UCO2M−UMR CNRS n°6011 Université du Maine LCOM−Chimie des Polymères Faculté des Sciences et Techniques
THESE
Présentée en vue de l’obtention du grade de
DOCTEUR Spécialité: Chimie et Physicochimie des Polymères
par
Nitinart SAETUNG
Synthetic- and natural rubber-based telechelic polyisoprenes:
preparation and use for block copolymers via RAFT polymerization
Soutenue le 25 novembre 2010, devant le jury composé de:
Mme Pranee PHINYOCHEEP Assoc. Professeur, Mahidol University, Thaïlande Rapporteur M. Christophe BOISSON Directeur de Recherche-HDR CNRS, Université Lyon 1 Rapporteur Mme Sophie BISTAC Professeur, Université de Haute Alsace, Mulhouse Présidente M. Frédéric PERUCH Chargé de Recherche-HDR CNRS, Université de Bordeaux 1 Examinateur Mme Irène CAMPISTRON Ingénieur CNRS à l’Université du Maine Co-encadrante Mme Sagrario PASCUAL Maître de Conférences, Université du Maine Co-encadrante M. Laurent FONTAINE Professeur, Université du Maine Directeur M. Jean-François PILARD Professeur, Université du Maine Co-directeur
For my grandparents For my parents For my family members For my teachers
The present thesis is the result of my PhD research at the Université du Maine,
France. I will never forget this time in my life and, most importantly, the people I met here
and who helped me to create, develop and finish this thesis. First of all, I would like to
acknowledge the financial support from Prince of Songkla University, Thailand and from the
French Ministry of Education and Research. Taking this opportunity, I would like to express
my sincere gratitude to Assistance Professor Dr. Orasa PATARAPAIBOOLCHAI for her
advice and recommendation letter that brought me study for a Ph.D. at Université du Maine.
I would like to thank my advisor: Professor Laurent FONTAINE for giving me an
opportunity to do my PhD work within his group, as well as for his support and professional
guidance during my PhD period. Professor Laurent has been a wonderful advisor, providing
me with support, encouragement, patience and an endless source of ideas. His breadth of
knowledge and his enthusiasm for research inspires me. I thank him for the countless hours
he has spent with me, discussing everything from research to career choices, reading my
manuscript and correcting my presentation.
I would also like to thank Professor Jean-François PILARD, my Ph. D. co-advisor.
Professor Jean-François has been a great advisor. His enthusiasm for research and his vision
for the future have been an inspiration. He has given me support and encouragement and his
advice about my research have greatly enhanced the work. I thank him for his assistance and
for all the support provided to both me and to my husband, Anuwat SAETUNG.
I would like to express my sincere gratitude to Dr. Irène CAMPISTRON, whose
enthusiasm for the controlled oxidative and metathesis degradations of natural rubber and
her knowledge of the subject has helped me understand many aspects of controlled
degradation of natural rubber, especially the metathesis degradation that was foreign to me
beforehand, and for correcting my manuscript. Most importantly, I would like to thank her for
her encouragement, patience and also much assistance in my personal life for the past 4
years.
I am extremely grateful to Dr. Sagrario PASCUAL for the time spent discussing the
results related to living radical polymerization, especially RAFT polymerization that was new
to me at the start of this thesis. Most importantly, I would like to thank her for her
encouragement and for having confidence in me and my abilities and for finding the time to
read through the manuscripts and correct my manuscript.
Next, I would like to thank members of my thesis committee, Assoc. Professor Pranee
PHINYOCHEEP, Professor Sophie BISTAC, Dr. Christophe BOISSON and Dr. Frédéric
PERUCH who have been generous with their time and have assisted with the successful
completion of this work. I would especially like to thank to Professor Sophie BISTAC for her
help with preliminary wedge tests.
I am grateful to Dr. Jean-Claude SOUTIF for his assistance and useful discussions on
MALDI-TOF MS over the last year. Furthermore, I would especially like thank to Madame
Evette SOUTIF, his wife, for all the love, kindness and help offered to my family throughout,
in particular to my daughter, Alisa SAETUNG. Evette took care of my daughter like she was
her own granddaughter.
Many thanks to Mme Cécile CHAMIGNON and Mme Amélie DURAND for help
interpreting liquid 1H NMR spectra and 13C NMR spectra. I would also like to thank to Dr.
Monique BODY for the analysis of solid-state 13C NMR spectra of my samples.
I am greatly indebted to Dr.Véronique MONTEMBAULT, Dr. Michel THOMAS and
Dr. Charles COUGNON, Anita LOISEAU, Jean-Luc MONEGER and Aline LAMBERT for
their guidance and helpful in providing advice many times during my work here. I would
especially like thank to Dr. Fédéric GOHIER and his wife, Dr. Stephanie LEGOUPY, for
their kindness and support shown to my family throughout by lending me their baby clothes
and baby accessories for the past 4 years.
I am also grateful to Professor Jean-Claude BROSSE, Dr. Daniel DEROUET and
Dr. Albert LAGUERRE for their helpful, guidance and support for my study here.
Thank you all friends in LCOM laboratory, Chuanpit, Faten, Hoa, Sandie, Charles,
Dao, Ekasit, Ekkawit, Hien, Jean-Marc, Martin and Rachid for their friendship and good
atmosphere in laboratory. I would like to give special thanks to Martin for his helpful
discussions related to living radical polymerization and also for helping me to improve my,
English. I would also like to give special thanks to Chuanpit for her help in my personal life,
especially during my first year in France, and thanks to Faten for her help improving my
French.
Finally, I would like to thank my grandparents, my family for all their advice, support
and love. I am very lucky to have such wonderful family members. I especially thank my
wonderful husband, Anuwat SAETUNG who is my best friend and turn to ‘soul-mate’. He has
kept me happy and positive throughout the Ph.D. process, and I thank him for all his patience,
support, encouragement and love. I truly thank Anuwat for sticking by my side, even during
the difficult days. Most importantly, I am very lucky to have a wonderful daughter, Alisa
SAETUNG who was an inspiration during my graduate Ph. D. studies, and in future always
will be.
Synthetic- and natural rubber-based telechelic polyisoprenes: preparation and use for block copolymers via RAFT polymerization ABSTRACT: The aim of this research work is to develop new strategies to synthesize well-
defined block copolymers from natural rubber (NR) based telechelic polyisoprene (PI) by
reversible addition-fragmentation chain transfer (RAFT) polymerization. The tert-butyl
acrylate (t-BA) has been chosen as comonomer which is further modified to obtain acrylic
acid (AA) units. To target such block copolymers, two original synthetic routes have been
developed to target NR-based PIs which are further employed as macromolecular chain
transfer agents (macroCTAs) for the RAFT polymerization of t-BA.
In the first approach, a trithiocarbonate functionalized telechelic cis-1,4-PI was synthesized
via the oxidative degradation of NR followed by reductive amination and amidation. The
microstructure of the functionalized PI is strictly cis-1,4. The end-functionality was
determined by 1H-NMR spectroscopy and clearly demonstrated that telechelic cis-1,4-PI
chains carry the trithiocarbonate moiety. We demonstrated that the chain extension of the
trithiocarbonate functionalized cis-1,4-PI starting block resulted in an efficient block
copolymer formation. PI-b-P(t-BA) diblock copolymer presents an unimodal SEC trace and
polydispersity index equal to 1.76. The copolymer has a nM equal to 26,000 g.mol-1 as
determined by SEC and a nDP (PI) equal to 62 and a nDP (P(t-BA)) equal to 87 as
determined by 1H NMR spectroscopy.
In the second approach, a well-defined α,ω-bistrithiocarbonyl-end functionalized telechelic
cis-1,4-polyisoprene was synthesized via functional metathesis degradation from NR in the
presence of second generation Grubbs catalyst (GII) and a bistrithiocarbonyl-end
functionalized olefin as CTA. Formation of telechelic natural rubber occurs rapidly in a
single-step process. The nM was equal to 8,200 g. mol-1 as determined by SEC after 4h of
reaction at 25 °C. A perfectly bifunctional telechelic PI was obtained using a ratio of
[NR]0/[GII] 0/[CTA]0 to 100/1/2 at 25°C. Moreover, the difunctional telechelic PI has a strictly
cis-1,4-microstructure. It was successfully used as macroCTA for the RAFT polymerization
of t-BA to form well-defined P(t-BA)-b-PI-b-P(t-BA) triblock copolymer. The final
copolymer has a nM equal to 23,300 g.mol-1, PDI equal to 1.50 as determined by SEC and a
nDP (PI) equal to 80 and nDP (P(t-BA)) equal to 100 as determined by 1H NMR
spectroscopy.
Finally, the tert-butyl ester groups of the P(t-BA) blocks were chemically cleaved to acrylic
acid groups using iodotrimethylsilane at room temperature in order to get PI-b-PAA diblock
and PAA-b-PI-b-PAA triblock copolymers. The thermal properties of block copolymers
before and after dealkylation of tert-butyl ester groups have been investigated by DSC and
TGA analyses.
Keyword: natural rubber, polyisoprene, oxidative degradation, functional metathesis
degradation, telechelics, reversible addition-fragmentation chain transfer (RAFT)
polymerization.
List of abbreviations
AA Acrylic acid
ACVA Azobiscyanovaleric acid
AFM Atomic force microscopy
AIBN 2,2′-Azobis(2-methylpropionitrile)
AROP Anionic ring−opening polymerization
ATR Attenuated total reflectance
ATRP Atom transfer radical polymerization
BriBBr 2-Bromoisobutyryl bromide
CA Coupling agent
CNTs Carbon nanotubes
COSY 2D-correlation spectroscopy
CPDB 2-(2-Cyanopropyl)dithiobenzoate
CP-MAS Cross-polarisation combined with magic angle spining
CRP Controlled/living radical polymerization
CTA Chain transfer agent
D3 Hexamethylcyclotrisiloxane
DCP Dicumyl peroxide
DDAT S-1-Dodecyl-S’-(α,α’-dimethyl-α”-acetic acid)trithiocarbonate
DEPT Distortionless enhancement of polarisation transfer
DLS Dynamic light scattering
DMA N,N-Dimethylacrylamide
DPE Diphenylethylene
nDP Number-average degree of polymerization
DRC Dry rubber content
DSC Differential scanning calorimetry
DTG First derivative thermogravimetry
EO Ethylene oxide
ETSPE 2-Ethylsulfanylthiocarbonyl sulfanyl propionic acid ethyl ester
nf Average functionality
FTIR Fourier transform infrared spectroscopy
GII Second generation of Grubbs catalyst
HSQC Heteronuclear single-quantum correlation
I Isoprene
List of abbreviations
macroCTA Macromolecular chain transfer agent
MALDI-TOF Matrix-assisted laser desorption ionisation time-of-flight
m-CPBA meta-Chloroperbenzoic acid
MMA Methyl methacrylate
nM Number-average molecular weight
n,NMRM Number-average molecular weight determined by 1H NMR spectroscopy
SECnM , Number-average molecular weight determined by SEC
MPEB 1,4-Bis(4-methyl-1-phenylethyl)benzene
wM Weight-average molecular weight
NMP Nitroxide-mediated radical polymerization
NMR Nuclear magnetic resonance spectroscopy
NR Natural rubber
NVP N-Vinylpyrrolidinone
PAA Poly(acrylic acid)
PD3 Poly(hexamethylcyclotrisiloxane)
PDI Polydispersity index
PDMA Poly(N,N-dimethylacrylamide)
PEO Poly(ethylene oxide)
PI Polyisoprene
PLA Polylactide
PI-Li+ Polyisoprenyllithium
PMDETA N, N, N’, N’, N’’-Pentamethyldiethylenetriamine
PNVP Poly(N-vinylpyrrolidinone)
PS Polystyrene
PS-Li+ Polystyrenyllithium
P(t-BA) Poly(tert-butyl acrylate)
P(2-VP) Poly(2-vinylpyridine)
RAFT Reversible addition/fragmentation chain transfer
ROMP Ring-opening metathesis polymerization
rrPT Regioregular hydroxyl-functionalized poly(3-hexylthiophene)
SAXS Small angle X-ray scattering
s-BuLi sec-Butyllithium
List of abbreviations
SCK Shell-crosslinked
SEC Size exclusion chromatography
SLS Static light scatterting
t-BA tert-Butyl acrylate
t-bp tert-Butyl peroxide
t-BuP4 1-tert-Butyl-4,4,4-tris(dimethylamino)-2,2-bis-[tris(dimethylamino)-
phosphoranylidenamino]-2λ5,4λ5-catenadi(phosphazene)]
Tg Glass transition temperature
TGA Thermogravimetric analysis
THF Tetrahydrofuran
TIPNO 2,2,5-Trimethyl-4-phenyl-3-azahexane-3-nitroxide
Tmax Maximum degradation temperature
TNR Telechelic cis-1,4-polyisoprene
TPC Terephthaloyl chloride
2-VP 2-Vinylpyridine
WAXS Wide-angle X-ray scattering
Table of contents
General introduction...…….......………………..………………………………..1
Chapter I : Literature on block copolymers based on PI
Introduction....................................................................................................................... ..........5
I. General strategies to synthesize block copolymers.................................................. ...........5 I.1 Synthesis of well-defined linear AB diblock copolymers...................................... ............6 I.2 Synthesis of well-defined ABA triblock copolymers............................................. ............8
II. Synthesis of block copolymers based on polyisoprene.......................................... ..........11 II.1 Using anionic polymerization.............................................................................. ..........11
II.1.1 Synthesis of AB diblock copolymers............................................................ ..........12 II.1.2 Synthesis of ABA triblock copolymers.......................................................... ..........19
II.2 Using controlled/living radical polymerizations................................................. ..........22 II.2.1 Nitroxide-Mediated Radical Polymerization (NMP)..................................... ..........23
II.2.1.1 Synthesis of AB diblock copolymers......................................................... ..........23 II.2.1.2 Synthesis of ABA triblock copolymers................................................... ..........30
II.2.2 Reversible Addition-Fragmentation Chain transfer Polymerization (RAFT).............32 II.3 Using a combination of various polymerizations................................................... ........36
II.3.1 Synthesis of AB diblock copolymers.............................................................. ........36 II.3.2 Synthesis of ABA triblock copolymers........................................................... ........39
Conclusion......................................................................................................................... ........41
References.......................................................................................................................... ........42
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
Introduction....................................................................................................................... .........45
I. Synthesis and characterization of polyisoprene........................................................ ........46
II. Synthesis and characterization of polyisoprene-b-poly(tert-butyl acrylate) block
copolymers....................................................................................................................
;........50
Conclusion......................................................................................................................... ........54
Experimental section...................................................................................................................55
References.......................................................................................................................... ........59
Table of contents
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
Introduction....................................................................................................................... .........61
I. Synthesis of αααα-trithiocarbonyl- ωωωω-carbonyl-cis-1,4-polyisoprene............................ ........63
II. Synthesis of PI-b-P(t-BA) diblock copolymer............................................................ ;........69
Conclusion......................................................................................................................... ........72
Experimental section...................................................................................................................73
References.......................................................................................................................... ........77
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
Introduction....................................................................................................................... .........80
I. Functional Metathesis Degradation............................................................................ ........83
II. Synthesis of P(t-BA)-b-PI-b-(P(t-BA) triblock copolymers...................................... ;........93
Conclusion......................................................................................................................... ........97
Experimental section...................................................................................................................98
References.......................................................................................................................... ........102
Chapter V : Thermal properties of block copolymers based on PI/P(P(t-BA) and PI/PAA
Introduction....................................................................................................................... ........104
I. Comparison between PI-macroCTA and block copolymers based on PI/P(t-BA) ........104
II. Influence of the PI microstructure............................................................................ ;......114
III. Deprotection of t-BA group and thermal stability of resulting block
copolymers based on PI/PAA.....................................................................................
......115
Conclusion......................................................................................................................... ........125
Experimental section...................................................................................................................126
References.......................................................................................................................... ........128
General conclusion...............................................................................................129
General introduction
General introduction
- 1 -
In the 20th century, natural polymers such as cellulose, cotton and rubber have attracted
considerable attention from polymer scientists. Increasing environmental consciousness
and demands of consumers have created significant opportunities for improved materials
and development of new preparation methods. Developing polymers from renewable
resources will support environmental request. The current challenge of polymers from
renewable resources is a growing area of reseach.1
Natural rubber (NR) is a polymer of great interest for use in producing new polymeric
materials as it is a polymer which comes form a renewable resource. Moreover, it is well
known that NR consists of a long sequence of cis-1,4-polyisoprene that provides the
material with unique and special properties, including good elastomeric properties, low
glass transition temperature, excellent flexibility, good “green” strength and building tack.2
Due to its excellent properties, polymer scientists have developed new synthetic routes to
obtain polyisoprene with very similar structure.3 The polymerization using Ziegler-Natta
catalysts leads to PIs with 98% of cis-1,4-polyisoprene units.4 However, these synthetic PIs
showed different properties from NR, especially in terms of processability. The living
anionic polymerization5 leads to PIs with 95% of cis-1,4-polyisoprene units, 1% of trans-
1,4-polyisoprene units and 4% of 3,4-polyisoprene units. The controlled/living radical
polymerizations (CRPs)6 of isoprene gave 80% of 1,4-polyisoprene, between 5% and 15%
of 3,4-polyisoprene and between 5% and 15% of 1,2-polyisoprene depending on the
reaction conditions. The microstructure influences the properties of the polyisoprene; for
example, the trans-1,4-polyisoprene has a higher degree of crystallinity and a higher glass
transition temperature than the cis-1,4-polyisoprene.7 Therefore, the synthesis of telechelic
strictly cis-1,4-polyisoprene from natural rubber (TNR) will give rise to original polymers
and copolymers with new potential applications. The most widely used methods to produce
TNR derivatives are controlled oxidative degradation8 or metathesis degradation.9
[1] Joseph, S.; John, M.; Pothen, L.; Thomas, S., Raw and Renewable Polymers. In Polymers-Opportunities and Risks II, Eyerer, P.;
Weller, M.; Hubner, C., Eds. Springer Berlin: Heidelberg, 2010; Vol. 12, p 55-80. [2] Morton, M., Rubber Technology. Van Nostrand Reinhold: New York, 1973. p 152. [3] Puskas, E. J.; Gautriaud, E.; Deffieux, A.; Kennedy, P. J., Prog. Polym. Sci. 2006, 31, 533-548. [4] Van Amerongen G, J., Transition Metal catalyst systems for polymerization Butadiene and Isoprene. In Elastomer Stereospecific
polymerization, Johnson, L. B.; Goodman, M., Eds. American chemical society: Washington, D.C., 1966; Vol. 52, p 136-152. [5] Young, N. R.; Quirk, R. P.; Fetters, J. L., Anionic Polymerizations of Non-Polar Monomers Involving Lithium. In Anionic
polymerization, Fetters, J. L.; Luston, J.; Quirk, R. P.; Vass, F.; Young, N. R., Eds. Springer-Verlag NewYork Heidelberg Berlin, 1984; Vol. 56, p 53.
[6] Jitchum, V.; Perrier, S., Macromolecules 2007, 40, 1408-1412. [7] Kent, E. G.; Swinney, F. B., I&EC Product Research and Development 1966, 5, 134-138. [8] Nor, H. M.; Ebdon, J. R., Prog. Polym. Sci. 1998, 23, 143-177. [9] Ivin, K. J.; Mol, J. C., Olefin metathesis and metathesis polymerisation. Academic Press: London, 1997. p 375.
General introduction
- 2 -
Oxidative degradation of NR has been widely used in our laboratory to develop precursors
for thermoplastic elastomers,10 biomaterials11 and polyurethane materials.12-15 In addition,
we have also developed a method for the preparation of TNR in a single-step process via
the metathesis degradation of cis-1,4-polyisoprene.16 Therefore, it is possible to prepare
functional TNR by combining chain cleavage reaction of NR with a post-functionalization
reaction to form original block copolymers with new potential applications. To best of our
knowledge, no work has been previously reported on the synthesis of telechelic cis-1,4-
polyisoprene from natural rubber as precursor for CRPs in order to obtain well-defined
block copolymers. Among CRP techniques, Reversible Addition/Fragmentation chain
transfer (RAFT) polymerization17 is recognized as one of the most versatile method for the
synthesis of block copolymers since it is effective for a wide range of monomers and thus
leads to a wide range of block copolymers.
The objective of this research work is to develop new strategies to synthesize well-defined
diblock copolymers and triblock copolymers from NR-based cis-1,4-PI by RAFT
polymerization in order to obtain new polymeric materials. In this work, the tert-butyl
acrylate (t-BA) has been chosen as a comonomer. To target such block copolymers, new
synthetic routes (Figure 1) are developed to prepare NR-based cis-1,4-PI which could
further be employed as macromolecular chain transfer agent (macroCTAs) for the RAFT
polymerization of t-BA. In the first approach, the PI-macroCTA was synthesized via the
oxidative degradation of NR followed by reductive amination and amidation. In the second
approach, the PI-macroCTA was synthesized via one-pot metathesis degradation from NR.
In order to compare the properties of final block copolymers, the preparation of synthetic
PI-macroCTAs has also been performed by RAFT polymerization.
[10] Derouet, D.; Nguyen, T. M. G.; Brosse, J.-C., J. Appl. Polym. Sci. 2007, 106, 2843-2858. [11] Kébir, N.; Campistron, I.; Laguerre, A.; Pilard, J.-F.; Bunel, C.; Jouenne, T., Biomaterials 2007, 28, 4200-4208. [12] Kébir, N.; Morandi, G.; Campistron, I.; Laguerre, A.; Pilard, J.-F., Polymer 2005, 46, 6844-6854. [13] Kébir, N.; Campistron, I.; Laguerre, A.; Pilard, J.-F.; Bunel, C.; Couvercelle, J.-P.; Gondard, C., Polymer 2005, 46, 6869-6877. [14] Saetung, A.; Rungvichaniwat, A.; Campistron, I.; Klinpituksa, P.; Laguerre, A.; Phinyocheep, P.; Pilard, J. F., J. Appl. Polym.
Sci. 2010, 117, 1279-1289. [15] Saetung, A.; Rungvichaniwat, A.; Campistron, I.; Klinpituksa, P.; Laguerre, A.; Phinyocheep, P.; Doutres, O.; Pilard, J.-F., J.
Appl. Polym. Sci. 2010, 117, 828-837. [16] Solanky, S. S.; Campistron, I.; Laguerre, A.; Pilard, J.-F., Macromol. Chem. Phys. 2005, 206, 1057-1063. [17] Moad, G.; Thang, S. H., Aust. J. Chem. 2009, 62, 1379-1381.
General introduction
- 3 -
Natural Rubber
Degradation
= RAFT agent moiety
Oxidation
amination and amidation Metathesis
PI-b-P(t-BA) P( t-BA)-b-PI-b-P(t-BA)
RAFT polymerization RAFT polymerization
Figure 1. Synthetic routes to target block copolymers based on cis-1,4-PI from NR.
This PhD. manuscript is based on five chapters.
The first chapter is a literature survey about the synthesis and characterization of block
copolymers based on PI.
The second chapter describes the preparation of synthetic polyisoprene via RAFT
polymerization and then its use for the formation of PI-b-P(t-BA) diblock copolymer via
RAFT polymerization.
The third chapter describes the synthesis of a new trithiocarbonate functionalized NR-
based cis-1,4-polyisoprene via the oxidative degradation of natural rubber followed by
reductive amination and amidation. The well-defined α-trithiocarbonyl-ω-carbonyl-cis-
1,4-polyisoprene was used as a monofunctional macroCTA to mediate the RAFT
polymerization of t-BA to form well-defined PI-b-P(t-BA) diblock copolymers.
General introduction
- 4 -
The fourth chapter describes the one-pot synthesis of a new α,ω-bistrithiocarbonyl-end
functionalized telechelic cis-1,4-polyisoprene via metathesis degradation from NR. The
new well-defined α,ω-bistrithiocarbonyl-end functionalized telechelic NR-based cis-1,4-
polyisoprene was used as macroCTA to mediate the RAFT polymerization of t-BA leading
to well-defined P(t-BA)-b-PI-b-P(t-BA) triblock copolymers.
The final chapter is devoted to thermal characterizations of PI-macroCTAs, PI-b-P(t-BA)
diblock copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers and, to the study of
the thermal stability of block copolymers before and after dealkylation of tert-butyl ester
groups of the P(t-BA).
Chapter I
Literature on block copolymers
based on PI
Chapter I : Literature on block copolymers based on PI
- 5 -
Introduction
Block copolymers are a fascinating class of materials made by covalent bonding of two or
more chemically different polymeric chains (blocks) that, in most cases, are
thermodynamically incompatible giving rise to a rich variety of microstructures in bulk and
in solution. Therefore, they are materials with unique chemical and physical properties:
they combine the properties of individual blocks in one molecule.1 They have attracted a
great deal of attention both academically and industrially due to their wide range of
potential applications2-3.
Block copolymers which contain polyisoprene (PI) as a block have found applications as
nanofibers,4 thermoplastic elastomers,5 pressure sensitive adhesives,6-7 and biocompatible
materials.8-9 This is due to the fact that PI is of great interest for its low glass transition
temperature (Tg), for its double bond rich composition, for its 1,4-microstructure and
because it has been classified as a biopolymer.10
The objective of our research work is the synthesis of AB diblock copolymers and
symmetric ABA triblock copolymers based on PI block (A) and a polar poly(tert-butyl
acrylate) P(t-BA) block (B) in order to get novel polymeric materials. Therefore, in this
chapter, we report on the general strategies to synthesize block copolymers that lead to
well-defined linear AB and ABA block copolymers and focus on the preparation of
architecturally well-defined linear AB diblock and ABA triblock copolymers based on PI.
I. General strategies to synthesize block copolymers
Various architectures of linear block copolymers such as AB diblock, ABA and ABC
triblocks, (AB)n multiblock are shown in Figure I-1.
Chapter I : Literature on block copolymers based on PI
- 6 -
AB diblock (AB)n multiblock
ABA triblock ABC triblock
Figure I-1. Linear block copolymers architectures.
The use of controlled/living polymerization techniques are the most convenient and
efficient methodology to target well-defined block copolymers. In this section, the
synthetic strategies based on controlled/living polymerization techniques that lead to the
preparation of linear AB diblock and ABA triblock copolymers will be presented.
I.1 Synthesis of well-defined linear AB diblock copolymers
A summary of block copolymer synthesis techniques has been provided by Hillmyer11 and
Matyjaszewski.12 Four methods have been reported for the preparation of AB linear
diblock copolymers:
A) the sequential monomer addition,
B) site-transformation technique,
C) the use of a dual initiator and,
D) by coupling two well-defined telechelic polymers.
Chapter I : Literature on block copolymers based on PI
- 7 -
telechelic oligomer
n
telechelic oligomer
+ n
n
__ _ _ __ _
nn+
_n
_I
mechanism I Site transformation
n
mechanism IIm+n m
nn+ _I m
n
_ _m
YXn
n
mechanism IY
mechanism II
mn
_ _m
A)
B)
C)
D)
dual initiator
AB diblock copolymer
_
I : initiator; X and Y : initiator sites; : monomer A, and : monomer B
AB diblock copolymer
AB diblock copolymer
AB diblock copolymer
X Y
Y
coupling
Figure I-2. Schematic representation of synthetic strategies toward well-defined AB
diblock copolymers: A) sequential monomer addition using controlled/living
polymerizations, B) site-transformation technique, C) using a dual initiator, and D) by
coupling two well-defined telechelic polymers.
In the first case, sequential addition of monomer can be performed in a one-pot
polymerization reaction using controlled/living polymerizations (Figure I-2A).
Provided that termination and/or transfer reactions are negligible, after the consumption of
the first monomer A, the remaining functionality at the chain-end of polymer A must be
able to initiate the polymerization of the new incoming second monomer B. This crossover
reaction must proceed fast and quantitatively to prevent side reactions. In addition to well-
established living ionic polymerization,13-14 other living polymerization systems such as
controlled/living radical polymerizations,15-16 have been developed during the past years.
Well-defined block copolymers are prepared by these controlled/living systems, but the
sequential monomer addition technique excludes monomers that polymerize by different
mechanisms.17
Chapter I : Literature on block copolymers based on PI
- 8 -
The second process is the so-called site-transformation technique which is applied when
the involved monomers cannot undergo polymerization with the same type of active sites
(Figure I-2B). In this technique, the monomer A is polymerized by the mechanism I via
the active center X. The active center X is then transformed to the active center Y and
monomer B is polymerized by a second mechanism. Extensive reviews about the site-
transformation technique have been published1,18-22 and this technique was recently
updated by Hadjichristidis et al.23
The third route involves the use of a dual bifunctional initiator that is able to start
simultaneously two polymerizations with two monomers by different mechanisms (i.e.,
ring-opening metathesis polymerization (ROMP) and nitroxide-mediated polymerization
(NMP). The two active sites must be compatible and tolerate each other (Figure I-2C).
Recently, Du Prez et al.24 published a review about dual and heterofunctional initiator to
prepare well-defined block copolymers.
The fourth synthetic route relies on the coupling reaction of two different well-defined
telechelic homopolymers (Figure I-2D). This strategy involves that the different functions
at the chain-ends must be highly reactive.25 Recently, a lot of progress has been made in
this field by the application of “click chemistry”26 and metal-ligand couplings.27-28
I.2 Synthesis of well-defined ABA triblock copolymers
The synthesis of ABA triblock copolymers can be accomplished using one of the following
methods:
A) the use of a difunctional initiator and a two-step sequential addition of monomers,
B) two-step sequential addition of monomers followed by a coupling reaction,
C) three-step sequential addition of monomers and,
D) by site-transformation technique.
Chapter I : Literature on block copolymers based on PI
- 9 -
nn+ _I
XXn
nX
m
_
m
A)
B)
C)
D)
difunctionalinitiator ABA triblock copolymer
Xn
_
m
_m
m
n
coupling agent
_
mn
+
mn*
m n
CA
CA
nn+
_I _
m
m
n
n
nm
nn
_Y
mechanism Isite transformation
mechanism II
m
+
nXX
difunctionalmacroinitiator
XX
difunctionalinitiator
Y
n
_m
_m
I : initiator; X and Y: initiator sites; : monomer A and : monomer B
ABA triblock copolymer
ABA triblock copolymer
ABA triblock copolymer
n
Figure I-3. Schematic representation of synthetic strategies toward well-defined ABA
triblock copolymers: A) use of a difunctional initiator and a two-step sequential addition of
monomers, B) two-step sequential addition of monomers followed by a coupling reaction,
C) three-step sequential addition of monomers, and D) by site-transformation technique.
Chapter I : Literature on block copolymers based on PI
- 10 -
The most straightforward method and widely explored so far is the use of a difunctional
initiator. The middle block (Polymer A) is made first, bearing at both ends active sites
capable of initiating the polymerization of the second monomer B, which is added
sequentially in the reaction medium after the consumption of the first monomer A (Figure
I-3A) . This procedure can be performed in a one-pot reaction. Living ionic polymerization
techniques13-14 and controlled/living radical polymerizations15-16 have been successfully
used to synthesize ABA triblock copolymers using such strategy.
In the second method, a well-defined linear AB diblock copolymer is synthesized by
sequential addition of monomers A and B. This diblock copolymer is reacted in
stoichiometric amount with a difunctional coupling agent (CA) in order to form the ABA
triblock copolymers25 (Figure I-3B). Recently, “click chemistry” has been used for
coupling blocks together and, quantitative reactions of functional end-groups for the
construction of well-defined block copolymers have been obtained.29-31
The third method involves sequential monomers additions using a monofunctional
initiator. The first monomer A is polymerized followed by the polymerization of the
second one B. After complete consumption of the second monomer B, the first monomer A
is added to the reaction mixture resulting in an ABA triblock copolymer (Figure I-3C).
Finally, ABA can be prepared by a combination of polymerization techniques. This
procedure is needed when the two monomers A and B cannot be polymerized by the same
polymerization technique and have to carried out in a two-step reaction using a
difunctional initiator. The monomer A is polymerized by mechanism 1 via active centers
X. The active centers X are then transformed to active centers Y and the resulting
difunctional macroinitiator can be employed for the polymerization of monomer B by
mechanism II (Figure I-3D). This technique is extremely convenient for the formation of
mechanistically incompatible block copolymers.24
Chapter I : Literature on block copolymers based on PI
- 11 -
II. Synthesis of block copolymers based on polyisoprene
The general strategies to synthesize block copolymers presented in the section I of this
chapter are widely used for the synthesis of well-defined linear AB diblock and ABA
triblock copolymers based on polyisoprene (PI). PI is generally synthesized by anionic
polymerization, by Ziegler-Natta polymerization and by controlled/living radical
polymerization. It could also be obtained by ring-opening metathesis polymerization
(ROMP) and from natural rubber (NR). However, only anionic polymerization,
controlled/living radical polymerizations and a combination of various polymerizations
have been employed to synthesize block copolymers based on PI. Then, in this section, the
preparation of linear block copolymers based on polyisoprene by anionic polymerization,
controlled/living radical polymerizations and a combination of various polymerization
techniques is presented.
II.1 Using anionic polymerization
The anionic polymerization of isoprene has been widely reported.1,11,13,32 Anionic
polymerization proceeds efficiently via organometallic sites, carbanions (or oxanions) with
metallic counterions. Due to the fact that carbanions are nucleophiles, the monomers that
can undergo polymerization by anionic polymerization are those bearing an electron
withdrawing group at the polymerizable double bond. The most widely used initiators for
anionic polymerization are organolithiums.33 The primary reason for the employment of
these organometallic compounds as an anionic initiator is due to their rapid reaction with
the monomer at the initiation step of the polymerization reaction. With a rate of initiation
greater than that of the propagation step, the use of organometallic compounds leads to the
formation of the desired polymer with a narrow molecular weight distribution because all
active polymer chains start growing at almost the same time. Propagation proceeds through
the nucleophilic attack of a carbanionic site onto a monomer molecule with reformation of
the anionic active center. Under the appropriate experimental conditions, anionic
polymerization is associated with the absence of either spontaneous termination or chain
transfer reaction. Additionally, carbanions still remain active after the monomer is
completely consumed leading to well-defined block copolymers once a second monomer is
added to the reaction.
Chapter I : Literature on block copolymers based on PI
- 12 -
II.1.1 Synthesis of AB diblock copolymers
Two conditions are necessary in order to obtain well-defined diblock copolymers by
anionic polymerization:
a) the nucleophilicity of the macroanion A− must be high enough to initiate the
incoming monomer B without attacking its pendant groups (e.g., ester group of
acrylates);
b) the initiation of monomer A must be faster than the propagation rate of the
second monomer B. In general, sequential anionic polymerization requires the
following order of addition: dienes/styrene > vinylpyridines > (meth)acrylates >
oxiranes > siloxanes.13
The anionic polymerization of isoprene using sec-butyllithium (s-BuLi) as initiator in
hydrocarbon solvents at low temperature (−78 °C) is the most widely used and reported.
This is due to the fact that the use of hydrocarbon solvents and Li as counterion in the
initiator are essential for the production of polyisoprene having a high 1,4-microstructure
leading to a low Tg of the polymer and good elastomeric properties.
Various diblock copolymers based on isoprene and styrenic monomers or (meth)acrylic
monomers have been synthesized1,12-13 and used for many applications.34-38 Thus, the
synthesis of block copolymers containing an isoprenic block and other types of monomers
e.g. styrene, ethylene oxide (EO), 2-vinylpyridine (2-VP) and (meth)acrylic monomers
such as methyl methacrylate (MMA), tert-butyl acrylate (t-BA) will be studied in this part.
A wide variety of diblock copolymers of styrene and isoprene have been synthesized by
sequential addition of monomers.13,39 Polyisoprene was synthesized as the first block using
s-BuLi in benzene at low temperature (−78 °C) to form polyisoprenyllithium (PI−Li+)
active ion. The polymer was chain extended by the addition of styrene in the presence of a
small amount of a polar solvent (usually tetrahydrofuran (THF) (Scheme I-1A).
Alternatively, isoprene can be polymerized as the second block by generating
polystyrenyllithium (PS−Li +) active ion with s-BuLi in hydrocarbon solvent at low
Chapter I : Literature on block copolymers based on PI
- 13 -
temperature. Then, isoprene monomer was added to form a well-defined diblock
copolymer (Scheme I-1B). These reactions were terminated by the addition of methanol.
+ s BuLi Benzene78 °C
LiPITHF, LI78 °C
PI bCH3OH
+ s BuLi Benzene78 °C
LiPSBenzene,
LI78 °C CH3OH
A)
B)
PS
PS b PI
PI b PS
PS b PI
n
m
n
m
Scheme I-1. Synthesis of PI-b-PS via anionic polymerization: A) PI was synthesized as the
first block, and B) PI was synthesized as the second block.1.
The preparation of well-defined diblock copolymers based on isoprene and a polar
monomer (e.g. ethylene oxide, 2-vinylpyridine, and (meth)acrylates) is more complex than
that of the PI-b-PS or PS-b-PI diblock copolymers. Generally, the preparation of diblock
copolymers containing isoprene and ethylene oxide can be achieved in a two-steps
reaction1 (Scheme I-2A). First, isoprene monomer is polymerized in benzene with s-BuLi
as initiator at −78 °C. The living chain-end is then capped with one ethylene oxide unit.
After addition of ethanoic acid, an intermediate polymer containing hydroxyl group at the
chain-end (PI-OH) is obtained. Then, cumyl potassium was used to deprotonate the OH
group, leading to the macroinitiator PI-O−K+ which was further employed for the
polymerization of EO in THF at 50 °C. In this case K+ counterion has been used and not
Li+ because the strong ionic interaction between C-O− and Li+ leads to a low delocalization
of the negative charge on the oxygen and finally the insertion of monomers is
not possible.39-40 Förster et al.41 successfully used 1-tert-butyl-4,4,4-tris (dimethylamino)-
2,2-bis-[tris(dimethylamino)-phosphoranylidenamino]-2λ5,4λ5-catenadi(phosphazene)]
(t-BuP4) with s-BuLi to prepare well-defined PI-b-PEO diblock copolymers in a one-pot
synthesis (Scheme I-2B). This strong phosphazene base can efficiently complex lithium
ions, thereby suppressing the strong ionic interaction between C-O− and Li+ facilitating the
polymerization of ethylene oxide. To synthesize this diblock copolymer, isoprene was first
polymerized, using s-BuLi/t-BuP4 system as the initiator in THF. Afterward, a small
amount of ethylene oxide is added at −40 °C to cap the living PI chain-end and the reaction
Chapter I : Literature on block copolymers based on PI
- 14 -
solution is heated to 40 °C to start chain propagation with EO. This reaction was finally
terminated by the addition of a carboxylic acid (Scheme I-2B).
+ s BuLi Benzene78 °C
LiPI PI
LI
O1.
2.CH3COOHOH
First step
PI OH
C
CH3
CH3
K
THFPI O K
THF, 50 °C
OCH3COOH
Second step
A)
+s BuLi/
78 °CLiPI PI
OO
THF,
OB)
BuP4tin hexane
40 °C 40 °C
N
P
N
NNP P
P
N(CH3)2
N(CH3)2
N(CH3)2
N(CH3)2N(CH3)2
N(CH3)2
(H3C)2Nt BuP4 :
Li BuP4t
PI b PEO PI b PEO
PI b PEO
n
m
nm
Scheme I-2. Synthesis of PI-b-PEO via anionic polymerization: A) in a two-step process,1
and B) in a one-pot reaction.41
In addition to the employment of ethylene oxide as a monomer, the use of 2-vinylpyridine
(2-VP) as monomer is also reported. For example, well-defined diblock copolymers
containing isoprene and 2-VP monomers were obtained by altering solvent from a non
polar to a polar solvent during the copolymerization.42 To make this diblock copolymer the
polyisoprenyl lithium was first synthesized in n-heptane at −78 °C and s-BuLi was used as
initiator. Afterward, the solvent was removed and the polar solvent (THF) was added for
the polymerization step of 2-VP. The reaction was quenched with methanol (Scheme I-
3A). Quirk et al.36 prepared well-defined PI-b-P(2-VP) diblock copolymers in benzene.
The PI block was synthesized in benzene at 45 °C using s-BuLi as initiator. LiCl was used
Chapter I : Literature on block copolymers based on PI
- 15 -
as cross-associator in benzene at 8 °C to reduce reactivity at the chain-end of well-defined
P(2-VP) from polymerization and then the reaction mixture was rapidly terminated by
adding acetic acid in methanol (Scheme I-3B).
N
+ s BuLi 78 °C LiPI LI
n-heptane THF, CH3OH
N
+ s BuLi, 45 °C
LiPI8 °C CH3CO2HBenzene Benzene,
CH3OHLiCl
LiCl,
78 °C
A)
B)
PI b P(2 VP) PI b P(2 VP)
PI b P(2 VP)LIPI b P(2 VP)
n
m
n
m
Scheme I-3. Synthesis of PI-b-P(2-VP) via anionic polymerization; A) by changing
solvents,42 and B) in benzene.36
The synthesis of block copolymers composed of polyisoprene and poly(meth)acrylates by
anionic polymerization has been reported. The anionic polymerization of (meth)acrylates
frequently produces side reactions due to the fact that the anionic propagating centers can
react with the carbonyl groups of the (meth)acrylate monomers. To avoid this problem,
the active site chain is usually modified to reduce the reactivity of the anion at the
chain-end.13,43-44
As our current investigation is concerned by the synthesis of block copolymers based on
polyisoprene and poly(tert-butyl acrylate), the anionic polymerization of block copolymers
involving PI and P(t-BA) was studied. Previously, Ünal et al.45 synthesized PI-b-P(t-BA)
by sequential addition of monomers by anionic polymerization using s-BuLi as the
initiator. The first block was synthesized by polymerization of isoprene using s-BuLi in
THF at 0°C. Then, the t-BA was added to the solution at –78°C. The reaction mixture was
stirred for a further 48 hours. The reaction was terminated by addition of methanol
(Scheme I-4). Characterization of block copolymers were carried out using size exclusion
chromatography (SEC) and elemental analysis (Table I-1).
Chapter I : Literature on block copolymers based on PI
- 16 -
+ s BuLi 0°C
LiPI LICH3OH 78 °CTHF
OO
bPI P(t BA)bPI P(t BA)n
m
Scheme I-4. Synthesis of PI-b-P(t-BA) by sequential addition of monomers via anionic
polymerization using s-BuLi as initiator.45
It was found that the block copolymers formed micelles consisting of a PI shell and a
P(t-BA) core in n-octane which is a poor solvent for the P(t-BA) block and a good solvent
for PI block. The micelle formation was studied by static light scattering (SLS). The light
scattering results showed that an increase of temperature led to a shift in the micelle/free-
chain equilibrium in favour of free-chains. Furthermore, the standard Gibbs energy of
micellization was evaluated and it was found that a large negative standard enthalpy of
micellization was obtained which is one of the important driving forces for micellization.
Table I-1. Characteristics of PI-b-P(t-BA) synthesized by sequential addition of monomer
using anionic polymerization.45
Polymer nM *
(g.mol-1) wM *
(g.mol-1) wM / nM * Weight (%) **
isoprene
COP3a 100 000 123 000 1.23 19.0±0.6
PI−3b 31 000 35 000 1.13 −
COP5a 70 000 77 000 1.09 35.0±1.1
PI−5b 36 000 42 000 1.15 −
*determined by SEC, ** determined by elemental analysis, aCOP for PI-b-P(t-BA) diblock copolymer, bPI for polyisoprene.
Wooley et al.46 use the advantages of micelle formation via diblock copolymer containing
polyisoprene unit to build nanocage structures. The polyisoprene-b-poly(acrylic acid)
(PI-b-PAA) block copolymer was prepared by the hydrolysis of PI-b-P(t-BA) copolymer
precursor. This precursor was synthesized by anionic polymerization of isoprene using s-
BuLi as initiator in hexane at room temperature, followed by addition of 1,1-
diphenylethylene (DPE) and then polymerization of t-BA in hexane/THF containing LiCl
Chapter I : Literature on block copolymers based on PI
- 17 -
at −78 °C (Scheme I-5). The copolymer composition of the amphiphilic diblock
copolymer PI-b-PAA was determined by 1H NMR spectroscopy ( nDP (PI) = 30 and
nDP (PAA) = 170). This copolymer formed micelles in aqueous solution consisting of a
hydrophobic core of PI and a hydrophilic shell of PAA. Chemical cross-linking of the PAA
segments with an α,ω-diaminopoly(ethylene oxide) led to the formation of shell cross-
linked particles. Interestingly, the double bonds moiety of the cis-1,4-polyisoprene
backbone contained within the micelle core were degraded by ozonolysis. Hollow
nanocages were obtained with different sizes that vary from 83 nm to 130 nm depending
the length of the α,ω-diaminopoly(ethylene oxide) cross-linker.
+ s BuLi LiPI
LICH3OH 78 °C
Hexane
RT PILi
Hexane/THF,
LiCl
bPI P(t BA) bPI P(t BA)
n
OO
m
Scheme I-5. Synthesis of PI-b-P(t-BA) via anionic polymerization using DPE and LiCl.46
Similarly, Terao et al.38 investigated the synthesis of PI-b-PAA via anionic polymerization.
The first block, polyisoprene was polymerized using the previous described procedure by
Wooley et al.46 and trimethylsilylacrylate monomer as second monomer was introduced at
−78 °C in THF. The trimethylsilyl groups were hydrolyzed using dilute hydrochloric acid.
The resulting copolymer was precipitated in methanol and washed with cyclohexane. The
polymer composition was determined by 1H NMR spectroscopy ( nDP (PI) = 40 and nDP
(PAA) = 40). Next, the PI40-b-PAA40 was dispersed into 0.3% aqueous solution to form
micelles; such nanoparticles were cross-linked by gamma-ray irradiation. The size
distribution of the core-shell nanoparticles was determined by dynamic light scattering
(DLS) and atomic force microscopy (AFM) and it was found that the size distribution was
Chapter I : Literature on block copolymers based on PI
- 18 -
very narrow. The average diameter of the particles decreased from 48 nm for the non-
irradiated micelles to 26 nm after irradiation with 30 kGy. The core size of this
nanostructure was determined by small angle X-ray scattering (SAXS) combined with
DLS and it was roughly constant of 10 nm, irrespective of irradiation dose. Whereas the
shell thickness of the micelles was twice as large as the core size and the size decreased
with increasing the irradiation dose.
Lu et al.47 reported the preparation of microspheres using PI-b-PAA as the surfactant to
disperse a solution of PI-b-P(t-BA) and a P(t-BA) homopolymer (hP(t-BA)) in
dichloromethane. The PI-b-P(t-BA) and the precursor of PI-b-PAA were prepared by
sequential anionic polymerization. A solution of t-BuP4 and s-BuLi at a molar ratio of
1.05/1.00 in hexane was used to initiate the polymerization of isoprene at −78 °C in THF.
After five hours DPE was added, followed by the addition of t-BA. The polymerization
was continued for a further three hours at −78 oC, where upon the reaction was terminated
by the addition of methanol (Scheme I-6). The PI-b-P(t-BA) had an average molecular
weight ( wM ) of 92,000 g.mol-1 as determined by light scattering (LS) and a PDI = 1.22
determined by SEC. The tert-butyl ester groups of the precursor of PI-b-PAA were
removed quantitatively under acidic hydrolysis by treatment with trifluoroacetic acid in dry
dichloromethane to form PI-b-PAA and then used as the surfactant. Permanent
microspheres were produced after PI domains were cross-linked with sulphur
monochloride (S2Cl2). Porous microspheres were produced after the hydrolysis of P(t-BA)
and extraction of the homopoly(acrylic acid) chains. The shape and connectivity of the
poly(acrylic acid)-lined pores could be adjusted by changing in the P(t-BA)/hP(t-BA)
content in precursor microspheres.
Chapter I : Literature on block copolymers based on PI
- 19 -
+ LiPI
LIP(tPICH3OH
BA) P(tPI BA)
PILi
THF, LiCl
BuP4/s
78 °C
THF, 78 °C
t BuLi
OO
m
n
Scheme I-6. Synthesis of PI-b-P(t-BA) by sequential addition of monomers via anionic
polymerization using t-BuP4/s-BuLi system as initiator.47
Bouropoulos and co-workers48 used the amphiphilic block copolymers (PI-b-PAA) to
modify the surface of muti-walled carbon nanotubes (CNTs) and the growth of calcium
carbonate on these modified CNTs was investigated. The amphiphilic block copolymers
were synthesized using the procedure previously described by Pipas.37 It was found that
wM = 42,400 g.mol-1, PDI = 1.16 determined by SEC and that the copolymer contains 10
wt % PI determined by 1H NMR spectroscopy. The morphology of calcite crystals on
CNTs treated with PI-b-PAA exhibited both a spherical and an ellipsoidal crystal while the
untreated CNTs were found only a rhombohedral calcite.
II.1.2 Synthesis of ABA triblock copolymers
The most reported methods to synthesize symmetric ABA triblock copolymer based on
polyisoprene by anionic polymerization are the use of a coupling agent and the use of a
difunctional initiator. These procedures were described in the section I.2 of this chapter.
PS-b-PI-b-PS triblock copolymer has been prepared by Morton and coworkers39 using a
coupling method that is developed for the preparation of PS-b-PI-b-PS thermoplastic
elastomers used in industries (Scheme I-7A). A PS block was firstly prepared in benzene
at −78 °C using s-BuLi as initiator, followed by the addition of isoprene. Then, an excess
of the living diblock is used for coupling with dichlorodimethylsilane (CH3)2SiCl2)
Chapter I : Literature on block copolymers based on PI
- 20 -
employed as the coupling agent to form PS-b-PI-Si(CH3)2-PI-b-PS triblock copolymer.
Recently, Li et al.49 have reported the synthesis of difunctional organolithium initiators for
the polymerization of the PS-b-PI-b-PS triblock copolymer in a non polar solvent. The
difunctional initiator (DiMPEBLi) (Scheme I-7B). was synthesized in cyclohexane by the
reaction between t-BuLi and 1,4-bis(4-methyl-1-phenylethenyl)benzene (MPEB). The
resulting compound is then employed as a difunctional initiator for the polymerization of
isoprene in cyclohexane. After that, styrene was added to continue the polymerization and
methanol was used to terminate the reaction.
+ s BuLiBenzene
78 °CLiPS LI
CH3OHSi
CH3
CH3
Cl Cl(excess)
+
Benzene
CH3CLi
CH2
CLi
CH2
CH3
Bu Bu
DiMPEBLi
+
CH3C
CH2
C
CH2
CH3
MPEB
t BuLi2
Cyclohexane
DiMPEBLiCyclohexane
PI LiLiCyclohexane
A)
B)
bPS PI b PS
bPS PI Si(CH3)2 PI b PS
bPS PI
LIbPS PI
m
n
m
n
Scheme I-7. Synthesis of PS-b-PI-b-PS triblock copolymers via anionic polymerization:
A) using dichlorodimethylsilane as the coupling agent,39 and B) using a difunctional
initiator.49
The synthesis of ABA triblock copolymers based on isoprene and EO50 were achieved
using sodium or potassium naphthalene as the difunctional initiator in which Na+ or K+
counterions were formed by electron transfer from the Na or K atom to the naphthalene
molecule. Isoprene was first polymerized in THF at −78 °C. Next, the difunctional
macroinitiator was employed for the polymerization of EO in THF at 50 °C and the
reaction was terminated by the addition of methanol (Scheme I-8). The molecular weight
Chapter I : Literature on block copolymers based on PI
- 21 -
distributions of the triblock copolymers were narrow and monomodal. Since Na or K
naphthalenide is soluble only in polar solvents (e.g. THF), the microstructure of PI
obtained was mostly 3,4 (approximately 80%) with remainder 1,2.
O
40 °C
K THFK
K 78 °CTHF,
K KCH3OH
PEO b b PEOPI PEO b b PEOPI
K KPI+ n
m
Scheme I-8. Synthesis of PEO-b-PI-b-PEO triblock copolymer via anionic polymerization
using a difunctional initiator.50
To the best of our knowledge, there are only a few reports about the synthesis of ABA
triblock copolymers with isoprene and t-BA monomers via anionic polymerization.
However, employment of general polydienes as the middle block (B) with
poly(meth)acrylates has been previously reported. In this part, the synthesis of triblock
copolymers based on polydienes and poly(tert-butyl acrylate) is particularly studied as it is
one of the topics of this PhD thesis project.
Varshney51 have successfully synthesized well-defined ABA triblock copolymer consisting
of PS or P(2-VP) or polydienes rich in 1,4-microstructure as the middle block and P(t-BA)
as the end block by using terephthaloyl chloride (TPC) as the coupling agent (Scheme I-9).
A PS-b-P(t-BA) diblock copolymer is first formed by the polymerization of styrene in THF
at −78 °C, followed by the addition of LiCl and t-BA. The living macroanion (PS-b-P(t-
BA)−Li+) was linked with TPC at −30 °C to form PS-b-P(t-BA)-b-PS triblock copolymers.
This procedure can be modified and used to synthesize of PI-b-P(t-BA)-b-PI triblock
copolymers by forming PI-b-P(t-BA) diblock copolymers first and their coupling with
TPC.
Chapter I : Literature on block copolymers based on PI
- 22 -
+ s BuLi LiPS
LI
78 °C
THFPS Li
LiCl
30 °CTPC
P(t BA) PS
DPE
TPC : Cl CO
CO
Cl
78 °CTHF,
78 °CTHF,
bPS P(t BA) bPS P(t BA) TPC
OO
m
n
Scheme I-9. Synthesis of PS-b-P(t-BA)-b-PS using TPC as coupling agent.51
II.2 Using controlled/living radical polymerizations
Living anionic polymerization is one synthetic technique that is widely employed to
produce well-defined block copolymers, however this technique has a number of
drawbacks. Firstly, there is a limitation on the types of monomers that may be polymerized
due to the incompatibility between the reactive centers and monomers. Secondly, living
anionic polymerization requires extremely stringent conditions. To overcome these
drawbacks, there has been considerable interest in polymerization processes that mimic
“living” systems with the versatility and ease of the radical process; moving toward a
controlled/living radical polymerization.15,52 These methods have emerged as powerful
tools for the preparation of block copolymers as they produce well-defined polymers with
a narrow molecular weight distribution and high chain-end functionality. Moreover, the
reactions may be adapted to a wide range of olefin monomers and are tolerant to traces of
impurities. Within the controlled/living radical polymerization, the nitroxide-mediated
radical polymerization (NMP)53 and the reversible addition-fragmentation chain transfer
(RAFT) polymerization54 are the most widely used to synthesize PI and PI-based block
copolymers. A preliminary study was performed on the atom transfer radical
polymerization (ATRP) of isoprene.55 In this study, it was shown that the ATRP of
isoprene proceeded to only 5% conversion, meaning that the reaction was unsuccessful.
The authors explained this result by suggesting that the Cu(I) active species necessary to
promote ATRP are low in the reaction medium due to a competitive chelation of the
copper catalyst by diene monomer units.
Chapter I : Literature on block copolymers based on PI
- 23 -
II.2.1 Nitroxide-Mediated Radical Polymerization (NMP)
A number of recent reports have described the preparation of PI and diblock copolymers
containing PI with a range of polar and non-polar monomers using NMP.53
II.2.1.1 Synthesis of AB diblock copolymers
Hawker and coworkers56 have developed a rod-coil block copolymer containing
polyisoprene via NMP. The formation of the rod-coil block copolymer was accomplished
by using a biphenyl ester oligomer (rod segment) as an alkoxyamine-terminated
macroinitiator (A, Scheme I-10) for the polymerization of isoprene in o-dichlorobenzene
as a solvent at 120 °C. The resulting block copolymer had a number-average molecular
weight ( nM ) of 3,100 g.mol−1 determined by 1H NMR spectroscopy and a polydispersity
index of 1.08 determined by SEC. The phase behaviour of the rod-coil block copolymer
was detected by wide-angle X-ray scattering (WAXS). The rod-coil block copolymer
containing 35 wt % polyisoprene coil segments did not show any crystallization at room
temperature and it exhibits a lamellar microstructure with short rigid domains.
O
OO
OO
OO
O ON
macroinitiator ( A)
n120 °C
o dichlorobenzene
n
O NA
Scheme I-10. Synthesis of rod-coil block copolymer containing a polyisoprene coil
segment via NMP.56
Chapter I : Literature on block copolymers based on PI
- 24 -
Grubbs et al.57 reported the synthesis of amphiphilic PEO-b-PI diblock copolymers via
NMP. First, PEO monomethyl ether (MeO-PEO, nM ≈ 5,200 g.mol-1) was functionalized
by esterification with 2-bromopropionyl bromide. Reaction with a copper bromide (I)
complexed and N, N, N’, N’, N’’-pentamethyldiethylenetriamine (PMDETA) abstracted the
bromine atom from bromoester that was subsequently trapped by 2,2,5-trimethyl-4-phenyl-
3-azahexane-3-nitroxide (TIPNO) at 80 °C to form a PEO macroinitiator (B, Scheme I-
11). The PEO macroinitiator (B) used to initiate the polymerization of isoprene in m-
xylene at 125 °C. The resulting PEO-b-PI diblock copolymer had a number-average
molecular weight ( nM ) of 11.4 kg.mol-1 and a low polydispersity index (PDI < 1.1) as
determined by SEC. Compositional analysis of the copolymer showed that it contained 54
wt % PI with approximately 90% of 1,4-microstructure as determined by 1H NMR
spectroscopy.
OHMeO
DMAP, CH2Cl2
OMeO
OBr
OMeO
OO N
PhEt3N,
BrCOCH(CH3)Br
0 °C to RT
CuBr, Cu(0), TIPNO
PMDETA,toluene, 80 °C
m-xylene, 125 °COMeO
O
O N
Phn
(B)
TIPNO : ON
n n
m
n
m
Scheme I-11. Synthesis of PEO-b-PI diblock copolymer via NMP 57
More recently the same group synthesized an efficient unimolecular initiator for
the polymerization of styrene, isoprene and n-butyl acrylate and their subsequent
block copolymers via NMP.58 An ester-functional alkoxyamine initiator (C, Scheme I-12)
was synthesized by the addition of 1-(4-(methoxycarbonyl)-phenyl)ethyl radicals to the
nitroso group of 2-methyl-2-nitrosopropane in high yield (85%). This alkoxyamine was
then used to initiate and mediate the polymerization of styrene in bulk at 125 °C. After the
polystyrene was purified by precipitation into methanol, it was used as a macroinitiator for
the polymerization of isoprene. The resulting diblock copolymer had a number-average
molecular weight ( nM ) of 10.1 kg.mol-1 and a PDI equal to 1.13 as determined by SEC. It
Chapter I : Literature on block copolymers based on PI
- 25 -
contains 58 wt % PI with approximately 89% of 1,4-microstructure as determined by 1H
NMR spectroscopy.
N
O
Br
CO2Me
+CuBr, Cu(0), PMDETA
toluene, N2, 60 °C, 85%
N OMeO2C
CO2Me(C)
N OMeO2C
CO2Me
125 °C
N OMeO2C
CO2Mem
n
m
125 °C
n
m
Scheme I-12. Synthesis of PS-b-PI diblock copolymer via NMP 58
McCullough et al.59 investigated conducting polymers by end-capping a regioregular
hydroxyl-functionalized poly(3-hexylthiophene) (rrPT)60 with 2,2,5-trimethyl-4-phenyl-3-
azahexane-3-nitroxide (TIPNO) (Scheme I-13). This polymer was then employed as a
macroinitiator for the polymerization of isoprene via NMP using previously reported
conditions.61 The polymerization reaction was performed at 110 °C in 50% v/v of toluene
The resulting rrPT-b-PI diblock copolymer had a number-average molecular weight ( nM )
of 20,300 g.mol-1 and a PDI equal to 1.8 as determined by SEC. The copolymer contained
65 wt % of PI with approximately 90% 1,4-microstructure as determined by 1H NMR
spectroscopy.
Chapter I : Literature on block copolymers based on PI
- 26 -
S
C6H13
OHBr
m
Br
O
Br1.
2. TIPNO S
C6H13
OBr m
OO N
Ph
50% toluene, 110 °C S
C6H13
OBr m
OO
n
nN
Ph
TIPNO : ON
Scheme I-13. Synthesis of rrPT-b-PI diblock copolymer via NMP.59
Moreover, the synthesis of PI-b-PS and PI-b-P(t-BA) block copolymers were investigated
and reported.61 For the preparation of PI-b-PS diblock copolymers, isoprene was
polymerized first using 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane (I,
Scheme I-14A) as an unimolecular alkoxyamine initiator at 120 °C. After the reaction was
complete, polyisoprene was purified by precipitation into methanol and used as a PI-
macroinitiator for the polymerization of styrene in bulk at 120 °C under argon. The
characteristics of the PI-b-PS after purification showed a nM equal to
6,600 g.mol-1 and a PDI of 1.19 determined by SEC, with predominately 1,4-
microstructure as calculated by 1H NMR spectroscopy. Alternatively, a copolymer based
on PI and PS can be synthesized starting with the PS as the first block. In this case, styrene
was polymerized first, followed by the polymerization of isoprene in the same conditions
(Scheme I-14B). The polydispersity index of the PS-b-PI block copolymer is equal to 1.16.
In the case of P(t-BA)-b-PI block copolymer, the 2,2,5-trimethyl-3-(1-phenylethoxy)-4-
phenyl-3-azahexane (I, Scheme I-14C) and TIPNO were used to polymerize the t-BA at
125 °C under argon. The P(t-BA)-macroinitiator was purified by precipitation into
methanol and then used to initiate the polymerization of isoprene at 125 °C under argon.
The macromolecular characteristics of P(t-BA)-b-PI after purification were: nM = 9,700
g.mol-1 and PDI = 1.19 as determined by SEC, with predominantly a 1,4-microstucture as
calculated by 1H NMR spectroscopy. The authors showed that the PI-macroinitiatior is not
Chapter I : Literature on block copolymers based on PI
- 27 -
efficient for the polymerization of t-BA (Scheme I-14D) as incomplete initiation was
observed leading to a polydisperse sample.
I120 °C
ON
n
120 °C
120 °C
m ON
n m
A)
B)
m
ON
m m
ON
n120 °C
n
n
ON
n
x
I
ON
O O
x
n
125 °C
125 °C
ON
nO O
x
ON
n125 °C
ON
125 °C
C)
D)
I : initiator :
n
TIPNO : ON
+ TIPNO O O
OO
x
OO
x
Scheme I-14. Different strategies for the synthesis of AB diblock copolymers based on
polyisoprene via NMP: A) PI-b-PS diblock copolymer, B) PS-b-PI diblock copolymer,
C) P(t-BA)-b-PI diblock copolymer, and D) PI-b-P(t-BA) diblock copolymer.61
Chapter I : Literature on block copolymers based on PI
- 28 -
Wooley and co-workers62 have investigated the synthesis of amphiphilic shell-crosslinked
(SCK) nanoparticles consisting of a polyisoprene core and a poly(acrylic acid) shell from
block copolymers prepared via NMP, whereas previously this group used anionic
polymerization46,63 to prepare these structures (as mentioned in page 16 of this Chapter I).
Two amphiphilic diblock copolymers, one consisting of an unmodified PI block
(PAA-b-PI) and the other composed a hydrochlorinated PI block (PAA-b-PI(HCl)) were
prepared by the cleavage of the tert-butyl ester unit in P(t-BA)-b-PI block copolymer
precursors. The P(t-BA)-b-PI precursors were synthesized via NMP, using conditions
similar to that of Benoit.61 The P(t-BA) was polymerized first using an alkoxyamine (I,
Scheme I-14C) and TIPNO at 125 °C and then was used as a macroinitiator for the
polymerization of isoprene at 125 °C in bulk to form P(t-BA)-b-PI. The
copolymer composition was determined by 1H NMR spectroscopy ( nDP (PI) = 128, nDP
(P(t-BA)) = 64) and a number-average molecular weight and a polydispersity index
determined by SEC ( nM = 13 600 g.mol-1 and PDI = 1.18). The PI block contained
predominantly 86% of 1,4-microstructure.
The cleavage reaction of the tert-butyl ester unit was performed in toluene/acetic acid
using methanesulfonic acid as catalyst at 110 °C. This PAA-b-PI copolymer formed
micelles in aqueous solution and their micelle structure is based on a hydrophobic core of
PI and a hydrophilic shell of PAA. Chemical cross-linking of the PAA segments with an
α,ω-diaminopoly(ethylene oxide) led to the formation of shell cross-linked particles
increasing their rigidity and preventing their shape deformation when they are in contact
with substrates. An SCK containing a PI core untreated with HCl had a Tg of −63 °C, while
PI core treated with HCl had a Tg of 33 °C. These SCK showed little deformation from the
solution-state spherical shape upon deposition onto a mica substrate.
The same group64 further extended the synthesis of PI-b-P(t-BA) copolymers to the
synthesis of core-shell brush copolymers. A norbornene functional alkoxyamine (I,
Scheme 1-15) was first prepared. The norbornene group was polymerized via ring opening
metathesis (ROMP) using Grubbs catalyst to form a polynorbornene backbone with
pendant alkoxyamine functionalities. It was then used as a polyfunctional NMP
macroinitiator in the sequential polymerization of isoprene and t-BA in presence of TIPNO
to suppress biradical couplings.65 A brush copolymer consisting of a PI-b-P(t-BA) diblock
copolymer grafts and a polynorbornene backbone is obtained. The PI-b-P(t-BA) grafts
Chapter I : Literature on block copolymers based on PI
- 29 -
were characterized by 1H NMR spectroscopy ( nDP (PI) = 18 and nDP (P(t-BA)) = 41).
The P(t-BA) units are hydrolysed using HCl to form PAA units that were subsequently
crosslinked with 2,2-(ethylenedioxy)bis(ethylamine) to form a crosslinked brush
copolymer with hydrodynamic diameter of 17.2 nm as determined by DLS. Hollow
nanostructures were then formed by degradation of the PI core using ozonolysis.
O O
ON
198
10
O OO
N
198
10
18
n
(I)
ON
120 °C
x122 °C + TIPNO
+ TIPNO
ON
18O O
41
O O
198
10
TIPNO :
O OO
N10
ROMP Grubbs' catalyst
OO
Scheme I-15. Synthesis of brush copolymers based on PI-b-P(t-BA) grafts and on a
polynorbene backbone via NMP.64
Chapter I : Literature on block copolymers based on PI
- 30 -
II.2.1.2 Synthesis of ABA triblock copolymers
In addition to the synthesis of AB diblock copolymers via NMP, the synthesis of linear
ABA triblock copolymers based on polyisoprene has been reported recently.
Braslau et al.66 used the advantage of an unimolecular alkoxyamine to synthesize a
dialkoxyamine (I, Scheme I-16) used as an initiator to target a range of symmetrical ABA
triblock copolymers based on polyisoprene and poly(N,N-dimethylacrylamide) (PDMA)
(Scheme I-16A). The PI-macroinitiator was obtained using the bidirectional initiator at
123 °C under argon and then was employed for the polymerization of DMA to form
PDMA-b-PI-b-PDMA. The characteristics of PDMA-b-PI-b-PDMA triblock copolymer
were determined by SEC (nM = 7,000 g.mol-1, PDI = 1.23) and 1H NMR spectroscopy
( nM = 6,000 g.mol-1). In addition, the bidirectional initiator was used to prepare PI-b-P(t-
BA)-b-PI triblock copolymers. The polymerization of t-BA was performed first in bulk
with the bidirectional initiator and TIPNO at 125 °C under argon. Then the P(t-BA) with
the nitroxide cap at both chain-ends was used as a difunctional macroinitiator for the
polymerization of isoprene to form PI-b-P(t-BA)-b-PI triblock copolymers (Scheme I-
16B). nM of PI-b-P(t-BA)-b-PI after isolation was determined by SEC and it was found
equal to 29,800 g.mol-1 and PDI = 1.15. The polymer contained 10 wt% PI as determined
by 1H NMR spectroscopy.
Chapter I : Literature on block copolymers based on PI
- 31 -
ONPh nO
O NPh
NO
m m
124 °C
ONPh n
O NPh
ONm
I
n
124 °C
OOx
A)
125 °C
O
O O
x
ON
Ph
NPh
n
125 °C
O O
x
n
O NPhON
Ph n
B)
+ TIPNO
ON
TIPNO :
N
O NPh
ONPhI : initiator :
Scheme I-16. Synthesis of ABA triblock copolymers based on polyisoprene using a
bidirectional alkoxyamine initiator (I) via NMP; A) PDMA-b-PI-b-PDMA triblock
copolymer, and B) PI-b-P(t-BA)-b-PI triblock copolymer.66
Chapter I : Literature on block copolymers based on PI
- 32 -
II.2.2 Reversible Addition-Fragmentation Chain transfer (RAFT) Polymerization
The RAFT polymerization technique is recognized as one of the most versatile methods for
the synthesis of block copolymers since it is compatible with a wide range of unprotected
polar monomers54 including acrylic acid.67 The first successful polymerization of isoprene
via the RAFT process was reported by Jitchum and Perrier.68 The authors found the
optimum reaction conditions to synthesize well-defined polyisoprene homopolymers. In
this study, two different types of chain transfer agent (CTA) were investigated. The first
one was a dithiobenzoate derivative (2-(2-cyanopropyl)dithiobenzoate, CPDB).69 The
polymerization of isoprene mediated by CPDB at 60 °C and using 2,2′-azobis(2-
methylpropionitrile) (AIBN) as an initiator proceeded to low conversion (<15%).
Increasing the reaction temperature to 120 °C and using dicumyl peroxide (DCP) as an
initiator lead to an uncontrolled polymerization, shown by the broad polydispersity
(PDI = 4.07) of the product. It was proposed that the CPDB decomposed at this higher
temperature. By contrast the second trithiocarbonate derivative used as CTA, (2-
ethylsulfanylthiocarbonyl sulfanyl propionic acid ethyl ester, ETSPE)70 was able to control
the polymerization at 120 °C as ETSPE is stable at this reaction temperature. When a ratio
[ETSPE]0/[DCP]0 of 1/0.5 was used, a slightly broad polydispersity index (PDI ≈1.47-
1.67) was obtained, but reducing the [ETSPE]0/[DCP]0 ratio to 1/0.2 at 115 °C improved
the control and PDIs of less than 1.3 were obtained. (Scheme I-17A). Following this, the
optimized reaction conditions were used to produce AB diblock copolymers based on
polyisoprene using the RAFT process. Both P(t-BA) and PS were prepared and use as
macroCTA to mediate the polymerization of isoprene under previously mentioned
conditions (Scheme I-17B-C). The characteristics of PS-b-PI were determined by SEC and
found to be equal to nM = 44 300 g.mol-1, PDI = 1.19 and the copolymer contained 23
wt% PI as determined by 1H NMR spectroscopy. The characteristics of P(t-BA)-b-PI as
determined by SEC were found to be nM = 21 500 g.mol-1, PDI = 1.20 and the copolymer
contained 49 wt % PI. All of the PI blocks were found to feature a high proportion
(approximately 75%) of 1,4-microstructure products as determined by 1H NMR
spectroscopy.
Chapter I : Literature on block copolymers based on PI
- 33 -
S On S
S
S
ETSPE
115 °C
n
+
OOx
ETSPE
S
S
S
OOO
O
O
S
S
x
S
S
S
n
OO
O
O
x
O
O
n
m
S
S
S
n O
O
m
S
S
SO
O
m
DCP
DCP+
115 °C
115 °C
115 °CDCP,
n
115 °CDCP,
DCP+
A)
B)
C)
DCP : dicumyl peroxide
Scheme I-17. Synthesis of block copolymers based on polyisoprene using ETSPE as CTA
via RAFT process: A) synthesis of PI-macroCTA, B) synthesis of P(t-BA)-b-PI block
copolymer, and C) synthesis of PS-b-PI block copolymer.68
Wooley et al.71 have also prepared well-defined PI-b-PS diblock copolymers using the
RAFT process. In this synthesis, the polyisoprene block was obtained first using S-1-
dodecyl-S’-(α,α’-dimethyl-α”-acetic acid)trithiocarbonate72 (DDAT, Scheme I-18) as a
CTA and tert-butyl peroxide (t-bp) as an initiator at 125 °C under argon. The PI-
macroCTA was then chain extended by the addition of styrene in 1,4-dioxane using AIBN
as an initiator and a reaction temperature of 60 °C under argon. The copolymer was
recovered by precipitation in an excess of methanol. The characteristics of PI-b-PS were
determined by SEC ( nM = 15,590 g.mol-1, and PDI = 1.28). The final copolymer
contained 39 wt % PI with predominantly 1,4-microstructure as determined by 1H NMR
spectroscopy.
Chapter I : Literature on block copolymers based on PI
- 34 -
S
S
S
O
OH+ n125 °C
t-butyl peroxideS
S
S
n
O
OH
mAIBN, 60 °C
n
O
OHS
S
S
m
DDAT
C12H25 C12H25
C12H25
Scheme I-18. Synthesis of PI-b-PS block copolymer using DDAT as CTA via RAFT
process.71
Wooley et al. 73 also reported the preparation of P(t-BA)-b-PI via the RAFT process. The
P(t-BA) block was synthesized first using DDAT (Scheme I-19) as CTA at 80 °C using
AIBN as initiator. The polymer was recovered by precipitation into a cold 1:1 mixture of
water and methanol. The P(t-BA) was then used as a macroCTA for the polymerization of
isoprene in bulk performed at a reaction temperature of 125 °C to form P(t-BA)-b-PI
diblock copolymer. The characteristics of P(t-BA)-b-PI were determined by SEC to be
equal to nM = 34,500 g.mol-1 and PDI = 1.5. Analysis by 1H NMR spectroscopy revealed
that nM = 21,100 g.mol-1, nDP (P(t-BA)) = 53, nDP (PI) = 48 and that predominantly
1,4-microstructure for PI block is presented. Additionally, the synthesis of P(t-BA)-b-PI-b-
PS and P(t-BA)-b-PS-b-PI triblock copolymers were also reported.
Chapter I : Literature on block copolymers based on PI
- 35 -
S
S
S
O
OH +
125 °C
t-butyl peroxide
AIBN
60 °C
n
S
S
S
DDAT
OOx
S
S
S
OO
OH
O
x
n
OO
OH
O
x
C12H25
C12H25
C12H25
Scheme I-19. Synthesis of P(t-BA)-b-PI block copolymer using DDAT as CTA via RAFT
process.73
Recently, Wooley et al.74 used the RAFT process to form amphiphilic diblock copolymers
consisting of poly(N-vinylpyrrolidinone) (PNVP) and polyisoprene. The synthesis began
with the polymerization of NVP employing conditions similar to Gnanou75, using
azobiscyanovaleric acid (ACVA) as initiator and DDAT as CTA in 1,4-dioxane at 80 °C.
After precipitation, the PNVP-macroCTA was then employed to mediate the
polymerization of isoprene using tert-butyl peroxide as the initiator at 125 °C (Scheme I-
20). The conditions used were similar to those employed by Jichum and Perrier68 and
Wooley and Germack71. The molecular weight characteristics of PNVP-b-PI were
determined by SEC: wM = 226,000 g.mol-1, nM = 77,800 g.mol-1and PDI = 2.90. The
copolymer contained 30 wt % of PI. Analysis of the copolymer by 1H NMR spectroscopy
showed also that the 1,4-microstructure is predominant. These block copolymers were
cross-linked with sulphur monochloride (S2Cl2) to produce a complex amphiphilic
network.
Chapter I : Literature on block copolymers based on PI
- 36 -
S
S
S
O
OH +
125 °C
t-butyl peroxide
ACVA
1,4-dioxane, 60 °C
n
S
S
S
DDAT
Ny
S
S
SOH
O
y
n
NOH
O
y
O N O
O
C12H25
C12H25
C12H25
Scheme I-20. Synthesis of PNVP-b-PI block copolymer using DDAT as CTA via RAFT
process.74
II.3 Using a combination of various polymerizations
In each of the polymerization systems described above, the formation of block copolymers
requires the same polymerization mechanism for two (or more) monomers. In some cases,
the preparation of well-defined block copolymers cannot undergo polymerization with the
same method. The site-transformation technique as described in section I of this Chapter
allows to obtain well-defined block copolymers by the combination of various
polymerization mechanisms.
II.3.1 Synthesis of AB diblock copolymers
Only a few reports described the preparation of AB diblock copolymers containing
polyisoprene using the combination of various polymerizations.
Hilllmyer et al.76 investigated the synthesis of polyisoprene-b-polylactide (PI-b-PLA)
diblock copolymers by a combination of living anionic polymerization and controlled
coordination-insertion polymerization (Scheme I-21). To make these diblock copolymers,
the polyisoprenyl lithium was first synthesized in cyclohexane with s-BuLi as the initiator
Chapter I : Literature on block copolymers based on PI
- 37 -
at 40 °C. The living chain-end is then capped with one ethylene oxide unit. After the
addition of hydrochloric acid, an intermediate polymer containing hydroxyl group at the
chain-end (PI-OH) is obtained. Then, the PI-OH polymer was dissolved in toluene
followed by the addition of triethylaluminum (AlEt3) under an argon atmosphere at 70 °C
leading to the macroinitiator PI-OAlEt2 which was further employed for the
polymerization of D,L-lactide. This reaction was finally terminated by the addition of
hydrochloric acid. Characteristics of the copolymer were determined by 1H NMR
spectroscopy ( nM = 3,600 g.mol-1) and SEC (PDI = 1.26).
+ s BuLi40 °C
Cyclohexanen
n-1Li
1.
2. HClOH
n
OHn
AlEt3, toluene
70 °COAlEt2
n
+ C2H6
OAlEt2n
D,L lactide
O
2. HCl
toluene, 70 °C1.
On
O
O
O
O
m
Scheme I-21. Synthesis of PI-b-PLA block copolymer by the combination of living
anionic polymerization and controlled coordination-insertion polymerization.76
Recently, Carpentier and coworkers77 reported the synthesis of a well-defined PI-b-PLA
diblock copolymer by a combination of living anionic polymerization of isoprene and the
stereoselective ring-opening polymerization of rac-lactide. The copolymer was synthesized
by a two-step sequential procedure.76,78-79 The first step involves the living anionic
polymerization of isoprene, followed by addition of ethylene oxide to end-capped
polymers (PI-OH). In the second step, an aluminium (1, Scheme I-22A) or yttrium (2,
Scheme I-22B) organometallic moiety is grafted onto PI-OH to get PI-O-[Al] or PI-O-[Y]
macroinitiators. The polymerization of rac-lactide with the macroinitiator PI-O-[Y]
occurred under much milder conditions (THF, 20 °C, 1 h) than those required for
PI-O-[Al] (toluene, 70 °C, 96 h). Moreover, the PI-O-[Al] macroinitiator undergoes an
isotactic PLA block as the PI-O-[Y] macroinitiator undergoes a heterotactic PLA block.
The resulting PI-b-PLA copolymers with an isotactic or a heterotactic PLA segment have
nM ≈ 13,600 g.mol-1and polydispersity index of 1.19 determined by SEC.
Chapter I : Literature on block copolymers based on PI
- 38 -
A)
OH
n R-Y[X2]
Me-Al[X'2]
O
n
Y[X2]
O
n
Al[X'2]
O
n
O
O O
O
O
O
OO
H
m
O
n
O
O O
O
O
O
OO
H
m
1. D,L-lactide
2. H+
PI b (het D,L PLA)
THF
20 °C
PI b (iso D,L PLA)
1. D,L-lactide
2. H+
toluene
70 °C
p q
t-Bu O
t-Bu
N N
O t-Bu
t-Bu
Al
Me
t-Bu
t-Bu
N
O Y O
t-Bu
t-BuO
THF
RMe
R = N(SiHMe2)2
B)
1
2
1
2
Scheme I-22. Synthesis of PI-b-PLA block copolymers by a combination of living anionic
polymerization and controlled organometallic-insertion polymerization: A) using an
aluminium based organometallic, and B) using an yttrium based organometallic.77
Miura and Miyake80 investigated the synthesis of polydimethylsiloxane-b-polyisoprene
diblock copolymers by the combination of anionic ring-opening polymerization (AROP) of
hexamethylcyclotrisiloxane (D3) and NMP of isoprene (Scheme I-23). In the first step, an
alkoxyamine (A, Scheme I-23) was treated with Li powder in ether (B, Scheme I-23)
suitable for the AROP of D3. The resulting functional PD3 was employed for the
polymerization of isoprene in bulk at 120 °C in order to obtain PD3-b-PI diblock
copolymer. Characteristics of the copolymer were determined by SEC ( nM = 10,100
g.mol-1, PDI = 1.15) and 1H NMR spectroscopy ( nM = 13,000 g.mol-1). In addition, the
PD3-b-PI was also used as a macroinitiator to prepare PD3-b-PI-b-PS triblock copolymers.
Chapter I : Literature on block copolymers based on PI
- 39 -
BrO N
PhLi, ether
RTLi
O N
Ph(+ LiBr)
D3
O N
PhCH3
m
n
D3
O N
Ph
CH3m
D3, THF
RT
n120 °C
D3 :
(A) (B)
SiO
SiO
Si
O
m
Scheme I-23. Synthesis of PD3-b-PI block copolymer by combination of AROP and
NMP.80
II.3.2 Synthesis of ABA triblock copolymers
The synthesis of ABA triblock copolymers based on isoprene and styrene by a
combination of anionic polymerization and atom transfer radical polymerization81-82
(ATRP) has been described by Matyjaszewski et al.83. The macroinitiator, polystyrene-b-
polyisoprene containing a 2-bromoisobutyryl bromide (BriBBr) chain-end (PS-b-PI-Br)
(Scheme I-24A) was prepared by anionic polymerization. For that, styrene was first
polymerized in toluene at −30°C using BuLi as initiator in dry box. Afterward, isoprene
was added to the solution. The living PS-b-PI−Li+ was chain extended with styrene epoxide
and then terminated by addition of BriBBr (Scheme I-24B). The macromolecular
characteristics of PS-b-PI-Br were determined by SEC ( nM = 16,800 g.mol-1 and
PDI = 1.03). The copolymer composition was determined by 1H NMR spectroscopy ( nDP
(PS) = 58 and nDP (PI) = 160). The PS-b-PI-Br was then used to initiate the
polymerization of styrene by ATRP in bulk at 110 °C using copper bromide (I) complexed
with N, N, N’, N’, N’’-pentamethyldiethylenetriamine (PMDETA) as a catalytic system to
form PS-b-PI-b-PS triblock copolymer. The resulting triblock copolymer had a number-
average molecular weight nM = 32,800 g.mol-1 and a PDI of 1.20.
Chapter I : Literature on block copolymers based on PI
- 40 -
+ s BuLi30 °C
LiPSTHF,
LI30 °C
PS b PITHFH2C CH
O
LIPS b PI CH2 CH O BrPS b PI CH2 CH O C
OBrBr C
O
CuBr, PMDETA, 110 °CPS b PI b PS
A)
BrPS b PI CH2 CH O C
OB)
m
n
x
Scheme I-24. Synthesis of PS-b-PI-b-PS block copolymer by combination of anionic
polymerization and ATRP: A) PS-b-PI-Br diblock copolymer, and B) PS-b-PI-b-PS
triblock copolymers.83
Chapter I : Literature on block copolymers based on PI
- 41 -
Conclusion
Well-defined block copolymers based on polyisoprene and other polymers can be
synthesized either by anionic polymerization, controlled/living radical polymerization or a
combination of various polymerizations. Of these techniques, controlled/living radical
polymerization methods have numerous advantages over the anionic polymerization as the
reactions can be performed under less stringent conditions and they can be applied to a
wide range of functional monomers. These advantages drive us to use controlled/living
radical polymerization and more precisely the RAFT polymerization to synthesize block
copolymers based on polyisoprene as NMP necessitates high temperatures for some
monomers such as styrene and the challenging synthesis of difunctional initiators. The
polyisoprene block is often obtained starting from the isoprene monomer but it can also be
obtained from a biomacromolecule, cis-1,4-polyisoprene, or so called natural rubber (NR).
In this case, telechelics from natural rubber (TNR) are necessary to synthesize block
copolymers. The transformation of NR into TNR can be obtained by chain cleavage
reaction of NR with a functionalization.
In this work, we propose two strategies to prepare AB diblock copolymers based on PI
using the RAFT process:
− starting from synthetic isoprene monomer,
− starting with TNR obtained by oxidative chain cleavage of NR and then chemically
modified by coupling reaction with a RAFT agent.
These PIs are used as macromolecular chain transfer agents (macroCTAs), and then chain
extended with t-BA using RAFT polymerization to make AB diblock copolymers. In
addition, we will demonstrate the synthesis of ABA triblock copolymers based on PI
obtained from a functional metathesis degradation of NR. Such degradation leads to
difunctional PI-macroCTAs which were employed for the RAFT polymerization of t-BA
to form ABA triblock copolymers.
Chapter I : Literature on block copolymers based on PI
- 42 -
References
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Macromolecules 1999, 32, 235-237. [52] Davis, K. A.; Matyjaszewski, K., Adv. Polym. Sci. 2002, 159, 1. [53] Hawker, C. J.; Bosman, A. W.; Harth, E., Chem. Rev. 2001, 101, 3661-3688. [54] Moad, G.; Rizzardo, E.; Thang, S. H., Polymer 2008, 49, 1079-1131. [55] Wootthikanokkhan, J.; Tongrubbai, B., J. Appl. Polym. Sci. 2003, 88, 921-927. [56] Gopalan, P.; Li, X.; Li, M.; Ober, C. K.; Gonzales, C. P.; Hawker, C. J., J. Polym.
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[62] Murthy, K. S.; Ma, Q.; Remsen, E. E.; Tomasz, K.; Wooley, L. K., J. Mater. Chem. 2003, 13, 2785.
[63] Huang, H.; Kowalewski, T.; Wooley, K. L., J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 1659-1668.
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[65] Benoit, D.; Chaplinski, V.; Braslau, R.; Hawker, C. J., J. Am. Chem. Soc. 1999, 121, 3904-3920.
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[67] Yin, X.; Hoffman, A. S.; Stayton, P. S., Biomacromolecules 2006, 7, 1381-1385. [68] Jitchum, V.; Perrier, S., Macromolecules 2007, 40, 1408-1412. [69] Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P. T.;
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[70] Wood, M. R.; Duncalf, D. J.; Rannard, S. P.; Perrier, S., Org. Lett. 2006, 8, 553-556. [71] Germack, D. S.; Wooley, K. L., J. Polym. Sci., Part A: Polym. Chem. 2007, 45,
4100-4108. [72] Lai, J. T.; Filla, D.; Shea, R., Macromolecules 2002, 35, 6754-6756. [73] Germack, D. S.; Wooley, K. L., Macromol. Chem. Phys. 2007, 208, 2481-2491. [74] Bartels, J. W.; Billings, P. L.; Ghosh, B.; Urban, M. W.; Greenlief, C. M.; Wooley,
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Chapter II
Synthesis of block copolymers based
on PI by RAFT process
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 45 -
Introduction
As mentioned in the previous chapter, the successful polymerization of isoprene via the
RAFT process was reported by Perrier et al.1 and by Wooley et al.2-3 Moreover, these
groups demonstrated the ability of RAFT polymerization to prepare AB diblock
copolymers and ABC triblock copolymers. For instance, Perrier et al.1 have prepared well-
defined poly(tert-butyl acrylate)-b-polyisoprene (P(t-BA)-b-PI) and polystyrene-b-
polyisoprene (PS-b-PI) block copolymers. In this study,1 P(t-BA) or PS is first prepared
and then used as a molecular chain transfer agent (macroCTA) to chain extend with
isoprene in order to prepare P(t-BA)-b-PI or PS-b-PI block copolymers. Moreover,
Wooley et al.2 have reported the RAFT polymerization of isoprene to target PI and chain
extended the PI-macroCTA with styrene to form PI-b-PS diblock copolymer. The same
group3 also reported the preparation of P(t-BA)-b-PI-b-PS triblock copolymers via RAFT
polymerization. In this case, P(t-BA) is synthesized first followed by RAFT
polymerization of isoprene. The resulting P(t-BA)-b-PI is then used as a macroCTA for
the RAFT polymerization of styrene.
The aim of the research work described in this chapter is to develop synthetic routes to
obtain well-defined block copolymers based on PI and P(t-BA) via RAFT polymerization.
These copolymers may find applications as compatibilizers for polymer blends,4 surface
modifiers5 and adhesive applications when the tert-butyl group is cleaved in order to form
acrylic acid.
Herein, PI-b-P(t-BA) diblock copolymer was prepared via RAFT polymerization. The
method of synthesis differs from the work by Wooley. et al3 as the blocks are prepared in
the reverse order. In this work, well-defined polyisoprene is first synthesized by RAFT
polymerization using S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid) trithiocarbonate6 (1,
Scheme II-1) as a chain transfer agent. The resulting PI was used as macroCTA to mediate
the RAFT polymerization of t-BA to form PI-b-P(t-BA) block copolymers.
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 46 -
I. Synthesis and characterization of polyisoprene
RAFT polymerization of isoprene was carried out using S-1-dodecyl-S’-(α-α’-dimethyl-
α’’-acetic acid) trithiocarbonate (1, Scheme II-1) and tert-butyl peroxide (t-bp) as initiator
at 125 °C for 25h. Monomer conversion was determined via gravimetry and calculated to
be 49 % conversion.
C12H25S
S
SOH
O
1
C12H25S
S
SO
OH
x y z
0.2 eq t-bp
125 °C, 25h
190 eq1 eq
+
2
Scheme II-1. Synthesis of polyisoprene via RAFT polymerization of isoprene in bulk at
125 °C ([I]0/([1]0/([t-bp]0=190/1/0.2).
The resulting polymer was characterized by 1H NMR spectroscopy and 13C NMR
spectroscopy (Figure II-1) . 1H NMR spectroscopy of a representative polymer (Figure II-
1A) revealed the presence of polyisoprene resonances arising from all three major repeat
unit isomers.7-8 Peaks at 5.84-5.67 ppm, at 5.12 ppm, 4.98-4.81 ppm and at 4.75-4.61 ppm
are corresponding to methine protons, 11 (1,2-polyisoprene, -HC=CH2), methine protons,
7 (1,4-polyisoprene, C(CH3)=CH ), methylene protons 12 (1,2-polyisoprene backbone, -
HC=CH2) and methylene protons 16 (3,4-polyisoprene backbone, (CH3)C=CH2),
respectively. The ratio of each isomer was calculated from integrals of the peaks of the 1,2-
polyisoprene at the range of 5.84-5.67 ppm, integrals the peaks of the 3,4-polyisoprene at
the range of 4.75-4.61 ppm and integrals of the 1,4-polyisoprene at 5.12 ppm by 1H NMR
spectroscopy. The polymer obtained had a ratio of 90% of 1,4-polyisoprene, 6% of 3,4-
polyisoprene and 4% of 1,2-polyisoprene. This ratio is essentially the same as previously
reported for polyisoprene prepared by NMP9-10 and RAFT1-3 which showed a
microstructure of predominately 1,4-addition units.
The arrangement of the internal trans and cis units can be determined by the 13C NMR
spectroscopy.11-14 Figure II-1 shows the 13C NMR spectrum (Figure II-1C) and the
DEPT-135 spectrum (Figure II-1B ) of polyisoprene. The signals at 125.11 and at 124.46
ppm are assigned to the methine carbon, 7 (-C(CH3)=CH-) of the trans and cis-1,4-
polyisoprene units, respectively. The signal at 40.03 ppm corresponds to the methylene
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 47 -
carbon (4, -CH2-(CH3)C=CH-) in the trans-1,4-polyisoprene and the signal at 32.26 ppm
corresponds to methylene carbon (4, -CH2-(CH3)C=CH-) in the cis-1,4-polyisoprene. In
addition, it was observed the signal at 23.36 ppm corresponding to methyl carbon in cis-
1,4-polyisoprene (6, -C(CH3)=CH-), while it appears at 16.00 ppm in trans-1,4-
polyisoprene. 13C NMR spectroscopy (Figure II-1C ) was used to estimate the relative
contents of the cis- and trans-1,4-polyisoprene. The signal at 23.36 ppm corresponds to the
methyl carbon (6, -C(CH3)=CH-) in the cis-1,4-polyisoprene and the signal at 16.00 ppm
corresponds to the methyl carbon (6, -C(CH3)=CH-) in the trans-1,4-polyisoprene. The
areas under those peaks at 23.36 ppm and at 16.00 ppm obtained by inverse gated
decoupling are used to estimate the ratio of the cis- and trans-1,4-polyisoprene. The area
ratio indicates that there is about 40% of the cis- and 60% of the trans-1,4-polyisoprene.
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 48 -
CH2
S
S
SO
OH
x y z
C10H20CH3
1
2
34
5
6
7
89
11
10
12
13 14
15
1617
1819
20 21
22
11 10 9 8 7 6 5 4 3 2 1 ppm
1
2
311
7
12 16 -CHSC(S)S
9
6(trans-), 17
6(cis-)
14
4, 8, 13, 18
210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm
210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm
1
2210,15
5 (trans-)
5 (cis-)
7 (cis-)
7 (trans-)
1216
CDCl3
1318
19
4 (trans-)
6 (trans-)6 (cis-)
17
8(cis-)
8(trans-)
3
4 (cis-)
-CH
-CH
3
2
-CH
Figure II-1. A) 1H NMR spectrum, B) DEPT-135 spectrum and C) 13C NMR spectrum of
polyisoprene synthesized by RAFT polymerization of isoprene in bulk at 125 °C
([I] 0/([1]0/([t-bp]0=190/1/0.2).
Confirmation of successful RAFT polymerization of isoprene was further provided by
FTIR spectroscopy (Figure II-2) . A band was observed at 1700 cm-1 corresponding to the
C=O stretching band of carbonyl group and a band was observed at 1070 cm-1
A)
B)
C)
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 49 -
corresponding to the stretching band of C=S trithiocarbonate group15-16 at the chain-end. A
strong band at 1664 cm-1 was observed which corresponds to the C=C double bonds in
polyisoprene.
4000 3500 3000 2500 2000 1500 1000 500
-20
0
20
40
60
80
100
120
C=S
1070-C=C-
1664
-C=O
1700
Tra
nsm
ittan
ce (
%)
Wavenumber (cm-1)
Figure II-2. FTIR spectrum of polyisoprene synthesized by RAFT polymerization of
isoprene in bulk at 125 °C ([I]0/[1]0/[t-bp]0=190/1/0.2).
The number-average degree of polymerization of PI is equal to 90 ( nM = 6,500 g. mol-1)
by comparing the integration of methylene protons of the chain-ends, 3 (Figure II-1A) at
3.32 ppm to the integrations of the methine protons of the 1,4-polyisoprene repeating unit,
7 (Figure II-1A) at 5.12 ppm, of the 1,2-polyisoprene repeating unit, 11 (Figure II-1A) at
5.84-5.67 ppm and of the methylene protons of the 3,4-polyisoprene repeating unit, 16
(Figure II-1A) at 4.98-4.81 ppm. A molecular weight of nM = 9,200 g. mol-1 and
polydispersity index (PDI) = 1.23 was determined by SEC.
The 1H NMR spectroscopy, 13C NMR spectroscopy, FT-IR and SEC data,
show that the RAFT polymerization of isoprene has been successful and leads to a well-
defined ω-trithiocarbonyl-polyisoprene which can further be used as a macroCTA to target
new well-defined block copolymers.
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 50 -
II. Synthesis and characterization of polyisoprene-b-poly(tert-butyl
acrylate) block copolymers
We investigated the synthesis of a PI-b-P(t-BA) diblock copolymer using a PI as a
macroCTA (2, Scheme II-2). The reaction was performed in bulk at 60 oC and AIBN was
used as an initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0=250/1/0.2). Monomer conversion was
determined by following the disappearance of the vinyl peaks of t-BA at the range of 6.40
to 5.60 ppm in comparison with methyl protons of anisole used as an internal standard at
3.75 ppm by 1H NMR spectroscopy.
CH2
S
S
SO
OH
81 4 5
C10H20CH3
CH2
S
S
SO
OH
81
C10H20CH3
O O
72
54
0.2 eq AIBN
60 °C, 2.5h
O O250 eq
90
90
2
3
Scheme II-2. Synthesis of PI-b-P(t-BA) via RAFT polymerization of t-BA in bulk at
60 °C ([t-BA] 0/[PI-macroCTA]0/[AIBN] 0=250/1/0.2).
After a polymerization time of 4h, the t-BA conversion reaches 48% (Table II-1). The
block copolymer had a number-average molecular weight of 24,400 g. mol-1 and a
polydispersity index of 1.55 as determined by SEC. The overlaid of the SEC traces of
copolymers obtained at different reaction times is presented in Figure II-3 . It shows a shift
of the SEC chromatograms toward earlier retention times corresponding to higher
molecular weights when the reaction time increases (Table II-1 and Figure II-3) .
However, a high molecular weight shoulder appeared on SEC traces (Figure II-3) when
the monomer conversion reaches 48%. This indicates that the level of control is slightly
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 51 -
deteriorated; this is confirmed by PDI values, which increase from 1.23 to 1.55. This
phenomenon could be explained by the presence of termination by combination between
growing radical chains. This feature has already been observed in RAFT polymerizations
of acrylates (e.g. methyl acrylate, butyl acrylate).17-18 Previous work has shown that the
shoulder became more pronounced with conversion and was most evident for higher
molecular weight polymers. The Table II-1 shows that the best result in terms of monomer
conversion, nM and PDI was obtained after 2.5h. The number-average molecular weights
determined experimentally using SEC (Table II-1) for the diblock copolymers are in good
agreement with the theoretical calculated values. This confirms that there is a good control
over molecular weights.
Table II-1. Synthesis of PI-b-P(t-BA) diblock copolymers via RAFT polymerization of
t-BA in bulk at 60°C ([t-BA] 0/[PI-macroCTA]0/[AIBN] 0 = 250/1/0.2).
Copolymer Reaction time
(h)
conv.a
(%)
bcalnM ,
(g. mol-1)
cSECnM ,
(g. mol-1)
PDId
S-0 0.00 0 9200 9200 1.23
S-1 1.50 8 11 760 12 000 1.26
S-2 2.50 22 16 240 16 000 1.40
S-3 3.25 37 21 040 21 000 1.55
S-4 4.00 48 24 560 24 000 1.55 aMonomer conversion determined using 1H NMR spectroscopy. bNumber-average molecular weight
calculated using: calnM , = (conversion (%)×[M] 0/[MacroCTA]0×MM)+MmacroCTA where [M]0, [MacroCTA]0,
MM and MmacroCTA are the initial concentration of t-BA monomer, the initial concentration of polyisoprene macroCTA, the molecular weight of t-BA monomer and the molecular weight of the polyisoprene macroCTA respectively. cNumber-average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards. dPolydispersity index measured by SEC.
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 52 -
9 10 11 12 13 14 15 16 17 18
Retention time (mins)
PI
PI-b-P(t-BA)_1.5h
PI-b-P(t-BA)_2.5h
PI-b-P(t-BA)_3.25h
PI-b-P(t-BA)_4h
Figure II-3. Overlaid SEC traces of PI-macroCTA and PI-b-P(t-BA) diblock
copolymers synthesized via RAFT polymerization of t-BA in bulk at 60 °C
([t-BA] 0/[PI-macroCTA]0/[AIBN] 0 = 250/1/0.2).
The molar composition of the diblock copolymer was determined by comparing the
integral of the ethylenic proton, 7 (Figure II-4A) , of the 1,4-polyisoprene backbone (set
equivalent to the degree of polymerization of 81) at resonance at 5.12 ppm to the methine
proton, 23 (Figure II-4A), of P(t-BA) resonances at 2.4-2.1 ppm on the 1H NMR spectrum
of the copolymer (Figure II-4A) . It was found that the diblock copolymer contains 47% of
P(t-BA) for 53% of 1,4-polyisoprene. Therefore, the number-average degree of
polymerization )DP( n of PI is equal to 90 and the nDP of P(t-BA) is equal to 72. Finally,
the molar composition of the diblock copolymer is equal to 55.5% of PI and 44.5% of
P(t-BA).
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 53 -
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 ppm
1
2
3
4, 8, 13, 18
23
27
26
7
6 (trans-), 17
6 (cis-)
9
11 12 16
CH2
S
S
SO
OH
81
C10H20CH3
1
2
34
5
6
7
89
11
10
12
13 14
15
1617
1819
20 21
22
O O
72
54
2327
25
26
24
2626 90
A)
B)
Figure II-4. A) 1H NMR spectrum, and B) 13C NMR spectrum of PI-b-P(t-BA) diblock
copolymer (S-2, Table II-1) synthesized via RAFT polymerization of t-BA in bulk at
60 °C ([t-BA] 0/[PI-macroCTA]0/[AIBN] 0 = 250/1/0.2).
The copolymer structure was further confirmed by the 13C NMR spectrum, (Figure II-4B)
which showed the carbonyl carbon resonance at 174.16 ppm and the quaternary carbon at
80.41 ppm corresponding to P(t-BA) and also presented carbon resonances at 135.39,
135.22, 125.30, and 124.50 ppm, corresponding to those observed for polyisoprene earlier
in this chapter. The data obtained from SEC, 1H NMR spectroscopy and 13C NMR
spectroscopy provides additional evidence for the formation of the AB diblock copolymer.
210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm
5 (trans-)5 (cis-)
7 (cis-)
7 (trans-)
1
6 (trans-)
6 (cis-)
17
4 (trans-)
26
2524
23
4 (cis-)
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 54 -
Conclusion
We have demonstrated that the RAFT polymerization of isoprene leads to well-defined
polyisoprenes (PI) with 90% of 1,4-PI (60% trans and 40% cis), 4% of 1,2-PI and 6% of
3,4-PI as determined by 1H NMR spectroscopy and 13C NMR spectroscopy. The nM is
equal to 6,500 g. mol-1 and PDI to 1.23 as determined by SEC. The formation of block
copolymers PI-b-P(t-BA) via RAFT mediated polymerization using the resulting PI as
macroCTA, was investigated. We found that the used of [t-BA] 0/[macroCTA]0/[AIBN] 0
equal to 250/1/0.2 in bulk at 60°C for 2.5h leads to a block copolymer with a good control
over molecular weight and relatively low polydispersity index (1.40). The copolymer had a
nM equal to 16,000 g. mol-1 as determined by SEC and a nDP (PI) of 90 and a nDP
(P(t-BA)) of 72 as determined by 1H NMR spectroscopy.
The optimized conditions previously determined to produce PI-b-P(t-BA) block
copolymers were employed to produce original block copolymers from natural rubber and
P(t-BA). In that case, polyisoprene was obtained by oxidative chain cleavage of natural
rubber and then chemically modified by coupling reaction with a RAFT agent. The results
are described in Chapter III.
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 55 -
Experimental section
General Characterization. NMR spectra were recorded on a Bruker Avance 400
spectrometer for 1H NMR (400 MHz) and 13C NMR (100 MHz). Chemical shifts are
reported in ppm relative to the deuterated solvent resonances. Molecular weights and
molecular weight distributions were measured using size exclusion chromatography (SEC)
on a system equipped with a SpectraSYSTEM AS 1000 autosampler, with a Guard column
(Polymer Laboratories, PL gel 5 µm Guard column, 50 × 7.5 mm) followed by two
columns (Polymer Laboratories, 2 PL gel 5 µm MIXED-D columns, 2 × 300 × 7.5) and
with a SpectraSYSTEM RI-150 detector. The eluent used was tetrahydrofuran (THF) at a
flow rate of 1 mL min-1 at 35°C. Narrow molecular weight linear polystyrene standards
(ranging from 580 g. mol-1 to 4.83 × 105 g. mol-1) were used to calibrate the SEC. Infrared
spectra were recorded on a Nicolet Avatar 370 DTGS FT-IR spectrometer in the 4000–500
cm-1 range with KBr pellets and controlled by OMNIC software.
.
Materials. All chemicals were purchased from Aldrich unless otherwise noted. Isoprene
monomer (I, Acros, 99%), tert-butyl acrylate (t-BA), 99%) was purified by passing
through neutral alumina column to remove inhibitor. 2,2-Azobis(2-methylpropionitrile)
(AIBN, 98%) was recrystallized into methanol prior to use. Anisole (99%) were used as
received. Dichloromethane (99%+) and methanol (99%) were distilled over CaH2 prior to
use. The RAFT agent, S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid) trithiocarbonate, (1,
Scheme II-1) was synthesized as described in an earlier publication.6
General method for the preparation of polyisoprene by RAFT polymerization. RAFT
polymerization of isoprene was conducted with S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic
acid) trithiocarbonate (1, Scheme II-1) as RAFT agent and tert-butyl peroxide (t-bp) as the
initiator in a manner similar to that previously reported,2-3 ([I] 0/[1]0/[t-bp]0 = 190/1/0.2).
Because of the high volatility of isoprene and the high temperatures employed in the
polymerization thereof, only thick-walled glass flasks, free of visible defects, were used for
these experiments, each conducted with at least 50% of the volume of the flask remaining
free. Briefly, a solution of 6 mL (59.9 mmol) of isoprene, 0.115 g (0.3158 mmol) of 1,
0.0115 mL (0.0615 mmol) of t-bp were deoxygenated by bubbling with argon for 15 min,
and then changed from a rubber septum to a Teflon screw cock. Polymerization was
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 56 -
initiated by immersion in oil bath at 125°C. After 25 h, the reaction mixture was removed
from the oil bath and cooled under cold running water for 15 min. The polymer was
isolated by removal of excess isoprene in vacuo to give a crude product (2.1279 g) as clear
yellow oil. The crude product was diluted with 10 mL CH2Cl2 and precipitated twice into
methanol and dried in vacuo to give the final product as viscous, clear yellow oil. It was
then analyzed by 1H NMR spectroscopy, 13C NMR spectroscopy, FTIR spectroscopy and
SEC. The final product consisted of 1.7779 g (83% yield based on 49% conversion via
gravimetry).
1H-NMR (CDCl3): δ (ppm) 5.84-5.67 (m, 1,2-polyisoprene backbone, -HC=CH2), 5.12
(br, cis-1,4-polyisoprene backbone, -C(CH3)=CH), 4.98-4.81 (m, 1,2-polyisoprene
backbone, -HC=CH2), 4.75-4.61 (m, 3,4-polyisoprene backbone, (CH3)C=CH2), 4.1-4.0
(br, chain-end, (-CH-SC(S)-S-), 3.32 (t, chain-end, -C(S)-SCH2(CH2)10CH3), 2.42–1.93
(br, polyisoprene backbone, -CH2C(CH3)=CH-CH2), 1.87 (br, 3,4-polyisoprene backbone,
-CH2-CH-) 1.67 (t, cis-1,4-polyisoprene backbone, -C(CH3)=CH) 1.60 (t, trans-1,4 and
3,4-polyisoprene backbone, -C(CH3)=CH), 1.13-1.48 (m, chain-end, -C(S)-SCH2-(CH2)10-
CH3), 0.98 (1,2-polyisoprene backbone, -C(CH3)-CH2), 0.88 (t, chain-end, -C(S)-S-
(CH2)11CH3).
13C NMR (CDCl3): δ (ppm) 184.37 (chain-end, -C=O), 147.78 (3,4-polyisoprene
backbone, -C(CH3)=CH2), 147.69 (1,2-polyisoprene backbone, -CH=CH2), 135.39 (trans-
1,4-polyisoprene backbone, -C(CH3)=CH-), 135.22 (cis-1,4-polyisoprene backbone,
-C(CH3)=CH-), 125.11 (cis-1,4-polyisoprene, -C(CH3)=CH-), 124.46 (trans-1,4-
polyisoprene, -C(CH3)=CH-), 115.93 (1,2-polyisoprene, -CH=CH2), 111.30 (3,4-
polyisoprene backbone, C(CH3)=CH2), 51.83 (1,2-polyisoprene backbone, -CH2-C(CH3)-),
50.27 (3,4-polyisoprene backbone, -CH2-CH-), 42.21 (chain-end, -C(CH3)2-),
40.03 (trans-1,4-polyisoprene, -CH2-(CH3)C=CH-), 38.48 (3,4-polyisoprene,
-HC(C(CH3)=CH2)-CH2), 36.89 (chain-end, C(S)-SCH2CH2-), 32.26 (cis-1,4-polyisoprene,
-CH2C(CH3)=CH-), 31.92, 29.64, 29.63, 29.57, 29.46, 29.35, 29.12, 28.95, 27.86 (chain-
end, -SCH2(CH2)9CH2CH3), 26.71 (trans-1,4-polyisoprene backbone, -C(CH3)=CH-CH2-),
26.38 (cis-1,4-polyisoprene, -C(CH3)=CH-CH2-), 23.36 (cis-1,4-polyisoprene,
-C(CH3)=CH-), 22.87 (3,4-polyisoprene, C(CH3)=CH2), 22.70 (chain-end,
-S(CH2)9CH2CH3), 16.0 (trans-1,4-polyisoprene, ,-CH2-C(CH3)=CH-), 14.14 (chain-end,
-C(S)-S-(CH2)11-CH3).
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 57 -
FTIR: ν (cm-1) 3035 (H-C=C), 2900−2730 (CH2, CH3), 1700 (chain-end, -C=O),
1665 (polyisoprene backbone, -C=C-), 1448 (polyisoprene backbone, -CH2), 1376
(polyisoprene backbone, -CH2), 1070 (chain-end, C=S), 836 (polyisoprene backbone, -CH)
SEC: nM = 9,200 g. mol-1, wM = 11,200 g. mol-1, PDI =1.23
RAFT polymerization of tert-butyl acrylate using PI-macroCTA. A typical procedure
is given for the polymerization of tert-butyl acrylate (t-BA) mediated by polyisoprene (2,
Scheme II-1) used as macroCTA and using AIBN as initiator
([t-BA] 0/[PI-macroCTA]0/[AIBN] 0 = 250/1/0.2). A magnetic stir bar was charged to a
Schlenk tube together with the PI-macroCTA (0.3216 g, 0.0495 mmol), t-BA (1.5832 g,
12.37 mmol), AIBN (0.0016 g, 0.0098 mmol), and anisole (0.09 mL, 5% v/v). Then, the
reaction mixture was degassed by three cycles of freeze pump-thaw, back-filled with Ar,
and sealed. The polymerization was initiated (t = 0) by immersion in a thermostatted oil
bath at 60°C. Samples were withdrawn from the reaction mixture via a degassed syringe
for conversion monitoring (by 1H NMR spectroscopy) and molecular weight analysis (by
SEC). At the end of reaction, the polymer solution was concentrated under vacuum using
rotary evaporation and was purified by a series of precipitations from dichloromethane
(minimum volume) into an ice cold 1:1 mixture of water and methanol. The copolymer
was separated by filtration and dried under vacuum until constant weight. It was then
further analyzed by 1H NMR spectroscopy, 13C NMR spectroscopy and SEC. Yield: 78%.
1H NMR (CDCl3): δ (ppm) 5.84-5.67 (m, 1,2-polyisoprene, -HC=CH2), 5.12 (br, 1,4-
polyisoprene, -C(CH3)=CH), 4.98-4.81 (m, 1,2-polyisoprene, -HC=CH2), 4.75-4.61
(m, 3,4-polyisoprene, (CH3)C=CH2), 3.32 (t, chain-end, -C(S)-SCH2(CH2)10CH3), 2.40-
2.15 (br, P(t-BA), -CH2-CHC(O)-), 2.42–1.93 (br, polyisoprene, -CH2C(CH3)=CH-CH2),
1.90-1.70 (br, P(t-BA), -CH2-CHC(O)-), 1.67 (t, cis-1,4-polyisoprene, -C(CH3)=CH),
1.60 (t, trans-1,4 and 3,4-polyisoprene, -C(CH3)=CH), 1.48-1.38 (br, P(t-BA),
-OC(CH3)3), 1.35-1.25 (m, chain-end, -C(S)-S-CH2-(CH2)10CH3), 1.22 (m, 1,2-
polyisoprene -CH2-C(CH3)-, and 3,4-polyisoprene, -CH2-CH-), 0.98 (1,2-polyisoprene, -
C(CH3)-CH2), 0.88 (t, chain-end, -C(S)-S-(CH2)11CH3).
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 58 -
13C NMR (CDCl3): δ (ppm) 174.16 (P(t-BA) backbone, -C(O)-O-), 135.39 (trans-1,4-
polyisoprene backbone, -C(CH3)=CH-), 135.22 (cis-1,4-polyisoprene backbone,
-C(CH3)=CH-) 125.11 (cis-1,4-polyisoprene, -C(CH3)=CH-), 124.27 (trans-1,4-
polyisoprene, -C(CH3)=CH-), 80.41 (P(t-BA) backbone, -C(O)-O-C(CH3)3), 42.42
(P(t-BA) backbone, -CHC(O)-O-C(CH3)3), 38.78 (trans 1,4-polyisoprene,
-CH2-(CH3)C=CH-), 38.48 (3,4-polyisoprene, -HC(C(CH3)=CH2)-CH2), 36.89 (chain-end,
C(S)-SCH2CH2-), 32.26 (cis-1,4-polyisoprene, -CH2C(CH3)=CH-), 31.92, 29.64, 29.63,
29.57, 29.46, 29.35, 29.12, 28.95, 27.86 (chain-end, -SCH2(CH2)9CH2CH3), 28.10 (P(t-
BA) backbone, -O-C(CH3)3), 26.75 (cis- 1,4-polyisoprene backbone, -CH2C(CH3)=CH-),
23.47 (cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 22.87 (3,4-polyisoprene,
C(CH3)=CH2), 22.70 (chain-end, -S(CH2)9CH2CH3), 16.0 (trans-1,4-polyisoprene, -CH2-
C(CH3)=CH- ), 14.14 (chain-end, -C(S)-S-(CH2)11-CH3).
SEC: nM = 16,000 g. mol-1, wM = 22,000 g. mol-1, PDI =1.40
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 59 -
References [1] Jitchum, V.; Perrier, S., Macromolecules 2007, 40, 1408-1412. [2] Germack, D. S.; Wooley, K. L., J. Polym. Sci., Part A: Polym. Chem. 2007, 45,
4100-4108. [3] Germack, D. S.; Wooley, K. L., Macromol. Chem. Phys. 2007, 208, 2481-2491. [4] Wootthikanokkhan, J.; Tongrubbai, B., J. Appl. Polym. Sci. 2003, 88, 921-927. [5] Lu, Z.; Liu, G.; Liu, F., J. Appl. Polym. Sci. 2003, 90, 2785-2793. [6] Lai, J. T.; Filla, D.; Shea, R., Macromolecules 2002, 35, 6754-6756. [7] Chen, H. Y., Anal. Chem. 1962, 34, 1134-1136. [8] Chen, H. Y., Anal. Chem. 1962, 34, 1793-1795. [9] Benoit, D.; Harth, E.; Fox, P.; Waymouth, R. M.; Hawker, C. J., Macromolecules
2000, 33, 363-370. [10] Wegrzyn, J. K.; Stephan, T.; Lau, R.; Grubbs, R. B., J. Polym. Sci., Part A: Polym.
Chem. 2005, 43, 2977-2984. [11] Tanaka, Y.; Sato, H.; Kageyu, A., Polymer 1982, 23, 1087-1090. [12] Tanaka, Y.; Takagi, M., Biochem. J 1979, 183, 163-165. [13] Tanaka, Y.; Sato, H.; Kageyu, A.; Tomita, T., Biochem. J 1987, 243, 481-485. [14] Dai, L., Macromol. Chem. Phys. 1997, 198, 1723-1738. [15] Whalley, E., Can. J. Chem. 1960, 38, 2105-2108. [16] You, Y. Z.; Hong, C. Y.; Pan, C. Y., Macromol. Rapid Commun. 2002, 23, 776-780. [17] Chong, Y. K.; Krstina, J.; Le, T. P. T.; Moad, G.; Postma, A.; Rizzardo, E.; Thang, S.
H., Macromolecules 2003, 36, 2256-2272. [18] Moad, G.; Mayadunne Roshan, T. A.; Rizzardo, E.; Skidmore, M.; Thang San, H.,
ACS Symp. Ser. 2003, 854, 520-535.
Chapter III
Synthesis of natural rubber-based
telechelic cis-1,4-polyisoprenes and
their use to prepare block copolymers
via RAFT polymerization
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 60 -
Synthesis of natural rubber-based telechelic cis-1,4 polyisoprenes and
their use to prepare block copolymers via RAFT polymerization
Nitinart Saetung, Irène Campistron, Sagrario Pascual, Jean-Claude Soutif, Jean-François Pilard* and Laurent Fontaine*
LCOM-Chimie des Polymères, UCO2M, UMR CNRS 6011, Université du Maine, Avenue Olivier. Messiaen, 72085 Le Mans Cedex 09, France.
Fax: (+33 (0)2 43 83 37 54)
E-mail: [email protected]; [email protected]
Publication accepted in European Polymer Journal, Ref. No. EUROPOL-D-10-01369R1
Graphical abstract
(COCl)2n
mCPBAH5IO6
C12H25S
S
S OH
O
NH4(OAc)
m
OC12H25
S
S
SO
NH
m
OH2N
m
OC12H25
S
S
SO
NH
O O
k
60 °C, toluene
AIBN, t-BA
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 61 -
ABSTRACT : A new trithiocarbonate functionalized cis-1,4-polyisoprene was obtained
from oxidative degradation of natural rubber followed by reductive amination and
amidation. The structure of the resulting functionalized cis-1,4-polyisoprene was
confirmed by a combination of 1H NMR spectroscopy, 13C NMR spectroscopy, MALDI-
TOF mass spectrometry and FTIR spectroscopy. 1H NMR spectroscopy showed that the
trithiocarbonate functionality was equal to 1. The well-defined trithiocarbonyl-end
functionalized cis-1,4-polyisoprene was used as a macromolecular chain transfer agent
(macroCTA) to mediate the RAFT polymerization of t-BA using AIBN as the initiator ([t-
BA] 0/[macroCTA]0/[AIBN] 0 = 250/1/0.2) in toluene at 60 °C. The resulting PI-b-P(t-BA)
diblock copolymer presents an unimodal SEC trace shifted toward higher molecular weight
in comparison with the SEC trace of the macroCTA, indicating that the polymerization of
the second block is effective. The characteristics of the copolymer were determined by
SEC nM( = 26,000 g.mol-1, PDI = 1.76) and 1H NMR spectroscopy ( nDP (PI) = 62 and
nDP (P(t-BA) = 87).
Keywords: natural rubber, cis-1,4-polyisoprene, oxidative degradation, telechelics,
reversible addition fragmentation chain transfer (RAFT).
Introduction
The synthesis of functional polymers from renewable resources1-2 has attracted
considerable attention from polymer scientists throughout the world because of
environmental problems. Natural rubber (NR) is interesting to use for producing new
polymeric materials because it can be recyclable or degradable when exposed to
sunlight3-4, ozone5, and long term heating6-9 due to the unsaturation of the carbon-carbon
double bonds within the isoprene backbone. NR is also interesting for its strictly cis-1,4-
microstructure that provides materials with unique and special properties including good
elastomeric properties. In order to enhance potential applications of NR, numerous new
telechelic oligoisoprenes from NR with high content in cis-1,4-structure with precise
chain-end functionalities have been developed10. Redox reaction11-12, photochemical
reaction13-14, chemical oxidation15-18, as well as ozonolysis19, have been widely exploited to
produce telechelic cis-1,4-polyisoprene from natural rubber. In this respect, our group has
developed a selective degradation of natural rubber leading to new carbonyl telechelic cis-
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 62 -
1,4-polyisoprene via a two-step procedure20-22. These carbonyl telechelic polyisoprenes are
useful functional materials used as precursors for thermoplastic elastomers23,
biomaterials24 and polyurethane materials.21-22,25-26 Moreover, telechelic polyisoprene
could be obtained from synthetic cis-1,4-polyisoprene either by oxidative degradation25,27
or by metathesis degradation28-29. Telechelic polyisoprene could also be synthesized via the
ring-opening metathesis polymerization of 1,5-dimethyl-1,5-cyclooctadiene30. However,
by this method Grubbs et al.30 showed that there is a formation of a random distribution of
the various isomeric units along the chain resulting from cis-1,4 and trans-1,4-addition. By
contrast, natural rubber features only the cis-1,4-microstructure. To the best of our
knowledge, no work has been reported yet to prepare telechelic cis-1,4-polyisoprene from
natural rubber as precursor for controlled/living radical polymerization (CRP) in order to
obtain well-defined block copolymers.
Amongst CRP techniques, Nitroxide Mediated Radical Polymerization (NMP)31, Atom
Transfer Radical Polymerization (ATRP)32 and Reversible Addition/Fragmentation chain
transfer (RAFT)33-34 polymerization have been intensively used during the last decades to
produce block copolymers. The RAFT polymerization is probably the most versatile of the
commonly used CRP techniques as it is effective for a wide range of monomers and then,
leads to a wide range of block copolymers. In the RAFT process, generally block
copolymers are synthesized in two steps35. The first block was synthesized using a chain
transfer agent to control the number-average molecular weight, the molecular weight
distribution and the chain-end functionality of the polymer. Then, this well-defined block
is used as a macromolecular chain transfer agent (macroCTA) to synthesize the second
block.
In the present work, we report an original strategy for the synthesis of α-trithiocarbonyl-ω-
carbonyl-cis-1,4-polyisoprene (4, Scheme III-1) suitable to be used as macroCTA for
RAFT polymerization. The functionalized cis-1,4-polyisoprene (4, Scheme III-1) is then
used as monofunctional macroCTA to mediate the RAFT polymerization of tert-
butylacrylate to form AB diblock copolymers. To the best of our knowledge, no previous
studies have been reported on the synthesis of telechelic cis-1,4-polyisoprene suitable to be
used as macroCTA for RAFT polymerization.
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 63 -
n n-mm
O
1
mCPBA
CH2Cl2
H5IO6
THF m
OO
2
NH4(OAC)/NaBH(OAC)3
CH2Cl2, 24h, 25°Cm
OH2N3
C12H25S
S
S OH
O
2. (COCl)2,
CH2Cl2, 24h, 25°C
1.
m
OHN
OSS
C12H25
S
4
Scheme III-1. Synthesis of α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene.
I. Synthesis of αααα-trithiocarbonyl- ωωωω-carbonyl-cis-1,4-polyisoprene
Herein, α-amino-ω-carbonylpolyisoprene21,25,37 (2, Scheme III-1) was reacted with S-1-
dodecyl-S’-(α-α’-dimehyl-α’’-acetic acid) trithiocarbonate (3, Scheme III-1) in the
presence of oxalyl chloride in dichloromethane at 25 °C for 24h. The resulting
functionalized polyisoprene (4, Scheme III-1) was characterized by 1H NMR
spectroscopy, 2D HSQC (Heteronuclear Single-Quantum Correlation) experiment, 13C
NMR spectroscopy and MALDI TOF mass spectrometry. The 1H NMR spectroscopy
(Figure III-1) showed new signals at 3.05 ppm and at 2.80-2.70 ppm corresponding to
methylene protons 7 (-CH2NHC(O)) and proton 6 (-NHC(O)), respectively. This result
indicated that the amidation between the amino group of oligoisoprene (2, Scheme III-1)
and in situ formed carboxylic chloride of RAFT agent (3, Scheme III-1) occurred and the
α-trithiocarbonyl-ω-carbonylpolyisoprene (4, Scheme III-1) was formed. 2D HSQC
experiment was used to confirm the structure of the functionalized polyisoprene. The 2D
HSQC spectrum is shown in Figure III-1. The signal at 3.05 ppm corresponding to
methylene protons in the 1H NMR spectrum was reasonably correlated with the signal at
45.00 ppm in the 13C NMR spectrum. Thus, it was confirmed that a new functionalized α-
trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene (4, Scheme III-1) was formed. Moreover,
an intense signal at 5.12 ppm in 1H NMR spectrum (Figure III-1) corresponding to vinylic
protons (9,-(CH3)C=CHCH2-) was observed, indicating that the 1,4-microstructure is
prominent. The 13C NMR spectroscopy (Figure III-2) was used to identify the 1,4-
microstructure of telechelic polyisoprenes.38 The signals observed at 135.23 (10,
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 64 -
-C(CH3)=CH-), 125.28 (9, -C(CH3)=CH-), 32.13 ppm (8’, -CH2C(CH3)=CH-), 26.36 (8, -
C(CH3)=CHCH2-), and 23.36 ppm (11, -C(CH3)=CH-) correspond to cis-1,4-polyisoprene
units.39 There are no signals at 131.20 ppm (-C(CH3)=CH-), 124.27 (-C(CH3)=CH-), 40.02
ppm (-C(CH3)=CHCH2-), 16.00 (-C(CH3)=CH-) characteristics of trans-1,4-polyisoprene
units40. This result confirmed that α-triocarbonyl-ω-carbonylpolyisoprene has a cis-1,4-
microstructure.
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 65 -
m
OHN
O
SS
SCH2
CH2
(CH2)9
1
2 3
4
5
68'
7
8
914
13
12
5
10
11
H3C
2'
10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 ppm
2.62.83.03.23.4 ppm
2.04
2.00
1
2
36
9
11
12
8,8'
145
7 , 2’
ppm
8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 ppm
140
130
120
110
100
90
80
70
60
50
40
30
20
10
1
1
3
3
7
12
12
7
Figure III-1. 1H NMR spectrum and 2D HSQC spectrum of α-trithiocarbonyl-ω-carbonyl-
cis-1,4-polyisoprene (4, Scheme III-1).
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 66 -
m
OHN
O
SS
SCH2
(CH2)10
CH3
1
2
3
4
5
68'
7
8
914
13
12
5
10
11
220 210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm
1
88'10 9
12
3
11
134
14
27
Figure III-2. 13C NMR spectrum of α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene (4,
Scheme III-1).
The reaction between the in situ formed carboxylic chloride of the RAFT agent (3, Scheme
III-1) and the α-amino group of functionalized polyisoprene (2, Scheme III-1) was further
studied by MALDI-TOF MS analysis by using dithranol as matrix with silver
trifluoroacetate as added salt. Figure III-3 shows an enlargement from 800 to 1400 g mol-1
of the MALDI-TOF-MS spectrum of α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene.
There are two sets of peaks separated by an identical peak-to-peak mass increment, which
is equal to the molecular weight of the isoprene repeating unit (68 Da). Here, the two sets
of molecular ions are labelled as A’ and B’ (Figure III-3) in ascending order of m/z
magnitude. Each peak of set A’ is higher in intensity than the corresponding peak of set B’,
separated by 16 in m/z corresponding to the presence of an epoxide unit in the main chain.
These epoxide units come from the uncomplete oxidative chain cleavage reaction used to
prepare the initial carbonyl telechelic cis-1,4-polyisoprene and have been previously
observed25,41. The fragment ion at m/z = 814.62 of series A’ (Figure III-2) corresponds to
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 67 -
a polymer chain consisting of n =9 isoprene units ionized by a hydrogen atom with a
sulfonium (EG1, Scheme III-2) at one chain-end and a ketone group (EG2, Scheme III-2)
at the other chain-end. The theoretical mass calculated with the equation (1) is 814.65 Da
(monisotopic peak) in good agreement with the experimental values of 814.62 Da,
confirming the formation of such a structure. The occurrence of fragmentation during
ionization in the MALDI-TOF analysis of dithiocarbamate-terminated polymers has
already been reported42-46. A fragmentation pathway involving the protonation of the
trithiocarbonyl group followed by the heterolytic cleavage of S-C(S)S group could
occurred (Scheme III-2). This cleavage leads to the formation of the sulfonium species
(EG1, Scheme III-2) and a neutral molecule (5, Scheme III-2). This is in a good
agreement with the analysis in negative mode, which did not show C12H25 nor
C12H25SCS species. Each peak value was calculated according to the following equation
(1):
Mcal = MEG + nMisoprene (1)
where MEG is the mass of the end groups (⊕S-C6H11NO, EG1 and C3H5O, EG2) with an
average molecular mass = 202.09,) in the telechelic cis-1,4-polymer, Misoprene is the mass of
isoprene unit (molecular mass = 68) and n is the number of repeating units.
m
ONHC12H25S
S
SO
m
ONHS
Ouν+ C13H26S2
EG1
19 kV
EG2H
4 4' 5
Scheme III-2. End groups observed during MALDI-TOF MS measurements.
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 68 -
Figure III-3. MALDI-TOF mass spectrum of α-trithiocarbonyl-ω-carbonyl-cis-1,4-
polyisoprene
The data obtained from 1H NMR spectroscopy and MALDI TOF mass spectrometry
provide evidence for the formation of the new α-trithiocarbonyl-ω-carbonyl-cis-1,4-
polyisoprene with a number-average molecular weight ( nM ) of 12,000 g mol-1and
polydispersity index of 1.60 as determined by SEC. The number-average degree of
polymerization equal to 62 ( nM = 4650 g mol-1) was calculated from 1H NMR spectrum
by comparing the integration of methylene protons of the chain-ends at 2.43 ppm (12,
Figure III-1) to the integration of the methine proton of the isoprene backbone at 5.12
ppm (9, Figure III-1) . The different nM values between SEC and 1H NMR spectroscopy
are attributed to the fact that polystyrene standards calibration was used to determine the
average molecular weights.
The average trithiocarbonyl functionality )( nf of α-trithiocarbonyl-ω-carbonyl-cis-1,4-
polyisoprene was determined by 1H NMR spectroscopy, by comparing the integration of
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 69 -
the methylene protons at 2.43 ppm (12, Figure III-1) with the one of the methylene
protons at 3.25 ppm (3, Figure III-1) . The integration of their respective peaks showed
complete trithiocarbonate functionality by 1H NMR spectroscopy (Figure III-1) that
agrees with a 1:1 theoretical ratio. Therefore, α-trithiocarbonyl-ω-carbonyl-cis-1,4-
polyisoprene can subsequently be used as a monofunctional macroCTA for the chain
extension reaction in order to form diblock copolymers.
II. Synthesis of PI-b-P(t-BA) diblock copolymer
We investigated the synthesis of a PI-b-P(t-BA) diblock copolymer using a purified α-
trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene (4, Scheme III-3) as a macromolecular
chain transfer agent (macroCTA). The reaction was performed in toluene at 60 oC and
AIBN was used as an initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 = 250/1/0.2) (6, Scheme
III-3) . Monomer conversion was determined by following the disappearance of the vinyl
peaks of t-BA at the range of 6.40 to 5.60 ppm in comparison with methyl protons of
anisole used as an internal standard at 3.75 ppm by 1H NMR spectroscopy. Table III-1
shows that the t-BA conversion increases with time and reaches 39% after 5h. Moreover,
the number-average molecular weights of the block copolymer increase with t-BA
conversion. SEC traces in Figure III-4 shows a shift towards higher number-average
molecular weights indicating that the α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene
(4, Scheme III-3) was extended into a block copolymer. Moreover, the SEC traces of the
so obtained block copolymers are unimodals illustrating that the polymerization of the
second block underwent chain transfer quantitatively. The molar composition of block
copolymer (S-4, Table III-1) was analyzed by 1H-NMR spectroscopy. The number
average degree of polymerization )DP( n of PI was equal to 62 and that of P(t-BA) was
equal to 87 as calculated by comparing the integral of the ethylenic proton, (8, Figure III-
5) of the polyisoprene backbone at 5.12 ppm to the methine proton, (4, Figure III-5) of
P(t-BA) at 2.4-2.1 ppm on the 1H NMR spectrum of the copolymer (Figure III-5) . The
data obtained from SEC and 1H NMR spectroscopy provide additional evidence for the
formation of the AB diblock copolymer based on the cis-1,4-polyisoprene from natural
rubber.
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 70 -
m
OC12H25
S
S
SO
NH
4
60 °C, toluene
O O
0.2 eq. AIBN
m
OC12H25
S
S
SO
NH
O O
k
6
250 eq.
Scheme III-3. Synthesis of PI-b-P(t-BA) by RAFT polymerization using α-trithiocarbonyl-
ω-carbonyl-cis-1,4-polyisoprene as macroCTA.
Table III-1. Synthesis of AB diblock copolymers via RAFT polymerization of tert-butyl
acrylate (t-BA) using the PI as macroCTA and AIBN as initiator at 60°C in toluene.
Copolymer
Reaction time
(h)
conv.a
(%)
b,calnM
(g mol-1)
c,SECnM
(g mol-1)
PDId
S-1 1 2 12 640 13 000 1.55
S-2 2 4 13 280 13 500 1.55
S-3 4 21 18 720 19 000 1.55
S-4 5 39 24 480 26 000 1.76 aMonomer conversion determined using 1H NMR spectroscopy. bNumber average molecular weight
calculated using: calcnM , = (conversion (%)×[M] 0/[MacroCTA]0×MM)+MmacroCTA where [M]0, [MacroCTA]0, MM and MmacroCTA are the initial concentration of t-BA monomer, the initial concentration of ∝-trithicarbonyl-ω-carbonyl-cis-1,4-polyisoprene macroCTA, the molecular weight of t-BA monomer and the molecular weight of the ∝-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene macroCTA respectively. cNumber average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards. dPolydispersity index measured by SEC.
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 71 -
Figure III-4. Overlaid SEC traces using UV detection at a wavelength of 309 nm of PI
macroCTA and PI-b-P(t-BA) diblock copolymers.
1
2
3
4
6
7
895
62
OCH2
S
S
SO
NH
O O
87
(CH2)10
66
7' 10
11
H3C
1.01.52.02.53.03.54.04.55.05.56.0 ppm
3.33.43.5 ppm
3
9
4
5 1
2
1011
7,7' 6
8
Figure III-5. 1H NMR spectrum of PI-b-P(t-BA) diblock copolymer (S-4, Table III-1).
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 72 -
Conclusion
A new well-defined α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene was successfully
synthesized from α-amino-ω-carbonyl-cis-1,4-polyisoprene through coupling reaction with
S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid) trithiocarbonate. The chain-end
functionality was confirmed by 1H NMR spectroscopy: the average trithiocarbonyl
functionality was equal to 1. The controlled chain extension of so obtained trithiocarbonyl-
functionalized-cis-1,4-polyisoprene with t-BA successfully formed PI-b-P(t-BA) diblock
copolymers through the RAFT polymerization process. This report is the first example of
diblock copolymer based on natural rubber-based polyisoprene, thus providing valuable
building blocks from a renewable raw material.
Acknowledgments: The authors wish to thank French Ministry of Education and Research
and Prince of Songkla University, Thailand, for their financial support.
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 73 -
Experimental Section
General Characterization. NMR spectra were recorded on a Bruker Avance 400
spectrometer for 1H NMR (400 MHz) and 13C NMR (100 MHz). Chemical shifts are
reported in ppm relative to the deuterated solvent resonances. Molecular weights and
molecular weight distributions were measured using size exclusion chromatography (SEC)
on a system equipped with a SpectraSYSTEM AS 1000 autosampler, with a Guard column
(Polymer Laboratories, PL gel 5 µm Guard column, 50 × 7.5 mm) followed by two
columns (Polymer Laboratories, 2 PL gel 5 µm MIXED-D columns, 2 × 300 × 7.5) and
with a SpectraSYSTEM RI-150 detector. The eluent used was tetrahydrofuran (THF) at a
flow rate of 1 mL min-1 at 35°C. Narrow molecular weight linear polystyrene standards
(ranging from 580 g mol-1 to 4.83 × 105 g mol-1) were used to calibrate the SEC. Infrared
spectra were recorded on a Nicolet Avatar 370 DTGS FT-IR spectrometer in the 4000-500
cm-1 range with KBr pellets and controlled by OMNIC software. Matrix-assisted laser
desorption ionization time-of-flight (MALDI-TOF) mass spectra were recorded on a
Bruker Biflex III equipped with a nitrogen laser (lZ337 nm). Solutions of dithranol (20
mg/ml), end-functional polymer (10 mg/ml), and silver trifluoroacetate (10 mg/ml) were
made in tetrahydrofuran. These solutions were mixed in the ratio matrix:cationizing
salt:polymer as for 10:1:2, and 1 ml of the solution was deposited on the sample holder. All
mass spectra were obtained in the linear mode with an acceleration voltage of 19 kV. The
delay time was 200 ns. Typically, 100 single-shot acquisitions were summed to give a
composite mass spectrum. All data were reprocessed using the Bruker XTOF software.
Materials. All chemicals were purchased from Aldrich unless otherwise noted. Toluene
(99%), 2-propanol (99%) (Fisher Scientific) and anisole (99%) were used as received.
Dichloromethane (99%+) and methanol (99%) were distilled over CaH2 prior to use. tert-
Butyl acrylate (t-BA, 99%) was purified by passing through neutral alumina column to
remove inhibitor. 2,2-Azobis(2-methylpropionitrile) (AIBN, 98%) was recrystallized into
methanol prior to use. The RAFT agent, S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid)
trithiocarbonate, (3, Scheme III-1) was synthesized as described in an earlier publication.36
The α-amino-ω-carbonyl-cis-1,4-polyisoprenes (2, Scheme III-1) were obtained from
initial carbonyl telechelic cis-1,4-polyisoprene (1, Scheme III-1) through reductive
amination according to procedure previously reported by our group.21,25,37
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 74 -
Synthesis of αααα-trithiocarbonyl- ωωωω-carbonyl-cis-1,4-polyisoprene. Under an argon
atmosphere, (COCl)2 (1.5 mL, 17 mmol) was added dropwise to S-1-dodecyl-S’-(α-α’-
dimehyl-α’’-acetic acid) trithiocarbonate (3, Scheme III-1) (0.57 g, 1.56 mmol) at 25°C
under a rapid stirring. After 4.5 h, the excess of (COCl)2 was removed under vacuum. A
solution of α-amino-ω-carbonyl cis-1,4-polyisoprene (2, Scheme III-1) (4.5 g, 1.05 mmol)
dissolved in 20 mL dichloromethane was added to the previous solution under an argon
atmosphere. The resulting solution was stirred at 25 °C for 24 h and then, concentrated
under vacuum. The polymer was precipitated twice by dissolving it in dichloromethane
(minimum volume) and precipitated into methanol (50 mL). The isolated polymer was
dried under vacuum to remove any traces of solvent. It was then analyzed by 1H NMR
spectroscopy, 13C NMR spectroscopy, FTIR spectroscopy and SEC. Yield: 76%.
1H-NMR (CDCl3): δ (ppm) 5.12 (br, polyisoprene backbone -(CH3)C=CHCH2), 3.25 (t,
chain-end, -SCH2CH2(CH2)9CH3), 3.05 (m, chain-end, -CH2NHC(O)) 2.80-2.70 (br, chain-
end, -NHC(O)), 2.43 (t, chain-end, CH3COCH2CH2), 2.25 (m, -C(O)CH2CH2), 2.13 (s,
chain-end, CH3COCH2), 2.04 (br, polyisoprene backbone, -CH2C(CH3)=CH-CH2 ), 1.75
(s, chain-end, -SC(CH3)2C(O)NH-), 1.70-1.60 (s, polyisoprene backbone, -C(CH3)=CH
and chain-end, -SCH2CH2(CH2)9CH3), 1.18-1.4 (m, chain-end, - SCH2CH2(CH2)9CH3),
0.88 (t, chain-end,(-CH2)10)CH3).
13C NMR (CDCl3): δ (ppm) 208.45 (chain-end, -(CH3)C(O)), 135.23 (cis-1,4-polyisoprene
backbone, -C(CH3)=CH-), 125.28 (cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 45.00
(chain-end, -CH2NHC(O)), 43.91 (chain-end, -(CH3)C(O)CH2), 37.41, (chain-end,
-SCH2CH2(CH2)9CH3), 32.13 (cis-1,4- isoprene backbone, -CH2C(CH3)=CH-), 31.85
(chain-end, -S(CH2)2CH2(CH2)8CH3), 29.77 (chain-end, -S(CH2)3CH2(CH2)7CH3), 29.57
(chain-end, -S(CH2)4CH2(CH2)6CH3), 29.46 (chain-end, -S(CH2)5CH2(CH2)5CH3), 29.28
(chain-end, -S(CH2)6CH2(CH2)4CH3), 29.12 (chain-end, -S(CH2)7CH2(CH2)3CH3), 28.95
(chain-end, -S(CH2)8CH2(CH2)2CH3), 28.86 (chain-end, -S(CH2)10CH2CH3), 27.92 (chain-
end, -SCH2CH2 (CH2)9CH3), 26.36 (cis-1,4-polyisoprene backbone, -C(CH3)=CHCH2-),
23.36 (1,4-cis-polyisoprene backbone -C(CH3)=CH-), 22.63 (chain-end, -
S(CH2)9CH2CH2CH3), 22.22 (chain-end, (CH3)C(O)-), 14.06 (chain-end, -CH3).
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 75 -
FTIR: ν (cm-1) 3400 (HN), 3035 (H-C=C), 2900-2730 (CH2, CH3), 1721 (chain-end, -
C=O), 1666 (polyisoprene backbone, -C=C-), 1448 (polyisoprene backbone, -CH2), 1376
(polyisoprene backbone, -CH2), 1075 (chain-end, -C-S), 836 (isoprene backbone, -CH),
SEC: nM = 12,000 g/mol-1, wM = 19,200 g/mol-1, PDI =1.60
A typical RAFT polymerization. A typical procedure is given for the polymerization of
tert-butyl acrylate (t-BA) mediated by the α-trithiocarbonyl-ω-carbonyl-cis-1,4-
polyisoprene. (4, Scheme III-1) used as macromolecular chain transfer agent (macroCTA)
and using AIBN as initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 = 250/1/0.2). A magnetic stir
bar was charged to a Schlenk tube together with the macroCTA (0.4337 g, 0.093 mmol), t-
BA (2.976 g, 23.25 mmol), AIBN (0.0030 g, 0.018 mmol), toluene (0.8 mL, 20% v/v) and
anisole (0.17 mL, 5% v/v). Then, the reaction mixture was deoxygenated by bubbling with
argon for 15 min. The polymerization was initiated (t = 0) by immersion in a thermostated
oil bath at 60°C. Samples were withdrawn from the reaction mixture via a degassed
syringe for conversion monitoring (by 1H NMR spectroscopy) and molecular weight
analysis (by SEC). At the end of reaction, the polymer solution was concentrated under
vacuum using rotary evaporation and was purified by a series of precipitations from
dichloromethane (minimum volume) into an ice cold 1:1 mixture of water and methanol.
The copolymer was separated by filtration and dried under vacuum until constant weight. It
was then further analyzed by 1H NMR spectroscopy, 13C NMR spectroscopy and SEC. 1H NMR (CDCl3): δ (ppm) 5.12 (br, polyisoprene backbone -C(CH3)=CH), 3.25 (t, chain-
end, -SCH2CH2(CH2)9CH3), 2.43 (t, chain-end, CH3COCH2CH2), 2.40-2.15 (br, P(t-BA)
backbone -CH2-CHC(O)-), 2.13 (s, chain-end, CH3COCH2), 2.12-1.95 (br, polyisoprene
backbone, -CH2C(CH3)=CH- and -C(CH3)=CHCH2-), 1.90-1.75 (br, P(t-BA) backbone -
CH2-CHC(O)-), 1.72 (s, chain-end, -SC(CH3)2C(O)NH-), 1.70-1.60 (br, polyisoprene
backbone, -C(CH3)=CH-, and chain-end, -SCH2CH2(CH2)9CH3), 1.55-1.30 (br, P(t-BA)
backbone -OC(CH3)3), 1.20-1.40 (chain-end, -SCH2CH2(CH2)9CH3), 0.86 (chain-end,
S(CH2)11CH3).
13C NMR (CDCl3): δ(ppm) 174.16 (P(t-BA) backbone, -C(O)-O-), 135.23 (cis-1,4-
polyisoprene backbone, -C(CH3)=CH-), 125.28 (cis-1,4-polyisoprene backbone,
-C(CH3)=CH-) 80.20 (P(t-BA) backbone, -C(O)-O-C(CH3)3), 42.16 (P(t-BA) backbone,
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 76 -
-CHC(O)-O-C(CH3)3), 37.20, -SCH2CH2(CH2)9CH3), 32.03 (cis-1,4-polyisoprene
backbone, -CH2C(CH3)=CH-), 31.85 (chain-end, -S(CH2)2CH2(CH2)8CH3), 29.77 (chain-
end, -S(CH2)3CH2(CH2)7CH3), 29.57 (chain-end, -S(CH2)4CH2(CH2)6CH3), 29.46 (chain-
end, -S(CH2)5CH2(CH2)5CH3), 29.28 (chain-end, -S(CH2)6CH2(CH2)4CH3), 29.12 (chain-
end, -S(CH2)7CH2(CH2)3CH3), 28.95 (chain-end, -S(CH2)8CH2(CH2)2CH3), 28.86 (chain-
end, -S(CH2)10CH2CH3), 27.92 (chain-end, -SCH2CH2(CH2)9CH3), 26.36 (1,4-cis-
polyisoprene backbone -C(CH3)=CHCH2-), 23.44 (cis-1,4-polyisoprene backbone -
C(CH3)=CH-), 22.70 (chain-end, -S(CH2)9CH2CH2CH3), 22.22 (chain-end, (CH3)C(O)-),
14.14 (chain-end, -CH3).
SEC: : nM = 26,000 g.mol-1, wM = 45,800, PDI = 1.76
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 77 -
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71, 795-802. [18] Reyx, D.; Campistron, I., Angew. Makromol. Chem. 1997, 247, 197-211. [19] Anachkov, M. P.; Rakovski, S. K.; Stefanova, R. V., Polym. Degrad. Stab. 2000, 67,
355-363. [20] Phinyocheep, P.; Phetphaisit, C. W.; Derouet, D.; Campistron, I.; Brosse, J. C., J.
Appl. Polym. Sci. 2005, 95, 6-15. [21] Saetung, A.; Rungvichaniwat, A.; Campistron, I.; Klinpituksa, P.; Laguerre, A.;
Phinyocheep, P.; Pilard, J. F., J. Appl. Polym. Sci. 2010, 117, 1279-1289. [22] Saetung, A.; Rungvichaniwat, A.; Campistron, I.; Klinpituksa, P.; Laguerre, A.;
Phinyocheep, P.; Doutres, O.; Pilard, J.-F., J. Appl. Polym. Sci. 2010, 117, 828-837. [23] Derouet, D.; Nguyen, T. M. G.; Brosse, J.-C., J. Appl. Polym. Sci. 2007, 106, 2843-
2858. [24] Kébir, N.; Campistron, I.; Laguerre, A.; Pilard, J.-F.; Bunel, C.; Jouenne, T.,
Biomaterials 2007, 28, 4200-4208. [25] Kébir, N.; Morandi, G.; Campistron, I.; Laguerre, A.; Pilard, J.-F., Polymer 2005,
46, 6844-6854. [26] Kébir, N.; Campistron, I.; Laguerre, A.; Pilard, J.-F.; Bunel, C.; Couvercelle, J.-P.;
Gondard, C., Polymer 2005, 46, 6869-6877.
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 78 -
[27] Gillier-Ritoit, S.; Reyx, D.; Campistron, I.; Laguerre, A.; Singh, R. P., J. Appl. Polym. Sci. 2003, 87, 42-46.
[28] Lapinte, V.; Fontaine, L.; Montembault, V.; Campistron, I.; Reyx, D., J. Mol. Catal. A: Chem. 2002, 190, 117-129.
[29] Solanky, S. S.; Campistron, I.; Laguerre, A.; Pilard, J.-F., Macromol. Chem. Phys. 2005, 206, 1057-1063.
[30] Thomas, R. M.; Grubbs, R. H., Macromolecules 2010, 43, 3705-3709. [31] Hawker, C. J.; Bosman, A. W.; Harth, E., Chem. Rev. 2001, 101, 3661-3688. [32] Matyjaszewski, K.; Xia, J., Chem. Rev. 2001, 101, 2921-2990. [33] Moad, G.; Rizzardo, E.; Thang, S. H., Polymer 2008, 49, 1079-1131. [34] Moad, G.; Thang, S. H., Aust. J. Chem. 2009, 62, 1379-1381. [35] Moad, G.; Barner-Kowollik, C., Handbook of RAFT polymerization. WILEY-VCH
Verlag GmbH & Co. KGaA: Weinheim, 2008. p 51-104. [36] Lai, J. T.; Filla, D.; Shea, R., Macromolecules 2002, 35, 6754-6756. [37] Morandi, G.; Kebir, N.; Campistron, I.; Gohier, F.; Laguerre, A.; Pilard, J.-F.,
Tetrahedron Lett. 2007, 48, 7726-7730. [38] Khatchaturov, A. S.; Dolinskaya, E. R.; Prozenko, L. K.; Abramenko, E. L.; Kormer,
V. A., Polymer 1977, 18, 871-877. [39] Dejean de la Batie, R.; Laupretre, F.; Monnerie, L., Macromolecules 1989, 22, 122-
129. [40] Morese-Seguela, B.; St-Jacques, M.; Renaud, J. M.; Prud'homme, J.,
Macromolecules 1977, 10, 431-432. [41] Saetung, A.; Rungvichaniwat, A.; Campistron, I.; Klinpituksa, P.; Laguerre, A.;
Phinyocheep, P.; Pilard, J.-F., J. Appl. Polym. Sci. 2010, 117, 1279-1289. [42] Schilli, C.; Lanzendörfer, M. G.; Müller, A. H. E., Macromolecules 2002, 35, 6819-
6827. [43] Vosloo, J. J.; De Wet-Roos, D.; Tonge, M. P.; Sanderson, R. D., Macromolecules
2002, 35, 4894-4902. [44] Loiseau, J.; Doërr, N.; Suau, J. M.; Egraz, J. B.; Llauro, M. F.; Ladavière, C.;
Claverie, J., Macromolecules 2003, 36, 3066-3077. [45] Favier, A.; Ladavière, C.; Charreyre, M.-T.; Pichot, C., Macromolecules 2004, 37,
2026-2034. [46] Ladavière, C.; Lacroix-Desmazes, P.; Delolme, F., Macromolecules 2009, 42, 70-84.
Chapter IV
One-pot synthesis of natural rubber-
based telechelic cis-1,4-polyisoprene
and their use to prepare block
copolymers by RAFT polymerization
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 79 -
One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes
and their use to prepare block copolymers by RAFT polymerization.
Nitinart Saetung, Irène Campistron, Sagrario Pascual, Jean-Claude Soutif, Jean-François
Pilard* and Laurent Fontaine*
LCOM-Chimie des Polymères, UCO2M, UMR CNRS 6011, Université du Maine, Avenue
Olivier. Messiaen, 72085 Le Mans Cedex 09, France.
Fax: (+33 (0)2 43 83 37 54)
E-mail: [email protected]; [email protected]
Publication accepted in Macromolecules, DOI: 10.1021/ma102406w
Graphical abstract
n
C12H25S S
OS
O
OS S
C12H25
O
S
C12H25S S
S
S SC12H25
SqO O O O
m m
1) Grubbs II catalyst
2) t-butyl acrylate/ AIBN
+
P(t-BA)-b-PI-b-P(t-BA) triblock copolymer
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 80 -
ABSTRACT : We investigate the one-pot synthesis of a new α,ω-bistrithiocarbonyl-end
functionalized telechelic cis-1,4-polyisoprene (PIp) via metathesis degradation from
natural rubber (NR) in the presence of the Grubbs second generation catalyst (GII) and a
bistrithiocarbonyl-end functionalized olefin as a chain transfer agent (CTA). When the
metathesis degradation of the NR of 2x106 g mol-1 molecular weight is performed in
toluene at 25 °C using the ratio of [Ip]0/[GII] 0/[CTA] 0 = 100/1/1, a cis-1,4-polyisoprene of
14,000 g mol-1 after 4h is obtained. The functionality estimated by 1H NMR spectroscopy
is equal to 1.5±0.1. The structure of telechelic cis-1,4-polyisoprene was confirmed by
combination of 1H NMR, 13C NMR spectroscopy and FTIR. The influence of the CTA
concentration was investigated. It was found that using concentrations of catalyst
([Ip] 0/[GII] 0/[CTA] 0 of 100/1/2 and 100/1/5 lead to form a perfectly telechelic cis-1,4-
polyisoprene with a functionality of 2 with no significant difference in nM values
(approximately 6,400 g mol-1) and in polydispersity indices (∼1.70). The new well-defined
α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprenes were used
successfully as macromolecular chain transfer agents (macroCTA) to mediate the RAFT
polymerization of t-BA using AIBN as the initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 =
500/1/0.4) in toluene at 60 °C leading to well-defined P(t-BA)-b-PIp-b-P(t-BA) triblock
copolymers.
Keywords: natural rubber, cis-1,4-polyisoprene, metathesis degradation, telechelics,
triblock copolymers, RAFT polymerization.
Introduction
Telechelic unsaturated polymers are good candidates to obtain block copolymers with a
wide range of applications. For instance, block copolymers containing polyisoprene (PIp)
as a constituent have found applications as nanofibers1, thermoplastic elastomers,2 pressure
sensitive adhesives,3-4 and biocompatible materials.5-6 The PIp block is essentially
synthesized by living anionic polymerization of isoprene (Ip),7-16 by controlled/living
radical polymerization (CRP) of isoprene,17-27 or ring-opening metathesis polymerization
of 1,5-dimethyl-1,5-cyclooctadiene.28 The cis-1,4-polyisoprene block can be obtained from
natural rubber (NR) which is a biomacromolecule and a renewable resource. It is well
known that strictly cis-1,4-microstructure of NR provides unique and special properties,
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 81 -
including good elastomeric properties, very low glass transition temperature, excellent
flexibility, good “green” strength and building tack. Therefore, the synthesis of telechelic
cis-1,4-polyisoprene from NR (TNR) opens new synthetic routes to develop materials
based on a biopolymer from a renewable resource. The block copolymers obtained from
NR can lead to new materials with properties suitable for a number of potential
applications including microemulsion elastomers29 for the paint industry, adhesives3-4 and.
nanoporous materials.30 The transformation of NR into TNR can be obtained by combining
chain cleavage reaction of NR with a postfunctionalization reaction. The most widely used
methods to produce TNR derivatives are controlled oxidative degradation,
photodegradation or metathesis degradation.31 Our group has focused on selective
degradation of synthetic cis-1,4-polyisoprene using well-controlled oxidative chain
cleavage reaction leading to new carbonyl telechelic cis-1,4-polyisoprene32 and the
chemical modification of carbonyl end-groups has led to the development of new
hydroxyl6,33 and amino telechelic polyisoprenes.34 The hydroxyl telechelic polyisoprene
was engaged as a precursor in the synthesis of linear polyurethanes for biological
materials6 and foams applications.35-36 However, this technique requires several steps to
obtain the precursor of the desired products. Alternatively, we have also developed a
method for the preparation of acetoxy-telechelic polyisoprene in a single-step process via
the metathesis degradation of cis-1,4-polyisoprene.37-38 To the best of our knowledge, no
study has been reported on the single-step synthesis of telechelic cis-1,4-polyisoprene
suitable to be employed as precursors for controlled/living radical polymerizations (CRPs)
in order to obtain block copolymers. Among CRP techniques,39 Reversible
Addition/Fragmentation chain Transfer (RAFT) polymerization40 is recognized as one of
the most versatile method for the synthesis of block copolymers since it is compatible with
a wide range of unprotected polar monomers41 including acrylic acid.42 The most common
RAFT chain transfer agent (CTA) contains thiocarbonylthio groups that are easily removed
or modified by a variety of methods.43
Herein, we have investigated the one-pot synthesis of original telechelic cis-1,4-
polyisoprenes (PIp) through a metathesis degradation of NR using Grubbs second
generation catalyst and a bistrithiocarbonyl-end functionalized olefin as a CTA (2, Scheme
IV-1A ). The resulting PIp were used as difunctional macroCTAs to mediate the
polymerization of tert-butyl acrylate to form ABA triblock copolymers via the RAFT
process. To the best of our knowledge, no previous studies have been reported on the one-
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 82 -
pot synthesis of α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene
suitable to be used in RAFT polymerization.
n
[Ru]
+
[Ru]O
S SC12H25
O
S+
C12H25S S
OS
O
OS S
C12H25
O
S
p6
3
5'
4
5
B)
[Ru] [Ru]
m m'
C12H25S S
OS
O
n
p'6'
C12H25S S
OS
O
[Ru]
n'
+
7
C12H25S S
OS
O
OS S
C12H25
O
Sq
NN
Ru
PCy3
Ph
Cl
Cl
[Ru]Ph
:
[Ru]Ph
1. (COCl)2, 20 °C
HO OH1
2
C12H25S S
OHS
O
C12H25S S
OS
O
OS S
C12H25
O
S2.
Toluene, 25 °C
15 min.
A)
[Ru]O
S SC12H25
O
S33'
C12H25S S
OS
O Ph
+
Scheme IV-1. A) Synthesis of a bistrithiocarbonyl-end functionalized CTA and, B)
synthesis of α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene from
NR via metathesis degradation.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 83 -
I. Functional Metathesis Degradation.
Herein, we investigated the synthesis of α,ω-bistrithiocarbonyl-end functionalized
telechelic cis-1,4-polyisoprene via metathesis degradation of NR using Grubbs second
generation catalyst (GII) and a bistrithiocarbonyl-end functionalized olefin (2) as the CTA
(Scheme IV-1). The difunctional CTA was reacted with Grubbs II catalyst in a
stoichiometrical ratio in toluene-d8 at 25 °C and the resulting product analyzed by 1H NMR
spectroscopy (Figure IV-1) and 2D-correlation spectroscopy (COSY) (Figure IV-2). New
peaks were observed in 1H NMR spectrum (Figure IV-1) at 5.35 ppm and 4.14 ppm that
are attributed to the olefinic proton, 1’([Ru]=CHCH2OC(O)-R) and to aliphatic proton, 2’
([Ru]=CHCH2OC(O)-R), respectively. In addition, new peaks were found at 4.36 ppm, at
5.87-5.80 ppm and at 6.15-6.10 ppm corresponding to 2’’ (Ph-CH=CHCH2OC(O)-R), to 4
(Ph-CH=CHCH2OC(O)-R), and to 4’ (Ph-CH=CHCH2OC(O)-R), respectively. COSY
two-dimensional NMR experiment was used to confirm these structures. In the COSY
spectrum (Figure IV-2), the signal at 4.14 ppm corresponding to aliphatic proton 2’ is
correlated with the signal centred at 5.35 ppm, corresponding to the olefinic proton, 1’. We
can also observe the correlation between the signals 6.15-6.10 ppm and 5.87-5.80 ppm,
corresponding to alkenes proton 4’ and 4, with the signal at 4.36 ppm, corresponding to
aliphatic proton 2” . Thus it was confirmed that the Grubbs II catalyst reacts with
difunctional CTA (2, Scheme IV-1A) to result in the new ruthenium carbene molecule (3,
Scheme IV-1A). This new catalyst (3, Scheme IV-1A) undergoes the metathesis
degradation at 25 °C with double bonds of NR (4, Scheme IV-1B) to form α,ω-
bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene (7, Scheme IV-1B).
Therefore, the one-pot degradation and functionalization reactions can continuously take
place in a catalytic fashion.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 84 -
[Ru]
C12H25S
S
SO
O O
OS
S
SC12H25
O
OS
S
SC12H25
[Ru]
Ph
+
+
C12H25S
S
SO
O
Ph1
2
3
2'
2"
4
1'
4'
25 °C
Toluene-d8
4.55.05.56.06.57.07.5 ppm
4.55.05.56.06.57.07.5 ppm
4.55.05.56.06.57.07.5 ppm192021 ppm
192021 ppm
192021 ppm
1
1'
3
2
2'
2"44'
1'
Figure IV-1. 1H NMR spectra (toluene-d8), A) the resulting mixture solution between
CTA and Grubbs II catalyst, B) CTA, and C) Grubbs II catalyst.
A)
B)
C)
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 85 -
[Ru]
C12H25S
S
SO
O O
OS
S
SC12H25
O
OS
S
SC12H25
[Ru]
Ph
+
+
C12H25S
S
SO
O
Ph1
2
3
2'
2"
4
1'
4'
25 °C
Toluene-d8
ppm
4.04.55.05.56.06.57.0 ppm
4.0
4.5
5.0
5.5
6.0
6.5
7.0
2'
2"44'
1'
2'
2"
4
4'
1'
Figure IV-2. COSY spectrum (toluene-d8) of the resulting mixture solution between CTA
and Grubbs II catalyst.
A first attempt for the preparation of telechelic NR (entry A-2, Table IV-1) was
performed in toluene using Grubbs II catalyst and bistrithiocarbonyl-end functionalized
olefin (2, Scheme IV-1A) as the CTA. The reaction was carried out at room temperature
for 4h with a ratio [Ip]0/[GII] 0/[CTA] = 100/1/1. The resulting polymer was characterized
by 1H NMR spectroscopy (Figure IV-3) and 2D-correlation spectroscopy (COSY) (Figure
IV-4) . An intense signal corresponding to vinylic protons at 5.16 ppm (4,
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 86 -
-(CH3)C=CHCH2-) was observed in 1H NMR spectroscopy (Figure IV-3). This result
indicates that telechelic polyisoprenes with 1,4-microstructure are obtained. In addition,
new peeks were also observed at 5.86-5.70 ppm, at 5.60-5.50 ppm, at 5.38-5.28 ppm and at
4.72-4.50 ppm corresponding to 5 (cis -CH=CH), 5 (trans –CH=CH), 3 (-C(CH3)=CH)
and 2 (-C(CH3)=CH-CH2OC(O)-) or 6 (-CH=CH-CH2OC(O)-), respectively. COSY two-
dimensional NMR experiment was used to confirm these structures. In the COSY spectrum
(Figure IV-4), the signals centred at 5.78 ppm and at 5.55 ppm corresponding to cis- and
trans-ethylenic protons, 5, are correlated with the signal centred at 4.53 ppm corresponding
to aliphatic proton 6. We can also observe the correlation of the signal at 5.83 ppm, the
signal centred at 5.55 ppm and the signal centred at 5.34 ppm corresponding respectively
to cis- ethylenic proton, 5(cis-), trans- ethylenic proton, 5(trans-) and isoprenic proton, 3,
with the signal centred at 4.62 ppm corresponding to aliphatic protons, 6 and 2. In addition,
we can observe the correlation of the signal at 5.34 ppm corresponding to isoprenic proton,
3 with the signal centred at 4.68 ppm corresponding to aliphatic protons, 2. 13C NMR spectroscopy (Figure IV-5) was used to identify the 1,4-microstructure of
telechelic polyisoprenes. The signals observed at 135.21 (1, -C(CH3)=CH-), 125.02 (2,
-C(CH3)=CH-), 32.2 ppm (3, -CH2C(CH3)=CH-), 26.39 (5, -C(CH3)=CHCH2-), and 23.44
ppm (7, -C(CH3)=CH-) correspond to the cis-1,4- polyisoprene unit. There are no signals at
131.2 ppm (-C(CH3) =CH-), 124.27 (-C(CH3)=CH-), 40.02 ppm (-C(CH3)=CHCH2-),
16.00 (-C(CH3)=CH-) corresponding to the trans-1,4-polyisoprene unit.47 This result
confirmed that the telechelic polyisoprene is a strictly cis-1,4-polyisoprene. By contrast,
the synthesis of telechelic polyisoprene through anionic polymerization,48-49 NMP21 or
RAFT polymerization24-26 gives a mixture of 1,4-addition, 1,2-addition and 3,4-addition
products. On the other hand, the synthesis of telechelic polyisoprene via the Ring-Opening
Metathesis polymerization of 1,5-dimethyl-1,5-cyclooctadiene gives a mixture of telechelic
cis-1,4 and trans-1,4-polyisoprene.28
In order to determine the average functionality )( nf of telechelic cis-1,4-polyisoprene, the
number average polymerization degree (nDP ) of the oligomers determined by 1H NMR
spectroscopy was compared with the nDP determined by SEC. The nDP of cis-1,4-
polyisoprene from 1H NMR spectroscopy was calculated by comparing the relatives
integrations of the methylene protons (2 and 6, Figure IV-3) of the chain-ends at 4.72-
4.50 ppm, with those of the isoprenic protons (4, Figure IV-3) of polyisoprene backbone
at 5.16 ppm. The functionality was then calculated according to equation (1) which is an
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 87 -
adaptation of the equation used by Pham et al.50-51 for hydroxytelechelic polybutadiene
obtained by radical or anionic polymerization.
isopreneM
BSECnM
I
IInf
××
+++=
*,
4
62/)26( 2I (1)
with 2I corresponding to the relative integration of aliphatic protons 2 of isoprene chain-
end unit at 4.72-4.68 ppm (Figure IV-3);
26+I corresponding to the relative integration of aliphatic protons 6+2 of isoprene and
butadiene chain-ends unit at 4.68-4.56 ppm (Figure IV-3);
6I corresponding to the relative integration of aliphatic protons 6 of butadiene chain-end
unit at 4.56-4.50 ppm (Figure IV-3);
4I corresponding to the relative integration of vinylic protons 4 of isoprene backbone unit
at 5.16 ppm (Figure IV-3);
*,SECnM is the number average molecular weight of telechelic cis-1,4-polyisoprene
determined by SEC at 25 °C;
B is Benoît factor value52 of polyisoprene equal to 0.67;
Misoprene is the molar mass of isoprene unit equal to 68 g mol-1.
The resulting functionality for the cis-1,4-polyisoprene telechelic (entry A-2, Table IV-1)
was equal to 1.5±0.1. We believe that under these conditions the low concentration of CTA
gives rise to some active free ruthenium carbene (8, Scheme IV-2), which could be
involved in backbiting reactions leading to the formation of non-functional cyclic products
(8’, Scheme IV-2). Finally, ethyl vinyl ether used to stop the reaction leads to oligomer
vinylic chain-ends (8’’, Scheme IV-2). These reactions limit the functionality of the so-
obtained polyisoprenes.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 88 -
+[Ru]
O
[Ru]O
+
8'
8''
Termination
Backbiting reaction
n
8
[Ru]
qC12H25
S SO
S
O
Scheme IV-2. The formation of non-functional chain-ends.
The evolution of number-average molecular weight of telechelic cis-1,4-polyisoprene with
reaction time is presented in Figure IV-6. It illustrates that metathesis degradation
proceeds in two relatively distinct steps. A very rapid decrease of the molecular weights of
the cis-1,4-polyisoprene, corresponding to a drop from 2×106 g mol-1 to 14,000 g mol-1, is
observed over the first two hours. In the initial stage of the reaction, an active ruthenium
carbene reacts rapidly with the double bonds of the cis-1,4-polyisoprene backbone leading
to a decrease of molecular weight. In addition, the active ruthenium carbene at the chain-
end can also react with the double bonds of cis-1,4-polyisoprene via intermolecular
metathesis reactions. Then, in a second period from 2h to 8h, the molecular weight of the
polymer decreases slowly but continually to form telechelic cis-1,4-polyisoprene with a
final molecular weight of approximately 5,800 g mol-1. This is also proved53-55 by the fact
that at very long reaction times intramolecular metathesis reactions can occur to form
cyclic oligomers. The resulting cyclic oligomers were confirmed by MALDI-TOF MS
analysis (Figure IV-7). The Ag+ ionized MALDI spectrum of oligomers isolated after
precipitation of the higher molecular weight fraction using 2-propranol reveals cyclic
polyisoprenic species. For example, the signal at m/z = 583 corresponds to a cyclic
polyisoprene consisting of n = 7 isoprene units ionized by Ag+ (Mcal = 107 + 7×68 = 583 g
mol-1; where 107 g mol-1 is the mass of silver atom and 68 g mol-1 is the mass of isoprene
unit) This experimental value is good agreement with the theoretical mass calculated (583
Da, monoisotopic peak), confirming the formation of cyclic oligomers via backbiting
reaction.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 89 -
In order to obtain better control of the molecular weight and chain-end functionality of
telechelic cis-1,4-polyisoprene, the effect of changing the ratio of [Ip]0/[GII] 0/[CTA] 0
(entries A-1 to A-4, Table IV-1) was studied. When the ratio of [Ip]0/[GII] 0/[CTA] 0 is
equal to 200/1/1(entry A-1, Table IV-1), it was found that the evolution of the number-
average molecular weight of telechelic cis-1,4-polyisoprene with time followed a similar
two-step profile to that observed for sample A-2 (Table IV-1). During the first stage, a
period of two hours, the nM decreased rapidly from 2×106 g mol-1 to 34,000 g mol-1. After
2h, the nM decreased slowly to form telechelic cis-1,4-polyisoprene with a final
molecular weight of about 10,000 g mol-1 after a period of 8h (Figure IV-6). However, the
final telechelic cis-1,4-polyisoprene has a higher molecular weight corresponding to a
higher initial ratio of [Ip]0/[GII] 0/[CTA] 0. Moreover, the functionality of telechelic cis-1,4-
polyisoprene obtained was unaffected and remained less than 2. In order to form a
perfectly difunctional telechelic cis-1,4-polyisoprene, the influence of the CTA
concentration was investigated. The ratio of [GII]0/[CTA] 0 was set to 1/2 and 1/5, and the
ratio of [Ip]0/[GII] 0 was fixed at 100/1 (entries A-3 and A-4, Table IV-1). We observed
that ratios of [GII]0/[CTA] 0 of 1/2 and 1/5 formed polymers with a chain-end functionality
of 2 as shown by 1H NMR spectrum (Figure IV-3B) with no significant difference in
nM values and in polydispersity indices of the final telechelic cis-1,4-polyisoprene. This is
probably due to the fact that the CTA which have not reacted with the Grubbs II catalyst
may react with the ruthenium carbene at the chain-end (8, Scheme IV-3) leading to
difunctionalized cis-1,4-polyisoprene (7, Scheme IV-3).
[Ru]
qC12H25
S SO
S
O
C12H25S S
OS
O
OS S
C12H25
O
S
C12H25S S
OS
O
OS S
C12H25
O
Sq
8
7
difunctional CTA
Scheme IV-3. Formation of difunctionalized telechelic cis-1,4-polyisoprene.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 90 -
Table IV-1. Metathesis degradation of NR using Grubbs II catalyst and difunctional chain
transfer agent in toluene at 25 °C after 4h.
Entry
[Ip] 0/[GII] 0/[CTA] 0 SECnM ,
a
(g mol-1)
NMRnM ,
b
(g mol-1)
Functionalityc
PDId
Yield
(%)
A-1 200/1/1 23 000 16 400 1.4±0.1 1.83 78
A-2 100/1/1 10 200e 7 200 1.5±0.1 1.76 76
A-3 100/1/2 8 200e 6 200 2.0±0.1 1.70 76
A-4 100/1/5 8 200 6 400 2.0±0.1 1.67 70 aExperimental number average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards at 35 °C, bDetermined by 1H NMR spectroscopy according to nM =
[(I4×68)/(I1/4)] + 848, cDetermined by 1H NMR spectroscopy and using equation (1). dPolydispersity index measured by SEC, eExperimental number average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards at 25 °C.
qO
O
S SCH2H2CS SO
OC11H23
12
345
6C11H23
1
5
S S7 7
8
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 ppm
0.08
0.21
0.09
10.4
6
1
43
4.64.8 ppm5.45.65.86.0 ppm
5(cis-)
5(trans-)
2
2+66
7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 ppm
0.05
0.13
0.05
10.8
5
5.45.65.86.0 ppm 4.64.8 ppm
5(cis-)
5(trans-)
32
2+66
7 8
7 84
1
Figure IV-3. 1H NMR spectra of difunctional telechelic cis-1,4-polyisoprenes, A) entry
A-2, Table IV-1 and B) entry A-3, Table IV-1.
A)
B)
5.1=nf
0.2=nf
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 91 -
qO
O
S SCH2H2CS SO
OC11H23
12
345
6C11H23
1
5
S S
ppm
4.24.44.64.85.05.25.45.65.86.0 ppm
4.2
4.4
4.6
4.8
5.0
5.2
5.4
5.6
5.8
6.0
2
6+2
6
3
5(trans-)
5(cis-)
2+6
Figure IV-4. COSY spectrum of the difunctional telechelic cis-1,4-polyisoprene (entry A-
2, Table IV-1).
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 92 -
qO
O
S
S
S(CH2)11CH3
S
SO
O8
2
34
7
6
CH3(CH2)11S 15 4
6 6 6
7
8
210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm
1 2 3 5 7
4 6 8
Figure IV-5. 13C NMR spectrum of telechelic cis-1,4-polyisoprene (entry A-2, Table IV-
1).
0 2 4 6 800
10000
2000020000
30000
19000001900000
1950000
20000002000000
Mn
(g.m
ol-1)
Reaction time (hours)
A-1 A-2 A-3
Figure IV-6. Evolution of the telechelic cis-1,4-polyisoprene number-average molecular
weight as a function of reaction time (entries A-1 to A-3, Table IV-1).
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 93 -
573 578 583 588 593 598m/z
a.i.
Figure IV-7. MALDI-TOF mass spectrum of the cyclic polyisoprene oligomers obtained
via backbiting reaction. The insert shows the theoretical distribution at m/z 538.
II. Synthesis of P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers.
We investigated the synthesis of ABA triblock copolymers containing polyisoprene as the
central block using a purified α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-
polyisoprene as macroCTA (7, Scheme IV-4). The P(t-BA)-b-PIp-b-P(t-BA) (9, Scheme
IV-4 ) was prepared from the RAFT polymerization of tert-butyl acrylate using the
difunctional telechelic cis-1,4-polyisoprene (A-3, Table IV-1) as a macroCTA. The
reaction was performed in toluene at 60 oC and AIBN was used as an initiator ([t-BA] 0/[
macroCTA]0/[AIBN] 0 = 500/1/0.4). Monomer conversion was determined by 1H NMR
spectroscopy by following the disappearance of the vinyl protons of t-BA at 6.40 to 5.60
ppm which were compared with methyl protons of anisole used as an internal standard at
3.75 ppm. The macromolecular characteristics of block copolymers were determined by
SEC.
580 650 720 m/z
1000
2000
3000
4000
5000
6000
7000
a.i.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 94 -
After a polymerization time of 5h, the t-BA conversion reaches 26% (Table IV-2). The
block copolymer had a number-average molecular weight of 23,300 g mol-1 and a
polydispersity index of 1.50 by SEC. The SEC trace of the copolymer (Figure IV-8A )
showed the absence of a peak corresponding to the PIp-macroCTA and a unimodal curve,
illustrating that the polymerization of the second block underwent chain transfer
quantitatively. The number average degree of polymerization of the PIp block is equal to
80 and the one of P(t-BA) is equal to 100 as calculated by comparing the integral of the
ethylenic protons 4 of the polyisoprene backbone resonance at 5.14 ppm to the methine
protons 2 of P(t-BA) resonances at 2.4-2.1 ppm on the 1H NMR spectrum of the copolymer
(Figure IV-8B). The data obtained from SEC and 1H NMR spectroscopy provide
additional evidence for the formation of the ABA triblock copolymer based on the cis-1,4-
polyisoprene from NR with the desired topology.
Glass transition temperature (Tg) of PIp-macroCTA and P(t-BA)-b-PIp-b-P(t-BA) triblock
copolymer were investigated by thermal analysis by differential scanning calorimetry
(DSC) under nitrogen at 10 °C/min heating rate. A single Tg of PIp-macroCTA is observed
at −65 °C. Whereas, the P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers show two values of
Tg which the low temperature at −37 °C corresponds to the glass transition temperature of
PIp and the higher temperature at 32 °C corresponds to the glass transition temperature of
P(t-BA) as the Tg of P(t-BA) is equal to 48 °C.56 This is a supplementary proof of the
successful synthesis of P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 95 -
Table IV-2. Synthesis of ABA triblock copolymers via RAFT polymerization of tert-butyl
acrylate (t-BA) using the macroCTA (A-3, Table IV-1) and AIBN as initiator at 60°C in
toluene.
Copolymer
Reaction time
(h)
conv.a
(%)
b,calnM
(g mol-1)
c,SECnM
(g mol-1)
PDId
S-1 2 2 9 080 8 200 1.75
S-2 4 15 17 400 16 000 1.50
S-3 4.5 21 21 240 20 000 1.50
S-4 5 26 24 440 23 300 1.50 aMonomer conversion determined using 1H NMR spectroscopy. bNumber average molecular weight calculated using: Mn,calc = (conversion (%)×[M] 0/[MacroCTA]0×MM)+MmacroCTA where [M]0, [MacroCTA]0, MM and MmacroCTA are the initial concentration of monomer, the initial concentration of difunctional telechelic cis-1,4-polyisoprene macroCTA, the molecular weight of monomer and the molecular weight of the difunctional telechelic cis-1,4-polyisoprene macroCTA respectively. cNumber average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards at 35°C. dPolydispersity index measured by SEC.
C12H25S S
OS
O
OS S
C12H25
O
S80
toluene, 60 °C, 5h O O0.4 eq. AIBN,
500 eq.
C12H25S S
S
S SC12H25
S80
O O O O
50 50
7
9
Scheme IV-4. Synthesis of P(t-BA)-b-PIp-b-P(t-BA) by RAFT polymerization using α,ω-
bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene as macroCTA.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 96 -
A)
B)
1.01.52.02.53.03.54.04.55.05.56.0 ppm
3.33.43.5 ppm
1
4
2
3
Figure IV-8. A) Overlaid SEC traces of the telechelic cis-1,4-polyisoprene and of the P(t-
BA)-b-PIp-b-P(t-BA) triblock copolymers, and B) 1H NMR spectrum of P(t-BA)-b-PIp-b-
P(t-BA) triblock copolymers.
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Retention time (mins)
P(t-BA)-b-PI-b-P(t-BA)
PI
CH2S S
S
S SCH2
S80O O O O
50 50
C11H23C11H232
3 42
3
1 1
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 97 -
Conclusion
A new α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene was
successfully synthesized in one-pot reaction via metathesis degradation of NR using the
Grubbs II catalyst and a bistrithiocarbonyl-end functionalized olefin as a CTA. The
influence of the Grubbs II catalyst concentration and the CTA concentration were
investigated. The functionality of telechelic cis-1,4-polyisoprene reaches 2 when the ratio
of [GII] 0/[CTA] 0 is equal to 1/2 or/and 1/5 as demonstrated by 1H NMR spectroscopy. The
resulting α,ω-bistrithiocarbonyl-end functionalized telechlelic cis-1,4-polyisoprene was
successfully used as macroCTA for the RAFT polymerization of tert-butyl acrylate to form
P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers. This polymer precursor could be of great
interest in various block copolymers applications especially regarding adhesive properties
which are still in studies currently in our laboratory. This interest is also reinforced by the
fact that such functionalized oligomers are an alternative to few analogues coming from
petroleum origin.
Acknowledgments. The authors wish to thank French Ministry of education and research
and Prince of Songkla University, Thailand for their financial support. Thanks to Dr. Jean-
Claude Soutif for MALDI-TOF MS analysis.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 98 -
Experimental Section
General Characterization. NMR spectra were recorded on a Bruker Avance 400
spectrometer for 1H NMR (400 MHz), 13C NMR (100 MHz). Chemical shifts are reported
in ppm down-field from tetramethylsilane (TMS). Molecular weights and molecular
weight distributions were measured using size exclusion chromatography (SEC) on a
system equipped with a SpectraSYSTEM AS 1000 autosampler, with a Guard column
(Polymer Laboratories, PL gel 5 µm Guard column, 50×7.5 mm) followed by two columns
(Polymer Laboratories, 2 PL gel 5 µm MIXED-D columns, 2×300×7.5) and with a
SpectraSYSTEM RI-150 detector. The eluent used was tetrahydrofuran (THF) at a flow
rate of 1 mL min-1 at 25 °C or 35°C. Narrow molecular weight linear polystyrene standards
(ranging from 580 g mol-1 to 4.83×105 g mol-1) were used to calibrate the SEC. Infrared
spectra were recorded on a Nicolet Avatar 370 DTGS FT-IR spectrometer in the 4000-500
cm-1 range with KBr pellets and controlled by OMNIC software. Matrix-assisted laser
desorption ionization time-of-flight (MALDI-TOF) mass spectra were recorded on a
Bruker Biflex III equipped with a nitrogen laser (lZ337 nm). All mass spectra were
obtained in the linear mode with an acceleration voltage of 19 kV. The delay time was 200
ns. Typically, 100 single-shot acquisitions were summed to give a composite mass
spectrum. All data were reprocessed using the Bruker XTOF software. Thermal transition
of samples was measured by DSC Q100 (TA Instrument) Differential Scanning
Calorimeter equipped with the cooling system that temperature can be decrease to −90°C.
Samples were put in the aluminium capsule and empty capsule was used as inert reference.
All experiments were carried out under nitrogen atmosphere at flow rate 50 mL/min with
weight of sample 5 to 10 mg. Two scans from −80 to 60°C were performed with a heating
and cooling rate of 10°C/min and the glass transition temperature was recorded.
Materials. All chemicals were purchased from Aldrich unless otherwise noted. Oxalyl
chloride (99%), cis-but-2-ene-1,4-diol (97%), toluene (99%), ethyl vinyl ether (99%),
tricyclohexylphosphine [1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene]
benzylidineruthenium (IV) dichloride (99%+) (Grubbs second generation catalyst, GII), 2-
propanol (99%) (Fisher Scientific) and anisole (99%) were used as received.
Dichloromethane (99%+) and methanol (99%) were distilled over CaH2 prior to use. tert-
butyl acrylate (t-BA, 99%) was purified by passing through neutral alumina column to
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 99 -
remove inhibitor. 2,2-Azobis(2-methylpropionitrile) (AIBN, 98%) was recrystallized into
methanol prior to use. NR latex was preserved with ammonia solution 0.7% (w/w) (Dry
rubber content, DRC = 60%, wM = 2×106 g mol-1, Pattani Industrial, Thailand) and non
rubber impurities were removed by urea treatment, nonionic surfactant washing and double
centrifugation followed by coagulation with methanol and dried.44 The RAFT agent, S-1-
dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid) trithiocarbonate, (1, Scheme IV-1A) was
prepared according to a procedure reported in the literature.45 The bistrithiocarbonyl-end
functionalized olefin used as CTA (2, Scheme IV-1A) was synthesized as described
previously.46
Functional Metathesis Degradation Procedure. A general procedure for metathesis
degradation of NR to obtain difunctional telechelic cis-1,4-polyisoprene (7, Scheme IV-
1B) is described. A magnetic stirrer was charged to a dry Schlenk tube fitted with a rubber
septum. A degassed solution of purified NR (0.7 g, 0.0103 mol) dissolved in toluene (20
mL) was added. Separately, a solution of the difunctional CTA (2, Scheme IV-1A)
(0.1606 g, 0.2056 mmol) and Grubbs II catalyst (GII, 0.0873 g, 0.1028 mmol) in toluene (4
mL) was degassed by sparging with argon and stirred for 15 min. The resulting solution of
difunctional CTA and Grubbs II catalyst was transferred into the solution of NR using a
degassed syringe (defining t = 0) at 25 °C. Aliquots were withdrawn from the reaction
solution after 2, 4, 6 and 8 h. When this time had elapsed the metathesis reaction was
quenched by adding ethyl vinyl ether into the reaction solution under an argon atmosphere.
The resulting solution was concentrated under vacuum at room temperature and was
purified by a series of precipitations from dichloromethane (minimum volume) into 2-
propanol (100 mL) at room temperature. The isolated polymer was dried under vacuum to
remove any trace of solvent. It was then further analyzed by 1H NMR spectroscopy, 13C
NMR spectroscopy, FTIR spectroscopy and SEC. Yield: 76%.
1H NMR (CDCl3): δ (ppm) 5.86-5.70 (br, chain-end, cis -CH=CH), 5.60-5.50 (br, chain-
end, trans -CH=CH), 5.38-5.28 (br, chain-end; -C(CH3)=CH-), 5.14 (br, polyisoprene
backbone, -C(CH3)=CH), 4.72-4.65 (d, chain-end, -C(CH3)=CH-CH2OC(O)-), 4.65-4.56
(d, chain-end, -C(CH3)=CH-CH2OC(O)- and -CH=CH-CH2OC(O)-), 4.56-4.50 (d, chain-
end, -CH=CH-CH2OC(O)-), 3.25 (t, C(S)-SCH2CH2R), 2.12-1.95 (br, polyisoprene
backbone, -CH2C(CH3)=CH- and -C(CH3)=CHCH2), 1.70-1.60 (br, polyisoprene
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 100 -
backbone, -C(CH3)=CH, and chain-end -SC(CH3)2C(O)O-), 1.20-1.40 (br, chain-end, -
SCH2(CH2)10CH3), 0.86 (t, -S(CH2)11CH3).
13C NMR (CDCl3): δ(ppm) 135.21(cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 125.02
(cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 36.8 (chain-end, C(S)-SCH2CH2-), 32.2
(cis-1,4-polyisoprene backbone, -CH2C(CH3)=CH-), 31.92, 29.64, 29.63, 29.57, 29.46,
29.35, 29.12, 28.95, 27.86 (chain-end, -SCH2(CH2)9CH2CH3, 26.39 (cis-1,4-polyisoprene
backbone, -C(CH3)=CH-CH2-), 25.36 (chain-end, -SC(CH3)2C(O)O-), 23.44 (cis-1,4-
polyisoprene backbone -C(CH3)=CH-), 22.70 (chain-end, -SCH2(CH2)8CH2CH3), 14.14
(chain-end, -CH3)
FTIR: ν (cm-1) 3032 (H-C=C), 2962-2854 (CH2, CH3), 1735 (chain-end, -C=O), 1666
(polyisoprene backbone-C=C-), 1448 (polyisoprene backbone -CH2), 1376 (polyisoprene
backbone, -CH2), 1259 (chain-end, C-O-), 1082 (chain-end, -C-S), 836 (polyisoprene
backbone, -CH),
A typical RAFT polymerization. A typical procedure is given for the polymerization of
tert-butyl acrylate (t-BA) mediated by α,ω-bistrithiocarbonyl-end functionalized telechelic
cis-1,4-polyisoprene (7, Scheme IV-1B) used as macroCTA and using AIBN as the
initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 = 500/1/0.4). A magnetic stir bar was charged to a
Schlenk tube together with the CTA (0.3160 g, 0.051 mmol), t-BA (3.65 mL, 0.028 mol),
AIBN (0.0033 g, 0.020 mmol), toluene (1 mL, 20% v/v) and anisole (0.17 mL, 5% v/v).
Then, the reaction mixture was deoxygenated by bubbling with argon for 15 min. The
polymerization was initiated by immersion in a thermostatted oil bath at 60°C. Samples
were withdrawn from the reaction mixture via a degassed syringe for conversion
monitoring (by 1H NMR spectroscopy) and molecular weight analysis (by SEC). At the
end of reaction, the polymer solution was concentrated under vacuum using rotary
evaporation and was purified by a series of precipitations from dichloromethane (minimum
volume) into an ice cold 1:1 mixture of water and methanol. The copolymer was separated
by filtration and dried under vacuum until constant weight. It was then further analyzed by 1H NMR spectroscopy, 13C NMR spectroscopy and SEC.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 101 -
1H NMR (CDCl3): δ (ppm) 5.86-5.70 (br, chain-end, cis -CH=CH-), 5.60-5.50 (br, chain-
end, trans-CH=CH-), 5.16 (br, polyisoprene backbone, -C(CH3)=CH), 4.72-4.65 (d, chain-
end, -C(CH3)=CH-CH2OC(O)-), 4.65-4.56 (d, chain-end, -C(CH3)=CH-CH2OC(O)- and -
CH=CH-CH2OC(O)-), 4.56-4.50 (d, chain-end, -CH=CH-CH2OC(O)-) 3.32 (t, C(S)-
SCH2CH2R), 2.40-2.15 (br, P(t-BA) backbone, -CH2-CHC(O)-), 2.12-1.95 (br,
polyisoprene backbone, -CH2C(CH3)=CH- and -C(CH3)=CHCH2-), 1.90-1.70 (br, P(t-BA)
backbone -CH2-CHC(O)-), 1.70-1.60 (br, polyisoprene backbone, -C(CH3)=CH-, and
chain-end -SC(CH3)2-C(O)O-), 1.55-1.30 (br, P(t-BA) backbone -OC(CH3)3), 1.20-1.40
(br, chain-end -SCH2CH2-(CH2)9CH3), 0.86 (t, S(CH2)11CH3).
13C NMR (CDCl3): δ(ppm) 174.16 (P(t-BA) backbone, -C(O)-O-), 135.21 (cis-1,4-
polyisoprene backbone, -C(CH3)=CH-), 125.02 (cis-1,4-polyisoprene backbone, -
C(CH3)=CH-), 80.41 (P(t-BA) backbone, -C(O)-O-C(CH3)3), 42.42 (P(t-BA) backbone, -
CHC(O)-O-C(CH3)3), 37.41, (chain-end, C(S)-SCH2CH2-), 32.20 (cis-1,4-polyisoprene
backbone, -CH2C(CH3)=CH-), 31.92, 29.64, 29.63, 29.57, 29.46, 29.35, 29.12, 28.95,
27.86 (chain-end, -SCH2(CH2)9CH2CH3, 28.14 (P(t-BA) backbone, -O-C(CH3)3), 26.39
(1,4-cis- polyisoprene backbone -C(CH3)=CH-CH2-), 23.44 (cis-1,4-polyisoprene
backbone -C(CH3)=CH-), 22.70 (chain-end, -S(CH2)9CH2CH3), 14.14 (chain-end, -CH3).
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 102 -
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Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 103 -
[29] Meier, W.; Falk, A.; Odenwald, M.; Stieber, F., Colloid. Polym. Sci. 1996, 274, 218-226.
[30] Hillmyer, M. A., Adv. Polym. Sci. 2005, 190, 137-181. [31] Nor, H. M.; Ebdon, J. R., Prog. Polym. Sci. 1998, 23, 143-177. [32] Gillier-Ritoit, S.; Reyx, D.; Campistron, I.; Laguerre, A.; Singh, R. P., J. Appl.
Polym. Sci. 2003, 87, 42-46. [33] Kébir, N.; Campistron, I.; Laguerre, A.; Pilard, J.-F.; Bunel, C.; Couvercelle, J.-P.;
Gondard, C., Polymer 2005, 46, 6869-6877. [34] Morandi, G.; Kebir, N.; Campistron, I.; Gohier, F.; Laguerre, A.; Pilard, J.-F.,
Tetrahedron Lett. 2007, 48, 7726-7730. [35] Saetung, A.; Rungvichaniwat, A.; Campistron, I.; Klinpituksa, P.; Laguerre, A.;
Phinyocheep, P.; Pilard, J.-F., J. Appl. Polym. Sci. 2010, 117, 1279-1289. [36] Saetung, A.; Rungvichaniwat, A.; Campistron, I.; Klinpituksa, P.; Laguerre, A.;
Phinyocheep, P.; Doutres, O.; Pilard, J.-F., J. Appl. Polym. Sci. 2010, 117, 828-837. [37] Solanky, S. S.; Campistron, I.; Laguerre, A.; Pilard, J.-F., Macromol. Chem. Phys.
2005, 206, 1057-1063. [38] Lapinte, V.; Fontaine, L.; Montembault, V.; Campistron, I.; Reyx, D., J. Mol.
Catal. A: Chem. 2002, 190, 117-129. [39] Matyjaszewski, K., Controlled/Living Radical Polymerization. ACS Symposium
Series Washington, DC, 2000. Vol. 768, p 2. [40] Moad, G.; Thang, S. H., Aust. J. Chem. 2009, 62, 1379-1381. [41] Moad, G.; Rizzardo, E.; Thang, S. H., Polymer 2008, 49, 1079-1131. [42] Yin, X.; Hoffman, A. S.; Stayton, P. S., Biomacromolecules 2006, 7, 1381-1385. [43] Barner-Kowollik, C., Handbook of RAFT polymerization. WILEY-VCH Verlag
GmbH & Co. KGaA: Weinheim, 2008; p 455. [44] Klinklai, W.; Saito, T.; Kawahara, S.; Tashiro, K.; Suzuki, Y.; Sakdapipanich, J. T.;
Isono, Y., J. Appl. Polym. Sci. 2004, 93, 555-559. [45] Lai, J. T.; Filla, D.; Shea, R., Macromolecules 2002, 35, 6754-6756. [46] Mahanthappa, M. K.; Bates, F. S.; Hillmyer, M. A., Macromolecules 2005, 38,
7890-7894. [47] Tanaka, Y.; Sato, H.; Kageyu, A.; Tomita, T., Biochem. J 1987, 243, 481. [48] Lu, Z.; Huang, X.; Huang, J.; Pan, G., Macromol. Rapid Commun. 1998, 19, 527-
531. [49] Hou, S.; Chan, W. K., Macromolecules 2001, 35, 850-856. [50] Fages, G.; Pham, T., Q., Makromol. Chem. 1978, 179, 1011-1023. [51] Camberlin, Y.; Pascault, J.-P.; Pham, T., Q., Makromol. Chem. 1979, 180, 397. [52] Busnel, J. P., Polymer 1982, 23, 137-141. [53] Tlenkopatchev, M. A.; Barcenas, A.; Fomine, S., Macromol. Theory Simul. 2001,
10, 441-446. [54] Ivin, K. J.; Mol, J. C., Olefin metathesis and metathesis polymerisation. Academic
Press: London, 1997. p 375. [55] Bielawski, C. W.; Grubbs, R. H., Prog. Polym. Sci. 2007, 32, 1-29. [56] Fernández-García, M.; Fuente, J. L. d. l.; Cerrada, M. L.; Madruga, E. L., Polymer
2002, 43, 3173-3179.
Chapter V
Thermal properties of block
copolymers based on PI/P(t-BA) and
PI/PAA
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 104 -
Introduction
In order to have a better knowledge on the potential use of previously synthesized well-
defined block copolymers containing polyisoprene (PI) from synthetic- and natural rubber
(NR) with poly(tert-butyl acrylate) (P(t-BA)), the thermal properties of PI macromolecular
chain transfer agent (PI-macroCTAs), PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-
b-P(t-BA) triblock copolymers are studied in the first part. In the second part, the influence
of the PI microstructure on thermal properties was studied. The last part describes the
investigation on the cleavage reaction of the tert-butyl ester units of P(t-BA) to form
poly(acrylic acid) (PAA) and the determination of the thermal properties of resulting block
copolymers based on PI and PAA.
I. Comparison between PI-macroCTA and block copolymers based on
PI/P(t-BA)
In this section, the thermal properties of previous PI-macroCTAs, well-defined PI-b-P(t-
BA) diblock copolymers synthesized from successive RAFT polymerizations of isoprene
and t-BA (2, Scheme V-I) and from oxidative degradation of NR followed by reductive
amination, amidation and RAFT polymerization of t-BA (2’, Scheme V-I) are
investigated. Moreover, thermal analysis of well-defined P(t-BA)-b-PI-b-P(t-BA) triblock
copolymers (5, Scheme V-II) prepared via metathesis degradation of NR followed by the
RAFT polymerization of t-BA are carried out by differential scanning calorimetry (DSC)
and thermogravimetric analysis (TGA). The results are summarized in Table V-1.
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 105 -
A) B)
62
OC12H25
S
S
SO
NH
O O
87
C12H25
S
S
SO
OH
80O O
65
64
and
2 2'
C12H25
S
S
SO
OH
81 4 5
901
0.2 eq AIBN
60 °C, 2.5h250 eq t-BA
62
OC12H25
S
S
SO
NH
1'
62
OC12H25
S
S
SO
NH
O OH
87
iodotrimethylsilane25 °C, 4h
3'
0.2 eq AIBN
60 °C, 4h250 eq t-BA
C12H25
S
S
SO
OH
80O OH
6564
3
iodotrimethylsilane25 °C, 4h
CH2Cl2
CH2Cl2
Scheme V-1. Synthesis of PI-b-PAA diblock copolymers; A) PI block obtained by RAFT
polymerization of isoprene and B) PI block obtained by oxidative degradation of NR
followed by reductive amination and amidation.
80
50
OOOO
50
S
S
SC12H25
S
S
SC12H25
80
50
OHOOHO
50
S
S
SC12H25
S
S
SC12H25
25 °C, 4h
5
6
4
C12H25S S
OS
O
OS S
C12H25
O
S80
0.4 eq AIBN
60 °C, 5h500 eq t-BA
iodotrimethylsilane CH2Cl2
Scheme V-2. Synthesis of PAA-b-PI-b-PAA based on PI block obtained by metathesis
degradation of NR.
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 106 -
Table V-1. Thermal properties of PI-macroCTAs and block copolymers based on PI Glass transition Thermal degradation stage
Entry Sample temperature 1st stage 2nd stage 3rd stage Tg
1 Tg2 Tmax Weight
loss Tmax Weight
loss Tmax Weight
loss (°C) (°C) (°C) (%) (°C) (%) (°C) (%)
A-1 PI-macroCTA (1)a −60 - * 5.5 376 94.3 - -
A-2 PI-b-P(t-BA) (2) −35 37 181 34.5 272 14.3 425 42.4
A-3 PI-macroCTA (1’)b −64 - * 6.1 375 91.8 - -
A-4 PI-b-P(t-BA) (2) −40 30 240 38.0 264 9.0 380-434 46.5
A-5 PI-macroCTA (4)c −64 - * 9.7 375 87.7 - -
A-6 P(t-BA)-b-PI-b-
P(t-BA) (5)
−37 32 189 37.0 272 14.2 424 40.4
aPI-macroCTA obtained by polymerization of isoprene via RAFT polymerization, bPI-macroCTA obtained
by oxidative degradation of NR followed by reductive amination and amidation, cPI-macroCTA obtained by
metathesis degradation of NR. * Not determined (Thermal decomposition began ∼ 120 °C)
Glass transition temperature (Tg) of PI-macroCTAs, PI-b-P(t-BA) diblock copolymers and
P(t-BA)-b-PI-b-P(t-BA) triblock copolymers were investigated by DSC under nitrogen at
10 °C/min heating rate.
A single Tg is detected in all the DSC thermograms of PI-macroCTA except in block
copolymers that exhibit two glass transition temperatures. The DSC curve of PI-
macroCTA obtained by RAFT polymerization of isoprene (Figure V-1) shows a single
glass transition temperature (Tg) at −60 °C. This result confirms that the PI microstructure
is predominantly 1,4 as the Tg of cis-1,4-PI is equal to −73 °C1 and the one of trans-1,4-PI
is equal to −58 °C1 while the Tg of 3,4-PI is equal to 33 °C.2 The PI-b-P(t-BA) diblock
copolymer (entry A-2, Table V-1) shows two values of Tg, the low one at −35 °C
corresponding to the glass transition temperature of PI and the higher one at 37 °C
corresponding to the glass transition temperature of P(t-BA) as the Tg of P(t-BA) is equal
to 48 °C.3 The glass transition temperature assigned to the PI backbone is significantly
moved toward higher temperatures in the block copolymer compared to the PI-macroCTA.
This shift is expected since the introduction of rigid P(t-BA) reduces the mobility of the PI
backbone leading to an increase of the Tg value.
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 107 -
Similar results are seen in DSC curves (Figure V-2) of PI-macroCTA obtained by
oxidative degradation of NR followed by reductive amination and amidation (entry A-3,
Table V-1). A single Tg of PI-macroCTA is observed at −64 °C. Whereas, the PI-b-P(t-
BA) diblock copolymer (entry A-4, Table V-1) shows two values of Tg which the low
temperature at −40 °C corresponds to the glass transition temperature of PI and the higher
temperature at 30 °C corresponds to the glass transition temperature of P(t-BA).
In addition, similar curves could be observed on the DSC analysis (Figure V-3) of PI-
macroCTA obtained by metathesis degradation of NR (entry A-5, Table V-1) and P(t-
BA)-b-PI-b-P(t-BA) (entry A-6, Table V-1). We observe a single Tg of PI-macroCTA at
−64 °C and two values of Tg of P(t-BA)-b-PI-b-P(t-BA) triblock copolymers with the low
temperature at −37 °C corresponds to the glass transition temperature of PI and the higher
temperature at 32 °C corresponds to the glass transition temperature of P(t-BA).
This is a supplementary proof of the successful synthesis of PI-b-P(t-BA) diblock
copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers.
Figure V-1. DSC thermograms of PI-macroCTA (entry A-1, Table V-1) and PI-b-P(t-
BA) diblock copolymer (entry A-2, Table V-1).
PI-macroCTA --- PI-b-P(t-BA)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 108 -
Figure V-2. DSC thermograms of PI-macroCTA (entry A-3, Table V-1) and PI-b-P(t-
BA) diblock copolymer (entry A-4, Table V-1).
Figure V-3. DSC thermograms of PI-macroCTA (entry A-5, Table V-1) and P(t-BA)-b-
PI-b-P(t-BA) diblock copolymer (entry A-6, Table V-1).
PI-macroCTA --- PI-b-P(t-BA)
PI-macroCTA --- P(t-BA)-b-PI-b-P(t-BA)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 109 -
The thermal stability of PI-macroCTAs and block copolymers based on PI/P(t-BA) were
also studied using thermogravimetric analysis (TGA) under nitrogen at 10 °C/min heating
rate. The main TGA parameters are shown in Table V-1.
The thermogravimetric curve and its first derivative curve of PI-macroCTA obtained by
RAFT polymerization of isoprene is shown in Figure V-4. Results show that the thermal
decomposition starts at 120 °C with a weight loss of 5.5% and, then a weight loss of 94.3%
is obtained from 300 °C to 475 °C. The maximum temperature (Tmax) at 376 °C and a
shoulder at 420 °C were observed on the first derivative thermogravimetric curve. This
behaviour shows that the PI-macroCTA degradation involves many reactions. As
mentioned by Job et al.4 and Mattoso et al.5-6 during NR degradation, random scissions
occur with simultaneous crosslinkings and cycling reactions.
Similar behaviour were seen on thermogravimetric curve and its first derivative curve
(Figure V-5 and Figure V-6) of PI-macroCTA obtained from oxidative degradation of
NR followed by reductive amination and amidation (entry A-3, Table V-1) and PI-
macroCTA obtained by metathesis degradation of NR (entry A-5, Table V-1). The
thermal decomposition starts at 120 °C with a weight loss of 6.1% and of 9.7%,
respectively. A maximum temperature (Tmax) at 375 °C and a shoulder at 434 °C and at 420
°C with a weight loss of 91.8% and of 87.7% respectively, are attributed to the degradation
of polyisoprene part.
The thermogravimetric studies of block copolymers show that the PI-b-P(t-BA) diblock
copolymers (entry A-2, Table V-1) obtained from successive RAFT polymerizations of
isoprene and t-BA has a similar behaviour than the P(t-BA)-b-PI-b-P(t-BA) (entry A-6,
Table V-1). The first thermal degradation shows a Tmax at 180°C and at 189 °C with a
weight loss of 34.5% and of 37.0% respectively. This first stage is associated with the
elimination of tert-butyl ester group in P(t-BA) blocks3 (Scheme V-3). The second stage
has a Tmax at 272°C with a weight loss of 14.2% for both block copolymers. This is due to
the dehydration reactions between carboxylic groups to give six-member cyclic anhydride
structures3 (Scheme V-3). The final third stage is attributed to the degradation of
polyisoprene block with a Tmax at 425°C and a weight loss of 42.4% and of 40.4% for
diblock copolymer and triblock copolymer respectively.
The thermogravimetric curve of the PI-b-P(t-BA) diblock copolymers (entry A-4, Table
V-1) synthesized from the oxidative degradation of NR followed by reductive amination
and amidation and RAFT polymerization of t-BA shows a first degradation stage with a
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 110 -
Tmax at 240 °C and a weight loss of 38.0%. This Tmax is higher than the Tmax observed for
diblock copolymer issued from successive RAFT polymerization of isoprene and t-BA and
than Tmax observed for triblock copolymers. This is probably due to increasing intra- and
intermacromolecular interactions between the chains by hydrogen bonds between N-H
groups and C=O groups. At higher temperature that Tmax = 240 °C, the thermogravimetric
curve of the PI-b-P(t-BA) diblock copolymer (entry A-4, Table V-1) shows the thermal
degradations of P(t-BA) block and PI block as previously described.
O O O O
n
O OH O OH
n
O O O
n
+ H2O
+ 2
Scheme V-3. Mechanism of the first stage of P(t-BA) thermal degradation.3
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 111 -
Figure V-4. A) themogravimetric curves, B) first derivatives curve for PI-macroCTA
(entry A-1, Table V-1) and PI-b-P(t-BA) diblock copolymer (entry A-2, Table V-1)
under a nitrogen atmosphere, at a heating rate of 10 °C/min.
A)
B)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 112 -
Figure V-5. A) themogravimetric curves, B) first derivatives curve for PI-macroCTA
(entry A-3, Table V-1) and PI-b-P(t-BA) diblock copolymer (entry A-4, Table V-1)
under a nitrogen atmosphere, at a heating rate of 10 °C/min.
A)
B)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 113 -
Figure V-6. A) themogravimetric curves, B) first derivatives curve for PI-macroCTA
(entry A-5, Table V-1) and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers (entry A-6,
Table V-1) under a nitrogen atmosphere, at a heating rate of 10 °C/min.
B)
A)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 114 -
II. Influence of the PI microstructure
In this section, the influence of the PI microstructure on the thermal properties of PI-b-
P(t-BA) diblock copolymers is studied by comparing DSC curves and TGA curves
between PI-b-P(t-BA) diblock copolymer obtained from successive RAFT polymerizations
of isoprene and t-BA (2, Scheme V-1) and PI-b-P(t-BA) diblock copolymer obtained by
oxidative degradation of NR followed by reductive amination and amidation and RAFT
polymerization of t-BA (2’, Scheme V-1).
The Tg value of PI-macroCTA obtained by RAFT polymerization of isoprene (entry A-1,
Table V-1) was noted at −60°C that is a slightly higher than Tg noted (Tg= −64 °C) of PI-
macroCTA obtained by oxidative degradation of NR followed by reductive amination and
amidation (entry A-3, Table V-1). The PI-macroCTA (entry A-1, Table V-1) obtained by
RAFT polymerization of isoprene has a microstructure composed of 90% of 1,4-PI (60%
trans and 40% cis), 4% of 1,2-PI and 6% of 3,4-PI. By contrast, PI-macroCTA (entry A-3,
Table V-1) obtained by oxidative degradation of NR followed by reductive amination and
amidation leads to cis-1,4-PI units. It is well-known that the type of isomeric structures of
PI influences the degree of crystallinity and glass transition temperature of PI.7 Normally,
the Tg of cis-1,4-PI is lower than that of trans-1,4-PI and 3,4-PI due to the fact that the
lower the cis content, the less amount the crystallinity that the polymer can develop.8
However, the various PI microstructures in our work has no significant influence on their
thermal properties. This is probably due to the fact that the NR-based cis-1,4-PI obtained
after NR degradation have a low number-average molecular weight.
The Tg values assigned to the PI backbone of PI-b-P(t-BA) diblock copolymers (entry A-2
and entry A-4, Table V-1) increase from −60 °C to −35 °C and from −64 °C to −40 °C
respectively. This shift toward higher temperatures is expected since the introduction of
rigid P(t-BA) in the block copolymers reduces the mobility of the chains. This reduction of
mobility can also explained the thermal stability of PI-b-P(t-BA) diblock copolymers. It
can be observed that the Tmax (424 °C) in the second stage of PI-b-P(t-BA) diblock
copolymers from PI-macroCTA obtained by RAFT polymerization of isoprene (entry A-2,
Table V-1) is not different to the Tmax (425 °C) observed in the second stage of PI-b-P(t-
BA) diblock copolymers from PI-macroCTA obtained by oxidative degradation of NR
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 115 -
(entry A-4, Table V-1). Thus it can be concluded that the difference in microstructures of
low molecular weight PI has no effect on the thermal stability of the diblock copolymers.
III. Deprotection of t-BA group and thermal stability of resulting block
copolymers based PI/PAA
A number of recent reports have described the preparation of diblock copolymers
containing PI with poly(acrylic acid) (PAA) through the cleavage reaction of the tert-butyl
ester units to form PI-b-PAA. Wooley et al.9 have prepared PI-b-PAA by the hydrolysis of
PI-b-P(t-BA) copolymer precursor by heating the diblock polymers in 1,4-dioxane
containing concentrated HCl at reflux.
Lu et al.10 reported the preparation of microspheres using PI-b-PAA as the surfactant to
disperse a solution of PI-b-P(t-BA) and a P(t-BA) homopolymer (hP(t-BA)) in
dichloromethane. The PI-b-P(t-BA) and the precursor of PI-b-PAA were prepared by
sequential anionic polymerization. The tert-butyl ester groups of the precursor of PI-b-
PAA were removed quantitatively under acidic hydrolysis by treatment with trifluoroacetic
acid in dry dichloromethane to form PI-b-PAA and then used as the surfactant. More
recently Wooley and co-workers11 have investigated the synthesis of amphiphilic shell-
crosslinked (SCK) nanoparticles consisting of a PI core and a PAA shell from P(t-BA)-b-
PI block copolymers prepared via NMP. The cleavage reaction of the tert-butyl ester unit
was performed in toluene/acetic acid using methanesulfonic acid as catalyst at 110 °C. The
same group12 further extended the synthesis of PI-b-P(t-BA) copolymers to the synthesis of
core-shell brush copolymers. A brush copolymer consisting of a PI-b-P(t-BA) diblock
copolymer grafts and a polynorbornene backbone is obtained. The P(t-BA) units are
hydrolysed using HCl to form PAA units that were subsequently crosslinked with 2,2-
(ethylenedioxy)bis(ethylamine) to form a crosslinked brush. Full details of these
experiments were described in pages 15-28 of Chapter I.
Previous well-defined PI-b-P(t-BA) diblock copolymers synthesized from successive
RAFT polymerizations of isoprene and t-BA (2, Scheme V-I) and from oxidative
degradation of NR followed by reductive amination, amidation and RAFT polymerization
of t-BA (2’, Scheme V-I) were treated by iodotrimethylsilane at room temperature.13
After 4h, the excess solvent and reagent were removed and the copolymers were
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 116 -
redissolved in THF. The resulting solutions were dialyzed using nanopure water, followed
by lyophilisation to obtain the white solid product of PI-b-PAA diblock copolymers (3 and
3’, Scheme V-I). In addition, the previous P(t-BA)-b-PI-b-P(t-BA) triblock copolymers (5,
Scheme V-II) prepared via metathesis degradation of NR followed from the RAFT
polymerization of t-BA were treated with iodotrimethylsilane to form PAA-b-PI-b-PAA
triblock copolymers (6, Scheme V-II) following the same conditions as for the preparation
of PI-b-PAA diblock copolymers (3 and 3’, Scheme V-I).
All solid products of PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA triblock
copolymers obtained after lyophilisation are difficult to solubilize in polar solvents
(DMSO (d-6), D2O, pyridine (d-5)) at 25 °C. Due to this problem, ATR-FTIR analysis and 13Carbon Cross-Polarisation (CP) combined with Magic Angle Spinning (MAS) (13C-CP-
MAS) solid-state NMR spectroscopy were used to observe the cleavage of the tert-butyl
groups. The modification of PI-b-P(t-BA) (2 and 2’, Scheme V-I) to PI-b-PAA (3 and 3’,
Scheme V-I) and P(t-BA)-b-PI-b-P(t-BA) (5, Scheme V-II) to PAA-b-PI-b-PAA (6,
Scheme V-II) were confirmed by ATR-FTIR analysis (Figures V-7-9). After deprotection
of the tert-butyl ester, the ATR-FTIR spectra show a broad peak in the region ~2900-3400
cm-1 corresponding to O-H bond stretching vibrations in acrylic acid groups, a broadening
of carbonyl band that shifts from 1730 to 1700 cm-1 and the disappearance of the bands at
1368 and 1392 cm-1 characteristics of the pendant methyl group of tert-butyl acrylate. This
indicates that the tert-butyl groups were successfully cleaved.
Similar results are seen in the ATR-FTIR spectrum of PAA-b-PI-b-PAA triblock
copolymers (Figure V-10). This result confirmed that tert-butyl groups were cleaved to
acrylic acid groups.
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 117 -
Figure V-7. ATR-FTIR spectra of PI-b-P(t-BA) diblock copolymer (2, Scheme V-1) and
PI-b-PAA diblock copolymer (3, Scheme V-1).
Figure V-8. ATR-FTIR spectra of PI-b-P(t-BA) diblock copolymer (2’, Scheme V-1) and
PI-b-PAA diblock copolymer (3’, Scheme V-1).
PI-b-P(t-BA)
412,7 429,0
471,5
750,9
844,5
1142,6
1255,1 1366,0
1392,0
1447,7
1723,8
2928,2
2963,
417,8
439,4
476,2
503,6 607,9 755,7
842,0
1052,9
1168,2
1251,8
1451,7
1704,2
2954,8
PI-b -PAA
Abs
orba
nce
500 1000 1500 2000 2500 3000 3500 4000 Wavenumber (cm-1)
751,4
845,8
1149,6
1256,8 1367,3
1392,3
1448,8
1728,4
2929,7
2976,7
599,9
780,9 804,5
1041,2 1158,3
1229,5
1413,8
1450,0
1703,2
1756,6 2934,0
Abs
orba
nce
1000 1500 2000 2500 3000 3500
Wave number (cm-1)
PI-b-PAA
PI-b-P(t-BA)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 118 -
Figure V-9. ATR-FTIR spectra of P(t-BA)-b-PI-b-P(t-BA) triblock copolymer (5, Scheme
V-2) and PAA-b-PI-b-PAA triblock copolymer (6, Scheme V-2).
The PAA block was further confirmed by 13C solid-state NMR spectroscopy (performed by
Dr. Monique BODY, LPEC-UMR CNRS 6087, Université du Maine). The 13C solid-state
NMR spectroscopy was previously used by Mauritz, et al.14 who reported characteristics
of poly(tert-butyl acrylate)-b-polystyrene-b-poly(isobutylene)-b-polystyrene-b-poly(tert-
butyl acrylate) after tert-butyl ester deprotection to target acrylic acid end block
functionality by a thermal process.
A comparison between the 13C CP-MAS solid-state NMR spectrum of the PI-b-P(t-BA)
diblock copolymers (2’, Scheme V-1) and the 13C liquid NMR spectrum of the PI-b-PAA
is presented in Figure V-10. The 13C liquid NMR spectrum (Figure V-10B) shows the
carbonyl carbon at 174.16 ppm and the quaternary carbon at 80.41 ppm corresponding to
P(t-BA) and also presents carbon resonances at 135.90 and 127.15 ppm, corresponding to
polyisoprene. The cleavage of the tert-butyl acrylate to acrylic acid groups to form PI-b-
PAA diblock copolymers was confirmed by the 13C CP-MAS solid-state NMR
spectroscopy (Figure V-10A). We observe that the carbonyl carbon at 174.16 ppm shifts
to 180.00 ppm and the disappearance of the quaternary carbon of the tert-butyl group at
80.41 ppm. The result indicates that the tert-butyl ester group of P(t-BA) was successfully
cleaved to form PI-b-PAA. Similar results are seen in the 13C CP-MAS solid-state NMR
spectrum of PAA-b-PI-b-PAA triblock copolymers (Figure V-11). This result confirms
that tert-butyl ester groups were successfully cleaved.
751,7
844,4
1141,8
1254,8 1365,8
1446,1
1723,1
2977,4
401,1
411,0 792,3
1041,5
1160,5 1237,4
1413,9
1453,1
1698,5
1756,6 2848,4
2916,2 Abs
orba
nce
500 1000 1500 2000 2500 3000 3500
Wave number (cm-1)
PAA-b-PI-b-PAA
P(t-BA)-b-PI-b-P(t-BA)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 119 -
210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm
210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm
1
1'
2
CDCl3
3
4
3' 4'
Figure V-10. A) 13C solid-state NMR spectrum of PI-b-PAA diblock copolymer (3’,
Scheme V-1) and B) 13C liquid NMR spectrum of PI-b-P(t-BA) diblock copolymer (2’,
Scheme V-1).
210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm
210 200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 ppm
1
1'
2
CDCl33 4
3' 4'
Figure V-11. A) 13C solid-state NMR spectrum of PAA-b-PI-b-PAA triblock copolymers
(6, Scheme V-2) and B) 13C liquid NMR spectrum of P(t-BA)-b-PI-b-P(t-BA) triblock
copolymers (5, Scheme V-2).
62
OC12H25
S
S
SO
NH
O O
87
1
2
3
4
62
OC12H25
S
S
SO
NH
O OH
87
1' 3'
4'
80
50OHO
OHO50
S
S
SC12H25
S
S
SC12H25
1'
3'
4'
1'
A)
A)
B)
B)
80
50
OOOO
50
S
S
SS
S
SC12H25
1
2
3
4
1
2
C12H25
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 120 -
The thermal properties of block copolymers before and after dealkylation of the t-BA units
of the block copolymers to form polar acrylic acid (AA) units have been investigated by
TGA. The main TGA parameters are shown in Table V-2.
Table V-2. Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA Thermal degradation stage Entry Sample 1st stage 2nd stage 3rd stage Tmax Weight
loss Tmax Weight
loss Tmax Weight
loss (°C) (%) (°C) (%) (°C) (%)
A-2 PI-b-P(t-BA) (2)a 181 34.5 272 14.3 425 42.4
B-2 PI-b-PAA (3) 242 20.3 432 48.4
A-4 PI-b-P(t-BA) (2’)b 240 38.0 261 9.0 380 46.5
B-4 PI-b-PAA (3’) 261 21.1 427 55.6
A-6 P(t-BA)-b-PI-b-P(t-BA) (5)c 189 37 272 14.2 424 40.4
B-6 PAA-b-PI-b-PAA (6) 266 22.9 429 51.0 - - aentry A-2, Table V-1, bentry A-4, Table V-1, centry A-6, Table V-1.
It can be observed that Tmax of PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA
triblock copolymers (entry B-2, entry B-4 and entry B-6, Table V-2) in the first stage are
shifted to higher temperatures in comparison with Tmax of PI-b-P(t-BA) diblock
copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers (entry A-2, entry A-4 and
entry A-6, Table V-2). This result confirms the successful removing of the tert-butyl ester
groups. For the second step, Tmax of PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA
triblock copolymers (entry B-2, entry B-4 and entry B-6, Table V-2) is slightly shifted to
higher temperatures in comparison with Tmax of PI-b-P(t-BA) diblock copolymers and P(t-
BA)-b-PI-b-P(t-BA) triblock copolymers (entry A-2, entry A-4 and entry A-6, Table V-
2). This can be explained by hydrogen bonds interactions occurring between chains leading
to an increase of the thermal stability.
The thermogravimetric curve of the PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA
triblock copolymers (entry B-2, entry B-4 and entry B-6, Table V-2) show that the
thermal degradation takes place through two stages (Figure V-12, Figure V-13 and
Figure V-14). The first one is mainly associated with the dehydration and decarboxylation
reactions of carboxyl groups in PAA block copolymer15 (Scheme V-4) with a Tmax at
242°C, at 261 °C and at 266 °C with a weight loss of 20.3%, of 21.1% and of 22.9%
respectively. The second stage is associated with chain scissions of PAA15 (Scheme V-4)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 121 -
and attributed to the degradation of polyisoprene part with a Tmax at 432°C, at 427°C and at
429 °C, with a weight loss of 48.4 %, of 55.6% and of 51.6% respectively.
O OH O OHn O O O
n
+ H2O
Dehydration
O O On
Decarboxylation
On O
O O O O OHn
n > 1
O O O O O O
O O O O OHn-1
O O O O O OO OH
or
homolysis
O O O O O O OH
+
+ oligomer or monomer
Chain scission
n
Scheme V-4. Mechanism of the first stage of PAA thermal degradation.15
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 122 -
Figure V-12. Themogravimetric curves for PI-b-P(t-BA) diblock copolymer (entry A-2,
Table V-2) and PI-b-PAA diblock copolymer (entry B-2, Table V-2) under a nitrogen
atmosphere, at a heating rate of 10 °C/min.
A)
B)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 123 -
Figure V-13. Themogravimetric curves for PI-b-P(t-BA) diblock copolymer (entry A-4,
Table V-2) and PI-b-PAA diblock copolymer (entry B-4, Table V-2) under a nitrogen
atmosphere, at a heating rate of 10 °C/min.
A)
B)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 124 -
Figure V-14. Themogravimetric curves for P(t-BA)-b-PI-b-P(t-BA) triblock copolymers
(entry A-6, Table V-2) and PAA-b-PI-b-PAA triblock copolymers (entry B-6, Table V-
2) under a nitrogen atmosphere, at a heating rate of 10 °C/min.
A)
B)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 125 -
Conclusion
The thermal properties of PI-macroCTAs, PI-b-P(t-BA) diblock copolymers and P(t-BA)-
b-PI-b-P(t-BA) triblock copolymers were studied by DSC. The DSC results showed that a
single Tg of PI-macroCTA was observed between −64 °C and −60 °C. Moreover, the PI-b-
P(t-BA) diblock copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers exhibited
two values of Tg, one is attributed to the glass transition temperature of the PI block (Tg =
(−40 °C) to (−35 °C)), and the other is related to the glass transition temperature of the P(t-
BA) block (Tg = 37 °C).
The thermal stability of PI-macroCTAs, PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-
PI-b-P(t-BA) triblock copolymers were studied by TGA. The PI microstructures had no
effect on thermal stability of PI-macroCTAs and PI-b-P(t-BA) diblock copolymers. This is
probably due to the fact that the NR-based cis-1,4-polyisoprenes obtained after NR
degradation have low number-average molecular weights.
PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers exhibit
better thermal stability than PI-macroCTA by increasing the maximum degradation
temperature of PI block from 376 °C to 424 °C.
The polarity of P(t-BA) was improved though the cleavage reaction of the tert-butyl ester
units of P(t-BA) block to form PAA block. This leads to PI and PAA based block
copolymers with higher thermal stability than PI-b-P(t-BA) diblock copolymers and P(t-
BA)-b-PI-b-P(t-BA) triblock copolymers. Thus, block copolymers based on PI and
containing PAA blocks could be better suited for high temperature applications when
compared with PI-macroCTAs and PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-b-
P(t-BA) triblock copolymers.
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 126 -
Experimental section
General Characterization. Infrared spectra were recorded on a Nicolet Avatar 370 DTGS
FT-IR spectrometer in the 4000-500 cm-1 range with a diamond ATR device (attenuated
total reflection) and controlled by OMNIC software. NMR spectra were recorded on a
Bruker Avance 400 spectrometer for 13C liquid NMR (100 MHz). Chemical shifts are
reported in ppm relative to the deuterated solvent resonances. Solid-state 13C NMR spectra
were carried out at room temperature on a BRUKER AVANCE 300 MHz wide bore
spectrometer at 75.47 MHz using Cross-Polarisation (CP) combined with Magic Angle
Spinning (MAS). The spectra were recorded at spinning frequencies equal to 10 kHz.
Chemical shifts are referenced to tetramethylsilane (TMS). For CP-MAS experiments, we
chose the 1H radio frequency field strength such as the π/2 pulse duration was equal to 3.5
µs. The cross polarisation contact time was taken equal to 3.5 ms. A recycle delay of 3 s
between scans was used. A 1H decoupling field of 70 kHz was applied during acquisition.
Thermal transition of samples was measured by DSC Q100 (TA Instrument) Differential
Scanning Calorimeter equipped with the cooling system that temperature can be decrease
to −90°C. Samples were put in the aluminium capsule and empty capsule was used as inert
reference. All experiments were carried out under nitrogen atmosphere at flow rate 50
mL/min with weight of sample 5 to 10 mg. Two scans from −80 to 60°C were performed
with a heating and cooling rate of 10°C/min and the glass transition temperature was
recorded.
Thermogravimetric analysis (TGA) was performed on a TA Instruments (TGA Q 100)
with a heating rate of 10°C min-1 from room temperature to 600°C under nitrogen
atmosphere at a flow rate 90 mL min-1 using 10 mg of sample for analysis.
Materials. All chemicals were purchased from Aldrich unless otherwise noted.
Dichloromethane (99%+) was distilled over CaH2 prior to use. Tetrahydrofuran (99%) and
iodotrimethylsilane (97%) were used as received.
General procedure for deprotection of tert-butyl ester in block copolymers.
Synthesis of PI-b-PAA: The cleavage of the tert-butyl groups from PI-b-P(t-BA) (1,1’,
Scheme V-1) to PI-b-PAA (2, 2’ Scheme V-1) was performed according to a literature
method.13 A quantity of the diblock copolymer (0.2536 g, 0.013 mmol) was dissolved in
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 127 -
50mL of dichloromethane and a solution of iodotrimethylsilane (0.4 mL, 28.1 mmol,
diluted by 10 mL CH2Cl2) was added. The reaction was stirred at room temperature for 4h,
followed by the removal of the excess solvent and reagents under reduced pressure. The
residue was redissolved in THF. The solution was then dialyzed against nanopure water for
5 days, followed by lyophilisation to afford the final product. White solid polymer was
obtained in a 60% yield.
13C-CP-MAS solid-state NMR : δ (ppm) 180.00 (poly(acrylic acid) backbone, -C=O),
135.90 (cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 127.15 (cis-1,4-polyisoprene,
-C(CH3)=CH-) and the large board between 16.00 ppm and 55.00 ppm corresponding to
aliphatic carbon of the PI-chain, P(t-BA)-chain and the chain-end.
FTIR: ν(cm-1) 3400-2900 (-OH acid), 1704 (-C=O), 1451 (-CH2), 1168 (C-O), 842 (-CH)
Synthesis of PAA-b-PI-b-PAA: The tert-butyl groups of P(t-BA)-b-PI-b-P(t-BA) triblock
copolymer (1, Scheme V-2) were removed to yield poly(acrylic acid)-b-PI-b-poly(acrylic
acid) (PAA-b-PI-b-PAA) (2, Scheme V-2) following the same procedure as for PI-b-P(t-
BA) diblock copolymer. The P(t-BA)-b-PI-b-P(t-BA) triblock copolymer (0.1536 g,
0.0080 mmol) was dissolved in 50mL of dichloromethane and a solution of
iodotrimethylsilane (0.4 mL, 28.1 mmol, diluted by 10 mL CH2Cl2) was added. The
reaction was stirred at room temperature for 4h, followed by the removal of the excess
solvent and reagents under reduced pressure. The residue was redissolved in THF. The
solution was then dialyzed against nanopure water for 5 days, followed by lyophilisation to
afford the final product. White solid polymer was obtained in a 60% yield.
13C-CP-MAS solid-state NMR : δ (ppm) 180.20 (poly(acrylic acid) backbone, -C=O),
135.90 (cis-1,4-polyisoprene backbone, -C(CH3)=CH-), 126.40 (cis-1,4-polyisoprene,
-C(CH3)=CH-) and the large board between 16.00 ppm and 55.00 ppm corresponding to
aliphatic carbon of the PI-chain, P(t-BA)-chain and the chain-end.
FTIR: ν(cm-1) 3400-2900 (-OH acid), 1698 (-C=O), 1453 (-CH2), 1160 (C-O), 792 (-CH)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 128 -
References
[1] Brandrup, J. I., Edmund H.; Grulke, Eric A.; Abe, Akihiro; Bloch, Daniel R. , Polymer Handbook. 4th ed.; John Wiley & Sons New York, 2005. p V/208.
[2] Zhang, L.; Luo, Y.; Hou, Z., J. Am. Chem. Soc. 2005, 127, 14562-14563. [3] Fernández-García, M.; Fuente, J. L. d. l.; Cerrada, M. L.; Madruga, E. L., Polymer
2002, 43, 3173-3179. [4] Agostini, S. L. D.; Constantino, L. J. C.; Job, E. A., J. Therm. Anal. Calorim. 2008,
91, 703-707. [5] Moreno, R. M. B.; De Medeiros, E. S.; Ferreira, F. C.; Alves, N.; Goncalves, S. P.;
Mattoso, L. H. C., Plastics, Rubber and Composites 2006, 35, 15-21. [6] Medeiros, E.; Galiani, P.; Moreno, R.; Mattoso, L.; Malmonge, J., J. Therm. Anal.
Calorim. 2010, 100, 1045-1050. [7] Kent, E. G.; Swinney, F. B., I&EC Product Research and Development 1966, 5, 134-
138. [8] Brydson, J. A., Plastic Materials. 5th ed.; Butterworths: London, 1989. p 272. [9] Huang, H.; Remsen, E. E.; Kowalewski, T.; Wooley, K. L., J. Am. Chem. Soc. 1999,
121, 3805-3806. [10] Lu, Z.; Liu, G.; Liu, F., J. Appl. Polym. Sci. 2003, 90, 2785-2793. [11] Murthy, K. S.; Ma, Q.; Remsen, E. E.; Tomasz, K.; Wooley, L. K., J. Mater. Chem.
2003, 13, 2785. [12] Cheng, C.; Qi, K.; Khoshdel, E.; Wooley, K. L., J. Am. Chem. Soc. 2006, 128, 6808-
6809. [13] Li, Z.; Ma, J.; Cheng, C.; Zhang, K.; Wooley, K. L., Macromolecules 2010, 43,
1182-1184. [14] Kopchick, J. G.; Storey, R. F.; Jarrett, W. L.; Mauritz, K. A., Polymer 2008, 49,
5045-5052. [15] McNeill, C. I.; Sadeghi, T. M., Polym. Degrad. Stab. 1990, 29, 233-246.
General conclusion
General conclusion
- 129 -
The objective of our research work was the synthesis of well-defined diblock copolymers and
triblock copolymers based on a polyisoprene (PI) block obtained from natural rubber via
Reversible Addition-Fragmentation chain transfer (RAFT) polymerization. The PI block was
used as a macromolecular chain transfer agent (macroCTA) to perform the RAFT
polymerization of tert-butyl acrylate. Then, the synthesis of well-defined trithiocarbonate
functionalized telechelic PIs was developed using two different strategies. The first one is based
on the oxidative degradation of natural rubber followed by reductive amination and amidation,
and the second one is based on the functional metathesis degradation of NR. It is interesting to
observe that no previous studies have been reported on the synthesis of NR-based block
copolymers by RAFT polymerization.
In order to compare final thermal properties of block copolymers taking into account the PI
microstructure, we first synthesized block copolymers via successive RAFT polymerization of
isoprene and t-BA. Well-defined PI (PDI = 1.23) with a mixture of microstructures was
obtained via RAFT polymerization. The microstructures consist of 90% of 1,4-PI (60% trans
and 40% cis), 5% of 1,2-PI and 6% of 3,4-PI. We found that the use of PI as macroCTA to
mediate the RAFT polymerization of t-BA using AIBN as initiator ([t-BA] 0/[PI-
macroCTA]0/[AIBN] 0 = 250/1/0.2) at 60 °C for 2.5h leads to well-defined PI-b-P(t-BA) that
presents unimodal molecular weight distribution and low polydispersity index (1.40). The
copolymer has a nM equal to 16,000 g.mol-1 as determined by SEC and a nDP (PI) equal to
90 and a nDP P(t-BA) equal to 72 as determined by 1H NMR spectroscopy.
A new trithiocarbonate functionalized telechelic cis-1,4-polyisoprene was synthesized via the
oxidative degradation of natural rubber followed by reductive amination and amidation. The
microstructure of the functionalized PI is strictly cis-1,4. The end-functionality was determined
by 1H-NMR spectroscopy and clearly demonstrated that telechelic cis-1,4-polyisoprene chains
carry the trithiocarbonate moiety. We demonstrated that the chain extension of the
trithiocarbonate functionalized cis-1,4-PI starting block resulted in an efficient block copolymer
formation. PI-b-P(t-BA) diblock copolymer presents an unimodal SEC trace and polydispersity
index equal to 1.76. The copolymer has a nM equal to 26,000 g.mol-1 as determined by SEC
and a nDP (PI) equal to 62 and nDP (P(t-BA)) equal to 87 as determined by 1H NMR
spectroscopy.
General conclusion
- 130 -
In addition, a new α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene was
also prepared via functional metathesis degradation from NR in the presence of second
generation Grubbs catalyst (GII) and a bistrithiocarbonyl-end functionalized olefin as CTA.
Formation of telechelic natural rubber occurs rapidly in a single-step process. The nM was
equal to 8,200 g. mol-1 as determined by SEC after 4h of reaction at 25 °C. A perfectly
bifunctional telechelic PI was obtained using a ratio of [NR]0/[GII] 0/[CTA)] 0 to 100/1/2 at 25°C.
Moreover, the difunctional telechelic PI has a strictly cis-1,4-microstructure. It was successfully
used as macroCTA for the RAFT polymerization of t-BA to form well-defined P(t-BA)-b-PI-b-
P(t-BA) triblock copolymer. The final copolymer has a nM equal to 23,300 g.mol-1, PDI equal
to 1.50 as determined by SEC and a nDP (PI) equal to 80 and nDP (P(t-BA)) equal to 100 as
determined by 1H NMR spectroscopy.
A comparison can be made between the PI-macroCTAs obtained using the three different
techniques: RAFT polymerization of isoprene, oxidative degradation of natural rubber followed
by reductive amination/amidation and metathesis degradation from NR. All three techniques
produce PI with well-defined trithiocarbonate end groups that can be chain extended with t-BA
to form block copolymers. The PI-macroCTA obtained from polymerization of isoprene has a
PDI of 1.23. However, the microstructure of PI-macroCTA is not well-defined and consists of a
mixture of 1,4-PI, of 1,2-PI and of 3,4-PI. By contrast the PI-macroCTAs obtained from the
degradation of NR by either oxidative degradation or metathesis degradation features a strictly
cis-1,4-microstructure. Oxidative degradation produces α-trithiocarbonyl-ω-carbonyl-cis-1,4-PI
whilst metathesis degradation leads to α, ω-bistrithiocarbonyl-cis-1,4-PI. The PDIs of these PI-
macroCTAs are broader (PDI ∼1.60-1.70) but after chain extension with t-BA, copolymers of
similar characteristics were obtained regardless of the preparation of the starting PI-macroCTA.
Finally, the thermal properties were studied by DSC and TGA. The DSC results showed that a
single Tg of PI-macroCTA was observed between −64 °C and −60 °C. Moreover, DSC results
showed that PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers
have two glass transition temperatures characteristic of each block, one at −35 °C corresponding
to PI block and the other at 37 °C corresponding to P(t-BA) block. This increase of Tg of PI
block copolymers is a supplementary proof of the successful synthesis of PI-b-P(t-BA) diblock
copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers.
General conclusion
- 131 -
In this work, we have shown that block copolymers based on PI can be synthesized form NR as
a renewable raw material. These investigations show that PI-macroCTAs from NR can be used
successfully for the formation of well-defined block copolymers containing P(t-BA) by either
PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers. The
polarity of P(t-BA) block and PAA block improve the thermal stability of PI block copolymers,
with increased polarity of the second block leading to increased thermal stability by more
interactions between the chains.
A possible extension of this work is the study of the adhesive performance of block copolymers
based on PI/P(t-BA) and PI/PAA for adhesive application on polar substrate such as stainless
steel. This is because the polar groups can rearrange and there after, orients to the interface
between the adhesive and the polar substrate, so as to minimize interfacial free energy during
adhesion. At the same time, hydrogen bonds can form between the polar groups and those in the
substrate. In addition, block copolymers based on PI/P(t-BA) and based on PI/PAA showed a
higher thermal stability than PI that may be used for high temperature adhesive applications.
Moreover, the unsaturated repeating units of the polyisoprene block can be chemically modified
by epoxidation to improve adhesive strength via crosslinking reaction. In addition, polymers
containing epoxide groups, such as poly(glycidyl (meth)acrylate) suitable to be synthesized by
RAFT polymerization in a control way could be employed. The main interest in those polymers
is largely due to the ability of pendant epoxide groups to be crosslinked by amines such as
diethylenetriamine. These advantages led to its explosive use as adhesive in industries.
Another possible extension of this work can be the development of adhesives in form of
waterborne or dispersion adhesives. The dispersion adhesive form is interesting in many
industrial and research work due to the use of water which has no negative impact for the
environment. Moreover, it has many advantages such as a safe man-working, a save storage and
a save distribution. The PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA triblock
copolymers can be dispersed in aqueous medium to form micelle structures due to the
incorporation of two different block segments. The hydrophobic segment is a polyisoprene
block and the hydrophilic segment is a poly(acrylic acid) block.
General conclusion
- 132 -
In conclusion, we have established a new methodology for the formation of trithiocarbonyl-end
functionalized telechelic cis-1,4-PI obtained from natural rubber. This technique involves the
functional metathesis degradation on NR. It is unique and powerful as the degradation and the
functionalization of NR occurs in a one-pot process. In addition, the reactive functional
precursors could be further chain extended with a wide range of monomers by RAFT
polymerization. Such controlled/living radical polymerization is a powerful process to prepare
well-defined block copolymers containing a cis-1,4-PI issued from NR which has a great
interest as it is a renewable resource. Then, our results bring new synthetic routes to develop
materials based on a biopolymer which is a renewable resource.