Fully Biobased Aliphatic Anionic Oligoesters: Synthesis and Properties · 2019. 7. 30. · tylene...

Research ArticleFully Biobased Aliphatic Anionic Oligoesters: Synthesisand Properties

Yosra Hadj Kacem,1,2 Abdelkader Bougarech ,1 Souhir Abid,1,3 Majdi Abid ,1,3

and Etienne Fleury2

1Laboratoire de Chimie Appliquée H.C.G.P., Faculté des Sciences de Sfax, Université de Sfax, Bp 1171, 3000 Sfax, Tunisia2Université de Lyon, INSA LYON, Ingénierie des Matériaux Polymères IMP-UMR CNRS 5223, F 69621 Villeurbanne, France3Chemistry Department, College of Science and Arts, Jouf University, P.O. Box 756, Al-Gurayyat, Al Jouf, Saudi Arabia

Correspondence should be addressed to Majdi Abid; [email protected]

Received 10 October 2018; Accepted 15 January 2019; Published 31 March 2019

Academic Editor: Alessandro Pegoretti

Copyright © 2019 Yosra Hadj Kacem et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in anymedium, provided the original work is properly cited.

Biobased aliphatic sulfonated oligoesters with 10 to 30% of sulfonated units were synthesized by melt polycondensation of biobasedmonomers such as diethyl succinate, z-octadec-9-enedioic acid, dimer fatty acid, sodium (sulfonated dimethyl succinate), andvarious diols like 1,4-butane diol and isosorbide. Structural characterization of the resulting oligoesters was determined by 1HNMR spectroscopy and MALDI-TOF MS technique. Showing a regular structure, the nature of the different expected speciespresent in the macromolecular structure allowed the detection of etherification and cyclisation side reactions. The study of thethermal properties indicates that the resulting oligoesters are amorphous or semicrystalline that essentially depend on the natureof monomers. Films of oligoesters treated in acidic, basic, and natural media at 37°C indicate that the remaining weight dependsessentially on the composition of oligoesters. Finally, sulfonated oligoester was used to prepare a biobased poly(ester-urethane)thermoset, a material having tunable properties.

1. Introduction

The sulfonated polyesters constitute the most studied ionicpolymer family. Indeed, the incorporation of sulfonatedgroups into the structure of aromatic polyesters, mainlyPET and PBT, has been the subject of many researches fornearly three decades [1–3]. PET containing small amountsof sulfonated units has been known for a long time. Theyhave been exploited by DuPont as textile fibers withimproved dye ability to cationic dyes [4]. The pioneer workswere interested in the preparation of sulfonated PET con-taining Na+, K+, and Cs+ counterions [5–10]. In particu-lar, they were interested in the evolution of the thermalbehavior and the crystallinity following the modificationof the metallic counterion nature associated with thesulfonate group and the content of sulfonated units insidethe copolyesters. The melt polycondensation of dimethyl

terephthalate (DMT), dimethyl 5-sodiosulfoisophthalate(Na-DMSI), and 1,2-ethanediol has been successfully real-ized by Fleury et al. [11] who show that the formation ofdiethylene glycol (DEG) and triethylene glycol (TEG) unitsby etherification reaction was inevitable but can be used totune the thermal properties, stability, and mainly thehydrolytic degradation of these polymers. In addition tothe etherification side reactions, Guo et al. [12] have men-tioned that the molecular weight of copolyester ionomersdepends on the sulfonate content. Therefore, the copolye-sters that had the highest sulfonate content led to thelowest value of molecular weight. Sulfonated polyestersbased on 1,4-butane diol (BD) and 1,6-hexane diol (HD)[13–16] were also prepared; these studies clearly show themajor role of the sulfonated unit content on the copolymerchain mobility and as a consequence on Tg and hydrolyticdegradation behavior. The replacement of petrochemical

HindawiInternational Journal of Polymer ScienceVolume 2019, Article ID 3186202, 19 pageshttps://doi.org/10.1155/2019/3186202

http://orcid.org/0000-0002-4574-3786http://orcid.org/0000-0003-0456-0876https://creativecommons.org/licenses/by/4.0/https://creativecommons.org/licenses/by/4.0/https://doi.org/10.1155/2019/3186202

feedstocks by their biobased counterpart product fromrenewable resources in aromatic and aliphatic copolyestershas benefits relating to positive environmental impacts suchas reduced carbon dioxide emissions. In this context, ourteam has been interested in the preparation of new bio-based sulfonated copolyesters from furanic monomerderived from furfural, which can be easily obtained bychemical treatment of vegetal biomass. The original proper-ties of these materials involving thermal stability, watersorption, and hydrolytic degradation help them to be goodmaterials for a variety of demanding applications [17]. Inthe last few years, the synthesis of biobased aliphatic poly-esters such as poly(butylene succinate) (PBS) and poly(bu-tylene adipate) (PBA) received great interest from severalresearch projects [18, 19] due to their excellent physicalproperties. They are among the most promising materialsfor biomedical applications and environmental protection.Particular interest has been given to aliphatic polyestersbased on ionomers because of their potential biologicalproperties, such as biocompatibility and biodegradability,and their relatively easy synthesis. Two main methods havebeen applied to prepare these materials: (i) by polyconden-sation of succinic acid or adipic acid and sodium(sulfonated dimethyl succinate) (Na-DMSS) obtained bysulfonation of dimethyl maleate (DMM) and various diols[20–25] and (ii) by postsulfonation of unsaturated polyes-ters. The second method was carried out to prepare surfac-tants by sulfonation of unsaturated poly(silicone-esters)[26, 27]. A more detailed study was realized to describethe sulfonation of unsaturated polyesters based on dimethylmaleate and 1,2-ethane diol (ED) by the addition of sodiumbisulfite in an aqueous-alcoholic medium [28]. Resultingmaterials are soluble in an aqueous-organic medium andexhibit micellar behavior in an aqueous medium whichdepends on the concentration of the sulfonated units. It isalso noted that the presence of anionic aliphatic unitmodifies the thermal and mechanical properties of thepolyesters. Recently, a series of sulfonated poly(butylenesuccinate) (PBS) ionomers containing up to 14mol% ofsulfonated succinate units have been synthesized byBautista et al. [29]. They report the synthesis, NMR char-acterization, and mechanical and thermal properties ofPBS ionomers. The hydrolytic degradation of these iono-mers was also performed in an aqueous medium at dif-ferent pH to estimate their susceptibility to hydrolysis indifferent conditions.

This work is aimed at studying and characterizing fullybiobased aliphatic sulfonated oligoesters based on diethylsuccinate (DES), 1,18-octadec-9-enedioic acid with z con-figuration (C18), hydrogenated dimer fatty acid (DA),sodium (sulfonated dimethyl succinate) (Na-DMSS), andtwo biosourced diols: 1,4-butane (BD) diol and isosorbide(Is). The objective is to evaluate the effect of the nature ofthe aliphatic monomers on both thermal properties andhydrolytic degradation of these new oligoesters. Deepcharacterization by 1H NMR and MALDI-TOF analysis[30, 31] and hydrolytic stability of these materials bothin aqueous and oxidative media were investigated [32].Finally, in view of designing new ionic and biobased

thermosets, we have tested one oligoester as macrodiol ina polyurethane formulation and evaluated the thermaland hydrolysis properties of the correspondingcross-linked material.

2. Experimental

2.1. Materials. Diethyl succinate (DES) (98.00+ %);dimethyl maleate (DMM) (96.00+ %); 1,4-butane-diol(BD) (99.99+ %); isosorbide (Is) (98.00+ %); tetrabutoxyti-tanium (Ti(OBu)4) (97.00+ %); zinc acetate (Zn(OAc)2)(99.99%); trimethylolpropane (TMP) (98+ %); and 4,4′methylene bis-(cyclohexyl isocyanate) (HMDI) (90+ %) wereall purchased from Sigma-Aldrich. 1,18-Octadec-9-enedioicacid with z configuration (C18) was kindly provided by theInstitut Francais du Pétrole (IFP, France) and was used with-out purification. Hydrogenated distilled dimer acid (HDA)Radiacid 0976 was supplied by OLEON. It presents an iodinevalue of 196mg KOH/g.

2.2. Synthesis of Sodium (Sulfonated Dimethyl Succinate)(Na-DMSS). Sodium (sulfonated dimethyl succinate)(Na-DMSS) was prepared according to the proceduredescribed elsewhere [33]. First, dimethyl maleate (DMM)(10 g) and NaHSO3 were dissolved in a mixed methanol/-water (50/50 v/v) and were submitted to reflux at 80°C for8 h. Then, the reaction mixture was filtered in order toremove traces of NaHSO3 and evaporate to dryness. The res-idue was dissolved in DMSO, the liquid phase was precipi-tated with a large amount of acetone, and the precipitatewas collected by filtration and dried under vacuum at 80°Cfor 48 h.

2.3. Copolymerization

2.3.1. Synthesis of Poly(1,4-butylene succinate-co-1,4-butylenesodiosulfonate succinate) PBSuxSsy. PBSu70Ss30 was synthe-sized by the polycondensation of 5 g (29mmol) of DES and3.05 g (12.4mmol) of Na-DMSS with 11.17 g (124mmol) ofBD. Transesterification reactions were carried out at 190°Cunder a nitrogen flow in the presence of 0.1wt% of Ti(OBu)4for 6 h. Then, 0.1wt% Ti(OBu)4 was added to the resultingreaction medium and it was heated at a high temperature of220°C during 3 h under vacuum to remove the remainingdiol as efficiently as possible. The oligoesters PBSu100Ss0,PBSu80Ss20, and PBSu60Ss40 were obtained by perming thesame protocol but by adjusting the ratio (DES)/(Na-DMSS):(100 : 0)/(80 : 20)/(60 : 40), respectively.

2.3.2. Synthesis of Poly(1,4-butylene isosorbide succinate-co-1,4-butylene isosorbide sodiosulfonate succinate) PBISuxSsy.PBISu70Ss30 was synthesized according the same proceduredescribed above for PBSu70Ss30 but by substituting a partof BD (5.57 g; 61.9mmol) by Is (9.03 g; 61.9mmol). Theoligoesters PBISu100Ss0, PBISu90Ss10, and PBISu80Ss20 wereobtained by following a similar process but by adjustingthe ratio (DES)/(Na-DMSS): (100 : 0)/(90 : 10)/(80 : 20),respectively.

2 International Journal of Polymer Science

2.3.3. Synthesis of Ploy(1,4-butylene z-octadec-9-enedioate-co-1,4-butylene sodiosulfonate succinate) PBC18xSsy.PBC1870Ss30 oligoester was prepared using 5 g (16mmol) ofC18, 1.7 g (6.8mmol) of Na-DMSS, and 6.7 g (68mmol) ofBD. Transesterification reactions were carried out at 190°Cunder a nitrogen flow in the presence of 0.1wt% of Zn(OAc)2for 6 h. Then, 0.1wt % of Ti(OBu)4 was added to theresulting reaction medium and it was heated at 220°Cfor 3 h. The oligoesters PBC18100Ss0, PBC1890Ss10, andPBC1880Ss20 were obtained by following a similar processbut by adjusting the ratio (C18)/(Na-DMSS):(100 : 0)/(90 : 10)/(80 : 20), respectively.

2.3.4. Synthesis of Poly(1,4-butylene dimer acid-co-1,4-butylene sodiosulfonate succinate) PBDAxSsy. Theprevious procedure was used for the preparation of

PBDA100-70Ss0-30 but by introducing HDA instead ofC18 at different ratios (HDA)/(Na-DMSS):(100 : 0)/(90 : 10)/(80 : 20). For PBDA70Ss30, the raw materialsare as follows: 5 g (0.886mmol) of HDA, and 0.94 g(0.38mmol) of Na-DMSS were reacted with 3.42 g of(38mmol) of BD.

The resulting copolymers were used for characterizationwithout any purification.

2.3.5. Synthesis of Poly(ester-urethane) Network (Cross-Linked PBSu70Ss30 or cPBSu70Ss30). The poly(ester-urethane)network cPBSu70Ss30 was synthesized in a way that the ratioof OH / NCO = 1 09. First, 0.495 g (0.258mmol) ofPBSu70Ss30 oligoester with Mn = 1920 g/mol and 0.0346 g(0.25mmol) of TMP has been dissolved in a limited quantityof DMF (80 : 20 wt% :wt%) at 120°C under a nitrogen

RO C

O

R1 C

O

ORa + c+HO R2 OHb

HO R2 O C

O

R1 C

O

O CR2 O

O

CH

SO3 Na

CH2 C

O

O R2 O H

x y

N2,

190°C

6h

0.01mmHg

220°C

3h

CH3O C

O

CH

SO3 Na

CH2 C

O

OCH3

CH3OH, C2H5OH, H2O HO-R2-OH

0.1% Ti(OBu)4+0.1% Ti(OBu)4+or Zn(OAc)2

Scheme 1: Reaction scheme of biobased oligoester synthesis: (1) transesterification and (2) polyesterification.

Table 1: Biobased monomer list.

Monomers R1 R2

Diethyl succinate CH2 CH2

Z-Octadec-9-enedioic acidCH2 CH CH CH2

7 7

Dimer fatty acid

CH2CH2CH2CH2

CH2

CH2

CH3

CH3

5

5

7

7

1,4-Butanediol CH2 CH2 CH2 CH2

Isosorbide

O

O

3International Journal of Polymer Science

atmosphere, while the mixture was stirred for a few minutes.Then, 0.338 g (0.517mmol) of HDMI was added. After isocy-anate addition, the mixture was stirred again for a fewminutes and poured in a rectangular silicone mold andheated at 130°C for 48 under vacuum in order to eliminateDMF and air bubbles.

In the extractible rate, the resulting cPBSu70Ss30 was putin DMF for 24 h at ambient temperature. Then, the samplewas filtered and dried under vacuum at 120°C for 48h in

order to eliminate the traces of DMF. The extractible ratedetermined according to equation (1) was around 7.5%.

Extractible = mi −mfmf

× 100, 1

where mi and mf are the initial mass of matter and the finalmass of dry matter, respectively.

Structure

1H NMR spectrum

1

2

2 2

3

254

7

8 6

2′

1

7

3

4 5

2,6

8,H2O2′

3

DMSO

C

O

CH

SO3,Na

SO3,Na

CH2 C

O

O CH2 CH2 CH2 CH2 O

C

O

CH2 CH2 C

O

O CH2 CH2 CH2 CH2 O

HO CH2CH2 CH2 CH2 O

O CH2 CH2 CH2 CH2 O C

O

CH CH2 C

O

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 0.0

Figure 1: 1H NMR characterization of PBSu70Ss301H NMR spectrum (400MHz, DMSO-d6).


2.4. Solubility Tests. Qualitative solubility was determined bydissolving 100mg of oligoesters in 900mg of organic solventunder agitation at room temperature or upon heating.

2.5. Film Preparation. Films of oligoesters PBSu80Ss20,PBC1880Ss20, and PBDA80Ss20 were prepared by casting atroom temperature from a 10% (w/v) solution inCHCl3/MeOH (8/1v/v) on silanized Petri dish. The filmswere cut and dried in vacuum at 50°C to constant weight.

2.6. Analytical Techniques. 1H NMR spectra were recordedon a Bruker Avance III 400 spectrometer. Samples were dis-solved in DMSO-d6 or CDCl3 and analyzed at 80

°C or atroom temperature.

The MALDI-TOF MS spectra were recorded using 10 g/Lsolution of sample and in DMSO mixed with 2-(4-hydroxy-phenylazo)-benzoic acid of matrix solution (45/5 v/v) forPBSu70Ss30 and PBISu70Ss30. For PBDA70Ss30, the analysiswas recorded using 10 g/L solution of sample in CHCl3/THF(50/50 v/v) mixed with 2-(4-hydroxy-phenylazo)-benzoicacid of matrix solution (45/5 v/v).

Differential scanning calorimetry experiments (DSC)were performed with TA Instruments Q 22. The sampleswere cut and placed in a close hermetic aluminum cap-sule and were tested under the dry nitrogen condition,at a heating rate of 10°C/min. Tg was taken at theinflection point and Tm at the minimum of meltingendotherms.

The hydrolytic degradation essays were performed withfilms of oligoesters and cPBSu70Ss30: after immersion inwater (pH = 4 35, pH = 7 4, and pH = 11 5) at 37°C for onemonth, the samples were rinsed thoroughly in water anddried to constant weight. Sample weighting measurementswere used to follow the rate of hydrolysis.

The oxidative degradation was carried out with films ofoligoesters in a solution composed of 30 vol% H2O2 and in

a solution composed of 20 vol% H2O2 in combination with0.1M CoCl2 for 15 days at 37

°C [34]. Sample weighting wasused to follow the rate of oxidative degradation.

3. Results and Discussion

3.1. Copolymerization. A set of novel biobased aliphaticoligoesters: series of sulfonated poly(butylene succinate)(PBSuxSsy), sulfonated poly(butylene z-octadec-9-enedioate)(PBC18xSsy), sulfonated poly(butylene dimer acid)(PBDAxSsy), and sulfonated poly(butylene-co-isosorbidesuccinate) (PBISuxSsy), containing various concentrationsof sodiosulfosuccinate units were prepared according to aheating melt process with two successive steps: transesterifi-cation/esterification and polycondensation (Scheme 1). Inthe first one, the blend of monomers was mixed at a temper-ature raised to 190°C in a presence of catalyst: tetrabutoxyti-tanium (Ti(OBu)4) or zinc acetate (Zn(OAc)2) (Table 1). Thetemperature was maintained for 6 h to complete the transes-terification reaction by evaporating by-products: methanol,ethanol, and water, coming from the reaction between diolsand diesters (methyl and ethyl) and diacids. The second stepwas then performed at a higher temperature (220°C) undervacuum in order to release the excess of diol and thus dis-place the reaction equilibrium for getting higher molecularweight. This latter step was also catalyzed by an addition ofTi(OBu)4. These conditions (limited temperature and tita-nium catalyst) were chosen not only for avoiding the deg-radation of the sulfosuccinate moieties by β-eliminationand formation of the maleate or fumarate units [20]but also for facilitating the polycondensation of diacidsand isosorbide which are less reactive than diester mono-mers and 1,4-butanediol [35, 36]. In particular, the intro-duction of isosorbide together with 1,4-butanediol hasallowed the release of the excess of BD during the poly-condensation step [1].

3.2. Characterization of Aliphatic Biobased Oligoesters. Thechemical structure of oligoesters was investigated by 1HNMR and the MALDI-TOF MS method. As an example,the typical 1H NMR spectrum of PBSu70Ss30 is givenFigure 1. It reveals the presence of the characteristic signalsof the succinate proton H1 at 2.57 ppm and those ofsulfonated units H4 (-CH2) and H5 (-CH-) at 2.79 and3.70 ppm, respectively. This is different to what has beendescribed by Ishida et al. [20, 25] who reported the presenceof the -CH- signal at 6.77 ppm while the 1H NMR spectrumof Na-DMSS highlighted the presence of the -CH- signal at3.70 ppm. The weak pic at 1.48 ppm is related to the 1,4-buta-nediol internal groups -CH2-CH2-CH2-CH2-OH. Thesinglets at 1.62 and 4.03 ppm are associated with H3(-CH2-CH2-) and H2 (-CH2-O-) protons of 1,4-butanediolintegrated into the macromolecular chains. Finally, the smallsignal at 4.13 ppm is associated to the -CH2-O- adjacent tothe sulfonated units. One can point out that no signal ofmaleate proton was detected in the 1H NMR spectrum ofPBSu70Ss30 as well as that of the PBSuxSsy series. Thisindicates that β-elimination reaction of sulfosuccinate unitsand consecutive isomerization of maleate to fumarate

Table 2: Characterization of oligoesters: initial and finalcomposition and molecular weight (Mn).

SampleInitial

(diacid)/(Ss)NMR

(diacid)/(Ss)aMn (g·mol-1)b

PBSu100Ss0 100 : 0 100 : 0 6970

PBSu80Ss20 80 : 20 78 : 22 6789

PBSu70Ss30 70 : 30 71 : 29 9831

PBSu60Ss40 60 : 40 62 : 38 11459

PBC18100Ss0 100 : 0 100 : 0 d

PBC1890Ss10 90 : 10 88 : 12 7106

PBC1880Ss20 80 : 20 81 : 19 7652

PBC1870Ss30 70 : 30 72 : 28 8471

PBDA100Ss0 100: 0 100 : 0 c

PBDA90Ss10 90 : 10 80 : 20 c

PBDA80Ss20 80 : 20 77 : 23 c

PBDA70Ss30 70 : 30 71 : 29 caDiacid unit/sulfosuccinate unit molar ratio in oligoesters determined by 1HNMR. bMolecular weight (Mn) determined by 1H NMR. cEnd groups notdetected by 1H NMR.


conformation at temperature above 160°C did not occur inour conditions [29]. 1H NMR peak integrations allowed thequantization of succinate and sulfonated monomer units inoligoesters of the PBSuxSsy series (equation (2)) confirmingthat the experimental molar fraction is close to the theoret-ical one (Table 2). The number average molecular weights(Mn) calculated by 1H NMR are ranged between 6970and 11459 gmol-1. One can remark that the Mn slightlyincreases with the increase of the sulfonated unit content

as already reported in the literature for poly(ethylenefuroate-co-ethylene isophthalate sodiosulfonate) (PEFSI)copolyesters [17].

FSs = 1/3IH5 + IH4

1/3 IH5 + IH4 +1/4 IH1∗ 100

FSu = 1/4IH1

1/3 IH5 + IH4 +1/4 IH1

2

892.0 970.2 1048.4 1126.6 1204.8 1283.00

1993.1

0

10

20

30

40

50

60

70

80

90

100

% in

tens

ity

903.4

1075.5

1247.6

1076.5 1248.6

904.4973.5

985.41145.6

1249.61177.4974.5

1077.5 1146.61005.4905.4959.5

901.4 1073.51003.4 1157.5 1175.5986.4957.5 1131.5 1147.6975.5915.31061.4 1245.61229.51129.51087.4 1158.5902.4 987.4960.5 1025.4 1176.51006.4 1074.5 1246.71148.61059.4 1234.41127.4 1259.5958.4 971.5 988.4 1173.51079.5 1160.51001.6 1041.5 1089.4913.4 1144.5900.4 1213.6 1232.5980.3935.2 1117.51108.41023.7

L(3,1)Na+

L(4,1)Na+

L(5,0)Na+

C(2,2)Na+C(3,2)Na+

L′(3,1)Na+L′(4,1)Na+

C(4,1)Na+

L(2,2)Na+

L(3,2)Na+

L(6,0)Na+

L(5,1)Na+

C″(5,1)Na+

L″(2,2)Na+

C(5,1)Na+

L″(3,2)Na+

L″(1,2)Na+

C″(2,2)Na+

Δ = 172 uma

Δ = 172 uma

Δ = 274 uma

Δ = 172 uma

Δ = 172 umaΔ = 172 uma

Figure 2: MALDI-TOF MS spectrum of PBSu70Ss30.

HO CH2 O C

O

C

O

O O C

O

CH C

O

O O4 4

H, Na+4

3 1

CH2 CH2 CH2 CH2

SO3, Na

CH2

Figure 3

HO C

O

CH2 CH2 C

O

O O C

O

CH C

O

O O C

O

C

O3 14 4

SO3, Na

CH2 CH2 CH2 CH2 CH2 OC2H5, Na+

Figure 4

HO CH2CH2 CH2 CH2 OH

C

O

O CH2 CH2 CH2 CH2 OH

HO CH2CH2 CH2 CH2 O C

O

C

O

O CH2 CH2 CH2 CH2 CH2 CH2 O

- H2OO C

O

CH2 CH2 C

O

O CH2 O C

O

CH

SO3,Na

CH2 C

O

O CH2 O H4 4

H

x y

C

O

CH2 CH2 C

O

O CH2 O C

O

CH

SO3,Na

CH2 C

O

O CH2 O4 4

x y

Scheme 2: Possible side reactions involved in PBSu70Ss30 oligoester.


The MALDI-TOF MS spectrum of PBSu70Ss30 oligoe-ster is depicted in Figure 2. Five different peaks weredetected and noted: L x,y , L x,y′ , L x,y″ , C x,y , and C x,y″ withL and C for linear and cyclic whereas x and y are succinateand sulfonated repeating units.

More precisely, L x,y may correspond to linear oligomerscontaining hydroxyl end groups, as, for instance, the struc-ture of L 3,1 in Figure 3.

An increase of 172 uma corresponding to the molar massof one butylene succinate unit leads to the L 4,1 also detectedin the spectrum as well as the L 5,1 . One can highlight thatthe L 5,0 and the L 6,0 were detected which means that a partof the oligoester chains was not sulfonated. Finally, even ifthe MALDI-TOF method is not quantitative, the peaksL x,y having the highest intensity mean that their concentra-tions are logically higher than those of the other structures.

Structure

1H NMR spectrum

1

2

10

5 4 3 2 1 [ppm]

11

8

31

267 654 45

7 46

3

2

5

9

DMSO

H2O

7

2

3

10

HO CH2 CH2 CH2 CH2 O8

11

9 2

C

O

CH2 CH2 CH24

CH2 CH CH CH2 CH2 CH2 CH2 C4

O

O CH2 CH2 CH2 CH2 O

C

O

CH

SO3,Na

CH2 C

O

O CH2 CH2 CH2 CH2 O H

O CH2 CH2 CH2 CH2 O C

O

CH

SO3,Na

CH2 C

O

OCH3

Figure 5: 1H NMR characterization of PBC1870Ss301H NMR spectrum (400MHz, DMSO-d6).


L′ x, y are oligoesters with α hydroxyl and ω (carboxylicacid) functionalized as L 3,1′ in Figure 4.

As mentioned above, a gap of 172 uma is observed inFigure 2 stating the presence of L 4,1′ oligoesters. However,one can assume that both oligoesters are in a less concen-tration than L x,y oligoesters because of the weak intensityof signals.

In the series of peaks, noteC x,y was assigned to cyclicoligomers whichwere generated during the polycondensation

reaction (Scheme 2) [37]. Finally, some other species: L x,y″andC x,y″ resulting from side etherification reactions: etherifi-cation coupling between two 1,4-butanediol or one 1,4-buta-nediol and one hydroxyester end chain, already mentionedin the literature when 1,4-butanediol is used as comonomer[38] (Scheme 2), were highlighted in the MALDI-TOF MSspectrum. However, similar structures were not detected inthe 1HNMR spectra probably suggesting that their concentra-tions are too low, below 1mol %, to be detected.

Structure

1H NMR spectrum

7, 6

9

3

4

1 5

8

2

CDCl3

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 0.0

TMS

CH2 CH2 CH2 C

O

O CH2 CH2 CH2 CH2

CH2CH2CH2CH2CH2C

O

CH2

CH2

CH3

CH3

5

5

5

5

O6 2 2

3

1 4

5 6

6 5

6 4 1

7

77

7

77

22

3

89C

O

CH

SO3,Na

CH2 C

O

O CH2 CH2 CH2 CH2 O H

Figure 6: 1H NMR characterization of PBDA70Ss301H NMR spectrum (400MHz, CHCl3-d6).


With respect to specific 1H NMR signals for thePBC1870Ss30 series (Figure 5), one can point out that thealiphatic proton H5 from the C18 units is visible at1.29 ppm whereas those of protons in the α position ofethylenic proton H4 are located at 1.99 ppm, the ethylenic

proton H1 being located at 5.33 ppm. The signals at 2.26and 1.54 ppm were attributed, respectively, to H7 and H6located in the α and β position of the ester carbonylgroups integrated in fatty acid units. The difficulty to wellesterify was stressed by the presence of the methoxy end

905.0 983.2 1061.4 1139.6 1217.8 1296.00

1660.6

0

10

20

30

40

50

60

70

80

90

100 947.5

949.5

948.5 1073.1915.5

1163.5945.5

1165.5917.5 950.5 1221.51074.1

1005.5 1223.5916.5928.6 946.5 1222.5913.5 1164.51007.6

1067.0918.5 1161.51006.6 1089.0 1224.5951.5933.5909.4 1068.0 1215.51167.51008.6942.5 1097.0930.6 1149.5 1189.5 1262.0910.4 1124.9 1225.5 1279.61059.0 1207.51173.41077.91037.1963.5 1017.6 1109.0944.5925.1 1150.41001.5977.6 1188.8 1250.9 1272.91064.0

L′(1,1)Na+

L(1,1)Na+

C(1,1)Na+

L(0,3)Na+

L′(1,2)Na+

C(1,2)Na+ L(1,2)Na+

L′(0,3)Na+

L′(0,4)Na+

L″(1,1)Na+

Δ = 274 uma

Figure 7: TheMALDI-TOFMS spectrum of PBDA70Ss30. L x,y corresponds to linear species oligomer containing hydroxyl end groups with xand y fatty acid and sulfonated repeating units. C x,y corresponds to cyclic species oligomer with x and y fatty acid and sulfonated repeating

units. L x,y′ corresponds to linear species oligomer containing ester end groups with x and y fatty acid and sulfonated repeating units. L x,y″corresponds to linear species containing acid end groups with x and y fatty acid and sulfonated repeating units.

C

O

O

CH2 CH2 CH2 CH2C

O

5

5

5 x

O4

C

O

CH C

O

O O

SO3, Na4

y

5

,Na+

CH2

CH3 CH3

CH2 CH3

CH2 CH2 CH2 CH2 CH2 CH2

Figure 8

C

O

O

C

O

HO

5

5

5

5x

O C

O

CH

SO3, Na

C

O

O O H, Na+

44yCH2 CH2 CH2 CH2 CH2

CH3 CH3

CH2 CH2


Figure 9

C

O

CH C

O

O O

SO3, Na4

x

CH3O

C

O

O

C

O

5

5

5 y

O4

H, Na+

5


CH3

CH2 CH3

CH2

CH2

CH2 CH2 CH2 CH2

Figure 10


groups (CH3-O-) at 3.60 ppm. However, such feature didnot impact the good correspondence between the theoret-ical diacid C18/sulfosuccinate ratio and the experimentalone (equation (3)). In addition, the level of molecularweight which ranged between 6740 and 8105 g·mol-1 issimilar to the previous series (Table 2). These oligoestersare no longer soluble in DMSO, probably because it hasundergone a change over time, so the MALDI-TOFanalysis was not possible.

FSs = 1/3IH10 + IH9

1/3 IH10 + IH9 +1/4 IH7∗ 100

FC18 = 1/4IH7

1/3 IH10 + IH9 +1/4 IH7∗ 100

3

The presence of the dimer acid units in PBDA70Ss30oligoester (Figure 6) was set by the existence of character-istic 1H NMR peaks of the following cyclic protons: H7

Structure

1H NMR spectrum

HO CH2 CH2 CH2 CH2 O

C

O

CH

SO3,Na

CH2 C

O

O

OO

O

H

H

O

C

O

CH2 CH2 C

O

OO

O

H

H

O

OO

OHH

H

2

7

3

1

1′

12e, 11e810 14e 4

511, 12

10e9e

C

O

CH2 CH2 C

O

O CH2 CH2 CH2 CH2 O2 2

2 24

1′

5 4

9

8

7

6

11

13 14

9

10

11

14

12

13

10e

9e

11e

12e

13e 14e

14,13

5.6

4.20 4.15 4.10 4.05 4.00 3.95 3.95 3.85 3.80 3.75 3.70

5.4 5.2 5.0 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

913e

1

5

6

12, 11

C

O

CH

SO3,Na

CH2 C

O

O CH2 CH2 CH2 CH2 O

3

10

3

12

10e

Figure 11: 1H NMR characterization of PBISu70Ss301H NMR spectrum (400MHz, DMSO-d6).


(-CH-) and H6 (-CH2-) protons ascribed at 1.31 ppm andthose of the methyl (-CH3) protons at 0.9 ppm. Moreimportantly, signals at 2.31 and 1.64 ppm were attributed,respectively, to H1 and H4 protons located in the α andβ position of the ester carbonyl groups confirming theintegration of the dimer acid units inside the oligoesterbackbone. The experimental molar fractions of PBDAxSsywere determined from the following:

FSs = 1/3IH8 + IH9

1/3 IH8 + IH9 +1/4 IH1∗ 100,

FDA = 1/4IH1

1/3 IH8 + IH9 +1/4 IH1∗ 100

4

The MALDI-TOF analysis (Figure 7) shows the pres-ence of cyclic oligoesters C x,y in Figure 8.

Oligoesters with α hydroxyl and ω (carboxylic acid) func-tionalized L x,y″ in Figure 9.

Oligoesters with α hydroxyl and ω (ester) functionalizedL x,y′ in Figure 10.

Finally, with the respect to oligoester PBISu70Ss30(Figure 11), the isosorbide proton signals were clearlydetected at 5.11 for H14 and at 5.02 for H13, H10, and H9which were situated at 4.75 and 4.44 ppm; the signals from3.71 to 3.83 ppm were attributed to H11 and H12 incorpo-rated into the oligoester structures. The isosorbide endgroups H11e and H12e were set at 3.30 and 3.38 ppm. H10ewas situated at 4.15 ppm. The signal at 4.10 ppmwas assignedfor H9e protons. H14e and H13e were situated at 4.67 and4.39 ppm, respectively. The final compositions ((diacid)/(Ss),(butandiol)/(Is)) and molar masses of oligoesters PBISuxSsywere not determined because of the complexity of the 1HNMR spectra. However, the MALDI-TOF analysis(Figure 12) also confirmed the presence of isosorbide unitwithin the polymer chain. In addition, the MALDI-TOFspectra highlighted that all oligomers are dihydroxy func-tionalized and that the hydroxyl functions come in majority

939.0 1038.8 1138.6 1238.4 1338.2 1438.00

1116.7

0

10

20

30

40

50

60

70

80

90

100 1015.3

1071.3

1187.41243.4

1016.3

959.3

1072.31415.5

1085.5 1244.41017.3 1188.41359.5

1131.4960.3 1299.4 1416.51189.41073.3945.2 1025.4 1360.51257.51117.3 1142.4 1289.41197.4 1313.51061.3 1417.51173.3 1355.4971.4 1018.3 1143.4956.2 1081.3 1201.5 1258.5 1290.31118.31047.1999.3 1403.41371.51177.4 1323.51024.4

L(3,0,0,1) Na+

L′(3,0,0,1) Na+

L(0,3,1,0) Na+

L(0,4,1,0) Na+

L′(4,0,0,1) Na+

L′(5,0,0,1) Na+

L(3,0,0,2) Na+

L(1,3,1,0) Na+

L(2,3,1,0) Na+L′(4,1,0,0) Na+

L′(5,1,0,0) Na+L(3,3,0,0) Na+

L′(1,3,0,0) Na+ L(2,0,0,2) Na+

L′(4,0,1,0) Na+

Δ = 172 uma

Δ = 172 uma

Figure 12: The MALDI-TOF MS spectrum of PBISu70Ss30. L n,m,y,z corresponds to linear species oligomer containing 1,4-butanediol endgroups with n and y succinate and sulfonated repeating units associated to 1,4-butanediol, m and z succinate and sulfonated repeatingunits associated to isosorbide. L n,m,y,z′ corresponds to linear species oligomer containing isosorbide end groups with n and y succinate andsulfonated repeating units associated to the 1,4-butanediol, m and z succinate and sulfonated repeating units associated to isosorbide.

C

O

C

O

O ( ) O C

O

C

O O

OO

O C

O

CH

SO3, Na

C

O

O ( ) O C

O

CH C

O

O

O

OO

O HSO3, Na

44n

y mz

O(CH2 CH2 CH2 CH2 CH2 CH2CH2 CH2 CH2

)HO4

Figure 13

C

O

CH2 CH2 C

O

O (CH2) O C

O

CH2 CH2 C

O O

OO

O C

O

CH

SO3,Na

CH2 C

O

O (CH2) O C

O

CH

SO3,Na

CH2 C

O

O

O

OO

O H

44n

y mz

O

OO

HO

Figure 14


from the isosorbide moieties, those playing the role ofend-cappers. More precisely, L n,m,y,z are oligoesters with1,4-butanediol end groups in Figure 13.

L n,m,y,z′ oligoesters with isosorbide end groups in Figure 14.These results confirm the low reactivity of isosorbide due

to the steric hindrance and the nature of hydroxyl function;here secondary alcohol knowing that the reactivity ofhydroxyl functions on C2 and C5 is close even if not strictlyequivalent [39].

3.3. Thermal Properties of Aliphatic Biobased Oligoesters.Each DSC measurement was performed with a heatingrate of 10°C/min and a first heating cycle in order toreduce the presence of absorbed water molecules whichcould plasticized the polymer followed by a second onefor evaluating the thermal characteristics. Thus, the datareported in Table 3 and Figure 15(a) shows that sulfonatedpoly(butylene succinate) (PBSuxSsy), having 0 to 20% ofsulfonated units have a semicrystalline character and aglass transition temperatures increasing from −38 to−24°C with the increasing of sulfonated unit content. Thisis in good agreement with those ionomers containing upto 14mol% of sulfonated units [29]. Moreover, the authorsattributed the increasing of Tg to the intermolecular ionicinteractions between the sulfonates units. This trend isalso consistent with that of Bougarech et al. [17] who havereported on the role of sulfonated moieties which rigidifythe oligoester backbone limiting the flexibility of the mac-romolecular chains and thus leading to higher Tg. For

PBC18xSsy oligoesters, DSC traces (Figure 15(b))highlighted their semicrystalline character which clearlyindicates that the aliphatic units promote the arrangementof macromolecular chains so the crystallization phenome-non occurs. The melting point decreased from 18 to 6°Cwith the increasing of the sulfonated content. On the otherhand, both melting and recrystallization enthalpies appearto strongly depend on the ionic content (Table 3). It isnoteworthy to indicate that the presence of the ionicgroups reduces the regularity of macromolecular backbonegiving birth to a decrease in melting temperature, andmelting and recrystallization enthalpies as for the PBSionomer [29]. Tg values of PBC18xSsy oligoesters wereranged from −68 to −63°C that is lower than their homol-ogous PBSuxSsy. Indeed, the length of the aliphatic units ofthe fatty acid helps the segmental rotation of macromolec-ular chains and thus leads to a decrease of Tg. Concerningthe PBDAxSsy, the bulky character of the cyclic units gaverise to amorphous structures (Figure 15(c)) with Tg rang-ing between −56 and −54°C, the effect of sulfonated unitsbeing quite limited. The incorporation of isosorbide in theoligoester structures also generated amorphous oligomersand led to the increasing of the glass transition tempera-tures with a value up to 12°C for the PBISu70Ss30. Thiswas expected because the two fused tetrahydrofuran ringstend to impart a stiffness in the macromolecular backboneas already reported with other copolyesters [40].

Thermal decomposition of biobased sulfonated oligoe-sters was evaluated by TGA measurements under nitrogenatmosphere. Thermal gravimetrical traces from 30°C to600°C are reported in Figure 16, and the temperaturesfor 5% weight loss (Td (5%)) are gathered in Table 3 tocompare their thermal stabilities. First, it clearly appearsthat thermal stability of oligoesters decreased with theincreasing of the sulfonated unit content probably becauseof a possible acidic character of these units. Then, thethermal degradation depends obviously on the overallcomposition. Thus, stability of PBSuxSsy oligoesters(between 268 and 260°C) was found lower compared tothat of the PBC18xSsy and PBDAxSsy ones which showedstability up to 312°C and 353°C, respectively. As the trendfor chain scission should be higher in polyesters having ahigher number of methylene groups [41], one can supposethat the presence of double bond in C18 units and thecyclic character of HDA have limited the thermal degrada-tion by favoring cross-linking reactions. This is not thecase for PBISuxSsy containing isosorbide units in theirmacromolecular backbone which can undergo a hydrationreaction at a high temperature, leading to 1,4-sorbitan for-mation. Thus, the thermal degradation was close to that ofPBSuxSsy oligoesters [42].

The remaining weight of all oligoesters after the degra-dation at 500°C increased with the sulfonated content(Table 3). Indeed, PBSu70Ss30, PBC1870Ss30, PBDA70Ss30,and PBISu70Ss30 show a remaining weight value muchgreater than their homopolyesters. The remaining weightof PBSuxSsy goes from 2.7% to 24%. Residual weightdepends also on the chemical structure of oligoesters. Infact, oligoesters based on C18 and HAD presented a lower

Table 3: Thermal properties of biobased oligoesters.

SampleTd(5%)(°C)a

RW(%)b

Tg(°C)c

Tm(°C)d

ΔHm(J.g-1)e

ΔHr(J.g-1)f

PBSu100Ss0 277 2.7 −38 114 111 68PBSu80Ss20 268 16.3 −33 99 45 —PBSu70Ss30 263 17.8 −29 — — —PBSu60Ss40 260 24.2 −24 — — —cPBSu70Ss30 — — 53 — — —

PBC18100Ss0 360 1.15 −68 18 51 42PBC1890Ss10 312 5 −66 17 37 31PBC1880Ss20 298 10.8 −64 8 15 22PBC1870Ss30 289 10 −63 6 9 15PBDA100Ss0 384 0.5 −56 — — —PBDA90Ss10 353 2.1 −55 — — —PBDA80Ss20 335 3.3 −54 — — —PBDA70Ss30 288 6.9 −55 — — —PBISu100Ss0 308 4 −7 — — —PBISu90Ss10 286 13 −2 — — —PBISu80Ss20 269 16 9 — — —

PBISu70Ss30 227 24 12 — — —aDegradation temperature at which a 5% weight loss was observed in TGA.bRemaining weight at 500°C. cGlass transition temperature taken as theinflection point of the DSC traces. dMelting temperatures were registeredby DSC. eMelting enthalpies were registered by DSC. fCrystallizationenthalpies were registered by DSC.


residue value than PBSuxSsy. For PBISuxSsy, the remainingweight slightly increased compared to their homologousPBSuxSsy.

3.4. Degradation in Aqueous Solutions of Aliphatic BiobasedOligoesters. The solubility of oligoesters was first tested atroom temperature and/or upon heating in water and organicsolvents having various polarities. Most of the sulfonated oli-goesters were not soluble in water. Thus, in the PBSuxSsyseries, only the PBSu60Ss40 with the highest content ofsulfonate group was partially soluble in water and all oli-goesters from the PBISuxSsy series were hydrosolublewhich confirms the hydrophilic character of the isosorbideunits already highlighted in the literature. Indeed, isosor-bide was used for preparing hydrotropes [43]. Moreover,these results confirm that the macromolecular design of

water-soluble ionic polyesters or oligoesters needs at leasttwo hydrophilic monomers [11].

To assess their sensitivity to hydrolysis in acidic, neutral,and alkaline media, films of PBSu80Ss20, PBC1880Ss20, andPBDA80Ss20 oligoesters were soaked in water. The tempera-ture of bath was fixed at 37°C over a period of four weeks.The data presented in Figure 17 show that the remainingweight (RW%) of PBSu80Ss20 was decreased both in acidand basic media, 76 and 83, respectively. Contrarily, the deg-radation at pH7.4 was minor with a RW% of 94. These valuesshould be compared with those reported by Bautista et al.[29] in the case of high molecular weight polyester having aclose chemical composition (PBSu85Ss15). Data are differentwithin a particular higher degradation level at basic pH(RW% of 60 instead of 83) and at neutral pH (RW% of 85instead of 94). This might be caused by difference in the

0.2

0.0

−0.2

−0.4

−0.6

−0.8

Exo up−100 −50 0 50

Temperature (°C)100 150 200

Universal V4.2ETA instruments

PBSu100Ss0PBSu80Ss20


Hea

t flow

(W/g

)

(a)

0.5

0.0

−0.5

−1.0

−1.5

−2.0

Exo up

Hea

t flow

(W/g

)

−100 −50 0 50Temperature (°C)

100 150 200Universal V4.2ETA instruments

PBC18100Ss0PBC1890Ss10


(b)

0.2

0.0

−0.2

−0.4

−0.6

−0.8

−1.0

Exo up−100 −50 0 50

Temperature (°C)100 150 200

Universal V4.2ETA instruments

PBDA100Ss0PBDA90Ss10


Hea

t flow

(W/g

)

(c)

0.4

0.2

0.0

−0.2

−0.4

−0.6

−0.8

Exo up−100 −50 0 50

Temperature (°C)

Hea

t flow

(W/g

)

100 150Universal V4.2ETA instruments

PBISu100Ss0PBISu90Ss10


(d)

Figure 15: DSC curves of biobased oligoesters: (a) DSC curves of PBSuxSsy, (b) DSC curves of PBC18xSsy, (c) DSC curves of PBDAxSsy, and(d) DSC curves of PBISuxSsy.


hydrolysis protocol and/or by the molar mass effect. Never-theless, our results are expected because ester bonds are gen-erally more sensible to hydrolysis at extreme pH [44].

The hydrolytic degradation of oligoesters based on C18was high in basic conditions. However, in neutral condi-tions, hydrolytic degradation stayed higher than in acidicmedia. The 1H NMR analysis of the degraded sample inacidic media logically revealed the presence of acid endgroups at 12 ppm, proving the cleavage of the macromo-lecular backbone by hydrolysis of ester functions. In addi-tion, a residual resonance with very low intensities wasalso detected at 5.31 ppm and attributed to ethylenic pro-tons. Thus, the 1H NMR spectra suggested that in acidconditions, the ethylenic double bonds were affected bymigration in order to form carbocation located at the 4- or5-position on a fatty acid backbone. Probably, an intramolec-ular cyclization of a fatty acid carboxyl group with carboca-tions took place to form γ-and δ-stearolactone [45] because

of the presence of novel peaks at 4.62 ppm (Figure 18). Themechanism of the formation of γ- and δ-stearolactone isdetailed in Scheme 3 [46].

Finally, oligoester based on dimer acid HDA(PBDA80Ss20) remained as it is with nonvariation of RW%even after four weeks in water, whatever the pH. These dataclearly illustrate the protective role of the dimer acid whichhampers the ester accessibility by water molecules due to itshydrophobic character.

PBSu80Ss20, PBC1880Ss20 and PBDA80Ss20 films under-went an oxidative degradation for 15 days at 37°C in twosolutions composed of (i) 30 vol% H2O2 and (ii) a combina-tion of 20 vol% H2O2 and 0.1M CoCl2, respectively. The datapresented in Table 4 show that practically, films ofPBDA80Ss20 were very stable in both oxidative solutionswhich was expected because of the hydrophobic characterof that oligoester. Contrarily, a fall in sample weight tookplace for PBSu80Ss20 and PBC1880Ss20 in a solution

250

20

40

60

80

100

120

125 225 325Temperature (°C)

Wei

ght (

%)




(a)

0

20

40

60

80

100

120

Wei

ght (

%)

25 125 225 325Temperature (°C)

425 525 625Universal V4.2ETA Instruments



(b)

0

20

40

60

80

100

120

Wei

ght (

%)





(c)

0

20

40

60

80

100

120

Wei

ght (

%)





(d)

Figure 16: TGA curves of biobased oligoesters: (a) TGA curves of PBSuxSsy, (b) TGA curves of PBC18xSsy, (c) TGA curves PBDAxSsy, and (d)TGA curves of PBISuxSsy.


composed of 30 vol% of H2O2, which resulted in reduction of36% and 74% of the initial weight of the sample, respectively.In that case, one can assume that macromolecular chain’sscissions occurred concomitantly via hydrolysis and oxida-tive reactions. In H2O2/CoCl2 solution, the remaining weightwas close to 100wt% (films PBSu80Ss20 and PBC1880Ss20attained nearly 94% and 96%, respectively) suggesting thatproduction of reactive hydroxyl radicals by the oxidationreaction may lead to cross-linking because in the same pH,one can observe a higher degradation [34].

3.5. Toward the Preparation of Poly(ester-urethane) Network.The preparation of sulfonated aliphatic oligoesters α and ωhydroxyl functionalized represents an opportunity todevelop thermosets that are biosourced and have tunable

properties [47]. Thus, a poly(ester-urethane) thermoset(cPBSu70Ss30) was performed by reacting together theoligoester PBSu70Ss30 and 4,4-methylenebis(cyclohexyl iso-cyanate) (HMDI) in a presence of trimethylolpropane cho-sen as the cross-linker. The quantity of reagent wascalculated in order to have a stoichiometry OH/NCO closeto one. After blending, the components were cured in asilicon mold at 130°C under vacuum for 48 h. Such condi-tions were chosen in order to facilitate the evaporation ofthe DMF previously added to ensure the miscibilitybetween the reagents. The resulting material was not solu-ble in DMF, and the formation of network structures canbe assumed because the extractible rate was 7.5wt%. Inaddition, the glass transition temperature of thecPBSu70Ss30 was much higher compared to the PBSu70Ss30

0 5 10 15 20 25 30Time (day)

PBDA80Ss20PBSu80Ss20PBC1880Ss20

50

60

70

80

90

100Re

mai

ning

wei

ght %

(a)

0 5 10 15 20 25 30Time (day)


50

60

70

80

90

100

Rem

aini

ng w

eigh

t %

(b)

0 5 10 15 20 25 30Time (day)


50

60

70

80

90

100

Rem

aini

ng w

eigh

t %

(c)

0 5 10 15 20 25 3050

60

70

80

90

100

Time (day)

pH = 4,35pH = 11,5pH = 7,4

Rem

aini

ng w

eigh

t %

(d)

Figure 17: Hydrolysis of PBSu80Ss20, PBC1880Ss20, and PBDA80Ss20: evolution of the “remaining weight” in water at 37°C: (a) at pH = 4 35,

(b) at pH = 7 4, and (c) at pH = 11 5. Comparison with (d) “remaining weight” of cPBSu70Ss30 immersed in water (pH = 4 35, pH = 11 5, andpH = 7 4) at 37°C.


oligoester, 53°C and −29, respectively (Table 3). Thatincrease of Tg is obviously due to the presence of the ure-thane linkage together with the tridimensional cross-linkedstructures which can increase the rigidity of the macro-molecule backbone [48, 49]. The hydrolytic degradability ofthat cross-linkedmaterial was also determined inwater at var-ious pH and at 37°C and were found in the same range as anon-cross-linking material. In this case, cPBSu70Ss30 is moredegradable in acid and alkaline than neutral media because

of the presence of ester bonds which are more sensible tohydrolysis in acid and alkaline conditions.

4. Conclusion

A series of biobased oligoesters containing up to 30% ofsulfonated units, namely, sodium sulfonate succinate,were successfully prepared by melt polycondensationreaction using biobased monomers including isosorbide,

12.5 11.5 10.5 9.5 8.5 7.5 6.5 5.5 4.5 3.5 2.5 1.5 0.5(a)

C

O

OH

12.5 11.5 10.5 9.5 8.5 7.5 6.5 5.5 4.5 3.5 2.5 1.5 0.5

O O

H1

1

(b)

12.5 11.5 10.5 9.5 8.5 7.5 6.5 5.5 4.5 3.5 2.5 1.5 0.5(c)

12.5 11.5 10.5 9.5 8.5 7.5 6.5 5.5 4.5 3.5 2.5 1.5 0.5(d)

Figure 18: 1H NMR spectrum of degraded sample PBC1880Ss20 (400MHz, DMSO-d6): (a) initial sample; (b) degraded sample in water(pH = 4 35) at 37°C; (c) degraded sample in water (pH = 7 4) at 37°C, degraded sample in water (pH = 18 5) at 37°C.


hydrogenated dimer acid, and C18 diacid (1,18-octade-c-9-enedioic acid). The structures of the resulting oligoe-sters were studied by 1H NMR and their regularstructures were evidenced. Thus, the MALDI-TOF MSanalysis showed the presence of expected linear speciesbut also cyclic species resulting from cyclisation reactionscommonly observed in polycondensation. It was alsohighlighted that end groups are in majority hydroxylbut that acid functions can also be detected. The studyof the thermal properties clearly confirms the role ofthe oligoester compositions. Thus, a high content of sul-fonate unit as well as bulky units such as isosorbideand hydrogenated dimer acid leads to amorphous poly-mers whereas oligoesters containing a low level ofsulfonated units and long alkyl chains are semicrystalline.This study also clearly underlines that water solubility isonly achieved with oligoesters having both sulfonated

and isosorbide units or very high content of sulfonatemoieties (>30mol%). The degradation in aqueous solu-tion films of oligoesters was also correlated with the com-position, the most hydrophobic oligoester being morestable. Finally, a thermoset was prepared using sulfonatedoligoesters, opening the way to prepare biobased poly(es-ter-urethane) materials having tunable properties.

Data Availability

The figures and schemes used to support the findings of thisstudy are included within the article.

Conflicts of Interest

The authors confirm that this article content has no conflictof interest.

H

O

O

OO

O O

OO

OOH

OO

OO

O

O

O

O O

O

OO

O O

O

OO

O

�훿-stearolactone �훾-stearolactone

Scheme 3: Mechanism of the formation of δ-stearolactone and γ-stearolactone [46].

Table 4: Remaining weight (%) of PBSu80Ss20, PBC1880Ss20, and PBDA80Ss20 and the remaining weight for samples immersed in H2O2(30 vol%) and H2O2 (20 vol%) CoCl2 (0.1M) at 37

°C after 15 days of degradation.

SampleDegradation conditions

Hydrolysis OxidationpH = 4 35 pH = 11 5 pH = 7 4 H2O2 (30 vol%) H2O2 (20 vol%) CoCl2 (0.1M)

PBSu80Ss20 82 89 97 64 94

PBC1880Ss20 98 71 68 26 96

PBDA80Ss20 99 99.5 99 100 100


Acknowledgments

The authors acknowledge the financial support of theMinistry of Higher Education and Scientific Research inTunisia. The authors gratefully thankDr. Catherine Ladavièrefor the MALDI-TOF analysis.

Supplementary Materials

This is the 1H NMR spectrum of each series (SI.1-10)and the FT-IR spectra of prepared polyesters (SI.11).(Supplementary Materials)

References

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