New biodegradable polymers from renewable resources
Abstract: High molecular weight poly(ester-carbonate)s have beenprepared by a two-step chain-extension reaction performed onoligomeric αω-bishydroxyl-terminatedpoly(1,3-propylene succinate).αω-Bishydroxyl-terminated copolymeric oligomers of1,3-propylene succinate/1,4-cyclohexanedimethylene succinatewere obtained by thermal polycondensation of1,3-propanediol/1,4-cyclohexanedimethanol/succinic acidmixtures having different composition, and subsequently chainextended using phosgene as coupling agent, which leads toaliphatic/alicyclic copoly(ester-carbonate)s. New highmolecular weight amphiphilic block copolymers ofpoly(ester-ether-carbonate), containing poly(1,3-propylenesuccinate) and poly(ethylene glycol) (PEG) segments in theirmain chain, were synthesized by a two-step chain-extensionreaction performed on a thermally-polycondensed α,ω-bishydroxyl-terminated oligomeric poly(1,3-propylenesuccinate) with PEG1000 and PEG2000, respectively. The newpolymers, besides having a biodegradable backbone, derive fromtwo monomers, 1,3-propanediol and succinic acid respectively,which can be obtained from renewable resources. Therefore, theyhave a potential as environmental friendly materials.The molecular characterization by1H-NMR and IR spectroscopy, the molecular weight andmolecular weight distribution by SEC and the main thermalproperties by DSC of all synthesized materials are reported.Spectroscopic characterizations were in full agreement with theproposed structures. Thermal characterization demonstrated thatan increase in the cyclic ester unit content leads to anincrease in Tm and Tg of the copolymers. Solubility testsindicated that the introduction of hydrophilic PEG segmentsinto the high molecular weight polysuccinate imparts apparentamphiphilic character to the new materials. This is expected toinfluence even their biocompatibility and biodegradability.The properties of aliphatic homopolyesters from renewablemonomers, 1,3-propanediol and succinic acid, were improved byintroducing aromatic urethane into the main chain of polymers,which gives place to the formation of strong hydrogen bondsamong the macromolecular chains of the material. Segmentedpolyester-urethanes (PEU) were synthesizedfromdi-hydroxyl-terminated poly(trimethylene succinate), chainextended with 4,4'-diisophenylmethane diisocyanate (MDI). Thematerials were characterized using SEC, DSC,1H-NMR,13C-NMR and INSTRON. The maximum weight averagemolecular weight approached 7.5× 104. DSC detected the Tgof the soft segment from10 to19° C and the Tmof the hard segment from 175 to 210 ° C. Theaverage repeat number of hard segment ranges from 4.0 to 8.1,and the average repeat number of AnBmunit from 3.3 to 6.4. The average length of thehard segment decreases with increasing concentration ofpolyester in feeding.The results clearly show that within the studied series theincrease in soft segment content reduced both crystallinity andmelting temperature of hard segment microcrystalline phase,which is accompanied by decrease in modulus due to weakerinteraction among polymer chains in microcrystalline phase. Thedegree of crystallinity, Tg, Tm, tensile strength, elongation, and Youngsmodulus were influenced by the ratio between hard and softsegment as well as the molecular weight of thepolyester-urethane. The introduction of the polyurethanesegments significantly reduces the degradability ofcorresponding aliphatic polyester, although there is stillenzymatic attack detectable during the enzymatic degradation.All samples exhibited significant weight losses after twomonths of compost simulation incubation. The highersoft-segment contents resulted in higher degradability. Weconcluded that the segmented polyester-urethane from1,3-propanediol and succinic acid is a promising, processable,soluble, and biodegradable thermoplastic elastomer.Keywords:polycondensation, block copolymer, chainextension, isocyanate, phosgene, dichloroformatecharacterization, biodegradation, renewable resources,1,3-propanediol, succinic acid, polyurethane, polyester,thermoplastic elastomer.
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