Effect of Monomer Structure on Crystallization and Glass Transition of Flexible Copolyesters

Abstract

Amorphous flexible (co)polyesters with low glass transition temperature (T g) are very desirable in impact modification of biodegradable brittle polymers and synthesis of biodegradable elastomers. However, most flexible polyesters and binary copolyesters made from linear diacid(s) and diol(s) are crystalline polymers. In order to investigate the effect of monomer structure on the crystallization and T g of such copolyesters, novel ternary or multiple flexible copolyesters containing various structural units were designed and synthesized in this study, and characterized with 1HNMR, GPC, DSC, WAXD, TGA and tensile testing. Introducing aromatic diacid (especially asymmetric one) or short-chain branched diol is favorable to depress copolyester crystallization, and leads to higher T g at the same time. From easily crystallized to fully amorphous copolyesters with low T g were successfully synthesized by adopting different combination of structural units. In addition, the existence of aromatic structural unit in copolyesters is helpful to improve their tensile properties. Flexible copolyesters containing various structural units were designed and synthesized. Introducing asymmetric, rigid aromatic or short-chain branched unit is favorable to depress copolyester crystallization, and leads to higher T g at the same time. Crystalline to fully amorphous copolyesters with low enough T g have been successfully synthesized by adjusting the structural units.