Synthesis and Structure–Property Relationships of Novel High Molecular Weight Fully Biobased 2,5-Thiophenedicarboxylic Acid-Based Polyesters

Abstract

High molecular weight fully biobased poly(propylene succinate-co-2,5-thiophenedicarboxylate) (PPSTF) random copolyesters based on the emerging biobased aromatic diacid, 2,5-thiophenedicarboxylic acid (TFDCA), in full composition range were synthesized via melt polycondensation. Their crystallization behavior, thermal-mechanical, gas barrier, and biodegradable properties were systematically investigated. A certain level of comonomer cocrystallization was evidenced by XRD, and PTF units had stronger crystallization competitive capability compared to PS units due to the higher stiffness of TFDCA units. These copolyesters exhibited excellent thermal stability, and mechanical properties can be easily controlled by tuning the varied ratio of flexible to rigid segments. Gas barrier properties were studied from both theoretically calculated and experimental perspectives, and the copolyesters even with 50 mol % PS units still showed superior gas permeation resistance. The selected lipase from Aspergillus oryzae can degrade the copolyesters with up to 60 mol % PTF units. The nonbiodegradable-biodegradable transition was found to occur at the number-average sequence length of aromatic PTF units as low as about 3. Interestingly, when compared with their terephthalic acid-based (TA-based) and 2,5-furandicarboxylic acid-based (FDCA-based) analogues with the same content of aromatic units, the apparent degradation rate constant (k) and half period (t_1/2) of PPSTF60 were actually between them. These findings offer much promise for the application of polyesters containing odd-carbon diol monomers in green packaging and other fields.