Effects of Different Isomers of Thiophenedicarboxylic Acids on the Synthesis and Properties of Thiophene-Based Sustainable Polyesters

The need for high-performance bioplastics brings new challenges to the design and preparation of next-generation sustainable bioplastics. With the emergence of a number of biobased monomers with a similar chemical structure in recent years, it is necessary to conduct a systematic and in-depth study on the effects of different isomers of monomers on the final material properties. Considering the potential barrier and bacteriostatic properties of emerging thiophene-based polyesters, this work systematically investigated the effects of different isomers of thiophenedicarboxylic acids (TFDCAs), 2,5-TFDCA and 3,4-TFDCA, on the synthesis and properties of polyesters by a combination of experiments and molecular simulations. A novel biobased polyester based on the 3,4-TFDCA isomer was synthesized and compared with its analogue. Theoretical studies modeled through population balances were performed to simulate the polymerization kinetics of these two polyesters. Contrary to expectations, we successfully prepared high-molecular-weight poly(1,4-butylene 3,4-thiophenedicarboxylate) (3,4-P14BTF) via melt polycondensation. As we know, for the polyesters based on the analogous phthalic acid, high molecular weights cannot be obtained by this strategy. Barrier properties were further systematically studied from both theoretical calculation and experimental perspectives. The superior gas and water vapor barrier properties of semicrystalline poly(1,4-butylene 2,5-thiophenedicarboxylate) (2,5-P14BTF) could be attributed to the decreased chain mobility and smaller fractional free volume. More intriguingly, they exhibited improved bacteriostatic effect compared to poly(lactic acid) (PLA), while no notable difference was observed between 2,5-and 3,4-isomers. 3,4-P14BTF could be degraded under milder conditions than 2,5-P14BTF enabled by methanolysis with the imidazole acetate ionic liquid catalyst. Therefore, in-depth analysis of the effects of different isomers of monomers should be considered for the design and preparation of new high-barrier and antibacterial polymeric materials for advanced applications such as biobased active food packaging and electronic encapsulation.