Development of Thiophene-Based Copolyesters with a High Gas Barrier and Toughness by the Introduction of Diethylene Glycol

Abstract A bio-based poly (butylene thiophenedicarboxylate-co-diethylene glycol) (PBThD) copolyester was synthesized with 2,5-thiophenedicarboxylic acid (TDCA), 1,4-butandiol (BDO), and diethylene glycol (DEG). The free rotation of the ether bond in DEG is used to give the molecular chain good flexibility, and then combined with the barrier properties of the thiophene-based polyester to meet the requirements of plastic packaging. The influence of composition on its microstructure, crystallization behavior, thermal properties, mechanical properties, and gas barrier properties was studied. The results showed that the resulting copolyesters exhibited good toughness (elongation at break: 712% ∼ 1016%). Throughout the entire DEG molar fraction range of 10–50 mol %, both Tα and Tm exhibit minimal variation, fluctuating by less than 3 °C, while the copolyesters retain robust thermal stability. In addition, no crystallization peak was observed when the amount of DEG was higher than 10 mol %, indicating that the introduction of DEG significantly destroyed the crystal structure of the homopolymer. Unexpectedly, although PBThD20 is not easy to crystallize, its barrier performance to CO2 is 33.4 times higher than that of petroleum-based PET, and its barrier to O2 remains stable. This work contributes to the development of thiophene-based copolyesters with both high barrier and mechanical properties.