Synthesis and Performance Evaluation of Fully Bio‐Based Unsaturated Polyesters Derived From 2,5‐Thiophenedicarboxylic Acid and Itaconic Acid

ABSTRACT The fully bio‐based unsaturated copolyesters, poly(thiophenedicarboxylate‐ co ‐succinate‐ co ‐itaconate glycol) (PESITh), were synthesized via a one‐step polycondensation strategy. FTIR and 1 H NMR analyses confirmed the successful preparation of the unsaturated copolyesters with a micro‐crosslinked structure. For rheological investigations, the increased elastic response at higher IA contents further corroborated the presence of micro‐crosslinked networks. DSC analysis revealed that all copolyesters were amorphous, with the glass transition temperature ( T g ) gradually decreasing from 30.0°C to 17.8°C as the IA content increased. TGA data showed that with increasing IA content, the temperature for 5% weight loss ( T d, 5% ) decreased, whereas the maximum decomposition temperature ( T d, max ) increased to 392.1°C. For PESI10Th54 with IA actual content of 8 mol% by NMR, the copolyester exhibited optimal mechanical properties, with a tensile strength of 9.43 MPa and an elongation at break of 512.18%. Surface property analyses indicated that the water and diiodomethane contact angles decreased as the IA content increased, whereas the surface free energy increased from 35.37 to 48.82 mJ·m −2 , primarily driven by an increase in the dispersive component. This study presents a viable synthetic route and provides theoretical insights for designing fully bio‐based unsaturated polyesters with tunable properties.