A Sustainable Poly(butylene furandicarboxylate) (PBF)-Based Copolyester Containing a Cyclic Ether Structure: Integrated with High Thermal, Mechanical, and Hydrolytic Degradable Properties

Designing and synthesizing bio-based furandicarboxylic acid (FDCA)-based copolyesters with high thermal, mechanical, and modest hydrolytic properties present a significant challenge. In this study, poly(butylene furandicarboxylate) (PBF) was modified with the bio-based cyclic ether diol 2,5-tetrahydrofurandimethanol (THFDM). The resulting sustainable poly(butylene furandicarboxylate-co-hydroxymethyl tetrahydrofuran furandicarboxylate) (PBThFs) copolyesters displayed random microstructures with molecular weights (M_w) ranging from 20.8 to 62.6 × 10³ g/mol. PBThFs transitioned from a partially crystalline to a fully amorphous state while maintaining thermal stability above 367 °C. The tensile strength and modulus of PBF were 49 and 1479 MPa, respectively, while PBThF15 (with a feed molar ratio of THFDM units at 15 mol %) showed improved values of 77 and 1855 MPa. Adding THFDM units significantly increased the glass transition temperature from 39.9 to 74.7 °C. The presence of ether linkages in THFDM modified the hydrolytic degradation of PBThF copolyesters compared to pure PBF. The hydrolysis mechanisms were clarified using Fukui function analysis and DFT calculations, indicating the increased susceptibility of PBThFs to hydrolysis. This study demonstrates the feasibility of synthesizing high-performance FDCA-based copolyesters, facilitating a broad spectrum of applications.