A Bio-Based Branching Agent for Preparation of Crosslinked Poly(Butylene Succinate-Co-Terephthalate): Synthesis, Thermo-Mechanical and Rheological Properties

To improve the mechanical strength, melt strength, and degradation performance of PBAT,a novel bio-based polyalcohol branching agent (BA) was synthesized through a three-step reaction using isomannide (1,4:3,6-dianhydromannitol) as the precursor. This agent was subsequently employed to fabricate long-chain-branched poly(butylene succinate-co-terephthalate) (LCB PBAT) copolyesters via branching modification. The chemical structure of LCB PBAT was systematically characterized by 1 H NMR and 13 C NMR spectroscopy, while its thermal, mechanical, and rheological properties were comprehensively evaluated. Results demonstrate that the incorporation of a minor BA addition (0.2–0.8 mol%) significantly enhanced key thermal and mechanical parameters, including glass transition temperature (up to −25.1°C), melting point (up to 131.2°C), crystallization temperature (up to 103.2°C), and tensile strength (up to 23.26 Mpa). Notably, the crystallinity of LCB-PBAT remained largely unchanged compared to linear PBAT. Rheological analyses revealed substantial improvements in melt processability, with the modified PBAT demonstrating a reduced loss tangent angle, enhanced elastic energy storage, and increased melt strength.