Structure–property relationships in melt-synthesized poly(butylene succinate-co-suberate) copolyesters: influence of suberic acid content on crystallization and mechanical performance

Poly(butylene succinate) (PBS) is a promising bio-based aliphatic polyester, but its relatively limited thermal stability, moderate mechanical performance, and restricted toughness can limit the range of potential applications. To overcome these limitations, this work aims to tailor the physicochemical, thermal, and mechanical properties of PBS. In this study, a series of poly(butylene succinate-co-suberate) (PBS-co-SubA) copolymers containing 10–50 mol% suberic acid (SubA), were synthesized via melt polycondensation and comprehensively characterized. Gel permeation chromatography (GPC) revealed a significant decrease in both number-average (M_n) and weight-average (M_w) molecular weights, accompanied by an increase in polydispersity with increasing SubA content, indicating hindered polymerization kinetics. Structural analysis by ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy confirmed the successful incorporation of SubA into the polymer backbone, whereas diffusion-ordered spectroscopy (DOSY) NMR verified statistical copolymer formation, as evidenced by a single diffusion coefficients. Increasing SubA content resulted in higher diffusion coefficients, indicative of reduced molecular size and enhanced chain mobility. Differential scanning calorimetry (DSC) demonstrated a progressive decrease in glass transition (Tg), melting (Tm), and crystallization (Tc) temperatures with increasing SubA incorporation while Thermogravimetric analysis (TGA) showed enhanced thermal stability, with degradation onset temperatures rising from 385 °C for PBS to 403 °C for PBSubA. X-ray diffraction (XRD) analysis, together with the DSC melting behavior, suggests crystallization consistent with an isodimorphic copolymer system, characterized by the coexistence of PBS and PBSubA-rich crystalline phases across the studied composition range, however, the present data do not provide definitive proof of this crystallization mode. Mechanical testing indicated that SubA content reduced stiffness and yield strength but significantly improved ductility and impact resistance. Notably, PBS-co-10-SubA exhibited a strain at break of 418 % and resisted fracture under Charpy impact testing. Overall, these results demonstrate that SubA is an effective comonomer for tuning the thermal and mechanical properties of PBS, enabling the design of flexible, thermally stable and impact-resistant PBS-based copolyesters.