Highly flexible polyester macroinitiator enabled strength-retaining toughening of PLGA

Poly(lactic-co-glycolic acid) (PLGA) is a biodegradable aliphatic polyester with tunable composition and degradation behavior, but its intrinsic brittleness limits its broader use as a structural material. In this work, a highly flexible polyester macroinitiator (FPM) was introduced into PLGA through bulk ring-opening copolymerization of L-lactide and glycolide, followed by chain extension with hexamethylene diisocyanate (HDI), to construct PLGA FPM multiblock copolymers. FPM incorporation weakened the ordered packing of PLGA and progressively changed its tensile behavior from brittle fracture to pronounced ductile deformation. With increasing FPM content, PLGAFPM copolymers showed a gradual transition from brittle fracture to ductile deformation, accompanied by markedly improved elongation at break and tensile toughness. Among the investigated samples, PLGAFPM10 provided the most favorable balance between strength retention and toughness improvement, retaining a tensile strength of 55.6 MPa together with an elongation at break of 182.9 % and a toughness of 45.3 MJ/m 3 . Further increasing FPM content promoted extensibility but reduced tensile strength. Seawater immersion further showed a composition-dependent aqueous degradation response, with mass retention decreasing from 94.5 % for neat PLGA to 74.8 % for PLGA FPM20 after 126 d. This result indicates that FPM incorporation retained the hydrolyzable PLGA-based polyester framework while increasing water-related structural evolution. These results provide a chain-structure design strategy for toughening PLGA while maintaining its degradable polyester framework.