Molecular Engineering of Hard Segment Domains in Polyurethane Elastomers for Toughening Poly(Glycolic Acid)

Poly(glycolic acid) (PGA) is recognized as a premier biodegradable polyester, distinguished by its exceptional gas barrier properties and high tensile strength. However, its intrinsic brittleness severely restricts its practical applications. Achieving a synergy of stiffness, toughness, and biodegradability remains a formidable challenge, particularly without relying on complex reactive compatibilizers. Herein, we report a molecular architecture‐directed strategy to toughen PGA by precisely tailoring the hard segment content of thermoplastic polyurethane (TPU). By synthesizing a library of poly(ε‐caprolactone) (PCL)‐based TPUs with tunable hard segments, we successfully manipulated the interplay between interfacial compatibility and microphase separation. The incorporation of PCL significantly reduced interfacial tension, while the optimized hard segment domains functioned as rigid physical crosslinks. Consequently, the PGA/TPU blends exhibited a remarkable 5.1‐fold increase in elongation at break (61%) and a 3.8‐fold enhancement in tensile toughness (29.3 MJ·m −3 ) compared to neat PGA, alongside a 2.7‐fold improvement in impact strength (7.8 kJ·m −2 ). This work not only yields a high‐performance composite but also elucidates the mechanism by which elastic networks regulate the brittle‐ductile transition of stiff polyesters.