A Toughness‐Enhanced and Photoprogrammable Poly(L‐Lactide) Copolymer via L‐Lactide/4‐Phenyl‐ε‐Caprolactone

ABSTRACT Polylactic acid (PLA), a biodegradable and bio‐based polyester derived from renewable resources, has emerged as a promising sustainable alternative to conventional plastics. Nevertheless, its inherent brittleness has persistently hindered its broader utility. To address these challenges, we report a molecular design strategy through copolymerization of L‐lactide (L‐LA) with 4‐phenyl‐ε‐caprolactone (4‐Ph‐ε‐CL), yielding a novel biodegradable polyester with integrated toughness and photoresponsive functionality. In this study, the phenyl unit acts as a bifunctional modifier. Macroscopically, it serves as a toughening agent that effectively dissipates energy, significantly enhancing the material's ductility. At the surface level, it functions as a localized photosensitizer that, upon 254 nm ultraviolet (UV) irradiation, triggers selective cross‐linking and leads to the formation of tailored topological protrusions with distinct mechanical properties. This work demonstrates simultaneous and independent tuning of bulk mechanical performance and surface functionality within a single material, establishing a new paradigm for the design of intelligent biodegradable polymers for advanced biomedical and engineering applications.