Photo‐Switchable Molecular Module Programming PET Biodegradation in Aquatic Environments

Plastics face a durability paradox where their utility causes environmental intractability. We resolve this by embedding a photo‐controlled molecular module, a pyrrolidone carboxylamide derived from itaconic acid, directly into the polymer backbone. While stable during use, sunlight exposure in water triggers a precise degradation cascade: (1) Norrish Type I photonic ring‐opening to generate amino acid groups, (2) increased hydrophilicity and water dissolution, avoiding the formation of hydrophobic microplastics, (3) accelerated hydrolysis into monomers/oligomers, and (4) rapid biodegradation. This programmable lifecycle was first proven in pyrrolidone derivatives, which mineralize as fast as cellulose microfibers (70% in 2 weeks) after a single phototrigger, with safety confirmed via human microbiota and Organisation for Economic Co‐operation and Development standards‐compliant toxicity models (chronic toxicity for microalgae; 310 mg/L). Crucially, we integrated the diacid‐type pyrrolidone carboxylamide module into poly(ethylene terephthalate) (PET). The resulting copolymer maintains the physicochemical performance of conventional PET copolymers but achieves photo‐mediated biodegradation of PET segments into nontoxic minerals. This modular biodegradation platform is not a mere additive but a backbone‐integrated design possibly applicable to other polyesters, polyamides, polyurethanes, and so on, appearing to represent a viable option to help address plastic pollution, likely minimizing negative impacts on material integrity.