Catalyst-free, autoinductive photochemical upcycling of aromatic polymers and mixed plastics via autosensitization

Photochemical upcycling of polymers is a promising strategy for mitigating the plastic-waste crisis; however, many recent advances have centered on developing costly photocatalysts. In contrast, the auto-sensitized photoreactivity of aromatic polymers such as polystyrene (PS)—albeit documented for decades—has remained unexploited for practical upcycling. Here we leverage this overlooked reactivity to develop a catalyst-free platform that converts PS into benzoic acid under visible light irradiation in air. The approach extends to other aromatic polymers including polyethylene terephthalate (PET), polycarbonate, polyether sulfone (PES), and epoxy resins, as well as biomass feedstocks such as lignin. Mechanistic experiments combined with DFT calculations reveal a non-innocent role for the chloroalkane solvent, an aspect that has been underrecognized in related photochemical upcycling systems, as well as an autoinductive rate acceleration. This intrinsic PS photoreactivity further enables co-upcycling with non-aromatic polymers and remains effective in a waste-emulating halogenated solvent mixture, pointing to potential synergy between mixed plastics/biomass valorization and solvent waste management.