Ligand-Controlled Copper Photocatalysis for Polyethylene C–H Oxidation via Coupled Photothermal Activation

The selective functionalization of polyethylene (PE) C–H bonds under mild conditions remains a major challenge because PE is chemically inert and poorly soluble at room temperature. Here, we report a visible-light-driven copper-catalyzed strategy for the controlled oxidation of low-density polyethylene (LDPE), in which the copper catalyst couples photochemical C-H activation with photothermal polymer swelling. Under blue-light irradiation, diimine copper complexes absorb visible light and generate heat in situ, enabling LDPE oxidation without an external heating source. Systematic evaluation of four copper complexes revealed a clear ligand-dependent activity–selectivity relationship. The neocuproine-ligated complex Cu-4 exhibited the highest oxidation activity but also promoted chlorination and chain scission, whereas the 1,10-phenanthroline-ligated complex Cu-2 provided the most favorable balance among ketone formation, side-reaction suppression, and molecular-weight retention. Under optimized Cu-2 catalyzed conditions, ketone-functionalized LDPE was obtained with a largely preserved molecular weight and crystallinity. The resulting material showed remarkably improved tensile strength, tear resistance, wettability, paint adhesion, and adhesion to metal substrates. This work demonstrates that ligand-controlled copper photocatalysis, assisted by catalyst-induced photothermal heating, provides a practical platform for ketone-selective PE oxidation and the preparation of functional polyolefin materials.