Hybrid of Organophotoredox- and Cu-Mediated Pathways Enables Atom Transfer Radical Polymerization with Extremely Low Catalyst Loading

The rise of photoredox catalysis has extended the landscape of reversible-deactivation radical polymerization. Recently, visible-light-driven photoredox/Cu dual catalyzed atom transfer radical polymerization (photoATRP) has become an emerging trend, providing well-defined polymer under low copper catalyst loading. In this work, we described a dual catalyzed ATRP using CuBr2/tris(2-pyridinylmethyl)amine (TPMA) and donor–acceptor-type organophotoredox catalysts (OPCs) with visible light absorption. The excited state OPC can reduce both dormant polymer chain-end and CuBr2/TPMA, generating propagating radical species and CuBr/TPMA, respectively. This indicates that the mechanism is a hybrid of organophotoredox-mediated and Cu-mediated ATRP. The photoATRP driven by 425 nm light irradiation produced a series of well-defined polymethacrylates under extremely low catalyst loadings (5 or 10 ppm CuBr2 and 1 ppm OPC relative to monomer). The method also showed excellent temporal control over polymerization and oxygen tolerance.