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 landscapeofreversible-deactivation radical polymerization. Recently, visible-light-drivenphotoredox/Cu dual catalyzed atom transfer radical polymerization(photoATRP) has become an emerging trend, providing well-defined polymerunder low copper catalyst loading. In this work, we described a dualcatalyzed 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 bothdormant polymer chain-end and CuBr2/TPMA, generating propagatingradical species and CuBr/TPMA, respectively. This indicates that themechanism is a hybrid of organophotoredox-mediated and Cu-mediatedATRP. The photoATRP driven by 425 nm light irradiation produced aseries of well-defined polymethacrylates under extremely low catalystloadings (5 or 10 ppm CuBr2 and 1 ppm OPC relative to monomer).The method also showed excellent temporal control over polymerizationand oxygen tolerance.