Organic Photocatalyst for ppm-Level Visible-Light-Driven Reversible Addition–Fragmentation Chain-Transfer (RAFT) Polymerization with Excellent Oxygen Tolerance

A highly efficient organic photocatalyst (OPC) for photoinduced electron/energy-transfer reversible addition–fragmentation chain-transfer (PET-RAFT) polymerization was identified through a systematic catalyst design and discovery. The devised OPC offers excellent control over PET-RAFT polymerizations of methyl methacrylate at very low catalyst loadings (5 ppm), that is, ca. 5–50 times lower loadings than other OPCs reported so far. Moreover, excellent oxygen tolerance was achieved using the discovered OPC combined with trithiocarbonate-based chain-transfer agent (CTA) under low-energy light irradiation conditions. In depth experimental and computational investigations revealed that (1) strong visible-light absorption and efficient generation of long-lived triplet states of the OPC due to its unique molecular structure and (2) the oxidation stability and no rate retardation of trithiocarbonate-based CTA are the key to the outstanding oxygen tolerance and ppm-level catalyst loadings. Our approach is thus believed to address a variety of challenging tasks related to polymer synthesis and living additive manufacturing.