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.