Photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer(PET-RAFT) using purely organic photocatalysts in the presence of oxygen
Department of Materials Science and EngineeringThe necessity of a sustainable polymerization method renders a synthesis method to be more simple, efficient, and green. Reversible addition-fragmentation chain transfer (RAFT) polymerization is a typical method of living radical polymerization. This can control the degree of polymerization and the molecular weight depending on the reaction time and obtain the narrow molecular weight distribution. Recently, photoinduced electron/energy transfer (PET)-RAFT polymerization using photocatalysts has shown the excellent oxygen tolerance with use of transition metal-based catalysts, such as iridium or ruthenium complex. However, this approach is not effective for sustainable polymerization owing to the metal contaminations and hazards of toxicity, which necessitate the purification to remove residual transition metals after reaction.
Here, we discovered purely organic photocatalysts (OPC) with light absorption in the visible light region. The well-designed highly efficient OPC provides excellent control and narrow molecular weight distributions for PET-RAFT at extremely low catalyst loadings as well as low-energy light irradiation conditions, without additional reducing agents unlike other OPCs reported. In addition, by depth experimental and computational study, we present the following key factors showing the excellent oxygen tolerance with ppm-level catalyst loadings: the strong visible-light absorption and efficient generation of long-lived triplet states of the OPC, the oxidation stability and short retardation of chain-transfer agent (CTA), such as trithiocarbonate-based CTA.clos
