A well-defined, versatile photoinitiator (salen)Co–CO2CH3 for visible light-initiated living/controlled radical polymerization

Abstract

The control of the polymerization of a wide range of monomers under mild conditions by a single catalyst remains a major challenge in polymer science. We report a versatile, well-defined organocobalt salen complex to control living radical polymerization of different categories of monomers, including acrylates, acrylamides and vinyl acetate, under visible light irradiation at ambient temperature. Both household light and sunlight were effectively applied in the synthesis of polymers with controlled molecular weights and narrow polydispersities. Narrowly dispersed block copolymers (M_w/M_n < 1.2) were obtained under various conditions. The structures of the polymers were analyzed by ¹H NMR, ²D NMR, ¹³C NMR, GPC, MALDI-TOF-MS and isotopic labeling experiments, which showed that the ω and α ends of the polymer chains were capped with (salen)Co and –CO₂CH₃ segments, respectively, from the photoinitiator (salen)Co–CO₂CH₃. The ω end was easily functionalized through oxygen insertion followed by hydrolysis from ¹⁸O₂ to –¹⁸OH. This robust system can proceed without any additives, and offers a versatile and green way to produce well-defined homo and block copolymers.