Synergizing Visible Light-Mediated Cationic and Radical PET RAFT Through Electron-Rich Dithiobenzoates

Abstract

In this work, we developed a novel electron-rich dithiobenzoate chain transfer agent (CTA) with excellent control for both cationic and radical photoelectron/energy transfer-reversible addition–fragmentation chain transfer (PET RAFT) polymerizations. The 2,4-dimethoxydithiobenzoate-based CTA enables the optimized stabilization of chain transfer intermediates, outperforming trithiocarbonates in the control of cationic RAFT polymerizations and dithiocarbamates in radical RAFT polymerizations of more active monomers. The excellent control of cationic PET RAFT polymerization offered by this novel CTA was demonstrated by the blue-light-mediated synthesis of poly(isobutyl vinyl ether) of various chain lengths with sub-1.2 dispersities. Furthermore, to highlight its benefit over previously reported dithiocarbamate and trithiocarbonate CTAs, this new CTA was employed for the one-pot synthesis of poly(isobutyl vinyl ether)-block-poly(methyl acrylate) diblock copolymers. The prepared CTA-terminated poly(isobutyl vinyl ether) was chain-extended by methyl acrylate via red-light-mediated radical RAFT polymerization, which afforded a diblock copolymer with a dispersity of 1.26, which significantly surpassed the dispersities achieved with analogous trithiocarbonates. The radical polymerization step uses a zinc tetraphenylporphyrin photocatalyst to achieve complete wavelength orthogonality, with a tris(4-methoxyphenyl)pyrylium photocatalyst used for the cationic polymerization step. The optimized electron-rich dithiobenzoate can then be used as a universal agent in the synthesis of advanced copolymers involving radical-cationic RAFT crossover polymerization steps.