Catalyst-Free Selective Photoactivation of RAFT Polymerization: A Facile Route for Preparation of Comblike and Bottlebrush Polymers

We report a novel photoiniferter approach toward enabling chemoselective fragmentation of reversible addition-fragmentation chain transfer (RAFT) polymerization using two different RAFT agents. Methyl methacrylate (MMA) was polymerized in the presence of two different RAFT agents, 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDTPA) and 2-(dodecylthiocarbonothioylthio)propionic acid (DTPA). Both RAFT agents contain the same Z-groups but different R-leaving groups. Under photoiniferter conditions, only one RAFT agent was preferentially fragmented while the other remained inert. This led to the synthesis of poly(methyl methacrylate) (PMMA) with close correlations between theoretical and experimental molecular weights and narrow molecular weight distributions (M-w/M-n). This approach was then employed to homopolymerize and copolymerize a RAFT inimer, 2-(2-(n-butyltrithiocarbonate)propionate)ethyl methacrylate (BTPEMA), under green light with CDTPA with the trithiocarbonate functionality on the inimer incapacitated for chain transfer. Switching to blue light irradiation allowed for photolysis of BTPEMA and grafting of a second monomer. This novel approach provided a facile route for the synthesis of complex macromolecular architectures such as comblike and bottlebrush polymers without the need for intermediate steps, such as postmodification.