Anthraquinone-Mediated Reduction of a Trithiocarbonate Chain-Transfer Agent to Initiate Electrochemical Reversible Addition-Fragmentation Chain Transfer Polymerization

A goal in applying electrochemical methods to reversible addition-fragmentation chain transfer (RAFT) polymerization is to use electrochemical reduction to activate RAFT agents (SC(Z)S-R) to also act as initiators. The use of a mediator can limit side reactions that would otherwise inhibit polymerization. In this work, we present the use of anthraquinone (AQ) to mediate the electrochemical reduction of a trithiocarbonate RAFT agent, 4-cyano-4-(((dodecylthio)carbonothioyl)thio)pentanoic acid, and thereby initiate RAFT polymerization of methyl methacrylate (MMA). In a representative eRAFT reaction conducted in DMSO with a target degree of polymerization (DP) of 100, conversion reached 67% in 24 h at ambient temperature, with C = 1.19. The effect of reaction conditions on polymerization was studied - in general, the conversion rate was found to decrease as target DP increases. Dispersity increases as (i) target DP increases and (ii) mediator concentration increases. The livingness of AQ-mediated eRAFT polymerization was confirmed by eRAFT chain extension with MMA and by thermally initiated RAFT with styrene to form a block copolymer. AQ-mediated eRAFT was found to be unsuitable for polymerization of monosubstituted monomers (styrene, butyl acrylate, N,N-dimethylacrylamide, and N-vinylpyrrolidone). These results support the hypothesis that mediated electrochemical reduction of RAFT agents can yield an initiating species (R•), although polymerization is strongly dependent on diffusion and fragmentation kinetics.