Anthraquinone-Mediated Reduction of a Trithiocarbonate Chain-Transfer Agent to Initiate Electrochemical Reversible Addition–Fragmentation Chain Transfer Polymerization
2020
Strover, Lisa T. | Postma, Almar | Horne, Michael D. | Moad, Graeme
A goal in applying electrochemical methods to reversible addition–fragmentation chain transfer (RAFT) polymerization is to use electrochemical reduction to activate RAFT agents (S═C(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 Đ = 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.
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