RAFT miniemulsion polymerization: Influence of the structure of the RAFT agent

Reversible addition-fragmentation chain transfer polymerization (RAFT) of styrene has been successfully performed in miniemulsion, mediated by a very efficient RAFT agent: 1-phenylethyl phenyldithioacetate (PEPDTA). To gain a better understanding of this system, we compared the performance of this RAFT agent with those of cumyl dithiobenzoate (CDB) and 1-phenylethyl dithiobenzoate (PEDB) in bulk and found a superior performance for PEPDTA. This result is consistent with a more efficient reversible radical sink in this system. Miniemulsion polymerizations mediated by PEPDTA (initiated by potassium persulfate at 75 °C) were also found to proceed at a considerably higher rate than those mediated by CDB or PEDB mediated ones; however, all three systems showed a significant decrease in polymerization rate as compared to a conventional miniemulsion polymerization. This latter observation is conceivably related to entry and exit events, as a prepolymerized PEPDTA RAFT agent displayed rates close to the conventional nonliving miniemulsion system. All systems were found to produce polymers with relatively broad molar mass distributions, which is fully explained by consideration of initiator-derived chains.