Access to Chain Length Dependent Termination Rate Coefficients of Methyl Acrylate via Reversible Addition−Fragmentation Chain Transfer Polymerization

The reversible addition−fragmentation chain transfer chain length dependent termination (RAFT-CLD-T) method is employed to map out the chain length dependence of the termination rate coefficient in methyl acrylate (MA) bulk free radical polymerizations at 80 °C. Methoxycarbonylethyl phenyldithioacetate (MCEPDA) a novel RAFT agent carrying a methyl acryl leaving group is identified as suitable for the RAFT-CLD-T method applied to methyl acrylate, as interfering inhibition and rate retardation effects are avoided. The chain length dependency of the termination rate coefficient was constructed in a stepwise fashion since the MA/MCEPDA system displays hybrid behavior (between conventional and living free radical polymerization), resulting in initial high molecular weight polymers formed at low RAFT agent concentrations. The chain length dependency of k t in the MA system for chain lengths, i, ranging from 5 to 800 at 80 °C may be described by a value for α of 0.36 ± 0.05 (where α is the slope of the associated log k t i, i vs log i plot). An alternative RAFT agent, dimethoxycarbonylethyl trithiocarbonate (DMCETC), may not be as ideally applicable to map CLD dependent k t i, i in MA polymerizations. Since the leaving group of both RAFT reagents is identical to the propagating methyl acrylate radical, the addition rate coefficient of the methyl acrylate propagating radicals to the initial and polymeric RAFT agent, k β, was determined and found to be close to 1.4 × 10 6 L mol -1 s -1 for MCEPDA and 2.1 × 10 6 L mol -1 s -1 for DMCETC at 60 °C.