Kinetic investigations of reversible addition fragmentation chain transfer polymerizations: Cumyl phenyldithioacetate mediated homopolymerizations of styrene and methyl methacrylate

A previously published simulation and data fitting procedure for the reversible addition fragmentation chain transfer (RAFT) process using the PREDICI simulation program has been extended to cumyl phenyldithioacetate mediated styrene and methyl methacrylate (MMA) bulk homopolymerizations. The experimentally obtained molecular weight distributions (MWDs) for the styrene system are narrow and unimodal and shift linearly with monomer conversion to higher molecular weights. The MMA system displays a hybrid of conventional chain transfer and living behavior, leading to bimodal MWDs. The styrene system has been subjected to a combined experimental and modeling study at 60 °C, yielding a rate coefficient for the addition reaction of free macroradicals to polymeric RAFT agent, k_β, of approximately 5.6 × 10⁵ L mol^-1 s^-1 and a decomposition rate coefficient for macroradical RAFT species, k_-β, of about 2.7 × 10^-1 s^-1. The transfer rate coefficient to cumyl phenyldithioacetate is found to be close to 2.2 × 10⁵ L mol^-1 s^-1. The MMA system has been studied over the temperature range 25-60 °C. The hybrid behavior observed in the MMA polymerizations has been exploited (at low monomer conversions) to perform a Mayo analysis allowing the determination of the temperature dependence of the transfer to cumyl phenyldithioacetate reaction. The activation energy of this process is close to 26 kJ mol^-1. In contrast to the styrene system, the PREDICI simulation procedure cannot be successfully applied to cumyl phenyldithioacetate mediated MMA polymerizations for the deduction of k_β and k_-β. This inability is due to the hybrid nature of the cumyl phenyldithioacetate-MMA system, leading to a significantly reduced sensitivity toward k_β and k_-β.