Kinetic investigations of reversible addition fragmentation chain transferpolymerizations: Cumyl phenyldithioacetate mediated homopolymerizations ofstyrene and methyl methacrylate

A previously published simulation and data fitting procedure for the revers ible 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 experi mentally obtained molecular weight distributions (MWDs) for the styrene sys tem are narrow and unimodal and shift linearly with monomer conversion to h igher molecular weights. The MMA system displays a hybrid of conventional c hain transfer and living behavior, leading to bimodal MWDs. The styrene sys tem has been subjected to a combined experimental and modeling study at 60 degreesC, yielding a rate coefficient for the addition reaction of free mac roradicals to polymeric RAFT agent, k(beta), of approximately 5.6 x 10(-5) L mol(-1) s(-1) and a decomposition rate coefficient for macroradical RAFT species, k-(beta), of about 2.7 x 10(-1) s(-1). The transfer rate coefficie nt to cumyl phenyldithioacetate is found to be close to 2.2 x 10(5) L mol(- 1) s(-1). The MMA system has been studied over the temperature range 25-60 degreesC. 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 ph enyldithioacetate 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 medi ated MMA polymerizations for the deduction of k(beta) and k-(beta). This in ability is due to the hybrid nature of the cumyl phenyldithioacetate-MMA sy stem, leading to a significantly reduced sensitivity toward k(beta) and k(- beta).