Kinetics of Dithiobenzoate-Mediated Methyl Methacrylate Polymerization

The equilibrium constant, K-eq, of the reversible addition-fragmentation chain transfer (RAFT) model system methyl methacryl dithiobenzoate (MMADB) and of methyl methacrylate (MMA) polymerization mediated by MMADB is studied via electron paramagnetic resonance (EPR) spectroscopy in the range 70 to 110 degrees C and at -40 degrees C, respectively. The measured difference in activation energy of the addition and fragmentation steps is: E-a(k(ad)) - E-a(k(frag)) approximate to -36.6 kJ mol(-1). Significant amounts of missing step products from reaction of the cross-termination product with a methyl methacrylyl radical are found. The fast missing step reaction and low K-eq, due to slow k(ad), are responsible for rate retardation being absent in dithiobenzoate-mediated MMA polymerization.