EPR Study into Cross-Termination and Fragmentation with the PhenylethylPhenylethyl Dithiobenzoate RAFT Model System

The reversible additionfragmentation chain transfer (RAFT) equilibrium constant of the phenylethyl1-phenylethyl dithiobenzoate model system is deduced via EPR spectroscopy to be 31 +/- 4 L mol1 at 110 degrees C. The difference in activation energies of addition and fragmentation, Ea(kad) Ea(k) approximate to 45.6 kJ mol1, is close to that of the polystyrylpolystyryl dithiobenzoate system. Significant amounts of products from cross-termination and from missing step reaction of the cross-termination product with the phenylethyl radical demonstrate that intermediate radical termination, rather than slow fragmentation of the RAFT intermediate radical, is responsible for the rate retardation in the dithiobenzoate-mediated styrene polymerization.