Kinetic analysis of controlled/"living" radical polymerizations by simulations. 1. The importance of diffusion-controlled reactions

Controlled/"living" atom transfer radical polymerization (ATRP), which is subject to the persistent radical effect, has been examined through computer simulations. It was found that the peculiar time-dependent rates predicted by the persistent radical effect may not be observed experimentally because termination is dependent on chain length and viscosity. In the early stages of the polymerizations the deactivating species is produced very fast through irreversible radical-radical termination; however, as the polymerization progresses, less deactivator is produced because termination reactions are slowed, thus resulting in a steady rate of polymerization. Thermal initiation of styrene was found to be insignificant in ATRP under the conditions examined, in contrast to systems characterized by a low equilibrium constant, such as TEMPO-mediated polymerization, where the rate of styrene polymerization is dominated by thermal initiation. Inclusion of termination rate coefficients that decrease during polymerization in the simulation model led to adequate reproduction of experimental results.