Kinetics of living radical polymerization

This review covers fundamental kinetic features of living radical polymerization (LRP). Theories on polymerization rate R_p and polydispersity index (PDI) and experimental investigations into individual LRP systems are summarized. The presence of bimolecular termination, which is unavoidable in LRP as well as in conventional radical polymerization, provides LRP with the characteristic time dependence of radical concentrations and hence R_p and PDI, depending on experimental conditions, such as the presence or absence of conventional initiation. Despite the presence of termination (and initiation, in some cases), the product from LRP can have a low polydispersity, provided that the number of terminated chains is small compared to the number of potentially active, i.e. living, chains. On the premise that an activation-deactivation quasi-equilibrium holds, a large rate constant of activation, k_act, is another fundamental requisite for low polydispersities. The kinetic parameters related to reversible activation reactions are tabulated. Treated in this review are nitroxide-mediated polymerization, atom transfer radical polymerization, iodide-mediated polymerization, reversible addition-fragmentation chain transfer polymerization, and organotellurium-mediated radical polymerization.