Kinetics of living radical polymerization

Activation processes and polymerization rates of several variants of living radical polymerization (LRP) are discussed. Despite the presence of side reactions such as termination and initiation, the products from LRP can have a low polydispersity, provided that the number of terminated chains is small compared to the number of potentially active chains. A large rate constant of activation, k_act, is another fundamental requisite for low polydispersities. Experimental studies on k_act have clarified the exact mechanisms of activation in several LRP systems. The magnitudes of k_act have been found to largely differ from system to system. Because of bimolecular termination, which is inevitable in LRP as well as in conventional radical polymerization, the time-conversion curves of LRP have several characteristic features depending on experimental conditions, such as the presence or absence of conventional initiation and/or an extra amount of stable free radicals or the like. A new analytical rate equation applicable to such general cases is presented.