Kinetic Analysis of “Living” Polymerization Processes Exhibiting Slow Equilibria. 6. Cationic Polymerization Involving Covalent Species, Ion Pairs, and Free Cations

Abstract

The kinetics of cationic polymerization is studied theoretically in accordance with a three-state mechanism which consists of two successive equilibria: the ionization/ion collapse equilibrium between covalent species and ion pairs, and the subsequent dissociation/association equilibrium between ion pairs and free ions. The number- and weight-average degrees of polymerization and the polydispersity index (PDI), Pw/Pn, are derived. The molecular weight distribution of the polymer generated from this mechanism is generally broader than that of polymers formed via a two-state mechanism, i.e. with only one equilibrium either between covalent species and ion pairs or between covalent species and free ions. Under this general mechanism, the exchange rate parameter, β, is more complicated than that of two-state mechanisms and is a combination of the corresponding exchange rate parameters for these two mechanisms. The molecular weight distribution becomes narrower if dissociation is reduced by adding common co...