Chapter 2 Kinetics of Homogeneous Cationic Polymerization

Abstract

Publisher Summary Cationic polymerization is the conversion of low molecular weight monomeric molecules into high molecular weight polymeric ones, through a mechanism involving stepwise growth of a carbonium (R 3 C + ), carboxoniup, oxonium (R 3 0 + ), sulphonium (R 3 S + ), or immonium (R 2 N + =CŔ 2 ) ion. This chapter reviews the kinetic and mechanistic aspects of cationic polymerizations and analyzes the limited reliable kinetic data. The chapter outlines the complex nature of cationic systems and discusses that in any kinetic experiment of quantitative value, firstly data on the rate of propagation alone as opposed to an overall rate of polymerization must be ascertained. Secondly, the proportion of free ions and paired species ( α or K d ) must be known. Finally, in order to determine the two unknowns, that is, the rate coefficient for propagation by free ions, and the rate coefficient for propagation by ion pairs, either their approximate relative values must be known, or the proportion of each species must be altered by some arbitrary procedure (for instance, changing the total concentration, or use of “common ion” effect).