Ionic Chain Polymerization

This chapter describes anionic and cationic chain polymerization of carbon–carbon double bond monomers, with emphasis on the parameters that control polymer molecular weight. The rate and molecular weight in both reversible and irreversible polymerizations are discussed together with the process conditions needed for producing different polymers. Various initiators are discussed including Lewis acids and photoinitiators for cationic polymerization; metal alkyls, electron-transfer, and group-transfer for anionic polymerization; transition metal and other initiators. Molecular weight control depends on temperature, reactant concentrations, solvent, counterion, and various transfer and termination reactions. Solvents have large effects on polymerization rate and polymer molecular weight because of changes in the relative concentrations of free ions and ion pair propagating species. Living polymerization allows the synthesis of block, graft, star, and other polymer architectures. Ionic polymerization is commercially used for isobutylene polymers such as butyl rubber and various block polymers. The polymerization of carbonyl and other multiple-bond monomers are also considered.