Abstract
The development of simple, stable, and well defined catalyst systems for the initiation of ionic polymerisation is reviewed. The principles involved are illustrated by reference to the use of potassium t‐butoxide in dimethyl sulphoxide for initiating anionic polymerisation of ethylene oxide and of the hexachloroantimonate salt of the triphenyl methyl cation for polymerisation of tetrahydrofuran. Other stable organic cations initiate polymerisation via charge transfer complexes and can give rise to cation‐radicals as intermediates. It is suggested that related cation‐radicals may play a role in lignin biosynthesis.