Polymerization of ethylene oxide in dimethyl sulphoxide (DMS)

Abstract

Comparison of the reactivity of various types of centres, especially of ions and ionic pairs, can give very valuable information about the type of reactions with the monomer and the medium. The reactivity of free ions in the polymerization of styrene [1] or propylene sulphide [2], in tetrahydrofuran (THF) as solvent for example, is approximately 3 orders of magnitude greater than that of ionic pairs; this is due to steric hindrance of chain propagation by the strong solvation of the latter and also to the greater capacity of the anion to polarize the attack monomer. The reaction capacity of ions and ionic pairs in the polymerization of epoxides is basically still an open question. The reaction kinetics of the oxo anions was detected only in hexamethylphosphorus triamide [3]. The free ions do not play any outstanding part in the ethylene oxide (EO) polymerization in ether-type solvents (THF, dimethoxyethane, dimethylene glycol and in the bulk process) when alkali metal cations are present [4, 5]. The aim of this work was to study the polymerization of this monomer in a more polar medium to establish the part played by the oxo anions in chain propagation. The selected monomer was ethylene oxide (EO) in DMS, because it was the most suitable.