Anionic polymerization of ethylene oxide in dimethyl sulphoxide

The polymerization of ethylene oxide has been investigated in anhydrous DMSO using potassium tert-butoxide as initiator. At low conversion the polymerization obeys the rate expression R3=k3[ethylene oxide][K+−OBut] where kp=0.10±0.03 litre mole−1 sec−1, ΔH‡p=6.4 kcal mole−1, and ΔS‡p=−41 cal mole−1deg−1, at 25°C. Values of kp obtained are thought to represent propagation by free alkoxide ion, and are much greater than previously reported values. At 25°C polyethylene oxide is only slightly soluble in DMSO and hence the polymerizations develop the characteristics of colloidal systems as conversion and molecular weight increase. Raising the temperature to 50°C or addition of 1,2-dimethoxy ethane helps to maintain homogeneity in the reaction mixtures. Molecular weights increase with increasing [monomer] and decreasing [catalyst].