The polymerisation of propylene oxide by organomagnesium compounds

Abstract

AbstractDiethyl magnesium as a diethyl etherate‐dioxanate complex polymerises propylene oxide in a diethyl ether solution to very high molecular weight crystalline polymer. Magnesium dibromide diethyl etherate polymerises propylene oxide in diethyl ether to low polymer. Ethyl magnesium bromide diethyl etherate polymerises propylene oxide in diethyl ether in four distinct kinetic stages. In the first two kinetic stages, polymer similar to that produced by diethyl magnesium is obtained in very low yield. Polymer of Mv ≈ 10,000 to 15,000 in yields up to 50% is produced in the next two stages. Above a certain catalyst concentration, the second stage is characterised by gel formation and precipitation. The third kinetic stage, during which most of the eventual polymer yield is produced, occurs with breakdown of the gel and redissolution of the precipitate, a similarity with polymerisation of propylene oxide by magnesium dibromide. With the ethyl magnesium bromide polymerisation, above the aforementioned catalyst concentration, change of catalyst concentration or solvent affects only the initial polymerisation stage kinetically.