Abstract
Propylene oxide (PO) was polymerized by some diphenylzinc-ketone systems. Cocatalytic effects of nine ketones were examined. The systems are greatly influenced by the nature of the ketone and by the molar ratio of ketone to diphenylzinc. Methyl and cyclic ketones were the most effective as cocatalyst and the maximum catalyst activity was found, in most cases, for a molar ratio of unity. The difference in cocatalyst activities for methyl ketones is attributed to electronic effects, while steric hindrance is not relevant. Similar effects were found for PO polymerization initiated by diphenylzinc in combination with cyclic and with non-halogenated methyl ketones. However the activity of the diphenylzinc-diethyl ketone system increases with increase of the molar ratio. The diphenylzinc-benzophenone system shows a small dependence on the molar ratio. The activity of the diphenylzinc-acetylacetone decreases with increase of the molar ratio showing maximum conversion to polymer when no ketone was added. Polymerization of ethylene oxide by some of these systems showed behaviour similar to that found for PO.
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