Highly Active Catalysts for the Ring-Opening Polymerization of Ethylene Oxide and Propylene Oxide Based on Products of Alkylaluminum Compounds with Bulky Tetraphenol Ligands

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Abstract

Mixtures of hindered (poly)phenols and alkylaluminum compounds have been evaluated as catalysts for the polymerization of ethylene oxide (EO) and propylene oxide (PO). Certain ligands bearing four phenol groups form particularly active catalysts when combined with triisobutylaluminum (2 equiv) and triethylamine (1 equiv) as initiator. Productivities of >100 g/mmol Al have been achieved in both EO and PO polymerizations by use of a dibenzothiophene-bridged tetraphenol. In general, catalyst activity increases with the increasing bulk of the substituents ortho to the phenol hydroxyl groups. Mechanistic investigations support a dinuclear insertion process. Chain transfer to alcohol (2-propanol or benzyl alcohol) has been demonstrated. Poly(propylene oxide) produced in this manner is atactic and highly regioirregular.

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