Mixtures of hindered (poly)phenols and alkylaluminum compounds have 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, catalysts activity increases iwth the increasing bulk of the substituents ortho to the phenol (2-propanol or benzyl alcohol) has been demonstrated. Poly(propylene oxide) produced in this manner is atactic and highly regionirregular.