Polymerization of ethylene oxide using metal cyanide catalysts

A process for preparing a block polyether, comprising forming a mixture of an initiator compound having one or more oxyalkylatable groups, an initial charge of ethylene oxide and a metal cyanide catalyst complex, and subjecting the mixture to conditions sufficient to ethoxylate the oxyalkalatable groups of the initiator, and feeding another alkylene oxide or mixture of another alkylene oxide and a copolymerizable monomer to the reactor under polymerization conditions once the catalyst has been activated and the initial charge of ethylene oxide has begun to polymerize.