A method for making a polyether monomer having at least one unsaturated site per molecule and having a desired number of alkoxyl repeating units includes the steps of reacting an active hydrogen-containing monomer having at least one unsaturated site per molecule with an alkyl oxide in the presence of an alkoxylation catalyst and a polymerization inhibitor at a temperature from about 30° C. to less than 45° C. to produce a polyether monomer. In one embodiment, from about 5 to about 1000 parts by weight of a phenothiazine polymerization inhibitor per one million parts by weight of the active hydrogen-containing monomer phenothiazine compound is used as the polymerization inhibitor.