Describes terminally ethylenically unsaturated poly(alkyleneoxy) surfactant compounds of the general formula, R--O--(R'O).sub.m --(EO).sub.n-1 --CH.sub.2 CH.sub.2 --X, wherein R is the ethylenically unsaturated hydrocarbon group, e.g., allyl, R' is the bivalent radical derived from butylene oxide, E is the bivalent ethylene radical, m and n are numbers of from 10 to 15 and 10 to 40 respectively, and X is chloride, tertiaryamino, sulfonate, sulfate, phosphate, isethionate and alkali metal salts of the anionic groups. These surfactant compounds may be used in emulsion polymerization of ethylenically unsaturated, e.g., vinyl, monomers.