Abstract: Novel aqueous liquid emulsion polymers are prepared by the copolymerization of (A) about 15-60 weight percent of a C.sub.3 -C.sub.8 .alpha.,.beta.-ethylenically unsaturated carboxylic acid monomer, preferably acrylic or methacrylic acid or a mixture thereof with itaconic or fumaric acid, (B) about 15-80 weight percent of a nonionic copolymerizable C.sub.2 -C.sub.12 .alpha.,.beta.-ethylenically unsaturated monomer, preferably a monovinyl ester such as ethyl acrylate or a mixture thereof with styrene, acrylonitrile, vinyl chloride or vinyl acetate, and (C) about 1-30 weight percent of certain nonionic vinyl surfactant esters, such as nonylphenoxypoly(ethyleneoxy).sub.9 ethyl acrylate, to give an emulsion copolymer stable as an aqueous colloidal dispersion at an acid pH lower than about 5.0 but responsive to pH adjustment with base. These emulsion polymers adjusted to a pH of about 5.