Latex of an interpolymer composed of (1) a copolymer A of butadiene, styrene and at least one ethylenically unsaturated carboxylic acid, and (2) a polymer B of at least one halogenoalkyl or halogenoacetoxyalkyl ester of an ethylenically unsaturated monocarboxylic or dicarboxylic acid, polymer B being at least partially grafted onto the copolymer A.The latex is prepared by the emulsion polymerization of butadiene, styrene and at least one copolymerizable, ethylenically unsaturated carboxylic acid to form a copolymer latex, followed by the polymerization in the presence of the copolymer latex of a halogenoalkyl or halogenoacetoxyalkyl ester of an ethylenically unsaturated monocarboxylic or dicarboxylic acid.The latex may be used as a binder in aqueous compositions for coating paper.