Abstract: There is provided a binder for coating compositions based on a mixture of an unsaturated .beta.-hydroxy ester with copolymerizable monomers. The binder consists essentially of, on a total weight basis,(A) 25 to 60 weight percent of an unsaturated .beta.-hydroxy ester which is produced by reacting an epoxy resin based on bisphenol A and epichlorohydrin with a molecular weight between 800 and 3000 and an epoxide equivalent weight between 400 and 2500 with a mixture of(a) 74 to 64 mole percent of methacrylic acid and/or acrylic acid and(b) 26 to 36 mole percent of at least one saturated monocarboxylic acid having 8 to 20 carbon atoms or a mixture of at least one saturated monocarboxylic acid having 8 to 20 carbon atoms with up to 20 mole percent of an unsaturated monocarboxylic acid having 8 to 20 carbon atoms, and(B) 75 to 40 weight percent of a mixture based on the weight of component (B) of(a) 70 to 95 weight percent methyl methacrylate,(b) 30 to 5 weight percent of at least one monomer of the formula CH.sub.