Graft and block copolymers with a weight average molecular weight below 20,000, a hydroxy value more than 200 and acid value below 50 which copolymers comprise (a) 20-98% by weight of a water soluble macromonomer having a hydroxy value of at least 300, a weight average molecular weight below 6000, containing less than 10% by weight of an acid functional monomer and having a terminal unsaturated double bond; and (b) 2 to 80% of polymerized monomers selected from vinyl monomers, acrylate monomers, methacrylate monomers and mixtures thereof, form stable coating compositions that are compatible with polyisocyanate crosslinking agents and provide improved properties and appearance in automotive finishes.