The present invention relates to aqueous copolymer dispersions containing A) one or more hydroxy-functional copolymers synthesized from a) one or more OH-free (meth)acrylic esters and/or vinylaromatics, b) one or more hydroxy-functional (meth)acrylic esters, c) one or more ionic and/or potential ionic monomers capable of free-radical copolymerization, and d) one or more optionally monomers other than components a) to c) that are capable of free-radical copolymerization, and B) one or more hydroxy-functional polycarbonate polyols as reactive diluent. The present invention also relates to a process for preparing these aqueous copolymer dispersions and to their use in coating compositions.