The invention relates to a coating composition comprising an acetal-functional binder and a thiol-functional cross-linker, wherein the acetal-functional binder is represented by the following formula ##STR1##

wherein P is a binder backbone, K is a divalent and/or trivalent organic moiety having 1 to 30 carbon atoms and having one or two links to the binder backbone, A is selected from oxygen, sulphur, and NR^VII, wherein R^VII is hydrogen or an alkyl group with 1 to 4 carbon atoms, m is an integer from 1 to 50, n is an integer from 1 to 10, and R and R may be the same or different and represent alkyl groups with 1 to 4 carbon atoms. In a further aspect, the invention relates to acetal-functional binders, acetal-functional monomers, a process for the preparation of said monomers, coating compositions comprising said acetal-functional binders, and to a process for the preparation of a coating composition comprising an acetal-functional polyurethane dispersion and a thiol-functional cross-linker.