Abstract: A process of bonding a plastic is provided. The process comprises applying to a plastic surface an aqueous dispersion of a hydroxyl-functional polyurethane prepolymer obtained by:(1) reaction of:a polyol component containing a polyester polyol,a compound selected from the group of compounds containing groups capable of salt formation and at least two isocyanate-reactive groups,an isocyanate component in a stoichiometric excess, at least 20% by weight of said component consisting of tetramethyl xylylene diisocyanate, and(2) subsequent dispersion in water and at least partial reaction of the remaining NCO groups with an aminoalcohol and, optionally, subsequent chain extension. The process further comprises drying said applied aqueous dispersion to form a primer and bonding said plastic surface having said primer to a part to be joined thereto. The process is particularly useful for priming plastics such as polyvinyl chloride.