Modified polyolefins are produced by reacting a functionalized polyolefin with one or more ethylenically unsaturated compounds having a functional group reactive with the functional group on the polyolefin. These modified polyolefins may then polymerize in the presence of a photoinitiator upon exposure to ultraviolet radiation and also have the capability of copolymerizing in the presence of a photoinitiator with other ethylenically unsaturated crosslinking agents upon exposure to ultraviolet radiation. These modified polyolefins may also contain pendant carboxyl groups, which have the propensity to form hydrophilic salts with amines, and therefore may be rendered water-dispersible. The modified polyolefins of the present invention significantly improve the adhesion of paints, inks, and adhesives to various plastic and metal substrates.