In accordance with the present invention, there are provided novel coupling agents which are compatible with a wide variety of adhesive formulations and which provide substantial adhesion enhancement relative to base formulations to which they are added. Invention compounds comprise at least one free-radically polymerizable group (other than acrylate) and at least one reactive moiety which forms covalent bond(s) with substrates having free hydroxyl groups on the surface thereof. Thus, invention compounds are covalently linked to adhesive formulations upon free radical cure, while at the same time providing “residual” functionality which is capable of undergoing reaction with any substrate having reactive (e.g., hydroxyl) groups in the surface thereof.