er (having a plurality of pendent polymerizable functional groups) may comprise any of the free radically polymerizable ethylenically-unsaturated monomers, examples of which include one or more of the vinyl aromatic monomers such as styrene, ??-methylstyrene, 2- and 4-vinyl pyridine, and the like; ??,??-unsaturated carboxylic acids and their derivatives such as acrylic acid, methacrylic acid, itac