Abstract: Crosslinked homopolymers and copolymers of N-vinyl-2-pyrrolidone formed by addition polymerization through ethylenically unsaturated groups are polymerized on solid, inert carriers. Heavy crosslinking is employed to render the polymers insoluble. The polymers can be made by copolymerizing, with N-vinyl-2-pyrrolidone, amides or substituted amides of unsaturated carboxylic acids, such as acrylamide, substituted and unsubstituted unsaturated carboxylic acids, such as methacrylic acid or halfacid maleates. Also included are comonomers containing basic nitrogen groups therein, such as vinyl pyridine, or alkylamino acrylates and methacrylates. The polymers are formed on inert substrates of both solid and porous types.