Polyfunctional N-chloramide derivatives of homo-or copolymers of acrylamide or methacrylamide. These may be copolymers of methacrylamide and acrylamide; or of either of these with any of styrene, methylstyrene, dimethylstyrene, chlorostyrene and alkylacrylate. Preferred alkylacrylate include methyl-, methylmeth-, ethyl-, ethylmethyl-, butylmeth-, hexyl-, hexylmeth-, decyl-, decylmeth-, dodecyl- and dodecylmeth- species. The derivatives may be cross-linked by divinylbenzene or divinylether.