This invention pertains to a water-insolubilized resin of a polymer of at least one monomer selected from N-alkyl- or N-alkylene-substituted acrylamides or methacrylamides represented by the following general formula (I): ##STR1## wherein R1 and R2 mean individually a hydrogen atom or methyl group and R3 denotes a methyl, ethyl or propyl group, with the proviso that R3 is an ethyl or propyl group