Abstract: Method for avoiding network defects due to unwanted secondary reactions during the polymerization in water-swellable hydrophilic polymers which contain polymers prepared by free radical (co)polymerization of one or more hydrophilic monomers of the formula I ##STR1## wherein R.sup.1 is hydrogen, methyl or ethyl,R.sup.2 is the group --COOR.sup.4, the sulphonyl group, the phosphonyl group, the phosphonyl group-esterified by (C.sub.1 -C.sub.4)-alkanol or a group of the formula ##STR2## R.sup.3 is hydrogen, methyl, ethyl or the carboxyl group, R.sup.4 is hydrogen, amino or hydroxy-(C.sub.1 -C.sub.4)-alkyl andR.sup.5 is the sulphonyl group, the phosphonyl group or the carboxyl group, or grafting (co)polymerization of one or more hydrophilic monomers of the formula I onto a grafting base, using a free radical initiator which forms three or more free radical sites per molecule.