Abstract: An absorbent resin exhibiting a high absorption ratio, having only a small water-soluble component content, and have excellent gel stability to withstand the effect of aging is produced. The production of the absorbent resin comprises a step of polymerizing a water-soluble monoethylenically unsaturated monomer by using, in a proportion of 0.01-0.3 mol % based on the amount of the water-soluble monoethylenically unsaturated monomer, a cross-linking agent having at least one group of the following formula I: ##STR1## wherein R.sup.1 is an alkylene group of 2 to 4 carbon atoms interposed between two polymerizing unsaturated groups in the molecular unit thereof and then heat-treating the resin produced by the polymerization at a temperature in the range of from 160.degree. to 230.degree. C.

Abstract: A method for the production of an absorbent resin retaining at a high level an absorption capacity without load, one of the basic physical properties of absorbent resin, and excelling in an absorption capacity under load is provided. The production is attained by mixing an absorbent resin as a base polymer possessing a carboxyl group with a first cross-linking agent possessing a solubility parameter (SP value) of not less than 12.5 (cal/cm.sup.3).sup.1/2 and exhibiting reactivity with the carboxyl group and a second cross-linking agent possessing a solubility parameter (SP value) of less than 12.5 (cal/cm.sup.3).sup.1/2 and exhibiting reactivity with the carboxyl group and then subjecting the resultant mixture to a heat treatment at a temperature not less than 160.degree. C.

Abstract: A water-absorbent resin having high absorption capacity and a slight amount of water-soluble ingredients is produced by a process, which includes polymerizing a water-soluble monoethylenic unsaturated monomer in the presence of a crosslinking agent, and using a bifunctional compound represented by the following general formula 1 as the crosslinking agent; ##STR1## wherein R.sup.1 and R.sup.2 are a hydrogen atom or a methyl group independently, and --(X)-- is a divalent organic group combined in a straight chain type by an optional arrangement of a structural unit (A) of --(CO--CH.dbd.CH--CO--O).sub.L -- and l=1-5, a structural unit (B) of --(CH.sub.2 CH.sub.2 O).sub.m -- and m=2-100, and a structural unit (C) of --(R.sup.3 O).sub.n -- and n=0-20, in which R.sup.3 is a C.sub.3 -C.sub.4 alkylene.