WATER-ABSORBING RESIN AND ITS PRODUCTION

摘要

PROBLEM TO BE SOLVED: To produce the subject resin having high and stable absorbability of salt-containing water by polymerizing a water-soluble ethylenic unsaturated monomer by polymerization operations including three steps. SOLUTION: (A) An aqueous solution of a water-soluble ethylenic unsaturated monomer [preferably (meth)acrylic acid, etc.] is subjected to reverse-phase suspension polymerization in (B) a hydrocarbon solvent in the presence of (C) a surfactant and/or a polymeric protecting colloid. The action of the component C is eliminated after the polymerization. The polymerization reaction system is incorporated with (D) an aqueous solution of a water-soluble ethylenic unsaturated monomer containing nonionic macromonomer and again subjected to reverse-phase suspension polymerization. The final stage is preferably repeated twice or more. The macromonomer of the component D is preferably selected from carbamyl esters of the formula [R<1> is H or methyl; R<2> is H, methyl or ethyl; R<3> is a 1-8C hydrocarbon group; (n) is 1-500 on an average; (m) is 0-200 on an average; n>=m;Σ(n+m)=1 to 500], etc.