cooled in ice 147 6 g of a 20 9 by mass sodium hydroxide aqueous solution was dropwise added for 75 mol neutralization then 0 101 g 0 00037 mol of potassium persulfate was added and dissolved therein thereby preparing a monomer aqueous solution for the first polymerization the monomer aqueous solution had a mass of 91 0 g of the water soluble ethylenically unsaturated monomer and a moisture amount of 148 6 g the monomer aqueous solution for the first polymerization was added to the separable flask in which the rotation frequency of the stirrer was set to 450 r min the system was replaced with nitrogen gas for 30 minutes and heated by immersion in a water bath at 70 u00b0 c the first reversed phase suspension polymerization was carried out for one hour after the first reversed phase suspension polymerization added to the resulting reaction mixture was 5 0 g of a 2 by mass ethylene glycol diglycidyl ether aqueous solution 0 00057 mol as an intermediate crosslinking agent the mixture was subjected to an intermediate crosslinking reaction at 75 u00b0 c for 30 minutes apart from the monomers for the first polymerization to a 500 ml erlenmeyer flask containing 92 g of an 80 5 by mass acrylic acid aqueous solution 1 03 mol while being cooled in ice 147 6 g of a 20 9 by mass sodium hydroxide aqueous solution was dropwise added for 75 mol neutralization then 0 101 g 0.