80 u00b0 c while stirring to dissolve the surfactant and then cooled to 55 u00b0 c an 80 mass aqueous solution of acrylic acid 92 g 1 02 mol was then placed in a 500 ml erlenmeyer flask while cooling the flask from the outside a 30 mass aqueous solution of sodium hydroxide 68 1 g 0 51 mol was added dropwise thereto to perform 50 mol neutralization to the thus neutralized solution 1 15 g of a 2 0 mass aqueous solution of 2 2 u2032 azobis 2 amidinopropane dihydrochloride as a radical polymerization initiator 0 92 g of a 1 0 mass aqueous solution of sodium hypophosphite monohydrate and 51 6 g of ion exchanged water were added giving a monomer aqueous solution the entire quantity of this monomer aqueous solution was added to the cylindrical round bottom flask the flask was dipped in a 60 u00b0 c water bath to heat it to 58 u00b0 c the atmosphere inside the flask was replaced with nitrogen followed by conducting a polymerization reaction the contents reached the peak temperature 79 u00b0 c 30 minutes after the initiation of the polymerization reaction the flask was maintained in the state of being dipped in the 60 u00b0 c water bath for 0 5 hours and the reaction was continued the temperature.