thermometer stirrer and reflux condensed was charged with 196 parts of maleic anhydride 75 1 parts of water to make 232 parts of maleic acid and 0 01 parts of iron iii ammonium sulfate dodecahydrate equivalent to 5 ppm of fe 3 based on the amount of maleic acid charged the resulting aqueous solution was heated with stirring to the boiling point under normal pressure then 96 3 parts of 60 hydrogen peroxide equivalent to 28 9 g for 1 mol of maleic acid charged was added dropwise with stirring continuously over 3 hours during which polymerization proceeded stirring was continued for another 1 hour at the boiling point of the system after the completion of polymerization there was obtained sample 1 of acid type polymaleic acid containing 63 solids the sample was tested for molecular weight and molecular weight distribution by gel permeation chromatography under the following conditions the results are shown in table 1 column g 3000pw xl g 2500pw xl made by toso co ltd eluent phosphate buffer solution ph 7 and reference sample for molecular weight polyethylene glycol made by general science co ltd the same procedure as in example 1 was repeated to give samples 2 to 9 of acid type polymaleic acid except that the amounts of iron iii ammonium sulfate dodecahydrate and hydrogen peroxide were changed.