PRODUCTION OF GRAFT POLYMER

PURPOSE:To readily obtain a carboxyl group-containing graft polymer, by preparing a graft polymer by using a macromonomer containing a tertiary alcoholic ester of (meth)acrylic acid and then forming carboxyl group by hydrolysis. CONSTITUTION:A macromonomer (one having preferably 500-50,000 molecular weight number-average molecular weight) which usually contains >=2wt.% tertiary alcoholic ester unit of (meth)acrylic acid and 1 polymerizable unsaturated group [e.g., group shown by the formula (R is H, CH3 or C2H5; m is 1-5)] at one end is reacted with a main chain-forming monomer to give a graft polymer, which is hydrolyzed in the presence of an acid catalyst (e.g., sulfuric acid or hydrochloric acid) and the tertiary alcoholic ester unit of (meth)acrylic acid in the graft polymer is modified into a (meth)acrylic acid unit to give a graft polymer containing carboxyl group based on the (meth)acrylic acid unit in the side chain-forming polymer.