To a 1 L flask equipped with a stirrer, a nitrogen introducing tube, a thermometer and a condenser, 50 g of stearyl acrylate, 49 g of n-butylacrylate, 1 g of hydroxyethyl acrylate, 0.89 g of AIBN, 100 mL of toluene and 100 mL of ethyl acetate were added and subjected to polymerization reaction in a stream of nitrogen at 70° C. for 12 hr, to obtain a copolymer of stearyl acrylate, n-butyl acrylate and hydroxyacrylate (hereinafter sometimes referred to “PSABAHEA”. The resulting PSABAHEA had a weight average molecular weight of 170,000.
