Thus prepared was 10.33 grams of reaction products comprising graft copolymer of the aforementioned formula (I), in which R1 is hydrogen, R2 is --COO--CH2 --C(H) (CH3)O-- with its --COO bonded to the main chain, R3 is --CH2 CH3 OCO-- with its --CH2 bonded to the main chain, R4 is a methyl group, and R5 is hydrogen.