On the other hand, the kneading process is a process wherein the ethylenic copolymer (A) is allowed to react by kneading with about 0.01 to 1.0 part by weight (preferably 0.05 to 0.5 part by weight) on the basis of 100 parts by weight of the copolymer (A) of a tertiary amine and about 0.1 to 3.0 moles (preferably 1.0 to 2.0 moles) of an alcohol per mole of dicarboxylic acid anhydride unit in the c