. . . . "As the N-substituted acrylamide or N-substituted methacrylamide of the formula (IV), there can be used the compounds of the formula (IV) in which R1 is hydrogen atom or a methyl group, R2 is hydrogen atom or an alkyl group having 1 to 4 carbon atoms and R3 is an alkyl group having 1 to 4 carbon atoms or an oxoalkyl group having 4 to 8 carbon atoms." .