. . "ber selected from the group consisting of --COOR3, --CH, ##SPC5##--ocor6 and --CONHR7 and wherein R3 is an alkyl group having 1 to 8 carbon atoms, glycidyl group or a hydroxyalkyl group having 2 to 4 carbon atoms, R4, R5 and R6 are independently hydrogen, methyl group or ethyl group and R7 is a hydroxyalkyl group having 1 to 2 carbon atoms or ##STR14## a molar ratio of amide group in said amide-co" . .