oichiometric quantity of an halogenated ester having the general formula of: ##STR15## wherein X is a halogen, selected from the group consisting of chloro, bromo or iodo; R2 is a C1 to C6 alkyl group, and R3 is a monovalent, substituted or unsubstituted C1 to C20 alkyl, alkenyl or aryl substituent wherein R2 and R3 are the same as or different from each other, to form an N-substituted polybenzimi