Aminophthalic anhydride copolymers

The process of preparing a film forming polyamic acid which comprises reacting an aminophthalic anhydride of the formula H.sub.2 NC.sub.6 H.sub.n Y.sub.3-n (CO).sub.2 O wherein Y represents a halogen selected from the group consisting of F, Br and Cl and n represents an integer having a value of 0 to 3, in an inert organic solvent in which the polymer is soluble at a temperature of about 10-100.degree. C with 0.5 to 0.001 mole per mole of anhydride of a compound having the formula Ar(NH.sub.2).sub.2 in which Ar represents single, fused or heterocyclic aromatic ring, said heterocyclic ring being selected from the class consisting of pyridine, quinoline and quinoxaline or a multiplicity of such rings linked to each other directly ##STR19## in which R represents hydrocarbon group containing one to twelve carbon atoms and the remaining positions in the Ar groups being occupied by hydrogen and a halogen selected from the class consisting of F, Cl and Br.