A series of new poly(imide-hydrazide)s and poly(amide-imide-hydrazide)s were obtained by the direct polycondensation of N-[p-(or m-)carboxyphenyl] trimellitimide (p- or m-CPTMI) with terephthalic dihydrazide (TPH), isophthalic dihydrazide (IPH), and p-aminobenzhydrazide (p-ABH) by means of diphenyl phosphite and pyridine in the N-methyl-2-pyrrolidone (NMP) solutions containing dissolved CaCl2. The resulting hydrazide-containing polymers exhibited inherent viscosities in the 0.15-0.96 dL/g range. Except for that derived from p-CPTMI with TPH or p-ABH, the other hydrazide copolymers were readily soluble in polar solvents such as NMP and dimethyl sulfoxide (DMSO). As evidenced by X-ray diffraction patterns, the hydrazide copolymer obtained from TPH showed a moderate level of crystallinity, whereas the others were amorphous in nature. Most of the amorphous hydrazide copolymers formed flexible and tough films by solvent casting. The amorphous hydrazide copolymers had glass-transition temperatures (T-g) between 187 and 233 degrees C. All hydrazide copolymers could be thermally converted into the corresponding oxadiazole copolymers approximately in the region of 250-400 degrees C, as evidenced by the DSC thermograms. The oxadiazole copolymers showed a significantly decreased solubility when compared to their respective hydrazide precursors. They exhibited T-g's of 264-302 degrees C and did not show dramatic weight loss before 400 degrees C in air or nitrogen.