Novel aromatic poly(amide-hydrazide)s based on the bipyridine. Part I: Synthesis, characterization and thermal stability

A series of new poly(amide-hydrazide)s were obtained by the direct polycondensation of 5-amino 5′-carbohydrazido-2,2′-bipyridine with commercially available diacids by means of triphenyl phosphite and pyridine in the N-methyl-2-pyrrolidone (NMP) solutions containing dissolved LiCl. The resulting hydrazide containing polymers exhibited inherent viscosities in the 0.42-0.64 dL/g range. All copolymers were soluble in polar solvents such as NMP and dimethyl sulfoxide (DMSO). Most of the amorphous hydrazide copolymers formed flexible and tough films by solvent casting. The poly(amide-hydrazide)s had glass-transition temperatures (Tg) between 178 and 206 °C. All hydrazide copolymers could be thermally converted into the corresponding poly(amide-oxadiazole) approximately in the region of 300-400 °C, as evidenced by the DSC thermograms. The oxadiazole polymers and copolymers showed a dramatically decreased solubility and higher Tg when compared to their respective hydrazide prepolymers. They exhibited Tgs of 197-248 °C and were stable up to 450 °C in air or nitrogen.