Synthesis and properties of poly(amide-imide-hydrazide)s and poly(amide-imide-1,3,4-oxadiazole)s

A series of new wholly aromatic and aromatic-aliphatic poly(amide-imide-hydrazide)s were prepared by the direct polycondensation from p-aminobenzhydrazide with various imide ring-containing dicarboxylic acids by means of diphenyl phosphite and pyridine. These polymers had inherent viscosities between 0.60 and 1.17 dl g^-1. Most of the poly(amide-imide-hydrazide)s were readily soluble in polar aprotic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO) and could be solution cast into light yellow, transparent, flexible, and tough films. These poly(amide-imide-hydrazide)s had T_g in the range 122-211°C and could be thermally cyclodehydrated in the solid state to the corresponding poly(amide-imide-1,3,4-oxadiazole)s approximately in the range 250-400°C, as evidenced by the differential scanning calorimetry thermograms. The thermally converted oxadiazole copolymers exhibited T_g in the range 120-271°C and did not show significant weight loss before 380°C in air or nitrogen. Effects of structural changes such as polymethylene length and the nature of the diacid monomers on the properties of polymers were studied.