Synthesis and Properties of Novel Aromatic Poly(1,3,4-Oxadiazole)s and Poly(Amide-1,3,4-Oxadiazole)s having Ortho-Phenylenedioxy Units

Abstract

Two series of novel polyhydrazides and poly(amide-hydrazide)s are prepared from two ortho-linked bis(ether-carboxylic acid)s including 4,4′-(1,2-phenylenedioxy)dibenzoic acid and 4,4′-(4-tert-butyl-1,2-phenylenedioxy)dibenzoic acid, or their diacyl chlorides with terephthalic dihydrazide (TPH), isophthalic dihydrazide (IPH) and p-aminobenzoyl hydrazide (p-ABH) via the Yamazaki phosphorylation reaction or the low-temperature solution polycondensation. The resulting hydrazide-containing polymers exhibited inherent viscosities in the range of 0.27-0.62 dl g⁻¹. These hydrazide polymers were amorphous and soluble in various solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) and could be solution-cast into colorless, flexible, and tough films with good tensile strengths. Differential scanning calorimetry (DSC) indicated that the polyhydrazides and poly(amide-hydrazide)s had T _g s in the range of 172-200 °C and could be thermally cyclodehydrated into the corresponding oxadiazole polymers in the range of 270-370 °C. The oxadiazole polymers showed a slightly enhanced crystallinity and T _g, but a dramatically decreased solubility compared to their hydrazide prepolymers. The thermally converted oxadiazole polymers exhibited T _g s in the range of 205-221 °C and softening temperatures of 214-239 °C and showed insignificant weight loss up to 450 °C in air or nitrogen.

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