Two flexible dicarboxylic acid monomers, 4,4＇- [isopropylidenebis(1,4-phenylene) dioxy]dibenzoic acid (1) and 4,4＇-[hexafluoroisopropylidenebis(1,4-phenylene)-dioxy]dibenzoic acid (3), were synthesized from readily available compounds in two steps in high yields. High molecular-weight polyhydrazides and poly(amide-hydrazide)s were directly prepared from dicarboxylic acids 1 and 3 with terephthalic dihydrazide(5), isophthalic dihydrazide(6), and p-aminobenzhydrazide (7)by the phosphorylation reaction by means of diphenyl phosphite (DPP) and pyridine in N-methyl-2-pyrrolidone (NMP)/LiCl, or prepared from the diacyl chlorides of 1 and 3 with the hydrazide monomers 5-7 by the low-temperature solution polycondensation in NMP/LiCl. Less favorable results were obtained when using triphenyl phosphite (TPP) instead of DPP in the direct polycondensation reactions. Except for those derived from terephthalic dihydrazide, the resulting polyhydrazides and poly( amide-hydrazide)s could be cast into colorless, flexible, and tough films with good tensile strengths. All the hydrazide polymers and copolymers are amorphous in nature and are readily soluble in various polar solvents such as NMP and dimethyl sulfoxide (DMSO). Their T(g)s were recorded in the range of 162-198 degrees C and could be thermally cyclodehydrated into the corresponding polyoxadiazoles and poly( amide-oxadiazole)s approximately in the region of 300-380 degrees C, as evidenced by the DSC thermograms. The oxadiazole polymers and copolymers showed a dramatically decreased solubility and higher T-g when compared to their respective hydrazide prepolymers. They exhibited T(g)s of 190-216 degrees C and were stable up to 450 degrees C in air or nitrogen.