A new [(2-oxo-1,3-cyclopentanediylidene)bis(methylidyne-p-phenyleneoxy)]diacetic acid dihydrazide III has been prepared via interaction of 2,5-bis(p-hydroxybenzylidene) cyclopentanone I with ethyl chloroacetate in basic medium to give diester II, followed by hydrazinolysis with hydrazine. The synthesized compounds were confirmed by IR, NMR, and elemental analyses. Unreported polyhydrazides by the low temperature interfacial polycondensation technique of III with adipoyl, sebacoyl, 4,4'-diphenic, isophthaloyl, terephthaloyl, 4,4'-azodibenzoyl, 3,3'-azodibenzoyl, 4,4'[1,4-phenylene-bis(methylidynenitrilo)]dibenzoyl dichlorides, and 2,7-dichloroformylthianthrene-5,5',10,10'-teraoxwere prepared. In order to characterize the polymers, a model compound was synthesized from III and benzoyl chloride. The resulting polyhydrazides were confirmed by IR, UV, viscometry, DSC measurements, and thermogravimetric analysis. The crystallinities of all polyhydrazides were investigated by x-ray analysis. The effect of the nature of different moieties on the properties of these polyhydrazides was explored by comparing their physical, spectral, thermal, and x-ray analysis data.