Abstarct: The aim of this study was to synthesize 1-phenyl pyrazolidine-3,5-dione via the reaction of diethyl malonate with one mole of phenyl hydrazine in free solvent condition. 1,4-bis (1-phenyl pyrazolidine-3,5-dione-4-yiliden methyl) benzen was prepared via the of reaction 1-phenyl pyrazolidine-3,5-dione with one mole of terephthalaldehyde in glacial acetic acid. The structures of the monomer was identified and confirmed with the help of IR and 1H-NMR spectroscopy methods. The polymerization of the monomer with equal moles of various diisocyanates, hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), and isophorone diisocyanate (IPDI), led to new polymers, in high yields and inherent viscosities. The characterization of the polymers was achieved using IR and 1H-NMR spectroscopies, viscometery and thermal gravimetric analysis (TGA/DTG).