The present research work was performed to study the properties of polyurethanes (PU) based on aliphatic diisocayanate and the effect of chemical structure of chain extenders. Two series of PUs were synthesized via two steps polymerization technique. The PU samples constituted on hexamethylene diisocayanate (HDI), hydroxy-terminated polybutadiene (HTPB) and blends 1, 4 butanediol (BDO)/bisphenol A (BPA) and or 1, 4 butanediol (BDO)/bisphenol S (BPS) were prepared. Structural characterization was done using Fourier transform infrared spectroscopy during and after the synthesis. The FTIR analysis confirmed the existence of proposed bisphenol A (BPA) and bisphenol S (BPS) based PU structures. Differential scanning calorimeter (DSC) analysis gives information about the thermal transition of all the polymer samples. Because of the difference of polarity between hard and soft segments of PU, microphase separation can occur. The degree of phase separation in the prepared PU was confirmed using scanning electron microscope (SEM) technique. The SEM techniques present a distinctive chance to directly visualize the morphology of the polyurethanes.