A series of segmented polyurethanes based on hydroxylterminated polybutadienes (HTPBD) and their hydrogenated derivatives(HYPBD) has been synthesized. Thermal, mec:hanic:aL and spectrosc:opic: studies were c:arried out over a wide temperature range to elucidate the structure-property relationships existing in these polymers. Both thermal and dynamic mechanical response showed a soft segment Tu at-74°C forthe unsaturated polyurethanes and at -69"C for the hydrogenated samples. In addition, two hard segment transitions are. observed by differential scanning c:alorimetry (DSC) at 40 and 75°C and a softening region by thermal mechanical analysis (TMA) at 190"C. The low T,,. very dose to that of the free HTPBD and HYPBD and independent of hard segment c:ontent. indicated that these polymers were well phase separated. Results of infrared analysis revealed that at room temperature, 90-95 percent of the urethane N-H groups formed hydrogen bonds. Since hydrogen bonding resides only within the hard segment domain in these butadiene-c:ontaining polyurethanes the extent of H-bonding served as additional evidence for nearly complete phase segregation. From dynamic: mechanical studies, the plateau modulus above the soft segment Tu and stress-strain behavior depended upon the concentration of hard segments. A slight increase in the modulus, a moderate increase in stress (er,,), and decrease in elongation accompanied a higher hard segment content. The thermal and mechanical response of these polyurethanes appears to be consistent with behavior observed for other phase segregated systems. Variations in behavior resulting from hydrogenation of the precursor prepolymer are discussed.