Polyurethanes were prepared from poly(tetramethylene oxide) end-capped with MDI and PBT extenders. The PBT extenders were random-disperse in length and their length varied from three to seven repeating units. The structure of the polyurethanes was studied by FT-IR and AFM, their thermal and thermomechanical responses were measured by DSC and DMTA, and their elastic behavior was assessed by compression set measurements. The MDI-PBT-MDI hard segments had a ribbon-like crystalline morphology. Increasing the PBT length gave rise to an increase of the storage modulus at room temperature and the melting point. The storage modulus depended strongly on temperature.