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.
De, D., & Gaymans, R. J. (2008). Thermoplastic polyurethanes with poly(butylene terephthalate) as crystallizable hard phase. Macromolecular materials and engineering, 293(3), 228-234. https://doi.org/10.1002/mame.200700356