Polyols derived from renewable resources are good candidates for obtaining segmented polyurethane (PU) elastomers. Diisocyanates with different chemical structures, aliphatic and aromatic, were used to synthesize PU elastomers with different hard-segment (HS) contents by a two-step polymerization procedure. Microphase separation and thermal stability were studied with attenuated total reflection Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. The analysis of H-bonded and non-H-bonded urethane carbonyl stretching vibration in the amide I region, the glass-transition temperatures of the soft segments and HSs, and the melting temperature and enthalpies of the HSs revealed that aliphatic diisocyanate based PUs presented a higher phase separation degree and higher HS crystallinity and also a superior thermal stability to the aromatic diisocyanate-based PUs. The aromatic diisocyanate-based PU presented a higher ductility, higher tensile strength, and lower modulus than aliphatic diisocyanate-based PU for the same HS content because of the different morphology that they presented. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3677-3685, 2011