The degree of phase separation in several moisture-cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X-ray diffraction (WAXD), and temperature-modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol-based PUUs, whereas for triol-based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. (c) 2007 Wiley Periodicals, Inc.