The long-term confusing glass transition temperature, T-g, and specific heat capacity, Delta C-p, of the 4,4’-diisocyanatodiphenylmethane (MDI) and 1,4-butanediol (ED) hard segment in segment polyurethanes have been clearly evidenced by using a new series of completely phase-mixed polyurethanes while being extrapolated to 100% hard segment content. The hard segment T-g and Delta C-p, thus obtained are 108 degrees C and 0.38 J/g degrees C, respectively, which are equivalent to the reported Tg and Delta C-p of a high molecular weight MDI-BD homopolymer. In addition, if a single homogeneous phase is present, the observed Delta C-p and T-g are found to be given by the linear weighted combination of the pure constituent values. This provides a simple relationship to access the composition of the individual microdomain in segment polyurethanes, providing that the phase-separate morphology does not affect the microdomain glass transition behavior.