Polyurethanes were prepared from different molecular weight polycaprolactone-based polyols with varying amounts of hard segment made with toluene diisocyanate and butanediol. A theoretical model based on hard and soft segment miscibility was used to predict phase separation in these polyurethanes. Wide-angle X-ray diffraction, near-infrared spectroscopy, and Fourier transform infrared spectroscopy were used to determine phase separation. Good agreement was found between the experimental results and the theoretical predictions. The glass surfaces of the previously tested glass/polyurethane adhesion samples were analyzed by angular dependent X-ray photoelectron spectroscopy (ADXPS). ADXPS data revealed an interphase region of approximately 2-10 nm in thickness present between the polyurethane matrix and the glass substrate in each sample. The data also showed that the composition of the interphase region was influenced not only by the matrix composition, but also by the phase separation. The curve-fitted C 1s spectra of the interphase region showed the presence of C-O type linkages that could be due to the presence of C-OH from the polyols and/or the butanediols, and C-O-Si type bonds. These observations were supported by the adhesion results of various polyurethanes to glass test coupons primed with a 2% solution of butanediol in acetone.