The aim of this study was to investigate the structure and morphology of polyurethane (PU) foams at the interface with a thermoplastic material. Fourier transform infrared/attenuated total reflectance spectroscopy was used to study the reaction of 4,4'-diphenylmethane diisocyanate (MDI) with polyether-based polyols with water as a blowing agent via the absorption intensity of the v(NCO, 2265 cm(-1)) vibrational band of MDI in three different PU foam systems. The data revealed that MDI reacted simultaneously with two different species in the reaction mixture having different reaction rates. These were the reactions of isocyanate functional groups with water (fast reaction) and polyol (slow reaction). A structure analysis at the PU foam interface (i.e., PU formed a compact film 110 +/- 30 mu m thick at the interface) with a thermoplastic material plate was carried out with small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and neutron reflection (NR) techniques. From SAXS measurements, a typical hard-segment-segment distance of 10 +/- 0.3 nm was observed. The TEM and NR data of the compact PU film revealed an internal layered structure (parallel to the surface) with a typical layer thickness of 260-400 nm. The formation of a layered morphology (macrophase-separated structures) was assumed to be due to the difference in the polarities of the hard and soft segments. Furthermore, the layer thickness increased when D2O was used as the blowing agent instead of H2O. (c) 2005 Wiley Periodicals, Inc.