Depression of microphase-separated domain size of polyurethanes in confined geometry

The role of film thickness and interfacial interaction for controlling the size of microphase separation is described. XPS measurement was carried out to analyze the surface chemical composition of the PU films. The interdomain spacing of microphase-seaparated structure in the PU films were investigated by grazing incident small-angle X-ray scattering (GISAXS) measurement. As the film thickness decreases, the space for the crystallization of the hard segment chains become smaller. With decreasing film thickness, the size of the microphase-separated domains decrease, resulting in the amount of the interfacial region between hard segment domains and soft segment matrix increases. Fourier-transform infrared (FT-IR) spectra shows that the aggregation of the hard segment chains become weaker with decreasing film thickness. Strong polarity of the urethane groups leads to the strong interaction between the PU films and substrate surface, which results in the formation of the microphase-separated domain size.