Surface Composition of a Series of Dimethylsiloxane-Urea-Urethane Segmented Copolymers Studied by Electron Spectroscopy for Chemical Analysis

Surface composition of a series of segmented poly(siloxane-urea-urethane)s have been determined by angle- and energy-dependent ESCA. The polymers are based on aminopropyl end-capped dimethylsiloxane oligomers, isophorone diisocyanate, and 1,4-benzenedimethanol. Effects of segmental length and annealing on the surface composition weee investigated. It was found that when the average molecular weight of the siloxane segments reaches 27K, the topmost surface region (within 18 Å of the free surface) of a film cast from tetrahydrofuran solution is nearly pure siloxane phase. To achieve a comparable degree of surface phase concentration in films of copolymers with a siloxane segmental molecular weight of 10K, annealing at 120 °C for 15 min was required. Depth profiles based on these data showed that in as-cast films a siloxane deficient (hard-block enriched) phase several nanometers thick occuss beneath the siloxane surface layer. Annealing increases the thickness of both the siloxane-enriched and the siloxane-deficient regions.