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SYNOPSISX-ray photoelectron spectroscopy (XPS) is used to compare the surface behavior in various binary systems of poly (dimethylsiloxane) with poly( bisphenol A sulfone) and poly-(bisphenol A carbonate). All the systems studied show a pronounced surface enrichment in siloxane. At a fixed siloxane concentration in the bulk the lowest extent of surface enrichment is observed in the neat copolymers, next go the blends of copolymers in homopolymers, and the highest extent of surface enrichment is characteristic of the blends of homopolymers. The blends of two copolymers show an unexpected surface behavior: The addition of minor amounts of a siloxane-rich copolymer to another copolymer possessing a much lower siloxane content decreases (rather than increases) the surface siloxane concentration of the latter. A microscopic model is suggested to explain the observed surface behavior. The model involves the formation of a "quasi-two-dimensional" overlayer of additive's macromolecules on the blend surface, with the macromolecules oriented preferentially parallel to the sample surface.

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Simultaneous IPNs of poly(dimethyl siloxane‐urethane) (PDMSU)/poly(methyl methacrylate) (PMMA) and related isomers have been prepared by using new oligomers of bis(β‐hydroxyethoxymethyl)poly(dimethyl siloxane)s (PDMS diols) and new crosslinkers biuret triisocyanate (BTI) and tris(β‐hydroxylethoxymethyl dimethylsiloxy) phenylsilane (Si‐triol). Their phase morphology have been characterized by DSC and SEM. The SEM phase domain size is decreased by increasing crosslink density of the PDMSU network. A single phase IPN of PDMSU/PMMA can be made at an Mc = 1000 and 80 wt % of PDMSU. All of the pseudo‐ or semi‐IPNs and blends of PDMSU and PMMA were phase separated with phase domain sizes ranging from 0.2 to several micrometers. The full IPNs of PDMSU/PMMA have better thermal resistance compared to the blends of linear PDMSU and linear PMMA. © 1993 John Wiley & Sons, Inc.

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