Aryl-Bridged Polysilsesquioxanes - New Microporous Materials
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ARYL-BRIDGED POLYSILSESQUIOXANES MATERIALS.
- NEW MICROPOROUS
KENNETH J. SHEA,* OWEN WEBSTER**, AND DOUGLAS A. LOY* *Department of Chemistry, University of California, Irvine, Irvine, California, 92717. "**Central Research & Development, E.I. duPont de Nemours & Company, Experimental Station, Wilmington, Delaware, 19898. ABSTRACT The first representatives of a new family of microporous, aryl-bridged polysilsesquioxanes have been prepared by sol-gel processing of bis-1,4-(triethoxysilyl)benzene la, bis-4,4'(triethoxysilyl)biphenyl 2a, bis-4,4'-(triethoxysilyl)terphenyl 3a, and bis-9,10-triethoxysilyl anthracene 4a. The bis(trichlorosilyl) analogs of la and 2a (lb and 2b, respectively) were also examined. The materials produced by hydrolysis and condensation of the monomers provide an opportunity to fully condense to a network with rigid-rod organic spacers interspaced at regular intervals in the silicate-like framework. The xerogels produced upon subsesquent processing of the gels have extremely high surface areas (256-1100 m2 /g; BET) with porosities confined to the micropore domain (< 200 nm). Solid state (CP MAS) 13 C and 29 Si NMR were used to evaluate the extent of hydrolysis and degree of condensation in the xerogels. The porosity and thermal stability of the aryl bridged polysilsesquioxanes may lead to applications as chromatographic absorbents. The transparent materials may also have optical applications arising from both the gels' high refractive indices and the covalent incorporation of ultraviolet chromophores. INTRODUCTION Synthetic silicates (Figure 1, A) prepared by sol-gel processing of alkoxysilanes (eq. 1) allow for the preparation of amorphous materials (xerogels) that are precursors to high purity glasses, ceramics, coatings, and fibers [1]. In a similar fashion, organically modified silicates can be prepared by condensing tetraethoxysilane (TEOS) with hydroxy terminated poly(dimethylsiloxanes) [2] or replacing an ethoxy substituent with an alkyl or aryl group (polysilsesquioxanes or T-resins) [3].
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We report the preparation of a new class of microporous materials, aryl-bridged polysilsesquioxanes [4], through the sol-gel processing of bis(triethoxysilyl)aryl la-4a and
bis(trichlorosilyl)aryl lb, 2b monomers (Figure 2). These materials incorporate aryl groups in silsesquioxane networks with hexacoordinate connectivity (Figure 1, B). The xerogels would retain the useful optical properties of tricoordinate poly(arylsilsesquioxanes) in a more uniform, close packed network [7] The rigid aryl spacers [8] between the silicon atoms in the monomer may also provide control of the microarc
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