Structural Modification of Sol-Gel Materials through Retro Diels-Alder Reaction

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Hydrolysis and condensation of organically bridged bis-triethoxysilanes, (EtO){sub 3}Si-R-Si(OEt){sub 3}, results in the formation of three dimensional organic/inorganic hybrid networks (Equation 1). Properties of these materials, including porosity, are dependent on the nature of the bridging group, R. Flexible groups (akylene-spacers longer than five carbons in length) polymerize under acidic conditions to give non-porous materials. Rigid groups (such as arylene-, alkynylene-, or alkenylene) form non-porous, microporous, and macroporous gels. In many cases the pore size distributions are quite narrow. One of the motivations for preparing hybrid organic-inorganic materials is to extend the range of properties available with sol-gel systems by ... continued below

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2 p.

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SHALTOUT,RAAFAT M.; LOY,DOUGLAS A.; MCCLAIN,MARK D.; PRABAKAR,SHESHASAYANA; GREAVES,JOHN & SHEA,KENNETH J. December 8, 1999.

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  • Sandia National Laboratories
    Publisher Info: Sandia National Labs., Albuquerque, NM, and Livermore, CA (United States)
    Place of Publication: Albuquerque, New Mexico

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Hydrolysis and condensation of organically bridged bis-triethoxysilanes, (EtO){sub 3}Si-R-Si(OEt){sub 3}, results in the formation of three dimensional organic/inorganic hybrid networks (Equation 1). Properties of these materials, including porosity, are dependent on the nature of the bridging group, R. Flexible groups (akylene-spacers longer than five carbons in length) polymerize under acidic conditions to give non-porous materials. Rigid groups (such as arylene-, alkynylene-, or alkenylene) form non-porous, microporous, and macroporous gels. In many cases the pore size distributions are quite narrow. One of the motivations for preparing hybrid organic-inorganic materials is to extend the range of properties available with sol-gel systems by incorporating organic groups into the inorganic network. For example, organically modified silica gels arc either prepared by co-polymerizing an organoalkoxysilane with a silica precursor or surface silylating the inorganic gel. This can serve to increase hydrophobicity or to introduce some reactive organic functionality. However, the type and orientation of these organic functionalities is difficult to control. Furthermore, many organoalkoxysilanes can act to inhibitor even prevent gelation, limiting the final density of organic functionalities. We have devised a new route for preparing highly functionalized pores in hybrid materials using bridging groups that are thermally converted into the desired functionalities after the gel has been obtained. In this paper, we present the preparation and characterization of bridged polysilsesquioxanes with Diels-Alder adducts as the bridging groups from the sol-gel polymerization of monomers 2 and 4. The bridging groups are constructed such that the retro Diela-Alder reaction releases the dienes and leaves the dienophiles as integral parts of the network polymers. In the rigid architecture of a xerogel, this loss of organic functionality should liberate sufficient space to modify the overall porosity. Furthermore, the new porosity will be functionalized with the dienophilic olefin bridging group. We also demonstrate that by changing the type of Diels-Alder adduct used as the bridging group, we can change the temperature at which the retro-Diels-Alder reaction will occur.

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2 p.

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OSTI as DE00015180

Medium: P; Size: 2 pages

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  • Journal Name: Polymer Preprints; Other Information: Submitted to Polymer Preprints

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  • Report No.: SAND99-3124J
  • Grant Number: AC04-94AL85000
  • Office of Scientific & Technical Information Report Number: 15180
  • Archival Resource Key: ark:/67531/metadc618323

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  • December 8, 1999

Added to The UNT Digital Library

  • June 16, 2015, 7:43 a.m.

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  • April 10, 2017, 3:06 p.m.

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SHALTOUT,RAAFAT M.; LOY,DOUGLAS A.; MCCLAIN,MARK D.; PRABAKAR,SHESHASAYANA; GREAVES,JOHN & SHEA,KENNETH J. Structural Modification of Sol-Gel Materials through Retro Diels-Alder Reaction, article, December 8, 1999; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc618323/: accessed October 18, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.