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Arylene-bridged 2,2,5,5-tetramethyl2,5-disila-1-oxacyclopentanes as precursors to non-shrinking polysiloxanes. A new route to sol-gel type polymers

Description: Sol-gel chemistry has been the focus of much attention in the design and preparation of highly crosslinked polysiloxane gels. Preparation of sol-gel processed silica or polysilesquioxane gels is carried out by the hydrolysis and condensation of alkoxysilyl monomers, usually in the presence of catalytic acid or base and an excess of water. Removal of the alcohol and water byproducts of the condensation reactions, in addition to the alcohol needed to co-dissolve the hydrophobic monomers with water, leads to substantial shrinkage during drying of the resulting gels. This limits the utility of sol-gel processing for applications requiring net-shape casting of artifacts, crack free coatings, or low vaporous organic contaminants (VOCs). It would be advantageous to have a sol-gel process based on an organosilicon monomer that would not require water as a reactant or produce water and alcohol condensation products and still result in siloxane network polymers capable of forming gels. Here, the authors show the synthesis and preparation of a novel sol-gel monomer which can easily be polymerized by ring opening polymerization to give highly crosslinked polysiloxane gels with no condensation byproducts.
Date: November 1, 1998
Creator: Rahimian, K. & Loy, D.A.
Partner: UNT Libraries Government Documents Department

Non-Shrinking Sol-Gel Type Polymers by Ring Opening Polymerizations

Description: We have designed a new class of cyclic siloxane compounds that behave as sol-gel systems when ring open polymerized using a hydroxide base. These monomers polymerize through chain growth polymerization. unlike conventional alkoxysilane sol-gel precursors, to form sol-gel polymers. They do not require solvent or water for polymerization, show no visible shrinkage or cracking during polymerization and are thermally stable. We have successfully utilized these materials in encapsulation of microelectronics. Current efforts are focused toward expanding this family of ROP monomers and optimization of their mechanical properties.
Date: April 5, 1999
Creator: Loy, D.A. & Rahimian, K.
Partner: UNT Libraries Government Documents Department

Porosity in Polysilsesquioxane Xerolgels

Description: Polymerization of organotrialkoxysilanes is a convenient method for introducing organic functionality into hybrid organic-inorganic materials. However, not much is known about the effects of the organic substituent on the porosity of the resulting xerogels. In this study, we prepared a series of polysilsesquioxane xerogels from organotrialkoxysilanes, RSi(OR{sup 1}){sub 3}, with different organic groups (R = H, Me, Et dodecyl, hexadecyl, octadecyl, vinyl, chloromethyl, (p-chloromethyl) phenyl, cyanoethyl). Polymerizations of the monomers were carried out under a variety of conditions, varying monomer concentration, type of catalyst, and alkoxide substituent. The effect of the organic substituent on the sol-gel process was often dramatic. In many cases, gels were formed only at very high monomer concentration and/or with only one type of catalyst. All of the gels were processed as xerogels and characterized by scanning electron microscopy and nitrogen sorption porosimetry to evaluate their pore structure.
Date: August 17, 1999
Creator: Baugher, B.M.; Loy, D.A. & Rahimian, K.
Partner: UNT Libraries Government Documents Department