Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Utility Patent
1998-06-10
2001-01-02
Nguyen, Ngoc-Yen (Department: 1754)
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
C423S335000, C423S326000
Utility Patent
active
06168773
ABSTRACT:
FIELD OF THE INVENTION
This invention concerns a process for producing silica gel or silicate polymer by rapidly conducting sol-gel chemistry using a fluoroalkoxysilane as a starting material. Extremely low solids content silica gel produced by this process can posses large pore size.
BACKGROUND OF THE INVENTION
Inorganic gel can be generated from molecular precursors through room temperature hydrolytic and condensation sol-gel reactions. Such reactions generally require cosolvents for the essential reactants, water and the molecular precursor compound, such as a tetraalkoxysilane, and are catalyzed by either acid or base.
Very low density gels are useful as precursors to low density aerogels made by supercritical fluid drying and as separation media for large molecules such as proteins and polymers. Aerogels are the best acoustic and thermal insulating materials known. However, simple conventional gel precursors, such as tetramethoxysilane or tetraethoxysilane, are not useful direct sources of low density gels because of extremely long or infinite gelation times at very low concentrations. In “Transparent ultralow-density silica aerogels prepared by a two-step sol-gel process”, J. Non-Crystl. Solids 145, 44 (1992), T. M. Tillotson and L. W. Hrubesh describe the preparation of an aerogel. First polysilicate is produced from tetramethoxysilane in a 16 hour reaction followed by isolation of the polysilicate and preparation of the gel therefrom—a two step, slow process.
There are no known processes for forming silica gel from a tetrafluoroalkoxysilane and water with or without the use of a catalyst. EP-A 0 232 024 describes a room-temperature-curable organopolysiloxane composition which requires for its preparation both a diorganopolysiloxane (A) terminated at both molecular chain ends with a silanol group and an organosilane compound (B) represented by the general formula R
4-a
Si(OR
f
)
a
, wherein R is a monovalent hydrocarbon group and R
f
is a 2,2,2-trifluoroethyl group of the formula —CH
2
CF
3
or a di(trifluoromethyl)methyl group of the formula —CH(CF
3
)
2
and a is 2, 3 or 4, or a partial hydrolysis product of such an organosilane compound. An organic tin compound is also required as a catalyst to promote the condensation reaction between the components (A) and (B). U.S. Pat. No. 5,459,198 describes a fluoroinfused composite comprising a swellable polymeric material having all or a portion thereof interpenetrated with a fluoropolysilicate network prepared by contacting the swellable polymer with a solution comprising a swelling solvent, a gelling agent and at least one organofluorosilane having a perfluoroalkyl segment and three network forming groups and containing a fluoroalkyl group-silicon atom link or bond not subject to hydrolysis or thermal decomposition.
SUMMARY OF THE INVENTION
The present invention provides a rapid process for the preparation of a silica gel or a silicate polymer, comprising: contacting at least one fluoroalkoxysilane with a solution comprising water to form the silica gel or the silicate polymer. Optionally, the process can be conducted with a solvent and/or a catalyst.
The present invention also provides a low solids content wet silica gel. The present invention further provides a wet silica gel having a pore size greater than about 50 nm.
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E. I. Du Pont de Nemours and Company
Nguyen Ngoc-Yen
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