Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From silicon reactant having at least one...
Reexamination Certificate
1999-05-12
2001-05-22
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From silicon reactant having at least one...
C528S037000, C556S434000, C556S435000, C549S214000
Reexamination Certificate
active
06235864
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to highly-crosslinked polysiloxane gels made from non-shrinking siloxane materials and a process for making the same. More particularly, this invention relates to a new class of disilaoxacyclopentane monomers that do not shrink substantially when undergoing a ring-opening polymerization to form highly-crosslinked polysiloxane gels useful as encapsulants.
In the general sol-gel chemistry of alkoxysilanes to form highly-cross-linked polysiloxane gels, stoichiometric quantities of water are used as part of a step-growth polymerization process and solvents are used for monomer/water miscibility. Subsequent evaporation of the solvent results in fragile gels as well as shrinkage of up to 90%. The drying process itself must be carried out slowly to avoid cracking of the gel. Much of the shrinkage results from the evaporation of the solvent used in the process and from by-products of the polymerization reaction itself. For example, Gloffelter et al. (U.S. Pat. No. 5,120,811, issued on Jun. 9, 1992) describe a sol-gel process for producing a polymer/glass hybrid coating that encounters significant changes in volume of up to 8:1 during the drying stage. Likewise, Haruvy et al. (U.S. Pat. No. 5,272,240, issued on Dec. 21, 1993), in another method for the sol-gel preparation of glasses, note that sol-gel polymerization reactions commonly result in cracking and fragmentation due to the extensive volume-contraction which accompanies the condensation reaction and the corresponding expulsion of the solvent and the condensation products. Haruvy et al. address this problem in part by choice of monomer and choice of reaction conditions as the hydrolysis reaction proceeds. By-products are still produced and water and optional solvent are still added during the hydrolysis reaction step. Curing at room temperature takes from hours to days.
One method for reducing shrinkage is to eliminate solvent and condensation by-products by replacing the step growth polymerization with a chain growth polymerization such as ring opening polymerization (ROP). Sadhir et al. (Sadhir, R. K. and Luck, R. M., “Expanding Monomers: Synthesis, Characterization and Applications,” 1992, CRC Press, pp. 21-37) has shown that ROP is an effective means for reducing or, as with the polymerization of spiroorthocarbonates, completely eliminating, shrinkage in linear, hydrocarbon polymers. Suryanarayanan et al. (Suryanarayan, B., Peace, B. and Mayhan, K., J. Polym Sci.; Chem. Ed., 1974, 12, 1089) and Samara et al. (Samara, M. and Loy, D., Polym. Preprints, 1998, 39(1), 599) have shown that the simple monomer 2,2,5,5-tetramethyl-2,5-disilaoxacyclopentane can form a polymer under ROP in the presence of tetrabutylammonium hydroxide with shrinkage of less than 5%.
Useful would be highly-crosslinked gels that exhibit essentially no shrinkage and whose synthesis results in no condensation by-products. Loy et al. (Loy, D. A., Rahimian, K. and Samara, M., Angew. Chem., Int. Ed., 1999, 38, 555; incorporated herein by reference), Rahimian and Loy (Rahimian, K. and Loy, D., Polymer Preprints, 216th National Meeting of the American Chemical Society, Boston, Mass. 1998; incorporated herein by reference), and Rahimian and Loy (Rahimian, K. and Loy, D., Polymer Preprints, 217th National Meeting of the American Chemical Society, Anaheim, Calif. 1999; incorporated herein by reference) discuss novel monomers useful in preparing highly-crosslinked gels that exhibit little or no shrinkage during a ring opening polymerization process. The crosslinked gels produced have no porosity or surface area and can be used as encapsulants as well as coatings. The process used involves no solvents or water addition.
SUMMARY OF THE INVENTION
According to the present invention, a cross-linked polymer is provided containing recurring units of the general formula R
1
(Me
2
SiOCH
2
CHSiMe
2
)
2
wherein R
1
is an alkyl group containing at least two carbon atoms and Me represents a methyl group of the formula CH
3
. The polymer has less than approximately 1% porosity and is thermally stable at temperatures up to approximately 500° C. In the process for making this polymer, a precursor monomer of the general formula R[CH
2
CH(Si(Me)
2
)
2
O]
2
, wherein R is a phenyl group or an alkyl group having at least two carbon atoms, is converted in the presence of an anionic base to form the cross-linked polymer. The anionic base can be, for example, tetrabutylammonium hydroxide, sodium hydroxide or potassium hydroxide and is present in a quantity of less than approximately 1 mole %. The conversion to the cross-linked polymer occurs by ring opening polymerization and results in shrinkage of less than approximately 5% by volume.
Also provided is a cross-linked polymer containing recurring units of the general formula R(Me
2
SiOCH
2
CHSiMe
2
)
2
[CH
2
CHR
2
(SiMe
2
)
2
O]
n
, wherein R
2
is hydrogen, phenyl, ethyl, propyl or butyl and n is sufficient to solvate the monomer. In the process for making this polymer, a precursor monomer R[CH
2
CH(Si(Me)
2
)
2
O]
2
is admixed with a co-monomer CH
2
CHR
2
(SiMe
2
)
2
O in the presence of an anionic base to form a cross-linked polymer of the general formula R(Me
2
SiOCH
2
CHSiMe
2
)
2
[CH
2
CHR
2
(SiMe
2
)
2
O]
n
. The polymer is formed within approximately one minute and results in shrinkage compared with the reactants of less than approximately 5 percent by volume.
The precursor monomer used in the process of making the cross-linked polymers is a compound bearing at least two 2,2,5,5-tetramethyl-2,5-disila-1-oxacylcopentane groups of the general formula R[CH
2
CH(Si(Me)
2
)
2
O]
2
, wherein R is a phenyl group or an alkyl group having at least two carbon atoms. The precursor monomer is made by admixing a diacetylene compound of the general formula R(CCH)
2
with (CH
3
)
4
Si
2
(O(CH
3
))
2
and a catalyst to form a mixture that is refluxed and then solubilized in an aqueous acid solution and non-reacting solvent to form a subsequent mixture. This mixture is catalytically hydrogenated to synthesize the monomer R[CH
2
CH(Si(Me)
2
)
2
O]
2
.
REFERENCES:
patent: 3041362 (1962-06-01), Merker
patent: 3317456 (1967-05-01), Hansen
patent: 3338951 (1967-08-01), Knaub
patent: 3387015 (1968-06-01), Piccoli
patent: 3660449 (1972-05-01), Schaschel
patent: 5120811 (1992-06-01), Glotfelter et al.
patent: 5272240 (1993-12-01), Haruvy et al.
Phenylene-Bridged Cyclic Siloxanes as Precursors to Nonshrinking Sol-Gel Systems . . . Loy et al., Agnew. Chem. Int. Ed., 1999.*
Suryanarayanan, B., Peace, B. and Mayhan, K., “Anionic Polymerization of 2,2,5,5-Tetramethyl-l-oxa-2,5-disilacyclopentane,” J. Polymer Sci., 1974, 12, 1089-1107.
Samara, M. and Loy, D., “Shrinkage and Recyclability of Poly(1,2-ethylene-bis(dimethylsiloxane)),” Polym. Preprints, 1998, 39(1), 599.
Rahimian, K. and Loy, D., “Non-shrinking Sol-gel Type Polymers by Ring Opening Polymerization,” Polymer Preprints, 217th National Meeting of the American Chemical Society, Anaheim, CA, Mar. 21-25, 1999.
Rahimian, K. and Loy, D., “Arylene-Bridged 2,2,5,5-Tetramenthyl-2,5-Disila-l-Oxacyclopentanes as Precursors to Non-Shrinking Polysiloxanes. A New Route to Sol-Gel Type Polymers,” Polymer Preprints, 216th National Meeting of the American Chemical Society, Boston, Mass, Aug. 23-27, 1998.
Loy, D., Rahimian, K. and Samara, M., “Phenylene-Bridged Cyclic Siloxanes as Precursors to Non-Shrinking Sol-gel Systems and Their Use as Encapsulants,” Angew. Chem. Int. Ed., 1999, 38(4), 555-557.
Watanabe, H., Kobayashi, M, Saito, M. and Nagai, Y., “Reaction of Disilanes with Acetylenes II. Double Silylation of 1-Hexyne, Trimethylsilylacetylene and Acetylene with Methoxymethyldisilanes Catalyzed by Tetrakis(Triphenylphosphine)Palladium, ” J. of Organometallic Chemistry, 1981, 216, 149-157.
Sadhir, R. and Luck, R. (eds.), Expanding Monomers: Synthesis, Characterization, and Applications, 1992, CRC Press, Boca Raton, FL, 21-37.
Loy Douglas A.
Rahimian Kamyar
Klavetter Elmer A.
Moore Margaret G.
Sandia Corporation
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