Stock material or miscellaneous articles – Self-sustaining carbon mass or layer with impregnant or...
Reexamination Certificate
1999-10-25
2001-11-20
Teskin, Fred (Department: 1713)
Stock material or miscellaneous articles
Self-sustaining carbon mass or layer with impregnant or...
C524S855000, C524S856000
Reexamination Certificate
active
06319611
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to carbon—carbon composites and monomers used in their formation. More particularly, the invention relates to a new family of monomers used in the formation of carbon—carbon composites.
Interest in carbon—carbon composites has grown exponentially in recent years. The combination of high specific strength retention at elevated temperatures and chemical inertness have led to their use in applications such as aircraft brakes, space vehicle heatshields and rocket nozzles.
Although the properties of carbon—carbon composites make them very useful, there are inherent problems with typical precursors such as pitch and many thermoset resins used to fabricate these composites. One of the most severe limitations of the presently used precursors is low char yields during pyrolysis. Typical thermoset precursors yield 50-65 weight percent carbon after pyrolysis. This results in the need for repeated impregnation cycles with resin to achieve a void-free sample.
Another problem with typical thermoset and pitch based carbon precursors arises from the high viscosities and intractable nature of these materials. This often results in poor wetting of the reinforcing fiber and/or the need for higher pressures and temperatures during the impregnation cycles.
Accordingly, it would be a significant advancement in the art to provide a precursor for carbon—carbon composites which had a low viscosity. It would be a further advancement in the art if such a resin had a char yield of greater than about 75%.
SUMMARY OF THE INVENTION
One aspect of the present invention comprises a new family of monomers based on alkene and alkyne derivatives of cyclopentadiene useful in the formation of carbon—carbon composites. These monomers are synthesized by reacting freshly prepared cyclopentadiene with allyl halides or propargyl halides in the presence of excess aqueous base and an appropriate phase transfer catalyst. Suitable catalysts include crown ethers, polyoxyethylene and quaternary ammonium salts. Purification of the resulting monomers involves washing with aqueous acid and base, and in some cases, extraction distillation or chromatography.
In another aspect of the present invention, the cyclopentadiene derivative resins are used as a thermoset precursor for carbon—carbon composites. Carbon fibers are coated with the resin and thermally cured. In one preferred embodiment, carbon fibers were coated with a propargylated cyclopentadiene (PCP) resin in a stainless steel mold. Pressure was applied to squeeze out excess resin and consolidate the fibers. The resin was then cured at 165° C. for 6 hours and 250° C. for 6 hours.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention is directed to a new family of thermosetting resins and their use in the formation of carbon—carbon composites. The resins comprise substituted cyclopentadiene.
In a preferred embodiment, the resins are synthesized by reacting freshly prepared cyclopentadiene with propargyl halides in the presence of excess aqueous base and an appropriate phase transfer catalyst. Suitable catalysts include crown ethers, polyoxyethylene and quaternary ammonium salts. One preferred catalyst is tetrabutylammonium bromide. Suitable propargyl halides include propargyl chloride and propargyl bromide.
These new monomers are highly reactive and oxidatively unstable. Exposure to air leads to incorporation of alcohol, acid and aldehyde or ketone functionality. Accordingly, during preparation it is important to remove and exclude air from the reaction to prevent oxidation of the resin.
In one embodiment, propargyl chloride is reacted with cyclopentadiene with an excess aqueous base to form the compounds set for in equation 1 wherein n equals 2-6.
In a second embodiment propargyl bromide is reacted with cyclopentadiene in the presence of excess aqueous base and a suitable catalyst to form the reaction product set forth in Equation 1 where n=2-6.
After synthesis, the resins are extracted and purified. In a preferred embodiment, the resins are extracted with toluene and washed with dilute acid, water and brine to remove the phase transfer catalyst. Yields of resin are nearly quantitative with respect to the cyclopentadiene. The product consists of a mixture of isomers of multiply substituted cyclopentadienes with degrees of functionality ranging from 2 to 6 propargyl groups per ring.
Carbon-carbon composite formation involves simple impregnation of carbon fiber preforms or mats with the liquid resin followed by thermal cure. The thermal cure is generally carried out in the absence of air which can cause side reactions such as the incorporation of alcohol, acid and aldehyde or ketone functionality. The composites are cured at temperatures up to about 350° C.
In one preferred embodiment, the thermal cure is performed at 165° C. for 6 hours and 250° C. for 6 hours. The cure times and temperatures can be adjusted as necessary depending upon the size of the samples and their intended use.
In another preferred embodiment, initiators or catalysts can be used in the curing process including free radical initiators, cationic initiators and metal salts capable of catalyzing polyadditon and methathesis reactions. Such compounds are known to those skilled in the art.
Once cured, the composite products are thermally and oxidatively stable to high temperatures; e.g., heating to 1000° C. in the absence of air causes less than 25% weight loss for these composites. This is extremely low in comparison to other resins currently used for carbon—carbon composite formation.
The advantages of the monomers of the present invention are their low viscosity for ease if impregnation and handling, their facile cure through uncatalyzed thermal reaction or initiated/catalyzed reactions to give highly condensed carbon networks, and extremely good thermal and oxidative stability of cured materials.
The composites of the present invention have many applications including thermally conductive brake linings for automotive and aircraft brakes, high thermal stability engine parts (piston and cylinder walls) and aerospace components in both structural and non-structural applications.
REFERENCES:
patent: 2237825 (1941-04-01), Ralston et al.
patent: 2331869 (1943-10-01), Adelson et al.
patent: 4201702 (1980-05-01), Blount
1996:224079 CAPLUS abstract of Polym. Mat. Sci. Eng. (1996), 74, 53-54.*
“Synthesis and Characterization Of Propargylated Cyclopentadiene Resins for Use in Carbon/Carbon Composites,” by Gregory J. Tregre and Lon J. Mathias, Department of Polymer Science, University of Southern Mississippi, Hattiesburg, MS 39401, pp. 319-320.
Polymer Composites, Dec. 1994, vol. 15, No. 6, “Synthesis and Characterization of a New Class of Thermosetting Resins: Allyl and Propargyl Substituted Cyclopentadiene Derivatives,” by Lon J. Mathias and Jeno Muthiah, Department of Polymer Science, University of Southern Mississippi, Hattiesburg, Mississippi, pp. 464-473.
Mathias Lon J.
Tregre Gregory J.
Howrey Simon Arnold & White , LLP
Teskin Fred
The University of Southern Mississippi
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