Claims
- 1. A polyimide foam bun which is substantially free of solid blowing agent or residue thereof and has a density in the range from about 0.1 lb/ft.sup.3 to about 0.7 lb/ft.sup.3, wherein said bun is produced by:
- 1) combining i) a polyimide precursor, said precursor comprising the reaction product of at least open aromatic or heterocyclic aromatic diamine, and at least one lower alkyl ester of an aromatic tetracarboxylic acid, with ii) at least one polar protic foam-enhancing additive of the formula ROH, herein R is selected from the group consisting of hydrogen, and C.sub.1 to C.sub.12 linear or branched alkyl or cycloalkyl, optionally substituted with halo, aryl, alkoxy or hydroxy, with the proviso that said foam-enhancing additive is volatile at the foaming temperature employed and the polar protic foam enhancing additive is added to the precursor at a ratio of between about 200 parts by weight precursor to 1 part by weight ROH and about 2 parts by weight precursor to 1 part by weight ROH; thereby producing a slurry;
- 2) heating said slurry to a temperature of not more than about 105.degree. C. to form a melt;
- 3) foaming said melt at a temperature of from about 120.degree. C. to 188.degree. C.; and
- 4) curing said foam produced in Step 3 to form said polyimide foam bun.
- 2. The polyimide foam bun of claim 1 wherein said melt is prepared by heating a slurry comprising particulate polyimide precursor and said polar protic foam-enhancing additive at a temperature below that of foam production, forming a homogeneous transparent solution or opaque suspension.
- 3. The polyimide foam bun of claim 2 wherein said slurry is heated at a temperature between about 50.degree. C. and about 105.degree. C.
- 4. The polyimide foam bun of claim 1 wherein R is selected from hydrogen and lower alkyl.
- 5. The polyimide foam bun of claim 3 wherein ROH is water.
- 6. The polyimide foam bun of claim 5 wherein the water is added by exposing the precursor composition to water vapor.
- 7. A polyimide foam bun of claim 5 wherein the particulate polyimide precursor comprises the lower alkyl diester of at least one aromatic tetracarboxylic acid and at least one aromatic or heterocyclic primary diamine.
- 8. A polyimide foam bun of claim 7 wherein the diester is a lower alkyl ester of benzophenone tetracarboxylic acid.
- 9. A polyimide foam bun of claim 7 wherein the diamine comprises 4,4'-methylenedianiline.
- 10. A polyimide foam bun of claim 7 wherein the precursor includes a surfactant.
- 11. A polyimide foam bun of claim 7 wherein the diester is a lower alkyl ester of benzophenone tetracarboxylic acid and the diamine is predominantly or entirely 4,4'-methylenedianiline.
- 12. A polyimide foam bun of claim 11 wherein the particulate polyimide precursor has a free volatiles content of less than about 5 weight percent.
- 13. A polyimide foam bun of claim 11 wherein the polyimide precursor includes a silicone glycol surfactant.
- 14. A polyimide foam bun of claim 7 wherein the diester is the dimethyl ester of benzophenone tetracarboxylic acid or the diethyl ester of benzophenone tetracarboxylic acid, the diamine is predominantly a mixture of 4,4'-methylenedianiline and a diaminopyridine, and wherein the precursor includes a silicone glycol surfactant.
- 15. A polyimide foam bun of claim 14 wherein the particulate polyimide precursor has a free volatiles content of less than about 5 weight percent.
- 16. A polyimide foam bun of claim 14 wherein said slurry comprises about 17 wt % added water, and the density of said bun is about 0.15 lb/ft.sup.3.
- 17. A polyimide foam bun of claim 14 wherein said slurry comprises about 15 wt % added water, and the density of said bun is about 0.17 lb/ft.sup.3.
- 18. A polyimide foam bun of claim 14 wherein said slurry comprises about 13 wt % added water, and the density of said bun is about 0.21 lb/ft.sup.3.
- 19. A polyimide foam bun of claim 14 wherein said slurry comprises about 11 wt % added water, and the density of said bun is about 0.23 lb/ft.sup.3.
- 20. A polyimide foam bun of claim 14 wherein said slurry comprises about 9 wt % added water, and the density of said bun is about 0.25 lb/ft.sup.3.
- 21. A polyimide foam bun of claim 14 wherein said slurry comprises about 7 wt % added water, and the density of said bun is about 0.28 lb/ft.sup.3.
- 22. A polyimide foam bun of claim 14 wherein said slurry comprises about 5 wt % added water, and the density of said bun is about 0.38 lb/ft.sup.3.
- 23. A polyimide foam bun of claim 14 wherein said slurry comprises about 3 wt % added water, and the density of said bun is about 0.48 lb/ft.sup.3.
- 24. A polyimide foam bun of claim 14 wherein said slurry comprises about 0 wt % added water, and the density of said bun is about 0.54lb/ft.sup.3.
Parent Case Info
This is a continuation of copending application Ser. No. 07/719,919 filed on Jun. 24, 1991, now abandoned, which is a division of application Ser. No. 07/575,982, filed Aug. 31, 1990, now U.S. Pat. No. 5,096,932 which is a continuation-in-part of Application Ser. No. 07/466,122, filed Jan. 16, 1990, now abandoned.
US Referenced Citations (6)
Divisions (1)
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Number |
Date |
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Parent |
575982 |
Aug 1990 |
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Continuations (1)
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Number |
Date |
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Parent |
719919 |
Jun 1991 |
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Continuation in Parts (1)
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466122 |
Jan 1990 |
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