USE OF AND METHOD FOR PREPARING POLYIMIDE AEROGELS

Abstract

The present invention pertains to the use of a polyimide aerogel, wherein the polyimide aerogel comprises polyimide spheres having a diameter of 250 nm to 20 m, as an insulating, sorption or filter material, as well as to methods for the preparation of the same.

Claims

1.-16. (canceled)

17. A thermal or electrical insulating material comprising a polyimide aerogel including polyimide spheres having a diameter of 250 nm to 20 m, wherein the material is applied as thermal or electrical insulation.

18. The thermal or electrical insulating material according to claim 17, wherein the polyimide spheres have a diameter of 1 m to 10 m; the polyimide aerogel further comprises pores between polyimide spheres that range from 0.2 m to 500 m; or a combination thereof.

19. The thermal or electrical insulating material according to claim 17, wherein the polyimide spheres are porous.

20. The thermal or electrical insulating material according to claim 19, wherein the polyimide spheres have pores with diameters between 1 nm to 100 nm.

21. The thermal or electrical insulating material according to claim 17, wherein the polyimide aerogel is halogen-free.

22. The thermal or electrical insulating material according to claim 17, wherein: a. the polyimide aerogel has a thermal conductivity measured at 25 C. and 50% relative humidity of less than about 40 mW/(m*K); b. the polyimide aerogel is hydrophobic; c. the water contact angles on the polyimide aerogel are between 90 and 140; or d. a combination thereof.

23. The thermal or electrical insulating material according to claim 17, wherein the polyimide aerogel has: a. a density of 0.06 to 0.2 g/cm.sup.3; b. a porosity of 80 to 98%; c. a Brunauer-Emmett-Teller specific surface area of 1 to 350 m.sup.2/g; d. a Young's Modulus of 0.2 to 5 MPa; or e. a combination thereof.

24. The thermal or electrical insulating material according to claim 17, wherein the polyimide aerogel is cross-linked.

25. The thermal or electrical insulating material according to claim 24, wherein the polyimide aerogel has a degree of crosslinking of 1 to 100%.

26. The thermal or electrical insulating material according to claim 17, wherein the polyimide aerogel comprises (a) a diamine monomer selected from the group consisting of 4,4-diaminodiphenyl ether (ODA); 2,2-dimethylbenzidine (DMBZ); 9,9-bis(4-aminophenyl)fluorene (BAPF); 2-bis [4-(4-aminophenoxy) phenyl]propane (BAPP); p-phenylene diamine (PPDA); 4,4-diaminodiphenylmethane (MDA); and combinations thereof; (b) a dianhydride monomer selected from the group consisting of 3,3,4,4-biphenyltetracarboxylic dianhydride (BPDA); 4,4-diphenyl ether dianhydride (ODPA); pyromellitic dianhydride (PMDA); 3,3,4,4-benzophenonetetracarboxylic dianhydride (BTDA); and a combination thereof; (c) a crosslinker selected from the group consisting of 1,3,5-benzenetricarbonyl trichloride (BTC); tris(2-aminoethyl)amine (TREN); 1,3,5-tris(4-aminophenoxy)benzene (TAB); polymaleic anhydride (PMA); tris(4-aminophenyl amine) (TAPA); and triisocyanate, or (d) a combination thereof.

27. The thermal or electrical insulating material according to claim 26, wherein the molar ratio of diamine monomer to dianhydride monomer within the polyimide is n:(n+1) or (n+1):n, wherein n is an integer 5.

28. An electronic device, robotic, aviation, astronautic, refrigeration, industrial installation, or pipeline comprising the thermal or electrical insulating material according to claim 17.

29. A low dielectric constant material comprising the polyimide aerogel according to claim 17.

30. A method for preparing the polyimide aerogel as described in claim 17, the method comprising the steps: (i) providing a polyamic acid in an aprotic solvent comprising (a) dimethylacetamide (DMAc), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or a mixture thereof; or (b) a mixture of N-methyl-2-pyrrolidone (NMP) with DMAc, DMF, DMSO, or a combination thereof; (ii) adding acetic anhydride and triethylamine to the polyamic acid of (i) to form a polyimide sol and to induce phase separation of the polyimide from the aprotic solvent; and (v) drying the mixture.

31. The method according to claim 30, wherein: (a) before or after step (ii) and before step (v), the method further comprises step (iii), adding a crosslinker before gelation of the polyimide sol, optionally BTC or TREN, to form a crosslinked polyimide sol; (b) after step (iii) and before step (v), the method further comprises step (iv), aging the gelled polyimide sol of step (ii) and/or step (iii); or (c) both (a) and (b).

32. The method according to claim 30, wherein in step (v), the drying is performed under supercritical CO.sub.2 or under atmospheric pressure at temperatures between 1 and 200 C.

33. The method according to claim 30, wherein the aprotic solvent in steps (i) and (ii) is dimethylacetamide (DMAc) or a mixture of DMAc and a further aprotic solvent.

34. The method according to claim 33, wherein the further aprotic solvent is selected from the group consisting of N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO).

35. The method according to claim 30, wherein: a. the concentration of the polyamic acid in steps (i) and/or (ii) is about 3 to 15 wt. %; b. in step (ii), the mixture is agitated for about 1 to 10 minutes; or c. both.

36. The method according to claim 31, wherein after step (iv) and before step (v) the solvent is exchanged with (a) dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or a mixture thereof, or (b) acetone in combination with heptane, hexane, or one or more alcoholic solvents.

37. A polyimide aerogel produced according to the method according of claim 30.

38. An electronic component comprising the thermal or insulating material of claim 17 applied thereon.

39. A method of insulating an electrical component comprising the steps of: providing an electrical component; and applying a coating comprising the thermal or insulating material of claim 17.

Description

FIGURES

[0077] FIG. 1A-D shows SEM images of polyimide aerogels as described herein: A and B are from ambient pressure drying; C and D are from supercritical CO.sub.2 drying. Both are ethanol-based gels before drying.

[0078] FIG. 2 shows SEM images of polyimide aerogels from ambient pressure drying (corresponding to A (left) and B (right) in FIG. 1) after thermal aging treatment (350 C. and 1 hour).

EXAMPLES

Example 1: Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Supercritical CO.SUB.2 .Drying

[0079] 2.0214 g biphenyl-3,3,4,4-tetracarboxylic dianhydride (BPDA), 0.7536 g 2,2-dimethylbenzidine (DMBZ) and 0.7108 g 4,4-oxidianiline (ODA) (the molar ratio between DMBZ and ODA is 5:5) was mixed with a molar ratio between dianhydride and diamine of respectively 30:31 in 40 ml dimethylacetamide (DMAc) solvent, the concentration of the polymer in the solution was about 7 wt. %, after 30 minutes polymerization under room temperature (S.T.P.) (step 1). The pre-mixed mixture of 5.20 mL acetic anhydride and 7.66 mL trimethylamine (TEA) was added slowly to the solution followed by stirring for 2 minutes (step 2). In the meantime, the 0.0405 g BTC was dissolved in 10 ml DMAc, the BTC solution was added in the polymer solution, and was stirred 2 more minutes (step 3). The sols were transferred into silicon molds and the gelation occurred within 10 minutes. Samples were aged 24 hours at room temperature (S.T.P.), and the solvent exchanged with 75/25, 25/75, and 0/100 DMAC/ethanol in 12 hours intervals (step 4). The wet gels were finally dried under supercritical CO.sub.2 (step 5), at 50 C. and 120 bar for 7 hours.

[0080] Materials properties: bulk density 0.14 g/cm.sup.3, BET specific surface area 47.6 m.sup.2/g, thermal conductivity of 33.0 mW/(m*K), 7% and 20% volumetric shrinkage at 200 C. and 300 C. for 24 hours, respectively, the compression Young's Modulus is 0.75 MPa.

Example 2: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Ambient Pressure Drying

[0081] A procedure identical to that of example 1 was used, with the exception that during step 5, ambient pressure drying was chosen to replace the supercritical CO.sub.2 drying for the drying out of ethanol from wet gels, which was carried out at ambient pressure, 75 C. for 5 hours.

[0082] Materials properties: bulk density 0.16 g/cm.sup.3, BET specific surface area 1.6 m.sup.2/g, thermal conductivity of 35.0 mW/(m*K), 8% and 18% volumetric shrinkage at 200 C. and 300 C. for 24 hours, respectively, the compression Young's Modulus is 0.78 MPa.

Example 3: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Supercritical CO.SUB.2 .Drying

[0083] A procedure identical to that of example 1 was used, with the exception that during step 1, instead of pure DMAc solvent, the mixture of 20 v % NMP/80 v % DMAc were used for the synthesis of polymer.

[0084] Materials properties: bulk density 0.11 g/cm.sup.3, BET specific surface area 107.0 m.sup.2/g, thermal conductivity of 32.1 mW/(m*K), the compression Young's Modulus is 0.40 MPa, 30% and 35% volumetric shrinkage at 200 C. and 300 C. for 24 hours.

Example 4: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Supercritical CO.SUB.2 .Drying

[0085] A procedure identical to that of example 1 was used, with the exception that during step 1, instead of the copolymerization of BPDA-ODA/DMBZ, only one diamine DMBZ was used for the synthesis of BPDA-DMBZ polymer.

[0086] Materials properties: bulk density 0.15 g/cm.sup.3, BET specific surface area 367.4 m.sup.2/g, thermal conductivity of 33.3 mW/(m*K), 15% and 25% volumetric shrinkage at 200 C. and 300 C. for 24 hours.

Example 5: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Ambient Pressure Drying

[0087] A procedure identical to that of example 2 was used, with the exception that during step 4, instead of ethanol for solvent exchange, the solvent hexane was used for solvent exchange, which was solvent exchanged with 75/25, 25/75, and 0/100 DMAC/hexane in 12 hours intervals (step 4), and ambient pressure drying afterwards.

[0088] Materials properties: bulk density 0.16 g/cm.sup.3, BET specific surface area 12.9 m.sup.2/g, thermal conductivity of 34.4 mW/(m*K), 10% and 20% volumetric shrinkage at 200 C. and 300 C. for 24 hours.

Example 6: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Ambient Pressure Drying

[0089] A procedure identical to that of example 2 was used, with the exception that during step 1, instead of using 50 mL DMAC for the synthesis, 800 mL DMAC was used to make a bigger gels (200 mm*200 mm*14 mm), in this case, the amount of all the chemicals used are scaled up, respectively.

[0090] Materials properties: bulk density 0.16 g/cm.sup.3, BET specific surface area 2.5 m.sup.2/g, thermal conductivity of 35.0 mW/(m*K), 8% and 18% volumetric shrinkage at 200 C. and 300 C. for 24 hours.

Example 7: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Ambient Pressure Drying

[0091] A procedure identical to that of example 2 was used, with the exception that during step 4, instead of ethanol for solvent exchange, the solvent heptane was used for solvent exchange, which was solvent exchanged with 75/25, 25/75, and 0/100 DMAC/heptane in 12 hours intervals (step 4), and ambient pressure drying afterwards.

[0092] Materials properties: bulk density 0.17 g/cm.sup.3, BET specific surface area 8.0 m.sup.2/g, thermal conductivity of 38.0 mW/(m*K), 10% and 18% volumetric shrinkage at 200 C. and 300 C. for 24 hours.

Example 8: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Supercritical CO.SUB.2 .Drying

[0093] A procedure identical to that of example 1 was used, with the exception that during step 3, instead of the cross-linker of BTC, cross-linker TREN was used to make the gels.

[0094] Materials properties: bulk density 0.15 g/cm.sup.3, BET specific surface area 3.0 m.sup.2/g, thermal conductivity of 34.3 mW/(m*K), 7% and 19% volumetric shrinkage at 200 C. and 300 C. for 24 hours.

Example 9: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Supercritical CO.SUB.2 .Drying

[0095] A procedure identical to that of example 1 was used, with the exception that during step 1, instead of pure DMAc solvent, the mixture of 30 v % NMP/70 v % DMAc were used for the synthesis of polymer.

[0096] Materials properties: bulk density 0.15 g/cm.sup.3, BET specific surface area 168.1 m.sup.2/g, thermal conductivity of 33.4 mW/(m*K), the compression Young's Modulus is 0.71 MPa, 30% and 40% volumetric shrinkage at 200 C. and 300 C. for 24 hours.

Example 10: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Supercritical CO.SUB.2 .Drying

[0097] A procedure identical to that of example 1 was used, with the exception that during step 1, instead of pure DMAc solvent, the mixture of 10 v % NMP/90 v % DMAc were used for the synthesis of polymer.

[0098] Materials properties: bulk density 0.16 g/cm.sup.3, BET specific surface area 53.6 m.sup.2/g, thermal conductivity of 30.2 mW/(m*K), the compression Young's Modulus is 0.54 MPa, 25% and 36% volumetric shrinkage at 200 C. and 300 C. for 24 hours.

Example 11: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Supercritical CO.SUB.2 .Drying

[0099] A procedure identical to that of example 1 was used, with the exception that during step 1, instead of pure DMAc solvent, pure DMF was used for the synthesis of polymer.

[0100] Materials properties: bulk density 0.12 g/cm.sup.3, BET specific surface area 3.5 m.sup.2/g, thermal conductivity of 34.2 mW/(m*K), the compression Young's Modulus is 1.05 MPa, 9% and 18% volumetric shrinkage at 200 C. and 300 C. for 24 hours.

Example 12: Alternative Preparation of Polyimide Aerogels with Spherical Structure in the Polyimide Matrix Via Supercritical CO.SUB.2 .Drying

[0101] A procedure identical to that of example 1 was used, with the exception that during step 1, instead of pure DMAc solvent, the mixture of 50 v % DMAc/50 v % DMSO were used for the synthesis of polymer.

[0102] Materials properties: bulk density 0.13 g/cm.sup.3, BET specific surface area 30.5 m.sup.2/g, thermal conductivity of 32.2 mW/(m*K), the compression Young's Modulus is 0.65 MPa, 15% and 22% volumetric shrinkage at 200 C. and 300 C. for 24 hours.

Comparative Example 13: Preparation of Polyimide Aerogels with Conventional Mesoporous Structure in the Polyimide Matrix Via Supercritical CO.SUB.2 .Drying

[0103] A procedure identical to that of example 1 was used, with the exception that during step 1, instead of pure DMAc solvent, pure NMP was used for the synthesis of polymer.

[0104] Materials properties: bulk density 0.07 g/cm.sup.3, BET specific surface area 433.9 m.sup.2/g, thermal conductivity of 24.7 mW/(m*K), the compression Young's Modulus is 7.00 MPa, 95% and 95% volumetric shrinkage at 200 C. and 300 C. for 24 hours.