A polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity and its preparation method

Abstract

The present invention discloses a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity, and a preparation method thereof. The polyimide is prepared using a diamine monomer containing an indeno[1,2-b]fluorene-6,12-dione structure and an aromatic dianhydride as raw materials. The indeno[1,2-b]fluorene-6,12-dione structure facilitates closer packing of polyimide molecular chains, thereby improving the barrier properties of the polyimide and reducing its thermal expansion coefficient. Based on this type of intrinsic high-barrier polyimide containing indeno[1,2-b]fluorene-6,12-dione structure, a polyimide / boron nitride nanosheet composite material is prepared. The high aspect ratio boron nitride nanosheets can extend the permeation path of oxygen and water vapor in the polyimide, which can further improve the barrier performance. Boron nitride nanosheets can also increase the thermal conductivity of polyimide, thereby obtaining a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity.

Description

Technical Field

[0001] The present invention belongs to the field of material science and technology, and specifically relates to a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity and a preparation method thereof. Background Art

[0002] Polyimide has excellent thermal properties due to the imide ring in its main chain. It is one of the best heat-resistant varieties of industrialized engineering plastics. It has comprehensive properties that other engineering plastics cannot match, such as high mechanical strength, good high and low temperature resistance, excellent dielectric properties, and good film-forming properties. It can be widely used in many fields, especially in flexible displays, aerospace, microelectronics and military industries.

[0003] With the rapid development of the flexible display industry, polyimide should have higher quality to meet the requirements of modern industry. Therefore, polyimide should not only have excellent thermal properties, but also have efficient barrier properties. Taking OLED devices as an example, the performance requirements of OLED devices for packaging materials include: ① Thermal performance: can withstand high temperatures of at least 300℃, and the thermal expansion coefficient is less than 10ppm / ℃; ② Barrier performance: water vapor transmission rate is less than 10 -6 g / m 2 day, oxygen transmission rate is less than 10 -5 cm 3 / m 2 ·day; ③ Thermal conductivity greater than 4.5W·m -1 ·K -1 Since most polyimides can meet the thermal performance requirements, but there are few studies on polyimides that simultaneously meet good thermal performance, barrier properties and thermal conductivity, it is of great significance to develop polyimide / boron nitride nanosheet composites with both ultra-high barrier and high thermal conductivity.

[0004] Polyimide has excellent thermal properties, so improving its barrier properties is key. The main approaches to improving polyimide barrier properties include synthesizing novel intrinsic polyimides and preparing polyimide nanocomposites. Fundamentally, these two approaches complement and synergize each other: synthesizing a novel intrinsic high-barrier polyimide structure and, based on this intrinsic polyimide, preparing polyimide materials with even higher barrier properties through nanocomposites.

[0005] Boron nitride is commonly used to improve the thermal conductivity of polyimide. Doping polyimide with nanosheets with a high aspect ratio can extend the gas permeation path in the polyimide matrix, thereby further improving the barrier properties of the polyimide. If the boron nitride nanosheets are simply modified and introduced into the intrinsic high-barrier polyimide matrix, not only can the thermal conductivity of the polyimide be improved, but the barrier properties of the polyimide can also be further improved, thereby preparing a polyimide composite material with both ultra-high barrier and high thermal conductivity. Therefore, it is necessary to conduct research on the design and synthesis of polyimide composite materials with both ultra-high barrier and high thermal conductivity based on intrinsic high-barrier polyimide. Summary of the Invention

[0006] Technical Problem to Be Solved: To address the aforementioned technical issues, the present invention discloses a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity, and its preparation method. The polyimide is prepared using a diamine monomer containing an indeno[1,2-b]fluorene-6,12-dione structure and an aromatic dianhydride as raw materials. The indeno[1,2-b]fluorene-6,12-dione structure facilitates closer packing of polyimide molecular chains, thereby improving the barrier properties of the polyimide and reducing its thermal expansion coefficient. Based on this type of intrinsic high-barrier polyimide containing indeno[1,2-b]fluorene-6,12-dione structure, a polyimide / boron nitride nanosheet composite material is prepared. The high aspect ratio boron nitride nanosheets can extend the permeation path of oxygen and water vapor in the polyimide, which can further improve the barrier performance. In addition, the boron nitride nanosheets can increase the thermal conductivity of the polyimide, thereby obtaining a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity.

[0007] Technical solution: A polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity. The polyimide / boron nitride nanosheet composite material with both high barrier and high thermal conductivity is prepared from polyimide and boron nitride nanosheets. The molecular structure of the polyimide is shown below:

[0008]

[0009] Where n is 1-10000.

[0010] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0011] S1. Boron nitride nanosheets are modified with a silane coupling agent to obtain modified boron nitride nanosheets;

[0012] S2. In an argon atmosphere, the modified boron nitride nanosheets were ultrasonically dispersed in a strongly polar aprotic organic solvent for 1-4 hours. A diketone-containing diamine and a dianhydride were added to the dispersion in a molar ratio of 1:(0.98-1.02). The mixture was stirred at -5-25°C for 4-24 hours to obtain a homogeneous, viscous polyamic acid composite adhesive.

[0013] S3. Dehydrating the polyamic acid in the polyamic acid composite adhesive containing boron nitride nanosheets to obtain a polyimide / boron nitride nanosheet composite material.

[0014] Furthermore, the molecular formula of the diketone structure in the diamine is as follows:

[0015]

[0016] The preparation method thereof comprises the following steps:

[0017] S1. 2,8-dibromo-indeno[1,2-b]fluorene-6,12-dione and p-aminophenylboronic acid hydrochloride are sequentially added to tetrahydrofuran and dissolved;

[0018] S2. Potassium carbonate solution and methyl trioctyl ammonium chloride were added sequentially, stirred magnetically and purged with argon, and heated in an oil bath to 60-80 ° C;

[0019] S3 was added tetrakistriphenylphosphine palladium and refluxed for 12-48h, and then the reaction solution was poured into ice water to precipitate;

[0020] S4. Filter, wash and dry to obtain.

[0021] Furthermore, the aspect ratio of the boron nitride nanosheets in step S1 is (400-2000):1.

[0022] Furthermore, in step S1, the silane coupling agent is one or more of γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

[0023] Furthermore, the dianhydride in step S2 includes pyromellitic dianhydride, 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride, and the polyimide synthesis reaction formula is as follows:

[0024]

[0025] Where R is One of them.

[0026] Furthermore, the highly polar aprotic organic solvent in step S2 is one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0027] Furthermore, in step S2, the total mass of the diamine and dianhydride is 10-40% of the mass of the glue.

[0028] Furthermore, the dehydration method of the polyamic acid in step S3 includes thermal imidization and chemical imidization.

[0029] Furthermore, the mass of the boron nitride nanosheets is 2-10% of the mass of the polyimide material.

[0030] Beneficial effects:

[0031] 1. The present invention synthesizes a novel diamine monomer containing an indeno[1,2-b]fluorene-6,12-dione structure. Introducing the diamine monomer into polyimide can make the stacking between polyimide molecular chains more compact and the arrangement more orderly, giving the polyimide a smaller free volume and weakening the creeping property of the polyimide molecular chains, making it difficult for gas molecules to diffuse inside the polyimide, thereby improving the barrier properties of the polyimide and reducing its thermal expansion coefficient, while having no effect on the water absorption rate.

[0032] 2. The diamine monomer in the present invention contains an indeno[1,2-b]fluorene-6,12-dione structure. The two carbonyl groups can give the diamine molecule stronger molecular polarity, change the stacking mode and interaction force between molecules, and make it easier to form intermolecular hydrogen bonds, π-π stacking and other interactions. In addition, the fluorene dione structure has good rigid plane and symmetry, which can further improve the stability and performance of polyimide.

[0033] 3. Boron nitride nanosheets have high thermal conductivity, but they are also electrically insulating. Adding them to polyimide will significantly improve the thermal conductivity of the polyimide composite material without reducing the electrical insulation of the polyimide. In addition, boron nitride nanosheets have the characteristics of a high aspect ratio, which can increase the tortuous path inside the polyimide, making the gas molecules face more obstacles when penetrating and diffusing. At the same time, they can reduce the diffusion channels of oxygen and water vapor in the polyimide, extend the permeation path of oxygen and water vapor in the polyimide, and further improve the barrier performance of the composite material; thereby achieving ultra-high barrier performance and high thermal conductivity at the same time.

[0034] 4. The ultra-high barrier and high thermal conductivity polyimide / boron nitride nanosheet composite materials prepared by the present invention can be widely used in various fields, especially in the electronic information industry such as flexible display, microelectronics and electronic device packaging, providing an excellent data basis for the design and synthesis of high-performance polyimide composite materials, which has important theoretical and practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The nuclear magnetic resonance of Example 1 1 H spectrum;

[0036] Figure 2 is the mass spectrum of Example 1;

[0037] Figure 3 are infrared spectra of Examples 2-7 and Comparative Example 4, where a represents Example 2, b represents Example 4, c represents Example 5, d represents 2,7-bis(4-aminophenyl)-9H-fluorene-9-one (FOPDA) in Comparative Example 4, e represents the polyimide film (PMDA-FOPDA) in Comparative Example 4, f represents Example 6, and g represents Example 7;

[0038] Figure 4 The NMR of 2,7-bis(4-aminophenyl)-9H-fluoren-9-one (FOPDA) in Comparative Example 4 is 1 H spectrum;

[0039] Figure 5 The NMR of 2,7-bis(4-aminophenyl)-9H-fluoren-9-one (FOPDA) in Comparative Example 4 is 13 C spectrum;

[0040] Figure 6 This is the mass spectrum of 2,7-bis(4-aminophenyl)-9H-fluoren-9-one (FOPDA) in Comparative Example 4. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with examples, which are provided to explain the present invention and are not limited to the following examples:

[0042] Example 1

[0043] Synthesis of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione

[0044] 4.40 g of 2,8-dibromo-indeno[1,2-b]fluorene-6,12-dione and 4.3353 g of p-aminophenylboronic acid hydrochloride were added to a 500 mL three-necked flask using tetrahydrofuran (THF) as the solvent. 37.5 mL of a 2 mol / L potassium carbonate solution and an appropriate amount of methyltrioctylammonium chloride were then added. The mixture was stirred magnetically and purged with argon. After heating to 75°C in an oil bath, 0.050 g of tetrakistriphenylphosphine palladium was added. After reflux for 24 hours, the reaction solution was poured into ice water, resulting in the formation of a large amount of precipitate. The residue was collected by filtration using a funnel and washed twice with tetrahydrofuran and deionized water, respectively. After drying, the product, 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA), was obtained in an 85% yield.

[0045] Example 2

[0046] Synthesis of polyimide PMDA-BDFPDA

[0047] S1. At room temperature, 4.6452 g (0.01 mol) of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione and 42.62 g of N,N-dimethylformamide were added to a 100 ml three-necked flask. Argon was introduced and stirred until completely dissolved. Then, 2.1812 g (0.01 mol) of 1,2,4,5-pyromellitic dianhydride (PMDA) was added and the reaction was stirred for 6 h to obtain a homogeneous, transparent, viscous polyamic acid solution.

[0048] S2. After removing bubbles from the polyamic acid solution, apply it to a glass plate with a knife. Then, place the glass plate in a vacuum oven and evacuate the air. The heating program is as follows: heating from room temperature to 100°C and then holding the temperature constant for 1 hour; heating from 100°C to 200°C and then holding the temperature constant for 1 hour; heating from 200°C to 300°C and then holding the temperature constant for 1 hour; heating from 300°C to 420°C and then holding the temperature constant for 1 hour. After cooling, a polyimide film (PMDA-BDFPDA) is obtained. The molecular structure of the PMDA-BDFPDA is as follows:

[0049]

[0050] Example 3

[0051] The method for preparing polyimide PMDA-BDFPDA by chemical imidization comprises the following steps:

[0052] S1. At room temperature, 4.6452 g (0.01 mol) of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione and 42.62 g of N,N-dimethylformamide were added to a 100 ml three-necked flask. Argon was introduced and stirred until completely dissolved. Then, 2.1812 g (0.01 mol) of 1,2,4,5-pyromellitic dianhydride (PMDA) was added and the reaction was stirred for 6 h to obtain a homogeneous, transparent, viscous polyamic acid solution.

[0053] S2. Add 4 mL of acetic anhydride to the obtained polyamic acid solution, continue stirring, then slowly add 3 mL of triethylamine, and raise the temperature to 75°C. Continue stirring for 6 hours, then apply the solution on a clean glass plate. Then place the glass plate in a vacuum oven, evacuate the vacuum, and dry at 150°C for 6 hours. After cooling, a polyimide film (PMDA-BDFPDA) can be obtained.

[0054] Example 4

[0055] The synthesis of polyimide BTDA-BDFPDA comprises the following steps:

[0056] S1. At room temperature, 4.6452 g (0.01 mol) of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione and 44.58 g of N,N-dimethylformamide were added to a 100 ml three-necked flask, purged with argon, and stirred. After complete dissolution, 3.2222 g (0.01 mol) of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) was added. The reaction was stirred for 7 h to obtain a homogeneous, transparent, viscous polyamic acid solution.

[0057] S2. After removing bubbles from the polyamic acid solution, the solution was scraped onto a glass plate, and the glass plate was placed in a vacuum oven and evacuated. The heating program was as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 430°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide film (BTDA-BDFPDA) was obtained.

[0058] The molecular structure of the polyimide BTDA-BDFPDA is as follows:

[0059]

[0060] Example 5

[0061] The synthesis of polyimide BPDA-BDFPDA comprises the following steps:

[0062] S1. At room temperature, 4.6452 g (0.01 mol) of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione and 30.35 g of N,N-dimethylformamide were added to a 50 ml three-necked flask, purged with argon, and stirred. After complete dissolution, 2.9422 g (0.01 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added and the reaction was continued with stirring for 6 h to obtain a homogeneous, transparent, viscous solution. The polyamic acid solution was removed by scraping the polyamic acid solution onto a glass plate, and the glass plate was placed in a vacuum oven and evacuated. The heating program was as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour, heating from 100°C to 200°C and then keeping the temperature constant for 1 hour, heating from 200°C to 300°C and then keeping the temperature constant for 1 hour, heating from 300°C to 420°C and then keeping the temperature constant for 1 hour, and cooling to obtain a polyimide film (BPDA-BDFPDA).

[0063] The molecular structure of the polyimide BPDA-BDFPDA is as follows:

[0064]

[0065] Example 6

[0066] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0067] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0068] S2. At room temperature and under an argon atmosphere, 0.4341 g of modified boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0069] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0070] Example 7

[0071] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0072] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0073] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0074] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0075] Example 8

[0076] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0077] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0078] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0079] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0080] Example 9

[0081] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0082] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 500:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir and react at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0083] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 500:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0084] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0085] Example 10

[0086] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0087] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 550:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0088] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 550:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0089] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0090] Example 11

[0091] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0092] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 600:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0093] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 600:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0094] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0095] Example 12

[0096] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0097] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 650:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0098] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 650:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0099] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0100] Example 13

[0101] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0102] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0103] S2. At room temperature and under an argon atmosphere, 0.3413 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0104] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0105] Example 14

[0106] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0107] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0108] S2. At room temperature and under an argon atmosphere, 0.4778 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0109] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0110] Example 15

[0111] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0112] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0113] S2. At room temperature and under an argon atmosphere, 0.5461 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0114] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0115] Example 16

[0116] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0117] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0118] S2. At room temperature and under an argon atmosphere, 0.6144 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0119] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0120] Example 17

[0121] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0122] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0123] S2. At room temperature and under an argon atmosphere, 0.6826 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0124] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0125] Example 18

[0126] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0127] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0128] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 1 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0129] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0130] Example 19

[0131] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0132] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0133] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 3 h. Then, 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was added to a three-necked flask and purged with argon. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added and stirred for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0134] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0135] Example 20

[0136] A method for preparing a polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity comprises the following steps:

[0137] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0138] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 4 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0139] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0140] Comparative Example 1

[0141] The difference between this comparative example and Example 2 is that 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) is replaced by 4,4'-diaminodiphenyl ether (ODA), as follows:

[0142] S1. At room temperature, under an argon atmosphere, 0.01 mol of 4,4'-diaminodiphenyl ether (ODA) and 2.1812 g (0.01 mol) of 1,2,4,5-pyromellitic dianhydride (PMDA) were added to 42.62 g of N,N-dimethylformamide and the reaction was stirred for 6 h to obtain a homogeneous, transparent, viscous polyamic acid solution;

[0143] S2. After removing bubbles from the polyamic acid solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven and evacuate it. The heating program is as follows: heat from room temperature to 100°C and keep it constant at that temperature for 1 hour, heat from 100°C to 200°C and keep it constant at that temperature for 1 hour, heat from 200°C to 300°C and keep it constant at that temperature for 1 hour, heat from 300°C to 400°C and keep it constant at that temperature for 1 hour. After cooling, the polyimide film (PMDA-ODA) can be obtained.

[0144] The molecular structure of the polyimide film (PMDA-ODA) is as follows:

[0145]

[0146] Comparative Example 2

[0147] The difference between this comparative example and Example 4 is that 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) is replaced by 4,4'-diaminodiphenyl ether (ODA), as follows:

[0148] S1. At room temperature, under an argon atmosphere, 0.01 mol of 4,4'-diaminodiphenyl ether (ODA) and 3.2222 g (0.01 mol) of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) were added to 44.58 g of N,N-dimethylformamide and the reaction was stirred for 6 h to obtain a homogeneous, transparent, viscous polyamic acid solution.

[0149] S2. After removing bubbles from the polyamic acid solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven and evacuate it. The heating program is as follows: heat from room temperature to 100°C and keep it constant for 1 hour, heat from 100°C to 200°C and keep it constant for 1 hour, heat from 200°C to 300°C and keep it constant for 1 hour, heat from 300°C to 400°C and keep it constant for 1 hour. After cooling, the polyimide film (BTDA-ODA) can be obtained.

[0150] The molecular structure of the polyimide film (BTDA-ODA) is as follows:

[0151]

[0152] Comparative Example 3

[0153] The difference between this comparative example and Example 5 is that 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) is replaced by 4,4'-diaminodiphenyl ether (ODA), as follows:

[0154] S1. At room temperature, under an argon atmosphere, 0.01 mol of 4,4'-diaminodiphenyl ether (ODA) and 2.9422 g (0.01 mol) of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) were added to N,N-dimethylformamide and the reaction was stirred for 6 h to obtain a homogeneous, transparent, viscous polyamic acid solution;

[0155] S2. After removing bubbles from the polyamic acid solution, the solution is scraped onto a glass plate. The glass plate is then placed in a vacuum oven and evacuated. The heating program is as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour, heating from 100°C to 200°C and then keeping the temperature constant for 1 hour, heating from 200°C to 300°C and then keeping the temperature constant for 1 hour, heating from 300°C to 400°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide film (BPDA-ODA) can be obtained.

[0156] The molecular structure of the polyimide film (BPDA-ODA) is as follows:

[0157]

[0158] Comparative Example 4

[0159] The difference between this comparative example and Example 2 is that 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) is replaced by 2,7-bis(4-aminophenyl)-9H-fluorene-9-one (FOPDA), as follows:

[0160] S1. Synthesis of 2,7-bis(4-aminophenyl)-9H-fluoren-9-one (FOPDA):

[0161] 10.140 g of 2,7-dibromofluorenone and 13.006 g of p-aminophenylboronic acid hydrochloride were added to a 500 mL three-necked flask. 350 mL of tetrahydrofuran was added, followed by 112.5 mL of a 2 mol / L potassium carbonate solution and an appropriate amount of Aliquat 336. The mixture was stirred magnetically and purged with argon. After heating to 75°C in an oil bath, 0.150 g of tetrakistriphenylphosphine palladium was added and the mixture was refluxed for 24 hours. The reaction solution was poured into water, whereupon a large amount of precipitate formed. This precipitate was then filtered using a funnel and the solvent was evaporated under reduced pressure. The product was purified by column chromatography using a mobile phase of dichloromethane:n-hexane (2:1) and a silica gel stationary phase. The product was collected and dried to a reddish-brown solid, which was then dried in vacuo at 80°C for 24 hours. The yield was 87%.

[0162] The molecular structure of the 2,7-bis(4-aminophenyl)-9H-fluorene-9-one (FOPDA) is as follows:

[0163]

[0164] S2. Synthesis of Polyimide PMDA-FOPDA

[0165] 0.3624 g of 2,7-bis(4-aminophenyl)-9H-fluoren-9-one was placed in a 50 mL round-bottom flask and dissolved in 10 mL of dimethylformamide (DMF). 0.2181 g of dianhydride monomer PMDA was then added to achieve a solid content of approximately 6 wt %. After purging with argon, the mixture was reacted at room temperature for 6 h to obtain a homogeneous, transparent, and viscous polyamic acid solution.

[0166] After removing bubbles from the polyamic acid solution, the solution was scraped onto a glass plate, and then the glass plate was placed in a vacuum oven and evacuated. The heating program was as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour, heating from 100°C to 200°C and then keeping the temperature constant for 1 hour, heating from 200°C to 300°C and then keeping the temperature constant for 1 hour, heating from 300°C to 400°C and then keeping the temperature constant for 1 hour. After cooling, a polyimide film (PMDA-FOPDA) was obtained.

[0167] The molecular structure of the polyimide film (PMDA-FOPDA) is as follows:

[0168]

[0169] Depend on Figure 4 and Figure 5 It can be seen that the number of hydrogen atoms, carbon atoms and chemical shifts of the synthetic substance 2,7-bis(4-aminophenyl)-9H-fluorene-9-one (FOPDA) in Comparative Example 4 are consistent with the target structure; Figure 6 It can be seen that the molecular weight of the synthetic substance 2,7-bis(4-aminophenyl)-9H-fluorene-9-one (FOPDA) in Comparative Example 4 is almost the same as the molecular weight (362.14) corresponding to the target structure. Based on the above characterization structure, it can be determined that the synthetic substance in Comparative Example 4 is 2,7-bis(4-aminophenyl)-9H-fluorene-9-one (FOPDA).

[0170] Comparative Example 5

[0171] The difference between this comparative example and Example 6 is that the aspect ratio of boron nitride is 2500:1, as follows:

[0172] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 2500:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, wash the precipitate with 100 mL of anhydrous ethanol, and repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0173] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 2500:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0174] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0175] Comparative Example 6

[0176] The difference between this comparative example and Example 6 is that the silane coupling agent modification is replaced by hydroxylation modification, as follows:

[0177] S1. Weigh 1.0 g of boron nitride nanosheets with an aspect ratio of 700:1 and add them to 10 mL of 5 mol / L sodium hydroxide solution. Magnetic stirring is carried out at 80°C for 48 h. After filtration, the precipitate is washed with deionized water. This cycle is repeated until the pH of the filtrate is neutral. The precipitate is dried in a drying oven at 120°C for 24 h to obtain hydroxylated boron nitride nanosheets.

[0178] S2. At room temperature and under an argon atmosphere, 0.4341 g of hydroxylated boron nitride nanosheets were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask and purged with argon. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added and stirred for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0179] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

[0180] Comparative Example 7

[0181] The difference between this comparative example and Example 6 is that the gradient heating in step S2 is replaced by direct heating, as follows:

[0182] S1. Dissolve 3 g of aminopropyltriethoxysilane in 100 mL of anhydrous ethanol and stir evenly; then add 10 g of boron nitride nanosheets with an aspect ratio of 700:1 to the silane coupling agent solution and use ultrasonic treatment for 30 minutes to ensure that the boron nitride nanosheets are evenly dispersed; stir the reaction at 60°C for 4 hours to ensure that the silane coupling agent and the boron nitride nanosheets are fully reacted; after the reaction is completed, centrifuge the mixture, pour off the supernatant, and wash the precipitate with 100 mL of anhydrous ethanol. Repeat the washing three times to remove unreacted silane coupling agent; dry the modified boron nitride nanosheets in a vacuum drying oven at 60°C for 12 hours to obtain modified boron nitride nanosheets;

[0183] S2. At room temperature and under an argon atmosphere, 0.4341 g of boron nitride nanosheets with an aspect ratio of 700:1 were ultrasonically dispersed in 62.4 mL of N,N-dimethylformamide for 2 h. 0.01 mol of 2,8-bis(4-aminophenyl)indeno[1,2-b]fluorene-6-12-dione (BDFPDA) was then added to a three-necked flask. Argon was introduced and stirred. After complete dissolution, 0.01 mol of pyromellitic dianhydride (PMDA) was added. Stirring was continued and the reaction was allowed to proceed for 12 h to obtain a homogeneous, transparent, and viscous polyamic acid / boron nitride nanosheet composite solution.

[0184] S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, apply it to a glass plate with a scraper. The glass plate is then placed in a vacuum oven, evacuated, and heated to 420°C and maintained for 1 hour. After cooling, a polyimide / boron nitride nanosheet composite material is obtained.

[0185] Structural characterization

[0186] Depend on Figure 1 It can be seen that the number of hydrogen atoms and chemical shift of the synthetic substance in Example 1 are consistent with the target structure; Figure 2 It can be seen that the molecular weight of the synthetic substance in Example 1 is almost the same as the molecular weight corresponding to the target structure (464.14); based on the above characterization structure, it can be determined that the synthetic substance in Example 1 is BDFPDA. The molecular structure of BDFPDA is as follows:

[0187]

[0188] from Figure 3 It can be seen from the infrared spectra in Example 2, Example 4, Example 5 and Comparative Example 4 that the polyimide prepared has an infrared spectrum of 1778 cm -1 and 1710cm -1 Nearby are the asymmetric and symmetric stretching vibrations of the carbonyl group, 1356 cm -1 The stretching vibration of the imide ring is nearby, indicating that Examples 2-5 have successfully synthesized polyimide. -1The NH bond bending vibration is at 3500-3000cm -1 Between them are characteristic absorption peaks of hydroxyl and -NH, which indicate that the aminopropyltriethoxysilane-modified boron nitride / polyimide composite materials in Examples 6 and 7 have been successfully synthesized.

[0189] Performance Testing

[0190] (1) Dynamic mechanical properties (DMA) analysis

[0191] The glass transition temperature (T) of PI was tested using a DMAQ850 dynamic thermal mechanical properties analyzer from TA, USA. g ), the position of the DMA instrument was calibrated before the test, and the sample was clamped into the DMA fixture according to the specification of effective size of 20×6mm (length×width), the heating rate was 5℃ / min, the test temperature range was 25-510℃, the amplitude was 20μm, and the frequency was 1Hz.

[0192] (2) Static thermomechanical (TMA) analysis

[0193] The dimensional stability (thermal expansion coefficient) of the polyimide film was characterized using a TMAQ400 thermomechanical properties analyzer from TA Corporation of the United States. A film stretching fixture was used, the sample size (length × width) was 18 × 4.5 mm, the heating rate was 5 ° C / min, and the test temperature range was 50-300 ° C from room temperature.

[0194] (3) Barrier properties

[0195] The water vapor transmission coefficient (WVP) of polyimide film was tested using a PERMATRAN-W3 / 33 water vapor transmission rate tester from MOCON, USA. The test conditions were in accordance with ASTM F-1249, with a relative humidity of 90% and a test area of ​​5 cm. 2 The oxygen permeability coefficient (OP) of polyimide film was tested using MOCON2 / 21 oxygen permeability tester from MOCON Company of the United States in accordance with ASTM D3985. The test conditions were: relative humidity 0%, test area 5 cm 2 .

[0196] (4) Water absorption

[0197] Cut the polyimide film into 3cm x 3cm in length and width respectively. Place the sample in an 80℃ blast drying oven to remove the residual organic solvent and moisture. The measured mass is recorded as M0. Immerse the sample in deionized water and measure its mass at intervals. n According to the calculation formula, the water absorption rate change curve of the porous composite film at different immersion times can be obtained. Each group of samples needs to be measured five times to obtain the average value. The calculation formula is as follows:

[0198] W(%)=(M n -M0) / M0×100%

[0199] Where: W is the water absorption rate of polyimide film, M0 and M n Represent the mass of the sample before and after immersion, respectively.

[0200] (5) Thermal conductivity

[0201] The thermal conductivity of polyimide film was tested using a TC3000 thermal conductivity tester. The test temperature was room temperature, using the fast mode, a test voltage of 1.2V, and a measurement interval of 3 minutes. The calculation formula is as follows:

[0202]

[0203] Where: K is the thermal conductivity; q is the heat generated per unit length of metal wire; ΔT is the temperature change of the metal wire; t is the test time.

[0204] Table 1 Performance parameters of the polyimides synthesized in Examples and Comparative Examples

[0205]

[0206]

[0207] As shown in Table 1, Comparative Examples 1-3 are polyimides prepared by conventional methods, Comparative Example 4 is a polyimide containing a fluorenone structure, and the moisture permeability coefficient, oxygen permeability coefficient and thermal expansion coefficient of the polyimide containing indeno[1,2-b]fluorene-6,12-dione structure prepared in Examples 2, 4 and 5 are all lower than those in Comparative Examples 1-4, and the glass transition temperature is higher than that in Comparative Examples 1-4; the moisture permeability coefficient, oxygen permeability coefficient and thermal expansion coefficient of the polyimide / boron nitride nanosheet composite material in Example 6-20 are further reduced, the glass transition temperature is further increased, and the thermal conductivity is increased by more than 3 times, indicating that the polyimide / boron nitride nanosheet composite material containing indeno[1,2-b]fluorene-6,12-dione structure has ultra-high water vapor and oxygen barrier properties, high thermal conductivity, high dimensional stability and heat resistance. The moisture permeability coefficient, oxygen permeability coefficient, thermal expansion coefficient and water absorption of Comparative Examples 5-7 are all higher than those of the examples, and the thermal conductivity and T gThese values ​​are lower than those in the examples, demonstrating that an appropriate aspect ratio and boron nitride nanosheet modification method can improve the barrier properties of the composite material. Furthermore, the gradient temperature increase can stabilize the imidization process, alleviate thermal stress experienced during composite preparation, improve thermal stability, and thus enhance the thermal conductivity of the composite material. In summary, the polyimide composite material prepared by the present invention exhibits ultra-high barrier properties, high thermal conductivity, a low thermal expansion coefficient, low water absorption, and a high glass transition temperature, meeting the requirements of various applications.

[0208] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any person skilled in the art can, without departing from the spirit and technical solution of the present invention, use the methods and technical contents disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity, characterized in that: The polyimide / boron nitride nanosheet composite material with both high barrier and high thermal conductivity is prepared from polyimide and boron nitride nanosheets. The molecular structure of the polyimide is shown below: wherein n is 1-10000, and X is a dianhydride residue; The preparation method of the polyimide / boron nitride nanosheet composite material comprises the following steps: S1. Boron nitride nanosheets modified with a silane coupling agent to obtain modified boron nitride nanosheets; the aspect ratio of the boron nitride nanosheets is (400-2000):1; S2. In an argon atmosphere, the modified boron nitride nanosheets are ultrasonically dispersed in a strongly polar aprotic organic solvent for 1-4 hours. A diketone-containing diamine and a dianhydride are added to the dispersion at a molar ratio of 1:(0.98-1.02). The mixture is stirred at -5-25°C for 4-24 hours to obtain a homogeneous, viscous polyamic acid composite adhesive. S3. After removing bubbles from the polyamic acid / boron nitride nanosheet solution, scrape it onto a glass plate, then place the glass plate in a vacuum oven, evacuate the oven, and perform gradient temperature increase. The temperature increase is controlled as follows: heating from room temperature to 100°C and then keeping the temperature constant for 1 hour; heating from 100°C to 200°C and then keeping the temperature constant for 1 hour; heating from 200°C to 300°C and then keeping the temperature constant for 1 hour; heating from 300°C to 420°C and then keeping the temperature constant for 1 hour. After cooling, the polyimide / boron nitride nanosheet composite material can be obtained.

2. The polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity according to claim 1, characterized in that: The molecular formula of the diamine containing a diketone structure is shown below: The preparation method thereof comprises the following steps: S1. 2,8-dibromo-indeno[1,2-b]fluorene-6,12-dione and p-aminophenylboronic acid hydrochloride are sequentially added to tetrahydrofuran and dissolved; S2. Potassium carbonate solution and methyl trioctyl ammonium chloride were added sequentially, stirred magnetically and purged with argon, and heated in an oil bath to 60-80 ° C; S3. Tetrakis triphenylphosphine palladium was added and the reaction was refluxed for 12-48 h, and then the reaction solution was poured into ice water to precipitate; S4. Filter, wash and dry to obtain.

3. The polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity according to claim 1, characterized in that: The silane coupling agent in step S1 is one or more of γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane.

4. The polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity according to claim 1, characterized in that: The dianhydride in step S2 includes pyromellitic dianhydride, 3,3',4,4'-dibenzophenone tetracarboxylic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride.

5. The polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity according to claim 1, characterized in that: In step S2, the highly polar aprotic organic solvent is one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylacetamide, and N,N-dimethylformamide.

6. The polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity according to claim 1, characterized in that: In step S2, the total mass of the diamine and dianhydride is 10-40% of the mass of the glue.

7. The polyimide / boron nitride nanosheet composite material with both ultra-high barrier and high thermal conductivity according to claim 1, characterized in that: The mass of the boron nitride nanosheets is 2-10% of the mass of the polyimide material.

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