Modified polyimide aerogel as well as preparation method and application thereof

Abstract

The invention provides modified polyimide aerogel and a preparation method and application thereof.The preparation method comprises the steps that a polysiloxane solution and a polyamic acid solution are mixed, sol reaction is conducted in the presence of a dehydrating agent and a catalyst, polysiloxane-polyimide sol is obtained, standing is conducted, and the modified polyimide aerogel is obtained. The modified polyimide aerogel is obtained through solvent replacement, and the volume ratio of the polysiloxane solution to the polyamide acid solution is 1: 1; the modified flexible high-temperature-resistant polysiloxane-polyimide aerogel provided by the invention can still keep excellent mechanical properties in an extreme temperature environment, the flexibility of the material at an extremely low temperature is remarkably improved by virtue of a sphere-chain structure, and the problem of low-temperature brittle failure of the traditional polyimide aerogel is effectively solved; and excellent bending performance and heat insulation performance are realized.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, specifically to a modified polyimide aerogel, its preparation method, and its applications. Background Technology

[0002] Aerogel is a three-dimensional porous solid material rich in a gas dispersion medium (air accounts for up to 99.8% of the total volume of the material), characterized by its low density (0.16 mg / cm³). 3 High porosity (90~99.8%), high specific surface area (100-1600 m²) 2 / g), low thermal conductivity (10-40 mW·(m·K)). -1 Its advantages, such as low dielectric constant (close to that of air, 1.0), make it a promising candidate for applications in aerospace, building insulation, microwave insulation, biomedicine, adsorption catalysis and other fields.

[0003] With the continuous development and in-depth research in the field of aerogels, various types of aerogels have been developed. Based on their chemical structure, aerogels can be divided into three categories: inorganic aerogels, organic aerogels, and organic-inorganic hybrid aerogels. Although traditional inorganic aerogels (such as SiO2, Al2O3, and ZrO2) are among the most widely used aerogels due to their advantages of low density, high porosity, low thermal conductivity, and high temperature resistance, their high brittleness, poor mechanical properties, and cumbersome preparation process greatly limit their application in many fields. There is an urgent need for an aerogel with good mechanical properties and easy processing. Conventional organic aerogel materials, such as organosiloxane aerogels, polyurethane aerogels, and cellulose aerogels, while possessing relatively good mechanical strength and flexibility, suffer from poor performance and cannot meet the requirements for thermal insulation and load-bearing in high-temperature environments.

[0004] Polyimide is a polymer containing an imide ring in its molecular backbone. The conjugation effect of the imide ring enhances the bond energy of the backbone and the intermolecular forces, giving polyimide high-temperature resistance properties not found in other polymers. Due to its excellent thermal stability, mechanical properties, dimensional stability, chemical resistance, and insulation, polyimide is widely used in aerospace, microelectronics, and other fields, such as high-temperature coatings for spacecraft, lightweight spacecraft structural support materials, solar cell substrates, flexible printed circuit boards, and insulating layers for large-scale integrated circuits.

[0005] Polyimide aerogels not only inherit the excellent mechanical strength, high-temperature stability, and flexible synthesis methods of polyimide materials, but also possess the unique properties of aerogel materials, such as light weight, high specific surface area, high porosity, and low thermal conductivity, making them a class of porous materials with excellent comprehensive properties. Compared with conventional polymer aerogels, polyimide aerogels exhibit superior high-temperature thermal stability; compared with brittle inorganic aerogels, polyimide aerogels have high mechanical strength and good flexibility, and the aerogel films made from them can be bent, folded, and have a low relative permittivity. Moreover, the monomers used to synthesize polyimides are highly selective, and the synthesis methods are diverse. By controlling the types and proportions of monomers and employing different synthesis methods, polyimides with different chemical structures can be obtained, demonstrating strong molecular structure designability. Introducing functional groups into the polyimide molecular chain can endow it with multifunctionality.

[0006] When polyimide aerogels are applied in fields such as foldable spacecraft, spacesuits, and patch antennas, the combination of high-temperature resistance and flexibility at extreme high and low temperatures becomes particularly important. However, most existing high-temperature resistant polyimide aerogels have a large number of rigid benzene ring structures. This rigid structure can provide good support during aerogel molding, ensuring a stable microstructure and good high-temperature resistance. But excessive rigidity can also lead to problems such as large deformation and shrinkage of polyimide aerogels in high-temperature environments, severe collapse and shrinkage of the internal structure, and brittle fracture in extreme low-temperature environments.

[0007] Therefore, it is necessary to develop a polyimide-based aerogel material that maintains the high-temperature thermal stability of polyimide, while ensuring a complete and stable aerogel microstructure and exhibiting good flexibility and thermal insulation properties under extreme high and low temperature conditions. Summary of the Invention

[0008] The technical problem that this invention aims to solve is that existing aerogels are brittle and have poor resistance to high and low temperatures.

[0009] To address the aforementioned technical problems, in a first aspect, the present invention provides a method for preparing modified polyimide aerogel. The method comprises: mixing a polysiloxane solution and a polyamic acid solution, and carrying out a sol-gel reaction in the presence of a dehydrating agent and a catalyst to obtain a polysiloxane-polyimide sol. After standing, the modified polyimide aerogel is obtained by solvent displacement. The volume ratio of the polysiloxane solution to the polyamic acid solution is 1:(0.02~0.04).

[0010] The preparation method provided by this invention is simple. It involves synthesizing nanoscale polysiloxane particles using a specific surfactant and in-situ polymerization, thereby coating the surface of the polyimide particles with polyimide molecular chains to construct a unique "sphere-chain" composite structure. This structural design endows the material with excellent flexibility while ensuring a stable skeletal structure and superior mechanical properties. The resulting aerogel possesses an interpenetrating "sphere-chain" structure and excellent high-temperature resistance and flexibility, meeting the application requirements in extreme temperature environments.

[0011] Preferably, the polysiloxane solution is composed of a mixture of alkyltrialkoxysilane, ethanol, water, acetic acid, and a surfactant.

[0012] In this invention, during the preparation of the polysiloxane solution, after adding the surfactant, the mixture is stirred for 10-30 minutes to achieve a full reaction.

[0013] Preferably, the volume ratio of the alkyltrialkoxysilane, ethanol, water and acetic acid is (1~2):(1~2):(1~2):(0.02~0.04), for example, it can be 1:1:1:0.02, 1:2:1:2:0.03, 1:1:1:0.04, etc., and the amount of surfactant used is 4~6 mL of water per 1g of surfactant.

[0014] Preferably, the alkyltrialkoxysilane includes methyltrimethoxysilane; the surfactant is a combination of hexadecyltrimethylammonium bromide and / or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer F127.

[0015] Preferably, the surfactant is polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer F127.

[0016] Hexadecyltrimethylammonium bromide is widely used in industrial fields. For example, it is used as a mineral flotation agent to improve the flotation efficiency of sulfide and oxide ores, and as an asphalt emulsifier to disperse asphalt into a stable emulsion for road paving. Due to its cationic properties, hexadecyltrimethylammonium bromide can be adsorbed onto fiber surfaces to reduce the coefficient of friction, and is widely used in hair conditioners, fabric treatment agents, and leather fatliquoring agents, but not in the preparation of aerogels.

[0017] The high biocompatibility of F127, a triblock copolymer of polyethylene oxide, polypropylene oxide, and polyethylene oxide, makes it commonly used for sustained-release and targeted drug delivery. Furthermore, F127 hydrogel possesses excellent moisture retention, breathability, and biocompatibility, forming a protective film to cover wounds, prevent bacterial infection, and promote wound healing. It is frequently used in wound dressings for burns, trauma, and chronic ulcers, and can also be loaded with growth factors to enhance repair effects. It should not be used in the preparation of aerogels.

[0018] Preferably, the polyamic acid is obtained by reacting aromatic dianhydride, aromatic diamine and solvent; the dehydrating agent is acetic anhydride; and the catalyst is triethylamine.

[0019] In this invention, the dehydrating agent and the catalyst are added to the reaction system simultaneously, or they can be added separately, but the interval between them should not exceed 2 minutes.

[0020] Preferably, the aromatic dianhydride comprises pyromellitic dianhydride or 3,3',4,4'-biphenyltetracarboxylic dianhydride; the aromatic diamine comprises 4,4'-diaminodiphenyl ether; and the solvent comprises N,N-dimethylacetamide and / or N-methylpyrrolidone.

[0021] In this invention, the flexible high-temperature resistant polysiloxane-polyimide aerogel uses 4,4'-diaminodiphenyl ether as a diamine monomer, and combines it with pyromellitic (pyromellitic dianhydride) and biphenyl (3,3',4,4'-biphenyltetracarboxylic dianhydride) dianhydride monomers to form a macromolecular chain structure with alternating flexible and rigid segments.

[0022] Preferably, the molar ratio of the aromatic dianhydride, catalyst and dehydrating agent is 1:(7~10):(7~10), for example, it can be 1:7:7, 1:8:8, 1:10:9, or 1:9:10, etc.

[0023] The mass ratio of the aromatic diamine to the solvent is 1:(20~30), for example, it can be 1:20, 1:25 or 1:30, etc.

[0024] Preferably, the solvent replacement is performed by washing the settled polysiloxane-polyimide sol, immersing the washed polysiloxane-polyimide sol in anhydrous ethanol and a polar aprotic solvent with increasing volume ratios, and finally drying to obtain modified polyimide aerogel.

[0025] Polar aprotic solvents can be N,N-dimethylacetamide, N-methylpyrrolidone, etc.

[0026] In this invention, the meaning of increasing the volume ratio of anhydrous ethanol and polar aprotic solvent is as follows: For example, when washing the polysiloxane-polyimide sol after it has been left to stand, the washing solvent is N,N-dimethylacetamide, and the replacement solvent is ethanol; first, 25% ethanol is added to N,N-dimethylacetamide, and after a period of time, 75% ethanol is added, and after a period of time, 100% ethanol is added, so that the solvent eventually becomes ethanol, that is, the volume ratio of ethanol to N,N-dimethylacetamide gradually increases until ethanol becomes 100%.

[0027] The drying process uses supercritical carbon dioxide drying, and the drying conditions are generally 8-10 MPa, 37-42℃, and the drying time is 8-10 hours.

[0028] Preferably, the sol-gel reaction time is 5-15 minutes; the settling time is 10-15 hours; and the solvent replacement time is 2-4 days.

[0029] Secondly, this invention provides a modified polyimide aerogel prepared by the method described in the first aspect. The aerogel provided by this invention has a "sphere-chain" structure that significantly improves the flexibility of the material at extremely low temperatures, effectively solving the problem of low-temperature brittleness in traditional polyimide aerogels, and achieving excellent bendability and thermal insulation properties.

[0030] The modified polyimide aerogel provided by this invention can be applied to fields such as structural support materials for satellites, solar cell substrates, flexible printed circuit boards, and large-scale integrated circuits.

[0031] Implementing this invention has the following beneficial effects: (1) The flexible, high-temperature resistant modified polysiloxane-polyimide aerogel provided by this invention uses 4,4'-diaminodiphenyl ether as a diamine monomer, combined with pyromellitic (pyromellitic dianhydride) and biphenyl (3,3',4,4'-biphenyltetracarboxylic dianhydride) dianhydride monomers to form a macromolecular chain structure with alternating flexible and rigid segments. Simultaneously, nanoscale polysiloxane particles are synthesized using in-situ polymerization, allowing polyimide molecular chains to coat the surface of the polysiloxane particles, constructing a unique "sphere-chain" composite structure. This structural design endows the material with excellent flexibility while ensuring its stable skeletal structure and superior mechanical properties.

[0032] (2) The flexible high-temperature modified polysiloxane-polyimide aerogel provided by the present invention has a significantly improved temperature resistance and a greatly reduced high-temperature shrinkage rate, enabling it to maintain stable performance in high-temperature environments for a long time. Its unique "ball-chain" structure particularly enhances the material's bendability under extreme temperature conditions.

[0033] (3) The modified flexible high-temperature resistant polysiloxane-polyimide aerogel provided by the present invention can still maintain excellent mechanical properties under extreme temperature conditions. Its "ball-chain" structure significantly improves the flexibility of the material at extremely low temperatures, effectively solves the problem of low-temperature brittle fracture of traditional polyimide aerogels, and achieves excellent bendability and thermal insulation performance.

[0034] (4) The preparation method of the modified flexible high temperature resistant polysiloxane-polyimide aerogel provided in this application is simple and convenient to operate. Attached Figure Description

[0035] Figure 1 This is the FTIR spectrum of the flexible high-temperature resistant polysiloxane-polyimide aerogel prepared in Example 1.

[0036] Figure 2 This is a scanning electron microscope image of the flexible high-temperature resistant polysiloxane-polyimide aerogel prepared in Example 1.

[0037] Figure 3 This is a thermogravimetric analysis diagram of the flexible high-temperature resistant polysiloxane-polyimide aerogel prepared in Example 1.

[0038] Figure 4 This is a physical illustration of the bendability test of the flexible high-temperature resistant polysiloxane-polyimide aerogel prepared in Example 1. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1 This embodiment provides a method for preparing modified polysiloxane-polyimide aerogel. (1) In a nitrogen atmosphere, add 100 ml of dehydrated N,N dimethylacetamide solvent to a 250 ml three-necked flask, then add diamine monomer 4,4'-diaminodiphenyl ether (3.248 g) and dianhydride monomer pyromellitic dianhydride (0.804 g) to obtain a mixed solution, and stir at room temperature until the reaction is complete.

[0041] (2) Mix 5ml water, 5ml ethanol, 5ml methyltrimethoxysilane and 0.15ml glacial acetic acid evenly, stir until a homogeneous solution is formed, add surfactant F127 (1.1g) and continue stirring until the solution is clear, and record it as solution A.

[0042] (3) Add 2.948 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride to the solution prepared in step (1) and continue the reaction at room temperature.

[0043] (4) Add 3 ml of solution A to the solution in step (3) and continue stirring until a homogeneous polysiloxane-polyamic acid solution is formed.

[0044] (5) Add acetic anhydride (the molar ratio of acetic anhydride to diamine is 8:1) and triethylamine (the molar ratio of triethylamine to acetic anhydride is 1:1) to the polysiloxane-polyamic acid solution prepared in step (4) to carry out a chemical imidization reaction to obtain polysiloxane-polyimide sol. Then pour it into a mold and let it stand for 15 minutes to obtain flexible polysiloxane-polyimide wet gel.

[0045] (6) Wash the wet gel with the solvent N,N-dimethylacetamide. After washing, perform solvent replacement. Ethanol is selected as the replacement solvent. The reaction solvent is completely replaced with the replacement solvent. The specific operation is as follows: First, add 25% ethanol to N,N-dimethylacetamide and place the sample in it for 12 hours. Then, add 75% ethanol to N,N-dimethylacetamide and soak the sample in it for 12 hours. Finally, place the sample in a 100% ethanol bath for another 48 hours.

[0046] (7) The wet gel after replacement is subjected to supercritical carbon dioxide drying. The wet gel sample is placed in a supercritical drying vessel and dried for 10 hours at 10 MPa and 40 °C to obtain flexible high-temperature resistant polysiloxane-polyimide aerogel.

[0047] Figure 1 This is the infrared spectrum of Example 1. In the infrared spectrum, 1780 cm⁻¹ -1 and 1720cm -1 The corresponding C=O group is located at 1380 cm. -1 The corresponding CNC bond at this location, along with this set of characteristic peaks, collectively confirms the presence of a typical polyimide structure in the material. 2973 cm⁻¹ -1 The location originates from the CH bond, 1275cm -1 and 844cm -1 The position belongs to the Si-O-CH3 group, while 1170 and 1115 cm -1 The presence of Si-O-Si bonds indicates that the polysiloxane structure has been successfully incorporated into the polyimide aerogel.

[0048] Figure 2 This is a cross-sectional scanning electron microscope image of Example 1, showing that the polysiloxane-polyimide aerogel has a multi-level hierarchical porous network structure. Flexible polyimide molecular chains are cross-linked via imidization to form a network backbone, with 300-400 nm polysiloxane nanoparticles uniformly encapsulated at the nodes, constituting a "chain-like backbone-spherical particle" topology, significantly reducing drying and high-temperature shrinkage. Figure 2 (cd) forms a "core-shell" structure. The irregularly folded shell buffers bending stress through modulus gradient, giving the material both high specific surface area and excellent flexibility, enabling repeated bending without cracking.

[0049] Figure 3 The thermogravimetric analysis diagram of Example 1 shows that the sample mass loss is mainly divided into three stages: the first stage (25~400℃) is when adsorbed H2O or residual solvent in the sample evaporates; the second stage (400~500℃) is when the methyl groups on the surface of the polysiloxane collapse and decompose, as well as some residual surfactants decompose; and the third stage (520~800℃) is when the imide ring in the sample breaks, and the imine bonds and carbon-carbon bonds in the main chain break at high temperatures.

[0050] Figure 4 This is a physical illustration of the bendability test of the polysiloxane-polyimide aerogel obtained in Example 1. It can be seen that Example 1 exhibits good bendability, capable of being bent in both forward and reverse directions, and does not show any cracks after repeated bending. This is because nano-sized polysiloxane particles are introduced into the polyimide molecular chain, allowing the stress during bending to be evenly distributed and resulting in more coordinated deformation.

[0051] Example 2 This embodiment provides a method for preparing modified polysiloxane-polyimide aerogel. (1) In a nitrogen atmosphere, N,N-dimethylacetamide solvent (without water) was added to a 250 ml three-necked flask. Then, the diamine monomer 4,4'-diaminodiphenyl ether and the dianhydride monomer pyromellitic dianhydride were added to the flask in a molar ratio of 1:1 to obtain a mixed solution with a solid content of 7 wt%. The solution was stirred at room temperature until the reaction was complete.

[0052] (2) Mix 5ml water, 5ml ethanol, 5ml methyltrimethoxysilane and 0.15ml glacial acetic acid evenly, stir until a homogeneous solution is formed, add surfactant F127 (1.1g) and continue stirring until the solution is clear, and record it as solution A.

[0053] (3) Add 3 ml of solution A to the solution in step (1) and continue stirring until a homogeneous polysiloxane-polyamic acid solution is formed.

[0054] (4) Add acetic anhydride (the molar ratio of acetic anhydride to diamine is 8:1) and triethylamine (the molar ratio of triethylamine to acetic anhydride is 1:1) to the polysiloxane-polyamic acid solution prepared in step (3) to carry out a chemical imidization reaction to obtain polysiloxane-polyimide sol. Then pour it into a mold and let it stand for 15 minutes to obtain flexible polysiloxane-polyimide wet gel.

[0055] (5) Wash the wet gel with the solvent N,N-dimethylacetamide. After washing, perform solvent replacement. Ethanol is selected as the replacement solvent. The reaction solvent is completely replaced with the replacement solvent. The specific operation is as follows: First, add 25% ethanol to N,N-dimethylacetamide and place the sample in it for 12 hours. Then, add 75% ethanol to N,N-dimethylacetamide and soak the sample in it for 12 hours. Finally, place the sample in a 100% ethanol bath for another 48 hours.

[0056] (6) The wet gel after replacement is subjected to supercritical carbon dioxide drying. The wet gel sample is placed in a supercritical drying vessel and dried for 10 hours at 10 MPa and 40 °C to obtain flexible high-temperature resistant polysiloxane-polyimide aerogel.

[0057] Example 3 This embodiment is basically the same as embodiment 1, except that the amount of solution A added in step (3) is 2 ml.

[0058] Example 4 This embodiment is basically the same as that of embodiment 1, except that the amount of solution A added in step (3) is 4 ml.

[0059] Example 5 This embodiment is basically the same as that of embodiment 1, except that the surfactant mentioned in step (2) is hexadecyltrimethylammonium bromide (0.2g).

[0060] Example 6 This embodiment is basically the same as that of embodiment 1, except that the surfactant in step (2) is replaced with Tween 80.

[0061] Comparative Example 1 The difference between this comparative example and Example 1 is that the solution A described in step (4) is not added, but instead an equal amount of N,N-dimethylacetamide is added and stirring is continued for 1 hour. Otherwise, it is the same as Example 1.

[0062] Comparative Example 2 The difference between this comparative example and Example 1 is that the surfactant described in step (2) is not added; otherwise, it is the same as Example 1.

[0063] The samples prepared in the above embodiments and comparative examples were subjected to performance tests. Specifically, the shrinkage rate was obtained by dividing the volume change after drying by the volume before drying, and the thermal conductivity was measured at room temperature using a flat plate heat flow meter with square samples. The thermal decomposition temperature was defined as Td5% on the thermogravimetric curve.

[0064] The test results are shown in Table 1 below: Table 1 As shown in Table 1, the polysiloxane-polyimide aerogels prepared in Examples 1-3 of this invention are superior to those in Comparative Examples 1-2 in terms of key performance indicators such as shrinkage rate, thermal conductivity, and thermal decomposition temperature. Among them, Example 1 exhibits the best overall performance, with a shrinkage rate as low as 2.31%, a thermal decomposition temperature as high as 518.7℃, and a thermal conductivity of only 0.0332 W / (m·K), demonstrating excellent thermal insulation, dimensional stability, and high-temperature resistance. Furthermore, Example 4 shows that when the amount of polysiloxane solution is too large, the temperature resistance of the aerogel will decrease significantly.

[0065] A comparison between Example 1 and Example 6 shows that the aerogel prepared with conventional surfactants has poor performance, while the aerogel prepared with polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer F127 is preferred.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a modified polyimide aerogel, characterized by, The preparation method is: mixing a polysiloxane solution and a polyamide acid solution, carrying out a sol reaction in the presence of a dehydrating agent and a catalyst to obtain a polysiloxane-polyimide sol, then standing, and then carrying out solvent replacement to obtain the modified polyimide aerogel, the volume ratio of the polysiloxane solution to the polyamide acid solution being 1:(0.02-0.04).

2. The production method according to claim 1, characterized by, The polysiloxane solution is formed by mixing alkyltrialkoxysilane, ethanol, water, acetic acid and a surfactant.

3. The production method according to claim 2, characterized by, The volume ratio of the alkyltrialkoxysilane, ethanol, water and acetic acid is (1-2):(1-2):(1-2):(0.02-0.04), and the amount of the surfactant is 4-6 mL of water per 1 g of the surfactant.

4. The production method according to claim 2, characterized by, The alkyltrialkoxysilane includes methyltrimethoxysilane; and the surfactant is a combination of cetyltrimethylammonium bromide and / or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer F127. Preferably, the surfactant is polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer F127.

5. The preparation method according to claim 1, characterized in that, The polyamide acid is obtained by mixing reaction of an aromatic dianhydride, an aromatic diamine and a solvent; the dehydrating agent is acetic anhydride; and the catalyst is triethylamine.

6. The production method according to claim 5, wherein The aromatic dianhydride includes pyromellitic dianhydride or 3,3',4,4'-diphenyltetracarboxylic dianhydride; the aromatic diamine includes 4,4'-oxydianiline; and the solvent includes N,N-dimethylacetamide and / or N-methylpyrrolidone.

7. The preparation method according to claim 5, characterized in that, The molar ratio of the aromatic dianhydride, the catalyst and the dehydrating agent is 1:(7-10):(7-10). The mass ratio of the aromatic diamine to the solvent is 1:(20-30).

8. The method of claim 1, wherein, The solvent replacement is: washing the polysiloxane-polyimide sol after standing, then sequentially immersing the washed polysiloxane-polyimide sol in anhydrous ethanol and a polar aprotic solvent with increasing volume ratios, and finally drying to obtain the modified polyimide aerogel.

9. The method of claim 1, wherein, The time of the sol reaction is 5-15 minutes; the time of the standing is 10-15 hours; and the time of the solvent replacement is 2-4 days.

10. The modified polyimide aerogel prepared by the preparation method according to any one of claims 1-9.

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