A shape memory polyimide aerogel and its preparation method

Abstract

This invention relates to a shape memory polyimide aerogel and its preparation method. A polyimide precursor is prepared via a polycondensation reaction using diamine and dianhydride as monomers, followed by sol-gelation, freeze-drying, and thermal imidization to obtain the final product. This invention prepares a polyimide aerogel with excellent shape memory and thermal insulation properties by increasing the thermal conductivity of the aerogel framework while reducing gas phase and radiative thermal conductivity, thus resolving the contradiction between thermal insulation and shape memory in aerogels and showing promising market application prospects.

Description

Technical Field

[0001] This invention belongs to the field of aerogels, and specifically relates to a shape memory polyimide aerogel and its preparation method. Background Technology

[0002] Aerogels are porous gel-like materials with a three-dimensional network structure, dispersed by a gas medium. Their porosity is typically 80–99.8%, and their specific surface area is generally 200–1000 m². 2 / g, density is usually less than 0.1g / cm³ 3 It is precisely because of this unique porous structure that aerogels possess many excellent properties in terms of mechanics, acoustics, and thermals. Therefore, aerogels have broad application prospects in areas such as thermal insulation, flame retardancy, and sound insulation.

[0003] With the development and advancement of science and technology, there are increasingly higher demands on the performance of materials in all aspects. The research and development of smart materials has attracted great attention from relevant personnel both domestically and internationally. Shape memory materials are a promising new type of smart material that can adjust its structural parameters under controllable external stimuli such as heat, light, water, electricity, magnetism, and chemical induction, thereby returning to its initial shape or state. By endowing aerogel materials with shape thermal memory effects, the intelligence and diversity of aerogel applications can be improved, providing a new direction for aerogel applications.

[0004] Currently, there are few publicly disclosed patents related to shape memory aerogels. Patents CN 113651992 A and CN113694843 A each disclose a method for preparing shape memory aerogels. The aerogels reported in these patents have low excitation temperatures and poor thermal stability, making them unsuitable for harsh environments such as aerospace. Patent CN 113980342 A uses organosilicon as a matrix to prepare shape memory aerogels, which exhibit better high-temperature resistance and can be used in the extreme environments required by aerospace and other fields. In all these patents, the shape memory of the aerogels is achieved through Joule heating; however, the good thermal insulation properties of the aerogel itself hinder heat transfer, resulting in poor shape memory performance and limitations in practical applications. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a shape memory polyimide aerogel and its preparation method, which resolves the contradiction between aerogel heat insulation and shape memory, greatly improves the shape memory performance of aerogel, and realizes the integration of shape memory and heat insulation functions.

[0006] This invention provides a shape memory polyimide aerogel, which is prepared by polycondensation reaction of diamine and dianhydride to obtain a polyimide precursor (polyamic acid PAA), followed by sol-gelation, freeze-drying and thermal imidization; wherein, a filler is added during the sol-gelation process, the filler content in the aerogel is 0% to 50% by weight, and the polyimide precursor content is 50% to 100% by weight.

[0007] The polyamic acid molecular chain contains flexible groups and has a molecular weight of 200,000 to 1,800,000.

[0008] The diamine is one or more of 3,4-diaminodiphenyl ether (3,4'-ODA), 4,4'-diaminodiphenyl ether (4,4'-ODA), and 1,3-bis(4'-aminophenoxy)benzene (BAPB); the dianhydride is one or more of bisphenol A diether dianhydride (BPADA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), and 4,4'-oxophthalic anhydride (ODPA). Other conventional diamines and dianhydrides are also applicable to this invention.

[0009] The organic solvent used in the polycondensation reaction is one or more of N,N-dimethylacetamide (DMAc), chloroform (CHCl3), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF).

[0010] The filler includes zero-dimensional filler, one-dimensional filler, or two-dimensional filler; wherein, the zero-dimensional filler is metal nanoparticles, metal oxide nanoparticles, carbon black, C 60 The filler is one or more of titanium dioxide; the one-dimensional filler is one or more of carbon nanotubes, carbon nanofibers, metal nanowires, carbon fibers, and silicon nitride; the two-dimensional filler is one or more of graphene oxide, transition metal carbonitrides, and boron nitride.

[0011] This invention also provides a method for preparing shape memory polyimide aerogel, comprising the following steps:

[0012] (1) Polyamic acid was prepared by polycondensation of diamine and dianhydride in an organic solvent at room temperature. Then, the prepared polyamic acid was deposited in deionized water, washed, and freeze-dried to obtain solid polyamic acid.

[0013] (2) The above-mentioned solid polyamic acid is dissolved in water with alkali and mixed with filler to form a uniform aqueous solution. It is then frozen in a low-temperature environment and freeze-dried to obtain polyamic acid aerogel. Then, it is thermally imidized to obtain shape memory polyimide aerogel.

[0014] The molar ratio of diamine to dianhydride in step (1) is 1:0.7-1:1.3; the reaction time of the polycondensation reaction is 10-48h, and the reaction temperature is 0-40℃.

[0015] The aqueous solution in step (2) is composed of: by weight fraction, 2-10% polyamic acid, 0-5% filler, 2-10% alkali, and 98-90% water.

[0016] The alkali in step (2) is an organic alkali or an inorganic alkali; wherein the organic alkali is one or more of pyridine, methylamine, ethylamine, and triethylamine; and the inorganic alkali is one or more of sodium hydroxide, magnesium hydroxide, potassium hydroxide, calcium hydroxide, and ammonia water.

[0017] The low temperature environment in step (2) is -4 to -196°C; the freezing method is one of random freezing, directional freezing, bidirectional freezing and tridirectional freezing.

[0018] The freezing process is performed with ultrasound assistance, and the power of the ultrasound is between 20W and 1000W.

[0019] The thermal imidization temperature in step (2) is near the glass transition temperature of the corresponding polyimide (200-350℃). The thermal imidization adopts a gradient heating method with a heating rate of 1-5℃ / min and an imidization time of 1-3h.

[0020] This invention also provides an application of shape memory polyimide aerogel in fields such as fire suits, new energy vehicles, spacesuits, and intelligent sensing.

[0021] The thermal conductivity of aerogels can generally be divided into three parts: gas phase thermal conductivity, solid phase thermal conductivity, and radiative thermal conductivity. This invention reduces the gas phase thermal conductivity of the aerogel by controlling the pore structure. Adding fillers increases solid phase thermal conductivity and reduces radiative thermal conductivity, thereby improving shape memory properties while maintaining good thermal insulation performance. By adjusting the direction and size of ice crystal growth, the prepared aerogel possesses a controllable pore structure.

[0022] Beneficial effects

[0023] This invention prepares polyimide aerogels with excellent shape memory and thermal insulation properties by increasing the skeletal thermal conductivity of the aerogel structure while reducing gas-phase and radiative thermal conductivity. Specifically, firstly, a polyimide with excellent shape memory is prepared based on molecular structure design. Secondly, based on the thermal conductivity mechanism of aerogels, the pore structure is controlled using the ice crystal template method to reduce the gas-phase thermal conductivity of the aerogel (improving thermal insulation performance). Then, by adding fillers with high thermal conductivity and radiation absorption functions, the radiative thermal conductivity of the aerogel is reduced (improving thermal insulation performance) while increasing its skeletal thermal conductivity (improving shape memory performance), thus resolving the contradiction between thermal insulation and shape memory in aerogels and preparing a polyimide aerogel with integrated shape memory and thermal insulation properties. Attached Figure Description

[0024] Figure 1 This is a schematic diagram and microstructure diagram of the shape memory polyimide aerogel of the present invention; wherein, 1 is the original state polyimide aerogel, 2 is the high-temperature compressed state polyimide aerogel, 3 is the fixed state polyimide aerogel, 4 is the recovered state polyimide aerogel, 5 is the microstructure of the polyimide aerogel, 6 is the filler, 7 is the pore of the polyimide aerogel, 8 is the skeleton of the polyimide aerogel, 9 is solid phase thermal conductivity, 10 is radiative thermal conductivity, and 11 is gas phase thermal conductivity.

[0025] Figure 2 SEM images of the shape memory polyimide aerogels prepared in Examples 1-4.

[0026] Figure 3 The size of the pores in the shape memory polyimide aerogels prepared in Examples 1-4 was statistically analyzed using ImageJ software.

[0027] Figure 4 The thermal conductivity data of the shape memory polyimide aerogels prepared in Examples 1-4 are shown in the figure.

[0028] Figure 5 The shape memory properties of the shape memory polyimide aerogels prepared in Examples 1-4.

[0029] Figure 6 Digital photographs of the shape memory process of the shape memory polyimide aerogel prepared in Example 3.

[0030] Figure 7 FT-IR tests of CNT-COOH, CNT, and CNT-NH2 prepared in Example 5.

[0031] Figure 8 SEM images of the shape memory polyimide aerogel prepared in Example 5 and the pore size statistics were performed using ImageJ software.

[0032] Figure 9Thermal conductivity test of the shape memory polyimide aerogel prepared in Example 5.

[0033] Figure 10 The shape memory properties of the shape memory polyimide aerogel prepared in Example 5 were tested.

[0034] Figure 11 Digital photographs of the shape memory process of the shape memory polyimide aerogel prepared in Example 5.

[0035] Figure 12 Thermal conductivity data and shape memory data of the shape memory polyimide aerogel prepared in Example 6.

[0036] Figure 13 Digital photograph of the flame-excited shape memory recovery process of the shape memory polyimide aerogel prepared in Example 6. Detailed Implementation

[0037] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0038] Example 1

[0039] Preparation of PAA: Nitrogen gas was introduced into a 250 ml three-necked flask to purge air. 40 ml of solvent DMAC was added. Then, 1.6 g of ODA was accurately weighed and stirred under nitrogen atmosphere for 30 min until ODA was completely dissolved. 4.164 g of BPADA was accurately weighed and added to the three-necked flask in batches over one hour. After reacting at room temperature for 20 h, the mixture was deposited in deionized water at 0 °C. The resulting product was centrifuged, washed, and then freeze-dried to obtain polyamic acid (PAA).

[0040] Preparation of ultra-small porous PI aerogel: 1.5g of TEA was added to 19g of deionized water, followed by 1.0g of PAA to prepare a 5wt% solid content PAA aqueous solution. The PAA aqueous solution was allowed to stand for 4 hours to obtain PAA hydrogel. The PAA hydrogel was then pre-frozen at 4℃ and then ultrasonically assisted at -130℃ for 20 minutes using 100W. The sample was then freeze-dried to obtain an ultra-small porous PAA aerogel. The obtained PAA aerogel was thermally imidized at 200–250℃ to obtain a shape memory polyimide aerogel, denoted as PI-US.

[0041] Example 2

[0042] PAA powder was prepared using the same method as in Example 1.

[0043] Preparation of small-pore PI aerogel: 1.5g TEA was added to 19g deionized water, followed by 1.0g PAA to prepare a 5wt% solids content PAA aqueous solution. The PAA aqueous solution was allowed to stand for 4 hours to obtain PAA hydrogel. The PAA hydrogel was then pre-frozen at 4℃ and then frozen at -130℃. The samples were placed in a freeze dryer and freeze-dried to obtain small-pore PAA aerogel. The obtained PAA aerogel was thermally imidized at 200-250℃ to obtain shape memory polyimide aerogel, denoted as PI-S.

[0044] Example 3

[0045] PAA powder was prepared using the same method as in Example 1.

[0046] Preparation of mesoporous PI aerogel: 1.5g of TEA was added to 19g of deionized water, followed by 1.0g of PAA to prepare a PAA aqueous solution with a solid content of 5wt%. The PAA aqueous solution was allowed to stand for 4 hours to obtain PAA hydrogel. The PAA hydrogel was then pre-frozen at 4℃ and subsequently frozen at -80℃. The samples were then placed in a freeze dryer and freeze-dried to obtain mesoporous PAA aerogel. The prepared PAA aerogel was thermally imidized at 200–250℃ to obtain shape memory polyimide aerogel, denoted as PI-M.

[0047] Example 4

[0048] PAA powder was prepared using the same method as in Example 1.

[0049] Preparation of macroporous PI aerogel: 1.5g of TEA was added to 19g of deionized water, followed by 1.0g of PAA to prepare a PAA aqueous solution with a solid content of 5wt%. The PAA aqueous solution was allowed to stand for 4 hours to obtain PAA hydrogel. The PAA hydrogel was then pre-frozen at 4℃ and subsequently frozen at -30℃. The samples were then placed in a freeze dryer and freeze-dried to obtain macroporous PAA aerogel. The prepared PAA aerogel was thermally imidized at 200–250℃ to obtain shape memory polyimide aerogel, denoted as PI-L.

[0050] The pore structure of the shape memory polyimide aerogels prepared in Examples 1-4 was observed using scanning electron microscopy (SEM), and the pore size was statistically analyzed using ImageJ software. The experimental results are as follows: Figure 2 and Figure 3As shown, the samples obtained in different embodiments have different pore structures. The average pore size of the prepared aerogels increases with increasing freezing temperature; the average pore sizes of the aerogels prepared in Examples 2-4 are 73 μm, 131 μm, and 225 μm, respectively. The aerogel prepared with ultrasonic assistance in Example 1 has an average pore size of only 31 μm, smaller than that of the aerogel prepared without ultrasonic assistance in Example 2.

[0051] The physical properties of the samples prepared in Examples 1-4 are shown in Table 1. As the pore size of the aerogel increases, the density of the aerogel decreases, while the corresponding porosity increases. This may be because the larger the pore size of the aerogel, the thicker the pore wall, and the stronger the supporting effect of the pore wall. During freeze-drying, this can reduce the collapse or shrinkage of the aerogel pore structure, which would otherwise lead to high porosity.

[0052] Table 1

[0053] sample PI-US PI-S PI-M PI-D Aperture (µm) 31.0 73.0 131.0 225.0 <![CDATA[Density (mg / cm 3 )]]> 98.0 93.0 87.7 79.0 Porosity (%) 93.2 93.6 93.9 94.5

[0054] The thermal conductivity of the prepared aerogel samples PI-US, PI-S, PI-M, and PI-L was tested using a Hotdisk TPS2500S thermal constant analyzer, based on the transient hot wire method.

[0055] Thermal conductivity of aerogels (λ) t It can be divided into vapor phase heat conduction (λ) g Solid-state thermal conductivity (λ) s ) and radiative thermal conductivity (λ) r The three parts are: λ, λ, and λ, ... g , λ s and λ r Perform the calculation.

[0056] λ t =λ g +λ s +λ r (1)

[0057]

[0058]

[0059] Where λ0 is the thermal conductivity of the solid skeleton, λ air =26.0mW / (m- 1 K- 1 ) is the thermal conductivity of air, Φ is the porosity, and f is the thermal conductivity of air. s The volume fraction of the bonding points in the aerogel skeleton is β≈2 for air, l is the mean free path of the gas (approximately 70 nm), and D is the average pore size of the aerogel.

[0060] Figure 4The graph shows the thermal conductivity data of samples PI-US, PI-S, PI-M, and PI-L. As can be seen from the graph, all four samples exhibit excellent thermal insulation performance, with thermal conductivity all less than 50 mW / m². -1 K -1 It outperforms most commercial insulation materials. Furthermore, as the pore size increases... g Only a tiny change, while λ s The porosity decreases as it increases. It is worth noting that λ... r It plays a crucial role in the thermal conduction process of aerogels, even surpassing λ. s Therefore, reducing radiative thermal conductivity is crucial for lowering the thermal conductivity of aerogels.

[0061] The shape memory properties of the prepared aerogel samples PI-S, PI-M, and PI-L were tested using a TA DMA Q800 instrument. The test was conducted using a controllable force mode with a compression clamp, and the load force used for the test was 1N.

[0062] like Figure 5 As shown, 'ad' represents the shape memory performance of PI-US, PI-S, PI-M, and PI-L, respectively. It can be seen that PI-US, PI-S, and PI-M aerogels all exhibit good fixation and recovery capabilities, while the PI-L sample shows poor recovery ability. This is attributed to the larger pore size leading to poorer mechanical properties, and the pore structure is easily damaged during high-temperature compression, resulting in poor recovery performance. PI-S and PI-M both exhibit excellent recovery performance, with recovery rates of 94.2%, 94.3%, and 94.6%, respectively. Furthermore, PI-M exhibits a larger shape memory strain than PI-S and PI-US, which is more beneficial for its applications.

[0063] Figure 6 The image shows a digital photograph of the shape memory process of the shape memory aerogel. It can be seen that the shape memory aerogel can be compressed and cooled to fix at a high temperature of 250℃, and can return to its original shape when the aerogel is reheated.

[0064] Example 5

[0065] Nitrogen gas was introduced into a 250ml three-necked flask to purge air. 40ml of solvent DMAC was added, and then 1.6g of ODA was accurately weighed and stirred under nitrogen atmosphere for 30min until ODA was completely dissolved. 4.164g of BPADA was accurately weighed and added to the three-necked flask in batches over one hour. After reacting at room temperature for 20h, the mixture was deposited in deionized water at 0℃. The resulting product was centrifuged, washed, and then freeze-dried to obtain PAA powder for later use.

[0066] Preparation of amination-modified CNT (CNT-NH2): Weigh 2g of CNT and add it in batches of 0.5g to a mixed acid solution (H2SO4:HNO3 = 3:1). Stir at 63℃ for 3 hours to obtain acidified CNT (CNT-COOH). After the reaction is complete, cool the mixture to room temperature and dilute it to 1000ml with deionized water under ice-water bath protection. After waiting for CNT to settle in the solution, separate the supernatant and continue to dilute to 1000ml. Repeat this process until the acidified CNT is difficult to separate into layers in the solution. At this point, transfer the mixed solution to a 50ml centrifuge tube and centrifuge at 8500r / min for 8min in a refrigerated centrifuge until neutral. Then, dry it into powder in a freeze dryer for later use. Weigh 0.4 g of acidified CNTs and disperse them in 300 ml of deionized water. Then, add 0.11 mL of N2H4·H2O and 0.75 mL of NH3·H2O respectively, and reflux at 95 °C for 6 h to obtain a CNT-NH2 mixed solution. Wash and dry the CNT-NH2 mixed solution for later use.

[0067] Preparation of polyimide composite aerogel: 0.95g PAA, 0.05g CNT-NH2, and 1ml TEA were added to 19ml deionized water, stirred and sonicated for 2 hours, and then allowed to stand for 4 hours to obtain PAA / CNT-NH2 hydrogel. The PAA / CNT-NH2 hydrogel was then frozen and freeze-dried at -80℃ to obtain a PAA / CNT-NH2 composite aerogel with a CNT-NH2 content of 5wt%. The obtained PAA / CNT-NH2 composite aerogel was thermally imidized at 200–250℃ to obtain a shape memory polyimide aerogel, denoted as PC-5.

[0068] The obtained CNT-COOH, CNT, and CNT-NH2 were subjected to FT-IR testing using a Thermo Fisher Scientific Nicolet Fourier transform infrared spectrometer, and the testing method was the KBr pellet method. Figure 7 It can be observed that the original CNTs have almost no functional groups. They appear at ~1720cm. -1 and ~3450cm -1 The peak values ​​are attributed to the stretching vibrations of C=O and -OH, respectively, confirming the presence of COOH. Meanwhile, at ~1400 cm⁻¹... -1 The peak value corresponds to the CN stretching vibration of CNT-NH2, revealing that amino (-NH2) is attached to CNT.

[0069] The pore structure of the shape memory polyimide aerogel prepared in Example 5 was observed using scanning electron microscopy (SEM), and the pore size was statistically analyzed using ImageJ software. The experimental results are as follows: Figure 8The aerogel exhibits a uniform honeycomb porous structure. Compared to the aerogel prepared in Example 2, the introduction of CNT-NH2 inhibits shrinkage, reducing the aerogel density from 87.7 mg / cm³. 3 Reduced to 75.2 mg / cm³ 3 The average pore size decreased from 131 μm to 124 μm.

[0070] The thermal conductivity of the shape memory polyimide aerogel prepared in Example 5 was tested using a Hotdisk TPS2500S thermal constant analyzer. The test principle was the transient hot wire method, and the thermal conductivity of the aerogel was analyzed and calculated according to formulas (1) to (3). Figure 9 As shown, compared to PI-M in Example 2, this aerogel λ r The proportion decreased significantly while λ s The proportion has increased significantly, while the overall thermal conductivity is 41.5 mW / m. -1 K -1 43.2mWm lower than PI-M -1 K -1 This is because CNT-NH2 can effectively absorb infrared radiation and reduce the λ of aerocondensation. r The high thermal conductivity of CNT-NH2 itself increases the λ of the aerogel to some extent. s .

[0071] The shape memory performance of the shape memory polyimide aerogel prepared in Example 5 was tested using a TA DMA Q800 instrument. The test employed a controllable force mode with a compression clamp, and the load force was 1 N. Figure 10 The composite aerogel exhibits excellent shape memory properties, with a fixation rate of 98.8% and a recovery rate of 97.2%. This is because the amino groups on the carbon nanotube surface can form physicochemical crosslinks with PI molecules, increasing the stationary phase.

[0072] Figure 11 The digital photographs show the shape memory process of the shape memory polyimide aerogel prepared in Example 5. It can be seen that the shape memory aerogel can be compressed at a high temperature of 250°C and fixed by cooling at room temperature. When it is reheated to 250°C in a tube furnace, the aerogel can return to its original shape.

[0073] Example 6

[0074] PAA powder was prepared using the same method as in Example 5.

[0075] MXene preparation: 1.0 g LiF was added to a 9 M HCl solution, and the mixture was magnetically stirred for 10 minutes until the LiF was completely dissolved. Next, 1.0 g of MAX phase powder was slowly added to the solution to avoid overheating, and the mixture was then kept at 35 °C for 24 h with magnetic stirring at 550 rpm. The mixture was then combined, reduced in size, and centrifuged with deionized water until the pH of the supernatant was close to 6. Finally, the diluted mixture was filtered under vacuum using a polytetrafluoroethylene (PTFE) membrane, and the resulting sample was collected by freeze-drying.

[0076] Preparation of PI / MXene composite aerogel: 0.8 g PAA, 0.2 g MXene, and 1 ml TEA were added to 19 ml deionized water, stirred and sonicated for 2 h, and then allowed to stand for 4 h to obtain PAA / MXene hydrogel. The PAA / MXene hydrogel was then freeze-dried at -80℃ to obtain a PAA / MXene composite aerogel with an MXene content of 20 wt%. The obtained PAA / MXene composite aerogel was thermally imidized at 200–250℃ to obtain a polyimide composite aerogel, designated PM-20.

[0077] The thermal conductivity of the prepared PI / MXene composite aerogel was tested using the same instruments and methods as in Example 5, and the thermal conductivity of the aerogel was analyzed and calculated according to formulas 1-3. Figure 12 The overall thermal conductivity of the PM-20 aerogel shown in figure a is 48.2 mW / m. -1 K -1 Furthermore, the addition of 20wt% MXene can not only reduce the radiative thermal conductivity but also increase the solid-phase thermal conductivity, which is beneficial for shape memory excitation.

[0078] The shape memory properties of the prepared PI / MXene composite aerogel were tested using the same instruments and methods as in Example 5. Figure 12 b indicates that the composite aerogel also exhibits good shape memory performance, with a fixation rate of 99.4% and a recovery rate of 97.8%. MXene's good thermal conductivity facilitates heat transfer through the aerogel framework, which is beneficial for improving the shape memory performance of the aerogel.

[0079] Figure 13 This is a digital photograph of the shape memory recovery process of the shape memory PI / MXene composite aerogel under flame excitation conditions. It can be seen that the shape memory aerogel can recover to its original shape in 40 seconds under the excitation of an alcohol lamp flame.

Claims

1. A shape memory / thermal insulation function integrated polyimide aerogel, characterized in that: The polyamide acid is prepared by polycondensation reaction of diamine and dianhydride as monomers, and then is prepared by sol-gel, freeze-drying and thermal imidization; wherein, the filler with high thermal conductivity and radiation absorption function is added in the sol-gel process, the weight percentage of the filler in aerogel is 0-50% and the weight percentage is not 0; the diamine is one or more of 3,4-diamino diphenyl ether, 4,4'-diamino diphenyl ether and 1,3-bis(4-aminophenoxy) benzene; the dianhydride is one or more of bisphenol A type diether dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride; the polyamide acid molecular chain contains flexible groups, and the molecular weight is 200,000-1,800,000; the filler is one or more of aminated carbon nanotubes, graphene oxide and MXene.

2. The aerogel of claim 1, wherein: The organic solvent used in the polycondensation reaction is one or more of N,N-dimethylacetamide, chloroform, dimethyl sulfoxide, tetrahydrofuran, N-methyl pyrrolidone and N,N-dimethylformamide.

3. A preparation method of the shape memory / thermal insulation function integrated polyimide aerogel according to any one of claims 1-2, comprising the following steps: (1) diamine and dianhydride are prepared into polyamide acid by polycondensation reaction in an organic solvent at room temperature under nitrogen atmosphere, and then the prepared polyamide acid is deposited in deionized water, washed, and freeze-dried to obtain polyamide acid solid; (2) the polyamide acid solid is dissolved in water by adding alkali, mixed with fillers to form a uniform aqueous solution, frozen in a low temperature environment, and then freeze-dried to obtain polyamide acid aerogel, and then thermal imidization is performed to obtain shape memory polyimide aerogel.

4. The method of claim 3, wherein: The molar ratio of diamine to dianhydride in step (1) is 1:0.7-1:1.3; the reaction time of the polycondensation reaction is 10-48 h, and the reaction temperature is 0-40 ℃.

5. The method of claim 3, wherein: The alkali in step (2) is an organic alkali or an inorganic alkali; wherein the organic alkali is one or more of pyridine, methylamine, ethylamine and triethylamine; the inorganic alkali is one or more of sodium hydroxide, magnesium hydroxide, potassium hydroxide, calcium hydroxide and ammonia.

6. The method of claim 3, wherein: The low temperature environment in step (2) is -4 to -196 ℃; the freezing mode is one of random freezing, directional freezing, bidirectional freezing and three-way freezing.

7. The method of claim 6, wherein: The freezing adopts ultrasonic assistance, and the power of the ultrasonic is between 20 W and 1000 W.

8. The method of claim 3, wherein: The thermal imidization temperature in step (2) is near the corresponding polyimide glass transition temperature, the thermal imidization adopts gradient heating method, the heating rate is 1-5 ℃ / min, and the imidization time is 1-3 h.

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