Polyimide aerogel with shape memory function and preparation method thereof

Abstract

The application discloses a polyimide aerogel with a shape memory function and a preparation method thereof, and belongs to the technical field of aerogel preparation.The preparation method comprises the following steps: 1) polymerizing diamine and dianhydride in dimethyl sulfoxide to obtain a polyamide acid precursor; 2) pouring the polyamide acid solution into a mold for cold forming and performing freeze drying to remove solvent; and 3) placing the polyamide acid block after freeze drying into a tube furnace for thermal imidization to obtain the polyimide aerogel.The polyimide aerogel is prepared by using a freeze drying method.The polyimide aerogel has the shape memory performance of high shape fixing rate and high shape recovery rate while realizing three-dimensional skeleton forming of the aerogel.

Description

Technical Field

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

[0002] Shape memory materials are a new type of smart material that can maintain a temporary shape under certain external forces and environmental conditions, and can return to their initial shape under specific external stimuli (such as heat, light, electricity, magnetism, etc.). Therefore, they have broad application prospects in spacecraft structural materials with self-deploying, self-deforming, and self-propelled characteristics. In recent years, with the continuous development of aerospace technology, higher requirements have been placed on the lightweight and functionality (such as thermal insulation and low dielectric constant) of materials. However, existing shape memory materials cannot meet the requirements of lightweight and intelligent operation.

[0003] Aerogels are a typical class of lightweight, thermally insulating materials used in aerospace. They are solid materials composed of a three-dimensional network structure with air as the dispersion medium, and have a low density (as low as 0.0002 g / cm³). -3 High porosity (80%–99.8%), low thermal conductivity (0.01–0.05 W / m²). -1 K -1 With its characteristics such as heat protection / insulation systems for advanced weapons and spacecraft, interplanetary entry-descent-landing systems for spacecraft, and thermal insulation for spacesuits, shape memory aerogels have significant application prospects. Shape memory aerogels combine the low density, high porosity, and low dielectric properties of aerogel materials with the deformability and recoverability of shape memory materials. Therefore, they can endow smart deformable materials with numerous properties such as lightweight, heat insulation, shock absorption and noise reduction, and low dielectric constant, thus potentially further improving the overall performance of smart materials for aerospace applications. However, shape memory aerogels currently suffer from poor high-temperature resistance, poor mechanical properties, and poor tolerance to harsh environments.

[0004] Polyimide is a general term for a class of polymers containing imide rings (-CO-N-CO-) in their main chain. It possesses high thermal stability, good mechanical properties, excellent weather resistance, high insulation, and superior radiation resistance, meeting the application requirements of harsh environments (such as high temperatures and space irradiation), thus making it highly favored in the aerospace field. Furthermore, the flexible designability of the polyimide molecular chain structure allows for the acquisition of a series of shape memory polyimide materials with tunable glass transition temperatures (typically above 200℃) by controlling the molecular structure, thereby meeting the needs of space applications. Therefore, the design and development of high-performance shape memory polyimide aerogel materials is expected to promote the intelligent development of functional materials for aerospace applications, and has become a key focus and hot topic in the future development of aerospace materials.

[0005] Existing technologies include the preparation of shape memory polyimides using traditional methods, but these methods do not possess the advantages of aerogels, such as lightweight, heat insulation, and sound absorption. Shape memory porous materials made by adding foaming agents to this traditional polyimide will exhibit defects such as cracking, collapse, uneven pore size, and incomplete imidization of the material, and the shape memory performance is not ideal. Summary of the Invention

[0006] To address the problems of existing technologies, this invention designs the molecular structure of polyimide, dissolves polyamic acid using dimethyl sulfoxide as a solvent, and forms an aerogel by freeze-drying to create pores. The final shape-memory polyimide aerogel is then produced through thermal imidization. Simultaneously, by controlling the flexibility of the diamine and dianhydride, as well as the number of benzene rings, to balance the ratio of soft and hard segments within the polyimide molecular structure, the mobility and physical entanglement of molecular chain segments are further controlled. This results in a low-density, high-porosity, and high shape fixation / recovery rate shape-memory polyimide aerogel, overcoming the difficulties in molding and poor shape-memory performance of existing shape-memory polyimide aerogels. This invention provides a simple-to-operate, space-corrosion-resistant polyimide aerogel with excellent shape-memory properties achieved through physical cross-linking of molecular chain segments, along with its preparation method and applications.

[0007] The technical solution of the present invention is as follows:

[0008] This invention provides a polyimide aerogel with shape memory function and its preparation method. The polyimide aerogel can program its own shape in an environment above its glass transition temperature, fix its programmed shape after the temperature is lowered, and restore its initial shape after reaching its glass transition temperature again.

[0009] According to the preferred embodiment of the present invention, the glass transition temperature of the shape memory polyimide aerogel is 210-225°C, the thermal decomposition temperature is 450-500°C, the shape memory fixation rate is 98-100%, and the shape recovery rate is 95-99%.

[0010] This invention provides a method for preparing shape memory polyimide aerogel, comprising the following steps:

[0011] 1) Preparation of polyamic acid precursor: Polyamic acid precursor solution was obtained by polymerizing diamine and dianhydride in dimethyl sulfoxide (DMSO);

[0012] 2) The polyamic acid precursor solution was further diluted with dimethyl sulfoxide, then poured into a mold and frozen to form a solid shape. Subsequently, the solvent was removed by freeze drying to obtain polyamic acid blocks.

[0013] 3) The obtained polyamic acid block is subjected to high temperature treatment to undergo thermal imidization, resulting in shape memory polyimide aerogel.

[0014] In an embodiment of the present invention, the molar ratio of diamine to dianhydride in step 1) is (0.8-1.2):1.

[0015] In an embodiment of the present invention, the diamine monomer in step 1) is selected from any one or more of the following: 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP, 98%), 4,4'-diaminodiphenyl ether (ODA, 98%), and 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP, 98%).

[0016] In an embodiment of the present invention, the dianhydride monomer in step 1) is selected from any one or more of the following: bisphenol A diether dianhydride (BPADA, 98%), pyromellitic dianhydride (PMDA, 98%), and hexafluoroisopropylphthalic anhydride (6FDA, 98%).

[0017] In an embodiment of the present invention, in step 1), the diamine monomer is first dissolved in DMSO, and after the diamine monomer is completely dissolved, the dianhydride monomer is added, and the reaction is continued to obtain polyamic acid; after the polyamic acid exhibits the phenomenon of rod climbing, the mixture is stirred for 1-2 hours to obtain the target polyamic acid precursor solution.

[0018] In an embodiment of the present invention, the solid content in the polyamic acid precursor solution in step 1) is 10-20 wt%.

[0019] In an embodiment of the present invention, in step 2), dimethyl sulfoxide is added to the polyamic acid precursor solution to dilute it so that the solid content in the polyamic acid solution is 5-8 wt%.

[0020] In an embodiment of the present invention, in step 2), the freeze-forming process involves placing the mold in a liquid nitrogen atmosphere for 1 to 2 hours to completely freeze the polyamic acid.

[0021] In an embodiment of the present invention, in step 2), liquid nitrogen is first poured into a foam box to create a low-temperature liquid nitrogen atmosphere. After the temperature atmosphere is relatively stable, the mold containing the diluted polyamic acid precursor solution is placed into the foam box for freezing.

[0022] In an embodiment of the present invention, when placing the mold into the foam box in step 2), foam or similar heat-insulating material is first placed at the bottom to ensure that the mold does not come into direct contact with liquid nitrogen, so that the polyamic acid solution is cooled evenly inside the mold.

[0023] In an embodiment of the present invention, in step 2), the temperature during freeze-drying is -40 to -50°C, the freeze-drying time is 36 to 72 hours, and the vacuum degree is 15 to 25 Pa.

[0024] In an embodiment of the present invention, the high temperature in step 3) is 150-300°C.

[0025] In an embodiment of the present invention, in step 3), the thermal imidization process is carried out in a tubular furnace with a heating rate of 1 to 2 K / min, and the furnace is held at 150°C, 250°C, and 300°C for half an hour in sequence. The process ends when the tubular furnace is heated to 300°C and held at that temperature.

[0026] In an embodiment of the present invention, the method specifically includes the following steps:

[0027] S1: Prepare the reaction materials, including the following:

[0028] Dihydride monomers: Bisphenol A type diether dianhydride (BPADA, 98%), pyromellitic dianhydride (PMDA, 98%), hexafluoroisopropylphthalic anhydride (6FDA, 98%).

[0029] Diamine monomers: 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP, 98%), 4,4'-diaminodiphenyl ether (ODA, 98%), 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP, 98%);

[0030] Polar solvent: dimethyl sulfoxide (DMSO, analytical grade);

[0031] S2: Preparation of polyamic acid precursor: Polymerize diamine and dianhydride in dimethyl sulfoxide in a molar ratio of (1:1.02) to obtain polyamic acid precursor;

[0032] S3: Pour the polyamic acid solution into a mold, freeze it to form a solid shape, and then freeze-dry it to remove the solvent;

[0033] S4: The freeze-dried polyamic acid block is placed in a tube furnace for thermal imidization to obtain the final shape memory polyimide aerogel;

[0034] The above solution solves the problem of poor shape memory performance in porous materials made from traditional shape memory polyimide, with a shape memory fixation rate of 98-100% and a shape recovery rate of 95-99%.

[0035] This invention provides a shape memory polyimide aerogel prepared based on the above method.

[0036] The present invention also provides the application of the above-described shape memory polyimide aerogel in aerospace equipment.

[0037] This invention also provides the application of the above-mentioned shape memory polyimide aerogel in advanced weapons, spacecraft, and spacesuits.

[0038]

Beneficial Effects of the Invention

[0039] This invention utilizes dimethyl sulfoxide (DMSO) as a solvent to dissolve polyamic acid, forming ice crystals within the solution through freezing, and then removing the ice crystals via freeze-drying to create pores and produce a polyamic acid aerogel. Finally, thermal imidization treatment yields the final polyimide aerogel. This method provides a low-cost and simple polyimide aerogel preparation process, avoiding the complex steps of polyamic acid precipitation and re-dissolution. It overcomes the limitation of non-crosslinked polyimide aerogels in forming a stable three-dimensional framework, and allows for the induction and control of the ice crystal growth process to create different pore structures within the aerogel.

[0040] This invention designs the molecular structure of polyimide and balances the ratio of soft and hard segments within the polyimide molecular structure by regulating the flexibility of the diamine and dianhydride that make up the polyimide and the number of benzene rings. This further regulates the mobility and physical entanglement of molecular chain segments, greatly improving the shape memory performance of polyimide aerogel.

[0041] The shape memory polyimide aerogel prepared by this invention has high porosity (94-97%) and excellent thermal stability (450-500℃), making it suitable for extreme environments. Attached Figure Description

[0042] Figure 1 The shape memory curves of the shape memory polyimide aerogels prepared in Example 1(a), Comparative Example 1(b), Comparative Example 2(c), and Comparative Example 3(d) were measured in a dynamic thermomechanical analyzer.

[0043] Figure 2 Scanning electron microscope images of the shape memory polyimide aerogels prepared in Example 1(a), Comparative Example 1(b), Comparative Example 2(c), and Comparative Example 3(d);

[0044] Figure 3 The images show a comparison of the original shape (a), temporary shape (b), and shape (c) after shape recovery under thermal stimulation of the shape memory polyimide aerogel prepared in Example 1 of this invention. Detailed Implementation

[0045] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0046] In addition, the experimental methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0047] The preparation steps of a shape memory polyimide aerogel are as follows:

[0048] 1) Preparation of polyamic acid precursor: Polyamic acid precursor was obtained by polymerizing diamine and dianhydride in a molar ratio of (1:1.02) in dimethyl sulfoxide.

[0049] 2) Pour the polyamic acid solution into a mold, freeze it to form a solid shape, and then freeze-dry it to remove the solvent.

[0050] 3) The freeze-dried polyamic acid block was placed in a tube furnace for thermal imidization to obtain the final shape memory polyimide aerogel.

[0051] In step 1), the diamine monomer is first dissolved in DMSO. After the diamine monomer is completely dissolved, the dianhydride monomer is added and the reaction continues to obtain polyamic acid. The solid content of the polyamic acid solution is 10-20%. The dianhydride monomers include: bisphenol A type diether dianhydride (BPADA, 98%), pyromellitic dianhydride (PMDA, 98%), and hexafluoroisopropylphthalic anhydride (6FDA, 98%). The diamine monomers include: 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP, 98%), 4,4'-diaminodiphenyl ether (ODA, 98%), and 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP, 98%). After the polyamic acid in the three-necked flask exhibits the phenomenon of rod climbing, the mixture is stirred continuously for 1-2 hours to obtain the target polyamic acid.

[0052] In step 2), dimethyl sulfoxide is added to the polyamic acid filament for dilution, resulting in a polyamic acid solution with a solid content of 5-8%. Liquid nitrogen is first poured into a foam box to create a low-temperature liquid nitrogen atmosphere. When placing the mold into the foam box, foam-like insulating material is placed at the bottom to ensure the mold does not directly contact the liquid nitrogen, allowing the polyamic acid solution to cool evenly within the mold. After the temperature atmosphere stabilizes, the mold containing the polyamic acid solution is placed in the foam box for freezing. Once the polyamic acid is completely frozen, it is placed in a freeze dryer for freeze-drying. During freeze-drying, the temperature is -40 to -50°C, the freeze-drying time is 36 to 72 hours, and the vacuum degree is 15 to 25 Pa.

[0053] In step 3), the freeze-dried polyamic acid is removed from the mold, wrapped in aluminum foil, and placed in a tube furnace for thermal imidization. During thermal imidization, the tube furnace heats up at a rate of 1–2 K / min, and is held at 150°C, 250°C, and 300°C for half an hour each. The process ends when the tube furnace reaches 300°C and holds at that temperature. The aerogel is then removed, and the shape memory polyimide aerogel is complete.

[0054] The relevant testing process is as follows:

[0055] Thermal insulation performance test: The thermal conductivity of the aerogel was tested using a thermal constant analyzer at room temperature (30℃). The heating power was 5mW and the heating time was 10s.

[0056] High temperature resistance test: The thermal stability of PI-1, PI-2, PI-3 and PI-4 was analyzed using a thermogravimetric analyzer. The gas atmosphere was nitrogen and the heating rate was 10℃ / min.

[0057] Shrinkage test: The shrinkage rate is calculated using the formula "Shrinkage(%)=(V0-V) / V0×100%", where V0 is the volume of polyamic acid after lyophilization and V is the volume of the final aerogel sample.

[0058] Apparent density: The apparent density of aerogels is calculated using the formula... Calculate, where ρ0 is the apparent density of the sample; m is the mass of the sample; and V is the volume of the final aerogel sample.

[0059] Porosity: The porosity of aerogels can be calculated using the following formula: P = (1 - ρ0 / ρ) × 100%, where ρ0 is the apparent density of the aerogel, ρ is the bulk density of the material, and the bulk density of PI is 1.38 g / cm³. 3 .

[0060] Example 1

[0061] 4.18 g of 2,2-bis[4-(4-aminophenoxy)phenyl]propane (10 mmol) was placed in a three-necked flask, followed by the addition of 45 ml of dimethyl sulfoxide. The mixture was mechanically stirred until the 2,2-bis[4-(4-aminophenoxy)phenyl]propane was completely dissolved. Stirring continued, and 5.42 g of bisphenol A diether dianhydride (10.2 mmol) was slowly added, followed by the addition of 10 ml of dimethyl sulfoxide. After the polyamic acid in the three-necked flask exhibited a rod-climbing phenomenon, stirring was continued for 1 hour to obtain the target polyamic acid.

[0062] 127 ml of dimethyl sulfoxide was added to a three-necked flask for dilution, resulting in a polyamic acid solution with a solid content of 5 wt%. The solution was poured into a mold, which was then placed in a liquid nitrogen atmosphere for freezing for 1 hour. After the polyamic acid solution was completely frozen, it was placed in a freeze dryer for freeze-drying. During freeze-drying, the temperature was -50°C, the freeze-drying time was 72 hours, and the vacuum degree was 15 Pa. The freeze-dried polyamic acid was removed from the mold, wrapped in aluminum foil, and placed in a tube furnace for thermal imidization. During thermal imidization, the tube furnace temperature rise rate was 2 K / min, and the temperature was successively held at 150°C, 250°C, and 300°C for half an hour. The process ended when the tube furnace reached 300°C and held at that temperature. The aerogel was then removed, and the shape memory polyimide aerogel was prepared and designated as PI-1. The apparent density of the obtained aerogel was 0.0764 g / cm³.3 The porosity is 94.45%.

[0063] Comparative Example 1

[0064] A method for preparing shape memory polyimide aerogel material is disclosed, as described in Example 1, except that 10 mmol / L 2,2-bis[4-(4-aminophenoxy)phenyl]propane is replaced with 10 mmol / L 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane. All other steps and conditions are the same as in Example 1. The resulting polyimide aerogel is designated as PI-2. The apparent density of the obtained aerogel is 0.0835 g / cm³. 3 The porosity is 94%.

[0065] Comparative Example 2

[0066] A method for preparing shape memory polyimide aerogel material is disclosed, as described in Example 1, except that 10.2 mmol / L bisphenol A type diether dianhydride is replaced with 10.2 mmol / L pyromellitic dianhydride; the other steps and conditions are the same as in Example 1. The polyimide aerogel is designated as PI-3 upon completion. The apparent density of the obtained aerogel is 0.1157 g / cm³. 3 The porosity is 91.17%.

[0067] Comparative Example 3

[0068] A method for preparing shape memory polyimide aerogel material is disclosed, as described in Example 1, except that 10.2 mol / L bisphenol A type diether dianhydride is replaced with 10.2 mol / L hexafluoroisopropylphthalic anhydride, and 10 mol / L 2,2-bis[4-(4-aminophenoxy)phenyl]propane is replaced with 10 mol / L 4,4'-diaminodiphenyl ether. All other steps and conditions are the same as in Example 1. The polyimide aerogel is designated as PI-4. The apparent density of the obtained aerogel is 0.1135 g / cm³. 3 The porosity is 91.78%.

[0069] Experimental Example 1

[0070] The shape memory polyimide aerogel materials prepared in the examples and comparative examples were tested for thermal insulation performance, high temperature resistance, and shrinkage rate. The test data are shown in Table 1 below.

[0071] Table 1

[0072] PI-1 0.044 470 215 22 PI-2 0.058 480 220 24 PI-3 0.074 420 320 35 PI-4 0.070 460 330 31

[0073] Experimental Example 2

[0074] The shape memory function of the polyimide aerogels prepared in the examples and comparative examples was tested. The test methods are as follows:

[0075] Polyimide aerogel samples measuring 7mm x 2mm x 25mm were placed in a dynamic thermomechanical analyzer and fixed using a tensile clamp. The heating program was initiated, raising the temperature to 10°C above the glass transition temperature (GTH). The temperature was held for 10 minutes to allow the polyimide aerogel to soften sufficiently. Then, a 0.5N force was applied to the polyimide aerogel to stretch it. A cooling program was then initiated, lowering the temperature inside the test chamber to 100°C (GTH) and holding for 2 minutes to fix the aerogel shape. The length change of the stretched polyimide aerogel was recorded. After removing the additional force, the temperature was raised again at 5K / min to 10°C above the GTH and held for 10 minutes. The recovery process of the sample length as the temperature increased was recorded. This process is called one cycle of shape memory testing. Each sample undergoes three cycles per test.

[0076] The results of the shape memory test under thermal stimulation are as follows Figure 1 As shown, Figure 1 (a) is the shape memory loop diagram of PI-1. Figure 1 (b) Shape memory cycle diagram of PI-2 Figure 1 (c) Shape memory loop diagram of PI-3. Figure 1 (d) Shape memory loop diagram of PI-4.

[0077] Based on the shape memory cycle diagram analysis, the shape fixation rate and recovery rate of PI-1, PI-2, PI-3, and PI-4 are recorded in Table 2.

[0078] Table 2

[0079]

[0080] As can be seen, the polyimide aerogel prepared in Example 1 of this invention achieved a fixation rate of over 98% and over 96% in three cycles, demonstrating excellent shape memory properties.

[0081] Experimental Example 3

[0082] The polyimide aerogels prepared in the examples and comparative examples were observed using a scanning electron microscope as follows: Figure 2 As shown. Among them. Figure 2 (a) Corresponding to Example 1, Figure 2 (b) For Comparative Example 1, Figure 2 (c) Corresponding to ratio 2, Figure 2 (d) Response ratio 3.

[0083] It can be seen that the aerogel obtained in Example 1 has a relatively regular and uniform pore structure formed inside it due to the growth of ice crystals, and the pore size is distributed between 50-100μm.

[0084] Test Example 4

[0085] The test method is as follows: In Example 1, the polyimide aerogel was placed in a 240°C oven for 5 minutes until it was completely softened. Pressure was then applied to the polyimide aerogel to deform it, maintaining its shape. The aerogel was then placed in a liquid nitrogen atmosphere to fix its temporary shape. Subsequently, the aerogel was returned to the 240°C oven atmosphere to thaw the internal molecular chain segments of the polyimide aerogel, releasing the stored stress and restoring its shape.

[0086] Test results are as follows Figure 3 As shown, Figure 3 (a) shows the initial shape of the polyimide aerogel. Figure 3 (b) is the temporary shape after deformation. Figure 3 (c) The shape after returning to the glass transition temperature for 3 seconds.

[0087] Effect of different solvents in Comparative Example 4

[0088] Referring to Example 1, dimethyl sulfoxide was replaced with an equal volume of another aprotic polar solvent, while other aspects remained unchanged. The results are shown in Table 3.

[0089] Table 3

[0090] N,Nˋ-Dimethylformamide no N,Nˋ-Dimethylacetamide no N-Methylpyrrolidone no

[0091] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A method for preparing shape memory polyimide aerogel, characterized in that, Polyamic acid was dissolved using dimethyl sulfoxide as a solvent, ice crystals were formed inside the solution by freezing, and the ice crystals were removed by freeze drying to create pores and produce polyamic acid aerogel. Finally, the final polyimide aerogel was produced by thermal imidization treatment. Includes the following steps: 1) Preparation of polyamic acid precursor: Polyamic acid precursor solution is obtained by polymerizing diamine and dianhydride in dimethyl sulfoxide. 2) The polyamic acid precursor solution was further diluted with dimethyl sulfoxide, then poured into a mold and frozen to form a solid shape. Subsequently, the solvent was removed by freeze drying to obtain a polyamic acid block. 3) The obtained polyamic acid block is subjected to high-temperature treatment to undergo thermal imidization, resulting in shape memory polyimide aerogel; In step 1), the molar ratio of diamine to dianhydride is (0.8-1.2):1; In step 1), the diamine monomer is 2,2-bis[4-(4-aminophenoxy)phenyl]propane; the dianhydride monomer is bisphenol A type diether dianhydride; In step 2), dimethyl sulfoxide is added to the polyamic acid precursor solution to dilute it so that the solid content in the polyamic acid solution is 5-8 wt%.

2. The preparation method according to claim 1, characterized in that, In step 1), the diamine monomer is first dissolved in dimethyl sulfoxide. After the diamine monomer is completely dissolved, the dianhydride monomer is added, and the reaction continues to obtain polyamic acid. When the polyamic acid exhibits the rod-climbing phenomenon, stirring is continued for 1-2 hours to obtain a polyamic acid precursor solution. The solid content in the polyamic acid precursor solution is 10~20wt%.

3. The preparation method according to claim 1, characterized in that, In step 2), the freeze-drying process is carried out at a temperature of -40 to -50°C, a freeze-drying time of 36 to 72 hours, and a vacuum degree of 15 to 25 Pa.

4. The preparation method according to any one of claims 1-3, characterized in that, In step 3), the high temperature is 150-300℃.

5. A shape memory polyimide aerogel prepared by the method according to any one of claims 1-4.

6. The application of the shape memory polyimide aerogel according to claim 5 in aerospace equipment.

7. The application of the shape memory polyimide aerogel according to claim 5 in advanced weapons, spacecraft, and spacesuits.

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