Preparation method of an atomic oxygen resistant polyimide composite film

Abstract

The application relates to a preparation method of an atomic oxygen-resistant polyimide composite film, which comprises the following steps: (1) preparing a polyamide acid PAA stock solution; (2) preparing a polyamide acid salt PAAS aqueous solution; (3) adding a silicon source into the PAAS aqueous solution and fully stirring to form a homogeneous solution; (4) preparing a semi-cured gel film; and (5) preparing the atomic oxygen-resistant polyimide composite film. The composite film has the characteristics of a SiO2 / PI interpenetrating network structure, has excellent atomic oxygen resistance, solves the problems of poor dispersion of silicon dioxide in the polyimide film, poor blending compatibility, poor interface effect and poor performance of the composite film, and the prepared film has excellent optical performance and mechanical performance and can be used as a material of a near-earth orbit space spacecraft.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and particularly relates to a preparation method of an atomic oxygen resistant polyimide composite film. BACKGROUND

[0002] Polyimide material refers to a kind of organic high-performance material containing imide structure in a molecular chain. The unique molecular structure makes it have superior mechanical properties, heat resistance and radiation resistance, which are outstanding. Therefore, the material becomes one of the important key strategic materials in the field of space exploration, and is widely used in spacecraft thermal control components, electronic devices, substrates of solar cells and the like.

[0003] However, space stations, space ships, space shuttles and most satellites and other space vehicles mainly operate in the earth orbit (Low Earth Orbit, LEO) with a height of 200-700 km. At this height, due to the high-vacuum state, atomic oxygen (Atomic Oxygen, AO) with strong oxidation formed by the photodissociation of oxygen by ultraviolet light with a wavelength of 160-240 nm cannot collide with the third particle capable of taking away the energy released by the combination of two free-state atomic oxygen to maintain the form of atomic oxygen. In the case that the spacecraft orbits at a speed of about 7 km / s, the beam density of atomic oxygen impacting the spacecraft can reach 10 12 ~10 16 cm -2 s -1 , the impact kinetic energy is as high as 4-5 eV, which can cause the chemical bonds of many spacecraft materials to break, and further cause the surface morphology of the material to change, the mass loss and the degradation of various properties, which seriously affects the chemical structure and service performance of the material. Therefore, improving the atomic oxygen resistance of polyimide film is of great significance for the application of the material in the low earth orbit environment.

[0004] At present, there are mainly three ways to improve the atomic oxygen resistance of PI film.

[0005] (1) Directly coating or evaporating an atomic oxygen resistant protective film such as SiO2, Al2O3, TiO2, SnO2 and the like inorganic coating on the surface of PI substrate. The inorganic oxide coating has high atomic oxygen resistance, can protect the film substrate, and will not affect the performance of the substrate. However, the coating is prone to cracking or peeling off, which can cause the atomic oxygen to impact the material surface with a certain probability to produce the etching effect, and cause greater damage to the PI substrate.

[0006] (2) Introducing some groups containing specific elements (e.g. P, Si, F, etc.) into the molecular structure of PI, using the characteristics of improving the oxidation resistance of PI or generating a passivation layer with atomic oxygen to improve the atomic oxygen resistance of PI. Although this method can improve the atomic oxygen resistance of PI to some extent, the phosphorus-containing thin film has high brittleness and low glass transition temperature (T g ), the silicon-containing thin film has low modulus and high thermal expansion coefficient, and the fluorine-containing thin film is sensitive to ultraviolet light and is prone to degradation, which are difficult to be practically applied.

[0007] (3) Mixing the AO-resistant filler with PI through physical or chemical blending to improve the AO resistance of PI film. For example, SiO2, Al2O3, polyhedral oligomeric silsesquioxane (POSS), graphene (GO), etc. are mixed with polyamic acid (PAA) or PI polymerization solution, the mixed solution is coated into a film, and after heat treatment, a composite film with good AO resistance is obtained. Some researches and patents use sol-gel method to prepare SiO2 (e.g. CN104603183A). Common silicon sources include silicates and silicates, and solvents can be selected from water or alcohols. First, the silicon source is mixed with the solvent in a certain proportion to form a sol. Then, by adjusting the pH value (7-11.5), temperature and time, the silicon source is gradually polymerized in the sol to form a gel. After the gel is formed, drying and sintering treatment are required to remove the solvent in the gel, and finally the silicon dioxide powder is formed. However, the addition of fillers will significantly affect the processing performance and impact toughness of the material, and the fillers often agglomerate, which is difficult to achieve a highly dispersed state, thus it is not conducive to providing comprehensive protection to the PI film. SUMMARY

[0008] The technical problem to be solved by the present application is to provide a preparation method of an atomic oxygen-resistant polyimide composite film, which solves the problems of poor dispersion of silicon dioxide in the polyimide film, poor blending compatibility, poor interfacial action and poor performance of the composite film, and the prepared film has excellent optical and mechanical properties and can be used as a material for near-earth orbit space spacecraft.

[0009] The present application provides a preparation method of an atomic oxygen-resistant polyimide composite film, comprising the following steps:

[0010] (1) mixing diamine and dianhydride, then putting them into a solvent and reacting under nitrogen protection and ice water bath conditions to obtain polyamic acid PAA stock solution;

[0011] (2) adding a poor solvent to the polyamic acid stock solution prepared in step (1) to precipitate PAA solid, and after drying treatment, dissolving it in a water solution containing a tertiary amine compound to obtain a polyamic acid salt PAAS aqueous solution;

[0012] (3) adding a silicon source into the PAAS aqueous solution prepared in step (2) and stirring thoroughly for 6-12 h to form a homogeneous solution;

[0013] (4) forming a film on a substrate from the homogeneous solution prepared in step (3), drying to obtain a semi-cured gel film;

[0014] (5) placing the semi-cured gel film prepared in step (4) on a super-clean bench for standing, and after the silanol is converted into a SiO2 network structure, placing it in an oven to remove water to obtain a SiO2 / PAA composite film; finally, heat treatment is performed, and after the temperature drops to room temperature, an atomic oxygen resistant polyimide composite film is obtained.

[0015] Preferably, the diamine in step (1) includes one or more of p-phenylenediamine (PDA), diaminodiphenylmethane (MDA), 4,4'-diaminodiphenyl ether (ODA), 2-(4-aminophenyl)-5-aminobenzimidazole (BIA), and 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB).

[0016] Preferably, the dianhydride in step (1) includes one or more of pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), and hexafluoro dianhydride (6FDA).

[0017] Preferably, the solvent in step (1) includes one or more of N,N'-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and N,N'-dimethylformamide (DMF).

[0018] Preferably, the molar ratio of the diamine to the dianhydride in step (1) is 1:0.98-1.02; and the sum of the mass of the diamine and the dianhydride accounts for 5-20% of the total mass of the reaction system.

[0019] Preferably, the poor solvent in step (2) includes one or more of acetone, ethanol, methanol, and tert-butanol.

[0020] Preferably, the tertiary amine compound in step (2) includes one or more of 1,2-dimethylimidazole (DMIZ), isoquinoline, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and N,N-dimethylaniline, and the molar ratio of the tertiary amine compound to the diamine is 2-4:1. The tertiary amine compound has a high boiling point to ensure that it remains in the gel film during the gradual evaporation of the deionized water, thereby gradually increasing the pH value and promoting the formation of a silica network structure.

[0021] Preferably, the silicon source in the step (3) comprises one or more of tetraethoxysilane (TEOS), methyltriethoxysilane (MTES), and propyltrimethoxysilane (PTS), and the mass ratio of the silicon source to the polyamic acid is 0.2-2:1.

[0022] Preferably, the process conditions for the drying in the step (4) are as follows: the vacuum pressure is-0.06--0.1 MPa, the temperature is 40-80 ℃, the holding time is 2-4 h, and the pH of the semi-cured gel film ranges from 7 to 11.5, at which the silica gel can be stably present. By adjusting the vacuum degree and the temperature of the oven, the evaporation speed of the solvent and the volatilization of the organic base can be finely controlled, and the semi-cured gel film is obtained.

[0023] Preferably, the process conditions for the heat treatment in the step (5) are as follows: under vacuum or nitrogen protection, a gradient heating process is adopted, the temperature ranges from 100 to 350 ℃, the heating rate is 1-5 ℃ / min, the holding time is 30 min per 100 ℃, and the holding time is 30-60 min when the final temperature is reached.

[0024] Preferably, the standing time in the step (5) is 12-24 h.

[0025] Advantages

[0026] The present application can be applied to various polyimide structures, and the reaction conditions are mild and the product is stable, which is conducive to batch production and product quality control. The prepared composite film has the characteristics of SiO2 / PI interpenetrating network structure, and solves the problems of poor dispersion, poor blending compatibility, poor interface effect, and poor performance of the composite film. The film has excellent optical and mechanical properties and excellent atomic oxygen resistance, and can be used as a material for near-earth orbit spacecraft. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The photograph of the PAAS aqueous solution obtained in Example 1.

[0028] Figure 2 From left to right are digital photographs of the composite films of Example 1 (a), Comparative Example 1 (b), and Comparative Example 2 (c).

[0029] Figure 3 The mechanical strength diagram of the composite films of Example 1, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION

[0030] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not used to limit the scope of the application. Furthermore, it should be understood that after reading the content of the application, those skilled in the art can make various modifications or changes to the application, and these equivalent forms also fall within the scope of the appended claims.

[0031] Example 1

[0032] A clean 100 mL three-necked flask was selected, 0.7072 g PDA and 1.9243 g BPDA and 50 g N,N'-dimethylacetamide (DMAc) were added, and stirring was carried out under N2 protection and ice water bath conditions for 24 h to obtain a PAA solution; the obtained PAA solution was precipitated in ethanol, washed multiple times and dried to obtain PAA powder; then the PAA powder was added into an aqueous solution containing 1.5718 g DMIZ (solid content was calculated as 5%), and stirring was carried out at 40 ℃ for 6 h to obtain a uniform polyamide acid salt aqueous solution; 1.3157 g TEOS was added into the polyamide acid salt aqueous solution, and after uniform stirring, the solution was scraped and coated into a 500 μm thin film, and placed in a vacuum oven for 4 h to obtain a gel film, and the pH was measured as 11, the vacuum pressure was-0.1 MPa, and the temperature was 40 ℃; then it was placed in an ultra-clean bench for 24 h, and the obtained thin film was gradiently heated at 100-350 ℃ at a rate of 3 ℃ / min, and finally heat treated at 350 ℃ for one hour to obtain a composite thin film. The tensile strength was 236 MPa, the modulus was 3.55 GPa, and the atomic oxygen erosion rate of the thin film was 0.15×10 20 atoms / cm 2 when the cumulative flux of atomic oxygen was 8.1×10 -24 cm 3 / atom.

[0033] Comparative Example 1

[0034] A clean 100 mL three-necked flask was selected, 0.7072 g PDA and 1.9243 g BPDA and 50 g N,N'-dimethylacetamide (DMAc) were added, and stirring was performed under N2 protection and ice water bath conditions for 24 h to obtain a uniform polyamide acid solution; 1.3157 g TEOS was added to the polyamide acid solution, and after uniform stirring, the solution was scraped to form a 500 μm film, which was placed in a vacuum oven for 4 h to obtain a gel film, the vacuum pressure was -0.1 MPa, and the temperature was 40 ℃; then it was placed in a super-clean bench for 24 h, and the obtained film was gradiently heated at 100-350 ℃, the rate was 3 ℃ / min, and finally it was kept at 350 ℃ for 1 h, to obtain a composite film. The tensile strength was 130 MPa, the modulus was 2.29 GPa, and when the cumulative atomic oxygen flux was 8.1×10 20 atoms / cm 2 , the atomic oxygen erosion rate of the film was 0.89×10 -24 cm 3 / atom.

[0035] Comparative Example 2

[0036] A clean 100 mL three-necked flask was selected, 0.7072 g PDA and 1.9243 g BPDA and 50 g N,N'-dimethylacetamide (DMAc) were added, and stirring was performed under N2 protection and ice water bath conditions for 24 h to obtain a uniform polyamide acid solution; the obtained PAA solution was precipitated in ethanol, and after multiple washing and drying, PAA powder was obtained; then the PAA powder was added to an aqueous solution containing 1.6545 g triethylamine (the solid content was calculated as 5%), and stirring was performed at 40 ℃ for 6 h; then 1.3157 g TEOS was added, and after uniform stirring, the solution was scraped to form a 500 μm film, which was placed in a vacuum oven for 4 h to obtain a gel film, the vacuum pressure was -0.1 MPa, and the temperature was 40 ℃, and the pH was measured to be 4.5; it was placed in a super-clean bench for 24 h, and the obtained film was gradiently heated at 100-350 ℃, the rate was 3 ℃ / min, and finally it was kept at 350 ℃ for 1 h, to obtain a composite film. The tensile strength was 163 MPa, the modulus was 2.46 GPa, and when the cumulative atomic oxygen flux was 8.1×10 20 atoms / cm 2 , the atomic oxygen erosion rate of the film was 0.76×10 -24 cm 3 / atom.

[0037] Comparative Example 3

[0038] A clean 100 mL three-necked flask was filled with 0.7072 g of PDA, 1.9243 g of BPDA, and 50 g of N,N'-dimethylacetamide (DMAc). The mixture was stirred under nitrogen in an ice-water bath for 24 h to obtain a PAA solution. The resulting PAA solution was precipitated in ethanol, washed multiple times, and dried to obtain a PAA powder. The PAA powder was then added to an aqueous solution containing 1.6545 g of triethylamine (5% solids content) and stirred at 40°C for 6 h. 1.3157 g of TEOS was then added and stirred until homogeneous. The solution was then doctor-coated to form a 500 μm film and allowed to stand in a clean bench for 24 h. The resulting film was then heated gradually from 40 to 350°C at a rate of 3°C / min, and finally held at 350°C for one hour to obtain a composite film. The composite film exhibited a tensile strength of 112 MPa, a modulus of 1.33 GPa, and a cumulative atomic oxygen flux of 8.1×10 20 atoms / cm 2 When the atomic oxygen erosion rate of the film is 0.83×10 -24 cm 3 / atom.

[0039] Example 2

[0040] A clean 100 mL three-necked flask was added with 0.7072 g PDA, 1.9243 g BPDA, and 50 g N,N'-dimethylacetamide (DMAc). The mixture was stirred under N2 protection and an ice-water bath for 24 h to obtain a PAA solution. The PAA solution was precipitated in ethanol, washed several times, and dried to obtain a PAA powder. The PAA powder was then added to an aqueous solution containing 1.5718 g DMIZ (solid content calculated as 5%) and stirred at 40 °C for 6 h to obtain a uniform mixed solution. 1.3157 g TEOS was then added and stirred until uniform. The solution was then doctor-coated into a 500 μm film and placed in a vacuum oven for 1 h at a vacuum pressure of -0.1 MPa and a temperature of 40 °C to obtain a gel film. The measured pH was 9. After standing for 24 h, the obtained film was gradually heated from 100 to 350 °C at a heating rate of 3 °C / min and finally at 350 °C. ℃ for one hour to obtain a composite film with a tensile strength of 225 MPa, a modulus of 3.08 GPa, and an atomic oxygen cumulative flux of 8.1×10 20 atoms / cm 2 When the atomic oxygen erosion rate of the film is 0.26×10 -24 cm 3 / atom.

[0041] Example 3

[0042] A clean 100 mL three-necked flask was added with 1.2595 g ODA, 1.3721 g PMDA, and 50 g N,N'-dimethylacetamide (DMAc). The mixture was stirred under N2 protection and an ice-water bath for 24 h to obtain a PAA solution. The PAA solution was precipitated in ethanol, washed several times, and dried to obtain a PAA powder. The PAA powder was then added to an aqueous solution containing 1.5718 g DMIZ (solid content calculated as 5%) and stirred at 40 °C for 6 h to obtain a uniform mixed solution. 1.3157 g TEOS was then added and stirred evenly. The solution was then doctor-coated into a 500 μm film and placed in a vacuum oven for 4 h to obtain a gel film with a measured pH of 11. The vacuum pressure was -0.1 MPa and the temperature was 40 °C. After standing for 24 h, the obtained film was gradually heated from 100 to 350 °C at a rate of 3 °C / min and finally at 350 °C. ℃ for one hour to obtain a composite film with a tensile strength of 212 MPa, a modulus of 3.02 GPa, and an atomic oxygen cumulative flux of 8.1×10 20 atoms / cm 2 When the atomic oxygen erosion rate of the film is 0.35×10 -24 cm 3 / atom.

[0043] Comparative Example 4

[0044] A clean 100 mL three-necked flask was added with 1.2595 g of ODA, 1.3721 g of PMDA, and 50 g of N,N'-dimethylacetamide (DMAc). The mixture was stirred under N2 protection and an ice-water bath for 24 h to obtain a PAA solution. The PAA solution was then applied as a 500 μm film. The film was then placed in a vacuum oven for 24 h to obtain a PAA film. The vacuum pressure was -0.1 MPa and the temperature was 80 °C. The film was then heated gradually from 100 to 350 °C at a rate of 3 °C / min and finally held at 350 °C for one hour to obtain a composite film. The composite film had a tensile strength of 159 MPa, a modulus of 2.76 GPa, and a cumulative flux of 8.1×10 20 atoms / cm 2 When the atomic oxygen erosion rate of the film is 3.02×10 -24 cm 3 / atom.

[0045] Example 4

[0046] A clean 100 mL three-necked flask was added with 1.1023 g TFMB, 1.5292 g 6FDA, and 50 g N,N'-dimethylacetamide (DMAc). The mixture was stirred under N2 protection and an ice-water bath for 24 h to obtain a PAA solution. The PAA solution was precipitated in ethanol, washed several times, and dried to obtain a PAA powder. The PAA powder was then added to an aqueous solution containing 1.5718 g DMIZ (solid content calculated as 5%) and stirred at 40 °C for 6 h to obtain a uniform mixed solution. 1.3157 g TEOS was then added and stirred evenly. The solution was then doctor-coated into a 500 μm film and placed in a vacuum oven for 4 h to obtain a gel film. The measured pH was 11, the vacuum pressure was -0.1 MPa, and the temperature was 40 °C. After standing for 24 h, the obtained film was gradually heated from 100 to 350 °C at a rate of 3. ℃ / min, and finally kept at 350 ℃ for one hour to obtain a composite film with a tensile strength of 192 MPa, a modulus of 2.85 GPa, and an atomic oxygen cumulative flux of 8.1×10 20 atoms / cm 2 When the atomic oxygen erosion rate of the film is 0.09×10 -24 cm 3 / atom.

[0047] Example 5

[0048] A clean 100 mL three-necked flask was added with 1.6230 g BTDA, 1.008 g ODA, and 50 g N,N'-dimethylacetamide (DMAc). The mixture was stirred under N2 protection and an ice-water bath for 24 h to obtain a PAA solution. The PAA solution was precipitated in ethanol, washed several times, and dried to obtain a PAA powder. The PAA powder was then added to an aqueous solution containing 1.2105 g DMIZ (solid content calculated as 5%) and stirred at 40 °C for 6 h to obtain a uniform mixed solution. 1.3157 g TEOS was then added and stirred evenly. The solution was then doctor-coated into a 500 μm film and placed in a vacuum oven for 4 h to obtain a gel film. The measured pH was 11, the vacuum pressure was -0.1 MPa, and the temperature was 40 °C. After standing for 24 h, the obtained film was gradually heated from 100 to 350 °C at a rate of 3 ℃ / min, and finally kept at 350 ℃ for one hour to obtain a composite film with a tensile strength of 154 MPa, a modulus of 1.97 GPa, and an atomic oxygen cumulative flux of 8.1×10 20 atoms / cm 2 When the atomic oxygen erosion rate of the film is 0.43×10 -24 cm3 atoms / cm 20 atoms / cm 2 atoms / cm -24 atoms / cm 3 atoms / cm

[0049] Example 6

[0050] A clean 100 mL flask was selected, 1.9703 g of BTDA and 0.6612 g of PDA were added, and 50 g of N,N'-dimethylacetamide (DMAc) was added. The mixture was stirred under N2 protection and ice water bath conditions for 24 h to obtain a PAA solution. The obtained PAA solution was precipitated in ethanol, washed repeatedly and dried to obtain PAA powder. Then the PAA powder was added to an aqueous solution containing 1.4695 g of DMIZ (solid content was calculated as 5%), and stirred at 40°C for 6 h to obtain a uniform mixed solution. Then 1.3157 g of TEOS was added, and the solution was uniformly stirred and scraped to form a 500 μm thin film. The solution was scraped to form a 500 μm thin film, and the solution was placed in a vacuum oven for 4 h to obtain a gel film. The pH was measured to be 11, the vacuum pressure was -0.1 MPa, and the temperature was 40°C. After standing for 24 h, the obtained thin film was gradiently heated at 100-350°C at a rate of 3°C / min, and finally heat treated at 350°C for one hour to obtain a composite film. The tensile strength was 215 MPa, the modulus was 2.66 GPa, and the atomic oxygen erosion rate of the film was 0.29×10 20 atoms / cm 2 atoms / cm -24 atoms / cm 3 atoms / cm

[0051] Example 7

[0052] A clean 100 mL flask was selected, 1.4933 g of BTDA and 1.1382 g of BIA were added, and 50 g of N,N'-dimethylacetamide (DMAc) was added. The mixture was stirred under N2 protection and ice water bath conditions for 24 h to obtain a PAA solution. The obtained PAA solution was precipitated in ethanol, washed repeatedly and dried to obtain PAA powder. Then the PAA powder was added to an aqueous solution containing 1.2198 g of DMIZ (solid content was calculated as 5%), and stirred at 40°C for 6 h to obtain a uniform mixed solution. Then 1.3157 g of TEOS was added, and the solution was uniformly stirred and scraped to form a 500 μm thin film. The solution was scraped to form a 500 μm thin film, and the solution was placed in a vacuum oven for 4 h to obtain a gel film. The pH was measured to be 11, the vacuum pressure was -0.1 MPa, and the temperature was 40°C. After standing for 24 h, the obtained thin film was gradiently heated at 100-350°C at a rate of 3°C / min, and finally heat treated at 350°C for one hour to obtain a composite film. The tensile strength was 215 MPa, the modulus was 2.66 GPa, and the atomic oxygen erosion rate of the film was 0.29×10 20 atoms / cm 2 atoms / cm -24 atoms / cm 3 atoms / cm20 atoms / cm 2 When the thin film is exposed to the atomic oxygen for 1 hour, the atomic oxygen erosion rate of the thin film is 0.35 x 10 -24 cm 3 / atom.

Claims

1. A method for preparing an atomic oxygen resistant polyimide composite film, characterized in that: The steps include: (1) mixing diamine and dianhydride and adding them into a solvent, reacting them under nitrogen protection and ice water bath conditions to obtain polyamic acid PAA stock solution; (2) adding a poor solvent to the polyamic acid stock solution obtained in step (1) to precipitate PAA solid, drying the solid, and dissolving the solid in an aqueous solution containing a tertiary amine compound to obtain a polyamic acid salt PAAS aqueous solution; wherein the tertiary amine compound includes one or more of 1,2-dimethylimidazole, isoquinoline, 1,8-diazabicyclo[5.4.0]undec-7-ene, and N,N-dimethylaniline; (3) adding a silicon source to the PAAS aqueous solution obtained in step (2) and stirring the mixture for 6-12 hours to form a PAAS / silanol mixed solution; (4) forming a film of the PAAS / silanol mixed solution obtained in step (3) on a substrate and drying the film to obtain a semi-cured gel film; (5) The semi-cured gel film obtained in step (4) is placed on a clean bench for standing. After the silanol is converted into a SiO2 network structure, it is placed in an oven to remove moisture to obtain a SiO2 / PAA composite film; finally, heat treatment is performed, and after the temperature drops to room temperature, an atomic oxygen-resistant polyimide composite film is obtained.

2. The preparation method according to claim 1, wherein: The diamine in step (1) includes one or more of p-phenylenediamine, diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, and 2,2'-bis(trifluoromethyl)diaminobiphenyl.

3. The preparation method according to claim 1, wherein: The dianhydride in step (1) includes one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and hexafluorodianhydride.

4. The preparation method according to claim 1, wherein: The solvent in step (1) includes one or more of N,N′-dimethylacetamide, N-methylpyrrolidone, and N,N′-dimethylformamide.

5. The preparation method according to claim 1, wherein: The molar ratio of the diamine to the dianhydride in the step (1) is 1:0.98-1.02; the sum of the masses of the diamine and the dianhydride accounts for 5-20% of the total mass of the reaction system.

6. The preparation method according to claim 1, wherein: The poor solvent in step (2) includes one or more of acetone, ethanol, methanol, and tert-butanol.

7. The preparation method according to claim 1, wherein: The molar ratio of the tertiary amine compound to the diamine in step (2) is 2 to 4:

1.

8. The preparation method according to claim 1, wherein: The silicon source in step (3) includes one or more of tetraethoxysilane, methyltriethoxysilane, and propyltrimethoxysilane, and the mass ratio of the silicon source to the polyamic acid is 0.2 to 2:

1.

9. The preparation method according to claim 1, wherein: The process conditions for drying in step (4) are: The vacuum pressure is -0.06 to -0.1 MPa, the temperature is 40 to 80° C., and it is maintained for 2 to 4 hours. The pH range of the semi-cured gel film is 7 to 11.

5.

10. The preparation method according to claim 1, characterized in that: The process conditions of the heat treatment in step (5) are: Under vacuum or nitrogen protection conditions, a gradient heating process is adopted with a temperature range of 100-350°C, a heating rate of 1-5°C / min, and a holding time of 30 minutes for each 100°C. When the final temperature is reached, the temperature is kept for 30-60 minutes.

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