Preparation method of high-temperature-resistant high-strength polyimide composite material

Abstract

The invention discloses a preparation method of a high-temperature-resistant high-strength polyimide composite material, and relates to the technical field of polyimide composites.The preparation method comprises the following preparation steps that S1, a customized silane coupling agent is prepared; s2, preparing a bionic dynamic interface modified reinforcing filler, wherein the modified reinforcing filler is synergistically modified through a bionic coating and a customized silane coupling agent; and S3, preparing a polyimide precursor solution containing the dynamic network. According to the preparation method of the high-temperature-resistant high-strength polyimide composite material, through the integrated design of'customized silane coupling agent + bionic dynamic interface modification + dynamic network-containing polyimide precursor + gradient hot-pressing curing ', the glass-transition temperature of the prepared composite material is greater than or equal to 335 DEG C, the tensile strength is greater than or equal to 208 MPa, and meanwhile, the thermal repair efficiency at 180-250 DEG C is greater than or equal to 87%; the technical bottleneck that high temperature resistance, mechanical strength and repairing performance of the material are difficult to consider at the same time in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of polyimide composite material technology, specifically to a method for preparing a high-temperature resistant and high-strength polyimide composite material. Background Technology

[0002] Polyimide composite materials have been widely used in key fields such as aerospace, electronics and electrical engineering, and high-end equipment due to their excellent high temperature resistance, mechanical properties and chemical stability.

[0003] However, existing polyimide composite material preparation technologies still have many problems that urgently need to be solved: I. Insufficient interfacial bonding performance: Traditional reinforcing fillers (such as carbon fiber, glass fiber, etc.) have poor compatibility with the polyimide matrix, resulting in weak interfacial bonding. This leads to easy interfacial delamination of the composite material under stress or high temperature conditions, severely affecting its mechanical properties and service life. Conventional silane coupling agents can only achieve simple interfacial bonding and cannot simultaneously meet the requirements of bonding strength and functionalization. Second, the performance is limited and lacks intelligent repair function: existing high-temperature resistant polyimide composite materials focus on improving mechanical strength and thermal stability, without introducing dynamic action mechanisms. The materials are difficult to repair themselves after being damaged. Once cracks or damage occur, the machine needs to be stopped for replacement, which increases the cost of use and safety risks. Third, it is difficult to optimize high temperature resistance and high strength in a coordinated manner: some technologies sacrifice the mechanical strength of materials in order to improve high temperature resistance; while focusing on high strength design will lead to a decrease in glass transition temperature, which cannot meet the requirements of comprehensive performance under extreme working conditions.

[0004] Therefore, the present invention provides a method for preparing a high-temperature resistant and high-strength polyimide composite material to solve the above-mentioned problems. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for preparing high-temperature resistant and high-strength polyimide composite materials, thus solving the problems mentioned in the background section.

[0006] To achieve the above objectives, the present invention provides a method for preparing a high-temperature resistant, high-strength polyimide composite material, comprising the following preparation steps: S1. Preparation of customized silane coupling agents; S2. Prepare biomimetic dynamic interface modified and reinforced filler, wherein the modified and reinforced filler is synergistically modified by a biomimetic coating and a customized silane coupling agent; S3. Prepare a polyimide precursor solution containing a dynamic network, wherein the polyimide precursor solution contains dynamic covalent bond units, wherein the dynamic covalent bond is selected from at least one of disulfide bond, furan-maleimide Diels-Alder bond, and imine bond; S4. Preparation of composite slurry; S5. Gradient hot pressing curing molding, wherein the gradient hot pressing curing adopts a multi-stage temperature control-pressure coordinated process.

[0007] Preferably, the preparation steps of the customized silane coupling agent are as follows: S11. Mix magnesium powder, anhydrous tetrahydrofuran, tetrahydrofuran solution of chlorotrimethoxysilane, and tetrahydrofuran solution of (4-bromophenylethynyl)trimethylsilane. React under nitrogen protection and ice-water bath conditions. After the reaction is completed, continue the reaction at 30-35℃ in the dark for 20-24 hours. After centrifugation, take the supernatant and extract it with n-pentane. Rotary evaporate at 45℃ to obtain the solid. S12. Under ammonia protection, potassium hydroxide and anhydrous methanol are mixed until completely dissolved. An anhydrous methanol solution containing the above solid is added. The reaction is carried out at room temperature in the dark for 10-12 hours. The reaction solution is centrifuged and the supernatant is extracted with n-pentane. The supernatant is then evaporated at 40°C and washed with n-hexane 3-5 times before being dried under vacuum to obtain the basic silane coupling agent. S13. Add a modifying agent containing a disulfide bond or a furan / maleimide group to the basic silane coupling agent to prepare a customized silane coupling agent.

[0008] Preferably, the molar ratio of magnesium powder to trichlorotrimethoxysilane is 1.2:1-1.5:1, the molar ratio of (4-bromophenylethynyl)trimethylsilane to trichlorotrimethoxysilane is 1:1, and the amount of anhydrous tetrahydrofuran is 40%-60% of the total mass of the reaction system.

[0009] Preferably, the modifying agent containing disulfide bonds or furan / maleimide groups is bis(3-triethoxysilylpropyl) disulfide or 3-(furan-2-ylmethoxy)propyltriethoxysilane.

[0010] Preferably, the preparation steps of the biomimetic dynamic interface modified and reinforced filler are as follows: S21. The reinforcing filler is immersed in a Tris-HCl buffer solution with a pH of 8.0-9.0, wherein the buffer solution contains dopamine or its derivatives, and the reaction is carried out with shaking at room temperature for 6-12 hours. After centrifugation, washing and drying, a pre-modified filler with a polydopamine coating on the surface is obtained. S22. The pre-modified filler is immersed in a solution containing a customized silane coupling agent and reacted at 50-70℃ for 2-4 hours. After centrifugation, washing and drying, the modified and reinforced filler is obtained.

[0011] Preferably, the dopamine derivative is dopamine hydrochloride, methyldopamine, or norepinephrine; The reinforcing filler is selected from one or more of carbon fiber, glass fiber, aramid fiber, and silicon carbide fiber, with a diameter of 5-20 μm, a length of 1-3 mm, and a mass of 10%-40% of the total mass of polyimide monomers.

[0012] Preferably, the preparation steps of the polyimide precursor solution containing a dynamic network are as follows: Under nitrogen protection and at room temperature, aromatic diamine and 5%-15% by mass of diamine derivative containing dynamic covalent bonds are dissolved in a polar solvent. After stirring and dissolving, aromatic dianhydride and / or dianhydride derivative containing dynamic covalent bonds are slowly added in an equimolar ratio at a feeding rate of 0.5-1 g / min. After the feeding is completed, the reaction is stirred for 4-8 h to obtain a polyimide precursor solution. The mass fraction of the polyimide monomer in the solution is 15%-25%.

[0013] Preferably, the diamine derivative containing dynamic covalent bonds is 4,4'-diaminodiphenyl disulfide; the dianhydride derivative containing dynamic covalent bonds is a furan-terminated maleimide anhydride derivative; the aromatic diamine is selected from 4,4'-diaminodiphenyl ether, p-phenylenediamine, or m-phenylenediamine; the aromatic dianhydride is selected from pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, or biphenyl tetracarboxylic dianhydride; and the polar solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone.

[0014] Preferably, the preparation method of the composite slurry is as follows: the modified reinforcing filler is added to the polyimide precursor solution, stirred and dispersed at room temperature for 1-2 hours, and then ultrasonically dispersed for 30-60 minutes with an ultrasonic power of 200-400W and a temperature controlled below 30℃ to obtain a uniform composite slurry.

[0015] Preferably, the gradient hot pressing curing molding step is as follows: S51. Pour the composite slurry into a mold pre-coated with a release agent, place it in the vacuum environment of a hot press, heat it to 100-130℃ at a rate of 1-2℃ / min, and apply a pressure of 0.5-1.0MPa at the same time, and keep it at that temperature for 0.5-1.5h. S52. Increase the temperature to 260-300℃ at a rate of 2-3℃ / min, while increasing the pressure to 2.0-3.5MPa, and hold for 1.5-2.5h. S53. Heat to 380-420℃, maintain or finely adjust the pressure, and keep warm for 1-2 hours; S54. Allow to cool naturally to room temperature, then demold to obtain the finished product.

[0016] Beneficial effects This invention provides a method for preparing a high-temperature resistant, high-strength polyimide composite material. Compared with the prior art, it has the following advantages: (1) The present invention achieves synergistic optimization of high temperature resistance, high strength and intelligent repair: Through the integrated design of "customized silane coupling agent + biomimetic dynamic interface modification + polyimide precursor with dynamic network + gradient hot pressing curing", the glass transition temperature of the prepared composite material is ≥335℃, the tensile strength is ≥208MPa, and the heat repair efficiency at 180-250℃ is ≥87%, which solves the technical bottleneck of the prior art that it is difficult to balance the high temperature resistance, mechanical strength and repair performance of the material.

[0017] (2) This invention significantly improves the interfacial bonding strength and stability: By using a biomimetic polydopamine coating and a customized silane coupling agent to synergistically modify and reinforce the filler, the polydopamine coating achieves a strong bond with the filler through biomimetic adhesion, while the customized silane coupling agent connects the polydopamine coating and the polyimide matrix through chemical bonds, and introduces dynamic covalent bond sites to form a stable interfacial structure of "filler-coating-coupling agent-matrix". Compared with materials using only a single modification method, the interfacial shear strength is increased by more than 30%, effectively avoiding the problem of interfacial delamination under high temperature or stress conditions.

[0018] (3) The present invention constructs a highly efficient dual dynamic repair network: by introducing monomers containing dynamic covalent bonds into the polyimide matrix, and introducing dynamic action sites at the interface through customized silane coupling agents, a “matrix-interface dual dynamic network” is formed; under thermal stimulation, the dynamic covalent bonds can achieve breakage-recombination, which can not only quickly repair surface cracks of the material, but also repair internal micro-damage. The repair efficiency is more than 25% higher than that of a single dynamic network, and the service life of the material is significantly extended. Attached Figure Description

[0019] Figure 1 SEM image of the cross-section of the polyimide composite material provided by the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0021] Example 1 S1. Preparation of customized silane coupling agents: S11. Mix 1.2 mol magnesium powder, 40% of the total mass of anhydrous tetrahydrofuran, 1 mol tetrahydrofuran solution of chlorotrimethoxysilane, and 1 mol tetrahydrofuran solution of (4-bromophenylethynyl)trimethylsilane. React in an ice-water bath under nitrogen protection for 2 h, and then continue the reaction at 30 °C in the dark for 24 h. After centrifugation, take the supernatant and extract it three times with n-pentane. Rotary evaporate at 45 °C to obtain the solid. Under S12 and ammonia protection, 2 mol of potassium hydroxide was dissolved in 8 times the solid mass of anhydrous methanol, and an anhydrous methanol solution containing the above solid was added. The reaction was carried out at room temperature in the dark for 12 hours. After centrifugation, the supernatant was extracted three times with n-pentane, rotary evaporated at 40°C, washed three times with n-hexane, and then vacuum dried for 8 hours to obtain the basic silane coupling agent. S13. Add bis(3-triethoxysilylpropyl) disulfide (molar ratio of 1:1 to the basic silane coupling agent) to the basic silane coupling agent and react at 60°C for 3 h to obtain a customized silane coupling agent containing disulfide bonds.

[0022] S2. Preparation of biomimetic dynamic interface modified and reinforced fillers: S21. Carbon fiber (particle size 50nm) was impregnated in a Tris-HCl buffer solution with pH 8.5 containing dopamine hydrochloride (mass concentration 2g / L). The mixture was shaken at room temperature for 8 hours, centrifuged, washed three times with deionized water, and vacuum dried at 80℃ for 6 hours to obtain the pre-modified filler. S22. The pre-modified filler is immersed in an ethanol solution containing a customized silane coupling agent (coupling agent mass fraction 5%), reacted at 60°C for 3 hours, centrifuged, washed with ethanol 3 times, and vacuum dried at 100°C for 8 hours to obtain modified carbon fiber; its amount is 20% of the total mass of polyimide monomer.

[0023] S3. Preparation of polyimide precursor solution containing dynamic network: Under nitrogen protection and at room temperature, 85 g of 4,4'-diaminodiphenyl ether (an aromatic diamine) and 15 g of 4,4'-diaminodiphenyl disulfide (containing a dynamically covalently bonded diamine derivative, accounting for 15% of the total monomer mass) were dissolved in N,N-dimethylformamide. After stirring and dissolving, 100 g of pyromellitic dianhydride was added at a rate of 0.5 g / min, and the reaction was continued with stirring for 6 h to obtain a polyimide precursor solution; the mass fraction of the polyimide monomer in the solution was 20%.

[0024] S4. Preparation of composite slurry: The modified carbon fiber above is added to the precursor solution, stirred and dispersed at room temperature for 1.5 h, and then ultrasonically dispersed at 300 W for 45 min (temperature controlled at 25℃) to obtain a uniform composite slurry.

[0025] S5, Gradient hot pressing curing molding: S51. Under vacuum conditions, the temperature is increased to 120°C at a rate of 1°C / min, a pressure of 0.8MPa is applied, and the temperature is maintained for 1 hour. S52, Heat to 280℃ at a rate of 2.5℃ / min, increase pressure to 2.5MPa, and hold for 2 hours; S53. Heat to 400℃, maintain constant pressure, and hold for 1.5 hours; S54. After naturally cooling to room temperature, demold to obtain the polyimide composite material.

[0026] Example 2 S1. Preparation of customized silane coupling agent: The modifying reagent is replaced with 3-(furan-2-ylmethoxy)propyltriethoxysilane, and the remaining steps are the same as in Example 1 to prepare a customized silane coupling agent containing furan groups.

[0027] S2. Preparation of biomimetic dynamic interface modified reinforcing filler: Take glass fiber (particle size 100nm), replace the dopamine derivative with methyl dopamine, the amount of which is 30% of the total mass of polyimide monomer, and the remaining steps are the same as in Example 1 to obtain modified glass fiber.

[0028] S3. Preparation of polyimide precursor solution containing dynamic network: p-phenylenediamine is selected as the aromatic diamine, the amount of the diamine derivative containing dynamic covalent bond accounts for 10% of the total mass of the monomer, the aromatic dianhydride is replaced with benzophenone tetracarboxylic dianhydride, and furan-terminated maleimide anhydride derivative (molar ratio with benzophenone tetracarboxylic dianhydride 1:4) is added. N-methylpyrrolidone is selected as the polar solvent, and the remaining steps are the same as in Example 1.

[0029] S4. Preparation of composite slurry: ultrasonic power 400W, ultrasonic time 30min, the remaining steps are the same as in Example 1.

[0030] S5, Gradient hot pressing curing molding: S51. Heat to 130℃ and hold for 1.5 hours; S52, heat to 300℃, pressure 3.0MPa, hold for 2.5h; S53. Heat to 420℃ and keep warm for 2 hours. The remaining steps are the same as in Example 1.

[0031] Example 3 S1. Preparation of customized silane coupling agent: 1.5 mol of magnesium powder, 60% of the total mass of anhydrous tetrahydrofuran in the reaction system, 2.5 mol of potassium hydroxide in S12, 10 times the solid mass of anhydrous methanol, and the remaining steps are the same as in Example 1.

[0032] S2. Preparation of biomimetic dynamic interface modified reinforcing filler: The reinforcing filler is a mixture of carbon fiber and silicon carbide fiber (mass ratio 1:1), and the dopamine derivative is norepinephrine, which is used in an amount of 40% of the total mass of polyimide monomers. The remaining steps are the same as in Example 1.

[0033] S3. Preparation of polyimide precursor solution containing dynamic network: The amount of diamine derivative containing dynamic covalent bond accounts for 5% of the total mass of monomer. The aromatic diamine is m-phenylenediamine, the aromatic dianhydride is biphenyltetracarboxylic dianhydride, and the polar solvent is N,N-dimethylacetamide. The remaining steps are the same as in Example 1.

[0034] S4. Preparation of composite slurry: Ultrasonic power 200W, ultrasonic time 60min, the remaining steps are the same as in Example 1.

[0035] S5, Gradient hot pressing curing molding: S41. Heat to 100℃ and hold for 0.5 hours; S42. Heat to 260℃, pressure 2.0MPa, and hold for 1.5h; S43. Heat to 380℃ and keep warm for 1 hour. The remaining steps are the same as in Example 1.

[0036] Comparative Example 1 Compared to Example 1, the difference is that a customized silane coupling agent was not used; only polydopamine modification was employed. Everything else remains the same. The reinforcing filler was subjected to only step S21 of Example 1, without step S22 (without adding a customized silane coupling agent), resulting in carbon fibers coated only with polydopamine; the remaining steps were completely consistent with those in Example 1.

[0037] Comparative Example 2 Compared to Example 1, the difference lies in that the polyimide precursor does not contain dynamic covalent bond units; everything else remains the same; that is: In the preparation of the polyimide precursor solution, 4,4'-diaminodiphenyl disulfide was not added; instead, 100g of 4,4'-diaminodiphenyl ether was reacted with 100g of pyromellitic dianhydride. The remaining steps were completely consistent with those in Example 1.

[0038] Comparative Example 3 Compared with Example 1, the difference lies in the use of a conventional hot-press curing process, which is a non-gradient procedure; everything else remains the same. After the composite slurry is poured into the mold, it is vacuum dried at 80°C for 4 hours, then directly heated to 380°C and kept at that temperature for 3 hours without gradient temperature control or pressure adjustment. After natural cooling, it is demolded. The remaining steps are completely consistent with those in Example 1.

[0039] Comparative Example 4 Compared to Example 1, the difference lies in the absence of biomimetic modification and dynamic network; everything else remains the same; that is: The silane coupling agent used is conventional γ-aminopropyltriethoxysilane, which does not introduce dynamic covalent bonds; The reinforcing filler (carbon fiber) was ultrasonically dispersed in anhydrous ethanol and then reacted with a silane coupling agent at 70°C for 5 hours without polydopamine biomimetic coating modification. The polyimide precursor solution was prepared from 4,4'-diaminodiphenyl ether and pyromellitic dianhydride and does not contain dynamic covalent units. Curing process: Dry at 80℃ for 3 hours, dry at 150℃ for 2 hours, dry at 250℃ for 1 hour, keep warm at 380℃ for 2 hours, apply without pressure.

[0040] Performance testing Tensile strength test: using a universal testing machine, tensile rate 5 mm / min.

[0041] Thermal repair efficiency: The sample is cut to form a 1mm gap, kept at 200℃ for 1h for repair, and the tensile strength after repair is tested. Repair efficiency = (tensile strength after repair / original tensile strength) × 100%.

[0042] Glass transition temperature (Tg): Differential scanning calorimetry (DSC) was used at a heating rate of 10℃ / min under a nitrogen atmosphere.

[0043] As shown in the table above, in Comparative Example 1, the lack of a customized silane coupling agent resulted in insufficient interfacial bonding between the filler and the matrix, leading to a significant decrease in tensile strength and repair efficiency. Comparative Example 2, because the precursor does not contain dynamic covalent bond units, relies solely on the dynamic interaction sites at the interface between the reinforcing filler and the matrix to achieve repair, lacking the synergistic support of the dynamic network inside the matrix, resulting in extremely low repair efficiency. Comparative Example 3, due to the use of conventional curing processes, has internal pores and internal stress, resulting in a decrease in tensile strength. Comparative Example 4, without biomimetic modification, dynamic network, and gradient hot pressing process, has the worst high temperature resistance and mechanical properties, and has no repair function.

[0044] The samples in Examples 1-3 showed excellent performance in terms of glass transition temperature (≥335℃), tensile strength (≥208MPa), and thermal repair efficiency (≥87%), significantly outperforming the comparative examples. This demonstrates that the integrated technical solution of "customized coupling agent + biomimetic dynamic modification + dynamic network precursor + gradient hot pressing curing" can achieve a synergistic improvement in high temperature resistance, high strength, and intelligent repair performance.

[0045] Depend on Figure 1 It can be known that: (1) Interface bonding state: The modified carbon fiber and the polyimide matrix are tightly bonded together without gaps or peeling, and the matrix forms a complete coating on the fiber; (2) Internal structure density: The cross-section has no obvious pores, bubbles or cracks, and presents a uniform and continuous microstructure; (3) Fracture characteristics: The fiber and the matrix fractured synchronously without debonding, which is a typical "ductile fracture".

[0046] Furthermore, any content not described in detail in this specification is existing technology known to those skilled in the art.

[0047] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0048] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-temperature resistant, high-strength polyimide composite material, characterized in that, The preparation steps include the following: S1. Preparation of customized silane coupling agents; S2. Prepare biomimetic dynamic interface modified and reinforced filler, wherein the modified and reinforced filler is synergistically modified by a biomimetic coating and a customized silane coupling agent; S3. Prepare a polyimide precursor solution containing a dynamic network, wherein the polyimide precursor solution contains dynamic covalent bond units, wherein the dynamic covalent bond is selected from at least one of disulfide bond, furan-maleimide Diels-Alder bond, and imine bond; S4. Preparation of composite slurry; S5. Gradient hot pressing curing molding, wherein the gradient hot pressing curing adopts a multi-stage temperature control-pressure coordinated process.

2. The method for preparing a high-temperature resistant, high-strength polyimide composite material according to claim 1, characterized in that: The preparation steps of the customized silane coupling agent are as follows: S11. Mix magnesium powder, anhydrous tetrahydrofuran, tetrahydrofuran solution of chlorotrimethoxysilane, and tetrahydrofuran solution of (4-bromophenylethynyl)trimethylsilane. React under nitrogen protection and ice-water bath conditions. After the reaction is completed, continue the reaction at 30-35℃ in the dark for 20-24 hours. After centrifugation, take the supernatant and extract it with n-pentane. Rotary evaporate at 45℃ to obtain the solid. S12. Under ammonia protection, potassium hydroxide and anhydrous methanol are mixed until completely dissolved. An anhydrous methanol solution containing the above solid is added. The reaction is carried out at room temperature in the dark for 10-12 hours. The reaction solution is centrifuged and the supernatant is extracted with n-pentane. The supernatant is then evaporated at 40°C and washed with n-hexane 3-5 times before being dried under vacuum to obtain the basic silane coupling agent. S13. Add a modifying agent containing a disulfide bond or a furan / maleimide group to the basic silane coupling agent to prepare a customized silane coupling agent.

3. The method for preparing a high-temperature resistant, high-strength polyimide composite material according to claim 2, characterized in that: in, The molar ratio of magnesium powder to trichlorotrimethoxysilane is 1.2:1-1.5:1, the molar ratio of (4-bromophenylethynyl)trimethylsilane to trichlorotrimethoxysilane is 1:1, and the amount of anhydrous tetrahydrofuran is 40%-60% of the total mass of the reaction system.

4. The method for preparing a high-temperature resistant, high-strength polyimide composite material according to claim 2, characterized in that: The modifying agent containing disulfide bonds or furan / maleimide groups is bis(3-triethoxysilylpropyl) disulfide or 3-(furan-2-ylmethoxy)propyltriethoxysilane.

5. The method for preparing a high-temperature resistant, high-strength polyimide composite material according to claim 1, characterized in that: The preparation steps of the biomimetic dynamic interface modified and reinforced filler are as follows: S21. The reinforcing filler is immersed in a Tris-HCl buffer solution with a pH of 8.0-9.0, wherein the buffer solution contains dopamine or its derivatives, and the reaction is carried out with shaking at room temperature for 6-12 hours. After centrifugation, washing and drying, a pre-modified filler with a polydopamine coating on the surface is obtained. S22. The pre-modified filler is immersed in a solution containing a customized silane coupling agent and reacted at 50-70℃ for 2-4 hours. After centrifugation, washing and drying, the modified and reinforced filler is obtained.

6. The method for preparing a high-temperature resistant, high-strength polyimide composite material according to claim 1, characterized in that: The dopamine derivative is dopamine hydrochloride, methyl dopamine, or norepinephrine; The reinforcing filler is selected from one or more of carbon fiber, glass fiber, aramid fiber, and silicon carbide fiber, with a diameter of 5-20 μm, a length of 1-3 mm, and a mass of 10%-40% of the total mass of polyimide monomers.

7. The method for preparing a high-temperature resistant, high-strength polyimide composite material according to claim 1, characterized in that: The preparation steps of the polyimide precursor solution containing a dynamic network are as follows: Under nitrogen protection and at room temperature, aromatic diamine and 5%-15% by mass of diamine derivative containing dynamic covalent bonds are dissolved in a polar solvent. After stirring and dissolving, aromatic dianhydride and / or dianhydride derivative containing dynamic covalent bonds are slowly added in an equimolar ratio at a feeding rate of 0.5-1 g / min. After the feeding is completed, the reaction is stirred for 4-8 h to obtain a polyimide precursor solution. The mass fraction of the polyimide monomer in the solution is 15%-25%.

8. The method for preparing a high-temperature resistant, high-strength polyimide composite material according to claim 7, characterized in that: The diamine derivative containing dynamic covalent bonds is 4,4'-diaminodiphenyl disulfide; the dianhydride derivative containing dynamic covalent bonds is a furan-terminated maleimide anhydride derivative; the aromatic diamine is selected from 4,4'-diaminodiphenyl ether, p-phenylenediamine, or m-phenylenediamine; the aromatic dianhydride is selected from pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, or biphenyl tetracarboxylic dianhydride; the polar solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, or N-methylpyrrolidone.

9. The method for preparing a high-temperature resistant and high-strength material according to claim 8, characterized in that: The method for preparing the composite slurry is as follows: the modified reinforcing filler is added to the polyimide precursor solution, stirred and dispersed at room temperature for 1-2 hours, and then ultrasonically dispersed for 30-60 minutes with an ultrasonic power of 200-400W and a temperature controlled below 30℃ to obtain a uniform composite slurry.

10. The method for preparing a high-temperature resistant, high-strength polyimide composite material according to claim 9, characterized in that: The gradient hot-press curing molding process is as follows: S51. Pour the composite slurry into a mold pre-coated with a release agent, place it in the vacuum environment of a hot press, heat it to 100-130℃ at a rate of 1-2℃ / min, and apply a pressure of 0.5-1.0MPa at the same time, and keep it at that temperature for 0.5-1.5h. S52. Increase the temperature to 260-300℃ at a rate of 2-3℃ / min, while increasing the pressure to 2.0-3.5MPa, and hold for 1.5-2.5h. S53. Heat to 380-420℃, maintain or finely adjust the pressure, and keep warm for 1-2 hours; S54. Allow to cool naturally to room temperature, then demold to obtain the finished product.

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