Preparation method and application of crosslinked network polyimide composite based on double-suction electron group

Abstract

A method for preparing and applying a cross-linked network polyimide composite material based on electron-withdrawing groups is disclosed, relating to the field of high-temperature energy storage technology for electrolyte capacitors. Method: 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene is added to a polyimide colloidal solution and stirred uniformly under a nitrogen atmosphere to obtain solution b; solution b is evacuated and then uniformly coated onto one side of a pretreated substrate. After curing, the substrate is subjected to gradient heating, and finally the film on the substrate is peeled off to obtain the cross-linked network polyimide composite material based on electron-withdrawing groups; the application of the cross-linked network polyimide composite material based on electron-withdrawing groups in dielectric capacitors. This invention provides a method for preparing and applying a cross-linked network polyimide composite material based on electron-withdrawing groups.

Description

Technical Field

[0001] This invention relates to the field of high-temperature energy storage technology for electrolyte capacitors, specifically to a method for preparing and applying a cross-linked network polyimide composite material based on double electron-withdrawing groups. Background Technology

[0002] With the rapid development of new energy vehicles, aerospace, and oil and gas exploration, the demand for high-performance dielectric capacitors is constantly increasing. There is an urgent need for capacitors that can operate stably under harsh environmental conditions. Inverters in hybrid and electric vehicles need to operate stably within a temperature range of 140℃-150℃. Aircraft electrification requires power converters located inside or near turbine engines, operating at temperatures as high as 180℃. However, the upper limit of the long-term stable operating temperature for biaxially oriented polypropylene (BOPP), commonly used in the manufacture of dielectric capacitors, is 80℃. When this upper limit is exceeded, the conductivity increases sharply, leakage current increases dramatically, leading to a sharp deterioration in energy storage performance. Therefore, researchers are considering polymers with high glass transition temperatures (Tg) as candidate materials for capacitive energy storage in harsh environments, such as polyimide (PI), polyetherimide (PEI), polycarbonate (PC), and polyetheretherketone (PEEK). However, these polymer dielectrics with high Tg still face challenges such as increased leakage current and a sharp decrease in charge and discharge efficiency under the influence of an external electric field. The root cause of this problem lies in the enhanced injection, excitation, and migration of charge carriers under the coupling effect of the high-temperature electric field, leading to a significant increase in conduction losses. Therefore, limiting the injection and transport of charge carriers to reduce conduction losses has become the main principle in the design of high-temperature dielectrics.

[0003] To address these challenges, researchers have primarily employed two strategies to suppress conduction losses. The first strategy involves developing composite materials by doping with wide-bandgap fillers or molecular semiconductors to construct charge traps and suppress carrier transport within the polymer. While this strategy improves the energy storage performance of the polymer, the dispersibility of the filler, the bandgap, and surface defects all require careful control; otherwise, agglomeration and other defects can occur, making the composite medium more susceptible to breakdown. The second strategy involves designing different molecular structures to suppress carrier migration. However, the preparation process of fully alicyclic polymers is complex and sometimes requires high-temperature treatment, undoubtedly negatively impacting preparation efficiency. To simultaneously address both the preparation process and filler dispersibility, a cross-linked network was proposed to effectively suppress polymer chain movement, thereby inhibiting carrier migration and improving energy storage performance. The construction of the cross-linked network ensures the consistency and reliability of the polymer dielectric properties without requiring consideration of dispersion uniformity. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems by providing a method for preparing and applying a cross-linked network polyimide composite material based on double electron-withdrawing groups.

[0005] A method for preparing a cross-linked network polyimide composite material based on electron-withdrawing groups, comprising the following steps:

[0006] Step S1: Prepare polyimide colloid;

[0007] Hexafluoroisopropylphthalic anhydride and 2,2'-di(trifluoromethyl)diaminobiphenyl were added to N-methylpyrrolidone and stirred at 0-5°C until the reaction was complete to obtain solution a;

[0008] Step S2: Prepare cross-linked polyimide with electron-withdrawing double groups;

[0009] 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene was added to solution a obtained in step S1 and stirred evenly under a nitrogen atmosphere to obtain solution b. Solution b was evacuated and then uniformly coated on one side of a pretreated substrate. After curing, the substrate was subjected to gradient heating and finally the film on the substrate was peeled off to obtain a cross-linked network polyimide composite material based on double electron-withdrawing groups.

[0010] The mass fraction of polyimide in the 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene solution a is 3%, 6%, 9%, or 12%.

[0011] An application of a cross-linked network polyimide composite material based on electron-withdrawing groups, specifically its application in dielectric capacitors.

[0012] The beneficial effects of this invention are:

[0013] (1) Compared with commercial polymeric materials (PIs), free radical polymeric materials (FPIs) have a higher band gap. Therefore, this invention introduces a crosslinking agent (1,3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene) (TF) with electron-withdrawing groups. While constructing a crosslinking network inside the FPI, electron-withdrawing groups are also introduced into the formed CFPI, further improving the band gap of the CFPI. It is worth noting that the CFPI exhibits excellent energy storage performance at both 150℃ and 200℃, with CFPI-9%TF showing the best Ue and η, superior to currently reported pure polymers and most polymer dielectrics. The results indicate that establishing a dense crosslinking network structure with electron-withdrawing groups in polymer dielectrics is an effective strategy that can significantly suppress the migration of carriers at high temperatures, thereby reducing leakage current and improving the energy storage performance of polymer dielectrics at high temperatures.

[0014] (2) The preparation process of this invention is simple, economical and practical, effectively saves resources, is suitable for large-scale industrial production, and can be widely applied in advanced fields such as electrical, electronic and new energy vehicles, providing a good strategy for developing new application paths for polyimide energy storage.

[0015] This invention provides a method for preparing and applying a cross-linked network polyimide composite material based on electron-withdrawing groups. Attached Figure Description

[0016] Figure 1 This shows a cross-sectional SEM image of the PI film prepared in Example 6;

[0017] Figure 2 This shows a cross-sectional SEM image of the FPI film prepared in Example 5;

[0018] Figure 3 This shows a cross-sectional SEM image of the CFPI-3%TF film in Example 1.

[0019] Figure 4 This shows a cross-sectional SEM image of the CFPI-6%TF film in Example 2;

[0020] Figure 5 This shows a cross-sectional SEM image of the CFPI-9%TF film in Example 3;

[0021] Figure 6 This shows a cross-sectional SEM image of the CFPI-12%TF film in Example 4;

[0022] Figure 7 Fourier transform infrared spectra of cross-linked polyimide composites with electron-withdrawing groups of different TF mass fractions, as well as FPI films and PI films.

[0023] Figure 8 XRD patterns of cross-linked polyimide composites with electron-withdrawing groups of different TF mass fractions, as well as FPI and PI films;

[0024] Figure 9 DSC spectra of cross-linked polyimide composites with electron-withdrawing groups of different TF mass fractions, as well as FPI films and PI films;

[0025] Figure 10 Thermogravimetric spectra of cross-linked polyimide composites with electron-withdrawing groups of different TF mass fractions, as well as FPI films and PI films;

[0026] Figure 11 This represents the band structure and density of states diagrams of PI, FPI, and CFPI thin films simulated using DFT.

[0027] Figure 12 This diagram shows the surface electrostatic potential distribution of the PI film prepared in Example 6.

[0028] Figure 13 This diagram shows the surface electrostatic potential distribution of the FPI film prepared in Example 5.

[0029] Figure 14 This diagram shows the surface electrostatic potential distribution of the CFPI thin film.

[0030] Figure 15 Dielectric constant and dielectric loss of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups under a test environment of 150℃.

[0031] Figure 16 Dielectric constant and dielectric loss of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups under a test environment of 200℃;

[0032] Figure 17 Breakdown field diagrams of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups under a 150°C test environment;

[0033] Figure 18 Breakdown field diagrams of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups under a 200°C test environment.

[0034] Figure 19 The energy storage density and efficiency of cross-linked polyimide composites with electron-withdrawing groups of different TF mass fractions are shown in the figure at 150℃.

[0035] Figure 20 The energy storage density and efficiency of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups are shown in the figure at 200℃.

[0036] Figure 21 The curves showing the change of discharge energy density and efficiency of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups as a function of cycle number under a test environment of 150℃.

[0037] Figure 22 The graph shows the discharge energy density and efficiency of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups as a function of the number of cycles under a test environment of 200℃. Detailed Implementation

[0038] Specific Implementation Method 1: This implementation method describes a method for preparing a cross-linked network polyimide composite material based on electron-withdrawing groups, which is carried out according to the following steps:

[0039] Step S1: Prepare polyimide colloid;

[0040] Hexafluoroisopropylphthalic anhydride and 2,2'-di(trifluoromethyl)diaminobiphenyl were added to N-methylpyrrolidone and stirred at 0-5°C until the reaction was complete to obtain solution a;

[0041] Step S2: Prepare cross-linked polyimide with electron-withdrawing double groups;

[0042] 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene was added to solution a obtained in step S1 and stirred evenly under a nitrogen atmosphere to obtain solution b. Solution b was evacuated and then uniformly coated on one side of a pretreated substrate. After curing, the substrate was subjected to gradient heating and finally the film on the substrate was peeled off to obtain a cross-linked network polyimide composite material based on double electron-withdrawing groups.

[0043] The mass fraction of polyimide in the 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene solution a is 3%, 6%, 9%, or 12%.

[0044] Specific Implementation Method Two: The difference between this implementation method and Specific Implementation Method One is that the molar ratio of hexafluoroisopropylphthalic anhydride to 2,2'-bis(trifluoromethyl)diaminobiphenyl in step S1 is 1:(1.01~1.05).

[0045] The other steps are the same as in Specific Implementation Method 1.

[0046] Specific Implementation Method 3: The difference between this implementation method and Specific Implementation Method 1 or 2 is that the hexafluoroisopropylphthalic anhydride mentioned in step S1 is added to N-methylpyrrolidone in three parts: 1 / 2 of the total mass is added in the first part, 1 / 4 of the total mass is added in the second part, and 1 / 4 of the total mass is added in the third part, with an interval of 1.5 to 3 hours between each addition.

[0047] The other steps are the same as in specific implementation method one or two.

[0048] Specific Implementation Method Four: The difference between this implementation method and Specific Implementation Methods One to Three is that the reaction in step S1 is carried out in a nitrogen atmosphere and kept dry.

[0049] The other steps are the same as those in Specific Implementation Methods One to Three.

[0050] Specific Implementation Method 5: The difference between this implementation method and Specific Implementation Methods 1 to 4 is that the 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene described in step S2 is dried under vacuum at 70~90℃ for 6~9h before use.

[0051] The other steps are the same as those in Specific Implementation Methods One through Four.

[0052] Specific Implementation Method Six: The difference between this implementation method and Specific Implementation Methods One to Five is that the stirring time in step S2 is 5 to 8 hours.

[0053] The other steps are the same as those in Specific Implementation Methods 1 to 5.

[0054] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Six is ​​that the pretreated substrate described in step S2 is processed according to the following steps: first, the substrate is washed with deionized water 2 to 3 times, then wiped with non-woven cloth, then washed with ethanol 3 to 4 times, and finally dried at 60 to 70°C for 7 to 9 hours to obtain the pretreated substrate, wherein the substrate is a high-temperature resistant silicon board.

[0055] The other steps are the same as those in Specific Implementation Methods 1 to 6.

[0056] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the curing temperature in step S2 is 55~90℃.

[0057] The other steps are the same as those in Specific Implementation Methods 1 to 7.

[0058] Specific Implementation Method Nine: The difference between this implementation method and Specific Implementation Methods One to Eight is that: first, the substrate is kept at 70~90℃ for 5~8 hours, then at 140~180℃ for 0.5~2 hours, then at 180~220℃ for 1.5~3 hours, then at 260~300℃ for 1.5~3 hours, and finally at 320~340℃ for 0.5~2 hours; after the gradient heating, the substrate is placed in water at 0~2℃ to cool down.

[0059] The other steps are the same as those in Specific Implementation Methods 1 to 8.

[0060] Specific Implementation Method 10: This implementation method describes the application of a cross-linked network polyimide composite material based on double electron-withdrawing groups in a dielectric capacitor.

[0061] The beneficial effects of the present invention are verified using the following embodiments:

[0062] Example 1: A method for preparing a cross-linked network polyimide composite material based on electron-withdrawing groups, comprising the following steps:

[0063] Step S1: Prepare polyimide colloid;

[0064] Hexafluoroisopropyl phthalic anhydride and 2,2'-di(trifluoromethyl)diaminobiphenyl were added to N-methylpyrrolidone. Note that the hexafluoroisopropyl phthalic anhydride was added in three portions: half the total mass in the first portion, one-quarter in the second portion, and one-quarter in the third portion, with each portion added 2 hours apart. The mixture was then mechanically stirred under nitrogen at 0–5°C until the reaction was complete (keeping the environment dry), yielding solution a.

[0065] The molar ratio of hexafluoroisopropylphthalic anhydride to 2,2'-bis(trifluoromethyl)diaminobiphenyl is 1:1.01;

[0066] Step S2: Prepare cross-linked polyimide with electron-withdrawing double groups;

[0067] First, 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene (TF) was dried under vacuum at 70°C for 6 h, then added to solution a, and stirred under nitrogen atmosphere for 6.5 h to obtain solution b. Solution b was then evacuated and uniformly coated onto one side of a pretreated substrate. After curing at 80°C, the substrate was placed in a forced-air oven and kept at 80°C for 6 h, then at 150°C for 1 h, then at 200°C for 2 h, then at 280°C for 2 h, and finally at 330°C for 1 h. After gradient heating, the substrate was placed in water at 1°C to cool down, and finally the film on the substrate was peeled off to obtain a cross-linked network polyimide composite material (CFPI) based on electron-withdrawing groups.

[0068] The pretreated substrate is processed according to the following steps: first, the substrate is washed twice with deionized water, then the water droplets are wiped clean with non-woven cloth, then washed three times with ethanol, and finally dried at 65°C for 7 hours to obtain the pretreated substrate. The substrate is a high-temperature resistant silicon board.

[0069] The mass fraction of polyimide in the 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene solution a is 3%.

[0070] Example 2: In this example, the mass fraction of polyimide in solution a of 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene was 6%. All other experimental conditions were the same as in Example 1.

[0071] Example 3: In this example, the mass fraction of polyimide in solution a of 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene was 9%. All other experimental conditions were the same as in Example 1.

[0072] Example 4: In this example, the mass fraction of polyimide in solution a of 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene was 12%. All other experimental conditions were the same as in Example 1.

[0073] Example 5: No 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene was added in this example.

[0074] Example 6: In this example, the polyimide matrix was obtained by reacting pyromellitic anhydride and diaminodiphenyl ether. All other experimental conditions were the same as in Example 1.

[0075] Figure 1 This shows a cross-sectional SEM image of the PI film prepared in Example 6. Figure 2 This shows a cross-sectional SEM image of the FPI film prepared in Example 5. Figure 3 This shows a cross-sectional SEM image of the CFPI-3%TF film in Example 1. Figure 4 This shows a cross-sectional SEM image of the CFPI-6%TF film in Example 2. Figure 5 This shows a cross-sectional SEM image of the CFPI-9%TF film in Example 3. Figure 6 This shows a cross-sectional SEM image of the CFPI-12%TF film in Example 4.

[0076] like Figure 1-6 As shown, all samples have a relatively uniform thickness, approximately 6-10 μm, and there are no defects such as pores on the surface and cross-section of the film.

[0077] Figure 7 Fourier transform infrared spectra of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups, as well as FPI and PI films; such as Figure 7 As shown, 1780 cm can be seen. -1 1760 cm -1 and 1360 cm -1 It has obvious characteristic peaks, including the 1780 cm peak. -1 and 1760 cm -1 These correspond to the C=O stretching vibration peak, 1360 cm⁻¹. -1 The corresponding CN stretching vibration peak indicates that the chemical bond structure of the characteristic peaks was not changed during the successful synthesis of PI, FPI, and CFPI.

[0078] Figure 8 XRD patterns of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups, as well as FPI and PI films; such as Figure 8As shown, it can be seen that all polymer dielectric films exhibit the typical broad peaks (2θ in the range of 10°-20°) present in amorphous polymers, and the amorphous structure has not been altered.

[0079] Figure 9 DSC spectra of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups, as well as FPI and PI films; such as Figure 9 As shown, all samples exhibit excellent thermal stability.

[0080] Figure 10 Thermogravimetric (TGA) spectra of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups, as well as FPI and PI films, are shown. The TGA curves reveal the relationship between the mass of the material and temperature during heating. Figure 10 As shown, it is evident that the thermal decomposition temperatures of the samples all exceed 400℃. However, with the construction of the cross-linked network, the decomposition temperature increases accordingly, demonstrating the improved thermal stability of the polymer.

[0081] Figure 11 This represents the band structure and density of states diagrams of PI, FPI, and CFPI thin films simulated using DFT. Figure 12 This diagram shows the surface electrostatic potential distribution of the PI film prepared in Example 6. Figure 13 This diagram shows the surface electrostatic potential distribution of the FPI film prepared in Example 5. Figure 14 This diagram shows the surface electrostatic potential distribution of the CFPI thin film. For example... Figure 11-14 As shown, the band gaps of PI, FPI and CFPI are 2.74 eV, 4 eV and 4.71 eV, respectively, and the electrostatic potential of CFPI is significantly greater than that of PI and FPI. This change in electrostatic potential also inhibits the transport of charge carriers.

[0082] Figure 15 The dielectric constant and dielectric loss of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups are shown in the figure at 150°C. Figure 16 The dielectric constant and dielectric loss of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups are shown in the figure at 200℃.

[0083] like Figure 15-16 As shown, the dielectric constant of the FPI film is smaller than that of the PI film, for example, in 10... 3At Hz, the dielectric constant of PI is 3.3, while that of FPI is 2.83. This is because the PI molecular chain contains flexible ether bonds (-o-), which have a large dipole moment, while the FPI molecular chain contains trifluoromethyl groups (-CF3), and fluorine (F) has low polarizability, thus resulting in a higher dielectric constant for PI. The dielectric constant of CFPI films initially increases and then decreases with increasing crosslinking degree. This is due to the introduction of TF into CFPI. TF not only contains ether bonds but also forms amide bonds with high dipole moments (3.7D) during the crosslinking process, which enhances the polarizability of the CFPI molecular chain. Therefore, the dielectric constant of CFPI increases with increasing crosslinking degree. However, with further increases in crosslinking degree, dipole reorientation polarization is further suppressed, leading to a decrease in dielectric constant. In summary, the dielectric constants of PI, FPI, and CFPI remain relatively stable across the entire frequency range.

[0084] Figure 17 Breakdown field diagrams representing cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups under a 150°C test environment. Figure 18 Breakdown field diagrams representing cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups under a 200°C test environment.

[0085] like Figure 17-18 As shown, among all CFPI films, CFPI-9%TF exhibits the highest breakdown field strength. The breakdown strength of CFPI decreases significantly at 200℃ compared to 150℃. For example, the breakdown field strengths of the CFPI-9%TF film at 150℃ and 200℃ are 798.59 MV / m and 707.84 MV / m, respectively, which are 1.598 times and 1.558 times that of FPI. This demonstrates that the formed crosslinked network with double electron-withdrawing groups effectively suppresses carrier transport at high temperatures, inhibits electrical tree growth, and significantly improves the breakdown field strength.

[0086] Figure 19 The graph shows the energy storage density and efficiency of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups under a test environment of 150℃. Figure 20 The graph shows the energy storage density and efficiency of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups under a test environment of 200℃.

[0087] like Figures 19-20As shown, both FPI and CFPI outperform PI. In terms of energy storage performance, CFPI films exhibit significant improvements in both Ue and η. This is mainly due to the construction of a cross-linked network with double electron-withdrawing groups, which suppresses carrier migration and increases trap density. With increasing cross-linking degree, at 150℃ and 200℃, CFPI's Ue shows a trend of first increasing and then decreasing. This indicates that moderate cross-linking is beneficial to improving CFPI's energy storage performance, while excessive TF reduces the effective connections of the cross-linked network, leading to the breakage of polymer dielectric chains.

[0088] Figure 21 The graph shows the discharge energy density and efficiency of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups as a function of cycle number under a test environment of 150℃. Figure 22 The graph shows the discharge energy density and efficiency of cross-linked polyimide composites with different TF mass fractions and electron-withdrawing groups as a function of the number of cycles under a test environment of 200℃.

[0089] like Figure 20-21 As shown, it can be seen that 10 5 A comparison of the DE hysteresis loops after each cycle shows that, at 150°C, the energy density decreases from 0.56 J / cm³. 3 It dropped slightly to 0.54 J / cm 3 η decreased by 3%; while at 200℃, the energy density decreased from 0.55 J / cm³. 3 It dropped slightly to 0.53 J / cm 3 η decreased by 3%.

Claims

1. A method for preparing a cross-linked network polyimide composite material based on electron-withdrawing groups, characterized in that, The preparation method is carried out according to the following steps: Step S1: Prepare polyimide colloid; Hexafluoroisopropylphthalic anhydride and 2,2'-di(trifluoromethyl)diaminobiphenyl were added to N-methylpyrrolidone and stirred at 0-5°C until the reaction was complete to obtain solution a; Step S2: Prepare cross-linked polyimide with electron-withdrawing double groups; 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene was added to solution a obtained in step S1 and stirred evenly under a nitrogen atmosphere to obtain solution b. Solution b was evacuated and then uniformly coated on one side of a pretreated substrate. After curing, the substrate was subjected to gradient heating and finally the film on the substrate was peeled off to obtain a cross-linked network polyimide composite material based on double electron-withdrawing groups. The mass fraction of polyimide in the 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene solution a is 3%, 6%, 9%, or 12%.

2. The method for preparing a cross-linked network polyimide composite material based on double electron-withdrawing groups according to claim 1, characterized in that, The molar ratio of hexafluoroisopropylphthalic anhydride to 2,2'-bis(trifluoromethyl)diaminobiphenyl in step S1 is 1:(1.01~1.05).

3. The method for preparing a cross-linked network polyimide composite material based on electron-withdrawing groups according to claim 1, characterized in that, The hexafluoroisopropylphthalic anhydride mentioned in step S1 is added to N-methylpyrrolidone in three parts: half of the total mass is added in the first part, one-quarter of the total mass is added in the second part, and one-quarter of the total mass is added in the third part, with an interval of 1.5 to 3 hours between each addition.

4. The method for preparing a cross-linked network polyimide composite material based on double electron-withdrawing groups according to claim 1, characterized in that, The reaction in step S1 is carried out under nitrogen atmosphere and kept dry.

5. The method for preparing a cross-linked network polyimide composite material based on double electron-withdrawing groups according to claim 1, characterized in that, The 3,5-tris(4-amino-2-trifluoromethylphenoxy)benzene described in step S2 should be dried under vacuum at 70-90°C for 6-9 hours before use.

6. The method for preparing a cross-linked network polyimide composite material based on double electron-withdrawing groups according to claim 1, characterized in that, The stirring time in step S2 is 5-8 hours.

7. The method for preparing a cross-linked network polyimide composite material based on double electron-withdrawing groups according to claim 1, characterized in that, The pretreated substrate described in step S2 is processed according to the following steps: first, the substrate is washed with deionized water 2-3 times, then wiped with non-woven cloth, then washed with ethanol 3-4 times, and finally dried at 60-70℃ for 7-9 hours to obtain the pretreated substrate, wherein the substrate is a high-temperature resistant silicon board.

8. The method for preparing a cross-linked network polyimide composite material based on electron-withdrawing groups according to claim 1, characterized in that, The curing temperature in step S2 is 55~90℃.

9. The method for preparing a cross-linked network polyimide composite material based on electron-withdrawing groups according to claim 1, characterized in that, The gradient heating steps in step S2 are as follows: first, maintain the temperature at 70~90℃ for 5~8 h, then maintain the temperature at 140~180℃ for 0.5~2 h, then maintain the temperature at 180~220℃ for 1.5~3 h, continue to maintain the temperature at 260~300℃ for 1.5~3 h, and finally maintain the temperature at 320~340℃ for 0.5~2 h; after the gradient heating, the substrate is placed in water at 0~2℃ to cool down.

10. The application of a cross-linked network polyimide composite material based on double electron-withdrawing groups prepared by the method according to any one of claims 1-9, characterized in that, The application of the cross-linked network polyimide composite material based on double electron-withdrawing groups in dielectric capacitors.

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