Method for regulating and controlling high-temperature energy storage of polyimide film by adjusting molecular structure

Abstract

The invention discloses a method for regulating and controlling high-temperature energy storage of a polyimide film by adjusting a molecular structure, and belongs to the application field of embedded capacitors, pulse power devices and the like. The invention aims to solve the problem that the existing polyimide is difficult to meet the requirement of long-term stable work in extreme environments such as high temperature, high frequency and strong electric field. The method comprises the following steps: dissolving diamine in a solvent, placing in an ice-water bath, and uniformly stirring; adding dianhydride in batches, and continuously stirring until the materials are uniform after the materials are added, so as to obtain a PAA glue solution; and paving the film, and carrying out gradient heating for imidization. According to the invention, a high-polarity group is introduced into a polyimide skeleton to induce dipolar polarization of the polyimide skeleton, and interaction between adjacent conjugate planes is optimized to obtain the polyimide film with excellent high temperature, high power and high stability. And the material can be used as a raw material for manufacturing modern embedded capacitors, semiconductor memory devices and the like.

Description

Technical Field

[0001] The present invention belongs to the application fields of embedded capacitors, pulse power devices, etc. Specifically, it relates to a method for regulating the high-temperature energy storage of polyimide films by adjusting the molecular structure. The polyimide film used as a dielectric in extremely harsh environments has excellent high temperature, high power, and high stability, and can work stably for a long time in extreme environments such as high temperature, high frequency, and strong electric field. Background Art

[0002] Polymer dielectrics can be applied to energy storage capacitors due to their advantages such as good flexibility, low density, and easy processing; dielectric capacitors have the advantages of fast charge and discharge speed, high energy storage density, long life, etc., and have been widely used in advanced microelectronics technologies and high-tech industries such as smart grid frequency modulation, electronic products, and high-speed trains.

[0003] At present, the highest working temperature of commercial electrolyte films is limited by the thermal stability of the materials, and problems such as low energy density (U e ), poor thermal conductivity, etc., make it difficult for polymer dielectrics to quickly eliminate the heat generated by energy loss and achieve efficient thermal management. This severely restricts their emergency applications in mainstream technologies such as renewable energy, electrified transportation, and advanced propulsion systems, where electronic devices need to operate stably under harsh temperature conditions above 150 to 200 °C. Therefore, developing high-temperature polymer dielectric materials with high dielectric constant, low dielectric loss, and high breakdown strength (E b ) has become the primary problem to be solved at present. Polyimide (PI) is considered a potential candidate for realizing its application in the field of high-temperature energy storage due to its excellent mechanical properties, good thermal stability, low dielectric loss, and high E b .

[0004] The interaction between the benzene ring and the imide ring in polyimide can withstand a relatively high Tg (>300 °C), indicating its good thermal stability and high-temperature resistance. However, materials used in the field of high-temperature energy storage usually require high dielectric constant, low dielectric loss, and excellent high-temperature resistance. To improve the energy storage performance of polyimide films, the introduction of fillers can improve the energy storage performance of polymers, but the complex synthesis and precise control of fillers lead to time-consuming experiments and low efficiency. Compared with polyimide composites, intrinsic polyimide avoids problems such as increased energy loss, reduction of E b and reduced service life during the preparation directly through molecular structure design. Summary of the Invention

[0005] To improve the possibility of polyimide application in high-temperature energy storage, polyimide films with high energy storage density at high temperatures can be obtained by adjusting the internal structure. It is imperative to study the method of adjusting the molecular structure to regulate the high-temperature energy storage of polyimide films.

[0006] The implementation of the present invention has important theoretical and practical significance for systematically regulating the high-temperature energy storage performance of dielectric films. At the same time, it can strengthen and deepen the research and development of the application of power electronic devices in harsh environments.

[0007] The present invention aims to solve the problem that existing polyimides are still difficult to meet the requirements of long-term stable operation in extreme environments such as high temperature, high frequency, and strong electric field.

[0008] In the present invention, by tailoring and designing the molecular structure of polyimide, high-polarity groups are introduced into the polyimide backbone to induce its dipole polarization, and at the same time, the interaction between adjacent conjugated planes is optimized to improve the high-temperature energy storage performance of polyimide.

[0009] The polyimide film prepared by the method of the present invention has excellent high-temperature, high-power, and high-stability performance.

[0010] The present invention provides a method for regulating the high-temperature energy storage of polyimide films by adjusting the molecular structure. The basic idea is to introduce different polar groups into polyimide and simultaneously regulate the dihedral angle of conjugated benzene rings to achieve the energy storage performance of polyimide at high temperatures, providing an opportunity for designing polymer dielectrics with excellent energy storage performance at high temperatures.

[0011] To achieve the above technical problems, the present invention adopts the following technical solutions:

[0012] The purpose of the present invention is to provide a method for regulating the energy storage density of polyimide films at high temperatures by adjusting the molecular structure, including the following steps:

[0013] Step 1: Dissolve diamine in a solvent, place it in an ice-water bath, and stir until uniform.

[0014] Step 2: Add dianhydride in batches while stirring. After the addition is complete, continue to stir until uniform to obtain a PAA solution.

[0015] Step 3: Spread the PAA solution to form a film, and perform imidization by gradient heating to obtain a polyimide film.

[0016] Further defined, in step 1, the diamine is one or a combination of several of 4,4-diaminodiphenyl ether, 5-amino-2-(4-aminophenyl)benzimidazole, 2-(4-aminophenyl)-5-aminobenzoxazole, 4,4'-diaminobenzanilide, 2,4-diaminotoluene, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 2,2'-bis(trifluoromethyl)diaminobiphenyl, 4,4'-diaminodiphenyl sulfone.

[0017] Further defined, in step 1, the solvent is one or an arbitrary ratio combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone.

[0018] Further defined, in step 2, the dianhydride is added in 4 to 10 batches, and the addition amount of each subsequent batch is 20% to 60% of the previous batch, with an interval time of 15 min to 30 min.

[0019] Further defined, in step 2, the dianhydride is one or a combination of several of cyclobutanetetracarboxylic dianhydride, pyromellitic dianhydride, bisphenol A dianhydride, cyclohexanetetracarboxylic dianhydride, 4,4'-(hexafluoroisopropyl)diphthalic anhydride.

[0020] Further defined, in step 2, the molar ratio of diamine to dianhydride is (0.6 to 1.3):1.

[0021] Further defined, in step 2, the solid content of the prepared PAA solution is 10% to 20%.

[0022] Further limitation: in step two, imidization is carried out by gradient heating from 60°C to 400°C; it can be maintained at 60°C for 1 hour and at 100°C, 150°C, 200°C, 250°C, 300°C, 350°C for 0.5 hour respectively for imidization; it can be maintained at 80°C for 1 hour and at 120°C, 160°C, 200°C, 240°C, 280°C for 0.5 hour respectively for imidization; it can be maintained at 80°C for 1 hour, at 120°C, 160°C, 200°C, 240°C, 280°C for 0.5 hour respectively, and at 350°C for 1 hour for imidization; it can be maintained at 80°C for 1 hour, at 120°C, 160°C, 200°C, 240°C for 0.5 hour respectively, and at 300°C for 1 hour for imidization; it can be maintained at 80°C for 1 hour and at 100°C, 150°C, 200°C, 250°C, 300°C, 350°C for 0.5 hour respectively for imidization; it can be maintained at 80°C for 1 hour and at 100°C, 150°C, 200°C, 250°C, 300°C for 0.5 hour respectively for imidization; it can be maintained at 80°C for 1 hour, at 120°C, 160°C, 200°C, 240°C, 300°C for 0.5 hour respectively, and at 350°C for 1 hour for imidization; it can be maintained at 60°C for 1 hour and at 100°C, 150°C, 200°C, 250°C, 300°C for 0.5 hour respectively for imidization.

[0023] Further limitation: the thickness of the polyimide film obtained by the method of the present invention is 0.5 mm - 2 mm. The purity of all chemical reagents used is not less than analytical pure.

[0024] Another object of the present invention is to provide a polyimide film prepared by any of the above methods as claimed.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The polyimide film prepared by the method for regulating the high-temperature energy storage of polyimide film by regulating the molecular structure provided by the present invention, which is used as the raw material for making modern embedded capacitors and semiconductor memory devices, etc., can effectively improve the electricity storage capacity of capacitors and the storage function of semiconductor memory devices, and can maintain stability at high temperatures.

[0027] The polyimide film prepared by the method for regulating the high-temperature energy storage of polyimide film by regulating the molecular structure provided by the present invention introduces polar groups into polyimide by using different monomers, and while maintaining the high-temperature stability of polyimide, greatly improves the energy storage performance of polyimide.

[0028] The polyimide film prepared by the method of regulating molecular structure to control the high-temperature energy storage of polyimide film provided by the present invention has an energy storage density of not less than 4 J / cm at 200 °C 3 The preparation process provided by this method is simple, pollution-free, low in energy consumption, low in cost, high in safety factor, and suitable for industrial production.

[0029] The polyimide film prepared by the present invention can be used as raw materials for making modern embedded capacitors, semiconductor storage devices, etc.

[0030] In order to further understand the features and technical content of the present invention, please refer to the following detailed description of the present invention and the drawings. However, the attached drawings are only for reference and illustration, and are not used to limit the present invention. Description of the Drawings

[0031] Figure 1 It is the infrared spectrogram of eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8

[0032] Figure 2 It is the X-ray diffraction pattern of eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8

[0033] Figure 3 It is the thermogravimetric analysis diagram of eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8

[0034] Figure 4 is the relationship diagram of dielectric constant, dielectric loss and frequency of eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8 at different temperatures. a is the relationship diagram of dielectric constant, dielectric loss and frequency of polyimide film at room temperature, and b is the relationship diagram of dielectric constant, dielectric loss and frequency at 200 °C

[0035] Figure 5 It is the relationship diagram of dielectric constant, dielectric loss and temperature of eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8 at 1 kHz

[0036] Figure 6 is the Weibull distribution diagram of breakdown field strength of eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8 at different temperatures. a is the Weibull distribution diagram of breakdown field strength of polyimide at room temperature, and b is the Weibull distribution diagram of breakdown field strength at 200 °C

[0037] Figure 7 is the change diagram of energy storage density and transmission efficiency with breakdown field strength of eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8 at different temperatures. a is the change diagram of energy storage density and transmission efficiency of polyimide with breakdown field strength at room temperature, and b is the change diagram of energy storage density and transmission efficiency with breakdown field strength at 200 °C. Detailed implementation manners

[0038] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, and at the same time do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several modifications and improvements can be made. These all belong to the protection scope of the present invention.

[0039] Embodiment 1: The method for regulating the energy storage density of a polyimide film at high temperature by adjusting the molecular structure in this embodiment is achieved through the following steps:

[0040] Step 1: Weigh 2.0026 g of 4,4-diaminodiphenyl ether and place it in a three-necked flask. Add 20 g of N,N-dimethylacetamide. Place the three-necked flask in an ice-water bath and mechanically stir at a speed of 1000 revolutions per minute until uniform.

[0041] Step 2: Add pyromellitic dianhydride in 6 portions, each time adding 50% of the current total mass, with an interval of 20 minutes each time. The total addition amount is 2.1812 g. Mechanically stir at a speed of 1000 revolutions per minute for 4 hours to obtain a PAA colloidal solution.

[0042] Step 3: Cast the PAA colloidal solution on a film casting machine. The casting thickness is 1 mm. Perform imidization by gradient heating, and then obtain a polyimide film after natural cooling.

[0043] Among them, in Step 3, the specific process of imidization is as follows: Heat up to 60 °C at a rate of 5 °C / minute, hold at 60 °C for 1 hour, heat up to 100 °C at a rate of 5 °C / minute, hold at 100 °C for 0.5 hour, heat up to 150 °C at a rate of 5 °C / minute, hold at 150 °C for 0.5 hour, heat up to 200 °C at a rate of 5 °C / minute, hold at 200 °C for 0.5 hour, heat up to 250 °C at a rate of 5 °C / minute, hold at 250 °C for 0.5 hour, heat up to 300 °C at a rate of 5 °C / minute, hold at 300 °C for 0.5 hour, heat up to 350 °C at a rate of 5 °C / minute, and hold at 350 °C for 0.5 hour.

[0044] Embodiment 2: The method for regulating the energy storage density of a polyimide film at high temperature by adjusting the molecular structure in this embodiment is achieved through the following steps:

[0045] Step 1: Weigh 1.0012 g of 4,4-diaminodiphenyl ether and place it in a three-necked flask. Add 22 g of N,N-dimethylacetamide. Place the three-necked flask in an ice-water bath and mechanically stir at a speed of 1000 revolutions per minute until uniform.

[0046] Step 2: Add bisphenol A dianhydride in 10 portions, each time adding 50% of the current total mass, with an interval of 20 minutes each time. The total addition amount is 2.6545 g. After mechanical stirring at a speed of 1000 revolutions per minute for 6 hours, a PAA solution is obtained;

[0047] Step 3: Spread the PAA solution on a film spreading machine with a spreading thickness of 1.2 mm, and perform imidization by gradient heating. After natural cooling, a polyimide film is obtained;

[0048] Among them, in Step 3, the specific process of imidization is as follows: Heat up to 80°C at a rate of 5°C per minute, hold at 80°C for 1 hour, heat up to 120°C at a rate of 5°C per minute, hold at 120°C for 0.5 hour, heat up to 160°C at a rate of 5°C per minute, hold at 160°C for 0.5 hour, heat up to 200°C at a rate of 5°C per minute, hold at 200°C for 0.5 hour, heat up to 240°C at a rate of 5°C per minute, hold at 240°C for 0.5 hour, heat up to 280°C at a rate of 5°C per minute, and hold at 280°C for 0.5 hour.

[0049] Example 3: The method for regulating the energy storage density of a polyimide film at high temperature by adjusting the molecular structure in this example is achieved through the following steps:

[0050] Step 1: Weigh 2.2436 g of 5-amino-2-(4-aminophenyl)benzimidazole and place it in a three-necked flask. Add 20 g of N,N-dimethylacetamide. Place the three-necked flask in an ice-water bath and mechanically stir at a speed of 1000 revolutions per minute until uniform;

[0051] Step 2: Add bisphenol A dianhydride in 8 portions, each time adding 50% of the current total mass, with an interval of 20 minutes each time. The total addition amount is 2.2810 g. After mechanical stirring at a speed of 1000 revolutions per minute for 5 hours, a PAA solution is obtained;

[0052] Step 3: Spread the PAA solution on a film spreading machine with a spreading thickness of 1.5 mm, and perform imidization by gradient heating. After natural cooling, a polyimide film is obtained;

[0053] Among them, in step 3, the imidization process is as follows: Heat up to 80°C at a rate of 5°C per minute, hold at 80°C for 1 hour, heat up to 120°C at a rate of 5°C per minute, hold at 120°C for 0.5 hour, heat up to 160°C at a rate of 5°C per minute, hold at 160°C for 0.5 hour, heat up to 200°C at a rate of 5°C per minute, hold at 200°C for 0.5 hour, heat up to 240°C at a rate of 5°C per minute, hold at 240°C for 0.5 hour, heat up to 280°C at a rate of 5°C per minute, hold at 280°C for 0.5 hour, heat up to 350°C at a rate of 5°C per minute, hold at 350°C for 0.5 hour.

[0054] Example 4: The method for regulating the energy storage density of the polyimide film at high temperature by adjusting the molecular structure in this example is achieved through the following steps:

[0055] Step 1: Weigh 1.1217 g of 5-amino-2-(4-aminophenyl)benzimidazole and place it in a three-necked flask. Add 20 g of N,N-dimethylacetamide. Place the three-necked flask in an ice-water bath and mechanically stir at a speed of 1000 revolutions per minute until homogeneous.

[0056] Step 2: Add bisphenol A dianhydride in 8 portions, each time adding 40% of the current total mass, with an interval of 25 minutes each time. The total addition amount is 2.6545 g. Mechanically stir at a speed of 1000 revolutions per minute for 6 hours to obtain a PAA glue solution.

[0057] Step 3: Spread the PAA glue solution on a film spreading machine with a spreading thickness of 1 mm, perform imidization by gradient heating, and obtain a polyimide film after natural cooling.

[0058] Among them, in step 3, the imidization process is as follows: Heat up to 80°C at a rate of 5°C per minute, hold at 80°C for 1 hour, heat up to 120°C at a rate of 5°C per minute, hold at 120°C for 0.5 hour, heat up to 160°C at a rate of 5°C per minute, hold at 160°C for 0.5 hour, heat up to 200°C at a rate of 5°C per minute, hold at 200°C for 0.5 hour, heat up to 240°C at a rate of 5°C per minute, hold at 240°C for 0.5 hour, heat up to 300°C at a rate of 5°C per minute, hold at 300°C for 1 hour.

[0059] Example 5: The method for regulating the energy storage density of the polyimide film at high temperature by adjusting the molecular structure in this example is achieved through the following steps:

[0060] Step 1: Weigh 2.2525 of 2-(4-aminophenyl)-5-aminobenzoxazole and place it in a three-necked flask. Add 18 g of N,N-dimethylacetamide. Place the three-necked flask in an ice-water bath and mechanically stir at a speed of 1000 revolutions per minute until homogeneous.

[0061] Step 2: Add pyromellitic dianhydride in 6 portions, each time adding 50% of the current total mass, with an interval of 15 minutes each time. The total addition amount is 2.2443 g. Mechanically stir at a speed of 1000 revolutions per minute for 4 hours to obtain a PAA solution.

[0062] Step 3: Spread the PAA solution on a film coater with a film thickness of 1.8 mm, and perform imidization by gradient heating. After natural cooling, a polyimide film is obtained.

[0063] Among them, in Step 3, the specific imidization process is as follows: Heat up to 80°C at a rate of 5°C per minute, hold at 80°C for 1 hour, heat up to 100°C at a rate of 5°C per minute, hold at 100°C for 0.5 hour, heat up to 150°C at a rate of 5°C per minute, hold at 150°C for 0.5 hour, heat up to 200°C at a rate of 5°C per minute, hold at 200°C for 0.5 hour, heat up to 250°C at a rate of 5°C per minute, hold at 250°C for 0.5 hour, heat up to 300°C at a rate of 5°C per minute, hold at 300°C for 0.5 hour, heat up to 350°C at a rate of 5°C per minute, and hold at 350°C for 0.5 hour.

[0064] Example 6: The method for regulating the energy storage density of a polyimide film at high temperature by adjusting the molecular structure in this example is achieved through the following steps:

[0065] Step 1: Weigh 1.1314 of 2-(4-aminophenyl)-5-aminobenzoxazole and place it in a three-necked flask. Add 18 g of N,N-dimethylacetamide. Place the three-necked flask in an ice-water bath and mechanically stir at a speed of 1000 revolutions per minute until homogeneous.

[0066] Step 2: Add bisphenol A dianhydride in 6 portions, each time adding 50% of the current total mass, with an interval of 20 minutes each time. The total addition amount is 2.6548 g. Mechanically stir at a speed of 1000 revolutions per minute for 6 hours to obtain a PAA solution.

[0067] Step 3: Spread the PAA solution on a film coater with a film thickness of 1.2 mm, and perform imidization by gradient heating. After natural cooling, a polyimide film is obtained.

[0068] Among them, in step 3, the imidization process is as follows: Heat up to 80°C at a rate of 5°C per minute, hold at 80°C for 1 hour, heat up to 100°C at a rate of 5°C per minute, hold at 100°C for 0.5 hour, heat up to 150°C at a rate of 5°C per minute, hold at 150°C for 0.5 hour, heat up to 200°C at a rate of 5°C per minute, hold at 200°C for 0.5 hour, heat up to 250°C at a rate of 5°C per minute, hold at 250°C for 0.5 hour, heat up to 300°C at a rate of 5°C per minute, hold at 300°C for 0.5 hour.

[0069] Example 7: The method for regulating the energy storage density of the polyimide film at high temperature by adjusting the molecular structure in this example is achieved through the following steps:

[0070] Step 1: Weigh 2.2726 g of 4,4'-diaminobenzanilide and place it in a three-necked flask. Add 20 g of N,N-dimethylacetamide. Place the three-necked flask in an ice-water bath and mechanically stir at a speed of 1000 revolutions per minute until homogeneous.

[0071] Step 2: Add pyromellitic dianhydride in 7 portions, each time adding 60% of the current total mass, with an interval of 15 minutes each time. The total addition amount is 2.2243 g. Mechanically stir at a speed of 1000 revolutions per minute for 4 hours to obtain a PAA glue solution.

[0072] Step 3: Spread the PAA glue solution on a film spreading machine. The film spreading thickness is 1.3 mm. Perform imidization by gradient heating, and after natural cooling, obtain a polyimide film.

[0073] Among them, in step 3, the imidization process is as follows: Heat up to 80°C at a rate of 5°C per minute, hold at 80°C for 1 hour, heat up to 120°C at a rate of 5°C per minute, hold at 120°C for 0.5 hour, heat up to 160°C at a rate of 5°C per minute, hold at 160°C for 0.5 hour, heat up to 200°C at a rate of 5°C per minute, hold at 200°C for 0.5 hour, heat up to 240°C at a rate of 5°C per minute, hold at 240°C for 0.5 hour, heat up to 300°C at a rate of 5°C per minute, hold at 300°C for 0.5 hour, heat up to 350°C at a rate of 5°C per minute, hold at 350°C for 1 hour.

[0074] Example 8: The method for regulating the energy storage density of the polyimide film at high temperature by adjusting the molecular structure in this example is achieved through the following steps:

[0075] Step 1: Weigh 1.1345 g of 4,4'-diaminobenzanilide and place it in a three-necked flask. Add 18 g of N,N-dimethylacetamide. Place the three-necked flask in an ice-water bath and mechanically stir at a speed of 1000 revolutions per minute until homogeneous.

[0076] Step 2: Add bisphenol A dianhydride in 9 portions, with each portion being 60% of the current total mass, and with a 15-minute interval between each addition. The total addition amount is 2.6550 g. After mechanical stirring at a speed of 1000 revolutions per minute for 10 hours, a PAA solution is obtained.

[0077] Step 3: Spread the PAA solution on a film spreading machine with a film thickness of 1.6 mm, and perform imidization by gradient heating. After natural cooling, a polyimide film is obtained.

[0078] Among them, in Step 3, the specific imidization process is as follows: Heat up to 80°C at a rate of 5°C per minute, hold at 80°C for 1 hour, heat up to 100°C at a rate of 5°C per minute, hold at 100°C for 0.5 hour, heat up to 150°C at a rate of 5°C per minute, hold at 150°C for 0.5 hour, heat up to 200°C at a rate of 5°C per minute, hold at 200°C for 0.5 hour, heat up to 250°C at a rate of 5°C per minute, hold at 250°C for 0.5 hour, heat up to 300°C at a rate of 5°C per minute, and hold at 300°C for 0.5 hour.

[0079] The infrared spectra of the eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8 are as Figure 1 shown. From Figure 1 the absorption bands at 1775 cm -1 , 1726 cm -1 , 1373 cm -1 , and 725 cm -1 are considered to be the characteristics of polyimide. It should be noted that no characteristic peaks of polyamic acid (PAA) are observed in the range of 3200 cm -1 to 2800 cm -1 . These findings confirm that all PI films have undergone complete thermal imidization during the critical high-temperature process, further ensuring the improvement of the final product performance and industrial feasibility.

[0080] The X-ray diffraction patterns of the eight polyimide (PI) films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8 are as Figure 2 shown. Obvious broad peaks can be observed from the figure, confirming that these eight PIs are amorphous polymers. The spacing (d) values of the eight PIs are calculated, and the results show that the spacing of the PI based on bisphenol A dianhydride (BPADA) is greater than that of the PI based on pyromellitic dianhydride (PMDA), indicating that the twisted long-chain structure in BPADA increases the interchain spacing.

[0081] The thermogravimetric analysis of the eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8 is as Figure 3As shown. The thermal decomposition temperature of the PMDA-based PI film is higher than that of the BPADA-based PI film. This difference is mainly attributed to the longer and softer chain segments of BPADA, while PMDA exhibits greater rigidity and a denser polymer arrangement. Obviously, the T of all eight PIs d5％ all exceed 500 °C, far exceeding the operating temperature of high-temperature dielectric capacitors, indicating excellent high-temperature resistance performance.

[0082] The graphs of the relationship between the dielectric constant, dielectric loss and frequency of the eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8 at room temperature and 200 °C are shown in Figure 4. From Figure 4, with the change of diamine, as the dielectric constant increases, the dielectric loss also increases, but the increase amplitude is less than 0.03. With the increase of temperature, the frequency stability of the dielectric loss also gradually increases, but the overall values are concentrated in a relatively low (<0.04, 50 Hz) range.

[0083] The graphs of the relationship between the dielectric constant, dielectric loss and temperature of the eight polyimide films prepared in Examples 1, 2, 3, 4, 5, 6, 7, and 8 at 50 Hz are as Figure 5 shown. From Figure 5 it can be seen that as the temperature gradually increases, the ε r and tanδ of the eight polyimide films remain relatively stable. This stability can be attributed to the advantage of electronic polarization and the strong rigidity of the molecular chain segments, resulting in a more compact overall arrangement and weaker temperature dependence. The overall change does not exceed 10%, indicating that the PI film has good dielectric thermal stability. The frequency stability of the dielectric loss also gradually increases, while the overall value still remains concentrated in a relatively low range (<0.04, 1 kHz). This indicates that these films can be effectively applied to high-temperature environments.

[0084] The Weibull distribution graphs of the breakdown field strength of the eight polyimide films in Examples 1, 2, 3, 4, 5, 6, 7, and 8 at room temperature and 200 °C are shown in Figure 6. From Figure 6, it can be seen that the breakdown field strength (E b ) of all eight polymers is higher than 450 MV / m, and the β value is relatively high, indicating that these films have high stability. Adding bisphenol A dianhydride significantly improves the Weibull characteristic breakdown strength (E b ) of PI. The electron conjugation effect in the polymer weakens, resulting in an enlarged band gap and restricted molecular motion and charge transport. At room temperature, the film in Example 8 exhibits the highest breakdown field strength of 598 MV / m. In addition, the film in Example 8 shows excellent performance stability at high temperature and high electric field. As the temperature increases from room temperature to 200 °C, the E b of the film slightly decreases, but still remains at 538 MV / m.

[0085] The variations of the energy storage density and the transfer efficiency of eight polyimide films in Examples 1, 2, 3, 4, 5, 6, 7, and 8 with the breakdown field strength at room temperature and 200 °C are shown in Figure 7. As can be seen from Figure 7, compared with Example 1 (4.32 J / cm 3 ), when we introduced polar groups and adjusted the conjugated dihedral angle in Example 8 (7.87 J / cm 3 ), the energy storage density increased by nearly 82% (η > 80%). This proves that it is completely feasible to adjust the dihedral angle between conjugated benzene rings in the molecular structure to improve the energy storage performance of dielectric materials. At 200 °C, Example 8 exhibited the highest energy storage density (U e ) of 7.37 J / cm 3 at 500 MV / m. As the temperature increased to 200 °C, the decrease in the energy storage density of PI was not significant. When η ≥ 80%, the U e of Example 8 reached 5.99 J / cm3. This indicates that it has high practical value. These results will lay a foundation for future research and applications.

[0086] The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for regulating high-temperature energy storage of polyimide film by adjusting molecular structure, characterized in that: The following steps are involved: Step 1, dissolve the diamine in a solvent, place in an ice water bath, and stir until uniform; Step 2, adding dianhydride in batches while stirring, and continuing to stir until uniform after the addition is completed to obtain PAA glue solution; Step 3: Spread the PAA glue solution on a film and perform imidization by increasing the temperature in a gradient manner to obtain a polyimide film.

2. The method according to claim 1, characterized in that: The diamine is one or a combination of 4,4-diaminodiphenyl ether, 5-amino-2-(4-aminophenyl)benzimidazole, 2-(4-aminophenyl)-5-aminobenzoxazole, 4,4'-diaminobenzanilide, 2,4-diaminotoluene, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 2,2'-bis(trifluoromethyl)diaminobiphenyl, and 4,4'-diaminodiphenyl sulfone.

3. The method according to claim 1, characterized in that: The solvent is one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone.

4. The method according to claim 1, characterized in that: The dianhydride is added in 4 to 10 batches, with the amount of each subsequent batch being 20% ​​to 60% of the previous batch, and the interval time being 15 minutes to 30 minutes.

5. The method according to claim 1, characterized in that: The dianhydride is one or a combination of cyclobutanetetracarboxylic dianhydride, pyromellitic dianhydride, bisphenol A dianhydride, cyclohexanetetracarboxylic dianhydride, and 4,4'-(hexafluoroisopropyl)phthalic anhydride.

6. The method according to claim 1, characterized in that: The molar ratio of diamine to dianhydride is (0.6-1.3):

1.

7. The method according to claim 1, characterized in that: The solid content of PAA glue is 10% to 20%.

8. The method according to claim 1, characterized in that: The temperature was increased gradually from 60°C to 400°C.

9. The method according to claim 1, characterized in that: The thickness of the polyimide film is 0.5mm-2mm.

10. A polyimide film prepared by the method according to any one of claims 1 to 9.

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