Multi-element random copolymerization polyimide dielectric film as well as preparation method and application thereof

Abstract

The invention discloses a multi-element random copolymerization polyimide dielectric film as well as a preparation method and application thereof, and belongs to the technical field of dielectric materials. The thin film material is prepared from at least one diamine monomer and at least two dianhydride monomers through a random copolymerization reaction. The specific method comprises the following steps: randomly copolymerizing one or more diamine monomers and two or more anhydride monomers through a conventional two-step method to synthesize a pure polymer, casting and coating the copolymerized polyamide acid synthesized by the reaction into a film shape, carrying out thermal imidization, demolding with deionized water, and drying to obtain the material. The film is suitable for high-temperature dielectric energy storage in high-temperature film capacitors, vehicle-mounted power electronics, aerospace power supplies and oil well / geothermal power systems. Compared with the existing filler modified or monomer homopolymerized PI, the preparation process is simple, the dielectric property is stable, the energy storage density and the breakdown strength at the high temperature of 200 DEG C and the high field are remarkably improved, and excellent stability and manufacturability are achieved.

Description

Technical Field

[0001] This invention belongs to the field of dielectric materials technology, and particularly relates to a multi-component random copolymer polyimide dielectric film, its preparation method and application. Background Technology

[0002] Polymers, with their excellent mechanical and insulating properties, have been widely used in the dielectric field, and dielectric capacitors made from them are widely used in key areas such as aerospace, oil exploration, hybrid vehicles, and wind power generation. However, the limited heat resistance of most polymers greatly restricts their application in high-temperature environments. Polyimide (PI), as a polymer with excellent heat resistance, is recognized as one of the most promising high-temperature dielectric materials. In addition to its excellent heat resistance, it also possesses comprehensive advantages such as outstanding chemical stability, high mechanical strength, and radiation resistance.

[0003] However, under the combined effects of high temperature and high electric field, the donor-acceptor (DA) structural units in the PI molecular chain easily form charge transfer complexes (CTCs), leading to a significant increase in conduction losses and severely limiting its application in high-temperature capacitor energy storage. This problem is even more pronounced when there is a large difference in electron density between the dianhydride and diamine monomers. Commercially available PI products, represented by Kapton, possess excellent high-temperature resistance due to the presence of numerous benzene rings and aromatic heterocycles in their molecular structure. However, these conjugated structures result in a relatively low band gap (Eg < 3.0 eV), which easily induces long-distance delocalization of π electrons even at lower electric fields, leading to increased conduction losses and decreased electric field tolerance. High-temperature environments further exacerbate these problems, limiting energy storage density and efficiency, and ultimately causing premature failure of traditional homopolymer PI.

[0004] To suppress the formation of chromatinized tert-terminated complexes (CTCs) between and within PI molecules, researchers have developed various modification strategies, including introducing strongly electronegative groups, constructing asymmetric rigid non-coplanar structures, and alicyclic structures. Among these, strongly electronegative groups can act as permanent dipoles, increasing both polarizability and the free volume between molecular chains, thereby suppressing CTC formation. However, the polarization loss associated with dipole groups still limits their application effectiveness in high-temperature scenarios.

[0005] Conventional homopolymer PI dielectric films still suffer from several inherent defects: First, the dianhydride and diamine units in a homogeneous structure tend to form regular molecular chain structures with high linear segment symmetry, making them prone to local crystallization. Defects easily form at the interface between crystalline and amorphous regions, leading to electric field concentration and ultimately a decrease in breakdown strength. Second, the homogeneous structure is prone to forming strong CTC under high temperature and high electric field conditions, resulting in deterioration of insulation performance and increased conduction loss. This defect can easily cause catastrophic failures in polymer film capacitors. Third, while introducing highly polar groups can increase the dielectric constant and enhance dipole polarization, thereby increasing the energy density at the same field strength, it may lead to excessively strong intermolecular interactions, causing crystallization or microphase separation, which in turn reduces the breakdown strength. Fourth, in high-frequency or high-temperature environments, homopolymer PI with excessively high polarity or high chain segment regularity is more likely to induce carrier transport and dielectric relaxation, exacerbating energy loss and dielectric loss, resulting in a significant decrease in charge and discharge efficiency, ultimately affecting energy utilization and long-term device stability. In summary, conventional homopolymer PI cannot simultaneously achieve high breakdown field strength (…). E b High energy density U d ) and high charge / discharge efficiency and cycle efficiency ( η ( ) synergistic consideration.

[0006] Therefore, there is an urgent need to develop a preparation method that enables precise molecular-level design, allowing for the synergistic regulation of the dielectric properties of materials by flexibly introducing different functional groups or segments, ultimately achieving high dielectric strength. E b ,high U d With Gao η Simultaneous consideration. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a multi-component random copolymer polyimide dielectric film, its preparation method, and its applications.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A multi-component random copolymer polyimide dielectric film is prepared by random copolymerization of at least one diamine monomer and at least two dianhydride monomers; the chemical structural formula of the multi-component random copolymer polyimide dielectric film is shown in formula (I): Equation (I) In the formula, m and n represent the molar fraction or the number of repeating units of the structural unit; wherein, both m and n are positive numbers, and satisfy 0 < m / (m + n) < 1. Preferably, the molar ratio (m∶n) of m to n is 5∶95 - 95∶5, more preferably 30∶70 to 70∶30. It should be noted that formula (I) is only a schematic expression of the chemical composition, and the polyimide is a random copolymer, and the two repeating units are randomly statistically distributed in the molecular chain, rather than a block distribution; Ar1 represents a dianhydride monomer; Ar2 represents a diamine monomer.

[0009] Through the selective random copolymerization of multiple monomers, the present invention introduces "structural perturbation", making the material not easy to crystallize, significantly reducing the crystallization tendency of polyimide, improving the film uniformity, making the electric field distribution uniform, and enhancing the breakdown strength. The copolymerization system improves the degree of electron localization, blocks the long-range migration path of carriers, reduces the leakage current, and thus can still maintain high efficiency at high temperatures. It has strong controllability and scalability. The random copolymerization of multiple monomers can adjust the polarity and rigidity in proportion to achieve the balance of energy density and charge-discharge efficiency. The copolymerization monomer combination of the present invention is flexible. According to the structural combination of different diamine or dianhydride monomers, the main chain of polyimide can be designed from the molecular structure, and the dielectric properties of different application scenarios can be regulated by adjusting the ratio of diamine and dianhydride monomers. On the premise of ensuring thermal stability, the dielectric properties can be optimized. It can achieve high E b 、high U d and high η . The prepared thin film can work for a long time at 200°C, has high reliability and application value as a high-temperature energy storage capacitor thin film, and is superior to traditional conventional homopolymer polyimide thin films.

[0010] Furthermore, the molar ratio of the diamine monomer to the dianhydride monomer is (0.95 - 1.05)∶(1.05 - 0.95).

[0011] Further, the diamine monomer is selected from 2,2'-bis(trifluoromethyl)diaminobiphenyl (TFMB), 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether (6FODA), 4,4'-diaminodiphenyl ether (4,4'-ODA), 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane (HFBAPP), 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane, N,N'-(2,2'-bis(trifluoromethyl)-[1,1'-di... [Biphenyl]-4,4'-diyl)bis(4-aminobenzamide) (AB-TFMB), 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl (6FAPBP), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 2,2-bis(3-aminophenyl)hexafluoropropane, 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline] (6FAPB), 2,2-bis(3-amino-4-tolyl)hexafluoropropane, 1,1-bis(4-aminophenyl)cyclohexane, 9,9- Bis(4-aminophenyl)fluorene (BAFL), 9,9-bis(4-amino-3-fluorophenyl)fluorene, 9,9-bis(4-amino-3-chlorophenyl)fluorene, 9,9-bis(4-amino-3-tolyl)fluorene, sulfone aminophenylene (DDS), 4,4'-bis(3-aminophenoxy)diphenyl sulfone (M-BAPS), 4,4'-bis(4-aminophenoxy)diphenyl sulfone (BAPS), 3,3'-diaminodiphenyl sulfone, 3,3'-diamino-4,4'-dihydroxydiphenyl sulfone, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane (BA) At least one of PP), 2,2'-bis[4-(3-aminophenoxy)phenyl]propane (m-BAPP), A,A'-bis(4-aminophenyl)-1,4-diisopropylbenzene, 4,4'-bis(4-aminophenoxy)biphenyl (BAPOBP), 4,4'-diaminodicyclohexylmethane (PACM), 1,4-cyclohexanediamine, 3,3'-dimethyl-4,4-diaminodicyclohexylmethane (MACM), bis(4-aminocyclohexyl) ether and 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindene.

[0012] Furthermore, the structural formula of the 2,2'-bis(trifluoromethyl)diaminobiphenyl is: The structural formula of the 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether is: The structural formula of the 4,4'-diaminodiphenyl ether is: The structural formula of the 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane is: The structural formula of the 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)benzene]hexafluoropropane is: The structural formula of N,N'-(2,2'-bis(trifluoromethyl)-[1,1'-diphenyl]-4,4'-diyl)bis(4-aminobenzamide) is as follows: The structural formula of the 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl is: The structural formula of the 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane is: The structural formula of the 2,2-bis(3-aminophenyl)hexafluoropropane is: The structural formula of the 4,4'-[1,4-phenylbis(oxy)]bis[3-(trifluoromethyl)aniline] is: The structural formula of the 2,2-bis(3-amino-4-tolyl)hexafluoropropane is: The structural formula of the 1,1-bis(4-aminophenyl)cyclohexane is: The structural formula of the 9,9-bis(4-aminophenyl)fluorene is: The structural formula of the 9,9-bis(4-amino-3-fluorophenyl)fluorene is: The structural formula of the 9,9-bis(4-amino-3-chlorophenyl)fluorene is: The structural formula of the 9,9-bis(4-amino-3-tolyl)fluorene is: The structural formula of the aminophenyl sulfone is: The structural formula of the 4,4'-bis(3-aminophenoxy)diphenyl sulfone is: The structural formula of the 4,4'-bis(4-aminophenoxy)diphenyl sulfone is: The structural formula of the 3,3'-diaminodiphenyl sulfone is as follows: The structural formula of the 3,3'-diamino-4,4'-dihydroxydiphenyl sulfone is: The structural formula of the 2,2'-bis[4-(4-aminophenoxyphenyl)]propane is: The structural formula of the 2,2'-bis[4-(3-aminophenoxy)phenyl]propane is: The structural formula of the aforementioned A,A'-bis(4-aminophenyl)-1,4-diisopropylbenzene is: The structural formula of the 4,4'-bis(4-aminophenoxy)biphenyl is: The structural formula of the 4,4'-diaminodicyclohexylmethane is: The structural formula of the 1,4-cyclohexanediamine is: The structural formula of the 3,3'-dimethyl-4,4-diaminodicyclohexylmethane is: The structural formula of the bis(4-aminocyclohexyl) ether is: The structural formula of the 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindene is: .

[0013] Further, the dianhydride monomer is selected from 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA), 4,4'-oxobisphthalic anhydride (ODPA), pyromellitic dianhydride (PMDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (A-BPDA), 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride (A-ODPA), hexafluorodianhydride (6FDA), 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic dianhydride (6FCDA), 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride (DSDA), bisphenol A type diether dianhydride (BPADA), and 4,4'-terephthalobisphthalic anhydride (HQ). The following are at least two of the following: DA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA), 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), 1,2,3,4-cyclopentanetetracarboxylic dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride (HBPDA), 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride (BPAF), tetrachloroperyl anhydride, 3,4,9,10-tetracarboxylic anhydride, bicyclo[2.2.2]octane-2,3:5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, and dimethylcyclobutanetetracarboxylic anhydride (DMCBDA).

[0014] Furthermore, the structural formula of the 3,3',4,4'-benzophenone tetracarboxylic dianhydride is: The structural formula of 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is: The structural formula of 4,4'-oxophthalic anhydride is: The structural formula of pyromellitic dianhydride is: The structural formula of 2,3,3',4'-biphenyltetracarboxylic dianhydride is: The structural formula of 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride is: The structural formula of hexafluorodianhydride is: The structural formula of 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic dianhydride is: The structural formula of 3,3,4,4-diphenylsulfone tetracarboxylic acid dianhydride is: The structural formula of bisphenol A type diether dianhydride is: The structural formula of 4,4'-terephthalodioxydiphthalic anhydride is: The structural formula of 1,2,4,5-cyclohexanetetracarboxylic dianhydride is: The structural formula of 1,2,3,4-cyclobutanediol dianhydride is: The structural formula of 1,2,3,4-cyclopentacarboxylic acid dianhydride is: The structural formula of dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride is: The structural formula of 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride is: The structural formula of 9,9-bis(3,4-dicarboxyphenyl)fluorene dihydric anhydride is: The structural formula of tetrachloroperyl anhydride is: The structural formula of 3,4,9,10-tetracarboxylic anhydride is: The structural formula of bicyclic [2.2.2]octane-2,3:5,6-tetracarboxylic dianhydride is: The structural formula of bicyclic [2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride is: The structural formula of dimethylcyclobutanetetracarboxylic anhydride is: .

[0015] This invention also provides a method for preparing a multi-component random copolymer polyimide dielectric film, comprising the following steps: The diamine monomer is dissolved in an organic solvent and stirred under an inert gas (nitrogen) atmosphere to obtain a diamine solution; The dianhydride monomer is added to the diamine solution to prevent local viscosity jumps and side reactions. The polymerization reaction is carried out under a nitrogen atmosphere to obtain a high-viscosity, semi-transparent copolyamic acid solution. The copolyamic acid solution is coated onto a substrate using spin coating, slot die coating, doctor blade coating, casting, or extrusion to form a wet film. The wet film is subjected to thermal imidization treatment, followed by demolding and drying to obtain the multi-component random copolymer polyimide dielectric film.

[0016] This invention employs a random copolymerization method. Unlike homopolymerization or block copolymerization, random copolymerization introduces component disorder at the nanoscale, which can disrupt long-range regularity and potential microcrystallization tendency, reduce local field distortion caused by the interface between ordered and disordered domains, and help improve Weibull shape parameters and E b ,improve U d and ηRandom copolymerization can introduce various imide units with different volumes and significant differences in symmetry, which can disrupt the regularity of chain segments, the planar stacking and periodic sequence of molecular chains, reduce defect conduction paths, and make the system tend towards a stable amorphous state. This reduces crystal interfaces, improves the density and uniformity of the film, and increases the dielectric breakdown field strength. The proportion of polar groups can be controlled, and different diamine or dianhydride monomers can be selected according to the desired film performance. While ensuring high-temperature stability, the dielectric constant and energy storage density can be controlled, thus simultaneously achieving high performance. E b ,high U d With Gao η Different combinations of diamine or dianhydride monomers can regulate [the effect / condition]. T g It regulates processability and film uniformity.

[0017] Furthermore, the stirring and dissolving temperature is 0-40℃ and the time is 0.5-2 hours; the polymerization reaction temperature is 0-90℃ and the time is 6-36 hours.

[0018] Furthermore, the organic solvent is selected from any one of N,N-dimethylacetamide (DMAc), N,N-dimethylpyrrolidone (NMP), and N,N-dimethylformamide (DMF).

[0019] Furthermore, the solid content of the copolyamic acid solution is 8-26 wt%, preferably 15 wt%.

[0020] Furthermore, the substrate is a pre-treated ultra-clean glass plate, which is treated by: washing with alcohol, wiping dry with lint-free paper, and preheating in an oven at 65°C for 10-30 minutes.

[0021] Furthermore, the specific steps of the thermal imidization treatment are as follows: treat at 80℃, 120℃, 150℃, 200℃ and 260℃ for 0.5-3 hours respectively.

[0022] Furthermore, the demolding is carried out in deionized water.

[0023] Furthermore, the drying process is carried out at 50-90°C for 3-16 hours.

[0024] The thickness of the thin film prepared by the method of the present invention is 0.2-50 micrometers (preferably 6-12 micrometers).

[0025] In the field of dielectric thin films, the preferred range of 6-12 μm is often considered the "golden balance" between breakdown strength and machinability. Controlling the film thickness within this range significantly suppresses the formation of critical size defects within the material. Precursor solutions with different solid contents require different doctor blade graduations to test film formation. This invention uses either a 150-micron or 100-micron graduation doctor blade to cast a 15wt% polyamic acid solution, resulting in excellent film quality and a film thickness range of 6-12 microns. When the film thickness is below 6 μm, the tensile strength and tensile properties of the material decrease significantly, failing to meet the minimum mechanical strength requirements of high-speed winding processes for capacitor elements. This leads to a sharp increase in the breakage rate during processing, hindering large-scale production. When the film thickness is above 12 μm: ① The probability of structural defects within the material increases significantly, resulting in a substantial decrease in the breakdown field strength (Eb). Compared to a 10 μm film, the breakdown field strength of a 50 μm film typically decreases by more than 30%-50%. ② As the film thickness increases, the thermal resistance increases, which is not conducive to the internal heat dissipation of the capacitor in high-power charge and discharge cycles. It is easy to cause thermal breakdown due to heat accumulation, reduce the reliability of the device, and cannot meet the miniaturization requirements of high-energy-density energy storage devices.

[0026] This invention also provides an application of a multi-component random copolymer polyimide dielectric film in the field of dielectric energy storage materials. The application environment temperature is 25-200℃.

[0027] Compared with the prior art, the present invention has the following advantages and technical effects: The copolyimide film prepared by this invention is synthesized by random copolymerization of one or more diamine monomers and two or more acid anhydride monomers in a conventional two-step method. The synthesized copolyimide is then cast and coated into a film, followed by thermal imidization, demolding with deionized water, and drying to obtain the material. This invention, through random copolymerization, allows for molecular-level design, with arbitrarily adjustable ratios of rigid and flexible segments, and controllable parameters such as dielectric constant, breakdown strength, and thermal stability, effectively improving the breakdown strength and discharge energy density of the polyimide dielectric film. This film is suitable for high-temperature film capacitors, automotive power electronics, aerospace power supplies, and high-temperature dielectric energy storage in oil well / geothermal power systems. Compared with existing filler-modified or monomer-homogenized PI, this invention has a simple preparation process, stable dielectric properties, significantly improved energy storage density and breakdown strength at 200℃ and high field, and exhibits excellent stability and manufacturability. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The dielectric constant and dielectric loss diagrams are shown for the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2. Figure 2 The graph shows the discharge energy density and discharge efficiency of the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2, tested at room temperature. Figure 3 The graph shows the PE hysteresis loop, representing the maximum electric field measured at room temperature for the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2. Figure 4 The graph shows the discharge energy density and discharge efficiency of the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2 at 200°C. Figure 5 The diagram shows the maximum electric field "PE hysteresis loop" of the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2 at 200°C. Detailed Implementation

[0029] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0030] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0032] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0033] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0034] This invention utilizes random copolymerization to enable molecular-level design, allowing for arbitrary adjustment of the ratio of rigid to flexible segments. This allows for control over parameters such as dielectric constant, breakdown strength, and thermal stability, effectively improving the breakdown strength and discharge energy density of polyimide dielectric films.

[0035] This invention provides a method for preparing a multi-component random copolymer polyimide dielectric film, comprising the following steps: (1) Preparation of diamine solution: Select at least one diamine monomer and dissolve it in an organic solvent (selected from any one of N,N-dimethylacetamide (DMAc), N,N-dimethylpyrrolidone (NMP), N,N-dimethylformamide (DMF), preferably NMP); under a nitrogen inert gas atmosphere, control the stirring temperature at 0-40℃ (preferably room temperature 25℃ or 40℃) and stir for 0.5-2 hours (preferably 0.5 hours) until the diamine monomer is completely dissolved to obtain a homogeneous diamine solution.

[0036] (2) Preparation of copolyamic acid solution by polymerization reaction: Select at least two dianhydride monomers and slowly add them to the above diamine solution (to avoid local viscosity jump and side reaction); maintain a nitrogen atmosphere and control the polymerization reaction temperature at 0-90℃ (e.g., 40℃ or 90℃), react for 6-36 hours (e.g., 6 hours, 12 hours or 18 hours), and finally obtain a high viscosity semi-transparent copolyamic acid solution with a solid content of 8-26wt% (preferably 15wt%).

[0037] (3) Preparation of wet film: First, the ultra-clean glass substrate is pretreated (washed with alcohol, wiped dry with lint-free paper, and then preheated in a 65°C oven for 10-30 minutes, preferably 10 minutes); the above copolyamic acid solution is uniformly coated on the pretreated substrate by any of the following methods: spin coating, slot die coating, scraping coating, casting or extrusion (the casting method is selected as an example in the following examples to verify the effect), forming a continuous wet film.

[0038] (4) Thermal imidization, demolding and drying: The substrate with wet film is placed in a forced-air drying oven and subjected to gradient heating thermal imidization treatment, specifically at 80℃, 120℃, 150℃, 200℃ and 260℃ for 0.5-3 hours (preferably 1 hour) to ensure complete imidization reaction; after the film cools to room temperature, it is placed in deionized water for demolding; finally, the demolded film is placed in an environment of 50-90℃ (e.g. 80℃) for 3-16 hours (e.g. 3 hours) to remove residual moisture and obtain a multi-component random copolymer polyimide dielectric film.

[0039] In the following preferred embodiments of the present invention, the molar ratio of diamine monomer to dianhydride monomer is (0.95-1.05):(1.05-0.95), preferably 1:1. The diamine monomer may be a mixture of HFBAPP, HFBAPP, and DDS (molar ratio of 0.6:0.4); the dianhydride monomer may be a mixture of HBPDA and 6FDA (molar ratio of 1:1 or 0.3:0.7) or a mixture of 6FDA, BPADA, and CBDA (molar ratio of 0.46:0.34:0.2).

[0040] Unless otherwise specified, "room temperature" in this invention refers to 25°C.

[0041] All raw materials used in this invention were purchased from the market.

[0042] The technical solution of the present invention will be further illustrated by the following embodiments. It should be noted that any aspects not described in detail in this invention are conventional practices in the art and are not the focus of this invention.

[0043] Example 1 A method for preparing a multi-component random copolymer polyimide dielectric film includes the following steps: (1) Weigh 3 mmol of diamine monomer (HFBAPP) and dissolve it in N,N-dimethylpyrrolidone (NMP). Stir at 25°C for 30 minutes under a nitrogen atmosphere until completely dissolved to obtain a diamine solution. (2) Under a nitrogen atmosphere, 1.5 mmol of dianhydride monomer (6FDA) and 1.5 mmol of dianhydride monomer (HBPDA) were added to the diamine solution obtained in step (1). The polymerization reaction was stirred at 0°C for 18 hours to obtain a copolyamic acid solution with a solid content of 15 wt%. (3) The copolyamic acid solution obtained in step (2) is coated onto the preheated clean glass substrate by casting to form a wet film. (4) The wet film obtained in step (3) is subjected to gradient heating imidization treatment in a forced-air drying oven, that is, it is treated for 1 hour at 80℃, 120℃, 150℃, 200℃ and 260℃ respectively to ensure complete imidization; then the film is cooled to room temperature, peeled off in deionized water, and vacuum dried in an oven at 80℃ for 3 hours to remove excess moisture, so as to obtain a ternary random copolymer polyimide dielectric film with a thickness of 11 micrometers.

[0044] Example 2 A method for preparing a multi-component random copolymer polyimide dielectric film includes the following steps: (1) Weigh 1.8 mmol of diamine monomer (HFBAPP) and dissolve it in N,N-dimethylpyrrolidone (NMP), then add 1.2 mmol of diamine monomer (DDS), and stir at 40°C for 30 minutes under a nitrogen atmosphere until completely dissolved to obtain a diamine solution; (2) Under a nitrogen atmosphere, 2.1 mmol of dianhydride monomer (6FDA) and 0.9 mmol of dianhydride monomer (HBPDA) were added to the diamine solution obtained in step (1). The polymerization reaction was stirred at 40°C for 12 hours to obtain a copolyamic acid solution with a solid content of 15 wt%. (3) The copolyamic acid solution obtained in step (2) is coated onto the preheated clean glass substrate by casting to form a wet film. (4) The wet film obtained in step (3) is subjected to gradient heating imidization treatment in a forced-air drying oven, that is, it is treated for 1 hour at 80℃, 120℃, 150℃, 200℃ and 260℃ respectively to ensure complete imidization; then the film is cooled to room temperature, peeled off in deionized water, and vacuum dried in an oven at 80℃ for 3 hours to remove excess moisture, to obtain a quaternary random copolymer polyimide dielectric film with a thickness of 10 micrometers.

[0045] Example 3 A method for preparing a multi-component random copolymer polyimide dielectric film includes the following steps: (1) Weigh 1.8 mmol of diamine monomer (HFBAPP) and dissolve it in N,N-dimethylpyrrolidone (NMP). Stir at 25°C for 30 minutes under a nitrogen atmosphere until completely dissolved to obtain a diamine solution. (2) Under a nitrogen atmosphere, 1.38 mmol of dianhydride monomer (6FDA) was added to the diamine solution obtained in step (1), followed by 1.02 mmol of dianhydride monomer (BPADA) and then 0.6 mmol of dianhydride monomer (CBDA). The polymerization reaction was carried out at 90°C for 6 hours to obtain a copolyamic acid solution with a solid content of 15 wt%. (3) The copolyamic acid solution obtained in step (2) is coated onto the preheated clean glass substrate by casting to form a wet film. (4) The wet film obtained in step (3) is subjected to gradient heating imidization treatment in a forced-air drying oven, that is, it is treated for 1 hour at 80℃, 120℃, 150℃, 200℃ and 260℃ respectively to ensure complete imidization; then the film is cooled to room temperature, peeled off in deionized water, and vacuum dried in an oven at 80℃ for 3 hours to remove excess moisture, to obtain a pentagonal random copolymer polyimide dielectric film with a thickness of 12 micrometers.

[0046] Comparative Example 1 A method for preparing a homopolymer polyimide (PI) includes the following steps: (1) Weigh 3 mmol of diamine monomer (ODA) and dissolve it in N,N-dimethylpyrrolidone (NMP). Then add 3 mmol of dianhydride monomer (PMDA) to the resulting mixed solution and stir at 10°C for 18 hours to obtain a polyamic acid solution with a solid content of 15 wt%. (2) The polyamic acid solution obtained in step (1) is coated onto the preheated clean glass substrate by casting to form a wet film. (3) The wet film obtained in step (2) is subjected to gradient heating imidization treatment in a forced-air drying oven, that is, treated for 1 hour at 80℃, 120℃, 150℃, 200℃ and 260℃ respectively, so as to complete imidization; then the film is cooled to room temperature, peeled in deionized water, and vacuum dried in an oven at 80℃ for 3 hours to remove excess moisture, so as to obtain a homopolymer polyimide polymer (PI) with a thickness of 10 micrometers.

[0047] Comparative Example 2 Same as Example 1, except that no dianhydride monomer (HBPDA) was added. A thin film material with a thickness of 9 micrometers was prepared, denoted as: FPI.

[0048] Performance testing: The electrical properties of the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2 were characterized using the following methods: Copper plating was performed on both sides of the thin film using a high-vacuum evaporation deposition machine to deposit copper electrodes with a diameter of 10 mm on both sides of the film for dielectric property measurement; the dielectric constant and dielectric loss were measured using a broadband dielectric impedance spectrometer with a frequency range of 10 Hz. 0 -10 6 Hz; In the energy storage performance test, copper electrodes with a diameter of 3 mm were deposited on both sides of the thin film to measure the PE hysteresis loop: the polarization-electric field (PE) hysteresis loop test was performed using a ferroelectric analyzer to measure the high-temperature energy storage performance and breakdown strength. The test sample was placed in heat-resistant silicone oil to control the temperature.

[0049] Discharge energy density of dielectric polymers ( U d The parameters () and efficiency (η) are derived from their PE hysteresis loops. The parameters are expressed as: Among them, P max (maximum polarization), P r (Residual polarization), E (applied electric field), and U loss (Energy loss density) is data measured by the PE hysteresis loop, and the discharge energy density is obtained through calculation. Ud ) and efficiency (η).

[0050] The results are shown in Tables 1 and 2. Figures 1-5 .

[0051] Table 1 Breakdown field strength of thin film materials at room temperature ( E b ) and discharge energy density ( U d ) As shown in Table 1, the room-temperature breakdown field strength of the multi-monomer random copolymer polyimide films of this invention (Examples 1-3) is greater than 600 MV / m, with Example 1 (ternary random copolymer) reaching 760 MV / m, far exceeding that of homopolymer PI (Comparative Example 1, 450 MV / m) and binary copolymer PI (Comparative Example 2, 630 MV / m). This verifies the design logic of "introducing structural perturbation through multi-monomer random copolymerization, disrupting molecular chain regularity, and reducing crystallization defects," effectively improving the electric field tolerance of the film. The room-temperature discharge energy density of Examples 1-3 is greater than 6.0 J / cm². 3 (Example 1 reaches 8.42 J / cm) 3 Furthermore, the charging and discharging efficiency remains above 90%; while Comparative Example 1 only achieves 2.5 J / cm². 3 Comparative Example 2 has a value of 5.55 J / cm³. 3 This demonstrates that multi-component random copolymerization can synergistically regulate the dielectric constant and breakdown field strength, achieving a significant increase in discharge energy density without sacrificing charge-discharge efficiency. Comparing Example 1 (1 type of diamine + 2 types of dianhydrides), Example 2 (2 types of diamine + 2 types of dianhydrides), and Example 3 (1 type of diamine + 3 types of dianhydrides), it is evident that the ternary random copolymerization (Example 1) exhibits the best overall performance. This indicates that a reasonable monomer combination (especially the binary combination of dianhydride monomers) can more precisely balance the rigidity and polarity of the molecular chain, avoiding structural disorder caused by the introduction of excessive monomers, thereby maximizing performance.

[0052] Table 2. Dielectric loss of thin film materials at room temperature and breakdown field strength at 200°C ( E b ) and discharge energy density ( U d ) As can be seen from Table 2, the dielectric loss of the thin film materials prepared in Comparative Examples 1-2 at room temperature, as well as the breakdown strength and discharge energy density tested at 200℃, are not as good as those in Examples 1, 2, and 3. This shows that the random copolymer polyimide film can effectively improve the high-temperature dielectric energy storage performance.

[0053] Figure 1The dielectric constant and dielectric loss diagrams for the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2 are shown below. Figure 1 As can be seen, at the critical test frequency of 1kHz, the dielectric losses of Examples 1-3 are all lower than those of Comparative Examples 1 and 2, and at 10... 0 -10 6 Within a wide frequency range (Hz), the dielectric loss curves of the embodiments are flatter with no significant fluctuations. This indicates that multi-component random copolymerization suppresses the formation of intermolecular charge transfer complexes (CTCs), inhibits carrier transport, and improves the frequency stability of dielectric properties. The dielectric constants of Examples 1-3 do not decrease significantly with frequency, while the dielectric constant of Comparative Example 1 is slightly higher, but the dielectric loss increases synchronously. This shows that the high dielectric constant of homopolymer PI comes at the cost of low loss, while the random copolymerization system of the present invention achieves a synergistic effect of "low loss + stable dielectric constant".

[0054] Figure 2 The graphs show the discharge energy density and discharge efficiency of the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2, tested at room temperature. Figure 2 As can be seen, the discharge energy density of Example 1 increases linearly with the increase of electric field strength, reaching nearly 8 J / cm at around 730 MV / m. 3 Furthermore, the charge / discharge efficiency remained consistently above 90%, without any sudden drop in efficiency; in Examples 2 and 3, the energy density both exceeded 6 J / cm³ at 600 MV / m. 3 The efficiency meets practical requirements. The discharge energy density of Comparative Example 1 increases slowly with increasing electric field, tends to saturate after 450 MV / m, and the efficiency is less than 60%. The discharge energy density growth slope of Comparative Example 2 is lower than that of the Example, indicating that binary copolymerization cannot optimize the dielectric constant through electron cloud rearrangement and synergistic polarization between different monomers, as the multi-component random copolymerization system of this invention does.

[0055] Figure 3 The graph shows the maximum electric field "PE hysteresis loop" of the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2, tested at room temperature. Figure 3 As can be seen, the PE loops of Examples 1-3 all exhibit the characteristics of "narrow width and low remanent polarization". Among them, the loop of Example 1 is the narrowest, and the remanent polarization intensity is close to 0, indicating that the film has low charge loss and good charge-discharge reversibility during the polarization-reversal process. The loops of Comparative Examples 1 and 2 are wider and have higher remanent polarization intensity. In particular, Comparative Example 1 has a large loop area, indicating that the conduction loss caused by CTC in the homopolymer PI is significant, resulting in large energy loss during the polarization reversal process, which is consistent with the dielectric loss data.

[0056] Figure 4The graph shows the discharge energy density and discharge efficiency of the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2, tested at 200°C. Figure 4 As can be seen from the data, Example 1 achieved a discharge energy density of 5.72 J / cm² at 200°C and 670 MV / m. 3 Example 2 achieved 4.95 J / cm at 600 MV / m. 3 Example 3 achieved 3.49 J / cm at 500 MV / m. 3 Furthermore, the efficiency remains above 70%, meeting the practical requirements of high-temperature energy storage scenarios. Comparative Example 1, however, exhibits a breakdown field strength of only 200 MV / m and a discharge energy density of only 0.09 J / cm² at 200℃. 3 It almost completely loses its energy storage function; the high-temperature discharge energy density of Comparative Example 2 (2.87 J / cm³) 3 The results were also much lower than in the examples, indicating that conventional homopolymer or binary copolymer PI cannot suppress CTC formation and carrier transport at high temperatures, while multi-component random copolymers achieve performance retention at high temperatures by localizing electrons and blocking long-range carrier migration paths.

[0057] Figure 5 The graph shows the hysteresis loop (PE) of the maximum electric field measured at 200°C for the thin film materials prepared in Examples 1-3 and Comparative Examples 1-2. Figure 5 As can be seen, the high-temperature PE loops of Examples 1-3 still maintain a narrow amplitude, with low residual polarization. The maximum electric field achievable is higher than that of the comparative examples, and the dielectric loss remains low even with increased polarization. This indicates that even at 200°C, the molecular chain structure of the film remains stable, with no obvious thermally induced defects and low energy loss during the polarization-reversal process. The high-temperature loop of Comparative Example 1 is wide and has low polarization intensity, indicating that the leakage current density increases sharply at high temperatures, and the breakdown field strength decreases significantly. The loop of Comparative Example 2 can only reach 470 MV / m, which is lower than that of the examples. This indicates that the binary copolymer system has limited inhibitory effect on CTC formation at high temperatures, and its withstand voltage is not as good as that of multi-component random copolymers. Furthermore, the "structural perturbation" effect of multi-component random copolymers can still be effectively exerted at high temperatures, ensuring the stability of dielectric properties.

[0058] Experimental results show that, at room temperature, the breakdown field of the random copolymer polyimide dielectric film prepared in this invention is greater than 600 MV / m, and the energy density is greater than 6.0 J / cm². 3 At a high temperature of 200℃, the breakdown field strength of the random copolymer polyimide film is greater than 500 MV / m, and the energy density is greater than 3.4 J / cm². 3 The random copolymer polyimide film prepared by this invention still has high breakdown field strength and high energy density at a high temperature of 200℃.

[0059] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-component random copolymer polyimide dielectric film, characterized in that, It is prepared by the random copolymerization of at least one diamine monomer and at least two dianhydride monomers; the chemical structural formula of the multi-component random copolymer polyimide dielectric film is shown in Formula (Ⅰ): Formula (Ⅰ) In the formula, m and n represent the molar number or the repeating unit number of the structural unit, where m and n are both positive numbers and satisfy 0 < m / (m + n) < 1; Ar1 represents a dianhydride monomer; Ar2 represents a diamine monomer.

2. The multi-component random copolymer polyimide dielectric film according to claim 1, characterized in that, The molar ratio of the diamine monomer to the dianhydride monomer is (0.95 - 1.05)∶(1.05 - 0.95).

3. The multi-component random copolymer polyimide dielectric film according to claim 2, characterized in that, The diamine monomer is selected from at least one of 2,2'-bis(trifluoromethyl)diaminobiphenyl, 2,2'-bis(trifluoromethyl)-4,4'-diaminophenyl ether, 4,4'-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 2,2'-bis[4-(4-amino-2-trifluoromethylphenoxy)benzene]hexafluoropropane, N,N'-(2,2'-bis(trifluoromethyl)-[1,1'-biphenyl]-4,4'-diyl)bis(4-aminobenzamide), 4,4'-bis(4-amino-2-trifluoromethylphenoxy)biphenyl, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,2-bis(3-aminophenyl)hexafluoropropane, 4,4'-[1,4-phenylenebis(oxy)]bis[3-(trifluoromethyl)aniline], 2,2-bis(3-amino-4-tolyl)hexafluoropropane, 1,1-bis(4-aminophenyl)cyclohexane, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3-fluorophenyl)fluorene, 9,9-bis(4-amino-3-chlorophenyl)fluorene, 9,9-bis(4-amino-3-tolyl)fluorene, dapsone, 4,4'-bis(3-aminophenoxy)diphenyl sulfone, 4,4'-bis(4-aminophenoxy)diphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 3,3'-diamino-4,4'-dihydroxydiphenyl sulfone, 2,2'-bis[4-(4-aminophenoxyphenyl)]propane, 2,2'-bis[4-(3-aminophenoxy)phenyl]propane, Α,Α'-bis(4-aminophenyl)-1,4-diisopropylbenzene, 4,4'-bis(4-aminophenoxy)biphenyl, 4,4'-diaminodicyclohexylmethane, 1,4-cyclohexanediamine, 3,3'-dimethyl-4,4-diaminodicyclohexylmethane, bis(4-aminocyclohexyl)ether, and 5(6)-amino-1-(4-aminophenyl)-1,3,3-trimethylindane.

4. The multi-component random copolymer polyimide dielectric film according to claim 2, characterized in that, The dianhydride monomer is selected from 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxobisphthalic anhydride, pyromellitic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, hexafluorodianhydride, 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic dianhydride, 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride, bisphenol A type diether dianhydride, 4,4'-terephthalobisphthalic anhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1, At least two of the following: 2,3,4-cyclobutanetetracarboxylic dianhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, dicyclohexyl-3,4,3',4'-tetracarboxylic dianhydride, 4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicarboxylic anhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, tetrachloroperyl anhydride, 3,4,9,10-tetracarboxylic anhydride, bicyclo[2.2.2]octane-2,3:5,6-tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, and dimethylcyclobutanetetracarboxylic anhydride.

5. A method for preparing a multi-component random copolymer polyimide dielectric film as described in any one of claims 1-4, characterized in that, Includes the following steps: The diamine monomer was dissolved in an organic solvent and stirred under an inert gas atmosphere to obtain a diamine solution. The dianhydride monomer is added to the diamine solution, and a polymerization reaction is carried out under an inert gas atmosphere to obtain a copolyamic acid solution. The copolyamic acid solution is coated onto a substrate to form a wet film; The wet film is subjected to thermal imidization treatment, followed by demolding and drying to obtain the multi-component random copolymer polyimide dielectric film.

6. The preparation method according to claim 5, characterized in that, The stirring and dissolving process takes place at a temperature of 0-40℃ for 0.5-2 hours. The polymerization reaction is carried out at a temperature of 0-90℃ for a duration of 6-36 hours.

7. The preparation method according to claim 5, characterized in that, The organic solvent is selected from any one of N,N-dimethylacetamide, N,N-dimethylpyrrolidone, and N,N-dimethylformamide.

8. The preparation method according to claim 5, characterized in that, The solid content of the copolyamic acid solution is 8-26 wt.%.

9. The preparation method according to claim 5, characterized in that, The specific steps of the thermal imidization treatment are as follows: treat at 80℃, 120℃, 150℃, 200℃ and 260℃ for 0.5-3 hours each.

10. The application of a multi-component random copolymer polyimide dielectric film as described in any one of claims 1-4 in the field of dielectric energy storage materials.

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