A method for preparing a polymer dielectric film

Abstract

The present invention relates to the technical field of dielectric material preparation, and in particular to a method for preparing a polymer dielectric film. In the present invention, a diamine monomer, a dianhydride monomer, and an organic solvent are mixed under an inert atmosphere, and then subjected to a condensation reaction to obtain a prepolymer solution; wherein, one of the diamine monomer and the dianhydride monomer contains a benzyl group; the prepolymer solution is subjected to an imidization reaction and a benzyl free radical cross-linking reaction to obtain a polymer dielectric film. The glass transition temperature (Tg) of the polymer dielectric film obtained by this preparation method is improved, and the modified film can have an excellent breakdown electric field and energy storage density under a high temperature environment of 250°C. Moreover, this method does not add other complex and high-tech processes on the basis of the process for synthesizing commercial polymer dielectric films, and does not require vacuum environment cross-linking, is environmentally friendly and energy-saving, and the reaction degree is controllable. The surface of the obtained polymer dielectric film is smooth and the cross-section has no obvious defects.

Description

Technical Field

[0001] The present invention relates to the technical field of dielectric material preparation, and in particular to a method for preparing a polymer dielectric film. Background Art

[0002] Modern new energy vehicles, oil and gas exploration, aerospace equipment, and high-voltage power systems urgently require polymer-based dielectric materials with excellent high-temperature capacitance performance. However, due to the poor heat resistance of commonly used biaxially oriented polypropylene (BOPP), its operating temperature cannot exceed 105°C. In particular, when the actual operating temperature exceeds 85°C, its internal conductivity losses increase exponentially, and additional cooling systems are usually required to maintain the stable operation of BOPP capacitors and prevent the degradation of their breakdown strength (Eb) and energy storage efficiency (η). Therefore, polymer dielectrics with high glass transition temperature (Tg) and high melting point (Tm), such as polyimide (PI), polyetherimide (PEI), and fluorene polyester (FPE), have been selected as candidates for high-temperature energy storage materials. However, the highly conjugated polymer backbone of high-temperature polymer dielectrics leads to a rapid increase in conduction losses at high temperatures and high fields, resulting in a significant decrease in their energy storage density (Ue) and energy storage efficiency (η).

[0003] Although polyimide (PI) and polyetherimide (PEI) are considered important dielectric materials for high-temperature energy storage and are widely used in high-tech fields such as electronic power systems and aerospace, the high-temperature capacitance performance of current polyimide and polyetherimide films still cannot meet the growing demand. Therefore, there is an urgent need to develop and prepare polymer dielectric films with excellent high-temperature capacitance performance. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing a polymer dielectric film to improve the high temperature resistance of the polymer dielectric film and reduce the charge transfer complex (CTC) effect, thereby optimizing the high temperature capacitance performance of the polymer dielectric film.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a polymer dielectric film, comprising the following steps:

[0007] 1) mixing a diamine monomer, a dianhydride monomer, and an organic solvent under an inert atmosphere and performing a polycondensation reaction to obtain a prepolymer solution; wherein one of the diamine monomer and the dianhydride monomer contains a benzyl group;

[0008] 2) subjecting the precursor solution to imidization reaction and benzyl radical cross-linking reaction to obtain a polymer dielectric film.

[0009] Alternatively, when the diamine monomer contains a benzyl group, the diamine monomer includes at least one of 2,2'-dimethyl-4,4'-diaminobibenzyl, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 2,5-dimethyl-1,4-phenylenediamine, 4,4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3,3',5,5'-tetramethylbiphenyl, 3,6-diamino-1,2,4,5-tetramethylbenzene, o-tolidine sulfone, 4,4'-diamino-2,2'-dimethylbiphenyl, 2-methyl-1,4-phenylenediamine, 4,4'-methylenebis(2,6-dimethylaniline) and 2,4-diamino-1,3,5-trimethylbenzene;

[0010] When the dianhydride monomer does not contain a benzyl group, the dianhydride monomer includes at least one of pyromellitic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 4,4'-diphthalic anhydride, 4,4'-oxydiphthalic anhydride, 1,4-phenylene bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), 4,4'-(4,4'-isopropyldiphenoxy)diphthalic anhydride, 4,4'-(hexafluoroisopropyl)diphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3,4,4-diphenylsulfonetetracarboxylic dianhydride and 1,2,5,6-naphthalenetetracarboxylic dianhydride.

[0011] Optionally, when the dianhydride monomer contains a benzyl group, it includes at least one of 5,5'-(2,2',3,3'-tetramethyl[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dihydro-1,3-dioxopyrimidine-5-isobenzofuran-4-carboxylate) and 4-[[4-[4-(3,4-dicarboxybenzoyloxy)-2,3,5-trimethylbenzene]-2,3,6-trimethylbenzene]oxycarbonyl]benzene-1,2-dicarboxylic acid;

[0012] When the diamine monomer does not contain a benzyl group, the diamine monomer includes at least one of 1,4-phenylenediamine, 1,3-phenylenediamine, 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone.

[0013] Optionally, the molar ratio of the diamine monomer to the dianhydride monomer is 1:0.9-1.1; and the usage ratio of the dianhydride monomer to the organic solvent is 1 mmol:4.42-5.21 mL.

[0014] Optionally, the organic solvent includes at least one of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide and m-phenol.

[0015] Optionally, the polycondensation reaction is carried out at room temperature for 24 to 48 hours.

[0016] Optionally, the precursor solution is subjected to imidization reaction and benzyl radical cross-linking reaction by the following steps:

[0017] The precursor solution is coated on a substrate to obtain a precursor solution film,

[0018] The precursor solution film is heat-treated, wherein the heat treatment is the following programmed temperature increase process: 70°C / 0.5h, 85°C / 2-3h, 110°C / 0.8-1.5h, 160°C / 0.8-15h, 220°C / 0.8-1.5h, 260°C / 0.8-1.5h, 290°C / 0.8-2h.

[0019] Optionally, the precursor solution is subjected to imidization reaction and benzyl radical cross-linking reaction by the following steps:

[0020] The precursor solution and the catalyst are mixed to carry out an imidization reaction to obtain an imidization reaction solution.

[0021] The imidization reaction solution is precipitated, the obtained precipitate is washed and dried, and then dissolved in an organic solvent to obtain a polymer solution,

[0022] coating the polymer solution on a substrate to obtain a polymer solution film,

[0023] The polymer solution film is subjected to a benzyl radical cross-linking reaction.

[0024] Optionally, the volume ratio of the precursor solution and the catalyst is 100-200:1, the catalyst is a mixture of isoquinoline or pyridine and acetic anhydride; the volume ratio of pyridine and acetic anhydride is 1:1; the temperature of the imidization reaction is 140-200°C, and the time is 2-10 hours.

[0025] Optionally, the benzyl radical cross-linking reaction is carried out at a temperature of 250 to 320° C. and for a time of 1 to 3 hours.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention provides a method for preparing a polymer dielectric film. Generally, the CTC effect is beneficial to the transport of carriers, causing high-temperature resistant polymer dielectrics to generate huge conduction losses under high temperature and high field conditions, increasing leakage current density, and seriously reducing energy storage density and energy storage efficiency. The present invention selects one of the diamine monomers or dianhydride monomers to contain a benzyl functional group, and co-condenses it with another dianhydride monomer or diamine monomer that does not contain a benzyl group. Due to the presence of the benzyl functional group, benzyl radicals can be generated under air conditions above 250°C to achieve cross-linking between molecular chains, further achieving preferential interlayer stacking (PLP) between molecular chains, thereby improving the high-temperature resistance of the polymer dielectric and weakening the charge transfer complex (CTC) effect, thereby optimizing the high-temperature capacitance performance of the polymer dielectric. Using this preparation method and optimization strategy, the glass transition temperature (Tg) of the polyetherimide film prepared in the embodiment is increased from 230°C to about 280°C, and the modified film can have excellent breakdown electric field and energy storage density in a high-temperature environment of 150°C to 250°C.

[0028] The method for preparing a polymer dielectric film provided by the present invention does not add other complex and high-tech processes to the process of synthesizing commercial polymer dielectric films, does not require vacuum environment cross-linking, is environmentally friendly and energy-saving, has a controllable reaction degree, and produces a polymer dielectric film with a smooth surface and no obvious defects in the cross section. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Optimization schematic for polyimide dielectric film.

[0030] Figure 2 Schematic diagram of the chemical reaction of benzyl cross-linked polyetherimide (TPEI) of Example 1 and polyetherimide (PEI) of Comparative Example 1.

[0031] Figure 3 FTIR graphs of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 and the polyetherimide dielectric film (PEI) of Comparative Example 1.

[0032] Figure 4 3 are TGA graphs of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 and the polyetherimide dielectric film (PEI) of Comparative Example 1.

[0033] Figure 5 1 and 2 are AFM images of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 and the polyetherimide dielectric film (PEI) of Comparative Example 1.

[0034] Figure 61 and 2 are SEM images of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 and the polyetherimide dielectric film (PEI) of Comparative Example 1.

[0035] Figure 7 3 are DSC graphs of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 and the polyetherimide dielectric film (PEI) of Comparative Example 1.

[0036] Figure 8 3 are TMA images of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 and the polyetherimide dielectric film (PEI) of Comparative Example 1.

[0037] Figure 9 1 is the dielectric spectrum of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 and the polyetherimide dielectric film (PEI) of Comparative Example 1.

[0038] Figure 10 1 and 2 are dielectric temperature spectra of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 and the polyetherimide dielectric film (PEI) of Comparative Example 1.

[0039] Figure 11 3 is a graph showing the energy storage performance of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 and the polyetherimide dielectric film (PEI) of Comparative Example 1 at 200°C.

[0040] Figure 12 1 is a graph showing the energy storage performance of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 at 250°C. DETAILED DESCRIPTION

[0041] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0042] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0043] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0044] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the present invention. The present description and examples are intended to be illustrative only.

[0045] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0046] The raw materials used in the present invention can be obtained commercially or prepared using existing technologies.

[0047] Unless otherwise specified, the "room temperature" in the present invention is 25±2°C.

[0048] The present invention provides a method for preparing a polymer dielectric film, comprising the following steps:

[0049] 1) mixing a diamine monomer, a dianhydride monomer, and an organic solvent under an inert atmosphere and performing a polycondensation reaction to obtain a prepolymer solution; wherein one of the diamine monomer and the dianhydride monomer contains a benzyl group;

[0050] 2) subjecting the precursor solution to imidization reaction and benzyl radical cross-linking reaction to obtain a polymer dielectric film.

[0051] When the polymer dielectric film is a polyimide dielectric film, the optimization principle is as follows: Figure 1As shown, when using electron-donating diamine and electron-accepting dianhydride to prepare polyimide dielectric films, there is a strong charge transfer complex (CTC) effect between the molecular chains. The present invention selects a monomer in the diamine monomer or dianhydride monomer containing a benzyl functional group, and co-condenses with another dianhydride monomer or diamine monomer that does not contain a benzyl group. After cross-linking, benzyl radicals are generated to prepare a polymer dielectric material with a preferred layer stacking (PLP) structure, which reduces the charge transfer complex (CTC) effect between molecules. Wherein, the CTC effect is beneficial to carrier transport, and the PLP structure is to slow down the CTC effect so as to reduce electron transport. Therefore, this strategy can simultaneously suppress the conductivity at high temperature and improve the heat resistance of the polymer dielectric material.

[0052] The present invention firstly mixes a diamine monomer, a dianhydride monomer and an organic solvent under an inert atmosphere, and then performs a polycondensation reaction to obtain a prepolymer solution; wherein one of the diamine monomer and the dianhydride monomer contains a benzyl group.

[0053] The present invention has no particular limitation on the gas of the inert atmosphere, as long as the diamine monomer, the dianhydride monomer and the organic solvent are mixed in an oxygen-free environment. In the embodiment of the present invention, the mixture is carried out in a nitrogen atmosphere.

[0054] In the present invention, there is no particular limitation on the mixing method, as long as the raw materials can be mixed uniformly. In an embodiment of the present invention, mixing is performed in a step-by-step manner, specifically: first, the diamine monomer and a portion of the organic solvent are uniformly mixed, and then the dianhydride monomer and another portion of the organic solvent are added and mixed uniformly.

[0055] In the present invention, there is no particular limitation on the type of organic solvent, as long as it can dissolve the reaction raw materials and carry out the above reaction. It is preferably a high-boiling point anhydrous organic solvent. In an embodiment of the present invention, the organic solvent comprises at least one of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide and m-phenol, and one of them is preferably used.

[0056] In some embodiments of the present invention, the molar ratio of the diamine monomer to the dianhydride monomer is 1:0.9-1.1, preferably 1:1; the usage ratio of the dianhydride monomer to the organic solvent is 1 mmol:4.42-5.21 mL, preferably 1 mmol:5.21 mL.

[0057] In the present invention, when the diamine monomer contains a benzyl group, the dianhydride monomer does not contain a benzyl group.

[0058] In some embodiments of the present invention, when the diamine monomer contains a benzyl group, the diamine monomer includes at least one of 2,2'-dimethyl-4,4'-diaminobibenzyl, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 2,5-dimethyl-1,4-phenylenediamine, 4,4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, 4,4'-diamino-3,3'-dimethylbiphenyl, 3,3',5,5'-tetramethyl-p-diaminobiphenyl, 3,6-diamino-1,2,4,5-tetramethylbenzene, o-tolidine sulfone, 4,4'-diamino-2,2'-dimethylbiphenyl, 2-methyl-1,4-phenylenediamine, 4,4'-methylenebis(2,6-dimethylaniline) and 2,4-diamino-1,3,5-trimethylbenzene.

[0059] When the dianhydride monomer does not contain a benzyl group, the dianhydride monomer includes at least one of pyromellitic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 4,4'-diphthalic anhydride, 4,4'-oxydiphthalic anhydride, 1,4-phenylene bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylate), 4,4'-(4,4'-isopropyldiphenoxy)diphthalic anhydride, 4,4'-(hexafluoroisopropyl)diphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3,4,4-diphenylsulfonetetracarboxylic dianhydride and 1,2,5,6-naphthalenetetracarboxylic dianhydride.

[0060] In the present invention, when the diamine monomer does not contain a benzyl group, the dianhydride monomer contains a benzyl group.

[0061] In some embodiments of the present invention, when the dianhydride monomer contains a benzyl group, the dianhydride monomer includes at least one of 5,5'-(2,2',3,3'-tetramethyl[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dihydro-1,3-dioxopyrimidine-5-isobenzofuran-4-carboxylate) and 4-[[4-[4-(3,4-dicarboxybenzoyloxy)-2,3,5-trimethylbenzene]-2,3,6-trimethylbenzene]oxycarbonyl]benzene-1,2-dicarboxylic acid.

[0062] Wherein, the 5,5'-(2,2',3,3'-tetramethyl[1,1'-biphenyl]-4,4'-diyl)bis(1,3-dihydro-1,3-dioxopyrimidine-5-isobenzofuran-4-carboxylate) is prepared by the preparation method of TA-35TMBP disclosed in "Optically transparent aromatic poly(ester imide)s with low coefficient soft hermal expansion.2: Effect of the introduction of alkyl-substituted p-biphenylene units";

[0063] The 4-[[4-[4-(3,4-dicarboxybenzoyloxy)-2,3,5-trimethylbenzene]-2,3,6-trimethylbenzene]oxycarbonyl]benzene-1,2-dicarboxylic acid is prepared by the preparation method of TA-235HMBP disclosed in "Optically transparent aromatic poly(ester imide)s with low coefficient soft hermal expansion.2: Effect of the introduction of alkyl-substituted p-biphenylene units";

[0064] When the diamine monomer does not contain a benzyl group, the diamine monomer includes at least one of 1,4-phenylenediamine, 1,3-phenylenediamine, 4,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl sulfone.

[0065] In some embodiments of the present invention, the polycondensation reaction is carried out at room temperature, and the polycondensation reaction time is preferably 36 hours; the precursor solution is a binary or multi-component copolymer.

[0066] After the precursor solution is obtained, imidization and free radical cross-linking are performed on the precursor solution to obtain a polymer dielectric film.

[0067] In the present invention, the prepolymer solution is subjected to imidization reaction and radical crosslinking reaction by the following steps:

[0068] The precursor solution is coated on a substrate to obtain a precursor solution film,

[0069] The precursor solution film is heat-treated, wherein the heat treatment is the following programmed temperature increase process: 70°C / 0.5h, 85°C / 2-3h, 110°C / 0.8-1.5h, 160°C / 0.8-15h, 220°C / 0.8-1.5h, 260°C / 0.8-1.5h, 290°C / 0.8-2h.

[0070] In some embodiments of the present invention, the gas in the precursor solution is removed before coating the precursor solution on the substrate. The present invention does not specifically limit the method of removing the gas. In the embodiments of the present invention, the precursor solution is placed under vacuum conditions to remove the gas.

[0071] In the temperature rising program of the present invention, "70°C / 0.5h" can be understood as "keeping at 70°C for 0.5h", and the remaining temperatures and times are also understood in the same way.

[0072] In some embodiments of the present invention, the heating rate during the temperature program is 1° C. / min.

[0073] In some embodiments of the present invention, after the imidization reaction and benzyl radical crosslinking reaction are completed, the polymer dielectric film is preferably cooled naturally, stripped with 40°C water, and then dried to obtain a cross-linked polyetherimide film. In this embodiment of the present invention, the drying temperature is 110°C for 24 hours.

[0074] In the present invention, the imidization reaction and the benzyl radical cross-linking reaction of the precursor solution can also be carried out by the following steps:

[0075] The precursor solution and the catalyst are mixed to carry out an imidization reaction to obtain an imidization reaction solution.

[0076] The imidization reaction solution is precipitated, the obtained precipitate is washed and dried, and then dissolved in an organic solvent to obtain a polymer solution,

[0077] coating the polymer solution on a substrate to obtain a polymer solution film,

[0078] The polymer solution film is subjected to a benzyl radical cross-linking reaction.

[0079] The present invention has no particular limitation on the method for precipitation of the imidization reaction solution, as long as the catalyst can be removed. In an embodiment of the present invention, the catalyst is removed by precipitation. Specifically, the imidization reaction solution is dripped dropwise into a stirred solvent, the catalyst is dissolved in the solvent, and the polymer is precipitated. The solvent is ethanol, and the temperature of the ethanol is 40°C.

[0080] The washing is to wash the polymer precipitate with ethanol, and the purpose of washing is to remove the catalyst remaining in the polymer precipitate.

[0081] The purpose of the drying is to further remove the residual ethanol solvent in the polymer precipitate. In the embodiment of the present invention, the drying temperature is 100-120° C. and the drying time is 24 hours.

[0082] The specific type of the organic solvent is not particularly limited, as long as it can form a viscous solvent suitable for coating after drying the polymer. It is preferably an anhydrous organic solvent. In an embodiment of the present invention, the organic solvent includes at least one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF) and m-phenol.

[0083] In some embodiments of the present invention, gas is removed from the precursor solution before coating it on the substrate. The present invention does not particularly limit the method of removing gas. In the embodiments of the present invention, the precursor solution is placed under vacuum conditions to remove gas.

[0084] After the polymer solution is evenly coated on the substrate, it is first dried to remove the organic solvent, and then heated in air to the temperature required for the benzyl radical cross-linking reaction. In the embodiment of the present invention, the drying temperature is 200° C. and the temperature is kept for 12 hours.

[0085] In some embodiments of the present invention, the volume ratio of the precursor solution and the catalyst is 100 to 200:1, and the catalyst is a mixture of isoquinoline or pyridine and acetic anhydride; the temperature of the imidization reaction is 140 to 200°C, and the time is 2 to 10 hours; the temperature of the benzyl radical cross-linking is ≥250 to 320°C, and the time is 1 to 3 hours.

[0086] In the present invention, there is no particular limitation on the thickness of the polymer dielectric film, as long as it can meet the application requirements of practical dielectric capacitors. In an embodiment of the present invention, the thickness of the polymer dielectric film is 7 to 20 μm, preferably 10 to 18 μm, and more preferably 12 to 15 μm.

[0087] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0088] Example 1

[0089] Preparation of polyetheramic acid (PAA) precursor: Under a nitrogen atmosphere, add 0.384 mmol of 3,6-diamino-1,2,4,5-tetramethylbenzene and 1 mL of N-methylpyrrolidone, and stir to dissolve at 25°C; add 0.384 mmol of 4,4'-(4,4'-isopropyldiphenyloxy)diphthalic anhydride to the above mixed solution, and then add 0.7 mL of N-methylpyrrolidone solution, followed by stirring and reacting at room temperature for 36 hours to obtain a PAA precursor solution.

[0090] The prepared PAA precursor solution was placed under vacuum conditions to remove excess gas, then poured onto a clean glass plate for coating, and then reacted according to the following temperature ramp: heating to 70°C at 1°C / min and holding for 1 hour, heating to 85°C at 1°C / min and holding for 1 hour, heating to 110°C at 1°C / min and holding for 1 hour, heating to 160°C at 1°C / min and holding for 1 hour, heating to 220°C at 1°C / min and holding for 1 hour, heating to 260°C at 1°C / min and holding for 1 hour, and heating to 290°C at 1°C / min and holding for 1 hour. The solution was then cooled naturally, and the polymer film was peeled off with 40°C water. The film was then baked at 110°C for 24 hours to obtain a benzyl cross-linked polyetherimide (TPEI) film with a thickness of 12 μm, i.e., a polymer dielectric film.

[0091] Example 2

[0092] The only difference from Example 1 is that after obtaining the prepolymer solution, 100 mL of the prepolymer solution is mixed with 1 mL of a mixture of pyridine and acetic anhydride in a volume ratio of 1:1, and the mixture is reacted at 160 ° C for 8 h to catalyze the imine ring formation of the polymer chain to obtain a polymer solution. The obtained polymer solution is dripped dropwise into ethanol with stirring at a temperature of 40 ° C., pyridine and acetic anhydride are dissolved in ethanol, and a polymer is precipitated. The polymer precipitate is washed with ethanol, and the polymer precipitate is placed in an oven at 120 ° C for 24 h to remove the solvent. The product is then dissolved in NMP solvent, vacuumed to remove the gas in the solution, and the viscous polymer solution is evenly coated on a clean substrate and baked at below 200 ° C for 12 h to remove a large amount of organic solvent. Then, the temperature was raised to 290°C in an air environment and kept for 1.5 hours to complete the benzyl radical crosslinking. The film was cooled naturally and the polymer film was peeled off with 40°C water. The film was then placed at 110°C and baked for 24 hours to obtain a polyetherimide film (TPEI) with a thickness of 10 μm.

[0093] Comparative Example 1

[0094] The only difference from Example 1 is that the diamine monomer is replaced by 1,4-phenylenediamine, and the remaining steps are the same as those in Example 1 to prepare a polyetherimide film (PEI).

[0095] The chemical reaction diagram of TPEI of Example 1 and PEI of Comparative Example 1 is as follows: Figure 2 As shown in FIG, when preparing TPEI, the benzyl group in the diamine monomer is used to generate benzyl radicals in an air and heated environment, which induces chemical crosslinking between the molecular chains of the diamine units in the skeleton. Since the benzyl radicals only exist on the diamine monomer, this crosslinking can promote the aggregation state of the polyetherimide polymer, which is the dominant interlayer stacking (PLP) that tends to weaken the intermolecular CTC effect.

[0096] The chemical structure properties and morphological characteristics of the obtained cross-linked polyetherimide film and polyetherimide were tested, and the results were as follows: Figures 3 to 8 shown.

[0097] Depend on Figure 3 The FTIR pattern can prove the existence of benzyl cross-linking structure in the cross-linked polyetherimide film.

[0098] Depend on Figure 4 From the thermogravimetric analysis diagram, it can be seen that the weight loss curve of TPEI in air shows a mass increase at 280-370°C, while the thermogravimetric curve of TPEI in nitrogen atmosphere only shows the degradation of the molecular main chain, indicating that oxygen is the key factor in thermal oxidative crosslinking.

[0099] Depend on Figure 5 The AFM image shows that the roughness of the PEI surface is 16.4nm, and the roughness of the TPEI surface is 3.16nm, indicating that the TPEI surface is smoother and has no obvious defects. Figure 6 From the SEM image, it can be seen that the film thickness of PEI is 8.33 μm, the film thickness of TPEI is 9.90 μm, and there are no obvious defects in the cross-section of the polymer film, indicating that the surface of the cross-linked polyetherimide film is flatter and has no obvious defects.

[0100] Depend on Figure 7 The DSC graph of shows that the glass transition temperature (Tg) of TPEI reaches 294.46°C, while that of PEI is only 236.31°C, indicating that the TPEI prepared by the preparation method of the present invention has a high glass transition temperature and can be used as a high-temperature energy storage material. The TMA graph of 8 shows that the thermal expansion coefficient of TPEI is 59.13 at 30-200°C and 63.4 at 30-250°C, while the thermal expansion coefficient of PEI is 66.53 at 30-200°C, indicating that the cross-linked polyetherimide film prepared by the present invention has better thermal dimensional stability.

[0101] Electrical performance test of polymer dielectric material: Design a metal mask with a circular hole diameter of 3mm, sandwich the prepared film between two metal masks, and symmetrically sputter gold electrodes on the upper and lower surfaces. The upper and lower surfaces are sputtered at a sputtering current of 30mA for 300s. The dielectric spectrum, dielectric temperature spectrum and high-temperature energy storage performance of the polymer dielectric material are tested using a ferroelectric workstation and an impedance analyzer. The results are as follows: Figures 9-12 shown.

[0102] Figure 9 The relationship between the dielectric constant and dielectric loss of PEI prepared in Comparative Example 1 and TPEI prepared in Example 1 at room temperature and the electric field frequency is shown in FIG. Figure 9 The results show that PEI is 10 3 ~10 7 In the frequency range of 10 3 ~10 7 In the frequency range, the dielectric constant decreases from 3.9 to 3.6, and the dielectric loss increases from 0.008 to 0.031. That is, compared with PEI, the formation of ether bonds between TPEI molecular chains and the introduction of short fatty chains make it show a higher dielectric constant in a wide frequency range. Because cross-linking will lead to an increase in the relaxation loss of the polymer film, that is, the flipping of the dipole cannot keep up with the change in the direction of the electric field, the dielectric loss of TPEI shows a slight increase in a wide frequency range.

[0103] Figure 10 The figure shows the relationship between the dielectric constant and dielectric loss of PEI prepared in Comparative Example 1 and TPEI prepared in Example 1 and the electric field frequency at 1 kHz. Figure 10 The results show that the dielectric constant of TPEI decreases slightly with increasing temperature, and the dielectric loss is relatively stable, while the dielectric constant and dielectric loss of PEI increase sharply at 200°C. That is, compared with pure PEI, TPEI shows more stable dielectric properties in the range of 30-250°C.

[0104] Depend on Figure 11 It can be seen that at 200 ° C, compared with pure PEI (energy storage density of 2.85 J / cm -3 , energy storage efficiency is 74.02%), TPEI has 7.16J / cm -3 The energy storage density and energy storage efficiency of 82.89% indicate that the preparation method of the present invention successfully improves the energy storage effect of polyetherimide.

[0105] Depend on Figure 12 It can be seen that the benzyl radical-induced cross-linking structure (TPEI) achieved 4.8 J / cm at 250 °C. 3The energy storage density is around 90%, while maintaining an energy storage efficiency of more than 90%. What is more worth mentioning is that the breakdown electric field of the modified polyetherimide reaches 570.8MV / m at 250°C, indicating that the existence of the cross-linked structure is beneficial for commercial polymers to highlight the operating temperature limit of energy storage applications and suppress losses, thereby improving energy storage performance in extreme environments.

[0106] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a polymer dielectric film, characterized in that: The following steps are involved: 1) mixing a diamine monomer, a dianhydride monomer, and an organic solvent under an inert atmosphere and performing a polycondensation reaction to obtain a prepolymer solution; wherein one of the diamine monomer and the dianhydride monomer contains a benzyl group; 2) subjecting the precursor solution to imidization reaction and benzyl radical cross-linking reaction to obtain a polymer dielectric film; The imidization reaction and benzyl radical cross-linking reaction of the precursor solution are carried out by the following steps: The prepolymer solution is coated on a substrate to obtain a prepolymer solution film, and the prepolymer solution film is subjected to heat treatment, wherein the heat treatment is a programmed temperature increase process of 70° C. / 0.5 h, 85° C. / 2-3 h, 110° C. / 0.8-1.5 h, 160° C. / 0.8-15 h, 220° C. / 0.8-1.5 h, 260° C. / 0.8-1.5 h, and 290° C. / 0.8-2 h; Alternatively, the precursor solution undergoes imidization reaction and benzyl radical cross-linking reaction by the following steps: The precursor solution and the catalyst are mixed, and an imidization reaction is carried out to obtain an imidization reaction solution. The imidization reaction solution is precipitated, and the obtained precipitate is washed and dried, and then dissolved in an organic solvent to obtain a polymer solution. The polymer solution is coated on a substrate to obtain a polymer solution film, and the polymer solution film is subjected to a benzyl radical cross-linking reaction; the temperature of the imidization reaction is 140 to 200° C. and the time is 2 to 10 hours, and the temperature of the benzyl radical cross-linking reaction is 250 to 320° C. and the time is 1 to 3 hours.

2. The preparation method according to claim 1, characterized in that When the diamine monomer contains a benzyl group, the diamine monomer includes 2,2'-dimethyl-4,4'-diaminobibenzyl, 4,4'-diamino-3,3'-dimethyldiphenylmethane, 2,5-dimethyl-1,4-phenylenediamine, 4,4'-diamino-3,3'-diethyl-5,5'-dimethyldiphenylmethane, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-3,3',5,5'-tetramethylbiphenyl, 3,6-diamino-1,2,4,5-tetramethylbenzene, o-tolidine sulfone, 4,4'-diamino-2,2'-dimethylbiphenyl, 2-methyl-1,4-phenylenediamine, 4,4'-methylenebis(2,6-dimethylaniline) ) and 2,4-diamino-1,3,5-trimethylbenzene; when the dianhydride monomer does not contain a benzyl group, the dianhydride monomer includes at least one of pyromellitic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 4,4'-diphthalic anhydride, 4,4'-oxydiphthalic anhydride, bis(1,3-dioxo-1,3-dihydroisobenzofuran-5-carboxylic acid) 1,4-phenylene ester, 4,4'-(4,4'-isopropyldiphenoxy) diphthalic anhydride, 4,4'-(hexafluoroisopropyl) diphthalic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3,4,4-diphenylsulfonetetracarboxylic dianhydride and 1,2,5,6-naphthalenetetracarboxylic dianhydride.

3. The preparation method according to claim 1, characterized in that When the dianhydride monomer contains a benzyl group, it includes at least one of 5,5′-(2,2′,3,3′-tetramethyl[1,1′-biphenyl]-4,4′-diyl)bis(1,3-dihydro-1,3-dioxopyrimidine-5-isobenzofuran-4-carboxylate) and 4-[[4-[4-(3,4-dicarboxybenzoyloxy)-2,3,5-trimethylbenzene]-2,3,6-trimethylbenzene]oxycarbonyl]benzene-1,2-dicarboxylic acid; when the diamine monomer does not contain a benzyl group, it includes at least one of 1,4-phenylenediamine, 1,3-phenylenediamine, 4,4′-diaminodiphenyl ether and 4,4′-diaminodiphenyl sulfone.

4. The preparation method according to claim 1, characterized in that The molar ratio of the diamine monomer to the dianhydride monomer is 1:0.9-1.1; the usage ratio of the dianhydride monomer to the organic solvent is 1 mmol:4.42-5.21 mL.

5. The preparation method according to claim 1 or 4, characterized in that The organic solvent includes at least one of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide and m-phenol.

6. The preparation method according to claim 1, characterized in that The polycondensation reaction is carried out at room temperature, and the polycondensation reaction time is 24 to 48 hours.

7. The preparation method according to claim 1, characterized in that The volume ratio of the prepolymer solution to the catalyst is 100-200:1, the catalyst is a mixture of isoquinoline or pyridine and acetic anhydride; and the volume ratio of the pyridine to acetic anhydride is 1:1.

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