Preparation method of polymer dielectric film

Abstract

The invention relates to the technical field of dielectric material preparation, in particular to a preparation method of a polymer dielectric film. The preparation method comprises the following steps: in an inert atmosphere, mixing a diamine monomer, a dianhydride monomer and an organic solvent, and carrying out condensation polymerization to obtain a precursor solution; wherein one of the diamine monomer and the dianhydride monomer contains benzyl groups; and carrying out imidization reaction and benzyl free radical cross-linking reaction on the precursor solution to obtain the polymer dielectric film. The glass transition temperature (Tg) of the polymer dielectric film prepared by the preparation method is improved, the modified film has excellent breakdown electric field and energy storage density in a high-temperature environment of 250 DEG C, and other complicated and high-technical-content processes are not added on the basis of a process for synthesizing a commercial polymer dielectric film; vacuum environment crosslinking is not needed, environmental protection and energy saving are achieved, the reaction degree is controllable, the surface of the prepared polymer dielectric film is smooth, and the cross section has no obvious defects.

Description

Technical Field

[0001] The 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 need polymer-based dielectric materials with excellent high-temperature capacitance performance. However, due to the poor heat resistance of the 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 loss increases exponentially, and an additional cooling system is usually required to maintain the stable operation of the BOPP capacitor and prevent its breakdown strength (Eb) and energy storage efficiency (η) from decreasing. Therefore. Polymer dielectrics with high glass transition temperature (Tg) and high melting point (Tm) are selected as candidates for high-temperature energy storage materials, such as polyimide (PI), polyetherimide (PEI), fluorene polyester (FPE), etc. However, the high-temperature resistant polymer dielectrics have a rapidly increased conduction loss at high temperature and high field due to their highly conjugated polymer skeleton, which seriously reduces their energy storage density (Ue) and energy storage efficiency (η).

[0003] Although polyimide (PI) and polyetherimide (PEI) are considered to be an important class of dielectric materials that can be applied to 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 films and polyetherimide films still cannot meet people's growing needs. 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 preparation method of a polymer dielectric film to improve the high temperature resistance of the polymer dielectric film and weaken 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) in an inert atmosphere, mixing a diamine monomer, a dianhydride monomer, and an organic solvent, 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] Optionally, 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'-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, 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.

[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, and the polycondensation reaction time is 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 2-10h.

[0025] Optionally, the temperature of the benzyl free radical cross-linking reaction is 250-320° C., and the time is 1-3 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 conducive to the transmission of carriers, causing the high temperature resistant polymer dielectric to produce huge conduction loss under high temperature and high field, increasing the leakage current density, and seriously reducing the energy storage density and energy storage efficiency. The present invention selects a diamine monomer or a dianhydride monomer containing a benzyl functional group, and co-condenses with another dianhydride monomer or a diamine monomer without a benzyl group. Due to the presence of the benzyl functional group, benzyl radicals can be generated under the condition of an air environment above 250°C to achieve cross-linking between molecular chains, and further achieve the advantageous 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 under a high temperature environment of 150°C to 250°C.

[0028] The preparation method of the polymer dielectric film provided by the present invention does not add other complex and high-tech processes on the basis of 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 the surface of the prepared polymer dielectric film is smooth and the cross-section has no obvious defects. 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] Fig. 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] Fig.10 1 is the dielectric temperature spectrum of the benzyl cross-linked polyetherimide dielectric film (TPEI) of Example 1 and the polyetherimide dielectric film (PEI) of Comparative Example 1.

[0039] Fig.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] Fig.12 3 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 should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

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

[0043] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation 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 a conflict with any incorporated document, the content 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 description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary 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 from the market or prepared by the existing technology.

[0047] The "room temperature" mentioned in the present invention is 25±2°C unless otherwise specified.

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

[0049] 1) in an inert atmosphere, mixing a diamine monomer, a dianhydride monomer, and an organic solvent, 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 film, there is a strong charge transfer complex (CTC) effect between molecular chains, the present invention selects a monomer in diamine monomer or dianhydride monomer containing benzyl functional group, and co-condenses with another dianhydride monomer or diamine monomer without benzyl, and generates benzyl radicals after cross-linking, and prepares 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 conducive to carrier transport, and the PLP structure is to slow down the CTC effect so as to achieve the reduction of electron transport. Therefore, this strategy can simultaneously suppress the conductivity at high temperature and improve the heat resistance of polymer dielectric materials.

[0052] The 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 evenly. In the embodiment of the present invention, the mixing is performed in a step-by-step manner, specifically: firstly, the diamine monomer and a part of the organic solvent are mixed evenly, and then the dianhydride monomer and another part of the organic solvent are added and mixed evenly.

[0055] In the present invention, there is no special 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 preferably one of them is 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, 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.

[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 polymer solution is obtained, the precursor polymer solution is subjected to imidization and free radical cross-linking to obtain a polymer dielectric film.

[0067] In the present invention, the prepolymer solution is subjected to imidization reaction and radical cross-linking 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 rising program is 1° C. / min.

[0073] In some embodiments of the present invention, after the imidization reaction and the benzyl radical crosslinking reaction are completed, the temperature is preferably naturally cooled, and the polymer dielectric film is peeled off with 40° C. water, and then dried to obtain a crosslinked polyetherimide film. In an embodiment of the present invention, the drying temperature is 110° C. and the drying time is 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, 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 special limitation on the method of 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 solution after the imidization reaction is dripped drop by drop 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, and it only needs to be a viscous solvent that can form the dried polymer into a suitable coating. 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, 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.

[0084] After the polymer solution is uniformly coated on the substrate, it is first dried to remove the organic solvent, and then heated to the temperature required for the benzyl free radical cross-linking reaction in an air environment. In an 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 100-200:1, and the catalyst is a mixture of isoquinoline or pyridine and acetic anhydride; the temperature of the imidization reaction is 140-200°C, and the time is 2-10 hours; the temperature of the benzyl radical cross-linking is ≥250-320°C, and the time is 1-3 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 in the actual dielectric capacitor. In an embodiment of the present invention, the thickness of the polymer dielectric film is 7-20 μm, preferably 10-18 μm, and more preferably 12-15 μm.

[0087] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope 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, then add 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, then add 0.7 mL of N-methylpyrrolidone solution, and then stir the reaction at room temperature for 36 hours to obtain a PAA precursor solution.

[0090] The prepared PAA precursor solution is 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 increase program: increase to 70°C at 1°C / min and keep warm for 1h, increase to 85°C at 1°C / min and keep warm for 1h, increase to 110°C at 1°C / min and keep warm for 1h, increase to 160°C at 1°C / min and keep warm for 1h, increase to 220°C at 1°C / min and keep warm for 1h, increase to 260°C at 1°C / min and keep warm for 1h, increase to 290°C at 1°C / min and keep warm for 1h, cool naturally, peel off the polymer film with 40°C water, and then bake it at 110°C for 24h to obtain a benzyl cross-linked polyetherimide (TPEI) with a thickness of 12μm, that is, 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 imide ring formation of the polymer chain to obtain a polymer solution. The obtained polymer solution is dripped dropwise into ethanol at a stirring temperature of 40° C., pyridine and acetic anhydride are dissolved in ethanol, a polymer is precipitated, the polymer precipitate is washed with ethanol, the polymer precipitate is placed in an oven at 120° C. and dried for 24 h to remove the solvent, and the product is dissolved in NMP solvent, vacuum is evacuated to remove the gas in the solution, 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, and the film was cooled naturally. The polymer film was peeled off with 40°C water and then baked at 110°C 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, when preparing TPEI, the benzyl group in the diamine monomer is used to generate benzyl radicals in an air and heated environment, which induces the 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 to be the dominant interlayer stacking (PLP) that tends to weaken the CTC effect between molecules.

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

[0097] Depend on Figure 3 The FTIR graph 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 a nitrogen atmosphere only shows the degradation of the main chain of the molecule, 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 From the DSC graph of , it can be seen that the glass transition temperature (Tg) of TPEI reaches 294.46°C, while the glass transition temperature (Tg) of PEI is only 236.31, 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. From the TMA graph of 8, it can be seen 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 materials: Design a metal mask with a circular hole diameter of 3mm, sandwich the prepared film between two metal mask plates, symmetrically sputter gold electrodes on the upper and lower surfaces, and sputter the upper and lower surfaces for 300s at a sputtering current of 30mA. The dielectric spectrum, dielectric temperature spectrum and high-temperature energy storage performance of polymer dielectric materials were tested using a ferroelectric workstation and an impedance analyzer. The results are as follows: Figures 9 to 12 shown.

[0102] Fig. 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. Fig. 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] Fig.10 The figure is a relationship diagram between the dielectric constant and dielectric loss of the PEI prepared in Comparative Example 1 and the TPEI prepared in Example 1 and the electric field frequency at 1 kHz. Fig.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 to 250°C.

[0104] Depend on Fig.11 It can be seen that at 200°C, compared with pure PEI (energy storage density is 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 Fig.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 about 20%, 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 inhibit 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 principle of the present invention. These improvements and modifications should also be regarded as 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) in an inert atmosphere, mixing a diamine monomer, a dianhydride monomer, and an organic solvent, 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.

2. The preparation method according to claim 1, characterized in that: 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'-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, the diamine monomer 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 meta-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 or 6, characterized in that: The precursor solution is subjected to imidization reaction and benzyl free radical crosslinking reaction by the following steps: The precursor solution is coated on a substrate to obtain a precursor solution film, 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.

8. The preparation method according to claim 1 or 6, characterized in that: The precursor solution is subjected to imidization reaction and benzyl free radical crosslinking reaction by the following steps: The precursor solution and the catalyst are mixed to carry out an imidization reaction to obtain an imidization reaction solution, 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, coating the polymer solution on a substrate to obtain a polymer solution film, The polymer solution film is subjected to a benzyl radical cross-linking reaction.

9. The preparation method according to claim 8, characterized in that: The volume ratio of the precursor solution to the catalyst is 100-200:1, the catalyst is a mixture of isoquinoline or pyridine and acetic anhydride; the volume ratio of pyridine to acetic anhydride is 1:1; the temperature of the imidization reaction is 140-200°C, and the time is 2-10 hours.

10. The preparation method according to claim 8, characterized in that: The temperature of the benzyl free radical cross-linking reaction is 250-320° C., and the time is 1-3 hours.

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