Polyimide dielectric film containing carboxyl betaine and preparation method thereof

Abstract

The invention discloses a polyimide dielectric film containing carboxyl betaine and a preparation method thereof. The carboxyl betaine-containing polyimide dielectric film is prepared from carboxyl betaine-containing polyimide, and the carboxyl betaine-containing polyimide is prepared by the following steps: firstly, taking a precursor of carboxyl betaine, m-phenylenediamine and bisphenol a type diether dianhydride as monomers, and carrying out condensation polymerization to obtain polyamide acid; carrying out complete imidization on the polyamide acid under the action of a catalyst isoquinoline to obtain polyimide containing a precursor; and reacting the polyimide containing the precursor with sodium bromoacetate to obtain polyimide containing carboxyl betaine. The zwitterions are introduced into the polyimide structure to improve the dielectric and energy storage performance of the polyimide dielectric film, and meanwhile, the preparation method has the advantages of being low in cost, simple in process, controllable and adjustable in performance, suitable for large-scale application and the like.

Description

Technical Field

[0001] This invention relates to a polyimide dielectric film containing carboxybetaine and its preparation method. Background Technology

[0002] Dielectric capacitors are among the most widely used components in electronic and electrical systems, found in numerous fields such as energy storage, pulsed power systems, power regulation devices, and even power factor correction equipment. Polymer capacitors are widely used in capacitor applications due to their low cost, high breakdown strength, and unique self-healing capabilities. Achieving both high energy density and low dielectric loss simultaneously is a major challenge for polymer films. In existing polymer dielectrics, either non-ferroelectric polymers have low energy density, or ferroelectric polymers have high dielectric loss, thus severely limiting their applications.

[0003] As is well known, the maximum electrostatic energy stored in a dielectric can be simply estimated using the following formula:

[0004] U e = (1)

[0005] Where ε0 represents the vacuum permittivity, ε r and E b These are the dielectric constant and electrical breakdown strength, respectively. Equation (1) implies that high energy density requires the polymer to simultaneously possess high ε... r and E b .

[0006] Currently, the widely used biaxially oriented polypropylene (BOPP) film capacitors on the market have a high T... g Its low dielectric constant results in an operating temperature <105℃, making it unsuitable for stable operation in complex environments such as high temperature and high pressure. Furthermore, its low dielectric constant limits energy density, failing to meet the demands for miniaturization and lightweight design. In contrast, the polyimide backbone, composed of imide and benzene rings, exhibits excellent high-temperature resistance (T...). g (>250℃), and dielectric properties. Furthermore, due to its good flexibility, ease of processing, good thermal stability, and freedom in structural design, it has attracted widespread attention from researchers. However, due to the π-π conjugation effect between polyimide segments, the band gap is low, resulting in poor energy storage performance. In terms of dielectric energy storage, ionic groups are generally considered detrimental because they lead to a significant increase in dielectric loss and conductivity. In addition, ionic groups tend to aggregate into large ionic domains, which cannot follow high-frequency alternating electric fields, resulting in a much lower-than-expected increase in dielectric constant. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a polyimide dielectric film containing carboxybetaine and its preparation method. By introducing zwitterions into the polyimide structure, the dielectric properties and energy storage properties of the polyimide dielectric film are improved. At the same time, the preparation has the advantages of low cost, simple process, controllable and adjustable performance, and suitability for large-scale application.

[0008] The technical solution adopted in this invention will be described in detail below.

[0009] In a first aspect, the present invention provides a polyimide dielectric film containing carboxybetaine, wherein the carboxybetaine-containing polyimide dielectric film is made of carboxybetaine-containing polyimide, which is prepared by the following method: firstly, using a carboxybetaine precursor, m-phenylenediamine (MPD), and bisphenol A diether dianhydride (BPADA) as monomers, the total molar ratio of the carboxybetaine precursor and m-phenylenediamine to the molar ratio of bisphenol A diether dianhydride (BPADA) is 1:1. The molar amount of the base precursor accounts for 1-10% of the total molar amount of the carboxybetaine precursor and m-phenylenediamine. A reaction solution with a solid content of 10-12% is prepared and subjected to polycondensation to obtain polyamic acid. The polyamic acid is then completely imidized under the action of the catalyst isoquinoline to obtain a polyimide containing the precursor. The polyimide containing the precursor is reacted with sodium bromoacetate to obtain a polyimide containing carboxybetaine, wherein the molar amount of sodium bromoacetate added is 3-6 times the molar amount of the precursor unit contained in the polyimide containing the precursor.

[0010] The precursor of the carboxybetaine is 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA), with the structure shown below:

[0011]

[0012] The structure of the bisphenol a type diether dianhydride is shown below:

[0013] .

[0014] Preferably, the polycondensation reaction conditions are: a reaction temperature of 0-10℃ and a reaction time of 18-30h, preferably 24h.

[0015] Preferably, the molar amount of the carboxybetaine precursor accounts for 2-5% of the total molar amount of the carboxybetaine precursor and m-phenylenediamine, more preferably 5%. This optimization enables the dielectric film to achieve higher breakdown field strength and energy storage efficiency, as well as lower leakage current density.

[0016] Preferably, the solvent of the reaction solution for the polycondensation reaction is anhydrous NMP.

[0017] Preferably, the feed ratio of the polyimide containing the precursor to sodium bromoacetate is 1:4-6, more preferably 1:4, calculated by the molar ratio of the precursor unit to sodium bromoacetate.

[0018] In a second aspect, the present invention provides a method for preparing the polyimide dielectric film containing carboxybetaine as described in the first aspect, comprising the following steps:

[0019] Step 1: Using carboxybetaine precursor, m-phenylenediamine (MPD), and bisphenol a diether dianhydride (BPADA) as monomers, the total molar ratio of the carboxybetaine precursor and m-phenylenediamine to the molar ratio of bisphenol a diether dianhydride (BPADA) is 1:1, and the molar amount of the carboxybetaine precursor accounts for 1-10% of the total molar amount of the carboxybetaine precursor and m-phenylenediamine. A reaction solution with a solid content of 10-12% is prepared, and polyamic acid is obtained through polycondensation reaction.

[0020] Step 2: The polyamic acid obtained in Step 1 is completely imidized under the action of the catalyst isoquinoline to obtain a polyimide containing a precursor;

[0021] Step 3: React the polyimide containing the precursor with sodium bromoacetate to obtain a polyimide containing carboxybetaine; wherein the molar amount of sodium bromoacetate added is 3-6 times the molar amount of the precursor unit contained in the polyimide containing the precursor;

[0022] Step 4: The polyimide containing carboxy betaine obtained in Step 3 is used to form a polyimide dielectric film containing carboxy betaine by solution film formation method;

[0023] The reaction equation is shown below:

[0024]

[0025] Preferably, in step 1, the molar amount of the carboxybetaine precursor accounts for 2-5% of the total molar amount of the carboxybetaine precursor and m-phenylenediamine, more preferably 5%.

[0026] Preferably, in step 1, the solvent of the reaction solution for the polycondensation reaction is anhydrous NMP.

[0027] Preferably, in step 1, the polycondensation reaction conditions are: a reaction temperature of 0-10℃ and a reaction time of 18-30h, preferably 24h.

[0028] Preferably, in step 1, anhydrous NMP is used as a solvent to prepare a reaction solution with a solid content of 10-12% for the precursor of carboxybetaine, m-phenylenediamine (MPD) and bisphenol a diether dianhydride (BPADA); more preferably, the solid content is 10.5-11.5%.

[0029] In some embodiments, step 1 is specifically carried out as follows: under a nitrogen atmosphere, anhydrous N-methylpyrrolidone (NMP), 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA), m-phenylenediamine (MPD) and bisphenol a diether dianhydride (BPADA) are added to a reaction vessel, stirred thoroughly and reacted at a temperature of 0-10°C for 18-30 h (preferably 24 h). After the reaction is completed, a reaction solution containing polyamic acid is obtained.

[0030] In some embodiments, step 2 of the present invention is specifically implemented as follows:

[0031] The catalyst isoquinoline is added dropwise to the reaction solution containing polyamic acid obtained from the first step of the polycondensation reaction. The mixture is stirred thoroughly and the temperature is controlled at 160-200℃ for 6-24 hours. After the reaction is completed, polyimide powder containing the precursor is obtained by separation and purification.

[0032] Preferably, in step 2, the amount of catalyst added is 0.5-0.15 mL: 0.005 mol, calculated by the ratio of catalyst to bisphenol A type diether dianhydride, and more preferably 0.1 mL: 0.005 mol.

[0033] Preferably, in step 2, the reaction temperature is 180°C and the reaction time is 12 hours.

[0034] Preferably, in step 2, the separation and purification steps are carried out as follows: the solution obtained from the reaction is transferred to ethanol at a volume ratio of 1:4-8, the precipitate is collected, and the precipitate is washed repeatedly with ethanol. Then, it is dried under vacuum to obtain polyimide powder containing the precursor.

[0035] In some embodiments, step 3 of the present invention is specifically implemented as follows:

[0036] Anhydrous solvent and polyimide containing the precursor were added to a reaction vessel under a nitrogen atmosphere and stirred thoroughly until completely dissolved to obtain a polyimide solution containing the precursor. Then, sodium bromoacetate solution was added dropwise, and the reaction was carried out at 80-90℃ for 24-72 hours. After the reaction was completed, polyimide powder containing carboxybetaine was obtained by separation and purification.

[0037] Preferably, in step 3, the feed ratio of the polyimide containing the precursor to sodium bromoacetate is 1:4-6, more preferably 1:4, calculated by the molar ratio of the precursor unit to sodium bromoacetate.

[0038] Preferably, in step 3, the anhydrous solvent is anhydrous NMP or anhydrous DMSO.

[0039] Preferably, in step 3, the solid content of the polyimide precursor solution is 5-8 wt%.

[0040] Preferably, in step 3, the solid content of the sodium bromoacetate solution is 1-2 wt%.

[0041] Preferably, in step 3, the reaction temperature is 85°C and the reaction time is 24-72 hours, more preferably 48 hours.

[0042] Preferably, in step 3, the separation and purification steps are carried out as follows: the solution obtained from the reaction is transferred to deionized water at a volume ratio of 1:4-8, the precipitate is collected, and it is repeatedly washed with deionized water several times, and then vacuum dried to obtain polyimide containing carboxybetaine.

[0043] Preferably, in step 4, the anhydrous organic solvent is anhydrous NMP.

[0044] In some implementations, step 4 is specifically performed as follows:

[0045] Polyimide powder containing carboxybetaine was dissolved in anhydrous NMP to obtain a casting solution, which was then cast into a film and dried to obtain a polyimide dielectric film containing carboxybetaine.

[0046] Preferably, in step 4, the drying temperature is 70-90℃, and the drying time can be determined according to the film thickness.

[0047] The present invention has the following advantages over the prior art:

[0048] (1) Compared to polyimide films without carboxybetaine, the polyimide films containing carboxybetaine described in this invention have higher dielectric constant, polarization intensity, and energy density. This is because zwitterions are dipolar ions of covalently bonded ions with opposite charges. Unlike traditional ionomers where ions are connected to polymer chains by electrostatic attraction, the presence of stronger covalent bonds not only restricts the free movement of ions but also prevents the formation of large ion clusters, which helps to prevent the generation of dielectric losses in zwitterion-functionalized polymers. At the same time, zwitterions themselves have a higher dipole moment, which can improve the dielectric constant, polarization intensity, and energy density.

[0049] (2) By controlling the content of carboxybetaine units, the polyimide film containing carboxybetaine described in this invention can achieve higher breakdown field strength and energy storage efficiency, as well as lower leakage current density, than polyimide films without carboxybetaine. This is because zwitterions, acting as charge trapping sites, can confine charge carriers to the ionic group-polymer interface, significantly reducing the number of free charge carriers and preventing charge migration, thereby reducing leakage current generation and improving breakdown field strength and energy storage efficiency.

[0050] (3) Compared to polyimide films without carboxybetaine, the polyimide film containing carboxybetaine described in this invention has a higher glass transition temperature. This is because there is a strong Coulomb force between zwitterions, which can act as physical crosslinking points to restrict nearby polymer chains, thereby increasing the glass transition temperature (T0) of the polymer. g This allows the polymer film to maintain good thermal stability at high temperatures.

[0051] (4) Compared with polyimide films that do not contain carboxy betaine, the polyimide films containing carboxy betaine described in this invention have a higher energy storage density under the same charge and discharge time, which is beneficial for the film capacitor to achieve a faster response in inverters or high-frequency filter circuits.

[0052] (5) The polyimide film containing carboxybetaine described in this invention, after more than 100,000 charge-discharge cycles, P max and P r It remains stable, exhibits good cyclic stability, and can operate stably at room temperature. Attached Figure Description

[0053] Figure 1 These are the infrared spectra of the thin films prepared in Examples 2, 3, 3, 4, and 5.

[0054] Figure 2 The thermodynamic properties of the thin films prepared in Examples 2, 3, 4 and 5 are: (a) storage modulus, (b) loss factor;

[0055] Figure 3 This describes the relationship between the dielectric properties and frequency of the thin films prepared in Examples 2, 3, 4, and 5.

[0056] Figure 4 The polarization behavior statistics of the thin films prepared in Examples 2, 3, 4 and 5 are as follows: (a) maximum polarization, (b) remanent polarization;

[0057] Figure 5The breakdown field strength distribution of the films prepared in Examples 2, 3, 4 and 5 is shown.

[0058] Figure 6 The energy storage performance of the thin films prepared in Examples 2, 3, 4 and 5;

[0059] Figure 7 The leakage current density is the same as that of the films prepared in Examples 2, 3, 4 and 5.

[0060] Figure 8 The cycling performance of the thin film prepared in Example 3;

[0061] Figure 9 The charge-discharge performance of the films prepared in Examples 2 and 3 is shown. Detailed Implementation

[0062] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the scope of protection of the present invention is not limited thereto.

[0063] Unless otherwise specified in the embodiments of this invention, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained through conventional technical means or commercially available.

[0064] The raw materials used in the embodiments of the present invention are commercially available analytical grade or chemically pure products.

[0065] Example 1, Comparative Examples 1 and 2

[0066] 1. Sample preparation

[0067] (1) Example 1

[0068] Step 1: Under a nitrogen atmosphere, add 0.005 mol MPD and 0.005 mol BPADA monomers, along with 25 mL of anhydrous NMP, to a 50 mL three-necked flask. After the addition is complete, react at 0-10 °C for 24 h.

[0069] Step 2: Dilute the polyamic acid solution obtained from the reaction with anhydrous NMP to a solid content (mass ratio) of 2%, then drop it onto a glass plate and place it in an oven to dry at 80°C for 8 hours to finally obtain a polyamic acid film.

[0070] (2) Comparison of Examples 1 and 2

[0071] Polyamic acid films were prepared according to the processes described in steps 1 and 2 of Example 1, except that in step 1, 35 mL and 15 mL of anhydrous NMP were added, respectively.

[0072] 2. Results Comparison and Analysis

[0073] Example 1 yielded a complete film with a smooth surface and a thickness of 10-15 μm. In Comparative Example 1, the low solid content of the reaction solution resulted in a low molecular weight polymer, preventing film formation. In Comparative Example 2, the high solid content of the reaction solution led to excessive viscosity after 6 hours, causing the reaction to stop and also preventing film formation. Therefore, the above results demonstrate that a complete polyamic acid film can be prepared using the process described in Example 1.

[0074] Example 2

[0075] 1. Sample preparation

[0076] Example 2

[0077] Step 1: Prepare a polyamic acid solution by referring to the process described in Step 1 of Example 1.

[0078] Step 2: Continue to add 0.1 mL of isoquinoline to the three-necked flask, stir thoroughly and control the temperature at 180℃ for 12 h. Transfer the resulting solution to ethanol at a ratio of 1:7, collect the precipitate, wash it repeatedly with ethanol, and then dry it in a vacuum oven at 60℃ for 24 h to finally obtain polyimide powder.

[0079] Step 3: Dissolve 0.15g of the polyimide powder obtained above in 10mL of anhydrous NMP, and drop the solution onto a glass plate. Place the plate in an 80℃ oven for 8 hours to obtain a polyimide film.

[0080] 2. Testing and Characterization

[0081] Fourier transform infrared spectroscopy analysis:

[0082] The structure of the thin film was analyzed using a Nicolet 6700 Fourier transform infrared spectrometer (TEIR) purchased from Nicolet Inc., USA. Attenuated total reflectance mode was used at a 4 cm⁻¹. -1 At a resolution of 3500 cm -1 up to 500cm -1 Within the wavelength range, 32 scans were performed.

[0083] 3. Results Comparison and Analysis

[0084] The structure of the polyimide prepared in Example 2 was characterized using Fourier transform infrared spectroscopy. Figure 1 As shown, at 1780cm -1 With 1720cm -1 Asymmetric and symmetric stretching vibrations of polyimide C=O were observed at 740 cm⁻¹.-1 The bending vibration peak at C=O is observed at 1360 cm⁻¹. -1 The appearance of the CN stretching vibration peak at 1550 cm⁻¹ indicates that the polyimide has been successfully synthesized. Simultaneously, a peak for the CN stretching vibration was observed at 1550 cm⁻¹. -1 The absence of characteristic absorption peaks of PAA indicates that the polyimide has been completely imidized.

[0085] Example 3, Comparative Example 3

[0086] 1. Sample preparation

[0087] (1) Example 3

[0088] Step 1: Prepare a polyamic acid solution containing the precursor using the process described in Step 1 of Example 1, except that the monomers added are: 0.00025 mol APBIA, 0.00475 mol MPD and 0.005 mol BPADA.

[0089] Step 2: Prepare polyimide powder containing the precursor by referring to the process described in Step 2 of Example 2.

[0090] Step 3: Under a nitrogen atmosphere, add 15 mL of anhydrous NMP and 1 g of polyimide powder containing the precursor (containing 0.00008 mol of APBIA precursor units) to a 50 mL three-necked flask, and stir thoroughly until completely dissolved. Then, dissolve 0.0512 g (0.00032 mol) of sodium bromoacetate in 5 mL of anhydrous DMSO and add it dropwise to the three-necked flask, controlling the temperature at 85 °C for 48 h. After the reaction is complete, transfer the resulting solution to deionized water at a ratio of 1:7, collect the precipitate, wash it repeatedly with deionized water, and then dry it in a vacuum oven at 60 °C for 24 h to finally obtain polyimide powder containing carboxybetaine.

[0091] Step 4: Prepare a polyimide film containing carboxybetaine according to the process described in Step 3 of Example 2.

[0092] (2) Comparative Example 3

[0093] The polyimide powder containing carboxybetaine was prepared according to the process described in steps 1, 2 and 3 of Example 3, except that in step 3, 0.0256 g of sodium bromoacetate was dissolved in 2.5 mL of anhydrous DMSO (the molar ratio of sodium bromoacetate to precursor unit was 2:1), and the reaction time was 24 h.

[0094] 2. Testing and Characterization

[0095] Fourier transform infrared spectroscopy analysis:

[0096] Refer to Example 2.

[0097] 3. Results Comparison and Analysis

[0098] The structures of the polyimides prepared in Example 3 and Comparative Example 3 were characterized using Fourier transform infrared spectroscopy. Figure 1 As shown, at 1780cm -1 The peak value is enhanced at 3480 cm⁻¹, which is attributed to the introduction of carboxyl groups. -1 A relatively wide absorption band was also observed, indicating the formation of hydrogen bonds. Therefore, it can be proven that Example 3 successfully constructed carboxybetaine, while Comparative Example 3 did not succeed.

[0099] Examples 4 and 5

[0100] 1. Sample preparation

[0101] A polyimide film containing carboxybetaine was prepared according to the process described in Example 3, except that the monomers fed in step 1 were: 0.0001 mol APBIA, 0.0049 mol MPD and 0.005 mol BPADA (Example 4), and 0.0005 mol APBIA, 0.0045 mol MPD and 0.005 mol BPADA (Example 5).

[0102] 2. Testing and Characterization

[0103] (1) Fourier transform infrared spectroscopy analysis:

[0104] Refer to Example 2.

[0105] (2) Dynamic thermomechanical analysis:

[0106] The thermodynamic properties of polyimide films were tested using a DMA 242 dynamic thermomechanical analyzer purchased from Netzsch, Germany. A 10 μm thick polyimide film was selected and cut into pieces 10 mm long and 5 mm wide. The test conditions were: frequency 1 Hz, amplitude 20 μm, and the experimental temperature increased from 35℃ to 300℃ at a heating rate of 10℃ / min.

[0107] (3) Dielectric property testing:

[0108] The dielectric properties of polyimide films were tested using an Agilent Technologies 4990LCR impedance analyzer. A 0.6cm × 0.6cm polyimide film was selected, and its top and bottom surfaces were electroplated (Au layer) using an ion sputtering apparatus. Then, at 10... 2 -10 6 Tests were conducted within the Hz range. The formula ε=C was then used subsequently. sThe dielectric constant is calculated using A / ε0 d. Where C... s A is the capacitance value; A is the conductive area, m 2 ε0 is the vacuum permittivity, 8.854 × 10⁻⁶. 12 F / m; d is the film thickness before spraying, in meters.

[0109] (4) Ferroelectric performance testing:

[0110] The ferroelectric properties of polyimide films were tested using a TREK09B-3-K-CE677 ferroelectric testing system from Radiant Technologies, USA. These tests included hysteresis loop (PE curve) and charge-discharge cycle performance testing. Prior to testing, an Au layer was electroplated onto the top and bottom surfaces of the polyimide film using an ion sputtering apparatus, with an area of ​​0.0707 cm². 2 The test frequency was 50Hz.

[0111] (5) Charge and discharge performance test

[0112] The charge-discharge performance of polyimide films was tested using a CPR1901 charge-discharge performance tester from Polyk Technologies, USA. The resistance R was measured. L It is 1000Ω. Discharge time (τ) 0.9 It is defined as the time required to release 90% of the stored energy.

[0113] 3. Results Comparison and Analysis

[0114] The structures of the thin films prepared in Examples 4 and 5 were characterized using Fourier transform infrared spectroscopy, and the results are as follows: Figure 1 As shown, at 1780cm -1 and 3480cm -1 The peak value at the point showed an upward trend with the increase of carboxybetaine content.

[0115] The thermodynamic properties of the thin films prepared in Examples 2-5 were characterized using a dynamic thermomechanical analyzer, and the results are as follows: Figure 2 As shown, with the increase of carboxybetaine content, T g The trend is upward. This is because there is a strong Coulomb force between zwitterions, which can act as physical cross-linking points to restrict the movement of nearby polymer chains, thereby increasing T. g The temperature rose from 173°C to 191°C. Meanwhile, the energy storage modulus was 10. 3 Above M, it exhibits good mechanical properties.

[0116] The dielectric properties of the thin films prepared in Examples 2-5 were characterized using an impedance analyzer, and the results are as follows: Figure 3As shown, the dielectric constant increases with increasing carboxybetaine content. The dielectric loss remains consistently low at 0.003. This is because zwitterions are dipolar ions with opposite charges and covalent bonds. Unlike traditional ionomers where ions are linked to polymer chains via electrostatic attraction, the stronger covalent bonds not only restrict the free movement of ions but also prevent the formation of large ion clusters, thus maintaining the dielectric loss of zwitterionic-functionalized polymers. Simultaneously, zwitterions themselves possess higher dipole moments and polarization responses, enhancing the overall dipole polarization of the polymer and increasing the dielectric constant from 3.5 to 4.5.

[0117] The polarization properties, breakdown properties, energy storage properties, and leakage current density of the thin films prepared in Examples 2-5 were characterized using a ferroelectric testing instrument. Figure 4 As shown, the addition of carboxybetaine increases the maximum polarization of the polyimide film while the residual polarization remains essentially unchanged. This is due to the high dipole moment and good polarization response of zwitterions. Figure 5 As shown, this is the fitting curve of breakdown strength using the Weibull distribution formula, an important standard for evaluating breakdown performance. The figure shows that the introduction of carboxybetaine significantly increases the breakdown field strength, from 512 MV / m to 666 MV / m. This is because zwitterions act as charge trapping sites, confining charge carriers at the ionic group-polymer interface, significantly reducing the number of free charge carriers and preventing charge migration, thereby increasing the breakdown field strength. Figure 6 As shown, in terms of energy storage performance, Example 3 can maintain an efficiency of 75% under a field strength of 650 MV / m, while the energy storage density can reach 22 J / cm³. 3 Compared to Example 2, the efficiency increased from 80% to 83% at a field strength of 500 MV / m, and the energy density increased from 12 J / cm². 3 Increased to 13J / cm 3 On the one hand, zwitterions can act as charge traps; on the other hand, zwitterions have high polarity. However, in Example 5, the breakdown field strength only reached 500 MV / m, with an efficiency of only 81%. This may be because when the amount of carboxybetaine added increased, random polycondensation failed to uniformly distribute the self-assembled nanoscale ion clusters on the polymer, leading to the formation of ionic phase domains. Figure 7 As shown in the results, carboxybetaine has a certain inhibitory effect on leakage current. At 25°C, the leakage current density in Example 2 was 8.6 × 10⁻⁶. -8 A / cm 2 The leakage current in Example 3 was 5.16 × 10⁻⁶. -8 A / cm 2Because zwitterions act as charge-trapping sites, they reduce the probability of electrical tree formation, thus lowering the leakage current density. The cycling performance of Example 3 was characterized using a ferroelectric testing instrument. Figure 8 As shown, in Example 3, after more than 100,000 charge-discharge cycles, P max and P r It remains stable, exhibiting good cycle stability and capable of stable operation at room temperature. The charge-discharge performance of Examples 2 and 3 was characterized using a charge-discharge performance tester. Figure 9 As shown, compared with Example 2, Example 3 has a higher energy storage density under the same charge and discharge time, which is beneficial for thin film capacitors to achieve faster response in inverters or high-frequency filter circuits.

Claims

1. A polyimide dielectric film containing carboxybetaine, characterized in that: The carboxybetaine-containing polyimide dielectric film is made of carboxybetaine-containing polyimide, which is prepared by the following method: First, using a carboxybetaine precursor, m-phenylenediamine, and bisphenol A diether dianhydride as monomers, the total molar ratio of the carboxybetaine precursor and m-phenylenediamine to the molar ratio of bisphenol A diether dianhydride is 1:

1. The molar amount of the carboxybetaine precursor accounts for 1-10% of the total molar amount of the carboxybetaine precursor and m-phenylenediamine. A reaction solution with a solid content of 10-12% is prepared, and polyamic acid is obtained through a polycondensation reaction. The polyamic acid is then completely imidized under the action of the catalyst isoquinoline to obtain a polyimide containing the precursor. The polyimide containing the precursor is reacted with sodium bromoacetate to obtain a polyimide containing carboxybetaine, wherein the molar amount of sodium bromoacetate added is 3-6 times the molar amount of the precursor unit in the polyimide containing the precursor. The precursor of the carboxybetaine is 2-(4-aminophenyl)-5-aminobenzimidazole, with the structure shown below: The structure of the bisphenol a type diether dianhydride is shown below: 。 2. The polyimide dielectric film containing carboxybetaine as described in claim 1, characterized in that: The molar amount of the precursor of carboxybetaine accounts for 2-5% of the total molar amount of the precursor of carboxybetaine and m-phenylenediamine, preferably 5%.

3. The polyimide dielectric film containing carboxybetaine as described in claim 1 or 2, characterized in that: The solvent for the polycondensation reaction solution is anhydrous NMP, and the polycondensation reaction conditions are: reaction temperature of 0-10℃, reaction time of 18-30h, preferably 24h.

4. The polyimide dielectric film containing carboxybetaine as described in claim 1 or 2, characterized in that: The feed ratio of the polyimide containing the precursor to sodium bromoacetate is 1:4-6, preferably 1:4, based on the molar ratio of the precursor unit to sodium bromoacetate.

5. A method for preparing a polyimide dielectric film containing carboxybetaine as described in any one of claims 1-4, comprising the following steps: Step 1: Using carboxybetaine precursor, m-phenylenediamine, and bisphenol A diether dianhydride as monomers, the total molar ratio of the carboxybetaine precursor and m-phenylenediamine to the molar ratio of bisphenol A diether dianhydride is 1:1, and the molar amount of the carboxybetaine precursor accounts for 1-10% of the total molar amount of the carboxybetaine precursor and m-phenylenediamine, a reaction solution with a solid content of 10-12% is prepared, and polyamic acid is obtained through polycondensation reaction; Step 2: The polyamic acid obtained in Step 1 is completely imidized under the action of the catalyst isoquinoline to obtain a polyimide containing a precursor; Step 3: React the polyimide containing the precursor with sodium bromoacetate to obtain a polyimide containing carboxybetaine; wherein the molar amount of sodium bromoacetate added is 3-6 times the molar amount of the precursor unit contained in the polyimide containing the precursor; Step 4: The polyimide containing carboxy betaine obtained in Step 3 is used to form a polyimide dielectric film containing carboxy betaine by solution film formation method.

6. The preparation method according to claim 5, characterized in that: Step 2 is implemented as follows: The catalyst isoquinoline is added dropwise to the reaction solution containing polyamic acid obtained from the first step of the polycondensation reaction. The mixture is stirred thoroughly and the temperature is controlled at 160-200℃ for 6-24 hours. After the reaction is completed, polyimide powder containing the precursor is obtained by separation and purification.

7. The preparation method according to claim 5, characterized in that: Step 3 is implemented as follows: Anhydrous solvent and polyimide containing the precursor were added to a reaction vessel under a nitrogen atmosphere and stirred thoroughly until completely dissolved to obtain a polyimide solution containing the precursor. Then, sodium bromoacetate solution was added dropwise, and the reaction was carried out at 80-90℃ for 24-72 hours. After the reaction was completed, polyimide powder containing carboxybetaine was obtained by separation and purification.

8. The preparation method according to claim 7, characterized in that: In step 3, the anhydrous solvent is anhydrous NMP or anhydrous DMSO, so that the solid content of the solution containing the precursor polyimide is 5-8 wt%.

9. The preparation method according to claim 7, characterized in that: In step 3, the solvent for the sodium bromoacetate solution is anhydrous DMSO, and the solid content is 1-2 wt%.

10. The preparation method according to claim 9, characterized in that: In step 3, the reaction temperature is 85°C and the reaction time is 24-72 hours.

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