A method for producing a halogenated olefin graft-modified poly-4-methyl-1-pentene dielectric film for a capacitor

Abstract

The application relates to a preparation method of a halogenated olefin graft-modified poly-4-methyl-1-pentene dielectric film for capacitors, and relates to the technical fields of polymer dielectric materials and thin-film capacitor. The application aims to solve the problems of the existing PMP dielectric film, such as the increase of dielectric loss, the limitation of breakdown strength and energy storage performance, and the insufficient service reliability under high-temperature and strong electric field conditions. The application introduces trans-1,3-dichloropropene into the PMP molecular chain through grafting, constructs controllable polarization sites and trap structures, realizes the inhibition of carrier injection and migration behavior and the regulation of space charge accumulation, thereby improving the dielectric stability and insulation reliability of the film under high-temperature conditions while maintaining the low-loss advantage of the polyolefin system. The halogenated olefin graft-modified poly-4-methyl-1-pentene dielectric film for capacitors is used as a dielectric layer of a thin-film capacitor.

Description

Technical Field

[0001] This invention relates to the field of polymer dielectric materials and thin-film capacitors, specifically to a method for preparing a poly4-methyl-1-pentene dielectric thin film grafted with halogenated olefins for capacitors. Background Technology

[0002] Polymer film capacitors are widely used in advanced power electronics, electric vehicles, aerospace systems, and deep well drilling due to their advantages such as low loss, self-healing, and fast charging and discharging. Currently, the most mature and widely used dielectric film in engineering is still biaxially oriented polypropylene (BOPP), whose outstanding advantages are low intrinsic loss and high breakdown strength. However, BOPP's conductivity and loss increase significantly with rising temperatures, thus limiting its usable operating temperature. This necessitates derating at higher temperatures, making it difficult to meet the high-power-density power electronics' requirements for miniaturization at high temperatures.

[0003] To improve the applicability of polymer dielectric films under high-temperature conditions, various modification approaches have been proposed, such as selecting engineering polymers with higher heat resistance, enhancing dielectric response by introducing polar structures, or using multilayer structures and nanocomposites to regulate dielectric properties. However, in practical applications of film capacitors, in addition to possessing certain temperature resistance, dielectric materials emphasize long-term low dielectric loss and high insulation reliability. Excessive enhancement of polarity or introduction of numerous interface structures often leads to increased dielectric loss, more complex carrier transport behavior, and an increase in potential defects, thus adversely affecting breakdown strength and service life under high-temperature and strong field conditions. Based on the aforementioned engineering requirements and constraints, selecting polyolefin materials with higher heat resistance potential as the dielectric matrix while maintaining the low-loss advantage of polyolefin systems is considered a more reasonable and engineering-feasible transitional path.

[0004] Poly(4-methyl-1-pentene) (PMP) is a nonpolar polyolefin with a high melting point (approximately 230-240°C) and good electrical insulation properties. It has been studied to evaluate its feasibility as a high-temperature dielectric film. However, PMP also suffers from the common challenges of typical polyolefins: its low dielectric constant (approximately 2.2) limits the discharge energy density, and under high temperature and strong field conditions, it may still experience increased losses and breakdown risks due to charge injection / migration and space charge accumulation.

[0005] Therefore, it is necessary to design a dielectric thin film based on PMP and introduce tunable functional structures through grafting to regulate trapping and charge transport, as well as its preparation method, in order to solve problems such as increased dielectric loss, space charge accumulation and decreased breakdown reliability under high temperature and strong field conditions. Summary of the Invention

[0006] The purpose of this invention is to solve the problems of increased dielectric loss, limited breakdown strength and energy storage performance, and insufficient service reliability of PMP dielectric films under high temperature and strong electric field conditions in the prior art. The invention provides a method for preparing a poly(4-methyl-1-pentene) dielectric film grafted with halogenated olefins for capacitors.

[0007] This invention provides a technical solution for optimizing the performance of dielectric thin films based on PMP graft modification. By grafting halogenated propylene structural units (trans-1,3-dichloropropylene) onto the PMP molecular chain, this invention constructs tunable polarization sites and trap structures to suppress carrier injection and migration behavior and regulate space charge accumulation. This improves the dielectric stability and insulation reliability of the thin film under high-temperature conditions while maintaining the low-loss advantage of the polyolefin system.

[0008] A method for preparing a poly(4-methyl-1-pentene) dielectric film grafted with a haloolefin for capacitors is specifically carried out according to the following steps:

[0009] 1. Under an anhydrous and oxygen-free nitrogen atmosphere, poly-4-methyl-1-pentene is mixed with a solvent, heated and stirred to dissolve, to obtain solution A;

[0010] 2. Under an anhydrous and oxygen-free nitrogen atmosphere, azobisisobutyronitrile and trans-1,3-dichloropropene were mixed and dissolved by ultrasonication to obtain solution B;

[0011] 3. Under an anhydrous and oxygen-free nitrogen environment, solution A and solution B are mixed, heated and stirred to react, and a PMP grafting reaction precursor solution is obtained.

[0012] IV. Preparation of poly-4-methyl-1-pentene dielectric thin films:

[0013] ① Pour the PMP grafting reaction precursor solution onto a preheated clean glass plate and scrape it to a certain thickness using a scraper to obtain the coated glass plate.

[0014] ② Place the coated glass plate into a vacuum drying oven to remove the solvent through a drying process;

[0015] ③ Place the glass plate in a vacuum drying oven for annealing, then allow it to cool naturally to room temperature. Next, place the glass plate in deionized water, and the film will naturally detach from the glass plate. Finally, place the film in a vacuum drying oven to completely remove moisture, thus obtaining a poly(4-methyl-1-pentene) dielectric film grafted with halogenated olefins for capacitors.

[0016] A poly4-methyl-1-pentene dielectric film grafted with a halogenated olefin is used as the dielectric layer of a thin-film capacitor.

[0017] The beneficial effects of this invention are:

[0018] This invention uses poly(4-methyl-1-pentene) as a matrix and grafts haloolefin monomers onto the PMP molecular chain under free radical initiation conditions to achieve directional control of the PMP side chain structure. The introduced halogen functional group (-Cl) has strong polarization characteristics and electron attraction effects, which can form tunable polarization sites and trap structures within the polymer. On the one hand, this improves the carrier injection and migration barrier, suppresses space charge accumulation, and reduces leakage current density and dielectric loss under high temperature conditions. On the other hand, it reduces electric field distortion by homogenizing the local electric field distribution, thereby improving the breakdown strength and energy storage performance of the film under high temperature and strong electric field conditions. Compared with the prior art, this invention has at least the following advantages:

[0019] (1) The halogenated olefin-grafted modified poly(4-methyl-1-pentene) dielectric film for capacitors prepared in this invention still exhibits good dielectric stability and insulation properties at 150 °C, showing a low dielectric loss (tanδ=1.01×10⁻⁶). -4 @1 kHz), and a low leakage current density (1.71 × 10⁻⁶). -8 A / cm 2 It operates stably under high temperature and strong field conditions (@200 kV / mm) and is suitable for the preparation of dielectric layers in high temperature energy storage thin film capacitors.

[0020] (2) The halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric film for capacitors prepared by this invention has better energy storage performance and charge / discharge efficiency, and can achieve a discharge energy density U at 150 °C and 740 kV / mm electric field. e It is 5.42 J / cm 3 The charge / discharge efficiency η is 92.9%, demonstrating excellent high-temperature energy storage stability;

[0021] (3) The preparation process provided by the present invention is clear and highly controllable, effectively suppressing the interference of oxygen and moisture on the free radical grafting reaction, avoiding the occurrence of side reactions, resulting in films with fewer defects and easy thickness control (typical thickness is about 10 μm), good batch consistency of products, and suitable for continuous and large-scale preparation.

[0022] (4) The raw materials used in this invention are readily available, the process conditions are mild, the solvent coating and vacuum heat treatment equipment are highly versatile, the process is environmentally friendly and controllable, and the resulting film can be directly used in applications such as the dielectric layer of film capacitors, which has good engineering promotion value and application prospects.

[0023] The present invention provides a poly4-methyl-1-pentene dielectric film grafted with halogenated olefins for use in capacitors. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the grafting reaction principle of the present invention;

[0025] Figure 2 XRD patterns of the halogenated olefin graft-modified poly(4-methyl-1-pentene) dielectric films for capacitors prepared in Examples 1-4 and the comparative examples.

[0026] Figure 3 Fourier transform infrared spectra of the halogenated olefin graft-modified poly(4-methyl-1-pentene) dielectric films for capacitors prepared in Examples 1-4 and the comparative examples.

[0027] Figure 4 The dielectric spectra of the haloolefin-grafted modified poly4-methyl-1-pentene dielectric films for capacitors prepared in Examples 1-4 and the comparative examples at 150 °C.

[0028] Figure 5 The dielectric constant of the haloolefin-grafted modified poly4-methyl-1-pentene dielectric films for capacitors prepared in Examples 1-4 and the comparative examples varies with temperature at 1 kHz.

[0029] Figure 6 The dielectric loss of the haloolefin-grafted modified poly4-methyl-1-pentene dielectric films for capacitors prepared in Examples 1-4 and the comparative examples is shown as a function of temperature at 1 kHz.

[0030] Figure 7 The diagram shows a comparison of the leakage current density of the halogenated olefin-grafted modified poly(4-methyl-1-pentene) dielectric films for capacitors prepared in Examples 1-4 with that of the comparative examples.

[0031] Figure 8 The graph shows a comparison of the energy storage performance of the halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric films for capacitors prepared in Examples 1-4 with those of the comparative examples. Detailed Implementation

[0032] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. All materials, reagents, methods, and instruments used are conventional materials, reagents, methods, and instruments in the art and are commercially available to those skilled in the art.

[0033] Specific Implementation Method 1: This implementation method is a method for preparing a poly4-methyl-1-pentene dielectric film grafted with haloolefins for capacitors, specifically carried out according to the following steps:

[0034] 1. Under an anhydrous and oxygen-free nitrogen atmosphere, poly-4-methyl-1-pentene is mixed with a solvent, heated and stirred to dissolve, to obtain solution A;

[0035] 2. Under an anhydrous and oxygen-free nitrogen atmosphere, azobisisobutyronitrile and trans-1,3-dichloropropene were mixed and dissolved by ultrasonication to obtain solution B;

[0036] 3. Under an anhydrous and oxygen-free nitrogen environment, solution A and solution B are mixed, heated and stirred to react, and a PMP grafting reaction precursor solution is obtained.

[0037] IV. Preparation of poly-4-methyl-1-pentene dielectric thin films:

[0038] ① Pour the PMP grafting reaction precursor solution onto a preheated clean glass plate and scrape it to a certain thickness using a scraper to obtain the coated glass plate.

[0039] ② Place the coated glass plate into a vacuum drying oven to remove the solvent through a drying process;

[0040] ③ Place the glass plate in a vacuum drying oven for annealing, then allow it to cool naturally to room temperature. Next, place the glass plate in deionized water, and the film will naturally detach from the glass plate. Finally, place the film in a vacuum drying oven to completely remove moisture, thus obtaining a poly(4-methyl-1-pentene) dielectric film grafted with halogenated olefins for capacitors.

[0041] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the solvent used in step one is cyclohexane, decahydronaphthalene, or trichloroethylene; the dissolution temperature in step one is 60 ℃~150 ℃, and the dissolution time is 3 h~5 h. Other steps are the same as in Specific Implementation Method One.

[0042] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that the mass ratio of poly-4-methyl-1-pentene to solvent in step 1 is (0.03~0.1):1. Other steps are the same as in Specific Implementation Method 1 or 2.

[0043] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: the dissolution temperature in step two is room temperature, and the dissolution time is 15 min to 20 min; the heating and stirring reaction temperature in step three is 60 ℃ to 80 ℃, and the reaction time is 2 h to 4 h. Other steps are the same as in Specific Implementation Methods One to Three.

[0044] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the mass ratio of azobisisobutyronitrile in step two to poly4-methyl-1-pentene in step one is (0.003~0.005):1. The other steps are the same as in Specific Implementation Methods One to Four.

[0045] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the mass ratio of trans-1,3-dichloropropene in step two to poly-4-methyl-1-pentene in step one is (0.025~0.1):1. The other steps are the same as in Specific Implementation Methods One to Five.

[0046] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the temperature of the preheated clean glass plate in step four① is 25 ℃, 40 ℃, or 60 ℃; in step four①, the PMP grafting reaction precursor solution is poured onto the preheated clean glass plate, the gap of the coating applicator blade is adjusted to 20 μm, and a uniform coating is formed to obtain the coated glass plate. Other steps are the same as in Specific Implementation Methods One to Six.

[0047] Specific Implementation Method Eight: The difference between this implementation method and Specific Implementation Methods One to Seven is that the drying process described in step four ② is as follows: vacuum drying at 60 ℃ for 3 hours or first drying at room temperature for 1 hour, then drying at 30 ℃ for 30 minutes, then drying at 45 ℃ for 30 minutes, and finally drying at 60 ℃ for 1 hour. Other steps are the same as in Specific Implementation Methods One to Seven.

[0048] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in the following ways: the annealing temperature in step four ③ is 90℃, 130℃, 150℃, or 180℃; the annealing time is 1 h to 3 h; in step four ③, the film is placed in a vacuum drying oven at 60℃ for 12 h to 24 h to completely remove moisture; the thickness of the halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric film for the capacitor in step four ③ is 8 to 12 μm. Other steps are the same as in Specific Implementation Methods One to Eight.

[0049] Specific Implementation Method 10: This implementation method is to use a poly4-methyl-1-pentene dielectric film grafted with halogenated olefins as the dielectric layer of a thin film capacitor.

[0050] The beneficial effects of the present invention are verified using the following embodiments:

[0051] Example 1: A method for preparing a poly4-methyl-1-pentene dielectric film grafted with haloolefins for capacitors, specifically comprising the following steps:

[0052] 1. Weigh out poly(4-methyl-1-pentene) (PMP) and place it in a Shrek bottle. Evacuate the system three times to ensure that the entire reaction system is sealed and under a nitrogen atmosphere free of water and oxygen. Then, inject cyclohexane into the Shrek bottle and place the Shrek bottle in a constant temperature oil bath at 60 °C. Heat and stir for 4 h to fully dissolve the PMP, resulting in a clear and homogeneous solution A.

[0053] The mass ratio of poly(4-methyl-1-pentene) to solvent in step one is 0.064:1;

[0054] 2. Azobisisobutyronitrile (AIBN) was added to a Shrek tube at a mass ratio of 0.005:1 to poly(4-methyl-1-pentene). The tube was then evacuated and purged with nitrogen three times to ensure the entire reaction system was under a sealed, anhydrous, and oxygen-free nitrogen atmosphere. Subsequently, trans-1,3-dichloropropene was injected into the Shrek tube at a mass ratio of 0.025:1 to poly(4-methyl-1-pentene). The solution was then sonicated at room temperature for 15 minutes until fully dissolved, yielding solution B.

[0055] 3. Under an anhydrous and oxygen-free nitrogen atmosphere, solution B was added dropwise to a Shrek bottle containing solution A. The mixture was then placed in a constant temperature oil bath and heated and stirred at 65 °C for 4 h to obtain the PMP grafting reaction precursor solution.

[0056] IV. Preparation of poly-4-methyl-1-pentene dielectric thin films:

[0057] ① PMP grafting reaction precursor solution is poured onto the surface of a clean glass plate preheated to 60 ℃. Then the gap of the coating tool is adjusted to 20 μm, and a film is uniformly coated to obtain the coated glass plate.

[0058] ② Place the coated glass plate into a vacuum drying oven and evacuate it. Remove the solvent by drying according to the following process: First, dry at room temperature for 1 hour, then dry at 30°C for 30 minutes, then dry at 45°C for 30 minutes, and finally dry at 60°C for 1 hour to fully remove the solvent and residual monomer.

[0059] ③ Place the glass plate in a vacuum drying oven and anneal at 150 °C for 1.5 h to promote the relaxation and rearrangement of the poly(4-methyl-1-pentene) molecular chain segments, further improve the crystalline and amorphous structure of the film and further reduce film defects. After annealing and cooling to room temperature, place the glass plate in deionized water to allow the film to detach automatically. After removing the film, place it in a vacuum drying oven and evacuate it. Dry it at 60 °C for 12 h to completely remove moisture, obtaining a poly(4-methyl-1-pentene) dielectric film grafted with haloolefin for capacitors (denoted as PMP-g-2.5Cl).

[0060] The thickness of the poly4-methyl-1-pentene dielectric film grafted with halogenated olefins described in step 4③ is approximately 10 μm.

[0061] In this embodiment, all operations involving solution preparation, mixing reaction and transfer are carried out in an anhydrous and oxygen-free nitrogen protective environment to avoid the quenching of free radicals by oxygen and interference from side reactions caused by water, thereby ensuring the stability and repeatability of the grafting reaction process.

[0062] Example 2: The difference between this example and Example 1 is that in step two, trans-1,3-dichloropropene is injected into a Shrek tube at a mass ratio of 0.05:1 to poly4-methyl-1-pentene; the capacitor obtained in step four ③ is labeled as PMP-g-5Cl, which is a poly4-methyl-1-pentene dielectric film grafted with a haloolefin. All other steps and parameters are the same as in Example 1.

[0063] Example 3: The difference between this example and Example 1 is that in step two, trans-1,3-dichloropropene is injected into a Shrek tube at a mass ratio of 0.075:1 to poly4-methyl-1-pentene; the capacitor obtained in step four ③ is labeled as PMP-g-7.5Cl, which is a poly4-methyl-1-pentene dielectric film grafted with a haloolefin. All other steps and parameters are the same as in Example 1.

[0064] Example 4: The difference between this example and Example 1 is that in step two, trans-1,3-dichloropropene is injected into the Shrek tube at a mass ratio of 0.1:1 to poly4-methyl-1-pentene; the capacitor obtained in step four ③ is labeled as PMP-g-10Cl, which is a poly4-methyl-1-pentene dielectric film grafted with a haloolefin. All other steps and parameters are the same as in Example 1.

[0065] Comparative Example: The preparation method of poly(4-methyl-1-pentene) dielectric thin film is carried out according to the following steps:

[0066] Step 1: Weigh 0.5 g of poly(4-methyl-1-pentene) (PMP) into a Shrek bottle, and continuously evacuate the system three times to ensure that the entire reaction system is sealed and under a nitrogen atmosphere free of water and oxygen. Then, add 10 mL of cyclohexane into the Shrek bottle through a disposable syringe, and heat and stir in a constant temperature oil bath at 60 °C for 4 h to fully dissolve the PMP and obtain a PMP solution.

[0067] Step 2: Pour the PMP solution onto the surface of a clean glass plate preheated to 60 °C, then adjust the gap of the coating tool to 20 μm and uniformly coat the glass plate to obtain the coated glass plate.

[0068] Step 3: Place the coated glass plate in a vacuum drying oven and evacuate it. Remove the solvent according to the following drying process: place at room temperature for 1 hour, at 30 ℃ for 30 minutes, at 45 ℃ for 30 minutes, and at 60 ℃ for 1 hour.

[0069] Step 4: After removing residual reagents, anneal the vacuum drying oven at 150 °C for 1.5 h;

[0070] Step 5: After the annealing in Step 4 is completed and cooled to room temperature, place the glass plate in deionized water to allow the film to detach automatically; after removing the film, place it in a vacuum drying oven and evacuate it, then dry it at 60 °C for 12 h to completely remove moisture, obtaining a poly(4-methyl-1-pentene) dielectric film with a typical thickness of about 10 μm, denoted as PMP.

[0071] Figure 2 XRD patterns of the halogenated olefin graft-modified poly(4-methyl-1-pentene) dielectric films for capacitors prepared in Examples 1-4 and the comparative examples.

[0072] from Figure 2 As can be seen, all samples exhibit a clear diffuse scattering background in the 10–40° range, indicating that the film is predominantly amorphous. However, in the low-angle region (around 10° and 17°), several weak and relatively sharp characteristic diffraction peaks superimposed on the diffuse peaks can still be observed, indicating that a small number of locally ordered microcrystalline regions were formed within the film after annealing. Meanwhile, no new strong diffraction peaks appeared in the grafted samples, indicating that no detectable crystalline byproducts or new crystalline phases were formed during the modification process, thus ensuring the uniformity and stability of the film phase structure.

[0073] Figure 3 Fourier transform infrared spectra of the halogenated olefin graft-modified poly(4-methyl-1-pentene) dielectric films for capacitors prepared in Examples 1-4 and the comparative examples.

[0074] As can be seen from the figure, 2950–2860 cm -1 The vibration is a stretching vibration of -CH3 / -CH2, at ~1460 cm. -1 With ~1375cm -1 It is a bending vibration of -CH3 / -CH2, and 1167 cm -1 These are characteristic absorption peaks of the CC skeleton vibration. After grafting, the spectrum still shows the aforementioned PMP intrinsic peaks as the main body, and the peak positions remain basically unchanged, indicating that the backbone skeleton remains stable and no significant structural damage has occurred. Theoretically, after grafting, the peaks should typically be located at ~800–600 cm⁻¹. -1 An absorption peak of C-Cl was observed, but no clear new peak was seen. This may be due to the following factors: First, the figure shows the mass fraction of monomer and PMP fed, not the actual grafting rate. The actual grafting amount is often much lower than the feed amount, resulting in a very weak C-Cl signal. Second, C-Cl itself has a weak absorption intensity and is located near the background fluctuations of the polyolefin fingerprint region, making it easily overwhelmed by the PMP peaks. Furthermore, no obvious peak was observed at 1800–1700 cm⁻¹. -1Carbonyl absorption band or 3600–3200 cm -1 The broad hydroxyl peak indicates that no significant oxidation side reactions or detectable oxygen-containing functional groups were introduced during the modification process, thus ensuring the stability and purity of the film's chemical structure.

[0075] Figure 4 The dielectric spectra of the haloolefin-grafted modified poly4-methyl-1-pentene dielectric films for capacitors prepared in Examples 1-4 and the comparative examples at 150 °C.

[0076] As can be seen from the graph: at 10 2 -10 6 Within the Hz frequency range, the dielectric constant of each sample did not change significantly with frequency, exhibiting good frequency stability. Compared with the comparative PMP sample, the overall dielectric constant of the grafted sample increased from approximately 2.07 to 2.28, indicating that the introduction of chlorine-containing side groups formed polarizable sites, enhancing polarization capability and thus effectively improving the dielectric constant. Meanwhile, the dielectric loss of each sample remained at a very low level at 150 °C, with a slight increase at higher frequencies. The loss level of the sample with a medium grafting amount was generally lower than that of the comparative sample, indicating that the grafted structure can suppress carrier injection / migration at high temperatures and reduce the contribution of conductivity and interface polarization. This allows for the improvement of the dielectric constant while maintaining low loss characteristics, demonstrating excellent high-temperature dielectric stability and insulation reliability.

[0077] Figure 5 The dielectric constant of the haloolefin-grafted modified poly4-methyl-1-pentene dielectric films for capacitors prepared in Examples 1-4 and the comparative examples varies with temperature at 1 kHz.

[0078] As shown in the figure, within the temperature range of 20–200 °C, the dielectric constant of each sample decreases slowly with increasing temperature. For example, at 20 °C, the dielectric constants of PMP, PMP-g-2.5Cl, PMP-g-5Cl, PMP-g-7.5Cl, and PMP-g-10Cl are 2.22, 2.32, 2.38, 2.47, and 2.42, respectively; when the temperature rises to 200 °C, their dielectric constants decrease to 1.95, 2.04, 2.13, 2.18, and 2.15, respectively. The main reason for this is that the increase in temperature causes thermal expansion of the polymer and an increase in free volume, which reduces the number density of polarizable groups per unit volume. At the same time, the more intense the molecular thermal motion, the easier it is for the dipoles to be thermally disturbed, making it difficult to maintain a relatively ordered orientation under an applied electric field. This weakens the contribution of orientation polarization, resulting in a decrease in the dielectric constant. The dielectric constant increases with the increase of grafting content because the strong polar side groups introduced by grafting significantly increase the number of dipoles and polarization intensity of the system. However, when the grafting amount continues to increase, the steric hindrance of the side groups and the rigidity of the chain segments increase, which restricts the effective polarization of some dipoles and causes the dielectric constant to decrease slightly.

[0079] Figure 6 The dielectric loss of the haloolefin-grafted modified poly4-methyl-1-pentene dielectric films for capacitors prepared in Examples 1-4 and the comparative examples is shown as a function of temperature at 1 kHz.

[0080] As shown in the figure, each sample exhibits a significant dielectric loss peak around 70 °C. This is mainly because at low temperatures, the chain segments and grafted dipoles are almost immobile, resulting in minimal work done by the electric field and low losses. As the temperature increases, the chain segments and grafted dipoles gradually activate, causing the dipoles to flip and lag in response to the electric field. This lag is greatest around 70 °C, leading to the strongest energy dissipation. Further heating accelerates the movement of the dipoles and chain segments, enabling them to keep up with electric field changes of 1 kHz, reducing lag and dissipation. Consequently, tanδ begins to decrease and tends to a lower level. The figure also indicates a controllable relaxation dissipation process in the mid-temperature region, while maintaining a low loss level at higher temperatures, which is beneficial for the stability of high-temperature dielectric applications.

[0081] Figure 7 The diagram shows a comparison of the leakage current density of the halogenated olefin-grafted modified poly(4-methyl-1-pentene) dielectric films for capacitors prepared in Examples 1-4 with that of the comparative examples.

[0082] As shown in the figure, the JE curve shifted downwards after grafting modification, indicating that leakage current was effectively suppressed. Specifically, at 150 ℃ and 200 kV / mm, the leakage current densities of PMP, PMP-g-2.5Cl, PMP-g-5Cl, PMP-g-7.5Cl, and PMP-g-10Cl were 2.85, 2.1, 1.7, 2.34, and 2.82 × 10⁻⁶, respectively. -8 A / cm 2 Further fitting results showed that the jump distances λ for each sample were 0.557, 0.521, 0.443, 0.612, and 0.603, respectively. This is because, in the low to medium grafting stage, the increased number density of trap sites makes carriers more inclined to jump between closer local states, shortening the equivalent jump distance, further suppressing conductivity, and minimizing leakage current. However, when the grafting amount is too high, the crowding of side groups leads to looser chain stacking, increased free volume, and may introduce microscopic inhomogeneities, making the distribution of effective transport sites discontinuous. Carriers often need to cross longer local low-density regions to reach the next occupiable state, thus increasing the equivalent jump distance. Therefore, the leakage current suppression effect decreases slightly, indicating that there is an optimal window for medium grafting content in this system.

[0083] Figure 8 The graph shows a comparison of the energy storage performance of the halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric films for capacitors prepared in Examples 1-4 with those of the comparative examples.

[0084] As shown in the figure, at 150 °C, the breakdown field strengths achievable by PMP, PMP-g-2.5Cl, PMP-g-5Cl, PMP-g-7.5Cl, and PMP-g-10Cl are approximately 580, 700, 740, 660, and 520 kV / mm, respectively. Under the same electric field strength, the charge-discharge efficiency of the grafted samples is generally higher than that of the comparative PMP film, indicating that grafting modification can effectively reduce energy loss. This is because the grafting of trans-1,3-dichloropropene introduces C-Cl polar groups onto the PMP molecular chain. The electron attraction effect of -Cl and its induced local energy level / trap structure can improve the carrier injection and migration barrier, suppress the accumulation of space charge and the formation of conductive channels, thereby reducing conductive loss and interface-related dissipation. At the same time, the introduction of the grafted structure helps to improve the uniformity of the film microstructure and defect control, reduce local loss hotspots under strong fields, and enable the film to maintain high charge-discharge efficiency even at 150 °C. Ultimately, even at a high temperature of 150 °C, the grafted film of this invention can still achieve a significantly improved discharge energy density under a high electric field, for example, a discharge energy density of 5.42 J / cm² at 740 kV / mm. 3 This is 1.62 times the ratio, demonstrating its high energy output capability and application potential under high temperature and strong field conditions.

[0085] The above description is only a preferred embodiment of the present invention. Given that those skilled in the art can make appropriate changes and modifications to the above embodiments, the present invention is not limited to the specific embodiments described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a poly(4-methyl-1-pentene) dielectric film grafted with a haloolefin for capacitors, characterized in that... The preparation method is specifically carried out according to the following steps:

1. Under an anhydrous and oxygen-free nitrogen atmosphere, poly-4-methyl-1-pentene is mixed with a solvent, heated and stirred to dissolve, to obtain solution A; 2. Under an anhydrous and oxygen-free nitrogen atmosphere, azobisisobutyronitrile and trans-1,3-dichloropropene were mixed and dissolved by ultrasonication to obtain solution B; 3. Under an anhydrous and oxygen-free nitrogen environment, solution A and solution B are mixed, heated and stirred to react, and a PMP grafting reaction precursor solution is obtained. IV. Preparation of poly-4-methyl-1-pentene dielectric thin films: ① Pour the PMP grafting reaction precursor solution onto a preheated clean glass plate and scrape it to a certain thickness using a scraper to obtain the coated glass plate. ② Place the coated glass plate into a vacuum drying oven to remove the solvent through a drying process; ③ Place the glass plate in a vacuum drying oven for annealing, then allow it to cool naturally to room temperature. Next, place the glass plate in deionized water, and the film will naturally detach from the glass plate. Finally, place the film in a vacuum drying oven to completely remove moisture, thus obtaining a poly(4-methyl-1-pentene) dielectric film grafted with halogenated olefins for capacitors.

2. The method for preparing a halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric film for capacitors according to claim 1, characterized in that... The solvent used in step one is cyclohexane, decahydronaphthalene, or trichloroethylene; the dissolution temperature in step one is 60 ℃~150 ℃, and the dissolution time is 3 h~5 h.

3. The method for preparing a halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric film for capacitors according to claim 1, characterized in that... The mass ratio of poly(4-methyl-1-pentene) to solvent in step one is (0.03~0.1):

1.

4. The method for preparing a halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric film for capacitors according to claim 1, characterized in that... The dissolution temperature in step two is room temperature, and the dissolution time is 15 min to 20 min; the heating and stirring reaction temperature in step three is 60 ℃ to 80 ℃, and the reaction time is 2 h to 4 h.

5. The method for preparing a halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric film for capacitors according to claim 1, characterized in that... The mass ratio of azobisisobutyronitrile in step two to poly4-methyl-1-pentene in step one is (0.003~0.005):

1.

6. The method for preparing a halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric film for capacitors according to claim 1, characterized in that... The mass ratio of trans-1,3-dichloropropene in step two to poly-4-methyl-1-pentene in step one is (0.025~0.1):

1.

7. The method for preparing a halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric film for capacitors according to claim 1, characterized in that... The temperature of the preheated clean glass plate mentioned in step 4① is 25 ℃, 40 ℃ or 60 ℃; in step 4①, the PMP grafting reaction precursor solution is poured onto the preheated clean glass plate, the gap of the coating tool is adjusted to 20 μm, and a film is uniformly coated to obtain the coated glass plate.

8. The method for preparing a halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric film for capacitors according to claim 1, characterized in that... The drying process described in step 4② is as follows: vacuum drying at 60 ℃ for 3 h or first drying at room temperature for 1 h, then drying at 30 ℃ for 30 min, then drying at 45 ℃ for 30 min, and finally drying at 60 ℃ for 1 h.

9. The method for preparing a halogenated olefin-grafted modified poly4-methyl-1-pentene dielectric film for capacitors according to claim 1, characterized in that... The annealing temperature in step 4.③ is 90 ℃, 130 ℃, 150 ℃ or 180 ℃; the annealing time is 1 h to 3 h; in step 4.③, the film is placed in a vacuum drying oven at 60 ℃ for 12 h to 24 h to completely remove moisture; the thickness of the poly4-methyl-1-pentene dielectric film for capacitors modified with halogenated olefins in step 4.③ is 8 to 12 μm.

10. The method for preparing a halogenated olefin-grafted modified poly(4-methyl-1-pentene) dielectric film for capacitors according to claim 1, characterized in that... A poly4-methyl-1-pentene dielectric film grafted with a halogenated olefin is used as the dielectric layer of a thin-film capacitor.

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