Crosslinkable cycloolefin copolymer as well as preparation method and application thereof

Abstract

The invention relates to a crosslinkable cycloolefin copolymer as well as a preparation method and application thereof. The preparation method comprises the following steps: copolymerizing norbornene and derivatives thereof with dicyclopentadiene, preparing a film from the obtained polymer in a solution casting manner, and finally initiating formation of a polymer cross-linked structure through heat treatment. The polymer is prepared by initiating monomers to perform ring-opening metathesis polymerization by a second-generation Grubbs catalyst, norbornene and derivatives thereof in the polymer can adjust the polarization intensity of the polymer in a high electric field, and dicyclopentadiene can provide crosslinking sites, so that a crosslinking structure is formed in a polymer film. The dielectric film prepared by the invention has excellent thermal stability and energy storage performance, still keeps high breakdown strength, high energy storage density, high charge-discharge efficiency and good structural stability at 150 DEG C, and is suitable for electronic devices such as energy storage capacitors working in a high-temperature environment.

Description

Technical Field

[0001] The invention belongs to the technical field of film capacitors, and in particular relates to a cross-linkable cycloolefin copolymer and a preparation method and application thereof. Background Art

[0002] As an indispensable component in advanced electrical and electronic systems, dielectric capacitors are now widely used in energy, transportation, military and aerospace. Compared with energy storage devices such as batteries and supercapacitors, although the energy density of dielectric capacitors is relatively small, it has significant advantages such as high power density, high withstand voltage, safety and reliability. At present, the dielectric materials in commercial dielectric capacitors are mainly divided into two types: ceramics and polymers. Dielectric ceramics have high dielectric constant, high hardness and good thermal stability. However, dielectric ceramics are also limited in practical applications due to their defects such as low breakdown strength, difficult processing and poor flexibility. On the other hand, dielectric polymers have attracted attention due to their advantages such as high breakdown strength, good processability and low cost. In addition, dielectric polymers also have their unique self-healing ability. In metallized film capacitors, self-healing can isolate the breakdown point from the rest of the metallized film electrode, thereby ensuring the stable operation of the film capacitor. Due to the above advantages, polymer film capacitors have been widely used in modern electronic and electrical systems.

[0003] A key issue with polymer dielectrics is that their dielectric constant is relatively low. The dielectric constant of polymer materials is generally below 10, which is 1 to 3 orders of magnitude lower than that of dielectric ceramics. The low dielectric constant limits the polarization ability of polymers under high electric fields, which directly affects their energy storage density. Another key issue is their low operating temperature. Due to the rapid development of aerospace, oil and gas exploration, and new energy power generation, higher requirements are placed on the working conditions of polymer film capacitors: in the inverter of hybrid vehicles, capacitors are required to operate at 140 to 150°C; in the field of oil and gas resource exploration, depending on the drilling depth, the operating temperature of capacitors is required to be 170 to 300°C; and in aerospace, the operating temperature requirement is above 250°C. These all require polymer materials to have good thermal stability and high-temperature dielectric energy storage performance. The most commonly used polymer dielectric material is biaxially oriented polypropylene (BOPP). Film capacitors made of this material have the above two problems: on the one hand, due to the low dielectric constant of BOPP (about 2.2), the energy storage density of the capacitor cannot meet the needs of most applications; on the other hand, due to its poor thermal stability, BOPP cannot adapt to high-temperature working environments. When used at high temperatures, it must be equipped with a matching cooling system, which makes it difficult to miniaturize the equipment and increases energy consumption. The long-term operating temperature of BOPP film capacitors cannot exceed 85°C, and the maximum operating temperature cannot exceed 105°C, otherwise the capacitor capacity will decrease rapidly, greatly reducing the service life of the capacitor.

[0004] To solve this problem, people have developed various high T g Engineering polymers such as polyimide (PI), polyethyleneimine (PEI) and polyethylene terephthalate (PET) are used as high-temperature film capacitor dielectrics. g Polymers have good thermal stability, but they can only work well under relatively low electric fields. When polymers are affected by high temperature and high electric field at the same time, their discharge energy density and charge and discharge efficiency are greatly reduced, making it difficult to meet the needs of practical applications.

[0005] In summary, the demand for high-temperature resistant and high-energy storage polymer dielectric materials is increasing day by day, and there is an urgent need to develop more new polymer dielectrics. Summary of the invention

[0006] In view of the deficiencies in the above-mentioned existing polymer energy storage dielectrics, the object of the present invention is to design and provide a cross-linkable cycloolefin copolymer and a preparation method thereof. This cross-linkable cycloolefin copolymer can be synthesized by ring-opening metathesis polymerization (ROMP) of monomers initiated by a second-generation Grubbs catalyst, and then a polymer film is obtained by a cast film forming method. Further heat treatment of the film can induce the formation of a cross-linked network structure inside the polymer, thereby significantly improving its breakdown strength and thermal stability, reducing its leakage current under high temperature and high electric field, and improving its charge and discharge efficiency.

[0007] The scheme of the present invention is:

[0008] The first aspect of the present invention provides a cross-linkable cycloolefin copolymer, and the structure of the cross-linkable cycloolefin copolymer is as follows:

[0009]

[0010] In the structural formula, a, b, and c are the numbers of repeating units;

[0011] Where R 1 and R 2 Select one of the following structures:

[0012] R 1 :

[0013] R 2 :

[0014] The second aspect of the present invention provides a method for preparing the cross-linkable cycloolefin copolymer, which comprises the following steps: (1) 1 and R 2 The two monomers of norbornene and dicyclopentadiene were completely dissolved in anhydrous dichloromethane and then heated to N 2 The invention relates to a method for preparing a cross-linked cycloolefin copolymer, wherein the cross-linked cycloolefin copolymer is prepared by mixing the cross-linked cycloolefin copolymer with the cross-linked cycloolefin copolymer in anhydrous dichloromethane. The ...

[0015] Furthermore, in step (1), the second generation Grubbs catalyst is 1,3-bis(2,4,6-trimethylphenyl)-2-(imidazolidinyl) (dichlorobenzylidene) (tricyclohexylphosphine) ruthenium.

[0016] Furthermore, the ratio of the total molar amount of the polymerized monomers to the molar amount of the second-generation Grubbs catalyst is (500-4000):1.

[0017] Furthermore, in the step (1), the molar amount of dicyclopentadiene accounts for 5% to 50% of the total molar amount of the polymerizable monomers.

[0018] Furthermore, in the step (1), the temperature of the ROMP reaction is 20 to 30° C., and the reaction time is 0.5 to 4 hours.

[0019] Furthermore, in the step (2), the terminator is ethoxyethylene.

[0020] The third aspect of the present invention provides a method for preparing a cross-linkable cycloolefin copolymer dielectric film, which is made of the cross-linkable cycloolefin copolymer as claimed in claim 1; the preparation method comprises: fully dissolving the cross-linkable cycloolefin copolymer in anhydrous chloroform to obtain a polymer solution; uniformly dripping the polymer solution on a carrier, and after the solvent is completely volatilized at room temperature, heat treating at 150°C for 1h to 3h to obtain a uniform cross-linkable cycloolefin copolymer dielectric film; wherein the concentration of the polymer solution is 1wt% to 3wt%.

[0021] A fourth aspect of the present invention provides a cross-linkable cycloolefin copolymer dielectric film obtained by the method for preparing the cross-linkable cycloolefin copolymer dielectric film as described above.

[0022] A fifth aspect of the present invention provides use of the cross-linkable cycloolefin copolymer described above in the field of high temperature resistant polymer dielectrics.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The cross-linkable cycloolefin copolymer prepared by the present invention has a rigid main chain and can be induced to form a cross-linked network structure through heat treatment, thereby ensuring that it has excellent thermal stability.

[0025] By introducing highly polar norbornene derivatives into the copolymer, its dielectric constant is effectively improved, giving it a high energy storage density. The formation of a cross-linked network can also effectively inhibit the increase in its leakage loss, giving it good high-temperature energy storage performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments consistent with the present invention and, together with the description, serve to explain the principles of the present invention, in which:

[0027] Figure 1A preparation route for a cross-linkable cycloolefin copolymer provided in an embodiment of the present invention;

[0028] Figure 2 1 is a breakdown field strength diagram of poly(norbornene-dicyclopentadiene) with different components in Example 1 of the present invention;

[0029] Figure 3 Graph showing the change in dielectric constant and loss of poly(norbornene-dicyclopentadiene) with different components as a function of frequency in Example 1 of the present invention;

[0030] Figure 4 Graph showing the energy storage density and charge-discharge efficiency of poly(norbornene-dicyclopentadiene) with different components at room temperature in Example 1 of the present invention;

[0031] Figure 5 Graph showing energy storage density and charge-discharge efficiency of poly(norbornene-dicyclopentadiene) with different components at 150° C. in Example 1 of the present invention;

[0032] Figure 6 1 is a breakdown field strength diagram of poly((2-cyano-5-norbornene)-dicyclopentadiene) with different components in Example 2 of the present invention;

[0033] Figure 7 Graph showing the change in dielectric constant and loss of poly((2-cyano-5-norbornene)-dicyclopentadiene) with different components in Example 2 of the present invention as a function of frequency;

[0034] Figure 8 Graph showing the energy storage density and charge-discharge efficiency of poly((2-cyano-5-norbornene)-dicyclopentadiene) with different components at room temperature in Example 2 of the present invention;

[0035] Fig. 9 Graph showing the energy storage density and charge-discharge efficiency of poly((2-cyano-5-norbornene)-dicyclopentadiene) with different components at 150°C in Example 2 of the present invention. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The present invention provides a method for preparing a cross-linkable cycloolefin copolymer. The synthetic route is as follows: Figure 1 As shown, the method comprises the following steps:

[0038] (1) The R 1 and R 2The two monomers of norbornene and dicyclopentadiene were completely dissolved in anhydrous dichloromethane and then heated to N 2 The mixture was added into a Shrek bottle equipped with a magnetic stirrer under anhydrous atmosphere, and the second-generation Grubbs catalyst was dissolved in anhydrous dichloromethane and then added into the Shrek bottle to carry out a ring-opening metathesis polymerization reaction under anhydrous and oxygen-free conditions.

[0039] (2) After a certain reaction time, a terminator is added, and the reaction is terminated after stirring for 1 hour; the obtained product is washed and dried to obtain the cross-linkable cycloolefin copolymer.

[0040] Example 1

[0041] This embodiment provides a cross-linkable cycloolefin copolymer, the structure of which is as follows:

[0042]

[0043] The preparation method thereof comprises the following steps:

[0044] 1. Dissolve 0.005 mol of a mixture of norbornene (NB) and dicyclopentadiene (DCPD) in 40 mL of anhydrous dichloromethane and 2 The mixture was added to a Schlenk bottle equipped with a magnetic stirrer under an atmosphere of 40 °C. 0.001 mmol of the second-generation Grubbs catalyst was completely dissolved in 5 mL of anhydrous dichloromethane and added to the Schlenk bottle to carry out a ROMP reaction at room temperature.

[0045] 2. After the reaction was continued for 1 hour, 0.3 mL of ethoxyethylene was added and the reaction was terminated after stirring for another 1 hour. The obtained product was washed and dried to obtain the target product.

[0046] The method of preparing the cross-linkable cycloolefin copolymer dielectric film further comprises the following steps:

[0047] 3. Dissolve 100 mg of the copolymer in 6 mL of anhydrous chloroform to obtain a polymer solution, and evenly drop the polymer solution onto a glass plate. After the solvent is completely evaporated at room temperature, heat treat the solution at 150° C. for 3 h to obtain a uniform cross-linkable cycloolefin copolymer dielectric film.

[0048] like Figure 2As shown in the figure, the addition of dicyclopentadiene allows the copolymer to form a cross-linked structure by thermal initiation, thereby significantly enhancing the breakdown strength of the film. Compared with polynorbornene, the breakdown strength of poly(norbornene-dicyclopentadiene) copolymer at different temperatures is significantly improved, among which the breakdown strength of poly(norbornene-dicyclopentadiene) copolymer with the best composition is increased by about 200 MV m compared with polynorbornene. -1 The dielectric constant and loss of poly(norbornene-dicyclopentadiene) with different components vary with frequency. Figure 3 As shown in the figure, since the addition of dicyclopentadiene does not significantly change the polarity of the copolymer, the dielectric constant and dielectric loss of the poly(norbornene-dicyclopentadiene) copolymer at room temperature do not change significantly compared to polynorbornene. The energy storage density and charge-discharge efficiency of poly(norbornene-dicyclopentadiene) with different components are shown in the figure. Figure 4 , 5 As shown in the figure, the breakdown strength of the copolymer is significantly improved due to the introduction of dicyclopentadiene, but its dielectric constant has no obvious change. Therefore, the improvement of the copolymer's energy storage density is almost entirely dependent on the increase in its breakdown strength. On the other hand, the formation of a cross-linked network helps to reduce leakage current and reduce the loss during the charge and discharge process of the film, thereby effectively improving its energy conversion efficiency. Compared with polynorbornene, the maximum discharge energy density of the optimal composition poly (norbornene-dicyclopentadiene) copolymer at room temperature reaches 9.88 J / cm -3 At 150°C, the maximum discharge energy density reaches 7.48 J / cm -3 .

[0049] Example 2

[0050] This embodiment provides a method for preparing a cross-linkable cycloolefin copolymer, the structure of which is as follows:

[0051]

[0052] The preparation method thereof comprises the following steps:

[0053] 1. Dissolve 0.005 mol of a mixture of 2-cyano-5-norbornene (NBCN) and dicyclopentadiene in 40 mL of anhydrous dichloromethane and 2 The mixture was added to a Schlenk bottle equipped with a magnetic stirrer under an atmosphere of 40 °C. 0.001 mmol of the second-generation Grubbs catalyst was completely dissolved in 5 mL of anhydrous dichloromethane and added to the Schlenk bottle to carry out a ROMP reaction at room temperature.

[0054] 2. After 4 hours of reaction, 0.3 mL of ethoxyethylene was added and the reaction was terminated after stirring for 1 hour. The obtained product was washed and dried to obtain the target product.

[0055] The method of preparing the cross-linkable cycloolefin copolymer dielectric film further comprises the following steps:

[0056] 3. Dissolve 100 mg of the copolymer in 6 mL of anhydrous chloroform to obtain a polymer solution, and evenly drop the polymer solution onto a glass plate. After the solvent is completely evaporated at room temperature, heat treat the solution at 150° C. for 3 h to obtain a uniform cross-linkable cycloolefin copolymer dielectric film.

[0057] like Figure 6 As shown in Figure 2, the breakdown strength of poly((2-cyano-5-norbornene)-dicyclopentadiene) copolymer film is significantly improved compared to poly(2-cyano-5-norbornene), which can also be attributed to the formation of a cross-linked network in the film. The dielectric constant and loss of poly(norbornene-dicyclopentadiene) with different components vary with frequency as shown in Figure 2. Figure 7 As shown in the figure, due to the introduction of high polar norbornene derivatives, the copolymer has a higher dielectric constant, and the increase in the proportion of dicyclopentadiene in the copolymer leads to a slight decrease in its dielectric constant. The energy storage density and charge-discharge efficiency of poly((2-cyano-5-norbornene)-dicyclopentadiene) with different components are shown in the figure. Figure 8 , 9 As shown in the figure, by adjusting the dielectric constant and cross-linking degree of the copolymer, the optimal dielectric energy storage performance can be obtained. Compared with poly(2-cyano-5-norbornene), the maximum discharge energy density of the optimal composition poly((2-cyano-5-norbornene)-dicyclopentadiene) copolymer at room temperature reaches 11.81 J / cm -3 At 150°C, the maximum discharge energy density reaches 8.69 J / cm -3 .

[0058] In summary, the present invention provides a cross-linkable cycloolefin copolymer and a preparation method thereof. This cross-linkable cycloolefin copolymer is synthesized by a second-generation Grubbs catalyst initiating a monomer to undergo a ROMP reaction, and then a cross-linkable cycloolefin copolymer dielectric film is obtained by a film casting method. The film is further heat-treated, and the polymer itself can be induced to form a cross-linked network structure without adding a cross-linking agent. On the one hand, this can effectively inhibit the movement of polymer segments at high temperatures, increase the glass transition temperature of the material, and make it have excellent thermal stability; on the other hand, the formation of a cross-linked structure can significantly inhibit the increase of leakage current, thereby ensuring that it has high breakdown strength and high charge and discharge efficiency. At the same time, the introduction of high-polarity norbornene derivatives significantly increases the dielectric constant of the copolymer, thereby increasing its energy storage density. The cross-linkable cycloolefin copolymer provided by the present invention is suitable for application in the field of high temperature resistant polymer dielectrics.

[0059] Those skilled in the art will readily appreciate other embodiments of the invention after considering the specification and practicing the invention herein. The invention is intended to cover any variations, uses or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art of the invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the claims.

[0060] It should be understood that the present invention is not limited to the exact construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A cross-linkable cycloolefin copolymer, characterized in that: The structure of the cross-linkable cycloolefin copolymer is as follows: In the structural formula, a, b, and c are the numbers of repeating units; Wherein R1 and R2 are selected from one of the following structures: R1： R2： 2. The method for preparing a crosslinkable cycloolefin copolymer according to claim 1, wherein: The method comprises the following steps: (1) completely dissolving two polymerization monomers of norbornene and dicyclopentadiene containing the R1 and R2 in anhydrous dichloromethane, and then adding the two monomers into a Shrek bottle equipped with a magnetic stirrer under a N2 atmosphere, and dissolving a second-generation Grubbs catalyst in anhydrous dichloromethane and then adding the two monomers into the Shrek bottle, and performing a ring-opening metathesis polymerization reaction under anhydrous and oxygen-free conditions; (2) After a certain reaction time, a terminator is added, and the reaction is terminated after stirring for 1 hour; the obtained product is washed and dried to obtain the cross-linkable cycloolefin copolymer.

3. The method for preparing a crosslinkable cycloolefin copolymer according to claim 2, characterized in that: In the step (1), the second generation Grubbs catalyst is 1,3-bis(2,4,6-trimethylphenyl)-2-(imidazolidinylidene)(dichlorobenzylidene)(tricyclohexylphosphine)ruthenium.

4. The method for preparing a crosslinkable cycloolefin copolymer according to claim 2, wherein: The ratio of the total molar amount of the polymerization monomers to the molar amount of the second-generation Grubbs catalyst is (500-4000):

1.

5. The method for preparing a crosslinkable cycloolefin copolymer according to claim 2, characterized in that: In the step (1), the molar amount of dicyclopentadiene accounts for 5% to 50% of the total molar amount of the polymerizable monomers.

6. The method for preparing a crosslinkable cycloolefin copolymer according to claim 2, characterized in that: In the step (1), the temperature of the ring-opening metathesis polymerization reaction is 20 to 30° C., and the reaction time is 0.5 to 4 hours.

7. The method for preparing a crosslinkable cycloolefin copolymer according to claim 2, characterized in that: In the step (2), the terminator is ethoxyethylene.

8. A method for preparing a cross-linkable cycloolefin copolymer dielectric film, characterized in that: The cross-linkable cycloolefin copolymer dielectric film is made of the cross-linkable cycloolefin copolymer as claimed in claim 1; The preparation method comprises: fully dissolving the cross-linkable cycloolefin copolymer in anhydrous chloroform to obtain a polymer solution; uniformly dripping the polymer solution on a carrier, and after the solvent is completely volatilized at room temperature, heat-treating at 150° C. for 1 h to 3 h to obtain a uniform cross-linkable cycloolefin copolymer dielectric film; Wherein, the concentration of the polymer solution is 1wt% to 3wt%. 9 . The cross-linkable cycloolefin copolymer dielectric film obtained by the method for preparing the cross-linkable cycloolefin copolymer dielectric film according to claim 8 .

10. Use of the cross-linkable cycloolefin copolymer according to claim 1 in the field of high temperature resistant polymer dielectrics.

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