A method for preparing a liquid-crystal-polyarylate-based low-dielectric epoxy resin composite

Abstract

The application relates to a preparation method of a liquid crystal polyarylate-based low-dielectric epoxy resin composite, and relates to a preparation method of an epoxy resin composite. The application aims to solve the problem that the epoxy resin composite prepared by the existing method cannot have low dielectric constant, low dielectric loss and excellent electric insulation performance. The application adopts 4,4'-dihydroxydiphenyl, terephthaloyl chloride, isophthaloyl chloride and bisphenol A as monomers to synthesize liquid crystal polyarylate with reduced structural regularity; on this basis, the prepared liquid crystal polyarylate is introduced into an epoxy resin system to construct a low-dielectric epoxy resin composite, the balance of low dielectric, low dielectric loss and high insulation of the epoxy resin is realized, and the low-dielectric epoxy resin composite shows wide application prospects in the fields of high-frequency high-speed electronic devices and electronic packaging insulation.

Description

Technical Field

[0001] This invention relates to a method for preparing epoxy resin composite materials, specifically a method for preparing low-dielectric epoxy resin composite materials based on liquid crystal polyarylate. Background Technology

[0002] With the continuous development of electronic information technology, high-frequency and high-speed signal transmission, and advanced integrated circuit packaging technology, electronic materials are evolving towards miniaturization, high integration, and high signal transmission efficiency. In this process, the dielectric and electrical insulation properties of materials have gradually become key factors affecting the signal integrity and operational stability of devices. Epoxy resin, due to its excellent mechanical properties, good adhesion, high thermal stability, excellent electrical insulation properties, and mature processing technology, is widely used in electronic packaging, printed circuit boards, insulating materials, and composite materials, and is currently one of the most important thermosetting resin matrix materials in the electronic packaging field. However, the traditional epoxy resin molecular structure contains many polar groups, which easily undergo dipole polarization under the influence of an electric field, resulting in a dielectric constant typically in the range of 3.5–4.5. While this results in relatively high dielectric loss, it is insufficient to meet the requirements of conventional electronic devices and the low dielectric properties required for high-frequency and high-speed electronic materials. Currently, the development trend of high-frequency and high-speed electronic materials is to use low-dielectric materials with a dielectric constant below 3.0 to reduce signal transmission delay and dielectric loss. Meanwhile, as an electronic packaging and insulating material, it is also required to have good electrical insulation properties and long-term reliability. Therefore, the development of high-performance epoxy resin composite materials with low dielectric constant, low dielectric loss, and excellent electrical insulation properties is of great research significance.

[0003] Currently, the main methods for reducing the dielectric constant of epoxy resins include fluorine-containing modification, siloxane modification, inorganic nanofiller filling, and porous structure construction. Fluorine-containing structures, due to their low polarizability, can significantly reduce the dielectric constant of materials, with some systems reducing it to approximately 2.0–3.0. However, they also suffer from high raw material costs, complex synthesis processes, and insufficient environmental friendliness. Siloxane modification can reduce the dielectric constant by increasing the free volume of the system, typically reducing it to approximately 2.7–3.3, but it easily leads to a decrease in the thermal and mechanical properties of the material. Inorganic nanofillers such as SiO2 and BN have good thermal stability and insulation properties, but due to problems such as easy agglomeration, poor interfacial compatibility, and difficulty in dispersion, it is often difficult to simultaneously optimize dielectric properties and structural stability. In addition, although porous structures can further reduce the dielectric constant, with some porous systems even achieving dielectric constants below 2.0, the introduction of porous structures can easily lead to an increase in internal defects and local electric field distortion, thereby adversely affecting the mechanical properties, electrical insulation properties, and long-term stability of the material. Therefore, how to achieve synergistic optimization of low dielectric constant, low dielectric loss and excellent electrical insulation performance remains an important challenge in the current research on low dielectric properties of epoxy resins. Summary of the Invention

[0004] The purpose of this invention is to solve the problem that epoxy resin composite materials prepared by existing methods cannot simultaneously possess low dielectric constant, low dielectric loss, and excellent electrical insulation properties, and to provide a method for preparing low dielectric epoxy resin composite materials based on liquid crystal polyarylate.

[0005] To address the aforementioned technical problems, this invention uses 4,4′-dihydroxybiphenyl, terephthaloyl chloride, isophthaloyl chloride, and bisphenol A as monomers to synthesize liquid crystal polyarylates with reduced structural regularity. Based on this, the prepared liquid crystal polyarylates are introduced into an epoxy resin system to construct a low-dielectric epoxy resin composite material. The effects of the amount of liquid crystal polyarylate added on the dielectric properties and electrical breakdown properties of the composite material are systematically studied, providing a new approach for the design of low-dielectric, high-electric-insulation epoxy resin composite materials.

[0006] A method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate includes the following steps:

[0007] I. Preparation of liquid crystal polyarylate:

[0008] ① Add sodium hydroxide, 4,4′-dihydroxybiphenyl, bisphenol A, benzyltriethylammonium chloride and sodium bisulfite to deionized water and stir at room temperature to obtain an aqueous solution;

[0009] ② Add terephthaloyl chloride and isophthaloyl chloride to an organic solvent and stir at room temperature to obtain an organic phase solution;

[0010] ③ Add the organic phase solution dropwise to the aqueous phase solution and stir at low temperature. After the low temperature reaction is completed, continue stirring the reaction system at room temperature. After the room temperature reaction is completed, pour it into methanol, and then filter, wash and dry the precipitated polymer to obtain liquid crystal polyarylate.

[0011] II. Preparation of liquid crystal polyarylate / epoxy resin composite materials:

[0012] ① Mix epoxy resin and liquid crystal polyarylate, heat and stir, then add curing agent, heat and stir, then add accelerator, continue heating and stirring, and finally transfer to vacuum oven for degassing treatment to obtain slurry;

[0013] ② Pour the slurry into the mold, and then place the mold in a flat vulcanizing machine to cure it, thereby obtaining a low dielectric epoxy resin composite material based on liquid crystal polyarylate.

[0014] The principle of this invention:

[0015] This invention introduces liquid crystal polyarylate into an epoxy resin system. Utilizing the synergistic effect of the unique rigid rod-like molecular structure of the liquid crystal polyarylate and the cross-linking network of the epoxy resin, the dielectric and insulating properties of the material are simultaneously improved. The mechanism of action can be explained as follows: First, the molecular chains of the liquid crystal polyarylate have high rigidity and regularity, with a high proportion of nonpolar aromatic rings and a low overall polarizability. Under an alternating electric field, it is not prone to orientation polarization, thus reducing the dielectric response of the material. Simultaneously, the introduction of the liquid crystal polyarylate reduces the effective mobility of polarizable groups in the system, decreasing energy loss during polarization relaxation, which is beneficial for reducing the dielectric constant and dielectric loss of the composite material. Second, during the curing process, the liquid crystal polyarylate can form a locally ordered orientation structure in the epoxy resin matrix and interact with the epoxy resin... The interaction of the lipid cross-linking network promotes the formation of a denser and more ordered microstructure. This ordered structure can effectively reduce the free volume and micro-defects inside the material, reduce charge accumulation and interfacial polarization at the interface, and thus further suppress dielectric loss. In terms of insulation performance, the ordered orientation of the liquid crystal structure effectively regulates the electric field distribution inside the material, suppressing local electric field distortion and concentration. On the other hand, the rigid ordered phase formed by the liquid crystal polyarylate can act as a barrier layer for charge transport, increasing the carrier migration barrier and limiting the migration and accumulation of electrons and ions inside the material, thereby reducing leakage current and conductivity loss. In addition, the multiphase synergistic structure formed by the liquid crystal polyarylate and epoxy resin helps to disperse the local stress and energy caused by the applied electric field, suppress the initiation and expansion of electrical trees, and delay the formation of breakdown channels.

[0016] In summary, this invention, through the low polarizability of liquid crystal polyarylate, the ordered structure effect of liquid crystal, and the regulation of the epoxy resin curing network, synergistically reduces the dielectric constant and dielectric loss of the composite material, while effectively improving the insulation performance and breakdown strength of the material.

[0017] Advantages of this invention:

[0018] I. This invention synthesizes a nematic liquid crystal polyarylate and introduces it into epoxy resin to prepare a high-performance, low-dielectric epoxy resin composite material. Studies show that the crystallinity of the liquid crystal polyarylate is reduced after regulation by meta-phenyl and side-chain methyl groups, the melting point is lowered to 325℃, and the processing performance is significantly improved, while the material still maintains excellent thermal stability. Regarding dielectric and insulation properties, the liquid crystal polyarylate prepared by this invention can effectively limit the dipole orientation polarization of the matrix polar groups. At a frequency of 1MHz, the dielectric constant of the composite material with 10% (by mass) of the epoxy resin added to the liquid crystal polyarylate decreases from 3.27 of pure epoxy resin to 2.65, a reduction of 18.96%, and the dielectric loss decreases from 0.0245 to 0.0178, a reduction of 27.35%. Simultaneously, its power frequency AC breakdown field strength also increases to 79.22 kV / mm, an increase of 19.27% ​​compared to pure epoxy resin.

[0019] II. The low-dielectric epoxy resin composite material based on liquid crystal polyarylate prepared by this invention achieves a balance between low dielectric strength, low dielectric loss and high insulation of epoxy resin, showing broad application prospects in the field of high-frequency and high-speed electronic devices and electronic packaging insulation. Attached Figure Description

[0020] Figure 1 The synthesis diagrams are for the liquid crystal polyarylates in Example 1 and Comparative Examples 1-2;

[0021] Figure 2 The infrared spectra of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 are shown below.

[0022] Figure 3 X-ray diffraction patterns of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2;

[0023] Figure 4 The DSC temperature curves of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 are shown.

[0024] Figure 5 The DSC cooling curves of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 are shown.

[0025] Figure 6 Thermogravimetric curves of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 are shown.

[0026] Figure 7 The images are polarized light microscope images of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 at 400°C, from left to right: LCP1, LCP2, and LCP3.

[0027] Figure 8 The bar chart shows the tensile strength of the low dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Example 1 and Comparative Examples 1-2.

[0028] Figure 9 The stress-strain curves of the low-dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Example 1 and Comparative Examples 1-2 are shown.

[0029] Figure 10 The dielectric constant curves of the low-dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2 at 25°C are shown.

[0030] Figure 11 The dielectric constant of the low-dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2 at 25°C is the dielectric constant at a frequency of 1MHz.

[0031] Figure 12 The dielectric loss curves of the low-dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2 at 25°C are shown.

[0032] Figure 13 The dielectric loss of the low dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2 at 25°C at a frequency of 1MHz.

[0033] Figure 14 The breakdown field strength Weibull plots are shown for the low dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2.

[0034] Figure 15 The breakdown field strength histograms are for the low-dielectric epoxy resin composite materials based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2. Detailed Implementation

[0035] Specific Implementation Method 1: This implementation method is a method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate, including the following steps:

[0036] I. Preparation of liquid crystal polyarylate:

[0037] ① Add sodium hydroxide, 4,4′-dihydroxybiphenyl, bisphenol A, benzyltriethylammonium chloride and sodium bisulfite to deionized water and stir at room temperature to obtain an aqueous solution;

[0038] ② Add terephthaloyl chloride and isophthaloyl chloride to an organic solvent and stir at room temperature to obtain an organic phase solution;

[0039] ③ Add the organic phase solution dropwise to the aqueous phase solution and stir at low temperature. After the low temperature reaction is completed, continue stirring the reaction system at room temperature. After the room temperature reaction is completed, pour it into methanol, and then filter, wash and dry the precipitated polymer to obtain liquid crystal polyarylate.

[0040] II. Preparation of liquid crystal polyarylate / epoxy resin composite materials:

[0041] ① Mix epoxy resin and liquid crystal polyarylate, heat and stir, then add curing agent, heat and stir, then add accelerator, continue heating and stirring, and finally transfer to vacuum oven for degassing treatment to obtain slurry;

[0042] ② Pour the slurry into the mold, and then place the mold in a flat vulcanizing machine to cure it, thereby obtaining a low dielectric epoxy resin composite material based on liquid crystal polyarylate.

[0043] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the molar ratio of sodium hydroxide, 4,4′-dihydroxybiphenyl, bisphenol A, benzyltriethylammonium chloride, and sodium bisulfite in step one ① is (0.1~0.2):(0.04~0.05):(0.007~0.008):(0.001~0.002):(0.002~0.003). The other steps are the same as in Specific Implementation Method One.

[0044] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the molar ratio of sodium hydroxide, 4,4′-dihydroxybiphenyl, bisphenol A, benzyltriethylammonium chloride, and sodium bisulfite in step one ① is 0.11:0.0425:0.0075:0.001:0.0025. The other steps are the same as in Specific Implementation Method One or Two.

[0045] Specific Implementation Method Four: The difference between this implementation method and Specific Implementation Methods One to Three is that the amount of 4,4′-dihydroxybiphenyl mentioned in step one ① is in the volume ratio of (0.04mol~0.05mol):(100mL~150mL). The other steps are the same as in Specific Implementation Methods One to Three.

[0046] Specific Implementation Method Five: The difference between this implementation method and Specific Implementation Methods One to Four is that the stirring time in step one ① is 20 min to 40 min at room temperature. The other steps are the same as in Specific Implementation Methods One to Four.

[0047] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the molar ratio of 4,4′-dihydroxybiphenyl mentioned in step one ① to terephthaloyl chloride and isophthaloyl chloride mentioned in step one ② is (0.04~0.05):(0.04~0.05):(0.007~0.008). The other steps are the same as in Specific Implementation Methods One to Five.

[0048] Specific Implementation Method Seven: The difference between this implementation method and Specific Implementation Methods One to Six is ​​that the volume ratio of the amount of terephthaloyl chloride to the organic solvent in step one, step two, is (0.04 mol ~ 0.05 mol): 100 mL. The other steps are the same as in Specific Implementation Methods One to Six.

[0049] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the organic solvent mentioned in step one, step two, is dichloromethane. The other steps are the same as in Specific Implementation Methods One to Seven.

[0050] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the stirring time in step one ② is 20-40 minutes at room temperature. The other steps are the same as in Specific Implementation Methods One to Eight.

[0051] Specific Implementation Method Ten: The difference between this implementation method and Specific Implementation Methods One to Nine is that the stirring time at low temperature in step 1③ is 1 to 2 hours. The other steps are the same as those in Specific Implementation Methods One to Nine.

[0052] Specific Implementation Method Eleven: The difference between this implementation method and Specific Implementation Methods One through Ten is that the low temperature mentioned in step one ③ is an ice-water bath with a temperature of -5℃ to 0℃. The other steps are the same as in Specific Implementation Methods One through Ten.

[0053] Specific Implementation Method Twelve: The difference between this implementation method and Specific Implementation Methods One to Eleven is that the stirring reaction time in step one ③ is 3 to 4 hours at room temperature. The other steps are the same as in Specific Implementation Methods One to Eleven.

[0054] Specific Implementation Method Thirteen: The difference between this implementation method and Specific Implementation Methods One to Twelve is that the washing described in step one ③ involves washing with anhydrous ethanol and deionized water 2 to 4 times respectively. The other steps are the same as in Specific Implementation Methods One to Twelve.

[0055] Specific Implementation Method Fourteen: The difference between this implementation method and Specific Implementation Methods One to Thirteen is that the drying described in step one ③ is performed at 60°C for 24 hours. The other steps are the same as in Specific Implementation Methods One to Thirteen.

[0056] Specific Implementation Method Fifteen: The difference between this implementation method and one of Specific Implementation Methods One to Fourteen is that the epoxy resin mentioned in step two① is E51 epoxy resin. The other steps are the same as those in Specific Implementation Methods One to Fourteen.

[0057] Specific Implementation Method Sixteen: The difference between this implementation method and Specific Implementation Methods One to Fifteen is that the heating and stirring temperature in step two① is 60℃~80℃, and the time is 10min~60min. The other steps are the same as those in Specific Implementation Methods One to Fifteen.

[0058] Specific Implementation Method Seventeen: The difference between this implementation method and Specific Implementation Methods One to Sixteen is that the accelerator mentioned in step two① is DMP-30. The other steps are the same as those in Specific Implementation Methods One to Sixteen.

[0059] Specific Implementation Method 18: The difference between this implementation method and Specific Implementation Methods 1 to 17 is that the degassing treatment in step 2① is carried out at a temperature of 80℃ for 15 to 30 minutes. The other steps are the same as those in Specific Implementation Methods 1 to 17.

[0060] Specific Implementation Method Nineteen: The difference between this implementation method and Specific Implementation Methods One to Eighteen is that the curing agent mentioned in step two① is methylhexahydrophthalic anhydride. The other steps are the same as those in Specific Implementation Methods One to Eighteen.

[0061] Specific Implementation Method Twenty: This implementation method differs from Specific Implementation Methods One to Nineteen in that the mass ratio of epoxy resin, liquid crystal polyarylate, curing agent, and accelerator in step two① is 100:(2.5~10):80:0.3. The other steps are the same as in Specific Implementation Methods One to Nineteen.

[0062] Specific Implementation Method 21: This implementation method differs from Specific Implementation Methods 1 to 21 in that the curing described in step 2② is constant temperature and pressure curing or segmented curing. The other steps are the same as in Specific Implementation Methods 1 to 20.

[0063] Specific Implementation Method 22: This implementation method differs from Specific Implementation Methods 1 to 21 in that the constant temperature and pressure curing method is as follows: curing is carried out at 160℃ and 10MPa for 2 hours. Other steps are the same as in Specific Implementation Methods 1 to 21.

[0064] Specific Implementation Method 23: This implementation method differs from Specific Implementation Methods 1 to 22 in that the segmented curing method is as follows: first, maintain the temperature at 120°C for 2 hours, then maintain the temperature at 140°C for 2 hours, and finally maintain the temperature at 160°C for 1 hour. Other steps are the same as in Specific Implementation Methods 1 to 22.

[0065] The beneficial effects of the present invention are verified using the following embodiments:

[0066] Comparative Example 1: A method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate (LCP1), specifically comprising the following steps:

[0067] I. Preparation of liquid crystal polyarylate:

[0068] ① Preparation of aqueous solution:

[0069] 0.11 mol sodium hydroxide, 0.05 mol 4,4′-dihydroxybiphenyl, 0.001 mol benzyltriethylammonium chloride and 0.0025 mol sodium bisulfite were added to 110 mL of deionized water and stirred at room temperature for 30 min to obtain an aqueous solution.

[0070] ② Preparation of organic phase solution:

[0071] 0.05 mol terephthaloyl chloride was dissolved in 100 mL dichloromethane and stirred at room temperature for 30 min to obtain an organic phase solution;

[0072] ③ Add the organic phase solution prepared in step 1 ② dropwise to the aqueous phase solution prepared in step 1 ①, and react for 1 hour under ice-water bath (-5~0℃) and stirring conditions. After the reaction is completed, remove the reaction system from the ice-water bath and continue to stir the reaction at room temperature for 4 hours. After the reaction is completed, pour it into 200 mL of methanol, filter the precipitated polymer, wash it twice with anhydrous ethanol and deionized water respectively, and finally dry it in a drying oven at 60℃ for 24 hours to obtain liquid crystal polyarylate (denoted as LCP1).

[0073] II. Preparation of liquid crystal polyarylate / epoxy resin composite materials:

[0074] ① Mix 100g of E51 epoxy resin and liquid crystal polyarylate, heat and stir in a constant temperature water bath at 80℃ for 1h. After the reaction is complete, add methyl hexahydrophthalic anhydride (MeHHPA), continue heating and stirring for 1h, then add 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), heat and stir for 10min, and finally transfer to a vacuum oven at 80℃ for degassing treatment for 30min to obtain slurry;

[0075] The amount of liquid crystal polyarylate used in step 2① is 0g, 2.5g, 5g or 10g;

[0076] ② Pour the slurry into the mold, and then place the mold in a flat vulcanizing machine to cure it, thereby obtaining a low dielectric epoxy resin composite material based on liquid crystal polyarylate (LCP1).

[0077] The curing method described in step 2② is as follows: first, keep warm at 120℃ for 2 hours, then keep warm at 140℃ for 2 hours, and finally keep warm at 160℃ for 1 hour.

[0078] When the amount of liquid crystal polyarylate used in step two ① of Comparative Example 1 is 0g, the product obtained in step two ② is pure epoxy resin, denoted as EP.

[0079] When the amount of liquid crystal polyarylate used in step two ① of Comparative Example 1 is 2.5g, the low dielectric epoxy resin composite material obtained in step two ② is based on liquid crystal polyarylate, denoted as LCP1-2.5.

[0080] When the amount of liquid crystal polyarylate used in step two ① of Comparative Example 1 is 5g, the low dielectric epoxy resin composite material based on liquid crystal polyarylate obtained in step two ② is denoted as LCP1-5.

[0081] When the amount of liquid crystal polyarylate used in step two ① of Comparative Example 1 is 10g, the low dielectric epoxy resin composite material obtained in step two ② is based on liquid crystal polyarylate and is denoted as LCP1-10.

[0082] Comparative Example 2: A method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate (LCP2), specifically comprising the following steps:

[0083] I. Preparation of liquid crystal polyarylate:

[0084] ① Preparation of aqueous solution:

[0085] 0.11 mol sodium hydroxide, 0.05 mol 4,4′-dihydroxybiphenyl, 0.001 mol benzyltriethylammonium chloride and 0.0025 mol sodium bisulfite were added to 110 mL of deionized water and stirred at room temperature for 30 min to obtain an aqueous solution.

[0086] ② Preparation of organic phase solution:

[0087] 0.0425 mol terephthaloyl chloride and 0.0075 mol isophthaloyl chloride were dissolved in 100 mL dichloromethane and stirred at room temperature for 30 min to obtain an organic phase solution;

[0088] ③ Add the organic phase solution prepared in step 1 ② dropwise to the aqueous phase solution prepared in step 1 ①, and react for 1 hour under ice-water bath (-5~0℃) and stirring conditions. After the reaction is completed, remove the reaction system from the ice-water bath and continue to stir the reaction at room temperature for 4 hours. After the reaction is completed, pour it into 200 mL of methanol, filter the precipitated polymer, wash it twice with anhydrous ethanol and deionized water respectively, and finally dry it in a drying oven at 60℃ for 24 hours to obtain liquid crystal polyarylate (denoted as LCP2).

[0089] II. Preparation of liquid crystal polyarylate / epoxy resin composite materials:

[0090] ① Mix 100g of E51 epoxy resin and liquid crystal polyarylate, heat and stir in a constant temperature water bath at 80℃ for 1h. After the reaction is complete, add methyl hexahydrophthalic anhydride (MeHHPA), continue heating and stirring for 1h, then add 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), heat and stir for 10min, and finally transfer to a vacuum oven at 80℃ for degassing treatment for 30min to obtain slurry;

[0091] The amount of liquid crystal polyarylate used in step 2① is 0g, 2.5g, 5g or 10g;

[0092] ② Pour the slurry into the mold, and then place the mold in a flat vulcanizing machine to cure it, thereby obtaining a low dielectric epoxy resin composite material based on liquid crystal polyarylate (LCP2).

[0093] The curing method described in step 2② is as follows: first, keep warm at 120℃ for 2 hours, then keep warm at 140℃ for 2 hours, and finally keep warm at 160℃ for 1 hour.

[0094] When the amount of liquid crystal polyarylate used in step 2① of Comparative Example 2 is 0g, the product obtained in step 2② is pure epoxy resin, denoted as EP.

[0095] When the amount of liquid crystal polyarylate used in step two ① of Comparative Example 2 is 2.5g, the low dielectric epoxy resin composite material obtained in step two ② is based on liquid crystal polyarylate, denoted as LCP2-2.5.

[0096] When the amount of liquid crystal polyarylate used in step 2① of Comparative Example 2 is 5g, the low dielectric epoxy resin composite material based on liquid crystal polyarylate obtained in step 2② is denoted as LCP2-5.

[0097] When the amount of liquid crystal polyarylate used in step 2① of Comparative Example 2 is 10g, the low dielectric epoxy resin composite material based on liquid crystal polyarylate obtained in step 2② is denoted as LCP2-10.

[0098] Example 1: A method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate (LCP3), specifically carried out according to the following steps:

[0099] I. Preparation of liquid crystal polyarylate:

[0100] ① Preparation of aqueous solution:

[0101] 0.11 mol sodium hydroxide, 0.0425 mol 4,4′-dihydroxybiphenyl, 0.0075 mol bisphenol A, 0.001 mol benzyltriethylammonium chloride and 0.0025 mol sodium bisulfite were added to 110 mL of deionized water and stirred at room temperature for 30 min to obtain an aqueous solution.

[0102] ② Preparation of organic phase solution:

[0103] 0.0425 mol terephthaloyl chloride and 0.0075 mol isophthaloyl chloride were added to 100 mL of dichloromethane and stirred at room temperature for 30 min to obtain an organic phase solution.

[0104] ③ Add the organic phase solution prepared in step 1 ② dropwise to the aqueous phase solution prepared in step 1 ①, and react for 1 hour under ice-water bath (-5~0℃) and stirring conditions. After the reaction is completed, remove the reaction system from the ice-water bath and continue to stir the reaction at room temperature for 4 hours. After the reaction is completed, pour it into 200 mL of methanol, filter the precipitated polymer, wash it twice with anhydrous ethanol and deionized water respectively, and finally dry it in a drying oven at 60℃ for 24 hours to obtain liquid crystal polyarylate (denoted as LCP3).

[0105] II. Preparation of liquid crystal polyarylate / epoxy resin composite materials:

[0106] ① Mix 100g of E51 epoxy resin and liquid crystal polyarylate, heat and stir in a constant temperature water bath at 80℃ for 1h. After the reaction is complete, add methyl hexahydrophthalic anhydride (MeHHPA), continue heating and stirring for 1h, then add 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30), heat and stir for 10min, and finally transfer to a vacuum oven at 80℃ for degassing treatment for 30min to obtain slurry;

[0107] The amount of liquid crystal polyarylate used in step 2① is 0g, 2.5g, 5g or 10g;

[0108] ② Pour the slurry into the mold, and then place the mold in a flat vulcanizing machine to cure it, thereby obtaining a low dielectric epoxy resin composite material based on liquid crystal polyarylate.

[0109] The curing method described in step 2② is as follows: first, keep warm at 120℃ for 2 hours, then keep warm at 140℃ for 2 hours, and finally keep warm at 160℃ for 1 hour.

[0110] When the amount of liquid crystal polyarylate used in step two ① of Example 1 is 0g, the pure epoxy resin obtained in step two ② is denoted as EP.

[0111] When the amount of liquid crystal polyarylate used in step two ① of Example 1 is 2.5g, the low dielectric epoxy resin composite material obtained in step two ② is based on liquid crystal polyarylate and is denoted as LCP3-2.5.

[0112] When the amount of liquid crystal polyarylate used in step two ① of Example 1 is 5g, the low dielectric epoxy resin composite material based on liquid crystal polyarylate obtained in step two ② is denoted as LCP3-5.

[0113] When the amount of liquid crystal polyarylate used in step two ① of Example 1 is 10g, the low dielectric epoxy resin composite material obtained in step two ② is based on liquid crystal polyarylate and is denoted as LCP3-10.

[0114] The liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 were tested using Fourier transform infrared spectroscopy, and the results are as follows: Figure 2 As shown;

[0115] Figure 2 The infrared spectra of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 are shown below.

[0116] Figure 2 The figure shows 1732 cm. -1 An absorption peak for the stretching vibration of C=O appeared at 1261 cm⁻¹. -1 The peak at 2968 cm⁻¹ corresponds to the asymmetric stretching vibration of COC, which preliminarily proves that a condensation reaction occurred between the bisphenol monomer and the acyl chloride monomer. -1 2924cm -1 2853cm -1 The peak represents the methyl stretching vibration of bisphenol A. In summary, the synthesized polymer is a liquid crystal polyarylate with the expected structure.

[0117] Figure 3 X-ray diffraction patterns of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2;

[0118] Figure 3 The results show that all three liquid crystal polyarylates exhibit relatively sharp diffraction peaks at a 2θ angle of approximately 20°, indicating that they are all nematic crystalline polymers. With the introduction of isophthaloyl chloride and bisphenol A, the diffraction peaks become increasingly broad, and the crystallinity decreases. This is mainly because the introduction of the torsional meta-phenyl group and the methyl group with a side chain of bisphenol A leads to a more disordered arrangement of the polymer molecular chains, resulting in a decrease in crystallinity. However, it has not yet transformed into the diffuse broad peaks characteristic of an amorphous polymer, thus retaining its liquid crystal properties.

[0119] The thermal behavior of the synthesized liquid crystal polyarylate was analyzed and tested using differential scanning calorimetry (DSC). Figure 4 and Figure 5 As shown;

[0120] Figure 4 The DSC temperature curves of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 are shown.

[0121] Figure 5 The DSC cooling curves of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 are shown.

[0122] exist Figure 4 The melting point (T) of liquid crystal polyarylate in the heating curve m The DSC curves of the liquid crystal polyarylate were obtained at 384°C, 359°C, and 325°C, respectively. The introduction of a torsion-structured meta-phenyl group and a bisphenol A group with a side-chain methyl group led to a TT of the LCP. m The melting point was significantly reduced due to the increase in flexible segments, which altered the original linear structure and decreased the crystallinity of the liquid crystal polyarylate, thus leading to a significant decrease in its melting point, consistent with the XRD results. Meanwhile... Figure 5 The difficulty in observing crystallization peaks in the cooling curve may be due to the wide molecular weight distribution of the liquid crystal polyarylate itself.

[0123] The TGA and DTG curves of liquid crystal polyarylate were obtained under a nitrogen atmosphere, as shown in the figure. Figure 6 As shown;

[0124] Figure 6 Thermogravimetric curves of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 are shown.

[0125] The degradation of liquid crystal polyarylate exhibited two steps, corresponding to two peaks in the DTG plot, indicating that the thermal degradation process consisted of two stages. The first stage primarily involved the oxidative degradation of unreacted monomers or low-molecular-weight monomers. The second stage was the oxidative degradation of the liquid crystal polyarylate, which best demonstrated its heat resistance. In this stage, with the introduction of isophthaloyl chloride and bisphenol A, the maximum decomposition temperature (T0) increased. max The temperature decreased slightly, from 591℃ to 586℃, indicating that it still possesses high thermal stability. This is in line with the 10% decrease in decomposition temperature (T). 10% The temperature was decreased from 560℃ to 518℃. It was found that with the introduction of isophthaloyl chloride and bisphenol A, its 100% decomposition temperature decreased, indicating that its structural regularity decreased, which is consistent with the previous XRD and DSC curves.

[0126] When liquid crystal polyarylate is heated to the melt, its molecular chains tend to align regularly along the shear direction under shear force. Under a polarizing microscope, this material exhibits a textured structure with colored patterns due to birefringence, demonstrating significant anisotropy. Figure 7 As shown;

[0127] Figure 7 The images are polarized light microscope images of the liquid crystal polyarylates synthesized in Example 1 and Comparative Examples 1-2 at 400°C, from left to right: LCP1, LCP2, and LCP3.

[0128] from Figure 7 It can be seen that all three liquid crystal polyarylates exhibit colored textures of liquid crystals. This phenomenon indicates that the addition of the nonlinear monomer isophthaloyl chloride and bisphenol A with side chains does not destroy the original liquid crystal properties. It also means that the three nematic liquid crystal polyarylates were successfully synthesized.

[0129] Figure 8 The bar chart shows the tensile strength of the low dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Example 1 and Comparative Examples 1-2.

[0130] Depend on Figure 8 It can be seen that the tensile strength of pure E51 epoxy resin is 56.13 MPa. The tensile strength of the composite material increases slightly with the increase of the liquid crystal polyarylate content. When the content of liquid crystal polyarylate in the composite material is 10% of the mass of epoxy resin, the tensile strength of the composite material reaches the maximum value. The tensile strengths of LCP1-10, LCP2-10, and LCP3-10 are 58.04, 57.87, and 57.90 MPa, respectively.

[0131] Figure 9 The stress-strain curves of the low-dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Example 1 and Comparative Examples 1-2 are shown.

[0132] pass Figure 9 The stress-strain curves show that the addition of liquid crystal polyarylate increases the strain of the epoxy resin, demonstrating that the composite material has improved toughness compared to pure E51 epoxy resin. This is because when liquid crystal molecules are subjected to external force, they orient themselves along the direction of the force, which in turn causes the matrix to also have an orientation tendency. Combined with the self-reinforcing effect of the liquid crystal molecules themselves, the tensile strength of the material increases. The end groups of the liquid crystal molecules are hydroxyl and carboxyl groups, which can form hydrogen bonds with oxygen atoms in the epoxy resin, tightly binding with the cured network. Its special molecular structure can change the properties of the continuous phase of the resin, which is conducive to the generation of shear bands and crazes under external force, relaxing the stress concentration at the crack tip and hindering propagation. The fibrous mesocrystalline domains act like bridges across the fracture surface of the matrix, preventing the propagation of crazes. Simultaneously, the mesocrystalline domains also act as anchors between crazes, preventing their propagation and thus improving the toughness of the material.

[0133] Dielectric properties mainly include dielectric constant and dielectric loss. Dielectric constant reflects a material's ability to store electrical energy in an electric field, while dielectric loss reflects the amount of energy lost by a material in an alternating electric field.

[0134] Figure 10The dielectric constant curves of the low-dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2 at 25°C are shown.

[0135] Overall, the dielectric constant of all samples decreased with increasing frequency. At low frequencies, the polar groups within the material have ample time to follow the changes in the electric field, resulting in a relatively high dielectric constant. As the frequency increases, the electric field changes more rapidly, and some polar groups cannot keep up with the changes, leading to a decrease in the material's polarization ability and thus a gradual decrease in the dielectric constant. With increasing proportions of liquid crystal polyarylate (LCP3), the dielectric constant of the composite material showed a decreasing trend, reaching its lowest value when the LCP3 content reached 10% of the epoxy resin mass.

[0136] Figure 11 The dielectric constant of the low-dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2 at 25°C is the dielectric constant at a frequency of 1MHz.

[0137] from Figure 11 It can be seen that at a frequency of 1MHz, the dielectric constant of E51 epoxy resin is 3.27, while the measured value of LCP3-10 composite material decreases to 2.65. E51 epoxy resin belongs to the bisphenol A type epoxy resin, containing a large number of polar groups in its molecule. These groups are prone to dipole orientation polarization under an electric field, resulting in a high dielectric constant. LCP1 molecular chains contain many rigid aromatic structures, making chain segments less mobile. Adding epoxy resin can restrict the movement of some epoxy resin chain segments and polar groups, reducing the overall polarization ability of the material. Compared to LCP1, LCP2 and LCP3 have certain meta-structures and side-chain structures, gradually reducing the regularity of the molecular chain and decreasing the number of polar groups per unit space, thus further reducing the dielectric constant. In contrast, E51 epoxy resin has an amorphous structure with randomly distributed molecular chains, resulting in more significant dipole polarization and a higher dielectric constant.

[0138] Figure 12 The dielectric loss curves of the low-dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2 at 25°C are shown.

[0139] from Figure 12 It can be seen that the dielectric loss of composite materials increases with increasing frequency, but is still less than that of pure E51 epoxy resin. This is mainly because as the rate of change of the applied electric field increases, the dipole orientation motion and interface charge migration within the material gradually lag behind the change in electric field, and the energy dissipation generated during polarization relaxation increases, thus increasing the dielectric loss.

[0140] Figure 13The dielectric loss of the low dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2 at 25°C at a frequency of 1MHz.

[0141] from Figure 13 It can be seen that at a frequency of 1MHz, the dielectric loss of E51 epoxy resin is 0.0245, while the measured value of LCP3-10 composite material decreases to 0.0178. This is mainly because liquid crystal polyarylate has a highly ordered liquid crystal structure, with regular molecular chain arrangement and strong intermolecular forces. This structural characteristic can effectively reduce dipole reorientation polarization, and the rigid segments of liquid crystal polyarylate can suppress the free movement of molecular chain segments, reducing energy loss. E51 epoxy resin has a relatively loose molecular chain structure, and more polar groups may be formed in the cross-linked network. These polar groups are prone to reorientation polarization under an electric field, resulting in a higher dielectric loss for E51 epoxy resin than that of the composite material.

[0142] Epoxy resin composites are widely used in the field of electronic packaging for applications such as electric vehicle inverters, distribution transformers, and power control boards in power frequency AC voltage scenarios. Therefore, the influence of liquid crystal polyarylate on the insulation properties of the matrix resin was studied. Figure 14-15 The effects of three liquid crystal polyarylate contents on the AC breakdown of composite materials were demonstrated.

[0143] Figure 14 The breakdown field strength Weibull plots are shown for the low dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2.

[0144] Figure 15 The breakdown field strength histograms are for the low-dielectric epoxy resin composites based on liquid crystal polyarylate prepared in Examples 1 and Comparative Examples 1-2.

[0145] Figures 14-15 The results show that the insulation strength of the composite system increases with the increase in the proportion of liquid crystal polyarylate. When the amount of liquid crystal polyarylate added is 10% of the epoxy resin mass, the composite material exhibits the best electrical properties, with its breakdown field strength significantly increased from the baseline value of 66.42 kV / mm for pure E51 resin to 79.22 kV / mm. This performance change is mainly due to the change in the internal structure of the material. The good compatibility between liquid crystal polyarylate and the matrix resin allows it to form a three-dimensional network structure during the curing process, effectively compensating for the inherent defects of E51 epoxy resin. The tight cross-linked structure not only inhibits the free movement of molecular chain segments but also hinders the formation of charge conduction pathways, thereby significantly improving the breakdown field strength.

Claims

1. A method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate, characterized in that, The preparation method includes the following steps: I. Preparation of liquid crystal polyarylate: ① Add sodium hydroxide, 4,4′-dihydroxybiphenyl, bisphenol A, benzyltriethylammonium chloride and sodium bisulfite to deionized water and stir at room temperature to obtain an aqueous solution; ② Add terephthaloyl chloride and isophthaloyl chloride to an organic solvent and stir at room temperature to obtain an organic phase solution; ③ Add the organic phase solution dropwise to the aqueous phase solution and stir at low temperature. After the low temperature reaction is completed, continue stirring the reaction system at room temperature. After the room temperature reaction is completed, pour it into methanol, and then filter, wash and dry the precipitated polymer to obtain liquid crystal polyarylate. II. Preparation of liquid crystal polyarylate / epoxy resin composite materials: ① Mix epoxy resin and liquid crystal polyarylate, heat and stir, then add curing agent, heat and stir, then add accelerator, continue heating and stirring, and finally transfer to vacuum oven for degassing treatment to obtain slurry; ② Pour the slurry into the mold, and then place the mold in a flat vulcanizing machine to cure it, thereby obtaining a low dielectric epoxy resin composite material based on liquid crystal polyarylate.

2. The method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate according to claim 1, characterized in that, The molar ratio of sodium hydroxide, 4,4′-dihydroxybiphenyl, bisphenol A, benzyltriethylammonium chloride and sodium bisulfite mentioned in step 1① is (0.1~0.2):(0.04~0.05):(0.007~0.008):(0.001~0.002):(0.002~0.003).

3. The method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate according to claim 1, characterized in that, In step 1①, the stirring time at room temperature is 20-40 minutes.

4. The method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate according to claim 1, characterized in that, The molar ratio of 4,4′-dihydroxybiphenyl mentioned in step 1① to terephthaloyl chloride and isophthaloyl chloride mentioned in step 1② is (0.04~0.05):(0.04~0.05):(0.007~0.008).

5. The method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate according to claim 1, characterized in that, In step 1②, the stirring time at room temperature is 20 min to 40 min.

6. The method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate according to claim 1, characterized in that, In step 1, ③, the stirring time at low temperature is 1 to 2 hours.

7. The method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate according to claim 1, characterized in that, In step 1, the stirring reaction time at room temperature is 3 to 4 hours.

8. The method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate according to claim 1, characterized in that, The mass ratio of epoxy resin, liquid crystal polyarylate, curing agent and accelerator mentioned in step 2① is 100:(2.5~10):80:0.

3.

9. The method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate according to claim 1, characterized in that, The heating and stirring process in step 2① is carried out at a temperature of 60℃~80℃ for 10min~60min.

10. The method for preparing a low-dielectric epoxy resin composite material based on liquid crystal polyarylate according to claim 1, characterized in that, The curing process described in step 2② is constant temperature and pressure curing or segmented curing.

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