Liquid crystal monomer, liquid crystal epoxy resin and preparation method and application thereof

Abstract

The invention discloses a liquid crystal monomer, a liquid crystal epoxy resin and a preparation method and application of the liquid crystal monomer, the liquid crystal monomer has a structure shown as a formula (I): # imgabs0 # imgabs1 #, fluorine atoms are introduced into the liquid crystal monomer to enter an epoxy system, dipole polarization can be remarkably reduced, and therefore the dielectric constant and dielectric loss of the system are reduced; according to the liquid crystal epoxy resin prepared from the liquid crystal monomer, the heat-conducting property of the epoxy resin is intrinsically improved, a homogeneous phase system can be formed, the volume resistivity is also increased while the heat conductivity is increased, and the insulating property is improved.

Description

Technical Field

[0001] The present application relates to the technical field of epoxy resin materials, and particularly relates to a liquid crystal monomer, a liquid crystal epoxy resin, a preparation method thereof, and an application thereof. Background Art

[0002] Epoxy resin (EP) has been widely used in the fields of electronic packaging, printed circuit boards, light-emitting diodes, gas-insulated pipes, etc. due to its excellent electrical insulation performance, good thermal stability, easy processing, low cost, etc. However, the thermal conductivity of pure epoxy resin is only 0.17 - 0.23 W / (m·K). Therefore, it is particularly important to improve the thermal conductivity of epoxy resin materials while maintaining electrical insulation performance. Developing epoxy resin-based composite insulating materials with both high thermal conductivity and excellent electrical insulation has become one of the important research directions in the current field of insulating materials. Currently, the research on the modification of the thermal conductivity of epoxy resin is mainly based on the doping of inorganic high-thermal-conductivity fillers, that is, by adding some high-thermal-conductivity inorganic micro- and nano-fillers, such as alumina (Al2O3), boron nitride (BN), carbon nanotubes (CNTs), etc., into the epoxy resin material, and combining with the optimization of the preparation process to obtain filled thermally conductive epoxy resin.

[0003] At present, although the filled thermally conductive epoxy resin can effectively increase the thermal conductivity of epoxy resin, the fillers will increase the internal defects and pores of the material, resulting in the migration of electric ions and reducing the electrical insulation performance. At the same time, the fillers will significantly increase the viscosity of the epoxy slurry. Under the influence of the above two reasons, the amount of filler added is limited, which is not conducive to the further improvement of the thermal conductivity.

[0004] Therefore, there is a need for in-depth research on liquid crystal epoxy resin. Summary of the Invention

[0005] The present application aims to solve at least one of the technical problems existing in the prior art to some extent. For this purpose, the present application provides a liquid crystal monomer, a liquid crystal epoxy resin, a preparation method thereof, and an application thereof. The liquid crystal monomer intrinsically improves the thermal conductivity of epoxy resin, and the two can form a homogeneous phase system. At the same time, it can also effectively improve the insulation of the obtained liquid crystal epoxy resin, so that the liquid crystal epoxy resin has both good thermal conductivity and insulation, and the overall performance is excellent.

[0006] In the first aspect of the present application, the present application proposes a liquid crystal monomer having a structure shown in formula (Ⅰ):

[0007] After curing, the above liquid crystal monomer can significantly improve the thermal conductivity of the material. At the same time, due to the fluorine-containing characteristics of the liquid crystal monomer, it can also reduce the dielectric constant and dielectric loss of the system, increase the volume resistivity, thereby improving the insulation performance of the material. Thus, the material has both good thermal conductivity and insulation performance.

[0008] In the second aspect of the present application, a method for preparing the liquid crystal monomer described in the first aspect is proposed, including: chlorinating 3,3',5,5'-tetramethylbiphenyl diglycidyl ether to obtain 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether; fluorinating the 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether to obtain the liquid crystal monomer.

[0009] According to an embodiment of the present application, the chlorination treatment includes: mixing 3,3',5,5'-tetramethylbiphenyl diglycidyl ether, benzoyl peroxide and triethanolamine, and performing heat treatment to obtain a first intermediate product; the mass ratio of 3,3',5,5'-tetramethylbiphenyl diglycidyl ether, benzoyl peroxide and triethanolamine is (1600 - 1400):(20 - 30):1; the temperature of the heat treatment is 90 - 110 °C; contacting the first intermediate product with chlorine gas to obtain a second intermediate product; the contacting treatment is carried out under light conditions; the temperature of the contacting treatment is 100 - 300 °C, and the time is 5 - 8 h; washing and drying the second intermediate product, and performing a first vacuum distillation treatment to collect the fraction at 125 - 135 °C to obtain the 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether.

[0010] According to an embodiment of the present application, the fluorination treatment includes: mixing the 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether with hydrofluoric acid to obtain a third intermediate product; the mass ratio of 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether to hydrofluoric acid is (7 - 8):1; the temperature of the mixing treatment is 130 - 140 °C, the pressure is 1.4 - 2 MPa, and the time is 2 - 3 h; washing and drying the third intermediate product, and performing a second vacuum distillation treatment to collect the fraction at 117 - 125 °C to obtain the 3,3',5,5'-tetrakis(trifluoromethyl)biphenyl diglycidyl ether.

[0011] In the third aspect of the present application, a liquid crystal epoxy resin is proposed, and the raw materials of the liquid crystal epoxy resin include the liquid crystal monomer, epoxy resin and curing agent described in claim 1.

[0012] According to an embodiment of the present application, the epoxy resin includes bisphenol A epoxy resin E-51.

[0013] According to an embodiment of the present application, the curing agent includes 4,4'-diaminodiphenyl sulfone.

[0014] According to an embodiment of the present application, based on the total mass of the liquid crystal monomer and the epoxy resin, the mass proportion of the liquid crystal monomer is 30% to 30%.

[0015] According to an embodiment of the present application, the raw materials of the liquid crystal epoxy resin include: 50 to 70 parts by weight of epoxy resin; 30 to 50 parts by weight of liquid crystal monomer; 80 to 90 parts by weight of curing agent.

[0016] According to an embodiment of the present application, the raw materials of the liquid crystal epoxy resin further include: a promoter and a diluent.

[0017] According to an embodiment of the present application, the raw materials of the liquid crystal epoxy resin include: 50 to 70 parts by weight of epoxy resin; 30 to 50 parts by weight of liquid crystal monomer; 80 to 90 parts by weight of curing agent; 0.1 to 2 parts by weight of promoter; 2 to 8 parts by weight of diluent.

[0018] According to an embodiment of the present application, the promoter includes 2-methylimidazole; the diluent includes phenyl glycidyl ether.

[0019] In the fourth aspect of the present application, the present application provides a method for preparing the liquid crystal epoxy resin described in the third aspect, including: melting the liquid crystal monomer into a liquid state to obtain a liquid crystal monomer in a liquid state; stirring the liquid crystal monomer in a liquid state, epoxy resin, and curing agent to obtain a mixture; subjecting the mixture to a curing treatment to obtain a liquid crystal epoxy resin.

[0020] According to an embodiment of the present application, it further includes: performing the stirring treatment on the liquid crystal monomer in a liquid state, epoxy resin, curing agent, promoter, and diluent.

[0021] According to an embodiment of the present application, the temperature of the stirring treatment is 90 to 100 °C, and the time is 1 to 2 h.

[0022] According to an embodiment of the present application, the temperature of the curing treatment is 100 to 150 °C, and the time is 3 to 5 h.

[0023] In the fifth aspect of the present application, the present application provides an application of the liquid crystal monomer described in the first aspect in improving the thermal conductivity and volume resistivity of epoxy resin.

[0024] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be understood through the practice of the present application. Description of the Drawings

[0025] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, where:

[0026] Figure 1 It is the reaction schematic diagram in Embodiment 1 of the present application;

[0027] Figure 2 It is the physical product diagram in Embodiment 2 of the present application. Detailed Embodiments

[0028] The embodiments of the present application are described in detail below. The described embodiments are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application.

[0029] It should be noted that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. Further, in the description of the present application, unless otherwise stated, the meaning of "a plurality" is two or more.

[0030] The endpoints and any values within the ranges disclosed herein are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and a single point value, and between single point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0031] In this document, the term "comprising" or "including" is an open expression, that is, it includes the content specified in the present application, but does not exclude other aspects.

[0032] In this document, the terms "optionally", "optional" or "option" generally mean that the subsequent events or conditions may or may not occur, and the description includes the cases where such events or conditions occur, as well as the cases where such events or conditions do not occur.

[0033] Liquid crystal monomer

[0034] In the first aspect of the present application, the present application provides a liquid crystal monomer having a structure shown in formula (Ⅰ):

[0035]

[0036] After curing, the above liquid crystal monomer can significantly improve the thermal conductivity of the material. At the same time, due to the fluorine-containing characteristics of the liquid crystal monomer, it can also reduce the dielectric constant and dielectric loss of the system, increase the volume resistivity, thereby improving the insulation performance of the material. Thus, the material has both good thermal conductivity and insulation performance.

[0037] Method for preparing liquid crystal monomer

[0038] In the second aspect of the present application, the present application proposes a method for preparing the liquid crystal monomer described in the first aspect, including: chlorinating 3,3',5,5'-tetramethylbiphenyl diglycidyl ether to obtain 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether; fluorinating the 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether to obtain the liquid crystal monomer. Thus, fluorine atoms are introduced through fluorination treatment. Due to the high electronegativity and low polarity characteristics of fluorine atoms, dipole polarization can be significantly reduced, thereby reducing the dielectric constant and dielectric loss of the system, while increasing the volume resistivity, so as to enhance the insulation performance of the material while improving the thermal conductivity, and achieve the synergistic improvement of thermal conductivity and insulation performance.

[0039] According to an embodiment of the present application, the chlorination treatment includes: mixing 3,3',5,5'-tetramethylbiphenyl diglycidyl ether, benzoyl peroxide and triethanolamine, and performing heat treatment to obtain a first intermediate product; the mass ratio of 3,3',5,5'-tetramethylbiphenyl diglycidyl ether, benzoyl peroxide and triethanolamine is (1600 - 1400):(20 - 30):1, for example, it can be 1600:20:1, 1500:25:1, 1400:30:1, etc.; the temperature of the heat treatment is 90 - 110 °C, for example, it can be 90 °C, 91 °C, 92 °C, 93 °C, 94 °C, 95 °C, 100 °C, 110 °C, etc.; contacting the first intermediate product with chlorine gas to obtain a second intermediate product; the contacting treatment is carried out under light conditions; the temperature of the contacting treatment is 100 - 300 °C, for example, it can be 100 °C, 200 °C, 300 °C, etc.; the time is 5 - 8 h, for example, it can be 5 h, 6 h, 7 h, 8 h, etc.; washing and drying the second intermediate product, and performing a first vacuum distillation treatment to collect the fraction at 125 - 135 °C to obtain the 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether. Thus, the chlorination treatment provides reaction sites for the subsequent fluorination reaction.

[0040] According to an embodiment of the present application, the fluorination treatment includes: mixing the 3,3',5,5'-tetrakis(trichloromethyl)biphenol diglycidyl ether with hydrofluoric acid to obtain a third intermediate product; the mass ratio of the 3,3',5,5'-tetrakis(trichloromethyl)biphenol diglycidyl ether to hydrofluoric acid is (7-8):1, for example, it can be 7:1, 7.5:1, 8:1, etc.; the temperature of the mixing treatment is 130-140°C, for example, it can be 130°C, 135°C, 140°C, etc., the pressure is 1.4-2 MPa, for example, it can be 1.4 MPa, 1.5 MPa, 1.6 MPa, 1.7 MPa, 1.8 MPa, 1.9 MPa, 2 MPa, etc., and the time is 2-3 h, for example, it can be 2 h, 3 h, etc.; washing and drying the third intermediate product, and performing a second vacuum distillation treatment to collect the fraction at 117-125°C to obtain the 3,3',5,5'-tetrakis(trifluoromethyl)biphenol diglycidyl ether. Thus, fluorine atoms can replace chlorine atoms to form a fluorinated liquid crystal monomer.

[0041] Liquid crystal epoxy resin

[0042] In the third aspect of the present application, the present application proposes a liquid crystal epoxy resin. According to an embodiment of the present application, the raw materials of the liquid crystal epoxy resin include the above-mentioned liquid crystal monomer, epoxy resin, and curing agent.

[0043] The epoxy resin itself has an amorphous structure. By selecting a liquid crystal monomer containing a biphenyl group, it can be oriented and arranged into liquid crystal domains during the curing process, inhibiting phonon scattering, and thus improving the thermal conductivity of the epoxy resin. The prepared liquid crystal epoxy resin is a thermosetting resin that has isotropic characteristics similar to ordinary epoxy resins macroscopically and an anisotropic liquid crystal structure composed of regular and ordered mesogenic units microscopically, and the epoxy resin that improves the performance by controlling the formation of higher-order structures to form mesogenic domains.

[0044] According to an embodiment of the present application, the epoxy resin includes bisphenol A epoxy resin E-51. Thus, bisphenol A epoxy resin E-51 is selected as the basic epoxy resin component, which has the advantages of good mechanical properties, chemical resistance, and processing performance. Acting synergistically with the liquid crystal monomer, it can not only maintain the basic properties of the epoxy resin system but also further optimize the thermal conductivity and insulation properties of the material through compounding with the liquid crystal monomer.

[0045] According to an embodiment of the present application, the curing agent includes 4,4'-diaminodiphenyl sulfone. Thus, 4,4'-diaminodiphenyl sulfone is selected as the curing agent to further promote the crosslinking and curing of the epoxy resin.

[0046] According to an embodiment of the present application, based on the total mass of the liquid crystal monomer and the epoxy resin, the mass ratio of the liquid crystal monomer is 30% to 30%. Thus, the thermal conductivity and insulation performance of the material are further optimized.

[0047] According to an embodiment of the present application, the liquid crystal epoxy resin, by weight, comprises: 50 to 70 parts by weight of an epoxy resin, such as 50 parts, 51 parts, 52 parts, 53 parts, 55 parts, 60 parts, 70 parts, etc.; 30 to 50 parts by weight of a liquid crystal monomer, such as 30 parts, 31 parts, 32 parts, 33 parts, 34 parts, 35 parts, 40 parts, 50 parts, etc.; 80 to 90 parts by weight of a curing agent, such as 80 parts, 81 parts, 82 parts, 83 parts, 84 parts, 85 parts, 90 parts, etc.; the liquid crystal monomer includes the liquid crystal monomer described in the first aspect. Thus, the liquid crystal monomer can be uniformly dispersed in the epoxy resin system and form an ordered liquid crystal structure, thereby significantly improving the thermal conductivity of the material after curing. At the same time, due to the fluorine-containing characteristics of the liquid crystal monomer, the dielectric constant and dielectric loss of the system can be reduced, and the volume resistivity can be increased, realizing the synergistic improvement of thermal conductivity and insulation performance. The curing agent can promote the cross-linking and curing of the epoxy resin.

[0048] According to an embodiment of the present application, the raw materials of the liquid crystal epoxy resin further include: an accelerator and a diluent.

[0049] According to an embodiment of the present application, the raw materials of the liquid crystal epoxy resin include: 50 to 70 parts by weight of an epoxy resin; 30 to 50 parts by weight of a liquid crystal monomer; 80 to 90 parts by weight of a curing agent; 0.1 to 2 parts by weight of an accelerator; 2 to 8 parts by weight of a diluent.

[0050] According to an embodiment of the present application, the accelerator includes 2-methylimidazole; the diluent includes phenyl glycidyl ether. Thus, the accelerator 2-methylimidazole can accelerate the curing reaction, improve the efficiency and uniformity of the curing reaction; the diluent phenyl glycidyl ether can reduce the viscosity of the epoxy resin system, enable each component to be more uniformly mixed, improve the filling property and processability of the material, and at the same time also helps to reduce the defects and pores inside the material, further improving the thermal conductivity and insulation performance of the material.

[0051] Method for preparing liquid crystal epoxy resin

[0052] In the fourth aspect of the present application, a method for preparing the liquid crystal epoxy resin described in the third aspect is proposed, including: melting the liquid crystal monomer into a liquid state to obtain a liquid crystal monomer in a liquid state; stirring the liquid crystal monomer in a liquid state, an epoxy resin, and a curing agent to obtain a mixture; subjecting the mixture to a curing treatment to obtain a liquid crystal epoxy resin. Thus, by melting the liquid crystal monomer and uniformly mixing it with the epoxy resin and the curing agent, an ordered liquid crystal structure can be formed by the liquid crystal monomer during the curing process, thereby achieving an improvement in thermal conductivity and an optimization of insulation performance in the cured epoxy resin.

[0053] According to an embodiment of the present application, it further includes: subjecting the liquid crystal monomer in a liquid state, an epoxy resin, a curing agent, an accelerator, and a diluent to the stirring treatment. Thus, the thermal conductivity and insulation performance of the material are further improved.

[0054] According to an embodiment of the present application, the temperature of the stirring treatment is 90 to 100 °C, for example, it can be 90 °C, 91 °C, 92 °C, 93 °C, 94 °C, 95 °C, 100 °C, etc., and the time is 1 to 2 h, for example, it can be 1 h, 2 h, etc. Thus, by controlling the temperature and time of the stirring treatment, the liquid crystal monomer in a liquid state, the epoxy resin, and the curing agent can be fully mixed to form a uniform mixture.

[0055] According to an embodiment of the present application, the temperature of the curing treatment is 100 to 150 °C, for example, it can be 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, etc., and the time is 3 to 5 h, for example, it can be 3 h, 4 h, 5 h, etc. By controlling the temperature and time of the curing treatment, the mixture can be fully cured to form a liquid crystal epoxy resin with a three-dimensional network structure.

[0056] Use

[0057] In the fifth aspect of the present application, an application of the liquid crystal monomer described in the first aspect in improving the thermal conductivity and volume resistivity of an epoxy resin is proposed. Thus, the liquid crystal monomer and the liquid crystal epoxy resin of the present application have a broader application prospect in the fields of electronic packaging, insulating materials, etc.

[0058] The solution of the present application will be explained below in conjunction with embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For reagents or instruments not specified as to the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0059] Example 1

[0060] In this embodiment, 3,3',5,5'-tetramethylbiphenyl diglycidyl ether (BLCER) is used as the raw material, and fluorinated BLCER is prepared by subjecting BLCER to a substitution reaction, including 3,3',5,5'-tetrakis(trifluoromethyl)biphenyl diglycidyl ether. The reaction principle is as shown in Figure 1 and the specific steps are as follows:

[0061] 1. Heat the solid spherical powder BLCER to 100 °C until it melts into a liquid state; add 150 g of the melted BLCER, 2.5 g of BPO, and 0.1 g of triethanolamine to a 250 ml three-necked flask, mix well, and heat with an oil bath. Set the initial temperature to 100 °C; place a 500 W iodine tungsten lamp 35 cm away from the reaction flask, and introduce chlorine gas from the bottom of the reactor under light irradiation. Control the chlorine gas speed by observing the color depth of the gas in the reaction tube to make it light green under lamp irradiation. As the reaction progresses, slowly increase the temperature, but the reaction temperature at the end of the reaction should not exceed 150 °C. The reaction time is about 7 h; after the reaction is completed, wash with 10% sodium carbonate solution, then wash with water until neutral, dry with anhydrous calcium chloride to remove water, and perform vacuum distillation to collect the fraction at 130 °C to obtain chlorinated biphenyl liquid crystal.

[0062] 2. Add 150 g of chlorinated biphenyl liquid crystal and 20 g of HF to the reaction kettle; heat to 135 °C and react at a pressure of 1.7 MPa for 3 h. After the reaction is completed, wash with 10% sodium carbonate solution, then wash with water until neutral, dry with anhydrous calcium chloride to remove water, and perform vacuum distillation to collect the fraction at 121 °C to obtain 3,3',5,5'-tetrakis(trifluoromethyl)biphenyl diglycidyl ether (fluorinated BLCER).

[0063] Example 2

[0064] 1. Weigh 30 g of fluorinated BLCER, 70 g of epoxy resin (bisphenol A epoxy resin E-51), 85 g of curing agent (4,4'-diaminodiphenyl sulfone), 1 g of accelerator (2-methylimidazole), and 5 g of diluent (phenyl glycidyl ether).

[0065] 2. Heat the solid spherical powder of fluorinated BLCER to 180 °C until it melts into a liquid state. At the same time, add E-51 to another beaker, heat to 70 °C to reduce the viscosity, then pour the obtained liquid fluorinated BLCER into the beaker, heat to 100 °C and stir. Slowly add the curing agent DDS, 2-methylimidazole, and diluent, and stir well until the curing agent is completely melted and the blend is in a homogeneous state.

[0066] 3. Transfer the blend obtained in the previous step to a vacuum drying oven to remove bubbles for 20 min.

[0067] 4. Pour the degassed blend from the previous step into a preheated mold, transfer it to an oven, cure at 100 °C for 2 h + 150 °C for 2 h, cool to room temperature, demold to obtain the composite material( Figure 2 ).

[0068] Example 3:

[0069] It is different from Example 2 in that 50 g of fluorinated BLCER, 50 g of epoxy resin (bisphenol A epoxy resin E-51), 85 g of curing agent (4,4'-diaminodiphenyl sulfone), 1 g of accelerator (2-methylimidazole), and 5 g of diluent (phenyl glycidyl ether) are weighed.

[0070] Comparative Example 1

[0071] It is different from Example 2 in that 100 g of epoxy resin (bisphenol A epoxy resin E-51), 85 g of curing agent (4,4'-diaminodiphenyl sulfone), 1 g of accelerator (2-methylimidazole), and 5 g of diluent (phenyl glycidyl ether) are weighed.

[0072] Comparative Example 2

[0073] It is different from Example 2 in that 30 g of BLCER, 70 g of epoxy resin (bisphenol A epoxy resin E-51), 85 g of curing agent (4,4'-diaminodiphenyl sulfone), 1 g of accelerator (2-methylimidazole), and 5 g of diluent (phenyl glycidyl ether) are weighed.

[0074] Comparative Example 3

[0075] It is different from Example 3 in that 50 g of BLCER, 50 g of epoxy resin (bisphenol A epoxy resin E-51), 85 g of curing agent (4,4'-diaminodiphenyl sulfone), 1 g of accelerator (2-methylimidazole), and 5 g of diluent (phenyl glycidyl ether) are weighed.

[0076] Test Example

[0077] Perform performance tests on the composite materials prepared in Examples 2 and 3 and Comparative Examples 1-3 respectively. The specific tests are as follows:

[0078] 1. Thermal conductivity test: The thermal conductivity of the sample is tested by the plate method. The material to be tested is made into a flat plate, a stable temperature difference is applied on both sides of the flat plate, so that heat passes through the material stably, measure the heat flux passing through and the material thickness, etc., and then calculate the thermal conductivity using Fourier's law of heat conduction.

[0079] The test results of thermal conductivity are shown in Table 1. As the content of liquid crystal monomer increases, the thermal conductivity gradually rises. Moreover, the fluorinated liquid crystal monomer can further enhance the thermal conductivity. When 50% of the fluorinated liquid crystal monomer (calculated based on the total mass of the fluorinated liquid crystal monomer and epoxy resin) is added, the thermal conductivity is 0.392 W / (m·K), which is 2.24 times that of E-51 epoxy resin.

[0080] Table 1. Test Results of Thermal Conductivity

[0081] Sample Thermal Conductivity / W / (m·K) Example 2 0.287 Example 3 0.392 Comparative Example 1 0.175 Comparative Example 2 0.215 Comparative Example 3 0.237

[0082] 2. Volume Resistivity Test: The DC leakage current of the sample is measured by a three-electrode platform and an electrometer. The sample thickness is 2 mm, and the applied electric field is 2 kV / mm. During each measurement cycle, the stable leakage current is recorded and used to calculate the volume resistivity according to IEC standard 60093. The test results of volume resistivity are shown in Table 2. It can be found from Table 2 that as the content of liquid crystal monomer increases, the volume resistivity of the sample rises, indicating that the liquid crystal content plays a synergistic role in the thermal conductivity and insulation of the whole system. At the same time, the fluorinated liquid crystal monomer can further increase the volume resistivity of the system. When 50% of the fluorinated liquid crystal monomer is added, the volume resistivity increases by two orders of magnitude.

[0083] Table 2. Test Results of Volume Resistivity

[0084] Sample Volume Resistivity / Ω·m Example 2 <![CDATA[9.93×10 14 > Example 3 <![CDATA[7.53×10 15 > Comparative Example 1 <![CDATA[2.98×10 13 > Comparative Example 2 <![CDATA[7.09×10 13 > Comparative Example 3 <![CDATA[4.20×10 14 >

[0085] 3. Dielectric Property Test: The dielectric properties of the sample at power frequency are tested by a YG9187 full-automatic high-precision high-voltage dielectric loss analyzer (Yanggao Electric Appliance, China). The average thickness of the sample is 2 mm, and the applied electric field strength is 1 kV / mm. The measurement results of dielectric constant and dielectric loss are shown in Tables 3 and 4. It can be seen from the tables that adding ordinary liquid crystal monomer (BLCER) has little effect on the dielectric properties of the sample, while adding fluorinated liquid crystal monomer greatly improves the dielectric properties of the sample.

[0086] Table 3. Test Results of Dielectric Constant

[0087] Sample Dielectric Constant Example 2 3.19 Example 3 2.76 Comparative Example 1 3.59 Comparative Example 2 3.43 Comparative Example 3 3.34

[0088] Table 4. Test Results of Dielectric Loss

[0089] Sample Dielectric Loss Example 2 0.013 Example 3 0.009 Comparative Example 1 0.032 Comparative Example 2 0.031 Comparative Example 3 0.029

[0090] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of this application. In this specification, the schematic representations of the above terms are not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0091] Although the embodiments of this application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting this application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of this application.

Claims

1. A liquid crystal monomer, characterized in that, It has the structure shown in formula (Ⅰ):

2. A method for preparing the liquid crystal monomer according to claim 1, characterized in that, Including: Chlorinating 3,3',5,5'-tetramethylbiphenyl diglycidyl ether to obtain 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether; Fluorinating the 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether to obtain the liquid crystal monomer.

3. The method according to claim 2, wherein The chlorination treatment includes: Mixing 3,3',5,5'-tetramethylbiphenyl diglycidyl ether, benzoyl peroxide and triethanolamine, and performing heat treatment to obtain a first intermediate product; the mass ratio of 3,3',5,5'-tetramethylbiphenyl diglycidyl ether, benzoyl peroxide and triethanolamine is (1600 - 1400):(20 - 30):1; the temperature of the heat treatment is 90 - 110 °C; Contacting the first intermediate product with chlorine gas to obtain a second intermediate product; the contacting treatment is carried out under light conditions; the temperature of the contacting treatment is 100 - 300 °C, and the time is 5 - 8 h; Washing and drying the second intermediate product, performing a first vacuum distillation treatment, and collecting the fraction at 125 - 135 °C to obtain the 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether; Optionally, the fluorination treatment includes: Mixing the 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether with hydrofluoric acid to obtain a third intermediate product; the mass ratio of 3,3',5,5'-tetrakis(trichloromethyl)biphenyl diglycidyl ether to hydrofluoric acid is (7 - 8):1; the temperature of the mixing treatment is 130 - 140 °C, the pressure is 1.4 - 2 MPa, and the time is 2 - 3 h; Washing and drying the third intermediate product, performing a second vacuum distillation treatment, and collecting the fraction at 117 - 125 °C to obtain the 3,3',5,5'-tetrakis(trifluoromethyl)biphenyl diglycidyl ether.

4. A liquid crystal epoxy resin, characterized in that, The raw materials of the liquid crystal epoxy resin include the liquid crystal monomer, epoxy resin and curing agent as claimed in claim 1.

5. The liquid crystal epoxy resin according to claim 4, wherein The epoxy resin includes bisphenol A epoxy resin E-51; Optionally, the curing agent includes 4,4'-diaminodiphenyl sulfone; Optionally, based on the total mass of the liquid crystal monomer and epoxy resin, the mass proportion of the liquid crystal monomer is 30% - 30%; Optionally, the raw materials of the liquid crystal epoxy resin include: 50 - 70 parts by weight of epoxy resin; 30 - 50 parts by weight of liquid crystal monomer; 80 - 90 parts by weight of curing agent.

6. The liquid crystal epoxy resin according to claim 4, wherein The raw materials of the liquid crystal epoxy resin further include: accelerator and diluent; Optionally, the raw materials of the liquid crystal epoxy resin include: 50 - 70 parts by weight of epoxy resin; 30 - 50 parts by weight of liquid crystal monomer; 80 - 90 parts by weight of curing agent; 0.1 - 2 parts by weight of accelerator; 2 - 8 parts by weight of diluent; Optionally, the accelerator includes 2-methylimidazole; The diluent includes phenyl glycidyl ether.

7. A method for preparing the liquid crystal epoxy resin according to any one of claims 4 to 6, characterized in that, Including: Melting the liquid crystal monomer to a liquid state to obtain a liquid crystal monomer in liquid state; Stirring the liquid crystal monomer in liquid state, epoxy resin and curing agent to obtain a mixture; The mixture is subjected to a curing treatment to obtain a liquid crystal epoxy resin.

8. The method according to claim 7, wherein Further comprising: The liquid crystal monomer, epoxy resin, curing agent, accelerator and diluent are subjected to the stirring treatment.

9. The method according to claim 7 or 8, characterized in that The temperature of the stirring treatment is 90 - 100 °C, and the time is 1 - 2 h; Optionally, the temperature of the curing treatment is 100 - 150 °C, and the time is 3 - 5 h.

10. Use of the liquid crystal monomer according to claim 1 in improving the thermal conductivity and volume resistivity of an epoxy resin.

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