Preparation method of liquid crystal polymer and composition thereof, and application of liquid crystal polymer and composition thereof in electromagnetic shielding material

Abstract

The invention discloses a preparation method of a liquid crystal polymer and a composition thereof and application of the liquid crystal polymer and the composition in electromagnetic shielding materials, and relates to the technical field of organic polymer materials. The invention aims to solve the problem that the conventional electromagnetic shielding material cannot have high mechanical property, conductivity and processability at the same time. According to the invention, thiophene molecules are introduced into the molecular structure of the liquid crystal polymer, so that the liquid crystal polymer has a certain conductive characteristic, and a pi electron cloud in the thiophene molecules forms a conjugated system in the molecules, so that electrons can be freely transmitted in the molecules, thereby generating a semiconductor characteristic. And then the liquid crystal polymer with the conductive property is compounded with a certain amount of carbon fibers, so that the surface resistivity of the material is further reduced, the conductive performance is improved, and the good electromagnetic shielding effectiveness is further obtained. The invention can obtain the preparation method of the liquid crystal polymer and the composition thereof and the application of the liquid crystal polymer and the composition thereof in an electromagnetic shielding material.

Description

Technical Field

[0001] The present invention relates to the technical field of organic polymer materials, and particularly relates to a preparation method of a liquid crystal polymer and its composition and an application thereof in an electromagnetic shielding material. Background Art

[0002] With the popularization of various electronic devices, electromagnetic waves, as carriers of information transmission, are involved in all aspects of human life. While these electronic devices bring convenience and speed to us, they also bring many negative problems, such as electromagnetic interference, electromagnetic leakage, and electromagnetic pollution, which seriously affect people's normal work, information security, and health safety. In order to avoid the negative impacts brought by electromagnetic waves, exploring efficient electromagnetic shielding materials has become an urgent problem that people need to solve currently.

[0003] Currently, there are mainly the following four types of shielding materials: (1) polymer-based electromagnetic shielding composites; (2) surface coating type shielding materials; (3) fiber composites; (4) foamed metals. High-conductivity metal materials are the preferred materials, but due to their high density, easy corrosion, and difficult processing, the application of metals in the field of electromagnetic shielding is restricted. In contrast, polymer electromagnetic shielding composites are composed of a polymer matrix and conductive fillers, and have excellent electrical conductivity, corrosion resistance, low density, high specific surface area, as well as excellent chemical stability, thermal stability, and easy processing, etc. They overcome the disadvantages of metal materials and can better meet the requirements of fields such as aerospace and electronic communication, showing great advantages in the field of electromagnetic shielding.

[0004] With the increase of conductive fillers in polymer-based electromagnetic shielding composites, the electrical conductivity of the polymer shows a certain trend, that is, when the filler increases to the percolation threshold, there will be a mutation of several orders of magnitude. At this time, the conductive fillers can form an effective conductive network in the matrix, greatly improving the electrical conductivity of the matrix. Carbon fiber is prepared by high-temperature carbonization of organic fibers in an inert gas, and has excellent electrical conductivity, thermal conductivity, and electromagnetic shielding performance, etc. At the same time, it has a large aspect ratio, and under appropriate dosage and process conditions, it has a bridging effect in the polymer matrix, enabling the polymer to obtain better electrical conductivity and mechanical properties. Therefore, it is widely used as a conductive filler for electromagnetic shielding materials. However, carbon fiber has the problem of poor compatibility with polymer materials, and often more carbon fiber needs to be added to achieve the required electrical conductivity, while the addition of too much carbon fiber will affect the mechanical properties of the material. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of a liquid crystal polymer and its composition and an application thereof in an electromagnetic shielding material to solve the problem that conventional electromagnetic shielding materials cannot have both high mechanical properties, electrical conductivity, and processing performance.

[0006] A preparation method of a liquid crystal polymer is carried out according to the following steps:

[0007] Step S1, preparing a reaction mixture:

[0008] Mix p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, hydroquinone, an acylating agent and a catalyst to obtain a reaction mixture;

[0009] The molar ratio of the p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid to hydroquinone is (66-80):(10-17):(10-17);

[0010] Step S2, preparing a prepolymer:

[0011] Place the reaction mixture obtained in step S1 in a reaction kettle, heat it up to 120-130 °C, and keep it warm at 120-130 °C for 3-5 h; continue to heat it up to 260-280 °C, and keep it warm at 260-280 °C for 2 h; continue to heat it up to 300-320 °C, and keep it warm at 300-320 °C for 2 h; continue to heat it up to 330-350 °C, and keep it warm at 330-350 °C for 2 h; after the heat preservation is completed, under a nitrogen atmosphere, crush and dry it to obtain a prepolymer;

[0012] Step S3, preparing a liquid crystal polymer:

[0013] Under an inert gas atmosphere, place the prepolymer obtained in step S2 in a rotary kiln, and react it at 280-320 °C for 12-48 h to obtain a liquid crystal polymer.

[0014] A preparation method of a liquid crystal polymer composition is carried out according to the following steps:

[0015] Mix 100 parts of a liquid crystal polymer, 20-50 parts of carbon fiber, 0-10 parts of graphite, 0-5 parts of wollastonite and 0-10 parts of carbon nanotubes by weight, then add them to a screw extruder, melt, extrude and granulate to obtain a liquid crystal polymer composition.

[0016] An application of a liquid crystal polymer composition, the application of the liquid crystal polymer composition in preparing an electromagnetic shielding material.

[0017] Advantages of the present invention:

[0018] (1) By introducing thiophene molecules into the molecular structure of the liquid crystal polymer, the liquid crystal polymer has certain conductive properties. This is mainly because the π-electron cloud in the thiophene molecule forms a conjugated system within the molecule, enabling electrons to freely transport within the molecule, thereby generating semiconductor properties. Then, the liquid crystal polymer with conductive properties is compounded with a certain amount of carbon fiber to further reduce the surface resistivity of the material, improve the conductive performance, and thus obtain good electromagnetic shielding effectiveness.

[0019] (2) The liquid crystal polymer of the present invention is polymerized from specific monomers and then compounded with a specific content of carbon fiber. In addition to having good conductive properties, it also has good mechanical properties and processability.

[0020] The present invention can obtain a preparation method of a liquid crystal polymer and its composition and an application in electromagnetic shielding materials. Specific embodiments

[0021] Specific embodiment 1: A preparation method of a liquid crystal polymer in this embodiment is carried out according to the following steps:

[0022] Step S1, preparing a reaction mixture:

[0023] Mix p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, hydroquinone, an acylating agent, and a catalyst to obtain a reaction mixture;

[0024] The molar ratio of the p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid to hydroquinone is (66 - 80):(10 - 17):(10 - 17);

[0025] Step S2, preparing a prepolymer:

[0026] Place the reaction mixture obtained in step S1 in a reaction kettle, heat it to 120 - 130 °C, and keep it warm at 120 - 130 °C for 3 - 5 h; continue to heat it to 260 - 280 °C, and keep it warm at 260 - 280 °C for 2 h; continue to heat it to 300 - 320 °C, and keep it warm at 300 - 320 °C for 2 h; continue to heat it to 330 - 350 °C, and keep it warm at 330 - 350 °C for 2 h; after the heat preservation is completed, pulverize and dry it under a nitrogen atmosphere to obtain a prepolymer;

[0027] Step S3, preparing a liquid crystal polymer:

[0028] Under an inert gas atmosphere, place the prepolymer obtained in step S2 in a rotary kiln and react it at 280 - 320 °C for 12 - 48 h to obtain a liquid crystal polymer.

[0029] Embodiment 2: The difference between this embodiment and Embodiment 1 is that: in step S1, the molar ratio of the thiophene[2,3-b]thiophene-2,5-dicarboxylic acid to hydroquinone is 1:1.

[0030] Other steps are the same as those in Embodiment 1.

[0031] Embodiment 3: The difference between this embodiment and Embodiment 1 or 2 is that: in step S1, the acylating agent is one or more of acetic anhydride, propionic anhydride and maleic anhydride, and the addition amount of the acylating agent is 1.0 - 1.1 times the total molar amount of hydroxyl groups in the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid and hydroquinone.

[0032] Other steps are the same as those in Embodiment 1 or 2.

[0033] Embodiment 4: The difference between this embodiment and any one of Embodiments 1 to 3 is that: in step S1, the catalyst is potassium acetate, and the addition amount is 0.012 - 0.02% of the total mass of the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid and hydroquinone.

[0034] Other steps are the same as those in Embodiments 1 to 3.

[0035] Embodiment 5: The difference between this embodiment and any one of Embodiments 1 to 4 is that: in step S2, the temperature is raised to 260 - 280°C at a rate of 1 - 5°C / min; the temperature is raised to 300 - 320°C at a rate of 1 - 3°C / min; the temperature is raised to 330 - 350°C at a rate of 1 - 5°C / min.

[0036] Other steps are the same as those in Embodiments 1 to 4.

[0037] Embodiment 6: The difference between this embodiment and any one of Embodiments 1 to 5 is that: in step S2, the pressure of nitrogen is 0.5 - 1.0 MPa.

[0038] Other steps are the same as those in Embodiments 1 to 5.

[0039] Embodiment 7: The difference between this embodiment and any one of Embodiments 1 to 6 is that: in step S2, the drying is carried out at 100 - 130°C for 1 - 4 h.

[0040] Other steps are the same as those in Embodiments 1 to 6.

[0041] Embodiment 8: A method for preparing a liquid crystal polymer composition is carried out according to the following steps:

[0042] Mix 100 parts of liquid crystal polymer, 20 - 50 parts of carbon fiber, 0 - 10 parts of graphite, 0 - 5 parts of wollastonite, and 0 - 10 parts of carbon nanotubes by weight, then add them to a screw extruder for melting, extrusion, and pelletizing to obtain a liquid crystal polymer composition.

[0043] Specific Embodiment Nine: The difference between this embodiment and Specific Embodiment Eight is:

[0044] Other steps are the same as those in Specific Embodiment Eight.

[0045] Specific Embodiment Ten: The application of a liquid crystal polymer composition, which is the application of the liquid crystal polymer composition in preparing an electromagnetic shielding material.

[0046] The following examples are used to verify the beneficial effects of the present invention:

[0047] Table 1 shows the monomer ratios in Examples 1 - 5;

[0048] Table 1

[0049] p-Hydroxybenzoic acid Thieno[2,3-b]thiophene-2,5-dicarboxylic acid Hydroquinone 1# 66 17 17 2# 70 15 15 3# 73 13.5 13.5 4# 76 12 12 5# 80 10 10

[0050] Example 1: A preparation method of a liquid crystal polymer composition is carried out according to the following steps:

[0051] Step S1: Prepare a reaction mixture:

[0052] Mix p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, hydroquinone, an acylating agent acetic anhydride, and a catalyst potassium acetate according to the 1# formula to obtain a reaction mixture;

[0053] The molar ratio of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid to hydroquinone is 66:17:17;

[0054] The addition amount of the acylating agent acetic anhydride is 1.0 times the total molar number of hydroxyl groups in the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, and hydroquinone; the addition amount of the catalyst potassium acetate is 0.012% of the total mass of the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, and hydroquinone;

[0055] Step S2: Prepare a prepolymer:

[0056] Place the reaction mixture in a reaction kettle, heat it up to 120 °C, and keep it at 120 °C for 4 h; continue to heat it up to 280 °C at a rate of 3 °C / min, and keep it at 280 °C for 2 h; continue to heat it up to 300 °C at a rate of 3 °C / min, and keep it at 300 °C for 2 h; continue to heat it up to 320 °C at a rate of 3 °C / min, and keep it at 320 °C for 2 h; continue to heat it up to 350 °C at a rate of 3 °C / min, and keep it at 350 °C for 2 h; after the heat preservation is completed, introduce 1.0 MPa of nitrogen into the reaction kettle, discharge the reactants through the discharging valve, pulverize them, and dry them at 110 °C for 3 h to obtain a prepolymer;

[0057] Step S3, prepare a liquid crystal polymer:

[0058] Under an inert gas atmosphere, place the prepolymer in a rotary kiln and carry out solid-phase polycondensation reaction at 280 °C for 48 h to obtain a liquid crystal polymer;

[0059] Step S4, prepare a liquid crystal polymer composition:

[0060] Mix 100 parts by weight of the liquid crystal polymer and 20 parts of carbon fibers with a length of 4 - 10 mm and a diameter of 5 - 8 μm, then add them to a screw extruder, melt them, extrude them at 300 °C, and finally granulate them to obtain a liquid crystal polymer composition; after measurement, the melt index of this liquid crystal polymer composition is 54 cm 3 / 10 min.

[0061] Example 2: A preparation method of a liquid crystal polymer composition is carried out according to the following steps:

[0062] Step S1, prepare a reaction mixture:

[0063] Mix p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, hydroquinone, an acylating agent acetic anhydride and a catalyst potassium acetate according to the 2# formula to obtain a reaction mixture;

[0064] The molar ratio of the p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid to hydroquinone is 70:15:15;

[0065] The addition amount of the acylating agent acetic anhydride is 1.02 times the total molar number of hydroxyl groups in the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid and hydroquinone; the addition amount of the catalyst potassium acetate is 0.015% of the total mass of the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid and hydroquinone;

[0066] Step S2, prepare a prepolymer:

[0067] Place the reaction mixture in a reaction kettle, heat it up to 130 °C, and keep it at 130 °C for 4 h; continue to heat it up to 280 °C at a rate of 3 °C / min, and keep it at 280 °C for 2 h; continue to heat it up to 300 °C at a rate of 3 °C / min, and keep it at 300 °C for 2 h; continue to heat it up to 320 °C at a rate of 3 °C / min, and keep it at 320 °C for 2 h; continue to heat it up to 350 °C at a rate of 3 °C / min, and keep it at 350 °C for 2 h; after the heat preservation is over, introduce 1.0 MPa of nitrogen into the reaction kettle, discharge the reactants through the discharging valve, crush them, and dry them at 120 °C for 2 h to obtain a prepolymer;

[0068] Step S3: Prepare a liquid crystal polymer:

[0069] Under an inert gas atmosphere, place the prepolymer in a rotary kiln and carry out solid-phase polycondensation reaction at 290 °C for 36 h to obtain a liquid crystal polymer;

[0070] Step S4: Prepare a liquid crystal polymer composition:

[0071] Mix 100 parts by weight of the liquid crystal polymer and 30 parts of carbon fibers with a length of 4 - 10 mm and a diameter of 5 - 8 μm, then add them to a screw extruder, melt them, extrude them at 320 °C, and finally pelletize them to obtain a liquid crystal polymer composition; it is measured that the melt index of this liquid crystal polymer composition is 58 cm 3 / 10 min.

[0072] Example 3: A method for preparing a liquid crystal polymer composition is carried out according to the following steps:

[0073] Step S1: Prepare a reaction mixture:

[0074] Mix p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, hydroquinone, an acylating agent acetic anhydride, and a catalyst potassium acetate according to Formula 3# to obtain a reaction mixture;

[0075] The molar ratio of the p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid to hydroquinone is 73:13.5:13.5;

[0076] The addition amount of the acylating agent acetic anhydride is 1.05 times the total molar number of hydroxyl groups in the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, and hydroquinone; the addition amount of the catalyst potassium acetate is 0.016% of the total mass of the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, and hydroquinone;

[0077] Step S2: Prepare a prepolymer:

[0078] Place the reaction mixture in a reaction kettle, heat it up to 120 °C, and keep it at 120 °C for 4 h; continue to heat it up to 280 °C at a rate of 3 °C / min and keep it at 280 °C for 2 h; continue to heat it up to 300 °C at a rate of 3 °C / min and keep it at 300 °C for 2 h; continue to heat it up to 320 °C at a rate of 3 °C / min and keep it at 320 °C for 2 h; continue to heat it up to 350 °C at a rate of 3 °C / min and keep it at 350 °C for 2 h; after the heat preservation is over, introduce 1.0 MPa of nitrogen into the reaction kettle, discharge the reactants through the discharging valve, crush them, and dry them at 110 °C for 3 h to obtain a prepolymer;

[0079] Step S3: Prepare a liquid crystal polymer:

[0080] Under an inert gas atmosphere, place the prepolymer in a rotary kiln and carry out solid-phase polycondensation reaction at 300 °C for 30 h to obtain a liquid crystal polymer;

[0081] Step S4: Prepare a liquid crystal polymer composition:

[0082] Mix 100 parts by weight of the liquid crystal polymer and 35 parts of carbon fibers with a length of 4 - 10 mm and a diameter of 5 - 8 μm, then add them to a screw extruder, melt them, extrude them at 330 °C, and finally granulate them to obtain a liquid crystal polymer composition; it is measured that the melt index of this liquid crystal polymer composition is 53 cm 3 / 10 min.

[0083] Example 4: A preparation method of a liquid crystal polymer composition is carried out according to the following steps:

[0084] Step S1: Prepare a reaction mixture:

[0085] Mix p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, hydroquinone, an acylating agent acetic anhydride and a catalyst potassium acetate according to the 4# formula to obtain a reaction mixture;

[0086] The molar ratio of the p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid to hydroquinone is 76:12:12;

[0087] The addition amount of the acylating agent acetic anhydride is 1.08 times the total molar amount of hydroxyl groups in the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid and hydroquinone; the addition amount of the catalyst potassium acetate is 0.018% of the total mass of the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid and hydroquinone;

[0088] Step S2: Prepare a prepolymer:

[0089] Place the reaction mixture in a reaction kettle, heat it up to 120 °C, and keep it at 120 °C for 4 h; continue to heat it up to 280 °C at a rate of 3 °C / min, and keep it at 280 °C for 2 h; continue to heat it up to 300 °C at a rate of 3 °C / min, and keep it at 300 °C for 2 h; continue to heat it up to 320 °C at a rate of 3 °C / min, and keep it at 320 °C for 2 h; continue to heat it up to 350 °C at a rate of 3 °C / min, and keep it at 350 °C for 2 h; after the heat preservation is over, introduce 1.0 MPa of nitrogen into the reaction kettle, discharge the reactants through the discharging valve, pulverize them, and dry them at 110 °C for 3 h to obtain a prepolymer;

[0090] Step S3: Prepare a liquid crystal polymer:

[0091] Under an inert gas atmosphere, place the prepolymer in a rotary kiln and carry out solid-phase polycondensation reaction at 310 °C for 24 h to obtain a liquid crystal polymer;

[0092] Step S4: Prepare a liquid crystal polymer composition:

[0093] Mix 100 parts by weight of the liquid crystal polymer and 40 parts of carbon fibers with a length of 4 - 10 mm and a diameter of 5 - 8 μm, then add them to a screw extruder, melt them, extrude them at 350 °C, and finally granulate them to obtain a liquid crystal polymer composition; it is measured that the melt index of this liquid crystal polymer composition is 61 cm 3 / 10 min.

[0094] Example 5: A method for preparing a liquid crystal polymer composition is carried out according to the following steps:

[0095] Step S1: Prepare a reaction mixture:

[0096] Mix p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, hydroquinone, an acylating agent acetic anhydride, and a catalyst potassium acetate according to the 5# formula to obtain a reaction mixture;

[0097] The molar ratio of the p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid to hydroquinone is 80:10:10;

[0098] The addition amount of the acylating agent acetic anhydride is 1.1 times the total molar number of hydroxyl groups in the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, and hydroquinone; the addition amount of the catalyst potassium acetate is 0.020% of the total mass of the three raw materials of p-hydroxybenzoic acid, thiophene[2,3-b]thiophene-2,5-dicarboxylic acid, and hydroquinone;

[0099] Step S2: Prepare a prepolymer:

[0100] Place the reaction mixture in a reaction kettle, heat it up to 120 °C, and keep it at 120 °C for 4 h; continue to heat it up to 280 °C at a rate of 3 °C / min, and keep it at 280 °C for 2 h; continue to heat it up to 300 °C at a rate of 3 °C / min, and keep it at 300 °C for 2 h; continue to heat it up to 320 °C at a rate of 3 °C / min, and keep it at 320 °C for 2 h; continue to heat it up to 350 °C at a rate of 3 °C / min, and keep it at 350 °C for 2 h; after the heat preservation is completed, introduce nitrogen gas at 1.0 MPa into the reaction kettle, discharge the reactants through the discharge valve, pulverize them, and dry them at 120 °C for 2 h to obtain a prepolymer;

[0101] Step S3: Prepare a liquid crystal polymer:

[0102] Under an inert gas atmosphere, place the prepolymer in a rotary kiln and carry out solid-phase polycondensation reaction at 320 °C for 12 h to obtain a liquid crystal polymer;

[0103] Step S4: Prepare a liquid crystal polymer composition:

[0104] Mix 100 parts of the liquid crystal polymer and 50 parts of carbon fibers with a length of 4 - 10 mm and a diameter of 5 - 8 μm by weight, then add them to a screw extruder, melt them, extrude them at 370 °C, and finally granulate them to obtain a liquid crystal polymer composition; after measurement, the melt index of this liquid crystal polymer composition is 64 cm 3 / 10 min.

[0105] Comparative Example 1:

[0106] The difference from Example 3 is that thiophene[2,3-b]thiophene-2,5-dicarboxylic acid is replaced with an equimolar amount of terephthalic acid, and the melt index of the prepared liquid crystal polymer composition is measured to be 59 cm 3 / 10 min. Other experimental conditions are the same as those in Example 3.

[0107] Comparative Example 2:

[0108] The difference from Example 3 is that thiophene[2,3-b]thiophene-2,5-dicarboxylic acid is replaced with an equimolar amount of biphenol, and the melt index of the prepared liquid crystal polymer composition is measured to be 46 cm 3 / 10 min. Other experimental conditions are the same as those in Example 3.

[0109] Comparative Example 3:

[0110] The difference from Example 3 is that no carbon fiber is added to this liquid crystal polymer composition, and the melt index of the prepared liquid crystal polymer composition is measured to be 52 cm 3 / 10 min. Other experimental conditions are the same as those in Example 3.

[0111] Comparative Example 4:

[0112] It is different from Example 3 in that 10 parts by weight of carbon fiber is added to the liquid crystal polymer composition, and the melt index of the prepared liquid crystal polymer composition is measured to be 57 cm 3 / 10 min. All other experimental conditions are the same as those in Example 3.

[0113] Comparative Example 5:

[0114] It is different from Example 3 in that 50 parts by weight of carbon fiber is added to the liquid crystal polymer composition, and the melt index of the prepared liquid crystal polymer composition is measured to be 43 cm 3 / 10 min.

[0115] The following are the relevant performance tests for the above Examples 1-5 and Comparative Examples 1-5. The specific test items and test methods are as follows:

[0116] (1) Tensile strength: According to the standard ISO 527-1 / -2, the liquid crystal polymer composition is injection molded into a specimen. After the specimen is conditioned in an environment of 23°C and 50% relative humidity (RH) for 24 h, the tensile strength is tested at a speed of 10 mm / min;

[0117] (2) The flexural modulus is determined according to the standard method of ISO 178;

[0118] (3) Surface resistivity: It is determined according to the method of IEC 60093;

[0119] (4) Processability: It is determined according to the standard of GB / T 3682.2. It is judged by the melt index data of the liquid crystal polymer composition. When the melt index is between 50 and 70 cm 3 / 10 min, the viscosity of the liquid crystal polymer composition is moderate, and the injection molding and extrusion are smooth, then the processability is judged to be OK; when the melt index is lower than 50 cm 3 / 10 min, the viscosity of the liquid crystal polymer composition is too large, and it is not easy to extrude during the injection molding process, then the processability is judged to be NG.

[0120] The performance parameters of the liquid crystal polymer compositions in Examples 1-5 and Comparative Examples 1-5 are shown in Table 2.

[0121] Table 2

[0122]

[0123] As can be seen from Table 2, the liquid crystal polymer composition obtained by adopting the technical scheme of the present invention not only has good electrical conductivity, but also has good mechanical properties and processability.

[0124] From the test data of Comparative Example 1, Comparative Example 3 and Example 3, it can be seen that when the liquid crystal polymer monomer does not contain thiophene[2,3-b]thiophene-2,5-dicarboxylic acid or carbon fiber is not added to the composition, the overall conductivity of the liquid crystal polymer composition is poor and does not meet the requirements of the high-frequency and high-speed electronic connector for the shielding material (surface resistivity < 10 4 Ohm). In Example 3, by introducing thiophene molecules into the molecular structure of the liquid crystal polymer, the liquid crystal polymer has certain conductive properties. This is mainly because the π electron cloud in the thiophene molecule forms a conjugated system within the molecule, enabling electrons to freely transport within the molecule, thereby generating semiconductor properties. Then, the liquid crystal polymer with conductive properties is compounded with a certain amount of carbon fiber to further reduce the surface resistivity of the material and improve the conductive performance, and thus obtain good electromagnetic shielding effectiveness.

[0125] From the test data of Comparative Example 1, Comparative Example 2 and Example 3, it can be seen that when adjusting the composition of the liquid crystal polymer monomer, it will affect the final performance of the composition, resulting in the material being unable to balance conductivity, mechanical properties and processability at the same time.

[0126] From the test data of Comparative Example 3, Comparative Example 4 and Comparative Example 5 and Example 3, it can be seen that not adding or adding too little carbon fiber will affect the conductivity of the composition. As the addition amount increases and reaches the percolation threshold, continuing to add in excess will not only not increase the conductivity but will instead cause a decrease in the mechanical properties of the composition. Therefore, it is crucial to strictly control the addition amount of carbon fiber in the composition.

[0127] Referring to the GJ6190-2008 standard, the electromagnetic shielding effectiveness of the liquid crystal polymer compositions in Examples 1-5 of the present invention was tested by the coaxial transmission line method in the frequency range of 30 MHz to 1.5 GHz, and its shielding effectiveness is above 30 dB, fully meeting the use requirements of the new generation of high-frequency and high-speed electronic connectors.

Claims

1. A method for preparing a liquid crystal polymer, characterized in that The preparation method is carried out according to the following steps: Step S1, preparing a reaction mixture: mixing p-hydroxybenzoic acid, thieno[2,3-b]thiophene-2,5-dicarboxylic acid, hydroquinone, an acylating agent and a catalyst to obtain a reaction mixture; The molar ratio of p-hydroxybenzoic acid, thieno[2,3-b]thiophene-2,5-dicarboxylic acid and hydroquinone is (66-80):(10-17):(10-17); Step S2, preparing prepolymer: The reaction mixture obtained in step S1 is placed in a reaction kettle, heated to 120-130°C, and kept at 120-130°C for 3-5 hours; further heated to 260-280°C, and kept at 260-280°C for 2 hours; further heated to 300-320°C, and kept at 300-320°C for 2 hours; further heated to 330-350°C, and kept at 330-350°C for 2 hours; after the insulation is completed, crush and dry in a nitrogen atmosphere to obtain a prepolymer; Step S3, preparing liquid crystal polymer: Under an inert gas atmosphere, the prepolymer obtained in step S2 is placed in a rotary kiln and reacted at 280 to 320° C. for 12 to 48 hours to obtain a liquid crystal polymer.

2. The method for preparing a liquid crystal polymer according to claim 1, characterized in that The molar ratio of thieno[2,3-b]thiophene-2,5-dicarboxylic acid to hydroquinone in step S1 is 1:

1.

3. The method for preparing a liquid crystal polymer according to claim 1, characterized in that The acylating agent described in step S1 is one or more of acetic anhydride, propionic anhydride and maleic anhydride, and the added amount of the acylating agent is 1.0 to 1.1 times the total molar number of hydroxyl groups in the three raw materials of p-hydroxybenzoic acid, thieno[2,3-b]thiophene-2,5-dicarboxylic acid and hydroquinone.

4. The method for preparing a liquid crystal polymer according to claim 1, characterized in that The catalyst in step S1 is potassium acetate, and the added amount is 0.012-0.02% of the total mass of the three raw materials of p-hydroxybenzoic acid, thieno[2,3-b]thiophene-2,5-dicarboxylic acid and hydroquinone.

5. The method for preparing a liquid crystal polymer according to claim 1, characterized in that In step S2, the temperature is increased to 260-280°C at a rate of 1-5°C / min; the temperature is increased to 300-320°C at a rate of 1-3°C / min; the temperature is increased to 330-350°C at a rate of 1-5°C / min.

6. The method for preparing a liquid crystal polymer according to claim 1, characterized in that The pressure of nitrogen in step S2 is 0.5-1.0 MPa.

7. The method for preparing a liquid crystal polymer according to claim 1, characterized in that The drying in step S2 is carried out at 100-130° C. for 1-4 hours.

8. A method for preparing a liquid crystal polymer composition, characterized in that The preparation method is carried out according to the following steps: 100 parts of liquid crystal polymer, 20-50 parts of carbon fiber, 0-10 parts of graphite, 0-5 parts of wollastonite and 0-10 parts of carbon nanotubes are mixed by weight, then added into a screw extruder, melted, extruded and granulated to obtain a liquid crystal polymer composition.

9. The method for preparing a liquid crystal polymer according to claim 8, characterized in that The length of the carbon fiber is 4-10 mm, the diameter is 5-8 μm, and the extrusion temperature is 300-370°C.

10. Use of a liquid crystal polymer composition prepared by the method according to any one of claims 8 to 9, characterized in that The application of the liquid crystal polymer composition in the preparation of electromagnetic shielding materials.

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