Liquid crystal polymer and preparation method and application thereof

Abstract

The application discloses a liquid crystal polymer and a preparation method and application thereof, and the liquid crystal polymer is a copolymer of a monomer containing a naphthalene ring structure, a fluorine-containing monomer and a liquid crystal monomer, and the liquid crystal polymer comprises the following structure: wherein A is selected from one or more of -O-, -NH-, -CO-, B is selected from one or two of -COO-, -CONH-, and C is selected from one or more of -H, -F, -CF3, wherein at least one C is -F or -CF3. The application simultaneously introduces the naphthalene ring structure and the fluorine-containing unit into the liquid crystal polymer, so that the liquid crystal polymer has extremely low and stable dielectric constant and dielectric loss at high frequency, excellent heat resistance, mechanical property and dimensional stability, extremely low moisture absorption and good processing performance, and can be widely applied in the field of 5G.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of liquid crystal polymer materials, in particular to a liquid crystal polymer and a preparation method and application thereof. BACKGROUND

[0002] 5G technology, that is, the fifth generation communication technology, includes a medium frequency band of 450MHz-6000MHz and a high frequency band (millimeter wave band) of 24250MHz-52600MHz. The signal transmission speed and signal transmission attenuation are related to the dielectric constant and dielectric loss of the base material: the lower the dielectric constant of the material, the faster the signal transmission speed; the smaller the dielectric constant and dielectric loss of the base material, the smaller the signal transmission loss. In the high frequency transmission scene, in order to ensure the high speed of signal transmission and the minimization of signal delay, crosstalk and loss, the dielectric material should have the characteristics of low dielectric constant and low dielectric loss. The traditional base material polyimide (PI) has excellent thermal performance, chemical stability and good mechanical properties, and is the most commonly used dielectric material for PCB, FPC, thin film antenna and other products. However, the dielectric constant and dielectric loss of PI are relatively high, especially the high frequency (>10GHz) transmission loss is large, and the hygroscopicity is high, which has been unable to adapt to the development trend of 5G high frequency and high speed. Polytetrafluoroethylene (PTFE) is currently the lowest dielectric constant non-porous material, and has good temperature and frequency stability of dielectric properties. However, the flexible main chain structure of PTFE limits its thermodynamic properties, and the PTFE film has low yield stress and elastic modulus, high thermal expansion coefficient (>100ppm / ℃), poor creep resistance, which makes the PTFE film difficult to form and subsequent processing, and limits its in-depth application in the microelectronic field.

[0003] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0004] In view of the above shortcomings of the prior art, the purpose of the present application is to provide a liquid crystal polymer and a preparation method and application thereof, aiming at solving the problems of poor high frequency dielectric performance, poor hygroscopicity and poor dimensional stability of PTFE material of conventional dielectric materials such as polyimide in the current 5G scene.

[0005] The technical scheme adopted by the present application to solve the above technical problems is as follows:

[0006] A liquid crystal polymer, wherein the liquid crystal polymer is a copolymer of a monomer containing a naphthalene ring structure, a fluorine-containing monomer and a liquid crystal monomer, and the liquid crystal polymer comprises the following structure:

[0007]

[0008] Wherein, A is selected from one or more of -O-, -NH-, -CO-, B is selected from one or both of -COO-, -CONH-, C is selected from one or more of -H, -F, -CF3, wherein at least one C is -F or -CF3.

[0009] The liquid crystal polymer, wherein the monomer containing naphthalene ring structure is selected from one or more of 6-hydroxy-2-naphthoic acid, 4-hydroxynaphthalene-2-carboxylic acid, 5-aminonaphthalene-1-carboxylic acid, 1,3-naphthalenediol, 1,5-naphthalenediamine, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, naphthalene-2,6-diamine, 1,8-diaminonaphthalene, 2,7-diaminonaphthalene, dibromonaphthalene, 5-bromonaphthalene-1-amine, 6-bromo-2-naphthol, 2-chloro-6-hydroxynaphthalene, 2-bromo-7-hydroxynaphthalene, 1,8-naphthalene dicarboxylic anhydride, 2,6-dihydroxymethylnaphthalene, 3-bromonaphthalene-2,7-diol, 6-bromonaphthalene-1,2-diamine, 1,4,5,8-naphthalenetetracarboxylic acid.

[0010] The liquid crystal polymer, wherein the fluorine-containing monomer includes one or both of a monomer containing a trifluoromethyl structure and a monomer containing a symmetric fluorine-substituted structure.

[0011] The liquid crystal polymer, wherein the monomer containing a trifluoromethyl structure is selected from one or more of 4-hydroxy-3-trifluoromethylbenzoic acid, 2-hydroxy-5-trifluoromethylbenzoic acid, 3-hydroxy-4-trifluoromethylbenzoic acid, 3-hydroxy-5-(trifluoromethyl)benzoic acid, 4-hydroxy-2-trifluoromethylbenzoic acid, 4-amino-3-trifluoromethylbenzoic acid, 4-amino-2-(trifluoromethyl)benzoic acid, 4-hydroxy-3-trifluoromethylbenzoic acid, 3-amino-4-trifluoromethylbenzoic acid, 2-amino-4-trifluoromethylphenol, 4-amino-3-trifluoromethylphenol.

[0012] The liquid crystal polymer, wherein the monomer containing a symmetric fluorine-substituted structure is selected from one or more of 2,3,5,6-tetrafluorohydroquinone, tetrafluoroterephthalic acid, tetrafluoroterephthalyl alcohol, 3,4,5,6-tetrafluorobenzene-1,2-diamine, 4-amino-2,3-difluorophenol.

[0013] The liquid crystal polymer, wherein the liquid crystal monomer is selected from one or more of p-hydroxybenzoic acid, isophthalic acid, hydroquinone, and terephthalic acid.

[0014] A method for preparing a liquid crystal polymer as described in the preceding paragraphs of the present application, comprising the steps of:

[0015] providing a monomer containing a naphthalene ring structure, a fluorine-containing monomer, and a liquid crystal monomer;

[0016] The monomer containing naphthalene ring structure, the fluorine-containing monomer and the liquid crystal monomer are mixed with acetic anhydride to obtain a mixed raw material;

[0017] The mixed raw material is heated to a first preset temperature and reacted for a first preset time, and then heated to a second preset temperature at a preset heating rate and reacted for a second preset time to obtain the liquid crystal polymer.

[0018] The preparation method, wherein the molar ratio of the monomer containing naphthalene ring structure, the fluorine-containing monomer and the liquid crystal monomer is (1-4) : (1-3) : (0-8).

[0019] The preparation method, wherein the first preset temperature is 120-220 DEG C, the first preset time is 1-4 h, the preset heating rate is 0.5-5 DEG C / min, and the second preset temperature is 270-350 DEG C; and the second preset time is 0.5 h-12 h.

[0020] The application of the liquid crystal polymer in the preparation of dielectric materials.

[0021] Advantages: The application discloses a liquid crystal polymer, a preparation method and application thereof, the naphthalene ring structure and the fluorine-containing unit are simultaneously introduced into the liquid crystal polymer, so that the liquid crystal polymer has extremely low and stable dielectric constant and dielectric loss at high frequency, excellent heat resistance, mechanical property, size stability, extremely low moisture absorption and good processing performance, and can be widely applied in the field of 5G; the charge density of the naphthalene ring structure is larger than that of the benzene ring structure, and the molecular accumulation is more compact; meanwhile, the width and length of the liquid crystal polymer synthesized by replacing the benzene ring structure with the naphthalene ring structure are changed, so that the liquid crystal polymer containing the naphthalene ring structure has a wider liquid crystal phase temperature and a wider processing temperature window, and has more excellent comprehensive performance; the fluorine atom has strong electronegativity and can fix electrons well; the trifluoromethyl group can reduce the regularity of the high molecular chain, so that the high molecular chain is not compact, the intermolecular gap is increased, and the dielectric constant of the high polymer is reduced; meanwhile, the fluorine atom has strong hydrophobicity, can further reduce the moisture absorption of the LCP, and improve the dielectric stability of the material; the fluorine-containing structure unit is introduced into the molecular structure, so that the liquid crystal polymer with low dielectric constant, low dielectric loss and low moisture absorption rate can be prepared. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The preparation method of the liquid crystal polymer provided by the application is shown in the flowchart of the preferred embodiment. DETAILED DESCRIPTION

[0023] The application provides a liquid crystal polymer and a preparation method and application thereof. To make the purpose, technical scheme and effects of the application more clear and explicit, the application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0024] The liquid crystal polymer (LCP) is a polymer formed by connecting flexible structures and rigid liquid crystal units, which has both the fluidity of liquid and the anisotropy of crystal under certain physical conditions. The LCP has good high-temperature resistance, radiation resistance, hydrolysis resistance, chemical resistance, flame resistance, low moisture absorption, low expansion coefficient and high dimensional stability. In addition, the LCP also has excellent dielectric properties: in the radio frequency range up to 110 GHz, the dielectric constant remains almost constant, and the dielectric loss only increases to 0.0045, which is very suitable for millimeter wave applications and stands out in the 5G field.

[0025] Based on this, the application provides a liquid crystal polymer, which is a copolymer of a monomer containing a naphthalene ring structure, a fluorine-containing monomer and a liquid crystal monomer, and the liquid crystal polymer comprises the following structure:

[0026]

[0027] wherein A is selected from one or more of -O-, -NH-, -CO-, B is selected from one or both of -COO-, -CONH-, and C is selected from one or more of -H, -F, -CF3, wherein at least one C is -F or -CF3, that is, the liquid crystal polymer of the application is obtained by copolymerization of a monomer containing a naphthalene ring structure, a fluorine-containing monomer and a liquid crystal monomer, and the copolymerization method comprises one or more of solution polymerization, melt polymerization and solid phase polymerization.

[0028] Specifically, the present application introduces naphthalene ring structure and fluorine-containing units into liquid crystal polymers at the same time, so that the liquid crystal polymers have extremely low and stable dielectric constant and dielectric loss at high frequency, excellent heat resistance, mechanical properties, dimensional stability, extremely low moisture absorption and good processing performance, and can be widely used in the field of 5G; the charge density of naphthalene ring structure is larger than that of benzene ring structure, and the molecules are more closely packed, at the same time, the width and length of the liquid crystal polymer synthesized by replacing benzene ring structure with naphthalene ring structure are changed, therefore, the liquid crystal polymer containing naphthalene ring structure has a wider liquid crystal phase temperature and a wider processing temperature window, and has better comprehensive performance, the introduction of units containing naphthalene ring structure into the molecular structure can prepare liquid crystal polymers with good heat resistance and better processing performance; the fluorine atom has strong electronegativity and can fix electrons well, the trifluoromethyl group can reduce the regularity of the polymer chain, so that the polymer chain is not closely packed, the intermolecular space is increased, thereby reducing the dielectric constant of the polymer, at the same time, the fluorine atom has strong hydrophobicity, which can further reduce the moisture absorption of the LCP and improve the dielectric stability of the material, the introduction of fluorine-containing structural units into the molecular structure can prepare liquid crystal polymers with low dielectric constant, low dielectric loss and low moisture absorption.

[0029] In some embodiments, the monomer containing naphthalene ring structure is selected from one or more of 6-hydroxy-2-naphthoic acid, 4-hydroxynaphthalene-2-carboxylic acid, 5-aminonaphthalene-1-carboxylic acid, 1,3-naphthalenediol, 1,5-naphthalenediamine, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 1,7-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 2,7-dihydroxynaphthalene, naphthalene-2,6-diamine, 1,8-diaminonaphthalene, 2,7-diaminonaphthalene, dibromonaphthalene, 5-bromonaphthalene-1-amine, 6-bromo-2-naphthol, 2-chloro-6-hydroxynaphthalene, 2-bromo-7-hydroxynaphthalene, 1,8-naphthalene dicarboxylic anhydride, 2,6-dihydroxymethylnaphthalene, 3-bromonaphthalene-2,7-diol, 6-bromonaphthalene-1,2-diamine, 1,4,5,8-naphthalenetetracarboxylic acid.

[0030] Specifically, the naphthalene ring structure is in the molecular main chain of the liquid crystal polymer, the charge density of the naphthalene ring structure is larger than that of the benzene ring structure, and the molecules are more closely packed, at the same time, the width and length of the liquid crystal polymer synthesized by replacing benzene ring structure with naphthalene ring structure are changed, therefore, the liquid crystal polymer containing naphthalene ring structure has a wider liquid crystal phase temperature and a wider processing temperature window, and has better comprehensive performance, the introduction of units containing naphthalene ring structure into the molecular structure can prepare liquid crystal polymers with good heat resistance and better processing performance.

[0031] In some embodiments, the fluorine-containing monomer includes one or both of a monomer containing a trifluoromethyl structure and a monomer containing a symmetrical fluorine-substituted structure.

[0032] Specifically, the fluorine atom has strong electronegativity and can fix electrons well, the trifluoromethyl group can reduce the regularity of the polymer chain, so that the polymer chain is not tightly packed, the intermolecular gap is increased, and thus the dielectric constant of the polymer is reduced, meanwhile, the fluorine atom has strong hydrophobicity, which can further reduce the moisture absorption of the LCP and improve the dielectric stability of the material, and the introduction of the fluorine-containing structural unit in the molecular structure can prepare the liquid crystal polymer with low dielectric constant, low dielectric loss and low moisture absorption.

[0033] In some embodiments, the monomer containing a trifluoromethyl structure is selected from one or more of 4-hydroxy-3-trifluoromethylbenzoic acid, 2-hydroxy-5-trifluoromethylbenzoic acid, 3-hydroxy-4-trifluoromethylbenzoic acid, 3-hydroxy-5-(trifluoromethyl)benzoic acid, 4-hydroxy-2-trifluoromethylbenzoic acid, 4-amino-3-trifluoromethylbenzoic acid, 4-amino-2-(trifluoromethyl)benzoic acid, 4-hydroxy-3-trifluoromethylbenzoic acid, 3-amino-4-trifluoromethylbenzoic acid, 2-amino-4-trifluoromethylphenol, and 4-amino-3-trifluoromethylphenol.

[0034] In some embodiments, the monomer containing a symmetric fluorine-substituted structure is selected from one or more of 2,3,5,6-tetrafluoro-p-benzenediol, tetrafluoro-p- benzenedicarboxylic acid, tetrafluoro-p-benzenediol, 3,4,5,6-tetrafluorobenzene-1,2-diamine, and 4-amino-2,3-difluorophenol.

[0035] In some embodiments, the liquid crystal monomer is selected from one or more of p-hydroxybenzoic acid, isophthalic acid, p-benzenediol, and p-terephthalic acid.

[0036] In some embodiments, the molecular weight of the liquid crystal polymer is 10,000-20,000.

[0037] The application also provides a preparation method of the liquid crystal polymer as described in the above solution of the application, see Figure 1 which comprises the steps of:

[0038] S10, providing a monomer containing a naphthalene ring structure, a fluorine-containing monomer, and a liquid crystal monomer;

[0039] S20, mixing the monomer containing the naphthalene ring structure, the fluorine-containing monomer, and the liquid crystal monomer with acetic anhydride to obtain a mixed raw material;

[0040] S30, heating the mixed raw material to a first preset temperature, reacting for a first preset time, then heating to a second preset temperature at a preset heating rate, and reacting for a second preset time to obtain the liquid crystal polymer.

[0041] Specifically, the amino-containing monomer and the carboxyl-containing monomer can be polymerized to generate a liquid crystal polymer containing an amide bond. The phenolic hydroxyl-containing monomer and the carboxyl-containing monomer are realized by acylation-polycondensation "one-pot method", acetic anhydride is first acetylated with the phenolic hydroxyl, and then the acetoxy group is ester-exchanged with the carboxyl group in a molten state to realize the growth of the molecular chain.

[0042] In some embodiments, the molar ratio of the monomer containing a naphthalene ring structure, the fluorine-containing monomer, and the liquid crystal monomer is (1-4):(1-3):(0-8).

[0043] In some embodiments, the first preset temperature is 120-220°C, the first preset time is 1-4h, the preset heating rate is 0.5-5°C / min, and the second preset temperature is 270-350°C; the second preset time is 0.5h-12h.

[0044] The application further provides a use of the liquid crystal polymer as described in the above-mentioned solution of the application in the preparation of a dielectric material.

[0045] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only some of the embodiments of the application, rather than all the embodiments of the application, and are only used to explain the application, but not to limit the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0046] Example 1: a liquid crystal polymer and a synthesis method thereof

[0047] A monomer containing a naphthalene ring structure, 6-hydroxy-2-naphthoic acid, a monomer containing a trifluoromethyl structure, 4-hydroxy-3-trifluoromethylbenzoic acid, and a conventional liquid crystal monomer, p-hydroxybenzoic acid, are copolymerized. The molar ratio of the three monomers is shown in Table 1:

[0048] Table 1: molar ratio of each raw material

[0049]

[0050] The above monomers are used to synthesize a liquid crystal polymer by a melt copolymerization method, and the specific synthesis steps are as follows:

[0051]

[0052] (1) Keep the reaction kettle airtight well, open the nitrogen inlet and outlet switch, and pass nitrogen for 30min to exhaust the air in the reaction kettle. At the same time, the reaction monomers 6-hydroxy-2-naphthoic acid, p-hydroxybenzoic acid, 4-hydroxy-3-trifluoromethylbenzoic acid, and excess acetic anhydride are weighed according to the proportion, and the raw materials are added into the reaction kettle;

[0053] (2) Turn on the stirring and heating switches, set the temperature program to rapidly heat the reactor to 185°C, and open the vertical condenser to allow the reaction materials to rapidly condense and flow back into the reactor;

[0054] (3) Hold the temperature at 185°C for 2 hours;

[0055] (4) Set the temperature program to increase the temperature from 185°C to 325°C at a rate of 1°C / min, while closing the vertical condenser, opening the horizontal condenser, and appropriately increasing the nitrogen flow rate to remove by-products and promote the forward progress of the polymerization reaction. During the reaction, observe the torque changes;

[0056] (5) Hold the temperature at 325°C for 30 minutes, then remove the nitrogen and replace it with a vacuum pump to remove the residual by-products in the reactor and piping. Observe the torque changes until it reaches the preset value, then turn off the vacuum pump, heating system, and stirring. Keep the nitrogen flowing until the product and reaction device cool to room temperature.

[0057] Example 2: A liquid crystal polymer and its synthesis method

[0058] Select monomer 6-hydroxy-2-naphthoic acid containing naphthalene ring structure, monomer 2,3,5,6-tetrafluorohydroquinone containing symmetric fluorine substitution structure, and copolymerize with conventional liquid crystal monomers isophthalic acid and hydroquinone. The molar ratio of the four monomers is shown in Table 2:

[0059] Table 2: Molar ratio of each raw material

[0060]

[0061]

[0062] The above monomers are synthesized into a liquid crystal polymer by a melt copolymerization method, and the specific synthesis steps are as follows:

[0063] (1) Keep the reactor airtight, open the nitrogen inlet and outlet switches, and flow nitrogen for 30 minutes to exhaust the air in the reactor. At the same time, weigh the reaction monomers, excess acetic anhydride, and 0.3wt% potassium acetate (catalyst), and add the raw materials into the reactor;

[0064] (2) Turn on the stirring and heating switches, set the temperature program to rapidly heat the reactor to 150°C (about 40 minutes), and open the vertical condenser to allow the reaction materials to rapidly condense and flow back into the reactor;

[0065] (3) Hold the temperature at 150°C for 2 hours;

[0066] (4) Set the temperature program to increase the temperature from 150°C to 320°C at a rate of 1°C / min, while closing the vertical condenser, opening the horizontal condenser, and appropriately increasing the nitrogen flow rate to remove byproducts and promote the forward progress of the polymerization reaction. During the reaction, the torque change is observed.

[0067] (5) Continue the reaction at 320°C for 30 min, then remove the nitrogen and replace it with a vacuum pump to remove the residual byproducts in the reaction kettle and pipeline. The torque change is observed until it reaches a preset value, then the vacuum pump, heating system, and stirring are turned off. The product and reaction device are cooled to room temperature under a nitrogen atmosphere.

[0068] Example 3: A liquid crystal polymer and a method for synthesizing the same

[0069] The monomer 6-hydroxy-2-naphthoic acid containing a naphthalene ring structure and the monomer 4-hydroxy-3-trifluoromethylbenzoic acid containing a trifluoromethyl substituent structure are copolymerized with the conventional liquid crystal monomers hydroquinone and terephthalic acid. The molar ratio of the four monomers is shown in Table 3:

[0070] Table 3: Molar ratio of each raw material

[0071]

[0072] The above monomers are used to synthesize a liquid crystal polymer by melt copolymerization and solid phase polymerization. The specific synthesis steps are as follows:

[0073] (1) Keep the reaction kettle closed well, open the nitrogen inlet and outlet switch, and pass nitrogen for 30 min to exhaust the air in the reaction kettle. At the same time, weigh the reaction monomers and excess acetic anhydride, and add the raw materials to the reaction kettle;

[0074] (2) Turn on the stirring and heating switches, set the temperature program to quickly heat the reaction kettle to 170°C, and open the vertical condenser to quickly condense the reaction raw materials back to the reaction kettle;

[0075] (3) Keep the temperature at 170°C for 150 min;

[0076] (4) Set the temperature program to increase the temperature from 150°C to 300°C at a rate of 1°C / min, while closing the vertical condenser, opening the horizontal condenser, and appropriately increasing the nitrogen flow rate to remove byproducts and promote the forward progress of the polymerization reaction. During the reaction, the torque change is observed.

[0077] (5) Continue the reaction at 300°C for 60 min, then remove the nitrogen and replace it with a vacuum pump to remove the residual byproducts in the reaction kettle and pipeline. The torque change is observed until it reaches a preset value, then the vacuum pump, heating system, and stirring are turned off. The product and reaction device are cooled to room temperature under a nitrogen atmosphere.

[0078] (6) The product obtained in step (5) is crushed and solid-phase polymerization is carried out at 300°C under nitrogen protection for 10h.

[0079] Example 4 Liquid crystal polymer and its synthesis method

[0080] The monomer naphthalene-2,6-diamine containing naphthalene ring structure, the monomer 2-hydroxy-5-trifluoromethylbenzoic acid containing trifluoromethyl substitution structure, and the conventional liquid crystal monomer terephthalic acid are copolymerized. The molar ratio of the four monomers is shown in Table 4:

[0081] Table 4 Molar ratio of each raw material

[0082]

[0083] The above monomers are synthesized into a liquid crystal polymer by a melt copolymerization method, and the specific synthesis steps are as follows:

[0084] (1) Keep the reaction kettle airtight well, open the nitrogen inlet and outlet switch, and pass nitrogen for 30min to exhaust the air in the reaction kettle. At the same time, the reaction monomers, excess acetic anhydride, and the raw materials are weighed and added into the reaction kettle;

[0085] (2) Turn on the stirring and heating switches, set the temperature rising program, and make the reaction kettle quickly heat to 165°C. Open the vertical condenser tube so that the reaction raw materials can quickly condense backflow to the reaction kettle;

[0086] (3) Keep the temperature at 165°C for 120min;

[0087] (4) Set the temperature rising program to heat from 165°C to 300°C at a rate of 1°C / min. At the same time, close the vertical condenser tube, open the horizontal condenser tube, and appropriately increase the nitrogen flow rate to facilitate the removal of by-products and promote the forward progress of the polymerization reaction. During the reaction process, the torque change is observed;

[0088] (5) Keep the temperature at 300°C for 30min, then remove the nitrogen and replace it with a vacuum pump to remove the residual by-products in the reaction kettle and pipeline. Observe the torque change until it rises to the preset value, then close the vacuum pump, heating system, and stirring. Keep the nitrogen flowing condition until the product and reaction device are cooled to room temperature.

[0089] Example 5 Liquid crystal polymer and its synthesis method

[0090] The monomer 1,3-naphthalenediol containing naphthalene ring structure, the monomer tetrafluoro terephthalic acid containing symmetrical fluorine substitution structure, and the conventional liquid crystal monomer terephthalic acid are copolymerized. The molar ratio of the three monomers is shown in Table 5:

[0091] Table 5 Molar ratio of each raw material

[0092]

[0093] The monomers are used to synthesize liquid crystal polymers by melt copolymerization, and the specific synthesis steps are as follows:

[0094] (1) Keep the reaction kettle airtight, open the nitrogen inlet and outlet switch, and pass nitrogen for 30 min to exhaust the air in the reaction kettle. At the same time, weigh the reaction monomers and excess acetic anhydride, and add the raw materials into the reaction kettle;

[0095] (2) Turn on the stirring and heating switches, set the temperature rising program, and make the reaction kettle quickly heat to 185°C. Open the vertical condenser tube so that the reaction raw materials can quickly condense backflow to the reaction kettle;

[0096] (3) Keep the temperature at 185°C for 120 min;

[0097] (4) Set the temperature rising program to heat from 185°C to 300°C at a rate of 1°C / min. At the same time, close the vertical condenser tube, open the horizontal condenser tube, and appropriately increase the nitrogen flow rate to remove by-products and promote the forward progress of the polymerization reaction. During the reaction process, observe the torque change;

[0098] (5) Keep the temperature at 300°C for 30 min, then remove the nitrogen and replace it with a vacuum pump to remove the residual by-products in the reaction kettle and pipeline. Observe the torque change until it rises to the preset value, then close the vacuum pump, heating system, and stirring. Keep the nitrogen flowing condition and cool the product and reaction device to room temperature;

[0099] (6) Crush the product obtained in step (5) and perform solid-phase polymerization at 280°C under nitrogen protection for 12 h.

[0100] Example 6: A liquid crystal polymer and a synthesis method thereof

[0101] Select monomer 2,7-dihydroxynaphthalene containing naphthalene ring structure and monomer tetrafluoro terephthalic acid containing symmetrical fluorine substitution structure. The molar ratio of the two monomers is shown in Table 6:

[0102] Table 6: Molar ratio of each raw material

[0103]

[0104] The monomers are used to synthesize liquid crystal polymers by melt copolymerization, and the specific synthesis steps are as follows:

[0105] (1) Keep the reaction kettle airtight, open the nitrogen inlet and outlet switch, and pass nitrogen for 30 min to exhaust the air in the reaction kettle. At the same time, weigh the reaction monomers and excess acetic anhydride, and add the raw materials into the reaction kettle;

[0106] (2) Turn on the stirring and heating switches, set the temperature program, and make the reactor rapidly heat to 185°C. Open the vertical condenser to allow the reaction materials to rapidly condense and flow back to the reactor;

[0107] (3) Keep the temperature at 185°C for 120 min;

[0108] (4) Set the temperature program to heat from 185°C to 300°C at a rate of 1°C / min. At the same time, close the vertical condenser, open the horizontal condenser, and appropriately increase the nitrogen flow rate to remove byproducts and promote the forward progress of the polymerization reaction. During the reaction, observe the change in torque;

[0109] (5) Keep the temperature at 300°C for 30 min, then remove the nitrogen and replace it with a vacuum pump to remove the residual byproducts in the reactor and pipes. Observe the change in torque until it reaches the preset value, then close the vacuum pump, heating system, and stirring. Keep the nitrogen flowing until the product and reaction device cool to room temperature;

[0110] (6) Crush the product obtained in step (5) and perform solid-phase polymerization at 300°C under nitrogen protection for 6 h.

[0111] Example 7 Liquid crystal polymer and method for synthesizing the same

[0112] Select monomers 6-hydroxy-2-naphthoic acid containing a naphthalene ring structure and 4-hydroxy-2-trifluoromethylbenzoic acid containing a trifluoromethyl substituent structure, and copolymerize them with the conventional liquid crystal monomer p-hydroxybenzoic acid. The molar ratio of the four monomers is shown in Table 7:

[0113] Table 7 Molar ratio of each raw material

[0114]

[0115] Synthesize the liquid crystal polymer by melt copolymerization of the above monomers. The specific synthesis steps are as follows:

[0116] (1) Keep the reactor airtight, open the nitrogen inlet and outlet switches, and flow nitrogen for 30 min to remove the air in the reactor. At the same time, weigh the reaction monomers and excess acetic anhydride, and add the raw materials to the reactor;

[0117] (2) Turn on the stirring and heating switches, set the temperature program, and make the reactor rapidly heat to 180°C. Open the vertical condenser to allow the reaction materials to rapidly condense and flow back to the reactor;

[0118] (3) Keep the temperature at 180°C for 90 min;

[0119] (4) Set the temperature program to increase the temperature from 180°C to 330°C at a rate of 1°C / min, while closing the vertical condenser, opening the horizontal condenser, and appropriately increasing the nitrogen flow rate to remove byproducts and promote the forward progress of the polymerization reaction. During the reaction, the torque change is observed.

[0120] (5) Continue the reaction at 330°C for 30 min, then remove the nitrogen and replace it with a vacuum pump to remove the residual byproducts in the reactor and piping. The torque change is observed until it reaches a preset value, at which point the vacuum pump, heating system, and stirring are turned off. The product and reaction device are allowed to cool to room temperature under a nitrogen atmosphere.

[0121] Example 8 Liquid crystal polymer and method for synthesizing the same

[0122] A monomer containing a naphthalene ring structure, 5-aminonaphthalene-1-carboxylic acid, a monomer containing a trifluoromethyl substituent structure, 2-amino-4-trifluoromethylphenol, and a conventional liquid crystal monomer, terephthalic acid, are copolymerized. The molar ratio of the three monomers is shown in Table 8:

[0123] Table 8 Molar ratio of each raw material

[0124]

[0125] The above monomers are used to synthesize a liquid crystal polymer by melt copolymerization. The specific synthesis steps are as follows:

[0126] (1) Keep the reactor closed and well sealed, open the nitrogen inlet and outlet switch, and pass nitrogen for 30 min to exhaust the air in the reactor. At the same time, weigh the reaction monomers and excess acetic anhydride, and add the raw materials to the reactor.

[0127] (2) Turn on the stirring and heating switches, and set the temperature program to quickly heat the reactor to 200°C. Open the vertical condenser to allow the reaction raw materials to quickly condense back to the reactor.

[0128] (3) React at 200°C for 90 min.

[0129] (4) Set the temperature program to increase the temperature from 200°C to 300°C at a rate of 2°C / min, while closing the vertical condenser, opening the horizontal condenser, and appropriately increasing the nitrogen flow rate to remove byproducts and promote the forward progress of the polymerization reaction. During the reaction, the torque change is observed.

[0130] (5) Continue the reaction at 300°C for 90 min, then remove the nitrogen and replace it with a vacuum pump to remove the residual byproducts in the reactor and piping. The torque change is observed until it reaches a preset value, at which point the vacuum pump, heating system, and stirring are turned off. The product and reaction device are allowed to cool to room temperature under a nitrogen atmosphere.

[0131] The liquid crystal polymers synthesized in Examples 1-8 have dielectric constant less than 3.0 at 10 GHz, dielectric loss less than 0.005, thermal decomposition temperature higher than 400 DEG C and water absorption less than 1% due to the introduction of naphthalene ring structure and fluorine-containing structure unit in the molecular structure.

[0132] In conclusion, the application discloses a liquid crystal polymer and a preparation method and application thereof, and the liquid crystal polymer is a copolymer of a monomer containing naphthalene ring structure, a fluorine-containing monomer and a liquid crystal monomer. The application introduces the naphthalene ring structure and the fluorine-containing unit into the liquid crystal polymer, so that the liquid crystal polymer has extremely low and stable dielectric constant and dielectric loss at high frequency, excellent heat resistance, mechanical property, dimensional stability, extremely low moisture absorption and good processing performance, and can be widely applied in the field of 5G. The charge density of the naphthalene ring structure is higher than that of the benzene ring structure, and the molecular accumulation is more compact. Meanwhile, the molecular width and length of the liquid crystal polymer synthesized by replacing the benzene ring structure with the naphthalene ring structure are changed. Therefore, the liquid crystal polymer containing the naphthalene ring structure has a wider liquid crystal phase temperature, a wider processing temperature window and better comprehensive performance. The introduction of the unit containing the naphthalene ring structure into the molecular structure can prepare the liquid crystal polymer with good heat resistance and better processing performance. The fluorine atom has strong electronegativity and can fix electrons well. The trifluoromethyl group can reduce the regularity of the polymer chain, so that the polymer chain is not compact, the intermolecular gap is increased, and the dielectric constant of the polymer is reduced. Meanwhile, the fluorine atom has strong hydrophobicity, and can further reduce the moisture absorption of the LCP and improve the dielectric stability of the material. The introduction of the fluorine-containing structure unit into the molecular structure can prepare the liquid crystal polymer with low dielectric constant, low dielectric loss and low moisture absorption.

[0133] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the application, but not to limit the same; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalent ones; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the application.

Claims

1. A liquid crystal polymer, characterized in that The liquid crystal polymer is a copolymer of a monomer containing a naphthalene ring structure, a fluorine-containing monomer and a liquid crystal monomer, and the liquid crystal polymer comprises the following structure: Wherein, A is selected from one or more of -O-, -NH-, -CO-, B is selected from -CONH-, C is selected from one or more of -H, -F, -CF3, wherein at least one C is -CF3.

2. The liquid crystal polymer according to claim 1, wherein The monomer containing a naphthalene ring structure is selected from one or more of 5-aminonaphthalene-1-carboxylic acid, 1,5-naphthalenediamine, naphthalene-2,6-diamine, 1,8-diaminonaphthalene, 2,7-diaminonaphthalene, 5-bromonaphthalene-1-amine, and 6-bromonaphthalene-1,2-diamine.

3. The liquid crystal polymer according to claim 1, wherein The fluorine-containing monomer includes a monomer containing a trifluoromethyl structure.

4. The liquid crystal polymer according to claim 3, wherein The monomer containing a trifluoromethyl structure is selected from one or more of 2-hydroxy-5-trifluoromethylbenzoic acid, 3-hydroxy-4-trifluoromethylbenzoic acid, 3-hydroxy-5-(trifluoromethyl)benzoic acid, 4-hydroxy-2-trifluoromethylbenzoic acid, 4-amino-3-trifluoromethylbenzoic acid, 4-amino-2-(trifluoromethyl)benzoic acid, 4-hydroxy-3-trifluoromethylbenzoic acid, 3-amino-4-trifluoromethylbenzoic acid, 2-amino-4-trifluoromethylphenol, and 4-amino-3-trifluoromethylphenol.

5. The liquid crystal polymer according to claim 1, wherein The liquid crystal monomer is selected from one or more of p-hydroxybenzoic acid, isophthalic acid, and terephthalic acid.

6. A method for preparing a liquid crystal polymer according to any one of claims 1 to 5, characterized in that: Including steps: Providing monomers containing naphthalene ring structures, fluorine-containing monomers and liquid crystal monomers; mixing the monomer containing a naphthalene ring structure, the fluorine-containing monomer, the liquid crystal monomer and acetic anhydride to obtain a mixed raw material; The mixed raw material is heated to a first preset temperature, reacted for a first preset time, and then heated to a second preset temperature at a preset heating rate, reacted for a second preset time, to obtain the liquid crystal polymer.

7. The preparation method according to claim 6, characterized in that The molar ratio of the monomer containing a naphthalene ring structure, the fluorine-containing monomer and the liquid crystal monomer is (1-4): (1-3): (0-8).

8. The preparation method according to claim 6, characterized in that The first preset temperature is 120-220° C., the first preset time is 1-4 hours, the preset heating rate is 0.5-5° C. / min, the second preset temperature is 270-350° C., and the second preset time is 0.5-12 hours.

9. Use of the liquid crystal polymer according to any one of claims 1 to 5 in the preparation of dielectric materials.

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