Liquid crystalline polyester and its preparation method and application

Abstract

This invention provides a liquid crystal polyester, its preparation method, and its applications. By simultaneously introducing a 2,6-naphthylene structure with a "side-stepping effect" and a 4,4-diphenyl ether group with a bending structure, and replacing the easily rotatable biphenyl structure with a readily sublimable p-phenylene structure (i.e., a structure containing 1,4-phenylene), these three elements work synergistically. On the one hand, they increase the energy barrier for chain segment movement at high temperatures, reduce the movement of the molecular chain ends at lead-free reflow soldering temperatures, inhibit end-chain transesterification reactions, and collectively reduce the generation of vaporized small molecules, thereby avoiding foaming. On the other hand, the 2,6-naphthylene structure and the 4,4-diphenyl ether group also lower the melting point and crystallization temperature of the liquid crystal polyester. The liquid crystal polyester prepared by this invention exhibits excellent foaming resistance, with an average foaming rate as low as 10% or less; and after melting at 300°C for 60 minutes, the weight loss is less than 0.3% below 360°C.

Description

Technical Field

[0001] This invention relates to the field of engineering plastics technology, and in particular to a liquid crystal polyester, its preparation method, and its application. Background Technology

[0002] With the rapid development of miniaturization and high-frequency operation of electronic and electrical equipment, the advancement of compact, miniaturized, and high-density assembly technologies for electronic components has been promoted. In particular, the use of surface mount technology (SMT) connectors places higher demands on the temperature resistance and dimensional stability of the plastic materials used. The widespread adoption of lead-free reflow soldering to meet environmental requirements further enhances the blistering resistance of the materials used at the high peak temperatures of the reflow soldering process. Thermotropic liquid crystal polyester (LCP), with its rigid chain structure and ordered molecular arrangement, possesses excellent comprehensive physical and mechanical properties. It exhibits superior mechanical properties, dielectric properties, self-flame retardant properties (no flame retardant required), and heat resistance, making it widely used in connector materials employing lead-free reflow soldering.

[0003] To meet the foaming resistance requirements of conventional LCPs under lead-free reflow soldering, the melting point and crystallization temperature of the resin are typically increased. This reduces the chain segment mobility at lead-free reflow soldering temperatures, inhibiting the diffusion of residual small molecules and achieving foaming resistance. However, increasing the melting point and crystallization temperature of the resin leads to a higher processing temperature required to maintain melt flow during injection molding. This can easily cause resin degradation during processing, resulting in deterioration of mechanical properties. Furthermore, it can lead to excessively rapid external cooling of the molded part after injection molding, resulting in uneven shrinkage and warping.

[0004] Therefore, there is a need for a thermotropic liquid crystal polyester that has both a low melting point and good foaming resistance. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing foam-resistant liquid crystal polyesters, such as high melting point and poor processing and mechanical properties, by providing a liquid crystal polyester that simultaneously has a low melting point, good mechanical properties, and foam resistance.

[0006] Another object of the present invention is to provide a method for preparing the liquid crystal polyester.

[0007] Another object of the present invention is to provide the use of the liquid crystal polyester in the preparation of foam-resistant and / or heat-resistant electronic devices.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A liquid crystal polyester comprising repeating units as shown in Formula I, Formula II and Formula III:

[0010] —O—Ar1—O— Formula I;

[0011] —OC—Ar2—CO— Formula II;

[0012] —O—Ar3—CO— Formula III;

[0013] Wherein, Ar1 is at least one of 1,4-phenylene, 1,3-phenylene, 4,4-biphenyl or 4,4-diphenyl ether; Ar2 is at least one of 1,4-phenylene, 1,3-phenylene, 2,6-naphthylene or 4,4-diphenyl ether; Ar3 is at least one of 2,6-naphthylene or 1,4-phenylene; and the liquid crystal polyester simultaneously contains 1,4-phenylene, 2,6-naphthylene and 4,4-diphenyl ether.

[0014] It should be noted that the repeating unit shown in Formula I corresponds to an aromatic diphenol monomer, the repeating unit shown in Formula II corresponds to an aromatic dicarboxylic acid monomer, and the repeating unit shown in Formula III corresponds to a hydroxy aromatic carboxylic acid monomer. Regarding the ratios in Formulas I to III: the monomers of Formula I and Formula II undergo dehydration condensation polymerization to form a polyester; Formula III can react with Formulas I and II, or with Formula III containing different Ar3 structural units; in the polyester structures formed by Formulas I to III, the number of —O— and —CO— is the same.

[0015] This invention simultaneously incorporates a 2,6-naphthylene structure with a "side-stepping effect" and a 4,4-diphenyl ether group with a bending structure, and replaces the easily rotatable biphenyl structure with a readily sublimable p-phenylene structure (i.e., a structure containing 1,4-phenylene). The three elements work together to increase the energy barrier for chain segment movement at high temperatures, reduce the movement of the molecular chain ends at lead-free reflow soldering temperatures, inhibit the transesterification reaction at the chain ends, and jointly reduce the generation of vaporized small molecules, thereby avoiding foaming. On the other hand, the 2,6-naphthylene structure and the 4,4-diphenyl ether group can also lower the melting point and crystallization temperature of the liquid crystal polyester. Furthermore, the inventors have creatively discovered that existing foam-resistant liquid crystal polyesters all contain a high content of biphenyl monomers. However, when 4,4-diphenyl ether groups are introduced, the content of biphenyl monomers can be significantly reduced (≤5 mol%), or even without the addition of biphenyl monomers, the movement of molecular chains can be significantly suppressed, the generation of small molecules can be reduced, and the foam resistance stability of the prepared liquid crystal polyester can be improved, with an average foaming rate as low as 10% or less.

[0016] Preferably, based on all repeating units of the liquid crystal polyester, one or more of the following conditions are met:

[0017] (1) The content of 1,4-phenylene structural units is >70 mol%, preferably >75 mol%;

[0018] (2) The content of the structural unit containing 2,6-naphthyl group is ≥8 mol%, preferably ≥10 mol%;

[0019] (3) The content of structural units containing 4,4-diphenyl ether groups is ≥0.2 mol%, preferably ≥0.5 mol%.

[0020] Preferably, based on all repeating units of the liquid crystal polyester, the following conditions are met:

[0021] 0 mol% ≤ Content of 1,3-phenylene structural units ≤ 1.2 mol%, preferably ≤ 1 mol%;

[0022] The content of 4,4-biphenyl structural units is ≤5 mol%, preferably ≤1 mol%.

[0023] Preferably, based on all repeating units of the liquid crystal polyester, the following conditions are met:

[0024] The content of the 1,4-phenylene structural unit is 79–90 mol%.

[0025] Alternatively, the content of structural units containing 2,6-naphthyl groups is 10–20 mol%.

[0026] Alternatively, the content of structural units containing 4,4-diphenyl ether groups is 0.5–1.5 mol%.

[0027] When the amount of the above-mentioned groups is within the above range, the resulting liquid crystal polyester has a low melting point, low foaming rate, and low thermal weight loss rate.

[0028] More preferably, the amount of each repeating unit in the liquid crystal polyester, based on the total molar percentage of all repeating units of the liquid crystal polyester (i.e., the sum of the molar percentages of the repeating units shown in Formula I, Formula II, and Formula III is 100 mol%), satisfies at least one of the following conditions:

[0029] 1) In the repeating unit shown in Formula I, 10 mol% ≤ the content of the structural unit containing 1,4-phenylene ≤ 20 mol%, or 0 mol% ≤ the content of the structural unit containing 1,3-phenylene ≤ 0.5 mol%, or 0 mol% ≤ the content of the structural unit containing 4,4-biphenyl ≤ 5 mol%, or 0 mol% ≤ the content of the structural unit containing 4,4-diphenyl ether group ≤ 1 mol%.

[0030] 2) In the repeating unit shown in Formula II, 12 mol% ≤ the content of the structural unit containing 1,4-phenylene ≤ 20 mol%, or 0 mol% ≤ the content of the structural unit containing 1,3-phenylene ≤ 1 mol%, or 0 mol% ≤ the content of the structural unit containing 2,6-naphthylene ≤ 0.5 mol%, or 0 mol% ≤ the content of the structural unit containing 4,4-diphenyl ether ≤ 1 mol%.

[0031] 3) In the repeating unit shown in Formula III, 40 mol% ≤ the content of the structural unit containing 1,4-phenylene ≤ 60 mol%, or 8 mol% ≤ the content of the structural unit containing 2,6-naphthylene ≤ 20 mol%.

[0032] More preferably, based on all repeating units of the liquid crystal polyester (i.e., the sum of the molar percentages of the repeating units shown in Formula I, Formula II, and Formula III is 100 mol%), at least one of the following conditions is satisfied:

[0033] (1) In the repeating unit shown in Formula I, 15.9 mol% ≤ the content of the structural unit containing 1,4-phenylene ≤ 18 mol%, or 0 mol% ≤ the content of the structural unit containing 1,3-phenylene ≤ 0.6 mol%, or 0 mol% ≤ the content of the structural unit containing 4,4-biphenyl ≤ 0.5 mol%, or 0 mol% ≤ the content of the structural unit containing 4,4-diphenyl ether group ≤ 0.5 mol%.

[0034] (2) In the repeating unit shown in Formula II, 12 mol% ≤ the content of the structural unit containing 1,4-phenylene ≤ 15 mol%, or 0 mol% ≤ the content of the structural unit containing 1,3-phenylene ≤ 0.6 mol%, or 0 mol% ≤ the content of the structural unit containing 2,6-naphthylene ≤ 0.5 mol%, or 0.5 mol% ≤ the content of the structural unit containing 4,4-diphenyl ether ≤ 1 mol%.

[0035] (3) In the repeating unit shown in Formula III, 50 mol% ≤ 1,4-phenylene structural units ≤ 55 mol%, and 13 mol% ≤ 2,6-naphthyl structural units ≤ 16 mol%.

[0036] Within the aforementioned monomer range, the resulting liquid crystal polyester has a low melting point and, in particular, excellent anti-foaming properties.

[0037] The melting point of the liquid crystal polyester is 328-360℃. The melting point is measured by DSC. Starting from room temperature (20-30℃), the temperature is increased to a maximum temperature 30℃ above the melting point at a heating rate of 20℃ / min. After holding at this temperature for 3 minutes, the temperature is decreased to room temperature at a rate of 20℃ / min. The test sample is held at room temperature for 3 minutes and then heated again to a maximum temperature 30℃ above the melting point at a heating rate of 20℃ / min. The second melting curve of the liquid crystal polyester is obtained, and the melting peak of this curve is selected as the melting point.

[0038] The crystallization temperature of the liquid crystal polyester is <300℃. The crystallization temperature is measured by DSC. Starting from room temperature, the temperature is increased to a maximum temperature 30℃ above the melting point at a heating rate of 20℃ / min. After holding at this temperature for 3 minutes, the temperature is then decreased to room temperature at a rate of 20℃ / min. The crystallization curve of the liquid crystal polyester is obtained, and the crystallization peak of this curve is selected as the crystallization temperature.

[0039] The melt viscosity of the liquid crystal polyester is 10–30 Pa·s. The melt viscosity was measured using a capillary rheometer at a temperature 0–30°C above the melting point and a shear rate of 1000 s⁻¹. -1 The measurement was performed using a die with an inner diameter of 1 mm and a length of 40 mm.

[0040] The liquid crystal polyester exhibits excellent foaming resistance, with an average foaming rate of 10% or less.

[0041] The liquid crystal polyester exhibits a thermal weight loss rate of ≤0.3% under conditions of 300℃ for 60 min, which can be as low as 0.21%. The thermal weight loss rate is measured using a TGA (Thermogravimetric Analysis) instrument in a nitrogen atmosphere. The sample is heated to 150℃ at a rate of 20℃ / min and held at 150℃ for 10 min, then heated to 300℃ at a rate of 20℃ / min and held at 300℃ for 60 min. The thermal weight loss rate (%) under 300℃ for 60 min is calculated as: (100%) - (Mass of sample at 300℃ for 60 min / Mass of sample at 300℃ for 0 min) * 100%.

[0042] This invention also protects the method for preparing the above-mentioned liquid crystal polyester. The method for preparing the liquid crystal polyester includes the following steps:

[0043] S1. The repeating unit monomers of Formula III and Formula I repeating unit monomers undergo an acylation reaction with an acylating agent under catalysis;

[0044] S2. The acylation reaction product of step S1 and the monomer of the repeating unit of formula II undergo melt polycondensation and decompression polycondensation under catalysis to obtain the prepolymer;

[0045] S3. After cooling the prepolymer obtained in step S2, granulate it and then perform solid-state polymerization under vacuum conditions to obtain the liquid crystal polyester.

[0046] In this invention, the hydroxyl group is first acylated, and the acylated acyl group is then further polycondensed and polymerized with the carboxyl group to obtain a liquid crystal polyester.

[0047] Preferably, the molar amount A of the repeating unit monomer of Formula I in step S1. and the molar amount B of the repeating unit monomer of Formula II in step S2. are A:B = (1.03~1.6):1.

[0048] In some preferred embodiments, by controlling the ratio of the monomers of Formula I repeating unit to the monomers of Formula II repeating unit, the ratio of terminal reactive groups (carboxyl groups and acyl groups) in the prepolymer molecules formed at the end of the prepolymerization reaction can be made unbalanced. This allows the viscosity to increase while the growth rate of the molecular chain to be slower and more controllable during solid-state polymerization (tackification stage). This not only reduces gas residue but also prolongs the deashing time of small molecules and reduces the content of small molecules. Therefore, it can further avoid the generation of bubbles due to the vaporization of small molecules at reflow soldering temperature, and further improve the foaming resistance of liquid crystal polyester.

[0049] Because aromatic diphenol monomers are easily volatile during polymerization, an excess of aromatic diphenol monomers (i.e., the molar amount of monomers in Formula I repeating units is greater than that in Formula II repeating units) can ensure a slower solid-state polymerization rate and also ensure that more gas is carried away during volatilization, thus guaranteeing the excellent foaming resistance of the polyester. If there is an excess of carboxylic acid groups, coupled with the volatilization of aromatic diphenol monomers, the polyester yield will be lower, resulting in a greater amount of small-molecule monomers remaining in the obtained polyester, leading to an increase in the thermal weight loss rate of the polyester material.

[0050] Preferably, the acylation reaction in step S1 is carried out in an inert atmosphere, which is an atmosphere formed by at least one gas selected from nitrogen, helium, argon, or carbon dioxide. To suppress side reactions, the inert atmosphere is preferably an atmosphere formed by carbon dioxide gas.

[0051] The acylation reaction is carried out at a temperature of 100–180°C; the acylation reaction takes 0.5–3 hours; and the acylation reaction is carried out at a pressure of 0.1–0.2 MPa.

[0052] The acylating agent is a conventional acylating agent in the art, including but not limited to at least one of acetic anhydride, propionic anhydride, butyric anhydride, or valeric anhydride, preferably acetic anhydride. The molar amount of the acylating agent is greater than the total molar amount of the hydroxy aromatic carboxylic acid monomer and the aromatic diphenol monomer. The molar amount of the acylating agent is preferably 1.01 to 1.03 times the total molar amount of the hydroxy aromatic carboxylic acid monomer and the aromatic diphenol monomer.

[0053] In step S2, before the melt polycondensation reaction, the pressure of the reaction system needs to be reduced to atmospheric pressure (100-101 kPa) before adding the monomer of the repeating unit of Formula II. During the melt polycondensation reaction, alkyl acids (the corresponding alkyl acids formed after the acylating agent reaction), unreacted acylating agents, and a small amount of hydroquinone acylates need to be discharged. The amount of alkyl acids received is used to determine whether the reaction has reached more than 90% of the theoretical value. When the melt polycondensation reaction reaches more than 90% of the theoretical value, depressurization polycondensation is then carried out.

[0054] The reaction temperature of the melt polycondensation is 200–400°C; the temperature of the reduced-pressure polycondensation is 300–400°C; and the pressure of the reduced-pressure polycondensation is 1–10 kPa.

[0055] In step S3, the solid-phase polymerization conditions are: vacuum degree of 0.1 Pa to 50 kPa, temperature of 160 to 350 °C, and polymerization time of 0.5 to 40 h.

[0056] Preferably, the acylation reaction and melt polycondensation are carried out under the action of a catalyst, which is a conventional polyester polymerization catalyst in the art. The catalyst is a metal salt catalyst, including but not limited to at least one selected from potassium acetate, sodium acetate, magnesium acetate, zinc acetate, antimony trioxide, or tetrabutyl titanate. The amount of catalyst added is 50 to 200 ppm of the total monomer.

[0057] The above reaction is carried out in a vertical polymerization tank equipped with a stirrer, which can be a turbine blade, a twin-helix blade, or a multi-stage paddle blade, preferably a twin-helix blade.

[0058] The application of the aforementioned liquid crystal polyester in the manufacture of foam-resistant and / or heat-resistant electronic devices is also within the scope of protection of this invention. These electronic devices include, but are not limited to, sensors, LEDs, connectors, sockets, resistors, relay housings, relay bases, relay winding spools, switches, coil shafts, capacitors, variable capacitor housings, optical pickups, resonators, various terminal blocks, transformers, plugs, printed circuit boards, tuners, speakers, microphones, headsets, small electric motors, magnetic head bases, power modules, housings, semiconductors, liquid crystal display components, FDD brackets, FDD chassis, HDD components, motor brush holders, parabolic antennas, computer-related components, and other products.

[0059] Compared with the prior art, the beneficial effects of the present invention are:

[0060] This invention introduces a 2,6-naphthylene structure with a "side-stepping effect" and a 4,4-diphenyl ether group with a flexural structure, and replaces the easily rotatable biphenyl structure with a readily sublimable p-phenylene structure (i.e., a structure containing 1,4-phenylene). The synergistic effect of these three elements lowers the melting point and crystallization temperature while reducing the generation of vaporized small molecules, thus preventing foaming. The introduction of the 4,4-diphenyl ether group also significantly improves the foaming resistance of liquid crystal polyesters during processing, while significantly reducing the content of biphenyl monomers.

[0061] The liquid crystal polyester prepared by this invention has excellent foaming resistance and stability, with an average foaming rate as low as 10% or less; moreover, the melting point is 360℃ or less, and can be as low as 328℃; it also has excellent heat loss resistance, with a weight loss rate as low as 0.3% or less after 60 minutes at 300℃. Detailed Implementation

[0062] To better illustrate the purpose, technical solution, and advantages of this invention, specific embodiments will be used to further describe the invention below. However, these embodiments do not limit the invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in this invention are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this invention are commercially available.

[0063] The following raw materials are selected in the embodiments of the present invention:

[0064] Hydroquinone: Yingchuansheng Chemical Co., Ltd.

[0065] Resorcinol: Shandong Tianshili Biotechnology Co., Ltd.;

[0066] 4,4′-Dihydroxydiphenyl ether: Zhengzhou Siji Chemical Products Co., Ltd.;

[0067] 4,4′-Biphenyldiol: Shanghai Yuanye Biotechnology Co., Ltd.;

[0068] 2,6-Naphthiodiol: Beijing Jianqiang Weiye Technology Co., Ltd.;

[0069] 4-Hydroxybenzoic acid: Tianjin Yifang Technology Co., Ltd.;

[0070] 3-Hydroxybenzoic acid: Chengdu Yuanda Chemical Co., Ltd.;

[0071] 6-Hydroxy-2-naphthoic acid: Shandong Lifan Chemical Co., Ltd.;

[0072] Terephthalic acid: Shanghai Kaiyin Chemical Co., Ltd.;

[0073] isophthalic acid: Shandong Fengtai Chemical Technology Co., Ltd.;

[0074] 2,6-Naphthalenedicarboxylic acid: Tesco Chemical (Hubei) Co., Ltd.;

[0075] 4,4′-Diphenyl ether dicarboxylic acid: Hubei Jiufenglong Chemical Co., Ltd.;

[0076] Potassium acetate catalyst: Sinopharm Group;

[0077] Acylating agent: Acetic anhydride; Nanjing Zhuocheng Petrochemical Co., Ltd.

[0078] Examples 1-15, Comparative Examples 1-6

[0079] The liquid crystal polyesters, monomers, and dosage formulations of the embodiments and comparative examples of the present invention are shown in Table 1, and were prepared according to a preparation method including the following steps:

[0080] S1. Acylation reaction:

[0081] In a vertical polymerization tank with twin propeller blades, hydroxy aromatic carboxylic acid monomers (monomers corresponding to the repeating units shown in Formula III), aromatic diphenol monomers (monomers corresponding to the repeating units shown in Formula I), and acetic anhydride (the molar amount of acetic anhydride is 1.03 times the total molar amount of hydroxy aromatic carboxylic acid monomers and aromatic diphenol monomers) are added in proportion. Then carbon dioxide gas is introduced, the pressure is increased to 0.12 MPa, and the reaction is stirred at 120°C for 3 hours to obtain the acylated monomers.

[0082] S2. Preparation of liquid crystal polyester prepolymer:

[0083] Step S1. After the reaction is complete, the pressure in the vertical polymerization tank is reduced to atmospheric pressure (0.1 MPa), and then an aromatic dicarboxylic acid monomer (the monomer corresponding to the repeating unit shown in Formula II) is added. After heating to 300°C, a melt polycondensation reaction is carried out under these conditions. During the reaction, acid (the product after the reaction of the acylating agent), unreacted acid anhydride molecules (acylating agent), and a small amount of acylate are discharged from the distillation column of the vertical polymerization tank. When the amount of acid collected reaches more than 90% of the theoretical value, the pressure in the polymerization tank is reduced to 1 kPa, and the temperature of the reaction system is raised to 300-400°C. The prepolymer is obtained by decompression polycondensation.

[0084] S3. Solid-state polymerization of prepolymers:

[0085] After cooling the prepolymer obtained in step S2, granulate it and carry out solid-state polymerization under vacuum conditions of 10 Pa and 280 °C until a stable melt viscosity is reached. Then, cool it down to obtain the liquid crystal polyester.

[0086] Table 1. Raw material formulation of liquid crystal polyester in the embodiments.

[0087]

[0088] Table 2. Raw material formulations for comparative examples of liquid crystal polyesters.

[0089]

[0090]

[0091] The properties of the prepared liquid crystal polyester were characterized. The specific test items and methods are as follows, and the test results are detailed in Table 3:

[0092] 1. Melting point: Measured using DSC, the sample was heated from room temperature to the melting point +30℃ at a heating rate of 20℃ / min, held at this temperature for 3 minutes, and then cooled back to room temperature at a rate of 20℃ / min. The test sample was then held at room temperature for 3 minutes and then heated again to the melting point +30℃ at a heating rate of 20℃ / min. This yielded the second melting curve of the liquid crystal polyester. The temperature corresponding to the melting peak of this curve was selected as the melting point.

[0093] 2. Crystallization temperature: The crystallization temperature was obtained by DSC measurement. The temperature was increased from room temperature to the melting point +30℃ at a heating rate of 20℃ / min, held at this temperature for 3 minutes, and then cooled back to room temperature at a rate of 20℃ / min. The temperature corresponding to the crystallization peak of this curve was selected as the crystallization temperature.

[0094] 3. Melt viscosity: Tested using a capillary rheometer at a temperature 0–30°C above the melting point and a shear rate of 1000 s⁻¹. -1 The measurement was performed using a die with an inner diameter of 1 mm and a length of 40 mm.

[0095] 4. Foaming Rate: At a melting temperature 5°C above the liquid crystal polyester and an injection speed of 60 mm / s, the liquid crystal polyester or its composition was thermostatically extruded into sheet-like samples with a thickness of 1.0 mm and a length and width of 60 mm. Samples were taken for injection molding at 1 min, 20 min, and the end of polymerization, yielding 10 samples per injection. Each set of 10 samples was placed in a 260°C oven and baked for 5 min. The samples were then removed, and the formation of bubbles on the surface of each sample was observed. Foaming rate = number of foamed pieces / 10. A lower foaming rate indicates better anti-foaming properties.

[0096] 5. Thermogravimetric analysis (TGA) at 300℃ for 60 min: The test atmosphere was nitrogen. The sample was heated to 150℃ at a rate of 20℃ / min and held at 150℃ for 10 min. Then, the temperature was increased to 300℃ at a rate of 20℃ / min and held at 300℃ for 60 min. The thermogravimetric analysis (%) at 300℃ for 60 min = 100% - (mass of sample at 300℃ for 60 min / mass at 300℃ for 0 min) * 100%.

[0097] Table 3 Performance test results of the examples and comparative examples

[0098]

[0099] The results in the table above show that:

[0100] The results of Examples 1-15 show that the liquid crystal polyester with a specific unit structure of the present invention has excellent performance, with a melting point of 360°C and below, which can be as low as 328°C, making it more conducive to processing; a crystallization temperature of 300°C and below, which can be as low as 270°C; a melt viscosity of 10-30 Pa·s; and good foaming stability during processing, with an average foaming rate (the average foaming rate of samples in the mixing section, homogenization section and discharge port of the extruder, and injection molding tests taken at 1 min, 20 min and the end of polymerization) of 10% and below; it also has good heat loss resistance, with a weight loss rate of 0.3% and below after 60 min at 300°C.

[0101] When the molar amount of aromatic diphenol monomers is greater than that of aromatic dicarboxylic acid monomers, better foaming resistance is achieved. This is because aromatic diphenol monomers are easily volatilized during polymerization. Therefore, an excess of aromatic diphenol monomers ensures a slower solid-state polymerization rate and allows for the removal of more gas during volatilization, thus guaranteeing the excellent foaming resistance of the polyester. However, if there is an excess of carboxylic acid groups (as in Example 8), coupled with the volatilization of aromatic diphenol monomers, the polyester yield is lower, resulting in more small-molecule monomers remaining in the obtained polyester. Although the foaming stability meets the requirements, the thermal weight loss rate is higher.

[0102] The comparison results between Example 3 and Comparative Examples 1-4 show that the excellent performance of liquid crystal polyester requires the synergistic effect of three structures in the polyester molecular chain: 1,4-phenylene, 2,6-naphthylene, and 4,4-diphenyl ether. In particular, the introduction of the 4,4-diphenyl ether group can significantly reduce the content of biphenyl repeating units, and even without the addition of biphenyl monomers, it can significantly inhibit molecular chain movement and reduce the generation of small molecules. The absence of any one of these structures (such as in Comparative Examples 1-3) significantly reduces the foaming resistance of the liquid crystal polyester or significantly increases its melting point. Furthermore, the liquid crystal polyester molecular chain in Comparative Example 4 does not contain either the 4,4-diphenyl ether group or the biphenyl group, resulting in significantly poorer foaming resistance or a still relatively high melting point.

[0103] Compared with Example 1, Comparative Example 5, which attached 2,6-naphthyl group to Ar1, and Comparative Example 6, which attached 4,4-diphenyl ether group to Ar3, still produced liquid crystal polyesters with higher melting points and crystallization temperatures, as well as poorer foaming resistance. This shows that the relative positions of the groups in the molecular chain have a significant impact on the performance of liquid crystal polyesters.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A liquid crystal polyester, characterized in that, Including the repeating units shown in Equations I, II, and III: —O—Ar1—O— Formula I; —OC—Ar2—CO— Formula II; —O—Ar3—CO— Formula III; Ar1 is at least one of 1,4-phenylene, 1,3-phenylene, 4,4-biphenyl or 4,4-diphenyl ether. Ar2 is at least one of 1,4-phenylene, 1,3-phenylene, 2,6-naphthylene, or 4,4-diphenyl ether. Ar3 is at least one of 2,6-naphthylene or 1,4-phenylene; Furthermore, the liquid crystal polyester simultaneously contains 1,4-phenylene, 2,6-naphthylene, and 4,4-diphenyl ether group; Based on all the repeating units of the liquid crystal polyester, in the repeating units shown in Formula I, 0 mol% ≤ the content of structural units containing 4,4-diphenyl ether groups ≤ 1 mol%; Based on all the repeating units of the liquid crystal polyester, in the repeating units shown in Formula II, 12 mol% ≤ the content of structural units containing 1,4-phenylene ≤ 20 mol% Based on all repeating units of the liquid crystal polyester, the content of structural units containing 4,4-diphenyl ether groups is 0.2~1.6 mol.

2. The liquid crystal polyester as described in claim 1, characterized in that, Based on all repeating units of the liquid crystal polyester, one or more of the following conditions are satisfied: The content of 1,4-phenylene structural units is >70 mol%; The content of structural units containing 2,6-naphthyl groups is ≥8 mol%; The content of structural units containing 4,4-diphenyl ether groups is 0.5~1.6 mol.

3. The liquid crystal polyester as described in claim 2, characterized in that, Based on all repeating units of the liquid crystal polyester, one or more of the following conditions are satisfied: The content of 1,4-phenylene structural units is >75 mol%; The content of structural units containing 2,6-naphthyl groups is ≥10 mol.

4. The liquid crystal polyester as described in claim 3, characterized in that, Based on all repeating units of the liquid crystal polyester, one or more of the following conditions are satisfied: The content of 1,4-phenylene structural units is 79~90 mol%; The content of structural units containing 2,6-naphthyl groups is 10~20 mol%; The content of structural units containing 4,4-diphenyl ether groups is 0.5~1.5 mol%; 0 mol% ≤ Content of 1,3-phenylene structural units ≤ 1.2 mol% 0 mol% ≤ Content of structural units containing 4,4-biphenyl ≤ 5 mol.

5. The liquid crystal polyester as described in claim 4, characterized in that, Based on all repeating units of the liquid crystal polyester, one or more of the following conditions are satisfied: 0 mol% ≤ Content of 1,3-phenylene structural units ≤ 1 mol% 0 mol% ≤ Content of structural units containing 4,4-biphenyl ≤ 1 mol.

6. The liquid crystal polyester according to any one of claims 1 to 5, characterized in that, Based on all repeating units of the liquid crystal polyester, one or more of the following conditions are satisfied: (1) In the repeating unit shown in Formula I, 15.9 mol% ≤ the content of structural units containing 1,4-phenylene ≤ 18 mol%, 0 mol% ≤ the content of structural units containing 1,3-phenylene ≤ 0.6 mol%, or 0 mol% ≤ the content of structural units containing 4,4-biphenyl ≤ 0.5 mol%, or 0 mol% ≤ the content of structural units containing 4,4-diphenyl ether ≤ 0.5 mol%; (2) In the repeating unit shown in Formula II, 12 mol% ≤ the content of the structural unit containing 1,4-phenylene ≤ 15 mol%, or 0 mol% ≤ the content of the structural unit containing 1,3-phenylene ≤ 0.6 mol%, or 0 mol% ≤ the content of the structural unit containing 2,6-naphthylene ≤ 0.5 mol%, or 0.5 mol% ≤ the content of the structural unit containing 4,4-diphenyl ether ≤ 1 mol%; (3) In the repeating unit shown in Formula III, 50 mol% ≤ 1,4-phenylene structural units ≤ 55 mol%, 13 mol% ≤ 2,6-naphthyl structural units ≤ 16 mol%; The sum of the mole percentages of the repeating units shown in Formulas I, II, and III is 100 mol.

7. The liquid crystal polyester according to any one of claims 1 to 5, characterized in that, Formula I repeating unit monomer is an aromatic diphenol monomer, Formula II repeating unit monomer is an aromatic dicarboxylic acid monomer, and Formula III repeating unit monomer is a hydroxy aromatic carboxylic acid monomer.

8. The liquid crystal polyester according to any one of claims 1 to 5, characterized in that, Meet one or more of the following conditions: (1) The average foaming rate of the liquid crystal polyester is 10% or less; (2) The melting point of the liquid crystal polyester is 328~360℃; (3) Crystallization temperature ≤ 300℃; (4) The thermal weight loss rate at 300℃ for 60 min is ≤0.3%.

9. The method for preparing the liquid crystal polyester according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. The monomers of Formula III repeating unit and Formula I repeating unit undergo an acylation reaction with an acylating agent under catalysis; S2. The acylation reaction product of step S1 and the monomer of the repeating unit of formula II undergo melt polycondensation and decompression polycondensation under catalysis to obtain the prepolymer; S3. After cooling the prepolymer obtained in step S2, granulate it and then perform solid-state polymerization under vacuum conditions to obtain the liquid crystal polyester.

10. The method for preparing liquid crystal polyester as described in claim 9, characterized in that, The molar amount A of the repeating unit monomer of Formula I in step S1. and the molar amount B of the repeating unit monomer of Formula II in step S2. are A:B = (1.03~1.6):

1.

11. The method for preparing liquid crystal polyester as described in claim 9, characterized in that, The acylation reaction and melt polycondensation are carried out in the presence of a catalyst, which is at least one of potassium acetate, sodium acetate, magnesium acetate, zinc acetate, antimony trioxide, or tetrabutyl titanate.

12. The use of the liquid crystal polyester according to any one of claims 1 to 8 in the preparation of foam-resistant and / or heat-resistant electronic devices.

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