A liquid crystal copolyester, its preparation method and applications

Abstract

The present invention belongs to the technical field of polymer materials, and particularly relates to a liquid crystal copolyester and its preparation method and application. The liquid crystal copolyester of the present invention has the following structure: wherein, 0% ≤ x ≤ 90%, 10% ≤ y ≤ 40%, 0.1% ≤ z ≤ 20%. The liquid crystal copolyester of the present invention introduces 2,7-acetoxynaphthalene and isophthalic acid into the main chain of the molecule, which destroys the regular integrity of the macromolecular main chain, effectively reduces the melting point of the liquid crystal copolyester, and expands the processing window. At the same time, a large number of benzene ring structures are retained on the main chain of the liquid crystal copolyester molecule, which has high thermal stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to a liquid crystal copolyester, a preparation method thereof and an application thereof. Background Art

[0002] Liquid crystal copolyesters refer to polymers that can exist in a liquid crystal phase state under certain environmental conditions. Compared with conventional polymer polymers, they have both the molecular orientation unique to the liquid crystal phase and the high modulus and high strength of polymer compounds. Thermotropic liquid crystal copolyesters refer to polymers that form a liquid crystal state in a certain temperature range, that is, the temperature range between the melting point and the clearing point. Such polymers enter the liquid crystal state when heated and melted. For polymers in the liquid crystal state, the rigid parts of the molecular chains are arranged in a certain direction, showing spatial order, but the average orientation (director) of the molecular chains in each micro-region is different. The performance of thermotropic liquid crystal copolyesters is very excellent. In the molten state, the entanglement between molecules is very small, and only a very small shear stress is required to orient it. The liquid form shows the properties of crystalline substances, and its form can exist stably after cooling and solidification. At the same time, during molding, the molecular chains are arranged along the direction of flow, producing an effect similar to self-reinforcement between molecules, and higher modulus and strength can be obtained. Thermotropic liquid crystal copolyesters have a wide range of applications. They can be used as engineering plastics through melt injection molding. The liquid crystal polyester has quite outstanding high-temperature resistance and mechanical properties, and can replace ceramics, glass and some metal materials in the fields of communication equipment, aerospace, automotive parts, etc.

[0003] However, during the industrialization practice of thermotropic liquid crystal polyarylates in China at present, many technical problems have been encountered, such as the polymerization reaction of thermotropic liquid crystal polymers is not easy to control, the melting temperature of the synthesized thermotropic liquid crystal polyarylates is very high, the processing window is narrow, etc. Basically, no effective production capacity has been formed, especially products with certain competitiveness.

[0004] Therefore, in recent years, the goal of scientific researchers has been to design and construct high-performance thermotropic liquid crystal copolyesters with well-defined structures, controllable polymerization reactions, and low melting temperatures. Currently, several research groups have prepared thermotropic liquid crystal polyarylates with different structures and properties through molecular design, providing ideas for the molecular design and property optimization of thermotropic liquid crystal polyarylates. The commonly used methods mainly involve disrupting the regularity of the chain segments through copolymerization, such as using monomers with different lengths, flexible chain monomers, monomers containing substituents, introducing rigid bent monomers into the chain segments, introducing monomers with parallel offsets into the chain, introducing rotating monomers into the chain, etc., to lower the melting point of the thermotropic liquid crystal copolyester. Relevant scholars used the nonlinear biphenyl diacid monomer 4,4'-(phenoxyphosphine) dibenzoic acid (PPDBA), biphenol (BP), and sebacic acid (DA) as raw materials to prepare a series of phosphorus-containing thermotropic liquid crystal polymers (TLCPs). As the content of PPDBA increased, the melting point of the copolyester of TLCP showed a downward trend, with the lowest melting point being 192.2 °C. Although the introduction of the nonlinear biphenyl diacid monomer can disrupt the regularity of the chain segments and lower the melting point, it will also deteriorate the heat resistance of the thermotropic liquid crystal copolyester, damage its mechanical properties, and randomization of the polymer main chain may occur during the reaction, making the reaction conditions uncontrollable. How to maintain good heat resistance while reducing the melting point of the liquid crystal copolyester is one of the problems that still need to be solved in this field. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. For this purpose, the present invention provides a liquid crystal copolyester material with a low melting point and high heat resistance.

[0006] The present invention also provides a preparation method and application of the liquid crystal copolyester material.

[0007] In the first aspect of the present invention, a liquid crystal copolyester is provided, having the following structure:

[0008]

[0009] Wherein, 0% ≤ x ≤ 90%, 10% ≤ y ≤ 40%, 0.1% ≤ z ≤ 20%.

[0010] In the liquid crystal copolyester of the present invention, introducing 2,7 - acetoxynaphthalene and isophthalic acid into the main molecular chain can effectively reduce the melting point. In 2,7 - acetoxynaphthalene, the lateral translation effect of the functional groups substituted at the 2,7 positions on the naphthalene ring enables this type of monomer to connect the polyester molecular chains as a "twisting spindle", disrupting the linear structure of the molecular chain and improving the strong rigidity of the molecular chain of the thermotropic liquid crystal copolyester. The meta - phenyl ring structure on isophthalic acid also causes a decrease in the packing density of the macromolecular main chain, disrupting the regular integrity of the macromolecular main chain, effectively reducing the melting point of the liquid crystal copolyester, and expanding the processing window. At the same time, a large number of benzene ring structures are retained on the main molecular chain of the liquid crystal copolyester, endowing it with high thermal stability.

[0011] Preferably, 50% ≤ x ≤ 90%, more preferably 60% ≤ x ≤ 80%, further preferably 65% ≤ x ≤ 75%, including but not limited to 65%, 69%, 70%, 71%, 73%, etc.

[0012] Preferably, 20% ≤ y ≤ 40%, more preferably 20% ≤ y ≤ 30%, further preferably 25% ≤ y ≤ 30%, including but not limited to 25%, 28%, 29%, 30%, etc.

[0013] Preferably, 0.1% ≤ z ≤ 10%, more preferably 0.1% ≤ z ≤ 5%, further preferably 0.4% ≤ z ≤ 2%, including but not limited to 0.4%, 0.5%, 1.0%, 2%, etc.

[0014] Preferably, the melting temperature (melting point) of the liquid crystal copolyester ≤ 280 °C, more preferably the melting temperature ≤ 267 °C, further preferably the melting temperature is 260 °C - 267 °C.

[0015] Preferably, the thermal decomposition temperature (T 5％ , the temperature at which the thermal weight loss is 5%) ≥ 400 °C, more preferably the thermal decomposition temperature ≥ 415 °C, further preferably the thermal decomposition temperature is 415 °C - 444 °C; the char residue rate of the liquid crystal copolyester at 800 °C ≥ 30%, more preferably the char residue rate at 800 °C ≥ 35%, further preferably the char residue rate at 800 °C is 35 - 40%.

[0016] Preferably, the texture structure of the liquid crystal copolyester is a nematic liquid crystal band.

[0017] In the second aspect of the present invention, a preparation method of the liquid crystal copolyester is proposed, which includes the following steps: adding a mixture of p - acetoxybenzoic acid, 6 - acetoxy - 2 - naphthoic acid, isophthalic acid, 2,7 - acetoxynaphthalene, and a catalyst in batches, and carrying out a melt polycondensation reaction to obtain the liquid crystal copolyester.

[0018] Preferably, the mixture of p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, isophthalic acid, 2,7-acetoxynaphthalene, and the catalyst is added in 3 to 5 portions, more preferably in 4 portions.

[0019] Preferably, the mixture of p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, isophthalic acid, 2,7-acetoxynaphthalene, and the catalyst is added in equal amounts in batches.

[0020] Preferably, the temperature of the melt polycondensation reaction is 200 to 370 °C, more preferably 230 to 350 °C, including but not limited to 230 °C, 240 °C, 250 °C, 260 °C, 340 °C, 350 °C, etc.; the time of the melt polycondensation is 2 to 10 h, more preferably 4 to 8 h.

[0021] Preferably, the melt polycondensation reaction is carried out under the protection of an inert gas, and the inert gas includes at least one of nitrogen and argon; the melt polycondensation reaction is carried out under stirring at a rotation speed of 100 rpm to 300 rpm.

[0022] Preferably, the mixture of p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, isophthalic acid, 2,7-acetoxynaphthalene, and the catalyst is added in four portions. Specifically, the first portion is added before the start of the reaction, and the temperature for adding the first portion of the mixture is 20 to 50 °C, more preferably 20 to 40 °C, such as room temperature; the second, third, and fourth portions are added during the reaction, and the time interval is 1 to 1.5 h. The temperature for adding the second, third, and fourth portions of the mixture is 170 to 210 °C, more preferably 170 to 200 °C, and further preferably 180 to 190 °C.

[0023] Preferably, the preparation process of the liquid crystal copolyester includes the following steps:

[0024] S1, Mix p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, isophthalic acid, 2,7-acetoxynaphthalene, and the catalyst according to the proportion of each chain segment in the chemical formula to obtain a mixture; add part of the mixture (the first feeding), heat up to 230 to 260 °C, and react for 0.5 to 2 h;

[0025] S2, Cool down to 180 to 210 °C, add the mixture for the second time, heat up to 230 to 260 °C, and react for 0.5 to 2 h;

[0026] S3, Cool down to 180 to 210 °C, add the mixture for the third time, heat up to 230 to 260 °C, and react for 0.5 to 2 h;

[0027] S4, Cool down to 180 to 210 °C, add the mixture for the fourth time, heat up to 230 to 260 °C, and react for 0.5 to 2 h;

[0028] In S5, heat up to 320 - 350 °C and react for 0.5 - 2 h to obtain the liquid crystal copolyester.

[0029] Preferably, step S1 further includes pre - treating p - acetoxybenzoic acid, 6 - acetoxy - 2 - naphthoic acid, isophthalic acid, and 2,7 - diacetoxynaphthalene. Specifically, vacuum - dry the p - acetoxybenzoic acid, 6 - acetoxy - 2 - naphthoic acid, isophthalic acid, and 2,7 - diacetoxynaphthalene. The drying temperature is 50 - 90 °C, more preferably 60 - 80 °C; the drying time is 5 - 8 h, more preferably 6 - 8 h.

[0030] Preferably, for the preparation method of the liquid crystal copolyester, after the melt polycondensation reaction, it further includes vacuum pumping and purification treatment. The vacuum pumping treatment is specifically as follows: after the melt polycondensation ends, pump vacuum at a pressure of 50 - 90 Pa for 1 - 3 h to remove by - products (such as acetic acid) in the system; the purification treatment is carried out by Soxhlet extraction method. Specifically, crush the product, put it into a Soxhlet extractor and extract with propanol for 5 - 8 h, and then dry to obtain the liquid crystal copolyester.

[0031] Preferably, the catalyst includes at least one of antimony trioxide, magnesium acetate, zinc acetate, tetrabutyl titanate, and manganese acetate. A more preferred catalyst includes at least one of antimony trioxide, magnesium acetate, and zinc acetate.

[0032] Preferably, the dosage of the catalyst is 0.1 - 1% of the total mass of p - acetoxybenzoic acid, 6 - acetoxy - 2 - naphthoic acid, isophthalic acid, and 2,7 - diacetoxynaphthalene, more preferably 0.1 - 0.5%.

[0033] Preferably, the molar ratio of p - acyloxybenzoic acid to 6 - acetoxy - 2 - naphthoic acid is 1 - 5:1, more preferably 2 - 4:1, further preferably 2 - 3:1, including but not limited to 2:1, 2.3:1, 2.5:1, 2.8:1, 3:1, etc.

[0034] Preferably, the molar ratio of 6 - acetoxy - 2 - naphthoic acid to isophthalic acid is 20 - 80:1, more preferably 30 - 60:1, including but not limited to 30:1, 50:1, 60:1, etc.

[0035] Preferably, the molar ratio of isophthalic acid to 2,7 - diacetoxynaphthalene is about 1:1.

[0036] In the third aspect of the present invention, the application of the liquid crystal copolyester in the preparation of communication equipment, aerospace, and automotive parts.

[0037] Compared with the prior art, the present invention has at least the following beneficial effects:

[0038] (1) Introducing 2,7 - acetoxynaphthalene and isophthalic acid into the main chain of the liquid crystal copolyester molecule can effectively reduce the melting point. In 2,7 - acetoxynaphthalene, the lateral translation effect of the functional groups substituted at the 2,7 positions on the naphthalene ring enables this type of monomer to connect the polyester molecular chains as a "twisting axis", disrupting the linear structure of the molecular chains, improving the strong rigidity of the thermotropic liquid crystal copolyester molecular chains. The meta - benzene ring structure on isophthalic acid also causes a decrease in the packing density of the macromolecular main chain, disrupting the regular integrity of the macromolecular main chain, and thus reducing the melting point of the copolyester. At the same time, it has relatively high thermal stability, which expands the processing window to a certain extent.

[0039] (2) In addition, a melt polycondensation method with step - by - step feeding and gradual temperature control is used to prepare high - performance thermotropic liquid crystal copolyesters. This method has the characteristics of controllable reaction, can accelerate the reaction rate, and allows the linear growth of molecular chains to be sufficient. By applying a vacuum or an inert gas atmosphere, the terminal functional groups between molecular chains can further collide and react, and high - molecular - weight products can be obtained.

[0040] (3) The preparation method of the present invention is simple, easy to operate and control, and has good reproducibility. Description of the Drawings

[0041] The following further describes the present invention in conjunction with the drawings and embodiments, where:

[0042] Figure 1 is a schematic diagram of the synthesis route for preparing the liquid crystal copolyester of the present invention;

[0043] Figure 2 is the infrared spectrum of the liquid crystal copolyester prepared in Example 1 of the present invention;

[0044] Figure 3 is the solid nuclear magnetic spectrum of the liquid crystal copolyester prepared in Example 1 of the present invention;

[0045] Figure 4 is the DSC spectrum of the liquid crystal copolyester prepared in Example 1 of the present invention;

[0046] Figure 5 is the TG and DTG spectra of the liquid crystal copolyester prepared in Example 1 of the present invention;

[0047] Figure 6 is the texture structure diagram of the liquid crystal copolyester prepared in Example 1 of the present invention. Detailed Embodiments

[0048] The concept of the present invention and the resulting technical effects will be clearly and completely described below in conjunction with embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts all fall within the scope of protection of the present invention.

[0049] In the following embodiments, the raw materials used, unless otherwise specified, can be obtained from conventional commercial channels; the processes used, unless otherwise specified, are conventional processes in the art; the operating temperatures used, unless otherwise specified, are room temperature (20 ± 5°C).

[0050] Example 1

[0051] In this example, a thermotropic liquid crystal copolyester was prepared. The specific process is as follows:

[0052] S1: First, place the polymer monomers in a vacuum drying oven at 60°C for 6 hours. Weigh 10.09 g (0.056 mol) of p-acetoxybenzoic acid, 5.53 g (0.024 mol) of 6-acetoxy-2-naphthoic acid, 0.0665 g (0.0004 mol) of isophthalic acid, 0.0977 g (0.0004 mol) of 2,7-acetoxynaphthalene, and 0.0789 g of zinc acetate, and then add them together into a container with stirring. Stir for 1 hour, and then add the stirred mixture to the reactor in four equal amounts. Add 3.9658 g of the mixed raw materials to the reactor for the first time, open the vacuum pump to apply a negative pressure environment to the reactor, and purge with nitrogen to remove the air in the system. Then introduce nitrogen, start stirring, and carry out the melt polycondensation reaction under stirring at 100 rpm. Heat the reactor to 260°C and react for 1 hour. When reflux appears in the system, then lower the temperature to 190°C. Add 3.9658 g of the mixed raw materials for the second time, heat up to 260°C again, react for 1 hour, and then lower the temperature to 190°C. Add 3.9658 g of the mixed raw materials for the third time, heat up to 260°C again, react for 1 hour, and then lower the temperature to 190°C. Add 3.9658 g of the mixed raw materials for the fourth time, heat up to 260°C again, react for 1 hour, and continue to heat up to 350°C and maintain for 0.5 hour. Close the nitrogen, connect the vacuum system, and take out as much by-product acetic acid as possible. After evacuating and maintaining for 2 hours, the vacuum degree can reach 60 - 90 Pa, and stop the reaction. Take out the product, crush it with a crusher, then extract it with acetone in a Soxhlet extractor for 6 hours, and finally dry it in an oven for testing. The synthesis route is as Figure 1As shown in the figure. The melting temperature of the liquid crystal copolyester prepared in this example is 263 °C, the decomposition temperature at 5% weight loss is 444 °C, the char yield at 800 °C is 36.51%, and it also exhibits a typical nematic liquid crystal band texture.

[0053] Example 2

[0054] In this example, a thermotropic liquid crystal copolyester was prepared. The specific process is as follows:

[0055] S1: First, place the polymer monomers in a vacuum drying oven at 65 °C for 6 hours. Weigh 10.09 g (0.056 mol) of p-acetoxybenzoic acid, 5.53 g (0.024 mol) of 6-acetoxy-2-naphthoic acid, 0.1329 g (0.0008 mol) of isophthalic acid, 0.1954 g (0.0008 mol) of 2,7-acetoxynaphthalene, and 0.0797 g of zinc acetate respectively, and then add them together into a container with stirring. Stir for 1 hour, and then add the stirred mixture into the reactor in four equal amounts. Add 4.0070 g of the mixed raw materials to the reactor for the first time, and turn on the vacuum pump to apply a negative pressure environment to the reactor, and purge with nitrogen to remove the air in the system. Then introduce nitrogen, turn on the stirring, and carry out the melt polycondensation reaction under stirring at 100 rpm. Heat the reactor to 260 °C and react for 1 hour. When reflux appears in the system, then lower the temperature to 190 °C. Add 4.0070 g of the mixed raw materials for the second time and then heat up to 260 °C and react for 1 hour. Then lower the temperature to 190 °C. Add 4.0070 g of the mixed raw materials for the third time and then heat up to 260 °C and react for 1 hour. Then lower the temperature to 190 °C. Add 4.0070 g of the mixed raw materials for the fourth time and then heat up to 260 °C and react for 1 hour, and continue to heat up to 350 °C and hold for 0.5 hour. Turn off the nitrogen, connect the vacuum system, and take out as much by-product acetic acid as possible. After evacuating and maintaining for 2 hours, the vacuum degree can reach 60 - 90 Pa, and stop the reaction. Take out the product and crush it with a crusher, then extract it with acetone in a Soxhlet extractor for 6 hours, and finally put it in an oven to dry for testing. The melting temperature of the novel liquid crystal copolyester prepared in this example is 262 °C, the decomposition temperature at 5% weight loss is 418 °C, the char yield at 800 °C is 37.60%, and it also exhibits a typical nematic liquid crystal band texture.

[0056] Example 3

[0057] In this example, a thermotropic liquid crystal copolyester was prepared. The specific process is as follows:

[0058] S1: First, place the polymer monomers in a vacuum drying oven at 70 °C for 7 hours. Weigh 10.09 g (0.056 mol) of p-acetoxybenzoic acid, 5.53 g (0.024 mol) of 6-acetoxy-2-naphthoic acid, 0.1329 g (0.0008 mol) of isophthalic acid, 0.1954 g (0.0008 mol) of 2,7-acetoxynaphthalene, and 0.0797 g of zinc acetate respectively, and then add them together into a container with stirring. Stir for 1 hour, and then add the stirred mixture into the reactor in four equal amounts. Add 4.0070 g of the mixed raw materials to the reactor for the first time, turn on the vacuum pump to create a negative pressure environment in the reactor, and purge with nitrogen to remove the air in the system. Then introduce nitrogen, start stirring, and carry out the melt polycondensation reaction under stirring at 100 rpm. Heat the reactor to 250 °C and react for 1 hour. When reflux appears in the system, then lower the temperature to 180 °C. Add 4.0070 g of the mixed raw materials for the second time, heat up to 250 °C again, react for 1 hour, and then lower the temperature to 180 °C. Add 4.0070 g of the mixed raw materials for the third time, heat up to 250 °C again, react for 1 hour, and then lower the temperature to 180 °C. Add 4.0070 g of the mixed raw materials for the fourth time, heat up to 250 °C again, react for 1 hour, and continue to heat up to 340 °C and hold for 0.5 hour. Turn off the nitrogen, connect the vacuum system, and bring out as much by-product acetic acid as possible. After evacuating and maintaining for 2 hours, the vacuum degree can reach 60 - 90 Pa, and stop the reaction. Take out the product and crush it with a crusher, then extract it with acetone in a Soxhlet extractor for 6 hours, and finally dry it in an oven for testing. The melting temperature of the liquid crystal copolyester prepared in this example is 260 °C, the decomposition temperature at 5% weight loss is 415 °C, the char yield at 800 °C is 37.30%, and it also exhibits a typical nematic liquid crystal band texture.

[0059] Example 4

[0060] In this example, a thermotropic liquid crystal copolyester was prepared, and the specific process is as follows:

[0061] S1: First, place the polymer monomers in a vacuum drying oven at 75°C for 7 hours. Weigh 10.81 g (0.06 mol) of p-acetoxybenzoic acid, 5.53 g (0.024 mol) of 6-acetoxy-2-naphthoic acid, 0.0665 g (0.0004 mol) of isophthalic acid, 0.0977 g (0.0004 mol) of 2,7-acetoxynaphthalene, and 0.0789 g of zinc acetate respectively. Then add them together into a container with stirring and stir for 1 hour. After that, add the stirred mixture into the reactor in four equal portions. Add 4.1458 g of the mixed raw materials to the reactor for the first time, turn on the vacuum pump to apply a negative pressure environment to the reactor, and purge with nitrogen to remove the air in the system. Then introduce nitrogen, start stirring, and carry out the melt polycondensation reaction under stirring at 200 rpm. Heat the reactor to 240°C and react for 1 hour. When reflux appears in the system, then lower the temperature to 190°C. Add 4.1458 g of the mixed raw materials for the second time and heat up to 240°C again, react for 1 hour, then lower the temperature to 190°C. Add 4.1458 g of the mixed raw materials for the third time and heat up to 240°C again, react for 1 hour, then lower the temperature to 190°C. Add 4.1458 g of the mixed raw materials for the fourth time and heat up to 240°C again, react for 1 hour, and continue to heat up to 340°C and hold for 1 hour. Turn off the nitrogen, connect the vacuum system, and take out as much by-product acetic acid as possible. After evacuating and maintaining for 3 hours, the vacuum degree can reach 60 - 90 Pa, and stop the reaction. Take out the product and crush it with a crusher, then extract it with acetone in a Soxhlet extractor for 6 hours, and finally put it in an oven to dry for testing. The melting temperature of the liquid crystal copolyester prepared in this example is 264°C, the decomposition temperature at 5% weight loss is 418°C, the char yield at 800°C is 37.44%, and it also shows a typical nematic liquid crystal band texture.

[0062] Example 5

[0063] In this example, a thermotropic liquid crystal copolyester was prepared, and the specific process is as follows:

[0064] S1: First, place the polymer monomer in a vacuum drying oven at 75°C for 7 hours. Weigh 10.81 g (0.06 mol) of p-acetoxybenzoic acid, 5.53 g (0.024 mol) of 6-acetoxy-2-naphthoic acid, 0.1329 g (0.0008 mol) of isophthalic acid, 0.1954 g (0.0008 mol) of 2,7-acetoxynaphthalene, and 0.0797 g of zinc acetate respectively, and then add them together into a container with stirring. Stir for 1 hour, and then add the stirred mixture into the reactor in four equal amounts. Add 4.1870 g of the mixed raw materials to the reactor for the first time, turn on the vacuum pump to create a negative pressure environment for the reactor, and purge with nitrogen to remove the air in the system. Then introduce nitrogen, start stirring, and carry out the melt polycondensation reaction under stirring at 100 rpm. Heat the reactor to 260°C and react for 1.5 hours. When reflux appears in the system, then lower the temperature to 190°C. Add 4.1870 g of the mixed raw materials for the second time, heat up to 260°C again, and react for 1.5 hours. Then lower the temperature to 190°C. Add 4.1870 g of the mixed raw materials for the third time, heat up to 260°C again, and react for 1.5 hours. Then lower the temperature to 190°C. Add 4.1870 g of the mixed raw materials for the fourth time, heat up to 260°C again, and react for 1.5 hours. Then continue to heat up to 350°C and hold for 0.5 hour. Turn off the nitrogen, connect the vacuum system, and take out as much by-product acetic acid as possible. After evacuating and maintaining for 2 hours, the vacuum degree can reach 60 - 90 Pa, and stop the reaction. Take out the product and crush it with a crusher, then extract it with acetone in a Soxhlet extractor for 6 hours, and finally dry it in an oven for testing. The melting temperature of the liquid crystal copolyester prepared in this example is 267°C, the decomposition temperature at 5% weight loss is 415°C, the char yield at 800°C is 37.30%, and it also shows a typical nematic liquid crystal band texture.

[0065] Example 6

[0066] In this example, a thermotropic liquid crystal copolyester was prepared, and the specific process is as follows:

[0067] S1: First, place the polymer monomer in a vacuum drying oven at 80°C for 8 hours. Weigh 10.81 g (0.06 mol) of p-acetoxybenzoic acid, 5.53 g (0.024 mol) of 6-acetoxy-2-naphthoic acid, 0.1329 g (0.0008 mol) of isophthalic acid, 0.1954 g (0.0008 mol) of 2,7-acetoxynaphthalene, and 0.0797 g of zinc acetate respectively. Then add them together into a container with stirring and stir for 1 hour. After that, divide the stirred mixture into four equal portions and add them to the reactor. Add 4.1870 g of the mixed raw materials to the reactor for the first time, turn on the vacuum pump to create a negative pressure environment in the reactor, and purge with nitrogen to remove the air in the system. Then introduce nitrogen, start stirring, and carry out the melt polycondensation reaction under stirring at 200 rpm. Heat the reactor to 250°C and react for 1.5 hours. When reflux appears in the system, then lower the temperature to 190°C. Add 4.1870 g of the mixed raw materials for the second time, then heat up to 250°C and react for 1.5 hours. After that, lower the temperature to 190°C. Add 4.1870 g of the mixed raw materials for the third time, then heat up to 250°C and react for 1.5 hours. After that, lower the temperature to 190°C. Add 4.1870 g of the mixed raw materials for the fourth time, then heat up to 250°C and react for 1.5 hours, and continue to heat up to 350°C and hold for 1 hour. Turn off the nitrogen, connect the vacuum system, and take out as much by-product acetic acid as possible. After evacuating and maintaining for 2 hours, the vacuum degree can reach 60 - 90 Pa, and stop the reaction. Take out the product and crush it with a crusher, then extract it with acetone in a Soxhlet extractor for 6 hours, and finally dry it in an oven for testing. The melting temperature of the liquid crystal copolyester prepared in this example is 265°C, the decomposition temperature at 5% weight loss is 417°C, the char yield at 800°C is 37.50%, and it also shows a typical nematic liquid crystal band texture.

[0068] Test Example

[0069] This test example tested the performance of the liquid crystal copolyester prepared in the example. Among them:

[0070] Use the Nicolet560 Fourier transform infrared spectrometer of Nicolet Company in the United States for infrared testing; use the Agilent 600M solid nuclear magnetic resonance of Agilent Company in the United States to test the sample. Use the Q 20 series DSC of TA Company and the Q 50 series thermogravimetric analyzer of TA Company to test the thermal properties of this liquid crystal copolyester. Use the XP-800 series polarizing microscope of Shanghai Guangmi Instrument to observe the liquid crystallinity of this liquid crystal polymer.

[0071] Result description:

[0072] (1) Infrared spectrum

[0073] The infrared spectrum of the liquid crystal copolyester prepared in Example 1 is as follows Figure 2 shown. There is a stretching vibration absorption peak of C-H of the benzene ring at 3075 cm -1 . There is a strong absorption vibration peak at 1732 cm -1 belonging to the C=O vibration of the ester. The absorption peak at 881 cm -1 indicates the presence of a p-disubstituted benzene structure in the copolyester. In addition, 1629 cm -1 , 1600 cm -1 , 1504 cm -1 and 1412 cm -1 are the absorption vibration peaks of the aromatic ring skeleton. 1260 cm -1 and 1141 cm -1 are the asymmetric stretching vibration peaks of C-O-C. 1046 cm -1 and 1011 cm -1 are the symmetric stretching vibration peaks of C-O-C. The presence of the above characteristic absorption peaks of functional groups indicates that 4-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, isophthalic acid, and 2,7-acetoxynaphthalene participated in the polymerization reaction, and the required high-performance liquid crystal copolyester was successfully obtained.

[0074] (2) Solid nuclear magnetic spectrum

[0075] The solid nuclear magnetic spectrum of the liquid crystal copolyester prepared in Example 1 is as follows Figure 3 shown. The peak at 157 ppm is the chemical shift peak of the ester carbonyl carbon (a, b) in the copolyester; the peaks at 148 ppm and 144 ppm are the chemical shifts of the carbon atoms (c, d) connected to the oxygen atom in the aromatic ring skeleton. There are multiple overlapping peaks between 118-125 ppm, which are the chemical shift peaks of other carbon atoms on the aromatic ring skeleton. It can be further confirmed from the solid nuclear magnetic spectrum that the obtained copolyester is the target product.

[0076] (3) Thermodynamic properties

[0077] Table 1 Thermodynamic properties of the liquid crystal copolyester of the examples

[0078] Melting temperature / °C <![CDATA[T 5％ / ℃]]> Residual carbon rate at 800 °C / % Structure Example 1 263 444 36.51 Nematic liquid crystal stripe texture Example 2 262 418 37.60 Nematic liquid crystal stripe texture Example 3 260 415 37.30 Nematic liquid crystal stripe texture Example 4 264 418 37.44 Nematic liquid crystal stripe texture Example 5 267 415 37.30 Nematic liquid crystal stripe texture Example 6 265 417 37.50 Nematic liquid crystal stripe texture

[0079] The DSC spectrum of the liquid crystal copolyester prepared in Example 1 is as follows Figure 4 shown. It can be seen from the figure that the melting temperature of the new liquid crystal copolyester is only 263 °C. As can be seen from Table 1, the melting temperatures of the copolyesters prepared in Examples 1-6 are 260-270 °C, which expands the processing window and matches the processing temperatures of most thermoplastic resins.

[0080] The TG and DTG spectra of the liquid crystal copolyester prepared in Example 1 are as follows Figure 5As shown, it can be seen from the figure that the decomposition temperature of the novel liquid crystal copolyester when the weight loss is 5% is 444 °C, which has a relatively high thermal decomposition temperature. At the same time, the char residue rate at 800 °C is 36.51%. Combining with Table 1, it can be known that the thermal decomposition temperature and T 5％ , char residue rate of the copolyesters prepared in Examples 2-6 are close, indicating that the copolyesters prepared in Examples 1-6 of the present invention have good processability and excellent heat resistance at the same time.

[0081] Figure 6 is the texture structure diagram (POM diagram) of the liquid crystal copolyester prepared in Example 1. From Figure 6 , it can be known that the liquid crystal copolyester of Example 1 shows a typical nematic liquid crystal band texture, indicating that the liquid crystal polymer prepared by the present invention has liquid crystallinity. The texture structures of Examples 2-6 are also nematic liquid crystal band textures.

[0082] The above has made a detailed description of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention. In addition, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Claims

1. A liquid crystal copolyester, characterized in that, It has the following structure: where 50% ≤ x ≤ 90%, 20% ≤ y ≤ 40%, 0.1% ≤ z ≤ 10%; The melting temperature of the liquid crystal copolyester ≤ 280°C; the thermal decomposition temperature of the liquid crystal copolyester ≥ 400°C; The liquid crystal copolyester is prepared by a method comprising the following steps: Adding a mixture of p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, isophthalic acid, 2,7-acetoxynaphthalene, and a catalyst in batches, and carrying out melt polycondensation reaction to obtain the liquid crystal copolyester; The molar ratio of p-acetoxybenzoic acid to 6-acetoxy-2-naphthoic acid is 1 - 5:1; the molar ratio of 6-acetoxy-2-naphthoic acid to isophthalic acid is 20 - 80:1; the molar ratio of isophthalic acid to 2,7-acetoxynaphthalene is 1:1; The mixture of p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, isophthalic acid, 2,7-acetoxynaphthalene, and the catalyst is added in four batches. The first batch is added before the reaction starts, and the temperature for adding the first batch of the mixture is 20 - 50°C; the second, third, and fourth batches are added during the reaction, with a time interval of 1 - 1.5 h, and the temperature for adding the second, third, and fourth batches of the mixture is 170 - 210°C.

2. The preparation method of the liquid crystal copolyester according to claim 1, characterized in that, It includes the following steps: adding a mixture of p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, isophthalic acid, 2,7-acetoxynaphthalene, and a catalyst in batches, and carrying out melt polycondensation reaction to obtain the liquid crystal copolyester.

3. The preparation method of the liquid crystal copolyester according to claim 2, characterized in that, The temperature of the melt polycondensation reaction is 200 - 370°C.

4. The preparation method of the liquid crystal copolyester according to claim 2, characterized in that, The preparation process of the liquid crystal copolyester includes the following steps: S1, mixing p-acetoxybenzoic acid, 6-acetoxy-2-naphthoic acid, isophthalic acid, 2,7-acetoxynaphthalene, and a catalyst according to the proportion of each chain segment in the chemical formula to obtain a mixture; adding part of the mixture, heating to 230 - 260°C, and reacting for 0.5 - 2 h; S2, cooling to 180 - 210°C, adding the mixture for the second time, heating to 230 - 260°C, and reacting for 0.5 - 2 h; S3, cooling to 180 - 210°C, adding the mixture for the third time, heating to 230 - 260°C, and reacting for 0.5 - 2 h; S4, cooling to 180 - 210°C, adding the mixture for the fourth time, heating to 230 - 260°C, and reacting for 0.5 - 2 h; S5, heating to 320 - 350°C, reacting for 0.5 - 2 h to obtain the liquid crystal copolyester.

5. The preparation method of the liquid crystal copolyester according to claim 2, wherein, For the preparation method of the liquid crystal copolyester, after the melt polycondensation reaction, it further includes vacuum pumping and purification treatment.

6. The preparation method of the liquid crystal copolyester according to claim 2, characterized in that The catalyst includes at least one of antimony trioxide, magnesium acetate, zinc acetate, tetrabutyl titanate, and manganese acetate.

7. Application of the liquid crystal copolyester according to claim 1 in the preparation of communication equipment, aerospace, and automotive parts.

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