Method for preparing high molecular weight thermotropic liquid crystal polyester through melt coupling solid phase polycondensation

Abstract

The invention discloses a method for preparing high molecular weight thermotropic liquid crystal polyester through melt coupling solid phase polycondensation. The method comprises the following steps: mixing p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid and a catalyst 1-methylimidazole according to a specific molar ratio of (70-75): (25-30) to synthesize a liquid crystal polyester prepolymer with specific logarithmic viscosity; the preparation method comprises the following steps: crushing and drying a liquid crystal polyester prepolymer, placing prepolymer particles in a solid phase polycondensation device, accurately controlling the time and temperature of the polycondensation reaction, carrying out heating reaction in a nitrogen atmosphere to obtain high molecular weight thermotropic liquid crystal polyester, taking out the high molecular weight liquid crystal polyester, and carrying out viscosity test. In the preparation process of the prepolymer, the prepolymer with proper logarithmic viscosity can be effectively prepared by controlling the reaction temperature and time, so that the controllable preparation of the polymer is realized; the solid-phase polycondensation time required for obtaining the high-molecular-weight polymer is shortened by crushing the prepolymer into particles with different diameters, so that the solid-phase polycondensation efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a method for preparing high-molecular-weight thermotropic liquid crystal polyester by melt coupling solid-phase polycondensation. Background Art

[0002] In recent years, with the continuous development of electronic communication technology towards high frequency, high speed and high integration, higher requirements have been put forward for the performance of copper clad laminates. Thermotropic liquid crystal polymers are a class of polymers that can exhibit liquid crystal phases in the molten state, and the main representative is aromatic thermotropic liquid crystal polyester (TLCP). TLCP exhibits stable low dielectric properties, low water absorption, extremely low thermal expansion coefficient, and excellent thermal stability in the 5G millimeter wave band, and is considered an ideal high-performance millimeter wave substrate and packaging material. Fully aromatic liquid crystal copolyesters containing p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) components are an important class of TLCP (the most famous of which is Vectra), and are widely used in the fields of electronics and electrical appliances, optical fibers, chemical equipment, and other instruments.

[0003] The prior art CN114292389A proposes "a liquid crystal polymer and its preparation method and application", and directly melts and prepares liquid crystal polyester by a one-pot method. The specific reaction conditions are: heating to 80-150°C and reacting for 0.5-3h for acetylation reaction, and then continuing to heat to 250-330°C for melt polycondensation reaction. Further optimization is carried out by reacting at 250-280°C for 1.5-3h and at 280-330°C for 0.5-3h to finally obtain liquid crystal polyester. The prior art CN112334508A proposes "a method for manufacturing liquid crystalline resin", and its specific implementation method is to add monomers, catalysts and acetylation reagents into a polymerization reaction kettle, raise the reaction temperature to 140°C and carry out an acetylation reaction for 3h at the same time. Then it is further heated to 360°C in 4h, and then evacuated to 1330 Pa in 15 min to distill out acetic acid, excessive acetic anhydride and by-products such as phenol while carrying out polycondensation. The time from the start of decompression to when the stirring torque reaches a predetermined value is 20 min. After the torque reaches the predetermined value, nitrogen is introduced, and the pressure is increased from the decompressed state through normal pressure to a pressurized state, and the polymer is discharged from the lower part of the polymerization kettle to obtain the final liquid crystal polyester.

[0004] As can be seen from the above patent documents, the preparation method of thermotropic liquid crystal polyester is the "one-pot method". However, there are currently major problems with this method. After the polymerization in the reaction kettle is completed, it takes about ten minutes to one hour to discharge the material. The viscosity difference between the polymer in the first part of the discharged material and the polymer in the later part of the discharged material is large, and subsequent mixing is required to improve the uniformity. The traditional stirring device of the reaction kettle is difficult to handle materials with high viscosity or extremely high viscosity. The material stirring is difficult, the motor is extremely prone to overload, and the discharging is not complete. A large amount of residual material seriously affects subsequent batches. Moreover, due to a large amount of residual material, the reaction kettle needs to be frequently cleaned. At the same time, staying at a high temperature for too long will cause serious oxidation problems, increasing the by-products of the product and making the color darker.

[0005] The two-step method of melt coupling solid-state polycondensation is an important way to solve the above problems. At present, the solid-state polycondensation method has been applied in the production of polyester, nylon, etc. and has achieved good results. Its main feature is to prepare prepolymer particles with a relatively low molecular weight through melt polycondensation, and then carry out the polymerization reaction in a solid state far below the melting point of the prepolymer by about 50 °C. Since the solid-state polycondensation reaction does not need to go through the high-temperature and high-vacuum stages above the melting point, the polymerization reaction process conditions are relatively easy to control, the feeding and discharging are convenient, and the product has good color and a narrow molecular weight distribution.

[0006] Using the solid-state polymerization method to synthesize liquid crystal copolyesters is a good choice.

[0007] The prior art CN103459461A records a method for preparing liquid crystal polyester with a high molecular weight. The method for preparing liquid crystal polyester includes the following steps: (1) Using p-hydroxybenzoic acid, 4,4'-dihydroxybiphenyl, and 1,4-cyclohexanedicarboxylic acid as reaction monomers, and obtaining a prepolymer with a suitable molecular weight by regulating the polymerization process; (2) Then, the prepolymer is crushed into prepolymer powder with a particle diameter of 2 mm by a crusher and placed in a vacuum oven for drying; (3) The 2-mm particles are subjected to solid-state polycondensation for 15 h to obtain the final liquid crystal polyester product. This patent does not consider the influence of particle size on the production efficiency of solid-state polycondensation when implementing solid-state polycondensation. Therefore, in order to provide more data support for solid-state polycondensation and provide data guidance for the selection of reactors, the present invention proposes a method for preparing high molecular weight thermotropic liquid crystal polyester by melt coupling solid-state polycondensation, including optimizing and controlling the melt polymerization process conditions, determining the discharging time of the reaction kettle in the melt polymerization section and the intrinsic viscosity of the prepolymer, and effectively improving the solid-state polycondensation efficiency by controlling the particle size of the prepolymer powder, and finally forming an efficient polymerization method for high molecular weight liquid crystal polyester. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing high molecular weight thermotropic liquid crystal polyester by melt coupling solid-state polycondensation, so as to shorten the solid-state reaction time and improve the reaction efficiency of solid-state polycondensation.

[0009] The object of the present invention is achieved by the following technical solutions:

[0010] A method for preparing high molecular weight thermotropic liquid crystal polyester by melt coupling solid-phase polycondensation, comprising the following steps:

[0011] (1) Carry out acetylation reactions on the monomers p-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA) and acetic anhydride respectively. After the acetylation reactions are completed, recrystallize the products to remove the excess acetic anhydride, and obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 6-acetoxy-2-naphthoic acid monomer (ANA) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization refinement;

[0012] (2) Carry out melt polycondensation reaction on the refined acetylated product and zinc acetate catalyst at high temperature to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure to discharge a liquid crystal polyester prepolymer with a certain molecular weight;

[0013] (3) Transport the liquid crystal polyester prepolymer to a pulverizer. In the pulverizer, the low molecular weight liquid crystal polyester prepolymer is pulverized into prepolymer particles with uniform size. Then place the prepolymer particles with uniform particle size in a vacuum oven for drying to remove a small amount of acetic acid, a by-product of melt polycondensation. Place the dried prepolymer particles in a solid-phase polycondensation device and carry out a reaction under heating in a nitrogen atmosphere to obtain high molecular weight HBA / HNA thermotropic liquid crystal polyester.

[0014] Preferably, in step (1), the molar percentage of p-hydroxybenzoic acid (HBA) to 6-hydroxy-2-naphthoic acid (HNA) is 70-75:25-30.

[0015] Preferably, in step (1), the conditions of the acetylation reaction are reaction at 140-150 °C for 1-2 h.

[0016] Preferably, in step (2), the conditions of the melt polycondensation reaction are reaction at 250 °C for 3-4 h, reaction at 280 °C for 1-2 h, reaction at 320 °C for 0.5-3 h, and evacuate to 2000 Pa vacuum at this temperature.

[0017] Preferably, in step (2), the inherent viscosity of the obtained liquid crystal polyester prepolymer is controlled at 3.5-4.5.

[0018] Preferably, in step (2), the dosage of the zinc acetate catalyst is 200-500 ppm.

[0019] Preferably, in step (3), the uniformly sized prepolymer particles are spherical particles with a diameter of 30 to 300 mesh. The prepolymer particles are placed in a vacuum oven at 120 °C and dried for 12 to 14 h. The dried prepolymer particles are placed in a solid-state polycondensation device and heated to 210 to 240 °C in a nitrogen atmosphere. After reacting for 2 to 8 h, a high molecular weight HBA / HNA thermotropic liquid crystal polyester is obtained.

[0020] Preferably, in step (3), the high molecular weight HBA / HNA thermotropic liquid crystal polyester is taken out for viscosity testing. The logarithmic viscosity is 4.7 to 8.5, the molecular weight distribution is relatively narrow, and the color of the liquid crystal polyester is light beige.

[0021] This application also claims to protect a high molecular weight HBA / HNA liquid crystal polyester, which is prepared by the method of preparing a high molecular weight HBA / HNA liquid crystal polyester by the above-mentioned melt coupling solid-state polycondensation.

[0022] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0023] In the process of preparing the prepolymer of the present invention, a prepolymer with an appropriate logarithmic viscosity can be effectively prepared by controlling the reaction temperature and time to achieve the controllable preparation of the polymer. By crushing the prepolymer into particles with different diameters, the solid-state polycondensation time required to obtain a high molecular weight polymer is shortened, so as to improve the efficiency of the solid-state polycondensation reaction. Description of the Drawings

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, some of the drawings below are embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is a physical diagram of the high molecular weight liquid crystal polyester in Example 1 of the present invention. Detailed Description of the Invention

[0026] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the specific implementation methods will be described in detail below.

[0027] The present invention will be further described below in conjunction with the embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use. The implementation conditions not specified are the conventional conditions in the industry. The technical features involved in each implementation manner of the present invention can be combined with each other as long as they do not conflict with each other.

[0028] Example 1

[0029] See the appendix Figure 1 This example provides a method for preparing high-molecular-weight thermotropic liquid crystal polyester by melt coupling solid-phase polycondensation, including the following steps:

[0030] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 6-hydroxy-2-naphthoic acid (HNA) at a molar ratio of 73:27, and mix with acetic anhydride which is 2.2 times the total molar number of monomer hydroxyl groups and 300 ppm of 1-methylimidazole based on the total weight of the monomers. Heat up to 150 °C and keep constant temperature for 1 h for acetylation reaction. After the acetylation reaction is completed, recrystallize the monomers to remove the excess acetic anhydride, and obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 6-acetoxy-2-naphthoic acid monomer (ANA) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization refinement;

[0031] (2) Place the refined acetylated product and 300 ppm of zinc acetate catalyst in a three-necked flask, heat up to 250 °C and react for 3 h, continue to heat up to 280 °C and react for 1 h, continue to heat up to 320 °C and react for 0.5 h, and evacuate to 2000 Pa vacuum at this temperature for melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure, discharge the liquid crystal polyester prepolymer, and test the viscosity of the obtained liquid crystal polyester prepolymer;

[0032] (3) Transport the liquid crystal polyester prepolymer to a pulverizer. In the pulverizer, the low-molecular-weight liquid crystal polyester prepolymer is pulverized into prepolymer particles with a size of 30 - 50 meshes (0.3 - 0.6 mm). Then place the prepolymer particles with different diameters in a vacuum oven at 120 °C and dry for 12 h. Place the dried prepolymer particles in a vacuum rotary drum, with a nitrogen flow rate of 0.013 m / s, and keep at 210 °C for 2 h for solid-phase polycondensation to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester. Take out the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester, cool it, and then test its viscosity.

[0033] Example 2

[0034] This example provides a method for preparing high-molecular-weight thermotropic liquid crystal polyester by melt coupling solid-phase polycondensation, including the following steps:

[0035] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 6-hydroxy-2-naphthoic acid (HNA) at a molar ratio of 73:27, with acetic anhydride accounting for 2.2 times the total molar amount of the hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole based on the total weight of the monomers. Heat the mixture to 150 °C and then keep it at a constant temperature for 1 h for the acetylation reaction. After the acetylation reaction is completed, recrystallize the monomers to remove the excess acetic anhydride, and obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 6-acetoxy-2-naphthoic acid monomer (ANA) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization refinement;

[0036] (2) Place the refined acetylated product and 300 ppm of zinc acetate catalyst in a three-necked flask, heat it to 250 °C and react for 3 h, continue to heat to 280 °C and react for 1 h, then continue to heat to 320 °C and react for 1 h, and evacuate to 2000 Pa vacuum at this temperature for melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure, discharge the liquid crystal polyester prepolymer, and test the viscosity of the obtained liquid crystal polyester prepolymer;

[0037] (3) Transport the liquid crystal polyester prepolymer to a pulverizer. In the pulverizer, the low-molecular-weight liquid crystal polyester prepolymer is pulverized into prepolymer particles with a size of 30 - 50 mesh (0.3 - 0.6 mm). Then place the prepolymer particles with different diameters in a vacuum oven at 120 °C and dry for 12 h. Place the dried prepolymer particles in a vacuum rotary drum, with a nitrogen flow rate of 0.013 m / s, and keep it at 210 °C for 2 h for solid-phase polycondensation to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester. Take out the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester, cool it, and then test its viscosity.

[0038] Example 3

[0039] This example provides a method for preparing high-molecular-weight thermotropic liquid crystal polyester by melt coupling solid-phase polycondensation, including the following steps:

[0040] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 6-hydroxy-2-naphthoic acid (HNA) at a molar ratio of 73:27, with acetic anhydride accounting for 2.2 times the total molar amount of the hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole based on the total weight of the monomers. Heat the mixture to 150 °C and then keep it at a constant temperature for 1 h for the acetylation reaction. After the acetylation reaction is completed, recrystallize the monomers to remove the excess acetic anhydride, and obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 6-acetoxy-2-naphthoic acid monomer (ANA) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization refinement;

[0041] (2) Place the refined acetylated product and a 300 ppm zinc acetate catalyst in a three-necked flask, heat it to 250 °C and react for 3 h, then continue to heat to 280 °C and react for 1 h, then continue to heat to 320 °C and react for 2 h, and evacuate to 2000 Pa vacuum at this temperature to carry out melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure, discharge the liquid crystal polyester prepolymer, and test the viscosity of the obtained liquid crystal polyester prepolymer;

[0042] (3) Transfer the liquid crystal polyester prepolymer to a pulverizer. In the pulverizer, the low-molecular-weight liquid crystal polyester prepolymer is pulverized into prepolymer particles with a size of 30 - 50 mesh (0.3 - 0.6 mm). Then, place the prepolymer particles with different diameters in a vacuum oven at 120 °C and dry for 12 h. Place the dried prepolymer particles in a vacuum rotary drum, with a nitrogen flow rate of 0.013 m / s, and keep at 210 °C for 2 h for solid-phase polycondensation to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester. Take out the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester, cool it, and then test its viscosity.

[0043] Example 4

[0044] This example provides a method for preparing high-molecular-weight thermotropic liquid crystal polyester by melt coupling solid-phase polycondensation, which includes the following steps:

[0045] (1) Mix monomer p-hydroxybenzoic acid (HBA) and monomer 6-hydroxy-2-naphthoic acid (HNA) at a molar ratio of 73:27, mix with acetic anhydride which is 2.2 times the total molar number of monomer hydroxyl groups and 300 ppm 1-methylimidazole based on the total weight of the monomers, heat to 150 °C and keep at a constant temperature for acetylation reaction for 1 h. After the acetylation reaction is completed, recrystallize the monomers to remove the excess acetic anhydride to obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 6-acetoxy-2-naphthoic acid monomer (ANA) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization refinement;

[0046] (2) Place the refined acetylated product and a 300 ppm zinc acetate catalyst in a three-necked flask, heat it to 250 °C and react for 3 h, then continue to heat to 280 °C and react for 2 h, then continue to heat to 320 °C and react for 2 h, and evacuate to 2000 Pa vacuum at this temperature to carry out melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure, discharge the liquid crystal polyester prepolymer, and test the viscosity of the obtained liquid crystal polyester prepolymer;

[0047] (3) Feed the liquid crystal polyester prepolymer to a grinder. In the grinder, the low molecular weight liquid crystal polyester prepolymer is ground into prepolymer particles with a mesh size of 30 - 50 (0.3 - 0.6 mm). Then, the prepolymer particles with different diameters are placed in a vacuum oven at 120 °C for drying for 12 h. The dried prepolymer particles are placed in a vacuum drum, with a nitrogen gas flow rate of 0.013 m / s, and subjected to solid-state polycondensation at 210 °C for 2 h to obtain the high molecular weight HBA / HNA thermotropic liquid crystal polyester. After taking out and cooling the high molecular weight HBA / HNA thermotropic liquid crystal polyester, perform a viscosity test.

[0048] Example 5

[0049] This example provides a method for preparing high molecular weight thermotropic liquid crystal polyester by melt coupling solid-state polycondensation, including the following steps:

[0050] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 6-hydroxy-2-naphthoic acid (HNA) at a molar ratio of 73:27, and mix with acetic anhydride at 2.2 times the total molar number of monomer hydroxyl groups and 300 ppm of 1-methylimidazole based on the total weight of the monomers. Heat up to 150 °C and keep at a constant temperature for acetylation reaction for 1 h. After the acetylation reaction is completed, recrystallize the monomers to remove the excess acetic anhydride, and obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 6-acetoxy-2-naphthoic acid monomer (ANA) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization refinement;

[0051] (2) Place the refined acetylated product and 300 ppm of zinc acetate catalyst in a three-necked flask, heat up to 250 °C and react for 3 h, continue to heat up to 280 °C and react for 2 h, continue to heat up to 320 °C and react for 0.5 h, and pump a vacuum of 2000 Pa at this temperature to perform a melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen gas to terminate the polymerization reaction; increase the nitrogen gas pressure, discharge the liquid crystal polyester prepolymer, and perform a viscosity test on the obtained liquid crystal polyester prepolymer;

[0052] (3) Feed the liquid crystal polyester prepolymer to a grinder. In the grinder, the low molecular weight liquid crystal polyester prepolymer is ground into prepolymer particles with a mesh size of 30 - 50 (0.3 - 0.6 mm). Then, the prepolymer particles with different diameters are placed in a vacuum oven at 120 °C for drying for 12 h. The dried prepolymer particles are placed in a vacuum drum, with a nitrogen gas flow rate of 0.013 m / s, and subjected to solid-state polycondensation at 210 °C for 2 h to obtain the high molecular weight HBA / HNA thermotropic liquid crystal polyester. After taking out and cooling the high molecular weight HBA / HNA thermotropic liquid crystal polyester, perform a viscosity test.

[0053] Example 6

[0054] This embodiment provides a method for preparing high molecular weight thermotropic liquid crystal polyester by melt coupling solid state polycondensation, which comprises the following steps:

[0055] (1) Mix p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) monomers in a molar ratio of 73:27, and mix them with acetic anhydride which is 2.2 times the total molar number of monomer hydroxyl groups and 300 ppm of 1-methylimidazole based on the total weight of the monomers. After heating to 150 °C, keep the temperature constant for 1 h for acetylation reaction. After the acetylation reaction is completed, recrystallize the monomers to remove the excess acetic anhydride, and obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 6-acetoxy-2-naphthoic acid monomer (ANA) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization refinement;

[0056] (2) Place the refined acetylated product and 300 ppm of zinc acetate catalyst in a three-necked flask, heat to 250 °C and react for 3 h, continue to heat to 280 °C and react for 2 h, then continue to heat to 320 °C and react for 1 h, and evacuate to 2000 Pa vacuum at this temperature for melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure, discharge the liquid crystal polyester prepolymer, and test the viscosity of the obtained liquid crystal polyester prepolymer;

[0057] (3) Transport the liquid crystal polyester prepolymer to a pulverizer. In the pulverizer, the low molecular weight liquid crystal polyester prepolymer is pulverized into prepolymer particles with a size of 30 - 50 mesh (0.3 - 0.6 mm). Then, place the prepolymer particles with different diameters in a vacuum oven at 120 °C and dry for 12 h. Place the dried prepolymer particles in a vacuum rotary drum, with a nitrogen flow rate of 0.013 m / s, and keep at 210 °C for 2 h for solid state polycondensation to obtain the high molecular weight HBA / HNA thermotropic liquid crystal polyester. Take out the high molecular weight HBA / HNA thermotropic liquid crystal polyester, cool it, and then test its viscosity.

[0058] Example 7

[0059] This embodiment provides a method for preparing high molecular weight thermotropic liquid crystal polyester by melt coupling solid state polycondensation, which comprises the following steps:

[0060] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 6-hydroxy-2-naphthoic acid (HNA) at a molar ratio of 73:27 with acetic anhydride that is 2.2 times the total molar amount of the hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole based on the total weight of the monomers. Heat the mixture to 150 °C and then keep it at a constant temperature for an acetylation reaction for 1 h. After the acetylation reaction is completed, recrystallize the monomers to remove the excess acetic anhydride, and obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 6-acetoxy-2-naphthoic acid monomer (ANA) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization refinement;

[0061] (2) Place the refined acetylated product and 300 ppm of zinc acetate catalyst in a three-necked flask, heat it to 250 °C and react for 3 h, continue to heat it to 280 °C and react for 1 h, continue to heat it to 320 °C and react for 3 h, and evacuate to 2000 Pa vacuum at this temperature for a melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure, discharge the liquid crystal polyester prepolymer, and test the viscosity of the obtained liquid crystal polyester prepolymer;

[0062] (3) Transfer the liquid crystal polyester prepolymer to a pulverizer. In the pulverizer, the low-molecular-weight liquid crystal polyester prepolymer is pulverized into prepolymer particles with a size of 30 - 50 mesh (0.3 - 0.6 mm). Then place the prepolymer particles with different diameters in a vacuum oven at 120 °C and dry them for 12 h. Place the dried prepolymer particles in a vacuum rotary drum, with a nitrogen flow rate of 0.013 m / s, and keep them at 210 °C for 2 h for solid-phase polycondensation to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester. Take out the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester, cool it, and then test its viscosity.

[0063] Example 8

[0064] This example provides a method for preparing high-molecular-weight thermotropic liquid crystal polyester by melt coupling solid-phase polycondensation, including the following steps:

[0065] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 6-hydroxy-2-naphthoic acid (HNA) at a molar ratio of 73:27 with acetic anhydride that is 2.2 times the total molar amount of the hydroxyl groups of the monomers and 300 ppm of 1-methylimidazole based on the total weight of the monomers. Heat the mixture to 150 °C and then keep it at a constant temperature for an acetylation reaction for 1 h. After the acetylation reaction is completed, recrystallize the monomers to remove the excess acetic anhydride, and obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 6-acetoxy-2-naphthoic acid monomer (ANA) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization refinement;

[0066] (2) Place the refined acetylated product and a 300 ppm zinc acetate catalyst in a three-necked flask, heat it to 250 °C and react for 3 h, then continue to heat to 280 °C and react for 2 h, and then continue to heat to 320 °C and react for 3 h. At this temperature, evacuate to 2000 Pa vacuum to carry out melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure, discharge the liquid crystal polyester prepolymer, and test the viscosity of the obtained liquid crystal polyester prepolymer;

[0067] (3) Transport the liquid crystal polyester prepolymer to a pulverizer. In the pulverizer, the low-molecular-weight liquid crystal polyester prepolymer is pulverized into prepolymer particles with a mesh size of 30 - 50 meshes (0.3 - 0.6 mm). Then, place the prepolymer particles with different diameters in a vacuum oven at 120 °C and dry for 12 h. Place the dried prepolymer particles in a vacuum rotary drum, with a nitrogen flow rate of 0.013 m / s, and hold at 210 °C for 2 h for solid-phase polycondensation to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester. Take out the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester, cool it, and then test its viscosity.

[0068] Example 9

[0069] This example is based on Example 1 above, and the same parts as those in the above example will not be elaborated.

[0070] In this example, in step (3), solid-phase polycondensation is carried out at 220 °C for 2 h to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester.

[0071] Example 10

[0072] This example is based on Example 1 above, and the same parts as those in the above example will not be elaborated.

[0073] In this example, in step (3), solid-phase polycondensation is carried out at 230 °C for 2 h to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester.

[0074] Example 11

[0075] This example is based on Example 1 above, and the same parts as those in the above example will not be elaborated.

[0076] In this example, in step (3), solid-phase polycondensation is carried out at 240 °C for 2 h to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester.

[0077] Example 12

[0078] This example is based on Example 1 above, and the same parts as those in the above example will not be elaborated.

[0079] In this embodiment, in step (3), solid-phase polycondensation is carried out at 210 °C for 4 h to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester.

[0080] Example 13

[0081] This embodiment is carried out on the basis of the above Example 1, and the same parts as the above embodiment will not be described in detail.

[0082] In this embodiment, in step (3), solid-phase polycondensation is carried out at 210 °C for 6 h to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester.

[0083] Example 14

[0084] This embodiment is carried out on the basis of the above Example 1, and the same parts as the above embodiment will not be described in detail.

[0085] In this embodiment, in step (3), solid-phase polycondensation is carried out at 210 °C for 8 h to obtain the high-molecular-weight HBA / HNA thermotropic liquid crystal polyester.

[0086] Example 15

[0087] This embodiment is carried out on the basis of the above Example 1, and the same parts as the above embodiment will not be described in detail.

[0088] In this embodiment, in step (3), the nitrogen gas flow rate is 0.026 m / s.

[0089] Example 16

[0090] This embodiment is carried out on the basis of the above Example 1, and the same parts as the above embodiment will not be described in detail.

[0091] In this embodiment, in step (3), the nitrogen gas flow rate is 0.039 m / s.

[0092] Example 17

[0093] This embodiment is carried out on the basis of the above Example 1, and the same parts as the above embodiment will not be described in detail.

[0094] In this embodiment, in step (3), in the pulverizer, the low-molecular-weight liquid crystal polyester prepolymer is pulverized into prepolymer particles with a size of 50 - 100 mesh (0.15 - 0.3 mm).

[0095] Example 18

[0096] This embodiment is carried out on the basis of the above Example 1, and the same parts as the above embodiment will not be described in detail.

[0097] In this embodiment, in step (3), in a pulverizer, the low molecular weight liquid crystal polyester prepolymer is pulverized into prepolymer particles with a size of 100 - 300 mesh (0.05 - 0.15 mm).

[0098] Comparative Example 1

[0099] This comparative example provides a method for preparing liquid crystal polyester, including the following steps:

[0100] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 6-hydroxy-2-naphthoic acid (HNA) at a molar ratio of 73:27 with acetic anhydride that is 2.2 times the total molar number of monomer hydroxyl groups and 300 ppm of 1-methylimidazole based on the total weight of the monomers, heat the mixture to 150 °C and keep it at a constant temperature for 1 h for acetylation reaction. After the acetylation reaction is completed, recrystallize the monomers to remove the excess acetic anhydride;

[0101] (2) Place the acetylated reactants in a three-necked flask, heat to 250 °C and react for 3 h, continue to heat to 280 °C and react for 2 h, and then continue to heat to 320 °C and react for 0.5 h for melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure, discharge the liquid crystal polyester prepolymer, and test the viscosity of the obtained liquid crystal polyester prepolymer;

[0102] (3) Place the liquid crystal polyester prepolymer in a vacuum oven at 120 °C and dry it for 12 h. Place the dried prepolymer in a twin-screw extruder for extrusion molding; the particles are cylinders with a diameter controlled within the range of 1 mm, and perform solid-state polycondensation at 210 °C for 8 h to obtain liquid crystal polyester, and then test the viscosity.

[0103] Comparative Example 2

[0104] This comparative example provides a method for preparing liquid crystal polyester, including the following steps:

[0105] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 6-hydroxy-2-naphthoic acid (HNA) at a molar ratio of 73:27 with acetic anhydride that is 2.2 times the total molar number of monomer hydroxyl groups and 300 ppm of 1-methylimidazole based on the total weight of the monomers, heat the mixture to 150 °C and keep it at a constant temperature for 1 h for acetylation reaction. After the acetylation reaction is completed, recrystallize the monomers to remove the excess acetic anhydride;

[0106] (2) Place the acetylated reactants in a three-necked flask, heat up to 250 °C and react for 3 h, then continue to heat up to 280 °C and react for 2 h, and then continue to heat up to 320 °C and react for 0.5 h to carry out melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure, discharge the liquid crystal polyester prepolymer, and test the viscosity of the obtained liquid crystal polyester prepolymer;

[0107] (3) Place the liquid crystal polyester prepolymer in a vacuum oven at 120 °C and dry for 12 h, then place the dried prepolymer in a twin-screw extruder for extrusion molding; the particles are cylinders with a diameter controlled within the range of 2 mm, and carry out solid-state polycondensation at 210 °C for 8 h to obtain liquid crystal polyester, and then test the viscosity.

[0108] Comparative Example 3

[0109] This comparative example provides a method for preparing liquid crystal polyester, including the following steps:

[0110] (1) Mix monomer p-hydroxybenzoic acid (HBA) and monomer 6-hydroxy-2-naphthoic acid (HNA) at a molar ratio of 73:27, mix with acetic anhydride which is 2.2 times the total molar number of monomer hydroxyl groups and 1-methylimidazole which is 300 ppm of the total monomer weight, heat up to 150 °C and keep it at a constant temperature for acetylation reaction for 1 h. After the acetylation reaction is completed, recrystallize the monomer to remove the excess acetic anhydride;

[0111] (2) Place the acetylated reactants in a three-necked flask, heat up to 250 °C and react for 3 h, then continue to heat up to 280 °C and react for 2 h, and then continue to heat up to 320 °C and react for 0.5 h to carry out melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure, discharge the liquid crystal polyester prepolymer, and test the viscosity of the obtained liquid crystal polyester prepolymer;

[0112] (3) Place the liquid crystal polyester prepolymer in a vacuum oven at 120 °C and dry for 12 h, then place the dried prepolymer in a twin-screw extruder for extrusion molding; the particles are cylinders with a diameter controlled within the range of 3 mm, and carry out solid-state polycondensation at 210 °C for 8 h to obtain liquid crystal polyester, and then test the viscosity.

[0113] The solid-state polycondensation reaction conditions of the above Examples 1-18 are shown in Table 1.

[0114] Table 1

[0115] Reaction conditions Reaction temperature / °C Reaction time / h Nitrogen flow rate / m / s Particle size / mesh Examples 1 - 8 210 2 0.013 30～50 Example 9 220 2 0.013 30～50 Example 10 230 2 0.013 30～50 Example 11 240 2 0.013 30～50 Example 12 210 4 0.013 30～50 Example 13 210 6 0.013 30～50 Example 14 210 8 0.013 30～50 Example 15 210 8 0.026 30～50 Example 16 210 8 0.039 30～50 Example 17 210 8 0.013 50～100 Example 18 210 8 0.013 100～300

[0116] Test the viscosities of the liquid crystal polyester prepolymers obtained in the above Examples 1-18, and the test results are shown in Table 2.

[0117] Table 2

[0118]

[0119] The high molecular weight HBA / HNA thermotropic liquid crystal polyesters obtained from the above Examples 1 to 18 and the liquid crystal polyesters obtained from Comparative Examples 1 to 3 were tested for viscosity, and the test results are shown in Table 3.

[0120] Table 3

[0121]

[0122] The test method for the viscosity of the above examples and comparative examples is specifically described as follows:

[0123] (I) Determination of inherent viscosity (I.V.):

[0124] The solvent is pentafluorophenol; 0.050 g of the liquid crystal copolyester sample is weighed into a clean and dry 50 ml conical flask, then 50 ml of pentafluorophenol is added thereto, the stopper is covered, and the conical flask is placed in a shaker at 80 °C for 8 hours to completely dissolve the sample. Then, the solution is filtered through a No. 2 sintered glass funnel into another clean and dry 25 ml volumetric flask and kept at a constant temperature in the above water bath for 1 hour; the efflux times t 溶剂 and t 溶液 of the pure solvent and the solution are measured respectively with an Ubbelohde viscometer (capillary diameter 0.63 mm) in a 60 °C water bath; then the I.V. is calculated using the following formula:

[0125]

[0126] By comparing Example 14 with Comparative Examples 1, 2, and 3, it can be found that when the diameter of the particles becomes larger, the efficiency of solid-phase polycondensation will decrease significantly. Generally, when other conditions remain unchanged, as the average particle size of the prepolymer decreases, the internal diffusion resistance decreases, the apparent reaction rate increases, and the relative viscosity of the product increases, which is mainly reflected in the molecular weight and mechanical properties of the liquid crystal polyester obtained under the same solid-phase polycondensation time and nitrogen gas flow rate. Increasing the specific surface area of the LCP particles is beneficial to the removal of by-products, making the equilibrium shift forward and increasing the reaction rate so as to achieve the purpose of improving the production efficiency of solid-phase polycondensation.

[0127] In summary, in the process of preparing the prepolymer of the present invention, a prepolymer with an appropriate logarithmic viscosity can be effectively prepared by controlling the reaction temperature and time to achieve the controllable preparation of the polymer; by crushing the prepolymer into particles with different diameters, the solid-phase polycondensation time required to obtain a high molecular weight polymer can be shortened to improve the efficiency of the solid-phase polycondensation reaction.

[0128] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for preparing high molecular weight thermotropic liquid crystal polyester by melt-coupled solid phase polycondensation, characterized in that: The following steps are involved: (1) subjecting p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid monomers to acetylation reaction with acetic anhydride, respectively; after the acetylation reaction, the product is recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomer and 6-acetoxy-2-naphthoic acid monomer, respectively; and the obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) subjecting the refined acetylated product to a melt polycondensation reaction with a zinc acetate catalyst at a high temperature to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to a predetermined level, nitrogen is immediately introduced to terminate the polymerization reaction; and the nitrogen pressure is increased to release the liquid crystal polyester prepolymer; (3) conveying the liquid crystal polyester prepolymer to a pulverizer, in which the low molecular weight liquid crystal polyester prepolymer is pulverized into prepolymer particles of uniform size, and then placing the prepolymer particles of uniform particle size in a vacuum oven for drying to remove a small amount of acetic acid, a by-product of melt polycondensation, and placing the dried prepolymer particles in a solid phase polycondensation device for heating reaction in a nitrogen atmosphere to obtain the high molecular weight thermotropic liquid crystal polyester; Wherein, in step (1), the molar percentage of p-hydroxybenzoic acid to 6-hydroxy-2-naphthoic acid is 70-75:25-30; In step (3), the high molecular weight thermotropic liquid crystal polyester is taken out for viscosity testing, wherein the logarithmic viscosity is between 4.7 and 8.5, and the color of the liquid crystal polyester is beige.

2. The method for preparing high molecular weight thermotropic liquid crystal polyester by melt-coupled solid phase polycondensation according to claim 1, characterized in that: In step (1), the acetylation reaction is carried out at 140-150° C. for 1-2 hours.

3. The method for preparing high molecular weight thermotropic liquid crystal polyester by melt-coupled solid phase polycondensation according to claim 1, characterized in that: In step (2), the conditions of the melt polycondensation reaction are 3 to 4 hours at 250°C, 1 to 2 hours at 280°C, and 0.5 to 3 hours at 320°C, and a vacuum of 2000 Pa is drawn at this temperature.

4. The method for preparing high molecular weight thermotropic liquid crystal polyester by melt-coupled solid phase polycondensation according to claim 1, characterized in that: In step (2), the amount of zinc acetate used is 100 to 500 ppm.

5. The method for preparing high molecular weight thermotropic liquid crystal polyester by melt-coupled solid phase polycondensation according to claim 1, characterized in that: In step (2), the logarithmic viscosity of the obtained liquid crystal polyester prepolymer is controlled at 3.5 to 4.

5.

6. The method for preparing high molecular weight thermotropic liquid crystal polyester by melt-coupled solid phase polycondensation according to claim 1, characterized in that: In step (3), the prepolymer particles of uniform size are spherical particles with a diameter of 30 to 300 meshes, and the prepolymer particles are placed in a 120° C. vacuum oven for drying for 12 to 14 hours; the dried prepolymer particles are placed in a solid phase polycondensation device, heated to 210 to 240° C. in a nitrogen atmosphere, and reacted for 2 to 8 hours to obtain a high molecular weight thermotropic liquid crystal polyester.

7. A high molecular weight thermotropic liquid crystal polyester, characterized in that: The polyester is prepared by the method for preparing high molecular weight thermotropic liquid crystal polyester by melt-coupled solid phase polycondensation as claimed in any one of claims 1 to 6.

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