A method for preparing biphenol-based high heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation

Abstract

The present invention discloses a method for preparing biphenol-based highly heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation. A liquid crystal polyester prepolymer with a specific logarithmic viscosity and melting point is synthesized from p-acetoxybenzoic acid monomer, 4,4'-diacetoxy biphenyl, and terephthalic acid in different molar ratios. The prepolymer particles after being pulverized and dried are placed in a solid-phase polycondensation device, and biphenol-based highly heat-resistant liquid crystal polyester is obtained by precisely controlling the time, temperature, and nitrogen gas flow rate of the polycondensation reaction. The biphenol-based highly heat-resistant liquid crystal polyester is taken out for DSC testing. During the process of preparing the prepolymer in the present invention, the molar percentage of biphenol monomer is effectively regulated to prepare a prepolymer with an appropriate logarithmic viscosity and high melting point, and the influence of different monomer ratios on the melting point of the polymer is studied; by pulverizing the prepolymer into particles with different diameters, the solid-phase polycondensation time required to obtain the biphenol-based highly heat-resistant polymer is shortened to improve the efficiency of the solid-phase polycondensation reaction.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a method for preparing biphenol-based high heat-resistant 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 a liquid crystal phase state 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. The wholly aromatic liquid crystal copolyester containing p-hydroxybenzoic acid (HBA), 4,4'-biphenol (BP) and terephthalic acid (TA) components is an important class in Xydar. As a type I LCP, Xydar has high heat resistance and a thermal decomposition temperature of 560°C, and is widely used in the fields of electronics and electrical appliances, optical fibers, chemical equipment, and other instruments.

[0003] However, due to the highly ordered rigid molecular chain structure of the Xydar series liquid crystal polyesters, the melting point of the polymer is often higher than 250°C. In the process of liquid crystal polyester polymerization, the relationship between the relatively complex chain structure and the product properties is often involved. In the later stage of polymerization, the rod climbing phenomenon will occur due to the too high viscosity of the product. At the same time, in the later stage of the reaction, it is difficult to remove small molecules due to the too high viscosity of the product. In the process of preparing high molecular weight type I liquid crystal polyester, the reaction temperature is relatively high, and the polymerization temperature is often above 350°C, which poses a certain test for the heat resistance of the reactor.

[0004] From the above content, it can be seen that there are relatively large problems when using the "one-step method" to directly melt-polymerize high molecular products of type I thermotropic liquid crystal polyester. 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 discharged first and the polymer discharged later is large, and subsequent mixing is required to improve the uniformity; the traditional reaction kettle stirring device is difficult to handle high-viscosity or extra-high-viscosity materials, the material stirring is difficult, the motor is extremely prone to overload, and the discharging is not complete. A large amount of residual materials seriously affect the subsequent batches. And due to a large amount of residual materials, the reaction kettle needs to be cleaned frequently. At the same time, staying at a high temperature for too long will cause serious oxidation problems, resulting in an increase in by-products of the product and a darker color; since the polymer main chain is composed of long rod-shaped molecular units connected together, the melting point of the polymer is relatively high. When directly melt-polycondensing to obtain the product, the selection requirements for the reactor equipment are relatively high, increasing the production cost.

[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 good results have been achieved. Its main feature is to prepare prepolymer particles with a relatively low molecular weight through melt polycondensation, and then conduct the polymerization reaction in a solid state at a temperature about 50 °C lower than the melting point of the prepolymer. Since the solid-state polycondensation reaction does not require 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] It is a good choice to use the solid-state polymerization method to synthesize liquid crystal copolyesters.

[0007] The prior art CN103459461A discloses a method for preparing a liquid crystal polyester with a high molecular weight. The method for preparing the 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, crushing the prepolymer into prepolymer powder with a particle diameter of 2 mm by a crusher and drying it in a vacuum oven; (3) Conducting solid-state polycondensation on the 2-mm particles 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 data guidance for the selection of reactors, the present invention provides a method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt coupling solid-state polycondensation, including optimizing and controlling the melt polymerization process conditions, determining the discharge 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 biphenol-type high heat-resistant liquid crystal polyester. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt coupling solid-state polycondensation, and to explore the solid-state polycondensation reaction conditions to shorten the solid-state reaction time and improve the reaction efficiency of solid-state polycondensation.

[0009] The purpose of the present invention is achieved through the following technical solutions:

[0010] A method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt coupling solid-state polycondensation, including the following steps:

[0011] (1)The monomers p-hydroxybenzoic acid (HBA) and 4,4-biphenol (BP) are respectively acetylated with acetic anhydride and a catalyst. After the acetylation reaction, the products are recrystallized to remove the excess acetic anhydride, and high-purity monomers of p-acetoxybenzoic acid (ABA) and 4,4-diacetoxybiphenyl (ABP) are obtained respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and refinement.

[0012] (2)The refined monomers of p-acetoxybenzoic acid (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid are subjected to melt polycondensation reaction according to the molar ratio to obtain a liquid crystal polyester prepolymer. When the torque of the stirrer rises to 10 N·m, nitrogen is immediately introduced to terminate the polymerization reaction. The nitrogen pressure is increased to discharge a liquid crystal polyester prepolymer with a certain molecular weight.

[0013] (3)The liquid crystal polyester prepolymer is transported to a pulverizer. In the pulverizer, the low-molecular-weight liquid crystal polyester prepolymer is pulverized into uniformly sized prepolymer particles. Then, the prepolymer particles with uniform particle size are placed in a vacuum oven for drying to remove a small amount of acetic acid, a by-product of melt polycondensation. The dried prepolymer particles are placed in a solid-state polycondensation device and heated in a nitrogen atmosphere to obtain a biphenol-type high heat-resistant liquid crystal polyester.

[0014] Among them, in step (2), the molar ratio of the p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid is 10~80:10~40:10~40.

[0015] In step (3), the uniformly sized prepolymer particles are spherical particles with a diameter of 30~300 mesh.

[0016] Preferably, in step (1), the amount of acetic anhydride used is 1.0~5.0 times the total molar amount of the monomer hydroxyl groups, the catalyst is 1-methylimidazole, and the amount of the catalyst used is 100~1000 ppm.

[0017] More preferably, in step (1), the amount of acetic anhydride used is 2.0~3.0 times the total molar amount of the monomer hydroxyl groups, and the amount of the catalyst 1-methylimidazole used is 150~300 ppm.

[0018] Preferably, in step (1), the conditions of the acetylation reaction are to react at 140~150 °C for 1~2 h.

[0019] Preferably, in step (2), the conditions of the melt polycondensation reaction are to react at 250 °C for 3~3.5 h, at 280 °C for 2~2.5 h, at 350 °C for 1~1.5 h, and evacuate to 2000 Pa vacuum at this temperature.

[0020] Preferably, in step (2), the obtained logarithmic viscosity of the liquid crystal polyester prepolymer is controlled to be 3.5 - 4.5.

[0021] Preferably, in step (3), the prepolymer particles are placed in a vacuum oven at 120 °C and dried for 12 - 14 h; the dried prepolymer particles are placed in a solid-state polycondensation device, heated to 280 - 310 °C in a nitrogen atmosphere, and after reacting for 2 - 12 h, a biphenol-type highly heat-resistant liquid crystal polyester is obtained.

[0022] This application also claims to protect a biphenol-type highly heat-resistant liquid crystal polyester, which is prepared by the method for preparing a biphenol-type highly heat-resistant liquid crystal polyester by melt coupling solid-state polycondensation as described above.

[0023] Preferably, the biphenol-type highly heat-resistant liquid crystal polyester is subjected to viscosity testing and DSC testing. The logarithmic viscosity of the biphenol-type highly heat-resistant liquid crystal polyester is 4.5 - 8.5, the melting point > 560 °C, the molecular weight distribution is narrow, and at the same time, the color of the biphenol-type highly heat-resistant liquid crystal polyester is light yellow.

[0024] Due to the application of the above technical solutions, the present invention has the following beneficial effects compared with the prior art:

[0025] In the process of preparing the prepolymer of the present invention, the molar percentage of the biphenol monomer is regulated to prepare a prepolymer with an appropriate logarithmic viscosity and a high melting point, and the influence of different monomer ratios on the melting point of the polymer is studied; by crushing the prepolymer into particles with different diameters, the solid-state polycondensation time required to obtain the biphenol-type highly heat-resistant polymer is shortened, so as to improve the efficiency of the solid-state polycondensation reaction. Detailed Embodiments

[0026] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the specific implementation embodiments are 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 adopted in the embodiments can be further adjusted according to different requirements of specific uses. The implementation conditions not specified are the conventional conditions in this 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] This example provides a method for preparing a biphenol-type highly heat-resistant liquid crystal polyester by melt coupling solid-state polycondensation, including the following steps:

[0030] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 4,4-biphenol (BP) with acetic anhydride that is 2.2 times the total molar amount of the hydroxyl groups of the monomers and 1-methylimidazole at 300 ppm of the total weight of the monomers, heat up to 150 °C, and then keep the temperature constant 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 4,4-diacetoxybiphenyl (ABP) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization and refinement;

[0031] (2) Place the refined p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a three-necked flask at a molar ratio of 80:10:10, 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 350 °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 10 N·m, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure and discharge the 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 of 30 - 50 mesh (0.3 - 0.6 mm), and then the prepolymer particles of different diameters are placed in a vacuum oven at 120 °C and dried 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 280 °C for 2 h for solid-phase polycondensation to obtain the biphenol-type high heat-resistant liquid crystal polyester.

[0033] Example 2

[0034] This example provides a method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation, which includes the following steps:

[0035] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 4,4-biphenol (BP) with acetic anhydride that is 2.2 times the total molar amount of the hydroxyl groups of the monomers and 1-methylimidazole at 300 ppm of the total weight of the monomers, heat up to 150 °C, and then keep the temperature constant 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 4,4-diacetoxybiphenyl (ABP) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization and refinement;

[0036] (2) Place the refined p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP), and terephthalic acid in a three-necked flask at a molar ratio of 70:15:15, heat to 250 °C and react for 3 h, continue to heat to 280 °C and react for 1 h, then continue to heat to 350 °C and react for 1 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 10 N·m, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure and discharge the 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 hold at 280 °C for 2 h for solid-phase polycondensation to obtain the biphenol-type high heat-resistant liquid crystal polyester.

[0038] Example 3

[0039] This example provides a method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation, which includes the following steps:

[0040] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 4,4-biphenol (BP) with acetic anhydride 2.2 times the total molar amount of the monomer hydroxyl groups and 1-methylimidazole 300 ppm of the total monomer weight, heat to 150 °C and keep 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 to obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 4,4-diacetoxybiphenyl (ABP) respectively. Filter and wash the obtained acetylated monomer in ice water for recrystallization refinement;

[0041] (2) Place the refined p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP), and terephthalic acid in a three-necked flask at a molar ratio of 60:20:20, heat to 250 °C and react for 3 h, continue to heat to 280 °C and react for 1 h, then continue to heat to 350 °C and react for 1 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 10 N·m, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure and discharge the 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 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 and dried for 12 h. The dried prepolymer particles are placed in a vacuum rotary drum, with a nitrogen gas flow rate of 0.013 m / s, and kept at 280°C for 2 h for solid-phase polycondensation to obtain the biphenol-type high heat-resistant liquid crystal polyester.

[0043] Example 4

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

[0045] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 4,4'-biphenol (BP) with acetic anhydride that is 2.2 times the total molar number of the monomer hydroxyl groups and 1-methylimidazole that is 300 ppm of the total monomer weight, heat up to 150°C, and keep the temperature constant for 1 h for acetylation reaction. After the acetylation reaction is completed, recrystallize the monomer to remove the excess acetic anhydride to obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 4,4'-diacetoxybiphenyl (ABP) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization and purification;

[0046] (2) Place the refined p-acetoxybenzoic acid monomer (ABA), 4,4'-diacetoxybiphenyl (ABP), and terephthalic acid in a three-necked flask at a molar ratio of 50:25:25, heat up to 250°C and react for 3 h, continue to heat up to 280°C and react for 1 h, then continue to heat up to 350°C and react for 1 h, and evacuate to 2000 Pa vacuum at this temperature for melt polycondensation reaction to obtain the liquid crystal polyester prepolymer; when the torque of the stirrer rises to 10 N·m, immediately introduce nitrogen gas to terminate the polymerization reaction; increase the nitrogen gas pressure and discharge the liquid crystal polyester prepolymer;

[0047] (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 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 and dried for 12 h. The dried prepolymer particles are placed in a vacuum rotary drum, with a nitrogen gas flow rate of 0.013 m / s, and kept at 280°C for 2 h for solid-phase polycondensation to obtain the biphenol-type high heat-resistant liquid crystal polyester.

[0048] Example 5

[0049] This example provides a method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation, which includes the following steps:

[0050] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 4,4-biphenol (BP) with acetic anhydride in an amount 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 4,4-diacetoxybiphenyl (ABP) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization and purification;

[0051] (2) Place the purified p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP), and terephthalic acid in a three-necked flask at a molar ratio of 40:30:30, heat the mixture to 250 °C and react for 3 h, continue to heat to 280 °C and react for 1 h, then continue to heat to 350 °C and react for 1 h, and evacuate to 2000 Pa under vacuum at this temperature for melt polycondensation reaction to obtain a liquid crystal polyester prepolymer; when the torque of the stirrer rises to 10 N·m, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure and discharge the liquid crystal polyester prepolymer;

[0052] (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 280 °C for 2 h for solid-phase polycondensation to obtain the biphenol-type high heat-resistant liquid crystal polyester.

[0053] Example 6

[0054] This example provides a method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation, including the following steps:

[0055] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 4,4-biphenol (BP) with acetic anhydride in an amount 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 4,4-diacetoxybiphenyl (ABP) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization and purification;

[0056] (2) Place the refined p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP), and terephthalic acid in a three-necked flask in a molar ratio of 30:35:35, heat up to 250 °C and react for 3 h, then continue to heat up to 280 °C and react for 1 h, then continue to heat up to 350 °C and react for 1 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 10 N·m, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure and discharge the 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 the prepolymer particles with different diameters are placed in a vacuum oven at 120 °C and dried for 12 h. The dried prepolymer particles are placed in a vacuum rotary drum, with a nitrogen flow rate of 0.013 m / s, and kept at 280 °C for 2 h for solid-state polycondensation to obtain the biphenol-type high heat-resistant liquid crystal polyester.

[0058] Example 7

[0059] This example provides a method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt coupling solid-state polycondensation, including the following steps:

[0060] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 4,4-biphenol (BP) with acetic anhydride 2.2 times the total molar amount of the monomer hydroxyl groups and 1-methylimidazole 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 to obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 4,4-diacetoxybiphenyl (ABP) respectively. Filter and wash the obtained acetylated monomer in ice water for recrystallization refinement;

[0061] (2) Place the refined p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP), and terephthalic acid in a three-necked flask in a molar ratio of 20:40:40, heat up to 250 °C and react for 3 h, then continue to heat up to 280 °C and react for 1 h, then continue to heat up to 350 °C and react for 1 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 10 N·m, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure and discharge the liquid crystal polyester prepolymer;

[0062] (3) Feed 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 (0.3 - 0.6 mm). Then, the prepolymer particles with different diameters are placed in a vacuum oven at 120 °C and dried for 12 h. The dried prepolymer particles are placed in a vacuum rotary drum, with a nitrogen gas flow rate of 0.013 m / s, and solid-phase polycondensation is carried out at 280 °C for 2 h to obtain the biphenol-type high heat-resistant liquid crystal polyester.

[0063] Example 8

[0064] This example provides a method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation, which includes the following steps:

[0065] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 4,4-biphenol (BP) with acetic anhydride which is 2.2 times the total molar number of the monomer hydroxyl groups and 1-methylimidazole which is 300 ppm of the total monomer weight, heat up to 150 °C and keep the temperature constant for acetylation reaction for 1 h. After the acetylation reaction is completed, the monomers are recrystallized to remove the excess acetic anhydride, and high-purity p-acetoxybenzoic acid monomer (ABA) and 4,4-diacetoxybiphenyl (ABP) are obtained respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization refinement;

[0066] (2) Place the refined p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a three-necked flask in a molar ratio of 10:40:40, heat up to 250 °C and react for 3 h, continue to heat up to 280 °C and react for 1 h, then continue to heat up to 350 °C and react for 1 h, and evacuate to 2000 Pa vacuum at this temperature to carry out melt polycondensation reaction to obtain the liquid crystal polyester prepolymer; when the torque of the stirrer rises to 10 N·m, immediately introduce nitrogen gas to terminate the polymerization reaction; increase the nitrogen gas pressure and discharge the liquid crystal polyester prepolymer;

[0067] (3) Feed 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 (0.3 - 0.6 mm). Then, the prepolymer particles with different diameters are placed in a vacuum oven at 120 °C and dried for 12 h. The dried prepolymer particles are placed in a vacuum rotary drum, with a nitrogen gas flow rate of 0.013 m / s, and solid-phase polycondensation is carried out at 280 °C for 2 h to obtain the biphenol-type high heat-resistant liquid crystal polyester.

[0068] Example 9

[0069] This example is based on the above Example 3, and the same parts as the above example will not be elaborated.

[0070] In this embodiment, in step (3), solid-phase polycondensation is carried out at 290 °C for 2 h to obtain the biphenol-based high heat-resistant liquid crystal polyester.

[0071] Example 10

[0072] This embodiment is carried out on the basis of the above-mentioned Example 3, and the same parts as the above-mentioned embodiment will not be described in detail.

[0073] In this embodiment, in step (3), solid-phase polycondensation is carried out at 300 °C for 2 h to obtain the biphenol-based high heat-resistant liquid crystal polyester.

[0074] Example 11

[0075] This embodiment is carried out on the basis of the above-mentioned Example 3, and the same parts as the above-mentioned embodiment will not be described in detail.

[0076] In this embodiment, in step (3), solid-phase polycondensation is carried out at 310 °C for 2 h to obtain the biphenol-based high heat-resistant liquid crystal polyester.

[0077] Example 12

[0078] This embodiment is carried out on the basis of the above-mentioned Example 3, and the same parts as the above-mentioned embodiment will not be described in detail.

[0079] In this embodiment, in step (3), solid-phase polycondensation is carried out at 280 °C for 4 h to obtain the biphenol-based high heat-resistant liquid crystal polyester.

[0080] Example 13

[0081] This embodiment is carried out on the basis of the above-mentioned Example 3, and the same parts as the above-mentioned embodiment will not be described in detail.

[0082] In this embodiment, in step (3), solid-phase polycondensation is carried out at 280 °C for 6 h to obtain the biphenol-based high heat-resistant liquid crystal polyester.

[0083] Example 14

[0084] This embodiment is carried out on the basis of the above-mentioned Example 3, and the same parts as the above-mentioned embodiment will not be described in detail.

[0085] In this embodiment, in step (3), solid-phase polycondensation is carried out at 280 °C for 8 h to obtain the biphenol-based high heat-resistant liquid crystal polyester.

[0086] Example 15

[0087] This embodiment is carried out on the basis of the above-mentioned Example 3, and the same parts as the above-mentioned 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 based on the above-mentioned Embodiment 3, and the same parts as the above-mentioned embodiment will not be repeated.

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

[0092] Example 17

[0093] This embodiment is based on the above-mentioned Embodiment 3, and the same parts as the above-mentioned embodiment will not be repeated.

[0094] 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 50 - 100 mesh (0.15 - 0.3 mm).

[0095] Example 18

[0096] This embodiment is based on the above-mentioned Embodiment 3, and the same parts as the above-mentioned embodiment will not be repeated.

[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 4,4-biphenol (BP) with acetic anhydride that is 2.2 times the total molar number of monomer hydroxyl groups and 1-methylimidazole that is 300 ppm of the total monomer weight, 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, and obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 4,4-diacetoxybiphenyl (ABP) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization refinement;

[0101] (2)Place the refined p-acetoxybenzoic acid monomer (ABA), 4,4'-diacetoxybiphenyl (ABP), and terephthalic acid in a three-necked flask at a molar ratio of 60:40:40, heat to 250 °C and react for 3 h, continue to heat to 280 °C and react for 1 h, then continue to heat to 350 °C and react for 1 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 10 N·m, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure and discharge the liquid crystal polyester prepolymer;

[0102] (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 1 mm, and solid-phase polycondensation is carried out at 280 °C for 8 h to obtain the liquid crystal polyester.

[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 4,4'-biphenol (BP) with acetic anhydride 2.2 times the total molar amount of the monomer hydroxyl groups and 1-methylimidazole 300 ppm of the total monomer weight, heat to 150 °C and keep the temperature constant for acetylation reaction for 1 h. After the acetylation reaction is completed, recrystallize the monomer to remove the excess acetic anhydride to obtain high-purity p-acetoxybenzoic acid monomer (ABA) and 4,4'-diacetoxybiphenyl (ABP) respectively. Filter and wash the obtained acetylated monomer in ice water for recrystallization refinement;

[0106] (2)Place the refined p-acetoxybenzoic acid monomer (ABA), 4,4'-diacetoxybiphenyl (ABP), and terephthalic acid in a three-necked flask at a molar ratio of 60:40:40, heat to 250 °C and react for 3 h, continue to heat to 280 °C and react for 1 h, then continue to heat to 350 °C and react for 1 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 10 N·m, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure and discharge the 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 solid-phase polycondensation is carried out at 280 °C for 8 h to obtain the liquid crystal polyester.

[0108] Comparative Example 3

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

[0110] (1) Mix the monomer p-hydroxybenzoic acid (HBA) and the monomer 4,4-biphenol (BP) with acetic anhydride which is 2.2 times the total molar number of the hydroxyl groups of the monomers and 1-methylimidazole which is 300 ppm of the total weight of the monomers. Heat the mixture to 150 °C and 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 4,4-diacetoxybiphenyl (ABP) respectively. Filter and wash the obtained acetylated monomers in ice water for recrystallization and refinement;

[0111] (2) Place the refined p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a three-necked flask at a molar ratio of 60:40:40, heat it to 250 °C and react for 3 h, continue to heat it to 280 °C and react for 1 h, then continue to heat it to 350 °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 10 N·m, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure and discharge the liquid crystal polyester prepolymer;

[0112] (3) Dry the liquid crystal polyester prepolymer in a vacuum oven at 120 °C 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 3 mm, and perform solid-state polycondensation at 280 °C for 8 h to obtain the liquid crystal polyester.

[0113] Comparative Example 4

[0114] This comparative example is based on Example 1 above, and the same parts as those in the above example will not be elaborated.

[0115] In this comparative example, in step (2), place the refined p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a three-necked flask at a molar ratio of 10:45:45.

[0116] Comparative Example 5

[0117] This comparative example is based on Example 1 above, and the same parts as those in the above example will not be elaborated.

[0118] In this comparative example, in step (2), place the refined p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a three-necked flask at a molar ratio of 90:40:40.

[0119] Comparative Example 6

[0120] This comparative example is based on the above-mentioned Example 1, and the same parts as those in the above example will not be elaborated.

[0121] In this comparative example, in step (2), the refined p-acetoxybenzoic acid monomer (ABA), 4,4'-diacetoxybiphenyl (ABP), and terephthalic acid were placed in a three-necked flask in a molar ratio of 90:10:10.

[0122] The solid-state polycondensation reaction conditions of the above Examples 1 to 18 are shown in Table 1.

[0123] Table 1

[0124]

[0125] The liquid crystal polyester prepolymers obtained in the above Examples 1 to 18 were tested for viscosity and DSC. Among them, Td5% refers to the temperature at which the mass loss of the material reaches 5% during the heating process; Tdmax refers to the temperature corresponding to the maximum mass change rate on the thermogravimetric curve (TG curve); the test results are shown in Table 2.

[0126] Table 2

[0127]

[0128] The biphenol-type highly heat-resistant liquid crystal polyesters obtained in the above Examples 1 to 18 and the liquid crystal polyesters obtained in Comparative Examples 1 to 3 were tested for viscosity and DSC. Among them, Td5% refers to the temperature at which the mass loss of the material reaches 5% during the heating process; Tdmax refers to the temperature corresponding to the maximum mass change rate on the thermogravimetric curve (TG curve); the test results are shown in Table 3.

[0129] Table 3

[0130]

[0131] The test method for the viscosity of the above examples and comparative examples is specifically described as follows:

[0132] (I) Determination of logarithmic viscosity concentration (I.V.):

[0133] The solvent is pentafluorophenol; 0.050 g of the liquid crystal copolyester sample was weighed into a clean and dry 50 ml conical flask, then 50 ml of pentafluorophenol was added thereto, the stopper was covered, and the conical flask was placed in a shaker at 80 °C for 8 hours to completely dissolve the sample. Then, the solution was 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 outflow times t 溶剂 and t 溶液; Then calculate the I.V. using the following formula:

[0134] .

[0135] By comparing Example 14 with Comparative Examples 1, 2, and 3, it can be found that when the diameter of the particles increases, 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. This 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, thereby achieving the purpose of improving the production efficiency of solid-phase polycondensation; from Examples 1 and Comparative Examples 4-6, it can be seen that the molar ratio of the refined p-acetoxybenzoic acid monomer (ABA), 4,4'-diacetoxybiphenyl (ABP), and terephthalic acid will also affect the properties of the final product.

[0136] In summary, in the process of preparing the prepolymer of the present invention, the molar percentage of the biphenol monomer is effectively regulated to prepare a prepolymer with an appropriate logarithmic viscosity and high melting point, and the influence of different monomer ratios on the melting point of the polymer is studied; by crushing the prepolymer into particles with different diameters, the solid-phase polycondensation time required to obtain the biphenol-based high heat-resistant polymer is shortened to improve the efficiency of the solid-phase polycondensation reaction.

[0137] The above-described embodiments merely represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting 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 belong to 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 biphenol-based highly heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation, characterized in that, It includes the following steps: (1) Respectively carry out acetylation reactions on the monomer p-hydroxybenzoic acid, 4,4'-biphenol, acetic anhydride and a catalyst. After the acetylation reactions are completed, recrystallize the products to remove the excess acetic anhydride, and respectively obtain high-purity p-acetoxybenzoic acid monomer and 4,4'-diacetoxybiphenyl monomer. Filter and wash the obtained acetylated monomers in ice water for recrystallization and refinement; (2) Carry out melt polycondensation reaction on the refined p-acetoxybenzoic acid monomer, 4,4'-diacetoxybiphenyl and terephthalic acid according to a molar ratio to obtain a high heat-resistant liquid crystal polyester prepolymer; when the torque of the stirrer rises to 10 N·m, immediately introduce nitrogen to terminate the polymerization reaction; increase the nitrogen pressure and discharge the high heat-resistant liquid crystal polyester prepolymer; (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 react by heating in a nitrogen atmosphere to obtain the biphenol-type high heat-resistant liquid crystal polyester; Among them, in step (2), the molar ratio of the p-acetoxybenzoic acid monomer, 4,4'-diacetoxybiphenyl and terephthalic acid is 10-80:10-40:10-40; In step (3), the prepolymer particles with uniform size are spherical particles with a diameter of 30-300 meshes; In step (1), the amount of acetic anhydride used is 1.0-5.0 times the total molar number of monomer hydroxyl groups, the catalyst is 1-methylimidazole, and the amount of the catalyst used is 100-1000 ppm; In step (2), the conditions of the melt polycondensation reaction are to react at 250 °C for 3-3.5 h, react at 280 °C for 2-2.5 h, react at 350 °C for 1-1.5 h, and pump a vacuum of 2000 Pa at this temperature.

2. The method for preparing biphenol-based highly heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation according to claim 1, wherein In step (1), the conditions of the acetylation reaction are to react at 140-150 °C for 1-2 h.

3. The method for preparing biphenol-type highly heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation according to claim 1, characterized in that, In step (2), the inherent viscosity of the obtained liquid crystal polyester prepolymer is controlled at 3.5-4.

5.

4. The method for preparing a biphenol-based highly heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation according to claim 1, characterized in that, In step (3), place the prepolymer particles in a vacuum oven at 120 °C for drying for 12-14 h; place the dried prepolymer particles in a solid-phase polycondensation device and heat up to 280-310 °C in a nitrogen atmosphere, and react for 2-8 h to obtain the biphenol-type high heat-resistant liquid crystal polyester.

5. A biphenol-type highly heat-resistant liquid crystal polyester, characterized in that, It is prepared by the method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt coupling solid-phase polycondensation as described in any one of claims 1-4.

6. A biphenol-type highly heat-resistant liquid crystal polyester according to claim 5, characterized in that, Carry out viscosity test and DSC test on the biphenol-type high heat-resistant liquid crystal polyester. The inherent viscosity of the biphenol-type high heat-resistant liquid crystal polyester is 4.5-8.5, the melting point > 560 °C, and at the same time, the color of the biphenol-type high heat-resistant liquid crystal polyester is light yellow.

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