Method for preparing biphenol type high-heat-resistance liquid crystal polyester through melt coupling solid-phase polycondensation

Abstract

The invention discloses a method for preparing biphenol type high-heat-resistance liquid crystal polyester through melt coupling solid-phase polycondensation, which comprises the following steps: synthesizing a liquid crystal polyester prepolymer with specific logarithmic viscosity and melting point from p-acetoxybenzoic acid monomer, 4, 4-diacetoxybiphenyl and terephthalic acid according to different molar ratios; placing the crushed and dried prepolymer particles in a solid phase polycondensation device, accurately controlling the time, temperature and nitrogen flow rate of the polycondensation reaction to obtain the biphenol type high-heat-resistance liquid crystal polyester, and taking out the biphenol type high-heat-resistance liquid crystal polyester for DSC (differential scanning calorimetry) test. In the preparation process of the prepolymer, the molar percentage of the biphenol monomer is effectively regulated and controlled to prepare the prepolymer with proper logarithmic viscosity and high melting point, and the influence of different monomer proportions on the melting point of the polymer is researched; the solid-phase polycondensation time required for obtaining the biphenol type high-heat-resistance 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 invention relates to the technical field of polymer materials, and in particular to a method for preparing biphenyl diphenol type high heat-resistant liquid crystal polyester through melt-coupled solid phase polycondensation. Background Art

[0002] In recent years, as electronic communication technology continues to develop towards high frequency, high speed and high integration, higher requirements have been placed on the performance of copper clad laminates. Thermotropic liquid crystal polymers are a type of polymer that can exhibit a liquid crystal phase in a molten state, mainly represented by aromatic thermotropic liquid crystal polyesters (TLCP). TLCP exhibits stable low dielectric properties, low water absorption, extremely low thermal expansion coefficient, and excellent thermal stability in the 5G millimeter wave frequency band, and is considered to be an ideal high-performance millimeter wave substrate and packaging material. Fully aromatic liquid crystal copolyesters containing parahydroxybenzoic acid (HBA), 4,4-biphenol (BP) and terephthalic acid (TA) components are a very important type of Xydar. As a type I LCP, Xydar has high heat resistance and a thermal decomposition temperature of 560°C. It is widely used in the fields of electronics and electrical appliances, optical fiber, chemical equipment, and other equipment.

[0003] However, since the Xydar series of liquid crystal polyesters have a highly ordered rigid molecular chain structure, the melting point of the polymer is often higher than 250°C. The polymerization process of liquid crystal polyesters often involves a relatively complex relationship between the chain structure and the product performance. In the later stages of the polymerization, the product viscosity is too high, which leads to pole climbing. At the same time, in the later stages of the reaction, the removal of small molecules becomes difficult due to the high viscosity of the product. In the process of preparing high molecular weight type I liquid crystal polyesters, the reaction temperature is relatively high, and the polymerization temperature is often above 350°C, which poses a certain test on the heat resistance of the reactor.

[0004] From the above content, it can be seen that there are major problems in the preparation of polymer products by direct melt polymerization of type I thermotropic liquid crystal polyester using the "one-step method". It takes more than ten minutes to an hour to discharge the material after the polymerization in the reactor is completed. The viscosity of the polymer discharged first and the polymer discharged later is very different, and subsequent mixing is required to improve the uniformity; traditional reactor stirring devices are difficult to handle high-viscosity or ultra-high-viscosity materials, material stirring is difficult, the motor is very easy to overload, and the discharge is not complete. A large amount of residual material seriously affects subsequent batches, and due to the large amount of residual material, the reactor needs to be cleaned frequently. At the same time, if the residence time at high temperature is too long, serious oxidation problems will occur, resulting in an increase in product by-products and a darker color; since the polymer main chain is composed of long steel rod-shaped molecular units connected, the polymer has a high melting point. When you want to directly melt-polycondense to obtain the product, the selection of reactor equipment has high requirements, which increases the production cost.

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

[0006] Solid-state polymerization is a good choice for synthesizing liquid crystal copolyesters.

[0007] The prior art CN103459461A describes a method for preparing a liquid crystal polyester with a high molecular weight. The method for preparing a liquid crystal polyester comprises 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 a prepolymer powder with a particle diameter of 2 mm by a crusher, and placing it in a vacuum oven for drying; (3) subjecting the 2 mm particles to solid phase polycondensation for 15 hours to obtain a liquid crystal polyester final polymer. This patent does not take into account the effect of particle size on the production efficiency of solid-phase polycondensation when implementing solid-phase polycondensation. In order to provide more data support for solid-phase polycondensation and provide data guidance for the selection of reactors, the present invention proposes a method for preparing diphenol-type high heat-resistant liquid crystal polyester by melt-coupled solid-phase polycondensation, including optimizing and controlling the melt polymerization process conditions, determining the discharge time of the reactor in the melt polymerization stage and the characteristic viscosity of the prepolymer, and effectively improving the solid-phase polycondensation efficiency by controlling the particle size of the prepolymer powder, and finally forming an efficient polymerization method for forming diphenol-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 highly heat-resistant liquid crystal polyester by melt-coupled solid-phase polycondensation, explore the solid-phase polycondensation reaction conditions to shorten the solid-phase reaction time, and improve the reaction efficiency of the solid-phase polycondensation.

[0009] The purpose of the present invention is achieved through the following technical solutions: A method for preparing biphenyl diphenol type highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation, comprising the following steps: (1) Acetylation reaction is performed on monomers of p-hydroxybenzoic acid (HBA) and 4,4-biphenyl (BP) with acetic anhydride and a catalyst respectively. After the acetylation reaction is completed, the product is recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) subjecting the purified p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid to a melt polycondensation reaction in a 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 release a liquid crystal polyester prepolymer of a certain molecular weight; (3) conveying the liquid crystal polyester prepolymer to a pulverizer, where 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 a biphenol-type high heat-resistant liquid crystal polyester; Wherein, in step (2), the molar ratio of the acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid is 10-80:10-40:10-40; In step (3), the prepolymer particles of uniform size are spherical particles with a diameter of 30 to 300 meshes.

[0010] Preferably, in step (1), the amount of acetic anhydride used is 1.0 to 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 to 1000 ppm.

[0011] Further preferably, in step (1), the amount of acetic anhydride used is 2.0 to 3.0 times the total molar number of monomer hydroxyl groups, and the amount of catalyst 1-methylimidazole used is 150 to 300 ppm.

[0012] Preferably, in step (1), the acetylation reaction is carried out at 140-150° C. for 1-2 h.

[0013] Preferably, in step (2), the conditions for the melt polycondensation reaction are 250°C for 3-3.5 h, 280°C for 2-2.5 h, and 350°C for 1-1.5 h, and a vacuum of 2000 Pa is applied at this temperature.

[0014] Preferably, in step (2), the logarithmic viscosity of the obtained liquid crystal polyester prepolymer is controlled at 3.5-4.5.

[0015] Preferably, in step (3), the prepolymer particles are placed in a 120° C. vacuum oven and dried for 12 to 14 hours; the dried prepolymer particles are placed in a solid phase polycondensation device, heated to 280 to 310° C. in a nitrogen atmosphere, and reacted for 2 to 12 hours to obtain a diphenol-based high heat-resistant liquid crystal polyester.

[0016] The present application also claims protection for a biphenol-type high heat-resistant liquid crystal polyester, which is prepared by the above-mentioned method for preparing the biphenol-type high heat-resistant liquid crystal polyester by melt-coupled solid-phase polycondensation.

[0017] Preferably, the biphenol-type high heat-resistant liquid crystal polyester is subjected to viscosity test and DSC test. The logarithmic viscosity of the biphenol-type high heat-resistant liquid crystal polyester is 4.5-8.5, the melting point is >560°C, the molecular weight distribution is narrow, and the color of the biphenol-type high heat-resistant liquid crystal polyester is beige.

[0018] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art: In the process of preparing the prepolymer, the molar percentage of biphenol monomer is adjusted to prepare a prepolymer with appropriate logarithmic viscosity and high melting point, and the influence of different monomer ratios on the melting point of the polymer is studied; the solid phase polycondensation time required for obtaining the biphenol type high heat-resistant polymer is shortened by crushing the prepolymer into particles of different diameters, so as to improve the efficiency of the solid phase polycondensation reaction. DETAILED DESCRIPTION

[0019] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, a specific implementation scheme is now described in detail.

[0020] The present invention is further described below in conjunction with the examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not indicated are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0021] Example 1 This embodiment provides a method for preparing a biphenyl diphenol type highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 80:10:10 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is conveyed to a pulverizer, in which 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. The dried prepolymer particles are placed in a vacuum drum at a nitrogen flow rate of 0.013 m / s and maintained at 280° C. for 2 h for solid phase polycondensation to obtain the diphenol-type high heat-resistant liquid crystal polyester.

[0022] Example 2 This embodiment provides a method for preparing a biphenyl diphenol type highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified 4-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 70:15:15 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is conveyed to a pulverizer, in which 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. The dried prepolymer particles are placed in a vacuum drum at a nitrogen flow rate of 0.013 m / s and maintained at 280° C. for 2 h for solid phase polycondensation to obtain the diphenol-type high heat-resistant liquid crystal polyester.

[0023] Example 3 This embodiment provides a method for preparing a biphenyl diphenol type highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified 4-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 60:20:20 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is conveyed to a pulverizer, in which 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. The dried prepolymer particles are placed in a vacuum drum at a nitrogen flow rate of 0.013 m / s and maintained at 280° C. for 2 h for solid phase polycondensation to obtain the diphenol-type high heat-resistant liquid crystal polyester.

[0024] Example 4 This embodiment provides a method for preparing a biphenyl diphenol type highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 50:25:25 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is conveyed to a pulverizer, in which 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. The dried prepolymer particles are placed in a vacuum drum at a nitrogen flow rate of 0.013 m / s and maintained at 280° C. for 2 h for solid phase polycondensation to obtain the diphenol-type high heat-resistant liquid crystal polyester.

[0025] Example 5 This embodiment provides a method for preparing a biphenyl diphenol type highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified 4-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 40:30:30 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is conveyed to a pulverizer, in which 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. The dried prepolymer particles are placed in a vacuum drum at a nitrogen flow rate of 0.013 m / s and maintained at 280° C. for 2 h for solid phase polycondensation to obtain the diphenol-type high heat-resistant liquid crystal polyester.

[0026] Example 6 This embodiment provides a method for preparing a biphenyl diphenol type highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified 4-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 30:35:35 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is conveyed to a pulverizer, in which 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. The dried prepolymer particles are placed in a vacuum drum at a nitrogen flow rate of 0.013 m / s and maintained at 280° C. for 2 h for solid phase polycondensation to obtain the diphenol-type high heat-resistant liquid crystal polyester.

[0027] Example 7 This embodiment provides a method for preparing a biphenyl diphenol type highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified 4-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 20:40:40 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is conveyed to a pulverizer, in which 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. The dried prepolymer particles are placed in a vacuum drum at a nitrogen flow rate of 0.013 m / s and maintained at 280° C. for 2 h for solid phase polycondensation to obtain the diphenol-type high heat-resistant liquid crystal polyester.

[0028] Example 8 This embodiment provides a method for preparing a biphenyl diphenol type highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified 4-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 10:40:40 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is conveyed to a pulverizer, in which 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. The dried prepolymer particles are placed in a vacuum drum at a nitrogen flow rate of 0.013 m / s and maintained at 280° C. for 2 h for solid phase polycondensation to obtain the diphenol-type high heat-resistant liquid crystal polyester.

[0029] Example 9 This embodiment is carried out on the basis of the above-mentioned embodiment 3, and the similarities with the above-mentioned embodiment are not repeated here.

[0030] In this embodiment, in step (3), solid phase polycondensation is carried out at 290° C. for 2 hours to obtain the biphenyl diphenol type high heat-resistant liquid crystal polyester.

[0031] Example 10 This embodiment is carried out on the basis of the above-mentioned embodiment 3, and the similarities with the above-mentioned embodiment are not repeated here.

[0032] In this embodiment, in step (3), solid phase polycondensation is carried out at 300° C. for 2 hours to obtain the biphenyl diphenol type high heat-resistant liquid crystal polyester.

[0033] Embodiment 11 This embodiment is carried out on the basis of the above-mentioned embodiment 3, and the similarities with the above-mentioned embodiment are not repeated here.

[0034] In this embodiment, in step (3), solid phase polycondensation is carried out at 310° C. for 2 hours to obtain the biphenyl diphenol type high heat-resistant liquid crystal polyester.

[0035] Example 12 This embodiment is carried out on the basis of the above-mentioned embodiment 3, and the similarities with the above-mentioned embodiment are not repeated here.

[0036] In this embodiment, in step (3), solid phase polycondensation is carried out at 280° C. for 4 hours to obtain the biphenyl diphenol type high heat-resistant liquid crystal polyester.

[0037] Embodiment 13 This embodiment is carried out on the basis of the above-mentioned embodiment 3, and the similarities with the above-mentioned embodiment are not repeated here.

[0038] In this embodiment, in step (3), solid phase polycondensation is carried out at 280° C. for 6 hours to obtain the biphenyl diphenol type high heat-resistant liquid crystal polyester.

[0039] Embodiment 14 This embodiment is carried out on the basis of the above-mentioned embodiment 3, and the similarities with the above-mentioned embodiment are not repeated here.

[0040] In this embodiment, in step (3), solid phase polycondensation is carried out at 280° C. for 8 hours to obtain the biphenyl diphenol type high heat-resistant liquid crystal polyester.

[0041] Embodiment 15 This embodiment is carried out on the basis of the above-mentioned embodiment 3, and the similarities with the above-mentioned embodiment are not repeated here.

[0042] In this embodiment, in step (3), the nitrogen flow rate is 0.026 m / s.

[0043] Example 16 This embodiment is carried out on the basis of the above-mentioned embodiment 3, and the similarities with the above-mentioned embodiment are not repeated here.

[0044] In this embodiment, in step (3), the nitrogen flow rate is 0.039 m / s.

[0045] Embodiment 17 This embodiment is carried out on the basis of the above-mentioned embodiment 3, and the similarities with the above-mentioned embodiment are not repeated here.

[0046] In this embodiment, in step (3), the low molecular weight liquid crystal polyester prepolymer is crushed into prepolymer particles of 50-100 mesh (0.15-0.3 mm) in a crusher.

[0047] Embodiment 18 This embodiment is carried out on the basis of the above-mentioned embodiment 3, and the similarities with the above-mentioned embodiment are not repeated here.

[0048] In this embodiment, in step (3), the low molecular weight liquid crystal polyester prepolymer is crushed into prepolymer particles of 100-300 mesh (0.05-0.15 mm) in a crusher.

[0049] Comparative Example 1 This comparative example provides a method for preparing a liquid crystal polyester, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified 4-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 60:40:40 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is placed in a vacuum oven at 120°C and dried for 12 hours. The dried prepolymer is placed in a twin-screw extruder and extruded into particles. The particles are cylindrical and have a diameter within the range of 1 mm. The liquid crystal polyester is obtained by solid phase polycondensation at 280°C for 8 hours.

[0050] Comparative Example 2 This comparative example provides a method for preparing a liquid crystal polyester, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified 4-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 60:40:40 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is placed in a vacuum oven at 120°C and dried for 12 hours. The dried prepolymer is placed in a twin-screw extruder and extruded into particles. The particles are cylindrical and have a diameter within the range of 2 mm. The liquid crystal polyester is obtained by solid phase polycondensation at 280°C for 8 hours.

[0051] Comparative Example 3 This comparative example provides a method for preparing a liquid crystal polyester, comprising the following steps: (1) Mixing monomers of p-hydroxybenzoic acid (HBA) and 4,4-diphenol (BP), acetic anhydride accounting for 2.2 times the total molar number of monomer hydroxyl groups, and 300 ppm of 1-methylimidazole accounting for the total weight of the monomers, heating to 150° C., and then carrying out acetylation reaction at a constant temperature for 1 hour. After the acetylation reaction is completed, the monomers are recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomers (ABA) and 4,4-diacetoxybiphenyl (ABP), respectively. The obtained acetylated monomers are filtered and washed in ice water for recrystallization and purification; (2) Place the purified 4-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid in a molar ratio of 60:40:40 in a three-necked flask, heat to 250°C for reaction for 3 hours, continue to heat to 280°C for reaction for 1 hour, continue to heat to 350°C for reaction for 1 hour, and draw a vacuum of 2000 Pa 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 to release the liquid crystal polyester prepolymer; (3) The liquid crystal polyester prepolymer is placed in a vacuum oven at 120°C and dried for 12 hours. The dried prepolymer is placed in a twin-screw extruder and extruded into particles. The particles are cylindrical and have a diameter within the range of 3 mm. The liquid crystal polyester is obtained by solid phase polycondensation at 280°C for 8 hours.

[0052] Comparative Example 4 This comparative example is carried out on the basis of the above-mentioned embodiment 1, and the similarities with the above-mentioned embodiment are not repeated here.

[0053] In this comparative example, in step (2), the purified p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid are placed in a three-necked flask at a molar ratio of 10:45:45.

[0054] Comparative Example 5 This comparative example is carried out on the basis of the above-mentioned embodiment 1, and the similarities with the above-mentioned embodiment are not repeated here.

[0055] In this comparative example, in step (2), the purified p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid are placed in a three-necked flask at a molar ratio of 90:40:40.

[0056] Comparative Example 6 This comparative example is carried out on the basis of the above-mentioned embodiment 1, and the similarities with the above-mentioned embodiment are not repeated here.

[0057] In this comparative example, in step (2), the purified p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid are placed in a three-necked flask at a molar ratio of 90:10:10.

[0058] The solid phase polycondensation reaction conditions of Examples 1 to 18 are shown in Table 1.

[0059] Table 1

[0060] The liquid crystal polyester prepolymers obtained in the above Examples 1 to 18 were subjected to viscosity and DSC tests, wherein Td5% refers to the temperature at which the mass loss of the material during heating reaches 5%; 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.

[0061] Table 2

[0062] The biphenol-type high 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 subjected to viscosity and DSC tests, wherein Td5% refers to the temperature at which the mass loss of the material during heating reaches 5%; 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.

[0063] Table 3

[0064] The test methods of the viscosity of the above embodiments and comparative examples are described in detail as follows: 1. Determination of inherent viscosity (IV): The solvent is pentafluorophenol; 0.050 g of a sample of liquid crystal copolyester is weighed into a clean and dry 50 ml conical flask, and then 50 ml of pentafluorophenol is added thereto, the flask is covered with a stopper, and the conical flask is placed in a shaking table at 80°C to dissolve for 8 hours to completely dissolve the sample, and then the solution is filtered into another clean and dry 25 ml volumetric flask using a No. 2 sand core funnel, and placed in the above water bath at a constant temperature for 1 hour; the outflow time t of the pure solvent and the solution is measured respectively using an Ubbelohde viscometer (capillary diameter is 0.63 mm) in a 60°C water bath 溶剂 and t 溶液 ; then calculate IV using the following formula: .

[0065] 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 the 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 accelerates, and the relative viscosity of the product increases, which is mainly reflected in the molecular weight and mechanical properties of the obtained liquid crystal polyester under the same solid phase polycondensation time and nitrogen flow rate. Increasing the specific surface area of ​​the LCP particles is conducive to the removal of by-products, so that the equilibrium moves forward and the reaction rate is increased, thereby achieving the purpose of improving the production efficiency of the solid phase polycondensation. It can be seen from Example 1 and Comparative Examples 4 to 6 that the molar ratio of the refined p-acetoxybenzoic acid monomer (ABA), 4,4-diacetoxybiphenyl (ABP) and terephthalic acid will also affect the performance of the final product.

[0066] In summary, in the process of preparing the prepolymer, the molar percentage of the biphenol monomer is effectively regulated to prepare a prepolymer with appropriate logarithmic viscosity and high melting point, and the influence of different monomer ratios on the melting point of the polymer is studied; the solid phase polycondensation time required to obtain the biphenol-type high heat-resistant polymer is shortened by crushing the prepolymer into particles of different diameters, so as to improve the efficiency of the solid phase polycondensation reaction.

[0067] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing biphenol-based high heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation, characterized in that: The following steps are involved: (1) subjecting monomers p-hydroxybenzoic acid and 4,4-diphenol to acetylation reaction with acetic anhydride and a catalyst respectively, and after the acetylation reaction is completed, the product is recrystallized to remove excess acetic anhydride, thereby obtaining high-purity p-acetoxybenzoic acid monomer and 4,4-diacetoxybiphenyl monomer respectively, and the obtained acetylated monomer is filtered and washed in ice water for recrystallization and purification; (2) subjecting the purified p-acetoxybenzoic acid monomer, 4,4-diacetoxybiphenyl and terephthalic acid to a melt polycondensation reaction in a molar ratio to obtain a high heat-resistant 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 release the high heat-resistant liquid crystal polyester prepolymer; (3) conveying the liquid crystal polyester prepolymer to a pulverizer, where 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 in a nitrogen atmosphere to obtain the biphenol-type high heat-resistant liquid crystal polyester; Wherein, 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 of uniform size are spherical particles with a diameter of 30 to 300 meshes.

2. The method for preparing biphenol-based highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation as claimed in claim 1, characterized in that: In step (1), the amount of acetic anhydride used is 1.0 to 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 to 1000 ppm.

3. The method for preparing biphenol-based highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation as claimed in claim 1, characterized in that: In step (1), the acetylation reaction is carried out at 140-150° C. for 1-2 h.

4. The method for preparing biphenol-based highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation as claimed in claim 1, characterized in that: In step (2), the conditions of the melt polycondensation reaction are: reaction at 250°C for 3-3.5 hours, reaction at 280°C for 2-2.5 hours, and reaction at 350°C for 1-1.5 hours, and a vacuum of 2000 Pa is drawn at this temperature.

5. The method for preparing biphenol-based highly heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation as claimed in claim 1, characterized in that: In step (2), the logarithmic viscosity of the obtained liquid crystal polyester prepolymer is controlled at 3.5-4.

5.

6. The method for preparing biphenol-based high heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation as claimed in claim 1, characterized in that: In step (3), the prepolymer particles are placed in a 120° C. vacuum oven and dried for 12 to 14 hours; the dried prepolymer particles are placed in a solid phase polycondensation device, heated to 280 to 310° C. in a nitrogen atmosphere, and reacted for 2 to 8 hours to obtain a diphenol-type high heat-resistant liquid crystal polyester.

7. A biphenol-based high heat-resistant liquid crystal polyester, characterized in that: The method for preparing biphenol-type high heat-resistant liquid crystal polyester by melt-coupled solid phase polycondensation as described in any one of claims 1 to 6 is adopted.

8. The biphenol-based high heat-resistant liquid crystal polyester according to claim 7, characterized in that: The biphenol type high heat resistant liquid crystal polyester was subjected to viscosity test and DSC test. The logarithmic viscosity of the biphenol type high heat resistant liquid crystal polyester was 4.5-8.5, the melting point was >560°C, and the color of the biphenol type high heat resistant liquid crystal polyester was beige.

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