Synthesis method of liquid crystal polyarylate and application of high boiling point imidazole catalyst in its synthesis

Abstract

The present invention belongs to the field of liquid crystal polyarylate synthesis, and specifically relates to a synthesis method of liquid crystal polyarylate and the application of a high boiling point imidazole catalyst in the synthesis thereof. The synthesis method is as follows: under nitrogen protection, a certain proportion of monomers, acylating agents and catalysts are mixed, and the temperature is raised to undergo acetylation and melt polycondensation to obtain a liquid crystal polyester melt, which is cooled to obtain a liquid crystal polyarylate finished product. In the liquid crystal polyester synthesis method provided by the present invention, by selecting a specific high boiling point imidazole catalyst, it can be sustainably and efficiently used for the synthesis of liquid crystal polyarylate, which can not only effectively catalyze the acetylation reaction, but also can continuously and efficiently catalyze the melt polycondensation reaction, greatly shortening the reaction time of the polycondensation and reducing the occurrence of side reactions.

Description

Technical Field

[0001] The invention belongs to the field of liquid crystal polyarylate synthesis, and in particular relates to a synthesis method of liquid crystal polyarylate and application of a high-boiling-point imidazole catalyst in the synthesis thereof. Background Art

[0002] Liquid crystal polyarylate (LCP) has the advantages of high strength, high modulus, excellent molding and processing performance, outstanding heat resistance, low water absorption, excellent flame retardancy, extremely small linear expansion coefficient, excellent flame retardancy, electrical insulation, chemical corrosion resistance, weathering resistance, microwave transmittance, low dielectric constant and dielectric loss factor. It has been widely used in high-tech industries such as electronics, 5G communications, consumer electronics, and automotive parts.

[0003] LCP materials can be divided into three types according to heat deformation temperature, namely type I, type II, and type III. Type I LCP material is a high heat-resistant grade with a high molding temperature and a heat deformation temperature of about 320 ℃ or higher. Its main components are p-hydroxybenzoic acid (HBA), 4-4'biphenol (BP), isophthalic acid (IPA), and terephthalic acid (TPA) in different proportions. Type II LCP material is a medium heat-resistant grade with a heat resistance grade and molding processing temperature similar to general-grade engineering plastics. Its heat deformation temperature is above 220 ℃, and due to its good processing performance, it is usually used to produce LCP films and fibers. Its main components are HBA and 6-hydroxy-2-naphthoic acid (HNA). Type III LCP material is a general heat-resistant grade with a low heat resistance temperature and a heat deformation temperature of about 120 ℃. It has good molding and processing performance and a low price. It can be used for cooling fans, connecting pipes, sensors, etc. It is mainly composed of HBA and polyethylene terephthalate (PET) copolymer.

[0004] The synthesis of LCP is a two-step process of acetylation of phenolic hydroxyl groups and melt polycondensation of acetoxyacetophenone and carboxyl deacetic acid. The melt polycondensation step is carried out under high temperature conditions. The reaction can occur without a catalyst, but due to the difference in reactivity between different monomers, the composition of the final polymer will be affected, and more by-products will be generated under a longer reaction time, which seriously affects the performance of the final polymer. Or, metal acetates such as sodium acetate, magnesium acetate, zinc acetate, potassium acetate, and stannous acetate are used as catalysts. Such organometallic catalysts can effectively catalyze polycondensation reactions, but do not have catalytic activity for acetylation reactions. The amount of catalyst charged is very small compared to the monomer. There is no purification device for the final resin in industrial production, and the catalyst cannot be separated from the system. Therefore, a trace amount of catalyst residue will be contained in the final resin, affecting the performance of the resin. This makes the improvement of catalysts a valuable industrial problem.

[0005] In response to this problem, with the continuous development of industry, organic base catalysts have emerged for the synthesis of LCP. It can not only effectively catalyze the acetylation reaction, but also has relatively excellent catalytic activity for polycondensation reaction. In the prior art, the organic base catalysts used are heterocyclic compounds containing N atoms such as N,N'-dimethylaminopyridine and N-methylimidazole, such as patent document CN111886276A. Compared with metal catalysts, organic base catalysts can be discharged from the reaction system together with the by-product acetic acid during the high-temperature melt polycondensation process that can usually reach more than 300°C, avoiding residues in the final polymer.

[0006] However, the problem that follows is that the organic base catalysts proposed in the patent literature generally have a low boiling point. For example, the boiling point of N-methylimidazole is only 198°C. Before reaching the temperature for the start of the polycondensation reaction or just reaching the temperature, it is discharged from the reaction system together with the byproduct acetic acid, and only plays the role of catalyzing acetylation, and cannot effectively catalyze the polycondensation reaction, which leads to the extension of reaction time and the instability of product quality, resulting in loss and waste of resources. Therefore, the optimization and selection of catalysts is still a very important and hot research direction in the field of liquid crystal polyarylate synthesis.

[0007] In view of this, the present invention is proposed. Summary of the invention

[0008] Based on this, the purpose of the present invention is to select a stable high-boiling point imidazole catalyst that can be sustainably and efficiently used in the synthesis of liquid crystal polyarylates, which can not only effectively catalyze the acetylation reaction, but also can continuously and efficiently catalyze the melt polycondensation reaction, greatly shorten the reaction time of the polycondensation, and reduce the occurrence of side reactions.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0010] The synthesis method of liquid crystal polyarylate comprises the following steps: under nitrogen protection conditions, a certain proportion of monomers, an acylation agent and a specific catalyst are subjected to an acylation reaction at an acylation temperature, and then the temperature is slowly raised for polycondensation, finally a liquid crystal polyarylate melt with a certain viscosity is obtained, and after cooling, a liquid crystal polyarylate finished product is obtained; the monomers are p-hydroxybenzoic acid and its derivatives, terephthalic acid or its derivatives, isophthalic acid or its derivatives, 6-hydroxy-2-naphthoic acid or its derivatives, and biphenyl dicarboxylic acid or its derivatives.

[0011] In a preferred embodiment, the high boiling point imidazole catalyst is as shown in formula (1):

[0012] Formula (1)

[0013]

[0014] In formula (1), the R substituent may be an alkyl group, a cycloalkyl group, or an aryl group containing five or more carbon atoms, each independently replacing one or more hydrogen atoms on the five-membered ring.

[0015] In a preferred embodiment, the addition amount of the high boiling point imidazole catalyst is 50-5000 ppm of the total weight of the monomers, 50-3000 ppm after optimization, and 100-1000 ppm after further optimization.

[0016] In a preferred embodiment, the heating rate of the heating process is 0.2-45°C / min. After optimization, it is 0.5-5°C / min, which can be a specific value of 0.5°C / min, 1°C / min, 1.5°C / min, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min or any value within the range of 0.5-5°C / min.

[0017] In a preferred embodiment, the acylating agent is a common acid anhydride compound, preferably acetic anhydride, and the added amount is 0.6-20 equivalents of the total molar amount of the two monomers, 0.8-10 equivalents after optimization, and 0.8-2.5 equivalents after further optimization.

[0018] In a preferred embodiment, the monomers may be p-hydroxybenzoic acid and its derivatives, terephthalic acid and its derivatives, isophthalic acid and its derivatives, 6-hydroxy-2-naphthoic acid and its derivatives, biphenyl dicarboxylic acid and its derivatives, etc., and the monomers may be added in any molar ratio. Preferably, p-hydroxybenzoic acid and its derivatives and 6-hydroxy-2-naphthoic acid and its derivatives are added in a molar ratio of 50:50-95:5, and after further optimization, they are added in a molar ratio of 70:30-85:15.

[0019] In a preferred embodiment, the acetylation temperature is 80-180°C, and the reaction time is 10 minutes to 4 hours. It is understood that the acetylation temperature can be a specific value of 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C or any value within the range of 80-180°C, and is optimized to be 100-160°C; further optimized to be 100-140°C.

[0020] In a preferred embodiment, the polycondensation reaction temperature is 200-345°C, and the pressure of the reaction system is reduced to 50-1000 Pa in the later stage of the polycondensation reaction. After optimization, it is 230-345°C.

[0021] The high boiling point imidazole catalyst, in formula (1), the R substituent can be an alkyl group, cycloalkyl group, aryl group, etc. containing five or more carbon atoms, and can be further refined into pentyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, phenyl, benzyl, benzoyl, biphenyl, etc., including but not limited to the substituents listed. And the R substituents can independently replace one or more hydrogen atoms on the five-membered ring.

[0022] Examples thereof include N-pentyl imidazole, N-hexyl imidazole, N-cyclohexyl imidazole, N-heptyl imidazole, N-phenyl imidazole, 2-pentyl imidazole, 2-hexyl imidazole, 2-cyclohexyl imidazole, 2-nonyl imidazole, 2-undecyl imidazole, 4-phenyl imidazole, benzimidazole, 1-benzyl imidazole, 1-phenylethyl imidazole, 2,5-diphenyl imidazole, 4,5-diphenyl imidazole, 5-amino-1-phenyl imidazole, 1-ethyl-2-methylbenzimidazole, etc., including but not limited to the high boiling point imidazole catalysts listed above.

[0023] After the catalyst was optimized, it was a monosubstituted imidazole. After further optimization, the substitution position was 1, and the best catalysts were N-hexylimidazole and N-phenylimidazole.

[0024] The present invention also discloses an application of a high boiling point imidazole catalyst in the synthesis of liquid crystal polyarylate. The high boiling point imidazole catalyst has a structure as shown in formula (1):

[0025] Formula (1)

[0026]

[0027] In formula (1), the R substituent may be an alkyl group, a cycloalkyl group, or an aryl group containing five or more carbon atoms, each independently replacing one or more hydrogen atoms on the five-membered ring;

[0028] When synthesizing liquid crystal polyarylate, under nitrogen protection conditions, a certain proportion of monomers, acylation agents and high-boiling point imidazole catalysts are subjected to acylation reaction at acylation temperature, and then the temperature is slowly raised for polycondensation, and finally a liquid crystal polyarylate melt with a certain viscosity is obtained, and after cooling, a liquid crystal polyarylate finished product is obtained; the monomers are p-hydroxybenzoic acid and its derivatives, terephthalic acid or its derivatives, isophthalic acid or its derivatives, 6-hydroxy-2-naphthoic acid or its derivatives, and biphenyl dicarboxylic acid or its derivatives.

[0029] The present invention also provides a liquid crystal polyarylate polymerization process used in combination with the above-mentioned high-boiling-point imidazole catalyst, and the implementation steps are as follows:

[0030] Under nitrogen protection conditions, a certain proportion of monomers, acylation agents and high-boiling-point imidazole catalysts are subjected to acylation reaction at an acylation temperature, and then the temperature is slowly raised and polycondensation is carried out (due to the high temperature during the polycondensation process, by-products are gradually removed, and the by-products are mainly acetic acid), and finally a liquid crystal polyarylate melt with a certain viscosity is obtained, and a liquid crystal polyarylate finished product is obtained after cooling; the monomers are p-hydroxybenzoic acid and its derivatives, terephthalic acid or its derivatives, isophthalic acid or its derivatives, 6-hydroxy-2-naphthoic acid or its derivatives, and biphenyl dicarboxylic acid or its derivatives.

[0031] More specifically, the monomer, acylation agent and high-boiling-point imidazole catalyst are added to the reactor, nitrogen is purged into the reactor, and the atmosphere is fully replaced with a nitrogen-protected atmosphere. Under nitrogen protection, the temperature is slowly and uniformly raised to 80-180°C for acetylation reaction, and the reaction time is 10 minutes to 4 hours. After the acetylation is completed, the reaction system is heated to start a melt polycondensation reaction at a temperature of 200-345°C, and the pressure of the system is gradually reduced to 50-1000 Pa. The reaction is terminated after the torque rises to obtain a liquid crystal copolyester.

[0032] It should be noted that the liquid crystal copolyester can be obtained by ending the reaction after the material reaches a certain viscosity. The material viscosity here is a measured value obtained by the feedback value such as power, current or torque generated by the material acting on the stirrer and can be displayed in real time. When the reaction is sufficient, the material viscosity increases to a certain degree, indicating that the reaction is complete.

[0033] Compared with the prior art, the invention has the following beneficial effects: the high-boiling-point imidazole catalyst can not only continuously and efficiently participate in the polymerization reaction (polymerization is completed in one step, and the final polymer is obtained only through melt polycondensation), but also effectively increase the polymerization rate in the polycondensation stage, improve the polymerization difference between different monomers, and reduce the residence time under high temperature conditions, thereby reducing the impact of the side reactions in the late stage of polymerization on the final product, and obtaining liquid crystal polyarylate with excellent performance. In addition, it can also volatilize from the reaction system in the late stage of polymerization and be collected together with the by-products. The collected liquid can also be purified and recovered by distillation and other methods, which is in line with the concept of green chemistry. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The gas chromatogram of Example 1 and the mass spectrum of the catalyst detected therein, a is the gas chromatogram, b is the mass spectrum;

[0035] Figure 2 The gas chromatogram of Example 5 and the mass spectrum of the catalyst detected therein, a is the gas chromatogram, b is the mass spectrum;

[0036] Figure 3The gas chromatogram of Comparative Example 2 and the mass spectrum of the catalyst detected therein, a is the gas chromatogram, b is the mass spectrum;

[0037] Figure 4 The gas chromatogram of Comparative Example 3 and the mass spectrum of the catalyst detected therein, a is the gas chromatogram, b is the mass spectrum;

[0038] Figure 5 This is the gas chromatogram of the liquid collected at 290°C in Example 3;

[0039] Figure 6 This is the gas chromatogram of the liquid collected at 290°C in Example 5;

[0040] Figure 7 The gas chromatogram and mass spectrometry of the N-hexylimidazole catalyst standard sample are shown in Figure 1, where a is the gas chromatogram and b is the mass spectrometry;

[0041] Figure 8 The gas chromatography and mass spectrometry spectra of the N-phenylimidazole catalyst standard sample, a is the gas chromatography, and b is the mass spectrometry spectra;

[0042] Fig. 9 The gas chromatogram and mass spectrometry of the N-methylimidazole catalyst standard sample are shown in Figure 1, where a is the gas chromatogram and b is the mass spectrometry;

[0043] Fig.10 The gas chromatography and mass spectrometry spectra of the N-butylimidazole catalyst standard sample, a is the gas chromatography, and b is the mass spectrometry spectra;

[0044] Fig.11 The collected liquid mass-reaction time curves of Example 1 and Comparative Example 1 are shown;

[0045] Fig.12 The collected liquid mass-reaction time curves of Example 1 and Comparative Example 3 are shown. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0047] In the embodiments of the present invention, a method for synthesizing liquid crystal polyarylate and the application of a high boiling point imidazole catalyst in its synthesis are provided, and the catalytic synthesis process is verified and analyzed; the specific test and analysis method is as follows:

[0048] The byproducts collected during the polymerization process at different polycondensation temperatures were weighed and the reaction rate curve was plotted together with the reaction time. The sampled samples were concentrated and diluted, and the samples were tested by GC-MS. The collected liquid data were compared with the catalyst standard data, and the residence time of the catalyst in the polycondensation reaction was fed back to indicate the degree of participation of the catalyst.

[0049] In the embodiment of the present invention, the sampling temperature of the collected liquid is 200-345° C., and after optimization, it is 200-310° C. The reaction distillate is continuously discharged from the reaction system into a specific collection tank and used as the collected liquid for subsequent weighing and processing.

[0050] In the examples and comparative examples of the present invention, the pressure of the reaction system was reduced to 200 Pa in the later stage of the polycondensation reaction.

[0051] In the process of liquid crystal copolyester synthesis, in order to analyze the corresponding reaction progress, the condensation collection liquid, that is, the by-product liquid evaporated from the polymerization reaction, will be taken at various temperature points, weighed and analyzed. The temperature points of each sampling are within the temperature range of the condensation reaction, and sampling can be selected at any temperature. Further refined into 200 ℃, 205 ℃, 210 ℃, 215 ℃, 220 ℃, 225 ℃, 230 ℃, 235 ℃, 240 ℃, 245 ℃, 250 ℃, 255 ℃, 260 ℃, 265 ℃, 270 ℃, 275 ℃, 280 ℃, 285 ℃, 290 ℃, 295 ℃, 300 ℃, 305 ℃, 310 ℃, and any temperature range can be selected for sampling. The five sampling temperature points were optimized to be 200 ℃, 230 ℃, 260 ℃, 290 ℃ and 310 ℃.

[0052] In the embodiments of the present invention, the continuous influence of the high boiling point catalyst on the synthesis of liquid crystal polyester is tested by GC-MS of the collected liquid of the byproducts produced during the polymerization process at different polycondensation temperatures, and the residence time of the catalyst in the polycondensation reaction is fed back to indicate the degree of participation of the catalyst. At the same time, a reaction rate diagram is drawn based on the mass of the collected liquid and the reaction time at the same temperature to indicate the degree of catalysis of the catalyst on the polymerization reaction.

[0053] The treatment method of the collected liquid is: the byproduct collected liquid samples at different temperatures are concentrated by distillation to remove a large amount of byproduct acetic acid, and the remaining sample is diluted to a specific concentration with a good solvent, and then the GC-MS test is performed. Among them, the good solvent can be a low boiling point solvent such as methanol, ethanol, ethylene glycol, acetone, chloroform, dichloromethane, 1,1,2,2-tetrachloroethane, tetrahydrofuran, ethyl acetate, etc., including but not limited to the listed solvents. Preferably, tetrahydrofuran and dichloromethane are used.

[0054] The data analysis method is: use the same good solvent to prepare the catalyst standard sample of the same concentration, use the same test method to perform GC-MS test, fit the chromatographic data graph of the collected liquid in each temperature section or the chromatographic data graph of the decomposition extract with the chromatographic data graph of the catalyst standard sample, and confirm the presence of the catalyst in the collected liquid sample by gas chromatography and mass spectrometry.

[0055] As the instrument and test conditions for GC-MS test, they can be listed as follows:

[0056] Test instrument: SHIMADZU Nexis GC-2030

[0057] Test concentration: The ratio of concentrate to good solvent is 1:4

[0058] Test temperature: 320 ℃

[0059] Analysis software: GCMS solution

[0060] The color value of liquid crystal polyarylate is detected by a colorimeter.

[0061] The instruments and test conditions for color value data can be listed as follows:

[0062] Test instrument: Hunterlab LabScan XE

[0063] Unless otherwise specified, all commodities or reagents in the present invention are purchased through market channels. Among them:

[0064] Parahydroxybenzoic acid: HBA, purchased from Shengxiao Company;

[0065] 6-Hydroxy-2-naphthoic acid: HNA, purchased from Shengxiao Company;

[0066] Acetic anhydride: purchased from Sinopharm Group;

[0067] Dichloromethane: purchased from Sinopharm Group

[0068] N-Hexylimidazole, N-phenylimidazole, N-methylimidazole, and N-butylimidazole were purchased from Sigma-Aldrich.

[0069] Example 1

[0070] 193.38 g of p-hydroxybenzoic acid, 112.91 g of 6-hydroxy-2-naphthoic acid, 214.39 g of acetic anhydride and 91.89 mg (300 ppm) of N-hexylimidazole were added to a reactor equipped with a stirring device, a nitrogen introduction device, a vacuum system, a thermometer and a reflux cooling device. Nitrogen was purged into the reactor to fully replace the atmosphere with nitrogen protection. Under nitrogen flow, the temperature was first raised to 130 °C at a heating rate of 2 °C / min for acetylation reaction for 1.5 hours. After the acetylation was completed, the temperature was raised at a heating rate of 2 °C / min to start the polycondensation reaction, and the collected liquid evaporated from the reaction was weighed and sampled at 200 °C, 230 °C, 260 °C, 290 °C and 310 °C, respectively, and finally the temperature was raised to above 320 °C. The pressure of the system was gradually reduced during the heating process, and the reaction was terminated after the torque increased. The obtained liquid crystal copolyester was taken out and tested by a colorimeter. The collected liquid sample was concentrated to remove a large amount of acetic acid, and then diluted with dichloromethane for GC-MS testing. The obtained GC-MS spectrum was qualitatively analyzed, and it was found that N-hexyl imidazole was detected only in the collected liquid at 310 °C.

[0071] Example 2

[0072] 193.38 g of p-hydroxybenzoic acid, 112.91 g of 6-hydroxy-2-naphthoic acid, 214.39 g of acetic anhydride and 183.77 mg (600 ppm) of N-hexylimidazole were added to a reactor equipped with a stirring device, a nitrogen introduction device, a vacuum system, a thermometer and a reflux cooling device. Nitrogen was purged into the reactor to fully replace the atmosphere with nitrogen protection. Under nitrogen flow, the temperature was first raised to 130 °C at a heating rate of 2 °C / min for acetylation reaction for 1.5 hours. After the acetylation was completed, the temperature was raised at a heating rate of 2 °C / min to start the polycondensation reaction, and the collected liquid evaporated from the reaction was weighed and sampled at 200 °C, 230 °C, 260 °C, 290 °C and 310 °C, respectively, and finally the temperature was raised to above 320 °C. The pressure of the system was gradually reduced during the heating process, and the reaction was terminated after the torque increased. The obtained liquid crystal copolyester was taken out and tested by a colorimeter. The collected liquid sample was concentrated to remove a large amount of acetic acid, and then diluted with dichloromethane for GC-MS testing. The obtained GC-MS spectrum was qualitatively analyzed, and it was found that N-hexyl imidazole was detected only in the collected liquid at 310 °C.

[0073] Example 3

[0074] 193.38 g of p-hydroxybenzoic acid, 112.91 g of 6-hydroxy-2-naphthoic acid, 214.39 g of acetic anhydride and 306.29 mg (1000 ppm) of N-hexylimidazole were added to a reactor equipped with a stirring device, a nitrogen introduction device, a vacuum system, a thermometer and a reflux cooling device. Nitrogen was purged into the reactor to fully replace the atmosphere with nitrogen protection. Under nitrogen flow, the temperature was first raised to 130 °C at a heating rate of 2 °C / min for acetylation reaction for 1.5 hours. After the acetylation was completed, the temperature was raised at a heating rate of 2 °C / min to start the polycondensation reaction. The collected liquid evaporated from the reaction was weighed and sampled at 200 °C, 230 °C, 260 °C, 290 °C and 310 °C, respectively, and finally the temperature was raised to above 320 °C. The pressure of the system was gradually reduced during the heating process, and the reaction was terminated after the torque increased. The obtained liquid crystal copolyester was taken out and tested by a colorimeter. The collected liquid sample was concentrated to remove a large amount of acetic acid, and then diluted with dichloromethane for GC-MS testing. The obtained GC-MS spectrum was qualitatively analyzed, and it was found that N-hexyl imidazole was detected only in the collected liquid at 310 °C.

[0075] Example 4

[0076] 193.38 g of p-hydroxybenzoic acid, 112.91 g of 6-hydroxy-2-naphthoic acid, 214.39 g of acetic anhydride and 91.89 mg (300 ppm) of N-phenylimidazole were added to a reactor equipped with a stirring device, a nitrogen introduction device, a vacuum system, a thermometer and a reflux cooling device. Nitrogen was purged into the reactor to fully replace the atmosphere with nitrogen protection. Under nitrogen flow, the temperature was first raised to 130 °C at a heating rate of 2 °C / min for acetylation reaction for 1.5 hours. After the acetylation was completed, the temperature was raised at a heating rate of 2 °C / min to start the polycondensation reaction, and the collected liquid evaporated from the reaction was weighed and sampled at 200 °C, 230 °C, 260 °C, 290 °C and 310 °C, respectively, and finally the temperature was raised to above 320 °C. The pressure of the system was gradually reduced during the heating process, and the reaction was terminated after the torque increased. The obtained liquid crystal copolyester was taken out and tested by a colorimeter. The collected liquid sample was concentrated to remove a large amount of acetic acid, and then diluted with dichloromethane for GC-MS testing. The obtained GC-MS spectrum was qualitatively analyzed, and it was found that N-phenylimidazole was detected only in the collected liquid at 310 °C.

[0077] Example 5

[0078] 193.38 g of p-hydroxybenzoic acid, 112.91 g of 6-hydroxy-2-naphthoic acid, 214.39 g of acetic anhydride and 306.29 mg (1000 ppm) of N-phenylimidazole were added to a reactor equipped with a stirring device, a nitrogen introduction device, a vacuum system, a thermometer and a reflux cooling device. Nitrogen was purged into the reactor to fully replace the atmosphere with nitrogen protection. Under nitrogen flow, the temperature was first raised to 130 °C at a heating rate of 2 °C / min for acetylation reaction for 1.5 hours. After the acetylation was completed, the temperature was raised at a heating rate of 2 °C / min to start the polycondensation reaction, and the collected liquid evaporated from the reaction was weighed and sampled at 200 °C, 230 °C, 260 °C, 290 °C and 310 °C, respectively, and finally the temperature was raised to above 320 °C. The pressure of the system was gradually reduced during the heating process, and the reaction was terminated after the torque increased. The obtained liquid crystal copolyester was taken out and tested by a colorimeter. The collected liquid sample was concentrated to remove a large amount of acetic acid, and then diluted with dichloromethane for GC-MS testing. The obtained GC-MS spectrum was qualitatively analyzed, and it was found that N-phenylimidazole was detected only in the collected liquid at 310 °C.

[0079] Example 6

[0080] 234.82 g of p-hydroxybenzoic acid, 56.45 g of 6-hydroxy-2-naphthoic acid, 214.39 g of acetic anhydride and 87.38 mg (300 ppm) of N-hexylimidazole were added to a reactor equipped with a stirring device, a nitrogen introduction device, a vacuum system, a thermometer and a reflux cooling device. Nitrogen was purged into the reactor to fully replace the atmosphere with nitrogen protection. Under nitrogen flow, the temperature was first raised to 130 °C at a heating rate of 2 °C / min for acetylation reaction for 1.5 hours. After the acetylation was completed, the temperature was raised at a heating rate of 2 °C / min to start the polycondensation reaction, and the collected liquid evaporated from the reaction was weighed and sampled at 200 °C, 230 °C, 260 °C, 290 °C and 310 °C, respectively, and finally the temperature was raised to above 320 °C. The pressure of the system was gradually reduced during the heating process, and the reaction was terminated after the torque increased. The obtained liquid crystal copolyester was taken out and tested by a colorimeter. The collected liquid sample was concentrated to remove a large amount of acetic acid, and then diluted with dichloromethane for GC-MS testing. The obtained GC-MS spectrum was qualitatively analyzed, and it was found that N-hexyl imidazole was detected only in the collected liquid at 310 °C.

[0081] Comparative Example 1

[0082] 193.38 g of p-hydroxybenzoic acid, 112.91 g of 6-hydroxy-2-naphthoic acid, 214.39 g of acetic anhydride and 91.89 mg (300 ppm) of N-methylimidazole were added to a reactor equipped with a stirring device, a nitrogen introduction device, a vacuum system, a thermometer and a reflux cooling device. Nitrogen was purged into the reactor to fully replace the atmosphere with nitrogen protection. Under nitrogen flow, the temperature was first raised to 130 °C at a heating rate of 2 °C / min for acetylation reaction for 1.5 hours. After the acetylation was completed, the temperature was raised at a heating rate of 2 °C / min to start the polycondensation reaction, and the collected liquid evaporated from the reaction was weighed and sampled at 200 °C, 230 °C, 260 °C, 290 °C and 310 °C, respectively, and finally the temperature was raised to above 320 °C. The pressure of the system was gradually reduced during the heating process, and the reaction was terminated after the torque increased. The obtained liquid crystal copolyester was taken out and tested by a colorimeter. The collected liquid sample was concentrated to remove a large amount of acetic acid, and then diluted with dichloromethane for GC-MS testing. The obtained GC-MS spectrum was qualitatively analyzed, and it was found that N-methylimidazole was detected in the collected liquid at 230 °C.

[0083] Comparative Example 2

[0084] 193.38 g of p-hydroxybenzoic acid, 112.91 g of 6-hydroxy-2-naphthoic acid, 214.39 g of acetic anhydride and 306.29 mg (1000 ppm) of N-methylimidazole were added to a reactor equipped with a stirring device, a nitrogen introduction device, a vacuum system, a thermometer and a reflux cooling device. Nitrogen was purged into the reactor to fully replace the atmosphere with nitrogen protection. Under nitrogen flow, the temperature was first raised to 130 °C at a heating rate of 2 °C / min for acetylation reaction for 1.5 hours. After the acetylation was completed, the temperature was raised at a heating rate of 2 °C / min to start the polycondensation reaction, and the collected liquid evaporated from the reaction was weighed and sampled at 200 °C, 230 °C, 260 °C, 290 °C and 310 °C, respectively, and finally the temperature was raised to above 320 °C. The pressure of the system was gradually reduced during the heating process, and the reaction was terminated after the torque increased. The obtained liquid crystal copolyester was taken out and tested by a colorimeter. The collected liquid sample was concentrated to remove a large amount of acetic acid, and then diluted with dichloromethane for GC-MS testing. The obtained GC-MS spectrum was qualitatively analyzed, and it was found that N-methylimidazole was detected in the collected liquid at 230 °C.

[0085] Comparative Example 3

[0086] 193.38 g of p-hydroxybenzoic acid, 112.91 g of 6-hydroxy-2-naphthoic acid, 214.39 g of acetic anhydride and 91.89 mg (300 ppm) of N-butylimidazole were added to a reactor equipped with a stirring device, a nitrogen introduction device, a vacuum system, a thermometer and a reflux cooling device. Nitrogen was purged into the reactor to fully replace the atmosphere with nitrogen protection. Under nitrogen flow, the temperature was first raised to 130 °C at a heating rate of 2 °C / min for acetylation reaction for 1.5 hours. After the acetylation was completed, the temperature was raised at a heating rate of 2 °C / min to start the polycondensation reaction, and the collected liquid evaporated from the reaction was weighed and sampled at 200 °C, 230 °C, 260 °C, 290 °C and 310 °C, respectively, and finally the temperature was raised to above 320 °C. The pressure of the system was gradually reduced during the heating process, and the reaction was terminated after the torque increased. The obtained liquid crystal copolyester was taken out and tested by a colorimeter. The collected liquid sample was concentrated to remove a large amount of acetic acid, and then diluted with dichloromethane for GC-MS testing. The obtained GC-MS spectrum was qualitatively analyzed, and it was found that N-butyl imidazole was detected in the collected liquid at 290 °C.

[0087] According to the results of Examples 1-3, 4-5 and Comparative Examples 1-2, it can be seen that the concentration of the catalyst has no obvious relationship with the time it stays in the synthesis process of liquid crystal polyarylate. Even the high catalyst concentration of 1000 ppm (Examples 3, 5 and Comparative Example 2) is consistent with the results obtained with the lower catalyst concentration of 300 ppm (Examples 1, 4 and Comparative Example 1), and the presence of the catalyst used for polymerization is detected in the liquid collected at the corresponding temperature. By comparing Examples 1 and 6, it is shown that the monomer ratio has no obvious relationship with the residence time of the catalyst, and the temperature of the overflow system remains consistent under different monomer ratios. This not only shows that the residence time of the high-boiling imidazole catalyst in the synthesis process of liquid crystal polyarylate is independent of the catalyst concentration and the monomer ratio, but also shows that the organic base catalyst is removed from the reaction system together with the by-product acetic acid during the synthesis process.

[0088] The retention time and mass-to-charge ratio m / z data of the target peaks detected in the 310°C collected liquid spectra in Example 1 and Example 5 and the 230°C collected liquid spectra in Comparative Example 2 and 290°C collected liquid spectra in Comparative Example 3 are shown in Table 1 below.

[0089] Table 1: Retention time and mass-to-charge ratio m / z data of the catalyst target peak detected in the examples and comparative examples

[0090]

[0091] The boiling point of hexylimidazole is 270 °C, which is within the temperature range of the polycondensation reaction. By comparing the GC-MS data of the collected liquid and the standard sample of N-hexylimidazole, no N-hexylimidazole was detected in the collected liquid at 200 °C, 230 °C, 260 °C, and even 290 °C. Figure 5 As shown in the figure, it is shown that N-hexylimidazole continues to exist in the polymerization reaction system within the polycondensation temperature range. Until N-hexylimidazole was detected in the collected liquid at 310 °C, as shown in the figure. Figure 1 As shown, it is shown that the catalyst does not volatilize from the polymerization reaction system until the temperature range of 310°C, and at this time, it has a considerable degree of polymerization. N-methylimidazole is reported as a catalyst for the synthesis of liquid crystal polyarylate in many patents, but its boiling point is only 198°C. It can be seen from the results of Comparative Examples 1-2 that N-methylimidazole is detected in the collected liquid at 230°C, such as Figure 3 As shown in the figure, and no further detection was made in the subsequent collected liquid, while the polycondensation reaction was just at the beginning stage. This indicates that the N-methylimidazole catalyst with a lower boiling point only played a catalytic role in the acetylation reaction stage, and volatilized from the reaction system before or at the beginning of the polycondensation reaction, before it played a catalytic role in polymerization. The curves of the collected liquid mass and reaction time of Example 1 and Comparative Example 1 are shown in the figure. Fig.11 As shown, it is very intuitive that when N-methylimidazole with a lower boiling point is used as a catalyst, it evaporates from the reaction system at a lower temperature, and the subsequent polymerization reaction is carried out without a catalyst, and the reaction time is significantly prolonged. The mass of the collected liquid represents the degree of polymerization (the higher the mass of the collected liquid, the more complete the polymerization), because for each molecule of ester bond generated in the polycondensation reaction, one molecule of acetic acid will be generated. The mass of the collected liquid can be used to calculate the overall degree of polycondensation reaction, which also indicates the speed of the reaction. Fig.11 The reaction time on the horizontal axis refers to the overall reaction time, including the heating, acylation reaction time and polycondensation reaction time. All the collected liquids distilled from Example 1 and Comparative Example 1 were weighed at 160 min, 180 min, 200 min, 220 min, 240 min and 260 min, respectively. The mass of the collected liquid is shown in FIG. Fig.11 shown.

[0092] The temperature of the polycondensation reaction is high, and a longer reaction time will cause more side reactions. The intuitive performance is that the a value of the polymer is higher and the L value is lower (Table 2, which measures the color value of the polymer slices obtained in Examples 1, 4 and Comparative Examples 1, 3). This is because at a higher temperature, the catalyst with a lower boiling point volatilizes and cannot play a more effective catalytic effect, resulting in a slower reaction rate. Over time, the monomer decomposes to generate vinyl ketone impurities, causing the polymer color to darken. At the same time, due to the influence of the substituent, the nucleophilicity of N-methylimidazole is significantly higher than that of compounds such as N-hexylimidazole or N-phenylimidazole. At the temperature at which it can play a catalytic role, the reaction rate is too fast, and the reaction exotherm causes the reaction temperature to become higher, further increasing the side reactions. In Comparative Example 3, N-butylimidazole has a higher boiling point than N-methylimidazole, about 240 ° C, but its nucleophilicity is higher than that of N-hexylimidazole. The temperature of the collected liquid of the catalyst is detected to reach 290 ° C, and there is a certain degree of polymerization at this temperature. The color value of the polymer catalyzed by N-butylimidazole also shows the same effect as that of N-methylimidazole, indicating that the nucleophilicity of the catalyst has a greater impact on the polymer during the polymerization stage. At the same time, according to the chromatogram, in addition to the catalyst, more types of impurity peaks appear in Comparative Example 3 compared with Example 1, and the types and contents of impurities are increased ( Figure 1 , Figure 4 ), indicating that catalysts with strong nucleophilicity also have a certain catalytic effect on side reactions. For polycondensation reactions, strong nucleophilicity does not bring better polymerization results. In addition, for polycondensation reactions, they can be carried out without catalysts, but there are differences in reactivity between different monomers, resulting in different monomer reaction rates at the same reaction temperature, and the appearance of longer homopolymer segments or even homopolymers, which seriously affects the sequence structure and uniformity of the final polymer, and thus leads to poor polymer performance. Catalysts with strong nucleophilicity are also prone to the appearance of longer homopolymer segments due to differences in monomer reaction rates. Choosing catalysts with moderate nucleophilicity can greatly alleviate the occurrence of this situation, which requires stable N-hexylimidazole and N-phenylimidazole catalysts to catalyze polymerization in polycondensation reactions in a sustainable and efficient manner.

[0093] Table 2: Color value data of examples and comparative examples

[0094]

[0095] Furthermore, when N-phenylimidazole with a higher boiling point is used as a catalyst, that is, Example 4-5, the results are consistent with those of N-hexylimidazole. Regardless of whether the catalyst concentration is lower or slightly higher, it is only detected in the collected liquid at 310°C. Figure 2 and 6As shown, it is shown that the high-boiling-point imidazole catalyst can stably and continuously catalyze the reaction efficiently within the polycondensation temperature range and be discharged from the polymerization system at the later stage of polycondensation at a higher temperature.

[0096] It can be clearly seen from the examples and comparative examples that the high-boiling-point and moderately nucleophilic imidazole catalyst can not only continuously and efficiently participate in the polymerization reaction, but also effectively increase the polymerization rate in the polycondensation stage, improve the polymerization difference between different monomers, and reduce the residence time under high temperature conditions, thereby reducing the impact of the side reactions in the late polymerization on the final product, and obtaining liquid crystal polyarylate with excellent performance. In addition, it can also volatilize from the reaction system in the late polymerization and be collected together with the by-products, and the collected liquid can also be purified and recovered by distillation and other methods, which is in line with the concept of green chemistry.

[0097] In summary, the present invention can provide a high-boiling-point imidazole catalyst for the synthesis of liquid crystal polyarylate, which can continuously and efficiently catalyze the polymerization reaction and discharge the reaction system in the later stage of polymerization to obtain liquid crystal polyarylate with excellent color, and has extremely high industrial value.

[0098] It should be understood that the above embodiments do not limit the present invention in any form, and any technical solutions obtained by equivalent replacement or equivalent transformation shall fall within the protection scope of the present invention.

Claims

1. A method for synthesizing liquid crystal polyarylate, characterized in that: Under nitrogen protection conditions, a certain proportion of monomers, an acylation agent and a specific catalyst are subjected to an acylation reaction at an acylation temperature, and then the temperature is slowly raised for polycondensation, and finally a liquid crystal polyarylate melt with a certain viscosity is obtained, and a liquid crystal polyarylate finished product is obtained after cooling; the monomers are p-hydroxybenzoic acid and its derivatives, terephthalic acid or its derivatives, isophthalic acid or its derivatives, 6-hydroxy-2-naphthoic acid or its derivatives, and biphenyl dicarboxylic acid or its derivatives; The specific catalyst used in the synthesis of liquid crystal polyarylate is a high boiling point imidazole catalyst, and its structure is shown in formula (1): Formula (1) In formula (1), the R substituent is an alkyl group, cycloalkyl group or aryl group containing five or more carbon atoms, each independently replacing one or more hydrogen atoms on the five-membered ring.

2. The method for synthesizing liquid crystal polyarylate according to claim 1, characterized in that: The addition amount of high boiling point imidazole catalyst is 100-1000ppm of the total weight of the monomer; the heating rate is 0.5-5℃ / min.

3. The method for synthesizing liquid crystal polyarylate according to claim 1, characterized in that: The acylating agent is an acid anhydride compound; the amount of the acylating agent added is 0.8-2.5 equivalents of the total molar amount of the monomers.

4. The method for synthesizing liquid crystal polyarylate according to claim 1, characterized in that: The monomers include p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid, and the p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid are added in a molar ratio of 70:30-85:

15.

5. The method for synthesizing liquid crystal polyarylate according to claim 1, characterized in that: The acylation temperature is 80-180°C, and the reaction time is 10 minutes to 4 hours.

6. The method for synthesizing liquid crystal polyarylate according to claim 1, characterized in that: The polycondensation reaction temperature is 200-345°C, and the pressure of the reaction system is reduced to 50-1000Pa in the later stage of the polycondensation reaction.

7. The method for synthesizing liquid crystal polyarylate according to claim 1, characterized in that: The high boiling point imidazole catalyst is a monosubstituted imidazole, and the substitution position is the 1st substitution position.

8. The method for synthesizing liquid crystal polyarylate according to claim 1, characterized in that: The R substituent of the high boiling point imidazole catalyst is pentyl, hexyl, cyclohexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, phenyl, benzyl, benzo or biphenyl.

9. The method for synthesizing liquid crystal polyarylate according to claim 1, characterized in that: The high boiling point imidazole catalyst is one or more of N-pentyl imidazole, N-hexyl imidazole, N-cyclohexyl imidazole, N-heptyl imidazole, N-phenyl imidazole, 2-pentyl imidazole, 2-hexyl imidazole, 2-cyclohexyl imidazole, 2-nonyl imidazole, 2-undecyl imidazole, 4-phenyl imidazole, benzimidazole, 1-benzyl imidazole, 1-phenylethyl imidazole, 2,5-diphenyl imidazole, 4,5-diphenyl imidazole, 5-amino-1-phenyl imidazole, and 1-ethyl-2-methyl benzimidazole.

10. Application of high boiling point imidazole catalyst in the synthesis of liquid crystal polyarylate, characterized in that: The high boiling point imidazole catalyst has a structure as shown in formula (1): Formula (1) In formula (1), the R substituent is an alkyl, cycloalkyl, or aryl group containing five or more carbon atoms, each independently replacing one or more hydrogen atoms on the five-membered ring; When synthesizing liquid crystal polyarylate, under nitrogen protection conditions, a certain proportion of monomers, acylation agents and high-boiling point imidazole catalysts are subjected to acylation reaction at acylation temperature, and then the temperature is slowly raised for polycondensation, and finally a liquid crystal polyarylate melt with a certain viscosity is obtained, and after cooling, a liquid crystal polyarylate finished product is obtained; the monomers are p-hydroxybenzoic acid and its derivatives, terephthalic acid or its derivatives, isophthalic acid or its derivatives, 6-hydroxy-2-naphthoic acid or its derivatives, and biphenyl dicarboxylic acid or its derivatives.

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