Titanium-containing composite catalyst and its use in the preparation of thermotropic liquid crystalline polymers

Abstract

The application discloses a titanium-containing composite catalyst and application thereof in preparation of thermotropic liquid crystal polymers, relates to the technical field of thermotropic liquid crystal polymer preparation, and comprises acetate and aromatic titanate, wherein the mass ratio of the acetate to the aromatic titanate is (1-9):(9-1), and the aromatic titanate is one or a combination of more than one of tetraphenyl titanate or tetra-monosubstituted phenyl titanate. The titanium-containing composite catalyst has the advantages of more environmentally-friendly raw materials, solid catalyst, small corrosion, good stability, and convenient addition. When the titanium-containing composite catalyst is used for preparing liquid crystal polymers, the obtained product has better color, and the acylation efficiency and the polycondensation efficiency are both high.

Description

Technical Field

[0001] This invention relates to the field of thermotropic liquid crystal polymer preparation technology, specifically to a titanium-containing composite catalyst and its application in the preparation of thermotropic liquid crystal polymers. Background Technology

[0002] Thermotropic liquid crystal polymers (TLCPs) mainly refer to main-chain polyesters containing mesocrystalline groups. They are mainly divided into three categories: high heat resistance (Type I), medium heat resistance (Type II), and low heat resistance (Type III). Type I TLCPs primarily consist of p-hydroxybenzoic acid (HBA), biphenyl (BP), and varying proportions of terephthalic acid (TA) / isophthalic acid (IA). Typically, Type I TLCPs have a heat distortion temperature ≥280℃ and can be used to manufacture electronic connectors, heat-resistant fans, antennas, printed circuit boards, etc. Type II TLCPs mainly consist of HBA and 6-hydroxy-2-naphthoic acid (HNA). Type II TLCPs have a heat distortion temperature of 240~280℃ and can be used to manufacture fibers and sheathing materials, etc. Type III TLCPs are mainly copolymers synthesized from HBA and polyethylene terephthalate (PET). Type III TLCPs have a heat distortion temperature ≤210℃ and can be used to manufacture barrier materials, high-strength mechanical parts, and PET crystallization nucleating agents, etc. Currently, thermotropic liquid crystal polymers (TLCPs) have a wide range of applications, and the market demand for them is substantial.

[0003] In existing technologies, the preparation of thermotropic liquid crystal polymers generally involves adding acetic anhydride and a catalyst to the reactive monomers of the liquid crystal polymer to induce an acylation reaction, followed by acid hydrolysis (or transesterification) and polycondensation to finally obtain the liquid crystal polymer. Existing technologies include those using acetate as a single catalyst. However, the presence of numerous metal ions in the reaction system can affect the electrical properties of the liquid crystal polymer during later applications. Furthermore, in the later stages of synthesis, the presence of more metals and acetate ions at high temperatures can increase side reactions, deteriorate the product color, and ultimately affect the application of the product.

[0004] In existing technologies, there are also schemes that use alkyl titanate as a catalyst in the synthesis of thermotropic liquid crystal polymers. However, due to its poor stability and side reactions during the high-temperature polycondensation reaction in the later stage of the liquid crystal polymer, the product color still darkens, making it difficult to obtain products with high molecular weight. Summary of the Invention

[0005] The purpose of this invention is to provide a titanium-containing composite catalyst and its application in the preparation of thermotropic liquid crystal polymers. The raw materials of this titanium-containing composite catalyst are more environmentally friendly, and the catalyst is solid, with low corrosivity, good stability, and convenient addition.

[0006] This invention is achieved through the following technical solution: A titanium-containing composite catalyst comprises acetate and an aromatic titanate ester, wherein the mass ratio of acetate to aromatic titanate ester is (1~9):(9~1), and the aromatic titanate ester is one or more of tetraphenyl titanate or tetramonosubstituted tetraphenyl titanate of general formula (I) or (II). (I), (II), wherein Y is one or more of methyl, halogen, nitro, and sulfonic acid groups. Y is preferably methyl.

[0007] Furthermore, the aromatic titanate is obtained by the following preparation method: by transesterification of a low-alkoxy titanate with phenol or a monosubstituted phenol in a solvent, wherein the alkyl group of the low-alkoxy titanate has ≤5 carbon atoms. The solvent is preferably a low-boiling-point solvent, such as ethanol.

[0008] Furthermore, in the preparation of aromatic titanate esters, the initial reaction temperature is controlled at 75-80℃, and the reaction time is 2-4 hours to obtain the product. Specifically, in the preparation of aromatic titanate esters, the initial reaction temperature is controlled near the boiling point of the solvent. For example, when the solvent is ethanol, the initial temperature is 75-80℃, and the reaction time is 2-4 hours. In the later stage, the reaction temperature is controlled 10-30℃ below the boiling point of the monosubstituted phenol, and the product is obtained after 1-4 hours of reaction, depending on the low melting point evaporation.

[0009] Furthermore, the acetate is a metal acetate salt, which includes one or a combination of sodium, potassium, magnesium, cobalt, zinc, and lithium salts of acetic acid. Potassium, magnesium, and zinc salts of acetic acid are preferred.

[0010] Furthermore, the tetramonosubstituted phenyl titanate is one of tetraphenyl titanate, tetrao-toluene titanate, and tetra-m-toluene titanate, with tetraphenyl titanate being preferred.

[0011] The aforementioned application of a titanium-containing composite catalyst in the preparation of thermotropic liquid crystal polymers.

[0012] Furthermore, the preparation method of the thermotropic liquid crystal polymer includes the following steps: I. Add the reactive monomers for synthesizing liquid crystal polymers and the titanium-containing composite catalyst to the reactor. The amount of titanium-containing composite catalyst added is 100~700 ppm of the total mass of the reactive monomers. Then add acetic anhydride and carry out the acylation reaction for 20~200 min at 130~150℃ under the protection of inert gases such as nitrogen. II. Then heat the material to 280~380℃, then evacuate the reactor, and finally maintain the vacuum residual pressure at 3000~20Pa. After reacting for a certain time, discharge the material to obtain the liquid crystal polymer.

[0013] Furthermore, the preferred mass ratio of acetate to titanium aromatic ester in the titanium-containing composite catalyst is (7~3):(3~7).

[0014] Furthermore, in step I, when adding the titanium-containing composite catalyst, the acetate and titanium aromatic ester are added simultaneously or separately.

[0015] Compared with the prior art, the present invention has the following advantages and beneficial effects: I. In this invention, a titanium-containing composite catalyst is proposed, which contains acetate and solid titanium aromatic ester. This catalytic system is solid, has low corrosivity, good stability, and is easy to add.

[0016] Second, this invention also discloses a method for obtaining one of the raw materials for the titanium-containing composite catalyst—an aromatic ester of titanate. This method involves transesterifying a low-alkoxy titanate ester with phenol or a monosubstituted phenol in a solvent. The low-alkoxy titanate ester has ≤5 carbon atoms in its alkyl group. The reaction temperature is controlled at 75-80°C, and the reaction time is 2-4 hours. The raw materials are more environmentally friendly, the process is simple and easy to implement, safe, and can be carried out under normal pressure, making it easy to promote to industrial production. In this reaction system, non-toxic reagents such as ethanol can be used as solvents, which are readily available and inexpensive.

[0017] Third, the titanium-containing composite catalyst proposed in this invention can be used as a reaction catalyst for thermotropic liquid crystal polymers. When applied to the synthesis of liquid crystal polymers, this titanium-containing composite catalyst exhibits high reaction efficiency in both the acylation and transesterification polycondensation stages, which is beneficial for improving production efficiency and reducing production costs. Simultaneously, the prepared liquid crystal polymer has a lighter color. Attached Figure Description

[0018] Figure 1 These are infrared spectroscopy images of acylate samples from Examples 6, 7 and Comparative Example 2, where: the green line represents Example 6, the blue line represents Example 7, and the red line represents Comparative Example 2. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to embodiments, but the implementation of the present invention is not limited thereto.

[0020] The analytical and testing methods involved in the following implementation are as follows: (1) Color determination Visual observation: The colors, from light to dark, are pale yellow, light yellow, yellow, yellowish brown, brown, and tan.

[0021] (2) Infrared analysis Infrared spectrometer: Nicolet, Thermo Fisher Scientific; Fourier transform infrared spectroscopy (FTIR): Analyzing acylated samples using a Fourier transform infrared spectrometer.

[0022] The FTIR was performed using the KBr pellet method, with 64 scans and a wavenumber range of 4000 cm⁻¹. -1 ~400 cm -1 .

[0023] (3) Nuclear magnetic resonance analysis Nuclear magnetic resonance spectrometer: Bruker AscavII 400, Bruker GmbH, Germany; 1H-NMR: The powdered acylated sample was dissolved in deuterated dimethyl sulfoxide (DMSO-d6) for analysis, with 16 scans. The acylation efficiency was calculated by the integral area ratio of carboxyl and hydroxyl groups in the NMR spectrum.

[0024] (4) Intrinsic viscosity test Using an Ubbelohde capillary viscometer, the TLCP-crushed sample was weighed (0.1000±0.0020g) and poured into a flask. A specified amount (50ml) of 60℃ pentafluorophenol was added to the flask using a pipette.

[0025] (1) Add the filtered pentafluorophenol solvent to the Ubbelohde capillary viscometer and place it in a constant temperature water bath at 60°C for more than 5 minutes. Draw the liquid up to the starting mark and use a stopwatch to record the time it takes for the liquid level to rise from the starting mark to the ending mark. Repeat twice and take the average value as t0.

[0026] (2) Add the filtered sample solution to the Ubbelohde capillary viscometer and place it in a constant temperature water bath at 60℃ for more than 5 minutes. Draw the liquid up to above the initial graduation line and use a stopwatch to record the time it takes for the liquid level to rise from the initial graduation line to the final graduation line. Repeat twice and take the average value as the t value. Substitute the t0 value and the t value into the intrinsic viscosity formula derived from the experiment to calculate the intrinsic viscosity value of the sample.

[0027] Intrinsic viscosity formula: [η] = [2(η] sp -lnη r )] 1 / 2 / C Where: η r =t / t0,η sp =η r -1, where C is the solution concentration.

[0028] Example 1 In this embodiment, tetraphenyl titanate solid was prepared using laboratory instruments. Then, a composite catalyst of tetraphenyl titanate and metal acetate salt was used as a composite catalyst for the preparation of thermotropic liquid crystal polymers. The effect of the titanium-containing composite catalyst on the synthesis process of thermotropic liquid crystal polymers was investigated.

[0029] I. Preparation of tetraphenyl titanate and aromatic monosubstituted titanate esters.

[0030] 1. Preparation of tetraphenyl titanate (1) Add 75.3g of phenol and 75.3g of ethanol to a reactor equipped with a stirrer, thermometer, dropping funnel and reflux condenser, and add 68.1g of tetrabutyl titanate to the dropping funnel for later use; (2) Under stirring conditions, the material in the reactor is heated from room temperature to 70~75℃. During the heating process, tetrabutyl titanate is added dropwise. When the temperature reaches the set temperature, the reaction is kept at the temperature for 1~3 hours. (3) Then replace the reflux condenser with a distillation device, raise the temperature to 80~85℃, and distill off the ethanol. When about 70~80% of the total amount of ethanol has been distilled off, continue to raise the temperature to 120~125℃ to further distill off the butanol produced in the reaction. When the amount of butanol distilled off reaches 60~80% of the total amount, continue to raise the temperature to 160~180℃ to distill off the residual butanol. Depending on the amount of butanol distilled off, a low vacuum can be applied appropriately to improve the distillation efficiency of the by-product butanol. Finally, the product is obtained. After cooling, it is a yellowish-gray blocky tetraphenyl titanate, denoted as Cat-1.

[0031] 2. Preparation of aromatic monosubstituted esters of titanate, comprising the following steps: (1) Add aromatic substituted monophenols and ethanol to the reactor, so that the aromatic monophenols dissolve in the ethanol, and then add titanate dropwise at a molar ratio of aromatic substituted monophenols to titanate ester of 4:1. Control the reaction temperature at 80℃ and react for 3h to obtain a reaction solution. The titanate ester is one of tetrabutyl titanate, tetraisopropyl titanate, and tetraethyl titanate.

[0032] In this step, it is advisable to control the reaction temperature at 75-80℃ after adding the reactants. When the temperature in the reactor is below 75℃, the reaction is incomplete and slow, resulting in a large amount of reactants remaining. When the temperature in the reactor is above 80℃, ethanol vaporization is severe, which can easily lead to pressure buildup and side reactions. The reaction time should be controlled at 2-4 hours to ensure both complete reaction and low by-product content.

[0033] (2) Raise the temperature of the reaction solution to 85°C to remove the residual ethanol and byproduct butanol in the reaction solution to obtain the aromatic monosubstituted ester of titanate.

[0034] In this step, the temperature of the reaction solution can be raised to 85°C or higher, while maintaining it at 10-30°C below the boiling point of the monosubstituted phenol.

[0035] II. Preparation of Titanium-Containing Composite Catalysts In this embodiment, raw materials were taken according to the proportions of each group of raw materials in Table 1 below to obtain titanium-containing composite catalysts Q1 to Q5, wherein raw material A is a preferred metal acetate salt and raw material B is an aromatic monoester of titanate.

[0036] Table 1 III. Preparation of thermotropic liquid crystal polymers.

[0037] (1) Add 180g of p-hydroxybenzoic acid (HBA), 257g of 6-hydroxy-2-naphthoic acid, 280g of acetic anhydride, 0.07g of tetraphenyl titanate Cat-1, and 0.07g of zinc acetate (i.e., use catalyst Q1) to a reactor equipped with a stirrer, nitrogen inlet pipe, torque sensor, thermometer, and reflux pipe. (2) Replace the air in the reactor with nitrogen, and then heat it to 140±5℃ under nitrogen protection. Under this temperature condition, reflux the reaction for 2 hours. 3. Then, within a time of more than 30 minutes, the temperature is raised to 260±5℃ to distill off the by-product acetic acid. The reaction is carried out at this temperature for 30~40 minutes. Then, within a time of more than 60 minutes, the temperature is raised to 320±5℃. Then, the nitrogen gas is stopped, and the vacuum is gradually evacuated to a high vacuum (residual pressure less than 1 mmHg). The reaction is carried out under high vacuum for 30 minutes, and then the reaction is stopped. The light yellow polymer is discharged.

[0038] Example 2 The difference between this embodiment and Example 1 is that in step (1) of preparing the thermotropic liquid crystal polymer, the catalyst used is catalyst Q2 from Table 1.

[0039] Example 3 The difference between this embodiment and Example 1 is that in step (1) of preparing the thermotropic liquid crystal polymer, the catalyst used is catalyst Q3 from Table 1.

[0040] Example 4 The difference between this embodiment and Example 1 is that in step (1) of preparing the thermotropic liquid crystal polymer, the catalyst used is catalyst Q4 from Table 1.

[0041] Example 5 The difference between this embodiment and Example 1 is that in step (1) of preparing the thermotropic liquid crystal polymer, the catalyst used is catalyst Q5 from Table 1.

[0042] Example 6 The difference between this embodiment and Example 1 is that in step (1) of preparing the thermotropic liquid crystal polymer, the catalyst used is catalyst Q6 from Table 1.

[0043] Example 7 Compared with Example 1, the catalyst in this embodiment is the same as in Example 1. In the preparation of the thermotropic liquid crystal polymer, the ratio of the polymerizing monomers was adjusted. Referring to Table 2, the liquid crystal polymer was obtained using the same process and steps.

[0044] Specifically, the following steps are included: 1. Add 351g of p-hydroxybenzoic acid (HBA), 177g of 6-hydroxy-2-naphthoic acid, 355g of acetic anhydride, 0.085g of tetraphenyl titanate Cat-1, and 0.085g of zinc acetate to a reactor equipped with a stirrer, nitrogen inlet pipe, torque sensor, thermometer, and reflux pipe. 2. Replace the air in the reactor with nitrogen, and then heat to 140±5℃ under nitrogen protection. Under this temperature condition, reflux for 1 hour. 3. Then, within a time of more than 30 minutes, the temperature is raised to 260±5℃ to distill off the by-product acetic acid. The reaction is carried out at this temperature for 30~40 minutes. Then, within a time of more than 60 minutes, the temperature is raised to 320±5℃. Then, the nitrogen gas is stopped, and the vacuum is gradually evacuated to a high vacuum (residual pressure less than 1 mmHg). The reaction is carried out under high vacuum for 30 minutes, and then the reaction is stopped. The product is a light yellow polymer.

[0045] Example 8 This embodiment describes a method for preparing a thermotropic liquid crystal polymer using a titanium-containing composite catalyst Q5.

[0046] The preparation method of thermotropic liquid crystal polymers includes the following steps: 1. Add 207g of p-hydroxybenzoic acid (HBA), 140g of 4,4'-dihydroxybiphenyl, 62g of terephthalic acid, 21g of isophthalic acid, 337g of acetic anhydride, 0.070g of tetraphenyl titanate C1, and 0.070g of magnesium acetate to a reactor equipped with a stirrer, nitrogen inlet pipe, torque sensor, thermometer, and reflux pipe. 2. Replace the air in the reactor with nitrogen, and then heat to 140±5℃ under nitrogen protection. Under this temperature condition, reflux for 1 hour. 3. Then, after 30 minutes, the temperature is raised to 260±5℃ to evaporate the by-product acetic acid. The reaction is carried out at this temperature for 30~40 minutes. Then, the temperature is raised to 360±5℃ within a time of more than 60 minutes. Then, the nitrogen gas is stopped, and the vacuum is gradually evacuated to a high vacuum (residual pressure less than 1 mmHg). The reaction is carried out under high vacuum for 30 minutes, and then the reaction is stopped. The yellow polymer is discharged.

[0047] Example 9 Compared with Example 7, this embodiment shortens the acylation reaction time for polymer preparation and examines the experimental results.

[0048] The preparation method of thermotropic liquid crystal polymers includes the following steps: 1. Add 351g of p-hydroxybenzoic acid (HBA), 177g of 6-hydroxy-2-naphthoic acid, 355g of acetic anhydride, 0.085g of tetraphenyl titanate Cat-1, and 0.085g of zinc acetate to a reactor equipped with a stirrer, nitrogen inlet pipe, torque sensor, thermometer, and reflux pipe. 2. Replace the air in the reactor with nitrogen, and then heat to 140±5℃ under nitrogen protection. Under this temperature condition, reflux the reaction for 0.5h. 3. Then, within a time of more than 30 minutes, the temperature is raised to 260±5℃ to distill off the by-product acetic acid. The reaction is carried out at this temperature for 30~40 minutes. Then, within a time of more than 60 minutes, the temperature is raised to 360±5℃. Then, the nitrogen gas is stopped, and the vacuum is gradually evacuated to a high vacuum (residual pressure less than 1 mmHg). The reaction is carried out under high vacuum for 30 minutes, and then the reaction is stopped. The yellow polymer is discharged.

[0049] Example 10 The only difference between this embodiment and Example 1 is that Cat-1 is added after the acylation reaction is completed, as detailed below: 1. Add 180g of p-hydroxybenzoic acid (HBA), 257g of 6-hydroxy-2-naphthoic acid, 280g of acetic anhydride, and 0.070g of zinc acetate to a reactor equipped with a stirrer, nitrogen inlet pipe, torque sensor, thermometer, and reflux pipe. 2. Replace the air in the reactor with nitrogen, then heat to 140±5℃ under nitrogen protection and reflux for 1 hour; then add 0.070g of tetraphenyl titanate (Cat-1). 3. Then, within a time of more than 30 minutes, the temperature is raised to 260±5℃ to distill off the by-product acetic acid. The reaction is carried out at this temperature for 35±5 minutes. Then, within a time of more than 60 minutes, the temperature is raised to 320±5℃. Then, the nitrogen gas is stopped, and the vacuum is gradually evacuated to a high vacuum (residual pressure less than 1 mmHg). The reaction is carried out under high vacuum for 30 minutes, and then the reaction is stopped. The light yellow polymer is discharged.

[0050] Comparative Example 1 The comparative example uses the same liquid crystal polymer preparation process as in Example 1, except that zinc acetate is used as the catalyst in all cases, with a catalyst dosage of 0.140 g, while the contents of other reactants and acylating agent acetic anhydride remain unchanged.

[0051] Comparative Example 2 The only difference between this comparative example and Comparative Example 1 is that the same mass of tetrabutyl titanate was used to replace the original titanium-containing composite catalyst, and the liquid crystal polymer was obtained using the same process.

[0052] Comparative Example 3 The comparative example uses the same liquid crystal polymer preparation process as in Example 1, except that tetraphenyl titanate is replaced with tetrabutyl titanate.

[0053] Comparative Example 4 Compared with Example 7, this comparative example differs in that, on the one hand, catalyst Q4 is replaced with an equal mass of potassium acetate, while the amounts of other monomers remain unchanged; on the other hand, in step 3, the reaction time under high vacuum in the later stage of the reaction is extended from 30 minutes to 50 minutes.

[0054] Comparative Example 5 The difference between this comparative example and Example 7 is that, on the one hand, catalyst Q4 is replaced with an equal mass of potassium acetate, while the amounts of other monomers remain unchanged; on the other hand, the reaction time in step 2 is extended from 1 hour to 2 hours, while other process conditions remain unchanged.

[0055] Comparative Example 6 Compared with Example 8, this comparative example differs in that catalyst Q5 is replaced with an equal mass of magnesium acetate, while other process conditions remain unchanged.

[0056] The formulations of each component in Examples 1-10 and Comparative Examples 1-6 are referenced in Table 2. The experimental results of monomer acylation rate, intrinsic viscosity of liquid crystal polymerization, and product color in Examples 1-10 and Comparative Examples 1-6 are referenced in Table 3.

[0057] Table 2: Liquid crystal polymer raw material ratio (catalyst is calculated as approximately 300 ppm of the total mass ratio of reactant monomers).

[0058] In Table 1, (1) HBA: p-hydroxybenzoic acid; (2) HNA: 6-hydroxy-2-naphthoic acid; (3) TPA: terephthalic acid; (4) IPA: isophthalic acid; (5) BP: 4,4'-dihydroxybiphenyl; (6) AC: acetic anhydride. “—” indicates that this monomer was not added.

[0059] Table 3: Results and phenomena of different experimental cases.

[0060] In Table 3, "—" indicates no abnormalities.

[0061] illustrate: (1) Acylation rate of phenolic hydroxyl groups: Using the HBA monomer in the experimental example as a standard, acylation was carried out under the corresponding catalyst conditions, and the acylation rate of HBA was calculated by NMR analysis, where acetic anhydride / HBA = 1.05 / 1 (molar ratio), and the process conditions correspond to the process conditions of the experimental example. (2) Residual peak height of phenolic hydroxyl groups: After acylation, samples are taken and subjected to infrared analysis. The peak height of the phenolic hydroxyl groups is compared to evaluate the relative acylation efficiency. The lower the peak height, the higher the acylation efficiency. (See attached diagram) Figure 1 The red, green, and blue curves in the mid-infrared spectrum show the high, medium, and low peaks of the phenolic hydroxyl group, respectively.

[0062] As shown in Table 3, compared with Comparative Examples 1-6, Examples 1-9, using the titanium-containing composite catalyst of this scheme, not only exhibit higher acylation efficiency, reaching a maximum of 93.7%, but also demonstrate higher catalytic efficiency in the subsequent acid hydrolysis and polycondensation reactions. In the same reaction time, polymers with higher molecular weights are obtained, and the product color is also lighter. When this titanium-containing composite catalyst system is promoted to industrial production, it can improve product production efficiency, reduce production costs, and the product has broader application prospects (lighter color). (Reference) Figure 1 , Figure 1 These are infrared spectroscopy images of acylate samples from Examples 6, 7, and Comparative Example 2, where: the green line represents Example 6, the blue line represents Example 7, and the red line represents Comparative Example 2. Infrared spectroscopy is useful for qualitatively comparing the acylation efficiency of different experimental examples. The higher the peak in the spectrum, the higher the content of residual phenolic hydroxyl groups, and the lower the acylation efficiency.

[0063] Compared with Comparative Examples 1-6, Examples 1-9 show that liquid crystal polymers with different structures have different intrinsic viscosity ranges. Relatively speaking, under roughly the same process conditions, the liquid crystal polymer containing naphthalene has a larger intrinsic viscosity. The titanium-containing composite catalyst used in this invention exhibits roughly the same trend in the synthesis of liquid crystal polymers with different structures. The acylation and subsequent acid hydrolysis-condensation reactions are highly efficient, with fewer side reactions and better color.

[0064] In Example 9, compared with Example 1, the acylation reaction time for polymer preparation was shortened. Due to insufficient acylation, a small amount of unacylated monomers were found to deposit a small amount of white substance on the test microscope of the kettle lid during the heating process.

[0065] In summary, the titanium-containing composite catalyst using this scheme has high acylation efficiency and polycondensation efficiency, and the prepared liquid crystal polymer has better color, showing great application prospects.

[0066] Furthermore, extensive experiments have demonstrated that controlling the mass ratio of acetate to aromatic titanate ester in the titanium-containing composite catalyst within the range of (7~3):(3~7) results in higher catalytic efficiency. Within this preferred ratio range, both the acylation catalytic effect of acetate in the initial stage of the reaction and the catalytic effect of aromatic titanate ester in the later acidolysis and polycondensation reactions are effectively utilized, while also minimizing side reactions. This ratio range achieves a better balance between synthesis efficiency and product performance.

[0067] According to Tables 2 and 3, it can be seen that the composite catalytic system of the present invention can synthesize liquid crystal polymers more efficiently with a shorter reaction time, thereby reducing production costs. On the other hand, there are fewer side reactions in the later stage of the reaction, the prepared liquid crystal polymers are lighter in color, contain fewer impurities, and have a wider range of applications.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A titanium-containing composite catalyst, characterized in that: The mixture comprises acetate and aromatic titanate esters, wherein the mass ratio of acetate to aromatic titanate ester is (1~9):(9~1), and the aromatic titanate ester is one or more of tetraphenyl titanate or tetramonosubstituted tetraphenyl titanate of the following general formula (I) or (II). (I), (II), where Y is one or more of methyl, halogen, nitro, and sulfonic acid groups.

2. The titanium-containing composite catalyst according to claim 1, characterized in that: Y stands for methyl.

3. The titanium-containing composite catalyst according to claim 1, characterized in that, The aromatic titanate is obtained by the following preparation method: by transesterification reaction of a low-alkoxy titanate with phenol or a monosubstituted phenol in a solvent, wherein the alkyl group of the low-alkoxy titanate has ≤5 carbon atoms.

4. The titanium-containing composite catalyst according to claim 3, characterized in that: When preparing aromatic titanate esters, the temperature in the initial stage of the reaction is controlled at 75~80℃, and the product is obtained after 2~4 hours of reaction.

5. The titanium-containing composite catalyst according to claim 1, characterized in that: The acetate is a metal acetate salt, which includes one or a combination of sodium, potassium, magnesium, cobalt, zinc, and lithium salts of acetic acid.

6. The titanium-containing composite catalyst according to claim 5, characterized in that: Tetra-monosubstituted phenyl titanate is one of tetraphenyl titanate, tetra-o-toluene titanate, and tetra-m-toluene titanate.

7. The application of a titanium-containing composite catalyst as described in any one of claims 1-6 in the preparation of thermotropic liquid crystal polymers.

8. The application according to claim 7, characterized in that, The preparation method of thermotropic liquid crystal polymers includes the following steps: Ⅰ. Add the reactive monomers for synthesizing liquid crystal polymers and the titanium-containing composite catalyst to the reactor. The amount of titanium-containing composite catalyst added is 100~700 ppm of the total mass of the reactive monomers. Then add acetic anhydride and carry out the acylation reaction for 20~200 min at 130~150℃ under inert gas protection. II. Then heat the material to 280~380℃, then evacuate the reactor, and finally maintain the vacuum residual pressure at 3000~20Pa. After reacting for a certain time, discharge the material to obtain the liquid crystal polymer.

9. The application according to claim 8, characterized in that: The mass ratio of acetate to titanium aromatic ester in the titanium-containing composite catalyst is (7~3):(3~7).

10. The application according to claim 8, characterized in that: In step I, when adding the titanium-containing composite catalyst, the acetate and titanium aromatic ester are added simultaneously or separately.

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