Catalyst for synthesizing liquid crystal polyarylester and application of catalyst

Abstract

The invention relates to the field of polymer preparation, in particular to a catalyst for liquid crystal polyarylester synthesis and application of the catalyst, the catalyst is a nitrogen-containing heterocyclic compound, and the nitrogen-containing heterocyclic ring in the molecular structure of the catalyst is a six-membered ring or a fused ring formed by the six-membered ring; the thermal stability of the catalyst is quantitatively evaluated by calculating the Gibbs free energy of the catalyst at the first set temperature and the second set temperature. By quantitatively evaluating the thermal stability of the catalyst, the experimental screening process of the liquid crystal polyarylester synthesis catalyst is simplified, and the raw material cost and time consumption are remarkably reduced. The catalyst has excellent performance in melt polycondensation reaction of liquid crystal polyarylester, is expected to omit subsequent energy-consuming and complex solid phase polycondensation process, simplifies the process flow, and reduces the overall production cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymer preparation, in particular to a catalyst for the synthesis of liquid crystal polyarylate and its application. BACKGROUND

[0002] Liquid crystal polyarylate (LCP) as a kind of high-performance engineering plastics, due to its excellent heat resistance, mechanical strength and dimensional stability, has a wide application prospect in the field of electronic components, automobile parts and precision instruments. The melt polycondensation method is generally used in industry to prepare this kind of polymer, which usually involves the step-by-step polymerization reaction of aromatic hydroxyl carboxylic acid or its ester derivative under high temperature conditions. In this process, the choice of catalyst plays a decisive role in the reaction rate, polymer molecular weight and the quality of the final product. The commonly used nitrogen-containing heterocyclic organic base catalysts, such as 1-methylimidazole or 4-dimethylaminopyridine, can promote ester exchange reaction to some extent, but still face some problems that have not been properly solved in actual industrial production.

[0003] Firstly, as the polycondensation reaction proceeds to the later stage, the system temperature is as high as 300 ℃ or above, and high vacuum conditions are used to remove small molecular by-products, promoting the reaction to proceed in the direction of high molecular weight. However, under such harsh conditions, the molecular structure stability of many traditional catalysts is challenged. Some catalysts are prone to volatilization or decomposition in long-term high-temperature environment due to their low boiling point or insufficient thermal decomposition temperature, resulting in a decrease in effective catalytic concentration, which not only prolongs the reaction period, but also may cause the molecular weight distribution of the polymer to be broadened due to the lack of catalytically active centers, affecting the processing performance of the product. In addition, the instability of the catalyst at high temperature may also cause unnecessary side reactions, such as polymer chain scission or crosslinking, which may adversely affect the color, thermal stability and other key indicators of the product.

[0004] To avoid the above-mentioned high-temperature catalytic failure problem, the existing technical solutions tend to introduce a solid-phase polycondensation process after melt polycondensation. This process can further increase the molecular weight of the polymer at relatively low temperature, but also significantly increases the complexity and energy consumption of the process. Not only does it require additional reaction equipment and longer production cycle, but also the mass transfer efficiency is low in the solid phase state, and the molecular chain segment movement is limited, which slows down the reaction rate and increases the production cost. Therefore, the industry has always expected to optimize the catalyst system to achieve the goal of obtaining high molecular weight and excellent color of liquid crystal polyarylate products in a single melt polycondensation stage, thereby simplifying the process and improving production efficiency.

[0005] Another significant challenge in catalyst development lies in the lack of reliable methods to effectively predict long-term thermal stability in real-world reaction environments. Traditional catalyst screening heavily relies on experimental verification, requiring numerous repetitive polycondensation experiments to compare the activity and stability of different catalysts. This trial-and-error approach is time-consuming, labor-intensive, and highly susceptible to fluctuations in experimental conditions. While computational simulations have been introduced into catalyst evaluation systems—for example, using molecular dynamics simulations or electronic structure analysis to predict the interaction energy between catalysts and reactants and thus assess initial catalytic activity—these methods offer new insights for screening highly active catalysts. However, their focus is largely limited to the short-term activity of the catalytic reaction, and their prediction of catalyst structural evolution, tolerance, and sustained catalytic capacity under prolonged high temperature and pressure remains relatively weak. Existing simulation methods have not yet fully addressed the crucial issue of how to quantitatively assess the thermal stability of catalysts throughout the entire polymerization process, which is precisely the core factor determining their suitability for high-temperature melt polycondensation processes.

[0006] In summary, the synthesis of liquid crystal polyarylates currently faces clear technological demands: on the one hand, there is an urgent need to develop novel catalysts that can maintain structural integrity and high catalytic activity under high-temperature and high-vacuum conditions; on the other hand, there is a greater need to establish a theoretical method or index system that can proactively and accurately assess the thermal stability of catalysts to guide rational catalyst design and reduce blind research and development. While existing technologies have made progress in improving catalyst activity, further exploration is needed to resolve the inherent contradiction between catalyst thermal stability and process simplification. Summary of the Invention

[0007] This application aims to overcome the shortcomings of existing liquid crystal polyarylate synthesis catalysts in terms of high-temperature resistance, and therefore provides a catalyst for the synthesis of liquid crystal polyarylates and its application to overcome the above-mentioned deficiencies.

[0008] As described in the background section, existing technologies rely heavily on characterization of catalytic activity in the screening of catalysts for the synthesis of liquid crystal polyarylates. There is a lack of an effective means to proactively and quantitatively assess the ability of catalyst molecular structures to withstand high temperatures. This makes it difficult to avoid a large number of repetitive experimental verifications, which are not only inefficient and difficult to track, but also difficult to guide the design of catalysts with high thermal stability.

[0009] Faced with this technological gap, this application shifts its research perspective, moving beyond a single dimension of catalytic activity to prioritize addressing the "survival" of catalysts during the reaction process. Catalysts with poor thermal stability, even with high initial activity, will fail in the later stages of the reaction due to volatilization or decomposition. This is one of the key factors preventing some traditional catalysts from meeting the requirements of high-performance LCP synthesis. Therefore, this invention aims to establish a physical quantity that can directly and reliably characterize the structural stability of catalyst molecules during the reaction. The Gibbs free energy, which combines enthalpy and entropy effects, sensitively reflects the stability of molecular structure with temperature: the more negative the relative change in Gibbs free energy of catalyst molecules at different temperatures, the more the molecular configuration evolves towards lower free energy under thermal perturbation. By comparing the relative Gibbs free energies of different catalyst molecules at the same temperature, thermal stability can be described. Therefore, by using the Gibbs free energy as a thermodynamic state function, the evaluation shifts from the traditional "activity" perspective, which focuses on intermolecular interactions, to a "stability" perspective, which focuses on the structural stability of the molecules themselves.

[0010] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a catalyst for the synthesis of liquid crystal polyarylates. The catalyst is a nitrogen-containing heterocyclic compound, and the nitrogen-containing heterocyclic ring in its molecular structure is a six-membered ring or a fused ring composed of six-membered rings; The thermal stability of the catalyst is quantitatively evaluated by calculating its Gibbs free energy at a first set temperature and a second set temperature; wherein... The second set temperature is higher than the first set temperature.

[0011] Preferably, the catalyst is one or more of 4-azacyclobutanepyridine, 4-pyrrolidinylpyridine, and 4-piperidinylpyridine.

[0012] Preferably, the quantitative evaluation includes the following steps: (S.1) Construct molecular models of candidate catalysts and perform structural optimization and frequency calculations to obtain the optimal molecular model; (S.2) Calculate the Gibbs free energy of the candidate catalyst at at least a first set temperature and a second set temperature; (S.3) Based on the relationship between the Gibbs free energy and temperature, the thermal stability of the candidate catalyst is quantitatively evaluated.

[0013] As a preferred embodiment, the specific method of quantitative evaluation described in (S.3) is as follows: using the Gibbs free energy at the first set temperature as a benchmark, calculate the relative Gibbs free energy at the second set temperature respectively; the value of the relative Gibbs free energy is used to characterize thermal stability, and the more negative the value, the higher the thermal stability.

[0014] In this application's technical solution, step (S.1) of molecular modeling and structural optimization is a prerequisite for accurate calculations, ensuring that subsequent energy calculations are based on a reasonable molecular configuration with the lowest energy. Step (S.2) calculates the Gibbs free energy at different temperatures, simulating the thermodynamic behavior of the catalyst within the actual reaction temperature range, providing raw data for quantitative evaluation. Step (S.3) calculates and compares relative Gibbs free energies, thereby transforming the abstract concept of thermal stability into concrete and comparable relative Gibbs free energy values. This avoids complex and time-consuming dynamic interaction simulations, directly focusing on the thermodynamic evaluation of the catalyst's intrinsic properties, making the evaluation process more direct and efficient.

[0015] Compared to the "interaction energy" focused on in existing technologies, the "Gibbs free energy" employed in this application considers the influence of temperature on energy, allowing for better correlation with experiments. First, this method enables quantitative prediction of catalyst thermal stability, significantly reducing the blind spots and resource consumption in experimental verification of candidate catalyst thermal stability, shifting catalyst screening from an experimental model relying on extensive trial and error to a rational design model guided by theoretical calculations. Second, because this method can effectively screen catalysts with high thermal stability, its application in LCP synthesis brings a chain of positive effects.

[0016] This feature, by introducing a quantitative comparison of relative Gibbs free energy, provides a concrete and standardized implementation path for the core evaluation method. Its role is to transform the abstract concept of thermal stability into a directly comparable numerical value: using the Gibbs free energy at a first set temperature (e.g., 298 K) as a benchmark, the relative value at high temperatures is calculated, thereby eliminating the interference of temperature changes on the absolute energy value and directly reflecting the catalyst's molecular structure's tolerance to thermal disturbances. The more negative the relative Gibbs free energy value, the more stable the catalyst's molecular structure is at a specific temperature. This qualitative relationship makes the assessment of thermal stability no longer dependent on subjective experience or cumbersome experiments, but rather an objective measurement based on thermodynamic principles.

[0017] Secondly, the present invention also provides the application of the catalyst in the synthesis of liquid crystal polyarylates. The catalyst was used in a melt polycondensation reaction to synthesize liquid crystal polyarylates.

[0018] Thirdly, the present invention also provides a method for preparing liquid crystal polyarylate, comprising catalyzing an aromatic hydroxycarboxylic acid or its acylated derivative to undergo a melt polycondensation reaction under the action of the catalyst.

[0019] Preferably, the liquid crystal polyarylate is obtained directly after the melt polycondensation reaction without going through a solid-phase polycondensation stage.

[0020] Preferably, the acylated derivative is prepared at a temperature of 100 ℃ to 200 ℃.

[0021] Preferably, the melt polycondensation reaction includes a pre-polycondensation stage and a final polycondensation stage.

[0022] Preferably, the pre-condensation stage is carried out under an inert atmosphere at a temperature of 200 ℃ to 290 ℃.

[0023] Preferably, the final polycondensation stage is carried out under a vacuum of 50 Pa to 10000 Pa and a temperature of 290 °C to 350 °C.

[0024] Preferably, the catalyst is added in an amount of 5 ppm to 1000 ppm of the total mass of the reactants.

[0025] Practical applications have shown that using catalysts optimized through this method (such as 4-piperidinylpyridine) can significantly shorten the total reaction time of melt polycondensation while maintaining the intrinsic viscosity of the polymer. More importantly, the highly thermally stable catalyst can function continuously and effectively, making it possible to obtain polymers of the target molecular weight through only the melt polycondensation stage. This potentially eliminates the need for subsequent energy-intensive and complex solid-state polycondensation steps, simplifying the process and reducing overall production costs. Ultimately, this is reflected in the product, where the polymer exhibits a better color value, indicating reduced side reactions and improved product quality.

[0026] Therefore, the present invention has the following beneficial effects: (1) This invention develops and optimizes the thermal stability evaluation method from the perspective of catalyst thermal stability evaluation, simplifies the experimental screening process of liquid crystal polyarylate synthesis catalyst, significantly reduces raw material costs and time consumption, and greatly shortens the research and development cycle; (2) A novel high-performance catalyst was screened by this method. It has excellent performance in melt condensation polymerization into liquid crystal polyarylate. The catalyst screening has achieved a closed loop from "theoretical prediction - experimental verification". The solid-phase polycondensation process can be eliminated, and the production cost can be reduced. (3) This technology has good scalability and can be adapted to the screening and exploration of catalysts for other polymer systems. Attached Figure Description

[0027] Figure 1 The optimized model structure for the catalyst.

[0028] Figure 2 represents the relative Gibbs free energy of the catalyst at different temperatures.

[0029] Figure 3 The percentage of distilled acetic acid in the examples and comparative examples is related to the reaction time. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0031] Example 1 (1) This embodiment first provides a method for evaluating the thermal stability of a catalyst (4-piperidinylpyridine) used in the synthesis of liquid crystal polyarylates, including the following steps: ① Use Gaussian View or Materials Studio to build a molecular model of 4-piperidinylpyridine. Use Gaussian 16 with `opt freq b3lyp 6-311g++` for structure optimization and vibrational frequency calculation until the structure has no imaginary frequencies, obtaining the final model. The optimized catalyst model is shown below. Figure 1 As shown; ② For the final model of 4-piperidinylpyridine described in ①, the Gibbs free energy at 298 K was calculated by setting opt freq b3lyp 6-311g++temperature=298, and the Gibbs free energy at a series of temperatures from 298 K to 623 K was calculated by changing the set temperature. ③ Using the Gibbs free energy at 298 K as a benchmark, calculate the relative Gibbs free energy at higher temperatures.

[0032] (2) This embodiment also provides an optimization method for the thermal stability evaluation steps of 4-piperidinylpyridine catalyst: ① The steps of model building, structural optimization and vibration frequency determination using Gaussian View or Materials Studio are the same as in (1); ② For the final model of 4-piperidinylpyridine described in ①, the Gibbs free energy at a series of temperatures from 298 K to 623 K can be calculated by submitting only one task using the frequency method of the Dmol3 module in Materials Studio, making the calculation process more efficient; ③ Using the Gibbs free energy at 298 K as a benchmark, calculate the relative Gibbs free energy at higher temperatures.

[0033] (3) This embodiment also provides the application of 4-piperidinylpyridine catalyst in the synthesis of liquid crystal polyarylates: specifically including the synthesis of liquid crystal polyarylates and the corresponding testing and analysis: 4-Acetoxybenzoic acid (ABA) and 6-acetoxy-2-naphtholic acid (ANA) were added to the polymerization reactor at a ratio of 73%:27%, and 4-piperidinylpyridine catalyst was added at 50 ppm of the total reactants. After the air in the reactor was fully replaced with nitrogen, the reactor was kept under nitrogen purging, and stirring was started to raise the temperature. The reactor was heated to 240 °C for pre-polymerization, during which the acetic acid distilled from the reaction was continuously collected and weighed. The pre-polymerization reaction ended when the amount of acetic acid collected reached 90% of the theoretical acceptable amount. The temperature was then raised to 325 °C, and the nitrogen purging was turned off. The reactor was slowly evacuated to a negative pressure, and the final polymerization reaction was carried out under a vacuum of 52 Pa until the specified stirring power was reached. The reactor stirrer was then stopped, and the reaction was terminated. The total time of the polymerization reaction was recorded after the reaction was completed. Nitrogen was introduced into the reactor to purge the polymer from the reactor and granulate it. The resulting polymer was cooled to room temperature, and its viscosity and color value were tested.

[0034] Example 2 The thermal stability evaluation steps for the 4-piperidinylpyridine catalyst described in (1) and (2) are the same as those in Example 1.

[0035] (3) Application of 4-piperidinylpyridine in the synthesis of liquid crystal polyarylates, specifically including the synthesis of liquid crystal polyarylates and corresponding testing and analysis. 4-Acetoxybenzoic acid (ABA) and 6-acetoxy-2-naphthoic acid (ANA) were added to the polymerization reactor at a ratio of 73%:27%, and 4-piperidinylpyridine catalyst was added at 100 ppm of the total reactants. After the air in the reactor was fully replaced by nitrogen, the reactor was kept under nitrogen purging, and stirring was started to raise the temperature. The reactor was heated to 240 °C for pre-condensation reaction, and the acetic acid distilled from the reaction was continuously collected and weighed. The endpoint of the pre-condensation reaction was defined as the amount of acetic acid collected reaching 90% of the theoretical receiving amount. Then the temperature was raised to 325 °C and the nitrogen was turned off. The reactor was slowly evacuated to a negative pressure, and the final condensation reaction was carried out under a vacuum of 60 Pa until the specified stirring power was reached. Then the reactor stirrer was stopped and the reaction was ended. The total time of the condensation reaction was recorded after the reaction was completed. Nitrogen gas was introduced into the reactor to expel the polymer from the reactor and granulate it. The resulting polymer was then cooled to room temperature and its viscosity and color value were tested.

[0036] Example 3 The thermal stability evaluation steps for the 4-piperidinylpyridine catalyst described in (1) and (2) are the same as those in Example 1.

[0037] (3) Application of 4-piperidinylpyridine in the synthesis of liquid crystal polyarylates, specifically including the synthesis of liquid crystal polyarylates and corresponding testing and analysis. 4-Acetoxybenzoic acid (ABA) and 6-acetoxy-2-naphthoic acid (ANA) were added to the polymerization reactor at a ratio of 73%:27%, and 4-piperidinylpyridine catalyst was added at 200 ppm of the total reactants. After the air in the reactor was fully replaced by nitrogen, the reactor was kept under nitrogen purging, and stirring was started to raise the temperature. The reactor was heated to 240 °C for pre-condensation reaction, and the acetic acid distilled from the reaction was continuously collected and weighed. The endpoint of the pre-condensation reaction was defined as the amount of acetic acid collected reaching 90% of the theoretical receiving amount. Then the temperature was raised to 325 °C and the nitrogen was turned off. The reactor was slowly evacuated to a negative pressure, and the final condensation reaction was carried out under a vacuum of 57 Pa until the specified stirring power was reached. Then the reactor stirrer was stopped and the reaction was ended. The total time of the condensation reaction was recorded after the reaction was completed. Nitrogen gas was introduced into the reactor to expel the polymer from the reactor and granulate it. The resulting polymer was then cooled to room temperature and its viscosity and color value were tested.

[0038] Example 4 (1) This embodiment first provides a method for evaluating the thermal stability of a catalyst (4-pyrrolidinylpyridine) used in the synthesis of liquid crystal polyarylates, including the following steps: ① Use Gaussian View or Materials Studio to build a molecular model of the 4-pyrrolidinylpyridine catalyst. Use Gaussian 16 software with `opt freq b3lyp 6-311g++` to perform structural optimization and vibrational frequency calculations until the structure has no imaginary frequencies, obtaining the final model. The optimized model is shown below. Figure 1 As shown; ② For the model after structural optimization and frequency analysis calculation described in ①, set opt ​​freq b3lyp 6-311g++ temperature=298 to calculate the Gibbs free energy at 298 K, and calculate the Gibbs free energy at a series of temperatures from 298 K to 623 K by changing the set temperature; ③ Using the Gibbs free energy at 298 K as a benchmark, calculate the relative Gibbs free energy at higher temperatures.

[0039] (2) This embodiment also provides an optimized method for evaluating the thermal stability of 4-pyrrolidinylpyridine catalysts: ① Use Gaussian View or Materials Studio to build the model, optimize the structure, and set the vibration frequency in the same way as in (1); ② For the final model of 4-pyrrolidinylpyridine described in ①, the Gibbs free energy at a series of temperatures from 298 K to 623 K can be calculated by submitting only one task using the frequency method of the Dmol3 module in Materials Studio, making the calculation process more efficient; ③ Using the Gibbs free energy at 298 K as a benchmark, calculate the relative Gibbs free energy at higher temperatures.

[0040] (3) This embodiment also provides the application of 4-pyrrolidinylpyridine catalyst in the synthesis of liquid crystal polyarylates: specifically including the synthesis of liquid crystal polyarylates and the corresponding testing and analysis: 4-Acetoxybenzoic acid (ABA) and 6-acetoxy-2-naphtholic acid (ANA) were added to the polymerization reactor at a ratio of 73%:27%, and a 4-pyrrolidinylpyridine catalyst was added at 200 ppm of the reactant amount. After the air in the reactor was fully replaced with nitrogen, the reactor was kept under nitrogen purging, and stirring was started to raise the temperature. The reactor was heated to 240 °C for pre-polymerization, during which the acetic acid distilled from the reaction was continuously collected and weighed. The pre-polymerization reaction ended when the amount of acetic acid collected reached 90% of the theoretical receiving amount. The temperature was then raised to 325 °C, and the nitrogen purging was turned off. The reactor was slowly evacuated to a negative pressure, and the final polymerization reaction was carried out under a vacuum of 54 Pa until the specified stirring power was reached. The reactor stirrer was then stopped, and the reaction was terminated. The total time of the polymerization reaction was recorded after the reaction was completed. Nitrogen was introduced into the reactor to purge the polymer from the reactor and granulate it. The resulting polymer was cooled to room temperature, and its viscosity and color value were tested.

[0041] Comparative Example 1 (1) Evaluation of the thermal stability of 4-azacyclobutanepyridine catalysts: ① Use Gaussian View or Materials Studio to build a molecular model of 4-azacyclic butylpyridine. Use Gaussian 16 software with `opt freq b3lyp 6-311g++` to perform structural optimization and vibrational frequency calculations until the structure has no imaginary frequencies, obtaining the final model. The optimized model is shown below. Figure 1 As shown; ② For the catalyst model after structural optimization and frequency analysis calculation described in ①, set the calculation parameters opt freq b3lyp6-311g++ temperature=298, calculate the Gibbs free energy at 298 K, and calculate the Gibbs free energy at a series of temperatures from 298 K to 623 K by changing the set temperature. ③ Using the Gibbs free energy at 298 K as a benchmark, calculate the relative Gibbs free energy at higher temperatures.

[0042] (2) Optimization of the thermal stability evaluation procedure for 4-azacyclobutanepyridine catalysts: ① The steps for model building, structural optimization, and vibration frequency determination using Gaussian View or Materials Studio are the same as in (1); ② For the final model of the catalyst mentioned in ①, the Gibbs free energy at a series of temperatures from 298 K to 623 K can be calculated by submitting only one task using the frequency method of the Dmol3 module in Materials Studio, making the calculation process more efficient; ③ Using the Gibbs free energy at 298 K as a benchmark, calculate the relative Gibbs free energy at higher temperatures.

[0043] (3) Application of 4-azacyclobutanepyridine in the synthesis of liquid crystal polyarylates, specifically including the synthesis of liquid crystal polyarylates and corresponding testing and analysis. 4-Acetoxybenzoic acid (ABA) and 6-acetoxy-2-naphthoic acid (ANA) were added to the polymerization reactor at a ratio of 73%:27%, and 4-azacyclobutanepyridine catalyst was added at 200 ppm of the total reactants. After the air in the reactor was fully replaced by nitrogen, the reactor was kept under nitrogen purging, and stirring was started to raise the temperature. The reactor was heated to 240 °C for pre-condensation reaction, during which the acetic acid distilled from the reaction was continuously collected and weighed. The endpoint of the pre-condensation reaction was determined when the amount of acetic acid collected reached 90% of the theoretical receiving amount. Then the temperature was raised to 325 °C and the nitrogen was turned off. The reactor was slowly evacuated to a negative pressure, and the final condensation reaction was carried out under a vacuum of 50 Pa until the specified stirring power was reached. Then the reactor stirrer was stopped and the reaction was ended. The total time of the condensation reaction was recorded after the reaction was completed. Nitrogen gas was introduced into the reactor to expel the polymer from the reactor and granulate it. The resulting polymer was then cooled to room temperature and its viscosity and color value were tested.

[0044] Comparative Example 2 The application of 1-methylimidazole in the synthesis of liquid crystal polyarylates specifically includes the synthesis and corresponding testing and analysis of liquid crystal polyarylates. 4-Acetoxybenzoic acid (ABA) and 6-acetoxy-2-naphtholic acid (ANA) were added to a polymerization reactor at a ratio of 73%:27%, and 1-methylimidazole catalyst was added at 200 ppm of the total reactants. After the air in the reactor was fully replaced by nitrogen, the reactor was kept under nitrogen purging, and stirring was started to raise the temperature. The reactor was heated to 240 °C for a pre-condensation reaction, during which the acetic acid distilled from the reaction was continuously collected and weighed. The pre-condensation reaction endpoint was defined as the amount of acetic acid collected reaching 90% of the theoretical acceptable amount. The temperature was then raised to 325 °C, and the nitrogen purging was turned off. The reactor was slowly evacuated to a negative pressure, and the final condensation reaction was carried out under a vacuum of 65 Pa until the specified stirring power was reached. The stirrer was then stopped, and the reaction was terminated. The condensation reaction time was recorded after the reaction was completed. Nitrogen gas was introduced into the reactor to expel the polymer from the reactor and granulate it. The resulting polymer was then cooled to room temperature and its viscosity and color value were tested.

[0045] Data Analysis: Depend on Figure 2 The relative Gibbs free energies calculated using the two methods shown in the left and right figures reveal that the relative Gibbs free energies of the 4-azacyclobutanepyridine, 4-pyrrolidinylpyridine, and 4-piperidinylpyridine catalysts all become more negative with increasing temperature. Furthermore, comparing the relative Gibbs free energies of the three catalysts at specific temperatures, the left figure shows that the numerical curves for 4-azacyclobutanepyridine and 4-pyrrolidinylpyridine consistently exceed those for 4-piperidinylpyridine, indicating that 4-piperidinylpyridine has a more negative relative Gibbs free energy. The right figure follows the same trend; within the temperature range of 400 K to 1000 K, 4-piperidinylpyridine exhibits a more negative relative Gibbs free energy compared to 4-azacyclobutanepyridine and 4-pyrrolidinylpyridine. Therefore, 4-piperidinylpyridine demonstrates better thermal stability at high temperatures.

[0046] Depend on Figure 3 As shown, by comparing Examples 1-3, it was found that within the same reaction time, the percentage of acetic acid distillation increased significantly with the increase of the amount of 4-piperidinylpyridine catalyst, indicating a significantly faster prepolymerization rate. Examples 3 and 4 showed that, with the same catalyst dosage and reaction time, the acetic acid distillation of 4-piperidinylpyridine was significantly higher than that of 4-pyrrolidinylpyridine. Similarly, in Examples 3 and Comparative Examples 1-2, after 100 min of reaction, the acetic acid distillation of 4-piperidinylpyridine was the highest, at 95%, while that of 4-azacyclobutaneylpyridine and 1-methylimidazolium was less than 70%, indicating that their conversion rates in catalyzing the prepolymerization reaction were lower, while 4-piperidinylpyridine exhibited higher catalytic efficiency. Therefore, compared to other catalysts, 4-piperidinylpyridine possesses relatively higher catalytic performance in the prepolymerization stage.

[0047] The application and test data of the catalyst in the synthesis of liquid crystal polyester are shown in Table 1: Table 1. Application of catalysts in the synthesis of liquid crystal polyarylates By comparing the total polycondensation reaction times of the examples and comparative examples, it can be seen that, at almost the same intrinsic viscosity, the 4-piperidinylpyridine catalyst has the shortest total polycondensation reaction time, while the 1-methylimidazole catalyst has the longest reaction time. This indicates that due to its high thermal stability, it can continuously and efficiently catalyze the polycondensation reaction, shortening the reaction time. Furthermore, comparing the color values ​​reveals that the polymer synthesized from 4-piperidinylpyridine has a higher L value and relatively lower a and b values, resulting in a significantly higher polymer color than polymers obtained with other catalysts, which is beneficial for improving the polymer's processing performance.

[0048] Therefore, by calculating the thermal stability of a catalyst, its catalytic performance during the reaction process can be predicted, and this method is simple and feasible. Furthermore, catalysts with high thermal stability perform better in polymerization reactions, enabling sustained and efficient catalysis. They can directly synthesize polymers of the desired viscosity through melt polymerization, significantly reducing time and costs.

[0049] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A catalyst for the synthesis of liquid crystal polyarylates, characterized in that, The catalyst is a nitrogen-containing heterocyclic compound, and the nitrogen-containing heterocyclic ring in its molecular structure is a six-membered ring or a fused ring composed of six-membered rings; The thermal stability of the catalyst is quantitatively evaluated by calculating its Gibbs free energy at a first set temperature and a second set temperature; wherein... The second set temperature is higher than the first set temperature.

2. The catalyst according to claim 1, characterized in that, The catalyst is one or more of 4-azacyclobutanepyridine, 4-pyrrolidinylpyridine, and 4-piperidinylpyridine.

3. The catalyst according to claim 1, characterized in that, The quantitative evaluation includes the following steps: (S.1) Construct molecular models of candidate catalysts and perform structural optimization and frequency calculations to obtain the optimal molecular model; (S.2) Calculate the Gibbs free energy of the candidate catalyst at at least a first set temperature and a second set temperature; (S.3) Based on the relationship between the Gibbs free energy and temperature, the thermal stability of the candidate catalyst is quantitatively evaluated.

4. The catalyst according to claim 1 or 3, characterized in that, The specific method of quantitative evaluation described in (S.3) is as follows: using the Gibbs free energy at the first set temperature as a benchmark, calculate the relative Gibbs free energy at the second set temperature respectively; the value of the relative Gibbs free energy is used to characterize thermal stability, and the more negative the value, the higher its thermal stability.

5. The catalyst according to any one of claims 1 to 3, characterized in that, The first set temperature is 298 K, and the second set temperature includes, but is not limited to, any temperature in the range of 473 K to 623 K.

6. The application of the catalyst according to any one of claims 1 to 5 in the synthesis of liquid crystal polyarylates, characterized in that, The catalyst was used in a melt polycondensation reaction to synthesize liquid crystal polyarylates.

7. A method for preparing liquid crystal polyarylate, characterized in that, The catalyst included in any one of claims 1 to 5 was used to catalyze the melt polycondensation reaction of an aromatic hydroxycarboxylic acid or its acylated derivative.

8. The preparation method according to claim 7, characterized in that, The acylated derivative is prepared at a temperature of 100 ℃ to 200 ℃; The melt polycondensation reaction includes a pre-polycondensation stage and a final polycondensation stage.

9. The preparation method according to claim 7, characterized in that, The pre-condensation stage is carried out under an inert atmosphere at a temperature of 200 ℃ to 290 ℃; The final polycondensation stage is carried out under a vacuum of 50 Pa to 10000 Pa and a temperature of 290 °C to 350 °C.

10. The preparation method according to claim 7, characterized in that, The catalyst is added at a rate of 5 ppm to 1000 ppm of the total mass of the reactants.

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