Carbon nanotube supported catalyst and its use in the preparation of liquid crystalline polyesters

Abstract

The application discloses a carbon nanotube supported catalyst and application thereof in preparation of liquid crystal polyester, wherein the catalyst is composed of a carrier carbon nanotube and a supported catalyst, the carrier is a multi-walled carbon nanotube with surface carboxylation after acid treatment, and the support is a metal salt or an organic small molecule catalyst. The preparation includes two steps of surface modification of the carbon nanotube and vacuum impregnation of the small molecule catalyst. In the preparation of the liquid crystal polyester, the supported catalyst is used to catalyze acetylation of aromatic hydroxyl monomers and subsequent melt polycondensation reaction. The catalyst is anchored on the high-thermal-conductivity carbon nanotube, so that the thermal stability and activity of the catalyst in a high-temperature environment are remarkably improved, the heat conduction network constructed by the carbon nanotube effectively solves the heat conduction problem of a liquid crystal state high-viscosity system, the polycondensation reaction time is shortened, the tensile strength of the obtained liquid crystal polyester is synchronously improved by virtue of the nano-enhancing effect of the carbon nanotube, and the comprehensive technical effects of high efficiency, energy saving and high quality are realized.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of high polymer material synthesis, and particularly relates to a carbon nanotube loaded catalyst and application thereof in preparation of liquid crystal polyester. BACKGROUND

[0002] Thermotropic liquid crystal polyester (TLCP) is a kind of high-performance engineering plastic that can maintain molecular order orientation in a molten state. With excellent high-temperature resistance, low dielectric constant, good mechanical strength and excellent chemical corrosion resistance, TLCP has become an indispensable key material in the fields of 5G communication, semiconductor packaging, aerospace and other high-end manufacturing fields. According to the long-term use temperature, TLCP is usually divided into type I, type II and type III, among which type I and type II can work stably at a high temperature of 180 DEG C or above and thus become the focus of research and industrialization.

[0003] The synthesis of TLCP usually takes aromatic monomers such as p-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA), diphenylol (BP) and terephthalic acid (TPA) as raw materials. The polymerization process mainly includes two core steps: first, the acetylation protection reaction of aromatic hydroxyl monomers, and then the melt polycondensation reaction of all copolymerization monomers at high temperature. However, TLCP forms a unique liquid crystal state during polymerization, and this characteristic leads to extremely high viscosity and significant flow anisotropy of the reaction system, thereby causing serious problems of low heat transfer efficiency. The accumulated reaction heat in the system is difficult to diffuse quickly and uniformly, which easily causes local overheating, broadens the molecular weight distribution and even causes thermal degradation and other side reactions, which makes the synthesis of TLCP have much higher requirements for the accuracy of temperature control, stirring efficiency and vacuum system than ordinary polyesters, greatly increasing the difficulty and cost of its industrial production.

[0004] On the other hand, the polycondensation reaction of TLCP needs to be carried out at a high temperature of 300 DEG C or above for a long time, which poses a severe challenge to the long-term thermal stability of the catalyst. The catalysts widely used in industry, such as zinc acetate or N-methyl imidazole, have obvious defects under such extreme conditions. Zinc acetate is easy to thermally decompose into zinc oxide which loses catalytic activity at high temperature; and organic small molecule catalysts such as N-methyl imidazole are easy to decompose or volatilize. The deactivation of the catalyst not only significantly prolongs the reaction period and increases the energy consumption, but also leads to the molecular weight of the product failing to reach the design index, ultimately affecting the comprehensive performance of TLCP materials.

[0005] In summary, the industrial synthesis of heat-resistant liquid crystal copolyester is facing two interrelated technical bottlenecks: one is that the heat transfer efficiency of the reaction system is low due to the high viscosity of the liquid crystal state, which restricts the reaction rate and product uniformity; the second is that the existing catalyst is not thermally stable at high temperature, which cannot guarantee sustained and efficient catalytic activity, affecting the depth and efficiency of the reaction. These two problems seriously restrict the preparation efficiency, product quality and cost control of high-performance TLCP.

[0006] Therefore, in order to solve the above problems, the application provides a carbon nanotube supported catalyst and its application in the preparation of liquid crystal polyester. By stably loading small molecule catalyst on carbon nanotube carrier with high thermal conductivity, the thermal stability of the catalyst itself is significantly improved, the heat transfer efficiency of the whole reaction system is strengthened by the excellent thermal conductivity of carbon nanotubes, and the catalytic activity is improved by the nanometer effect, so as to realize the efficient, stable and energy-saving synthesis of liquid crystal polyester. SUMMARY

[0007] The purpose of the application is to provide a carbon nanotube supported catalyst and its application in the preparation of liquid crystal polyester. The supported catalyst with carbon nanotube as carrier, its preparation method and its industrial application in the catalytic synthesis of thermotropic liquid crystal polyester (TLCP) utilize the excellent thermal conductivity of carbon nanotube and the good compatibility of the surface modified carbon nanotube with liquid crystal copolyester matrix, realize the uniform dispersion of the catalyst in the reaction system, and greatly improve the heat transfer efficiency in the polymerization process.

[0008] The purpose of the application is realized by the following technical solutions:

[0009] A carbon nanotube supported catalyst, which is composed of a carrier and a carrier; the carrier is carbon nanotube, and the carrier is metal salt catalyst or organic catalyst; the preparation method of the carbon nanotube supported catalyst comprises the following steps:

[0010] S1, surface modification of carbon nanotube: carbon nanotube is reacted with mixed acid of concentrated sulfuric acid and concentrated nitric acid at 60 DEG C for 2-10 hours, the volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixed acid is 3:1; after the reaction, dilute with water and filter and wash to remove residual acid, to obtain carboxylated carbon nanotube;

[0011] S2, small molecule loading: the modified carbon nanotubes obtained in step S1 are dispersed in a solution containing a supported catalyst to form a mixed system; the concentration of the supported catalyst in the solution is 30-300 g / L, and the mass ratio of the modified carbon nanotubes to the supported catalyst is 1:0.1-3; the mixed system is first subjected to mechanical stirring for preliminary dispersion, then ultrasonic dispersion treatment for 0.5-2 hours, and then kept at room temperature and under a negative pressure of 10-0.05 kPa for 0.5-2 hours; finally, the carbon nanotube supported catalyst is obtained by centrifugal separation and drying.

[0012] Preferably, the carbon nanotubes are multi-walled carbon nanotubes with a thermal conductivity coefficient not less than 500 W / (m·K) and a diameter of 5-100 nm; the metal salt catalyst is selected from one or more of zinc acetate, potassium acetate, magnesium acetate, aluminum acetate, manganese acetate, tetrabutyl titanate or germanium oxide; and the organic catalyst is selected from one or more of N-methyl imidazole, 4-dimethylamino pyridine, 4-pyrrolidinyl pyridine, 1,8-diazabicycloundec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, methylbenzenesulfonic acid or trifluoromethanesulfonic acid.

[0013] The present application also claims a use of the above-mentioned carbon nanotube supported catalyst in the preparation of liquid crystal polyester, wherein the carbon nanotube supported catalyst is used to catalyze the acetylation reaction of aromatic hydroxyl polymerization monomers and the subsequent melt polycondensation reaction.

[0014] The present application also claims a preparation method of liquid crystal polyester, which uses the above-mentioned carbon nanotube supported catalyst for catalysis, and the method comprises the following steps:

[0015] (1) feeding and acetylation: each polymerization monomer, acetic anhydride and the carbon nanotube supported catalyst are added into a reaction device; under the protection of an inert atmosphere, the temperature is raised to 100-160°C, preferably 120-150°C, and the acetylation reaction is carried out for 0.5-3.5 hours; the molar ratio of the total amount of acetic anhydride to all aromatic hydroxyl polymerization monomers in the system is 0.9-5:1;

[0016] (2) melt polycondensation: after the acetylation reaction is completed, the reaction system is uniformly heated to the polycondensation reaction temperature of 150-390°C at a heating rate of 0.1-100°C / min under an inert atmosphere; after reaching the polycondensation temperature, the pressure of the system is reduced to 0.01-300 kPa, and the polycondensation reaction is carried out under this condition for 0.5-5 hours, with the maximum stirring torque as the reaction endpoint;

[0017] (3) discharging and post-treatment: after the polycondensation reaction is completed, the obtained melt polyester material is extruded through a die, cooled by water, solidified and then cut into particles to obtain a liquid crystal polyester product.

[0018] Preferably, the total molar amount ratio of acetic anhydride to all aromatic hydroxyl polymeric monomers in the system is 0.9-5:1, preferably 2-4:1, and more preferably 3:1.

[0019] Preferably, after the acetylation reaction is completed, the reaction system is uniformly heated to a polycondensation reaction temperature of 300-380℃ at a heating rate of 0.5-25℃ / min under an inert atmosphere; after reaching the polycondensation temperature, the system pressure is reduced to 0.01-50kPa, and the polycondensation reaction is carried out under this condition for 0.5-5 hours, with the maximum stirring torque as the reaction endpoint.

[0020] Preferably, the amount of the carbon nanotube-supported catalyst added is 0.1-10wt% of the total mass of all polymeric monomers, preferably 0.5-5wt%, and the effective content of the supported catalyst is 50-5000ppm, preferably 100-500ppm.

[0021] Preferably, the polymeric monomers are selected from at least one of an aromatic diol, an aromatic hydroxyl carboxylic acid, and an aromatic dicarboxylic acid;

[0022] The aromatic diol is selected from one or more of 4,4'-diphenylol, hydroquinone, 2,6-dihydroxynaphthalene, 2,2-bis-p-phenylenol propane, or 4,4'- (1-phenylethyl) bisphenol;

[0023] The aromatic hydroxyl carboxylic acid is selected from one or more of 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, or 6-hydroxy-2-naphthoic acid;

[0024] The aromatic dicarboxylic acid is selected from one or more of terephthalic acid, isophthalic acid, or 2,6-naphthalene dicarboxylic acid.

[0025] Preferably, the polycondensation reaction temperature in step (2) is 20-40℃ higher than the melting point of the synthesized liquid crystal polyester.

[0026] The present application also claims a liquid crystal polyester prepared by the above-mentioned method for preparing a liquid crystal polyester.

[0027] Preferably, the liquid crystal polyester has an intrinsic viscosity of 4.0-4.7dL / g, a tensile strength of no less than 112MPa, and a melting point of 282-356℃.

[0028] The working mechanism of this invention lies in the multi-level synergistic effect generated among the carbon nanotube support, the catalytically active component, and the polymerization reaction system. First, the catalyst deactivation problem is solved through support anchoring and thermal stabilization mechanisms: the surface-pretreated carbon nanotubes, with their active functional groups, firmly "anchor" the small-molecule catalyst to the surface and inner cavity, effectively preventing its thermal decomposition, volatilization, or aggregation at high temperatures, thus maintaining catalytic activity during polycondensation reactions at temperatures above 300°C for several hours. Second, the reaction efficiency is improved through nano-confinement and synergistic catalysis mechanisms: the nano-confinement effect generated by the support enriches the reactant molecules, and the electronic interactions between the carbon nanotubes and the active component may modulate the performance of the catalytic center, collectively lowering the energy barriers of transesterification and polycondensation reactions, resulting in a significantly higher catalytic efficiency than free catalysts. Furthermore, the heat transfer bottleneck of the system is overcome by utilizing thermally conductive networks and mass transfer enhancement mechanisms: carbon nanotubes with high thermal conductivity (>500 W / (m·K)) construct microscopic thermally conductive pathways in high-viscosity melts, which can rapidly homogenize the heat of reaction, eliminate local overheating, and promote the removal of by-products by improving rheological behavior, thereby significantly shortening the reaction time and increasing the molecular weight of the product. Finally, the product performance is optimized through structural compatibility and in-situ reinforcement mechanisms: the good compatibility between modified carbon nanotubes and the liquid crystal polyester matrix ensures their uniform dispersion, allowing them to be retained in situ as nano-reinforcing phases in the product, promoting the orderly arrangement of liquid crystals while directly endowing the material with higher mechanical strength.

[0029] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0030] 1. This invention significantly improves catalytic efficiency and greatly shortens the reaction cycle. Based on the nano-confinence and synergistic catalytic effect of carbon nanotubes, this supported catalyst exhibits higher intrinsic activity than traditional catalysts. Experiments have shown that this catalyst can significantly accelerate the polycondensation reaction process. When achieving the same polymer molecular weight, it can effectively shorten the total reaction time by 5% to 35%, resulting in a leapfrog improvement in production efficiency.

[0031] 2. This invention significantly enhances thermal stability and ensures high-temperature catalytic activity. By firmly anchoring the small molecule catalyst to the carbon nanotube support, this invention fundamentally solves the key problem of its easy deactivation at high temperatures. The supported catalyst maintains structural stability and catalytic activity in harsh reaction environments exceeding 300 degrees Celsius, providing continuous and stable catalytic power for the entire polycondensation process, and ensuring the reaction depth and product molecular weight.

[0032] 3. This invention efficiently enhances the heat transfer of the system, ensuring the uniformity of the process and the product. By utilizing a microscopic heat-conducting network constructed from carbon nanotubes with high thermal conductivity, this invention greatly improves the heat transfer efficiency of high-viscosity liquid crystal melts. This mechanism can quickly eliminate local overheating in the reaction, ensuring uniform temperature throughout the entire reaction system, thereby effectively suppressing the occurrence of side reactions and improving the controllability of the process and the consistency of the final product performance.

[0033] 4. This invention simultaneously achieves in-situ reinforcement of the product and optimizes the final mechanical properties. The surface-modified carbon nanotubes have excellent compatibility with the liquid crystal polyester matrix and can be retained in-situ as a high-performance nano-reinforcing phase in the product. This not only significantly improves the tensile strength of the synthetic material without sacrificing processability, but also simultaneously optimizes the comprehensive physical and mechanical properties of the product.

[0034] 5. This invention highlights the potential for energy conservation and consumption reduction, and has broad prospects for industrialization. The significant reduction in reaction cycle directly reduces energy consumption and carbon emissions in the production process. At the same time, the extension of catalyst life and the enhancement of process stability lay a solid technical foundation for large-scale continuous and green production, making this invention both economically and environmentally valuable. Attached Figure Description

[0035] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, some of the drawings in the following description are some embodiments of the present invention. For those skilled in the art, other drawings can be made based on these drawings without creative effort.

[0036] Figure 1 These are the thermogravimetric curves of the supported catalysts used in Examples 1-3 of this invention;

[0037] Figure 2 This is a thermogravimetric curve of the supported catalyst used in Examples 4-5 of the present invention. Detailed Implementation

[0038] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific implementation schemes are now described in detail.

[0039] The present invention will be further described below with reference to embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0040] Synthesis example 1

[0041] This synthetic example describes the preparation of catalyst A (carbon nanotube-supported N-methylimidazole):

[0042] S1. Surface modification of carbon nanotubes: Multi-walled carbon nanotubes were added to a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 and reacted at 60°C for 6 hours. After the reaction was completed, the mixture was diluted, filtered, and repeatedly washed with deionized water until the filtrate was neutral, and finally surface carboxylated carbon nanotubes were obtained.

[0043] S2. Small molecule loading: The modified carbon nanotubes were dispersed in an ethanol solution of N-methylimidazole at a mass ratio of 1:1 (concentration of 200 g / L); the mixture was first mechanically stirred for 10 minutes, and then ultrasonically treated at 80 W power for 2 hours; subsequently, the mixture was placed in a vacuum oven and kept at room temperature and 0.1 kPa negative pressure for 30 minutes; finally, the mixture was centrifuged and vacuum dried to obtain catalyst A.

[0044] Synthesis example 2

[0045] This synthetic example describes the preparation of catalyst B (carbon nanotube-supported N-methylimidazole):

[0046] S1. Surface modification of carbon nanotubes: Multi-walled carbon nanotubes were added to a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 and reacted at 60°C for 6 hours. After the reaction was completed, the mixture was diluted, filtered, and repeatedly washed with deionized water until the filtrate was neutral, and finally surface carboxylated carbon nanotubes were obtained.

[0047] S2. Small molecule loading: The modified carbon nanotubes were dispersed in an ethanol solution of N-methylimidazole at a mass ratio of 1:1 (concentration of 150 g / L); the mixture was first mechanically stirred for 10 minutes, and then ultrasonically treated at 80 W power for 2 hours; subsequently, the mixture was placed in a vacuum oven and kept at room temperature and 0.1 kPa negative pressure for 30 minutes; finally, the mixture was centrifuged and vacuum dried to obtain catalyst B.

[0048] Synthesis example 3

[0049] This synthetic example describes the preparation of catalyst C (carbon nanotube-supported N-methylimidazole):

[0050] S1. Surface modification of carbon nanotubes: Multi-walled carbon nanotubes were added to a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 and reacted at 60°C for 6 hours. After the reaction was completed, the mixture was diluted, filtered, and repeatedly washed with deionized water until the filtrate was neutral, and finally surface carboxylated carbon nanotubes were obtained.

[0051] S2. Small molecule loading: The modified carbon nanotubes were dispersed in an ethanol solution of N-methylimidazole at a mass ratio of 1:1 (concentration of 100 g / L); the mixture was first mechanically stirred for 10 minutes, and then ultrasonically treated at 80 W power for 2 hours; subsequently, the mixture was placed in a vacuum oven and kept at room temperature and 0.1 kPa negative pressure for 30 minutes; finally, the mixture was centrifuged and vacuum dried to obtain catalyst C.

[0052] Synthesis example 4

[0053] This synthesis example describes the preparation of catalyst D (zinc acetate supported on carbon nanotubes):

[0054] S1. Surface modification of carbon nanotubes: The steps are the same as step S1 in synthesis example 1;

[0055] S2. Small molecule loading: Modified carbon nanotubes were dispersed in deionized water at a mass ratio of 1:1 to form a suspension; then sufficient zinc acetate was added to make its concentration in the system 100 g / L; the reaction was stirred at 60 °C for 4 hours to allow the carboxyl groups to exchange ions with zinc ions; after the reaction was completed, the unreacted substances were removed by centrifugation and washing with ethanol, and finally the catalyst D was obtained by vacuum drying.

[0056] Synthesis example 5

[0057] This synthetic example describes the preparation of catalyst E (zinc acetate supported on carbon nanotubes):

[0058] S1. Surface modification of carbon nanotubes: The steps are the same as step S1 in synthesis example 1;

[0059] S2. Small molecule loading: Modified carbon nanotubes were dispersed in deionized water at a mass ratio of 1:1 to form a suspension; then sufficient zinc acetate was added to make its concentration in the system 50 g / L; the reaction was stirred at 60 °C for 4 hours to allow the carboxyl groups to exchange ions with zinc ions; after the reaction was completed, the unreacted substances were removed by centrifugation and washing with ethanol, and finally the catalyst E was obtained by vacuum drying.

[0060] Example 1

[0061] See appendix Figure 1 This embodiment provides a method for preparing a liquid crystal copolyester (type II liquid crystal copolyester), including the following steps:

[0062] (1) Feeding and acetylation: Under nitrogen protection, 4-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA) (molar ratio 73:27) were added to the reactor as all the monomers for polymerization. At the same time, catalyst A (of which the effective content of N-methylimidazolium was 400 ppm) and acetic anhydride with an effective content of 0.44 wt% of the total monomers and 2.0 times the equivalent of the total molar amount of hydroxyl groups were added.

[0063] (2) Acetylation reaction: The reaction system was stirred at 140°C for 2 hours to complete the acetylation process;

[0064] (3) Melt polycondensation: After acetylation, the system is uniformly heated to 320°C at a heating rate of 3°C / min under a nitrogen atmosphere; after reaching the polycondensation temperature, the vacuum system is started to reduce the system pressure to below 50 kPa, and the polycondensation reaction is carried out under this condition until the stirring torque reaches the maximum value, and the reaction time is recorded.

[0065] (4) Discharge and post-processing: After the reaction is completed, heating and stirring are stopped, the molten polymer is extruded through the die, cooled with water, solidified and then granulated to obtain type II liquid crystal copolyester particles.

[0066] Example 2

[0067] See appendix Figure 1 This embodiment provides a method for preparing liquid crystal copolyester (type II liquid crystal copolyester). This embodiment is based on the above embodiment 1, and the similarities with the above embodiment 1 will not be repeated.

[0068] In this embodiment, the amount of catalyst B added is 1.43 wt% of the total monomer mass (the effective content of N-methylimidazole is still 400 ppm).

[0069] Example 3

[0070] See appendix Figure 1 This embodiment provides a method for preparing liquid crystal copolyester (type II liquid crystal copolyester). This embodiment is based on the above embodiment 1, and the similarities with the above embodiment 1 will not be repeated.

[0071] In this embodiment, the amount of catalyst C added is 2.85 wt% of the total mass of the monomer (the effective content of N-methylimidazole is still 400 ppm).

[0072] Example 4

[0073] See appendix Figure 2 This embodiment provides a method for preparing a liquid crystal copolyester (Type I liquid crystal copolyester), including the following steps:

[0074] (1) Feeding and acetylation: Under nitrogen protection, 4-hydroxybenzoic acid (HBA), biphenyl (BP), terephthalic acid (TPA) and isophthalic acid (IPA) (molar ratio 60:20:17:3) were added to the reactor as all the monomers for polymerization. At the same time, catalyst D (with an effective content of 400 ppm of zinc acetate) and acetic anhydride with an equivalent amount of 2.5 times the total molar amount of hydroxyl groups were added, accounting for 1.90 wt% of the total monomer mass.

[0075] (2) Acetylation reaction: The reaction system was stirred at 140°C for 2 hours;

[0076] (3) Melt polycondensation: After acetylation, the system is uniformly heated to 350°C at a heating rate of 3°C / min under a nitrogen atmosphere; after reaching the polycondensation temperature, the vacuum system is started to reduce the system pressure to below 50 kPa, and this condition is maintained to carry out the polycondensation reaction until the stirring torque reaches the maximum value.

[0077] (4) Discharge and post-processing: After the reaction is completed, the molten polymer is extruded, cooled with water, and granulated to obtain type I liquid crystal copolyester particles.

[0078] Example 5

[0079] See appendix Figure 2 This embodiment provides a method for preparing liquid crystal copolyester (type I liquid crystal copolyester). This embodiment is based on the above embodiment 4, and the similarities with the above embodiment 4 will not be repeated.

[0080] In this embodiment, the amount of catalyst E added is 3.64 wt% of the total mass of the monomer (the effective content of zinc acetate is still 400 ppm).

[0081] Comparative Example 1

[0082] This comparative example provides a method for preparing a liquid crystal copolyester (type II liquid crystal copolyester, conventional catalyst). This comparative example is based on the above Example 1, and the similarities with the above Example 1 will not be repeated.

[0083] In this comparative example: catalyst A was not used; instead, an unsupported N-methylimidazolium small molecule catalyst, accounting for 400 ppm of the total monomer, was directly added, and no carbon nanotube support was added.

[0084] Comparative Example 2

[0085] This comparative example provides a method for preparing a liquid crystal copolyester (type I liquid crystal copolyester, conventional catalyst). This comparative example is based on the above Example 4, and the similarities with the above Example 4 will not be repeated.

[0086] In this comparative example: catalyst D was not used; instead, 400 ppm of unsupported zinc acetate small molecule catalyst, accounting for 400 ppm of the total monomer, was directly added, and no carbon nanotube support was added.

[0087] Comparative Example 3

[0088] This comparative example provides a method for preparing a liquid crystal copolyester (type II liquid crystal copolyester), including the following steps:

[0089] Under nitrogen protection, 4-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid (molar ratio 73:27) were added to a reactor along with 2 equivalents of acetic anhydride, 400 ppm of N-methylimidazole (total monomers), and 2.81 wt% of carbon nanotubes. The reaction procedure was as follows: the reaction was first carried out at 140℃ for 2 hours, then the temperature was increased to 280℃ at 3℃ / min for 2 hours, and then increased to 320℃ at the same rate for 1 hour. Nitrogen gas was purged throughout the process, and the byproduct acetic acid was distilled off. Finally, the vacuum system was started at 320℃ to reduce the system pressure to below 50 kPa. This condition was maintained for polycondensation until the stirring torque reached its maximum value, and the reaction time was recorded. After the reaction, the molten polymer was extruded, water-cooled, and pelletized to obtain type II liquid crystal copolyester particles.

[0090] Comparative Example 4

[0091] This comparative example provides a method for preparing a liquid crystal copolyester (Type I liquid crystal copolyester), comprising the following steps:

[0092] Under nitrogen protection, 4-hydroxybenzoic acid, biphenyl, terephthalic acid, and isophthalic acid (molar ratio 60:20:17:3) were added to a reactor along with 2.5 equivalents of acetic anhydride, 400 ppm of zinc acetate (total monomers), and 3.6 wt% of carbon nanotubes. The reaction procedure was as follows: the reaction was first carried out at 140℃ for 2 hours, then the temperature was increased to 300℃ at 3℃ / min for 1.5 hours, and then increased to 320℃ at the same rate for 1.5 hours. Nitrogen gas was purged throughout the process, and the byproduct acetic acid was distilled off. Finally, a vacuum system was started at 350℃ to reduce the system pressure to below 50 kPa. This condition was maintained for polycondensation until the stirring torque reached its maximum value, and the reaction time was recorded. After the reaction, the molten polymer was extruded, water-cooled, and pelletized to obtain type I liquid crystal copolyester particles.

[0093] The liquid crystal copolyesters prepared in the above embodiments and comparative examples were tested, and the test results are shown in Table 1.

[0094] Table 1

[0095]

[0096] From Table 1 and Appendix Figure 1 and attached Figure 2It can be seen that for type II liquid crystal copolyesters (based on Comparative Examples 1, 3, and Examples 1-3): compared with Comparative Example 1 which only used unsupported N-methylimidazole, Comparative Example 3, which used a physically mixed catalyst, showed a shorter reaction time (75 min → 62 min), proving that the addition of free carbon nanotubes did indeed improve the heat transfer of the system through its thermal conductivity. However, the supported catalysts used in this invention (Examples 1-3) showed a more significant improvement in reaction efficiency, with the reaction time further shortened to 70, 64, and even 55 minutes. Among them, the reaction time of Example 3 was reduced by 27% compared to Comparative Example 1. It is worth noting that although Example 3 and Comparative Example 3 had the same carbon nanotube and methylimidazole content, the synergistic catalytic effect of the two was more prominent in Example 3, and the reaction time was further shortened by 11% compared to Comparative Example 3. In terms of product performance, the addition of carbon nanotubes did not affect the intrinsic viscosity of the liquid crystal polyester. Although the tensile strength of Comparative Example 3 was better than that of Comparative Example 1 due to the reinforcing effect of carbon nanotubes, it was still lower than that of Examples 2 and 3, which had the same carbon nanotube content and used supported catalysts. This indicates that the pre-loading process not only promotes the uniform dispersion of carbon nanotubes in the matrix but also improves the thermal stability of methylimidazole (see attached figure), thereby achieving more sustained catalytic activity. The synergistic effect of both significantly shortens the reaction time and further enhances the mechanical properties of the material. In this embodiment, the supported catalyst system reduced the reaction time by up to 27% and increased the tensile strength by up to 5%.

[0097] For Type I liquid crystal copolyesters (based on Comparative Examples 2, 4, and Examples 4-5): the same trend was again verified in the more demanding synthesis of Type I liquid crystal polyesters. In Comparative Example 4, the reaction time was reduced from 45 minutes to 32 minutes compared to Comparative Example 2 with physical mixing, further confirming the heat transfer contribution of carbon nanotubes. However, the supported catalyst of this invention (Examples 4-5) further significantly reduced the reaction time to 35 minutes and 27 minutes, respectively, with an efficiency improvement far exceeding that of physical mixing (Comparative Example 4), reducing the reaction time by up to 34%. In terms of mechanical properties, the tensile strength of Comparative Example 4 was close to that of Example 4 using a low-content supported catalyst, but significantly lower than that of Example 5 using a high-content supported catalyst. This collectively demonstrates that to achieve the same performance level, the supported catalyst requires a smaller total amount of carbon nanotubes, or in other words, it has a higher reinforcing efficiency at the same filling amount.

[0098] The aforementioned multi-level data comparison forms a complete chain of evidence. First, the supported catalyst of this invention has comprehensive advantages over traditional catalysts (Comparative Example 1, Comparative Example 2) in terms of reaction efficiency and product strength. More importantly, through direct comparison with physical mixing schemes (Comparative Example 3, Comparative Example 4), it is proven that the core process step of "pre-loading" is the fundamental reason for the synergistic effect (dual improvement in catalytic efficiency and enhancement efficiency) that goes beyond simple superposition. Therefore, this invention successfully solves the problems of catalyst deactivation and low system heat transfer efficiency pointed out in the background art, providing an innovative solution for the efficient and high-performance synthesis of liquid crystal polyesters.

[0099] In summary, based on the nanoconfining and synergistic catalytic effect of carbon nanotubes, the supported catalyst provided by this invention exhibits higher intrinsic activity and thermal stability than traditional catalysts in the preparation of liquid crystal polyesters. This catalyst effectively prevents the deactivation of small-molecule catalysts in high-temperature environments above 300℃ by firmly anchoring them, ensuring the depth of the polycondensation reaction and the molecular weight of the product. Simultaneously, the highly efficient thermally conductive network constructed using carbon nanotubes significantly improves the heat transfer efficiency of the high-viscosity system, eliminates local overheating, shortens the reaction time by 5%–35%, and improves process controllability and product consistency. Furthermore, the surface-modified carbon nanotubes are retained in situ as a nano-reinforcing phase in the product, significantly improving the tensile strength of the material without sacrificing processability. In conclusion, this invention achieves efficient, stable, and energy-saving synthesis of liquid crystal polyesters through synergistic optimization of catalysis, heat transfer, and reinforcement effects, and has broad prospects for industrial application.

[0100] The embodiments described above merely illustrate more specific and detailed implementations of the present invention, and should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A carbon nanotube-supported catalyst, characterized in that, It consists of a support and a substrate; the support is carbon nanotubes, and the substrate is an organic catalyst; the preparation method of the carbon nanotube-supported catalyst includes the following steps: S1. Surface modification of carbon nanotubes: Carbon nanotubes are reacted with a mixture of concentrated sulfuric acid and concentrated nitric acid at 60°C for 2 to 10 hours. The volume ratio of concentrated sulfuric acid to concentrated nitric acid in the mixture is 3:

1. After the reaction is completed, water is added for dilution, and the mixture is filtered and washed to remove residual acid, thereby obtaining surface carboxylated carbon nanotubes. S2. Small molecule loading: The modified carbon nanotubes obtained in step S1 are dispersed in a solution containing a catalyst support to form a mixed system; the concentration of the catalyst support in the solution is 30~300 g / L, and the mass ratio of modified carbon nanotubes to catalyst support is 1:0.1~3; the mixed system is first mechanically stirred for preliminary dispersion, then ultrasonically dispersed for 0.5~2 hours, and then kept at room temperature and negative pressure of 10~0.05 kPa for 0.5~2 hours; finally, the carbon nanotube supported catalyst is obtained by centrifugation and drying. The carbon nanotubes are multi-walled carbon nanotubes with a thermal conductivity of not less than 500 W / (m·K) and a diameter of 5~100 nm; the organic catalyst is N-methylimidazole. The carbon nanotube supported catalyst is used to catalyze the acetylation reaction of aromatic hydroxyl polymer monomers and the subsequent melt polycondensation reaction.

2. A method for preparing liquid crystal polyester, characterized in that, Catalysis using the carbon nanotube-supported catalyst as described in claim 1, the method comprising the following steps: (1) Feeding and acetylation: Add each polymer monomer, acetic anhydride and the carbon nanotube supported catalyst to the reaction apparatus; under the protection of an inert atmosphere, heat to 100~160℃ and carry out acetylation reaction for 0.5~3.5 hours; the total molar ratio of acetic anhydride to all aromatic hydroxy polymer monomers in the system is 0.9~5:1; (2) Melt polycondensation: After the acetylation reaction is completed, the reaction system is uniformly heated to the polycondensation reaction temperature of 150~390℃ at a heating rate of 0.1~100℃ / min under an inert atmosphere; after reaching the polycondensation temperature, the system pressure is reduced to 0.01~300kPa, and the polycondensation reaction is carried out under these conditions for 0.5~5 hours, with the reaction endpoint being when the stirring torque reaches its maximum value; (3) Discharge and post-processing: After the polycondensation reaction is completed, the obtained molten polyester material is extruded through a die, cooled with water, solidified and then granulated to obtain liquid crystal polyester products.

3. The method for preparing liquid crystal polyester according to claim 2, characterized in that, The amount of the carbon nanotube supported catalyst added is 0.1 to 10 wt% of the total mass of all polymer monomers, wherein the effective content of the supported catalyst is 50 to 5000 ppm.

4. The method for preparing liquid crystal polyester according to claim 2, characterized in that, The polymerizing monomer is selected from at least one of aromatic diols, aromatic hydroxycarboxylic acids, and aromatic dicarboxylic acids; The aromatic diol is selected from one or more of 4,4'-biphenyl hydroquinone, hydroquinone, 2,6-dihydroxynaphthalene, 2,2-bis(p-phenol propane) or 4,4'-(1-phenylethyl)bisphenol. The aromatic hydroxycarboxylic acid is selected from one or more of 4-hydroxybenzoic acid, 3-hydroxybenzoic acid or 6-hydroxy-2-naphthoic acid; The aromatic dicarboxylic acid is selected from one or more of terephthalic acid, isophthalic acid, or 2,6-naphthalenedicarboxylic acid.

5. The method for preparing liquid crystal polyester according to claim 2, characterized in that, The polycondensation reaction temperature in step (2) is 20~40℃ higher than the melting point of the synthesized liquid crystal polyester.

6. A liquid crystal polyester, characterized in that, It is prepared by the method of any one of claims 2 to 5 for preparing liquid crystal polyester.

7. The liquid crystal polyester according to claim 6, characterized in that, The intrinsic viscosity of the liquid crystal polyester is 4.0~4.7 dL / g, the tensile strength is not less than 112 MPa, and the melting point is between 282℃ and 356℃.

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