A method for preparing a thermotropic liquid crystal polymer

Abstract

This invention relates to a method for preparing thermotropic liquid crystal polymers, in which multiple catalysts are added in combination to the polymerization system of thermotropic liquid crystal polyarylates, which greatly accelerates the polymerization reaction rate and obtains a polymer product with high storage modulus, strong mechanical properties and low dielectric constant.

Description

Technical Field

[0001] This invention relates to the field of special engineering plastics technology, and more specifically, to a method for preparing thermotropic liquid crystal polymers. Background Technology

[0002] With the rapid development of science and technology, more engineering challenges have emerged, placing higher demands on material selection. Thermotropic liquid crystal polyarylate (TLCP) is a high-performance specialty engineering plastic with excellent thermal stability, low moisture absorption, and strong mechanical properties. Based on its various properties, it has been widely used in aerospace, automotive, and electronics industries.

[0003] Although many research institutions and enterprises have overcome polymerization challenges in recent years and can independently produce thermotropic liquid crystal polyarylates, their performance and processing procedures still lag behind those of leading international companies. CN120708738A discloses a method for determining the role of catalysts in the synthesis of liquid crystal polyarylates using molecular modeling. While this theoretically allows for the screening of highly efficient catalysts, it remains theoretical and its conclusions have not been proven. CN115894874A discloses a method for preparing thermotropic liquid crystal polyarylates using zinc acetate as a catalyst. Considering all factors, this method has a long reaction time, and the prepared thermotropic liquid crystal polyarylate has poor thermal stability.

[0004] Therefore, it is crucial to develop a catalyst suitable for thermotropic liquid crystal polyarylate systems. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to develop a catalyst suitable for the polymerization of thermotropic liquid crystal polyarylates, so as to solve the problems of long polymerization time and poor overall performance mentioned in the background art.

[0006] The technical solution adopted in this invention is: A thermotropic liquid crystal polyarylate, wherein the structural formula of the thermotropic liquid crystal polyarylate is:

[0007] The x+y+z=1, n=10~15.

[0008] This invention provides a method for preparing thermotropic liquid crystal polyarylates catalyzed by a multi-component catalyst, comprising: Monomer I, monomer II, monomer III, catalyst, and acetic anhydride were mixed and pre-reacted under a nitrogen atmosphere. Then, vacuum polymerization was carried out under programmed temperature rise to obtain a high-performance thermotropic liquid crystal polyarylate material containing a multi-component catalyst.

[0009] The monomers are: monomer I is p-hydroxybenzoic acid, monomer II is 2,6-naphthalenedicarboxylic acid, and monomer III is 4,4'-dihydroxydiphenylmethane.

[0010] The molar ratio of monomer I, monomer II, and monomer III is 60-70:10-20:10-30.

[0011] The catalyst comprises two of potassium acetate, triphenylphosphine, tetrabutyl titanate, and 1,5,7-triazabicyclo[4.4.0]decene-5-ene, and further comprises potassium acetate and triphenylphosphine.

[0012] The mass ratio of the catalyst is 30-70:70-30, and more specifically 50:50.

[0013] The catalyst feed rate is 0.1-0.5% of the total mass of the three monomers, and more specifically 0.15-0.25%.

[0014] The amount of acetic anhydride added is 1.2 to 1.3 times the total amount of hydroxyl groups contained in the monomer.

[0015] The programmed temperature rise includes reacting at 130~135 ℃ for 45-90 min; then, at 130~135 ℃, the temperature is increased to 300~330 ℃ at a rate of 1~2 ℃ / min, followed by vacuuming and holding at that temperature for 10~20 min.

[0016] Compared with the prior art, the technical effects and advantages provided by the present invention in the above technical solution are as follows: 1. Using p-hydroxybenzoic acid (monomer I), 2,6-naphthalenedicarboxylic acid (monomer II), and 4,4'-dihydroxydiphenylmethane (monomer III) as the main chain structure, and introducing crankshaft-structured monomer II and nonlinear-structured monomer III as raw materials, the melting point was lowered by utilizing monomers II and III. This is because monomers II and III disrupt the linear structure of rigid molecules, greatly reducing the regularity of the molecular backbone, thereby significantly lowering the melting point.

[0017] 2. Thermotropic liquid crystal polyarylates are synthesized using potassium acetate and triphenylphosphine as catalysts. On the one hand, the two catalysts are suitable for the special high-temperature synthesis conditions of thermotropic liquid crystal polyarylates. On the other hand, the synergistic catalysis of inorganic and organic catalysts in the acetylation process of monomers I, II and III and the melt transesterification process can greatly accelerate the reaction process and control the molecular weight and its distribution. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0019] Figure 1 The first cooling curves of differential scanning calorimetry (DSC) for Comparative Example 1 and Examples 1-3 of the present invention are shown.

[0020] Figure 2 The first temperature rise curves of differential scanning calorimetry (DSC) for Comparative Example 1 and Examples 1-3 of the present invention are shown.

[0021] Figure 3 Thermogravimetric analysis (TGA) curves of Comparative Example 1 and Examples 1-3 of the present invention. Figure 4 The energy storage modulus (E') curves obtained by dynamic thermomechanical analysis (DMA) for Comparative Example 1 and Examples 1-3 of the present invention are shown.

[0022] Figure 5 The loss tangent (Tan delta) is obtained by dynamic thermomechanical analysis (DMA) for Comparative Example 1 and Examples 1-3 of the present invention. Detailed Implementation

[0023] To better understand the content of this invention, further description is provided below with reference to specific embodiments and accompanying drawings. Obviously, these embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0024] The sources and specifications of the raw materials and reagents used in the experiment are shown in Table 1.

[0025] Table 1 Experimental materials and reagents

[0026] The present invention discloses a method for preparing a thermotropic liquid crystal polyarylate catalyzed by a multi-component catalyst, comprising: Monomer I (p-hydroxybenzoic acid), monomer II (2,6-naphthalenedicarboxylic acid), monomer III (4,4'-dihydroxydiphenylmethane), catalyst, and acetic anhydride were mixed and reacted at 130–135 °C for 45–90 min under a nitrogen atmosphere for acetylation. The temperature was then increased to 300–330 °C at a rate of 1–2 °C / min, followed by vacuuming and holding at this temperature for 10–20 min. After the reaction was complete, vacuuming and heating were stopped. The entire apparatus was then filled with nitrogen, and the product was allowed to cool naturally to room temperature under a nitrogen atmosphere to obtain a high-performance thermotropic liquid crystal polyarylate. The catalysts were potassium acetate and triphenylphosphine; the catalyst content was 0.15–0.25% of the total mass of the three monomers; the acetic anhydride content was 1.2–1.3 times the total amount of hydroxyl groups in the monomers.

[0027] Example 1 This embodiment describes the preparation of thermotropic liquid crystal polyarylates catalyzed by a multi-component catalyst, using the following method: 1) 0.7 mol (96.684 g) of p-hydroxybenzoic acid, 0.15 mol (32.428 g) of 2,6-naphthalenedicarboxylic acid, 0.15 mol (32.13 g) of 4,4'-dihydroxydiphenylmethane, 0.15 mol (32.13 g) of 1,5,7-triazabicyclo[4.4.0]decen-5-ene (0.161 g) of tetrabutyl titanate (0.161 g) and acetic anhydride (1 mol, 93.91 mL) were placed together in a 250 mL three-necked flask equipped with a mechanical stirrer. A nitrogen gas tube and control valve were installed on one side to control the nitrogen flow rate according to the reaction progress. A collection bottle for byproducts such as acetic acid was installed on the other side. After the apparatus was set up, the mechanical stirrer was turned on and the nitrogen valve was opened to replace the air in the apparatus with nitrogen. The heating device was turned on to raise the temperature to 130 °C within 30 min and hold it at the temperature for 60 min to carry out the acetylation reaction.

[0028] 2) Heat to 320 °C at a heating rate of 1.5 °C / min and hold at that temperature for 20 min. Observe the change in polymer viscosity inside the flask to determine the polymerization process. When the "stick climbing" phenomenon occurs, start evacuating until the polymer agglomerates. Then stop heating and continuously circulate nitrogen gas. After the flask cools naturally to room temperature, remove the product from the flask to obtain a thermotropic liquid crystal polyarylate catalyzed by a multi-component catalyst.

[0029] Its differential scanning calorimetry (DSC) curve is shown in the attached instruction manual. Figure 1-2 As shown; Thermogravimetric analysis (TGA) curves are attached to the instruction manual. Figure 3 As shown; the storage modulus (E') and loss tangent (Tan delta) curves obtained by dynamic thermomechanical analysis (DMA) are as shown in the attached manual. Figure 4-5 As shown.

[0030] Example 2 This embodiment describes the preparation of thermotropic liquid crystal polyarylates catalyzed by a multi-component catalyst, using the following method: 1) 0.7 mol (96.684 g) of p-hydroxybenzoic acid, 0.15 mol (32.428 g) of 2,6-naphthalenedicarboxylic acid, 0.15 mol (32.13 g) of 4,4'-dihydroxydiphenylmethane, 0.161 g of potassium acetate, 0.161 g of triphenylphosphine, and 1 mol (93.91 mL) of acetic anhydride were placed together in a 250 mL three-necked flask equipped with a mechanical stirrer. A nitrogen gas line and control valve were installed on one side to adjust the nitrogen flow rate according to the reaction progress. A collection bottle for byproducts such as acetic acid was installed on the other side. After the apparatus was set up, the mechanical stirrer was turned on and the nitrogen valve was opened to replace the air in the apparatus with nitrogen. The heating device was turned on to raise the temperature to 130 °C within 30 min and held at that temperature for 60 min to carry out the acetylation reaction.

[0031] 2) Heat to 320 °C at a heating rate of 1.5 °C / min and hold at that temperature for 20 min. Observe the change in polymer viscosity inside the flask to determine the polymerization process. When the "stick climbing" phenomenon occurs, start evacuating until the polymer agglomerates. Then stop heating and continuously circulate nitrogen gas. After the flask cools naturally to room temperature, remove the product from the flask to obtain a thermotropic liquid crystal polyarylate catalyzed by a multi-component catalyst.

[0032] Its differential scanning calorimetry (DSC) curve is shown in the attached instruction manual. Figure 1-2 As shown; Thermogravimetric analysis (TGA) curves are attached to the instruction manual. Figure 3 As shown; the storage modulus (E') and loss tangent (Tan delta) curves obtained by dynamic thermomechanical analysis (DMA) are as shown in the attached manual. Figure 4-5 As shown.

[0033] Example 3 This embodiment describes the preparation of thermotropic liquid crystal polyarylates catalyzed by a multi-component catalyst, using the following method: 1) 0.7 mol (96.684 g) of p-hydroxybenzoic acid, 0.15 mol (32.428 g) of 2,6-naphthalenedicarboxylic acid, 0.15 mol (32.13 g) of 4,4'-dihydroxydiphenylmethane, 0.161 g of potassium acetate, 0.161 g of 1,5,7-triazabicyclo[4.4.0]decen-5-ene (0.161 g) and acetic anhydride (1 mol, 93.91 mL) were placed together in a 250 mL three-necked flask equipped with a mechanical stirrer. A nitrogen gas tube and control valve were installed on one side to control the nitrogen flow rate according to the reaction progress. A collection bottle for byproducts such as acetic acid was installed on the other side. After the apparatus was set up, the mechanical stirrer was turned on and the nitrogen valve was opened to replace the air in the apparatus with nitrogen. The heating device was turned on to raise the temperature to 130 °C within 30 min and hold it at the temperature for 60 min to carry out the acetylation reaction.

[0034] 2) Heat to 320 °C at a heating rate of 1.5 °C / min and hold at that temperature for 20 min. Observe the change in polymer viscosity inside the flask to determine the polymerization process. When the "stick climbing" phenomenon occurs, start evacuating until the polymer agglomerates. Then stop heating and continuously circulate nitrogen gas. After the flask cools naturally to room temperature, remove the product from the flask to obtain a thermotropic liquid crystal polyarylate catalyzed by a multi-component catalyst.

[0035] Its differential scanning calorimetry (DSC) curve is shown in the attached instruction manual. Figure 1-2 As shown; Thermogravimetric analysis (TGA) curves are attached to the instruction manual. Figure 3 As shown; the storage modulus (E') and loss tangent (Tan delta) curves obtained by dynamic thermomechanical analysis (DMA) are as shown in the attached manual. Figure 4-5 As shown.

[0036] Comparative Example 1 This embodiment describes the preparation of thermotropic liquid crystal polyarylates catalyzed by a multi-component catalyst, using the following method: 1) 0.7 mol (96.684 g) of p-hydroxybenzoic acid, 0.15 mol (32.428 g) of 2,6-naphthalenedicarboxylic acid, 0.15 mol (32.13 g) of 4,4'-dihydroxydiphenylmethane, 0.15 mol (32.13 g) of tetrabutyl titanate, 0.161 g of triphenylphosphine, and 1 mol (93.91 mL) of acetic anhydride were placed together in a 250 mL three-necked flask equipped with a mechanical stirrer. A nitrogen gas line and control valve were installed on one side to adjust the nitrogen flow rate according to the reaction progress. A collection bottle for byproducts such as acetic acid was installed on the other side. After the apparatus was set up, the mechanical stirrer was turned on and the nitrogen valve was opened to replace the air in the apparatus with nitrogen. The heating device was turned on to raise the temperature to 130 °C within 30 min and held at that temperature for 60 min to carry out the acetylation reaction.

[0037] 2) Heat to 320 °C at a heating rate of 1.5 °C / min and hold at that temperature for 20 min. Observe the change in polymer viscosity inside the flask to determine the polymerization process. When the "stick climbing" phenomenon occurs, start evacuating until the polymer agglomerates. Then stop heating and continuously circulate nitrogen gas. After the flask cools naturally to room temperature, remove the product from the flask to obtain a thermotropic liquid crystal polyarylate catalyzed by a multi-component catalyst.

[0038] Its differential scanning calorimetry (DSC) curve is shown in the attached instruction manual. Figure 1-2 As shown; Thermogravimetric analysis (TGA) curves are attached to the instruction manual. Figure 3 As shown; the storage modulus (E') and loss tangent (Tan delta) curves obtained by dynamic thermomechanical analysis (DMA) are as shown in the attached manual. Figure 4-5 As shown.

[0039] Performance tests were conducted on Examples 1-3 and Comparative Example 1. 1) Differential Scanning Calorimetry (DSC) Test procedure: Under a nitrogen atmosphere, the temperature was increased from 30 ℃ to 350 ℃ at a heating rate of 20 ℃ / min and held for 2 min; then the temperature was decreased from 350 ℃ to 30 ℃ at a cooling rate of 20 ℃ / min and held for 2 min. This heating and cooling cycle was repeated twice. 5–10 mg of sample was accurately weighed into the crucible.

[0040] 2) Thermogravimetric analysis (TGA) Test procedure: Under a nitrogen atmosphere, the temperature is set from 30 ℃ to 600 ℃ at a heating rate of 10 ℃ / min. 1~5 mg of sample is accurately weighed into the crucible. The temperature corresponding to a 5% weight loss is defined as the thermal decomposition temperature (Td5%).

[0041] 3) Dynamic Thermomechanical Analysis (DMA) Test procedure: Under a nitrogen atmosphere, the temperature was set from 30 ℃ to 300 ℃ at a heating rate of 5 ℃ / min. The sample size was a thin film with dimensions of (20±1)×(5±0.1)×(0.5±0.1) mm.

[0042] Example 3, Comparative Example 1, underwent DSC testing in a nitrogen atmosphere as follows: Figures 1-2 The thermotropic liquid crystal polyarylate synthesized in this system exhibits amorphous properties due to the disruption of the molecular backbone regularity caused by the introduction of crankshaft structure and nonlinear monomers, and thus does not show a clear melting point. However, due to the different types of catalysts added, which promoted the increase in molecular weight and controlled the molecular weight distribution, Example 3 exhibited a higher glass transition temperature.

[0043] Example 3, Comparative Example 1, results measured by a thermogravimetric analyzer are as follows: Figure 3 As shown, the Td5% of the obtained thermo-induced liquid crystal polyarylates are all greater than 450 °C, and the highest is found in Example 3. This is because the catalyst has a significant impact on the growth and distribution control of molecular weight.

[0044] Example 3, the dynamic thermomechanical analysis results of Comparative Example 1 measured under a nitrogen atmosphere are as follows: Figure 4-5 As shown: it is clear that the glass transition temperatures are all greater than 120 °C. Example 3 has a storage modulus of 3.9 MPa at 250 °C and the smallest peak width of the loss tangent, exhibiting optimal control over molecular weight and its distribution.

[0045] This technical solution utilizes the synergistic catalytic effect of inorganic and organic catalysts to configure a catalyst system for the polymerization of thermotropic liquid crystal polyarylates. Compared with existing thermotropic liquid crystal polyarylates, the catalytic time is shortened, the catalytic effect is doubled, and the molecular weight and its distribution are more precisely controlled.

[0046] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0047] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes and modifications can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a thermotropic liquid crystal polymer, characterized in that, The general structural formula of the thermotropic liquid crystal polyarylate is: ； The x+y+z=1, n=10~15.

2. The thermotropic liquid crystal polyarylate material containing a multi-component catalyst according to claim 1, characterized in that, The catalyst comprises potassium acetate, triphenylphosphine, tetrabutyl titanate, and 1,5,7-triazabicyclo[4.4.0]decene-5-ene.

3. A method for preparing a thermotropic liquid crystal polyarylate material containing a multi-component catalyst, comprising: Monomer I, monomer II, monomer III, catalyst, and acetic anhydride were mixed and pre-reacted under a nitrogen atmosphere. Then, vacuum polymerization was carried out under programmed temperature rise to obtain a high-performance thermotropic liquid crystal polyarylate material containing a multi-component catalyst.

4. The preparation method according to claim 3, characterized in that, The monomer I is p-hydroxybenzoic acid, monomer II is 2,6-naphthalenedicarboxylic acid, and monomer III is 4,4'-dihydroxydiphenylmethane.

5. The preparation method according to claim 3, characterized in that, The molar ratio of monomer I, monomer II, and monomer III is 60-70:10-20:10-30.

6. The preparation method according to claim 3, characterized in that, The catalyst comprises two of the following: potassium acetate, triphenylphosphine, tetrabutyl titanate, and 1,5,7-triazabicyclo[4.4.0]decene-5-ene.

7. The preparation method according to claim 3, characterized in that, The mass ratio of the catalyst is 30-70:70-30.

8. The preparation method according to claim 3, characterized in that, The catalyst feed rate is 0.1-0.5% of the total mass of the three monomers.

9. The preparation method according to claim 3, characterized in that, The amount of acetic anhydride added is 1.2 to 1.3 times the total amount of hydroxyl groups contained in the monomer.

10. The preparation method according to claim 3, characterized in that, The programmed temperature rise includes reacting at 130~135 ℃ for 45-90 min; then, at 130~135 ℃, the temperature is increased to 300~330 ℃ at a rate of 1~2 ℃ / min, followed by vacuuming and holding at that temperature for 10~20 min.

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