A method for preparing thermotropic liquid crystal polymer

Abstract

The present invention relates to the technical field of special engineering plastics, and in particular to a method for preparing a thermotropic liquid crystal polymer, wherein the method comprises the following steps: S1, under the protection of an inert gas and under heating conditions, an aromatic liquid crystal monomer and acetic anhydride are subjected to an acetylation reaction under the action of a catalyst; S2, after the acetylation reaction is completed, a prepolymerization reaction is carried out under the conditions of a heating temperature of 210 to 230°C and a pressure of 1 to 3 MPa, after the reaction is completed, the reaction system is depressurized and the by-products are discharged; S3, after the prepolymerization reaction is completed, the temperature is raised to carry out a melt polymerization reaction; S4, under the conditions of an inert gas, a solid phase polymerization reaction is carried out on the product of step S3 to obtain a thermotropic liquid crystal polymer. The preparation method can solve the sublimation problem of liquid crystal monomers and acetylation products, is simple to operate, saves working hours, reduces the generation of by-products, is convenient for industrial production, and the obtained thermotropic liquid crystal polymer has good thermal stability, mechanical properties and processing properties.

Description

Technical Field

[0001] The invention relates to a method for preparing a thermotropic liquid crystal polymer, belonging to the technical field of special engineering plastics. Background Art

[0002] Liquid crystal polymer (LCP) refers to a polymer that can exist in a liquid crystal phase under certain conditions. It is characterized by a high molecular weight and orderly orientation. Liquid crystal polymer (LCP) can be divided into lyotropic liquid crystal polymer (LLCP) and thermotropic liquid crystal polymer (TLCP). LLCP forms a liquid crystal phase in an organic solution, and the typical representative is aromatic polyamide; TLCP forms a liquid crystal phase above the melting point or glass transition temperature, and the main representative is polyarylate.

[0003] TLCP has high strength, high modulus, high chemical corrosion resistance, good dimensional stability and self-flammability constant, low dielectric constant at high frequencies, excellent radiation resistance and good transparency to microwaves. TLCP is widely used in electronics, automobile manufacturing, aerospace, chemical industry, medical and other fields.

[0004] At present, the raw materials for preparing TLCP include p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, hydroquinone, biphenyl, terephthalic acid, 2,6-naphthalene dicarboxylic acid, biphenyl dicarboxylic acid, isophthalic acid, etc. The TLCP production process generally adopts the acetylation-melt polymerization-solid phase polymerization process. The melt polymerization temperature of most TLCP products will reach above 300°C. At high temperatures, the raw materials or acetylation products (such as 4-acetoxybenzoic acid, 4,4´-diacetoxybiphenyl, etc.) are prone to sublimation, and nitrogen needs to be introduced during melt polymerization to remove by-products. At the same time, nitrogen will also accelerate the sublimation of monomers, greatly reducing the utilization rate of raw materials, affecting the material ratio composition of the product, and causing problems such as poor batch stability during the TLCP production process.

[0005] Chinese patent CN109824876B discloses a method for preparing a thermotropic liquid crystal polymer, wherein during the synthesis of TLCP, the temperature is between 140°C and T m The -10℃ temperature range needs to control the heating rate to 0.8~1.2℃ / min. m -10℃~T m The +20°C temperature range requires a controlled heating rate of 0.2~0.5°C / min. The preparation process is complicated, the operation time is long, and the production efficiency is low. Summary of the invention

[0006] The present invention aims at the deficiencies in the prior art and provides a method for preparing a thermotropic liquid crystal polymer. The prepared thermotropic liquid crystal polymer has good thermal stability, mechanical properties and processing properties, and the preparation method is simple to operate and suitable for industrial production.

[0007] The technical solution of the present invention to solve the above technical problem is as follows: a method for preparing a thermotropic liquid crystal polymer, the preparation method comprising:

[0008] S1. Acetylation reaction:

[0009] Under the protection of inert gas and heating conditions, aromatic liquid crystal monomers and acetic anhydride undergo acetylation reaction under the action of a catalyst;

[0010] S2, prepolymerization reaction:

[0011] After the acetylation reaction is completed, a prepolymerization reaction is carried out at a heating temperature of 210-230°C and a pressure of 1-3Mpa. After the reaction is completed, the reaction system is depressurized to discharge the by-products acetic acid and acetic anhydride;

[0012] S3, melt polymerization reaction:

[0013] After the prepolymerization reaction is completed, the temperature is raised to carry out melt polymerization reaction;

[0014] S4. Solid phase polymerization:

[0015] Under inert gas conditions, the product obtained in step S3 is subjected to solid phase polymerization to obtain a thermotropic liquid crystal polymer.

[0016] Furthermore, the aromatic liquid crystal monomer is selected from at least one of an aromatic hydroxycarboxyl monomer, an aromatic diol monomer and an aromatic dicarboxylic acid monomer; and the molar amounts of the hydroxyl group and the carboxyl group in the aromatic liquid crystal monomer are equal.

[0017] Further, the aromatic hydroxycarboxyl monomer is at least one of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid;

[0018] The aromatic diol monomer is at least one of hydroquinone, 4,4'-biphenylene glycol, and 2,6-naphthalene diol;

[0019] The aromatic dicarboxylic acid monomer is at least one of terephthalic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-biphenyl dicarboxylic acid and isophthalic acid.

[0020] Furthermore, in terms of molar fractions, in the aromatic liquid crystal monomer, the aromatic hydroxycarboxyl monomer is 50-100 parts, the aromatic diol monomer is 0-25 parts, and the aromatic dicarboxylic acid monomer is 0-25 parts.

[0021] Furthermore, the catalyst is at least one of potassium acetate, sodium acetate, zinc acetate and magnesium acetate.

[0022] Furthermore, the amount of the catalyst is 0.01% to 0.5% of the total mass of the aromatic liquid crystal monomer; the amount of acetic anhydride is 1.05 to 1.3 times the molar amount of all hydroxyl groups in the aromatic liquid crystal monomer.

[0023] Furthermore, the acetylation reaction temperature of step S1 is 140-150° C., and the acetylation reaction time is 2-5 hours.

[0024] Furthermore, the melt polymerization reaction temperature of step S3 is 300°C~340°C, and the reaction is first carried out under inert gas conditions for 1-3 hours until no liquid flows out of the condenser, and then the vacuum conditions are changed to vacuum conditions with a vacuum degree of 0.01~1KPa and a vacuum time of 1~3 hours.

[0025] Further, the solid phase polymerization reaction temperature of step S4 is (T m -80)℃~(T m -40)℃, T m is the melting temperature of the thermotropic liquid crystal polymer, and the solid phase polymerization reaction time is 4 to 24 hours.

[0026] Furthermore, the melting temperature of the thermotropic liquid crystal polymer is m The temperature of the thermotropic liquid crystal polymer is 300-360°C, and the thermal decomposition temperature of the thermotropic liquid crystal polymer is greater than 500°C.

[0027] The beneficial effects of the present invention are:

[0028] The preparation method of the present invention adds a closed pressurized prepolymerization process to generate oligomers in advance, solves the problem of easy sublimation of liquid crystal monomers and acetylated products, improves the problem of poor batch stability in the production process of thermotropic liquid crystal polymers, and the obtained thermotropic liquid crystal polymers have good thermal stability, mechanical properties and processing properties.

[0029] The preparation method of the present invention can obtain a thermotropic liquid crystal polymer product with excellent performance by adding a prepolymerization process, without setting a programmed temperature rise, making the operation simpler, saving work time, reducing the generation of by-products, and facilitating industrial production.

[0030] In the preparation method of the present invention, by controlling the prepolymerization reaction temperature and pressure conditions, the polymerization in the reaction system is made more uniform, which is more conducive to the control of the melt polymerization and solid phase polymerization reaction processes, and finally a thermotropic liquid crystal polymer product with excellent performance is obtained. DETAILED DESCRIPTION

[0031] The specific implementation of the present invention is described in detail below. The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0033] A method for preparing a thermotropic liquid crystal polymer, the preparation method comprising:

[0034] S1. Acetylation reaction:

[0035] The aromatic liquid crystal monomers are mixed and poured into a pressure-resistant reactor, and a certain amount of acetic anhydride and a catalyst are added, the feeding port is closed, and the reactor is evacuated and nitrogen is introduced repeatedly for more than 5 times to make the reaction mixture under inert gas protection, and the acetylation reaction is carried out under heating conditions;

[0036] S2, prepolymerization reaction:

[0037] After the acetylation reaction is completed, the reflux valve is closed, and a prepolymerization reaction is carried out at a heating temperature of 210-230°C and a pressure of 1-3Mpa. After the reaction is kept warm for 2-4 hours, the pressure relief valve is opened to discharge the by-products acetic acid and acetic anhydride;

[0038] S3, melt polymerization reaction:

[0039] Turn on the nitrogen and condensation system, blow nitrogen into the reaction system, heat and raise the temperature to carry out melt polymerization reaction, and when the liquid flow in the condenser is reduced to zero, stop passing nitrogen, evacuate, and remove by-products acetic acid and acetic anhydride;

[0040] S4. Solid phase polymerization:

[0041] Under inert gas conditions, the product obtained in step S3 is subjected to solid phase polymerization to obtain a thermotropic liquid crystal polymer (TLCP).

[0042] Specifically, the aromatic liquid crystal monomer is selected from at least one of an aromatic hydroxycarboxyl monomer, an aromatic diol monomer and an aromatic dicarboxylic acid monomer; and the molar amounts of the hydroxyl group and the carboxyl group in the aromatic liquid crystal monomer are equal.

[0043] Specifically, the aromatic hydroxycarboxyl monomer is at least one of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid;

[0044] The aromatic diol monomer is at least one of hydroquinone, 4,4'-biphenylene glycol, and 2,6-naphthalene diol;

[0045] The aromatic dicarboxylic acid monomer is at least one of terephthalic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-biphenyl dicarboxylic acid and isophthalic acid.

[0046] Specifically, in terms of molar fractions, in the aromatic liquid crystal monomer, the aromatic hydroxycarboxyl monomer is 50-100 parts, the aromatic diol monomer is 0-25 parts, and the aromatic dicarboxylic acid monomer is 0-25 parts.

[0047] Specifically, the catalyst is at least one of potassium acetate, sodium acetate, zinc acetate, and magnesium acetate.

[0048] Specifically, the amount of the catalyst is 0.01% to 0.5% of the total mass of the aromatic liquid crystal monomer; the amount of acetic anhydride is 1.05 to 1.3 times the molar amount of all hydroxyl groups in the aromatic liquid crystal monomer.

[0049] Specifically, the acetylation reaction temperature of step S1 is 140-150° C., and the acetylation reaction time is 2-5 hours.

[0050] Specifically, the melt polymerization reaction temperature of step S3 is 300°C~340°C, and the reaction is first carried out under inert gas conditions for 1-3 hours until no liquid flows out of the condenser, and then the vacuum conditions are changed to vacuum conditions with a vacuum degree of 0.01~1KPa and a vacuum time of 1~3 hours.

[0051] Specifically, the solid phase polymerization reaction temperature of step S4 is (T m -80)℃~(T m -40)℃, T m is the melting temperature of the thermotropic liquid crystal polymer, and the solid phase polymerization reaction time is 4 to 24 hours.

[0052] Specifically, the melting temperature of the thermotropic liquid crystal polymer is m The temperature of the thermotropic liquid crystal polymer is 300-360°C, and the thermal decomposition temperature of the thermotropic liquid crystal polymer is greater than 500°C.

[0053] Example 1

[0054] (1) 3.0 mol of p-hydroxybenzoic acid, 1.0 mol of 4,4´-biphenol, 0.75 mol of terephthalic acid and 0.25 mol of isophthalic acid were mixed and poured into a pressure reactor, and 5.5 mol of acetic anhydride and 0.383 g of sodium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to keep the reaction mixture under inert gas protection. The temperature was then raised to 145°C and refluxed for acetylation reaction for 3 hours.

[0055] (2) After the acetylation is completed, the reflux valve is closed and the temperature is raised to 220°C for prepolymerization. At this time, the system pressure is 2.1 MPa. The temperature is kept for 2 hours. After the temperature is kept, the pressure relief valve is opened to discharge the by-products acetic acid and acetic anhydride;

[0056] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 320°C for melt polymerization. Keep the temperature for 2 hours until no liquid flows out of the condenser, stop introducing nitrogen, and evacuate the system. The vacuum degree is 0.1 KPa and maintained for 1 hour;

[0057] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 290 °C in a nitrogen atmosphere for 10 h to obtain a TLCP product.

[0058] Neither liquid crystal monomers nor acetylated products were found in the by-products.

[0059] The obtained TLCP was subjected to product performance testing, and the results are shown in Table 1.

[0060] Example 2

[0061] (1) 3.5 mol of p-hydroxybenzoic acid and 1.5 mol of 6-hydroxy-2-naphthoic acid were mixed and poured into a pressure-resistant reactor, and 5.5 mol of acetic anhydride and 0.382 g of potassium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to protect the reaction mixture under inert gas. The temperature was then raised to 140° C. and refluxed to carry out acetylation reaction for 2 hours;

[0062] (2) After the acetylation is completed, the reflux valve is closed and the temperature is raised to 210°C for prepolymerization. At this time, the system pressure is 1.3 MPa. The temperature is kept for 3 hours. After the temperature is kept, the pressure relief valve is opened to discharge the by-products acetic acid and acetic anhydride;

[0063] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 300°C for melt polymerization. Keep the temperature for 1.5 hours until no liquid flows out of the condenser. Stop the nitrogen flow, evacuate, and maintain the vacuum degree at 0.05 KPa for 1.5 hours;

[0064] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 270 °C for 12 h in a nitrogen atmosphere to obtain a TLCP product.

[0065] Neither liquid crystal monomers nor acetylated products were found in the by-products.

[0066] The obtained TLCP was subjected to product performance testing, and the results are shown in Table 1.

[0067] Example 3

[0068] (1) 2.0 mol of p-hydroxybenzoic acid, 1.0 mol of 6-hydroxy-2-naphthoic acid, 1.0 mol of hydroquinone and 1.0 mol of terephthalic acid were mixed and poured into a pressure reactor, and 6.0 mol of acetic anhydride and 0.370 g of zinc acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to keep the reaction mixture under inert gas protection. The temperature was then raised to 148° C. and refluxed for 4 hours to carry out acetylation reaction;

[0069] (2) After the acetylation is completed, the reflux valve is closed and the temperature is raised to 225°C for prepolymerization. At this time, the system pressure is 2.6 MPa. The temperature is kept for 2 hours. After the temperature is kept, the pressure relief valve is opened to discharge the by-products acetic acid and acetic anhydride;

[0070] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 340°C for melt polymerization. Keep the temperature for 1 hour until no liquid flows out of the condenser, stop introducing nitrogen, and evacuate the system. The vacuum degree is 0.2 KPa and maintained for 2 hours;

[0071] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 280 °C in a nitrogen atmosphere for 24 h to obtain a TLCP product.

[0072] Neither liquid crystal monomers nor acetylated products were found in the by-products.

[0073] The obtained TLCP was subjected to product performance testing, and the results are shown in Table 1.

[0074] Example 4

[0075] (1) 2.0 mol of p-hydroxybenzoic acid, 1.0 mol of 6-hydroxy-2-naphthoic acid, 1.0 mol of hydroquinone, 0.75 mol of terephthalic acid and 0.25 mol of isophthalic acid were mixed and poured into a pressure reactor, and 5.5 mol of acetic anhydride and 0.148 g of zinc acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to keep the reaction mixture under inert gas protection. The temperature was then raised to 150° C. and refluxed to carry out acetylation reaction for 2 hours;

[0076] (2) After the acetylation is completed, the reflux valve is closed and the temperature is raised to 210°C for prepolymerization. At this time, the system pressure is 1.3 MPa. The temperature is kept for 4 hours. After the temperature is kept, the pressure relief valve is opened to discharge the by-products acetic acid and acetic anhydride;

[0077] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 330°C for melt polymerization. Keep the temperature for 3 hours until no liquid flows out of the condenser, stop the nitrogen flow, and evacuate the system. The vacuum degree is 0.5 KPa and maintained for 1 hour;

[0078] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 290 °C in a nitrogen atmosphere for 8 h to obtain a TLCP product.

[0079] Neither liquid crystal monomers nor acetylated products were found in the by-products.

[0080] The obtained TLCP was subjected to product performance testing, and the results are shown in Table 1.

[0081] Example 5

[0082] (1) 1.0 mol of p-hydroxybenzoic acid, 1.0 mol of 6-hydroxy-2-naphthoic acid, 1.0 mol of 2,6-naphthalene diol and 1.0 mol of terephthalic acid were mixed and poured into a pressure-resistant reactor, and 4.8 mol of acetic anhydride and 0.392 g of magnesium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to protect the reaction mixture under inert gas. The temperature was then raised to 145° C. and refluxed to carry out acetylation reaction for 3 hours;

[0083] (2) After the acetylation is completed, the reflux valve is closed and the temperature is raised to 225°C for prepolymerization. At this time, the system pressure is 2.6 MPa. The temperature is kept for 2 hours. After the temperature is kept, the pressure relief valve is opened to discharge the by-products acetic acid and acetic anhydride;

[0084] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 320°C for melt polymerization. Keep the temperature for 2 hours until no liquid flows out of the condenser, stop the nitrogen flow, and evacuate the system. The vacuum degree is 0.1 KPa and maintained for 2 hours;

[0085] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 280 °C in a nitrogen atmosphere for 16 h to obtain a TLCP product.

[0086] Neither liquid crystal monomers nor acetylated products were found in the by-products.

[0087] The obtained TLCP was subjected to product performance testing, and the results are shown in Table 1.

[0088] Example 6

[0089] (1) 3.0 mol of 6-hydroxy-2-naphthoic acid, 1.0 mol of 2,6-naphthalenediol, 0.75 mol of terephthalic acid and 0.25 mol of 2,6-naphthalenedicarboxylic acid were mixed and poured into a pressure-resistant reactor, and 6.5 mol of acetic anhydride and 0.452 g of magnesium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to protect the reaction mixture under inert gas. The temperature was then raised to 142° C. and refluxed to carry out acetylation reaction for 3 hours;

[0090] (2) After the acetylation is completed, the reflux valve is closed and the temperature is raised to 220°C for prepolymerization. At this time, the system pressure is 2.1 MPa. The temperature is kept for 2 hours. After the temperature is kept, the pressure relief valve is opened to discharge the by-products acetic acid and acetic anhydride;

[0091] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 310°C for melt polymerization. Keep the temperature for 2 hours until no liquid flows out of the condenser, stop introducing nitrogen, and evacuate the system. The vacuum degree is 0.1 KPa and maintained for 1 hour;

[0092] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 280 °C for 12 h in a nitrogen atmosphere to obtain a TLCP product.

[0093] Neither liquid crystal monomers nor acetylated products were found in the by-products.

[0094] The obtained TLCP was subjected to product performance testing, and the results are shown in Table 1.

[0095] Example 7

[0096] (1) 3.0 mol of 6-hydroxy-2-naphthoic acid, 1.0 mol of 2,6-naphthalenediol, 0.75 mol of terephthalic acid and 0.25 mol of 2,6-naphthalenedicarboxylic acid were mixed and poured into a pressure reactor, and 6.5 mol of acetic anhydride and 0.452 g of magnesium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to protect the reaction mixture under inert gas. The temperature was then raised to 150° C. and refluxed to carry out acetylation reaction for 2 hours;

[0097] (2) After the acetylation is completed, the reflux valve is closed and the temperature is raised to 230°C for prepolymerization reaction. At this time, the system pressure is 3MPa and the temperature is kept for 2 hours. After the temperature is kept, the pressure relief valve is opened to discharge the by-products acetic acid and acetic anhydride;

[0098] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 340°C for melt polymerization. Keep the temperature for 1 hour until no liquid flows out of the condenser, stop introducing nitrogen, and evacuate the system. The vacuum degree is 1 KPa and maintained for 1 hour;

[0099] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 300 °C for 12 h in a nitrogen atmosphere to obtain a TLCP product.

[0100] Neither liquid crystal monomers nor acetylated products were found in the by-products.

[0101] The obtained TLCP was subjected to product performance testing, and the results are shown in Table 1.

[0102] Example 8

[0103] (1) 3.0 mol of p-hydroxybenzoic acid, 1.0 mol of 4,4´-biphenol, 0.75 mol of terephthalic acid and 0.25 mol of isophthalic acid were mixed and poured into a pressure-resistant reactor, and 6.5 mol of acetic anhydride and 0.383 g of potassium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to keep the reaction mixture under inert gas protection. The temperature was then raised to 140° C. and refluxed for acetylation reaction for 5 hours.

[0104] (2) After the acetylation is completed, the reflux valve is closed and the temperature is raised to 210°C for prepolymerization. At this time, the system pressure is 1.0 MPa and the temperature is kept for 2 hours. After the temperature is kept, the pressure relief valve is opened to discharge the by-products acetic acid and acetic anhydride;

[0105] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 300°C for melt polymerization. Keep the temperature for 3 hours until no liquid flows out of the condenser, stop the nitrogen flow, and evacuate the system. The vacuum degree is 0.01 KPa and maintained for 3 hours;

[0106] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 320 °C for 10 h in a nitrogen atmosphere to obtain a TLCP product.

[0107] Neither liquid crystal monomers nor acetylated products were found in the by-products.

[0108] The obtained TLCP was subjected to product performance testing, and the results are shown in Table 1.

[0109] Comparative Example 1

[0110] The TLCP was prepared by the same method as in Example 1, except that no prepolymerization reaction was performed. The specific operation process was as follows:

[0111] (1) 3.0 mol of p-hydroxybenzoic acid, 1.0 mol of 4,4´-biphenol, 0.75 mol of terephthalic acid and 0.25 mol of isophthalic acid were mixed and poured into a pressure reactor, and 5.5 mol of acetic anhydride and 0.383 g of sodium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to keep the reaction mixture under inert gas protection. The temperature was then raised to 145°C and refluxed for acetylation reaction for 3 hours.

[0112] (2) After the acetylation is completed, the nitrogen and condensation systems are turned on, nitrogen is blown into the reaction system, and the temperature is raised to 320°C at a heating rate of 1°C / min for melt polymerization. The temperature is kept for 2 hours until no liquid flows out of the condenser, and the nitrogen is stopped. The system is evacuated and the vacuum degree is maintained at 0.1 KPa for 1 hour;

[0113] (3) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 290 °C for 10 h in a nitrogen atmosphere to obtain a TLCP product.

[0114] In addition to acetic acid and acetic anhydride, two acetylated products, 4-acetoxybenzoic acid and 4,4´-diacetoxybiphenyl, were found in the by-products.

[0115] The obtained TLCP was subjected to product performance testing, and the results are shown in Table 1.

[0116] Comparative Example 2

[0117] The TLCP was prepared by the same method as in Example 2, except that no prepolymerization reaction was performed. The specific operation process was as follows:

[0118] (1) 3.5 mol of p-hydroxybenzoic acid and 1.5 mol of 6-hydroxy-2-naphthoic acid were mixed and poured into a pressure-resistant reactor, and 5.5 mol of acetic anhydride and 0.382 g of potassium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to protect the reaction mixture under inert gas. The temperature was then raised to 140° C. and refluxed to carry out acetylation reaction for 2 hours;

[0119] (2) After the acetylation is completed, the reflux valve is closed, the nitrogen and condensation systems are turned on, nitrogen is blown into the reaction system, and the temperature is raised to 300°C at a heating rate of 3°C / min for melt polymerization. The temperature is kept for 1.5 hours until no liquid flows out of the condenser, the nitrogen is stopped, and the system is evacuated. The vacuum degree is maintained at 0.05 KPa for 1.5 hours;

[0120] (3) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 270 °C for 12 h in a nitrogen atmosphere to obtain a TLCP product.

[0121] In addition to acetic acid and acetic anhydride, p-hydroxybenzoic acid, 4-acetoxybenzoic acid and 6-acetoxy-2-naphthoic acid were found in the by-products.

[0122] The obtained TLCP was subjected to product performance testing, and the results are shown in Table 1.

[0123] Comparative Example 3

[0124] The TLCP was prepared by the same method as in Example 1, except that the temperature during the prepolymerization reaction was 250° C. (higher than the temperature specified in the present invention). The specific operation process was as follows:

[0125] (1) 3.0 mol of p-hydroxybenzoic acid, 1.0 mol of 4,4´-biphenol, 0.75 mol of terephthalic acid and 0.25 mol of isophthalic acid were mixed and poured into a pressure reactor, and 5.5 mol of acetic anhydride and 0.383 g of sodium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to keep the reaction mixture under inert gas protection. The temperature was then raised to 145°C and refluxed for acetylation reaction for 3 hours.

[0126] (2) After the acetylation is completed, close the reflux valve, raise the temperature to 250°C, carry out the prepolymerization reaction, adjust the system pressure to 2.1MPa, and keep the temperature for 2 hours. After the temperature is maintained, open the pressure relief valve to discharge the by-products acetic acid and acetic anhydride;

[0127] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 320°C for melt polymerization. Keep the temperature for 2 hours until no liquid flows out of the condenser, stop introducing nitrogen, and evacuate the system. The vacuum degree is 0.1 KPa and maintained for 1 hour;

[0128] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 290 °C in a nitrogen atmosphere for 10 h to obtain a TLCP product.

[0129] Comparative Example 4

[0130] The TLCP was prepared by the same method as in Example 1, except that the temperature during the prepolymerization reaction was 200° C. (lower than the temperature specified in the present invention). The specific operation process was as follows:

[0131] (1) 3.0 mol of p-hydroxybenzoic acid, 1.0 mol of 4,4´-biphenol, 0.75 mol of terephthalic acid and 0.25 mol of isophthalic acid were mixed and poured into a pressure reactor, and 5.5 mol of acetic anhydride and 0.383 g of sodium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to keep the reaction mixture under inert gas protection. The temperature was then raised to 145°C and refluxed for acetylation reaction for 3 hours.

[0132] (2) After the acetylation is completed, close the reflux valve, raise the temperature to 200°C, carry out the prepolymerization reaction, adjust the system pressure to 2.1MPa, and keep the temperature for 2 hours. After the temperature is maintained, open the pressure relief valve to discharge the by-products acetic acid and acetic anhydride;

[0133] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 320°C for melt polymerization. Keep the temperature for 2 hours until no liquid flows out of the condenser, stop introducing nitrogen, and evacuate the system. The vacuum degree is 0.1 KPa and maintained for 1 hour;

[0134] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 290 °C in a nitrogen atmosphere for 10 h to obtain a TLCP product.

[0135] Comparative Example 5

[0136] The TLCP was prepared by the same method as in Example 1, except that the pressure during the prepolymerization reaction was 0.5 MPa (lower than the pressure conditions specified in the present invention). The specific operation process was as follows:

[0137] (1) 3.0 mol of p-hydroxybenzoic acid, 1.0 mol of 4,4´-biphenol, 0.75 mol of terephthalic acid and 0.25 mol of isophthalic acid were mixed and poured into a pressure reactor, and 5.5 mol of acetic anhydride and 0.383 g of sodium acetate were added. The feed port was closed, and the reactor was evacuated and nitrogen was introduced repeatedly for more than 5 times to keep the reaction mixture under inert gas protection. The temperature was then raised to 145°C and refluxed for acetylation reaction for 3 hours.

[0138] (2) After the acetylation is completed, close the reflux valve, raise the temperature to 220°C, carry out the prepolymerization reaction, adjust the system pressure to 0.5MPa, and keep the temperature for 2 hours. After the temperature is maintained, open the pressure relief valve to discharge the by-products acetic acid and acetic anhydride;

[0139] (3) After prepolymerization, turn on the nitrogen and condensation system, blow nitrogen into the reaction system, and raise the temperature to 320°C for melt polymerization. Keep the temperature for 2 hours until no liquid flows out of the condenser, stop introducing nitrogen, and evacuate the system. The vacuum degree is 0.1 KPa and maintained for 1 hour;

[0140] (4) After melt polymerization, the product was transferred to a solid phase polymerization device and subjected to solid phase polymerization at 290 °C in a nitrogen atmosphere for 10 h to obtain a TLCP product.

[0141] The TLCP prepared in the above examples and comparative examples was subjected to product performance tests, and the results are shown in Table 1.

[0142] Table 1 TLCP product performance test data

[0143]

[0144] Remark:

[0145] The melting temperature was obtained by using a differential scanning calorimeter (DSC) under the following test conditions: under nitrogen protection, the temperature range was 50°C to 500°C, and the temperature rise rate was 20°C / min.

[0146] The thermal decomposition temperature was obtained by using a thermogravimetric analyzer (TGA) under nitrogen protection conditions, with a heating range of 50°C to 700°C and a heating rate of 10°C / min. The 5% thermal weight loss temperature was the thermal decomposition temperature.

[0147] The tensile strength was tested using a universal material testing machine according to standard ASTM D638.

[0148] The flexural strength was tested using a universal material testing machine according to standard ASTM D790.

[0149] The melt index is obtained by testing with a melt indexer according to standard ASTM D1238, with the test condition being 350° C. and the weight being 2.16 kg.

[0150] It can be seen from Table 1 above that the TLCP products prepared by the method of the present invention in Examples 1 to 8 have high melting temperature and high thermal decomposition temperature, good thermal stability, good mechanical properties, and ideal processing performance (melt index 40~55g / 10min).

[0151] The data comparison between Example 1 and Comparative Example 1 (traditional preparation method) and the data comparison between Example 2 and Comparative Example 2 (traditional preparation method) show that, by adopting the preparation method of the present invention, no liquid crystal monomer and acetylation product are found in the by-products, which reduces the difficulty of handling the by-products. In addition, the traditional preparation method controls the temperature at a certain heating rate, while the present invention does not need to control the heating rate, which reduces the difficulty of operation, saves working hours, and facilitates industrial production.

[0152] From the data comparison between Example 1 and Comparative Example 3, it can be seen that if the prepolymerization reaction temperature is high, the performance of the TLCP product will decrease. If the prepolymerization reaction temperature is high, it will easily lead to a decrease in the uniformity of the polymerization reaction, which will ultimately affect the mechanical properties of the TLCP product.

[0153] From the data comparison of Example 1 and Comparative Example 4, it can be seen that if the prepolymerization reaction temperature is lowered, the performance of the TLCP product will decline. This is because if the prepolymerization reaction temperature is lowered, the prepolymerization reaction will be insufficient, which will affect the subsequent melt polymerization and solid phase polymerization reactions, and ultimately lead to a decline in the performance of the TLCP product.

[0154] From the data comparison of Example 1 and Comparative Example 5, it can be seen that if the prepolymerization reaction pressure is reduced, the performance of the TLCP product will decline. Because the prepolymerization reaction pressure is reduced, the prepolymerization reaction is not sufficient, which affects the subsequent melt polymerization and solid phase polymerization reactions, and ultimately leads to a decline in the performance of the TLCP product.

[0155] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0156] For those skilled in the art, several modifications and improvements may be made without departing from the concept of the present invention, all of which belong to the protection scope of the present invention. The protection scope of the present invention shall be based on the attached claims.

Claims

1. A method for preparing a thermotropic liquid crystal polymer, characterized in that: The preparation method is: S1. Acetylation reaction: Under the protection of inert gas and heating conditions, aromatic liquid crystal monomers and acetic anhydride undergo acetylation reaction under the action of a catalyst; S2, prepolymerization reaction: After the acetylation reaction is completed, a prepolymerization reaction is carried out at a heating temperature of 210-230°C and a pressure of 1-3MPa. After the reaction is completed, the reaction system is depressurized to discharge the by-products acetic acid and acetic anhydride; S3, melt polymerization reaction: After the prepolymerization reaction is completed, the temperature is raised to carry out melt polymerization reaction; S4. Solid phase polymerization: Under inert gas conditions, subjecting the product obtained in step S3 to solid phase polymerization to obtain a thermotropic liquid crystal polymer; The aromatic liquid crystal monomer is selected from at least one of an aromatic hydroxycarboxyl monomer, an aromatic diol monomer and an aromatic dicarboxylic acid monomer; and the molar amounts of the hydroxyl group and the carboxyl group in the aromatic liquid crystal monomer are equal.

2. The method for preparing a thermotropic liquid crystal polymer according to claim 1, characterized in that: The aromatic hydroxycarboxyl monomer is at least one of p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid; The aromatic diol monomer is at least one of hydroquinone, 4,4'-biphenylene glycol, and 2,6-naphthalene diol; The aromatic dicarboxylic acid monomer is at least one of terephthalic acid, 2,6-naphthalene dicarboxylic acid, 4,4'-biphenyl dicarboxylic acid and isophthalic acid.

3. The method for preparing a thermotropic liquid crystal polymer according to claim 1, characterized in that: In terms of molar fractions, in the aromatic liquid crystal monomers, the aromatic hydroxycarboxyl monomer accounts for 50-100 parts, the aromatic diol monomer accounts for 0-25 parts, and the aromatic dicarboxylic acid monomer accounts for 0-25 parts.

4. The method for preparing a thermotropic liquid crystal polymer according to claim 1, characterized in that: The catalyst is at least one of potassium acetate, sodium acetate, zinc acetate and magnesium acetate.

5. The method for preparing a thermotropic liquid crystal polymer according to claim 1, characterized in that: The amount of the catalyst used is 0.01% to 0.5% of the total mass of the aromatic liquid crystal monomer; the amount of acetic anhydride used is 1.05 to 1.3 times the molar amount of all hydroxyl groups in the aromatic liquid crystal monomer.

6. The method for preparing a thermotropic liquid crystal polymer according to claim 1, characterized in that: The acetylation reaction temperature of step S1 is 140-150° C., and the acetylation reaction time is 2-5 hours.

7. The method for preparing a thermotropic liquid crystal polymer according to claim 1, characterized in that: The melt polymerization reaction temperature of step S3 is 300°C~340°C. The reaction is first carried out under inert gas conditions for 1-3 hours until no liquid flows out of the condenser. The vacuum condition is then changed to a vacuum degree of 0.01~1kPa for 1~3 hours.

8. The method for preparing a thermotropic liquid crystal polymer according to claim 1, characterized in that: The solid phase polymerization reaction temperature of step S4 is (T m -80)℃~(T m -40)℃, T m is the melting temperature of the thermotropic liquid crystal polymer, and the solid phase polymerization reaction time is 4-24h.

9. The method for preparing a thermotropic liquid crystal polymer according to claim 8, characterized in that: The melting temperature T of the thermotropic liquid crystal polymer m The temperature of the thermotropic liquid crystal polymer is 300-360°C, and the thermal decomposition temperature of the thermotropic liquid crystal polymer is greater than 500°C.

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