A thermotropic liquid crystal polyester compound and a preparation method thereof

Abstract

The present invention discloses a thermotropic liquid crystal polyester compound, belonging to the field of special engineering plastics. This thermotropic liquid crystal polyester compound has a structure containing a five-membered ring imide structural unit as shown in the general structural formula (I), where n is a positive integer in formula (I); the structure containing the five-membered ring imide structural unit is obtained by polymerizing diacid-type monomers; the diacid-type monomers have a structure as shown in (II). The main chain of this thermotropic liquid crystal polyester compound contains a five-membered ring imide structural unit, and it is a thermotropic liquid crystal polyester with high melt strength and viscosity, solving the problem of difficult thermal processing caused by the high melt index and low melt strength of common thermotropic liquid crystal polyesters. The introduction of the five-membered ring imide unit can increase the melting temperature of the thermotropic liquid crystal polyester compound, improve the heat resistance, and can ensure that the tensile strength does not decrease while increasing the tensile toughness of the material, that is, the elongation at break.

Description

Technical Field

[0001] The present invention belongs to the field of special engineering plastics, and particularly relates to a thermotropic liquid crystal polyester compound and a preparation method thereof. Background Art

[0002] With the popularization of the fifth-generation communication technology (5G), the signal processing and transmission frequencies of electronic devices have increased rapidly, posing requirements for the flexible circuit substrates used for signal transmission to have a low dielectric constant (D k ) and a low dielectric loss tangent (D f ). Thermotropic liquid crystal polymers (TLCPs) have excellent dielectric properties, low moisture absorption, dimensional stability, etc. After being processed into films, they have low losses under high-frequency signal transmission conditions as flexible circuit board substrates and have become the mainstream of high-frequency communication substrates. Processing TLCPs into films requires them to have a certain melt strength and viscosity to ensure a high draw ratio during melting.

[0003] However, due to the rod-like rigid monomer structure of existing TLCPs, for example, the Chinese invention patent with the publication number CN101497796A discloses a thermotropic liquid crystal polymer and a preparation method thereof for a non-adhesive substrate coil, which is formed by rigid rod-like macromolecular chains and is melted by heating. The intermolecular force of its polymer molecules is weak, and there is less intermolecular entanglement. The melt viscosity and melt strength are often low, and it is easy to crystallize and orient along the die extrusion direction, bringing difficulties to the key biaxial stretching stage in the film drawing process, which is the main reason why it is difficult to improve the quality of TLCP films. Therefore, it is necessary to develop a new structure of thermotropic liquid crystal polymer that can have higher melt strength and viscosity to solve the processing problems of TLCP films. Summary of the Invention

[0004] The purpose of the present invention is to provide a thermotropic liquid crystal polyester compound that can improve the melt strength and viscosity to solve the processing problems of TLCP films.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A thermotropic liquid crystal polyester compound has a structure containing a five-membered ring imide structural unit as shown in the structural general formula (I),

[0007]

[0008] In formula (I), n is a positive integer;

[0009] The structure containing the five-membered ring imide structural unit is obtained by polymerizing diacid-type monomers; the diacid-type monomers have the structure shown in (II),

[0010]

[0011] In formulas (I) and (II), A represents a group containing an aromatic ring or a group containing an alicyclic ring. The group containing an aromatic ring is one of the following structures:

[0012]

[0013] The group containing an alicyclic ring is one of the following structures: The Ar 1 is a group containing a benzene ring.

[0014] The thermotropic liquid crystal polyester compound of the present invention contains a structural unit with a five-membered ring imide structure shown in the general structural formula (I) in its structural unit. The imide monomer exists in the diacid monomer. The structure of this five-membered ring imide has a relatively large polarity and high stability. Aryl imides are prone to form π-π stacking, increasing the friction inside the molecular chain during the melting process, improving the rheological viscosity and melt strength. Moreover, the molecular chain containing imide has relatively large mobility and is more likely to undergo spatial entanglement, maintaining a certain strength in the molten state. This thermotropic liquid crystal polyester compound can compensate for the processing disadvantages of low melt strength and melt viscosity brought by the linear structure of liquid crystal polyester.

[0015] Furthermore, in formulas (I) and (II), the Ar 1 and the group formed with the carboxyl group -COOH is an amino aromatic acid, and the amino aromatic acid is one of the following structures or any combination thereof:

[0016] Furthermore, the molecular weight of the thermotropic liquid crystal polyester compound is 100,000 - 600,000 g / mol. Based on 100 mol% of the total amount of repeating units, the number of repeating units N1 containing 1,4-phenylene and 2,6-naphthylene is: 50 mol% - 80 mol%; the number of repeating units N2 containing 1,3-phenylene, 1,4-phenylene or 4,4'-biphenylene is 10 mol% - 25 mol%; the number of repeating units N3 containing repeating units with imide units and 1,4-phenylene is 10 mol% - 25 mol%, and the repeating units are only connected by an ester bond (-(C=O)-O-).

[0017] Preferably, based on 100 mol% of the total amount of repeating units, the thermotropic liquid crystal polyester compound contains repeating units of 1,4-phenylene and 2,6-naphthylene with the number N1 being 60 mol% to 70 mol%; contains repeating units of 1,3-phenylene, 1,4-phenylene or 4,4'-biphenylene with the number N2 being 10 mol% to 15 mol%, and contains repeating units of 1,3-phenylene or 1,4-phenylene with the number N3 being 10 mol% to 15 mol%.

[0018] The present invention provides a method for preparing the above thermotropic liquid crystal polyester compound, comprising the following steps:

[0019] P1. Performing an acetylation reaction on the hydroxyl-containing aromatic monomer and acetic anhydride;

[0020] P2. Performing a melt polycondensation reaction on the reactant after the acetylation reaction and the above dicarboxylic acid monomer to obtain the thermotropic liquid crystal polyester compound.

[0021] Further, in step P1, the hydroxyl-containing aromatic monomer is one or more of 4-hydroxybenzoic acid (HBA), 2-hydroxy-6-naphthoic acid (HNA), resorcinol, hydroquinone, 4,4'-biphenol.

[0022] Further, in step P1, the hydroxyl-containing aromatic monomer further includes terephthalic acid and / or isophthalic acid.

[0023] Further, the conditions for the acetylation reaction in step P1 are: the initial operating temperature of the reaction is 80°C to 120°C, the heating rate is 1.0 to 1.5°C / min, and nitrogen is used to purge the by-products acetic acid and acetic anhydride generated during the acetylation reaction; in the polyaddition stage of step P2, the temperature is between T1 and T2, the heating rate is 0.5 to 0.8°C / min, and when the temperature reaches T2, a vacuum pump is used to pump to a negative pressure in the kettle to remove the remaining trace amounts of acetic acid and acetic anhydride again; wherein, T1 satisfies: T1 = the lowest melting point of the raw material monomers, and T2 satisfies: T2 = the designed melting temperature of the target product + 20°C.

[0024] Further, in step P1, the conditions for the acetylation reaction are: performing the acetylation reaction on the hydroxyl-containing aromatic monomer and acetic anhydride at 120 to 140°C under the catalysis of concentrated sulfuric acid.

[0025] Preferably, the concentration of the concentrated sulfuric acid is 1 mol%.

[0026] Further, the molar ratio of acetic anhydride to the total amount of hydroxyl groups in the hydroxyl-containing aromatic monomer in step P1 is 1.01 to 1.08:1.

[0027] Preferably, the molar ratio of acetic anhydride to the total amount of hydroxyl groups in the hydroxyl-containing aromatic monomer in step P1 is 1.02 to 1.05:1.

[0028] Further, the reaction product of step P2 is pressed out by introducing nitrogen gas.

[0029] Further, in step P2, the reaction kettle is evacuated to a negative pressure with a vacuum pump, and the vacuum degree after the negative pressure is 10 KPa to 100 Pa.

[0030] Preferably, in step P2, the reaction kettle is evacuated to a negative pressure with a vacuum pump, and the vacuum degree is reduced to 20 KPa to 20 Pa within 0.5 - 2 h.

[0031] The present invention provides a preparation method of the above - mentioned diacid - type monomer, comprising the following steps:

[0032] S1. A tetra - acid anhydride represented by the structural formula (III) and a carboxyl - substituted aromatic amine are dispersed in a polar solvent for a condensation reaction, and the carboxyl - substituted aromatic amine is combined with the tetra - acid anhydride through an amino group;

[0033]

[0034] The group represented by A in formula (III) is the same as the group represented by A in formula (II); the carboxyl - substituted aromatic amine is selected from the above - mentioned amino - aromatic acids;

[0035] S2. Under the conditions of a dehydrating agent and a catalyst, after the carboxyl - substituted aromatic amine is combined with the tetra - acid anhydride, an acyl - transfer reaction occurs to remove water, and a thermotropic liquid - crystal monomer compound is obtained.

[0036] Further, the conditions of the condensation reaction in step S1 are a temperature of 0 - 5 °C and stirring and mixing for 2 - 10 h.

[0037] Further, the polar solvent in step S1 is selected from N, N - dimethylacetamide, N, N - dimethylformamide, N - methylpyrrolidone, dimethyl sulfoxide, acetone, and acetonitrile.

[0038] Further, the molar ratio of the tetra - acid anhydride to the carboxyl - substituted aromatic acid in step S1 is 2.5 - 2.05:1.

[0039] Preferably, the molar ratio of the tetra - acid anhydride to the carboxyl - substituted aromatic acid in step S1 is 2.2 - 2.05:1.

[0040] Further, the dehydrating agent in step S2 is selected from acetic anhydride, propionic anhydride, oxalyl chloride, acetyl chloride, phosphorus oxychloride, phosphorus trichloride, phosphorus pentachloride, and thionyl chloride.

[0041] Further, the molar ratio of the dehydrating agent to the tetra - acid anhydride in step S2 is 2.5 - 2.05:1.

[0042] Preferably, the molar ratio of the dehydrating agent to the tetracarboxylic dianhydride in step S2 is 2.2 - 2.1:1.

[0043] Further, the catalyst in step S2 is selected from triethylamine, tributylamine, triisopropylamine, diethylamine, diisopropylamine, 4-dimethylaminopyridine, pyridine, 2-dimethylpyridine, 4-tert-butylpyridine, imidazole, pyrazole, quinoline, isoquinoline, benzimidazole, benzothiazole, carbazole, quinine.

[0044] Further, the molar ratio of the catalyst to the dehydrating agent in step S2 is 0.05 - 1.05:1.

[0045] Preferably, the molar ratio of the catalyst to the dehydrating agent in step S2 is 0.1 - 0.5:1.

[0046] Further, the reaction conditions for the acyl transfer reaction in step S2 are: heating to 80 - 150 °C and reacting for 0.5 - 2 h.

[0047] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0048] (1) The present invention provides a thermotropic liquid crystal polyester compound, which is obtained by polymerizing a diacid monomer containing a five-membered ring imide structure. The obtained thermotropic liquid crystal polyester compound has high melt strength and viscosity, solving the problem of difficult thermal processing caused by high melt index and low melt strength of common thermotropic liquid crystal polyesters.

[0049] (2) The introduction of a five-membered ring imide unit into the thermotropic liquid crystal polyester compound of the present invention significantly increases the melting temperature of the thermotropic liquid crystal polyester compound, improves the heat resistance, and can ensure that the tensile strength does not decrease while increasing the tensile toughness of the material, that is, the elongation at break. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is the appearance diagram of the thermotropic liquid crystal polyester compound prepared in Example 1 of the present invention.

[0051] Figure 2 It is the test result of the differential scanning calorimeter in Example 1 of the present invention.

[0052] Figure 3 It is the test dumbbell strip for preparing the compound material sample of the present invention.

[0053] Figure 4 It is the stress-strain test curve of the thermotropic liquid crystal polyester compound prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0054] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0055] Example 1

[0056] (1) Preparation of diacid monomer (Monomer 1)

[0057] A diacid monomer compound has a chemical structure shown in Formula (Ⅲ-1):

[0058]

[0059] The preparation method of the above thermotropic liquid crystal monomer compound includes the following steps:

[0060] S1. The tetracarboxylic anhydride with the structural formula shown in Formula (Ⅱ) and the carboxyl-substituted aromatic amine are dispersed in a polar solvent for condensation reaction. Among them, there are 100 mole parts of tetracarboxylic anhydride, 210 mole parts of carboxyl-substituted aromatic amine, and 3000 mole parts of polar solvent. The polar solvent is N,N-dimethylacetamide. The conditions for the condensation reaction are at a temperature of 0°C and stirring for 2 hours;

[0061]

[0062] The group represented by A in Formula (Ⅱ) is: phenyl, that is, the chemical structure of the tetracarboxylic anhydride is shown in Formula (Ⅳ):

[0063]

[0064] The carboxyl-substituted aromatic amine is shown in Formula (Ⅴ):

[0065]

[0066] S2. Under the conditions of a dehydrating agent and a catalyst, the carboxyl-substituted aromatic amine reacts with the tetracarboxylic anhydride to undergo an acyl transfer reaction to remove water. Among them, the dehydrating agent is 210 mole parts of acetic anhydride, and the catalyst is 20 mole parts of triethylamine. The reaction conditions for the acyl transfer reaction are: heating to 80°C and reacting for 2 hours. After the reaction, it is poured into an ethanol solution to precipitate a solid, and then the solid is filtered and dried at 80°C to obtain the target monomer 1.

[0067] The chemical reactions involved in the above preparation method are as follows:

[0068]

[0069] The 1H NMR detection result of formula (Ⅲ-1) is as follows: (400 MHz, DMSO-d6): δ 13.20 (br, 2H,), 8.77 (s, 2H), 8.34 (d, 4H), 7.66 (d, 4H), and the yield is: 96%.

[0070] (2) Synthesis of thermotropic liquid crystal polyester compound

[0071] A thermotropic liquid crystal polyester compound, and its preparation method includes the following steps:

[0072] P1. Carry out acetylation reaction on the hydroxyl-containing aromatic monomer and acetic anhydride; the hydroxyl-containing aromatic monomer is 4-hydroxybenzoic acid (HBA), 2-hydroxy-6-naphthoic acid (HNA) and hydroquinone. The conditions of the acetylation reaction are as follows: the initial operating temperature of the reaction is 140 °C to T1, where T1 is 330 °C; the heating rate is 1.0 - 1.5 °C / min, and in the reaction stage, nitrogen is used to purge the by-products acetic acid and acetic anhydride generated by the reaction; in the polyaddition stage, the temperature is between T1 and T2, and the heating rate is 0.5 - 0.8 °C / min. In the reaction stage, the vacuum pump is used to pump to a negative pressure in the kettle to remove the remaining trace acetic acid and acetic anhydride again; among them, T1 satisfies: T1 = the melting temperature of the target product - 10 °C, T2 satisfies: T2 = the melting temperature of the target product + 20 °C, T2 is 360 °C, and the melting temperature of the target product is 340 °C.

[0073] The conditions of the acetylation reaction are as follows: The hydroxyl-containing aromatic monomer and acetic anhydride are subjected to acetylation reaction at 120 - 140 °C under the catalysis of 1 mol% concentrated sulfuric acid. Preferably, the acetylation reaction temperature in this example is 120 °C. The molar ratio of acetic anhydride to the total amount of hydroxyl groups in the hydroxyl-containing aromatic monomer is 1.01 - 1.08:1. Preferably, the molar ratio in this example is 1.05:1.

[0074] P2. Carry out polycondensation reaction on the reactant after the acetylation reaction and monomer 1. The molar percentage contents of the above-mentioned hydroxyl-containing aromatic monomer, i.e., 4-hydroxybenzoic acid (HBA), 2-hydroxy-6-naphthoic acid (HNA), hydroquinone and monomer 1 are: 65%, 25%, 5% and 5% respectively. In the polyaddition stage, the decompression reaction is started, and the vacuum degree is reduced to 20 KPa - 20 Pa within 0.5 - 2 h. Preferably, the time is 2 h and the vacuum degree is reduced to 50 Pa. After the reaction is completed, the reaction product is extruded by introducing nitrogen gas, and the obtained thermotropic liquid crystal polyester compound is as Figure 1 shown.

[0075] The molecular weight of the thermotropic liquid crystal polyester compound was measured to be 326,000 g / mol using a capillary rheometer. Based on a total of 100 mol% of the repeating units, the number of repeating units N1 containing 1,4-phenylene and 2,6-naphthylene was: 90 mol%; the number of repeating units N2 containing 1,3-phenylene, 1,4-phenylene or 4,4'-biphenylene was 5 mol%; and the number of repeating units N3 containing repeating units with imide units and 1,4-phenylene was 5%.

[0076] Example 2

[0077] A thermotropic liquid crystal polyester compound, the preparation method of which is the same as that of Example 1, except that the molar percentage contents of the hydroxy aromatic monomers 4-hydroxybenzoic acid (HBA), 2-hydroxy-6-naphthoic acid (HNA), hydroquinone and monomer 1 are: 60%, 20%, 10% and 10% respectively.

[0078] The molecular weight of the thermotropic liquid crystal polyester compound was measured to be 228,000 g / mol using a capillary rheometer. Based on a total of 100 mol% of the repeating units, the number of repeating units N1 containing 1,4-phenylene and 2,6-naphthylene was: 80 mol%; the number of repeating units N2 containing 1,3-phenylene, 1,4-phenylene or 4,4'-biphenylene was 10 mol%; and the number of repeating units N3 containing repeating units with imide units and 1,4-phenylene was 10%.

[0079] Example 3

[0080] A thermotropic liquid crystal polyester compound, the preparation method of which is the same as that of Example 1, except that the specific ratio of monomer 1 is different, and the specific ratio is shown in Table 2.

[0081] The molecular weight of the thermotropic liquid crystal polyester compound was measured to be 291,000 using a capillary rheometer. Based on a total of 100 mol% of the repeating units, the number of repeating units N1 containing 1,4-phenylene and 2,6-naphthylene was: 40 mol%; the number of repeating units N2 containing 1,3-phenylene, 1,4-phenylene or 4,4'-biphenylene was 20 mol%; and the number of repeating units N3 containing repeating units with imide units and 1,4-phenylene was 20%.

[0082] Example 4

[0083] A thermotropic liquid crystal polyester compound, the preparation method of which is the same as that of Example 1, except that the specific monomer 2 and the ratio are different, and the specific ratio is shown in Table 2. The molecular weight of the thermotropic liquid crystal polyester compound is tested by a capillary rheometer to be 335000 g / mol. Based on the total amount of repeating units of 100 mol%, the number of repeating units N1 containing 1,4-phenylene and 2,6-naphthylene is: 80 mol%; the number of repeating units N2 containing 1,3-phenylene, 1,4-phenylene or 4,4'-biphenylene is 10 mol%; the number of repeating units N3 containing repeating units with imide units and 1,4-phenylene is 10%.

[0084] Monomer 2 has a chemical structure as shown in formula (Ⅲ-2):

[0085]

[0086] The preparation method of monomer 2 refers to Example 1, the difference is: using 100 parts of tetracarboxylic dianhydride and 210 parts of carboxyl-substituted aromatic amine are dispersed in 3000 parts of polar solvent N,N-dimethylacetamide, and condensation reaction is carried out with stirring at 0 °C for 2 h. Then 210 parts of dehydrating agent acetic anhydride and 25 parts of catalyst triethylamine are added, and the temperature is raised to 80 °C for reaction for 2 h. After the reaction is completed, it is poured into an ethanol solution to precipitate a solid, and then the solid is filtered and dried at 80 °C to obtain a thermotropic liquid crystal monomer compound, which is monomer 2 of the synthesis target.

[0087] The 1H NMR detection result of formula (Ⅲ-2) is: (400 MHz, DMSO-d6): δ 13.17 (br, 2H,), 8.50 (s, 2H), 8.44 (d, J = 7.1 Hz, 2H), 8.15 (d, J = 7.1 Hz, 2H), 8.13 (d, J = 7.8 Hz, 4H), 7.66 (d, J = 2 Hz, 4H), and the 1H NMR is as Figure 2 shown, and the yield is: 91%.

[0088] Example 5

[0089] A thermotropic liquid crystal polyester compound, the preparation method of which is the same as that of Example 1, except that the specific monomer 3 and the ratio are different, and the specific ratio is shown in Table 2.

[0090] The molecular weight of the thermotropic liquid crystal polyester compound was measured by a capillary rheometer to be 255,000 g / mol. Based on a total of 100 mol% of the repeating units, the number of repeating units N1 containing 1,4-phenylene and 2,6-naphthylene was 60 mol%; the number of repeating units N2 containing 1,3-phenylene, 1,4-phenylene or 4,4'-biphenylene was 20 mol%; and the number of repeating units N3 containing repeating units with imide units and 1,4-phenylene was 10%.

[0091] Monomer 3 has a chemical structure as shown in formula (Ⅲ-3):

[0092]

[0093] For the preparation method of the above thermotropic liquid crystal monomer compound, referring to Example 1, the difference is that 100 parts of tetracarboxylic dianhydride and 210 parts of carboxy-substituted aromatic amine were dispersed in 3000 parts of polar solvent N-methylpyrrolidone, and condensation reaction was carried out with stirring at 0 °C for 6 h. Then 210 parts of dehydrating agent acetic anhydride and 30 parts of catalyst triethylamine were added, and the temperature was raised to 100 °C for reaction for 4 h. After the reaction was completed, it was poured into an ice ethanol solution to precipitate a solid, and then the solid was filtered and dried at 80 °C to obtain the thermotropic liquid crystal monomer compound, which is monomer 3 as the synthesis target.

[0094] The 1H NMR detection result of formula (Ⅲ-3) is: 1H NMR (600 MHz, DMSO-d6): δ 8.21 (t, J = 10.3 Hz, 4H), 8.10 (d, J = 8.6 Hz, 2H), 7.99 (d, J = 8.1 Hz, 2H), 7.78 (s, 2H), 7.63 - 7.58 (m, 4H), and the yield is 95%.

[0095] Example 6

[0096] A thermotropic liquid crystal polyester compound, the preparation method of which is the same as that of Example 1, the difference is that the specific monomer 4 and its ratio are different, and the specific ratio is shown in Table 2.

[0097] The molecular weight of the thermotropic liquid crystal polyester compound was measured by a capillary rheometer to be 207,000 g / mol. Based on a total of 100 mol% of the repeating units, the number of repeating units N1 containing 1,4-phenylene and 2,6-naphthylene was 80 mol%; the number of repeating units N2 containing 1,3-phenylene, 1,4-phenylene or 4,4'-biphenylene was 10 mol%; and the number of repeating units N3 containing repeating units with imide units and 1,4-phenylene was 10%.

[0098] Monomer 4 has a chemical structure as shown in formula (Ⅲ-4):

[0099]

[0100] The preparation method of the above-mentioned thermotropic liquid crystal monomer compound is referred to Example 5, with the difference that: the tetracarboxylic dianhydride is The carboxyl-substituted aromatic amine is The thermotropic liquid crystal monomer compound is obtained, which is the monomer 4 of the synthesis target.

[0101] The preparation methods of monomers 5 - 15 are as follows:

[0102] The chemical structure of monomer 5 is shown in formula (Ⅲ-5):

[0103]

[0104] The preparation method of the above-mentioned thermotropic liquid crystal monomer compound is referred to Example 1, with the difference that: 100 parts of tetracarboxylic dianhydride and 210 parts of carboxyl-substituted aromatic amine are dispersed in 3000 parts of polar solvent N-methylpyrrolidone, and stirred and condensed at 0°C, and the reaction time is 2 h. Then 210 parts of dehydrating agent and 25 parts of catalyst are added. According to actual needs, the dehydrating agent can also be replaced with other dehydrating agents such as propionic anhydride, oxalyl chloride, acetyl chloride, phosphorus oxychloride, phosphorus trichloride, phosphorus pentachloride, thionyl chloride; other catalysts such as tributylamine, triisopropylamine, diethylamine, diisopropylamine, 4-dimethylaminopyridine, pyridine, 2-dimethylpyridine, 4-tert-butylpyridine, imidazole, pyrazole, quinoline, isoquinoline, benzimidazole, benzothiazole, carbazole, quinine can also be used. Then the temperature is raised to 80°C and the reaction is carried out for 2 h. After the reaction is completed, it is poured into an ethanol solution to precipitate a solid, and then the solid is filtered and dried at 80°C to obtain the thermotropic liquid crystal monomer compound, which is the monomer 5 of the synthesis target.

[0105] The chemical structures of monomers 6 - 15 are shown in Table 1. Their preparation refers to the preparation of monomer 3 in Example 5. The chemical structures of the monomers, the required tetracarboxylic dianhydrides, carboxyl-substituted aromatic amines and yields are shown in detail in Table 1.

[0106] Table 1 Monomer synthesis raw materials and yields

[0107]

[0108]

[0109] Comparative Examples 1 - 2

[0110] The preparation method is the same as that in Example 1, with the difference that the types and contents of monomers are different, as shown in Table 2 specifically.

[0111] Experimental Example 1 Performance evaluation of thermotropic liquid crystal polyester compound

[0112] 1. Experimental methods

[0113] (1) Melting temperature measurement

[0114] Measured by a differential scanning calorimeter of model METTLER DSC ONE, heating from 50°C to 400°C at a heating rate of 20°C / min, staying at this temperature for 3 min and then cooling to room temperature at a rate of 20°C / min. The test sample stays at 50°C for 3 min and then heats up to 400°C again at a heating rate of 20°C / min to obtain the second melting curve of the polyester compound, and the melting peak value is selected as the melting temperature. The test standard refers to GB / T 1634-2004.

[0115] (2) Melt index measurement

[0116] The melt mass flow rate MFR of the plastic melt was measured using a melt indexer of model HT-3682MV-RL. The test standard is ATSM D238 or GB / T3682.1-2018. The electric loading weight was used, and the test temperature was 20°C above the melting temperature. The standard orifice diameter of 2.1 mm was used.

[0117] (3) Tensile strength, tensile modulus and elongation at break measurement

[0118] The thermotropic liquid crystal polyester compound was made into dumbbell-shaped test specimens using an injection molding machine, as Figure 3 shown. The tensile strength, tensile modulus and elongation at break of the specimens were tested using a universal material testing machine. The test standard refers to GBT 1040.1-2018.

[0119] Among them, the samples used in the above order were the thermotropic liquid crystal polyester compounds prepared in Examples 1-6 and Comparative Examples 1-2 respectively.

[0120] 2. Experimental results

[0121] As can be seen from Example 1 in Table 2, when the proportion of imide units is 5%, the melt index drops to 16 - 18 g / 10 min. Compared with the melt index of 23 - 25 g / 10 min in Comparative Example 2, the viscosity of the melt increases significantly. Examples 2 - 6 show that except for fluorine-containing imide units, when the molar content of imide units is greater than or equal to 10%, the melt index of the prepared thermotropic liquid crystal polyester is ≤ 12 g / 10 min. Examples 2 and 6 are the most preferred proportions for melt viscosity. The melt index of the thermotropic liquid crystal polyester containing fluorine-containing imide units in Example 5 is higher than others, and the melt flow rate is faster, but the viscosity is higher than that of Comparative Examples 1 and 2 which contain no imide units at all. By using a diacid monomer containing a five-membered ring imide structure and introducing imide units into the structure of the thermotropic liquid crystal polyester compound, the melting temperature of the thermotropic liquid crystal polyester can be increased, and the heat resistance can be improved. As can be seen from Examples 1 to 6, the melting temperature generally increases. When 10% of monomer 1 is added, the melting temperature increases by 15 °C compared with Comparative Example 1. When 30% of monomer 1 is added, it increases significantly by 25 °C. In Example 6, when 10% of monomer 4 containing both naphthalene and imide units is added, the heat resistance temperature reaches 355 °C, which is the most optimal proportion for heat resistance. Introducing imide units into the structural unit of the thermotropic liquid crystal polyester compound can ensure that the tensile strength does not decrease while increasing the tensile toughness of the material, that is, the elongation at break. As Figure 4 Figure 1 shows the stress and strain test curves of Example 1. The stress and strain results of each material are summarized in Table 3. As can be seen from Examples 1 - 6 in Table 3, the tensile strength is about 200 MPa, with extremely small differences from Comparative Examples 1 and 2. When the molar content of imide units exceeds 10%, the elongation at break is generally above 13%, up to 22% at most, which is significantly higher than that of the thermotropic liquid crystal polyester without imide units (2% - 3%), providing a prerequisite for the cold drawing processing.

[0122] Table 2 Influence of monomer ratio of thermotropic liquid crystal polyester compound on thermal properties

[0123]

[0124]

[0125] Table 3 Influence of monomer ratio of thermotropic liquid crystal polyester compound on mechanical properties

[0126]

[0127]

[0128] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A thermotropic liquid crystal polyester compound, characterized in that: It has a structure containing a five-membered cyclic imide structural unit as shown in the general structural formula (I), In formula (I), n is a positive integer; The structure containing the five-membered cyclic imide structural unit is obtained by polymerizing a diacid-type monomer; the diacid-type monomer has a structure as shown in (II), In formula (I) and (II), A represents a group containing an aromatic ring or a group containing an aliphatic ring, and the group containing an aromatic ring is one of the following structures: The group containing an aliphatic ring is one of the following structures: The Ar 1 is a group containing a benzene ring; The molecular weight of the thermotropic liquid crystal polyester compound is 100000-600000 g / mol. Based on 100 mol% of the total amount of repeating units, the number of repeating units N1 containing 1,4-phenylene and 2,6-naphthylene is 50 mol%-80 mol%; the number of repeating units N2 containing 1,3-phenylene, 1,4-phenylene or 4,4'-biphenylene is 10 mol%-25 mol%; the number of repeating units N3 containing imide units and 1,4-phenylene is 10 mol%-25 mol%, and the repeating units are connected only by ester bonds. The preparation of the thermotropic liquid crystal polyester compound comprises the following steps: P1. Acetylation of a hydroxyl-containing aromatic monomer with acetic anhydride; P2. The reactant after the acetylation reaction is reacted with the diacid monomer in a melt polycondensation reaction to obtain a thermotropic liquid crystal polyester compound; In step P1, the hydroxyl-containing aromatic monomer is one or more of 4-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, resorcinol, hydroquinone, and 4,4'-biphenol; The hydroxyl-containing aromatic monomer further comprises terephthalic acid and / or isophthalic acid.

2. The thermotropic liquid crystal polyester compound according to claim 1, characterized in that: In formula (I) and (II), Ar 1 The group formed with the carboxyl group -COOH is an amino aromatic acid, and the amino aromatic acid is one of the following structures or any combination thereof:

3. The thermotropic liquid crystal polyester compound according to claim 1, characterized in that: The conditions of the acetylation reaction in step P1 are as follows: the reaction starting operating temperature is 80°C to 120°C, the heating rate is 1.0 to 1.5°C / min, and the by-products acetic acid and acetic anhydride produced by the reaction are purged with nitrogen during the reaction stage; the temperature during the addition polymerization stage is between T1 and T2, the heating rate is 0.5 to 0.8°C / min, and the reaction stage is evacuated to a negative pressure in the kettle by a vacuum pump to remove the residual trace acetic acid and acetic anhydride again; wherein, T1 satisfies: T1=the lowest melting point of the raw material monomer, and T2 satisfies: T2=the designed melting temperature of the target product+20°C.

4. The thermotropic liquid crystal polyester compound according to claim 1, characterized in that: In the step P1, the acetylation reaction is carried out under the conditions of: acetylation of the hydroxyl-containing aromatic monomer and acetic anhydride at 120-140° C. under the catalysis of concentrated sulfuric acid.

5. The thermotropic liquid crystal polyester compound according to claim 4, characterized in that: The molar ratio of the acetic anhydride to the total hydroxyl groups in the hydroxyl-containing aromatic monomer in step P1 is 1.01-1.08:

1.

6. The thermotropic liquid crystal polyester compound according to claim 1, characterized in that: The preparation method of the diacid type monomer comprises the following steps: S1. dispersing a tetraanhydride having a structural formula as shown in formula (III) and a carboxyl-substituted aromatic amine in a polar solvent for condensation reaction, and combining the carboxyl-substituted aromatic amine with the tetraanhydride via an amino group; The group represented by A in formula (III) is the same as the group represented by A in formula (II) in claim 1; the carboxyl-substituted aromatic amine is selected from the amino aromatic acid described in claim 2; S2. Under the conditions of a dehydrating agent and a catalyst, the carboxyl-substituted aromatic amine is combined with tetraanhydride to undergo an acyl transfer reaction to remove water, thereby obtaining a thermotropic liquid crystal monomer compound.

Images