Liquid crystal polymer as well as preparation method and application thereof

Abstract

The invention relates to the technical field of high polymer materials, and relates to a preparation method of a liquid crystal polymer. The preparation method specifically comprises the following steps: mixing p-hydroxybenzoic acid, 2, 5-di-tert-butylhydroquinone, 2, 2 '-hydroxy-9, 9'-spirobifluorene, terephthalic acid, an acylation reagent and a catalyst according to a specific ratio to obtain a reaction mixture; carrying out a prepolymerization reaction on the reaction mixture to obtain a prepolymer; and performing solid-phase polycondensation reaction on the prepolymer in an inert gas atmosphere to obtain the liquid crystal polymer. A proper amount of spirobifluorene structure is introduced to a molecular chain, so that the crystallization speed of the liquid crystal polymer can be properly slowed down, and the cooling speed of a liquid crystal polymer melt can be effectively reduced, so that the weld mark strength of the liquid crystal polymer is improved while the tensile strength of the liquid crystal polymer is ensured; meanwhile, the highly symmetrical biphenyl structure is matched with other molecular structures, so that the thermal stability and processability of the liquid crystal polymer can be further improved.

Description

Technical Field

[0001] The invention belongs to the field of organic polymer materials, and in particular relates to a liquid crystal polymer and a preparation method and application thereof. Background Art

[0002] With the rapid development of the manufacturing industry, China's automobile industry is facing the challenges of industrial transformation, emission reduction, energy crisis and low-carbon development. The development of new energy vehicles has become the only way to reduce the automobile industry's dependence on oil and exhaust pollution. Since the engine, gearbox and other components of new energy vehicles have become batteries, motors, electronic controls and reducers, their thermal management systems mainly include four parts: battery thermal management system, automobile air conditioning system, motor electronic control cooling system, and reducer cooling system. The main function of the thermal management system is to ensure that different parts can work at a suitable temperature through heat dissipation, heating, and heat preservation to ensure the functional safety and service life of the vehicle. Due to being in a high temperature environment for a long time, it is also necessary to resist possible deformation, cracking, etc., which puts forward more stringent requirements on the processing performance, mechanical properties, thermal stability and other aspects of the thermal management system component materials.

[0003] At present, most thermal management system components are made of polypropylene. Although polypropylene has the advantages of low relative density, low price, and good processing performance, it also has many defects. For example, the molecular chain of polypropylene is very flexible, which makes the polypropylene material have low tensile strength, low weld mark strength, poor heat resistance and other problems. It cannot meet the application requirements of high-performance automotive thermal management system parts.

[0004] Liquid crystal polymer is a kind of high molecular polymer composed of rigid molecular chains, which has liquid crystal properties under certain conditions. Its molecular arrangement tends to be orderly, which makes it have the advantages of high strength, high rigidity, thermal stability, high temperature resistance, etc. It has great potential for use as a material for thermal management system components. However, liquid crystal polymer molecules are very easy to cool and crystallize rapidly during the cooling process, resulting in different degrees of orientation and crystallinity in various directions, resulting in poor strength of the weld mark of the product, and the product is prone to deformation or cracking when subjected to external pressure, which is not conducive to the safety of the thermal management system. Based on this, the inventor tried to design the liquid crystal polymer molecular chain in order to obtain a liquid crystal polymer material with excellent mechanical properties, processing properties, and thermal stability that can be used for automotive thermal management system components. Summary of the invention

[0005] In order to solve the technical problem that conventional liquid crystal polymers cannot take into account mechanical properties, processing properties, and thermal stability, a liquid crystal polymer and a preparation method thereof are provided. The liquid crystal polymer is obtained by polymerizing p-hydroxybenzoic acid, 2,5-di-tert-butylhydroquinone, 2,2'-hydroxy-9,9'-spirobifluorene, and terephthalic acid in a specific ratio under the action of an acylating agent and a catalyst, wherein an appropriate amount of spirobifluorene structure is introduced into the molecular chain, which can not only slow down the crystallization speed of the liquid crystal polymer appropriately, but also effectively reduce the cooling speed of the liquid crystal polymer melt, thereby ensuring the tensile strength of the liquid crystal polymer while improving its weld mark strength; at the same time, its highly symmetrical biphenyl structure can further improve the thermal stability and processability of the liquid crystal polymer in combination with other molecular structures.

[0006] In order to achieve the above object, the present invention is implemented by the following technical scheme: a method for preparing a liquid crystal polymer, which comprises the following preparation steps:

[0007] S1: four monomers, p-hydroxybenzoic acid, 2,5-di-tert-butylhydroquinone, 2,2'-hydroxy-9,9'-spirobifluorene, terephthalic acid, an acylating agent, and a catalyst are mixed to obtain a reaction mixture; wherein, in terms of molar percentage, the proportion of each monomer in the four monomers is as follows: p-hydroxybenzoic acid 30-48 mol%, 2,5-di-tert-butylhydroquinone 24.2-30.5 mol%, 2,2'-hydroxy-9,9'-spirobifluorene 1.8-4.5 mol%, and terephthalic acid 26-35 mol%;

[0008] S2: subjecting the reaction mixture to a prepolymerization reaction to obtain a prepolymer;

[0009] S3: Under an inert gas atmosphere, subjecting the prepolymer to a solid phase polycondensation reaction to obtain a liquid crystal polymer.

[0010] Preferably, in step S1, the sum of the molar percentages of the monomers 2,5-di-tert-butylhydroquinone and 2,2'-hydroxy-9,9'-spirobifluorene is equal to the molar percentage of terephthalic acid.

[0011] Preferably, the acylating agent in step S1 includes at least one of acetic anhydride, propionic anhydride and maleic anhydride, and the added amount is 1.02-1.3 times the total molar number of hydroxyl groups in the four monomers.

[0012] Preferably, the catalyst in step S1 includes at least one of potassium acetate, sodium acetate and magnesium acetate, and the added amount is 400-500 ppm of the total weight of the four monomers.

[0013] Preferably, the step S2 specifically comprises: keeping the reaction mixture at 110-130°C for 3-6h, then heating to 310-330°C, keeping for 2-4h, crushing, and drying at 110-130°C for 2-3h to obtain the prepolymer.

[0014] Preferably, the prepolymer in step S2 has a melt index of 4160-4220 cm at 370°C. 3 / 10min.

[0015] Preferably, the melting point of the liquid crystal polymer at 370°C in step S3 is 50-70 cm 3 / 10min.

[0016] Preferably, the temperature of the solid phase polycondensation reaction in step S3 is 300-330° C. and the time is 12-48 hours.

[0017] In a second aspect, the present invention provides a liquid crystal polymer as described in the first aspect, which is prepared by the preparation method of the liquid crystal polymer described in the first aspect.

[0018] In a third aspect, the present invention provides a use of the liquid crystal polymer as described in the first aspect in a component of an automobile thermal management system.

[0019] Beneficial technical effects of the present invention:

[0020] Compared with the prior art, the present invention uses p-hydroxybenzoic acid, 2,5-di-tert-butylhydroquinone, 2,2'-hydroxy-9,9'-spirobifluorene and terephthalic acid in a specific ratio to polymerize under the action of an acylating agent and a catalyst to obtain a liquid crystal polymer, wherein an appropriate amount of spirobifluorene structure is introduced into the molecular chain, which can not only slow down the crystallization speed of the liquid crystal polymer appropriately, but also effectively reduce the cooling speed of the liquid crystal polymer melt, thereby improving the weld mark strength while ensuring the tensile strength of the liquid crystal polymer; at the same time, the highly symmetrical biphenyl structure linked with other molecular structures can further improve the thermal stability and processability of the liquid crystal polymer. DETAILED DESCRIPTION

[0021] The following is a further description of the implementation of the present invention in conjunction with specific embodiments. People familiar with the technology can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0022] Before further describing the specific embodiments of the present invention, it should be understood that the protection scope of the present invention includes but is not limited to the following specific embodiments. The experimental methods in the following examples without specific conditions are usually carried out under conventional conditions, and the materials, equipment and reagents without special instructions are all commercially available.

[0023] Table 1 shows the ratio of each monomer in Examples 1-5.

[0024] Table (1)

[0025]

[0026] Example 1

[0027] According to the ratio of formula 1#, four monomers, p-hydroxybenzoic acid, 2,5-di-tert-butylhydroquinone, 2,2'-hydroxy-9,9'-spirobifluorene, and terephthalic acid, are mixed with acetic anhydride, an acylating agent, which accounts for 1.02 times the total molar number of hydroxyl groups of the four monomers, and potassium acetate, a catalyst, which accounts for 400 ppm of the total weight of the four monomers, to obtain a reaction mixture.

[0028] The reaction mixture was kept at 110°C for 6 hours, then heated to 310°C at a rate of 5°C / min and kept at that temperature for 4 hours; 1.0 MPa nitrogen was injected into the polymerization kettle, and the reactants were discharged through a discharge valve with a diameter of 2 mm and 8 holes, crushed through a 20-mesh sieve, and dried at 110°C for 3 hours to obtain a prepolymer, and its melt index at 370°C was measured to be 4175 cm 3 / 10min.

[0029] In an inert gas atmosphere, the prepolymer was placed in a rotary kiln for solid phase polycondensation at 300°C for 36 hours to obtain a liquid crystal polymer. The melt index at 370°C was 55 cm 3 / 10min.

[0030] Example 2

[0031] According to the ratio of formula 2#, four monomers, p-hydroxybenzoic acid, 2,5-di-tert-butylhydroquinone, 2,2'-hydroxy-9,9'-spirobifluorene, and terephthalic acid, are mixed with an acylating agent, propionic anhydride, which accounts for 1.06 times the total molar number of hydroxyl groups of the four monomers, and a catalyst, sodium ethyl acetate, which accounts for 420 ppm of the total weight of the four monomers, to obtain a reaction mixture.

[0032] The reaction mixture was kept at 120°C for 5 hours, then heated to 315°C at a rate of 5°C / min and kept at this temperature for 3 hours; 1.0 MPa nitrogen was injected into the polymerization kettle, and the reactants were discharged through a discharge valve with a diameter of 2 mm and 8 holes, crushed through a 20-mesh sieve, and dried at 120°C for 2 hours to obtain a prepolymer, and its melt index at 370°C was measured to be 4220 cm 3 / 10min.

[0033] In an inert gas atmosphere, the prepolymer was placed in a rotary kiln for solid phase polycondensation reaction at 310°C for 12 hours to obtain a liquid crystal polymer. The melt index at 370°C was 70 cm 3 / 10min.

[0034] Example 3

[0035] According to the 3# formula ratio, four monomers, p-hydroxybenzoic acid, 2,5-di-tert-butylhydroquinone, 2,2'-hydroxy-9,9'-spirobifluorene, and terephthalic acid, are mixed with acetic anhydride, an acylating agent, which accounts for 1.1 times the total molar number of hydroxyl groups of the four monomers, and sodium acetate, a catalyst, which accounts for 440 ppm of the total weight of the four monomers, to obtain a reaction mixture.

[0036] The reaction mixture was kept at 120°C for 4 hours, then heated to 320°C at a rate of 5°C / min and kept at this temperature for 3 hours; 1.0 MPa nitrogen was injected into the polymerization kettle, and the reactants were discharged through a discharge valve with a diameter of 2 mm and 8 holes, crushed through a 20-mesh sieve, and dried at 120°C for 3 hours to obtain a prepolymer, and its melt index at 370°C was measured to be 4190 cm 3 / 10min.

[0037] In an inert gas atmosphere, the prepolymer was placed in a rotary kiln for solid phase polycondensation reaction at 320°C for 24 hours to obtain a liquid crystal polymer. The melting point of the liquid crystal polymer at 370°C was 60 cm 3 / 10min.

[0038] Example 4

[0039] According to the ratio of formula 4#, four monomers, p-hydroxybenzoic acid, 2,5-di-tert-butylhydroquinone, 2,2'-hydroxy-9,9'-spirobifluorene, and terephthalic acid, are mixed with an acylating agent, maleic anhydride, which accounts for 1.2 times the total molar number of hydroxyl groups of the four monomers, and a catalyst, potassium acetate, which accounts for 470 ppm of the total weight of the four monomers, to obtain a reaction mixture.

[0040] The reaction mixture was kept at 110°C for 6 hours, then heated to 330°C at a rate of 5°C / min and kept at that temperature for 4 hours; 1.0 MPa nitrogen was injected into the polymerization kettle, and the reactants were discharged through a discharge valve with a diameter of 2 mm and 8 holes, crushed through a 20-mesh sieve, and dried at 120°C for 2 hours to obtain a prepolymer, and its melt index at 370°C was measured to be 4205 cm 3 / 10min.

[0041] In an inert gas atmosphere, the prepolymer was placed in a rotary kiln for solid phase polycondensation reaction at 320°C for 15 hours to obtain a liquid crystal polymer. The melt index at 370°C was 67 cm 3 / 10min.

[0042] Example 5

[0043] According to the 5# formula ratio, four monomers, p-hydroxybenzoic acid, 2,5-di-tert-butylhydroquinone, 2,2'-hydroxy-9,9'-spirobifluorene, and terephthalic acid, are mixed with acetic anhydride, an acylating agent, which accounts for 1.3 times the total molar number of hydroxyl groups of the four monomers, and magnesium acetate, a catalyst, which accounts for 500 ppm of the total weight of the four monomers, to obtain a reaction mixture.

[0044] The reaction mixture was kept at 130°C for 3 hours, then heated to 330°C at a rate of 5°C / min and kept at this temperature for 4 hours; 1.0 MPa nitrogen was injected into the polymerization kettle, and the reactants were discharged through a discharge valve with a diameter of 2 mm and 8 holes, crushed through a 20-mesh sieve, and dried at 130°C for 2 hours to obtain a prepolymer, and its melt index at 370°C was measured to be 4160 cm 3 / 10min.

[0045] In an inert gas atmosphere, the prepolymer was placed in a rotary kiln for solid phase polycondensation reaction at 330°C for 48 hours to obtain a liquid crystal polymer. The melt index at 370°C was 50 cm 3 / 10min.

[0046] Comparative Example 1

[0047] The difference from Example 3 is that 2,5-di-tert-butylhydroquinone is replaced by an equal molar amount of hydroquinone to participate in the polymerization reaction, and the other steps are the same as those in Example 3; the obtained prepolymer has a melting point of 3950 cm at 370°C. 3 / 10min, the obtained liquid crystal polymer has a melting point of 42cm at 370℃ 3 / 10min.

[0048] Comparative Example 2

[0049] The difference from Example 3 is that 2,2'-hydroxy-9,9'-spirobifluorene is replaced by an equal molar amount of biphenyl diphenol to participate in the polymerization reaction, and the rest is the same as Example 3; the obtained prepolymer has a melting index of 4185 cm at 370°C. 3 / 10min, the obtained liquid crystal polymer has a melting point of 62cm at 370℃ 3 / 10min.

[0050] Comparative Example 3

[0051] The difference from Example 3 is that terephthalic acid is replaced by an equal molar amount of isophthalic acid to participate in the polymerization reaction, and the other steps are the same as those in Example 3; the obtained prepolymer has a melting point of 4300 cm at 370°C. 3 / 10min, the obtained liquid crystal polymer has a melting point of 78cm at 370℃ 3 / 10min.

[0052] Comparative Example 4

[0053] The difference from Example 3 is that the solid phase polycondensation time is 10 h. The other conditions are the same as those of Example 3. The obtained prepolymer has a melting index of 4192 cm at 370°C. 3 / 10min, the obtained liquid crystal polymer has a melting point of 74cm at 370℃ 3 / 10min.

[0054] Comparative Example 5

[0055] The difference from Example 3 is that the solid phase polycondensation time is 50 h. The other conditions are the same as those in Example 3. The obtained prepolymer has a melting index of 4189 cm at 370°C. 3 / 10min, the obtained liquid crystal polymer has a melting point of 46cm at 370℃ 3 / 10min.

[0056] The above-mentioned embodiments 1-5 and comparative examples 1-5 were subjected to relevant performance tests, and the specific test items and test methods are as follows:

[0057] (1) Tensile strength: According to ISO 527-2012, the liquid crystal polymer was injection molded into a specimen with unilateral injection, and the specimen was conditioned in an environment of 23°C and 50% RH for 24 h and then the tensile strength was tested at a speed of 50 mm / min;

[0058] (2) Weld mark strength: According to ISO 527-2012 standard, the liquid crystal polymer was injection molded into a strip with the weld line converging in the middle of the strip. The strip was conditioned in an environment of 23°C and 50% RH for 24 h and then the tensile strength was tested at a speed of 50 mm / min.

[0059] (3) Thermal stability: Use a differential thermal and thermogravimetric simultaneous measurement device to measure the amount of gas generated when 10 mg of liquid crystal polymer is kept at 370°C for 30 minutes under a nitrogen flow. If the amount of gas generated is less than 15,000 ppm, the thermal stability is considered to be good;

[0060] (4) Processability: The melt index of liquid crystal polymer measured according to GB / T 3682.2 standard is 50-70cm 3 / 10min, the viscosity of the liquid crystal polymer is moderate, and the injection extrusion is smooth, then the processability is judged to be OK; the melt index is lower than 50cm 3 / 10min, the viscosity of the liquid crystal polymer is too high and it is difficult to extrude during the injection molding process, so the processability is judged as NG.

[0061] (5) Appearance: Observe the color and uniformity of the liquid crystal polymer with the naked eye. If it is uniformly beige, it is qualified; otherwise, it is unqualified.

[0062] The performance parameters of the liquid crystal polymers in Examples 1-5 and Comparative Examples 1-5 are shown in Table 2.

[0063] Table (2)

[0064]

[0065]

[0066] It can be seen from the performance parameters in Table 2 that the liquid crystal polymer obtained by adopting the technical solution of the present invention has good mechanical properties, thermal stability, processability and appearance.

[0067] By comparing Comparative Example 1 with Example 3, it can be seen that when the monomer 2,5-di-tert-butylhydroquinone in the scheme of the present invention is replaced by an equal molar amount of hydroquinone to participate in the polymerization reaction, the obtained liquid crystal polymer has poor processability, mainly because the liquid crystal polymer obtained after the replacement has a low melt index and a high viscosity, and is not easy to extrude during the injection molding process.

[0068] By comparing Comparative Example 2 with Example 3, it can be seen that when the monomer 2,2'-hydroxy-9,9'-spirobifluorene in the scheme of the present invention is replaced with an equimolar amount of biphenyl diphenol to participate in the polymerization reaction, the tensile strength, weld mark strength and thermal stability of the obtained liquid crystal polymer are greatly reduced. Example 3 introduces an appropriate amount of spirobifluorene structure on the molecular chain, which can not only slow down the crystallization rate of the liquid crystal polymer appropriately, but also effectively reduce the cooling rate of the liquid crystal polymer melt, thereby ensuring the tensile strength of the liquid crystal polymer while improving its weld mark strength; at the same time, its highly symmetrical biphenyl structure is linked to other molecular structures to further improve the thermal stability and processability of the liquid crystal polymer; after replacing it with other molecular structures that do not contain spirobifluorene structure in Comparative Example 2, the performance drops sharply.

[0069] By comparing Comparative Example 3 with Example 3, it can be seen that when terephthalic acid is replaced by an equal molar amount of isophthalic acid to participate in the polymerization reaction, the tensile strength, weld mark strength and thermal stability of the obtained liquid crystal polymer are significantly reduced. This is mainly because after the para-position structure is replaced by the meta-position structure, the interchain force is reduced, the rigidity of the molecular chain is reduced, and the flexibility is increased, resulting in a decrease in mechanical properties and thermal stability.

[0070] By comparing Comparative Examples 4-5 with Example 3, it can be seen that the solid-phase polymerization time needs to be controlled within a certain range. If the solidification time is too short, the polymerization will be incomplete and the mechanical properties of the liquid crystal polymer will be affected. If the solidification time is too long, not only will the viscosity of the polymer increase significantly, which is not conducive to processing, but part of it will also carbonize and decompose, resulting in decreased mechanical properties and thermal stability, and the material will be doped with black spots formed by carbonization.

[0071] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a liquid crystal polymer, characterized in that: The following steps are involved: S1: four monomers, p-hydroxybenzoic acid, 2,5-di-tert-butylhydroquinone, 2,2'-hydroxy-9,9'-spirobifluorene, terephthalic acid, an acylating agent, and a catalyst are mixed to obtain a reaction mixture; wherein, in terms of molar percentage, the proportion of each monomer in the four monomers is as follows: p-hydroxybenzoic acid 30-48 mol%, 2,5-di-tert-butylhydroquinone 24.2-30.5 mol%, 2,2'-hydroxy-9,9'-spirobifluorene 1.8-4.5 mol%, and terephthalic acid 26-35 mol%; S2: subjecting the reaction mixture to a prepolymerization reaction to obtain a prepolymer; S3: Under an inert gas atmosphere, subjecting the prepolymer to a solid phase polycondensation reaction to obtain a liquid crystal polymer.

2. The method for preparing a liquid crystal polymer according to claim 1, characterized in that: In the step S1, the sum of the molar percentages of the monomers 2,5-di-tert-butylhydroquinone and 2,2'-hydroxy-9,9'-spirobifluorene is equal to the molar percentage of terephthalic acid.

3. The method for preparing a liquid crystal polymer according to claim 1, characterized in that: In step S1, the acylating agent includes at least one of acetic anhydride, propionic anhydride and maleic anhydride, and the added amount is 1.02-1.3 times the total molar number of hydroxyl groups in the four monomers.

4. The method for preparing a liquid crystal polymer according to claim 1, characterized in that: The catalyst in step S1 includes at least one of potassium acetate, sodium acetate and magnesium acetate, and the added amount is 400-500 ppm of the total weight of the four monomers.

5. The method for preparing a liquid crystal polymer according to claim 1, characterized in that: The step S2 specifically comprises: keeping the reaction mixture at 110-130° C. for 3-6 hours, then heating to 310-330° C., keeping the temperature for 2-4 hours, crushing, and drying at 110-130° C. for 2-3 hours to obtain the prepolymer.

6. The method for preparing a liquid crystal polymer according to claim 1, characterized in that: Preferably, the prepolymer in step S2 has a melt index of 4160-4220 cm at 370°C. 3 / 10min.

7. The method for preparing a liquid crystal polymer according to claim 1, characterized in that: The melting point of the liquid crystal polymer at 370° C. in step S3 is 50-70 cm 3 / 10min.

8. The method for preparing a liquid crystal polymer according to claim 1, characterized in that: The temperature of the solid phase polycondensation reaction in step S3 is 300-330° C. and the time is 12-48 hours.

9. A liquid crystal polymer, characterized in that: The liquid crystal polymer is prepared by the preparation method of the liquid crystal polymer according to any one of claims 1 to 8.

10. Use of the liquid crystal polymer according to claim 9 in a component of an automobile thermal management system.

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