Preparation method of high-heat-resistance high-strength self-lubricating polyimide microcapsule

Abstract

The application discloses a kind of preparation methods of high heat resistance high-strength self-lubricating polyimide microcapsules, mainly related to the field of self-lubricating materials. Including the following steps: S1. diamine, dianhydride monomer is mixed to obtain polyimide precursor, then the polyimide precursor is mixed with the solvent obtained by mixing anhydrous methanol, tetrahydrofuran, liquid lubricant, nano inorganic and emulsifier, to obtain a mixed solution containing core material and wall material;S2. dimethyl silicone oil is added dropwise to the mixed solution containing core material and wall material, and after stirring, washing, filtering, drying polyimide precursor microcapsules coated with liquid lubricant are obtained;S3. polyimide precursor microcapsules are imidized to obtain polyimide inorganic composite shell microcapsules coated with liquid lubricant. The beneficial effects of the application are that it can withstand higher temperatures, has high strength, good wear resistance and friction reduction, and the preparation method has simple synthesis process, raw materials and solvents are easy to recover and reuse.

Description

TECHNICAL FIELD

[0001] The application relates to the field of self-lubricating materials, and particularly relates to a preparation method of high-heat-resistance high-strength self-lubricating polyimide microcapsules. BACKGROUND

[0002] In recent years, modern industry has developed rapidly, and various mechanical equipment is widely used, and the problems of friction and wear generated thereby are becoming increasingly serious. Friction and wear not only cause a large amount of resource waste, but also cause problems such as mechanical efficiency reduction and component failure, resulting in economic losses. In order to save energy and improve production efficiency and prolong the service life of materials, it is necessary to solve the problems of friction, wear and lubrication protection in many fields, and the application of lubrication technology is one of effective measures to solve the problems.

[0003] The microcapsule is a micro-container with a core-shell structure. The shell material of the microcapsule is referred to as a wall material, and the material embedded in the cavity of the wall material is referred to as a core material. This structure enables the core material to be effectively separated from the external environment, avoiding the influence of external temperature, pressure, ultraviolet light and pH value and the like. This enables the stability and performance of the core material to be greatly improved under the protection of the outer wall. In the actual application process, due to the action of external force, friction, heating or radiation, the internal core material lubricant of the microcapsule is released, thereby playing a role and effect of reducing friction and wear.

[0004] Because the wall material of the microcapsule plays a very important sealing and protective role on the core material, the microcapsule has a long service life and recyclability in the actual application process, and therefore the wall material is required to have certain mechanical strength and compactness. At present, the wall material of the single-walled microcapsule is mainly composed of polysulfone, phenolic resin, urea-formaldehyde resin, melamine resin, melamine urea-formaldehyde resin, polyurea or polyurethane, polymethyl methacrylate, SiO2 and CaCO3. The microcapsules composed of the aforementioned organic wall materials generally have the shortcomings of poor compactness, poor high-temperature resistance and brittleness and fragility in the use process. For example, a microencapsulated ammonium polyphosphate flame-retardant ultrahigh molecular weight polyethylene fiber and a preparation method thereof are disclosed in Chinese patent CN202011213927.5. The prepared melamine resin shell microcapsule has a temperature resistance lower than 300 DEG C. As for the microcapsules composed of inorganic wall materials such as SiO2 and CaCO3, the synthesis process is relatively complex, although the temperature resistance of the capsule wall is greatly improved, but for the core material such as ionic liquid lubricant with high viscosity, the content of the synthesized microcapsule core material is low. Chinese patent CN202210687081.1 discloses an oil-containing microcapsule self-lubricating fabric pad and a preparation method thereof. Due to the high-temperature decomposition of the lubricating oil, the application temperature range of the hollow SiO2 microsphere loaded lubricating oil microcapsule is limited. SUMMARY

[0005] The application aims to provide a preparation method of high-heat-resistance high-strength self-lubricating polyimide microcapsules, which can resist high temperature, has high strength, good wear resistance and friction reduction, and simple synthesis process, and raw materials and solvents are easy to recycle and reuse.

[0006] To achieve the above-mentioned purpose, the application realizes the technical scheme as follows.

[0007] The application provides a preparation method of high-heat-resistance high-strength self-lubricating polyimide microcapsules, which comprises the following steps.

[0008] S1. mixing diamine and dianhydride monomers to prepare polyimide precursors under the condition of 20-40 DEG C, and then mixing the polyimide precursors with a solvent obtained by mixing anhydrous methanol, tetrahydrofuran, liquid lubricant, nano inorganic substance and emulsifier to prepare a mixed solution containing core material and wall material;

[0009] S2. adding dimethyl silicone oil dropwise to the mixed solution containing core material and wall material in the step S1, and then stirring under the condition of 60-90 DEG C, and then washing, filtering and drying to obtain polyimide precursor microcapsules coated with liquid lubricant;

[0010] S3. performing imidization on the polyimide precursor microcapsules in the step S2 to obtain polyimide inorganic composite shell microcapsules coated with liquid lubricant.

[0011] Further, the liquid lubricant is composed of one or more of ionic liquid lubricant, perfluoropolyether lubricant, polyolefin lubricant, drying oil lubricant and castor oil lubricant.

[0012] Further, in the step S1, the molar ratio of dianhydride to diamine is n:n or n+1, n>1 and is a natural number, the mass ratio of the emulsifier is 1wt%-5wt%, the mass ratio of the mixed solution of diamine and dianhydride to liquid lubricant is 1:1-5, and the mass ratio of anhydrous methanol to tetrahydrofuran is 1:1-6.

[0013] Further, in the step S2, the volume ratio of the mixed solution containing core material and wall material to dimethyl silicone oil is 1:1-4.

[0014] Further, in the step S3, when the precursor microcapsules are subjected to imidization, chemical imidization or thermal imidization can be performed, wherein the chemical imidization is to immerse the polyimide precursor microcapsules coated with liquid lubricant in an acetone solution containing 30wt%-60wt% acetic anhydride and pyridine for 12-24 hours to complete imidization; the thermal imidization is to perform thermal imidization under the condition of 80-100 DEG C for 3-6 hours, 150-170 DEG C for 2-4 hours and 280-300 DEG C for 1-2 hours.

[0015] Further, the diamine monomer is composed of one or more of the following: bisphenylamine-xylylene, 4,4'-diamino diphenyl ether, 4,4'-diamino diphenyl methane, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 3,3'-diamino diphenyl sulfone, 3,4'-diamino diphenyl ether.

[0016] Further, the dianhydride monomer is composed of one or more of the following: 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, 3,3'4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0017] Further, the lubricant includes the free ion liquid lubricant selected from the group consisting of 1-hexyl-2,3-dimethyl imidazole hexafluorophosphate, 1-hexyl-2,3-dimethyl imidazole bromide, 1-butyl-3-methyl imidazole hexafluorophosphate, and 1-dodecyl-3-methyl imidazole hexafluorophosphate; and the polyolefin lubricant is poly alpha-olefin PAO No. 6 lubricating oil.

[0018] Further, the liquid lubricant is resistant to a temperature of 200-350°C.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] 1. The polyimide microcapsules prepared by the present application can withstand high temperature, which is due to the fact that the wall material is polyimide, and the rigid heterocyclic imide ring and aromatic benzene ring on the macromolecular backbone of the polyimide, combined with the high heat resistance of inorganic matter, thus having excellent thermal stability. Therefore, selecting a high-temperature-resistant lubricant as the core material of the microcapsule can prepare a high-heat-resistant self-lubricating polyimide shell microcapsule.

[0021] 2. The polyimide microcapsules prepared by the present application have high strength, which is due to the fact that the rigid heterocyclic imide ring and aromatic benzene ring on the macromolecular backbone of the polyimide wall material have excellent mechanical properties, combined with the excellent strength and rigidity of nano inorganic matter. Therefore, selecting high-strength polyimide and nano inorganic matter as the composite wall material makes the prepared microcapsules have high strength.

[0022] 3. The polyimide microcapsules prepared by the present application have high wear resistance and friction reduction, which is due to the fact that the core material liquid lubricant has good wear resistance and friction reduction.

[0023] 4. The process of the present application has simple process steps, and the raw materials used are cheap and easy to obtain. In particular, the dimethyl silicone oil can be reused in the next microcapsule preparation after filtration, and has no effect on the performance of the prepared microcapsules. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a SEM image of the present application. Figure 1 Figure 1 is a SEM image of the present application.

[0025] Figure 1 is a SEM image of the present application. Figure 2 Figure 1 is a SEM image of the present application. DETAILED DESCRIPTION

[0026] The present application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application. Furthermore, it should be understood that those skilled in the art can make various modifications or changes to the present application after reading the content taught by the present application, and these equivalent forms also fall within the scope defined by the present application.

[0027] The present application relates to a kind of high heat resistance high strength self-lubricating polyimide microcapsule preparation method, comprising the following steps:

[0028] S1. Under the condition of 20-40 ℃, diamine, dianhydride monomer is mixed to prepare polyimide precursor, then polyimide precursor is mixed with solvent obtained by mixing anhydrous methanol, tetrahydrofuran, liquid lubricant, nano inorganic and emulsifier, and stirring, to obtain mixed solution containing core material and wall material, wherein, nano inorganic is one or several of nanosilica, graphene, carbon nanotube, and nano inorganic can be modified by coupling agent, coupling agent selects silane coupling agent KH-550, KH-560, KH-570, emulsifier selects the group consisting of span 40, span 60, span 80, tween 60 and tween 80;

[0029] S2. In the mixed solution containing core material and wall material in the step S1, dimethyl silicone oil is added dropwise, and after stirring under the condition of 60-90 ℃, washing, filtering, drying to obtain polyimide precursor microcapsule coated with liquid lubricant;

[0030] S3. The polyimide precursor microcapsule in the step S2 is imidized to obtain polyimide inorganic composite shell microcapsule coated with liquid lubricant.

[0031] Preferably, the liquid lubricant is composed of one or several of ionic liquid lubricant, perfluoropolyether lubricant, polyolefin lubricant, dry oil lubricant, castor oil and other lubricants.

[0032] Preferably, in the step S1, the molar ratio of dianhydride to diamine is n:n or n+1, n>1 and is a natural number, the mass ratio of emulsifier is 1wt%-5wt%, the mass ratio of mixed solution of diamine and dianhydride to liquid lubricant is 1:1-5, and the mass ratio of anhydrous methanol to tetrahydrofuran is 1:1-6.

[0033] Preferably, in the step S2, the volume ratio of the mixed solution containing the core material and the wall material to the dimethyl silicone oil is 1:1-4.

[0034] Preferably, in the step S3, when the precursor microcapsule is imidized, chemical imidization or thermal imidization can be performed, wherein the chemical imidization is to immerse the polyimide precursor microcapsule coated with the liquid lubricant in an acetone solution containing 30wt%-60wt% of acetic anhydride and pyridine by mass ratio for 12-24 hours to complete the imidization; the thermal imidization is to perform thermal imidization at 80-100℃ for 3-6 hours, at 150-170℃ for 2-4 hours, and at 280-300℃ for 1-2 hours.

[0035] Preferably, the diamine monomer is composed of one or more of bisphenylamine-phenylenedimethyl, 4,4'-diamino diphenyl ether, 4,4'-diamino diphenyl methane, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 3,3'-diamino diphenyl sulfone, and 3,4'-diamino diphenyl ether.

[0036] Preferably, the dianhydride monomer is composed of one or more of 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, 3,3'4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0037] Preferably, the lubricant includes the free ionic liquid lubricant selected from the group consisting of 1-hexyl-2,3-dimethyl imidazole hexafluorophosphate, 1-hexyl-2,3-dimethyl imidazole bromide, 1-butyl-3-methyl imidazole hexafluorophosphate, and 1-dodecyl-3-methyl imidazole hexafluorophosphate; and the polyolefin lubricant is poly-alpha-olefin PAO No. 6 lubricating oil.

[0038] Preferably, the liquid lubricant is resistant to a temperature of 200-350℃.

[0039] Embodiment 1: A method for preparing a high-heat-resistant and high-strength self-lubricating polyimide microcapsule, comprising the following steps: preparing 4,4'-diamino diphenyl ether and 3,3',4,4'-biphenyl tetracarboxylic dianhydride in a molar ratio of 1:1. At room temperature, 2wt% of the emulsifier Span80 and poly-alpha-olefin PAO No. 6 lubricating oil are dissolved in a mass ratio of 1:4 of anhydrous methanol and tetrahydrofuran mixed solvents with a core-to-wall ratio of 1:1, and then 4,4'-diamino diphenyl ether is added to the mixed solution, followed by adding 3,3',4,4'-biphenyl tetracarboxylic dianhydride after stirring for 5 minutes. The mixture is stirred for 5 hours under mechanical stirring or magnetic stirring to obtain a mixed solution containing the core material and the wall material.

[0040] The mixed solution containing the core material and the wall material is added to dimethyl silicone oil at a volume ratio of 1:6, stirred at room temperature at a speed of 600 rpm for 3 minutes, then washed, filtered, and dried to obtain polyimide precursor microcapsules coated with poly-alpha-olefin PAO No. 6 lubricating oil;

[0041] The polyimide precursor microcapsules coated with the liquid lubricant are soaked in a mixed solution of acetic anhydride and pyridine for 12 hours to complete imidization, thereby obtaining the polyimide inorganic composite shell microcapsules coated with the liquid lubricant.

[0042] Example 2: A method for preparing high-heat-resistance high-strength self-lubricating polyimide microcapsules, comprising the following steps: at room temperature, 4wt% of emulsifier Span80 and 1-butyl-3-methylimidazolium hexafluorophosphate are dissolved in a mixed solvent of anhydrous methanol and tetrahydrofuran at a mass ratio of 1:6 at a core-to-wall ratio of 11:10, 4,4'-diamino diphenyl ether is then added to the mixed solution, 3,3',4,4'-benzophenone tetracarboxylic dianhydride is added after sufficient stirring for 5 minutes, and the mixture is mechanically stirred for 1 hour before being mixed with SiO2 particles modified by KH-550, and the mixture is mechanically stirred for 5 hours to obtain a mixed solution containing the core material and the wall material;

[0043] The mixed solution containing the core material and the wall material is added to dimethyl silicone oil at a volume ratio of 1:6, stirred at room temperature at a speed of 600 rpm for 3 minutes, then washed, filtered, and dried to obtain polyimide precursor microcapsules coated with poly-alpha-olefin PAO No. 6 lubricating oil; The polyimide shell microcapsules coated with the liquid lubricant are subjected to thermal imidization at 100°C for 3 hours, at 170°C for 2 hours, and at 280°C for 1 hour to obtain SiO2 / polyimide double-shell microcapsules.

[0044] Example 3: A method for preparing high-heat-resistance high-strength self-lubricating polyimide microcapsules, comprising the following steps: 4,4'-diamino diphenyl ether and 3,3',4,4'-biphenyl tetracarboxylic dianhydride are prepared at a molar ratio of 11:10. At room temperature, 3wt% of emulsifier (a combination of Span40 and Tween20) and poly-alpha-olefin PAO No. 6 lubricating oil are dissolved in a mixed solvent of anhydrous methanol and tetrahydrofuran at a mass ratio of 1:4 at a core-to-wall ratio of 1:1, 4,4'-diamino diphenyl ether is then added to the mixed solution, 3,3',4,4'-biphenyl tetracarboxylic dianhydride is added after sufficient stirring for 5 minutes, and the mixture is stirred for 1 hour before being mixed with surface-modified graphene (GO), and the mixture is mechanically stirred for 5 hours to obtain a mixed solution containing the core material and the wall material;

[0045] The mixed solution containing core material and wall material is added to dimethyl silicone oil at a volume ratio of 1:3, stirred at room temperature at a speed of 600 rpm for 3 minutes, then washed, filtered, and dried to obtain polyimide precursor microcapsules coated with poly-alpha-olefin PAO No. 6 lubricating oil; immerse in acetic anhydride and pyridine 30 wt% acetone solution for 12 hours to complete imidization to obtain GO / polyimide double-shell microcapsules.

[0046] Example 4: A method for preparing high-heat-resistant high-strength self-lubricating polyimide microcapsules, comprising the following steps: using 3,3'-diaminodiphenyl sulfone as a diamine monomer, using 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride and / or bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetra-carboxylic dianhydride as a dianhydride monomer, and preparing at a diamine to dianhydride molar ratio of 11:10. At room temperature, 4 wt% of the emulsifier Span80 and castor oil lubricating oil are dissolved in a mass ratio of 1:4 of anhydrous methanol and tetrahydrofuran mixed solvents at a core to wall ratio of 2:1, 4,4'-diamino diphenyl ether is then added to the mixed solution, 3,3',4,4'-biphenyl tetracarboxylic dianhydride is added after stirring for 5 minutes, and the mixed solution containing core material and wall material is obtained after stirring for 5 hours under mechanical stirring or magnetic stirring.

[0047] The mixed solution containing core material and wall material is added to dimethyl silicone oil at a volume ratio of 1:3, stirred at room temperature at a speed of 600 rpm for 3 minutes, then washed, filtered, and dried to obtain polyimide precursor microcapsules coated with poly-alpha-olefin PAO No. 6 lubricating oil; immerse in acetic anhydride and pyridine 30 wt% acetone solution for 12 hours to complete imidization to obtain GO / polyimide double-shell microcapsules.

[0048] Example 5: A method for preparing high-heat-resistant high-strength self-lubricating polyimide microcapsules, comprising the following steps: using 3,3'-diaminodiphenyl sulfone as a diamine monomer, using 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride and / or bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetra-carboxylic dianhydride as a dianhydride monomer, and preparing at a diamine to dianhydride molar ratio of 11:10. At room temperature, 4 wt% of the emulsifier Span80 and castor oil lubricating oil are dissolved in a mass ratio of 1:4 of anhydrous methanol and tetrahydrofuran mixed solvents at a core to wall ratio of 2:1, 4,4'-diamino diphenyl ether is then added to the mixed solution, 3,3',4,4'-biphenyl tetracarboxylic dianhydride is added after stirring for 5 minutes, and the mixed solution containing core material and wall material is obtained after stirring for 5 hours under mechanical stirring or magnetic stirring.

[0049] The mixture containing the core material and the wall material is added to dimethyl silicone oil at a volume ratio of 1:4. After washing, filtering, and drying, polyimide precursor microcapsules coated with 1-butyl-3-methylimidazolium hexafluorophosphate are obtained; polyimide shell microcapsules coated with liquid lubricant are then obtained.

[0050] Example 6: A method for preparing a high-heat-resistant, high-strength, self-lubricating polyimide microcapsule, comprising the following steps: 4,4'-diaminodiphenyl ether and 3,3',4,4'-biphenyltetracarboxylic acid dianhydride are prepared at a molar ratio of 11:10. At room temperature, 2 wt% of a mixed emulsifier of Span80 and Tween80 and 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid are dissolved in a mixed solvent of anhydrous methanol and tetrahydrofuran at a core-to-wall ratio of 2:1. Then, 4,4'-diaminodiphenyl ether is added to the mixed solution, and after thorough stirring, carbon nanotubes are added. The mixture is stirred for 5 hours under mechanical or magnetic stirring to obtain a mixture containing core and wall materials.

[0051] The mixture containing the core material and the wall material was added to dimethyl silicone oil at a volume ratio of 1:3. After stirring at 400 rpm for 3 minutes at room temperature, the mixture was washed, filtered, and dried to obtain polyimide precursor microcapsules coated with 1-butyl-3-methylimidazolium hexafluorophosphate. The microcapsules were then soaked in a 30 wt% acetone solution of acetic anhydride and pyridine for 12 hours to complete imidization and obtain carbon nanotube / polyimide bishell microcapsules.

[0052] From the appendix Figure 2 It is known that the polyimide microcapsules prepared by the present invention can withstand high temperatures; the polyimide microcapsules prepared by the present invention also have high strength and wear and friction reduction properties; and the process steps of the present invention are simple, the raw materials used are inexpensive and readily available, especially the dimethyl silicone oil, which can be used in the next microcapsule preparation after filtration, and has no effect on the various properties of the prepared microcapsules.

Claims

1. A method for preparing high heat-resistant, high-strength, self-lubricating polyimide microcapsules, characterized in that: It comprises the following steps: S1. The polyimide precursor is prepared by mixing diamine and dianhydride monomers at 20-40℃, and then the polyimide precursor is mixed with a solvent obtained by mixing anhydrous methanol, tetrahydrofuran, liquid lubricant, nano inorganic matter and emulsifier to obtain a mixed solution containing core material and wall material; S2. Dimethyl silicone oil is added dropwise to the mixed solution containing core material and wall material in step S1, and after stirring at 60-90℃, the polyimide precursor microcapsule coated with liquid lubricant is obtained by washing, filtering and drying; S3. The polyimide precursor microcapsule in step S2 is imidized to obtain a polyimide inorganic composite shell microcapsule coated with liquid lubricant; The liquid lubricant comprises a free ion liquid lubricant selected from the group consisting of 1-hexyl-2,3-dimethyl imidazole hexafluorophosphate, 1-hexyl-2,3-dimethyl imidazole bromide, 1-butyl-3-methyl imidazole hexafluorophosphate and 1-dodecyl-3-methyl imidazole hexafluorophosphate; The nano inorganic matter is one or several of nano silicon dioxide, graphene and carbon nanotube, and the nano inorganic matter is modified by a coupling agent selected from silane coupling agents KH-550, KH-560 and KH-570.

2. The preparation method of the high-heat-resistant and high-strength self-lubricating polyimide microcapsules according to claim 1, characterized in that: In step S1, the molar ratio of dianhydride to diamine is n:n or n+1, n>1 and is a natural number, the mass ratio of emulsifier is 1wt%-5wt%, the mass ratio of the mixed solution of diamine and dianhydride to liquid lubricant is 1:1-5, and the mass ratio of anhydrous methanol to tetrahydrofuran is 1:1-6.

3. The method according to claim 1, wherein the method is characterized by: In step S2, the volume ratio of the mixed solution containing core material and wall material to dimethyl silicone oil is 1:1-4.

4. The preparation method of the high-heat-resistant and high-strength self-lubricating polyimide microcapsules according to claim 1, characterized in that: In step S3, when the precursor microcapsule is imidized, chemical imidization or thermal imidization can be performed, wherein the chemical imidization is to immerse the polyimide precursor microcapsule coated with liquid lubricant in an acetone solution containing 30wt%-60wt% acetic anhydride and pyridine for 12-24 hours to complete the imidization; the thermal imidization is to perform thermal imidization at 80-100℃ for 3-6 hours, at 150-170℃ for 2-4 hours and at 280-300℃ for 1-2 hours.

5. The method according to claim 1, wherein the method is characterized by: The diamine monomer is one or several of bisphenylamine-phenylenedimethyl, 4,4'-diamino diphenyl ether, 4,4'-diamino diphenyl methane, 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 3,3'-diamino diphenyl sulfone and 3,4'-diamino diphenyl ether.

6. The method according to claim 1, wherein the method is characterized by: The dianhydride monomer is one or several of 2,2'-bis(3,4-dicarboxylic acid) hexafluoropropane dianhydride, 3,3'4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

7. The method according to claim 1, wherein the method is characterized by: The liquid lubricant can withstand a temperature of 200-350℃.

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