Preparation method of polyimide hollow microspheres

Abstract

The present invention relates to a method for preparing polyimide hollow microspheres. The specific method is as follows: Mix and stir a polyamic acid solution with an oil phase to obtain a W / O emulsion (W is the polyamic acid solution); add this emulsion to a precipitant mixed solution containing a surfactant, a dispersant, and an organic solvent, stir and react at a certain rotation speed for a period of time, precipitate solid particles, filter, wash, and perform thermal imidization to obtain polyimide hollow microspheres; control the morphology and particle size distribution of the particles by adjusting process parameters. The average particle size distribution of the polyimide hollow microspheres prepared by this method is between 2 - 15 μm, and the thermal decomposition temperature is between 460°C - 500°C.

Description

Technical Field

[0001] The present invention relates to a technical method for preparing polyimide hollow microspheres, and particularly to a method for preparing polyimide hollow microspheres by an emulsion templating method. Background Art

[0002] Polyimide hollow microspheres not only have excellent mechanical strength of polyimide, but also have outstanding heat resistance, chemical resistance and other properties. At the same time, their hollow structure can be used to encapsulate small molecules or other substances with special functions such as proteins, drug molecules, lubricants, etc. Therefore, they have very broad application prospects in the fields of catalyst carriers, dielectrics, friction, liquid crystal displays, etc.

[0003] Currently, the main methods for preparing hollow polymer microspheres include interfacial polymerization, hard template method, microfluidics, W / O / W inverse emulsion method, etc. Interfacial polymerization is to emulsify and disperse one of the monomers in the continuous phase containing the other monomer, and then the two monomers undergo a polymerization reaction at the interface to form microcapsules. The microspheres prepared by the interfacial polymerization method have serious agglomeration and harsh conditions. It requires both monomers to be soluble in the solvent and the successfully polymerized microcapsules to precipitate from the solvent. The hard template method uses monodisperse particles as templates, and a polymer shell is formed on the surface of the templates, and then the templates are removed by physical or chemical means to obtain polymer microspheres with a hollow structure. Currently, commonly used templates include calcium carbonate microspheres, polystyrene microspheres, silica microspheres, etc. Such templates are difficult to remove completely and will cause the rupture of the shell. Microfluidics technology can prepare monodisperse hollow microspheres by strictly controlling the flow rates of the two phases, but the particle size is relatively large, and it is difficult to obtain microspheres with a size below 10 μm. The microspheres prepared by the W / O / W inverse emulsion method have a wide particle size distribution and a rough surface. The emulsion templating method better compensates for the above technical defects and can be used to prepare hollow microspheres with a size ranging from a few micrometers to dozens of micrometers, and the templates are easy to remove. However, there are many factors affecting the emulsion templating method, such as the concentration of emulsifiers, monomers, time, and stirring speed, etc. Therefore, how to reasonably design the preparation process has a great impact on the morphology and properties of the microspheres.

[0004] U.S. Patent US00608400A proposes a method for preparing hollow polyimide microspheres. The dianhydride is dissolved in alcohol, and dialkyl ester-diacid is synthesized under the conditions of alcohol and ether. Then it reacts with diamine monomers, and the solvent is removed by heating in a stainless steel container to obtain polyimide powder. The polyimide microspheres prepared by this method have a relatively large particle size and poor sphericity. Chinese Patent 201410377232.9 first prepared composite microspheres of polypyrrole-coated polystyrene, then calcined to obtain a hollow microsphere carbon skeleton, used it as a template to prepare polyamic acid microspheres, and finally obtained polyimide hollow microspheres through imidization. Shinjiwatanabe used polystyrene as a template, first prepared polystyrene-polyamic acid microspheres with a core-shell structure, obtained polystyrene-polyimide microspheres with a core-shell structure through imidization, and then removed the core with toluene to obtain polyimide microspheres with a core-shell structure. Both of these methods will cause the shell to break when removing the core. Chinese Patent 202011093271.8 mixes an ethanol solution containing diamine monomers with dichloromethane and water in a certain proportion to obtain a water-in-oil emulsion, then adds an oil phase containing dianhydride monomers, stirs and polymerizes for a period of time, and finally evaporates to remove the solvent and water to obtain polyimide hollow microspheres. The microspheres prepared by this method agglomerate seriously and have poor dispersibility. Keiji Nagai added a drop of polyamic acid solution to polydimethylsiloxane (PDMS), and used a micro syringe to inject PDMS as the core material into the polyamic acid microdroplets, then mechanically stirred at room temperature, removed the solvent and imidized to finally obtain polyimide hollow microspheres. This method can only obtain microspheres with a size of 0.5 - 5 mm, and the preparation efficiency is low. Jianqi Ji prepared polyimide hollow microspheres by the inverse emulsion method. This method utilizes the characteristic that polyamic acid salts can dissolve in water. First, an O / W emulsion is prepared with a polyamic acid salt solution as the continuous phase and liquid paraffin as the dispersed phase, then an O / W / O emulsion is prepared with the O / W emulsion as the dispersed phase and liquid paraffin as the continuous phase, and finally polyimide hollow microspheres are obtained through a series of steps such as chemical imidization. This method has cumbersome steps, difficult control of the microsphere morphology, and serious adhesion.

[0005] Based on the problems in the above technologies that the microsphere morphology and particle size distribution cannot be well controlled and the template removal is difficult, the present invention provides a method for preparing polyimide hollow microspheres using a polyamic acid solution as a raw material. By secondary emulsifying the emulsion formed by stirring the polyamic acid solution and the oil phase, then the polyamic acid solution and the oil phase undergo phase separation, and precipitate out in the form of microspheres from the system under the action of a precipitating agent, and the particle size and distribution of the hollow microspheres are effectively regulated by adjusting process parameters. Summary of the Invention

[0006] The object of the present invention is to provide a method for preparing polyimide hollow microspheres which uses a polyamic acid solution as a raw material, an emulsion as a template, and enables the precipitation of the polyamic acid solution in the form of microspheres from the solution, and can control the particle size and distribution of the microspheres, so as to improve the deficiencies of the prior art.

[0007] The technical solution of the present invention: A method for preparing polyimide hollow microspheres, the specific steps are as follows:

[0008] (1) Dissolve the monomer diamine in an organic solvent, stir until completely dissolved, and then add the monomer dianhydride in batches to prepare a polyamic acid solution;

[0009] (2) Mix the polyamic acid solution prepared in step (1) with an oil phase, and then stir for a period of time at a certain rotation speed to obtain a white emulsion;

[0010] (3) Add the emulsion prepared in step (2) to a precipitant mixed solution, stir and react for a period of time at a certain rotation speed to precipitate solid particles; the precipitant mixed solution is composed of adding a certain amount of emulsifier and dispersant to the precipitant, and the precipitant is composed of an organic solvent and deionized water;

[0011] (4) Filter the suspension microsphere solution obtained in step (3) to separate the polyamic acid microspheres, then wash with an organic solvent and deionized water in sequence, dry, and then place in an oven for gradient temperature rise and cyclization dehydration to finally obtain polyimide hollow microspheres.

[0012] Preferably, the mass solid content of the polyamic acid solution described in step (1) is 3%-20%.

[0013] Preferably, the diamine described in step (1) is one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether (ODA), 4,4'-bis(4-aminophenoxy)biphenyl, 1,3-bis(4'-aminophenoxy)benzene, 3-(3-aminophenoxy)aniline, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 2,6-diaminotoluene, 4,4'-diaminodiphenylmethane, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 1,2-phenylenediamine, 2,2'-biphenyldiamine or tetramethyl-p-phenylenediamine; the dianhydride is one or more of pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), bisphenol A type diether dianhydride, benzophenone tetracarboxylic dianhydride, 4,4'-oxydiphthalic anhydride (ODPA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), hexafluorodiacid anhydride (6FDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride, 4,4'-phenylenedioxydiphthalic anhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, hydrogenated biphenyltetracarboxylic dianhydride or 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride; the organic solvent is one or more of N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) or diethyl sulfoxide.

[0014] Preferably, the mass ratio of the polyamic acid solution to the oil phase described in step (2) is 1:(1 - 5); the stirring rate is 100 - 1000 r / min; the reaction time is 20 - 120 min.

[0015] Preferably, in the precipitant described in step (3), the organic solvent accounts for 20% - 80% of the mass of the precipitant; the addition amount of the emulsifier in the precipitant mixed solution is 5% - 20% of the mass of the precipitant; the addition amount of the dispersant is 0.5% - 5% of the mass of the precipitant; the addition mass of the emulsion is 10% - 15% of the mass of the precipitant; the stirring rate is 100 - 600 r / min; the reaction time is 1 - 12 h.

[0016] Preferably, the gradient heating in step (4) is as follows: the heating rate is 2 - 4 °C / min; heat up to 80 - 120 °C and keep it constant for 50 - 70 min; heat up to 180 - 220 °C and keep it constant for 50 - 70 min; heat up to 280 - 320 °C and keep it constant for 50 - 70 min.

[0017] Preferably, the oil phase described in step (2) is one or more of methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methyl vinyl silicone oil or synthetic grease.

[0018] Preferably, the emulsifier described in step (3) is one or more of sodium stearate, polyethylene glycol, sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, OP-10 or OP-15; the organic solvent is one or more of methanol, tetrahydrofuran, ethanol, acetone or methyl ethyl ketone; the dispersant is one or more of polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), polyacrylic acid, polymethacrylate, methyl cellulose or gelatin.

[0019] Preferably, the organic solvent described in step (4) is one or more of n-hexane, cyclohexane, kerosene, petroleum ether or acetone.

[0020] The average particle size of the polyimide hollow microspheres prepared by the present invention is distributed between 2 - 15 μm, and the thermal decomposition temperature is between 460°C - 500°C.

[0021] The operation method of the present invention is simple and controllable, and the conditions are mild, providing a simple and feasible new method for preparing polyimide hollow microspheres. Using the emulsion template method to prepare polyimide hollow microspheres, the size and distribution of the polyimide hollow microspheres can be controlled by controlling the solid content of the polyamic acid solution, the composition of the precipitant, and the rotation speed, etc.

[0022] Beneficial effects:

[0023] (1) Using the emulsion template method to prepare polyimide hollow microspheres, compared with the O / W / O inverse emulsion method, the emulsifier is used only once during the preparation process, so less impurities are introduced, and the prepared polyimide microspheres are purer.

[0024] (2) Most of the existing polyimide microsphere preparation processes require chemical imidization first and then thermal imidization. This method first prepares polyamic acid hollow microspheres, and then undergoes one-step thermal imidization without the need for chemical imidization, reducing the consumption of solvents.

[0025] (3) This method uses emulsion droplets as templates. During the microsphere forming process, part of the template is washed away, and the part of the template remaining in the internal cavity will also degrade during the thermal imidization process. Therefore, polyimide hollow microspheres with a relatively complete shell layer can be obtained. Description of the drawings

[0026] Figure 1 It is the infrared spectrum of the polyimide hollow microspheres prepared in Example 1.

[0027] Figure 2 It is the scanning electron microscope photo of the polyimide hollow microspheres prepared in Example 1.

[0028] Figure 3 It is the particle size distribution diagram of the polyimide hollow microspheres prepared in Example 1.

[0029] Figure 4 Thermogravimetric curve of the polyimide hollow microspheres prepared in Example 1. Detailed implementation mode

[0030] Example 1: Add 1.4359 g of 4,4'-diaminodiphenyl ether (ODA) to 57 g of DMAc, stir until ODA is dissolved, and add a total of 1.5641 g of PMDA under stirring. Polymerize at room temperature for 4 hours to obtain a polyamic acid solution with a solid content (mass percentage) of 3%. Take 5 g of the above-prepared polyamic acid solution and 5 g of methyl silicone oil (mass ratio of polyamic acid solution to silicone oil is 1:1), stir at 100 r / min for 20 min to obtain a white emulsion. Prepare 100 g of a precipitant, including 20 g of ethanol, 80 g of deionized water, and add 0.5 g of PVP and 5 g of sodium dodecyl sulfonate to obtain a precipitant mixed solution. Add the above white emulsion to the precipitant mixed solution and stir and react at a rotation speed of 100 r / min for 1 hour. Filter the obtained suspension microsphere solution, wash it 3 times with n-hexane and deionized water respectively, dry it, and perform thermal imidization with a heating rate of 2 °C / min (100 °C × 60 min, 200 °C × 60 min, 320 °C × 60 min) to obtain yellow powdery polyimide hollow microspheres. The infrared spectrum of the polyimide hollow microspheres prepared in this example is as Figure 1 shown, the symmetric and asymmetric stretching vibration peaks of C=O at 1771 cm -1 , 1717 cm -1 indicate the existence of the imide ring structure in the sample, that is, polyimide is generated. The surface morphology of the polyimide hollow microspheres prepared in this example is as Figure 2 shown, the surface of the microspheres is relatively smooth, without obvious agglomeration, and the hollow structure can be seen in some damaged microspheres. The particle size distribution of the polyimide hollow microspheres prepared in this example is as Figure 3 shown, the maximum particle size is about 10 μm, the minimum particle size is about 2 μm, and it is basically normally distributed, with an average particle size of 5.12 μm. The thermogravimetric curve of the polyimide hollow microspheres prepared in this example is as Figure 4 shown, the temperature at which the weight loss is 5% in a nitrogen atmosphere is 460 °C.

[0031] Example 2: 1.2901 g of p-phenylenediamine was added to 55.2 g of NEP, and stirred until the p-phenylenediamine was dissolved. Under stirring, a total of 3.5099 g of BPDA was added, and polymerization was carried out at room temperature for 4 hours to obtain a polyamic acid solution with a solid content (mass percentage) of 8%. 5 g of the above-prepared polyamic acid solution and 10 g of ethyl silicone oil (the mass ratio of the polyamic acid solution to the silicone oil is 1:2) were stirred at 200 r / min for 40 min to obtain a white emulsion. 100 g of a precipitating agent was prepared, including 30 g of tetrahydrofuran and 70 g of deionized water, and 1 g of PVA and 15 g of sodium dodecylbenzenesulfonate were added to obtain a mixed solution of the precipitating agent. The above white emulsion was added to the mixed solution of the precipitating agent, and stirred and reacted at a rotation speed of 300 r / min for 4 hours. The obtained suspension microsphere solution was filtered, washed 3 times with cyclohexane and deionized water respectively, dried, and thermally imidized with a heating rate of 2.5 °C / min (120 °C × 50 min, 220 °C × 50 min, 320 °C × 50 min) to obtain yellow powdery polyimide hollow microspheres. The polyimide hollow microspheres prepared in this example had a smooth surface and no agglomeration phenomenon. After testing, the maximum particle size of the microspheres was about 5 μm, the minimum particle size was about 1 μm, and they were basically normally distributed, with an average particle size of 2.51 μm, and the temperature at which the weight loss was 5% in a nitrogen atmosphere was 494 °C.

[0032] Example 3: 1.8611 g of m-phenylenediamine was added to 52.8 g of DMF, and stirred until the m-phenylenediamine was dissolved. Under stirring, a total of 5.3389 g of ODPA was added, and polymerization was carried out at room temperature for 4 hours to obtain a polyamic acid solution with a solid content (mass percentage) of 12%. 5 g of the above-prepared polyamic acid solution and 15 g of phenyl silicone oil (the mass ratio of the polyamic acid solution to the silicone oil is 1:3) were stirred at 300 r / min for 50 min to obtain a white emulsion. 200 g of a precipitating agent was prepared, including 160 g of ethanol and 40 g of deionized water, and 2 g of polyacrylic acid and 30 g of sodium dodecyl sulfate were added to obtain a mixed solution of the precipitating agent. The above white emulsion was added to the mixed solution of the precipitating agent, and stirred and reacted at a rotation speed of 300 r / min for 6 hours. The obtained suspension microsphere solution was filtered, washed 3 times with acetone and deionized water respectively, dried, and thermally imidized with a heating rate of 3 °C / min (80 °C × 70 min, 180 °C × 70 min, 280 °C × 70 min) to obtain yellow powdery polyimide hollow microspheres. After testing, the maximum particle size of the polyimide hollow microspheres prepared in this example was about 12 μm, the minimum particle size was about 2 μm, and they were overall normally distributed, with an average particle size of 7.92 μm, and the temperature at which the weight loss was 5% in a nitrogen atmosphere was 467 °C.

[0033] Example 4: 4.8010 g of 4,4'-bis(4-aminophenoxy)biphenyl was added to 51 g of DMSO and stirred until 4,4'-bis(4-aminophenoxy)biphenyl was dissolved. Under stirring, a total of 4.1990 g of BTDA was added, and polymerization was carried out at room temperature for 4 hours to obtain a polyamic acid solution with a solid content (mass percentage) of 15%. 5 g of the above-prepared polyamic acid solution and 20 g of methyl hydrogen silicone oil (the mass ratio of the polyamic acid solution to the silicone oil is 1:4) were stirred at 400 r / min for 60 min to obtain a white emulsion. 300 g of a precipitant was prepared, including 180 g of acetone and 120 g of deionized water, and 4 g of methylcellulose and 50 g of op-10 were added to obtain a precipitant mixed solution. The above white emulsion was added to the precipitant mixed solution, and stirring reaction was carried out at a rotation speed of 600 r / min for 6 hours. The obtained suspension microsphere solution was filtered, washed 3 times with kerosene and deionized water respectively, dried, and thermally imidized with a heating rate of 3.5 °C / min (90 °C × 50 min, 190 °C × 60 min, 300 °C × 70 min) to obtain yellow powdery polyimide hollow microspheres. After detection, the maximum particle size of the polyimide hollow microspheres prepared in this example was about 6 μm, the minimum particle size was about 2 μm, the overall was in a normal distribution, the average particle size was 3.66 μm, and the temperature at which the weight loss was 5% under a nitrogen atmosphere was 482 °C.

[0034] Example 5: 4.7626 g of 1,3-bis(4'-aminophenoxy)benzene was added to 48 g of NMP and stirred until 1,3-bis(4'-aminophenoxy)benzene was dissolved. Under stirring, a total of 7.2374 g of 6FDA was added, and polymerization was carried out at room temperature for 4 hours to obtain a polyamic acid solution with a solid content (mass percentage) of 20%. 5 g of the above-prepared polyamic acid solution and 25 g of methyl vinyl silicone oil (the mass ratio of the polyamic acid solution to the silicone oil is 1:5) were stirred at 1000 r / min for 120 min to obtain a white emulsion. 300 g of a precipitant was prepared, including 240 g of ethanol and 60 g of deionized water, and 15 g of PVP and 60 g of op-15 were added to obtain a precipitant mixed solution. The above white emulsion was added to the precipitant mixed solution, and stirring reaction was carried out at a rotation speed of 300 / min for 12 hours. The obtained suspension microsphere solution was filtered, washed 3 times with n-hexane and deionized water respectively, dried, and thermally imidized with a heating rate of 4 °C / min (100 °C × 50 min, 220 °C × 70 min, 310 °C × 60 min) to obtain yellow powdery polyimide hollow microspheres. After detection, the maximum particle size of the polyimide hollow microspheres prepared in this example was about 20 μm, the minimum particle size was about 8 μm, the overall was in a normal distribution, the average particle size was 15.49 μm, and the temperature at which the weight loss was 5% under a nitrogen atmosphere was 469 °C.

[0035] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, 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 method for preparing polyimide hollow microspheres, the specific steps are as follows: (1) Dissolve the monomer diamine in an organic solvent, stir until completely dissolved, and then add the monomer dianhydride in batches to prepare a polyamic acid solution; wherein the mass solid content of the polyamic acid solution is 3%-20%; (2) Mix the polyamic acid solution prepared in step (1) with an oil phase, and then stir at a certain rotation speed for a period of time to obtain a white emulsion; wherein the oil phase is one or more of methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methyl vinyl silicone oil or synthetic oil; the mass ratio of the polyamic acid solution to the oil phase is 1:(1-5); (3) Add the emulsion prepared in step (2) to a precipitant mixed solution, stir and react at a certain rotation speed for a period of time to precipitate solid particles; the precipitant mixed solution is composed of adding a certain amount of emulsifier and dispersant to the precipitant, wherein the precipitant is composed of an organic solvent and deionized water; wherein the organic solvent in the precipitant accounts for 20%-80% of the mass of the precipitant; the organic solvent is one or more of methanol, tetrahydrofuran, ethanol, acetone or butanone; (4) Filter the suspension microsphere solution obtained in step (3), separate the polyamic acid microspheres, then wash them successively with an organic solvent and deionized water, dry them, and then place them in an oven for gradient heating, cyclization dehydration, and finally obtain polyimide hollow microspheres.

2. The preparation method according to claim 1, characterized in that The diamine described in step (1) is one or more of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4'-bis(4-aminophenoxy)biphenyl, 1,3-bis(4'-aminophenoxy)benzene, 3-(3-aminophenoxy)aniline, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 2,6-diaminotoluene, 4,4'-diaminodiphenylmethane, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, 1,2-phenylenediamine, 2,2'-biphenyldiamine or tetramethyl-p-phenylenediamine; the dianhydride is one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, bisphenol A type diether dianhydride, benzophenone tetracarboxylic dianhydride, 4,4'-oxybisphthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, hexafluorodiacid anhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 4,4'-p-phenylenedioxybisphthalic anhydride, 1,2,3,4-cyclopentanetetracarboxylic dianhydride, hydrogenated biphenyltetracarboxylic dianhydride or 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride; the organic solvent is one or more of N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide or diethyl sulfoxide.

3. The preparation method according to claim 1, characterized in that The stirring rate in step (2) is 100-1000 r / min; the reaction time is 20-120 min.

4. The preparation method according to claim 1, characterized in that In the precipitant mixed solution described in step (3), the addition amount of the emulsifier is 5%-20% of the mass of the precipitant; the addition amount of the dispersant is 0.5%-5% of the mass of the precipitant; the added mass of the emulsion is 10%-15% of the mass of the precipitant; the stirring rate is 100-600 r / min; the reaction time is 1-12 h.

5. The preparation method according to claim 1, characterized in that In step (4), the gradient temperature increase is as follows: the temperature increase rate is 2-4 °C / min; it is heated to 80-120 °C and kept at a constant temperature for 50-70 min; it is heated to 180-220 °C and kept at a constant temperature for 50-70 min; it is heated to 280-320 °C and kept at a constant temperature for 50-70 min.

6. The preparation method according to claim 1, wherein In step (3), the emulsifier is one or more of sodium stearate, polyethylene glycol, sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, op-10 or op-15; the dispersant is one or more of polyvinyl alcohol, polyvinylpyrrolidone, polyacrylic acid, polymethacrylate, methyl cellulose or gelatin.

7. The production method according to claim 1, characterized in that In step (4), the organic solvent is one or more of n-hexane, cyclohexane, kerosene, petroleum ether or acetone.

8. The preparation method according to claim 1, characterized in that The average particle size of the prepared polyimide hollow microspheres is distributed between 2-15 μm, and the thermal decomposition temperature is between 460 °C - 500 °C.

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