阅读说明：本技术 一种聚酰亚胺/二氧化硅微球及其制备方法 (Polyimide/silicon dioxide microsphere and preparation method thereof ) 是由 贾南方 王杰 于 2021-10-21 设计创作，主要内容包括：本发明公开了一种表面包覆二氧化硅壳层的聚酰亚胺/二氧化硅复合微球及其制备方法,所述聚酰亚胺/二氧化硅具有聚酰亚胺@二氧化硅为复合核心、二氧化硅为壳的结构,采用静电喷雾技术制备出含二氧化硅前驱体的聚酰胺酸微球,经水解及热酰亚胺化处理,最终得到聚酰亚胺/二氧化硅复合微球。本发明方法制得的复合微球的直径在20nm-10μm范围内可控,二氧化硅无机纳米层包覆均匀,壳层厚度在5nm-500nm范围内可控,兼顾了聚酰亚胺材料的轻质高强耐高温的优良属性和二氧化硅耐热、耐磨、耐化学腐蚀的特性,可广泛应用于催化、制药、生物材料、电子器件、等领域,同时,其在锂电隔膜涂层材料及负极材料领域也表现出巨大的应用潜力。(The invention discloses a polyimide/silicon dioxide composite microsphere with a silicon dioxide shell layer coated on the surface and a preparation method thereof. The diameter of the composite microsphere prepared by the method is controllable within the range of 20nm-10 mu m, the inorganic nano-silica layer is uniformly coated, the thickness of the shell layer is controllable within the range of 5nm-500nm, the excellent properties of light weight, high strength and high temperature resistance of the polyimide material and the characteristics of heat resistance, wear resistance and chemical corrosion resistance of the silica are considered, the composite microsphere can be widely applied to the fields of catalysis, pharmacy, biological materials, electronic devices and the like, and meanwhile, the composite microsphere also has great application potential in the fields of lithium battery diaphragm coating materials and cathode materials.)

1. The polyimide/silicon dioxide microsphere is characterized by consisting of a polyimide microsphere @ silicon dioxide inner core and silicon dioxide particles or silicon dioxide shells coated on the surface, wherein the diameter of the silicon dioxide particles is 5-200nm, the thickness of the silicon dioxide shells is 5-500nm, and the diameter of the polyimide @ silicon dioxide inner core microsphere is 20nm-10 mu m, preferably 200nm-5 microns; the mass ratio of the silicon dioxide to the microspheres is 1-50 wt%, preferably 5-40 wt%.

2. A preparation method of polyimide/silicon dioxide microspheres is characterized by comprising the following steps:

a: selecting dianhydride and diamine, preparing a polyamic acid solution in an aprotic polar solvent through low-temperature condensation polymerization, then adding a silicon source precursor into the polyamic acid solution, uniformly mixing, and then performing electrostatic spraying to prepare a polyamic acid/silicon source precursor microsphere;

b: carrying out thermal induction treatment on the polyamic acid/silicon source precursor microspheres prepared in the step A to obtain polyamic acid composite microspheres with enriched silicon source precursors on the surface layers;

c: placing the microspheres subjected to heat treatment in hydrolysate for hydrolysis, cleaning with deionized water, and finally placing in a vacuum oven for drying;

d: and D, performing thermal imidization treatment on the microspheres treated in the step C to finally obtain the polyimide/silicon dioxide microspheres.

3. The method for producing a polyimide/silica microsphere according to claim 2, wherein the dianhydride in step A is one or a mixture of two or more selected from the group consisting of biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, benzophenonetetracarboxylic dianhydride, diphenyl ether tetracarboxylic dianhydride, hexafluoro dianhydride and bisphenol A type diether dianhydride, and the diamine is one or a mixture of two or more selected from the group consisting of diaminodiphenyl ether, p-phenylenediamine, 4 ' -diaminodiphenylmethane and 4,4 ' -diamino-2, 2 ' -bistrifluoromethylbiphenyl.

4. The method for preparing polyimide/silica microspheres according to claim 2, wherein the polyamic acid in the step a is prepared from at least one dianhydride and at least one diamine in a molar ratio of dianhydride to diamine of 0.95:1-1.05:1 is obtained by polycondensation in polar aprotic solvent; the polar aprotic solvent is one or more of DMF, DMAc, NMP and DMSO, and the solid content of the polyamic acid solution is 3-50 wt%, preferably 5-40 wt%.

5. The method for preparing polyimide/silica microspheres according to claim 2, wherein the silicon source precursor in step a is one or more of tetramethyl orthosilicate, tetraethyl orthosilicate, ethyl orthosilicate and tetrabutyl orthosilicate; the molar ratio of the added silicon source precursor to the dianhydride is 0.1:1-7: 1.

6. The method for preparing polyimide/silica microspheres according to claim 2, wherein the electrostatic spraying voltage in step a is 10 to 60kV, preferably 15 to 55 kV; the spraying distance is 8-35 cm, preferably 10-30 cm.

7. The method for preparing polyimide/silica microspheres as claimed in claim 2, wherein the heat-induced treatment temperature in step B is 150-.

8. The method for preparing polyimide/silica microspheres according to claim 2, wherein the hydrolysate in the step C is one or more of acid, alcohol and deionized water, and when mixed, the volume ratio of alcohol/water is 1: 0.25-1: and 4, the pH value of the mixed solution is 0-7, wherein the acid is one or more of formic acid, acetic acid, oxalic acid, propionic acid, butyric acid, hydrochloric acid, sulfuric acid and nitric acid, and the alcohol is one or more of methanol, ethanol, ethylene glycol, glycerol, n-propanol, isopropanol and n-butanol.

9. The method for preparing polyimide/silica microspheres according to claim 2, wherein the hydrolysis time in step C is 30min to 24h, the drying condition is 40 to 70 ℃, the drying time is 30min to 16h, and preferably the drying condition is 50 to 60 ℃ and the vacuum drying time is 1 to 12 h.

10. The method for preparing polyimide/silica microspheres according to claim 2, wherein the thermal imidization treatment conditions in step D are: the temperature is 280-450 ℃, the treatment time is 30min-3h, and the treatment time is preferably 300-350 ℃ for 1-2 h.

11. Polyimide/silica microspheres prepared by a process for the preparation of polyimide/silica microspheres according to any one of claims 2 to 10 and articles thereof.

Technical Field

The invention belongs to the technical field of polyimide microspheres, and particularly relates to a polyimide/silicon dioxide microsphere and a preparation method thereof.

Background

With the rise of nano materials in recent years, electrostatic spraying has attracted much attention as a commonly used technology for preparing polymer microspheres. Compared with the traditional methods such as a precipitation method, suspension polymerization, emulsion polymerization and the like, the electrostatic spraying method has the obvious advantages of simple operation, less post-treatment procedures, considerable efficiency and the like, and has the potential of macroscopic preparation and large-scale application. The nano-sized microspheres prepared by electrospray have unique small-size effect, surface effect and tunnel effect, and can endow materials with better performance and function. Therefore, the method has great development potential in the fields of energy, biology, environment, catalysis and the like, and has high application value.

The polyimide material is a high-performance polymer material with excellent characteristics of high and low temperature resistance, high strength and high modulus, high creep resistance, high dimensional stability, low thermal expansion coefficient, high electrical insulation, low dielectric constant and loss, radiation resistance, corrosion resistance and the like. The nano-sized polyimide microspheres not only have the characteristics of polyimide, but also have the advantages of light weight and large specific surface area, and are particularly suitable for application in the fields of energy storage and conversion, biomedicine, environmental protection and the like. In recent years, organic/inorganic composite materials have attracted much attention because of their combination with the light weight and high strength of organic materials and the acoustic, optical, electrical, magnetic, etc. properties of inorganic materials. Similarly, the polyimide/inorganic composite material prepared by the surface inorganic loading method endows the polyimide with the functionalized characteristic, and becomes a research hotspot in the current new energy field.

The lithium ion battery has the advantages of small volume, long service life, environmental protection and the like, and is widely applied to a plurality of fields of 3C, power automobiles, energy storage and the like. In recent years, accidents such as mobile phone explosion, electric vehicle spontaneous combustion and the like frequently occur, and more attention is paid to the requirement on the safety performance of the lithium ion battery. The current lithium battery diaphragm mostly adopts a ceramic particle coating method in order to improve the heat resistance and the electrolyte wettability of the traditional polyolefin diaphragm, but the loss of energy density can be caused due to the high density of the ceramic particles, and particularly, the thickness of the ceramic coating layer is more and more larger under the trend that the current diaphragm is thinner and thinner. Therefore, it has become a hot point of research in recent years to effectively improve the heat resistance and electrolyte wettability of the separator and reduce the energy density loss due to coating.

Disclosure of Invention

The method is simple to implement, the prepared polyimide/silica microsphere has uniform silica inorganic nano-layer coating and controllable thickness, the obtained composite nano-microsphere can play the same role as a ceramic coating, the weight of the coating is effectively reduced, the energy density of a battery can be ensured not to be greatly lost, the composite nano-microsphere is taken as an ideal candidate material of a high-temperature-resistant coating of a lithium ion battery diaphragm, and meanwhile, the microsphere has a good application prospect in the field of silicon carbon negative electrodes.

The polyimide/silicon dioxide microsphere is characterized by consisting of a polyimide microsphere inner core and silicon dioxide particles or a silicon dioxide shell layer coated on the surface.

Furthermore, the diameter of the silicon dioxide particle is 3-200nm, the thickness of a silicon dioxide shell layer is 3-500nm, and the diameter of the polyimide @ silicon dioxide inner core microsphere is 20nm-10 μm; preferably 200nm to 5 μm.

Further, the silica in the polyimide/silica microspheres accounts for 1 to 50 wt%, preferably 5 to 40 wt%, of the total mass.

Further, the density of the polyimide/silicon dioxide microspheres is 1.46-1.90g/cm³Preferably 1.47 to 1.70g/cm³。

A preparation method of polyimide/silicon dioxide microspheres is characterized by comprising the following steps:

a: preparing a polyamic acid solution using at least one dianhydride and at least one diamine, and then adding to the polyamic acid solution

Adding a silicon source precursor, and performing electrostatic spraying to obtain polyamic acid/silicon source precursor microspheres;

b: c, performing thermal induction treatment on the polyamic acid/silicon source precursor microspheres prepared in the step A to obtain a precursor with a silicon source enriched on the surface layer

Polyamic acid microspheres of a body;

c: b, placing the microspheres subjected to the heat treatment in the step B into hydrolysate for hydrolysis and drying;

d: and D, performing thermal imidization treatment on the microspheres treated in the step C to finally obtain the polyimide/silicon dioxide microspheres.

Further, the polyamic acid in the step A is prepared by low-temperature polycondensation of at least one dianhydride and at least one diamine in a polar aprotic solvent according to the mole ratio of the dianhydride to the diamine of 0.95:1-1.05: 1.

Further, the dibasic acid anhydride is one or a mixture of more than two of biphenyl tetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), Benzophenone Tetracarboxylic Dianhydride (BTDA), diphenyl ether tetracarboxylic dianhydride (ODPA), hexafluoro dianhydride (6FDA) and bisphenol A type diether dianhydride (BPADA), and the diamine is one or a mixture of more than two of diaminodiphenyl ether (ODA), p-Phenylenediamine (PDA), 4 ' -diaminodiphenylmethane (MDA) and 4,4 ' -diamino-2, 2 ' -bistrifluoromethylbiphenyl (TFDB).

Further, the polar aprotic solvent is one or more of DMF, DMAc, NMP and DMSO, and the solid content of the polyamic acid solution is 3-50%, preferably 5-40%.

Further, in the step a, the silicon source is one or more of tetramethyl orthosilicate, tetraethyl orthosilicate, ethyl orthosilicate and tetrabutyl orthosilicate.

Further, the molar ratio of the precursor silicon source and the dianhydride added in the step A is 0.1:1-7:1, preferably 0.5:1-6: 1.

Further, the electrostatic spraying voltage in the step A is 10-60 kV, preferably 15-55 kV; the spraying distance is 8-35 cm, preferably 10-30 cm.

Further, the heat-induced treatment temperature in the step B is 150-.

Further, the hydrolysate in the step C is one or a mixture of acid, alcohol and water, and when the hydrolysate is mixed and used, the volume ratio of the acid to the alcohol to the water is 1: 0.1-2: 2-6, preferably 1: 0.25-1: 3-5, wherein the pH value of the mixed solution is 0-7, the acid is one or more of formic acid, acetic acid, oxalic acid, propionic acid, butyric acid, hydrochloric acid, sulfuric acid and nitric acid, and the alcohol is one or more of methanol, ethanol, ethylene glycol, glycerol, n-propanol, isopropanol and n-butanol; preferably, water is used.

Further, the hydrolysis time in the step C is 10min-36h, preferably 30min-24 h; the hydrolysis temperature is 0-100 deg.C, preferably 10-60 deg.C; drying at 40-70 deg.C for 30min-16h, preferably 50-60 deg.C for 1-12 h. Further, the thermal imidization treatment conditions in the step D are as follows: the temperature is 250-450 ℃, the treatment time is 30min-3h, and the treatment time is preferably 300-350 ℃ for 1-2 h.

Compared with the prior art, the method has the following excellent effects:

1. compared with the traditional suspension polymerization, emulsion polymerization and precipitation methods, the method has the advantages of simple preparation process, less post-treatment procedures, simple and convenient operation, easy repetition and wide applicable system, and can be used for all systems for preparing the polyimide microspheres by a two-step method.

2. The method can realize the controllable adjustment of the core diameter and the shell thickness of the polyimide/silicon dioxide microsphere through the adjustment of the addition amount of the precursor and the preparation process parameters.

3. The polyimide nano-microsphere with the surface coated with the silicon dioxide, which is prepared by the method disclosed by the invention, effectively combines the advantages of polyimide and silicon dioxide, and has excellent thermal stability, wettability and flame retardant property.

4. The polyimide nano-microspheres coated with silicon dioxide and prepared by the method can be used for coating polyolefin diaphragms, and the thermal dimensional stability and the electrolyte wettability of the diaphragms are enhanced. The density of the microsphere coating surface of the diaphragm with the same thickness of the substrate and the coating layer is smaller than that of the ceramic coating diaphragm.

Drawings

FIG. 1 is a scanning electron micrograph of polyimide/silica microspheres prepared according to example 1 at 20000 times magnification.

FIG. 2 is a scanning electron micrograph of polyimide/silica microspheres prepared according to example 2, at 20000 times magnification.

FIG. 3 is a scanning electron micrograph of polyimide/silica microspheres prepared according to example 3 at 20000 times magnification.

FIG. 4 is a scanning electron micrograph of polyimide/silica microspheres prepared according to example 4 at 20000 times magnification.

FIG. 5 is an infrared spectrum of a polyimide/silica microsphere prepared according to example 4.

FIG. 6 is a scanning electron micrograph of polyimide/silica microspheres prepared according to example 5 at 20000 times magnification.

FIG. 7 is a scanning electron micrograph of polyimide/silica microspheres prepared according to example 6 at 20000 times magnification.

FIG. 8 is a scanning electron micrograph of polyimide/silica microspheres prepared according to example 7 at 20000 times magnification.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be noted that: the following examples are only for illustrating the present invention and are not intended to limit the technical solutions described in the present invention. Thus, while the present invention has been described in detail with reference to the following examples, it will be understood by those skilled in the art that the present invention may be modified and equivalents may be substituted; all such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.

Example 1

A. Weighing 3.359g of PMDA and 3.084g of ODA, completely dissolving ODA in 50ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step in an ice-water bath condition to obtain a polyamic acid (PAA) solution with the solid content of 12 wt%, mechanically stirring for 2h, dropwise adding 2.376g of TEOS (the addition amount is calculated inversely according to 10% of the total mass fraction of the polyimide and the silicon dioxide), stirring for 2h after dropwise adding is finished, uniformly mixing, then putting into an injector with the capacity of 20ml, and preparing the PAA/TEOS microsphere through electrostatic spraying. Specific parameters of electrostatic spraying are voltage: 25 kV; temperature: 25 ℃; humidity: 40 percent; diameter of syringe needle: number 12; receiving a flat plate; receiving distance: the tip-to-plate distance was 20 cm.

B. And carrying out heat treatment on the obtained microspheres, wherein the treatment temperature is 280 ℃, and the treatment time is 30 min.

C. Preparing hydrolysate: 40mL of deionized water and 20mL of ethanol are uniformly mixed, and hydrochloric acid is added dropwise to adjust the pH value to 5.

D. And D, putting the microspheres prepared in the step B into a hydrolysate with the pH value of 5 for hydrolysis for 12 hours, and putting the microspheres into an oven with the temperature of 60 ℃ for heat preservation for 10 hours.

E. And D, putting the microspheres obtained by the treatment in the step D into a forced air oven for complete imidization, wherein the treatment temperature is 300 ℃, and the time is 2 hours, so that the polyimide/silicon dioxide microspheres are finally obtained. The morphology of the obtained microspheres is shown in figure 1.

Example 2

A. Weighing 3.359g of PMDA and 3.084g of ODA, completely dissolving ODA in 50ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step in an ice-water bath condition to obtain a polyamic acid (PAA) solution with the solid content of 12 wt%, mechanically stirring for 2h, dropwise adding 5.345g of TEOS (the addition amount is calculated by the reverse calculation of the silica accounting for 20% of the total mass fraction of the polyimide and the silica), stirring for 2h after dropwise adding is finished, uniformly mixing, then putting into a syringe with the capacity of 20ml, and preparing the PAA/TEOS microsphere through electrostatic spraying. Specific parameters of electrostatic spraying are voltage: 25 kV; temperature: 25 ℃; humidity: 40 percent; diameter of syringe needle: number 12; receiving a flat plate; receiving distance: the tip-to-plate distance was 20 cm.

B. And carrying out heat treatment on the obtained microspheres, wherein the treatment temperature is 280 ℃, and the treatment time is 30 min.

C. Preparing hydrolysate: 40mL of deionized water and 20mL of ethanol are uniformly mixed, and hydrochloric acid is added dropwise to adjust the pH value to 5.

D. And D, putting the microspheres prepared in the step B into a hydrolysate with the pH value of 5 for hydrolysis for 12 hours, and putting the microspheres into an oven with the temperature of 60 ℃ for heat preservation for 10 hours.

E. And D, putting the microspheres obtained by the treatment in the step D into a forced air oven for complete imidization, wherein the treatment temperature is 300 ℃, and the time is 2 hours, so that the polyimide/silicon dioxide microspheres are finally obtained. The morphology of the obtained microspheres is shown in figure 2.

Example 3

A. Weighing 3.359g of PMDA and 3.084g of ODA, completely dissolving ODA in 50ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step in an ice-water bath condition to obtain a polyamic acid (PAA) solution with the solid content of 12 wt%, mechanically stirring for 2h, dropwise adding 9.163g of TEOS (the addition amount is calculated inversely according to 30% of the total mass fraction of the polyimide and the silicon dioxide), stirring for 2h after dropwise adding is finished, uniformly mixing, then putting into a syringe with the capacity of 20ml, and preparing the PAA/TEOS microsphere through electrostatic spraying. Specific parameters of electrostatic spraying are voltage: 25 kV; temperature: 25 ℃; humidity: 40 percent; diameter of syringe needle: number 12; receiving a flat plate; receiving distance: the tip-to-plate distance was 20 cm.

B. And carrying out heat treatment on the obtained microspheres, wherein the treatment temperature is 280 ℃, and the treatment time is 30 min.

C. Preparing hydrolysate: 40mL of deionized water and 20mL of ethanol are uniformly mixed, and hydrochloric acid is added dropwise to adjust the pH value to 5.

D. And D, putting the microspheres prepared in the step B into a hydrolysate with the pH value of 5 for hydrolysis for 12 hours, and putting the microspheres into an oven with the temperature of 60 ℃ for heat preservation for 10 hours.

E. And D, putting the microspheres obtained by the treatment in the step D into a forced air oven for complete imidization, wherein the treatment temperature is 300 ℃, and the time is 2 hours, so that the polyimide/silicon dioxide microspheres are finally obtained. The morphology of the obtained microspheres is shown in figure 3.

Example 4

A. Weighing 3.359g of PMDA and 3.084g of ODA, completely dissolving ODA in 50ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step in an ice-water bath condition to obtain a polyamic acid (PAA) solution with the solid content of 12 wt%, mechanically stirring for 2h, dropwise adding 14.253g of TEOS (the addition amount is calculated inversely according to 40% of the total mass fraction of the polyimide and the silicon dioxide), stirring for 2h after dropwise adding is finished, uniformly mixing, then putting into a syringe with the capacity of 20ml, and preparing the PAA/TEOS microsphere through electrostatic spraying. Specific parameters of electrostatic spraying are voltage: 25 kV; temperature: 25 ℃; humidity: 40 percent; diameter of syringe needle: number 12; receiving a flat plate; receiving distance: the tip-to-plate distance was 20 cm.

B. And carrying out heat treatment on the obtained microspheres, wherein the treatment temperature is 280 ℃, and the treatment time is 30 min.

C. Preparing hydrolysate: 40mL of deionized water and 20mL of ethanol are uniformly mixed, and hydrochloric acid is added dropwise to adjust the pH value to 5.

D. And D, putting the microspheres prepared in the step B into a hydrolysate with the pH value of 5 for hydrolysis for 12 hours, and putting the microspheres into an oven with the temperature of 60 ℃ for heat preservation for 10 hours.

E. And D, putting the microspheres obtained by the treatment in the step D into a forced air oven for complete imidization, wherein the treatment temperature is 300 ℃, and the time is 2 hours, so that the polyimide/silicon dioxide microspheres are finally obtained. The morphology of the obtained microspheres is shown in figure 4, and the infrared spectrogram is shown in figure 5. The curve in the infrared spectrum shows a distinct characteristic structure absorption peak at 1778cm^-1，1723cm^-1The absorption peak corresponds to the symmetric and asymmetric stretching vibration of C ═ O on the imide ring, 725cm^-1The absorption peak corresponds to the characteristic peak of the imide five-membered ring structure and is 1091cm^-1A very distinct characteristic absorption peak of Si — O bonds appears, thus demonstrating the successful preparation of polyimide/silica microspheres.

Example 5

A. Weighing 3.359g of PMDA and 3.084g of ODA, completely dissolving ODA in 50ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step in an ice-water bath condition to obtain a polyamic acid (PAA) solution with the solid content of 12 wt%, mechanically stirring for 2h, dropwise adding 7.126g of TEOS (the addition amount is calculated by the reverse calculation of the silicon dioxide accounting for 25% of the total mass fraction of polyimide and silicon dioxide), stirring for 2h after dropwise adding is finished, uniformly mixing, then putting into a syringe with the capacity of 20ml, and preparing the PAA/TEOS microsphere through electrostatic spraying. Specific parameters of electrostatic spraying are voltage: 25 kV; temperature: 25 ℃; humidity: 40 percent; diameter of syringe needle: number 12; receiving a flat plate; receiving distance: the tip-to-plate distance was 20 cm.

B. And carrying out heat treatment on the obtained microspheres, wherein the treatment temperature is 280 ℃, and the treatment time is 30 min.

C. Preparing hydrolysate: 40mL of deionized water and 20mL of ethanol are uniformly mixed, and hydrochloric acid is added dropwise to adjust the pH value to 5.

D. And D, putting the microspheres prepared in the step B into a hydrolysate with the pH value of 5 for hydrolysis for 12 hours, and putting the microspheres into an oven with the temperature of 60 ℃ for heat preservation for 10 hours.

E. And D, putting the microspheres obtained by the treatment in the step D into a forced air oven for complete imidization, wherein the treatment temperature is 300 ℃, and the time is 2 hours, so that the polyimide/silicon dioxide microspheres are finally obtained. The morphology of the obtained microspheres is shown in figure 6.

Example 6

A. Weighing 3.359g of PMDA and 3.084g of ODA, completely dissolving ODA in 50ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step in an ice-water bath condition to obtain a polyamic acid (PAA) solution with the solid content of 12 wt%, mechanically stirring for 2h, dropwise adding 9.163g of TEOS (the addition amount is calculated inversely according to 30% of the total mass fraction of the polyimide and the silicon dioxide), stirring for 2h after dropwise adding is finished, uniformly mixing, then putting into a syringe with the capacity of 20ml, and preparing the PAA/TEOS microsphere through electrostatic spraying. Specific parameters of electrostatic spraying are voltage: 25 kV; temperature: 25 ℃; humidity: 40 percent; diameter of syringe needle: number 12; receiving a flat plate; receiving distance: the tip-to-plate distance was 20 cm.

B. And carrying out heat treatment on the obtained microspheres, wherein the treatment temperature is 280 ℃, and the treatment time is 30 min.

C. Preparing hydrolysate: 40mL of deionized water and 20mL of ethanol are uniformly mixed, and hydrochloric acid is added dropwise to adjust the pH value to 5.

D. And D, putting the microspheres prepared in the step B into a hydrolysis solution with the pH value of 6 for hydrolysis for 12 hours, and putting the microspheres into an oven at the temperature of 60 ℃ for heat preservation for 10 hours.

E. And D, putting the microspheres obtained by the treatment in the step D into a forced air oven for complete imidization, wherein the treatment temperature is 300 ℃, and the time is 2 hours, so that the polyimide/silicon dioxide microspheres are finally obtained. The morphology of the obtained microspheres is shown in figure 7.

Example 7

A. Weighing 3.359g of PMDA and 3.084g of ODA, completely dissolving ODA in 50ml of N, N-Dimethylformamide (DMF) solvent, mechanically stirring, after completely dissolving ODA in DMF, adding PMDA step by step in an ice-water bath condition to obtain a polyamic acid (PAA) solution with the solid content of 12 wt%, mechanically stirring for 2h, dropwise adding 9.163g of TEOS (the addition amount is calculated inversely according to 30% of the total mass fraction of the polyimide and the silicon dioxide), stirring for 2h after dropwise adding is finished, uniformly mixing, then putting into a syringe with the capacity of 20ml, and preparing the PAA/TEOS microsphere through electrostatic spraying. Specific parameters of electrostatic spraying are voltage: 25 kV; temperature: 25 ℃; humidity: 40 percent; diameter of syringe needle: number 12; receiving a flat plate; receiving distance: the tip-to-plate distance was 20 cm.

B. And carrying out heat treatment on the obtained microspheres, wherein the treatment temperature is 280 ℃, and the treatment time is 30 min.

C. Preparing hydrolysate: 40mL of deionized water and 20mL of ethanol are uniformly mixed, and hydrochloric acid is added dropwise to adjust the pH value to 5.

D. And D, putting the microspheres prepared in the step B into a hydrolysis solution with the pH value of 6 for hydrolysis for 6 hours, and putting the microspheres into an oven at the temperature of 60 ℃ for heat preservation for 10 hours.

E. And D, putting the microspheres obtained by the treatment in the step D into a forced air oven for complete imidization, wherein the treatment temperature is 300 ℃, and the time is 2 hours, so that the polyimide/silicon dioxide microspheres are finally obtained. The morphology of the obtained microspheres is shown in figure 8.