阅读说明：本技术 一种纳米级聚酰亚胺微粉的合成工艺 (Synthesis process of nano polyimide micro powder ) 是由 周鸿文 杨伟明 于 2020-12-08 设计创作，主要内容包括：本发明公开了一种纳米级聚酰亚胺微粉的合成工艺,包括：S1.投入芳香族胺类单体和溶剂；S2.以二甲基乙酰胺冲洗加入均苯四甲酸二酐；S3.检测反应液粘度,当反应液粘度达到格式粘度100s时,升温到110℃恒温反应1h,再升温到115℃恒温反应30min；S4.当反应液粘度达到格式粘度20s时,加入苯酐,继续恒温反应30min；S5.反应完成,冷却降温,然后析出产物,过滤,再洗涤,最后通过喷雾干燥得到聚酰亚胺微粉。本发明对聚酰亚胺微粉的合成工艺不断调整优化,通过温度、粘度、搅拌剪切速率等工艺控制手段,合成一种纳米级聚酰亚胺微粉,再通过清洗、压滤、喷雾干燥等步骤得到纳米级聚酰亚胺微粉产品,反应收率高,粉末的粒径较易控制,性能稳定。(The invention discloses a synthesis process of nano polyimide micro powder, which comprises the following steps: s1, adding an aromatic amine monomer and a solvent; s2, washing with dimethyl acetamide and adding pyromellitic dianhydride; s3, detecting the viscosity of the reaction solution, raising the temperature to 110 ℃ for constant-temperature reaction for 1h when the viscosity of the reaction solution reaches the format viscosity of 100s, and raising the temperature to 115 ℃ for constant-temperature reaction for 30 min; s4, adding phthalic anhydride when the viscosity of the reaction solution reaches the format viscosity of 20s, and continuing to react for 30min at constant temperature; and S5, after the reaction is finished, cooling, separating out a product, filtering, washing, and finally performing spray drying to obtain the polyimide micro powder. The synthesis process of the polyimide micropowder is continuously adjusted and optimized, the nanoscale polyimide micropowder is synthesized by process control means such as temperature, viscosity, stirring shear rate and the like, and the nanoscale polyimide micropowder product is obtained by steps such as cleaning, filter pressing, spray drying and the like, so that the reaction yield is high, the particle size of the powder is easy to control, and the performance is stable.)

1. A synthesis process of nano polyimide micropowder is characterized by comprising the following steps:

s1, adding an aromatic amine monomer and a solvent into a reaction device, controlling the stirring speed at 380-400 rpm, and stirring for dissolving;

s2, gradually adding pyromellitic dianhydride, and adding N, N-dimethylacetamide by flushing; controlling the temperature of the system to be not more than 60 ℃ in the adding process, adjusting the stirring speed to be 600-700 rpm after the adding is finished, and reacting for 25-35min at the constant temperature of 55-65 ℃;

s3, detecting the viscosity of the reaction solution, when the viscosity of the reaction solution reaches 95-105 s, heating to 105-115 ℃, carrying out constant-temperature reflux reaction for 0.8-1.2 h, and then heating to 116-120 ℃, and carrying out constant-temperature reaction for 30 min;

s4, adding phthalic anhydride when the viscosity of the reaction solution reaches 18-22 s, and continuing to react for 30min at constant temperature;

and S5, after the reaction is finished, cooling, separating out a product, filtering, washing, and finally performing spray drying to obtain the polyimide micro powder.

2. The process for synthesizing nano-sized polyimide micropowder according to claim 1, wherein the aromatic amine monomer of S1 is 1, 3-bis (4-aminophenoxy) benzene and 4,4 '-diaminodiphenyl ether, or 4,4' -diaminodiphenyl ether.

3. The process for synthesizing nano-sized polyimide micropowder of claim 2, wherein the aromatic amine monomer of S1 is 1, 3-bis (4-aminophenoxy) benzene and 4,4' -diaminodiphenyl ether, and the solvent of S1 is N, N-dimethylacetamide.

4. The process for synthesizing nano-sized polyimide micropowder according to claim 3, wherein the mass ratio of the 1, 3-bis (4-aminophenoxy) benzene, 4' -diaminodiphenyl ether and N, N-dimethylacetamide of S1 is 28 to 35: 12-18: 500-600, S2, wherein the mass ratio of the pyromellitic dianhydride to the N, N-dimethylacetamide is 40-50: 55-65.

5. The process for synthesizing nano-sized polyimide micropowder according to claim 4, wherein the mass ratio of the 1, 3-bis (4-aminophenoxy) benzene, 4' -diaminodiphenyl ether and N, N-dimethylacetamide of S1 is 32: 15: 560, S2 the mass ratio of pyromellitic dianhydride to N, N-dimethylacetamide is 45.8: 60.

6. the process for synthesizing nano-sized polyimide micropowder of claim 2, wherein the aromatic amine monomer of S1 is 4,4' -diaminodiphenyl ether, and the solvent of S1 is N-methylpyrrolidone.

7. The process for synthesizing nano-sized polyimide micropowder according to claim 6, wherein the mass ratio of 4,4' -diaminodiphenyl ether to N-methylpyrrolidone is 102: 720, performing a test; s2, the mass ratio of the pyromellitic dianhydride to the N, N-dimethylacetamide is 53: 46.

8. the synthesis process of the nano-scale polyimide micropowder according to claim 1, wherein in S5, deionized water is adopted to completely separate out the polyimide, the polyimide is filtered, and then the polyimide is repeatedly washed with the deionized water for 4-6 times.

9. The synthesis process of the nano-scale polyimide micropowder as claimed in claim 1, wherein the particle size of the polyimide micropowder obtained in S5 is 500 to 950 nm, and the polyimide micropowder can be dissolved in N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone, and has a solubility of 20% or more.

10. The process for synthesizing a nano-sized polyimide micropowder according to claim 1, wherein the logarithmic viscosity number of the polyimide micropowder obtained in S5 is measured after dissolving the polyimide micropowder in a solvent, and the logarithmic viscosity number is measured to be 0.50dL/g to 1.50 dL/g.

Technical Field

The invention belongs to the technical field of polymer material synthesis, and mainly relates to a synthesis process of nano polyimide micro powder.

Background

Polyimide (Polyimide), abbreviated as PI, is a polymer having an imide group in the main chain. Polyimide is used as a special engineering material and has been widely applied to the fields of aviation, aerospace, microelectronics, nano-scale, liquid crystal, separation membranes, laser and the like. Recently, the research, development and utilization of polyimide are being carried out in various countries as one of the most promising engineering plastics in the 21 st century. Polyimide, because of its outstanding characteristics in terms of performance and synthesis, whether as a structural material or as a functional material, has great potential for applications that have been fully recognized and is known as "problem-solving" and is considered "without polyimide, there is no current microelectronics technology".

The existing polyimide synthesis methods can be divided into two main categories, wherein the first category is imide ring formation in the polymerization process or in the macromolecular reaction; the second type is the synthesis of polyimides from monomers containing imide rings. The first synthetic method mainly comprises the following steps: reacting a dianhydride and a diamine to form a polyimide; reacting a tetrabasic acid with a diamine to form a polyimide; polyimide is obtained by reacting dibasic ester of tetrabasic acid with diamine, polyimide is obtained by reacting dianhydride with diisocyanate, and the like. In the second type of synthesis, almost all of the general polycondensation reactions have been used to synthesize various imide ring-bearing polymers such as polyester imide, polyamide imide, polycarbonate imide, polyurethane imide, etc. from imide ring-bearing monomers.

CN102604093B discloses a preparation method of polyimide, which comprises the following steps: a) performing dehydration polymerization reaction on diamine and acid anhydride of organic acid in a nonpolar solvent to obtain a mixture, wherein the nonpolar solvent is one or more of aromatic hydrocarbon, aliphatic hydrocarbon, halogenated aromatic hydrocarbon or halogenated aliphatic hydrocarbon, and the acid anhydride of the organic acid is one or more of dianhydride and monoanhydride; b) filtering and drying the mixture obtained in the step a) to obtain polyimide. In the invention, diamine and anhydride of organic acid can directly generate dehydration polymerization reaction in a nonpolar solvent to obtain polyimide which is insoluble in the nonpolar solvent, so that the reaction mixture can be directly filtered without washing and dried to obtain fine-particle polyimide powder, a complex washing procedure and a crushing procedure are not needed, the production period is shortened, the production cost is reduced, and the large-scale production is facilitated. The preparation of the polyimide powder does not describe the synthesis process parameters in detail, the particle size of the obtained polyimide powder is difficult to control, side reactions are more, and the nano-grade polyimide micro powder product with stable performance is difficult to obtain.

Disclosure of Invention

The invention aims to provide a synthesis process of nano-grade polyimide micro powder, which is characterized in that 4,4-ODA, TPER, PMDA, PA and other raw materials are synthesized into the nano-grade polyimide micro powder in a polar solvent such as DMF/DMAC/NMP and other process control means such as temperature, viscosity, stirring shear rate and the like, and then the nano-grade polyimide micro powder product is obtained through the steps of cleaning, filter pressing, spray drying and the like.

The product synthesized by the process technology is a completely soluble Polyimide (PI) or an ultra-high temperature resistant insoluble product in the true sense, is golden yellow or brownish yellow powder, is blank in China, is produced only in the countries such as the United states, Japan and the like at present, and is expensive. The particle size of the product is 500-950 nanometers, and the product is in a pure solid powder state. Can be dissolved in organic solvents such as N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone at room temperature. The dissolving concentration can reach more than 20 percent. The process yield is between 93% and 96%, calculated as the weight of polyimide obtained divided by the theoretical yield (or total input of materials involved in the reaction).

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

a synthesis process of nano polyimide micropowder comprises the following steps:

s1, adding an aromatic amine monomer and a solvent into a reaction device, controlling the stirring speed at 380-400 rpm, and stirring for dissolving;

s2, gradually adding pyromellitic dianhydride, and adding N, N-dimethylacetamide by flushing; controlling the temperature of the system to be not more than 60 ℃ in the adding process, adjusting the stirring speed to be 600-700 rpm after the adding is finished, and reacting for 25-35min at the constant temperature of 55-65 ℃;

s3, detecting the viscosity of the reaction solution, when the viscosity of the reaction solution reaches 95-105 s, heating to 105-115 ℃, carrying out constant-temperature reflux reaction for 0.8-1.2 h, and then heating to 116-120 ℃, and carrying out constant-temperature reaction for 30 min;

s4, adding phthalic anhydride when the viscosity of the reaction solution reaches 18-22 s, and continuing to react for 30min at constant temperature;

and S5, after the reaction is finished, cooling, separating out a product, filtering, washing, and finally performing spray drying to obtain the polyimide micro powder.

In long-term experimental research, the inventor of the invention continuously adjusts and optimizes the synthesis process of the polyimide micro powder, synthesizes the nano-grade polyimide micro powder by process control means such as temperature, viscosity, stirring and shearing rate and the like, and obtains the nano-grade polyimide micro powder product by steps such as cleaning, filter pressing, spray drying and the like, and the nano-grade polyimide micro powder product has high reaction yield, easily controlled powder particle size and stable performance.

In the present invention, preferably, the aromatic amine monomer of S1 is 1, 3-bis (4-aminophenoxy) benzene and 4,4 '-diaminodiphenyl ether, or is 4,4' -diaminodiphenyl ether. The aromatic amine monomer has high amino activity, small reaction steric hindrance and less side reaction.

Wherein the structural formula of the 1, 3-bis (4-aminophenoxy) benzene is shown as the following

The structural formula of the 4,4' -diaminodiphenyl ether is shown in the specification

In the present invention, preferably, the aromatic amine monomer in S1 is 1, 3-bis (4-aminophenoxy) benzene and 4,4' -diaminodiphenyl ether, and the solvent in S1 is N, N-dimethylacetamide. The solvent is N, N-dimethylacetamide, the solubility to aromatic amine monomers is good, and the reaction is facilitated.

Further preferably, the mass ratio of the 1, 3-bis (4-aminophenoxy) benzene, the 4,4' -diaminodiphenyl ether and the N, N-dimethylacetamide in S1 is 28-35: 12-18: 500-600, S2, wherein the mass ratio of the pyromellitic dianhydride to the N, N-dimethylacetamide is 40-50: 55-65. More preferably, the mass ratio of the 1, 3-bis (4-aminophenoxy) benzene, the 4,4' -diaminodiphenyl ether and the N, N-dimethylacetamide in S1 is 32: 15: 560, S2 the mass ratio of pyromellitic dianhydride to N, N-dimethylacetamide is 45.8: 60. the mass ratio is a better mixture ratio obtained by the inventor through a large amount of experimental adjustment and calculation, and has the advantages of high reaction speed, less side reaction and high yield.

In the present invention, preferably, the aromatic amine monomer in S1 is 4,4' -diaminodiphenyl ether, and the solvent in S1 is N-methylpyrrolidone. Further preferably, the mass ratio of the 4,4' -diaminodiphenyl ether to the N-methylpyrrolidone is 102: 720, performing a test; s2, the mass ratio of the pyromellitic dianhydride to the N, N-dimethylacetamide is 53: 46. the selection of the solvent and the mass ratio are relatively excellent ratios obtained by the inventor through a large amount of experimental adjustment and calculation, and have the advantages of high reaction speed, less side reactions and high yield.

In the present invention, it is preferable that the amount of the phthalic anhydride added in S4 is 0.2% to 0.5% of the total amount of the raw materials. The phthalic anhydride is added as a blocking agent and the reaction process is stopped.

Specifically, the particle size of the polyimide micropowder obtained in S5 is 500-950 nanometers, and the polyimide micropowder can be dissolved in N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone, and the solubility of the polyimide micropowder is more than 20%.

Specifically, after obtaining the polyimide fine powder in S5, the polyimide fine powder is dissolved in a solvent, and the logarithmic viscosity number of the polyimide fine powder is measured, and the logarithmic viscosity number is 0.50dL/g to 1.50 dL/g.

Specifically, in the present invention, the reaction apparatus described in S1 is a four-necked flask with a reflux apparatus, and nitrogen gas is introduced during the reaction.

Compared with the method of singly carrying out polymerization reaction by diamine and anhydride of organic acid, the modification of polyimide can be realized by adding the filler at the initial stage of the polymerization reaction, namely, the filler is added as a raw material. The filler is not particularly limited in the present invention, and those skilled in the art can select the filler according to the application of the polyimide product, for example, conventional reinforcing and friction reducing materials such as graphite, polytetrafluoroethylene, molybdenum disulfide, organic fibers, glass fibers or carbon fibers, etc., or other conventional toughening materials can be used. The amount of the filler added in the present invention is not particularly limited, and can be determined by those skilled in the art according to the properties of the desired modified polyimide, and when a reinforcing material such as graphite, carbon fiber, etc. is used, the amount of the filler added is preferably 5% to 20% of the total amount of the acid anhydride and diamine of the organic acid.

Compared with the prior art, the invention has the beneficial effects that:

the synthesis process of the polyimide micropowder is continuously adjusted and optimized, the nanoscale polyimide micropowder is synthesized by process control means such as temperature, viscosity, stirring shear rate and the like, and the nanoscale polyimide micropowder product is obtained by steps such as cleaning, filter pressing, spray drying and the like, so that the reaction yield is high, the particle size of the powder is easy to control, and the performance is stable. The product synthesized by the process technology is a polyimide which is completely soluble in the true sense, is golden yellow or brownish yellow powder, is blank in China, is only produced in the countries of the United states, Japan and the like at present, and is expensive. The particle size of the product is 500-950 nanometers, the product is in a pure solid powder state, and the product can be dissolved in organic solvents such as N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone at room temperature. The dissolving concentration can reach more than 20 percent.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments, but the scope of the present invention is not limited to the embodiments.

The starting materials used in the following examples are all commercially available unless otherwise specified.

The invention adopts a laser particle size distribution instrument to test the particle size of the prepared polyimide micro powder.

Example 1:

and (3) synthesis of nano polyimide micro powder:

1. putting 32g of 1, 3-bis (4-aminophenoxy) benzene, 15g of 4,4' -diaminodiphenyl ether and 560g of N, N-dimethylacetamide into a 1000ml four-neck flask with a reflux device, introducing nitrogen, starting stirring, controlling the stirring speed at 380-400 rpm, gradually adding 45.8g of pyromellitic dianhydride (flushing and adding 60g of N, N-dimethylacetamide) after materials are completely dissolved, controlling the temperature of a process control system to be not more than 60 ℃, adjusting the stirring speed to be 600-700 rpm after the feeding is finished, keeping the temperature at 60 ℃ for about 30min, and detecting the viscosity of a reaction solution.

2. When the viscosity of the reaction solution reaches 100s (format viscosity), the temperature is raised to 110 ℃ for constant-temperature reflux reaction for 1h, and then the temperature is raised to 115 ℃ for constant-temperature reaction for about 30 min.

3. When the viscosity of the reaction solution reached 20s (format viscosity), 2.20g of phthalic anhydride was added, and the reaction was continued for 30min at constant temperature.

4. And after the reaction is finished, cooling, adding a proper amount of deionized water to completely separate out PI, filtering, repeatedly washing the product with the deionized water for 4-6 times, and finally performing spray drying to obtain golden yellow polyimide micropowder, wherein the particle size is 650-950 nanometers through detection, the product can be dissolved in organic solvents such as DMF/DMAC/NMP, and the solubility is more than 20%.

The reaction yield is 95%, the prepared nano polyimide micro powder is dissolved in m-cresol, and the logarithmic viscosity of the nano polyimide micro powder is measured to be 0.86 dL/g.

Example 2:

and (3) synthesis of nano polyimide micro powder:

1. putting 102g of 4,4' -diaminodiphenyl ether and 720g of N-methylpyrrolidone into a 1000ml four-neck flask with a reflux device, introducing nitrogen, starting stirring, controlling the stirring speed at 380-400 rpm, gradually adding 53g of pyromellitic dianhydride (flushing and adding 46g of N, N-dimethylacetamide) after materials are completely dissolved, controlling the temperature of a system to be not more than 60 ℃ in a process control system, adjusting the stirring speed to be 600-700 rpm after the materials are completely dissolved, keeping the temperature at 60 ℃ for about 30min, and detecting the viscosity of a reaction solution.

2. When the viscosity of the reaction solution reaches 100s-110s (format viscosity), heating to 110 ℃ for constant-temperature reflux reaction for 50min, and then heating to 115 ℃ for constant-temperature reaction for about 30 min.

3. When the viscosity of the reaction solution reached 20s (format viscosity), 2.60g of phthalic anhydride was added, and the reaction was continued for 30min at constant temperature.

4. And (3) after the reaction is finished, cooling, adding a proper amount of deionized water to completely separate out PI, filtering, repeatedly washing the product with the deionized water for 4-6 times, and finally performing spray drying to obtain brown yellow polyimide micro powder, wherein the particle size is 580-930 nanometers through detection.

The reaction yield is 96 percent, the prepared nano polyimide micro powder is dissolved in m-cresol, and the logarithmic viscosity is measured to be 0.91 dL/g.

Example 3:

and (3) synthesis of nano polyimide micro powder:

1. adding 28g of 1, 3-bis (4-aminophenoxy) benzene, 12g of 4,4' -diaminodiphenyl ether and 500g of N, N-dimethylacetamide into a 1000ml four-neck flask with a reflux device, introducing nitrogen, starting stirring, controlling the stirring speed at 380-400 rpm, gradually adding 40g of pyromellitic dianhydride (flushing and adding 55g of N, N-dimethylacetamide) after materials are completely dissolved, controlling the temperature of a process control system to be not more than 60 ℃, adjusting the stirring speed to be 600-700 rpm after the material addition is finished, keeping the temperature at 55 ℃ for about 35min, and detecting the viscosity of a reaction solution.

2. When the viscosity of the reaction solution reaches 95s (format viscosity), the temperature is raised to 105 ℃ for constant-temperature reflux reaction for 1.2h, and then the temperature is raised to 116 ℃ for constant-temperature reaction for about 30 min.

3. When the viscosity of the reaction solution reached 18s (format viscosity), 2.0g of phthalic anhydride was added, and the isothermal reaction was continued for 30 min.

4. And after the reaction is finished, cooling, adding a proper amount of deionized water to completely separate out PI, filtering, repeatedly washing the product with the deionized water for 4-6 times, and finally performing spray drying to obtain golden yellow polyimide micropowder, wherein the particle size is 540-750 nanometers through detection, the product can be dissolved in organic solvents such as DMF/DMAC/NMP, and the solubility is more than 20%.

The reaction yield is 95%, the prepared nano polyimide micro powder is dissolved in m-cresol, and the logarithmic viscosity is measured to be 0.96 dL/g.

Example 4:

and (3) synthesis of nano polyimide micro powder:

1. putting 98g of 4,4' -diaminodiphenyl ether and 700g of N-methylpyrrolidone into a 1000ml four-neck flask with a reflux device, introducing nitrogen, starting stirring, controlling the stirring speed at 380-400 rpm, gradually adding 50g of pyromellitic dianhydride (flushing and adding 42g of N, N-dimethylacetamide) after materials are completely dissolved, controlling the temperature of a system to be not more than 60 ℃ in the process, adjusting the stirring speed to be 600-700 rpm after the materials are completely dissolved, keeping the temperature at 55 ℃ for about 35min, and detecting the viscosity of a reaction solution.

2. When the viscosity of the reaction solution reaches 105s (format viscosity), the temperature is raised to 105 ℃ for constant-temperature reflux reaction for 1.2h, and then the temperature is raised to 116 ℃ for constant-temperature reaction for about 30 min.

3. When the viscosity of the reaction solution reached 18s (format viscosity), 2.20g of phthalic anhydride was added, and the isothermal reaction was continued for 30 min.

4. And (3) after the reaction is finished, cooling, adding a proper amount of deionized water to completely separate out PI, filtering, repeatedly washing the product with the deionized water for 4-6 times, and finally performing spray drying to obtain brown yellow polyimide micro powder, wherein the particle size is 580-930 nanometers through detection.

The reaction yield is 96 percent, the prepared nano polyimide micro powder is dissolved in m-cresol, and the logarithmic viscosity is measured to be 1.02 dL/g.

Example 5:

and (3) synthesis of nano polyimide micro powder:

1. adding 106g of 4,4' -diaminodiphenyl ether and 740g of N-methylpyrrolidone into a 1000ml four-neck flask with a reflux device, introducing nitrogen, starting stirring, controlling the stirring speed at 380-400 rpm, gradually adding 56g of pyromellitic dianhydride (flushing and adding 50g of N, N-dimethylacetamide) after materials are completely dissolved, controlling the temperature of a system to be not more than 60 ℃ in the process, adjusting the stirring speed to be 600-700 rpm after the materials are completely dissolved, keeping the temperature at 65 ℃ for about 25min, and detecting the viscosity of a reaction solution.

2. When the viscosity of the reaction solution reaches 95s (format viscosity), the temperature is raised to 115 ℃ for constant-temperature reflux reaction for 0.8h, and then the temperature is raised to 120 ℃ for constant-temperature reaction for about 30 min.

3. When the viscosity of the reaction solution reached 22s (format viscosity), 3.0g of phthalic anhydride was added, and the isothermal reaction was continued for 30 min.

4. And (3) after the reaction is finished, cooling, adding a proper amount of deionized water to completely separate out PI, filtering, repeatedly washing the product with the deionized water for 4-6 times, and finally performing spray drying to obtain brown yellow polyimide micro powder, wherein the particle size is 650-840 nanometers through detection.

The reaction yield is 97%, the prepared nano polyimide micro powder is dissolved in m-cresol, and the logarithmic viscosity is measured to be 1.20 dL/g.

Example 6:

1. adding 35g of 1, 3-bis (4-aminophenoxy) benzene, 18g of 4,4' -diaminodiphenyl ether and 600g of N, N-dimethylacetamide into a 1000ml four-neck flask with a reflux device, introducing nitrogen, starting stirring, controlling the stirring speed at 380-400 rpm, gradually adding 50g of pyromellitic dianhydride (flushing and adding 65g of N, N-dimethylacetamide) after materials are completely dissolved, controlling the temperature of a process control system to be not more than 60 ℃, adjusting the stirring speed to be 600-700 rpm after the material addition is finished, keeping the temperature at 65 ℃ for about 25min, and detecting the viscosity of a reaction solution.

2. When the viscosity of the reaction solution reaches 105s (format viscosity), the temperature is raised to 115 ℃ for constant-temperature reflux reaction for 0.8h, and then the temperature is raised to 120 ℃ for constant-temperature reaction for about 30 min.

3. When the viscosity of the reaction solution reached 22s (format viscosity), 2.80g of phthalic anhydride was added, and the isothermal reaction was continued for 30 min.

4. And after the reaction is finished, cooling, adding a proper amount of deionized water to completely separate out PI, filtering, repeatedly washing the product with the deionized water for 4-6 times, and finally performing spray drying to obtain golden yellow polyimide micropowder, wherein the particle size is 700-850 nanometers through detection, the product can be dissolved in organic solvents such as DMF (dimethyl formamide)/DMAC (dimethylacetamide)/NMP (N-methyl pyrrolidone), and the solubility reaches more than 20%.

The reaction yield is 96 percent, the prepared nano polyimide micro powder is dissolved in m-cresol, and the logarithmic viscosity is measured to be 1.26 dL/g.

Variations and modifications to the above-described embodiments may occur to those skilled in the art, which fall within the scope and spirit of the above description. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and variations of the present invention should fall within the scope of the claims of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.