Method for continuously synthesizing thermoplastic polyimide through polymerization extrusion granulation

Abstract

The invention discloses a method for continuously synthesizing thermoplastic polyimide through polymerization-extrusion granulation, and relates to the technical field of high-performance polymer synthesis, and the method comprises the following specific steps: mixing dianhydride and diamine monomer according to a ratio, and reacting in a water-containing solvent or a pure water phase to obtain an oligomer mixture; carrying out flash evaporation under the negative pressure of-0.01 to-0.1 MPa to recover the solvent / water, so as to obtain polyimide oligomer powder; drying the powder, mixing the dried powder with an auxiliary agent and other flexibilizers, carrying out stepped heat treatment in a nitrogen atmosphere, conveying the mixture into a screw machine through a screw, extruding, and pelletizing to obtain thermoplastic polyimide particles; the continuous production of the thermoplastic polyimide is realized by integrating core procedures, and the material loss and the time cost are reduced; and auxiliary materials such as the antioxidant and the flexibilizer are added, so that the product performance is improved, the application range is widened, and efficient and low-carbon production is realized.

Description

Technical Field

[0001] This invention relates to the field of high-performance polymer synthesis technology, specifically to a method for continuous synthesis of thermoplastic polyimide by polymerization, extrusion, and granulation. Background Technology

[0002] Thermoplastic polyimide, as a high-performance polymer material, possesses excellent high-temperature resistance, chemical corrosion resistance, mechanical strength, and good electrical insulation properties. These core characteristics make it occupy an important position in high-end industrial fields. As aerospace, electronics, and automotive industries continue to upgrade towards high performance, lightweight, and high-temperature resistance, the demand for this type of material, which combines stability and multifunctionality, continues to rise. In the aerospace field, structural components that need to withstand extreme temperatures and complex mechanical environments; insulation and protection components for high-precision components in the electronics and electrical field; and critical components near heat sources in the automotive industry all have urgent application needs for thermoplastic polyimide. Currently, the research and development of synthesis technology for thermoplastic polyimide remains a key focus in the industry. The core objective is to improve the stability of material performance by optimizing process design, while reducing energy consumption and costs in the production process, so as to better adapt to the ever-upgrading application requirements of various fields and promote the industrialization and widespread application of high-performance polymer materials.

[0003] The patent application CN103827174B, titled "Thermoplastic (co)polyimide and its synthesis method," presents a fragmented synthesis path. Solution polymerization relies on toxic polar aprotic solvents, which not only poses significant challenges in recycling and environmental burden but also easily leads to performance fluctuations caused by residual solvents in the product. Furthermore, it requires repeated purification, resulting in high energy consumption. Melt polymerization must be carried out at temperatures above the polymer's melting point, which can easily cause thermal decomposition and color defects in the material. While solid-state polymerization avoids some solvent issues, it can easily lead to uneven molecular weight distribution in the product. Some semi-crystalline products also suffer from melting points and decomposition temperatures that are close to each other, resulting in a narrow processing window, which limits their large-scale application in high-end fields such as aerospace and electronics. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for continuous synthesis of thermoplastic polyimide by polymerization, extrusion, and granulation. This method achieves efficient synthesis through steps such as oligomer synthesis, solvent / water flash evaporation recovery, powder heat treatment, and extrusion granulation. In the process, dianhydride and diamine monomers are carefully selected, reaction conditions and catalyst dosage are controlled, solvent is recovered by flash evaporation, and then performance is improved through heat treatment and extrusion granulation to finally obtain high-quality thermoplastic polyimide particles.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for synthesizing thermoplastic polyimide by continuous polymerization extrusion granulation, wherein the specific steps of the method are as follows: S1, Oligomer Synthesis: Dianone monomer and diamine monomer are mixed in a molar ratio of 1.03:1 to 1:1.03. Water or organic solvent is used as the reaction medium. The mixture is stirred at 40-150℃ and 0-1MPa for 2-4 hours. Then an imidization catalyst is added and the reaction is continued for 1-2 hours to obtain a polyimide oligomer reaction system. S2, Solvent / Water Flash Evaporation Recovery: The polyimide oligomer reaction system is placed in a vacuum environment with a pressure of -0.01 to -0.1 MPa for flash evaporation. The solvent or water is distilled off and collected. The collected liquid is returned to step S1 as a reaction medium and reused in the oligomer synthesis to obtain polyimide powder. S3, Powder Treatment: Polyimide powder is mixed evenly with toughening agent, reinforcing agent, and antioxidant. The mixture is then heated in an inert gas atmosphere, with a gradient temperature increase of 120-180°C. It is then dried in a nitrogen atmosphere at a temperature of 120-150°C for 1-2 hours, and then dried in a nitrogen atmosphere at a temperature of 150-180°C for 2-3 hours. Subsequently, it is fed into a screw extruder through a feeding device.

[0006] S4, Extrusion Granulation: The mixture is fed into a twin-screw extruder via a screw conveyor, and after zoned temperature-controlled extrusion, cooling, and pelletizing, thermoplastic polyimide particles are obtained.

[0007] Further, in S1, the oligomer synthesis, the organic solvent is selected from at least one of N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, ethanol, methanol, toluene, and xylene; wherein, the mixture of water and organic solvent is a medium in which the mass ratio of water to organic solvent is from 70:30 to 98:2; Furthermore, in the S1 oligomer synthesis, the dianhydride monomer is selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenyl ethertetracarboxylic dianhydride, or bisphenol A diether dianhydride; the diamine monomer is selected from 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, or m-phenylenediamine, or bisphenol A diether diamine.

[0008] Furthermore, in S1, during the oligomer synthesis, the total mass of the reaction medium and the monomer satisfies the following: the solid content of the system is 15-50%; the imidization catalyst is selected from a mixture of acetic anhydride and triethylamine, a mixture of acetic anhydride and pyridine, or zinc chloride, and the amount of catalyst added is 0.4%-0.6% of the total mass of the dianhydride monomer and the diamine monomer.

[0009] Furthermore, in S2, during the solvent / water flash evaporation recovery, the flash pressure is controlled at -0.01 to -0.1 MPa, and the flash temperature is 80-150°C. Furthermore, in step S3, during powder processing and mixing, the antioxidant is antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]) or antioxidant 1076 (octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), and the amount added is 0.2%-0.4% of the mass of the polyimide powder.

[0010] Furthermore, in step S3, the reinforcing agent is selected from at least one of glass fiber, carbon fiber, carbon nanotubes, graphene, nano-silica, nano-titanium dioxide, clay or polytetrafluoroethylene micropowder, and polyetheretherketone. The addition amount is 0%-30% of the mass of the polyimide. Mixing is performed using a high-speed mixer. After mixing, the mixture is further heat-treated in a nitrogen atmosphere furnace.

[0011] Furthermore, in S5, during extrusion granulation, the screw length-to-diameter ratio of the twin-screw extruder is 30:1 to 60:1, and the temperature is controlled in zones as follows: 180 to 260°C in the feeding section, 280 to 320°C in the melting section, 320 to 360°C in the mixing section, and 350 to 370°C in the die head section; the die head pressure during extrusion is 5 to 8 MPa.

[0012] Compared with existing technologies, this method for synthesizing thermoplastic polyimides via continuous polymerization extrusion granulation has the following advantages: I. This invention integrates core processes such as oligomer synthesis, solvent recovery, post-processing, and extrusion molding to achieve an integrated process for the production of thermoplastic polyimide. This solves the turnover problem in traditional production, reduces material loss and time costs during intermediate transportation, and uses a flash evaporation process in the solvent recovery stage to return the solvent to the oligomer synthesis step for reuse. The aim is to reduce energy consumption, align with green production guidelines, and improve overall production efficiency and resource utilization efficiency.

[0013] II. This invention, through the scientific combination of auxiliary materials and optimization of the processing environment, utilizes antioxidants to inhibit oxidative deterioration during material processing. The rational combination of toughening and reinforcing agents forms a synergistic effect with the polyimide matrix, significantly improving the product's key properties such as toughness and strength, meeting the needs of diverse application scenarios. The heat treatment process is carried out under an inert atmosphere, avoiding oxidative degradation problems during material processing. The zoned temperature control design and precise process regulation of the twin-screw extruder ensure that the materials reach the optimal reaction state at each processing stage, promoting uniform mixing and full reaction of each component, improving product uniformity. The entire process has good compatibility with various monomers and auxiliary materials, allowing for flexible adjustment of the formula composition according to application requirements, broadening the product's applicability, while reducing production energy consumption, achieving the goal of high-efficiency, low-carbon, and high-quality production.

[0014] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0016] Figure 1 Flowchart of a continuous method for synthesizing thermoplastic polyimide via polymerization, extrusion, and granulation; Figure 2 This is a schematic diagram of the process for synthesizing thermoplastic polyimide oligomers and recovering solvents by flash evaporation. Figure 3 This is a schematic diagram of the process of mixing, drying, and twin-screw extrusion granulation of thermoplastic polyimide powder. Detailed Implementation

[0017] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below. Example

[0018] S1, oligomer synthesis: Weigh the following materials: Dihydride monomer: Bisphenol A diether dianhydride (BPADA), molecular weight 520.5 g / mol, purity ≥99.5%, dosage 53.09 kg (0.102 kmol); Diamine monomer: 4,4'-diaminodiphenyl ether (ODA), molecular weight 200.24 g / mol, purity ≥99.5%, dosage 20.02 kg (0.100 kmol); Reaction medium: 80 kg N,N-dimethylacetamide (DMAc), 130 kg water; Imine catalyst: a mixture of acetic anhydride and triethylamine (mass ratio 1:1), used in an amount of 0.37 g (0.5% of the total mass of acetic anhydride and diamine).

[0019] Weighed BPADA and ODA were added to a 500L reactor equipped with a stirrer, thermometer, and reflux condenser. DMAc and water were added as the reaction medium, resulting in a solid content of 20% (total monomer mass 73.11 kg, reaction medium 210 kg, 73.11 / (73.11+210)≈20%). Nitrogen gas was introduced for protection. The reaction temperature was set to 80℃, and stirring was started (300 rpm) for 3 hours. Subsequently, the prepared acetic anhydride-triethylamine mixed catalyst was added, and the reaction was continued under the above temperature and pressure conditions for 1.5 hours to obtain a milky white polyimide oligomer.

[0020] S2, Solvent / Water Flash Evaporation Recovery: The above polyimide oligomer reaction system was transferred to a vacuum flash evaporator. The tank door was closed, and the vacuum pump was started to reduce the absolute pressure inside the tank to -0.03 MPa (gauge pressure, i.e., vacuum). The heating rate was set to 6 °C / min, and the temperature of the material inside the tank was raised to 120 °C by oil bath heating, maintaining this condition for flash evaporation. The flash-evaporated DMAc and water vapor were condensed by a condenser and collected in a receiving flask. After separation and dehydration, the collected mixed liquid could be returned to step S1 as a reaction medium for reuse. After flash evaporation, the remaining solids in the tank were pulverized to obtain a pale yellow polyimide powder.

[0021] S3, Powder Mixing and Heat Treatment: Weigh the following additives and prepare to mix them with the polyimide powder obtained in S2: Antioxidant: Pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (Antioxidant 1010), dosage 0.16 kg; Toughening agent: Polyetheretherketone (PEEK, molecular weight 50,000-80,000), dosage 4.32 kg; Reinforcing agent: glass fiber (3mm in length, 10μm in diameter), 10.37kg in dosage.

[0022] First, polyimide powder and antioxidant 1010 are initially mixed evenly at room temperature. Then, this premixed powder, along with toughening agent PEEK and reinforcing agent glass fiber, is added to a high-speed mixer and mixed at 800 rpm for 15 minutes to obtain a homogeneous mixture.

[0023] The mixture was transferred to a nitrogen atmosphere heat treatment furnace. High-purity nitrogen was introduced into the furnace to replace the air, and then the temperature was increased at a programmed rate of 5°C / min: first to 150°C and held for 1 hour; then further increased to 190°C and held for 1.5 hours. After heat treatment, the material was cooled to an operable temperature under nitrogen protection.

[0024] S4, extrusion granulation: The heat-treated mixture is fed into a twin-screw extruder via a screw feeder. The extruder temperatures are set as follows: feed section 240℃, melting section 280℃, mixing section 320℃, and die head section 350℃. The die head pressure is controlled at 6MPa, and the screw speed is 200rpm. The melt-extruded strip material is immediately cooled to room temperature and solidified in a water-cooling tank, and then cut by a pelletizer to obtain uniform polyimide particles with a diameter of approximately 3mm and a length of approximately 3mm. Example

[0025] S1, oligomer synthesis: Weigh the following materials: Dihydride monomer: 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), molecular weight 310.22 g / mol, purity ≥99.5%, dosage 31.33 kg (0.101 kmol). Diamine monomer: 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), molecular weight 410.5 g / mol, purity ≥99.5%, dosage 54.46 kg (0.101 kmol); Reaction medium: A mixture of water and organic solvent is used, including 12.30 kg of water, 98.42 kg of N,N-dimethylformamide (DMF), and 12.30 kg of toluene (the total mass ratio of water to organic solvent is 10:90, and the mass ratio of DMF to toluene is 8:2), with a total mass of 123.02 kg of reaction medium. Imine catalyst: a mixture of acetic anhydride and pyridine (mass ratio 2:1), used in an amount of 0.32 kg (0.5% of the total mass of dianhydride and diamine).

[0026] Weighed ODPA and BAPP were added to a 500L reactor equipped with a stirrer and thermometer, and then purged with nitrogen. The aforementioned mixed reaction solvent was added. At this point, the solid content of the system was 41.5% (total monomer mass 85.79 kg, reaction medium 123.02 kg, 85.79 / (85.79+123.02)=41.5%). The reaction temperature was set at 100℃, the reaction pressure at 0.8 MPa, and the stirring speed at 350 rpm for 2.5 hours. Subsequently, an acetic anhydride-pyridine mixed catalyst was added, and the reaction was continued at the above temperature and pressure for 1.2 hours to obtain a viscous polyimide oligomer reaction system.

[0027] S2, Solvent / Water Flash Evaporation Recovery: The oligomer reaction system was transferred to a vacuum flash evaporator. A vacuum was applied to maintain the system absolute pressure at -0.02 MPa (gauge pressure). The heating rate was set to 6.5 °C / min, and the material was heated to 90 °C. Flash evaporation was performed under these conditions for 1.2 hours. The mixed vapors of water, DMF, and toluene generated during flash evaporation were collected by condensation. The collected liquid was separated into aqueous and organic phases by liquid-liquid separation. The organic phase was dehydrated, filtered, and purified for later use, while the aqueous phase was purified by distillation and could be reused. A light brown polyimide powder was obtained after flash evaporation, as shown below. Figure 2 As shown.

[0028] S3, Powder Mixing and Heat Treatment: Weigh the following additives and prepare to mix them with the polyimide powder obtained in S2: Antioxidant: Antioxidant 1010, dosage 0.15kg; Toughening agent: Polyetheretherketone (PEEK, molecular weight 50,000-80,000), dosage 3.78 kg; Reinforcing agent: a mixture of carbon fiber (8μm in length) and nano-silica (50nm in particle size) in a mass ratio of 3:7, with a total dosage of 13.23kg.

[0029] Polyimide powder, antioxidant 1010, toughening agent PEEK, and reinforcing agent mixture were added to a high-speed mixer and mixed at 1000 rpm for 20 minutes to ensure uniform dispersion of each component.

[0030] The uniformly mixed powder was placed in a drying oven purged with high-purity nitrogen for heat treatment. The heat treatment conditions were set as follows: drying at 160°C for 4.5 hours under a nitrogen atmosphere.

[0031] S4, extrusion granulation: The heat-treated mixture is fed into a twin-screw extruder. The extruder temperatures are set as follows: feed section 260℃, melt section 320℃, mixing section 360℃, and die head section 370℃. The die head pressure is controlled at 7MPa, and the screw speed is 160rpm. After the extruded melt is cooled and solidified in a cooling water bath, it is pelletized by a pelletizer to obtain thermoplastic polyimide particles of the required specifications. Example

[0032] S1, oligomer synthesis: Weigh the following materials: Dihydride monomer: Bisphenol A diether dianhydride (BPADA), molecular weight 442.46 g / mol, purity ≥99.5%, dosage 44.69 kg (0.101 kmol). Diamine monomer: m-phenylenediamine (MPD), molecular weight 108.14 g / mol, purity ≥99.5%, dosage 10.92 kg (0.101 kmol). Reaction medium: a mixed organic solvent, consisting of N-methylpyrrolidone (NMP) and xylene in a mass ratio of 4:6, with a total mass of 185.70 kg; Imine catalyst: zinc chloride, purity ≥99.0%, dosage 0.33kg (0.6% of the total mass of dianhydride and diamine).

[0033] Weighed BPADA and MPD were added to an 800L reactor, along with a mixed reaction medium of NMP and xylene. At this point, the solid content of the system was 20% (total monomer mass 55.61 kg, reaction medium 185.70 kg, 55.61 / (55.61+185.70)=20%). A stirrer, thermometer, and reflux condenser were installed, and nitrogen gas was introduced for protection. The reaction temperature was set to 120℃, the reaction pressure to 0.3 MPa, and the stirring speed to 400 rpm for 3.5 hours. Then, zinc chloride catalyst was added, and the reaction was continued under the above conditions for another 1.8 hours to obtain a polymer solution.

[0034] S2, Solvent / Water Flash Evaporation Recovery: The reaction system was transferred to a vertical vacuum flash evaporator. The vacuum system was activated to maintain the absolute pressure inside the evaporator at 0.04 MPa (absolute pressure, equivalent to a vacuum of approximately -0.061 MPa gauge pressure). The material was heated to 130°C at a rate of 7°C / min and flashed under these conditions for 1.5 hours. The flash-evaporated NMP and xylene mixture vapors were collected by condensation, and the collected liquid was filtered and dehydrated for reuse. After flash evaporation, a yellow polyimide oligomer powder was obtained, with a yield of approximately 54.96 kg.

[0035] S3, Powder Mixing and Heat Treatment: Weigh the following additives and prepare to mix them with the polyimide powder obtained in S2: Antioxidant: Antioxidant 1010, dosage 0.20kg; Toughening agent: Polyetheretherketone (PEEK, molecular weight 50,000-80,000), dosage 4.44 kg; Reinforcing agent: A mixture of graphene (5-10 layers) and polytetrafluoroethylene micro powder (particle size 2μm) in a mass ratio of 2:8, with a total dosage of 16.65kg.

[0036] First, polyimide powder and antioxidant 1010 are premixed at room temperature. Then, this premix is ​​added to a high-speed mixer along with a toughening agent PEEK and a reinforcing agent mixture, and mixed at 900 rpm for 18 minutes to obtain a uniform composite powder.

[0037] The above-mentioned mixed powder was placed in a nitrogen atmosphere heat treatment furnace. High-purity nitrogen was introduced into the furnace, and the temperature was then raised to 310°C and held at that temperature for 3 hours to complete the heat treatment process. Figure 3 As shown.

[0038] S4, extrusion granulation: The heat-treated mixture is fed into a twin-screw extruder (in this example, the screw diameter is 35 mm, and the length-to-diameter ratio is 40:1). The temperatures of each section of the extruder are set as follows: feed section 245℃, melt section 285℃, mixing section 325℃, and die head section 335℃. The die head pressure is controlled at 8 MPa, and the screw speed is 220 rpm. After being cooled in a water cooling tank, the molten extruded material is cut into polyimide particles with a diameter of approximately 3.5 mm and a length of approximately 3.5 mm by a pelletizer.

[0039] Comparative example: Comparative example (traditional batch solution polymerization) Process route: In a reaction vessel, 10.8 kg of m-phenylenediamine and 52.05 kg of bisphenol A diether dianhydride (molar ratio 1:1) were reacted in 148 kg of NMP at 25 °C for 12 h to obtain polyamic acid (PAA). Using acetic anhydride / pyridine (3:1) as the imidizing agent, chemical imidization was performed at 25 °C for 4 h. The product was precipitated in methanol, pulverized, washed 16 times with water, filtered, and vacuum dried at 80 °C for 8 h to obtain polyimide powder. The powder was mixed with 0.3% antioxidant 1010, extruded, and granulated under cooling.

[0040] Process characteristics: The entire process is intermittent.

[0041] It requires a large amount of methanol precipitant, resulting in high VOC emissions.

[0042] Post-processing involves multiple washing steps, resulting in high energy consumption and significant batch-to-batch variations.

[0043] Without the introduction of toughening / reinforcing components, the product is highly brittle.

[0044] Performance data comparison index unit Example 1 Example 2 Example 3 Comparative Example Glass transition temperature Tg ℃ 225 238 218 217 Tensile strength MPa 118 125 110 95 Elongation at break % 14 12 11 6 Notched impact strength <![CDATA[kJ m -2 ]]> 9.2 10.5 11.0 4.5 Bending strength MPa 165 178 185 140 Flexural modulus GPa 3.1 3.4 3.6 3.0 5% thermogravimetric temperature ℃ 521 528 535 515 Melt flow index (360℃, 5kg) g / 10 min 8.5 7.2 6.8 3.0 Solvent recovery rate % 93 91 90 80 Single batch production cycle h 10 10 12 24 Unit product energy consumption* <![CDATA[kWh kg -1 ]]> 3.8 4.0 4.2 7.5 VOC emissions <![CDATA[kg t -1 ]]> <5 <5 <5 20 In summary, comparing the effects of traditional batch solution polymerization and the continuous polymerization-extrusion granulation method of this invention in the synthesis of thermoplastic polyimide reveals significant shortcomings in the traditional process: the entirely batch operation results in a production cycle of up to 24 hours; the large amount of methanol precipitant leads to VOC emissions as high as 20 kg / t; the multi-step washing process results in high energy consumption (7.5 kWh / kg); and the lack of toughening / reinforcing components results in brittle products with a tensile strength of only 95 MPa and a notched impact strength of 4.5 kJ / m², limiting overall performance. In contrast, the continuous process of this invention offers significant advantages. By integrating core processes, it achieves integrated production, shortening the production cycle to 10-12 hours, achieving a solvent recovery rate of 90%-93%, reducing VOC emissions to below 5 kg / t, and lowering unit product energy consumption to 3.8-4.2 kWh / kg, making it low-carbon, highly efficient, and environmentally friendly. Meanwhile, with the scientific formulation of antioxidants, toughening agents and reinforcing agents, and inert atmosphere heat treatment, the product performance is comprehensively improved, with a glass transition temperature of 218-238℃, tensile strength of 110-125MPa, and notched impact strength of 9.2-11.0kJ / m². The thermal stability and processing performance are also better, effectively solving many pain points of traditional processes and laying the foundation for the large-scale and high-quality application of thermoplastic polyimide.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for synthesizing thermoplastic polyimide via a continuous polymerization extrusion granulation process, characterized in that, The specific steps of this method are as follows: S1, Oligomer Synthesis: Dianone monomer and diamine monomer are mixed in a molar ratio of 1.03:1 to 1:1.03, and water or (and) organic solvent is used as the reaction medium. The mixture is stirred at 40-150℃ and 0-1MPa for 2-4 hours. Then, an imidization catalyst is added and the reaction is continued for 1-2 hours to obtain a polyimide oligomer reaction system. S2, Solvent / Water Flash Evaporation Recovery: The polyimide oligomer reaction system is placed in a vacuum environment with a pressure of -0.01 to -0.1 MPa, and the temperature is raised to 80-150℃ for flash evaporation. The solvent or water is flashed out and collected. The collected material is returned to step S1 as a reaction medium and reused in the oligomer synthesis. After flash evaporation, polyimide oligomer powder is obtained. S3, Powder mixing and drying: The polyimide oligomer powder is mixed with antioxidants and other additives, toughening agents, and reinforcing agents, and then vacuum dried at 120-200℃ for 4-6 hours with step temperature increase. S4, Extrusion Granulation: The above mixture is fed into a twin-screw extruder and extruded and granulated under controlled temperature in different zones to obtain thermoplastic polyimide particles.

2. The method for synthesizing thermoplastic polyimide by a continuous polymerization-extrusion granulation process according to claim 1, characterized in that, In S1, during the oligomer synthesis, the organic solvent is selected from at least one of N,N-dimethylacetamide, N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, ethanol, methanol, toluene, and xylene. The mixture of water and the organic solvent is used as a medium, wherein the mass ratio of water to the organic solvent is from 70:30 to 98:

2.

3. The method for synthesizing thermoplastic polyimide by continuous polymerization extrusion granulation according to claim 1, characterized in that, In the S1 oligomer synthesis, the dianhydride monomer is selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-diphenyl ethertetracarboxylic dianhydride, or bisphenol A diether dianhydride; the diamine monomer is selected from 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfide, bisphenol A diether diamine, or m-phenylenediamine.

4. The method for synthesizing thermoplastic polyimide by continuous polymerization extrusion granulation according to claim 1, characterized in that, In the S1 oligomer synthesis, the total mass of the reaction medium and the monomers satisfies the following: the solid content of the system is 15-50%; the imidization catalyst is selected from a mixture of acetic anhydride and triethylamine, a mixture of acetic anhydride and pyridine, or zinc chloride, and the amount of catalyst added is 0.4%-0.6% of the total mass of the dianhydride monomer and the diamine monomer.

5. The method for synthesizing thermoplastic polyimide by continuous polymerization extrusion granulation according to claim 1, characterized in that, In step S2, during the solvent / water flash evaporation recovery, the flash pressure is controlled between -0.01 and -0.1 MPa, and the flash temperature is 80-150°C.

6. The method for synthesizing thermoplastic polyimide by continuous polymerization extrusion granulation according to claim 1, characterized in that, In step S3, the antioxidant is antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] or antioxidant 1076 (octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), and the amount added is 0.2%-0.4% of the mass of the polyimide powder.

7. The method for synthesizing thermoplastic polyimide by continuous polymerization extrusion granulation according to claim 1, characterized in that, In step S3, the reinforcing agent is selected from at least one or a mixture of several of glass fiber, carbon fiber, carbon nanotubes, graphene, nano-silica, nano-titanium dioxide, clay or polytetrafluoroethylene micropowder, and polyetheretherketone. The amount added is 0%-30% of the mass of the polyimide.

8. The method for synthesizing thermoplastic polyimide by continuous polymerization extrusion granulation according to claim 1, characterized in that, In step S3, the mixture is then heated in a nitrogen dryer, with a gradient temperature increase of 120-180°C. The mixture is then dried in a nitrogen atmosphere at a temperature of 120-150°C for 1-2 hours, and then dried in a nitrogen atmosphere at a temperature of 150-180°C for 2-3 hours. Subsequently, it is fed into a screw extruder via a feeding device.

9. The method for synthesizing thermoplastic polyimide by continuous polymerization extrusion granulation according to claim 1, characterized in that, In step S4, extrusion granulation is performed. The screw length-to-diameter ratio of the twin-screw extruder is 30:1 to 60:1, and the temperature is controlled in zones as follows: feeding section 180 to 260°C, melting section 280 to 320°C, mixing section 320 to 360°C, and die head section 350 to 370°C. The die head pressure during extrusion is 5 to 8 MPa.

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