A method for the aqueous polymerization of polyimides

Abstract

The present application relates to a kind of polyimide aqueous phase polymerization method, belong to high-performance polymer synthesis technical field.It includes the following steps, 1), aqueous phase polymerization, dianhydride is mixed with diamine in deionized water, end-capping agent is added, and it is reacted for several hours in autoclave after nitrogen replacement, and polyamide acid oligomer water suspension solution is generated;2), spray drying, after reaction, by control switch valve, the above water suspension solution is passed through spray drying equipment, and the polyamide acid oligomer powder with good flowability of 1-200 microns uniform particle size is obtained;3), twin-screw vacuum devolatilization imidization and extrusion, the above dry powder is sent into same direction twin-screw extruder, and by screw shearing and step-by-step vacuum devolatilization effect, oligomer chain growth and dehydration cyclization are synchronously carried out, and high molecular weight polyetherimide is formed;4), extrusion granulation, in extruder, melt polyetherimide is extruded, cooled and cut into pellets in die, and polyetherimide plastic particle is obtained.The present technical solution is environmentally friendly and advanced: it is easy to realize continuous production;Greatly improve production efficiency.

Description

Technical Field

[0001] This invention relates to a method for aqueous polymerization of polyimide, belonging to the field of high-performance polymer synthesis technology. Background Technology

[0002] Polyetherimide (PI) and polyimide (PI) have become indispensable high-performance engineering plastics in high-end manufacturing fields such as aerospace, electronics, medical, and automotive due to their outstanding high-temperature resistance, mechanical strength, electrical insulation, and chemical corrosion resistance. Polyimides are typically obtained through the polymerization reaction of dianhydrides and diamines, and a wide variety of monomers are applicable. By changing the monomer structure, polymers with different thermal, mechanical, and optical properties can be obtained. Common polyimide synthesis methods are usually two-step processes (i.e., first preparing polyamic acid, followed by cyclization through thermal imidization or chemical imidization to obtain polyimide). Polar aprotic solvents such as N,N-dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF) are commonly used as reaction solvents. Although the technology is mature, it has the following common drawbacks: ① High-boiling-point solvent residues are difficult to remove completely, with high-boiling-point solvent residues ≥0.5 wt%, affecting the purity and long-term reliability of the products; ② High-temperature step drying is required after the reaction, which is energy-intensive and time-consuming, with step drying energy consumption ≥15 kWh•kg⁻¹ ​​and a cycle >12 h; ③ A large amount of toxic solvent volatilization causes environmental pollution, with high VOC emissions, and the cost of waste treatment accounts for more than 15% of the total cost; ④ The solution viscosity increases sharply with the increase of molecular weight, which easily forms gels or clumps, limiting heat / mass transfer during scale-up production, resulting in low continuity and poor batch stability.

[0003] The invention patent "Method for preparing polyetherimide by continuous extrusion reaction" published by Shanghai Synthetic Resin Research Institute, CN1563150A, uses direct melt extrusion to obtain polyetherimide with an intrinsic viscosity of only 0.45–0.65 dL / g in N-methylpyrrolidone. Moreover, direct extrusion requires uniform mixing of two monomer raw materials, and direct extrusion of monomers in a screw extruder is prone to oxidation, resulting in a dark product color.

[0004] The aforementioned methods generally suffer from the following problems: large amounts of organic solvents are used, making recycling difficult; high energy consumption, serious environmental pollution, and poor batch stability.

[0005] In recent years, some studies have attempted aqueous polymerization, but problems such as low reaction efficiency, poor product solubility, and the need for organic solvents in subsequent treatment have limited its industrial application. The invention patent CN201810787533.7 applied for by Sanpu Aqueous Technology Co., Ltd. uses a mixed solvent of ethanol and water as the reaction medium, and requires substances such as tetrabutylammonium bromide (TBAB) as catalysts. Catalyst residues are easily left, and post-treatment rinsing results in the residue entering the wastewater. Zhejiang Qinghe Technology Co., Ltd. CN112694614 B provides a highly efficient and green preparation method for polyimide. This method uses segmented high-temperature and pressure polymerization in an aqueous phase, solving the problem of black impurities generated in existing aqueous polymerization technologies and avoiding the use of high-boiling-point solvents. However, subsequent treatment still requires washing with ethanol-acetone solvents, increasing the complexity of the process.

[0006] Therefore, existing technologies suffer from problems such as high solvent residue, high energy consumption, and low continuity. Furthermore, the aqueous phase route has not yet solved the two core problems of "high Mw-dissolution / melting contradiction" and "continuous closed-loop dehydration." Therefore, developing a method for preparing polyetherimide plastic particles that is solvent-free throughout the entire process, can be continuously scaled up, has controllable molecular weight, and directly yields the particles has become a key technological direction that urgently needs to be broken through in this field. Summary of the Invention

[0007] The present invention aims to provide a green, efficient and continuous method for preparing polyetherimide, which solves the problems of excessive solvent use, high energy consumption and uncontrollable molecular weight in traditional processes.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for aqueous polymerization of polyimide includes the following four steps, and no organic solvents are used throughout the process: 1) The polycondensation reaction of material A and diamine is carried out by high-pressure polymerization in a deionized aqueous phase to generate an oligomer aqueous suspension slurry of polyamic acid; material A is dianhydride or tetracarboxylic acid; 2) After the reaction is complete, the above aqueous suspension is passed through a spray drying device to obtain polyamic acid oligomer powder with a particle size of 1-200 micrometers and good flowability; 3) The above-mentioned dried powder is fed into a twin-screw extruder. Through screw shearing and step-by-step vacuum devouring, the oligomer chain growth and dehydration imidization are carried out simultaneously to form high molecular weight polyetherimide. 4) The imidized melt is extruded through a die to form polyetherimide plastic particles.

[0009] A further improvement to the technical solution of the present invention is as follows: the method for synthesizing polyamic acid oligomers in step 1) is to add dianhydride and diamine to a high-pressure reactor after nitrogen purging, and simultaneously add a capping agent and deionized water for polymerization; the solute phase in step 1 contains dianhydride, diamine, and capping agent in a total mass ratio to the total mass of the entire solution, i.e., the solid content is 5~70%, preferably 25~50%, and more preferably 20~30%.

[0010] A further improvement to the technical solution of the present invention is as follows: the dianhydride monomer is selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), bisphenol A diether dianhydride (BPADA), and bisphenol S diether dianhydride (DSDA); the diamine monomer is selected from 4,4'-diaminodiphenyl ether (4,4ODA), 4,4'-diaminodiphenyl sulfide, bisphenol A diether diamine (BAPP), or m-phenylenediamine (mDA); the end-capping agent is phthalic anhydride or aniline; the tetracarboxylic acid is 3,3',4,4'-biphenyltetracarboxylic acid, 3,3',4,4'-diphenyl ether tetracarboxylic acid, bisphenol A diether diphenyltetracarboxylic acid, and bisphenol S diether diphenyltetracarboxylic acid.

[0011] A further improvement to the technical solution of the present invention is as follows: in step 1, the molar ratio of dianhydride to diamine is (0.98-1.02):1; the amount of capping agent is (0.1-3) of the molar amount of diamine.

[0012] A further improvement to the technical solution of the present invention is as follows: the reaction is carried out in a high-pressure reactor after nitrogen purging at 120℃~180℃ for 2~5 hours, the reaction pressure range is 0-1MPa, and the stirring speed is 80-300 rpm.

[0013] A further improvement to the technical solution of this invention is as follows: In step 2, the inlet temperature of the spray drying process is 150℃~220℃, and the outlet temperature is 80℃~120℃. Centrifugal atomization is used, with an atomizer speed of 10,000-40,000 rpm; nitrogen is used as the carrier gas for spray drying, and the spray drying pressure is 0.12-0.5 MPa. The moisture content of the powder after spray drying is between 1% and 5%. The weight-average molecular weight of the oligomers in the spray-dried polyamic acid powder is between 10,000 and 40,000, and the number-average molecular weight is between 5,000 and 20,000; the particle size D50 of the spray-dried powder is between 1 micrometer and 200 micrometers; and the loose packing density of the powder is ≥0.30 g / cm³.

[0014] A further improvement to the technical solution of this invention is as follows: In step 3, the screw extruder is a co-directional twin-screw structure with a screw length-to-diameter ratio L / D = 40~60. Three to four vacuum devouring ports are sequentially arranged along the screw axis. The first one to two vacuum ports have a range of 80–120 mbar, the second and third stages have 15–30 mbar, and the last stage has a vacuum port of 2–10 mbar, with an interstage pressure difference ≥ 5 times. The meshing block occupies 15~25% of the total area. The operating temperature range is 220℃~370℃, the vacuum degree is 2-30 mbar, and the rotation speed is 30–300 rpm. The twin-screw temperature zones are 220℃~250℃→250℃~280℃→280℃~320℃→310℃~350℃→350℃~360℃, and the extrusion residence time is 2-10 minutes.

[0015] A further improvement to the technical solution of the present invention is as follows: the imidized melt is extruded through a die, cooled, and pelletized to form thermoplastic polyetherimide plastic particles.

[0016] A further improvement to the technical solution of this invention is as follows: the polyetherimide particles obtained in step 8 have an intrinsic viscosity of 0.5–1.2 dL / g, Tg ≥ 210℃, and a thermal decomposition temperature (T5%) > 520℃. The molecular weight distribution range is: weight-average molecular weight between 60,000 and 150,000, and number-average molecular weight between 30,000 and 60,000. The degree of imidization is measured using FT-IR with a peak area ratio ≥ 0.98 at 1780 cm⁻¹ / 1500 cm⁻¹; the melt index test at 350℃ and 5KG pressure shows a melt index range of 5-50 g / 10min; the metal ion content is ≤ 5 ppm, and the VOC emission is ≤ 20 mg / m³.

[0017] A further improvement to the technical solution of this invention is that the entire process is free of organic solvents, the water recycling rate is ≥95%, the comprehensive energy consumption per unit product is ≤8 kWh / kg, and the continuous operation time is ≥72 h.

[0018] Due to the adoption of the above technical solution, the technical effects achieved by this invention are as follows: Green and environmentally friendly: Water is used as the reaction medium throughout the process, avoiding the problems of using and recycling organic solvents; the spray drying process has high thermal energy utilization; the co-rotating twin-screw extrusion reactor is used, and by precisely controlling the screw speed and feed rate, the polymerization process can be made continuous and stable, and the production efficiency is improved compared with the traditional batch reaction.

[0019] Continuous process: The imidization and thickening processes are completed simultaneously in the screw compressor, eliminating the need for subsequent high-temperature treatment or solvent extraction. The aqueous polymerization, spray drying, and extrusion granulation units can be connected in series, enabling continuous production from oligomers to finished particles; significantly improving production efficiency.

[0020] Controllable molecular weight: By adjusting the amount of end-capping agent and screw parameters, as well as by staged vacuum degassing, precise control of polymer chain length and molecular weight distribution can be achieved.

[0021] The product boasts superior performance: During melt polycondensation in a screw extruder, the reaction temperature is controlled between 220-360℃, with staged vacuum degassing and a maximum vacuum maintained at 10-30 mbar, effectively removing byproducts and promoting molecular chain growth. By adjusting polymerization conditions, spray drying parameters, and the type and amount of tackifier, the molecular weight, particle size distribution, and final mechanical properties of the polyetherimide can be precisely controlled. The resulting polyetherimide particles have a Tg ≥ 210℃, a thermal decomposition temperature (T5%) > 520℃, and a molecular weight distribution range of: weight-average molecular weight between 60,000 and 150,000, and number-average molecular weight between 30,000 and 60,000. The melt index at 350℃ and 5KG pressure ranges from 5-50 g / 10 min. The metal ion content is ≤ 5 ppm, making it suitable for various processing methods such as injection molding and extrusion.

[0022] The technical solution of this invention involves no organic solvents throughout the entire process, with VOC emissions ≤20 mg / m³, water recycling rate ≥95%, comprehensive energy consumption per unit product ≤8 kWh / kg, and continuous operation time ≥72 h. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0024] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0025] The present invention aims to provide a green preparation method for PEI particles that is solvent-free throughout the entire process, can be continuously scaled up, has controllable molecular weight, and directly obtains the particles, thus solving the problems of solvent residue, high energy consumption, intermittent production, and wide molecular weight distribution in the prior art.

[0026] The continuous preparation method of polyetherimide mainly includes the following steps in sequence: Aqueous phase polymerization - spray drying - imidization - extrusion granulation; no organic solvents are used throughout the process.

[0027] The following is a detailed explanation of each step: 1) Aqueous phase polymerization Deionized water, material A, diamine, and end-capping agent are added to a high-pressure reactor after nitrogen purging. The reaction is carried out for several hours to generate an aqueous suspension of polyamic acid oligomers.

[0028] Material A can be either dianhydride or tetracarboxylic acid.

[0029] Further, preferably, the dianhydride monomer is selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), bisphenol A diether dianhydride (BPADA), and bisphenol S diether dianhydride (DSDA); the diamine monomer is selected from 4,4'-diaminodiphenyl ether (4,4ODA), 4,4'-diaminodiphenyl sulfide, bisphenol A diether diamine (BAPP), or m-phenylenediamine (mDA); the end-capping agent is phthalic anhydride or aniline; the tetracarboxylic acid is preferably 3,3',4,4'-biphenyltetracarboxylic acid, 3,3',4,4'-diphenyl ether tetracarboxylic acid, bisphenol A diether diphenyltetracarboxylic acid, or bisphenol S diether diphenyltetracarboxylic acid.

[0030] The dianhydride and diamine are mixed in a molar ratio of (0.98–1.02):1. The capping agent is phthalic anhydride or aniline, and its amount is (0.1–3)% of the molar amount of diamine. The reaction conditions are 120℃–180℃ for 2–5 hours. The stirring speed is 80–300 rpm.

[0031] 2) Spray drying After the reaction, the aqueous suspension is passed through a spray dryer by controlling the switching valve to obtain a powdered material. Specifically, the inlet temperature of the spray dryer is controlled at 150℃~220℃, the outlet temperature at 80℃~120℃, nitrogen is used as the carrier gas, and the spray drying pressure is 0.12-0.5 MPa. The moisture content of the spray-dried powder is between 1% and 5%. The weight average molecular weight of the spray-dried oligomer powder is between 10,000 and 40,000, and the number average molecular weight is between 5,000 and 20,000. The particle size distribution of the spray-dried powder is between 1 and 200 micrometers, and the loose packing density is ≥0.30 g / cm³, allowing it to be directly fed into a screw compressor.

[0032] 3) Imine The powder synthesized and spray-dried from dianhydride and diamine or the powder synthesized and spray-dried from diacid and diamine is fed into a co-rotating twin-screw extruder. Through screw shearing and vacuum devolatilization, the oligomer undergoes further chain growth and dehydration cyclization simultaneously to form high molecular weight polyetherimide.

[0033] The screw extruder used is a co-rotating twin-screw structure equipped with a vacuum devolatilization device. Three to four vacuum devolatilization ports are sequentially arranged along the screw axis. The first one to two vacuum ports have a range of 80–120 mbar, the next two stages 15–30 mbar, and the final stage 2–10 mbar, with an interstage pressure difference ≥5 times and a rotational speed of 30–300 rpm. The powder is fed into the twin-screw extruder, where the oligomers undergo further chain growth and dehydration / cyclization simultaneously through screw shearing and vacuum devolatilization. The co-rotating twin-screw has an L / D ratio of 40–60, with five-stage temperature control at 220–250–280–310–350 ℃ (±10 ℃), and a residence time of 2–10 min. The interlocking block length is 15–25% to ensure simultaneous completion of powder melting, dehydration, and chain growth, achieving an imidization rate ≥98%. Imidization is tested using infrared spectroscopy with a standard sample comparison method. This results in a high molecular weight polyetherimide with a relatively uniform molecular weight distribution. Furthermore, specifically, the operating temperature range is 220℃~370℃, the vacuum degree is 2-30mbar, and the speed is 30–300rpm; the twin-screw temperature zones are 220℃~250℃→250℃~280℃→280℃~320℃→310℃~350℃→350℃~360℃, and the extrusion residence time is 2-10 minutes.

[0034] 4) Extrusion granulation The above-mentioned molten polyetherimide is extruded through a die, cooled, and granulated to obtain polyetherimide plastic particles.

[0035] The polyetherimide particles prepared using this technology have an intrinsic viscosity of 0.5–1.2 dL / g, a Tg ≥ 210℃, and a thermal decomposition temperature (T5%) > 520℃. The molecular weight distribution ranges from 60,000 to 150,000 in weight average and from 30,000 to 60,000 in number average. The melt index at 350℃ and 5KG pressure ranges from 5 to 50 g / 10 min. The metal ion content is ≤ 5 ppm, making it suitable for various processing methods such as injection molding and extrusion.

[0036] The technical solution of this invention involves no organic solvents throughout the entire process, with VOC emissions ≤20 mg / m³, water recycling rate ≥95%, comprehensive energy consumption per unit product ≤8 kWh / kg, and continuous operation time ≥72 h.

[0037] In this invention, material A can be either tetracarboxylic acid or dianhydride. Tetracarboxylic acid is preferred because, in actual production, dianhydride is also produced using tetracarboxylic acid as a raw material. Using tetracarboxylic acid directly in this method achieves the same product effect while saving the dehydration process from tetracarboxylic acid to dianhydride, reducing costs and improving process efficiency.

[0038] This technical solution can achieve continuous and stable process, enabling continuous production from oligomers to finished particles, and significantly improving production efficiency.

[0039] The following are specific examples. Example 1

[0040] Step 1, Aqueous Phase Polymerization: 1400 kg of deionized water was added to a 3 m³ nitrogen-purged reactor, along with 520 kg of bisphenol A type diether dianhydride and 108 kg of m-phenylenediamine, and 2.96 kg of phthalic anhydride as a capping agent. The solid content was 31%. The stirring speed was 160 rpm, and the reaction was carried out at 120℃ and 0.2 MPa for 5 hours.

[0041] Step 2, Spray Drying: The above aqueous suspension is piped into a centrifugal spray dryer. Nitrogen is used as the carrier gas. The inlet temperature of the spray dryer is controlled at 150℃, the outlet temperature at 100℃, and the centrifugal atomizer speed at 8000 rpm. A dried powder with a D50 of 150 µm is obtained and collected. The loose bulk density is 0.38 g / cm³, and the moisture content is 4.8%.

[0042] Step 3, Imidification: A co-rotating screw extruder with a screw length-to-diameter ratio (L / D) of 52 was used. The extrusion process employed four vacuum degassing ports with four levels of vacuum pressure (80→30→10→2 mbar). The temperature was controlled in five stages: 220-250-280-310-330 ℃, with a screw speed of 120 rpm and a residence time of 6 min. The imidization rate was 98.5%.

[0043] Step 4: Extrusion granulation. Molten polyetherimide is extruded through a die at the end of the screw extruder, cooled, and granulated to obtain polyetherimide plastic particles. The resulting cylindrical particles are 3 mm long and 2 mm in diameter, with IV = 0.80 dL / g, Mw = 84800, Mn = 45200, MFR = 18 g / 10min (350℃, 5 kg), Tg = 217 ℃, Td5% = 525 ℃, metal ions ≤ 3 ppm, VOC = 5 mg / m³, and a yield of 93.2%. The VOC level of the condensate after exhaust gas in the aqueous phase is 3 mg / m³. The water recycling rate is ≥95%, the comprehensive energy consumption per unit product is 6 kWh / kg, and the continuous operation time is ≥100 h. Example 2

[0044] Step 1, Aqueous Phase Polymerization: Add 300 kg of deionized water to a 3 m³ reactor, along with 520 kg of bisphenol A type diether dianhydride and 200 kg of 4,4′-diaminodiphenyl ether, and 0.1 kg (0.001 kmol) of aniline as a capping agent. The solid content is 70%. The reaction is carried out at 180℃, 0.8 MPa, and a stirring speed of 250 rpm for 1.5 hours.

[0045] Step 2, Spray Drying: The above aqueous suspension is piped into a spray drying device. The inlet temperature of the spray drying device is controlled at 190℃, the outlet temperature at 100℃, and the centrifugal atomizer speed at 30,000 rpm. A dried powder with a D50 of 100 µm is obtained and collected. The moisture content is 0.9%.

[0046] Step 3, Imidization: A co-rotating screw extruder with a screw length-to-diameter ratio (L / D) of 40 was used. The extrusion process was controlled with a five-stage heating process: 240-280-310-330-360℃ (±5℃). Vacuum level 4 was used (100→15→5→2 mbar), screw speed was 30 rpm, residence time was 10 min, and the imidization rate was 98.8%.

[0047] Step 4: Extrusion granulation. Molten polyetherimide is extruded through a die at the end of the screw extruder, cooled, and granulated to obtain polyetherimide plastic particles. The resulting cylindrical particles are 3 mm long and 2 mm in diameter, with IV = 0.60 dL / g, Mw = 98400, Mn = 35000, MFR = 8 g / 10 min (350℃, 5 kg), Tg = 225℃, Td5% = 530℃, metal ions ≤ 3 ppm, and a yield of 92%.

[0048] The VOC level of the condensate after exhaust gas in the aqueous phase is 5 mg / m³. The water recycling rate is ≥97%, the comprehensive energy consumption per unit product is 7.5 kWh / kg, and the continuous operation time is ≥80 h. Example 3

[0049] Step 1, Aqueous Phase Polymerization: Add 400 kg of deionized water to a 3 m³ reactor, then add 310.2 kg of 3,3′,4,4′-diphenyl ether tetracarboxylic dianhydride and 200 kg of 4,4-diaminodiphenyl ether, along with 1 kg of phthalic anhydride as a capping agent. The solid content is 56%. The reaction is carried out at 130℃ and 0.3 MPa for 2 hours.

[0050] Step 2, Spray Drying: The above aqueous suspension is piped into a spray drying device. The inlet temperature of the spray drying device is controlled at 220℃, the outlet temperature at 120℃, and the centrifugal atomizer speed at 25000 rpm. A dried powder with a D50 of 200 is obtained and collected. The moisture content is 1%.

[0051] Step 3, imidization: Using a co-rotating screw extruder with a screw length-to-diameter ratio (L / D) of 40, the extrusion process is controlled as a five-stage heating process: 240-280-310-330-360 ℃ (±5 ℃), 3-level vacuum (80→30→10 mbar), screw speed 100 rpm, residence time 8 min, imidization rate 98.2%.

[0052] Step 4: Extrusion granulation. Molten polyetherimide is extruded through a die at the end of the screw extruder, cooled, and granulated to obtain polyetherimide plastic particles. The resulting cylindrical particles are 3 mm long and 2 mm in diameter, with IV = 0.60 dL / g, Mw = 88400, Mn = 35000, MFR = 5 g / 10 min (330 ℃, 5 kg), Tg = 225 ℃, Td5% = 520 ℃, metal ions ≤ 3 ppm, and a yield of 92%.

[0053] The VOC level of the condensate after exhaust gas in the aqueous phase is 5 mg / m³. The water recycling rate is ≥97%, the comprehensive energy consumption per unit product is 5 kWh / kg, and the continuous operation time is 100 h. Example 4

[0054] Step 1, Aqueous Phase Polymerization: Add 1400 kg of deionized water to a 3 m³ reactor, along with 466 kg of 3,3′,4,4′-diphenyl ether tetracarboxylic dianhydride and 216 kg of 4,4-diaminodiphenyl sulfide, and 2.8 kg of aniline as a capping agent. The reaction is carried out at 130 °C for 4 hours with a solid content of 25%.

[0055] Step 2, Spray Drying: The above aqueous suspension is piped into a spray drying device. The inlet temperature of the spray drying device is controlled at 200℃, the outlet temperature at 100℃, and the centrifugal atomizer speed at 25,000 rpm. A dried powder with D50=200 is obtained and collected. The moisture content is less than 0.6%.

[0056] Step 3, Imidification: A co-rotating screw extruder with a screw length-to-diameter ratio (L / D) of 40 was used. The extrusion process was controlled as a five-stage heating process: 240-280-310-330-360 ℃ (±5 ℃). There were three vacuum ports with a maximum vacuum of -30 mbar. The screw speed was 120 rpm, and the residence time was 5 min. The imidization rate was 98.2%.

[0057] Step 4: Extrusion granulation. Molten polyetherimide is extruded through a die at the end of the screw extruder, cooled, and pelletized to obtain polyetherimide plastic particles. The resulting cylindrical particles are 3 mm long and 2 mm in diameter, with IV = 0.50 dL / g, Mw = 60400, Mn = 30300, MFR = 50 g / 10 min (330℃, 5 kg), Tg = 225℃, Td5% = 525℃, metal ions ≤ 3 ppm, and a yield of 92%.

[0058] The VOC level of the condensate after exhaust gas in the aqueous phase is 2 mg / m³. The water recycling rate is ≥97%, the comprehensive energy consumption per unit product is 6.5 kWh / kg, and the continuous operation time is 80 hours. Example 5

[0059] Step 1, Aqueous Phase Polymerization: Add 1400 kg of deionized water to a 3 m³ reactor, along with 466 kg of 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 200 kg of bisphenol A diether diamine, and 1 kg of phthalic anhydride as a capping agent. The reaction is carried out at 130 °C for 4 hours with a solid content of 25%.

[0060] Step 2, Spray Drying: The above aqueous suspension is piped into a spray drying device. The inlet temperature of the spray drying device is controlled at 200℃, the outlet temperature at 100℃, and the centrifugal atomizer speed at 25,000 rpm. A dried powder with D50=200 is obtained and collected. The moisture content is less than 0.6%.

[0061] Step 3, imidization: Using a co-rotating screw extruder with a screw length-to-diameter ratio (L / D) of 40, the extrusion process is controlled as a five-stage heating process: 240-280-310-330-360 ℃ (±5 ℃), 3-level vacuum (80→30→-30 mbar), screw speed 120 rpm, residence time 5 min, imidization rate 98.2%.

[0062] Step 4: Extrusion granulation. Molten polyetherimide is extruded through a die at the end of the screw extruder, cooled, and granulated to obtain polyetherimide plastic particles. The resulting cylindrical particles are 3 mm long and 2 mm in diameter, with IV = 0.60 dL / g, Mw = 88400, Mn = 35000, MFR = 18 g / 10 min (330 ℃, 5 kg), Tg = 225 ℃, Td5% = 525 ℃, metal ions ≤ 3 ppm, and a yield of 92%.

[0063] The VOC level of the condensate after exhaust gas in the aqueous phase is 5 mg / m³. The water recycling rate is ≥97%, the comprehensive energy consumption per unit product is 7 kWh / kg, and the continuous operation time is ≥80 h. Example 6

[0064] Step 1, Aqueous Phase Polymerization: Add 1235 kg of deionized water to a 3 m³ reactor, along with 466 kg of 3,3′,4,4′-diphenyl ether tetracarboxylic dianhydride and 200 kg of 4,4-diaminodiphenyl ether, and 2.5 kg of phthalic anhydride as a capping agent. The reaction is carried out at 130 °C for 4 hours with a solid content of 35%.

[0065] Step 2, Spray Drying: The above aqueous suspension is piped into a spray drying device. The inlet temperature of the spray drying device is controlled at 200℃, the outlet temperature at 100℃, and the centrifugal atomizer speed at 25,000 rpm. A dried powder with a D50 of 200 is obtained and collected. The moisture content is 4.8%.

[0066] Step 3, Imidification: Using a co-rotating screw extruder with a screw length-to-diameter ratio (L / D) of 40, the extrusion process is controlled as a five-stage heating process: 240-280-310-330-360 ℃ (±5 ℃), 4-level vacuum (80→30→10→2 mbar), screw speed 120 rpm, residence time 5 min, imidization rate 98.2%.

[0067] Step 4: Extrusion granulation. Molten polyetherimide is extruded through a die at the end of the screw extruder, cooled, and granulated to obtain polyetherimide plastic particles. The resulting cylindrical particles are 3 mm long and 2 mm in diameter, with IV = 0.80 dL / g, Mw = 60200, Mn = 30100, MFR = 50 g / 10 min (330 ℃, 5 kg), Tg = 235 ℃, Td5% = 520 ℃, metal ions ≤ 3 ppm, and a yield of 92%.

[0068] The VOC level of the condensate after exhaust gas in the aqueous phase was 5 mg / m³. The water recycling rate was 95%, the comprehensive energy consumption per unit product was 6 kWh / kg, and the continuous operation time was 100 h. Example 7

[0069] Step 1, Aqueous Phase Polymerization: Add 1400 kg of deionized water to a 2 m³ reactor, along with 466 kg of 3,3′,4,4′-diphenyl ether tetracarboxylic dianhydride and 200 kg of bisphenol A diphenyl ether diamine, and 1 kg of phthalic anhydride as a capping agent. The reaction is carried out at 130°C for 4 hours with a solid content of 25%.

[0070] Step 2, Spray Drying: The above aqueous suspension is piped into a spray drying device. The inlet temperature of the spray drying device is controlled at 200℃, the outlet temperature at 100℃, and the centrifugal atomizer speed at 25,000 rpm. A dried powder with D50=200 is obtained and collected. The moisture content is less than 0.6%.

[0071] Step 3, Imidification: A co-rotating screw extruder with a screw length-to-diameter ratio (L / D) of 40 was used. The extrusion process was controlled as a five-stage heating process: 240-280-310-330-360 ℃ (±5 ℃). There were three vacuum ports with a maximum vacuum of -30 mbar. The screw speed was 120 rpm, and the residence time was 5 min. The imidization rate was 98.2%.

[0072] Step 4: Extrusion granulation. Molten polyetherimide is extruded through a die at the end of the screw extruder, cooled, and pelletized to obtain polyetherimide plastic particles. The resulting cylindrical particles are 3 mm long and 2 mm in diameter, with IV = 0.60 dL / g, Mw = 88400, Mn = 35000, MFR = 18 g / 10 min (330 ℃, 5 kg), Tg = 210 ℃, Td5% = 525 ℃, metal ions ≤ 3 ppm, and a yield of 92%.

[0073] The VOC level of the condensate after exhaust gas in the aqueous phase is 5 mg / m³. The water recycling rate is ≥97%, the comprehensive energy consumption per unit product is ≤10 kWh / kg, and the continuous operation time is ≥80 h. Example 8

[0074] Step 1, Aqueous Phase Polymerization: 1400 kg of deionized water was added to a 3 m³ nitrogen-purged reactor, along with 556 kg of bisphenol A type diether tetracarboxylic acid and 108 kg of m-phenylenediamine, and 2.96 kg of phthalic anhydride capping agent with a solid content of 31%. The mixture was stirred at 160 rpm and reacted at 120 °C and 0.2 MPa for 5 hours.

[0075] Step 2, Spray Drying: The above aqueous suspension is piped into a centrifugal spray dryer. Nitrogen is used as the carrier gas. The inlet temperature of the spray dryer is controlled at 150℃, the outlet temperature at 100℃, and the centrifugal atomizer speed at 8000 rpm. A dried powder with a D50 of 150 µm is obtained and collected. The loose bulk density is 0.38 g / cm³, and the moisture content is 4.8%.

[0076] Step 3: The conditions for thickening polyamic acid synthesized from tetracarboxylic acid and diamine are as follows: temperature 150–210℃, stepped temperature increase, each step 5–10℃, pressure 13–60 Pa (vacuum) or N2 slight positive pressure, nitrogen flow rate 0.2–2 L·min⁻¹·kg⁻¹, total time 2–8 h, and the later thickening temperature < 210℃ for 2–6 h.

[0077] Step 3, Imidification: A co-rotating screw extruder with a screw length-to-diameter ratio (L / D) of 52 was used. The extrusion process employed four vacuum degassing ports with four levels of vacuum pressure (80→30→10→2 mbar). The temperature was controlled in five stages: 220-250-280-310-330 ℃, with a screw speed of 120 rpm and a residence time of 6 min. The imidization rate was 98.5%.

[0078] Step 4: Extrusion granulation. Molten polyetherimide is extruded through a die at the end of the screw extruder, cooled, and granulated to obtain polyetherimide plastic particles. The resulting cylindrical particles are 3 mm long and 2 mm in diameter, with IV = 0.80 dL / g, Mw = 84800, Mn = 45200, MFR = 18 g / 10 min (350 ℃, 5 kg), Tg = 217 ℃, Td5% = 525 ℃, metal ions ≤ 3 ppm, VOC = 5 mg / m³, and a yield of 93.2%. The VOC level of the condensate after exhaust gas in the aqueous phase is 3 mg / m³. The water recycling rate is ≥95%, the comprehensive energy consumption per unit product is 5 kWh / kg, and the continuous operation time is ≥100 h. Example 9

[0079] Step 1, Aqueous Phase Polymerization: Add 400 kg of deionized water to a 3 m³ reactor, along with 346 kg of 3,3′,4,4′-diphenyl ether tetracarboxylic acid and 200 kg of 4,4-diaminodiphenyl ether, and 1 kg of phthalic anhydride as a capping agent. The solid content is 56%. The reaction is carried out at 130℃ and 0.3 MPa for 2 hours.

[0080] Step 2, Spray Drying: The above aqueous suspension is piped into a spray drying device. The inlet temperature of the spray drying device is controlled at 220℃, the outlet temperature at 120℃, and the centrifugal atomizer speed at 25000 rpm. A dried powder with a D50 of 200 is obtained and collected. The moisture content is 1%.

[0081] Step 3, imidization: Using a co-rotating screw extruder with a screw length-to-diameter ratio (L / D) of 40, the extrusion process is controlled as a five-stage heating process: 240-280-310-330-360 ℃ (±5 ℃), 3-level vacuum (80→30→10 mbar), screw speed 100 rpm, residence time 8 min, imidization rate 98.2%.

[0082] Step 4: Extrusion granulation. Molten polyetherimide is extruded through a die at the end of the screw extruder, cooled, and granulated to obtain polyetherimide plastic particles. The resulting cylindrical particles are 3 mm long and 2 mm in diameter, with IV = 0.60 dL / g, Mw = 88400, Mn = 35000, MFR = 5 g / 10 min (330 ℃, 5 kg), Tg = 225 ℃, Td5% = 520 ℃, metal ions ≤ 3 ppm, and a yield of 92%.

[0083] The VOC level of the condensate after exhaust gas in the aqueous phase is 5 mg / m³. The water recycling rate is ≥97%, the comprehensive energy consumption per unit product is 4.5 kWh / kg, and the continuous operation time is 100 h.

[0084] Comparative example: Traditional NMP solution method First, in a nitrogen-protected reactor at 15 °C, 10.8 kg of m-phenylenediamine was dissolved in 180 kg of NMP. Then, 52.05 kg of bisphenol A diether dianhydride was added in three portions to form a viscous polyamic acid solution. Next, 0.2 kg of phthalic anhydride was added as a capping agent. Then, chemical imidization was completed by using a 0.3 kg acetic anhydride-pyridine catalytic system at 180 °C for 8 h, followed by dehydration at elevated temperature, to obtain a concentrated polyetherimide-NMP solution with Mw≈64,000 and IV 0.65 dL / g. The hot material was directly pressed into 10 times its volume of ethanol to precipitate a white solid. The solid was separated, pulverized, and boiled 12 times with pure water to remove the solvent. Then, it was vacuum dried at 80 °C and –0.09 MPa for 6 h. The final particles contained 0.5 wt% solvent, and the tail gas VOC was as high as 2000 mg / m³. Powder extrusion granulation involves extruded molten polyetherimide through a die at the end of a screw extruder, followed by cooling and pelletizing to obtain polyetherimide plastic particles. The resulting cylindrical particles are 3 mm long and 2 mm in diameter, with IV = 0.50 dL / g, Mw = 68400, Mn = 34000, MFR = 8 g / 10 min (330 ℃, 5 kg), Tg = 216 ℃, Td5% = 515 ℃, and metal ions ≤ 3 ppm. The yield is 87.3%.

[0085] The continuous preparation method of polyetherimide of the present invention, through aqueous phase polymerization-spray drying-extrusion granulation process, is superior to the traditional solvent method in terms of environmental protection, particle size control, thermal properties and yield.

[0086] Screw extrusion granulation has the most significant effect on increasing molecular weight, see Example 2.

[0087] All embodiments outperform the comparative examples in key indicators such as IV, Tg, and Td, demonstrating that this process has significant technical advantages.

[0088] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for aqueous polymerization of polyimide, characterized in that: It includes the following four steps, and no organic solvents are used throughout the process: 1) The polycondensation reaction of material A and diamine is carried out by high-pressure polymerization in a deionized aqueous phase to generate an oligomer aqueous suspension slurry of polyamic acid; material A is dianhydride or tetracarboxylic acid; 2) After the reaction is complete, the above aqueous suspension slurry is passed through a spray drying device to obtain polyamic acid oligomer powder with a particle size of 1-200 micrometers and good flowability; 3) The above-mentioned polyamic acid oligomer powder is fed into a twin-screw extruder. Through screw shearing and step-by-step vacuum devouring, the oligomer chain growth and dehydration imidization are carried out simultaneously to form high molecular weight polyimide. 4) The imidized melt is extruded through a die to form polyimide plastic particles.

2. The method for aqueous polymerization of polyimide according to claim 1, characterized in that: The synthesis method of polyamic acid oligomer in step 1) is to add dianhydride and diamine to a high-pressure reactor after nitrogen purging, and simultaneously add a capping agent and deionized water for polymerization; the solute phase in step 1 contains dianhydride, diamine, capping agent, and the total mass ratio of the total mass of the solution, i.e., the solid content, is 5~70%.

3. The method for aqueous polymerization of polyimide according to claim 2, characterized in that: The dianhydride monomer is selected from 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA), bisphenol A diether dianhydride (BPADA), and bisphenol S diether dianhydride (DSDA); the diamine monomer is selected from 4,4'-diaminodiphenyl ether (4,4ODA), 4,4'-diaminodiphenyl sulfide, bisphenol A diether diamine (BAPP), or m-phenylenediamine (mDA); the end-capping agent is phthalic anhydride or aniline; the tetracarboxylic acid is 3,3',4,4'-biphenyltetracarboxylic acid, 3,3',4,4'-diphenyl ether tetracarboxylic acid, bisphenol A diether diphenyltetracarboxylic acid, or bisphenol S diether diphenyltetracarboxylic acid.

4. The method for aqueous polymerization of polyimide according to claim 3, characterized in that: In step 1, the molar ratio of dianhydride to diamine is (0.98–1.02):1; the amount of capping agent is (0.1–3) of the molar amount of diamine.

5. The method for aqueous polymerization of polyimide according to claim 1, characterized in that: The reaction was carried out in a high-pressure reactor after nitrogen purging at 120℃~180℃ for 2~5 hours, with a reaction pressure range of 0-1MPa and a stirring speed of 80-300 rpm.

6. The method for aqueous polymerization of polyimide according to claim 2, characterized in that: In step 2, the inlet temperature of the spray dryer is 150℃~220℃, and the outlet temperature is 80℃~120℃; centrifugal atomization is used, and the atomizer speed is 10,000-40,000 rpm; nitrogen is used as the carrier gas for spray drying, and the spray drying pressure is 0.12-0.5 MPa; the moisture content of the spray-dried powder is between 1% and 5%; the molecular weight of the oligomers of the spray-dried polyamic acid powder is measured, with a weight average molecular weight between 10,000 and 40,000 and a number average molecular weight between 5,000 and 20,000; the particle size D50 of the spray-dried powder is between 1 micrometer and 200 micrometers; and the loose packing density of the powder is ≥0.30 g / cm³.

7. The method for aqueous polymerization of polyimide according to claim 1, characterized in that: In step 3, the screw extruder is a co-rotating twin-screw structure with a screw length-to-diameter ratio (L / D) of 40–60. Three to four vacuum degassing ports are sequentially arranged along the screw axis. The first one to two vacuum ports have a range of 80–120 mbar, the next two stages 15–30 mbar, and the last stage 2–10 mbar, with an interstage pressure difference ≥ 5 times. The meshing block occupies 15–25% of the total pressure. The operating temperature range is 220℃–370℃, the vacuum level is 2–30 mbar, and the rotational speed is 30–300 rpm. The twin-screw temperature zones are 220℃~250℃→250℃~280℃→280℃~320℃→310℃~350℃→350℃~360℃, and the extrusion residence time is 2–10 minutes.

8. The method for aqueous polymerization of polyimide according to claim 1, characterized in that: The imidized melt is extruded through a die, cooled, and pelletized to form thermoplastic polyimide plastic particles.

9. A method for aqueous polymerization of polyimide according to any one of claims 2 to 7, characterized in that: The polyimide particles obtained in step 4 have an intrinsic viscosity of 0.5–1.2 dL / g, Tg ≥ 210℃, and thermal decomposition temperature > 520℃; the molecular weight distribution range is: weight average molecular weight between 60,000 and 150,000, and number average molecular weight between 30,000 and 60,000; the degree of imidization is measured by FT-IR with a peak area ratio of 1780 cm⁻¹ / 1500 cm⁻¹ ≥ 0.98; the melt index test at 350℃ and 5KG pressure shows a melt index range of 5-50 g / 10min; the metal ion content is ≤ 5 ppm, and the VOC emission is ≤ 20 mg / m³.

10. The method for aqueous polymerization of polyimide according to claim 1, characterized in that: This method involves no organic solvents throughout the entire process, has a water recycling rate of ≥95%, a comprehensive energy consumption per unit product of ≤8 kWh / kg, and a continuous operation time of ≥72h.

11. The method for aqueous polymerization of polyimide according to claim 2, characterized in that: In step 1, the solute phase contains dianhydride, diamine, and capping agent. The ratio of the total mass of these components to the total mass of the solution, i.e., the solid content, is 25-50%.

12. The method for aqueous polymerization of polyimide according to claim 2, characterized in that: In step 1, the solute phase contains dianhydride, diamine, and capping agent. The ratio of the total mass of these components to the total mass of the solution, i.e., the solid content, is 20-30%.

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