A method for preparing polyimide and its aqueous phase polymerization

Abstract

This invention discloses a method for preparing polyimide and its aqueous phase polymerization, belonging to the field of polymer materials technology. The method uses deionized water as a medium, to which additives A, B, and C are added sequentially and stirred until homogeneous, resulting in an aqueous additive compound solution. Additive A is one or two of diethylene glycol dimethyl ether and betaine; additive B is one or two of 1-methylimidazole and urea; and additive C is one or two of pyridine and dimethyl sulfoxide. An aromatic diamine monomer and an aromatic dianhydride monomer are added to the aqueous additive compound solution, and the mixture is stirred for prepolymerization to obtain an aqueous polyamic acid solution. Then, gradient-temperature thermal imidization is performed to obtain polyimide. Through a synergistic strategy of water-soluble co-solvent solubilization, low-temperature aqueous phase polymerization, and stepwise thermal imidization, high-performance polyimide is prepared by aqueous phase polymerization. This preparation process balances environmental friendliness, economy, and material performance.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a polyimide and its aqueous phase polymerization preparation method. Background Technology

[0002] Polyimide (PI) is an ultra-high-performance polymer with an imide ring in its main chain. It possesses comprehensive properties such as ultra-high heat resistance, excellent mechanical properties, chemical corrosion resistance, and low dielectric loss, and is widely used in high-end fields such as aerospace, microelectronics, 5G communications, flexible displays, and new energy. Traditional polyimide synthesis heavily relies on high-boiling-point, highly polar organic solvents such as NMP, DMF, DMAC, and DMSO, which presents the following prominent problems: high toxicity of organic solvents, high VOC emissions, and enormous environmental pressure; complex solvent recovery and high energy consumption, resulting in high production costs; difficulty in completely removing solvents, leading to high residual stress, easy yellowing, and decreased electrical properties in polyimide products; and high flammability and explosiveness risks, posing significant safety challenges for large-scale production.

[0003] In recent years, aqueous synthesis of polyimides has become an important direction for green manufacturing. However, aqueous systems have bottlenecks such as poor monomer solubility, slow polymerization rate, low molecular weight, and incomplete imidization, making it difficult to obtain products with satisfactory overall performance. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the present invention aims to provide a method for preparing polyimide and its aqueous phase polymerization. Through a synergistic strategy of solubilization with water-soluble co-solvents, low-temperature aqueous phase polymerization, and stepwise thermal imidization, high-performance polyimide is prepared by aqueous phase polymerization. This preparation process takes into account environmental friendliness, economy, and material performance.

[0005] To achieve the above objectives, the present invention employs the following technical solution: One method for preparing polyimide by aqueous phase polymerization includes the following steps: S1, using deionized water as a medium, add auxiliary agent A, auxiliary agent B, and auxiliary agent C sequentially and stir until homogeneous to obtain an aqueous auxiliary agent compound solution; the ratio of deionized water, auxiliary agent A, auxiliary agent B, and auxiliary agent C is 100 mL:(0.1~4.0) g:(0.1~3.0) g:(0.1~20) mL; auxiliary agent A is one or two of diethylene glycol dimethyl ether and betaine; auxiliary agent B is one or two of 1-methylimidazole and urea; and auxiliary agent C is one or two of pyridine and dimethyl sulfoxide. S2, add aromatic diamine monomer and aromatic dianhydride monomer to the aqueous phase auxiliary agent compound solution, stir and prepolymerize to obtain polyamic acid aqueous solution; S3, the polyamic acid aqueous solution is subjected to gradient heating thermal imidization, dehydration and ring closure, followed by cooling, filtration, water washing and drying to obtain polyimide powder; Alternatively, an aqueous solution of polyamic acid can be coated onto a substrate, followed by gradient heating and thermal imidization to obtain a polyimide film. Alternatively, polyamic acid aqueous solution can be spun into polyamic acid nascent fibers, which are then subjected to gradient heating thermal imidization for dehydration and ring closure to generate polyimide fibers with rigid aromatic ring structures.

[0006] In one embodiment, the amount of diethylene glycol dimethyl ether in the adjuvant A is 0.1–2.0 g, and the amount of betaine is 0.1–2.0 g; The amount of 1-methylimidazole in adjuvant B is 0.1–2.0 g, and the amount of urea is 0.1–1.0 g; The amount of pyridine in the adjuvant C is 1-10 mL, and the amount of dimethyl sulfoxide is 0.1-10 mL.

[0007] In one embodiment, the prepolymerization temperature is 0–60°C, the stirring time is 6–12 h, and the stirring speed is 200–800 rpm.

[0008] In one embodiment, the molar ratio of the aromatic diamine monomer to the aromatic dianhydride monomer is (0.95–1.05):1; The mass ratio of the sum of the aromatic diamine monomer and the aromatic dianhydride monomer to the sum of auxiliaries A, B and C is 1:(0.2 to 1.5).

[0009] In one embodiment, the aromatic diamine monomer is one or more of p-phenylenediamine, m-phenylenediamine, 2,2-bis(trifluoromethyl)-4,4-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, and 2-(4-aminophenyl)-5-aminobenzimidazole.

[0010] In one embodiment, the aromatic dianhydride monomer is one or more of pyromellitic dianhydride, hexafluorodianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxobisphthalic anhydride, and benzophenone tetracarboxylic dianhydride.

[0011] In one embodiment, the ratio of the total mass of the aromatic diamine monomer and the aromatic dianhydride monomer to the amount of deionized water is 5.0 g to 20.0 g: 100 mL, and the ratio of the total mass of the aromatic diamine monomer and the aromatic dianhydride monomer to the mass of deionized water is approximately 1:19 to 1:5.70.

[0012] In one embodiment, the solid content of the polyamic acid aqueous solution is 5% to 15%.

[0013] In one embodiment, the gradient heating is performed in the following stages: The first stage involves holding the temperature at 80℃ for 1-2 hours, the second stage involves holding the temperature at 150℃ for 1-2 hours, and the third stage involves holding the temperature at 200-250℃ for 1-3 hours.

[0014] The present invention also provides a polyimide prepared by the aqueous phase polymerization method of the aforementioned polyimide.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a novel, green, efficient, stable, and scalable method for preparing polyimide through aqueous phase polymerization, achieving solvent-free, low-cost, and high-performance industrial production. Compared with existing organic phase synthesis technologies, this method is environmentally friendly, low-cost, safe, suitable for large-scale production, and produces products with excellent performance and broad applicability. This invention uses water as the sole primary reaction medium, completely replacing toxic organic solvents such as N-methylpyrrolidone (NMP) and N,N-dimethylformamide (DMF), eliminating volatile organic compound (VOC) emissions at the source and achieving a near-zero VOC emission green chemical synthesis process. Water is inexpensive and readily available as the reaction medium, and the process eliminates the need for additional steps such as organic solvent recovery, explosion-proof measures, and environmental post-treatment, significantly reducing equipment investment and operating costs. The entire polymerization process is carried out at room temperature and pressure, eliminating the risk of flammability and explosion, requiring minimal equipment, and is easy to operate, facilitating industrial scale-up and continuous production. The resulting polyimide product has no organic solvent residue and high purity. This method is applicable to combinations of various aromatic diamines and aromatic dianhydride monomers, and can prepare polyimide products in various forms such as films, coatings, powders, and fibers. It uses low amounts of organic solvents and does not require consideration of the solubility limitations of polyamic acid in organic solvents. At the same time, the all-aqueous process is green and environmentally friendly, low in cost, requires low equipment, and is simple to operate.

[0016] The technical mechanism behind these superior effects lies in the synergistic effect of "solubilization and activation" in this invention: The solubilization and dispersing effect is manifested in the diethylene glycol dimethyl ether in additive A, which is a polar ether-based co-solvent, and betaine, an amphoteric surfactant. The combination of these two can form a micelle structure in water, effectively encapsulating the hydrophobic aromatic dianhydride and diamine monomers, significantly increasing the solubility of the monomers in pure water. Dimethyl sulfoxide (DMSO) in additive C, as a strongly polar small molecule, can insert into the intermolecule gaps of monomers, weakening intermolecular hydrophobic aggregation, further inhibiting monomer precipitation, and achieving complete homogeneous dispersion of the monomers, providing a uniform reaction environment for the polymerization reaction. The total addition amount of the three additives is controlled at 1%–20% of the water mass, balancing solubilization effect and system viscosity, avoiding excessive additive use that would increase costs. The activation and catalytic effect is manifested in the 1-methylimidazole in additive B, which contains tertiary amine nitrogen atoms, and urea, which contains amide active sites. The combination of these two forms a composite organic base catalytic system. The catalytic mechanism lies in the following: the lone pair electrons of the nitrogen atom attack the carbonyl group of the aromatic dianhydride, lowering the carbonyl reaction energy barrier and effectively activating the anhydride group; simultaneously, it forms hydrogen bonds with the amino group of the aromatic diamine, enhancing the nucleophilic attack ability of the amino group, thereby significantly accelerating the acylation polycondensation reaction rate, increasing the molecular weight of polyamic acid, and facilitating the acquisition of high molecular weight polyamic acid. Furthermore, urea can stabilize the polymerization intermediate and inhibit the aggregation and precipitation of polyamic acid molecular chains. This synergistic closed-loop effect is reflected in the solubilization system ensuring uniform dispersion of monomer molecules in the aqueous phase, and the activation catalytic system simultaneously increasing the acylation reaction rate. The synergistic effect of these two systems effectively avoids the problem of instantaneous product precipitation caused by excessively high local monomer concentrations. DMSO also acts as a polar buffer medium, balancing the polarity of the micelles and stabilizing the intermediate polyamic acid, ensuring that the entire prepolymerization process is free of significant stratification or precipitation. Subsequent heating is sufficient for successful dehydration and imidization, truly achieving direct preparation of polyimide through all-aqueous phase polymerization.

[0017] Therefore, this invention is widely applicable to the manufacture of various types of polyimide fibers, films and other products, and can be used to expand the application of polyimide films in flexible electronics, microelectronic packaging, insulating materials, high-temperature coatings, display devices and other fields. Attached Figure Description

[0018] Appendix Figure 1 Graph of polyamic acid aqueous solution prepared by aqueous phase polymerization; Appendix Figure 2 Infrared spectrum of polyamic acid prepared by aqueous phase polymerization; Appendix Figure 3 Infrared spectrum of polyimide prepared by aqueous phase polymerization. Detailed Implementation

[0019] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0020] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0021] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0022] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0023] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0024] This invention provides a method for preparing polyimide through aqueous phase synthesis, comprising the following steps: (1) Preparation of aqueous phase additive compound solution: (1-1) Using deionized water as the main reaction medium, a compound functional additive system is prepared, with the total mass of all additives accounting for 1% to 20% of the mass of deionized water; the ratio of the amount of deionized water, additive A, additive B and additive C is 100 mL:(0.1~4.0) g:(0.1~3.0) g:(0.1~20) mL; additive A is one or two of diethylene glycol dimethyl ether and betaine; additive B is one or two of 1-methylimidazole and urea; and additive C is one or two of pyridine and dimethyl sulfoxide. The dosage of each monomer and auxiliary agent is explained below using 100 mL of deionized water as an example.

[0025] (1-2) The components of the auxiliary agent system are as follows: Additive A: Diethylene glycol dimethyl ether (ECM) and betaine, with the following addition mass ranges: 0.1–2.0 g for diethylene glycol dimethyl ether and 0.1–2.0 g for betaine. The two can be used alone or in combination. Additives B: 1-methylimidazole and urea, with the following addition ranges: 1-methylimidazole 0.1–2.0 g and urea 0.1–1.0 g. They can be used alone or in combination. Additive C: pyridine and dimethyl sulfoxide (DMSO), with the following addition ranges: pyridine 1-10 mL; DMSO 0.1-10 mL. The two can be used alone or in combination. (1-3) Place deionized water in a flask equipped with a stirrer, add 0.1-4.0 g of additive A in sequence under stirring at room temperature, and stir for 5-10 min until completely dissolved; then add 0.1-3.0 g of additive B, and continue stirring for 5-10 min; finally add 1.1-20 mL of additive C, and continue stirring for 5-10 min to obtain a homogeneous aqueous phase additive compound solution. (2) Preparation of aqueous polyamic acid solution: Add aromatic diamine and aromatic dianhydride monomer to the aqueous phase additive compound solution obtained in step (1), stir at room temperature for 6-8 h for prepolymerization, and generate polyamic acid aqueous solution; (3) Thermal imidization to form polyimide The aqueous polyamic acid solution is heated by gradient heating to dehydrate and close the ring, thus completing the imidization reaction. After the reaction, the solution is cooled, filtered, washed with water, and dried to obtain polyimide powder. Alternatively, the polyamic acid solution can be directly coated onto a glass plate and heated by gradient heating to obtain a polyimide film.

[0026] There are three types of post-processing solutions: Scheme A (polyimide powder): After the reaction is completed and cooled to room temperature, the solid is collected by filtration, washed repeatedly with deionized water to remove residual additives, and dried under vacuum at 80-120℃ to obtain high-purity polyimide powder; Scheme B (polyimide film): The aqueous polyamic acid solution is washed multiple times, filtered to remove the additives, coated into a wet film, and then subjected to thermal imidization with gradient heating to close the ring and dehydrate. The polyimide film is then peeled off.

[0027] Option C (polyimide fiber): The mainstream method is a two-step process. First, polyamic acid aqueous solution is spun into polyamic acid nascent fiber, and then cyclized imidized, dehydrated and closed the ring to finally generate polyimide fiber with a rigid aromatic ring structure.

[0028] In one embodiment, the mass ratio of the sum of the aromatic diamine monomer and the aromatic dianhydride monomer to the auxiliary agent is 1:(0.2-1.5). The molar ratio of diamine to dianhydride is controlled at (0.95-1.05):1, and the total mass of diamine and dianhydride is 5.0 g to 20.0 g.

[0029] In one embodiment, a mixed diamine monomer and a dianhydride monomer are mixed according to a reaction ratio, wherein the ratio of the total mass of the aromatic diamine monomer and the aromatic dianhydride monomer to the amount of deionized water is 5.0 g to 20.0 g: 100 mL. Further, the ratio of the total mass of the aromatic diamine monomer and the aromatic dianhydride monomer to the mass of deionized water is approximately 1:19 to 1:5.70. An aqueous solution of polyamic acid with a solid content of 5% to 15% is obtained.

[0030] In one embodiment, the diamine monomer may be one or a mixture of several commercially available 4,4'-diaminodiphenyl ether, 2,2-bis(trifluoromethyl)-4,4-diaminobiphenyl, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, and 2-(4-aminophenyl)-5-aminobenzimidazole in any proportion.

[0031] In one embodiment, the dianhydride monomer may be one or a mixture of several of the following in any proportion: commercially available pyromellitic dianhydride, hexafluorodianhydride, biphenyl dianhydride, 4,4'-oxobisphthalic anhydride, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0032] In one embodiment, the solution is environmentally friendly deionized water.

[0033] In one embodiment, the aqueous polymerization conditions are: polymerization temperature of 0–60°C; stirring time of 6–12 h; and stirring speed of 200–800 rpm.

[0034] In one embodiment, the thermal imidization treatment temperature is as follows: first stage: 80°C, holding for 1-2 hours; second stage: 150°C, holding for 1-2 hours; third stage: 200-250°C, holding for 1-3 hours.

[0035] In summary, the core of this invention relies on a synergistic "solventization + activation" mechanism to achieve efficient polymerization of polyimide in an aqueous system. Traditional polyimide polymerization depends on high-boiling-point toxic organic solvents, making it impossible to use pure water as the primary reaction medium. This results in drawbacks such as high solvent recovery costs, significant environmental burden, uneven polymerization, and poor molecular weight controllability. This invention uses deionized water as the reaction medium and employs water-soluble additives to assist in the dissolution of diamine and dianhydride monomers. Under mild conditions, it achieves aqueous synthesis of polyamic acid, followed by a step-by-step thermal imidization to obtain high-performance polyimide, eliminating the need for large quantities of highly toxic organic solvents. This invention features simple equipment, continuous production, green and low-toxic solvents, and high monomer conversion rates, enabling large-scale continuous production of polyimide materials.

[0036] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0037] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0038] Comparative Example 1 Preparation of traditional organic phase polyimides: First, 6.39 g of 4,4'-diaminodiphenyl ether (ODA) was added to 100 mL of N,N-dimethylformamide (DMF) and stirred at room temperature until a homogeneous solution was formed. Then, 10.28 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) was added and stirring was continued for 12 h to obtain a viscous liquid, i.e., a polyamic acid solution. Subsequently, imidization was performed at 120℃ / 150℃ / 200℃ for 2 h each to obtain a conventional polyimide.

[0039] Example 1 A method for preparing polyimide through aqueous phase synthesis: (1) Preparation of aqueous phase additive compound solution: Take 100 mL of deionized water, the total mass of all additives accounts for about 1.5% of the mass of deionized water; Additive A: 0.1 g diethylene glycol dimethyl ether, 0.1 g betaine; Additive B: 0.1 g 1-methylimidazole, 0.1 g urea; Additive C: 1 mL pyridine, 0.1 mL DMSO. Stir at room temperature for 30 min to obtain a homogeneous compound solution.

[0040] (2) Polymerization of aqueous polyamic acid: At room temperature, 3.50 g of p-phenylenediamine (p-PDA) and 3.95 g of pyromellitic dianhydride (PMDA) were added to the compound solution, controlling the molar ratio of diamine to dianhydride to be 1.01:1, and the total mass of diamine and dianhydride was 7.45 g. After the addition was completed, the mixture was stirred for 40 min to obtain a homogeneous monomer aqueous phase. Subsequently, the mixture was stirred at a constant temperature for 6 h, and an acylation reaction occurred under the synergistic effect of the additives to generate a stable homogeneous aqueous polyamic acid solution.

[0041] (3) Thermal imidization: The aqueous polyamic acid solution was thermally imidized according to the following gradient heating program: the first stage was held at 80℃ for 1 hour, the second stage was held at 150℃ for 1 hour, and the third stage was held at 200℃ for 2 hours. The water in the system was gradually removed, and the polyamic acid molecular chain underwent dehydration and ring closure to form polyimide. After cooling, the solution was filtered, washed 5 times with deionized water, and dried under vacuum at 100℃ to obtain polyimide powder.

[0042] Example 2 A method for preparing polyimide through aqueous phase synthesis: (1) Preparation of aqueous phase additive compound solution: Take 100 mL of deionized water, the total mass of all additives accounts for about 19.3% of the mass of deionized water; Additive A: 2.0 g diethylene glycol dimethyl ether, 2.0 g betaine; Additive B: 2.0 g 1-methylimidazole, 1.0 g urea; Additive C: 8 mL pyridine, 4 mL DMSO. Stir at room temperature for 30 min to obtain a homogeneous compound solution.

[0043] (2) Polymerization of aqueous polyamic acid: At room temperature, 7.08 g of 4,4'-diaminodiphenyl ether (ODA) and 10.45 g of 4,4'-oxophthalic anhydride (ODPA) were added to the compound solution, controlling the molar ratio of diamine to dianhydride to be 1.05:1, and the total mass of diamine and dianhydride to be 17.53 g. After the addition was completed, the mixture was stirred for 60 min to obtain a homogeneous monomer aqueous phase. Subsequently, the mixture was stirred at a constant temperature for 12 h, and an acylation reaction occurred under the synergistic effect of the additives to generate a stable homogeneous aqueous polyamic acid solution.

[0044] (3) Thermal imidization: An aqueous solution of polyamic acid is coated onto a clean glass plate, and thermal imidization is carried out according to the following gradient heating program: the first stage is held at 80°C for 2 hours, the second stage is held at 150°C for 2 hours, and the third stage is held at 250°C for 3 hours. The water in the system is gradually removed, and the polyamic acid molecular chain undergoes dehydration and ring closure to form a polyimide film. After cooling, the film is peeled off from the glass plate to obtain the polyimide film.

[0045] Example 3 A method for preparing polyimide through aqueous phase synthesis: (1) Preparation of aqueous phase additive compound solution: Take 100 mL of deionized water, the total mass of all additives accounts for about 17.7% of the mass of deionized water; Additive A: 1.0 g diethylene glycol dimethyl ether, 1.0 g betaine; Additive B: 1.0 g 1-methylimidazole, 0.5 g urea; Additive C: 10 mL pyridine, 4.0 mL DMSO. Stir at room temperature for 30 min to obtain a homogeneous compound solution.

[0046] (2) Polymerization of aqueous polyamic acid: At room temperature, 8.00 g of 2,2-bis(trifluoromethyl)-4,4-diaminobiphenyl (6FODA) and 7.00 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) were added to the compound solution, controlling the molar ratio of diamine to dianhydride to be 1.05:1, and the total mass of diamine and dianhydride was 15.00 g. After the addition was completed, the mixture was stirred for 50 min to obtain a homogeneous monomer aqueous phase. Subsequently, the temperature was raised to 40℃ and stirred for 10 h. Under the synergistic effect of the additives, an acylation reaction occurred to generate a stable homogeneous aqueous polyamic acid solution.

[0047] (3) Thermal imidization: The polyamic acid aqueous solution is spun into polyamic acid nascent fibers using a wet spinning process; the nascent fibers are then subjected to cyclization imidization, dehydration and ring closure according to the following gradient heating program: the first stage is held at 80℃ for 1.5 hours, the second stage is held at 150℃ for 1.5 hours, and the third stage is held at 220℃ for 2 hours, finally generating polyimide fibers with a rigid aromatic ring structure.

[0048] Example 4 A method for preparing polyimide through aqueous phase synthesis: (1) Preparation of aqueous phase additive compound solution: Take 100 ml of deionized water, the total mass of all additives accounts for 12.5% ​​of the mass of deionized water; Additive A: 1.0 g diethylene glycol dimethyl ether, 0.6 g betaine; Additive B: 0.3 g 1-methylimidazole, 0.8 g urea; Additive C: 10 mL pyridine. Stir for 30 min to obtain a homogeneous compound solution.

[0049] (2) Polymerization of aqueous polyamic acid: At room temperature, 6.19 g of 4,4-diaminodiphenyl ether (ODA) was added to the compound solution and stirred for 30 min until completely dissolved; 10.48 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) was slowly added, controlling the molar ratio of diamine to dianhydride at 0.95:1. After the addition was completed, the mixture was stirred for 40 min to obtain a homogeneous monomer aqueous phase without precipitation. Subsequently, the temperature was raised to 40℃ and stirred for 6 h. Under the synergistic effect of the additives, an acylation reaction occurred to generate a stable homogeneous aqueous polyamic acid solution.

[0050] (3) Thermal imidization: The aqueous polyamic acid solution was thermally imidized according to the following gradient heating program: the first stage was held at 80℃ for 1 hour, the second stage was held at 150℃ for 2 hours, and the third stage was held at 230℃ for 2 hours. Water was gradually removed from the system, and the polyamic acid molecular chain underwent dehydration and ring closure to form polyimide. After cooling, the solution was filtered, washed three times with deionized water, and dried under vacuum at 100℃ to obtain a light yellow polyimide powder.

[0051] Example 5 A method for preparing polyimide through aqueous phase synthesis: (1) Preparation of aqueous phase additive compound solution: Take 100 ml of deionized water, the total mass of the additive accounts for 17.2% of the water mass; add 10 mL of pyridine and 10 mL of DMSO only for additive C. Stir at 400 rpm and mix at room temperature to obtain the additive aqueous solution.

[0052] (2) Polymerization of aqueous polyamic acid: 6.34 g of ODA was added at room temperature and dissolved completely, followed by 9.36 g of 4,4'-oxophthalic anhydride (ODPA). The molar ratio of diamine to dianhydride was controlled at 1:1, and the mixture was stirred for 30 min to obtain a homogeneous monomer mixture. Subsequently, the temperature was raised to 60℃ and stirred for 6 h to prepare an aqueous polyamic acid solution. The system showed no stratification and no solid precipitation.

[0053] (3) Imidification treatment: The aqueous polyamic acid solution was thermally imidized according to the following gradient heating program: the first stage was held at 80℃ for 2 hours, the second stage was held at 150℃ for 1 hour, and the third stage was held at 200℃ for 3 hours. The water in the system was gradually removed, and the polyamic acid molecular chain underwent dehydration and ring closure to form polyimide. After cooling, the solution was filtered, washed three times with deionized water, and dried under vacuum at 100℃ to obtain a light yellow polyimide powder.

[0054] Example 6 A method for preparing polyimide through aqueous phase synthesis: (1) Preparation of aqueous phase additive compound solution: Take 100 ml of deionized water, the total mass of the additives accounts for 14.10% of the water mass; only 1.5 g of diethylene glycol dimethyl ether is added to additive A; additive B is a two-component compound of 0.6 g of 1-methylimidazole and 1.0 g of urea; add 10.0 mL of DMSO to additive C, stir and dissolve at room temperature for later use.

[0055] (2) Polymerization of aqueous polyamic acid: 10.59 g of 2,2-bis(trifluoromethyl)-4,4-diaminobiphenyl (6FODA) was added at room temperature, and the molar ratio of diamine to dianhydride was controlled at 1:1. The mixture was stirred for 30 min to dissolve, and 6.91 g of pyromellitic dianhydride (PMDA) was added in batches. The mixture was stirred continuously for 30 min to form a stable monomer aqueous phase. Polycondensation was then completed by stirring at a constant temperature for 6 h to obtain a semi-transparent aqueous polyamic acid solution.

[0056] (3) Imidification treatment: The aqueous polyamic acid solution was thermally imidized according to the following gradient heating program: the first stage was held at 80℃ for 1.5 hours, the second stage was held at 150℃ for 1.5 hours, and the third stage was held at 240℃ for 1.5 hours. Water was gradually removed from the system, and the polyamic acid molecular chain underwent dehydration and ring closure to form polyimide. After cooling, the solution was filtered, washed three times with deionized water, and dried under vacuum at 100℃ to obtain a light yellow polyimide powder.

[0057] Example 7 Preparation of a polyimide synthesized in aqueous phase: (1) Aqueous phase additive compounding: 100 ml deionized water, total additives account for 15.7%; Additive A is only 1.0 g betaine; Additive B: 1.2 g 1-methylimidazole and 0.4 g urea compounded together; Additive C: 10 mL pyridine and 3.0 mL DMSO.

[0058] (2) Polymerization of aqueous polyamic acid: 3.24 g of p-phenylenediamine (p-PDA) was added and stirred for 10 min at room temperature, followed by 8.82 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), with the molar ratio of diamine to dianhydride controlled at 1:1. Polycondensation was then carried out by heating to 60℃ and stirring for 6 h. The system was homogeneous and did not precipitate throughout the process.

[0059] (3) Imidification treatment: The aqueous polyamic acid solution was thermally imidized according to the following gradient heating program: the first stage was held at 80℃ for 2 hours, the second stage was held at 150℃ for 2 hours, and the third stage was held at 250℃ for 1 hour. The water in the system was gradually removed, and the polyamic acid molecular chain underwent dehydration and ring closure to form polyimide. After cooling, the solution was filtered, washed three times with deionized water, and dried under vacuum at 100℃ to obtain a light yellow polyimide powder.

[0060] Example 8 Preparation of a polyimide synthesized in aqueous phase: (1) Preparation of aqueous phase additive compound solution: Take 100 ml of deionized water, the total mass of all additives accounts for 10.5% of the mass of deionized water; Additive A: 1.0 g diethylene glycol dimethyl ether, 0.7 g betaine; Additive B: 0.15 g 1-methylimidazole, 0.4 g urea; Additive C: 5 mL pyridine, 3.0 mL DMSO. Add the additives sequentially at room temperature and stir for 30 min to obtain a homogeneous compound solution.

[0061] (2) Polymerization of aqueous polyamic acid: 7.56 g of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) was added to the compound solution at room temperature and stirred for 30 min; 9.94 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) was slowly added, and the molar ratio of diamine to dianhydride was controlled at 1:1. After the addition was completed, the mixture was stirred for 45 min, and then heated to 60℃ and stirred for 6 h. Under the synergistic effect of the additives, an acylation reaction occurred to generate a stable homogeneous aqueous polyamic acid solution.

[0062] (3) Imidification treatment: The aqueous polyamic acid solution was thermally imidized according to the following gradient heating program: the first stage was held at 80℃ for 1 hour, the second stage was held at 150℃ for 1.5 hours, and the third stage was held at 210℃ for 3 hours. The water in the system was gradually removed, and the polyamic acid molecular chain underwent dehydration and ring closure to form polyimide. After cooling, the solution was filtered, washed three times with deionized water, and dried under vacuum at 100℃ to obtain polyimide powder.

[0063] Example 9 A method for preparing polyimide through aqueous phase synthesis: (1) Preparation of aqueous phase additive compound solution: Take 100 mL of deionized water, the total mass of all additives accounts for about 1.38% of the mass of deionized water; Additive A: 0.1 g diethylene glycol dimethyl ether, 0.1 g betaine; Additive B: 0.1 g 1-methylimidazole, 0.1 g urea; Additive C: 1 mL pyridine. Stir at room temperature for 30 min to obtain a homogeneous compound solution.

[0064] (2) Polymerization of aqueous polyamic acid: At room temperature, 3.00 g of 4,4'-diaminodiphenyl ether (ODA) and 4.00 g of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) were added to the compound solution, controlling the molar ratio of diamine to dianhydride to be 1.02:1, and the total mass of diamine and dianhydride was 7.00 g. After the addition was completed, the mixture was stirred for 40 min to obtain a homogeneous monomer aqueous phase. Subsequently, the mixture was stirred at a constant temperature for 8 h, and an acylation reaction occurred under the synergistic effect of the additives to generate a stable homogeneous aqueous polyamic acid solution.

[0065] (3) Thermal imidization: The polyamic acid aqueous solution is spun into polyamic acid nascent fibers using a wet spinning process; the nascent fibers are then subjected to cyclization imidization, dehydration and ring closure according to the following gradient heating program: the first stage is held at 80℃ for 1 hour, the second stage is held at 150℃ for 2 hours, and the third stage is held at 230℃ for 2 hours, finally generating polyimide fibers with a rigid aromatic ring structure.

[0066] Example 10 A method for preparing polyimide through aqueous phase synthesis: (1) Preparation of aqueous phase additive compound solution: Take 100 mL of deionized water, the total mass of all additives accounts for about 10.2% of the mass of deionized water; Additive A: 0.1 g diethylene glycol dimethyl ether, 0.1 g betaine; Additive B: 0.1 g 1-methylimidazole, 0.1 g urea; Additive C: 10 mL DMSO. Stir at room temperature for 30 min to obtain a homogeneous compound solution.

[0067] (2) Polymerization of aqueous polyamic acid: At room temperature, 4.50 g of 2,2-bis(trifluoromethyl)-4,4-diaminobiphenyl (6FODA) and 5.50 g of hexafluorodianhydride (6FDA) were added to the compound solution, controlling the molar ratio of diamine to dianhydride to be 0.98:1, and the total mass of diamine and dianhydride was 10.00 g. After the addition was completed, the mixture was stirred for 50 min to obtain a homogeneous monomer aqueous phase. Subsequently, the temperature was raised to 40℃ and stirred for 10 h. Under the synergistic effect of the additives, an acylation reaction occurred to generate a stable homogeneous aqueous polyamic acid solution.

[0068] (3) Thermal imidization: An aqueous solution of polyamic acid was coated onto a clean glass plate, and thermal imidization was carried out according to the following gradient heating program: the first stage was held at 80°C for 1.5 hours, the second stage was held at 150°C for 1.5 hours, and the third stage was held at 200°C for 2.5 hours. The water in the system gradually disappeared, and the polyamic acid molecular chain underwent dehydration and ring closure to form a polyimide film. After cooling, the film was peeled off from the glass plate to obtain the polyimide film.

[0069] Example 11 A method for preparing polyimide through aqueous phase synthesis: (1) Preparation of aqueous phase additive compound solution: Take 100 mL of deionized water, the total mass of all additives accounts for about 19.55% of the mass of deionized water; Additive A: 2.0 g diethylene glycol dimethyl ether, 2.0 g betaine; Additive B: 2.0 g 1-methylimidazole, 1.0 g urea; Additive C: 10 mL pyridine, 2.5 mL DMSO. Stir at room temperature for 30 min to obtain a homogeneous compound solution.

[0070] (2) Polymerization of aqueous polyamic acid: At room temperature, 6.50 g of 4,4'-diaminodiphenyl ether (ODA) and 6.50 g of 4,4'-oxophthalic anhydride (ODPA) were added to the compound solution, controlling the molar ratio of diamine to dianhydride to be 1:1, and the total mass of diamine and dianhydride was 13.00 g. After the addition was completed, the mixture was stirred for 60 min, and then heated to 40 °C and stirred at a constant temperature for 12 h to generate a stable homogeneous aqueous polyamic acid solution.

[0071] (3) Thermal imidization: The polyamic acid aqueous solution is coated on a clean glass plate, and the temperature is increased in a gradient manner according to the first stage of 80℃ / 2h, the second stage of 150℃ / 2h, and the third stage of 250℃ / 3h. After cooling, the plate is peeled off to obtain a polyimide film.

[0072] Depend on Figure 1 It can be seen that the polyamic acid aqueous solution prepared by aqueous phase polymerization is in a uniform and transparent dispersion state, with no visible precipitation or layering, indicating that the additive compound system effectively achieves complete dissolution and stable dispersion of monomers.

[0073] Depend on Figure 2 It can be seen that in the infrared spectrum of polyamic acid, at approximately 1650 cm⁻¹... -1 An amide I band appears at approximately 1550 cm⁻¹ (C=O stretching vibration). -1 An amide II band (NH bending vibration and CN stretching vibration) appears at approximately 1720 cm. -1 The presence of a C=O absorption peak in the carboxylic acid structure confirms the formation of the polyamic acid structure.

[0074] Depend on Figure 3 It can be seen that in the infrared spectrum of polyimide, at approximately 1780 cm⁻¹... -1 and 1720 cm -1 Symmetric and asymmetric stretching vibration peaks of the C=O ring on the imide ring appear at approximately 1380 cm⁻¹. -1 A CN stretching vibration peak appears at approximately 725 cm⁻¹. -1 The appearance of the bending vibration peak of the imide ring, while the characteristic absorption peaks of amide and carboxylic acid have basically disappeared, indicates that after gradient heating and thermal imidization, polyamic acid has been completely dehydrated and closed into a polyimide structure.

[0075] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A method for preparing polyimide by aqueous phase polymerization, characterized in that, Includes the following steps: S1, using deionized water as a medium, add auxiliary agent A, auxiliary agent B, and auxiliary agent C sequentially and stir until homogeneous to obtain an aqueous auxiliary agent compound solution; the ratio of deionized water, auxiliary agent A, auxiliary agent B, and auxiliary agent C is 100 mL:(0.1~4.0) g:(0.1~3.0) g:(0.1~20) mL; auxiliary agent A is one or two of diethylene glycol dimethyl ether and betaine; auxiliary agent B is one or two of 1-methylimidazole and urea; and auxiliary agent C is one or two of pyridine and dimethyl sulfoxide. S2, add aromatic diamine monomer and aromatic dianhydride monomer to the aqueous phase auxiliary agent compound solution, stir and prepolymerize to obtain polyamic acid aqueous solution; S3, the polyamic acid aqueous solution is subjected to gradient heating thermal imidization, dehydration and ring closure, followed by cooling, filtration, water washing and drying to obtain polyimide powder; Alternatively, an aqueous solution of polyamic acid can be coated onto a substrate, followed by gradient heating and thermal imidization to obtain a polyimide film. Alternatively, polyamic acid aqueous solution can be spun into polyamic acid nascent fibers, which are then subjected to gradient heating thermal imidization for dehydration and ring closure to generate polyimide fibers with a rigid aromatic ring structure.

2. The method for preparing polyimide by aqueous phase polymerization according to claim 1, characterized in that, The amount of diethylene glycol dimethyl ether in the adjuvant A is 0.1–2.0 g, and the amount of betaine is 0.1–2.0 g; The amount of 1-methylimidazole in adjuvant B is 0.1–2.0 g, and the amount of urea is 0.1–1.0 g; The amount of pyridine in the adjuvant C is 1-10 mL, and the amount of dimethyl sulfoxide is 0.1-10 mL.

3. The method for preparing polyimide by aqueous phase polymerization according to claim 1, characterized in that, The prepolymerization temperature is 0–60°C, the stirring time is 6–12 h, and the stirring speed is 200–800 rpm.

4. The method for preparing polyimide by aqueous phase polymerization according to claim 1, characterized in that, The molar ratio of the aromatic diamine monomer to the aromatic dianhydride monomer is (0.95–1.05):1; The mass ratio of the sum of the aromatic diamine monomer and the aromatic dianhydride monomer to the sum of auxiliaries A, B and C is 1:(0.2 to 1.5).

5. The method for preparing polyimide by aqueous phase polymerization according to claim 1, characterized in that, The aromatic diamine monomer is one or more of p-phenylenediamine, m-phenylenediamine, 2,2-bis(trifluoromethyl)-4,4-diaminobiphenyl, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, and 2-(4-aminophenyl)-5-aminobenzimidazole.

6. The method for preparing polyimide by aqueous phase polymerization according to claim 1, characterized in that, The aromatic dianhydride monomer is one or more of the following: pyromellitic dianhydride, hexafluorodianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-oxobisphthalic anhydride, and benzophenone tetracarboxylic dianhydride.

7. The method for preparing polyimide by aqueous phase polymerization according to claim 1, characterized in that, The ratio of the total mass of the aromatic diamine monomer and the aromatic dianhydride monomer to the amount of deionized water is 5.0 g to 20.0 g: 100 mL.

8. The method for preparing polyimide by aqueous phase polymerization according to claim 1, characterized in that, The solid content of the polyamic acid aqueous solution is 5% to 15%.

9. The method for preparing polyimide by aqueous phase polymerization according to claim 1, characterized in that, The gradient heating is carried out in the following stages: The first stage involves holding the temperature at 80℃ for 1-2 hours, the second stage involves holding the temperature at 150℃ for 1-2 hours, and the third stage involves holding the temperature at 200-250℃ for 1-3 hours.

10. A polyimide prepared by aqueous phase polymerization of a polyimide according to any one of claims 1 to 9.

Images