Polyimide resin soluble in aqueous alkaline solution, process for its preparation and use

Abstract

This invention relates to the field of polymer materials technology, specifically to a polyimide resin soluble in alkaline aqueous solution, its preparation method, and its applications. The resin comprises structural unit I derived from a carboxyl-substituted diamine compound, structural unit II derived from a tetracarboxylic dianhydride compound, and structural unit III derived from a non-carboxyl-substituted diamine compound. The molar ratio of structural unit I, structural unit II, and structural unit III is 1:2~4:1~3. This polyimide resin possesses excellent water solubility, thermal stability, and mechanical properties, and its preparation process is environmentally friendly, meeting the application needs of various fields.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to polyimide resins soluble in alkaline aqueous solutions, their preparation methods, and applications. Background Technology

[0002] Polyimide (PI) is a class of high-performance polymer materials with imide rings as the main structural unit. It has excellent thermal stability, chemical stability, mechanical properties, and electrical properties, and is widely used in aerospace, electronics, new energy, biomedicine, and many other fields. However, due to the high rigidity of the molecular chain and strong intermolecular forces, traditional polyimides are usually insoluble and infusible. They can only be processed from their precursor polyamic acid solution, followed by high-temperature cyclization or chemical cyclization to obtain polyimide products. This "two-step" preparation process has problems such as high energy consumption, high pollution, high cost, and difficulty in achieving complete cyclization, which can easily lead to a decline in product performance.

[0003] To address the processing challenges of traditional polyimides, existing technologies introduce flexible structures, large-volume side groups, fluoromethyl substituents, or polar groups into the polyimide molecular chain to prepare soluble polyimides.

[0004] Currently reported soluble polyimides are mainly soluble in aprotic polar organic solvents such as N-methylpyrrolidone and N,N-dimethylformamide. However, most of these organic solvents have disadvantages such as toxicity, volatility, and serious environmental pollution, which do not conform to the development trend of green and environmental protection and limit their application in some fields with strict requirements for solvent environment (such as biomedicine and water treatment).

[0005] In recent years, the research and development of water-soluble polyimides has become a hot topic. These polyimides can dissolve in water or alkaline aqueous solutions, making the processing more environmentally friendly and gentler, and expanding the application range of polyimides. In existing technologies, the preparation of water-soluble polyimides often involves introducing hydrophilic groups such as sulfonates and quaternary ammonium salts. However, this preparation process is complex, requiring multiple reaction steps, and the introduction of hydrophilic groups can easily lead to a decrease in the thermal stability and mechanical properties of the polyimide. Furthermore, the solubility of existing water-soluble polyimides is limited, mostly existing in a colloidal dispersion state, making it difficult to form a uniform and transparent solution, thus affecting their processing performance and application effects.

[0006] In summary, there is an urgent need to provide a polyimide resin that possesses excellent water solubility, thermal stability, and mechanical properties, while also having a simple and environmentally friendly preparation process. Summary of the Invention

[0007] This invention addresses the technical problem of how to provide a polyimide resin that possesses excellent water solubility, thermal stability, and mechanical properties, while also having a simple and environmentally friendly preparation process.

[0008] To achieve the above objectives, the first aspect of the present invention provides a polyimide resin soluble in an alkaline aqueous solution, comprising structural unit I derived from a carboxyl-substituted diamine compound, structural unit II derived from a tetracarboxylic dianhydride compound, and structural unit III derived from a non-carboxyl-substituted diamine compound.

[0009] The molar ratio of structural unit I, structural unit II and structural unit III is 1:2~4:1~3.

[0010] A second aspect of the present invention provides a method for preparing the above-mentioned polyimide resin soluble in alkaline aqueous solution, comprising the following steps:

[0011] A carboxyl-substituted diamine compound, a tetracarboxylic acid dianhydride compound, a non-carboxyl-substituted diamine compound, and an aprotic polar solvent are mixed until dissolved. A catalyst and a dehydrating agent are then added to initiate a polymerization reaction, yielding a polyimide resin solution. The polyimide resin solution is then mixed with pure water, and the precipitate is collected, washed, filtered, and dried to obtain the polyimide resin.

[0012] A third aspect of the present invention provides the application of the above-mentioned polyimide resin soluble in alkaline aqueous solution, wherein the polyimide resin can be used to prepare water-soluble coatings, electronic packaging materials, optical waveguide materials, second-order nonlinear optical materials, photosensitive materials or water treatment membranes.

[0013] The beneficial effects of this invention are as follows:

[0014] The water-soluble polyimide resin provided by this invention possesses excellent water solubility, thermal stability, and mechanical properties, and its preparation process is environmentally friendly, meeting the application needs of various fields. For example, when used to prepare water-soluble coatings, it eliminates the need for toxic organic solvents, making it more environmentally friendly, and the coating exhibits excellent adhesion and weather resistance; when used in electronic packaging materials, it can be rapidly dissolved and molded in alkaline aqueous solutions, and possesses good insulation properties and thermal stability; when used in water treatment membranes, its hydrophilic properties and excellent chemical stability can be utilized to improve the membrane's water permeability and retention performance. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] In the existing technology, soluble polyimides are only soluble in most aprotic polar organic solvents such as N-methylpyrrolidone and N,N-dimethylformamide, which are mostly toxic, volatile, and cause serious environmental pollution. There is an urgent need for a polyimide that can be soluble in water or alkaline aqueous solutions.

[0017] The inventors of this invention have discovered that by introducing a carboxyl-substituted diamine compound with a suitable carboxyl group position and combining it with two specific monomers, a polyimide that can be completely soluble in water or alkaline aqueous solution can be prepared.

[0018] The first aspect of the present invention provides a polyimide resin soluble in an alkaline aqueous solution, wherein the resin comprises a structural unit I derived from a carboxyl-substituted diamine compound, a structural unit II derived from a tetracarboxylic acid dianhydride compound, and a structural unit III derived from a non-carboxyl-substituted diamine compound.

[0019] The molar ratio of structural unit I, structural unit II and structural unit III is 1:2~4:1~3.

[0020] In this invention, a one-step method was used to synthesize a polyimide resin that can dissolve in an alkaline aqueous solution. The specific mechanism is as follows:

[0021] The dianhydride and diamine monomers are heated in the high-boiling-point solvent NMP (200-250℃) with the aid of a catalyst (such as isoquinoline). The resulting polyamic acid oligomer undergoes dehydration and cyclization under high temperature and catalytic action to form an imine ring, promoting chain growth and ultimately generating a high molecular weight polyimide. During this process, the water generated is carried out of the reaction system by the nitrogen gas flow, causing the reaction equilibrium to shift towards the formation of polyimide, which is beneficial to the increase of molecular weight.

[0022] In this invention, the molar quantity of structural unit II is not less than the sum of the molar quantities of structural unit I and structural unit III.

[0023] In this invention, a one-step method is used to synthesize water-soluble polyimide resin, which has the following advantages:

[0024] The one-step method combines the monomer condensation and dehydration cyclization steps into one, eliminating the need for polyamic acid purification and significantly improving preparation efficiency. It also avoids the risk of degradation and deterioration of polyamic acid during storage. Furthermore, this method is suitable for high-solids systems, avoiding the problems of excessively high viscosity and poor processability during polyamic acid synthesis, reducing the use of organic solvents, and lowering preparation costs. Moreover, this synthesis method is applicable regardless of whether the final polyimide resin is soluble in organic solvents such as NMP, and the subsequent resin separation and purification process is simple and easy to implement.

[0025] According to some preferred embodiments of the present invention, the molar ratio of structural unit I, structural unit II, and structural unit III is 1:2~3:1~2.

[0026] According to the present invention, the carboxyl-substituted diamine compound is at least one of 2,4-diaminobenzoic acid (2,4-DABA), 4,4'-diamino-3,3'-dicarboxybiphenyl (3,3'-DCB), 4,4''-diamino-[1,1':4',1''-terphenyl]-2',5'-dicarboxylic acid (DATPDB), or 3,3'-dicarboxy-4,4'-diaminodiphenylmethane (MBAA).

[0027] In this invention, carboxyl-containing monomers with the above-mentioned specific structures are selected. Their carboxyl substitution positions are reasonable, allowing them to be uniformly introduced into the polyimide molecular chain during the polymerization reaction. This ensures the water solubility of the resin without affecting the smooth progress of the polymerization reaction, while simultaneously improving the resin's thermal stability and mechanical properties. Specifically, the 2,4-DABA monomer enhances the rigidity of the molecular chain, giving the water-soluble polyimide good thermal and mechanical properties as well as good water solubility. The 3,3'-DCB monomer contains two carboxyl groups, strengthening hydrophilicity and enhancing the water solubility of the water-soluble polyimide resin. The DATPDB monomer contains three benzene rings and two carboxyl groups, giving the water-soluble polyimide good water solubility while also enhancing the flexibility of the molecular chain, making it easier to dissolve in aqueous solutions. The MBAA monomer contains two carboxyl groups, effectively improving the water solubility of the polyimide resin.

[0028] According to the present invention, the carboxyl-free substituted diamine compound is at least one selected from 4,4'-diamino-2,2'-dimethylbiphenyl, 1,4-bis(2-trifluoromethyl-4-aminobenzene)benzene, 2,5-dichloro-p-phenylenediamine, 3,3'-diaminodiphenyl sulfone, (3-aminophenyl)-5-aminobenzimidazole, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine, 4,4'-diaminobenzoylaniline, 2,2-bis(4-aminophenyl)hexafluoropropane, 9,9-bis(4-aminophenyl)fluorene, (4-aminophenyl)-5-aminobenzoxazole, and 4,4'-diaminodiphenyl ether.

[0029] According to the present invention, the tetracarboxylic dianhydride compound is at least one selected from the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, hexafluorodianhydride, 4,4'-diphenyl ether dianhydride, bisphenol A type diether dianhydride, cyclobutanetetracarboxylic dianhydride, hydrogenated pyromellitic dianhydride, 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride, and p-phenylene-bisphenyltriester dianhydride.

[0030] According to the present invention, the polyimide resin is soluble in at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, or triethylamine aqueous solution.

[0031] According to the present invention, the polyimide resin has a solubility of ≥10g / 100mL in a 0.1mol / L sodium hydroxide aqueous solution at 25°C, and forms a uniform and transparent solution after dissolution without obvious precipitation.

[0032] In this invention, the solubility index of the polyimide resin ensures that the polyimide resin has good solubility in actual processing, and can quickly dissolve to form a uniform and transparent solution, which facilitates subsequent coating, molding and other processing operations, and solves the problems of low solubility and poor dispersibility of existing water-soluble polyimides.

[0033] According to the present invention, the polyimide resin has a particle size of 1~100 μm and a bulk density of 0.3~0.8 g / cm³. 3 .

[0034] The powdered polyimide resin provided by this invention is easy to store, transport and process. The specific particle size and bulk density can ensure that the resin has good flowability, which is convenient for dissolution and subsequent molding operations, while avoiding slow dissolution due to excessively large particle size or powder agglomeration due to excessively small particle size.

[0035] According to the present invention, the glass transition temperature of the polyimide resin is 180~280°C, and the 5% thermal weight loss temperature is 350~450°C under a nitrogen atmosphere.

[0036] According to the present invention, the polyimide resin has a number-average molecular weight of 1~100 kDa, a weight-average molecular weight of 1~100 kDa, and a molecular weight distribution of 1~2.

[0037] In this invention, the thermal performance indicators of the polyimide resin show that the polyimide resin provided by this invention has both good water solubility and retains the excellent thermal stability of polyimide, which can meet the requirements of aerospace, electronics and electrical appliances and other fields for the thermal performance of materials, and overcomes the defect of decreased thermal stability of existing water-soluble polyimides.

[0038] A second aspect of the present invention provides a method for preparing the above-mentioned polyimide resin soluble in alkaline aqueous solution, comprising the following steps:

[0039] A carboxyl-substituted diamine compound, a tetracarboxylic acid dianhydride compound, a non-carboxyl-substituted diamine compound, and an aprotic polar solvent are mixed until dissolved. A catalyst and a dehydrating agent are then added to initiate a polymerization reaction, yielding a polyimide resin solution. The polyimide resin solution is then mixed with pure water, and the precipitate is collected, washed, filtered, and dried to obtain the polyimide resin.

[0040] The preparation method provided by this invention is simple and has few steps, requiring no complex equipment or harsh reaction conditions, making it easy to industrialize. The washing step can remove residual solvent and unreacted monomers from the resin surface, improving product purity; the drying step can remove moisture and residual solvent from the resin, ensuring stable product performance.

[0041] The aprotic polar solvent used for dilution is the same as the aprotic polar solvent used to obtain the polyamic acid solution.

[0042] According to the present invention, the conditions for the polymerization reaction include: a reaction temperature of 200-250°C, a reaction time of 2-4 h, a solid content of 10-30% in the polyimide resin solution, and a dynamic viscosity of 1000-1000000 cps in the polyimide resin solution.

[0043] According to the present invention, the polyimide resin is insoluble in the reaction solvent.

[0044] According to the present invention, the solid content of the polyimide resin solution is 10-30%.

[0045] In this invention, the one-step polymerization reaction eliminates the need for a polyamic acid precursor stage, directly achieving monomer polymerization and imidization. This simplifies the preparation process, reduces energy consumption and pollution, and the specific polymerization conditions ensure that the polymerization reaction proceeds fully, avoiding side reactions and yielding a polyimide resin with uniform molecular weight distribution and stable performance. If the reaction temperature is too low, the reaction rate will be too slow and the reaction will be incomplete; if the temperature is too high, it may lead to molecular chain degradation, excessive crosslinking, and resin charring, affecting the resin's water solubility and mechanical properties.

[0046] According to the present invention, the carboxyl-substituted diamine compound is at least one selected from 2,4-diaminobenzoic acid, 4,4'-diamino-3,3'-dicarboxybiphenyl, 4,4''-diamino-[1,1':4',1''-terphenyl]-2',5'-dicarboxylic acid, or 3,3'-dicarboxy-4,4'-diaminodiphenylmethane;

[0047] According to the present invention, the carboxyl-free diamine compound is at least one selected from 4,4'-diamino-2,2'-dimethylbiphenyl, 1,4-bis(2-trifluoromethyl-4-aminobenzene)benzene, 2,5-dichloro-p-phenylenediamine, 3,3'-diaminodiphenyl sulfone, (3-aminophenyl)-5-aminobenzimidazole, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine, 4,4'-diaminobenzoylaniline, 2,2-bis(4-aminophenyl)hexafluoropropane, 9,9-bis(4-aminophenyl)fluorene, (4-aminophenyl)-5-aminobenzoxazole, and 4,4'-diaminodiphenyl ether.

[0048] According to the present invention, the tetracarboxylic dianhydride compound is at least one selected from the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, hexafluorodianhydride, 4,4'-diphenyl ether dianhydride, bisphenol A type diether dianhydride, cyclobutanetetracarboxylic dianhydride, hydrogenated pyromellitic dianhydride, 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride, and p-phenylene-bisphenyltriester dianhydride.

[0049] According to the present invention, the catalyst is at least one selected from triethylamine (TEA), 1-methylimidazole (1-MI), isoquinoline (IQL), N-ethylpiperidine (1-EP), carbonyl diimidazole (CDI), and pyridine (Py).

[0050] According to the present invention, the dehydrating agent is at least one of toluene (m-Tol), xylene (Xy), and acetic anhydride (Ac2O).

[0051] According to the present invention, the aprotic polar solvent is selected from at least one of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), γ-butyrolactone (GBL), and m-cresol.

[0052] According to the present invention, the molar ratio of the carboxyl-substituted diamine compound, the tetracarboxylic acid dianhydride compound, and the non-carboxyl-substituted diamine compound is 1:2~3:1~2.

[0053] According to the present invention, the mass of the aprotic polar solvent is 3 to 8 times the total mass of the carboxyl-substituted aromatic diamine compound, the tetracarboxylic dianhydride compound, and the non-carboxyl-substituted aromatic diamine compound.

[0054] In this invention, the aprotic polar solvent has good solubility, which can fully dissolve the carboxyl-containing monomers, providing a uniform reaction environment for the polymerization reaction. At the same time, it can stabilize the polyimide molecular chain and prevent it from agglomerating. The specific range of the amount of aprotic polar solvent can ensure the full dissolution of the monomers and the smooth progress of the reaction, while avoiding excessive solvent usage that would increase the cost of subsequent separation and drying.

[0055] According to the present invention, the washing conditions include: first adding acetic acid to the polyimide resin solution, the amount being 10% of the total mass of the monomer, stirring thoroughly, and then pouring it into a low-boiling-point solvent for washing, washing 2 to 4 times, and each washing time being 10 to 20 minutes.

[0056] According to the present invention, the low-boiling-point solvent is at least one selected from deionized water, ethanol, methanol, and acetone.

[0057] Specifically, in a preferred embodiment of the present invention, the washing process involves alternating between deionized water and ethanol for 2 to 4 washes.

[0058] In this invention, the polarity of the low-boiling-point solvent differs significantly from that of the aprotic polar solvent, enabling the polyimide resin to precipitate rapidly. Furthermore, the precipitant is widely available, low in cost, and easily volatile, facilitating subsequent removal. Alternating washing with deionized water and ethanol effectively removes residual solvents and monomers from the resin surface, improving product purity.

[0059] In this invention, the low-boiling-point solvent enables the polyimide resin to precipitate quickly and uniformly, facilitating separation and collection.

[0060] According to the present invention, the drying conditions include: vacuum drying, drying temperature of 80~120℃, drying time of 12~24h, and drying vacuum degree of 0.08~0.1MPa.

[0061] In this invention, vacuum drying can quickly remove moisture and residual solvents at a lower temperature, avoiding the degradation of resin molecular chains caused by high temperatures and ensuring stable product performance.

[0062] A third aspect of the present invention provides the application of the above-mentioned polyimide resin soluble in alkaline aqueous solution, wherein the polyimide resin can be used to prepare water-soluble coatings, electronic packaging materials, optical waveguide materials, second-order nonlinear optical materials, photosensitive materials or water treatment membranes.

[0063] The water-soluble polyimide resin of this invention possesses excellent water solubility, thermal stability, and mechanical properties, and its preparation process is environmentally friendly, meeting the application needs of various fields. For example, when used to prepare water-soluble coatings, it eliminates the need for toxic organic solvents, making it more environmentally friendly, and the coatings exhibit excellent adhesion and weather resistance. When used in electronic packaging materials, it can be rapidly dissolved and molded in alkaline aqueous solutions, and it possesses good insulation properties and thermal stability. When used in water treatment membranes, its hydrophilic properties and excellent chemical stability can be utilized to improve the membrane's water permeability and retention performance.

[0064] The CAS number for 2,4-diaminobenzoic acid is 611-03-0.

[0065] The CAS number for 3,3-diamino-4,4-dicarboxylic biphenyl is 1799740-97-8.

[0066] The CAS number for 4,4''-diamino-[1,1':4',1''-terphenyl]-2',5'-dicarboxylic acid is 2417234-65-0.

[0067] The CAS number for 3,3'-dicarboxy-4,4'-diaminodiphenylmethane is 7330-46-3.

[0068] The CAS number for pyromellitic dianhydride is 89-32-7.

[0069] The CAS number for 3,3',4,4'-biphenyltetracarboxylic acid dianhydride is 2450-87-3.

[0070] The CAS number for 3,3',4,4'-benzophenone tetracarboxylic dianhydride is 2421-28-5.

[0071] The CAS number for 2,3,3',4'-biphenyltetracarboxylic dianhydride is 36978-41-3.

[0072] The CAS number for hexafluorodianhydride is 1107-00-2.

[0073] The CAS number for 4,4'-diphenyl ether dianhydride is 1823-59-2.

[0074] The CAS number for bisphenol A type diether dianhydride is 38103-06-9.

[0075] The CAS number for cyclobutanetetracarboxylic dianhydride is 4415-87-6.

[0076] The CAS number for hydrogenated pyromellitic dianhydride is 2754-41-8.

[0077] The CAS number for 3,3,4,4-diphenylsulfone tetracarboxylic acid dianhydride is 2540-99-0.

[0078] The CAS number for p-phenylene-bisphenyltriester dianhydride is 2770-49-2.

[0079] The CAS number for 4,4'-diamino-2,2'-dimethylbiphenyl is 84-67-3.

[0080] The CAS number for 1,4-bis(2-trifluoromethyl-4-aminobenzene)benzene is 1815602-33-5.

[0081] The CAS number for 2,5-dichloro-p-phenylenediamine is 20103-09-7.

[0082] The CAS number for 3,3'-diaminodiphenyl sulfone is 599-61-1.

[0083] The CAS number for (3-aminophenyl)-5-aminobenzimidazole is 13676-49-8.

[0084] The CAS number for 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane is 83558-87-6.

[0085] The CAS number for 2,2'-bis[4-(4-aminophenoxy)phenyl]propane is 13080-86-9.

[0086] The CAS number for 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine is 341-58-2.

[0087] The CAS number for 4,4'-diaminobenzoyl aniline is 785-30-8.

[0088] The CAS number for 2,2-bis(4-aminophenyl)hexafluoropropane is 1095-78-9.

[0089] The CAS number for 9,9-bis(4-aminophenyl)fluorene is 15499-84-0.

[0090] The CAS number for (4-aminophenyl)-5-aminobenzoxazole is 13676-47-6.

[0091] The CAS number for 4,4'-diaminodiphenyl ether is 101-80-4.

[0092] Unless otherwise specified, the following examples and comparative examples were conducted under conventional conditions. Unless otherwise specified, the reagents or instruments used were all commercially available products.

[0093] Example 1

[0094] (1) 2,4-Diaminobenzoic acid, 4,4'-diamino-2,2'-dimethylbiphenyl and pyromellitic dianhydride were added to N-methylpyrrolidone in a molar ratio of 2:3:5 and stirred until completely dissolved to obtain a polyamic acid solution with high viscosity, wherein the monomer solid content was 25% and the viscosity was 51002cps;

[0095] (2) Heat the monomer solution to 250°C, add 5% isoquinoline as a catalyst and 10% toluene as a dehydrating agent, keep the reaction at the temperature for 2 hours, carry out a one-step polymerization reaction, and obtain a polyimide resin solution. The solution is yellow and the resin solid precipitates out.

[0096] (3) Add NMP to dilute the polyimide resin solution. After dilution, the solid content is 20%, and the amount of N-methylpyrrolidone is 4 times the total mass of the monomer.

[0097] (4) Add the polyimide resin solution to deionized water, stir to precipitate, filter and collect the precipitate; wash with deionized water and ethanol alternately 3 times, each time for 15 min; place the washed precipitate under vacuum drying at 100℃ and 0.09MPa for 18 h to obtain water-soluble polyimide resin powder A1.

[0098] In the water-soluble polyimide resin powder A1, the molar ratio of structural unit I, structural unit II and structural unit III is 1:2.5:1.5.

[0099] The water-soluble polyimide resin powder prepared in this embodiment has a particle size of 10~30 μm and a bulk density of 0.3 g / cm³. 3 The number-average molecular weight is 23 kDa, the weight-average molecular weight is 45 kDa, and the molecular weight distribution is 1.9.

[0100] The solubility of potassium hydroxide in a 0.1 mol / L aqueous solution at 25℃ is 20 g / 100 mL, and it forms a homogeneous and transparent solution after dissolution; the glass transition temperature is 296℃, and the 5% thermal weight loss temperature under a nitrogen atmosphere is 448℃.

[0101] Example 2

[0102] (1) 4,4'-diamino-3,3'-dicarboxybiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, and pyromellitic dianhydride were added to N-methylpyrrolidone in a molar ratio of 2:3:5 and stirred until completely dissolved to obtain a polyamic acid solution with a high viscosity, wherein the monomer solid content was 25% and the viscosity was 65420cps;

[0103] (2) The monomer solution was heated to 250°C and kept at that temperature for 2 hours to carry out a one-step polymerization reaction, resulting in a polyimide resin solution. The solution was yellow and the resin solid precipitated out.

[0104] (3) Add NMP to dilute the polyimide resin solution. After dilution, the solid content is 20%, and the amount of N-methylpyrrolidone is 4 times the total mass of the monomer.

[0105] (4) Add the polyimide resin solution to deionized water, stir to precipitate, filter and collect the precipitate; wash with deionized water and ethanol alternately 3 times, each time for 15 min; place the washed precipitate under vacuum drying at 100℃ and 0.09MPa for 18 h to obtain water-soluble polyimide resin powder A2.

[0106] In the water-soluble polyimide resin powder A2, the molar ratio of structural unit I, structural unit II and structural unit III is 1:2.5:1.5.

[0107] The water-soluble polyimide resin powder prepared in this embodiment has a particle size of 10~100 μm and a bulk density of 0.8 g / cm³. 3 The number-average molecular weight is 60 kDa, the weight-average molecular weight is 115 kDa, and the molecular weight distribution is 1.9. The solubility in a 0.1 mol / L tetramethylammonium hydroxide aqueous solution at 25 °C is 20 g / 100 mL, which forms a homogeneous and transparent solution after dissolution. The glass transition temperature is 315 °C, and the 5% thermal weight loss temperature under a nitrogen atmosphere is 482 °C.

[0108] Example 3

[0109] The preparation method of Example 2 was followed, except that 4,4'-diamino-3,3'-dicarboxylic biphenyl was replaced with 4,4''-diamino-[1,1':4',1''-terphenyl]-2',5'-dicarboxylic acid to obtain water-soluble polyimide resin powder A3.

[0110] In the water-soluble polyimide resin powder A3, the molar ratio of structural unit I, structural unit II and structural unit III is 1:2.5:1.5.

[0111] The water-soluble polyimide resin powder prepared in this embodiment has a particle size of 30-70 μm and a bulk density of 0.76 g / cm³. 3 The number-average molecular weight is 53 kDa, the weight-average molecular weight is 95 kDa, and the molecular weight distribution is 1.8. The solubility in a 0.1 mol / L tetramethylammonium hydroxide aqueous solution at 25 °C is 60 g / 100 mL, which forms a homogeneous and transparent solution after dissolution. The glass transition temperature is 287 °C, and the 5% thermal weight loss temperature under a nitrogen atmosphere is 426 °C.

[0112] Example 4

[0113] The preparation method of Example 2 was followed, except that 4,4'-diamino-3,3'-dicarboxybiphenyl was replaced with 3,3'-dicarboxy-4,4'-diaminodiphenylmethane to obtain water-soluble polyimide resin powder A4.

[0114] In the water-soluble polyimide resin powder A4, the molar ratio of structural unit I, structural unit II and structural unit III is 1:2.5:1.5.

[0115] The water-soluble polyimide resin powder prepared in this embodiment has a particle size of 20-80 μm and a bulk density of 0.67 g / cm³. 3 The number-average molecular weight is 42 kDa, the weight-average molecular weight is 75 kDa, and the molecular weight distribution is 1.79. The solubility in a 0.1 mol / L tetramethylammonium hydroxide aqueous solution at 25 °C is 74 g / 100 mL, which forms a homogeneous and transparent solution after dissolution. The glass transition temperature is 329 °C, and the 5% thermal weight loss temperature under a nitrogen atmosphere is 434 °C.

[0116] Example 5

[0117] Following the preparation method of Example 2, except that the molar ratio of 4,4'-diamino-3,3'-dicarboxybiphenyl, 4,4'-diamino-2,2'-dimethylbiphenyl, and pyromellitic dianhydride is 1:1:2, water-soluble polyimide resin powder A4 is prepared.

[0118] In the water-soluble polyimide resin powder A5, the molar ratio of structural unit I, structural unit II and structural unit III is 1:2:1.

[0119] The water-soluble polyimide resin powder prepared in this embodiment has a particle size of 30-50 μm and a bulk density of 0.75 g / cm³. 3 The number-average molecular weight is 56 kDa, the weight-average molecular weight is 96 kDa, and the molecular weight distribution is 1.71. The solubility in a 0.1 mol / L tetramethylammonium hydroxide aqueous solution at 25 °C is 35 g / 100 mL, which forms a homogeneous and transparent solution after dissolution. The glass transition temperature is 311 °C, and the 5% thermal weight loss temperature under a nitrogen atmosphere is 406 °C.

[0120] Example 6

[0121] Following the preparation method of Example 2, except that the molar ratio of 4,4'-diamino-3,3'-dicarboxylic biphenyl and pyromellitic dianhydride is 1:1, water-soluble polyimide resin powder A5 is prepared.

[0122] In the water-soluble polyimide resin powder A6, the molar ratio of structural unit I to structural unit II is 1:1.

[0123] The water-soluble polyimide resin powder prepared in this embodiment has a particle size of 40-80 μm and a bulk density of 0.66 g / cm³. 3 The number-average molecular weight is 52 kDa, the weight-average molecular weight is 94 kDa, and the molecular weight distribution is 1.8. The solubility in a 0.1 mol / L tetramethylammonium hydroxide aqueous solution at 25 °C is 80 g / 100 mL, which forms a homogeneous and transparent solution after dissolution. The glass transition temperature is 334 °C, and the 5% thermal weight loss temperature under a nitrogen atmosphere is 394 °C.

[0124] Comparative Example 1

[0125] The traditional two-step method is adopted: 4,4'-diaminodiphenyl ether and pyromellitic dianhydride are added to N-methylpyrrolidone and reacted at room temperature for 4 hours to obtain a polyamic acid solution; then acetic anhydride and pyridine catalyst are added, and chemical imidization reaction is carried out at 150°C for 24 hours to obtain a polyimide resin solution; after precipitation, washing and drying, polyimide resin powder DA1 is obtained.

[0126] The molar ratio of 4,4'-diaminodiphenyl ether to pyromellitic dianhydride is 1:1.

[0127] The polyimide resin powder DA1 prepared in Comparative Example 1 is almost insoluble in alkaline aqueous solutions such as sodium hydroxide and potassium hydroxide, and cannot be dissolved in aprotic polar organic solvents such as N-methylpyrrolidone.

[0128] Comparative Example 2

[0129] 4,4'-Diaminodiphenyl ether and pyromellitic dianhydride were added to N-methylpyrrolidone in a molar ratio of 1:1 and reacted at room temperature for 4 h to obtain a polyamic acid solution. Then sodium aminosulfonate was added and stirred for 2 h to introduce hydrophilic groups of sulfonate. Then imidization was carried out at 150 °C for 12 h to obtain a polyimide resin solution. After precipitation, washing and drying, polyimide resin powder DA2 was obtained.

[0130] Precipitation, washing, and drying were performed in accordance with the precipitation, washing, and drying procedures in Example 2.

[0131] The polyimide resin powder DA2 prepared in Comparative Example 2 has a solubility of 5 g / 100 mL in sodium hydroxide aqueous solution, a glass transition temperature of 267 °C, and a 5% thermal weight loss temperature of 388 °C under nitrogen atmosphere. Its thermal stability and mechanical properties are significantly lower than those of the products in Examples 1-5 of this invention, and the preparation process is complex and requires multiple reaction steps.

[0132] Comparative Example 3

[0133] The preparation method of Example 2 was followed, except that 4,4'-diamino-3,3'-dicarboxybiphenyl was replaced with 3,5-diaminobenzoic acid (3,5-DABA) to obtain water-soluble polyimide resin powder DA3.

[0134] In the water-soluble polyimide resin powder DA3, the molar ratio of structural unit I, structural unit II and structural unit III is 1:2.5:1.5.

[0135] The water-soluble polyimide resin powder DA3 has a particle size of 70~220 μm and a bulk density of 0.88 g / cm³. 3 The number-average molecular weight is 55 kDa, the weight-average molecular weight is 108 kDa, and the molecular weight distribution is 1.96. The solubility in a 0.1 mol / L tetramethylammonium hydroxide aqueous solution at 25 °C is 30 g / 100 mL, which forms a homogeneous and transparent solution after dissolution. The glass transition temperature is 284 °C, and the 5% thermal weight loss temperature under a nitrogen atmosphere is 397 °C.

[0136] Comparative Example 4

[0137] Following the preparation method of Example 2, except that 4,4'-diamino-3,3'-dicarboxybiphenyl was replaced with 4,4'-diamino-2,2'-dicarboxybiphenyl (2,2'-DCB), water-soluble polyimide resin powder DA4 was obtained.

[0138] In the water-soluble polyimide resin powder DA4, the molar ratio of structural unit I, structural unit II and structural unit III is 1:2.5:1.5.

[0139] The water-soluble polyimide resin powder DA4 has a particle size of 30~120 μm and a bulk density of 0.93 g / cm³. 3 The number-average molecular weight is 62 kDa, the weight-average molecular weight is 114 kDa, and the molecular weight distribution is 1.84. The solubility in a 0.1 mol / L tetramethylammonium hydroxide aqueous solution at 25 °C is 35 g / 100 mL, which forms a homogeneous and transparent solution after dissolution. The glass transition temperature is 306 °C, and the 5% thermal weight loss temperature under a nitrogen atmosphere is 393 °C.

[0140] As can be seen from the comparison of the above embodiments and comparative examples, the water-soluble polyimide resin of the present invention is synthesized in one step by a carboxyl-containing monomer in combination with two other specific monomers. The preparation process is simple and environmentally friendly. It can be rapidly dissolved in a variety of alkaline aqueous solutions, has high solubility, and also has excellent thermal stability and mechanical properties, which are significantly better than the soluble or water-soluble polyimide resins in the prior art.

[0141] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A polyimide resin soluble in alkaline aqueous solution, characterized in that, This includes structural unit I derived from carboxyl-substituted diamine compounds, structural unit II derived from tetracarboxylic dianhydride compounds, and structural unit III derived from non-carboxyl-substituted diamine compounds; The molar ratio of structural unit I, structural unit II and structural unit III is 1:2~4:1~3.

2. The polyimide resin soluble in alkaline aqueous solution according to claim 1, characterized in that, The molar ratio of structural unit I, structural unit II and structural unit III is 1:2~3:1~2.

3. The polyimide resin soluble in alkaline aqueous solution according to claim 2, characterized in that, The carboxyl-substituted diamine compound is at least one of 2,4-diaminobenzoic acid, 4,4'-diamino-3,3'-dicarboxybiphenyl or 4,4''-diamino-[1,1':4',1''-terphenyl]-2',5'-dicarboxylic acid, and 3,3'-dicarboxy-4,4'-diaminodiphenylmethane. The carboxyl-free diamine compound is at least one of the following: 4,4'-diamino-2,2'-dimethylbiphenyl, 1,4-bis(2-trifluoromethyl-4-aminophenyl)benzene, 2,5-dichloro-p-phenylenediamine, 3,3'-diaminodiphenyl sulfone, (3-aminophenyl)-5-aminobenzimidazole, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine, 4,4'-diaminobenzoylaniline, 2,2-bis(4-aminophenyl)hexafluoropropane, 9,9-bis(4-aminophenyl)fluorene, (4-aminophenyl)-5-aminobenzoxazole, and 4,4'-diaminodiphenyl ether. The tetracarboxylic dianhydride compound is at least one of the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, hexafluorodianhydride, 4,4'-diphenyl ether dianhydride, bisphenol A type diether dianhydride, cyclobutanetetracarboxylic dianhydride, hydrogenated pyromellitic dianhydride, 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride, and p-phenylene-bisphenyltriester dianhydride.

4. The polyimide resin soluble in alkaline aqueous solution according to claim 1, characterized in that, The polyimide resin can be dissolved in at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, tetramethylammonium hydroxide aqueous solution, tetraethylammonium hydroxide aqueous solution, or triethylamine aqueous solution; The polyimide resin has a solubility of ≥10g / 100mL in a 0.1mol / L sodium hydroxide aqueous solution at 25℃. The polyimide resin has a particle size of 1~100 μm and a bulk density of 0.3~0.8 g / cm³. 3 ; The glass transition temperature of the polyimide resin is 250~350℃, and the 5% thermal weight loss temperature is 350~450℃ under a nitrogen atmosphere. The polyimide resin has a number-average molecular weight of 1~100 kDa, a weight-average molecular weight of 1~100 kDa, and a molecular weight distribution of 1~2.

5. The method for preparing the polyimide resin soluble in alkaline aqueous solution according to any one of claims 1-4, characterized in that, Includes the following steps: A carboxyl-substituted diamine compound, a tetracarboxylic acid dianhydride compound, a non-carboxyl-substituted diamine compound, and an aprotic polar solvent are mixed until dissolved. A catalyst and a dehydrating agent are then added to initiate a polymerization reaction, yielding a polyimide resin solution. The polyimide resin solution is then mixed with pure water, and the precipitate is collected, washed, filtered, and dried to obtain the polyimide resin.

6. The preparation method according to claim 5, characterized in that, The conditions for the polymerization reaction include: a reaction temperature of 200-250℃, a reaction time of 2-4h, a solid content of 10-30% for the polyimide resin, and a dynamic viscosity of 1000-1000000cps for the polyimide resin. The solid content of the polyimide resin solution is 10-30%.

7. The preparation method according to claim 5, characterized in that, The carboxyl-substituted diamine compound is at least one of 2,4-diaminobenzoic acid, 4,4'-diamino-3,3'-dicarboxybiphenyl, or 4,4''-diamino-[1,1':4',1''-terphenyl]-2',5'-dicarboxylic acid, or 3,3'-dicarboxy-4,4'-diaminodiphenylmethane. The carboxyl-free diamine compound is at least one of the following: 4,4'-diamino-2,2'-dimethylbiphenyl, 1,4-bis(2-trifluoromethyl-4-aminophenyl)benzene, 2,5-dichloro-p-phenylenediamine, 3,3'-diaminodiphenyl sulfone, (3-aminophenyl)-5-aminobenzimidazole, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 2,2'-bis(trifluoromethyl)-(1,1'-diphenyl)-4,4'-diamine, 4,4'-diaminobenzoylaniline, 2,2-bis(4-aminophenyl)hexafluoropropane, 9,9-bis(4-aminophenyl)fluorene, (4-aminophenyl)-5-aminobenzoxazole, and 4,4'-diaminodiphenyl ether. The tetracarboxylic dianhydride compound is at least one of the following: pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, hexafluorodianhydride, 4,4'-diphenyl ether dianhydride, bisphenol A type diether dianhydride, cyclobutanetetracarboxylic dianhydride, hydrogenated pyromellitic dianhydride, 3,3,4,4-diphenyl sulfone tetracarboxylic dianhydride, and p-phenylene-bisphenyltriester dianhydride; The catalyst is at least one selected from triethylamine, 1-methylimidazolium, isoquinoline, N-ethylpiperidine, carbonyldiimidazole, and pyridine. The dehydrating agent is at least one of toluene (m-Tol), xylene (Xy), and acetic anhydride (Ac2O); The aprotic polar solvent is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, and m-methylphenol.

8. The preparation method according to claim 5, characterized in that, The molar ratio of the carboxyl-substituted diamine compound, the tetracarboxylic dianhydride compound, and the non-carboxyl-substituted diamine compound is 1:2~3:1~2; The catalyst is used at a rate of 2-10% of the total mass of the monomers, and the dehydrating agent is used at a rate of 1-3 times the mass of the catalyst. Preferably, the catalyst is used at a rate of 4-8% of the total mass of the monomers, the dehydrating agent is used at a rate of 1.5-2 times the mass of the catalyst, and the aprotic polar solvent is used at a rate of 3-8 times the total mass of the monomers.

9. The preparation method according to claim 5, characterized in that, The washing conditions include: first, adding acetic acid to the polyimide resin solution, the amount being 10% of the total mass of the monomer, stirring thoroughly, and then pouring it into a low-boiling-point solvent for washing, washing 2 to 4 times, with each washing time being 10 to 20 minutes; The low-boiling-point solvent is at least one of deionized water, ethanol, methanol, and acetone; The drying conditions include: vacuum drying, drying temperature of 80~120℃, drying time of 12~24h, and drying vacuum degree of 0.08~0.1MPa.

10. The application of the polyimide resin soluble in alkaline aqueous solution according to any one of claims 1-4, characterized in that, The polyimide resin can be used to prepare water-soluble coatings, electronic packaging materials, optical waveguide materials, second-order nonlinear optical materials, photosensitive materials, or water treatment membranes.