Water-soluble polyamide acid salt as well as water-phase one-pot preparation method and application thereof

Abstract

The invention belongs to the technical field of synthetic high polymer materials, and relates to water-soluble polyamide acid salt as well as a water-phase one-pot preparation method and application thereof. The preparation method comprises the following steps: completely dissolving an aromatic dianhydride monomer in water to obtain a first solution, completely dissolving an aromatic diamine monomer and an organic alkali in water to obtain a second solution, mixing the first solution and the second solution, carrying out a polymerization reaction, after the polymerization reaction is finished, adding an end-capping reagent, continuously stirring until the end-capping reagent is completely dissolved, and removing water to obtain a finished product. The water-soluble polyamide acid salt is obtained. According to the preparation method, water is used as a solvent, a single-step polymerization reaction is adopted, any subsequent purification treatment step is not needed, the production process is green and environment-friendly, the process is simple and convenient, the cost is low, and the preparation method is not limited by the feeding amount of aromatic dianhydride monomers and the scale of a reaction system. The viscosity average molecular weight of the finally prepared water-soluble polyamide acid salt is 8.0 * 10 < 3 >-2.0 * 10 < 4 > g / mol, the film forming effect is excellent, and the water-soluble polyamide acid salt can be used as sizing liquid.

Description

Technical Field

[0001] The present invention belongs to the technical field of synthetic polymer materials, and relates to a water-soluble polyamide salt, a one-pot preparation method thereof in an aqueous phase, and applications thereof. Background Art

[0002] Water-soluble polyamide salts use pure water as a solvent, and have better heat resistance and storage stability. The regular configuration formed by the hydrogen bond network between their molecular chains significantly increases the thermal decomposition threshold. At the same time, the solvation layer formed by the hydration effect effectively inhibits the hydrolysis degradation of the polymer. Verified by dynamic thermomechanical analysis (DMA), the glass transition temperature (Tg) of this system can reach above 220 °C, and the viscosity retention rate still exceeds 92% after 2000 hours of accelerated aging at 85 °C / 85% humidity. This unique two-phase interaction mechanism not only endows the material with excellent mechanical stability, but also enables it to exhibit extremely strong adhesion to metal substrates and ceramic interfaces in multi-layer composite structures. In particular, because they are soluble and dispersible at room temperature and can be thermally imidized into polyimides that are well compatible with the matrices of aerospace thermoplastic composites such as polyphenylene sulfide and polyether ether ketone at high temperatures, polyamic acids and polyamide salts have always been regarded as one of the best choices for high-temperature thermoplastic sizing agents for carbon fiber materials.

[0003] In view of the many drawbacks of traditional preparation processes in the use of organic solvents, in recent years, researchers have proposed a new strategy for synthesizing polyamide salts in an aqueous phase. This strategy uses water as the main medium and allows aromatic dianhydrides and diamines to polymerize stably under the catalysis of a suitable organic base to produce polyamide salts with excellent properties. This method avoids the use of organic solvents, greatly reduces pollution and costs, and has significant advantages in fields such as aerogels, flexible circuit boards, lithium-ion battery adhesives, and photoresists, becoming a research hotspot at the intersection of green chemistry and high-performance materials.

[0004] Reference 1 (Polymerization of poly-(amic acid) ammonium salt in aqueous solution and its use in flexible printed circuit boards. European Polymer Journal. 2017, 96, 393-402.) used dodecyltrimethylammonium chloride as a catalyst to successfully polymerize aromatic diamine and dianhydride in water at 10 °C, obtaining polyamide acid salt with a mass fraction of 18 wt%, and systematically studied its adhesion performance for flexible copper-clad laminates (FCCLs). Reference 2 (Simple and environmentally friendly approach for preparing high-performance polyimide precursor hydrogel with fully aromatic structures for strain sensor. European Polymer Journal. 2019, 114, 346-352.) used triethylamine and dodecyltrimethylammonium chloride as a mixed catalyst to polymerize aromatic diamine and dianhydride in water at 0 °C to prepare polyamide acid salt hydrogel, which has good stretching ability, an elongation rate of about 1350%, can not only self-heal, but also has good temperature responsiveness and adhesion to human skin, and is suitable as a sensitive strain sensor for motion detection. Reference 3 (Enhanced hydrolytic and electrical stability of eco-friendly processed polyimide gate dielectrics for organic transistor. Journal of Materials Chemistry C. 2020, 8, 14249-14612.) used 1,2-dimethylimidazole as an aqueous phase polymerization catalyst to polymerize aromatic diamine and dianhydride in water at 70 °C to obtain polyamide acid salt, and then prepared a large-volume submicron polyimide (PI) film, which has excellent insulation and electrical properties. Patent CN118515868A used an imidazole-based catalytic salt-forming agent to synthesize a polyimide adhesive with water as a solvent, and improved the solubility of the adhesive through acetic anhydride chemical imidization, and the bonding effect is good.Patent CN117247542A uses excessive triethylamine as a catalyst to improve the dispersibility and solubility of the product polyamic acid salt in aqueous solution, expands the types of monomers that can be used in the aqueous-phase polymerization to prepare polyimide, and the polyamic acid salt solution is frozen, vacuum-dried, and thermally imidized in a vacuum environment to obtain a polyimide aerogel with excellent properties.

[0005] Although the above studies have confirmed the feasibility of synthesizing polyamic acid salt by the aqueous-phase method, however, these current studies are all limited to laboratory-scale small-scale tests, with a small reaction scale. Generally, the total volume of the reaction system is less than 500 mL, and the feeding amount of aromatic dianhydride monomers is less than 0.2 mol. It has been found that once the reaction scale is expanded, the reaction becomes extremely difficult to control and is extremely likely to trigger the self-accelerating gelation phenomenon, resulting in the rapid solidification of the reaction system within a short time. In view of this, a process system that can be scaled up to industrial scale has not been successfully constructed so far. Summary of the Invention

[0006] The object of the present invention is to solve the problems existing in the prior art and provide a one-pot aqueous-phase preparation method of water-soluble polyamic acid salt, in which the feeding amount of aromatic dianhydride monomers and the scale of the reaction system are not restricted, and gelation will not occur regardless of whether it is a laboratory scale or an industrial scale. Furthermore, a water-soluble polyamic acid salt prepared by this preparation method and its applications are provided.

[0007] In view of the problem that when the aqueous phase method is used to synthesize polyamic acid on a large scale, the reaction is extremely difficult to control and is very likely to trigger self-accelerating gelation, causing the reaction system to solidify rapidly in a short period of time, the inventors have found through a large number of scale-up experiments that aromatic diamine / dianhydride monomers and polyamic acid products are completely miscible in traditional high-boiling point organic solvent systems, and the dissolution time is very short (less than 10 minutes); for aqueous phase polymerization, the current common operation is to directly add its powder into the reaction system for reaction. Since the aromatic dianhydride monomer dissolves very slowly in water, the dissolution time is 2-4 hours, which will cause the aromatic diamine / dianhydride monomer to dissolve in water. Before the anhydride monomer is completely dissolved, it mixes with the aromatic diamine monomer, making the reaction system present a solid-liquid multiphase coexistence state. It is this heterogeneity that causes multiple mass transfer restrictions. First, the surface of the aromatic dianhydride monomer particles contacts the dissolved aromatic diamine monomer, resulting in a violent local polycondensation reaction, which in turn triggers the self-accelerating gelation phenomenon; second, in the heterogeneous system, some of the dissolved aromatic dianhydride monomers react quickly with the aromatic diamine monomers to generate high molecular weight polymers. Due to the uneven reaction environment, the molecular weight distribution of the polymer becomes broad, and it is easy to form micelle aggregates, which eventually leads to gelation. When the feed amount increases (such as aromatic dianhydride monomer ≥ 2.5 mol), the proportion of undissolved aromatic dianhydride monomers will also increase, and the reaction will be very uncontrollable, which is very likely to trigger the self-accelerating gelation phenomenon, causing the reaction system to solidify instantly, seriously hindering the expansion of the reaction to an industrial scale. When the feeding amount of the reaction aromatic dianhydride monomer is ≥2.5mol, the inventors observed that a large amount of undissolved aromatic dianhydride monomers were wrapped in the product polyamic acid salt solid, which also confirmed the above viewpoint, and additional purification steps were required to remove these residual monomers in the follow-up, which increased the production cost. Although traditional aqueous polymerization research uses water as a solvent, it only focuses on parameters such as catalyst type and temperature control, and the operation process of directly mixing monomers is assumed. It does not recognize the uncontrollability of local polycondensation reactions in heterogeneous systems, resulting in the gelation problem being unable to be solved during scale-up. The present invention proposes a solution of pre-dissolving aromatic dianhydride monomers, eliminating the solid-liquid interface, and making the polymerization reaction system a homogeneous system, and for the first time reveals that the solid-liquid multiphase coexistence caused by the slow dissolution of aromatic dianhydride monomers is the core inducement of gelation, and proposes the correlation between the dissolution rate of aromatic dianhydride monomers and the uniformity of the reaction.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] The invention discloses an aqueous one-pot preparation method of water-soluble polyamic acid salt. The reaction medium is water, and the reaction raw materials are aromatic dianhydride monomer and aromatic diamine monomer. The aromatic dianhydride monomer is firstly completely dissolved in water and then mixed with the aromatic diamine monomer.

[0010] With the above technical solution, the reaction system of the present invention can always maintain a homogeneous state, effectively avoiding the problem of excessive local concentration, and enabling the polycondensation reaction to proceed smoothly. In the homogeneous system, the aromatic dianhydride monomer and the aromatic diamine monomer can contact evenly, the polycondensation reaction progresses step by step, the growth of the molecular weight is controlled, and the viscosity-average molecular weight distribution of the product is narrower. The homogeneous reaction of the present invention ensures the complete conversion of the monomers, the product has a higher purity, no subsequent purification steps are required, and the entire process is more environmentally friendly. Moreover, the method of pre-dissolving the aromatic dianhydride monomer in the present invention can eliminate the solid-liquid interface. Even when the feeding amount is as high as 11.6 mol or the system volume reaches 50 L, the homogeneous reaction can still be maintained, successfully breaking through the technical bottleneck of large-scale production.

[0011] As a preferred technical solution;

[0012] A one-pot aqueous-phase preparation method of a water-soluble polyamide salt as described above, the specific steps are as follows:

[0013] (a) Completely dissolve the aromatic dianhydride monomer in water to obtain a first solution. At the same time, completely dissolve the aromatic diamine monomer and the organic base in water to obtain a second solution;

[0014] (b) Mix the first solution and the second solution and carry out a polymerization reaction. After the polymerization reaction is completed, add a capping agent thereto and continue stirring until the capping agent is completely dissolved, and remove water to obtain the water-soluble polyamide salt.

[0015] The dissolution of the aromatic dianhydride monomer in water is extremely slow. Therefore, the current common practice is to directly add its powder to the reaction system for reaction. In this reaction system, there are two competing reactions: the amidation and hydrolysis of the acid anhydride. There is a literature (One-pot aqueous-phase synthesis of polyimides from typical monomer. Polymer.2024,313,127754.) indicating that once the acid anhydride undergoes hydrolysis to form an organic acid, it will no longer continue to react. However, in the present invention, even if the acid anhydride hydrolyzes to form an organic acid, under the catalytic action of the organic base, this organic acid can still undergo an amidation reaction to generate a polyamide salt. This is because, although the reaction rate of the organic acid is significantly lower than that of the acid anhydride, the decrease in the reaction temperature promotes a significant increase in the equilibrium constant of the reaction. This change actually compensates for the possible impact on the reaction conversion rate and yield, enabling the reaction to proceed smoothly.

[0016] A one-pot aqueous-phase preparation method of a water-soluble polyamide acid salt as described above, wherein the aromatic dianhydride monomer is one or more of 4,4'-biphenyl ether dianhydride, 3,3',4,4'-benzophenone dianhydride, 3,3',4,4'-biphenyl dianhydride, bisphenol A diether dianhydride, hexafluorodiacid dianhydride, pyromellitic dianhydride, methylpyromellitic dianhydride, dimethylpyromellitic dianhydride, ethylpyromellitic dianhydride, diethylpyromellitic dianhydride, phenylpyromellitic dianhydride, diphenylpyromellitic dianhydride, 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride;

[0017] The aromatic diamine monomer is one or more of p-phenylenediamine, m-phenylenediamine, 1,1-m-xylenediamine, 4,4-diaminodiphenyl sulfone, 3,3'-sulfonylbis-aniline, 4,4'-diaminobenzanilide, 3,3'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzoxazole, 2-(4-aminophenyl)-5-aminobenzimidazole, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl ethane, bisphenol A diether diamine, 2,7-diaminofluorene, 4,4-diaminoheptanediamine, 3,4-diaminothiophene;

[0018] The organic base is one or more of ammonia, diethanolamine, triethanolamine, triethylamine, N,N-dimethylethanolamine, benzimidazole, 1-methylimidazole, 1,2-dimethylimidazole, 1,8-diazabicycloundec-7-ene, dodecyltrimethylammonium chloride, quinoline, pyridine, 3-methylpyridine;

[0019] The capping agent is one or more of 4-methylphthalic anhydride, 4-tert-butylphthalic anhydride, 4-phenylethynylphthalic anhydride, 5-phenoxyisobenzofuran-1(3H)-one, 5-(4-(phenylethynyl)phenoxy)isobenzofuran-1,3-dione.

[0020] A one-pot aqueous-phase preparation method of a water-soluble polyamide acid salt as described above, the preparation process of the first solution is: after mixing the aromatic dianhydride monomer and water with a molar ratio of 1:12 - 30, under the protection of nitrogen or inert gas, stir at 100 - 180 °C for 1 - 5 h;

[0021] The aromatic dianhydride monomer (such as pyromellitic dianhydride, biphenyl ether dianhydride) contains a large aromatic ring structure, has strong hydrophobicity, and does not match the polarity of water molecules, which makes its solubility in water extremely low. Moreover, there are strong π-π stacking interactions and van der Waals forces between aromatic rings, resulting in strong intermolecular forces and molecules being prone to aggregation to form solid particles, further hindering the dissolution of the aromatic dianhydride monomer.

[0022] Since aromatic dianhydride monomers are extremely difficult to dissolve in water, the dissolution of aromatic dianhydride monomers only seems simple but is actually quite difficult. It is necessary to conduct a large number of experiments to determine the key process parameters during the dissolution process (such as dissolution temperature, pressure, time, concentration, etc.). These process conditions significantly exceed the scope of conventional dissolution operations (for example, the dissolution temperature of aromatic dianhydride monomers in the literature is usually ≤100°C). In actual operation, it is necessary to draw on the operation of hydrothermal reaction and ensure the complete dissolution of aromatic dianhydride monomers through long-term stirring under high temperature and high pressure. This operation method belongs to a non-obvious innovative means.

[0023] The preparation process of the second solution is as follows: After mixing the aromatic diamine monomer, the organic base and water, under the protection of nitrogen or inert gas, stir at 25 - 60°C for 5 - 30 min. The stirring time is related to the concentration of the aromatic diamine monomer. The higher the concentration, the longer the stirring time.

[0024] The polymerization reaction is carried out under the protection of nitrogen or inert gas, which can prevent other impurities from entering, avoid the oxidation and deterioration of the reaction monomers and reduce the occurrence of side reactions. The temperature of the polymerization reaction is 10 - 80°C. Temperature is the key factor determining the forward progress of the polycondensation to form salt reaction. Appropriately increasing the temperature can promote the energy transfer of reactant molecules and the increase of the collision frequency, thus accelerating the reaction rate, while decreasing the temperature is beneficial to the forward progress of the exothermic salt-forming reaction and greatly improves the reaction degree.

[0025] The molar ratio of the aromatic diamine monomer, the aromatic dianhydride monomer and the end-capping agent is 3 - 17:2 - 16:2; the molar ratio of the organic base to the aromatic dianhydride monomer is 1.6 - 2.4:1. Within this range, it can not only ensure that the aromatic diamine monomer and the aromatic dianhydride monomer are polymerized into polyamide acid salt in one step with a reasonable reaction rate and a high reaction degree, but also ensure that there is no volatile free amine in the final product of water-soluble polyamide acid salt; the solid content of the reaction system before removing water is 5 - 25 wt%.

[0026] When preparing polyamide acid salt by the aqueous one-pot method of the present invention, the organic base (catalytic salt-forming agent) added has a strong chelating effect with the carboxyl group (-COOH) in the polyamide acid structure, and there is almost no free amine in the system. Therefore, no subsequent treatment steps for absorbing the organic base are required; the content of volatile organic amine (taking triethylamine TEA as an example) in the obtained reaction solution is tested and verified by gas chromatography-mass spectrometry. The results show that there is almost no volatile organic amine in the obtained reaction solution, thus proving the rationality of the aqueous one-pot method of the present invention for preparing polyamide acid salt without any subsequent purification treatment steps.

[0027] A one-pot aqueous-phase preparation method of a water-soluble polyamide salt as described above, the feeding amount of the aromatic dianhydride monomer in the reaction system is at most 11.6 mol, and the total volume of the reaction system (i.e., the total volume of the reaction raw materials and the reaction medium) is at most 50 L. In the present invention, the feeding amount of the aromatic dianhydride monomer can be large or small, and the reaction system can be large or small, which can be of laboratory scale or industrial scale, and no gelation phenomenon will occur.

[0028] A one-pot aqueous-phase preparation method of a water-soluble polyamide salt as described in any one of the above, the viscosity-average molecular weight of the water-soluble polyamide salt is 8.0×10 3 -2.0×10 4 g / mol. The water-soluble polyamide salt with a viscosity-average molecular weight in this range has good redissolution property, and can be used as a sizing agent at the same time. It has excellent film-forming property, can form a complete and uniform film on the fiber surface, and there will be no entanglement phenomenon on the fiber surface, nor will it cause local aggregation of the sizing layer.

[0029] The present invention also provides a water-soluble polyamide salt prepared by using a one-pot aqueous-phase preparation method of a water-soluble polyamide salt as described in any one of the above.

[0030] The present invention also provides a one-pot aqueous-phase preparation method of a sizing agent of a water-soluble polyamide salt. During the process of preparing the water-soluble polyamide salt by using a one-pot aqueous-phase preparation method of a water-soluble polyamide salt as described above, the operation of removing water is omitted, and the sizing agent of the water-soluble polyamide salt is obtained.

[0031] The present invention also provides a sizing agent of a water-soluble polyamide salt prepared by using a one-pot aqueous-phase preparation method of a sizing agent of a water-soluble polyamide salt as described above; the sizing agent of the water-soluble polyamide salt can be stored in a bucket at low temperature (-20 - 4°C). When used, it is diluted with water, or after being coated and formed into a film on a polyester or polyimide release film during unwinding, it is dried at low temperature and wound up for storage. When used, it is redissolved in water and diluted to a concentration suitable for sizing. Among them, low-temperature drying means that the drying temperature is not higher than 60°C (preferably below 40°C or air-dried at room temperature), and the drying method can be through a low-temperature drying device during winding or drying overnight after winding.

[0032] The present invention also provides an application of a sizing agent of a water-soluble polyamide salt as described above for sizing carbon fibers.

[0033] As a preferred technical solution;

[0034] The application as described above has the following specific steps:

[0035] 1) Place the water-soluble polyamide salt sizing agent stored at low temperature into the sizing tank, and control the water volume in the sizing tank to dilute the water-soluble polyamide salt sizing agent to a concentration of 0.3 - 2.0 wt%.

[0036] 2) Directly size the carbon fiber after electrochemical treatment on the carbon fiber production line through the sizing tank, and the sizing time is 1 - 15 s.

[0037] 3) Dry and wind up the sized carbon fiber. The drying temperature is 60 - 160 °C, and the drying time is 15 s - 1 min.

[0038] For the application as described above, the specific steps are as follows:

[0039] 1) First, subject the carbon fiber sized with the thermosetting sizing agent to high-temperature ablation to remove the surface thermosetting sizing agent and then set it aside for later use.

[0040] 2) Activate the carbon fiber by plasma treatment, introduce oxygen-containing groups (such as carboxyl groups, hydroxyl groups, etc.) on its surface, and increase the surface roughness of the fiber.

[0041] 3) Redissolve the stored water-soluble polyamide salt sizing agent (at 25 - 60 °C) in water and dilute it to a concentration of 0.01 - 5 wt%. After impregnating the activated carbon fiber in it for 10 s - 4 h, take it out in sequence, drain the excess sizing agent, and dry it.

[0042] For the application as described above, the specific steps are as follows:

[0043] 1) Heat and reflux the carbon fiber sized with the thermosetting sizing agent in an acetone solution. After removing the surface thermosetting sizing agent, wash it with water (to remove the acetone on the surface of the carbon fiber) and then dry it.

[0044] 2) Activate the oxygen-containing groups on the surface of the carbon fiber with mesoxalic acid or acid anhydride, wash it with water until it is neutral, and then dry it.

[0045] 3) Redissolve the stored water-soluble polyamide salt sizing agent in water and dilute it to a concentration of 0.01 - 5 wt%. After impregnating the activated carbon fiber in it for 10 s - 4 h, take it out in sequence, drain the excess sizing agent, and dry it.

[0046] Beneficial effects:

[0047] The provided one-pot aqueous-phase preparation method of water-soluble polyamide salt of the present invention adopts a one-step polymerization reaction, without any subsequent purification treatment steps. The production process is green and environmentally friendly, the process is simple, and the cost is low.

[0048] The present invention innovatively uses a low-cost aqueous medium to replace traditional high-boiling organic solvents as the sole medium system for polymerization reactions, and has made remarkable progress in breaking through three major technical bottlenecks: First, it completely abandons the cumbersome processes and residual risks of organic solvent removal and recovery, and solves the problems of product safety and environmental protection of the sizing agent from the source; Second, through process optimization, controlled polymerization in the aqueous phase system is achieved, breaking through the shackles that the existing aqueous phase technology is difficult to achieve industrial-scale production; Third, a green and environmentally friendly one-step reaction process is constructed, with both high reaction efficiency and product purity, and high-quality products can be obtained without additional purification steps.

[0049] In the polymerization system of the present invention, an organic base is added, and the organic base will undergo a chelation reaction with the carboxyl groups (-COOH) in the polyamic acid structure, so that there is almost no free amine in the system, and no subsequent purification treatment steps for absorbing the organic base are required. The entire preparation process and the use process will not cause harm to the environment, which conforms to the development concept of green chemistry.

[0050] The one-pot aqueous-phase preparation method of the water-soluble polyamide salt provided by the present invention is not limited by the feeding amount of the aromatic dianhydride monomer and the scale of the reaction system. Whether it is a laboratory scale or an industrial scale, gelation will not occur, providing a technical basis for the large-scale preparation of water-soluble polyamide salts.

[0051] The water-soluble polyamide salt of the present invention has significant advantages. Its appearance is clear and transparent, its properties are uniform, and its flexibility is good. It has the characteristics of being green, efficient, pollution-free, and residue-free. It can penetrate into the fiber bundle interior faster. The narrow molecular weight distribution makes the film formation more uniform, and it has good redissolution property. When used as a sizing agent, it forms a complete film layer on the fiber surface, significantly improving the interfacial performance of carbon fiber composites. Compared with emulsion-type thermoplastic sizing agents, the water-soluble polyamide salt avoids the adverse effects on the temperature resistance of the sizing agent caused by the introduction of a large amount of emulsifiers, and also eliminates the hidden danger of instability after long-term storage.

[0052] The water-soluble polyamide salt of the present invention can be applied to the production process of high-performance thermoplastic composites and can significantly improve the performance of thermoplastic composite plates. For example, the porosity can be reduced to less than 1%, the interlaminar shear strength (ILSS) is increased by 70 - 100%, and the flexural strength and modulus are increased by about 70%.

[0053] The polyamide salt aqueous solution prepared by the present invention has a variety of uses. It can not only be used as a sizing agent to improve the interfacial performance of carbon fiber thermoplastic composites, but also be used as a suspension of prepreg and a resin matrix for preparing carbon-based material thermoplastic composite films, and has broad application prospects. Description of the Drawings

[0054] Figure 1This is the comparison chart of the total ion current chromatogram of the sizing agent prepared by the present invention and the traditional preparation process;

[0055] Figure 2 These are the infrared spectrograms of polyimide (PI) and the polyamic acid salts (PAAs) of the present invention;

[0056] Figure 3 This is the structural schematic diagram of the dilution type Ubbelohde viscometer used when testing the viscosity-average molecular weight of the water-soluble polyamic acid salt of the present invention;

[0057] Figure 4 These are the photos of the relatively hard solid product with gelation formed in Comparative Example 1. Detailed implementation manners

[0058] The present invention will be further described below in conjunction with the detailed implementation manners. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0059] In the examples, the test method for the viscosity-average molecular weight of the water-soluble polyamic acid salt: Use a dilution type Ubbelohde viscometer with a diameter of 0.59 mm (as Figure 3 shown), use water as the blank solvent, and test the efflux time of the polyamic acid salt with a concentration of 1 g / dL in a constant temperature water bath at 25 ± 0.1 °C. Take the average value of 5 groups of effective times with an error less than 0.3 s to obtain its viscosity-average molecular weight according to the formula; The steps for obtaining the efflux time are as follows:

[0060] (a) Clean the viscometer and adjust the water bath temperature to 25 0.1 °C;

[0061] (b) Prepare a test solution of the polyamic acid salt with a concentration of 1 dg / L;

[0062] (c) Clamp the viscometer and place it in the constant temperature water bath so that the G bulb is completely submerged below the water surface. Inject about 20 ml of the blank solvent from the A tube with a sintered glass funnel and balance it in the constant temperature water bath for 15 minutes;

[0063] (d) Clamp the C tube, use a syringe to draw the blank solvent from the B tube above the G bulb, open the C tube, and record the time t for the blank solvent to flow from the graduation line a to the graduation line b 0；

[0064] (e) Wash the viscometer with water, dry it, and place it in the water bath to balance;

[0065] (f) Repeat steps (c) and (d), replace the blank solvent with the test solution, and record the time t for the test solution to flow from graduation line a to graduation line b.

[0066] According to formulas (1)-(5), the viscosity-average molecular weight of the water-soluble polyamide salt can be obtained:

[0067] (1);

[0068] (2);

[0069] (3);

[0070] (4);

[0071] (5);

[0072] In the formulas:

[0073] t 0 is the efflux time of the blank solvent, s;

[0074] t is the efflux time of the test solution, s;

[0075] η sp is the specific viscosity of the test solution, dL / g;

[0076] η r is the relative viscosity of the test solution, dL / g;

[0077] η is the intrinsic viscosity of the test solution, dL / g;

[0078] c is the concentration of the test solution, g / dL;

[0079] K 、 α are constants, which can be obtained by referring to the polymer handbook, and are 0.079 and 0.72 respectively;

[0080] M v is the viscosity-average molecular weight, g / mol.

[0081] Example 1

[0082] A preparation method of a water-soluble polyamide salt, the specific steps are as follows:

[0083] (1) Raw material preparation:

[0084] Aromatic dianhydride monomer: 4,4'-oxydiphthalic dianhydride;

[0085] Aromatic diamine monomer: p-phenylenediamine;

[0086] End-capping agent: 4-methylphthalic anhydride;

[0087] Organic base: triethylamine;

[0088] Water;

[0089] (2) Preparation of water-soluble polyamide acid salt:

[0090] (2.1) Preparation of the first solution: Mix the aromatic dianhydride monomer and water at a molar ratio of 1:12, and stir at 140 °C for 3.5 h under the protection of nitrogen or inert gas;

[0091] Prepare the second solution: Mix the aromatic diamine monomer, organic base and water, and stir at 25 °C for 30 min under the protection of nitrogen or inert gas;

[0092] (2.2) After mixing the first solution and the second solution, carry out a polymerization reaction at 10 °C (under the protection of nitrogen or inert gas). When the viscosity-average molecular weight of the polyamide acid salt in the final polymerization system is 8.0×10 3 g / mol, stop the polymerization reaction, add the end-capping agent and continue stirring until the end-capping agent is completely dissolved, and remove water to obtain the water-soluble polyamide acid salt;

[0093] Among them, the feeding amount of the aromatic dianhydride monomer in the reaction system is 11.6 mol, and the molar ratio of the aromatic diamine monomer, aromatic dianhydride monomer and end-capping agent is 3:2:2, and the molar ratio of the organic base to the aromatic dianhydride monomer is 1.6:1; the total volume of the reaction system is 50 L, and the solid content of the reaction system before removing water is 18 wt%.

[0094] The characteristic functional groups of polyamide acid salt (PAAs) and polyimide (PI) were characterized by Fourier transform infrared spectroscopy (FTIR) analysis method (as Figure 2 shown), and the benzene ring absorption peak at 1525 cm -1 shared by PAAs and PI was used as the standard comparison for spectral analysis; from the FTIR curve of PAAs, the broad characteristic absorption band between 3100 - 3400 cm -1 represents the stretching vibration of the N-H bond, and this absorption peak disappears in the FTIR curve of PI. On the FTIR curve of PI, 1732 cm -1 , 1364 cm -1 , 745 cm -1The absorption bands respectively represent the symmetric stretching of -C=O, the stretching vibration of -C-N, and the bending vibration of -C=O (also known as the deformation vibration of the imide ring) in the imide group. These three absorption bands are the characteristic absorption bands of PI; an absorption peak generated by the stretching vibration of C=C in the benzene ring can be observed at 1531 cm -1 ; These series of results confirm that under the catalytic action of an organic base (triethylamine), the polyamic acid salt is successfully synthesized in the present invention, and this polyamic acid salt can be in-situ converted into heat-resistant and stable PI under the composite forming processing conditions of 320-350 °C.

[0095] A preparation method of a water-soluble polyamic acid salt sizing agent. In the process of preparing the water-soluble polyamic acid salt above, the water removal operation in step (2.2) is omitted, and the water-soluble polyamic acid salt sizing agent is obtained.

[0096] Comparative Example 1

[0097] A preparation method of a water-soluble polyamic acid salt is basically the same as that of Example 1, except that: there is no step (2.1), and in step (2.2), after directly mixing the aromatic dianhydride monomer, the aromatic diamine monomer, the organic base and water, the polymerization reaction is carried out at 10 °C (under the protection of nitrogen or inert gas).

[0098] The results show that after reacting for 4 h, gelation occurs (as Figure 4 shown), and the water-soluble polyamic acid salt cannot be successfully prepared. The above experiments also confirm that even if other conditions such as the feeding amount, temperature, catalyst, etc. are kept consistent, if the aromatic dianhydride monomer is not pre-dissolved, the reaction will still get out of control and gelation will occur. This fully shows that the dissolution order is not just a simple process adjustment, but a necessary condition to ensure the success of the technical solution.

[0099] Example 2

[0100] A preparation method of a water-soluble polyamic acid salt, the specific steps are as follows:

[0101] (1) Raw material preparation:

[0102] Aromatic dianhydride monomer: 3,3',4,4'-biphenyl dianhydride;

[0103] Aromatic diamine monomer: m-phenylenediamine;

[0104] End-capping agent: 4-tert-butylphthalic anhydride;

[0105] Organic base: ammonia;

[0106] Water;

[0107] (2) Preparation of water-soluble polyamic acid salt:

[0108] (2.1) Preparation of the first solution: Mix an aromatic dianhydride monomer and water at a molar ratio of 1:30, and under the protection of nitrogen or inert gas, stir at 150 °C for 2.5 h;

[0109] Preparation of the second solution: Mix an aromatic diamine monomer, an organic base and water, and under the protection of nitrogen or inert gas, stir at 40 °C for 15 min;

[0110] (2.2) After mixing the first solution and the second solution, carry out a polymerization reaction at 40 °C (under the protection of nitrogen or inert gas). When the viscosity-average molecular weight of the polyamic acid salt in the final polymerization system is 1.0×10 4 g / mol, stop the polymerization reaction, add a capping agent thereto and continue stirring until the capping agent is completely dissolved, and remove water to obtain a water-soluble polyamic acid salt;

[0111] Among them, the feeding amount of the aromatic dianhydride monomer in the reaction system is 3.16 mol, and the molar ratio of the aromatic diamine monomer, the aromatic dianhydride monomer and the capping agent is 5:4:2, and the molar ratio of the organic base to the aromatic dianhydride monomer is 2.4:1; the total volume of the reaction system is 40 L, and the solid content of the reaction system before removing water is 5 wt%.

[0112] A preparation method of a water-soluble polyamic acid salt sizing agent. In the process of preparing the water-soluble polyamic acid salt above, omit the water removal operation in step (2.2) to obtain the water-soluble polyamic acid salt sizing agent.

[0113] Example 3

[0114] A preparation method of a water-soluble polyamic acid salt, the specific steps are as follows:

[0115] (1) Raw material preparation:

[0116] Aromatic dianhydride monomer: Bisphenol A diether dianhydride;

[0117] Aromatic diamine monomer: 4,4-Diaminodiphenyl sulfone;

[0118] Capping agent: 4-Phenylethynylphthalic anhydride;

[0119] Organic base: Diethanolamine;

[0120] Water;

[0121] (2) Prepare a water-soluble polyamic acid salt;

[0122] (2.1) Preparation of the first solution: Mix an aromatic dianhydride monomer and water at a molar ratio of 1:25, and under the protection of nitrogen or inert gas, stir at 100 °C for 5 h;

[0123] Preparation of the second solution: Mix the aromatic diamine monomer, organic base and water, and then stir at 35 °C for 25 min under the protection of nitrogen or inert gas;

[0124] (2.2) Mix the first solution and the second solution, and then carry out a polymerization reaction at 70 °C (under the protection of nitrogen or inert gas). When the viscosity-average molecular weight of the polyamic acid salt in the final polymerization system reaches 1.1×10 4 g / mol, stop the polymerization reaction, add a capping agent thereto and continue stirring until the capping agent is completely dissolved, and remove water to obtain a water-soluble polyamic acid salt;

[0125] Among them, the feeding amount of the aromatic dianhydride monomer in the reaction system is 7.1 mol, the molar ratio of the aromatic diamine monomer, aromatic dianhydride monomer and capping agent is 10:9:2, and the molar ratio of the organic base to the aromatic dianhydride monomer is 1.8:1; the total volume of the reaction system is 33 L, and the solid content of the reaction system before water removal is 20 wt%.

[0126] A preparation method of a water-soluble polyamic acid salt sizing agent. In the process of preparing the water-soluble polyamic acid salt as described above, omit the water removal operation in step (2.2) to obtain the water-soluble polyamic acid salt sizing agent.

[0127] Example 4

[0128] A preparation method of a water-soluble polyamic acid salt, and the specific steps are as follows:

[0129] (1) Raw material preparation:

[0130] Aromatic dianhydride monomer: pyromellitic dianhydride;

[0131] Aromatic diamine monomer: 4,4'-diaminodiphenylmethane;

[0132] Capping agent: 5-phenoxyisobenzofuran-1(3H)-one;

[0133] Organic base: dodecyltrimethylammonium chloride;

[0134] Water;

[0135] (2) Prepare a water-soluble polyamic acid salt;

[0136] (2.1) Prepare the first solution: Mix the aromatic dianhydride monomer and water with a molar ratio of 1:28, and then stir at 180 °C for 1 h under the protection of nitrogen or inert gas;

[0137] Prepare the second solution: Mix the aromatic diamine monomer, organic base and water, and then stir at 60 °C for 5 min under the protection of nitrogen or inert gas;

[0138] (2.2) After mixing the first solution and the second solution, carry out a polymerization reaction at 60 °C (protected by nitrogen or inert gas). When the viscosity-average molecular weight of the polyamic acid salt in the final polymerization system is 2.0×10 4 g / mol, stop the polymerization reaction, add a capping agent thereto and continue stirring until the capping agent is completely dissolved, and remove water to obtain a water-soluble polyamic acid salt;

[0139] Among them, the feeding amount of the aromatic dianhydride monomer in the reaction system is 3.6 mol, and the molar ratio of the aromatic diamine monomer, the aromatic dianhydride monomer, and the capping agent is 17:16:2, and the molar ratio of the organic base to the aromatic dianhydride monomer is 2.0:1; the total volume of the reaction system is 44 L, and the solid content of the reaction system before removing water is 8 wt%.

[0140] A preparation method of a water-soluble polyamic acid salt sizing agent. In the process of preparing the water-soluble polyamic acid salt as described above, omit the water removal operation in step (2.2) to obtain the water-soluble polyamic acid salt sizing agent.

[0141] Comparative Example 2

[0142] A preparation method of a water-soluble polyamic acid salt, which is basically the same as Example 4, except that: there is no step (2.1), and in step (2.2), the aromatic dianhydride monomer, the aromatic diamine monomer, the organic base and water are directly mixed and then carried out at 60 °C A polymerization reaction (protected by nitrogen or inert gas).

[0143] The results show that after reacting for 8 h, a gelation phenomenon occurs and a water-soluble polyamic acid salt cannot be successfully prepared.

[0144] Example 5

[0145] A preparation method of a water-soluble polyamic acid salt, the specific steps are as follows:

[0146] (1) Raw material preparation:

[0147] Aromatic dianhydride monomer: 3,3',4,4'-benzophenone dianhydride;

[0148] Aromatic diamine monomer: 4,4'-diaminobenzanilide;

[0149] Capping agent: 5-(4-(phenylethynyl)phenoxy)isobenzofuran-1,3-dione;

[0150] Organic base: triethanolamine;

[0151] Water;

[0152] (2) Prepare a water-soluble polyamic acid salt;

[0153] (2.1) Preparation of the first solution: Mix an aromatic dianhydride monomer and water in a molar ratio of 1:16, and under the protection of nitrogen or inert gas, stir at 120 °C for 4 h;

[0154] Preparation of the second solution: Mix an aromatic diamine monomer, an organic base and water, and under the protection of nitrogen or inert gas, stir at 50 °C for 10 min;

[0155] (2.2) After mixing the first solution and the second solution, carry out a polymerization reaction at 80 °C (under the protection of nitrogen or inert gas). When the viscosity-average molecular weight of the polyamic acid salt in the final polymerization system is 1.3×10 4 g / mol, stop the polymerization reaction, add a capping agent and continue stirring until the capping agent is completely dissolved, and remove water to obtain a water-soluble polyamic acid salt;

[0156] Among them, the feeding amount of the aromatic dianhydride monomer in the reaction system is 2.4 mol, and the molar ratio of the aromatic diamine monomer, the aromatic dianhydride monomer and the capping agent is 12:11:2, and the molar ratio of the organic base to the aromatic dianhydride monomer is 2.2:1; the total volume of the reaction system is 13 L, and the solid content of the reaction system before removing water is 17 wt%.

[0157] A preparation method of a water-soluble polyamic acid salt sizing agent. In the process of preparing the water-soluble polyamic acid salt above, omit the water removal operation in step (2.2) to obtain the water-soluble polyamic acid salt sizing agent.

[0158] Example 6

[0159] A preparation method of a water-soluble polyamic acid salt, the specific steps are as follows:

[0160] (1) Raw material preparation:

[0161] Aromatic dianhydride monomer: methyl pyromellitic dianhydride;

[0162] Aromatic diamine monomer: 3,3'-sulfonylbisaniline;

[0163] Capping agent: a mixture of 4-methylphthalic anhydride and 4-phenylethynylphthalic anhydride with a mass ratio of 1:1;

[0164] Organic base: N,N-dimethylethanolamine;

[0165] Water;

[0166] (2) Preparation of water-soluble polyamic acid salt:

[0167] (2.1) Preparation of the first solution: Mix an aromatic dianhydride monomer and water in a molar ratio of 1:20, and under the protection of nitrogen or inert gas, stir at 160 °C for 1.5 h;

[0168] Preparation of the second solution: After mixing the aromatic diamine monomer, organic base and water, under the protection of nitrogen or inert gas, stir at 30 °C for 20 min;

[0169] (2.2) After mixing the first solution and the second solution, carry out a polymerization reaction at 20 °C (under the protection of nitrogen or inert gas). When the viscosity-average molecular weight of the polyamic acid salt in the final polymerization system is 1.6×10 4 g / mol, stop the polymerization reaction, add a capping agent thereto and continue stirring until the capping agent is completely dissolved, and remove water to obtain a water-soluble polyamic acid salt;

[0170] Among them, the feeding amount of the aromatic dianhydride monomer in the reaction system is 1.4 mol, and the molar ratio of the aromatic diamine monomer, aromatic dianhydride monomer and capping agent is 15:14:2, and the molar ratio of the organic base to the aromatic dianhydride monomer is 2.1:1; the total volume of the reaction system is 4 L, and the solid content of the reaction system before removing water is 25 wt%.

[0171] A preparation method of a water-soluble polyamic acid salt sizing agent. During the preparation of the water-soluble polyamic acid salt as described above, the water removal operation in step (2.2) is omitted to obtain a water-soluble polyamic acid salt sizing agent.

[0172] Example 7

[0173] A preparation method of a water-soluble polyamic acid salt, which is basically the same as Example 6, except that: the feeding amount of the aromatic dianhydride monomer in the reaction system of this example is 0.2 mol, and the total volume of the reaction system is 0.5 L;

[0174] The viscosity-average molecular weight of the finally prepared water-soluble polyamic acid salt is 1.4×10 4 g / mol.

[0175] A preparation method of a water-soluble polyamic acid salt sizing agent, the same as Example 6.

[0176] Example 8

[0177] A preparation method of a water-soluble polyamic acid salt, which is basically the same as Example 6, except that: the molar ratio of the aromatic diamine monomer, aromatic dianhydride monomer and capping agent in the reaction system of this example is 5:3:4;

[0178] The viscosity-average molecular weight of the finally prepared water-soluble polyamic acid salt is 6.0×10 3 g / mol.

[0179] Application Example 1

[0180] An application of a water-soluble polyamic acid salt sizing agent, sizing carbon fiber, and the specific steps are as follows:

[0181] 1) Take the water-soluble polyamide acid sizing agent stored at low temperature (prepared in Example 1) and place it in the sizing tank. Control the amount of water in the sizing tank to dilute the water-soluble polyamide acid sizing agent to a concentration of 2.0 wt%.

[0182] 2) Directly pass the carbon fiber after electrochemical treatment on the carbon fiber production line through the sizing tank for sizing, and the sizing time is 15 s.

[0183] 3) Dry and wind up the sized carbon fiber. The drying temperature is 120 °C and the drying time is 50 s.

[0184] Application Example 2

[0185] An application of a water-soluble polyamide acid sizing agent for sizing carbon fiber, and the specific steps are as follows:

[0186] 1) First, heat-ablatively remove the surface thermosetting sizing agent of the carbon fiber sized with the thermosetting sizing agent and set it aside for later use.

[0187] 2) Activate the carbon fiber by plasma treatment to introduce oxygen-containing groups (such as carboxyl groups, hydroxyl groups, etc.) on its surface and increase the surface roughness of the fiber.

[0188] 3) Dissolve the stored water-soluble polyamide acid sizing agent (prepared in Example 2) in water at 60 °C and dilute it to a concentration of 1.5 wt%. After impregnating the activated carbon fiber in it for 20 s, take it out in sequence, drain the excess sizing agent, and dry it.

[0189] Application Example 3

[0190] An application of a water-soluble polyamide acid sizing agent for sizing carbon fiber, and the specific steps are as follows:

[0191] 1) Heat and reflux the carbon fiber sized with the thermosetting sizing agent in an acetone solution. After removing the surface thermosetting sizing agent, wash it with water (to remove the acetone on the surface of the carbon fiber) and dry it in sequence.

[0192] 2) Activate the oxygen-containing groups on the surface of the carbon fiber with mesoxalic acid or acid anhydride, wash it with water until it is neutral, and then dry it.

[0193] 3) Dissolve the stored water-soluble polyamide acid sizing agent (prepared in Example 3) in water and dilute it to a concentration of 1.0 wt%. After impregnating the activated carbon fiber in it for 5 min, take it out in sequence, drain the excess sizing agent, and dry it.

[0194] The present invention further explores the environmental friendliness of the water-soluble polyamide acid sizing agent prepared by the present invention during use;

[0195] Using the polyamic acid salt obtained by polymerization in an organic solvent followed by ionization with the organic base triethylamine as the reference group (traditional preparation process), the sizing agent of the present invention is used as the experimental group; the sample amount of both groups is 1 g, and N-methylpyrrolidone (NMP) is added as a calibration substance at a ratio of 1 g / ml to test the content of triethylamine in the sizing agent; the test results are as Figure 1 shown. The relative proportions of the total amount of triethylamine in the reference group and the experimental group in the system are 7.53% and 3.27% respectively. This result indicates that the content of free amine in the sizing agent of the present invention is significantly reduced, verifying the environmental friendliness during its use (almost no amine smell can be detected during use).

Claims

1. A one-pot aqueous-phase preparation method of a water-soluble polyamide acid salt, with water as the reaction medium and aromatic dianhydride monomers and aromatic diamine monomers as the reaction raw materials, characterized in that, The aromatic dianhydride monomer is first completely dissolved in water and then mixed with the aromatic diamine monomer.

2. The aqueous one-pot preparation method of a water-soluble polyamide salt according to claim 1, characterized in that, The specific steps are as follows: (a) Completely dissolve the aromatic dianhydride monomer in water to obtain a first solution. At the same time, completely dissolve the aromatic diamine monomer and the organic base in water to obtain a second solution; (b) Mix the first solution and the second solution and carry out a polymerization reaction. After the polymerization reaction is completed, add a capping agent thereto and continue stirring until the capping agent is completely dissolved, and remove water to obtain a water-soluble polyamic acid salt.

3. The one-pot aqueous-phase preparation method of a water-soluble polyamide acid salt according to claim 2, characterized in that, The aromatic dianhydride monomer is one or more of 4,4'-biphenylene ether dianhydride, 3,3',4,4'-benzophenone dianhydride, 3,3',4,4'-biphenyl dianhydride, bisphenol A diether dianhydride, hexafluorodiacid dianhydride, pyromellitic dianhydride, methylpyromellitic dianhydride, dimethylpyromellitic dianhydride, ethylpyromellitic dianhydride, diethylpyromellitic dianhydride, phenylpyromellitic dianhydride, diphenylpyromellitic dianhydride, 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride; The aromatic diamine monomer is one or more of p-phenylenediamine, m-phenylenediamine, 1,1-m-xylenediamine, 4,4-diaminodiphenyl sulfone, 3,3'-sulfonylbisaniline, 4,4'-diaminobenzanilide, 3,3'-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzoxazole, 2-(4-aminophenyl)-5-aminobenzimidazole, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl ethane, bisphenol A diether diamine, 2,7-diaminofluorene, 4,4-diaminoheptanediamine, 3,4-diaminothiophene; The organic base is one or more of ammonia, diethanolamine, triethanolamine, triethylamine, N,N-dimethylethanolamine, benzimidazole, 1-methylimidazole, 1,2-dimethylimidazole, 1,8-diazabicycloundec-7-ene, dodecyltrimethylammonium chloride, quinoline, pyridine, 3-methylpyridine; The capping agent is one or more of 4-methylphthalic anhydride, 4-tert-butylphthalic anhydride, 4-phenylethynylphthalic anhydride, 5-phenoxyisobenzofuran-1(3H)-one, 5-(4-(phenylethynyl)phenoxy)isobenzofuran-1,3-dione; 4. The one-pot aqueous-phase preparation method of a water-soluble polyamide acid salt according to claim 2, characterized in that, The preparation process of the first solution is as follows: Mix the aromatic dianhydride monomer and water at a molar ratio of 1:12 - 30, and under the protection of nitrogen or inert gas, stir at 100 - 180 °C for 1 - 5 h; The preparation process of the second solution is as follows: Mix the aromatic diamine monomer, the organic base and water, and under the protection of nitrogen or inert gas, stir at 25 - 60 °C for 5 - 30 min; The polymerization reaction is carried out under the protection of nitrogen or inert gas, and the temperature of the polymerization reaction is 10 - 80 °C; The molar ratio of the aromatic diamine monomer, the aromatic dianhydride monomer, and the capping agent is 3 - 17:2 - 16:2; the molar ratio of the organic base to the aromatic dianhydride monomer is 1.6 - 2.4:1; the solid content of the reaction system before removing water is 5 - 25 wt%.

5. The one-pot aqueous-phase preparation method of a water-soluble polyamide acid salt according to claim 1, characterized in that, The highest feeding amount of the aromatic dianhydride monomer in the reaction system is 11.6 mol, and the highest total volume of the reaction system is 50 L.

6. A one-pot aqueous-phase preparation method of a water-soluble polyamide acid salt according to any one of claims 1-5, characterized in that, The viscosity-average molecular weight of the water-soluble polyamide salt is 8.0×10 3 -2.0×10 4 g / mol.

7. A water-soluble polyamide acid salt, characterized in that It is prepared by using the one-pot aqueous-phase preparation method of a water-soluble polyamide salt described in any one of claims 1-6.

8. A one-pot aqueous-phase preparation method of a water-soluble polyamide acid sizing agent, characterized in that, In the process of preparing the water-soluble polyamide salt by using the one-pot aqueous-phase preparation method of a water-soluble polyamide salt described in claim 6, the operation of removing water is omitted, and the water-soluble polyamide salt sizing agent is obtained.

9. A water-soluble polyamide acid sizing agent, characterized in that, It is prepared by using the one-pot aqueous-phase preparation method of a water-soluble polyamide salt sizing agent described in claim 8.

10. The application of a water-soluble polyamide salt sizing agent as described in claim 9, characterized in that, It is used for sizing carbon fibers.

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