Diamine monomer, polyamic acid salt, sizing agent, preparation methods of diamine monomer, polyamic acid salt and sizing agent, and resin / fiber composite material

Abstract

The invention relates to the field of organic materials, in particular to a diamine monomer, polyamide acid salt, a sizing agent, a preparation method and a resin / fiber composite material. According to the preparation method of the diamine monomer provided by the invention, a compound I and a compound II react to form the diamine monomer as shown in a formula III. The diamine monomer is used as a raw material for preparing the sizing agent, so that the obtained sizing agent has excellent thermal stability, storage and transportation stability and water solubility, interface bonding with CF and resin can be improved, and a composite material is endowed with excellent mechanical properties and interface properties.

Description

Technical Field

[0001] The present invention relates to the field of organic materials, and particularly to a diamine monomer, a polyamic acid salt, a sizing agent, a preparation method thereof, and a resin / fiber composite material. Background Art

[0002] High-performance resin / carbon fiber (CF) composite materials such as polyimide (PI), polyetheretherketone (PEEK), polyethersulfone (PES), and polyphenylene sulfide (PPS) have outstanding advantages such as high specific strength, high specific modulus, excellent thermal stability, and can be formed in various ways, and have important applications in high-tech fields such as ships, vehicles, and medical materials. In the resin / CF composite material, the sizing agent plays a role in transferring stress from the resin to the fiber. If the interfacial bonding is weak, the composite material will show delamination and slippage under fatigue load. Improving the bonding between CF and the resin matrix resin and reducing the energy consumption at the interface are the keys to improving the performance of composite products. At the same time, the sizing agent can effectively reduce the occurrence of carbon fiber fracture and the hairiness rate, and improve the bundling and wear resistance.

[0003] Currently, commonly used sizing agents are mostly prepared from main polymers such as epoxy resin and vinyl resin. The carbon fibers sized with them are suitable for thermosetting resin matrices. There are few reactive groups participating in the reaction in the molecular chains of resins such as PPS and PEEK, and it is difficult to undergo a chemical bonding reaction with thermosetting sizing agents, resulting in poor compatibility with the sizing agent and low interfacial bonding force. Moreover, the molding temperatures of PI, PES, PPS, and PEEK resins are above 300°C. The high temperature during the melt processing will cause the oxidation and decomposition of the thermosetting sizing agent, forming holes and defects at the interface, resulting in a decline in the comprehensive performance of composite products. Therefore, it is reasonable and necessary to design and develop a high heat-resistant sizing agent to meet the application requirements of high-performance composite materials.

[0004] Foreign CF manufacturers have invested a large amount of research in high-temperature thermoplastic sizing agents and have developed various series of sizing agents suitable for their own products. However, due to the components of the sizing agent belonging to the technical secrets of each company, only extremely limited information can be obtained through patents. The research on high-temperature thermoplastic sizing agents in China is still in its infancy, and there are no commercial sizing agent products. Summary of the Invention

[0005] In view of this, the present invention provides a diamine monomer, a polyamic acid salt, a sizing agent, a preparation method thereof, and a resin / fiber composite material. The diamine monomer provided by the present invention, as a raw material for preparing the sizing agent, can enable the obtained sizing agent to have excellent thermal stability, storage and transportation stability, water solubility, and can also improve the interfacial bonding with CF and the resin, endowing the composite material with excellent mechanical properties and interfacial properties.

[0006] The present invention provides a preparation method of a diamine monomer, comprising:

[0007] Compound I reacts with Compound II to form a diamine monomer represented by Formula III;

[0008] Wherein,

[0009] The structure of the said Compound I is as follows:

[0010]

[0011] R1 is selected from: -COOH, -COCl;

[0012] R2 is selected from: -NH2, -COOH, -COCl;

[0013] The said Compound II is selected from at least one of Formula II-1 to Formula II-4, the hydrochloride of Formula II-1 to the hydrochloride of Formula II-4:

[0014]

[0015] The obtained diamine monomer represented by Formula III includes at least one of the following Formula III-1a to Formula III-2b:

[0016]

[0017] Preferably, the molar ratio of the said Compound I to Compound II is 1.05:0.5 to 1:2.1;

[0018] The temperature of the said reaction is 170 - 220 °C, and the time is 5 - 16 h.

[0019] Preferably, it includes: under a protective atmosphere, adding a solvent, Compound I, a reducing agent and Compound II into a reactor, stirring until no more HCl gas volatilizes, adding a water absorbent, then heating to a first temperature, and then continuing to heat to the target reaction temperature for reaction to form a diamine monomer represented by Formula III.

[0020] The present invention also provides a diamine monomer prepared by the preparation method described in the above technical solution.

[0021] The present invention also provides a preparation method of a polyamic acid salt, including the following steps:

[0022] (A) A dianhydride monomer reacts with a diamine monomer to form a polyamic acid;

[0023] (B) The said polyamic acid reacts with an organic amine to form a polyamic acid salt;

[0024] Wherein,

[0025] The said diamine monomer includes the diamine monomer described in the above technical solution.

[0026] Preferably, the diamine monomer is the diamine monomer described in the above technical solution, or is the diamine monomer described in the above technical solution and the diamine monomer represented by Formula V;

[0027] The diamine monomer represented by Formula V is selected from at least one of Formula V-1 to Formula V-5:

[0028]

[0029] Among them,

[0030] X is selected from: O, S, C(CF3);

[0031] Y is selected from: O, N, S;

[0032] The dianhydride monomer is an aromatic dianhydride monomer, and is selected from at least one of Formula IV-1 to Formula IV-13:

[0033]

[0034] The organic amine is at least one of triethylamine and N,N-dimethylethanolamine.

[0035] The present invention also provides a polyamic acid salt prepared by the preparation method described in the above technical solution.

[0036] The present invention also provides a preparation method of a sizing agent, including: dissolving the polyamic acid salt in a solvent to obtain a sizing agent;

[0037] Among them, the polyamic acid salt is the polyamic acid salt described in the above technical solution.

[0038] The present invention also provides a sizing agent prepared by the preparation method described in the above technical solution.

[0039] The present invention also provides a resin / fiber composite material, and the sizing agent used therein is the sizing agent described in the above technical solution.

[0040] The present invention prepares a polyamic acid solution by polycondensation of a dianhydride and a diamine monomer, then adds an organic amine to the polyamic acid solution to prepare a polyamic acid salt solution, removes the solvent from the above solution to obtain a polyamic acid salt powder, and dissolves it in water to obtain an aqueous polyimide sizing agent; among them, the diamine monomer used includes the diamine monomer represented by Formula III. The sizing agent prepared by the present invention has excellent thermal stability, storage and transportation stability, and water solubility, can improve the bundling property and wear resistance of carbon fibers, improve the interfacial bonding with CF and resin, and endow the composite material with excellent mechanical properties and interfacial properties. Description of the Drawings

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0042] Figure 1 1H NMR spectrum of the diamine monomer obtained in Example 1 of the present invention 1 ;

[0043] Figure 2 Differential scanning calorimetry (DSC) curve of the sizing agent obtained in Example 2 of the present invention;

[0044] Figure 3 Thermogravimetric analysis (TGA) curve of the sizing agent obtained in Example 2 of the present invention;

[0045] Figure 4 Product drawing of CF sized with the sizing agent of Example 2 of the present invention. Detailed implementation manners

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in the description of this application herein are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0047] In this article, among the technical features described in an open-ended manner, it includes a closed technical solution composed of the listed features, and also includes an open technical solution containing the listed features.

[0048] The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0049] In this article, regarding numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to an integer, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0050] In this article, regarding the unit of a data range, if the unit is only attached after the right endpoint, it means that the units of the left endpoint and the right endpoint are the same. For example, 170~220 °C means that the units of the left endpoint "170" and the right endpoint "220" are both °C.

[0051] The present invention provides a method for preparing a diamine monomer, comprising:

[0052] Compound I reacts with Compound II to form a diamine monomer represented by Formula III;

[0053] Wherein,

[0054] The structure of the said Compound I is as follows:

[0055]

[0056] R1 is selected from: -COOH, -COCl;

[0057] R2 is selected from: -NH2, -COOH, -COCl;

[0058] The said Compound II is selected from at least one of Formula II-1 to Formula II-4, the hydrochloride of Formula II-1 to the hydrochloride of Formula II-4:

[0059]

[0060] The obtained diamine monomer represented by Formula III includes at least one of the following Formula III-1a to Formula III-2b:

[0061]

[0062] The present invention uses Compound I to react with Compound II to form a diamine monomer represented by Formula III; using the above diamine monomer as a raw material for preparing a sizing agent can enable the obtained sizing agent to have excellent thermal stability, storage and transportation stability, water solubility, can improve the bundling property and wear resistance of carbon fibers, and improve the interfacial properties of composite materials.

[0063] In the present invention, the structure of the said Compound I is as follows:

[0064]

[0065] R1 is selected from: -COOH (carboxyl group), -COCl (acyl chloride group, i.e., );

[0066] R2 is selected from: -NH2 (amino group), -COOH (carboxyl group), -COCl (acyl chloride group, i.e., ).

[0067] In the present invention, preferably, the said Compound I is at least one of 1,3-adamantanedicarboxylic acid and 1,3-adamantanediacyl chloride. The present invention has no special restrictions on the source of Compound I, and it can be a commercially available product or prepared according to known preparation methods in the art.

[0068] In the present invention, the compound II is selected from at least one of the formulas II-1 to II-4 shown above, and the hydrochloride salts of the formulas II-1 to II-4. The present invention has no special limitation on the source of the compound II, and it can be a commercially available product or prepared according to known preparation methods in the art.

[0069] In the present invention, the molar ratio of the compound I to the compound II is preferably 1.05:0.5 to 1:2.1.

[0070] In the present invention, the reaction is preferably carried out in a solvent medium. The solvent is preferably at least one of polyphosphoric acid and sulfuric acid. Among them, the sulfuric acid is preferably concentrated sulfuric acid. In the present invention, the amount of the solvent used is preferably 5 to 15 times the mass of the compound II, specifically 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times, 12 times, 13 times, 14 times, 15 times.

[0071] In the present invention, the reaction is preferably carried out in the presence of a reducing agent. In the present invention, the reducing agent is preferably at least one of tin powder and stannous chloride. Among them, the stannous chloride can be anhydrous stannous chloride or stannous chloride dihydrate. In the present invention, the amount of the reducing agent used is preferably 5% to 30% of the molar amount of the compound II, specifically 5%, 10%, 15%, 20%, 25%, 30%.

[0072] In the present invention, the reaction is preferably carried out in the presence of a water absorbent. In the present invention, the water absorbent is preferably at least one of phosphorus pentoxide (P2O5) and magnesium sulfate (MgSO4). In the present invention, the amount of the water absorbent used is preferably 0.5 to 2 times the molar amount of the compound I, specifically 0.5 times, 1 times, 1.5 times, 2 times.

[0073] In the present invention, the reaction is preferably carried out in a protective atmosphere. The present invention has no special limitation on the protective atmosphere, and it can be a conventional protective atmosphere in the art, preferably a nitrogen atmosphere or an argon atmosphere.

[0074] In the present invention, the temperature of the reaction is preferably 170 to 220 °C, specifically 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, 205 °C, 210 °C, 215 °C, 220 °C. The reaction time is preferably 5 to 16 h, specifically 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h.

[0075] In the present invention, preferably, the preparation method comprises: adding a solvent, Compound I, a reducing agent and Compound II into a reactor under a protective atmosphere, stirring until no more HCl gas volatilizes, adding a water absorbent, then heating to a first temperature, and further heating to a target reaction temperature for reaction to form a diamine monomer represented by Formula III.

[0076] Wherein:

[0077] When adding Compound II, it is preferably added in batches. After the feeding is completed, stirring is carried out until no more HCl gas volatilizes; wherein, the stirring rate is preferably 100 - 500 rpm. After adding the water absorbent, stirring is preferably carried out to mix the materials evenly, and then heating is started. When heating, first heat to the first temperature; the first temperature is preferably 150 - 170 °C, specifically 150 °C, 155 °C, 160 °C, 165 °C, 170 °C. After heating to the first temperature, keep warm for 3 - 5 h, specifically 3 h, 4 h, 5 h. During the heat preservation process, stirring is preferably carried out; the stirring rate is preferably 100 - 500 rpm. After the above treatment, further heat to the target reaction temperature for reaction; the target reaction temperature is the 170 - 220 °C described above, specifically 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, 200 °C, 205 °C, 210 °C, 215 °C, 220 °C. After rising to the target reaction temperature, the reaction time is the 5 - 16 h described above, specifically 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, 13 h, 14 h, 15 h, 16 h. After the reaction is complete, cooling is preferably carried out, specifically cooling to room temperature, to obtain a reaction solution containing the diamine monomer represented by Formula III.

[0078] In the present invention, after the reaction of Compound I and Compound II, post-treatment is preferably carried out. The post-treatment preferably comprises: adjusting the pH value of the obtained reaction solution to 8 - 9, then washing, filtering, and drying to obtain a crude diamine product; then, purifying to obtain the diamine monomer represented by Formula III. Among them, the regulator used for adjusting the pH value is preferably a basic regulator, more preferably a saturated sodium carbonate solution; the pH value is specifically 8, 8.5, 9. After adjusting the pH value, the reactants in the system precipitate out, and then washing and filtering are carried out. The washing is preferably carried out by washing with water and ethanol in sequence. After washing and filtering, drying is carried out; after drying, a crude diamine product is obtained, and then, further purification is carried out to obtain the diamine monomer represented by Formula III.

[0079] In the present invention, after the reaction of Compound I and Compound II, a diamine monomer represented by Formula III is formed, and its reaction route is as follows:

[0080]

[0081] The diamine monomers represented by the obtained formula III include, but are not limited to, at least one of the following formulas III-1a to III-2b:

[0082]

[0083] The present invention also provides a diamine monomer prepared by the preparation method described in the foregoing technical solution.

[0084] The present invention also provides a method for preparing a polyamic acid salt, comprising the following steps:

[0085] (A) Reacting a dianhydride monomer with a diamine monomer to form a polyamic acid;

[0086] (B) Reacting the polyamic acid with an organic amine to form a polyamic acid salt;

[0087] Wherein,

[0088] The diamine monomer includes the diamine monomer represented by formula III described in the above technical solution.

[0089] Regarding step (A):

[0090] In the present invention, the diamine monomer includes the diamine monomer represented by formula III described in the above technical solution. Preferably, the diamine monomer is the diamine monomer represented by formula III described in the above technical solution, or is the diamine monomer represented by formula III described in the above technical solution and the diamine monomer represented by formula V;

[0091] Wherein, the diamine monomer represented by formula V is selected from at least one of formulas V-1 to V-5:

[0092]

[0093] Wherein,

[0094] X is selected from: O, S, C(CF3);

[0095] Y is selected from: O, N, S.

[0096] Preferably, the diamine monomer represented by formula V is selected from at least one of p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The present invention has no special limitation on the source of the diamine monomer represented by formula V, and it can be a commercially available product or prepared according to the known preparation methods in the art.

[0097] In the present invention, when the diamine monomer is the diamine monomer represented by Formula III and the diamine monomer represented by Formula V, the molar ratio of the diamine monomer represented by Formula III to the diamine monomer represented by Formula V is preferably 1:(0.1 - 10), specifically 1:0.1, 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10.

[0098] In the present invention, the dianhydride monomer is an aromatic dianhydride monomer, denoted as dianhydride monomer IV, and is preferably at least one of Formula IV-1 to Formula IV-13:

[0099]

[0100] The name abbreviations corresponding to the above Formula IV-1 to Formula IV-13 are as follows:

[0101]

[0102] The present invention has no special restrictions on the source of the dianhydride monomer, and it can be a commercially available product or prepared according to known preparation methods in the art.

[0103] In the present invention, the molar ratio of the diamine monomer to the dianhydride monomer is preferably 0.9:1 - 1:0.9, specifically 0.9:1, 1:1, 1:0.9.

[0104] In the present invention, the reaction is preferably carried out in an organic solvent. Among them, the organic solvent is preferably an aprotic solvent, more preferably including at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO). In the present invention, the amount of the organic solvent used is preferably such that the solid content of the system is 5wt% - 30wt%, specifically 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%.

[0105] In the present invention, the reaction is preferably carried out in a protective atmosphere. The present invention has no special restrictions on the protective atmosphere, and it can be a conventional protective atmosphere in the art, preferably a nitrogen atmosphere or an argon atmosphere.

[0106] In the present invention, the temperature of the reaction is preferably -5 - 30°C, specifically -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, 30°C. The reaction time is preferably 6 - 24h, specifically 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h. In the present invention, a polymerization reaction occurs between the dianhydride monomer and the diamine monomer to form polyamic acid; specifically, the dianhydride monomer and the diamine monomer react in a solvent to obtain a polyamic acid solution.

[0107] Regarding step (B):

[0108] In the present invention, the organic amine is preferably at least one of triethylamine and N,N - dimethylethanolamine. In the present invention, preferably, the dosage of the organic amine is 3 - 4 times the molar number of the dianhydride monomer in step (A), specifically, it can be 3 times, 3.5 times, or 4 times.

[0109] In the present invention, the reaction is preferably carried out in a protective atmosphere. The present invention has no special limitation on the protective atmosphere, and it can be a conventional protective atmosphere in the art, preferably a nitrogen atmosphere or an argon atmosphere.

[0110] In the present invention, the temperature of the reaction is preferably - 5 to 30 °C, specifically, it can be - 5 °C, 0 °C, 5 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C; more preferably, it is the same as the reaction temperature of step (A). For example, if 25 °C is adopted in step (A), then step (B) continues to carry out the reaction at this temperature. In the present invention, the reaction time is preferably 5 - 10 h, specifically, it can be 5 h, 6 h, 7 h, 8 h, 9 h, 10 h. In the present invention, stirring is preferably accompanied during the reaction process. Through the reaction of polyamic acid and organic amine, polyamic acid salt is formed in the system; specifically, since it is carried out in a solvent medium, a polyamic acid salt solution is obtained in the system.

[0111] In the present invention, after the above reaction, post - treatment is preferably carried out. The post - treatment is post - treatment for removing the solvent, preferably including: drying. In the present invention, the drying preferably includes one of vacuum drying, spray drying, and precipitation drying. The present invention removes the solvent in the polyamic acid salt solution through drying to obtain polyamic acid salt powder. Among them, the process of the precipitation drying preferably includes: precipitating and separating out the precipitate from the reaction solution obtained from the reaction, followed by solid - liquid separation and drying to obtain polyamic acid salt powder. Among them, the precipitation and separation is realized by the solvent precipitation method. Specifically, the polyamic acid salt solution is transferred to a precipitation solvent to precipitate the precipitate; among them, the precipitation solvent used is preferably acetone. After the precipitate is separated out, solid - liquid separation is carried out; the method of solid - liquid separation has no special limitation and can be a conventional solid - liquid separation means in the art, such as filtration. After solid - liquid separation, it is preferable to break the obtained solid matter. After the above treatment, drying is carried out. After drying, polyamic acid salt powder is obtained.

[0112] In the present invention, preferably, the above overall steps (A) - (B) specifically include: under a protective atmosphere, adding a dianhydride monomer, a diamine monomer, and a solvent into a reactor to carry out a polymerization reaction to form a polyamic acid solution; then, adding an organic amine into the reactor to react to obtain a polyamic acid salt solution; removing the solvent from the polyamic acid salt solution to obtain polyamic acid salt. The types of substances, dosages, conditions, etc. are all the same as those described in the previous technical solutions and will not be elaborated here one by one.

[0113] The present invention also provides a polyamic acid salt, which is prepared by the preparation method described in the above technical solution.

[0114] The present invention also provides a preparation method of a sizing agent, comprising: dissolving the polyamic acid salt in a solvent to obtain the sizing agent; wherein, the polyamic acid salt is the polyamic acid salt described in the above technical solution. The solvent is preferably water, more preferably pure water. The obtained sizing agent is a polyimide sizing agent, preferably an aqueous polyimide sizing agent. The concentration of the sizing agent can be prepared according to needs. In the present invention, other auxiliaries can also be added according to needs during the preparation of the sizing agent; the auxiliaries include one or more of surfactants, coupling agents, plasticizers, etc.

[0115] The present invention also provides a sizing agent, which is prepared by the preparation method described in the above technical solution.

[0116] The present invention also provides a resin / fiber composite material, and the sizing agent used therein is the sizing agent described in the above technical solution. Among them, the fiber is preferably carbon fiber (CF). The type of the resin is not particularly limited and can be a conventional resin in the art.

[0117] The present invention also provides a preparation method of the resin / fiber composite material described in the above technical solution, which is prepared by a molding process. The specific preparation process of the molding process is not particularly limited and can be carried out according to the conventional process for preparing resin / fiber composite materials in the art.

[0118] The present invention prepares a polyamic acid solution by polycondensation of a dianhydride and a diamine monomer, then adds an organic amine to the polyamic acid solution to prepare a polyamic acid salt solution, removes the solvent from the above solution to obtain a polyamic acid salt powder, and dissolves it in water to obtain an aqueous polyimide sizing agent; wherein, the diamine monomer used includes the diamine monomer shown in Formula III. The sizing agent prepared by the present invention has excellent thermal stability, storage and transportation stability, and water solubility, can improve the bundling property and wear resistance of carbon fibers, improve the interfacial bonding with CF and resin, and endow the composite material with excellent mechanical properties and interfacial properties.

[0119] Compared with the prior art, the present invention has the following beneficial effects: 1. The sizing agent obtained by the present invention has excellent heat resistance and can withstand a processing temperature of more than 300 °C for the resin; 2. The carbon fibers after sizing have the characteristics of low fuzzing amount, excellent wear resistance and fibrillating property; 3. The sizing agent also forms a good interfacial bonding with CF and resin, effectively transmits the load, and thus endows the composite material with excellent mechanical properties and interfacial properties.

[0120] To further understand the present invention, the preferred embodiments of the present invention will be described below in conjunction with examples. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0121] Example 1

[0122] Preparation of diamine monomer III-1a:

[0123] Heat polyphosphoric acid to 60 °C. Under nitrogen protection, add preheated polyphosphoric acid (1000 g), 1,3-adamantanedicarboxylic acid (44.85 g, 0.2 mol), stannous chloride dihydrate (0.02 mol, 4.513 g) to a 2 L three-necked flask, and add 2,4-diaminophenol dihydrochloride (78.824 g, 0.4 mol) in batches. After the addition is complete, stir for 3 h until no more HCl gas is volatilized. Then add phosphorus pentoxide (P2O5) (28.388 g, 0.2 mol) and stir for 0.5 h. Slowly raise the temperature to 150 °C and stir for 3 h, then raise the temperature to 200 °C and react for 10 h. After the reaction is complete, cool the resulting reaction solution to room temperature. Then adjust the pH value of the solution to 8.5 using saturated sodium carbonate solution, wash three times with water and ethanol respectively, filter, and dry to obtain the crude diamine product. After purification, a white solid is obtained with a yield of 77%.

[0124] Perform 1H NMR characterization on the purified product, and the results are as follows: 1 H NMR (500 MHz, DMSO-d6) δ = 7.30 (d, J = 8.6, 1H), 6.80 (d, J = 2.2, 1H), 6.59 (dd, J = 8.6, 2.3, 1H), 5.00 (s, 2H), 2.38 (s, 1H), 2.26 (p, J = 3.0, 1H), 2.11 (dd, J = 12.9, 3.0, 2H), 2.04 (d, J = 13.4, 2H), 1.81 (d, J = 3.2, 1H). For details, see Figure 1 。

[0125] The results show that the obtained diamine monomer has the structure shown in formula III-1a:

[0126]

[0127] Example 2

[0128] 1. Preparation of polyamic acid salt:

[0129] (A) Under nitrogen protection, 52.1 g (0.1 mol) of the bisphenol A dianhydride monomer BPADA shown in Formula IV-13, 40.1 g (0.1 mol) of the diamine shown in Formula (III-1a) in Example 1, and 800 g of DMAc solvent were added to a three-necked flask, and the reaction was stirred at room temperature for 24 h to obtain a polyamic acid solution.

[0130] (B) 30 g of triethylamine was added to the above three-necked flask, and the reaction was continuously stirred at room temperature for 5 h to obtain a polyamide salt solution. The polyamide salt solution was transferred to acetone for precipitation, filtered, broken, and dried to obtain a polyamide salt powder.

[0131] 2. Preparation of sizing agent:

[0132] The polyamide salt powder was dissolved in water to obtain a polyimide sizing agent with a solid content of 1%.

[0133] 3. Testing:

[0134] (3.1) Sizing agent performance

[0135] Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were performed on the sizing agent respectively, and the results are shown in Figure 1-2 and Table 1. In addition, the water solubility of the sizing agent was observed, and the results are shown in Table 1. In addition, the stability of the sizing agent was also tested. Specifically, after the sizing agent was prepared, it was left standing for 7 days, and then whether there were color changes and precipitation in the sizing agent was observed, and the results are shown in Table 1. In addition, the apparent viscosity of 10% solid content was also tested. Specifically, the polyamide salt powder was dissolved in water to prepare a sizing agent with a solid content of 10%, and then its apparent viscosity was tested, and the results are shown in Table 1.

[0136] Table 1: Performance of the sizing agent in Example 2

[0137] Item Result <![CDATA[T g (DSC), °C]]> 280 5% Thermal weight loss temperature, °C 519 Water-based 100% water-soluble, no precipitation Stability After 7 days, the sizing agent has no color change and precipitation Apparent viscosity of 10% solid content, Pa.s ＜0.05

[0138] From the test results in the above table, it can be seen that the T of the sizing agent obtained in Example 2 g reached 280 °C, and the 5% thermogravimetric temperature reached 519 °C, showing excellent heat resistance. At the same time, it can be dissolved in water by 100% without precipitation, having good water solubility, and can be used to prepare a water-based sizing agent, which is safe and environmentally friendly. After the sizing agent was left standing for 7 days, there were no color changes and precipitation, showing excellent stability. In addition, the apparent viscosity < 0.05 Pa·s at 10% solid content proved that the sizing agent was convenient for construction operation.

[0139] (3.2) Performance of the sizing agent when used in composites

[0140] Using the sizing agent to prepare a resin / carbon fiber composite: The T800 carbon fiber / PEEK prepreg tape was prepared by the suspension method, and the composite material was prepared by the compression molding processing technology.

[0141] The above process was carried out with an epoxy sizing agent and the PI sizing agent of Example 2 respectively, and then various performance tests were carried out on the two resulting composites. The results are shown in Table 2. Figure 4 Product drawing of CF sized with the sizing agent of Example 2 of the present invention.

[0142] Table 2: Performance of composites

[0143]

[0144]

[0145] It can be seen from the test results in the above table that, under the same fiber content, compared with the carbon fiber composite sized with epoxy, the tensile strength, compressive strength and interlaminar shear strength of the carbon fiber composite sized with the PI sizing agent of Example 2 of the present invention are significantly improved, proving that the sizing agent of the present invention can improve the bonding between CF and the resin matrix, effectively transfer the load, and endow the composite with excellent mechanical properties and interfacial properties.

[0146] Example 3

[0147] 1. Preparation of polyamic acid salt:

[0148] (A) Under nitrogen protection, 3,3',4,4'-biphenyltetracarboxylic dianhydride monomer BPDA (29.4 g, 0.1 mol) shown in Formula IV-1, diamine shown in Formula (III-1a) of Example 1 (40.1 g, 0.1 mol), and 650 g of DMAc solvent were added to a three-necked flask, and the mixture was stirred at room temperature for 24 h to obtain a polyamic acid solution.

[0149] (B) 30 g of triethylamine was added to the above three-necked flask, and the mixture was continuously stirred at room temperature for 5 h to obtain a polyamic acid salt solution. The polyamic acid salt solution was transferred to acetone for precipitation, filtered, broken wall, and dried to obtain polyamic acid salt powder.

[0150] 2. Preparation of sizing agent:

[0151] The polyamic acid salt powder was dissolved in water to obtain a polyimide sizing agent with a solid content of 0.5%.

[0152] Example 4

[0153] 1. Preparation of polyamic acid salt:

[0154] (A) Under nitrogen protection, add pyromellitic dianhydride monomer PMDA shown in Formula IV-4 (21.8 g, 0.1 mol), diamine shown in Formula (III-1a) in Example 1 (40.1 g, 0.1 mol), and 600 g of DMAc solvent to a three-necked flask, and stir and react at room temperature for 10 h to obtain a polyamic acid solution.

[0155] (B) Add 30 g of triethylamine to the above three-necked flask, continue to stir and react at room temperature for 2 h to obtain a polyamide salt solution. Transfer the polyamide salt solution to acetone for precipitation, filter, break the wall, and dry to obtain polyamide salt powder.

[0156] 2. Preparation of sizing agent:

[0157] Dissolve the polyamide salt powder in water to obtain a polyimide sizing agent with a solid content of 0.6%.

[0158] Example 5

[0159] 1. Preparation of polyamide salt:

[0160] (A) Under nitrogen protection, add 3,3',4,4'-biphenyltetracarboxylic dianhydride monomer BPDA shown in Formula IV-1 (29.4 g, 0.1 mol), diamine shown in Formula (III-1a) in Example 1 (20.1 g, 0.05 mol), p-phenylenediamine shown in Formula V-1 (5.4 g, 0.05 mol), and 550 g of DMAc solvent to a three-necked flask, and stir and react at room temperature for 12 h to obtain a polyamic acid solution.

[0161] (B) Add 28 g of N,N-dimethylethanolamine to the above three-necked flask, continue to stir and react at room temperature for 5 h to obtain a polyamide salt solution. Transfer the polyamide salt solution to acetone for precipitation, filter, break the wall, and dry to obtain polyamide salt powder.

[0162] 2. Preparation of sizing agent:

[0163] Dissolve the polyamide salt powder in water to obtain a polyimide sizing agent with a solid content of 0.5%.

[0164] Example 6

[0165] 1. Preparation of polyamide salt:

[0166] (A) Under nitrogen protection, add 3,3',4,4'-biphenyltetracarboxylic dianhydride BPDA (29.4 g, 0.1 mol), diamine with the structure shown in Formula (III-1a) in Example 1 (20.1 g, 0.05 mol), m-phenylenediamine shown in Formula V-1 (5.4 g, 0.05 mol), and 560 g of DMAc solvent to a three-necked flask, and react at room temperature for 12 h to obtain a polyamic acid solution.

[0167] (B) Add 28 g of N,N-dimethylethanolamine to the above three-necked flask, and continue stirring at room temperature for 5 h to obtain a polyamide acid salt solution. Transfer the polyamide acid salt solution to acetone for precipitation, filter, break the wall, and dry to obtain polyamide acid salt powder.

[0168] 2. Preparation of sizing agent:

[0169] Dissolve the polyamide acid salt powder in water to obtain a polyimide sizing agent with a solid content of 0.6%.

[0170] Example 7

[0171] 1. Preparation of polyamide acid salt:

[0172] (A) Under nitrogen protection, add 3,3',4,4'-biphenyl ether tetracarboxylic dianhydride ODPA (31.0 g, 0.1 mol), the diamine shown in formula (III-1a) in Example 1 (20.0 g, 0.05 mol), 4,4'-diaminodiphenyl ether shown in formula V-4 (10.1 g, 0.05 mol), and 580 g of DMAc solvent to the three-necked flask, and react at room temperature for 12 h to obtain a polyamide acid solution.

[0173] (B) Add 28 g of N,N-dimethylethanolamine to the above three-necked flask, and continue stirring at room temperature for 5 h to obtain a polyamide acid salt solution. Transfer the polyamide acid salt solution to acetone for precipitation, filter, break the wall, and dry to obtain polyamide acid salt powder.

[0174] 2. Preparation of sizing agent:

[0175] Dissolve the polyamide acid salt powder in water to obtain a polyimide sizing agent with a solid content of 0.8%.

[0176] Test the products of Examples 3 to 7 respectively according to the test method in Example 2. The results show that the sizing agents obtained in Examples 3 to 7 exhibit excellent heat resistance, water solubility, and stability, and the carbon fiber composites sized with them exhibit excellent mechanical properties and interfacial properties.

[0177] In this article, specific examples are used to elaborate on the principles and implementation modes of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that for those of ordinary skill in the art in the technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The protection scope of the present invention patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that have no substantial difference from the literal description of the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A method for preparing a diamine monomer, characterized in that Comprising: Compound I reacts with Compound II to form a diamine monomer represented by Formula III; Wherein, The structure of said Compound I is as follows: R1 is selected from: -COOH, -COCl; R2 is selected from: -NH2, -COOH, -COCl; Said Compound II is selected from at least one of Formula II-1 to Formula II-4, the hydrochloride salt of Formula II-1 to the hydrochloride salt of Formula II-4: The obtained diamine monomer represented by Formula III includes at least one of the following Formula III-1a to Formula III-2b:

2. The preparation method according to claim 1, characterized in that, The molar ratio of said Compound I to Compound II is 1.05:0.5 to 1:2.1; The temperature of said reaction is 170 - 220 °C, and the time is 5 - 16 h.

3. The preparation method according to claim 1, characterized in that, Comprising: Under a protective atmosphere, a solvent, Compound I, a reducing agent and Compound II are added to a reactor, stirred until no more HCl gas volatilizes, an absorbent is added, then the temperature is raised to a first temperature, and then further raised to the target reaction temperature for reaction to form a diamine monomer represented by Formula III.

4. A diamine monomer, characterized in that, Prepared by the preparation method according to any one of Claims 1 - 3.

5. A method for preparing a polyamic acid salt, characterized in that, Comprising the following steps: (A) The dianhydride monomer reacts with the diamine monomer to form polyamic acid; (B) The polyamic acid reacts with an organic amine to form a polyamic acid salt; Wherein, Said diamine monomer includes the diamine monomer according to Claim 4.

6. The preparation method according to claim 5, characterized in that, Said diamine monomer is the diamine monomer according to Claim 4, or is the diamine monomer according to Claim 4 and the diamine monomer represented by Formula V; Said diamine monomer represented by Formula V is selected from at least one of Formula V-1 to Formula V-5: Wherein, X is selected from: O, S, C(CF3); Y is selected from: O, N, S; Said dianhydride monomer is an aromatic dianhydride monomer, selected from at least one of Formula IV-1 to Formula IV-13: Said organic amine is at least one of triethylamine and N,N-dimethylethanolamine.

7. A polyamic acid salt, characterized in that, Prepared by the preparation method according to any one of Claims 5 - 6.

8. A preparation method of a sizing agent, characterized in that, Comprising: Dissolve the polyamic acid salt in a solvent to obtain a sizing agent; Wherein, said polyamic acid salt is the polyamic acid salt according to Claim 7.

9. A sizing agent, characterized in that, Prepared by the preparation method according to Claim 8.

10. A resin / fiber composite material, characterized in that, The sizing agent used is the sizing agent according to Claim 10.

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