A method for synthesizing active ester curing agents

Abstract

This invention relates to the field of curing agent synthesis technology and provides a method for synthesizing an active ester curing agent, comprising the following steps: Step 1, mixing and dissolving a phenolic hydroxyl-containing resin and an acylating agent in a solvent, heating and controlling the reaction temperature to obtain mixture one; Step 2, adding a catalyst solution dropwise to mixture one while stirring to obtain mixture two; Step 3, separating the mixture, washing with water, and removing the solvent to obtain the active ester curing agent; wherein the acylating agent is one of an acyl halide, an anhydride, or a carboxylic acid; and the hydroxyl conversion rate is 60-95%. Therefore, this invention synthesizes an active ester curing agent by controlling the hydroxyl conversion rate and applies it to low-dielectric copper-clad laminates, exhibiting both high adhesion strength and low dielectric properties.

Description

Technical Field

[0001] This invention relates to the field of curing agent synthesis technology, and in particular to a method for synthesizing an active ester curing agent. Background Technology

[0002] With the rapid development of information technology, various electronic consumer products with high-speed information processing capabilities have become an indispensable part of daily life. The development of electronic products has placed more stringent requirements on the performance of copper-clad laminates: lower dielectric constant (Dk) and lower dielectric loss (Df) are required to ensure the speed and quality of signal transmission.

[0003] Conventional phenolic curing agents contain active hydroxyl groups, which, after curing with epoxy groups, produce alcohol hydroxyl groups. The polarity of alcohol hydroxyl groups leads to higher dielectric properties of the resin system, and alcohol hydroxyl groups easily adsorb water molecules, resulting in poor heat resistance of the board and easy board explosion during solder resistance tests.

[0004] Patent CN102985485A uses a polyarylene oxygen structure as the main framework and introduces an active ester structure at its end. Its cured product has a low dielectric constant, a low dielectric loss tangent, and excellent heat resistance and flame retardancy.

[0005] Patent CN104204031B introduces phosphorus into the phenolic active ester chain through chemical linkage. The resulting phosphorus-containing phenolic active ester, after curing epoxy resin, has the characteristics of low dielectric constant and low dielectric loss tangent, as well as excellent heat resistance and flame retardancy, thus solving the problem of non-flame retardancy of previous active ester products.

[0006] Patent CN107207703A uses a naphthalene ether structure as the main framework and introduces an active ester structure at the end. Its cured product has a low dielectric constant and a low dielectric loss tangent, and also has heat resistance, flame retardancy and decomposition resistance. It solves the problem of previous active ester products not being flame retardant by utilizing the intrinsic flame retardant properties of the naphthalene ring structure.

[0007] Patent CN104736598A points out that a modified phenolic compound, obtained by modifying part or even all of the aromatic core of a phenolic compound with an aliphatic cyclic hydrocarbon group by benzyl alcohol or naphthyl methanol, is esterified with an aromatic monohydroxy compound through an aromatic dicarboxylic acid or its halide to obtain an active ester resin. This active ester resin has high solubility in solvents with low environmental impact, such as butanol and ethyl acetate, and its cured product exhibits a very low dielectric constant and dielectric loss tangent, as well as low moisture absorption. This solves the solubility problem of previous phenolic active ester products in conventional solvents, making phenolic active esters suitable for various copper clad laminate formulations.

[0008] Patent CN105392817A addresses the problem that the presence of a dicyclopentadiene skeleton in the molecular structure of active ester compounds leads to the flammability of the cured product and insufficient heat resistance. It provides an active ester resin with a structural unit consisting of multiple aromatic nuclei linked by aliphatic cyclic hydrocarbon groups, and other structural units linked by aryl dicarbonyloxy groups. In this active ester resin, some or all of the aforementioned aromatic nuclei are used as substituents on the aromatic nuclei, which does not impair the excellent dielectric properties of the active ester. Furthermore, it also exhibits excellent heat resistance and flame retardancy, thereby solving the aforementioned problems.

[0009] Reactive ester curing agents are a type of epoxy resin curing agent used in high-frequency and high-speed copper-clad laminates. Existing patents mostly describe the structure of reactive ester curing agents and their application in copper-clad laminates, as well as the introduction of elements such as Si / P into the molecular structure to further reduce the dielectric constant or achieve flame retardancy, but do not control the hydroxyl conversion rate during the synthesis process of reactive esters.

[0010] In conclusion, the existing technology obviously has inconveniences and defects in practical use, so it is necessary to improve it. Summary of the Invention

[0011] To address the aforementioned shortcomings, the present invention aims to provide a method for synthesizing an active ester curing agent, which synthesizes an active ester curing agent by controlling the hydroxyl conversion rate and applies it to low-dielectric copper clad laminates, thus possessing both high bonding strength and low dielectric properties.

[0012] In order to achieve the above objectives,

[0013] This invention provides a method for synthesizing an active ester curing agent, comprising the following steps:

[0014] Step 1: Mix the resin containing phenolic hydroxyl groups and the acylating agent in a solvent, heat the mixture and control the reaction temperature to obtain mixture 1;

[0015] Step 2: While stirring, add the catalyst solution dropwise into mixture 1 and stir to obtain mixture 2;

[0016] Step 3: Separate the mixture, wash with water, and remove the solvent to obtain the active ester curing agent;

[0017] The acylating agent is one of an acyl halide, acid anhydride, or carboxylic acid; the hydroxyl conversion rate is 60-95%.

[0018] The reaction process between phenolic hydroxyl resin and acyl halide is as follows:

[0019]

[0020] The reaction process between phenolic hydroxyl resin and acid anhydride is as follows:

[0021]

[0022] The reaction process between phenolic hydroxyl resin and carboxylic acid is as follows:

[0023]

[0024] Esterification converts phenolic hydroxyl groups into ester structures, and after curing with epoxy groups, no new hydroxyl groups are generated, thereby reducing the dielectric constant and dielectric loss.

[0025] The molar ratio of the resin containing phenolic hydroxyl groups to the acyl halide or acid anhydride is 1:(0.3-0.48); the molar ratio of the resin containing phenolic hydroxyl groups to the carboxylic acid is 1:(0.6-0.95).

[0026] Resins containing phenolic hydroxyl groups react with acyl halides, acid anhydrides, or carboxylic acids to synthesize ester-containing curing agents. The hydroxyl content before and after the reaction is detected to control the feed ratio and the degree of reaction. As the hydroxyl conversion rate increases, the peel strength of copper foil tends to decrease, while the dielectric properties increase. By controlling the feed ratio to keep the hydroxyl conversion rate between 60% and 95%, and controlling the conversion rate below 95%, the board after resin curing can be guaranteed to have high peel strength.

[0027] Therefore, resins containing phenolic hydroxyl groups can be reacted with acyl halides, acid anhydrides, or carboxylic acids to synthesize resins. By controlling the feed ratio to achieve a hydroxyl conversion rate of 60-95%, the resulting resin-cured boards exhibit both low dielectric strength and high peel strength, making them suitable as active ester curing agents.

[0028] According to a method for synthesizing an active ester curing agent based on the present invention, the reaction temperature is between 40 and 70°C.

[0029] According to a method for synthesizing an active ester curing agent according to the present invention, the catalyst in step two is an alkaline catalyst, which is one or a combination of sodium hydroxide solution, potassium hydroxide solution, ammonia, and triethylamine, and the mass fraction of the alkaline catalyst solution is 15-25%.

[0030] According to a method for synthesizing an active ester curing agent of the present invention, in step one, the reaction system before heating is evacuated and the vacuum is broken with nitrogen gas, so that all the gas in the reaction system for synthesizing the active ester curing agent is replaced with nitrogen gas.

[0031] According to a method for synthesizing an active ester curing agent according to the present invention, the specific steps of separation, washing with water, and removing solvent in step three are as follows: after the reaction is completed, the mixture is allowed to stand and separated into an upper organic layer and a lower water layer, and the lower water layer is removed; the organic layer is washed twice with pure water until the pH value of the water layer is 7, and then the solvent is removed from the organic layer under reduced pressure to obtain the active ester curing agent.

[0032] According to a method for synthesizing an active ester curing agent according to the present invention, the solvent in step one is one or a combination of benzene, toluene, methyl isobutyl ketone, xylene, propylene glycol methyl ether, diethylene glycol dimethyl ether and cyclohexanone.

[0033] According to a method for synthesizing an active ester curing agent of the present invention, after the catalyst is added dropwise, stirring is continued for 1 hour at a stirring speed of 180-220 rad / min.

[0034] According to a method for synthesizing an active ester curing agent of the present invention, the resin containing phenolic hydroxyl groups is one or a combination of several of phenolic resin, o-cresol phenolic resin, bisphenol A phenolic resin, naphthol phenolic resin, and DCPD phenolic resin.

[0035] According to a method for synthesizing an active ester curing agent of the present invention, the acylating agent is one of isophthaloyl chloride and phthalic anhydride.

[0036] The purpose of this invention is to provide a method for synthesizing an active ester curing agent, thereby synthesizing an active ester resin that can be used as a curing agent for low-dielectric epoxy systems. When applied to low-dielectric copper-clad laminates, the active ester curing agent synthesized according to this invention significantly improves the dielectric properties of the product at 10GHz, and still maintains good peel strength compared to ordinary phenolic resin curing agents. By converting phenolic hydroxyl groups into ester groups through esterification, no new hydroxyl groups are generated after curing with epoxy groups, thus achieving the effect of reducing dielectric constant and dielectric loss. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] This invention provides a method for synthesizing an active ester curing agent, comprising the following steps:

[0039] Step 1: Mix the resin containing phenolic hydroxyl groups and the acylating agent in a solvent, heat the mixture and control the reaction temperature to obtain mixture 1;

[0040] Step 2: While stirring, add the catalyst solution dropwise into mixture 1 and stir to obtain mixture 2;

[0041] Step 3: Separate the mixture, wash with water, and remove the solvent to obtain the active ester curing agent.

[0042] The acylating agent is one of an acyl halide, acid anhydride, or carboxylic acid; the reaction process between the phenolic hydroxyl resin and the acyl halide is as follows:

[0043]

[0044] The reaction process between phenolic hydroxyl resin and acid anhydride is as follows:

[0045]

[0046] The reaction process between phenolic hydroxyl resin and carboxylic acid is as follows:

[0047]

[0048] Esterification converts phenolic hydroxyl groups into ester structures, and after curing with epoxy groups, no new hydroxyl groups are generated, thereby reducing the dielectric constant and dielectric loss.

[0049] The molar ratio of the resin containing phenolic hydroxyl groups to the acyl halide or acid anhydride is 1:(0.3-0.48); the molar ratio of the resin containing phenolic hydroxyl groups to the carboxylic acid is 1:(0.6-0.95).

[0050] Resins containing phenolic hydroxyl groups react with acyl halides, acid anhydrides, or carboxylic acids to synthesize ester-containing curing agents. The hydroxyl content before and after the reaction is detected to control the feed ratio and the degree of reaction. As the hydroxyl conversion rate increases, the peel strength of copper foil tends to decrease, while the dielectric properties increase. By controlling the feed ratio to keep the hydroxyl conversion rate between 60% and 95%, and controlling the conversion rate below 95%, the board after resin curing can be guaranteed to have high peel strength.

[0051] Therefore, resins containing phenolic hydroxyl groups can be reacted with acyl halides, acid anhydrides, or carboxylic acids to synthesize resins. By controlling the feed ratio to achieve a hydroxyl conversion rate of 60-95%, the resulting resin-cured boards exhibit both low dielectric strength and high peel strength, making them suitable as active ester curing agents.

[0052] Preferably, the reaction temperature is between 40 and 70°C. If the temperature is too low, the conversion rate will be too low, the produced active ester curing agent will be unqualified, and the dielectric constant (Dk) and dielectric loss (Df) values ​​will be too high. If the temperature is too high, the conversion rate will be qualified but the yield will be too low, resulting in waste of raw materials.

[0053] Preferably, the catalyst in step two is an alkaline catalyst, which is one or a combination of sodium hydroxide solution, potassium hydroxide solution, ammonia, and triethylamine. The mass fraction of the alkaline catalyst solution is 15-25%. After the catalyst is added dropwise, stirring is continued for 1 hour at a stirring speed of 180-220 rad / min.

[0054] Preferably, in step one, the reaction system before heating is evacuated and the vacuum is broken with nitrogen, so that all the gas in the reaction system for synthesizing the active ester curing agent is replaced with nitrogen.

[0055] Preferably, in step three, the specific steps of separation, washing with water, and removing solvent are as follows: after the reaction is completed, the mixture is allowed to stand and separated into an upper organic layer and a lower water layer. The lower water layer is then removed. The organic layer is washed twice with pure water until the pH of the water layer is 7. Subsequently, the solvent is removed from the organic layer under reduced pressure to obtain the active ester curing agent.

[0056] Preferably, the solvent in step one is one or a combination of benzene, toluene, methyl isobutyl ketone, xylene, propylene glycol methyl ether, diethylene glycol dimethyl ether, and cyclohexanone.

[0057] Preferably, the resin containing phenolic hydroxyl groups is one or a combination of several of phenolic resin, o-cresol phenolic resin, bisphenol A phenolic resin, naphthol phenolic resin, and DCPD phenolic resin, and the acylating agent is one of isophthaloyl chloride and phthalic anhydride.

[0058] The present invention will be better understood by referring to specific embodiments below, but the scope of protection of the present invention is not limited to these embodiments.

[0059] Example 1:

[0060] 153g of naphthol phenolic resin and 90g of isophthaloyl chloride were mixed and dissolved in 450g of toluene. The reactor was evacuated and the vacuum was broken with nitrogen to remove air. 177g of 20% sodium hydroxide solution was added dropwise to the reaction solution at 40℃ over 3 hours, and stirring was continued for 1 hour after the addition was complete. After the reaction was completed, the mixture was allowed to stand and the lower aqueous layer was separated. The organic layer was washed twice with pure water until the pH of the aqueous layer was 7. Subsequently, toluene was removed from the organic layer under reduced pressure to obtain the active ester curing agent (H-1). The reaction process is shown in the following reaction formula.

[0061] Before the reaction, the hydroxyl equivalent of the naphthol phenolic resin was 153. The hydroxyl equivalent of the product was adjusted by controlling the amount of isophthaloyl chloride added. After the reaction, the hydroxyl equivalent of the curing agent was 1850, the hydroxyl conversion rate was 88.1%, and the yield was 86.0%.

[0062]

[0063] Example 2:

[0064] 165g of DCPD phenol resin and 71g of isophthaloyl chloride were mixed and dissolved in 500g of toluene. The reactor was evacuated and the vacuum was broken with nitrogen to replace the air. 140g of 20% sodium hydroxide solution was added dropwise to the reaction mixture over 3 hours at 60°C, and stirring was continued for 1 hour after the addition was complete. After the reaction was complete, the mixture was allowed to stand and the lower aqueous layer was removed. The organic layer was washed twice with pure water until the pH of the aqueous layer reached 7. Subsequently, toluene was removed from the organic layer under reduced pressure to obtain the active ester curing agent (H-2). The reaction process is shown in the following reaction formula.

[0065] Before the reaction, the hydroxyl equivalent of DCPD phenol resin was 165. The hydroxyl equivalent of the product was adjusted by controlling the amount of isophthaloyl chloride added. After the reaction, the hydroxyl equivalent of the curing agent was 700, the hydroxyl conversion rate was 70.2%, and the yield was 83.1%.

[0066]

[0067] Example 3:

[0068] 165g of DCPD phenol resin, 72g of naphthol phenolic resin, and 144g of isophthaloyl chloride were mixed and dissolved in 630g of toluene. The reactor was evacuated and the vacuum was broken with nitrogen to replace the air. 280g of 20% sodium hydroxide solution was added dropwise to the reaction mixture at 55℃ over 4 hours, and stirring was continued for 0.5 hours after the addition was complete. After the reaction was complete, the mixture was allowed to stand and the lower aqueous layer was removed. The organic layer was washed twice with pure water until the pH of the aqueous layer reached 7. Subsequently, toluene was removed from the organic layer under reduced pressure to obtain the active ester curing agent (H-3).

[0069] Before the reaction, the hydroxyl equivalent of the mixture of DCPD phenol resin and naphthol phenolic resin was 155. The hydroxyl equivalent of the product was adjusted by controlling the amount of isophthaloyl chloride added. After the reaction, the hydroxyl equivalent of the curing agent was 6500, the hydroxyl conversion rate was 95.0%, and the yield was 84.5%.

[0070]

[0071] Example 4:

[0072] 165g of DCPD phenol resin, 72g of naphthol phenolic resin, and 92g of isophthaloyl chloride were mixed and dissolved in 630g of toluene. The reactor was evacuated and the vacuum was broken with nitrogen to replace the air. 280g of 20% sodium hydroxide solution was added dropwise to the reaction mixture at 70℃ over 4 hours, and stirring was continued for 0.5 hours after the addition was complete. After the reaction was complete, the mixture was allowed to stand and the lower aqueous layer was removed. The organic layer was washed twice with pure water until the pH of the aqueous layer reached 7. Subsequently, toluene was removed from the organic layer under reduced pressure to obtain the active ester curing agent (H-4), as shown in the following chemical formula.

[0073] Before the reaction, the hydroxyl equivalent of the mixture of DCPD phenol resin and naphthol phenolic resin was 155. The hydroxyl equivalent of the product was adjusted by controlling the amount of isophthaloyl chloride added. After the reaction, the hydroxyl equivalent of the curing agent was 540, the hydroxyl conversion rate was 60.8%, and the yield was 78.7%.

[0074]

[0075] Comparative Example 1

[0076] PF-8020 type phenolic resin curing agent.

[0077] Comparative Example 2

[0078] 165g of DCPD phenol resin, 72g of naphthol phenolic resin, and 147g of isophthaloyl chloride were mixed and dissolved in 630g of toluene. The reactor was evacuated and the vacuum was broken with nitrogen to replace the air. 280g of 20% sodium hydroxide solution was added dropwise to the reaction mixture at 70℃ over 4 hours, and stirring was continued for 0.5 hours after the addition was complete. After the reaction was complete, the mixture was allowed to stand and the lower aqueous layer was separated. The organic layer was washed twice with pure water until the pH of the aqueous layer reached 7. Subsequently, toluene was removed from the organic layer under reduced pressure to obtain the active ester curing agent (H-5), as shown in the following chemical formula.

[0079] Before the reaction, the hydroxyl equivalent of the mixture of DCPD phenol resin and naphthol phenolic resin was 155. The hydroxyl equivalent of the product was adjusted by controlling the amount of isophthaloyl chloride added. After the reaction, the theoretical hydroxyl equivalent of the curing agent was 14835, the hydroxyl conversion rate was 98.5%, and the yield was 78.4%.

[0080]

[0081] Comparative Example 3

[0082] The experimental steps and raw material formulation were the same as in Example 2. The reaction temperature was modified to 30°C, resulting in H-6 with a hydroxyl conversion rate of 33.4% and a yield of 96.2%.

[0083] Comparative Example 4

[0084] The experimental steps and raw material formulation were the same as in Example 2. The reaction temperature was modified to 80°C, resulting in H-7 with a hydroxyl conversion rate of 70.0% and a yield of 62.4%.

[0085] Performance testing:

[0086] The three active ester curing agents obtained in Examples 1, 2, 3, and 4 were mixed with the comparative examples of phenolic resin (Shengquan PF-8020) and epoxy resin (a 1:1 mass ratio mixture of Nanya NPPN438 and NPPN638) at an equivalent ratio of 1:1. 0.3 equivalents of curing accelerator (2-methylimidazole) and 0.3 equivalents of filler (aluminum hydroxide) were added, followed by the addition of solvent (toluene) until the solid content of the mixture reached 60%. The mixture was stirred until homogeneous to obtain the resin composition solution. Next, glass cloth was impregnated in the resin composition solution, and the impregnated glass was placed in an oven at 150°C for 5 minutes to form a semi-cured sheet. Eight semi-cured sheets were stacked together, and a layer of electrolytic copper foil was superimposed on each of the top and bottom sides. The sheets were then pressed in a vacuum hot press to obtain a copper-clad laminate under the following conditions: pressure 25 kg / cm². 2 Press at 220℃ for 2 hours.

[0087] The obtained copper-clad laminate was analyzed:

[0088] Interlayer bonding strength: Performed according to the standard method of Q / GDSY 6052-2016P01.

[0089] Thermogravimetric analysis (Td5%): The TGA test was performed according to the TGA test method specified in IPC-TM-6502.4.24.6.

[0090] Solder resistance at 288℃ (after 2 hours in a PCT pressure cooker): The test method is to immerse the pressure cooker test piece into a 288℃ soldering furnace and record the time required for the test piece to blister and delaminate. The evaluation can be completed when the substrate has been in the soldering furnace for more than 5 minutes without blistering or delamination.

[0091] Glass transition temperature test: Differential scanning calorimeter (DSC) was used with a heating rate of 20℃ / min.

[0092] Dielectric properties: Tested according to IEC-61189-2-721 (SPDR) method.

[0093] The performance test results for the comparative examples and various embodiments are shown in the table below:

[0094] Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Types of curing agents H-1 H-2 H-3 H-4 PF-8020 H-5 H-6 H-7 Interlayer bonding N / mm 1.0 1.0 0.9 1.1 1.1 0.5 1.0 1.0 T288 Solder-resistant >600 >600 >600 >600 >600 >600 >600 >600 Thermal weight loss Td5%℃ 438.1 407.3 420.1 438.2 425.4 428.1 408.2 407.5 Glass transition degree ℃ 185.4 167.1 178.3 182.3 173.3 179.2 168.4 167.7 Dielectric constant Dk (10 GHz) 3.3 3.1 2.9 3.5 4.3 2.8 4.0 3.1 Dielectric loss Df (10GHz) 0.006 0.005 0.004 0.010 0.021 0.003 0.019 0.005 hydroxyl conversion rate % 88.1 70.2 95.0 60.8 — 98.5 33.4 70.0 Yield % 86.0 83.1 84.5 78.7 — 78.4 96.2 62.4

[0095] The data in the table shows that the commonly used PF-8020 resin curing agent in the prior art has excessively high dielectric constant (Dk) and dielectric loss (Df) values ​​due to the easy generation of new hydroxyl groups, resulting in poor dielectric performance at 10GHz. As the hydroxyl conversion rate increases, the dielectric performance increases, but the copper foil peel strength tends to decrease. In Comparative Example 2, the hydroxyl conversion rate is 98.5%, and the interlayer bonding force is too low, resulting in low peel strength and easy board explosion. In Comparative Example 3, the temperature is too low, resulting in a low conversion rate and unqualified active ester curing agent with excessively high dielectric constant (Dk) and dielectric loss (Df) values. In Comparative Example 4, the temperature is too high, resulting in a qualified conversion rate but a low yield, causing waste of raw materials.

[0096] The active ester curing agent synthesized according to the method of the present invention can significantly improve the dielectric properties of low dielectric copper clad laminates at 10 GHz, and still has good peel strength compared with ordinary phenolic resin curing agents.

[0097] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A method for synthesizing an active ester curing agent, characterized in that, Includes the following steps: Step 1: Mix and dissolve the phenolic hydroxyl-containing resin and acylating agent in a solvent, heat and control the reaction temperature between 40 and 70°C; to obtain mixture 1. Step 2: While stirring, add the catalyst solution dropwise into mixture 1 and stir to obtain mixture 2; Step 3: Separate the mixture, wash with water, and remove the solvent to obtain the active ester curing agent; The resin containing phenolic hydroxyl groups is one or a combination of several of the following: phenolic resin, o-cresol resin, bisphenol A resin, naphthol resin, and DCPD resin; the acylating agent is isophthaloyl chloride. The hydroxyl conversion rate is 60-95%.

2. The method for synthesizing an active ester curing agent according to claim 1, characterized in that, The molar ratio of the phenolic hydroxyl-containing resin to the acylating agent is 1:(0.3~0.48).

3. The method for synthesizing an active ester curing agent according to claim 1, characterized in that, The catalyst in step two is an alkaline catalyst, which is one or a combination of sodium hydroxide solution, potassium hydroxide solution, ammonia, and triethylamine, and the mass fraction of the alkaline catalyst solution is 15-25%.

4. The method for synthesizing an active ester curing agent according to claim 1, characterized in that, In step one, the reaction system before heating is evacuated and the vacuum is broken with nitrogen gas, replacing all the gas in the reaction system with nitrogen gas.

5. The method for synthesizing an active ester curing agent according to claim 1, characterized in that, In step three, the specific steps of separation, washing with water, and solvent removal are as follows: After the reaction is completed, the mixture is allowed to stand and separated into an upper organic layer and a lower water layer. The lower water layer is then removed. The organic layer is washed twice with pure water until the pH of the water layer is 7. Subsequently, the solvent is removed from the organic layer under reduced pressure to obtain the active ester curing agent.

6. The method for synthesizing an active ester curing agent according to claim 1, characterized in that, The solvent in step one is one or a combination of benzene, toluene, methyl isobutyl ketone, xylene, propylene glycol methyl ether, diethylene glycol dimethyl ether, and cyclohexanone.

7. The method for synthesizing an active ester curing agent according to claim 1, characterized in that, After the catalyst is added dropwise, continue stirring for 1 hour at a stirring speed of 180~220 rad / min.

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