Multifunctional curing agent, preparation method and application thereof

Abstract

This invention discloses a multifunctional curing agent, its preparation method, and its applications, belonging to the field of flame-retardant curing agents. The curing agent of this invention contains both a piperazine ring and phosphorus in its structure, enabling a phosphorus-nitrogen synergistic flame-retardant effect. The flame-retardant structure also contains imino groups, which act as co-curing agents when applied to thermosetting polymers such as epoxy resins. When applied to epoxy resins, this multifunctional curing agent exhibits high flame-retardant efficiency, significantly improves the limiting oxygen index of the prepared epoxy resin material, achieves a V-0 rating during vertical burning, possesses excellent tensile and impact resistance, reduces the dielectric constant and dielectric loss of the cured epoxy, and simultaneously improves the moisture resistance and thermal conductivity of the cured epoxy.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant curing agents, specifically relating to a multifunctional curing agent, its preparation method, and its application. Background Technology

[0002] With the rapid development of new energy vehicles, electronic products, and high-frequency communication technologies, epoxy resins are widely used in structural components, electronic packaging materials, and electrical insulation systems. These applications require materials to possess not only high strength, heat resistance, and dimensional stability, but also good flame retardancy, low dielectric properties, and long-term service reliability. To improve the flame retardancy of bisphenol A type epoxy resins, existing technologies typically employ additive-based flame retardant systems, such as inorganic flame retardants like ammonium polyphosphate, aluminum hydroxide, and magnesium hydroxide. However, these systems generally suffer from poor compatibility, easy migration or precipitation, and adverse effects on mechanical and dielectric properties, making it difficult to meet the structural-functional integration requirements of the electronics and electrical fields. In recent years, intrinsic flame retardant strategies that chemically integrate flame-retardant groups into the epoxy resin crosslinking network have gained increasing attention. Furthermore, related research indicates that multi-element synergistic design (such as phosphorus-nitrogen, phosphorus-silicon, phosphorus-boron, and phosphorus-sulfur) helps improve flame retardant efficiency and enhance the overall performance of the material. Piperazine rings, as nitrogen-rich structural units, can enhance the density and thermal stability of char layers by promoting cross-linking of condensed phases and the formation of expanded char layers, thereby improving the char-forming ability and flame-retardant effect of materials. Furthermore, the nitrogen element in the piperazine ring can produce a synergistic effect with flame-retardant elements such as phosphorus and silicon, improving the flame-retardant properties of materials, and thus has broad application prospects in the preparation of flame retardants.

[0003] The research group led by Zhou Hong at Wuhan University of Technology synthesized a novel flame retardant, DOPMPA, using 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and piperazine as raw materials, and applied it to epoxy resin (EP). This flame retardant can give epoxy resin composites excellent flame retardant properties, improve char formation efficiency, and basically maintain the glass transition temperature (T0) of the composite material. g While the performance of epoxy resin remains unchanged, the introduction of DOPMPA reduces the mechanical properties of epoxy resin. The research group of Qu Hongqiang at Hebei University synthesized a novel reactive flame retardant, PBFA, using raw materials such as N-aminoethylpiperazine (AEP) and hexachlorocyclotriphosphazene (HCCP). When applied to epoxy resin, they obtained epoxy composite materials with good flame retardancy, smoke suppression, and mechanical properties. However, research on the dielectric properties of the material is relatively insufficient.

[0004] Therefore, developing a novel piperazine-based flame retardant that is simple to process, low in toxicity, and highly efficient, as well as preparing epoxy composite materials with excellent flame retardancy, mechanical properties, and dielectric properties, has become an important research direction for epoxy resins in the fields of new energy vehicles and high-end electronic and electrical engineering. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides a multifunctional curing agent, its preparation method, and its applications. This multifunctional curing agent integrates multiple functionalities such as flame retardancy, reinforcement, toughening, low dielectric properties, moisture resistance, and thermal conductivity.

[0006] The curing agent of this invention contains a piperazine ring structure, which can promote the dehydration and char formation of the polymer matrix, while phosphorus can play a flame-retardant role in both the condensed phase and the gas phase. In the condensed phase, the presence of phosphorus promotes the char formation of the polymer during combustion, while in the gas phase, phosphorus-containing free radicals quench active free radicals during combustion. The phosphorus content and aromatic ring number of this type of curing agent are adjustable, making it suitable for flame-retardant treatment of different polymer matrices. In addition, the curing agent of this invention contains imino groups, which can act as co-curing agents when applied to thermosetting polymers such as epoxy resins. The preparation process of the curing agent of this invention is simple, the conditions are relatively mild, and the yield is high, making it suitable for flame-retardant treatment and large-scale production and application of different polymer matrices, such as epoxy resins. Furthermore, without the introduction of additional conventional fluorescent groups, flame-retardant epoxy resin samples prepared with the curing agent of this invention exhibit photoluminescence properties.

[0007] The multifunctional curing agent of this invention has the following general structural formula:

[0008]

[0009] Wherein, R is selected from any of the following structures:

[0010] ;

[0011] * indicates the connection point.

[0012] The preparation method of the multifunctional curing agent of the present invention includes the following steps:

[0013] Step 1: Under inert gas protection, tris(2-aminoethyl)amine and 1-formaldehyde piperazine are mixed in anhydrous ethanol at a certain molar ratio and heated to 80°C for 6 hours.

[0014] Step 2: Slowly add the phosphorus-containing compound to the mixture obtained in Step 1. Under the protection of an inert gas, maintain the temperature at 60~80 ℃ and stir the reaction for 24~36 hours. After the reaction is completed, remove the solvent (liquid product) by rotary evaporation and dry to obtain the target product.

[0015] In step 1, the molar ratio of tris(2-aminoethyl)amine to 1-formaldehyde piperazine is 1:3.

[0016] In steps 1 and 2, the inert gas is any one of nitrogen, argon, or helium.

[0017] In step 2, the phosphorus-containing compound is selected from any one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine oxide, dimethyl phosphite, di-tert-butyl phosphonate, diphenyl phosphite, dibenzyl phosphite, and diethyl phosphite.

[0018] In step 2, the molar ratio of tris(2-aminoethyl)amine to the phosphorus-containing compound is 1:3.

[0019] The application of the multifunctional curing agent of this invention in the preparation of flame-retardant epoxy resin materials.

[0020] Furthermore, the multifunctional curing agent is used as a co-curing agent to partially replace conventional phosphorus-free amine curing agents.

[0021] The amount of the multifunctional curing agent added is determined by adjusting the phosphorus content, and the overall phosphorus content of the system is generally ≤2.0 wt%.

[0022] The appropriate molecular weight and number of functional groups have a significant impact on the reinforcing and toughening effects of flame retardants in epoxy resin systems. The piperazine-based phosphorus-containing flame retardant provided by this invention has a moderate molecular weight and contains multiple reactive -NH functional groups in its molecular structure, exhibiting high functionality. This facilitates its participation in the crosslinking reaction of epoxy resin during curing. Simultaneously, the uncured -NH groups in the piperazine ring structure can enhance interchain interactions through hydrogen bonding, thereby improving the tensile strength and impact strength of the material and enhancing its mechanical properties. In Examples 4, 5, and 6, the char residue of the flame-retardant epoxy resins at 700°C was higher than that of the unmodified epoxy resin in Comparative Example 1, indicating that the multifunctional curing agent of this invention can improve the thermal stability and char residue of epoxy resins at high temperatures, while also imparting good flame-retardant properties to the system while maintaining mechanical properties.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] 1. The curing agent of this invention contains piperazine rings, benzene rings, and phosphorus elements in its chemical structure. The phosphorus element can exert a flame-retardant effect in both the condensed phase and the gas phase. In the condensed phase, the presence of phosphorus promotes char formation of the polymer during combustion, while in the gas phase, phosphorus-containing free radicals quench active free radicals during combustion. Furthermore, the simultaneous presence of piperazine rings and phosphorus elements in the curing agent structure enables a phosphorus-nitrogen synergistic flame-retardant effect.

[0025] 2. The curing agent of this invention has imino groups in its chemical structure, which can react with epoxy resin to cure it. It has the advantages of intrinsic flame retardancy, high flame retardancy efficiency, and no migration or precipitation.

[0026] 3. The phosphorus content and number of aromatic rings in the chemical structure of the curing agent of the present invention can be adjusted, making it suitable for flame retardant treatment of different polymer matrices. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 Thermogravimetric analysis curves of each sample in Comparative Example 1, Example 4, Example 5 and Example 6 of this invention.

[0029] Figure 2 The heat release rate curves of each sample in Comparative Example 1, Example 4, Example 5 and Example 6 of this invention are shown.

[0030] Figure 3 The total heat release curves are for each sample in Comparative Example 1, Example 4, Example 5 and Example 6 of this invention.

[0031] Figure 4 These are photographs of the carbon residue from Comparative Examples 1, 4, 5, and 6 of this invention after testing with a cone calorimeter.

[0032] Figure 5 The stress-strain curves are for each sample in Comparative Example 1, Example 4, Example 5 and Example 6 of this invention.

[0033] Figure 6 This is a comparison chart of the impact strength of each sample in Comparative Example 1, Example 4, Example 5 and Example 6 of the present invention.

[0034] Figure 7 The dielectric constant curves of each sample in Comparative Example 1, Example 4, Example 5 and Example 6 of this invention are shown.

[0035] Figure 8 The dielectric loss curves of each sample in Comparative Example 1, Example 4, Example 5 and Example 6 of this invention are shown.

[0036] Figure 9 The images show the appearance of the samples from Comparative Example 1 and Example 6 of this invention under visible light and 365 nm ultraviolet light irradiation conditions. Detailed Implementation

[0037] To further illustrate the technical solution of the present invention, preferred embodiments are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0038] Example 1:

[0039] 1. Under nitrogen protection, tris(2-aminoethyl)amine and 1-formaldehyde piperazine were added to the solvent in a molar ratio of 1:3, and the mixture was magnetically stirred for 5-10 minutes. Then the system was heated to 80°C and reacted for 6 hours.

[0040] 2. Dimethyl phosphite was slowly added to the reaction mixture obtained in step 1, with a molar ratio of tris(2-aminoethyl)amine to dimethyl phosphite of 1:3. Under nitrogen atmosphere and at a temperature of 80°C, the mixture was stirred for 24 hours to obtain the target product a, whose chemical structure is shown below:

[0041]

[0042] Target product a was subjected to Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). 1 Characterized by 1H-NMR, its chemical structure was confirmed as follows: FT-IR (KBr, cm⁻¹) -1 ): 3530 (NH), 2960, 2850 (-CH3, -CH2-), 1190 (P=O), 1090 (PC), 1040 (POC). 1 H-NMR (400 MHz, DMSO-d6, ppm): 4.53 (d, 1H,piperazine-NH-), 4.41 (d, 1H, -CH-N-),4.26(s,1H,-NH-CH-),3.67(s,6H,-O-CH3),2.82 - 2.88 (m, 8H, piperazine-NH-CH2-CH2-N-), 2.66-2.79 (m, 4H, -NH-CH2-CH2-N-).

[0043] Example 2:

[0044] 1. Under nitrogen protection, tris(2-aminoethyl)amine and 1-formaldehyde piperazine were added to the solvent in a molar ratio of 1:3, and the mixture was magnetically stirred for 5-10 minutes. Then the system was heated to 80°C and reacted for 6 hours.

[0045] 2. 9,10-Dihydro-9-oxa-10-phosphaphenanthrene-10-oxide was slowly added to the reaction mixture obtained in step 1, with a molar ratio of tris(2-aminoethyl)amine to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide of 1:3. Under nitrogen atmosphere and at a temperature of 60°C, the mixture was stirred for 36 hours to obtain the target product b, whose chemical structure is shown below:

[0046]

[0047] Target product b was subjected to Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). 1 Characterized by 1H-NMR, its chemical structure was confirmed as follows: FT-IR (KBr, cm⁻¹) -1 ): 3530 (NH), 2850 (-CH2-), 1605, 1510 (benzenering), 1190 (P=O), 1090 (PC), 1040 (POC). 1 H-NMR (400 MHz, DMSO-d6, ppm):8.43 (dd, 1H, Ar-H), 8.03 (m, 1H, Ar-H), 7.86 (dd, 1H, Ar-H), 7.70 (td, 1H,Ar-H), 7.57-7.42 (m, 3H, Ar-H), 7.19 (m, 1H, Ar-H), 4.53 (d, 1H, piperazine-NH-), 4.54 (d, 1H, -CH-N-), 4.35 (s, 1H, -NH-CH-), 2.79 - 2.67 (m, 8H,piperazine-NH-CH2-CH2-N-), 2.66-2.62 (m, 4H, -NH-CH2-CH2-N-).

[0048] Example 3:

[0049] 1. Under nitrogen protection, tris(2-aminoethyl)amine and 1-formaldehyde piperazine were added to the solvent in a molar ratio of 1:3, and the mixture was magnetically stirred for 5-10 minutes. Then the system was heated to 80°C and reacted for 6 hours.

[0050] 2. Diphenylphosphine oxide was slowly added to the reaction mixture obtained in step 1, with a molar ratio of tris(2-aminoethyl)amine to diphenylphosphine oxide of 1:3. Under nitrogen atmosphere and at a temperature of 70°C, the mixture was stirred for 30 hours to obtain the target product c, whose chemical structure is shown below:

[0051]

[0052] The target product c was subjected to Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H NMR). 1 Characterized by 1H-NMR, its chemical structure was confirmed as follows: FT-IR (KBr, cm⁻¹) -1 ): 3530 (NH), 2850 (-CH2-), 1605, 1510 (benzenering), 1190 (P=O), 1090 (PC). 1 H-NMR (400 MHz, DMSO-d6, ppm): 8.06-7.64 (m,10H, Ar-H), 4.86 (d, 1H, piperazine-NH-), 4.68 (d, 1H, -CH-N-), 4.18 (s, 1H,-NH-CH-), 2.88-2.76 (m, 8H, piperazine-NH-CH2-CH2-N-), 2.76 - 2.63 (m, 4H, -NH-CH2-CH2-N-).

[0053] Example 4:

[0054] Accurately weigh 100.0 g of epoxy resin (DGEBA), 14.0 g of curing agent (diethyltoluene diamine, DETDA), and 16.0 g of flame-retardant curing agent a. Add DGEBA and flame-retardant curing agent a to a three-necked flask, heat to 100°C, and mechanically stir for 10-15 minutes to obtain an epoxy resin dispersion. Cool to 70-80°C, add the curing agent to the above epoxy resin dispersion, mechanically stir for 10 minutes, and immediately pour into a mold. Curing conditions are 80°C / 2 hours + 120°C / 2 hours + 150°C / 2 hours + 180°C / 2 hours. After demolding, allow to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.5% by mass.

[0055]

[0056] Example 5:

[0057] Accurately weigh 100.0 g of epoxy resin (DGEBA), 12.9 g of curing agent (DETDA), and 18.9 g of flame-retardant curing agent a. Add DGEBA and flame-retardant curing agent a to a three-necked flask, heat to 100°C, and mechanically stir for 10-15 minutes to obtain an epoxy resin dispersion. Cool to 70-80°C, add the curing agent to the above epoxy resin dispersion, mechanically stir for 10 minutes, and immediately pour into a mold. Curing conditions are 80°C / 2 hours + 120°C / 2 hours + 150°C / 2 hours + 180°C / 2 hours. After demolding, allow to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 1.75% by mass.

[0058] Example 6:

[0059] Accurately weigh 100.0 g of epoxy resin (DGEBA), 11.9 g of curing agent (DETDA), and 22.0 g of flame-retardant curing agent a. Add DGEBA and flame-retardant curing agent a to a three-necked flask, heat to 100°C, and mechanically stir for 10-15 minutes to obtain an epoxy resin dispersion. Cool to 70-80°C, add the curing agent to the above epoxy resin dispersion, and mechanically stir for 10 minutes. Immediately pour into a mold, and cure under the following conditions: 80°C / 2 hours + 120°C / 2 hours + 150°C / 2 hours + 180°C / 2 hours. After demolding, allow to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 2% by mass.

[0060] Example 7:

[0061] Accurately weigh 100.0 g of epoxy resin (DGEBA), 11.3 g of curing agent (DETDA), and 33.8 g of flame retardant curing agent b. Add DGEBA and flame retardant curing agent b to a three-necked flask, heat to 100°C, and mechanically stir for 10-15 minutes to obtain an epoxy resin dispersion. Cool to 70-80°C, add the curing agent to the above epoxy resin dispersion, mechanically stir for 10 minutes, and immediately pour into a mold. Curing conditions are 80°C / 2 hours + 120°C / 2 hours + 150°C / 2 hours + 180°C / 2 hours. After demolding, allow to cool naturally to room temperature to obtain a flame retardant epoxy resin sample with a phosphorus content of 2% by mass.

[0062] Example 8:

[0063] Accurately weigh 100.0 g of epoxy resin (DGEBA), 11.4 g of curing agent (DETDA), and 32.1 g of flame-retardant curing agent c. Add DGEBA and flame-retardant curing agent c to a three-necked flask, heat to 100°C, and mechanically stir for 10-15 minutes to obtain an epoxy resin dispersion. Cool to 70-80°C, add the curing agent to the above epoxy resin dispersion, mechanically stir for 10 minutes, and immediately pour into a mold. Curing conditions are 80°C / 2 hours + 120°C / 2 hours + 150°C / 2 hours + 180°C / 2 hours. After demolding, allow to cool naturally to room temperature to obtain a flame-retardant epoxy resin sample with a phosphorus content of 2% by mass.

[0064] Comparative Example 1:

[0065] Accurately weigh 100.0 g of epoxy resin (DGEBA) and 19.6 g of curing agent (DETDA). Add the epoxy resin and curing agent to a three-necked flask, heat to 70-80℃, and mechanically stir for 10-20 minutes. Immediately pour the mixture into a mold. Curing conditions are: 80℃ / 2 hours + 120℃ / 2 hours + 150℃ / 2 hours + 180℃ / 2 hours. After demolding, allow it to cool naturally to room temperature to obtain the epoxy resin sample.

[0066] The performance test results of the products obtained from the above embodiments and comparative examples are shown in Tables 1 to 3 below:

[0067] Table 1. Results of oxygen index, vertical burning, tensile impact test, thermogravimetric analysis (N2), and dielectric properties (1 MHz) of flame-retardant epoxy resin.

[0068]

[0069] Table 2. Cone calorimeter test results of flame-retardant epoxy resin

[0070]

[0071] Table 3. Results of water contact angle, water absorption rate, and thermal conductivity of flame-retardant epoxy resin.

[0072]

[0073] The oxygen index, vertical burning performance, mechanical properties, thermal stability, dielectric properties, and cone calorimeter test results of the samples in Tables 1 and 2 show that the oxygen index of DGEBA / DETDA type epoxy resin (Comparative Example 1) is only 21.0%, it has no rating in the UL-94 vertical burning test, a char residue of only 11.0% at 700℃, and tensile strength and impact strength of 37.3 MPa and 9.5 kJ / m², respectively. 2The dielectric constant and dielectric loss at 1 MHz were 3.114 and 0.04214, respectively. Compared with the unmodified epoxy resin (Comparative Example 1), the dielectric constant and dielectric loss of each flame-retardant epoxy resin in Examples 4-6 were reduced to a certain extent, and the oxygen index was all above 26.0%. The flame-retardant epoxy resins in Examples 5 and 6 could pass the UL-94 V-0 rating, and the tensile strength and impact strength were improved. This is because the piperazine ring molecular structure contains multiple reactive -NH functional groups, exhibiting high functionality, which helps to participate in the crosslinking reaction of epoxy resin during the curing process. At the same time, the -NH in the structure that does not participate in curing can also enhance the inter-chain interaction through hydrogen bonding, thereby improving mechanical properties. In addition, with the increase of the amount of multifunctional curing agent, the char residue of the flame-retardant epoxy resin increased significantly, indicating that the introduction of multifunctional curing agent improved the char formation performance of epoxy resin. Meanwhile, the peak heat release rate, total heat release, average effective heat of combustion, and fire spread index of each flame-retardant epoxy resin in Examples 4-8 were significantly reduced compared to Comparative Example 1. Among them, the flame-retardant properties of each epoxy resin in Examples 4-6 were superior. From the water contact angle, water absorption rate, and thermal conductivity results of each sample in Table 3, it can be seen that the water contact angle of Comparative Example 1 was 83.2°, the water absorption rate was 2.57 wt%, and the thermal conductivity was 0.101 W / (m·K). In contrast, all flame-retardant epoxy resins in Examples 4-6 achieved hydrophobic effects and reduced water absorption rates. This is mainly because the reactive multifunctional flame retardant reduced the free volume of the system after participating in the curing reaction, effectively limiting the diffusion and penetration of water molecules in the cured network. The thermal conductivity test results show that the thermal conductivity of each flame-retardant epoxy resin in Examples 4-6 was increased by 116.8%, 123.8%, and 125.7% compared to Comparative Example 1, respectively. Therefore, the multifunctional curing agent modified epoxy resin of this invention is suitable for applications requiring high flame retardancy, mechanical properties, moisture resistance and dielectric properties.

[0074] Thermogravimetric analysis curves of the samples in Comparative Example 1, Example 4, Example 5 and Example 6 under nitrogen atmosphere are shown below. Figure 1 As shown. It can be seen that the initial decomposition temperature (T) of the flame-retardant epoxy resin in Examples 4, 5, and 6 is... 5% ) and the temperature of maximum thermal decomposition rate (T max The char content of the flame-retardant epoxy resins in Examples 4, 5, and 6 was lower than that in Comparative Example 1, because the introduction of flame-retardant curing agent a promoted the earlier decomposition of the epoxy groups. However, at 700°C, the char residue of the flame-retardant epoxy resins in Examples 4, 5, and 6 increased to 18.0%, 18.1%, and 20.3 wt%, respectively, indicating that the introduction of the multifunctional curing agent improved the char-forming properties of the epoxy resin.

[0075] The heat release rate curves of each sample in Comparative Example 1, Example 4, Example 5, and Example 6 are shown below. Figure 2As shown in the figure, the peak heat release rate of the unmodified epoxy resin (Comparative Example 1) is approximately 1197.8 kW / m². 2 In Examples 4, 5, and 6, the peak heat release rates of the flame-retardant epoxy resins decreased to 426.1, 328.7, and 322.6 kW / m², respectively. 2 This indicates that the multifunctional curing agent can effectively suppress the heat release rate of epoxy resin.

[0076] The total heat release curves of each sample in Comparative Example 1, Example 4, Example 5, and Example 6 are shown below. Figure 3 As shown in the figure, it can be seen that the total heat release value of the unmodified epoxy resin (Comparative Example 1) within 0-600s is approximately 69.4 MJ / m². 2 The total heat release values ​​of the flame-retardant epoxy resins in Examples 4, 5, and 6 were 47.3, 41.3, and 35.8 MJ / m³, respectively. 2 This indicates that the multifunctional curing agent can promote the formation of a carbon layer in epoxy resin and effectively suppress the heat release during combustion.

[0077] Photographs of the char residue of each sample in Comparative Example 1, Example 4, Example 5, and Example 6 after testing with a cone calorimeter are shown below. Figure 4 As shown, the unmodified epoxy resin (Comparative Example 1) left almost no char residue after combustion, indicating poor oxidation resistance of the char layer. In contrast, the flame-retardant epoxy resins in Examples 4, 5, and 6 showed increasing amounts of char residue and more pronounced expansion effects, further demonstrating that the multifunctional curing agent has a good catalytic char formation effect.

[0078] The stress-strain curves of the samples in Comparative Example 1, Example 4, Example 5, and Example 6 are shown below. Figure 5 As shown, the flame-retardant epoxy resin sample in Comparative Example 1 fractured at a strain of 10.2%, with a tensile strength of 37.3 MPa. In Examples 4, 5, and 6, the flame-retardant epoxy resins fractured at strains of 15.6%, 21.9%, and 12.4%, respectively, with tensile strengths reaching 54.3, 56.5, and 52.7 MPa, respectively. These represent increases of 45.6%, 51.5%, and 41.3% compared to the flame-retardant epoxy resin sample in Comparative Example 1, indicating that the multifunctional curing agent of this invention can effectively maintain the tensile strength of epoxy resin materials.

[0079] The impact strength comparison diagram of each sample in Comparative Example 1, Example 4, Example 5 and Example 6 is shown in the figure below. Figure 6 As shown in the figure, the impact strength of the flame-retardant epoxy resin sample in Comparative Example 1 is 9.5 kJ / m. 2The impact strengths of the flame-retardant epoxy resins in Examples 4, 5, and 6 reached 14.8, 15.4, and 15.9 kJ / m, respectively. 2 Compared with the flame-retardant epoxy resin samples in Comparative Example 1, the flame-retardant properties were increased by 55.8%, 62.1%, and 67.4%, respectively, indicating that the multifunctional curing agent of the present invention can better maintain the impact strength of epoxy resin materials.

[0080] The dielectric constant curves of the samples in Comparative Example 1, Example 4, Example 5, and Example 6 are shown below. Figure 7 As shown, the dielectric constant of the flame-retardant epoxy resin sample in Comparative Example 1 is 3.114 at 1MHz; the dielectric constants of the flame-retardant epoxy resins in Examples 4, 5, and 6 at 1MHz reached 2.552, 2.473, and 2.424, respectively, which are 18.0%, 20.6%, and 22.2% lower than those in Comparative Example 1, indicating that the multifunctional curing agent of the present invention can effectively reduce the dielectric constant of epoxy resin materials.

[0081] The dielectric loss curves of the samples in Comparative Example 1, Example 4, Example 5, and Example 6 are shown below. Figure 8 As shown, the dielectric loss of the flame-retardant epoxy resin sample in Comparative Example 1 was 0.04214 at 1 MHz; the dielectric losses of the flame-retardant epoxy resins in Examples 4, 5, and 6 reached 0.03107, 0.02676, and 0.02424 at 1 MHz, respectively, which were reduced by 26.3%, 36.5%, and 42.5% compared with the flame-retardant epoxy resin sample in Comparative Example 1, respectively. This indicates that the multifunctional curing agent of the present invention can effectively reduce the dielectric loss of epoxy resin materials.

[0082] The appearance of the samples obtained in Comparative Example 1 and Example 6 under visible light and 365 nm ultraviolet light irradiation conditions is as follows: Figure 9 As shown in the figure, the flame-retardant epoxy resin sample in Comparative Example 1 did not exhibit obvious blue fluorescence under 365 nm ultraviolet light irradiation; while the sample obtained in Example 6, without the introduction of any additional conventional fluorescent groups, showed obvious blue fluorescence emission under 365 nm ultraviolet light irradiation. These results indicate that the flame-retardant epoxy resin material prepared in Example 6 possesses photoluminescence properties.

[0083] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A multifunctional curing agent characterized by Its general structural formula is as follows: ； Wherein, R is selected from any of the following structures: 。 2. The preparation method of the multifunctional curing agent according to claim 1, characterized in that... Includes the following steps: Step 1: Under inert gas protection, tris(2-aminoethyl)amine and 1-formaldehyde piperazine are mixed in anhydrous ethanol and heated to 80°C for reaction. Step 2: Slowly add the phosphorus-containing compound to the mixture obtained in Step 1, and stir the reaction under an inert gas at a temperature of 60~80℃. After the reaction is complete, remove the solvent by rotary evaporation and dry to obtain the target product. In step 2, the phosphorus-containing compound is selected from any one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine oxide, dimethyl phosphite, di-tert-butyl phosphonate, diphenyl phosphite, dibenzyl phosphite, and diethyl phosphite.

3. The preparation method according to claim 2, characterized in that: In step 1, the molar ratio of tris(2-aminoethyl)amine to 1-formaldehyde piperazine is 1:

3.

4. The preparation method according to claim 2, characterized in that: The inert gas is any one of nitrogen, argon, or helium.

5. The preparation method according to claim 2, characterized in that: The molar ratio of the tris(2-aminoethyl)amine to the phosphorus-containing compound is 1:

3.

6. The application of the multifunctional curing agent according to claim 1 in the preparation of flame-retardant epoxy resin materials.

7. The application according to claim 6, characterized in that: The multifunctional curing agent is used as a co-curing agent to partially replace conventional phosphorus-free amine curing agents.

8. The application according to claim 7, characterized in that: The amount of the multifunctional curing agent added is controlled by adjusting the phosphorus content, with the phosphorus content in the material controlled to be ≤2.0 wt%.

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