A triple charring piperazine flame retardant, a preparation method thereof and a flame-retardant polymer

Abstract

This invention relates to the field of flame retardant technology, and discloses a triple-carbonized piperazine flame retardant, its preparation method, and a flame-retardant polymer. The flame retardant provided by this invention has a multi-arm structure, with a triazine ring at its core. The branched structure of the multi-arm structure consists of DOPO and piperazine imine. Terephthalaldehyde and N-aminoethylpiperazine react via a Schiff base reaction to form a linear piperazine imine structure. DOPO then undergoes an addition reaction with the Schiff base bond of the piperazine imine to bind to the piperazine imine. The multi-arm structure, with a triazine ring as its core, significantly reduces the impact of the rigid triazine ring on the toughness of epoxy resin. The piperazine imine on the multi-arm structure is a flexible structure, which further increases the toughness of the epoxy resin. Furthermore, the piperazine imine on the multi-arm structure is also an excellent carbon source, and its combination with DOPO can produce a synergistic flame-retardant effect, significantly improving the flame-retardant performance of the flame retardant.

Description

Technical Field

[0001] This invention relates to the field of flame retardant technology, and in particular to a triple-carbonized piperazine flame retardant, its preparation method, and a flame-retardant polymer. Background Technology

[0002] Epoxy resin, as a class of high-performance thermosetting resins, has been widely used in electronics, aerospace, and new energy fields due to its excellent mechanical strength, chemical resistance, electrical insulation, and good molding and processability. However, epoxy resin has a low limiting oxygen index, classifying it as a flammable material. Furthermore, its combustion produces large amounts of toxic fumes and molten droplets, severely limiting its application in scenarios with high fire safety requirements and potentially causing secondary disasters that threaten personal and property safety. Therefore, developing efficient, low-smoke, low-toxicity additive epoxy resin flame retardants that do not impair the mechanical properties of the matrix has become an urgent need for the industry.

[0003] CN106543229A and CN110938235B indicate that 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is a novel environmentally friendly phosphorus-based flame retardant developed in the 1970s. It has a high phosphorus content and good flame retardant effect, significantly improving the flame retardant effect on thermosetting resins such as epoxy resins. However, DOPO itself has low thermal stability (below 200℃) and is prone to degradation under certain processing environments. Therefore, to address this issue, various DOPO derivatives have been developed in the prior art to increase its stability. Furthermore, while increasing the stability of DOPO, those skilled in the art have discovered that when a triazine ring structure is combined with DOPO, it can integrate a carbon source, a gas source, and a phosphorus source to produce a synergistic flame retardant effect, significantly improving both stability and the flame retardant effect.

[0004] Initially, most triazine-DOPO flame retardants had a single-arm structure, with a triazine ring to DOPO ratio of 1:1. However, the rigid structure of the triazine ring significantly improved flame retardant performance while significantly reducing the toughness of the epoxy resin. Therefore, to address this issue, existing technologies have developed triazine-DOPO flame retardants with a three-arm structure, achieving a triazine ring to DOPO ratio of 1:3. The three-arm structure solves the problem of excessive rigid triazine ring introduction by adjusting the ratio of triazine ring to DOPO. However, the triazine ring itself has excellent char-forming properties, and reducing the triazine ring ratio while increasing the proportion of phosphorus-containing structures also affects the synergistic flame retardant effect. Therefore, to further address this issue, existing technologies add flexible groups between the triazine ring and DOPO. For example, CN106543229A uses a combination of triallyl isocyanurate and DOPO, where a flexible propylene side chain acts as a bridge between the triazine ring and DOPO. For example, the flame retardant disclosed in publication number CN115925748B uses a methylpiperazine ring as a bridge between the triazine ring and DOPO. These flexible groups can reduce the impact of the rigid structure on the toughness of epoxy resin, while also providing a synergistic flame retardant effect by enhancing the carbon source. Although the above technical method alleviates the impact of the triazine-DOPO flame retardant on the toughness of epoxy resin, its impact on epoxy resin is still quite significant in practical applications. Therefore, further optimization of the triazine-DOPO flame retardant is still needed. Summary of the Invention

[0005] The purpose of this invention is to significantly suppress the effect of rigid triazine rings on the toughness of epoxy resin, significantly improve the synergistic flame retardant effect of flame retardants, and significantly increase the toughness of epoxy resin.

[0006] The flame retardant provided by this invention has a multi-arm structure. The core of this structure is a triazine ring, and the branched structure consists of DOPO and piperazine imine. Terephthalaldehyde and N-aminoethylpiperazine react via a Schiff base reaction to form a linear piperazine imine. DOPO then undergoes an addition reaction with the Schiff base bond of the piperazine imine, binding it to the piperazine imine. The multi-arm structure, with a triazine ring at its core, significantly reduces the impact of the rigid triazine ring on the toughness of the epoxy resin. The piperazine imine in the multi-arm structure is a flexible structure, which further increases the toughness of the epoxy resin. Furthermore, the piperazine imine in the multi-arm structure is also an excellent carbon source; its combination with DOPO produces a synergistic flame-retardant effect, significantly improving the flame-retardant performance of the flame retardant.

[0007] The specific technical solution of this invention is as follows: A triple-carbon piperazine flame retardant, the molecular structural formula of which is: .

[0008] As a preferred option, the raw materials for the triple char-forming piperazine flame retardant include terephthalaldehyde, N-aminoethyl piperazine, cyanuric chloride, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

[0009] A method for preparing the above-mentioned triple-carbonized piperazine flame retardant includes the following steps: (1) N-aminoethylpiperazine and terephthalaldehyde are mixed and heated to react. (2) After the heating reaction in step (1) is completed, cyanuric chloride is added under ice bath conditions to carry out a gradient heating reaction; (3) After the phased heating reaction in step (2) is completed, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is added to continue the heating reaction; (4) After the reaction in step (3) is completed, the solvent in the reaction product is removed to prepare a triple-carbonized piperazine flame retardant.

[0010] Preferably, the heating reaction conditions in step (1) include: a reaction temperature of 85~95℃ and a reaction time of 8~10h; and a molar ratio of terephthalaldehyde and N-aminoethylpiperazine of 1:2.

[0011] Preferably, the conditions for the gradient temperature reaction in step (2) include: 0~5℃ for 1~2h, 25~30℃ for 1~3h, and 80~90℃ for 3~5h; the molar ratio of cyanuric chloride and N-aminoethylpiperazine is 1:3~4.

[0012] Preferably, the solvent is one or more of methanol, ethanol, acetone, toluene, xylene, 1,4-dioxane, tetrahydrofuran, N,N-dimethylformamide, and dimethyl sulfoxide.

[0013] Preferably, the solvent in the reaction product is removed by rotary evaporation in step (4).

[0014] Preferably, the conditions for rotary evaporation include: temperature 40~60℃, rotation speed 50~200rpm, and vacuum degree 20~40mbar.

[0015] A flame-retardant polymer, comprising epoxy resin, 4,4'-diaminodiphenylmethane and a flame retardant, wherein the flame retardant is the above-mentioned triple-charring piperazine flame retardant or the triple-charring piperazine flame retardant prepared by the above preparation method.

[0016] Preferably, the mass ratio of epoxy resin, 4,4'-diaminodiphenylmethane, and flame retardant is 60:15:0.75~4.

[0017] This invention provides a multi-arm triazine-DOPO flame retardant that significantly inhibits the influence of rigid triazine rings on the toughness of epoxy resin, significantly increases the toughness of epoxy resin, and also has a synergistic flame retardant effect. Traditional single-arm triazine-DOPO flame retardants use triazine rings to improve the thermal stability of DOPO and serve as a carbon source for the flame retardant. However, the rigid structure of the triazine ring leads to a significant decrease in the toughness of the epoxy resin when introduced in excess. Therefore, those skilled in the art have proposed a three-arm triazine-DOPO flame retardant. The three-arm structure can reduce the proportion of triazine rings introduced, but this method prevents the effective charring effect of the triazine rings. Therefore, those skilled in the art have proposed adding flexible groups with excellent charring effects between the triazine rings and DOPO as a bridge. The flexible groups increase the toughness of the epoxy resin, weaken the influence of the rigid structure of the triazine rings to some extent, and supplement more charring groups, improving the synergistic flame retardant effect of the flame retardant. However, the effect of adding flexible groups on increasing toughness is limited. Therefore, this invention provides a triazine-DOPO flame retardant with a multi-arm structure. The core of the multi-arm structure is a triazine ring, and the branched structure consists of DOPO and piperazine imine. Terephthalaldehyde and N-aminoethylpiperazine react via a Schiff base reaction to form a linear piperazine imine structure. DOPO then undergoes an addition reaction with the Schiff base bond of the piperazine imine, binding it to the branched backbone of the piperazine imine. The triazine ring in this structure retains its ability to increase stability, but the amount of triazine ring introduced is significantly reduced. Furthermore, the piperazine imine is a flexible structure, which can further improve the toughness of epoxy resins. Piperazine imine is also an excellent carbon source, forming a synergistic flame retardant system with DOPO. With a phosphorus to nitrogen source ratio close to 1:1, the synergistic flame retardant effect is even better, significantly improving the char formation and flame retardancy of the flame retardant.

[0018] Furthermore, the reason for using piperazine imine as the branched structural framework in this invention is that the steric hindrance of the branched groups in the multi-arm structure synthesized directly from piperazine and DOPO reduces the stability of the multi-arm structure during synthesis, causing it to form a gel-like structure with significantly reduced solubility and processability. In contrast, the piperazine imine framework used in this invention is a flexible chain that allows the DOPO arms to diverge in three-dimensional space, avoiding structural instability caused by intramolecular tension. Simultaneously, piperazine imine increases the number of synthesis sites, significantly increasing the controllability of multi-arm synthesis. It also significantly improves stability, allowing it to remain intact during processing and at high temperatures, and provides flame retardancy.

[0019] Compared with the prior art, this application has the following technical effects: The flame retardant provided by this invention has a multi-arm structure. The core of this structure is a triazine ring, and the branched structure consists of DOPO and piperazine imine. Terephthalaldehyde and N-aminoethylpiperazine react via a Schiff base reaction to form a linear piperazine imine. DOPO then undergoes an addition reaction with the Schiff base bond of the piperazine imine, binding it to the piperazine imine. The multi-arm structure, with a triazine ring at its core, significantly reduces the impact of the rigid triazine ring on the toughness of the epoxy resin. The piperazine imine in the multi-arm structure is a flexible structure, which further increases the toughness of the epoxy resin. Furthermore, the piperazine imine in the multi-arm structure is also an excellent carbon source; its combination with DOPO produces a synergistic flame-retardant effect, significantly improving the flame-retardant performance of the flame retardant. Attached Figure Description

[0020] Figure 1 The Fourier transform infrared spectrum of detection example 1 is shown.

[0021] Figure 2 The images show the vertical combustion diagrams of Examples 1-3 and Comparative Example 1.

[0022] Figure 3 Macroscopic images of residual carbon after CCT testing of Examples 1-3 and Comparative Example 1. Detailed Implementation

[0023] The present invention will be further described below with reference to embodiments.

[0024] To better understand the content of this invention, further explanation is provided below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of this invention. Example 1:

[0025] A method for preparing a triple-carbonized piperazine flame retardant includes the following steps: (1) Mix 103.2 g of N-aminoethylpiperazine and 53.6 g of terephthalaldehyde and add them to 600 mL of solvent (1,4-dioxane), heat to 90 °C and react for 8 h; (2) Then place the reaction solution from step (1) in an ice bath and slowly add cyanuric chloride (47.8g cyanuric chloride and 200mL 1,4-dioxane mixture). After the addition is complete, carry out a gradient temperature reaction. The gradient temperature reaction conditions are: ice bath reaction for 2h, 25℃ reaction for 2h, and 80℃ reaction for 4h.

[0026] (3) After the reaction in step (2) is completed, add 129.6g of DOPO and heat to 90℃ for 8h. (4) Pour the reaction product of step (3) into the distillation flask of a rotary evaporator to remove the organic solvent and prepare triple carbonized piperazine flame retardant (ACP-DOPO). The parameters of rotary evaporation are: hot water bath set to 50°C, vacuum set to 30 mbar, and rotation speed set to 120 rpm.

[0027] The preparation method of the above flame-retardant polymer includes the following steps: Epoxy resin was added to a high-speed disperser and heated to 120°C, then stirred at 500 rpm. ACP-DOPO was added and stirring was continued to disperse it evenly. The temperature was then lowered to 70°C and 4,4'-diaminodiphenylmethane (DDM) was added and stirred for 10 min. The mixture was then degassed under a vacuum of -0.08 MPa for 10 min to remove air bubbles. During the curing reaction, the degassed system was poured into a mold pre-coated with a release agent and then cured at 120°C, 150°C, and 180°C for 2 h to complete the crosslinking reaction. After the reaction was completed, the mixture was cooled to produce flame-retardant epoxy resin. The mass ratio of epoxy resin:DDM:ACP-DOPO was 60:15:0.75. Example 2:

[0028] A method for preparing a triple-carbonized piperazine flame retardant includes the following steps: (1) Mix 103.2 g of N-aminoethylpiperazine and 53.6 g of terephthalaldehyde and add them to 600 mL of solvent (1,4-dioxane), heat to 90 °C and react for 8 h; (2) Then place the reaction solution from step (1) in an ice bath and slowly add cyanuric chloride (47.8g cyanuric chloride and 200mL 1,4-dioxane mixture). After the addition is complete, carry out a gradient temperature reaction. The gradient temperature reaction conditions are: ice bath reaction for 2h, 25℃ reaction for 2h, and 80℃ reaction for 4h.

[0029] (3) After the reaction in step (2) is completed, add 129.6g of DOPO and heat to 90℃ for 8h. (4) Pour the reaction product of step (3) into the distillation flask of a rotary evaporator to remove the organic solvent and prepare triple carbonized piperazine flame retardant (ACP-DOPO). The parameters of rotary evaporation are: hot water bath set to 50°C, vacuum set to 30 mbar, and rotation speed set to 120 rpm.

[0030] A method for preparing a flame-retardant polymer includes the following steps: Epoxy resin was added to a high-speed disperser and heated to 120°C, then stirred at 650 rpm. ACP-DOPO was then added and stirred to ensure uniform dispersion. The mixture was then cooled to 70°C and DDM was added and stirred for 10 minutes. After degassing under a vacuum of -0.09 MPa for 12 minutes, air bubbles were removed. During the curing reaction, the degassed system was poured into a mold pre-coated with a release agent and then cured at 120°C, 150°C, and 180°C for 2.5 hours to complete the crosslinking reaction. After the reaction, the mixture was cooled to produce flame-retardant epoxy resin. The mass ratio of epoxy resin to DDM to ACP-DOPO was 60:15:2.31. Example 3:

[0031] A method for preparing a triple-carbonized piperazine flame retardant includes the following steps: (1) Mix 103.2 g of N-aminoethylpiperazine and 53.6 g of terephthalaldehyde and add them to 600 mL of solvent (1,4-dioxane), heat to 90 °C and react for 8 h; (2) Then place the reaction solution from step (1) in an ice bath and slowly add cyanuric chloride (47.8g cyanuric chloride and 200mL 1,4-dioxane mixture). After the addition is complete, carry out a gradient temperature reaction. The gradient temperature reaction conditions are: ice bath reaction for 2h, 25℃ reaction for 2h, and 80℃ reaction for 4h.

[0032] (3) After the reaction in step (2) is completed, add 129.6g of DOPO and heat to 90℃ for 8h. (4) Pour the reaction product of step (3) into the distillation flask of a rotary evaporator to remove the organic solvent and prepare triple carbonized piperazine flame retardant (ACP-DOPO). The parameters of rotary evaporation are: hot water bath set to 50°C, vacuum set to 30 mbar, and rotation speed set to 120 rpm.

[0033] A method for preparing a flame-retardant polymer includes the following steps: Epoxy resin was added to a high-speed disperser and heated to 120°C, then stirred at 800 rpm. ACP-DOPO was then added and stirred to ensure uniform dispersion. The mixture was then cooled to 70°C, DDM was added, and stirred for 10 minutes. The mixture was then degassed under a vacuum of -0.1 MPa for 15 minutes to remove air bubbles. During the curing reaction, the degassed system was poured into a mold pre-coated with a release agent and then cured at 120°C, 150°C, and 180°C for 3 hours to complete the crosslinking reaction. After the reaction, the mixture was cooled to produce flame-retardant epoxy resin. The mass ratio of epoxy resin to DDM to ACP-DOPO was 60:15:3.94.

[0034] Comparative Example 1: The difference between Comparative Example 1 and Examples 1-3 is that no flame retardant was used, and the following steps were included: Epoxy resin was added to a high-speed disperser and heated to 70°C, then stirred at 650 rpm. DDM was then added and stirred for 10 min. The mixture was then degassed under a vacuum of -0.09 MPa for 12 min to remove air bubbles. The mass ratio of epoxy resin to DDM was 4:1. During the curing reaction, the degassed system was poured into a mold pre-coated with a release agent and then cured at 120°C, 150°C, and 180°C for 2.5 h to complete the crosslinking reaction. After the reaction was completed, the mixture was cooled to produce epoxy resin boards.

[0035] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that the flame retardant used is tri-(DOPO-hydroxymethylphenoxy)-triazine, as disclosed in the prior art "Preparation and Characterization of a Halogen-Free Flame Retardant Based on Phosphaphenanthrene and Triazine Groups"; Tri-(DOPO-hydroxymethylphenoxy)-triazine includes the following preparation steps: 167.4 g of p-hydroxybenzaldehyde and 145.5 g of anhydrous sodium carbonate were added to 400 mL of acetone and stirred for 1 h. Then, 83 g of cyanuric chloride was added and the mixture was slowly heated to 60 °C and refluxed for 6 h. After the reaction was completed, the mixture was cooled to room temperature and filtered under reduced pressure. The filter residue was washed with 80 °C water for 30 min with stirring. After washing three times, the product was dried to prepare tris-(4-aldehyde phenoxy)-triazine. 21.6 g of DOPO was added to 100 mL of 1,2-dichloroethane (stirred and heated to 85 °C) until completely dissolved. Then, 11 g of tris-(4-aldehyde phenoxy)-triazine was slowly added and refluxed at 85 °C for 4 h. After the reaction was completed, the mixture was filtered under reduced pressure. The filter residue was washed twice with 1,2-dichloroethane to remove excess DOPO. After washing, the product was dried to prepare tris-(DOPO-hydroxymethylphenoxy)-triazine flame retardant. A method for preparing a flame-retardant polymer includes the following steps: Epoxy resin was added to a high-speed disperser and heated to 120°C, then stirred at 800 rpm. Tris-(DOPO-hydroxymethylphenoxy)-triazine flame retardant was then added and stirred to ensure uniform dispersion. The temperature was then lowered to 70°C, DDM was added and stirred for 10 minutes, followed by degassing under -0.1 MPa vacuum for 15 minutes to remove air bubbles. During the curing reaction, the degassed system was poured into a mold pre-coated with a release agent and then cured at 120°C, 150°C, and 180°C for 3 hours to complete the crosslinking reaction. After the reaction, the system was cooled to produce flame-retardant epoxy resin. The mass ratio of epoxy resin:DDM:tris-(DOPO-hydroxymethylphenoxy)-triazine flame retardant was 60:15:0.75.

[0036] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that the flame retardant used is tri-(9-oxa-10-phosphaphenanthrene-10-oxide-10-propyl)-triazine trione (TAIC-DOPO) disclosed in CN106543229A. The preparation method of TAIC-DOPO includes the following steps: 24.9 g of triallyl isocyanurate and 60.48 g of DOPO were added to 12.5 g of dichloromethane and stirred and heated to 70 °C for 2 h. After the reaction was completed, the product was subjected to vacuum distillation to remove the solvent dichloromethane. After cooling, the product was added to 171 g of ethanol and stirred and washed for 0.5 h. The mixture was kept at 30 °C and allowed to stand and cool to room temperature. The crude product was then filtered and dried at 80 °C for 2 h to prepare TAIC-DOPO. A method for preparing a flame-retardant polymer includes the following steps: Epoxy resin was added to a high-speed disperser and heated to 120°C, then stirred at 800 rpm. TAIC-DOPO was then added and stirred to ensure uniform dispersion. The mixture was then cooled to 70°C, DDM was added, and stirred for 10 minutes. The mixture was then degassed under a -0.1 MPa vacuum for 15 minutes to remove air bubbles. During the curing reaction, the degassed system was poured into a mold pre-coated with a release agent, and then cured at 120°C, 150°C, and 180°C for 3 hours sequentially to complete the crosslinking reaction. After the reaction, the mixture was cooled to produce flame-retardant epoxy resin. The mass ratio of epoxy resin to DDM to TAIC-DOPO was 60:15:0.75.

[0037] Comparative Example 4: The difference between Comparative Example 4 and the Examples is that the flame retardant used is the triazine ring phosphorus-containing flame retardant disclosed in CN115925748B; The preparation method of triazine ring phosphorus-containing flame retardants includes the following steps: 3.3 mol of DOPO, 3.5 mol of triethylamine, and 1 mol of 1,3,5-(tripiperazine)-triazine were dissolved in 2 L of dichloromethane, stirred, and cooled to 0 °C. Then, 3.5 mol of carbon tetrachloride was added dropwise while maintaining the reaction temperature at 15 °C. The mixture was stirred during the addition, and the carbon tetrachloride was added over a period of 0.5 h. After the addition of carbon tetrachloride was complete, the mixture was heated to room temperature and stirred continuously for 2 h. After the reaction was completed, the reaction product was filtered and the precipitate was collected. The precipitate was washed three times with water and twice with acetone, and then vacuum dried to constant weight to prepare a triazine cyclic phosphorus-containing flame retardant. A method for preparing a flame-retardant polymer includes the following steps: Epoxy resin was added to a high-speed disperser and heated to 120°C, then stirred at 800 rpm. Triazine-based phosphorus-containing flame retardant was then added and stirred to ensure uniform dispersion. The mixture was then cooled to 70°C, DDM was added, and stirred for 10 minutes. The mixture was then degassed under a vacuum of -0.1 MPa for 15 minutes to remove air bubbles. During the curing reaction, the degassed system was poured into a mold pre-coated with a release agent and then cured at 120°C, 150°C, and 180°C for 3 hours to complete the crosslinking reaction. After the reaction, the mixture was cooled to produce flame-retardant epoxy resin. The mass ratio of epoxy resin to DDM to triazine-based phosphorus-containing flame retardant was 60:15:3.74.

[0038] Comparative Example 5: The difference between Comparative Example 5 and Example 1 is that the flame retardant used is the triazine hyperbranched charring agent disclosed in CN103333336B; 0.52 mol of piperazine was dissolved in 150 mL of water and added to a three-necked flask equipped with a reflux condenser, a constant pressure dropping funnel, and a stirrer. 0.25 mol of cyanuric chloride was dissolved in 80 mL of a mixed solvent of ethanol and water (volume ratio 4:1) and added dropwise to the system. The reaction was carried out at 0 °C for 4 hours. The temperature was then raised to 50 °C, and 0.78 mol of NaOH was dissolved in 80 mL of water and slowly added dropwise to the system. The reaction was carried out at this temperature for 6 hours. Finally, the temperature was raised to 95 °C and the reaction was carried out for 9 hours. Stirring was stopped, and the mixture was filtered while hot, washed three times with water, and dried under vacuum at 80 °C for 8 hours to obtain the hyperbranched triazine char agent. A method for preparing a flame-retardant polymer includes the following steps: Epoxy resin was added to a high-speed disperser and heated to 120°C, then stirred at 800 rpm. Triazine hyperbranched carbonizing agent was added and stirred to ensure uniform dispersion. The temperature was then lowered to 70°C, DDM was added and stirred for 10 minutes. The mixture was then degassed under a vacuum of -0.1 MPa for 15 minutes to remove air bubbles. During the curing reaction, the degassed system was poured into a mold pre-coated with a release agent and then cured at 120°C, 150°C, and 180°C for 3 hours to complete the crosslinking reaction. After the reaction, the mixture was cooled to produce flame-retardant epoxy resin. The mass ratio of epoxy resin to DDM to triazine hyperbranched carbonizing agent was 60:15:0.75.

[0039] Detection Example 1: The Fourier transform infrared spectra of the raw materials used in Examples 1-3 and the prepared ACP-DOPO were analyzed, and the test results are shown in [the table below]. Figure 1 ; like Figure 1 As shown, the characteristic peak of cyanuric chloride corresponds to 1275 cm⁻¹. -1 CN bond at the location and 850cm -1 The C-Cl bond at the position; N-aminoethylpiperazine at 1609 cm -1A characteristic -NH2 peak appears at 3284 cm⁻¹. -1 The characteristic peak of -NH- appears at 1692 cm⁻¹; the characteristic peak of -CHO for p-benzaldehyde is located at 1692 cm⁻¹. -1 DOPO is at 2394cm. -1 and 1236cm -1 Characteristic absorption peaks for PH and P=O bonds are observed at 1609 cm⁻¹, respectively. The FTIR spectrum of ACP-DOPO shows that the raw material contains peaks at 1609 cm⁻¹. -1 (-NH2), 3284cm -1 (-NH) - ), 850cm -1 (C-Cl), 1692cm -1 (-CHO) and 2394cm -1 The disappearance of the characteristic peaks of (pH) indicates that the reactive groups in the raw materials have fully participated in the reaction. Meanwhile, the peaks in the range of 2732~2979 cm⁻¹... -1 The characteristic absorption peaks appearing in the region correspond to the -CH2- structure on the piperazine ring, confirming that the piperazine skeleton has been successfully introduced into the target product; 1239 cm⁻¹ -1 The characteristic peaks of CN bonds at 751 cm⁻¹ -1 The characteristic peaks of the PC bonds indicate that the DOPO structure has been grafted into the molecular chain. Combining the above FTIR spectral analysis results, the disappearance of the characteristic active peaks of the raw material and the appearance of the characteristic structural peaks of the target product confirm that the flame retardant ACP-DOPO has been successfully synthesized.

[0040] Detection Example 2: The flame retardant properties and impact strength of the epoxy resins prepared in Examples 1-3 and Comparative Examples 1-5 were tested. The test items included: limiting oxygen index, vertical burning rating (UL-94), impact strength and CCT. The limiting oxygen index was tested according to the content published in GB / T 2406 93 Test Method for Burning Performance of Plastics - Oxygen Index Method; UL-94 tests were conducted in accordance with the content published in GB / T 2408-2008 "Determination of flammability of plastics - Horizontal and vertical methods"; The impact strength was tested in accordance with the content published in GB / T 1843-2008 "Determination of Impact Strength of Plastic Cantilever Beams"; CCT conducted the tests according to the content published in "GB / T 16172-2007 Test Method for Heat Release Rate of Building Materials"; The test results are shown in Table 1; Table 1 Test Results As shown in Table 1, the epoxy resins used in Examples 1-3 of this invention, made with ACP-DOPO, have a limiting oxygen index of over 29.5%, a vertical burning rating of V-0, and a dense char layer with expanded dense char layer after CCT testing. The molten strip burning time can be controlled within 15 seconds, and the impact strength can reach 34.84-47.55 kJ / m². 2 Compared with the epoxy resin without flame retardant in Comparative Example 1, the flame-retardant epoxy resin provided by this invention exhibits significantly improved flame retardant properties and impact strength. This result indicates that adding ACP-DOPO can significantly improve the synergistic flame-retardant properties of epoxy resin while also enhancing its toughness.

[0041] Comparative Examples 2, 3, 4, and 5 were prepared using triazine ring flame retardants with three-arm structures and triazine hyperbranched charring agents, respectively. The results showed that the impact strength of the epoxy resins prepared in Comparative Examples 2, 3, 4, and 5 was reduced compared to Comparative Example 1. Comparative Example 5 showed the greatest reduction in impact strength, followed by Comparative Examples 2 and 3, and then Comparative Example 4. Analysis of these results revealed that this phenomenon is significantly related to the amount of triazine ring introduced; the more triazine ring introduced, the lower the impact strength of the epoxy resin. Furthermore, the introduction of flexible groups can improve toughness and suppress the influence of triazine rings on the toughness of the epoxy resin. The multi-arm structure of this invention further overcomes the limitations of the three-arm structure, significantly reducing the influence of triazine rings. Simultaneously, the linear branching of piperazine imine provides more flexible structure, thereby achieving the technical effect of increasing both the flame retardant performance and toughness of the flame-retardant epoxy resin.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A triple-carbonized piperazine flame retardant, characterized in that, The molecular structure of the triple-carbon piperazine flame retardant is: 。 2. The triple-carbonized piperazine flame retardant according to claim 1, characterized in that, The raw materials for triple-carbonized piperazine flame retardant include terephthalaldehyde, N-aminoethyl piperazine, cyanuric chloride, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.

3. A method for preparing a triple-carbonized piperazine flame retardant according to any one of claims 1 to 2, characterized in that, Includes the following steps: (1) Mix N-aminoethylpiperazine and terephthalaldehyde and then heat to react; (2) After the heating reaction in step (1) is completed, cyanuric chloride is added under ice bath conditions to carry out a gradient heating reaction; (3) After the phased heating reaction in step (2) is completed, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide is added to continue the heating reaction; (4) After the reaction in step (3) is completed, the solvent in the reaction product is removed to prepare a triple-carbonized piperazine flame retardant.

4. The preparation method according to claim 3, characterized in that, The heating reaction conditions in step (1) include: a reaction temperature of 85~95℃ and a reaction time of 8~10h; and a molar ratio of terephthalaldehyde and N-aminoethylpiperazine of 1:

2.

5. The preparation method according to claim 3, characterized in that, The conditions for the gradient temperature reaction in step (2) include: 0~5℃ for 1~2h, 25~30℃ for 1~3h, and 80~90℃ for 3~5h; the molar ratio of cyanuric chloride and N-aminoethylpiperazine is 1:3~4.

6. The preparation method according to claim 3, characterized in that, The solvent is one or more of methanol, ethanol, acetone, toluene, xylene, 1,4-dioxane, tetrahydrofuran, N,N-dimethylformamide, and dimethyl sulfoxide.

7. The preparation method according to claim 3, characterized in that, In step (4), the solvent in the reaction product is removed by rotary evaporation.

8. The preparation method according to claim 7, characterized in that, The conditions for rotary evaporation include: temperature 40~60℃, rotation speed 50~200rpm, and vacuum degree 20~40mbar.

9. A flame-retardant polymer, characterized in that, The raw materials include epoxy resin, 4,4'-diaminodiphenylmethane and flame retardant, wherein the flame retardant is the triple char-forming piperazine flame retardant as described in any one of claims 1 to 2 or the triple char-forming piperazine flame retardant prepared by any one of claims 3 to 8.

10. The flame-retardant polymer according to claim 9, characterized in that, The mass ratio of epoxy resin, 4,4'-diaminodiphenylmethane and flame retardant is 60:15:0.75~4.

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