Preparation method and application of reactive flame retardant containing double DOPO groups and nitrogen heterocycles

Abstract

The invention discloses a preparation method and application of a reactive flame retardant containing double DOPO groups and nitrogen heterocycles, and the preparation method of the reactive flame retardant comprises the following steps: adding an amino compound R-NH2 and terephthalaldehyde into a reactor with a stirring device, adding a solvent, adding an acid to adjust the pH value to 6, then heating until the solvent is refluxed, keeping the refluxing temperature to react for a period of time, and cooling to room temperature to obtain the reactive flame retardant containing double DOPO groups and nitrogen heterocycles. Reaction liquid containing an imine intermediate product is obtained; then adding DOPO, controlling the reaction temperature to be the solvent reflux temperature, and keeping the reflux temperature to react for a period of time; after the reaction is finished, cooling, carrying out suction filtration, washing and drying to obtain a reaction type flame retardant containing double DOPO groups and nitrogen heterocyclic rings; the reaction formula is as follows: # imgabs0 # amino compound R-NH2 is 4-aminopyridine or 3-aminopyrazole, namely R is pyridyl or pyrazolyl. The synthesis and purification method of the flame retardant is simple, the reaction yield is high, and the flame retardant effect of epoxy resin can be remarkably improved by adding the flame retardant into bisphenol A epoxy resin through modification.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant materials, and specifically relates to a preparation method and application of a nitrogen-phosphorus-containing DOPO-based flame retardant. The flame retardant can be added to a polymer in a variety of ways and has excellent flame retardant properties. Background Art

[0002] Epoxy resin is a widely used thermosetting polymer material. It has the advantages of small shrinkage during the curing process, good electrical insulation, good heat resistance and corrosion resistance. It is one of the indispensable materials in industry. However, epoxy resin is a flammable material. It releases a lot of heat during combustion, which threatens people's lives and property safety, limiting its application and development. Therefore, it is very necessary to improve the flame retardant properties of epoxy resin.

[0003] The flame-retardant epoxy resin is made by introducing phosphorus into epoxy resin using reactive phosphorus flame retardants. Compared with traditional halogen flame retardants, it has the advantages of environmental protection and high flame retardant efficiency. Among them, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (hereinafter referred to as DOPO) contains active PH bonds, which can undergo addition reactions with many unsaturated groups to obtain DOPO derivatives. It has good flame retardant properties when applied to epoxy resin. Currently, DOPO-based flame retardants are a hot topic of research. At the same time, studies have found that multi-element synergistic flame retardants have the advantages of low addition amount and high flame retardant efficiency; in addition, nitrogen-containing compounds usually have the characteristics of high thermal decomposition temperature, environmental protection, and low corrosiveness, but the flame retardant effect of nitrogen-containing compounds is not outstanding, so they are often used in combination with phosphorus-based flame retardants to obtain good flame retardant effects. Lonela et al. used the imine obtained by condensation of 4-aminophenol and terephthalaldehyde and reacted it with DOPO to obtain a flame retardant PFR (Journal of Materials Chemistry A, 2014, 2 (38): 16230-16241.). After application to epoxy resin, it was found that the peak heat release rate of epoxy resin combustion was reduced by 45%, the flame retardancy level reached V-0 level, and the limiting oxygen index was increased to 40.05%. However, the P element content to reach this value was as high as 2wt%, which means that more PFR needs to be added. Wirasaputra et al. synthesized a flame retardant TDA (Macromolecular Materials and Engineering, 2016, 301 (8): 982-991.), using TDA as a flame retardant curing agent can effectively improve the reaction activity of the curing process, increase the crosslinking density of epoxy resin cured products, and when the phosphorus content in the epoxy cured product is 1.5wt%, the UL-94 fire rating test can reach V-0 level, and the limiting oxygen index reaches 32.7%, but the synthesis steps of TDA are relatively complicated and the preparation cost is high. Qian et al. synthesized a flame retardant TGIC-DOPO (Polymer, 2011, 52 (24): 5486-5493.), when the dosage is 4wt%, the limiting oxygen index of the epoxy resin reaches 35.6%, but its synthesis steps are also relatively complicated. Summary of the invention

[0004] The purpose of the present invention is to provide a preparation method and application of a flame retardant containing a double DOPO group and a nitrogen heterocycle. The preparation method of the flame retardant is simple, the reaction conditions are mild, and the reaction yield is high. At the same time, when applied to epoxy resin, it has a high flame retardant effect and a higher carbon residue rate.

[0005] The technical solution adopted by the present invention is as follows:

[0006] The preparation method of a reactive flame retardant containing a double DOPO group and a nitrogen heterocycle comprises the following steps:

[0007] S1: adding an amino compound R-NH2 and terephthalaldehyde to a reactor equipped with a stirring device, adding a solvent, adding an acid to adjust the pH to 6, then heating to reflux the solvent, maintaining the reflux temperature for a period of time to obtain a reaction solution containing an imine intermediate product;

[0008] S2: adding DOPO to the reaction solution of step S1, controlling the reaction temperature to the reflux temperature of the solvent, and maintaining the reflux temperature for a period of time;

[0009] S3: After the reaction is completed, the mixture is cooled to room temperature, filtered, washed with ethanol several times, and dried to obtain a reactive flame retardant containing a double DOPO group and a nitrogen heterocycle; the reaction formula is as follows:

[0010]

[0011] The amino compound R-NH2 is 4-aminopyridine or 3-aminopyrazole, that is, R is pyridyl or pyrazolyl, and the corresponding target products are named flame retardant I and flame retardant II, respectively.

[0012] Furthermore, in step S1, the molar ratio of the amino compound to terephthalaldehyde is 2-3:1; the solvent includes at least one of anhydrous ethanol, anhydrous methanol, acetone, and ethyl acetate; and the reaction time is 3 to 5 hours.

[0013] Furthermore, the molar ratio of DOPO in step S2 to terephthalaldehyde in step S1 is 2-2.5:1, and the reaction time is 3-5 hours.

[0014] The present invention also provides application of the reactive flame retardant containing a double DOPO group and a nitrogen heterocycle in bisphenol A type epoxy resin.

[0015] When flame retardant I is added in the preparation process of bisphenol A epoxy resin cured material at a dosage of 11.63% of the total amount of epoxy resin cured material, the vertical combustion UL-94 can reach V-0 level.

[0016] When flame retardant II is added in the preparation process of bisphenol A epoxy resin curing material at a dosage of 8.40% of the total amount of epoxy resin curing material, the vertical combustion UL-94 can reach V-0 level.

[0017] After flame retardant I was applied to modify bisphenol A epoxy resin, the residual carbon rate increased from 16.5% to 20.4% when heated to 800℃.

[0018] After flame retardant II was applied to modify bisphenol A epoxy resin, the residual carbon rate increased from 16.5% to 20.1% when heated to 800℃.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] 1) The flame retardant containing double DOPO groups and nitrogen heterocycles provided by the present invention is synthesized by a one-pot method using amino compounds, terephthalaldehyde and DOPO as raw materials. The synthesis and purification methods are simple and the reaction yield is high. At the same time, by modifying and adding to bisphenol A epoxy resin, the flame retardant effect of the epoxy resin can be significantly improved, and it has a wide range of application scenarios in the construction, electronic and electrical materials and other industries.

[0021] 2) Compared with the document Journal of Materials Chemistry A, 2014, 2 (38): 16230-16241, "using 4-aminophenol and terephthalaldehyde to condense imine and react with DOPO to obtain a flame retardant PFR", the flame retardant synthesized by the present invention is added to the bisphenol A epoxy resin cured product, the P element content is only 1wt%, and the limiting oxygen index is as high as about 40%. Under the condition of achieving similar flame retardant effect, the addition amount of the flame retardant of the present invention is much less than that of PFR. Compared with CN115612176A previously disclosed by the applicant, the invention name is "Reactive flame retardant containing DOPO group and nitrogen-containing heterocycle and its preparation method and application", under the condition of achieving about the same flame retardant effect, the addition amount of the flame retardant synthesized by the present invention is less, and the synthesis yield is higher. In summary, the present invention is more practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 1H-NMR diagram of the flame retardant I synthesized in the present invention;

[0023] Figure 2 The TG diagram of the flame retardant I synthesized in the present invention applied to epoxy resin and blank epoxy resin.

[0024] Figure 3 1H-NMR diagram of the flame retardant II synthesized in the present invention;

[0025] Figure 4 This is the TG diagram of the flame retardant II synthesized by the present invention applied to epoxy resin and blank epoxy resin. DETAILED DESCRIPTION

[0026] The DOPO-based nitrogen-containing flame retardant and the synthesis method thereof provided by the present invention are described in detail according to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0027] Example 1

[0028] The synthesis of flame retardant I is as follows:

[0029] In a 250mL three-necked flask equipped with a magnetic stirrer and a condenser, 13.4g (0.1mol) of terephthalaldehyde and 18.8g (0.2mol) of 4-aminopyridine were placed, and 150mL of anhydrous ethanol was added as a solvent. After the solid in the three-necked flask was fully dissolved, anhydrous formic acid was added dropwise to adjust the solution pH to 6, and the solution was slowly heated to the solvent reflux temperature, and the reaction temperature was maintained for 3h. After the reaction was completed, it was cooled to room temperature, and then 54g (0.25mol) of DOPO was added, and the temperature was raised to the solvent reflux temperature. The reaction temperature was maintained for 5h, and a large amount of white precipitate was generated during the reaction. After the reaction was completed, it was cooled to room temperature, filtered and washed with anhydrous ethanol (30mL×3) to obtain a white solid, and then the obtained white solid was dried in a vacuum drying oven at 70°C for 3h, and finally 66.73g of powdered white solid was obtained, with a yield of 92.81%.

[0030] Please refer to Figure 1 , Figure 1 The flame retardant I synthesized by the present invention is 1 H-NMR spectrum.

[0031] The results of the MRI test are as follows: 1 H NMR(500MHz, DMSO-d6)δ:8.22(dd,J=24.6,8.0Hz,4H),8.02(d,J=7.2Hz,2H),7.82(s,2H),7.72(dd,J=14.2,6.4Hz,2H),7.57(s,2H),7.49-7.44(m,2H ),7.41-7.36(m,4H),7.27(s,2H),7.05(d,J=7.4Hz,2H),6.87(s,2H),6.83 (dd,J=8.0,1.2Hz,2H),6.74(d,J=7.2Hz,4H),3.45(dd,J=14.0,7.0Hz,2H).

[0032] Example 2

[0033] The synthesis of flame retardant I is as follows:

[0034] In a 250mL three-necked flask equipped with a magnetic stirrer and a condenser, 13.4g (0.1mol) of terephthalaldehyde and 22.56g (0.24mol) of 4-aminopyridine were placed, and 150mL of anhydrous methanol was added as a solvent. After the solid in the three-necked flask was fully dissolved, glacial acetic acid was added dropwise to adjust the solution pH to 6, and the solution was slowly heated to the solvent reflux temperature, and the reaction temperature was maintained for 4h. After the reaction was completed, it was cooled to room temperature, and then 49.68g (0.23mol) of DOPO was added, and the temperature was raised to the solvent reflux temperature. The reaction temperature was maintained for 4h. A large amount of white precipitate was generated during the reaction. After the reaction was completed, it was cooled to room temperature, filtered and washed with anhydrous ethanol (30mL×3) to obtain a white solid, and then the obtained white solid was dried in a vacuum drying oven at 70°C for 3h, and finally 66.43g of powdered white solid was obtained, with a yield of 92.39%.

[0035] Example 3

[0036] The synthesis of flame retardant I is as follows:

[0037] In a 250mL three-necked flask equipped with a magnetic stirrer and a condenser, 13.4g (0.1mol) of terephthalaldehyde and 25.38g (0.27mol) of 4-aminopyridine were placed, and 150mL of acetone was added as a solvent. After the solid in the three-necked flask was fully dissolved, anhydrous formic acid was added dropwise to adjust the solution pH to 6, and the solution was slowly heated to the solvent reflux temperature, and the reaction temperature was maintained for 4h. After the reaction was completed, it was cooled to room temperature, and then 47.52g (0.22mol) of DOPO was added, and the temperature was raised to the solvent reflux temperature. The reaction temperature was maintained for 4h. A large amount of white precipitate was generated during the reaction. After the reaction was completed, it was cooled to room temperature, filtered and washed with anhydrous ethanol (30mL×3) to obtain a white solid, and then the obtained white solid was dried in a vacuum drying oven at 70°C for 3h, and finally 67.64g of powdered white solid was obtained, with a yield of 94.08%.

[0038] Example 4

[0039] The synthesis of flame retardant I is as follows:

[0040] 13.4g (0.1mol) of terephthalaldehyde and 28.2g (0.3mol) of 4-aminopyridine were placed in a 250mL three-necked flask equipped with a magnetic stirrer and a condenser, and 150mL of ethyl acetate was added as a solvent. After the solid in the three-necked flask was fully dissolved, glacial acetic acid was added dropwise to adjust the solution pH to 6, and the solution was slowly heated to the solvent reflux temperature and maintained at the reaction temperature for 5h. After the reaction was completed, it was cooled to room temperature, and then 43.2g (0.2mol) of DOPO was added, and the temperature was raised to the solvent reflux temperature. The reaction temperature was maintained for 3h. A large amount of white precipitate was generated during the reaction. After the reaction was completed, it was cooled to room temperature, filtered and washed with anhydrous ethanol (30mL×3) to obtain a white solid, and then the obtained white solid was dried in a vacuum drying oven at 70°C for 3h, and finally 67.20g of powdered white solid was obtained, with a yield of 93.46%.

[0041] Example 5

[0042] The synthesis steps of flame retardant II are as follows:

[0043] In a 250mL three-necked flask equipped with a magnetic stirrer and a condenser, 13.4g (0.1mol) of terephthalaldehyde and 16.6g (0.2mol) of 3-aminopyrazole were placed, and 150mL of anhydrous ethanol was added as a solvent. After the solid in the three-necked flask was fully dissolved, glacial acetic acid was added dropwise to adjust the solution pH to 6, and the solution was slowly heated to the solvent reflux temperature, and the reaction temperature was maintained for 5h. After the reaction was completed, it was cooled to room temperature, and then 54g (0.25mol) of DOPO was added, and the temperature was raised to the solvent reflux temperature, and the reaction temperature was maintained for 3h. A large amount of white precipitate was generated during the reaction. After the reaction was completed, it was cooled to room temperature, filtered and washed with anhydrous ethanol (30mL×3) to obtain a white solid, and then the obtained white solid was dried in a vacuum drying oven at 70°C for 3h, and finally 64.63g of powdered white solid was obtained, with a yield of 92.73%.

[0044] Please refer to Figure 3 , Figure 3 The flame retardant II synthesized by the present invention is 1 H-NMR spectrum.

[0045] The results of the MRI test are as follows: 1H NMR(500MHz, CDCl3)δ:9.87(s,2H),8.58(d,J=6.2Hz,2H),8.32(s,2H),8.22(d,J=6.4Hz,2H),8.11(s,2H),7.84(s,2H),7.83-7.81(m,2H ),7.81-7.79(m,2H),7.48(s,2H),7.07(d,J=6.2Hz,2H),6.97(d,J=8.6Hz,4H),6.80(s,2H),6.60(d,J=6.4Hz,2H),3.74(q,J=7.0Hz,2H).

[0046] Example 6

[0047] The synthesis steps of flame retardant II are as follows:

[0048] In a 250mL three-necked flask equipped with a magnetic stirrer and a condenser, 13.4g (0.1mol) of terephthalaldehyde and 19.92g (0.24mol) of 3-aminopyrazole were placed, and 150mL of anhydrous methanol was added as a solvent. After the solid in the three-necked flask was fully dissolved, anhydrous formic acid was added dropwise to adjust the solution pH to 6, and the solution was slowly heated to the solvent reflux temperature, and the reaction temperature was maintained for 4h. After the reaction was completed, it was cooled to room temperature, and then 49.68g (0.23mol) of DOPO was added, and the temperature was raised to the solvent reflux temperature. The reaction temperature was maintained for 4h. A large amount of white precipitate was generated during the reaction. After the reaction was completed, it was cooled to room temperature, filtered and washed with anhydrous ethanol (30mL×3) to obtain a white solid, and then the obtained white solid was dried in a vacuum drying oven at 70°C for 3h, and finally 64.90g of powdered white solid was obtained, with a yield of 93.11%.

[0049] Example 7

[0050] The synthesis steps of flame retardant II are as follows:

[0051] In a 250mL three-necked flask equipped with a magnetic stirrer and a condenser, 13.4g (0.1mol) of terephthalaldehyde and 22.41g (0.27mol) of 3-aminopyrazole were placed, and 150mL of acetone was added as a solvent. After the solid in the three-necked flask was fully dissolved, glacial acetic acid was added dropwise to adjust the solution pH to 6, and the solution was slowly heated to the solvent reflux temperature, and the reaction temperature was maintained for 4h. After the reaction was completed, it was cooled to room temperature, and then 47.52g (0.22mol) of DOPO was added, and the temperature was raised to the solvent reflux temperature. The reaction temperature was maintained for 4h. A large amount of white precipitate was generated during the reaction. After the reaction was completed, it was cooled to room temperature, filtered and washed with anhydrous ethanol (30mL×3) to obtain a white solid, and then the obtained white solid was dried in a vacuum drying oven at 70°C for 3h, and finally 65.46g of powdered white solid was obtained, with a yield of 93.92%.

[0052] Example 8

[0053] The synthesis steps of flame retardant II are as follows:

[0054] In a 250mL three-necked flask equipped with a magnetic stirrer and a condenser, 13.4g (0.1mol) of terephthalaldehyde and 24.9g (0.3mol) of 3-aminopyrazole were placed, and 150mL of ethyl acetate was added as a solvent. After the solid in the three-necked flask was fully dissolved, anhydrous formic acid was added dropwise to adjust the solution pH to 6, and the solution was slowly heated to the solvent reflux temperature, and the reaction temperature was maintained for 3h. After the reaction was completed, it was cooled to room temperature, and then 43.2g (0.2mol) of DOPO was added, and the temperature was raised to the solvent reflux temperature, and the reaction temperature was maintained for 5h. A large amount of white precipitate was generated during the reaction. After the reaction was completed, it was cooled to room temperature, filtered and washed with anhydrous ethanol (30mL×3) to obtain a white solid, and then the obtained white solid was dried in a vacuum drying oven at 70°C for 3h, and finally 64.08g of powdered white solid was obtained, with a yield of 91.94%.

[0055] Example 9

[0056] The flame retardant I prepared in Example 1 was applied to bisphenol A epoxy resin

[0057] Preparation of epoxy resin cured product: Mix flame retardant I with bisphenol A epoxy resin monomer (hereinafter referred to as EP), add a certain amount of acetone as a solvent, and when DP-SBD (flame retardant I) and EP are completely dissolved, stir thoroughly and remove acetone by rotary evaporation to obtain a viscous liquid, so that DP-SBD and EP are evenly dispersed. Then, add the curing agent diaminodiphenylmethane (DDM) after heating to 90°C, maintain the reaction temperature and stir for 30 minutes to obtain a clear and transparent solution. Finally, put the obtained clear and transparent solution into the mold for curing, and the curing conditions are: 120°C, 150°C, and 180°C for 2 hours each. After cooling to room temperature, the DP-SBD-modified epoxy resin cured product EP / DDM / I is obtained. The formula of EP / DDM / I is shown in Table 1:

[0058] Table 1: Formulation of EP / DDM / I

[0059]

[0060] Combustion performance test: The added samples were tested for limiting oxygen index (LOI) and fire rating (UL-94), and compared with the control samples EP / DDM and EP / DDM / DOPO to test their flame retardant properties. The test results are shown in Table 2:

[0061] Table 2: Limiting Oxygen Index (LOI) test and fire rating (UL-94) test data

[0062]

[0063]

[0064] In Table 2, the mass ratio of EP to DDM in the sample EP / DDM is 3.065, the mass ratio of EP to DDM in the sample EP / DDM / DOPO is 3.065, and the added amount of DOPO is controlled so that the P element content in the formula is 1%.

[0065] The limiting oxygen index (LOI) test is based on the ASTM D2863 standard, and the standard sample size is: 100mm×6.5mm×3mm. The fire rating (UL-94) test is based on the GBT2408-2008 standard, and the standard sample size is: 130mm×13mm×3mm.

[0066] From the test results in Table 2, it can be found that compared with the control blank sample EP / DDM, as the content of flame retardant I in EP increases, the limiting oxygen index of EP gradually increases, indicating that the flame retardant effect of flame retardant I is significantly enhanced. Compared with the control sample EP / DDM / DOPO with DOPO added as a flame retardant, the flame retardant performance of flame retardant I is better than that of DOPO under the condition of the same phosphorus content.

[0067] Thermal stability test: The thermal stability of epoxy resin cured products was tested using thermogravimetric analysis (TGA), and the temperature at which the epoxy resin cured product loses 5% of its mass (i.e., the initial decomposition temperature T 5％ ), the temperature at which 50% of the mass is lost is T 50％ , thermal weight loss rate peak T max , and the residual mass m at 800°C R The results are shown in Table 3:

[0068] Table 3: Thermogravimetric analysis data

[0069]

[0070]

[0071] According to the thermal stability experiment, the TG graphs of the flame retardant I synthesized in the present invention applied to epoxy resin and blank epoxy resin are as follows: Figure 2 As shown. Figure 2 It can be seen that the five curves roughly cross near 400℃, and the positions of the five curves before and after 400℃ are reversed. This shows that within 400℃, the thermal decomposition rate of epoxy resin cured material EP / DDM / I with flame retardant Ⅰ is greater than EP / DDM, because the thermal stability of the DOPO group is weaker than that of epoxy resin. However, within 400℃-800℃, the thermal decomposition rate of EP / DDM / I is less than that of EP / DDM, because after the thermal decomposition of the DOPO group, phosphorus-containing residues are generated, which slows down the thermal decomposition rate of the epoxy resin matrix, and at this time, the residual carbon rate of sample EP / DDM / I is higher than that of EP / DDM, which indicates that the sample EP / DDM / I has lower emissions of combustible gas and heat when thermally decomposed. The above results show that the application of flame retardant Ⅰ in epoxy resin can improve its thermal stability and has good flame retardant properties.

[0072] Example 10

[0073] The flame retardant II prepared in Example 5 was applied to bisphenol A epoxy resin

[0074] Preparation of epoxy resin cured product: Mix flame retardant II with bisphenol A epoxy resin monomer (hereinafter referred to as EP), add a certain amount of acetone as a solvent, and when DP-SBZ (flame retardant II) and EP are completely dissolved, stir thoroughly and remove acetone by rotary evaporation to obtain a viscous liquid, so that DP-SBZ and EP are evenly dispersed. Then, add DDM after heating to 90°C, maintain the reaction temperature and stir for 30 minutes to obtain a clear and transparent solution. Finally, put the obtained clear and transparent solution into a mold for curing, and the curing conditions are: 120°C, 150°C, and 180°C for 2 hours each. After cooling to room temperature, DP-SBZ-modified epoxy resin cured product EP / DDM / Ⅱ is obtained. The formula of EP / DDM / Ⅱ is shown in Table 4:

[0075] Table 4: EP / DDM / Ⅱ formula

[0076]

[0077]

[0078] Combustion performance test: The added samples were tested for limiting oxygen index (LOI) and fire rating (UL-94), and compared with the control samples EP / DDM and EP / DDM / DOPO to test their flame retardant properties. The test results are shown in Table 5:

[0079] Table 5: Limiting Oxygen Index (LOI) test and fire rating (UL-94) test data

[0080] Sample name Phosphorus content (%) LOI(%) UL-94(3mm) EP / DDM 0 25.3 Norating, producing droplets EP / DDM / DOPO 1 34.7 V-1, no droplets are produced EP / DDM / Ⅱ-0.25 0.25 31.7 V-1, no droplets are produced EP / DDM / Ⅱ-0.5 0.5 35.3 V-1, no droplets are produced EP / DDM / Ⅱ-0.75 0.75 37.6 V-0, no droplets are produced EP / DDM / Ⅱ-1.0 1.0 39.8 V-0, no droplets are produced

[0081] In Table 2, the mass ratio of EP to DDM in the sample EP / DDM is 3.065, the mass ratio of EP to DDM in the sample EP / DDM / DOPO is 3.065, and the added amount of DOPO is controlled so that the P element content in the formula is 1%.

[0082] The limiting oxygen index (LOI) test is based on the ASTM D2863 standard, and the standard sample size is: 100mm×6.5mm×3mm. The fire rating (UL-94) test is based on the GBT2408-2008 standard, and the standard sample size is: 130mm×13mm×3mm.

[0083] From the test results in Table 5, it can be found that compared with the control blank sample EP / DDM, as the content of flame retardant II in EP increases, the flame retardant effect is significantly enhanced. Compared with the control sample EP / DDM / DOPO with DOPO added as a flame retardant, the flame retardant performance of flame retardant II is better than that of DOPO under the condition of the same phosphorus content.

[0084] Thermal stability test: The thermal stability of epoxy resin cured products was tested using thermogravimetric analysis (TGA), and the temperature at which the epoxy resin cured product loses 5% of its mass (i.e., the initial decomposition temperature T 5％ ), the temperature at which 50% of the mass is lost is T 50％ , thermal weight loss rate peak T max , and the residual mass m at 800°C R The results are shown in Table 6:

[0085] Table 6: Thermogravimetric analysis data

[0086] Sample name <![CDATA[T 50％ (℃)]]> <![CDATA[T max (℃)]]> <![CDATA[T 50％ (℃)]]> <![CDATA[m R (wt%)]]> EP / DDM 353 385 392 16.5 EP / DDM / Ⅱ-0.25 341 364 382 17.6 EP / DDM / Ⅱ-0.5 336 362 379 18.3 EP / DDM / Ⅱ-0.75 331 359 376 19.0 EP / DDM / Ⅱ-1.0 328 355 374 20.1

[0087] According to the thermal stability experiment, the TG graphs of the flame retardant II synthesized in the present invention applied to epoxy resin and blank epoxy resin are as follows: Figure 4 As shown. Figure 4 It can be seen that the five curves roughly cross near 400℃, and the positions of the five curves before and after 400℃ are reversed. This shows that within 400℃, the thermal decomposition rate of epoxy resin cured material EP / DDM / Ⅱ with flame retardant Ⅱ is greater than EP / DDM, because the thermal stability of the DOPO group is weaker than that of epoxy resin. However, within 400℃-800℃, the thermal decomposition rate of EP / DDM / Ⅱ is less than EP / DDM, because after the thermal decomposition of the DOPO group, phosphorus-containing residues are generated, which slows down the thermal decomposition rate of the epoxy resin matrix, and at this time, the residual carbon rate of sample EP / DDM / Ⅱ is higher than that of EP / DDM, which indicates that the sample EP / DDM / Ⅱ has lower emissions of combustible gas and heat when thermally decomposed. The above results show that the application of flame retardant Ⅱ in epoxy resin can improve its thermal stability and has good flame retardant properties.

[0088] The contents described in this specification are merely an enumeration of implementation forms of the inventive concept, and the protection scope of the present invention should not be regarded as being limited to the specific forms described in the embodiments.

Claims

1. A method for preparing a reactive flame retardant containing a double DOPO group and a nitrogen heterocycle, characterized in that The following steps are involved: S1: adding an amino compound R-NH2 and terephthalaldehyde to a reactor equipped with a stirring device, adding a solvent, adding an acid to adjust the pH to 6, then heating to reflux the solvent, maintaining the reflux temperature for a period of time to obtain a reaction solution containing an imine intermediate product; S2: adding DOPO to the reaction solution of step S1, controlling the reaction temperature to the reflux temperature of the solvent, and maintaining the reflux temperature for a period of time; S3: After the reaction is completed, the mixture is cooled to room temperature, filtered, washed with ethanol several times, and dried to obtain a reactive flame retardant containing a double DOPO group and a nitrogen heterocycle; the reaction formula is as follows: The amino compound R-NH2 is 4-aminopyridine or 3-aminopyrazole, that is, R is pyridyl or pyrazolyl, and the corresponding target products are named flame retardant I and flame retardant II, respectively.

2. The method for preparing a reactive flame retardant containing a double DOPO group and a nitrogen heterocycle according to claim 1, characterized in that In step S1, the molar ratio of the amino compound to terephthalaldehyde is 2-3:1; the solvent includes at least one of anhydrous ethanol, anhydrous methanol, acetone, and ethyl acetate; and the reaction time is 3 to 5 hours.

3. The method for preparing a reactive flame retardant containing a double DOPO group and a nitrogen heterocycle according to claim 1, characterized in that The molar ratio of DOPO in step S2 to terephthalaldehyde in step S1 is 2-2.5:1, and the reaction time is 3-5 hours.

4. A reactive flame retardant containing a double DOPO group and a nitrogen heterocycle prepared by the method according to any one of claims 1 to 3.

5. Use of the reactive flame retardant containing a bis-DOPO group and a nitrogen heterocycle as claimed in claim 4 in bisphenol A type epoxy resin.

6. The use according to claim 5, characterized in that When flame retardant I is used in the preparation of bisphenol A epoxy resin cured material and its dosage is 11.63% of the total amount of epoxy resin cured material, the vertical combustion UL-94 can reach V-0 level.

7. The use according to claim 5, characterized in that When flame retardant II is used in the preparation of bisphenol A epoxy resin cured material and its dosage is 8.40% of the total amount of epoxy resin cured material, the vertical combustion UL-94 can reach V-0 level.

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