Phosphorus-nitrogen synergistic flame-retardant benzoxazine / epoxy resin composite material and preparation method thereof

Abstract

The invention discloses a phosphorus-nitrogen synergistic flame-retardant benzoxazine / epoxy resin composite material and a preparation method thereof. Firstly, a phenolic compound and DOPO react to generate an intermediate product, and then the intermediate product, an amine compound and paraformaldehyde are subjected to a dehydration condensation reaction to generate the phosphorus-nitrogen synergistic flame retardant benzoxazine. The phosphorus-nitrogen synergistic flame-retardant benzoxazine is added into epoxy resin for thermocuring to obtain the composite material. The prepared benzoxazine flame retardant contains phosphorus and nitrogen elements, the nitrogen-based flame retardant has the advantages of low pollution, low smoke, good compatibility with EP and the like, and a quenching effect, a dilution effect and a carbon layer barrier effect can be generated in the combustion process to prevent further combustion of flames. The composite material has better flame retardant property, can effectively reduce the risk of fire hazard caused by overheating or short circuit of equipment, and ensures the safe and stable operation of energy equipment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of flame-retardant materials, and particularly relates to a phosphorus-nitrogen synergistic flame-retardant benzoxazine / epoxy resin composite material and a preparation method thereof. BACKGROUND

[0002] Epoxy resin is an important thermosetting resin, which has excellent mechanical properties, thermal stability and chemical resistance. Epoxy resin contains two or more epoxy groups, which is a three-membered ring structure composed of one oxygen atom and two carbon atoms, and has high reactivity with bisphenol A, aliphatic, alicyclic and other organic compounds as the skeleton. Due to the unique molecular structure, it has a highly cross-linked three-dimensional network structure under the action of a curing agent. This structure provides rigidity and stability, and epoxy resin plays an indispensable role in the fields of electronics, aerospace, construction and other fields, and is one of the important basic materials for modern industry and technology development.

[0003] However, the inherent flammability, brittleness and high smoke emission during combustion of epoxy resin have become the main obstacles for the development of high-performance packaging materials. It is worth noting that the dense and possibly toxic smoke generated during the combustion of epoxy resin not only greatly hinders the escape and rescue at the fire scene, but also pollutes the environment. These short boards in comprehensive performance make it difficult for traditional epoxy resin systems to meet the increasingly stringent requirements of modern electronics, electric power and other fields for flame retardancy, long-term stability and environmental safety of packaging materials. Therefore, in order to meet higher performance requirements, it is necessary to modify the flame retardancy of epoxy resin and improve its flame retardant performance.

[0004] In recent years, P-N, P-Si, P-B and P-N-Si multi-element synergistic flame retardant systems have attracted increasing attention due to their excellent smoke suppression and flame retardant effect, high efficiency and good compatibility with polymer matrix. Most of the added flame retardants are solid or powder, and their compatibility with epoxy matrix must be carefully evaluated, and their amount must be strictly controlled. Poor compatibility or excessive addition may seriously affect the processing performance, flame retardancy and entire preparation process of epoxy resin composite material. In contrast, reactive epoxy flame retardants introduce flame retardant units into epoxy resin or curing agent molecules through direct or latent reaction, achieving high-efficiency flame retardation. Among the reactive flame retardants, a new type of liquid flame retardant benzoxazine containing a six-membered heterocyclic N-C-O structure appears in people's field of vision. Therefore, how to design and synthesize a phosphorus-nitrogen flame-retardant composite material based on benzoxazine / epoxy resin can effectively improve the flame retardant performance, and make up for the defects and risks of traditional epoxy resin in the field of electronic packaging, energy devices and other fields due to flammability and high smoke emission, which is an urgent problem to be solved by personnel in the field. SUMMARY

[0005] The purpose of the present application aims to overcome the poor flame retardancy of traditional epoxy resin, the poor compatibility of additive flame retardancy with epoxy resin, thereby affecting the flame retardant performance of the composite material. On this basis, the present application provides a phosphorus-nitrogen synergistic flame-retardant benzoxazine / epoxy resin composite material and a preparation method thereof. The phosphorus-nitrogen flame retardant obtained by the present application provides a promising halogen-free method for the flame retardance of future epoxy resin and its composite material, wherein DOPO has become one of the most important flame retardants in this field, and is used as a reactive or additive compound in several modifications, and DOPO exhibits excellent flame retardant performance in epoxy-based materials. The reactive P-H bond in DOPO can react with C=C bond, C=N bond, epoxy group and carbonyl group, which makes it have good molecular designability. However, DOPO will release phosphorus free radicals prematurely in the thermal degradation process, which seriously affects the thermal stability of the polymer. Therefore, additional flame-retardant elements such as silicon, nitrogen and sulfur are usually added in the phosphorus-derived flame retardant to enhance the flame-retardant performance.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions: The preparation method of the phosphorus-nitrogen synergistic flame-retardant benzoxazine comprises the following steps: (1) 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and phenolic compound are stirred under nitrogen atmosphere protection at 150-180°C for 18-20h, and then the intermediate product is obtained after washing and drying, and the reaction formula is as shown below, wherein R1-OH is a phenolic compound.

[0007] (2) The intermediate product, amine compound and polyformaldehyde are added into a flask, an organic solvent is added, and the reaction is carried out at 80-100°C for 6-8h, and then the phosphorus-nitrogen synergistic flame-retardant benzoxazine is obtained after the reaction is stopped, filtration, washing, rotary evaporation and drying, and the reaction formula is as shown below, wherein R2-NH2 is an amine compound, and (CH2O) is polyformaldehyde. n

[0008] Further, the molar ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and phenolic compound in step (1) is 1:1-1:1.2, and the phenolic compound is selected from one of the following structures: 、 、 .

[0009] Further, the structure of the intermediate product in step (1) is as shown below: .

[0010] ​Further, the molar ratio of the intermediate product, the amine compound and the paraformaldehyde in step (2) is 1:1:2-1:1:3.

[0011] Further, the amine compound in step (2) is any one of the following structures: .

[0012] Further, the organic solvent in step (2) is one of toluene, chloroform and tetrahydrofuran.

[0013] The application also provides a phosphorus-nitrogen synergistic flame-retardant benzoxazine prepared by the above preparation method, and the structure of the phosphorus-nitrogen synergistic flame-retardant benzoxazine is as follows: .

[0014] The application also provides a preparation method of a phosphorus-nitrogen synergistic flame-retardant benzoxazine / epoxy resin composite material, which specifically comprises the following steps: (1) uniformly mixing epoxy resin, a diluent and benzoxazine, then adding a curing agent and uniformly stirring; (2) vacuum deaerating the obtained mixture to remove air mixed in the stirring process to obtain a phosphorus-nitrogen synergistic flame-retardant benzoxazine / epoxy resin blend; (3) pouring the phosphorus-nitrogen synergistic flame-retardant benzoxazine / epoxy resin blend obtained in step (2) into a polytetrafluoroethylene mold, curing by programmed temperature rising and then slowly cooling to room temperature.

[0015] Further, the diluent is any one of dioctyl phthalate, dimethyl phthalate and diethyl phthalate; the curing agent is any one of polyether amine, 2-phenylimidazole and 4,4'-diaminodiphenyl methane; the mass fraction of benzoxazine in the composite material system is 10-40%, and the dosage ratio of epoxy resin, the diluent, benzoxazine and the curing agent is 100:10:0-84.58:16.87-25.28.

[0016] Further, the programmed temperature rising and curing process in step (3) is as follows: sequentially rising to 100°C for 1 h, 140°C for 2 h, 180°C for 2 h and 200°C for 1 h.

[0017] The working principle and advantages of the application are as follows: (1) On the basis of molecular design, the phosphorus-nitrogen synergistic flame-retardant benzoxazine flame retardant is prepared by Mannich condensation for flame-retardant modification of epoxy resin. Benzoxazine is crosslinked at high temperature, reacts with the epoxy groups of epoxy resin to form an interpenetrating network, and significantly improves the thermal stability of the material. This crosslinked network itself has a higher thermal decomposition temperature and lower flammability, and its nitrogen and oxygen heterocyclic structure preferentially absorbs heat and decomposes during combustion, consumes combustion energy, and further delays flame combustion. Therefore, the epoxy resin system modified by benzoxazine can better meet the stringent requirements of these fields for high flame-retardant grade, low smoke and non-toxic, and long-term reliability of materials, and expand its application potential in high-safety electronic energy products.

[0018] (2) The synthesized phosphorus-nitrogen synergistic flame-retardant benzoxazine is copolymerized with epoxy resin, and by introducing phosphorus and nitrogen flame-retardant elements into benzoxazine, the P-H bond in DOPO can adduct with the C=C bond in phenolic compounds to obtain an intermediate product, and the condensation reaction with amine compounds and polyformaldehyde forms a six-membered heterocyclic compound containing N-C-O structure. The phenolic hydroxyl group produced after heating or catalytic ring-opening can react with the epoxy group of epoxy resin to form a crosslinked structure, giving the polymer high thermal stability and excellent flame-retardant performance.

[0019] (3) The phosphorus-nitrogen synergistic flame-retardant benzoxazine provided by the present application can capture active free radicals such as H . and OH . in the atmosphere after decomposition, thereby interrupting the chain reaction and producing a quenching effect; the nitrogen-containing group can be oxidized to release inert gas, thereby diluting the concentration of flammable gas and oxygen, slowing down the degree of combustion, i.e. dilution effect; benzoxazine releases phosphoric acid and polyphosphoric acid when heated, accelerates the dehydration process on the surface of the polymer, promotes carbonization to form a physical barrier, and further hinders the entry of oxygen and the release of toxic gas, i.e. carbon layer barrier effect. The present application characterizes the successful synthesis of phosphorus-nitrogen synergistic flame-retardant benzoxazine by infrared spectrum and nuclear magnetic hydrogen spectrum; the combustion performance of the prepared phosphorus-nitrogen synergistic flame-retardant benzoxazine / epoxy resin composite material is studied by limiting oxygen index analysis and vertical combustion test analysis, and the composite material shows excellent flame-retardant performance. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The infrared spectrum of the benzoxazine prepared in Example 1.

[0021] Figure 2 The infrared spectrum of the benzoxazine prepared in Example 2.

[0022] Figure 3 The infrared spectrum of the benzoxazine prepared in Example 3.

[0023] Figure 4 Infrared spectrum of the benzoxazine prepared for Example 4.

[0024] Figure 5 Infrared spectrum of the benzoxazine prepared for Example 5.

[0025] Figure 6 NMR spectrum of the benzoxazine prepared for Example 1.

[0026] Figure 7 NMR spectrum of the benzoxazine prepared for Example 2.

[0027] Figure 8 NMR spectrum of the benzoxazine prepared for Example 3.

[0028] Figure 9 NMR spectrum of the benzoxazine prepared for Example 4.

[0029] Figure 10 NMR spectrum of the benzoxazine prepared for Example 5. DETAILED DESCRIPTION

[0030] In order to make the content of the present application more convenient to understand, the technical solutions described in the present application will be further described below in combination with specific embodiments, but the present application is not limited to this.

[0031] If not specifically indicated, the raw materials used in the examples of the present application can be commercially available; if not specifically indicated, the technical means used in the examples of the present application are conventional means well known to those skilled in the art.

[0032] Example 1 (1) Synthesis of phenolic reaction intermediate: 86.468 g of 9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide (DOPO, 0.4 mol) and 72.248 g (0.44 mol) of eugenol were placed in an oil bath pot and warmed to 180°C, and stirred for 20 h under the protection of nitrogen atmosphere, then 476.148 g of n-hexane was added and stirred for 30 min, and the operation was repeated three times. The reaction was dried in a vacuum oven at 100°C for 10 h, and the obtained intermediate had the following structural formula: .

[0033] (2) Synthesis of phosphorus-nitrogen synergistic flame-retardant benzoxazine monomer: 76.074 g (0.2 mol) of the intermediate product, 19.02 g (0.2 mol) of 2-aminopyrimidine, and 12.613 g (0.42 mol) of paraformaldehyde (purchased from Aldrich, MW: 30.03) were added to a flask, 300 ml of toluene was added, and the mixture was heated to 100 °C in an oil bath, and stirred for 8 h under nitrogen atmosphere. After the reaction was stopped, the mixture was washed with 0.2 mol / L NaOH solution and 0.1 mol / L HCl solution three times, respectively, and then washed with 50 °C water until neutral. The mixture was then rotary evaporated at 80 °C for 30 min, and dried in a vacuum oven for 10 h. The structure of the obtained benzoxazine is as follows: .

[0034] (3) The epoxy resin (20 g), diluent (dioctyl phthalate, 2 g), benzoxazine, and curing agent (4,4'-diaminodiphenylmethane, 4.362 g) were sequentially added, the amount of benzoxazine added was 20% of the total system, and the curing agent should be added after the solution was uniformly mixed and stirred. The total molar value of the epoxy groups in the epoxy resin should be equal to the sum of the molar values of -OH in the benzoxazine and -NH groups in the curing agent. The obtained mixture was vacuum degassed in a vacuum oven to remove air mixed during stirring. Then the mixture was poured into a polytetrafluoroethylene mold, and after warming and curing, the target product was obtained. The specific warming process of the warming and curing is as follows: warming to 100 °C for 1 h, 140 °C for 2 h, 180 °C for 2 h, and 200 °C for 1 h. After curing, the mold was removed, and the blended and cured product sample 1 was obtained.

[0035] Figure 1 The infrared spectrum of the benzoxazine monomer is shown in FIG. 1, in which the characteristic absorption peak of -CH3 is at 2900 cm-1, the characteristic absorption peak of the oxazine ring N-C-O is at 957 cm-1, the characteristic absorption peak of Ar-O-C on the oxazine ring is at 1220 cm-1. -1 -1 -1 The characteristic absorption peak of Ar-O-C on the oxazine ring is at 1220 cm-1.

[0036] Figure 6 The nuclear magnetic resonance hydrogen spectrum of the benzoxazine monomer is shown in FIG. 2, in which the characteristic hydrogen signals of O-CH2-N and Ar-CH2-N in the benzoxazine ring are at chemical shifts of 5.01 and 4.06 ppm.

[0037] Example 2 ​​(1) Synthesis of phenolic reaction intermediate: 86.468 g (0.4 mol) of DOPO and 72.248 g (0.44 mol) of isoeugenol were placed in an oil bath and heated to 180 °C, and stirred for 20 h under nitrogen atmosphere. Then 476.148 g of n-hexane was added and stirred for 30 min, and the process was repeated three times. The reaction was dried in a vacuum oven at 100 °C for 10 h. The structure of the obtained intermediate is as follows: .

[0038] (2) Synthesis of phosphorus-nitrogen synergistic flame-retardant benzoxazine monomer: 76.074 g (0.2 mol) of the intermediate, 19.02 g (0.2 mol) of 2-aminopyrimidine, and 12.613 g (0.42 mol) of paraformaldehyde (purchased from Aldrich, MW: 30.03) were added to a flask, and 300 ml of toluene was added. The mixture was heated to 100 °C in an oil bath and stirred for 8 h under nitrogen atmosphere. After the reaction was stopped, the mixture was washed with 0.2 mol / L NaOH solution and 0.1 mol / L HCl solution three times, respectively, and then washed with water at 50 °C until neutral. The mixture was rotary evaporated for 30 min and dried in a vacuum oven for 10 h. The structure of the obtained benzoxazine is as follows: .

[0039] (3) The epoxy resin (20 g), diluent (dioctyl phthalate, 2 g), benzoxazine, and curing agent (4,4'-diaminodiphenylmethane, 4.362 g) were added in sequence, and the amount of benzoxazine added accounted for 20% of the total system. The curing agent should be added after the solution was uniformly mixed and stirred. The total molar value of the epoxy groups in the epoxy resin should be equal to the sum of the molar values of -OH in the benzoxazine and -NH groups in the curing agent. The obtained mixture was vacuum degassed in a vacuum oven to remove the air mixed during stirring. Then the mixture was poured into a polytetrafluoroethylene mold, and after warming and curing, the target product was obtained. The specific warming process of the warming and curing is as follows: warming to 100 °C for 1 h, 140 °C for 2 h, 180 °C for 2 h, and 200 °C for 1 h. After curing, the mold was removed to obtain a blended and cured product sample 2.

[0040] Figure 2 The infrared spectrum of the benzoxazine monomer is shown in FIG. 1, in which 2911 cm -1 is the characteristic absorption peak of -CH3, 967 cm -1 is the characteristic absorption peak of the oxazine ring N-C-O, and 1214 cm -1 is the characteristic absorption peak of Ar-O-C on the oxazine ring.

[0041] Figure 7The NMR spectrum of the benzoxazine monomer has characteristic hydrogen signals of O-CH2-N and Ar-CH2-N in the benzoxazine ring at chemical shifts of 5.38 and 4.24 ppm.

[0042] Example 3 (1) Synthesis of phenolic reaction intermediate: 86.468 g (0.4 mol) of DOPO and 143.612 g (0.44 mol) of dehydrodiisoeugenol were placed in an oil bath pot and heated to 180°C under nitrogen atmosphere for 20 h of stirring. Then 690.24 g of n-hexane was added and stirred for 30 min, and this process was repeated three times. The reaction was dried in a vacuum oven at 100°C for 10 h. The structure of the obtained intermediate is as follows: .

[0043] (2) Synthesis of phosphorus-nitrogen synergistic flame-retardant benzoxazine monomer: 108.512 g (0.2 mol) of the intermediate, 19.02 g (0.2 mol) of 2-aminopyrimidine, and 12.613 g (0.42 mol) of paraformaldehyde (purchased from Aldrich, MW: 30.03) were added to a flask, 300 ml of toluene was added, and the mixture was heated to 100°C in an oil bath pot under nitrogen atmosphere for 8 h of stirring. After the reaction was stopped, the mixture was washed with 0.2 mol / L NaOH solution and 0.1 mol / L HCl solution three times, respectively, and then washed with water at 50°C until neutral. The mixture was then rotary evaporated for 30 min and dried in a vacuum oven for 10 h. The structure of the obtained benzoxazine is as follows: .

[0044] (3) The epoxy resin (20 g), diluent (dioctyl phthalate, 2 g), benzoxazine, and curing agent (4,4'-diaminodiphenylmethane, 4.362 g) were added in sequence, and the amount of benzoxazine added was 20% of the total system. The curing agent should be added after the solution is uniformly mixed and stirred. The total molar value of the epoxy groups in the epoxy resin should be equal to the sum of the molar values of -OH in the benzoxazine and -NH groups in the curing agent. The obtained mixture was vacuum degassed in a vacuum oven to remove air mixed during stirring. Then the mixture was poured into a polytetrafluoroethylene mold, and after warming and curing, the target product was obtained. The specific warming process of the warming and curing is as follows: warming to 100°C for 1 h, 140°C for 2 h, 180°C for 2 h, and 200°C for 1 h. After curing, the mold was removed to obtain a blended and cured product sample 3.

[0045] Figure 3 The infrared spectrum of the benzoxazine monomer has characteristic absorption peaks of -CH3 at 2913 cm -1 -CH3 at 913 cm -1characteristic absorption peak of the oxazine ring N-C-O at 1268 cm -1 characteristic absorption peak of the oxazine ring Ar-O-C.

[0046] Figure 8 NMR spectrum of the benzoxazine monomer, characteristic hydrogen signals of O-CH2-N and Ar-CH2-N in the benzoxazine ring at chemical shifts 5.28 and 4.41 ppm.

[0047] Example 4 (1) Synthesis of phenolic reaction intermediate: 86.468 g (0.4 mol) of DOPO and 72.248 g (0.44 mol) of eugenol were placed in an oil bath pot and heated to 180°C, stirred for 20 h under nitrogen atmosphere, then 476.148 g of n-hexane was added and stirred for 30 min, repeated three times. The reaction was dried in a 100°C vacuum oven for 10 h. The structure of the obtained intermediate is as follows: .

[0048] (2) Synthesis of phosphorus-nitrogen synergistic flame-retardant benzoxazine monomer: 76.074 g (0.2 mol) of the intermediate, 18.82 g (0.2 mol) of 2-aminopyridine, and 12.613 g (0.42 mol) of paraformaldehyde (purchased from Aldrich, MW: 30.03) were added to a flask, 300 ml of toluene was added, and the mixture was heated to 100°C in an oil bath pot and stirred for 8 h under nitrogen atmosphere. After the reaction was stopped, the mixture was washed with 0.2 mol / L NaOH solution and 0.1 mol / L HCl solution three times, then washed with 50°C water until neutral, and then rotary evaporated for 30 min and dried in a vacuum oven for 10 h. The structure of the obtained benzoxazine is as follows: .

[0049] (3) The epoxy resin (20 g), diluent (dioctyl phthalate, 2 g), benzoxazine, and curing agent (4,4'-diaminodiphenylmethane, 4.362 g) were added in sequence, the amount of benzoxazine added was 20% of the total system, and the curing agent should be added after the solution was uniformly mixed and stirred uniformly, and the total molar value of the epoxy groups in the epoxy resin should be equal to the sum of the molar values of -OH in the benzoxazine and -NH groups in the curing agent. The obtained mixture was vacuum degassed in a vacuum oven to remove air mixed during stirring. Then the mixture was poured into a polytetrafluoroethylene mold, and after warming and curing, the target product was obtained. The specific warming process of the warming and curing is as follows: warming to 100°C for 1 h, 140°C for 2 h, 180°C for 2 h, and 200°C for 1 h in sequence. After curing, the mold was removed to obtain the blended and cured product sample 4.

[0050] Figure 4 The infrared spectrum of the benzoxazine monomer, the characteristic absorption peak of -CH3 is at 2927 cm -1 -1 The characteristic absorption peak of the oxazine ring N-C-O is at 1272 cm -1 The characteristic absorption peak of Ar-O-C on the oxazine ring is at 1272 cm

[0051] Figure 9 The nuclear magnetic hydrogen spectrum of the benzoxazine monomer, the characteristic hydrogen signal of O-CH2-N and Ar-CH2-N in the benzoxazine ring is at chemical shift 5.06 and 4.10 ppm.

[0052] Example 5 (1) Synthesis of phenolic reaction intermediate: 86.468 g (0.4 mol) of DOPO and 72.248 g (0.44 mol) of eugenol were placed in an oil bath pot and heated to 180 °C, and stirred for 20 h under the protection of nitrogen atmosphere, then an appropriate amount of 476.148 g of n-hexane was added and stirred for 30 min, and the process was repeated three times. The reaction was dried in a 100 °C vacuum oven for 10 h. The structure of the obtained intermediate is as follows: .

[0053] (2) Synthesis of phosphorus-nitrogen synergistic flame-retardant benzoxazine monomer: 76.074 g (0.2 mol) of the intermediate, 19.02 g (0.2 mol) of 2-aminopyrazine, and 12.613 g (0.42 mol) of polyformaldehyde (purchased from Aldrich, MW: 30.03) were added to a flask, 300 ml of toluene was added, and the mixture was heated to 100 °C in an oil bath pot and stirred for 8 h under the protection of nitrogen atmosphere. After the reaction was stopped, the mixture was washed with 0.2 mol / L NaOH solution and 0.1 mol / L HCl solution three times, respectively, and then washed with water at 50 °C until neutral, and then rotary evaporated for 30 min and dried in a vacuum oven for 10 h. The structure of the obtained benzoxazine is as follows: .

[0054] ​(3) Add epoxy resin (20 g), diluent (dioctyl phthalate, 2 g), benzoxazine and curing agent (4,4'-diaminodiphenyl methane, 4.362 g) in sequence, the addition amount of benzoxazine accounts for 20% of the total system, wherein the curing agent should be added after the solution is uniformly mixed and stirred uniformly, and the total molar value of the epoxy group in the epoxy resin should be equal to the sum of the molar values of -OH in benzoxazine and -NH groups in the curing agent. The obtained mixture is vacuum degassed in a vacuum oven to remove the air mixed in the stirring process. Then the mixture is poured into a polytetrafluoroethylene mold, and after temperature curing, the target product is obtained. The specific temperature curing process of the temperature curing is as follows: sequentially heating to 100°C for 1 h, 140°C for 2 h, 180°C for 2 h, and 200°C for 1 h. After curing is completed, demolding is performed, and a blended and cured product sample 5 is obtained.

[0055] Figure 5 The infrared spectrum of the benzoxazine monomer is shown in the figure, and the characteristic absorption peak of -CH3 is at 2893 cm -1 -CH3 is at 955 cm -1 The characteristic absorption peak of the oxazine ring N-C-O is at 1222 cm -1 The characteristic absorption peak of Ar-O-C on the oxazine ring is at 1222 cm.

[0056] Figure 10 The nuclear magnetic hydrogen spectrum of the benzoxazine monomer is shown in the figure, and the characteristic hydrogen signals of O-CH2-N and Ar-CH2-N in the benzoxazine ring are at chemical shifts of 5.33 and 4.52 ppm.

[0057] Example 6 The remaining steps of this example are the same as those of Example 1, except that in step (3), the curing agent (4,4'-diaminodiphenyl methane, 4.758 g) and the addition amount of benzoxazine accounts for 10% of the total system, i.e. a blended and cured product sample 6 is obtained.

[0058] Example 7 The remaining steps of this example are the same as those of Example 1, except that in step (3), the curing agent (4,4'-diaminodiphenyl methane, 3.950 g) and the addition amount of benzoxazine accounts for 30% of the total system, i.e. a blended and cured product sample 7 is obtained.

[0059] Example 8 The remaining steps of this example are the same as those of Example 1, except that in step (3), the curing agent (4,4'-diaminodiphenyl methane, 3.374 g) and the addition amount of benzoxazine accounts for 40% of the total system, i.e. a blended and cured product sample 8 is obtained.

[0060] Comparative Example 1 For comparison with pure epoxy resin, the epoxy resin (20 g), diluent (dioctyl phthalate, 2 g) and curing agent (4,4'-diaminodiphenyl methane, 5.056 g) were added in sequence and stirred uniformly. The obtained mixture was vacuum degassed in a vacuum oven to remove the air mixed in the stirring process. Then the mixture was poured into a polytetrafluoroethylene mold to obtain the target product after curing at 90 °C for 2 h. After curing, demolding was performed to obtain the cured product sample 9.

[0061] The sample strips prepared in the above examples and comparative examples were subjected to limiting oxygen index and vertical burning analysis: Performance Test 1 Limiting Oxygen Index (LOI) Analysis was tested by an oxygen index tester (JF-3, Shanghai Precision Instruments and Meters Co., Ltd., Shanghai, China) according to ASTM D2863-17 standard. Before testing, each sample was processed into a cuboid sample strip of 100 x 6.5 x 3 mm 3 . The instrument was simply calibrated before testing. The LOI value of the sample to be tested was first estimated, and then the LOI value of the sample was determined by bisection method. All composite materials were tested for LOI for 5 times, and the average value was taken.

[0062] Table 1 is the LOI related data table of the benzoxazine and epoxy resin curing system and the pure epoxy resin curing system obtained after curing. As can be seen from the data in Table 1, the pure epoxy resin shows high flammability, with an LOI value of only 25.4%. Under the condition of benzoxazine synthesized by different amines and phenols, it is found that the benzoxazine synthesized by eugenol and 2-aminopyrimidine has the strongest flame retardancy. In addition, as the addition amount of benzoxazine increases, the limiting oxygen index first increases and then decreases. Excessive flame retardant may cause excessive or excessive reaction of the flame retardant element, so the optimal proportion of benzoxazine is 20% by mass fraction, which also shows that the addition of benzoxazine resin to the curing system described in the application improves the flame retardancy of the epoxy resin to a certain extent.

[0063] Table 1 is the limiting oxygen index of the benzoxazine / epoxy resin composite material and the pure epoxy resin material obtained from Examples 1-8 and Comparative Example 1

[0064] Performance Test 2 Vertical Burning Analysis was tested by a UL-94 vertical burning tester (YK-3050, Dongguan Yuke Automation Equipment Co., Ltd., Dongguan, China) according to ASTM D3801 standard. The size of the sample was 130 x 13 x 3 mm 3 . Each sample was burned for 5 times, and the average value was taken.

[0065] Table 2 is the experimental result data of the obtained benzoxazine and epoxy resin curing system and pure epoxy resin curing system after curing in the UL-94 vertical burning test, including vertical burning grade, whether there is melt dripping. From the table, it can be seen that the curing system of pure epoxy resin has solution dripping phenomenon, and the vertical burning grade is NR, so it does not have self-extinguishing property. After introducing the flame retardant, the improved epoxy resin passes the UL-94 test, and the vertical burning performance is also improved. And when the addition amount of benzoxazine prepared from eugenol and 2-aminopyrimidine is 20%, the vertical burning performance of the system is optimal, it can self-extinguish within 1s, there is no melt dripping phenomenon, and the burning grade reaches V-0 rating. This shows that the addition of benzoxazine can effectively improve the flame retardant effect of epoxy resin.

[0066] Table 2 is the vertical burning data of the benzoxazine / epoxy resin composite material obtained from examples 1-9 and comparative example 1 and the pure epoxy resin material In summary, the advantage of the present application is that the phosphorus-nitrogen synergistic flame-retardant benzoxazine is blended with epoxy resin to prepare a curable thermosetting resin system. Since the phosphorus and nitrogen flame-retardant elements are introduced into the benzoxazine, the quenching effect, dilution effect and carbon layer barrier effect can occur during the combustion process to limit the further combustion of the flame from three aspects, which can effectively delay the spread of fire inside the battery energy equipment, improve the use reliability and life of electronic products, and ensure the stable operation of the equipment and the safety of the user.

[0067] The above description is only the preferred embodiment of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. A method for preparing a phosphorus-nitrogen synergistic flame retardant benzoxazine, characterized in that: Specifically, the following steps are included: (1) 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and phenolic compounds were heated to 150-180°C and stirred for 18-20 h under nitrogen atmosphere protection, and then washed and dried to obtain intermediate products; (2) Add the intermediate product, amine compound, and paraformaldehyde to a flask, add organic solvent, and react at 80-100°C for 6-8 hours. After stopping the reaction, filter, wash, rotary evaporate, and dry to obtain phosphorus-nitrogen synergistic flame retardant benzoxazine.

2. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to the phenolic compound is 1:1 to 1:1.2, and the phenolic compound is selected from one of the following structures: 、 、 。 3. The preparation method according to claim 1, characterized in that: The structure of the intermediate product described in step (1) is shown below: 。 4. The preparation method according to claim 1, characterized in that: The molar ratio of the intermediate product, amine compound, and paraformaldehyde in step (2) is 1:1:2 to 1:1:

3.

5. The preparation method according to claim 1, characterized in that: The amine compound mentioned in step (2) has any one of the following structures: 。 6. The preparation method according to claim 1, characterized in that: The organic solvent mentioned in step (2) is one of toluene, chloroform, and tetrahydrofuran.

7. A phosphorus-nitrogen synergistic flame-retardant benzoxazine prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The structure of the phosphorus-nitrogen synergistic flame retardant benzoxazine is shown below: 。 8. A method for preparing a phosphorus-nitrogen synergistic flame-retardant benzoxazine / epoxy resin composite material, characterized in that: Specifically, the following steps are included: (1) After mixing the epoxy resin, diluent, and benzoxazine evenly, add the curing agent and stir evenly; (2) The mixture was subjected to vacuum degassing to remove the air mixed in during the stirring process to obtain a phosphorus-nitrogen synergistic flame retardant benzoxazine and epoxy resin blend; (3) Pour the phosphorus-nitrogen synergistic flame retardant benzoxazine and epoxy resin blend obtained in step (2) into a polytetrafluoroethylene mold, heat and cure according to the program and then slowly cool to room temperature.

9. The preparation method according to claim 8, characterized in that: The diluent is any one of dioctyl phthalate, dimethyl phthalate, and diethyl phthalate; the curing agent is any one of polyetheramine, 2-phenylimidazolium, and 4,4'-diaminodiphenylmethane; the mass fraction of benzoxazine in the composite material system is 10-40%, and the ratio of epoxy resin, diluent, benzoxazine, and curing agent is 100:10:0-84.58:16.87-25.

28.

10. The preparation method according to claim 1, characterized in that: The temperature rise curing process described in step (3) is as follows: sequentially raise the temperature to 100°C for 1 hour, 140°C for 2 hours, 180°C for 2 hours, and 200°C for 1 hour.

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