Hyperbranched benzoxazine resin containing P-N-Si and preparation method thereof

Abstract

The invention relates to hyperbranched benzoxazine resin containing P-N-Si and a preparation method of the hyperbranched benzoxazine resin. Belongs to the technical field of high-molecular compounds, and the hyperbranched flame-retardant toughened benzoxazine resin is obtained by synthesizing a toughened benzoxazine monomer containing three flame-retardant elements P-N-Si through a one-step method and then heating and carrying out a ring-opening crosslinking reaction. By virtue of a unique P-N-Si ternary flame-retardant system, the excellent flame-retardant property is shown. Compared with a traditional benzoxazine material, the benzoxazine material has the advantages that the thermal stability is remarkably improved, flame spreading can be effectively inhibited in a high-temperature environment, the combustion rate is reduced, and a solid guarantee is provided for safe application of the material. Meanwhile, the toughening property endows the material with more excellent mechanical properties, the brittleness of the material is effectively improved, the impact resistance of the material is enhanced, and the application range is widened.

Description

Technical Field

[0001] The present invention belongs to the technical field of high molecular compounds, and relates to a hyperbranched benzoxazine resin containing P-N-Si and a preparation method thereof. Background Art

[0002] Benzoxazine resin is a new type of thermosetting resin formed by the Mannich condensation reaction of phenolic compounds, primary amine compounds and aldehyde compounds. It has unique properties such as good heat resistance, flame retardancy, and flexibility in molecular design. Moreover, it does not require a catalyst during the curing process, has zero volume shrinkage, and does not release small molecules. Compared with many thermosetting resins, benzoxazine has flexible molecular designability, rich raw material sources and unique performance advantages, making it replace and surpass traditional thermosetting resins in many fields. However, the long-term heat resistance and toughness of benzoxazine resin are not high, and the material is prone to cause fires during use, resulting in economic losses and casualties, and cannot meet the requirements of high-performance materials. Therefore, it is necessary to explore a high-strength, high-toughness, high-temperature-resistant and high-flame-retardant benzoxazine resin. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems of insufficient long-term flame retardancy and toughness of high-performance benzoxazine resin. The present invention designs a type of flame-retardant and toughening benzoxazine resin with a hyperbranched structure, making it have excellent thermal stability, toughness and flame retardancy, and having the characteristics of hyperbranched polymers while retaining the advantages of traditional benzoxazine resin. The purpose of the present invention also lies in providing a preparation method for a type of flame-retardant and toughening benzoxazine with a hyperbranched structure.

[0004] To achieve the above purpose, the present invention provides the following technical solutions: A preparation method of a hyperbranched benzoxazine resin containing P-N-Si, the method comprising the following steps: S1. Preparation of hyperbranched benzoxazine monomer: The hyperbranched benzoxazine monomer is obtained by the Mannich reaction of a triphenol compound, a diamine compound and paraformaldehyde; S2. After the ring-opening crosslinking reaction of the hyperbranched benzoxazine monomer, a high flame-retardant and toughening hyperbranched benzoxazine resin containing P-N-Si is obtained.

[0005] The preparation of the hyperbranched benzoxazine monomer comprises the following steps: S11. Dissolve paraformaldehyde and the diamine compound in an organic solvent, and stir evenly under an ice-water bath condition for 20-60 min to uniformly mix the raw materials to form a solution. The diamine compound is a silicon-nitrogen-containing diamine compound or a phosphorus-silicon-containing diamine compound; S12. Dissolve the tri-phenol compound in an organic solvent, mix it with the solution in S11, and carry out a condensation reflux reaction at a temperature of 60 - 120 °C for 10 - 24 h until it becomes a light yellow solution. The tri-phenol compound is a phosphorus-containing tri-phenol compound or a nitrogen-containing tri-phenol compound; S13. After the reaction is completed, rotary evaporate the light yellow solution in S12 at 40 - 100 °C to remove most of the solvent. When the solution becomes slightly viscous, pour it into a petri dish to obtain the crude product of the hyperbranched benzoxazine monomer; S14. Dissolve the crude monomer product in an appropriate amount of organic solvent, filter it, collect and dry it to obtain the purified hyperbranched benzoxazine monomer.

[0006] This method prepares hyperbranched benzoxazine monomers through the Mannich reaction of phosphorus-containing or nitrogen-containing tri-phenol compounds, silicon nitride or phosphorus-containing silicon diamine compounds, and paraformaldehyde. Finally, the monomers are ring-opened and cross-linked to form a P-N-Si high flame-retardant and toughened hyperbranched benzoxazine resin. Hyperbranched polymers are dendritic branched macromolecules composed of a series of branched units. Compared with traditional linear polymers, hyperbranched polymers have characteristics such as good solubility, low viscosity, and a large number of terminal functional groups. Hyperbranched benzoxazine has high reactivity, which makes it easy to be functionalized or cross-linked and can play a unique role in different application scenarios. Its low viscosity characteristic greatly improves the processing performance, facilitating operation in actual production. It also has excellent solubility, is very suitable for solution processing, and has high thermal stability, showing outstanding performance in high-temperature resistance. In addition, it has excellent mechanical properties, presenting characteristics of high strength and good toughness, and has multifunctionality, which can be modified to meet diverse needs.

[0007] Furthermore, the weight-average molecular weight of the hyperbranched benzoxazine monomer is 1100 - 6000; Furthermore, the molecular weight distribution index of the P-N-Si hyperbranched benzoxazine resin is 1.7 - 3.5.

[0008] Furthermore, the phosphorus-containing tri-phenol compound is one of the following structures: .

[0009] Furthermore, the nitrogen-containing tri-phenol compound is one of the following structures: .

[0010] Furthermore, the silicon nitride diamine compound is one of the following structures: .

[0011] Furthermore, the phosphorus-containing silicon diamine compound is one of the following structures: 。

[0012] Further, the organic solvent is any one of 1,4-dioxane, ethanol, dimethyl sulfoxide, N,N-dimethylacetamide, petroleum ether, chloroform, ethyl acetate, tetrahydrofuran, dimethylformamide, methyl ethyl ketone, cyclohexanone, toluene, and xylene.

[0013] Further, in step S11, the molar ratio of the diamine compound to paraformaldehyde is 1:(2.2 - 2.4).

[0014] Further, in step S12, the molar ratio of the tri-phenol compound to the diamine compound is 2:3.

[0015] Further, in step S2, the hyperbranched benzoxazine resin is prepared from hyperbranched benzoxazine monomers, or can also be prepared by ring-opening cross-linking reaction of hyperbranched benzoxazine monomers with one or more small molecular structure benzoxazine monomers; the small molecular structure benzoxazine monomers are one or more of bisphenol A aniline type benzoxazine monomers, bisphenol A p-phenylenediamine type benzoxazine monomers, phenolphthalein aniline type benzoxazine monomers, phenolphthalein p-phenylenediamine type benzoxazine monomers, bisphenol S aniline type benzoxazine monomers, and bisphenol S p-phenylenediamine type benzoxazine monomers.

[0016] Further, the hyperbranched benzoxazine monomers and thermosetting resin monomers are matched in any proportion to form a modified combination.

[0017] Further, the thermosetting resin monomer is one of epoxy resin, bismaleimide resin, and phenolic resin; Further, the present invention provides a hyperbranched benzoxazine monomer, which is prepared by reacting a tri-phenol compound, a diamine compound, paraformaldehyde, and an organic solvent according to the following preparation method, and has a weight average molecular weight of 1100 - 6000.

[0018] The preparation method is as follows: Mix according to the molar ratio of phenol, amine, and paraformaldehyde of 2:3:(6.6 - 7.0) in an organic solvent, heat up to 80 - 120 °C, keep the temperature constant for reaction for 10 - 24 h, after the reaction is completed, cool the reaction mixture to room temperature, remove most of the solvent by rotary evaporation under reduced pressure to obtain a relatively viscous crude product, place the crude product in a vacuum drying oven and dry it at 60 - 80 °C to constant weight, then dissolve it with an organic solvent and purify it by recrystallization method to obtain hyperbranched benzoxazine.

[0019] Furthermore, the purified product of hyperbranched benzoxazine is ground into powder and placed in a forced-air drying oven for temperature curing. The temperature-time parameters are set at 150°C to 220°C, with a total time of 8 h, and the temperature is increased by 20°C every 2 h, obtaining a P-N-Si flame retardant toughened hyperbranched benzoxazine resin.

[0020] Another object of the present invention is to provide a P-N-Si highly flame retardant toughened hyperbranched benzoxazine resin. This resin is prepared by the above method, with a molecular weight distribution index of 1.7 to 3.5 P-N-Si, a maximum flexural strength of 177.00 MPa, a maximum tensile strength of 90.74 MPa, a longest ignition time of 210 S, a lowest peak heat release rate of 368.9 (W / g), an optimal total heat release rate of 32.80 (KJ / g), a maximum limiting oxygen index of 51%. The highest fracture toughness K IC is 1.76 MPa·m 1 / 2 , the maximum critical strain energy release G IC is 220.38 J·m², the highest glass transition temperature is 233ºC, and the maximum char residue rate is 63.90%.

[0021] Compared with the prior art, the present invention adopts the above technical solutions and has the following technical effects: 1. The present invention synthesizes a toughened benzoxazine monomer containing three flame retardant elements of P-N-Si by the "one-step method", and then obtains a hyperbranched benzoxazine resin through a heating ring-opening crosslinking reaction. With a unique P-N-Si ternary flame retardant system, it exhibits excellent flame retardant performance. Compared with traditional benzoxazine materials, its thermal stability is significantly improved, effectively inhibiting flame spread and reducing the combustion rate in a high-temperature environment, providing a solid guarantee for the safe application of materials. At the same time, the toughening characteristics endow the material with better mechanical properties, effectively improving the brittleness of the material, enhancing its impact resistance, and broadening the application range. Phosphorus- or nitrogen-containing tri-phenolic compounds and silicon nitride- or phosphorus-containing silicon diamine compounds are used as intrinsic flame retardants to build a stable flame retardant network inside the material, not only improving the flame retardant grade of the material, but also ensuring the stability of the material during processing and use, opening up a new path for the research and development of high-performance materials.

[0022] 2. The hyperbranched benzoxazine monomer provided by the present invention can be combined with traditional benzoxazine monomers such as bisphenol A-aniline type benzoxazine monomers, as well as thermosetting resin monomers such as epoxy resins and bismaleimides in any proportion to form a modified combination, and further cured and crosslinked to obtain a flame-retardant and toughened thermosetting composite material. This flexible matching characteristic enables the modified combination to precisely regulate its properties according to the requirements of different application scenarios. When facing strict fire safety standards and impact resistance performance requirements, increasing the proportion of the P-N-Si hyperbranched benzoxazine monomer can obtain a flame-retardant, high-strength and tough benzoxazine resin, reducing potential safety hazards and improving the practicality of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 (a) is the combustion test diagram of Example 1, Figure 1 (b) is the combustion test diagram of Comparative Example 1; Figure 2 is the flexural strength diagram of the prepared hyperbranched benzoxazine resin; Figure 3 is the tensile strength diagram of the prepared hyperbranched benzoxazine resin; Figure 4 is the preparation flow chart of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. The preparation flow chart of the present invention is as Figure 4 shown.

[0025] Example 1:

[0026] S1. Dissolve 0.033 mol of paraformaldehyde and 0.015 mol of the compound with the silicon-nitrogen diamine structural formula Ⅰ in 50 ml of 1,4-dioxane, and stir evenly under an ice-water bath condition for 30 min to uniformly mix the raw materials; S2. Dissolve 0.01 mol of the compound with the phosphorus-containing triol structural formula Ⅰ in 50 ml of 1,4-dioxane, mix it with the solution prepared in S1, and carry out a condensation reflux reaction at 110 °C for 24 h until the solution turns light yellow; S3. After the reaction, rotate and evaporate the light yellow solution at 60 °C to remove most of the solvent. When the solution becomes slightly viscous, pour it into a petri dish to obtain a crude product of the P-N-Si flame-retardant and toughened hyperbranched benzoxazine monomer; S4. Dissolve the crude product in N,N-dimethylformamide, filter out the insoluble impurities, collect and wash the solid. Dry the solid in vacuum at 100 °C for 6 h to remove the residual solvent and obtain the purified benzoxazine product.

[0027] S5. Heat and melt the purified benzoxazine monomer, then pour it into a mold coated with a release agent and preheated, and react in an oven at 180 °C for 4 h. After the ring-opening cross-linking reaction of the benzoxazine monomer, a P-N-Si flame-retardant and toughened hyperbranched benzoxazine resin is obtained.

[0028] The reaction formulas involved in Example 1 are as follows:

[0029] Example 2:

[0030] S1. Dissolve 0.033 mol of paraformaldehyde and 0.015 mol of the compound with the silicon-nitrogen diamine structural formula Ⅱ in 50 ml of 1,4-dioxane, and stir evenly in an ice-water bath for 20 min to mix the raw materials evenly. S2. Dissolve 0.01 mol of the compound with the phosphorus-containing triol structural formula Ⅱ in 50 ml of 1,4-dioxane, mix it with the solution prepared in S1, and carry out a reflux reaction at 110 °C for 20 h until the solution turns light yellow. S3. After the reaction is completed, rotary evaporate the light yellow solution at 60 °C to remove most of the solvent. When the solution becomes slightly viscous, pour it into a petri dish to obtain the crude product of the P-N-Si flame-retardant and toughened hyperbranched benzoxazine monomer. S4. Dissolve the crude product in ethanol, filter out the insoluble impurities, collect and wash the solid. Dry the solid in vacuum at 60 °C for 10 h to remove the residual solvent and obtain the purified benzoxazine product.

[0031] S5. Heat and melt the purified benzoxazine monomer, then pour it into a mold coated with a release agent and preheated, and react in an oven at 200 °C for 8 h. After the ring-opening cross-linking reaction of the benzoxazine monomer, a P-N-Si flame-retardant and toughened hyperbranched benzoxazine resin is obtained.

[0032] The reaction formulas involved in Example 2 are as follows:

[0033] Example 3: S1. Dissolve 0.033 mol of paraformaldehyde and 0.015 mol of the compound with the silicon-nitrogen diamine structural formula Ⅳ in 50 ml of 1,4-dioxane, and stir evenly in an ice-water bath for 40 min to mix the raw materials evenly. S2. Dissolve 0.01 mol of the compound with the structure of phosphotriphenol Ⅲ in 50 ml of 1,4-dioxane, mix it with the solution prepared in S1, and carry out a condensation reflux reaction at 100 °C for 18 h until the solution turns light yellow; S3. After the reaction is completed, rotate and evaporate the light yellow solution at 60 °C to remove most of the solvent. When the solution becomes slightly viscous, pour it into a petri dish to obtain a crude product of the P-N-Si flame retardant and toughened hyperbranched benzoxazine monomer; S4. Dissolve the crude product in tetrahydrofuran organic solvent and then filter to remove insoluble impurities. Collect and wash the solid. Dry the solid in a vacuum at 60 °C for 6 h to remove the residual solvent and obtain the purified benzoxazine product.

[0034] S5. Heat and melt the purified benzoxazine monomer and then pour it into a mold coated with a release agent and preheated. React in an oven at 150 - 220 °C for 4 - 8 h. After the ring-opening cross-linking reaction of the benzoxazine monomer, a P-N-Si flame retardant and toughened hyperbranched benzoxazine resin is obtained.

[0035] The reaction formulas involved in Example 3 are as follows:

[0036] Example 4: S1. Dissolve 0.033 mol of paraformaldehyde and 0.015 mol of the compound with the structure of silicon nitride diamine Ⅴ in 50 ml of 1,4-dioxane, and stir evenly under an ice-water bath condition for 30 min to make the raw materials well mixed; S2. Dissolve 0.01 mol of the compound with the structure of phosphotriphenol Ⅳ in 50 ml of 1,4-dioxane, mix it with the solution prepared in S1, and carry out a condensation reflux reaction at 100 °C for 20 h until the solution turns light yellow; S3. After the reaction is completed, rotate and evaporate the light yellow solution at 60 °C to remove most of the solvent. When the solution becomes slightly viscous, pour it into a petri dish to obtain a crude product of the P-N-Si flame retardant and toughened hyperbranched benzoxazine monomer; S4. Dissolve the crude product in ethyl acetate, filter insoluble impurities, collect and wash the solid. Dry the solid at 60 °C for 8 h to remove the residual solvent and obtain the purified benzoxazine product.

[0037] S5. Heat and melt the purified benzoxazine monomer and then pour it into a mold coated with a release agent and preheated. React in an oven at 180 °C for 8 h. After the ring-opening cross-linking reaction of the benzoxazine monomer, a P-N-Si flame retardant and toughened hyperbranched benzoxazine resin is obtained.

[0038] The reaction formulas involved in Example 4 are as follows:

[0039] Example 5: S1. Dissolve 0.033 mol of paraformaldehyde and 0.015 mol of the compound with the phosphorus-silicon diamine structural formula Ⅰ in 50 ml of 1,4-dioxane, and stir evenly under an ice-water bath condition for 30 min to uniformly mix the raw materials; S2. Dissolve 0.01 mol of the compound with the nitrogen-containing tri-phenol structural formula Ⅰ in 50 ml of 1,4-dioxane, mix it with the solution prepared in S1, and carry out a condensation reflux reaction at 110 °C for 24 h until the solution turns light yellow; S3. After the reaction is completed, rotate and evaporate the light yellow solution at 60 °C to remove most of the solvent. When the solution becomes slightly viscous, pour it into a petri dish to obtain a crude product of the P-N-Si flame-retardant and toughened hyperbranched benzoxazine monomer; S4. Dissolve the crude product in toluene, filter out insoluble impurities, collect and wash the solid. Dry the solid in an oven at 100 °C for 12 h to remove the residual solvent and obtain the purified benzoxazine product.

[0040] S5. Heat and melt the purified benzoxazine monomer and pour it into a mold coated with a release agent and preheated. React in an oven at 220 °C for 6 h. After the ring-opening cross-linking reaction of the benzoxazine monomer, a P-N-Si flame-retardant and toughened hyperbranched benzoxazine resin is obtained.

[0041] The reaction formulas involved in Example 5 are as follows:

[0042] Example 6: S1. Dissolve 0.033 mol of paraformaldehyde and 0.015 mol of the compound with the phosphorus-silicon diamine structural formula Ⅱ in 50 ml of 1,4-dioxane, and stir evenly under an ice-water bath condition for 30 min to uniformly mix the raw materials; S2. Dissolve 0.01 mol of the compound with the nitrogen-containing tri-phenol structural formula Ⅱ in 50 ml of 1,4-dioxane, mix it with the solution prepared in S1, and carry out a condensation reflux reaction at 120 °C for 20 h until the solution turns light yellow; S3. After the reaction is completed, rotate and evaporate the light yellow solution at 60 °C to remove most of the solvent. When the solution becomes slightly viscous, pour it into a petri dish to obtain a crude product of the P-N-Si flame-retardant and toughened hyperbranched benzoxazine monomer; S4. Dissolve the crude product in chloroform, filter out insoluble impurities, collect and wash the solid. Dry the solid under vacuum at 50 °C for 12 h to remove the residual solvent and obtain the purified benzoxazine product.

[0043] S5. Heat the purified benzoxazine monomer until it melts, then pour it into a mold coated with a release agent and preheated. React at 200 °C in an oven for 6 h. After the ring-opening cross-linking reaction of the benzoxazine monomer, a P-N-Si flame retardant and toughened hyperbranched benzoxazine resin is obtained.

[0044] The reaction formula involved in Example 6 is as follows:

[0045] Example 7: S1. Dissolve 0.033 mol of paraformaldehyde and 0.015 mol of the compound with the phosphorus-silicon diamine structural formula Ⅳ in 50 ml of 1,4-dioxane, and stir evenly under an ice-water bath condition for 60 min to make the raw materials well mixed. S2. Dissolve 0.01 mol of the compound with the nitrogen-containing triol structural formula Ⅲ in 50 ml of 1,4-dioxane, mix it with the solution prepared in S1, and carry out a reflux reaction at 120 °C for 24 h until the solution turns light yellow. S3. After the reaction, rotate and evaporate the light yellow solution at 60 °C to remove most of the solvent. When the solution becomes slightly viscous, pour it into a petri dish to obtain a crude product of the P-N-Si flame retardant and toughened hyperbranched benzoxazine monomer. S4. Dissolve the crude product in methyl ethyl ketone, filter out insoluble impurities, collect and wash the solid. Keep the solid at 80 °C for 8 h to remove the residual solvent and obtain the purified benzoxazine product.

[0046] S5. Heat the purified benzoxazine monomer until it melts, then pour it into a mold coated with a release agent and preheated. React at 180 °C in an oven for 8 h. After the ring-opening cross-linking reaction of the benzoxazine monomer, a P-N-Si flame retardant and toughened hyperbranched benzoxazine resin is obtained.

[0047] The reaction formula involved in Example 7 is as follows:

[0048] Comparative Example 1: Bisphenol A-aniline type benzoxazine resin: S1. Dissolve 0.042 mol of paraformaldehyde and 0.01 mol of bisphenol A in 50 ml of 1,4-dioxane, and stir evenly under an ice-water bath condition for 30 min to make the raw materials well mixed. S2. Dissolve 0.02 mol of aniline in 50 ml of 1,4-dioxane, mix it with the solution prepared in S1, and carry out a reflux reaction at 120 °C for 24 h until the solution turns light yellow. S3. After the reaction is completed, the light yellow solution is then subjected to rotary evaporation at 60 °C to remove most of the solvent. When the solution becomes slightly viscous, it is poured into a petri dish to obtain the crude product of bisphenol A-aniline type benzoxazine monomer; S4. The crude product is dissolved in a mixed solvent of toluene and acetone (organic solvent), and then filtered to remove insoluble impurities. The solid is collected and washed. The solid is dried in vacuo at 100 °C for 10 h to remove the residual solvent, obtaining the purified benzoxazine product.

[0049] S5. The purified bisphenol A / aniline benzoxazine product is heated and melted, and then poured into a mold coated with a release agent and preheated. The reaction is carried out in an oven at 220 °C for 8 h. After the ring-opening cross-linking reaction of the benzoxazine monomer, bisphenol A / aniline benzoxazine resin is obtained.

[0050] Comparative Example 2: Phenol-aniline-based benzoxazine: S1. 0.02 mol of paraformaldehyde and 0.01 mol of aniline are dissolved in 50 ml of 1,4-dioxane, and stirred evenly under an ice-water bath for 40 min to make the raw materials well mixed; S2. 0.01 mol of phenol is dissolved in 50 ml of 1,4-dioxane and mixed with the solution prepared in S1. The reaction is carried out under reflux condensation at 120 °C for 24 h until the solution turns light yellow; S3. After the reaction is completed, the light yellow solution is then subjected to rotary evaporation at 60 °C to remove most of the solvent. When the solution becomes slightly viscous, it is poured into a petri dish to obtain the crude product of benzoxazine monomer; S4. The crude product is dissolved in toluene and then filtered to remove insoluble impurities. The solid is collected and washed. The solid is dried in vacuo at 100 °C for 10 h to remove the residual solvent, obtaining the purified benzoxazine product.

[0051] S5. The purified benzoxazine product is heated and melted, and then poured into a mold coated with a release agent and preheated. The reaction is carried out in an oven at 220 °C for 8 h. After the ring-opening cross-linking reaction of the benzoxazine monomer, phenol-aniline-based benzoxazine resin is obtained.

[0052] Comparative Example 3: S1. 9 g of bisphenol A-aniline type benzoxazine and 1 g of the P-N-Si-containing highly flame-retardant and toughened hyperbranched benzoxazine prepared in Example 1 are added to a clean beaker, acetone is added, and ultrasonic treatment is carried out at room temperature for 30 min, followed by stirring for 30 min. The solvent is volatilized to obtain a mixed solution.

[0053] S2. Rotate and evaporate the mixed solution at 50 °C to remove most of the solvent. When the solution becomes slightly viscous, pour it into a mold coated with a release agent and preheated, and react in an oven at 180 °C for 12 h to obtain a blend benzoxazine resin of bisphenol A / aniline benzoxazine and a flame-retardant and toughened hyperbranched benzoxazine containing P-N-Si.

[0054] Performance comparison (1) Mechanical properties Test with a dynamic mechanical analyzer (DMA) at a heating rate of 10 °C / min from room temperature to 350 °C.

[0055] Tensile test: Use an Instron 5967 (30 kN) universal material testing machine from the United States to test the tensile properties of the cured specimens. The tensile specimens are prepared according to Type IV specimens (gauge length is 25 mm) in ASTM D638-10 standard, and the tensile rate is 5.08 mm / min. Each group of specimens is tested in parallel five times. Figure 1 (a) is the combustion test diagram of Example 1, Figure 1 (b) is the combustion test diagram of Comparative Example 1, Figure 2 is the bending strength result of the test, Figure 3 is the tensile strength result of the test.

[0056] Bending property test: Determine according to GB / T 2567-2008 standard using a microcomputer-controlled electronic universal testing machine.

[0057] Fracture toughness test: Prepare and test the cured specimens according to ASTM D5045 standard. The preparation process is as follows: Preparation of rough specimens: Use a cutting machine to cut the cured plate into specimens with dimensions of 50×12.5×3.2 mm³. Subsequently, use a grinding wheel and sandpapers of different meshes to grind the specimens until the surface is smooth. After grinding, let the specimens stand for more than 24 hours to eliminate the residual stress. 10 specimens need to be prepared in parallel for each group.

[0058] Notch processing: Clamp the ground specimens vertically with a fixture, and use a handsaw with a diameter of 0.3 mm to cut vertically at the center line position of the specimens to make a notch k. The notch depth should be controlled within 1 - 2 mm; Pre-crack preparation: First, place a sharp single-edge blade vertically in the notch k, and gently tap the blade with a hammer to prepare a crack with a length of ɑ (about 3.6 - 8.4 mm). After preparation, select the specimens that meet the crack length conditions for the fracture toughness test; The Instron 5967 (30kN) universal material testing machine made in the United States was used to test the fracture toughness of the specimens. The test temperature was room temperature and the test rate was 0.508 mm / min.

[0059] Wherein, W is the width of the spline, B is the length of the spline, and the fracture toughness K IC (MPa·m 1 / 2 ) is calculated by formula (1-1): Wherein , P Q is the maximum load, kN; f(x) is the geometric correction factor.

[0060] The critical strain energy release G IC (J·m²) is calculated by formula 1-2: Wherein, E is the Young's modulus, MPa, obtained from the tensile test; v is the Poisson's ratio (0.35).

[0061] (2) Thermogravimetric analysis (TGA) The Q50 thermogravimetric analyzer made by TA Company in the United States was used to test the thermal stability of the hyperbranched flame-retardant toughened benzoxazine resin. A sample with a mass of 5-10 mg was placed in a crucible. Under a nitrogen atmosphere, the flow rate was adjusted to 50 mL / min and the heating rate was 20ºC / min. The temperature test range was: 20-800ºC.

[0062] (3) Limiting oxygen index (LOI) The JF-3 oxygen index measuring instrument made by Nanjing Jiangning Analytical Instrument Factory was used for the test. The sample size was 100 mm×10 mm×10 mm. The oxygen index of the hyperbranched flame-retardant toughened benzoxazine resin was analyzed to determine the combustion degree of the material.

[0063] (4) Vertical burning analysis test (UL-94) The JF-3 oxygen index tester made in Nanjing Jiangning was used to analyze the combustion and dripping of the hyperbranched flame-retardant toughened benzoxazine resin.

[0064] (5) Cone calorimeter (CONE) The iCone classic cone calorimeter made by FTT Company was used to test the flame retardancy of the composite phase change material. During the test, the sample was wrapped with aluminum foil and carried out under a heat flux of 35 kW / m 2 .

[0065] Table 1 Element content table

[0066] Table 2 Mechanical property comparison

[0067] From the data in Table 2, the mechanical property test results of the high flame-retardant and toughened hyperbranched benzoxazine resin containing P-N-Si can be seen. The flexural strength and tensile strength of the high flame-retardant and toughened hyperbranched benzoxazine resin containing P-N-Si in Examples 1 to 7 all show an increasing trend (the flexural strength increases from 101.30 MPa to 177.00 MPa, and the tensile strength increases from 52.30 MPa to 91.68 MPa). Compared with the flexural strength and tensile strength of the high flame-retardant and toughened hyperbranched benzoxazine resin containing P-N-Si in Comparative Examples 1 to 2, it is increased to more than 90%. Although the flexural modulus and tensile modulus decrease, compared with the flexural modulus and tensile modulus of the high flame-retardant and toughened hyperbranched benzoxazine resin containing P-N-Si in Comparative Examples 1 to 2, it is as high as more than 100%. At the same time, the fracture toughness K IC and the critical strain energy release G IC have relatively large increases in value (the fracture toughness K IC increases from 0.81 MPa·m 1 / 2 to 1.76 MPa·m 1 / 2 , and the critical strain energy release G IC increases from 112.23 J·m² to 220.38 J·m²). These results fully prove that the benzoxazine resin has excellent toughening effects. The storage modulus of the hyperbranched benzoxazine resin shows a small decrease, indicating that the resin has good ductility and impact resistance; the increase in the glass transition temperature (from 205 °C to 233 °C) shows that the material can still maintain a stable glassy state in a high-temperature environment and has excellent thermal stability. From the mechanical property data of Comparative Example 3, it can be seen that the mixture of the resin in Example 1 and Comparative Example 1 endows it with excellent flexibility and deformation adaptability and has more excellent mechanical properties.

[0068] Comparison of Flame Retardant Properties in Table 3

[0069] As can be seen from the data in Table 3, the results of the flame retardancy performance test of the high flame retardant and toughened hyperbranched benzoxazine resin containing P-N-Si show that the synergistic thermal stability of the three elements P, N, and Si is greatly improved, and the flame retardant effect is remarkable. When burning, element P can form substances such as phosphoric acid with covering and isolating effects; element N can dilute the concentration of combustible gases in the gas phase and promote carbon formation at the same time; element Si can form a silicon oxide layer on the surface of the material, playing the role of heat insulation and oxygen isolation. The increase in the content of the three elements P, N, and Si enables the material to inhibit the combustion reaction in multiple aspects, thereby extending the ignition time from 37 s to 186 s, reducing the peak heat release rate from 511.60 (W / g) to 368.9 (W / g), and reducing the total heat release rate from 140.50 (KJ / g) to 40.6 (KJ / g). The long ignition time and low heat release rate of the high flame retardant and toughened hyperbranched benzoxazine resin containing P-N-Si indicate that when facing a fire, the material can remain non-combustible for a longer time, release less heat during combustion, and the fire spread speed is slower. This characteristic gives the material great application advantages in fields with high fire protection performance requirements, and can effectively improve the safety of related products. At the same time, the increase in LOI (from 30.4% to 51.00%) indicates an increase in the inherent flame retardancy of the high flame retardant and toughened hyperbranched benzoxazine resin containing P-N-Si. The increase in UL94 rating (from V1 to V0) shows that the high flame retardant and toughened hyperbranched benzoxazine resin containing P-N-Si is difficult to burn and drip during the vertical burning test, further proving the excellent flame retardancy performance of the resin, and can better meet the strict requirements for the fire protection and flame retardancy performance of materials in different fields in practical applications, thus expanding its potential application scope. From the flame retardancy performance data of Comparative Example 3, it can be seen that the resin mixture of Example 1 and Comparative Example 1 endows it with excellent flame retardancy performance and reaches the V0 level, indicating that the three elements P, N, and Si play a synergistic flame retardant role, making the modified Comparative Example 1 resin more difficult to ignite, significantly reducing the heat release during combustion, and comprehensively enhancing the flame retardancy performance to reach a relatively high flame retardant standard.

[0070] As can be seen from the data in Table 3, the results of the thermal stability performance test of the high flame retardant and toughened hyperbranched benzoxazine resin containing P-N-Si show that the introduction of elements P, N, and Si leads to a trend of first increasing and then decreasing in thermal stability. A certain amount of P, N, and Si can enhance the intermolecular interaction and better resist thermal motion. Therefore, a higher temperature is required to reach 5% weight loss (T 5% increase) and the temperature corresponding to the maximum weight loss rate (T maxIncreased), showing an improvement in thermal stability. When the P-N-Si content exceeds a certain value, it may lead to an overly complex molecular structure of the hyperbranched benzoxazine, which may disrupt the regularity and uniformity of the original molecular chain, making the intermolecular interactions uneven and causing a decrease in the structural stability in some regions. However, the P, N, and Si elements play a role in promoting char formation during the pyrolysis process of the hyperbranched benzoxazine. The presence of the P, N, and Si elements can enhance the stability and density of the char layer, prevent the transfer of heat and mass, and further promote the formation of residual carbon, resulting in a continuous increase in the residual carbon rate (from 28.70% to 63.90%), which is much higher than that of Comparative Examples 1 and 2. The high-flame-retardant and toughened hyperbranched benzoxazine resin containing P-N-Si having a high residual carbon rate means that the material can form more carbonaceous protective layers during combustion or in a high-temperature environment, which helps to improve the flame retardancy and heat insulation performance of the material. From the thermal stability performance data of Comparative Example 3, it can be seen that the mixture of Example 1 and the resin of Comparative Example 1 endows it with excellent thermal stability, and the increase in T 5% (from 368.1 °C to 402.7 °C) and T max (from 356.7 °C to 436.4 °C) directly reflects that the thermal stability of the modified bisphenol A-aniline type benzoxazine resin has been improved, indicating that within a certain temperature range, the addition of the P-N-Si hyperbranched benzoxazine resin effectively improves the resistance of the bisphenol A-aniline type benzoxazine resin during heating, enabling it to withstand higher temperatures without obvious thermal decomposition or performance degradation. At the same time, it has a relatively high residual carbon rate (48.6%) compared to Comparative Example 1, which is increased to 83%, indicating that the flame retardancy of the material has been effectively improved after the P-N-Si hyperbranched benzoxazine resin modifies the bisphenol A-aniline type benzoxazine resin.

[0071] In summary, the high-flame-retardant and toughened hyperbranched benzoxazine resin containing P-N-Si builds a multi-dimensional performance advantage matrix by virtue of the unique advantages of the P-N-Si ternary synergistic flame retardant system. At the mechanical level, the resin exhibits excellent high strength and high toughness, and can effectively resist external force impacts; in terms of thermal properties, it has excellent high-temperature resistance characteristics and can maintain a stable structure and performance in a high-temperature environment; particularly prominent is its flame retardancy. Thanks to the synergistic effect among the P, N, and Si elements, it significantly reduces the flammability and heat release rate of the material. In addition, when this resin is used as a modifier in other resin systems, it can specifically improve the flame retardancy efficiency and impact toughness of the matrix resin, realizing a leapfrog upgrade of the comprehensive performance of the material. Based on the above characteristics, the high-flame-retardant and toughened hyperbranched benzoxazine resin containing P-N-Si shows great technical potential and broad application prospects in many cutting-edge fields such as flame-retardant composites, safety protection equipment, medical polymer devices, and high-performance coatings, and is expected to provide new solutions for the material technology innovation in multiple industries.

[0072] Those skilled in the art can understand that the features recited in the various embodiments and / or claims of the present invention can be combined or / and combined in various ways, even if such combinations or combinations are not explicitly recited in the present invention. In particular, without departing from the spirit and teachings of the present invention, the features recited in the various embodiments and / or claims of the present invention can be combined and / or combined in various ways. All such combinations and / or combinations fall within the scope of the present invention.

Claims

1. A preparation method of a hyperbranched benzoxazine resin containing P-N-Si, characterized in that, The method comprises the following steps: S1. Preparation of hyperbranched benzoxazine monomer: The hyperbranched benzoxazine monomer is prepared by Mannich reaction of a triphenol compound, a diamine compound and paraformaldehyde; S2. After the ring-opening cross-linking reaction of the hyperbranched benzoxazine monomer, a P-N-Si-containing highly flame-retardant and toughened hyperbranched benzoxazine resin is obtained; The preparation of the hyperbranched benzoxazine monomer comprises the following steps: S11. Dissolve paraformaldehyde and the diamine compound in an organic solvent, and stir evenly under an ice-water bath condition for 20 - 60 min to make the raw materials mix evenly to form a solution. The diamine compound is a silicon-nitrogen-containing diamine compound or a phosphorus-silicon-containing diamine compound; S12. Dissolve the triphenol compound with an organic solvent, mix it with the solution in S11, and carry out a condensation reflux reaction at 60 - 120 °C for 10 - 24 h until it becomes a light yellow solution. The triphenol compound is a phosphorus-containing triphenol compound or a nitrogen-containing triphenol compound; S13. After the reaction is completed, rotate and evaporate the light yellow solution in S12 at 40 - 100 °C to remove most of the solvent. When the solution becomes slightly viscous, pour it into a petri dish to obtain a crude product of the hyperbranched benzoxazine monomer; S14. Dissolve the crude monomer product in an appropriate amount of organic solvent, then filter, collect and dry to obtain the purified hyperbranched benzoxazine monomer; The phosphorus-containing triphenol compound is one of the following structures: ； The nitrogen-containing triphenol compound is one of the following structures: ； The silicon-nitrogen-containing diamine compound is one of the following structures: ； The phosphorus-silicon-containing diamine compound is one of the following structures: 。 2. The preparation method of a hyperbranched benzoxazine resin containing P-N-Si according to claim 1, characterized in that, In step S11, the molar ratio of the diamine compound to paraformaldehyde is 1:(2.2 - 2.4); in step S12, the molar ratio of the triphenol compound to the diamine compound is 2:

3.

3. According to the preparation method of a P-N-Si-containing hyperbranched benzoxazine resin as claimed in claim 1, the organic solvent is any one of 1,4-dioxane, ethanol, dimethyl sulfoxide, N,N-dimethylacetamide, petroleum ether, chloroform, ethyl acetate, tetrahydrofuran, dimethylformamide, methyl ethyl ketone, cyclohexanone, toluene, xylene.

4. A P-N-Si-containing hyperbranched benzoxazine resin, obtained by using the preparation method as claimed in any one of claims 1 - 3, wherein the weight-average molecular weight of the hyperbranched benzoxazine monomer is 1100 - 6000, and the molecular weight distribution index of the hyperbranched benzoxazine resin is 1.7 - 3.

5.

5. A hyperbranched benzoxazine resin containing P-N-Si according to claim 4, characterized in that, The hyperbranched benzoxazine resin is prepared from hyperbranched benzoxazine monomers, or by subjecting hyperbranched benzoxazine monomers to ring-opening crosslinking reaction with one or more small molecule structure benzoxazine monomers; the small molecule structure benzoxazine monomers are one or more of bisphenol A aniline type benzoxazine monomers, bisphenol A p-phenylenediamine type benzoxazine monomers, phenolphthalein aniline type benzoxazine monomers, phenolphthalein p-phenylenediamine type benzoxazine monomers, bisphenol S aniline type benzoxazine monomers, bisphenol S p-phenylenediamine type benzoxazine monomers, or is prepared from hyperbranched benzoxazine monomers and thermosetting resin monomers, and the thermosetting resin is one of epoxy resin, bismaleimide resin, and phenolic resin.

6. The hyperbranched benzoxazine resin containing P-N-Si according to claim 4, wherein The maximum flexural strength is 177.00 MPa, the maximum tensile strength is 90.74 MPa, the longest ignition time is 210 S, the lowest peak heat release rate is 368.9 (W / g), the optimal total heat release rate is 32.80 (KJ / g), the maximum limiting oxygen index is 51%, and the highest fracture toughness K IC is 1.76 MPa·m 1 / 2 , the maximum critical strain energy release G IC is 220.38 J·m², the highest glass transition temperature is 233ºC, and the maximum char residue rate is 63.90%.

7. Use of a P-N-Si-containing hyperbranched benzoxazine resin according to claim 4 in a flame retardant material.

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