Polyorganosilicone cyclophosphazene modified epoxy resin and preparation method thereof

Abstract

The invention relates to a polyorganosilicone cyclophosphazene modified epoxy resin and a preparation method thereof, and belongs to the field of flame retardant materials, and the preparation method of the polyorganosilicone cyclophosphazene flame retardant comprises the following steps: taking hexachlorotripolyphosphazene, p-hydroxybenzaldehyde, p-aminobenzoic acid, DOPO and diphenyl silanediol as raw materials, and carrying out four-step reaction to prepare the polyorganosilicone cyclophosphazene modified epoxy resin. The preparation method comprises the following steps: by taking m-phenylenediamine as a curing agent, adding the series gradient polyorganosilicone cyclophosphazene flame retardant into the epoxy resin, and curing twice to obtain the modified epoxy resin. The preparation method is mainly used for preparing the polyorganosilicone cyclophosphazene flame retardant and the polyorganosilicone cyclophosphazene modified epoxy resin.

Description

Technical Field

[0001] The invention relates to a polysilicone cyclophosphazene modified epoxy resin and a preparation method thereof, and belongs to the field of flame retardant materials. Background Art

[0002] Epoxy resin has been widely used in many fields such as electronics, aerospace, construction and coatings due to its excellent mechanical properties, chemical stability and electrical insulation properties. However, it is highly flammable and produces toxic smoke when burned, which greatly limits its application in high temperature or flammable environments. This high flammability not only increases the safety hazards in use, but also restricts its promotion and application in fields with strict requirements on flame retardancy. In addition, the mechanical properties of epoxy resin are also a key factor in its use as a structural material, especially in occasions with large loads, which require the material to have not only good mechanical strength, but also good flame retardant properties when exposed to fire. Therefore, how to improve the flame retardant effect of epoxy resin without significantly reducing the mechanical properties has become a technical problem that needs to be solved urgently.

[0003] At present, the conventional method to improve the flame retardant properties of epoxy resin is to add various flame retardants thereto. Common flame retardants include phosphorus-containing, nitrogen-containing and other compounds. However, although the addition of a large amount of flame retardants can significantly improve the flame retardant properties of the material, this method often brings significant negative effects. First, adding a high proportion of flame retardants will significantly reduce the mechanical properties of epoxy resin, such as tensile strength, toughness, etc., causing the material to easily break or deform when subjected to mechanical stress. Secondly, the compatibility of flame retardants with epoxy resin matrix is ​​poor, and flame retardants are difficult to disperse evenly in the resin, which in turn affects the molding and processing properties of the material and may cause its internal structure to be uneven. In addition, adding a large amount of flame retardants will also increase the cost of the material and affect its application and promotion in industry. Therefore, how to balance the relationship between flame retardant effect and mechanical properties has become a huge challenge in current material modification.

[0004] The researchers further proposed a variety of improvement plans. For example, by reducing the particle size of the flame retardant, ultra-fine or nano-processing is carried out in order to improve its dispersibility and interface bonding performance with the matrix. However, it is found in practical applications that it is often difficult to obtain the desired effect through simple nano-processing alone. After the flame retardant reaches a certain mass or volume fraction, the performance improvement of the material tends to saturate. In addition, adding reinforcing fibers is also considered to be one of the effective means to improve mechanical properties, but some reinforcing fibers are flammable in themselves, which may aggravate the spread of flames and even cause a "wick effect", further reducing the flame retardant properties of epoxy resin. Therefore, optimizing the structure of the flame retardant, controlling its dispersibility, reducing the amount added, and improving the flame retardant efficiency on this basis have become the focus and difficulty in the research and development of epoxy resin composites. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a polysilicone cyclophosphazene modified epoxy resin to solve the problem that the flame retardant properties and mechanical properties of the existing modified epoxy resin are incompatible. The invention mainly includes a method for preparing a polysilicone cyclophosphazene flame retardant and a method for preparing a polysilicone cyclophosphazene modified epoxy resin.

[0006] There are many limitations in improving the mechanical properties of epoxy resin by adding nano flame retardants or doping reinforcing fibers. Therefore, the present invention proposes to design a flame retardant that contains special flame retardant elements of N, P, and Si and has high stability and high flexibility, and combines with the epoxy group of the epoxy resin through the active groups of the flame retardant itself to achieve the purpose of modifying the molecular structure of the epoxy resin and optimizing the flame retardant and mechanical properties of the modified epoxy resin.

[0007] Advantage 1: In order to ensure that a dense carbon layer can be formed during the combustion process and to give full play to the flame retardant effect of the condensed phase, existing researchers often design flame retardants into relatively complex polymer chain structures. The complex flame retardant structure will further make the cross-linked network formed by the ring-opening cross-linking reaction between the flame retardant and the epoxy group of the epoxy resin more complex, resulting in a decrease in the uniformity of the corresponding modified epoxy resin phase system and a decrease in the cross-linking density of the cured product, which in turn leads to a decrease in the mechanical properties of the modified epoxy resin. Therefore, the present invention designs the polysilicone cyclophosphazene flame retardant into a polymer structure with a certain number of active groups to better participate in the epoxy resin curing reaction and increase the cross-linking density between itself and the epoxy resin.

[0008] Advantage 2: Complex cross-linking networks and unevenly distributed cross-linking bonds may further lead to uneven stress distribution inside the material, and even stress concentration, which may cause the epoxy resin product to break. Therefore, the polysilicone cyclophosphazene flame retardant proposed in the present invention is based on hexachlorotripolyphosphazene as the core skeleton, and its stable six-membered ring conjugated structure can be used to further enhance the structural stability of the flame retardant. In addition, the reactive anchor points participating in the curing reaction during the epoxy resin curing process are evenly distributed on the six branches of the six-membered ring, which can improve the interaction between the flame retardant and the epoxy resin and reduce the phenomenon of uneven stress distribution. In addition, the present invention further introduces a high-stability DOPO group on its side chain to increase its steric hindrance and increase the cross-linking density of the system during the actual curing process, so as to effectively improve the compatibility between the polysilicone cyclophosphazene flame retardant and the epoxy resin, thereby promoting the polysilicone cyclophosphazene modified epoxy resin to have superior mechanical properties.

[0009] Advantage 3: The hexachlorotripolyphosphazene skeleton has a high content of N and P elements, and has the characteristics of easy derivatization of multiple side groups, which means that multiple flame retardant elements can be combined into the molecular structure of the flame retardant at the same time, so that it can have good flame retardant properties while ensuring the excellent mechanical properties of epoxy resin.

[0010] Advantage 4: The polysilicone cyclophosphazene flame retardant proposed in the present invention selects groups corresponding to chemical bonds with higher bond energy, such as benzene rings, as the main carbon structure on the extended skeleton branch of the flame retardant; diphenylsilanediol containing Si-O bonds with long bond length, large bond angle and better flexibility is selected to provide Si elements for the flame retardant proposed in the present invention. The purpose is to reduce the destructive effect of the flame retardant itself on the mechanical properties of epoxy resin while ensuring the flame retardant properties of epoxy resin by designing a high-stability flame retardant structure.

[0011] The structural formula of polysilicone cyclophosphazene flame retardant is:

[0012] The preparation method of the polysilicone cyclophosphazene flame retardant provided by the present invention is mainly completed according to the following steps: first, -OH in p-hydroxybenzaldehyde and -Cl in hexachlorotriphosphazene undergo substitution reaction to obtain intermediate 1; secondly, -CHO in intermediate 1 and -NH2 in p-aminobenzoic acid are used to generate intermediate 2 containing a Schiff base structure; DOPO is then used to undergo addition reaction with the Schiff base structure in intermediate 2 to obtain intermediate 3; finally, diphenylsilanediol and carboxylated intermediate 3 undergo esterification reaction, and since diphenylsilanediol has two symmetrically located -OH reaction sites, the polysilicone cyclophosphazene flame retardant is finally synthesized.

[0013] The preparation method of the polysilicone cyclophosphazene modified epoxy resin provided by the present invention is mainly completed according to the following steps: firstly, the epoxy resin (E-51) is heated to 100-120°C, the polysilicone cyclophosphazene flame retardant is added, the mixture is mixed evenly, then the mixture is cooled to a temperature of 60-80°C, a curing agent (m-phenylenediamine) is added, the mixture is mixed evenly, vacuum degassing is performed, and then a mold is poured, the mixture is cured twice, and the mixture is naturally cooled to obtain the polysilicone cyclophosphazene modified epoxy resin.

[0014] Technical effects of the present invention:

[0015] 1. The polysilicone cyclophosphazene flame retardant prepared by the present invention is a high molecular polymer, and there are various types of active hydrogen in its structure, which provides more active sites for the ring-opening reaction of epoxy groups of epoxy resin, so that the molecular chains are entangled with each other, and the cross-linking density of epoxy resin is increased, so the system is more tightly combined and the mechanical properties are more superior. The present invention successfully solves the problem of incompatibility between flame retardant properties and mechanical properties of existing modified epoxy resins.

[0016] 2. The polysilicone cyclophosphazene modified epoxy resins prepared by the present invention meet the test standards for flame retardant materials. When the addition amounts of the polysilicone cyclophosphazene flame retardant are 8% and 12% respectively, the corresponding modified epoxy resin LOI values ​​are 32.3% and 30.4% respectively, and the UL-94 test reaches V-0 grade, that is, the polysilicone cyclophosphazene modified epoxy resin has good flame retardant properties.

[0017] 3. The tensile properties and adhesive properties of the polysilicone cyclophosphazene modified epoxy resin prepared by the present invention are improved. When the addition amount of the polysilicone cyclophosphazene flame retardant is 4% and 8% respectively, the breaking strength of the corresponding modified epoxy resin is increased by 5.76MPa and 3.79MPa respectively compared with the unmodified epoxy resin, and the peel strength is increased by 0.2kN / m and 0.12kN / m respectively compared with the unmodified epoxy resin. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Infrared spectrum of the polysilicone cyclophosphazene flame retardant prepared in Example 5.

[0019] Figure 2 H NMR spectrum of the polysilicone cyclophosphazene flame retardant prepared in Example 5.

[0020] Figure 3 NMR phosphorus spectrum of the polysilicone cyclophosphazene flame retardant prepared in Example 5.

[0021] Figure 4 Video screenshot of the vertical combustion experiment process of the polysilicone cyclophosphazene modified epoxy resin in Example 6.

[0022] Figure 5 Stress-strain curve of the polysilicone cyclophosphazene modified epoxy resin in Example 6.

[0023] Figure 6 Peel strength bar graph of polysilicone cyclophosphazene modified epoxy resin in Example 6. DETAILED DESCRIPTION

[0024] The following examples are used to specifically describe the preparation method of the polysilicone cyclophosphazene flame retardant and the preparation method of the polysilicone cyclophosphazene modified epoxy resin proposed in the present invention, but the implementation mode is not limited thereto and the examples should not be regarded as limiting the present invention.

[0025] Example 1

[0026] A method for preparing a polysilicone cyclophosphazene modified epoxy resin, the preparation steps of the resin are: Step 1: p-Hydroxybenzaldehyde and hexachlorotriphosphazene undergo substitution reaction to obtain intermediate 1; Step 2: intermediate 1 undergoes a dehydration condensation reaction with p-aminobenzoic acid to generate intermediate 2 containing a Schiff base structure; Step 3: Use DOPO to react with intermediate 2 to obtain intermediate 3; Step 4: Esterification reaction is carried out between diphenylsilanediol and intermediate 3, and since diphenylsilanediol has two symmetrically located -OH reaction sites, polysilicone cyclophosphazene flame retardant 4 is obtained; Step 5: Heat the E-51 epoxy resin to 100-120°C, add the polysilicone cyclophosphazene flame retardant 4, mix evenly, then cool to 60-80°C, add the curing agent, mix evenly and perform vacuum degassing, then pour into a preheated mold and cure at 60-80°C in a vacuum drying oven for 1.5-2h, then cure at 130-150°C for 1.5-2h, and cool to room temperature to obtain a polysilicone cyclophosphazene modified epoxy resin, wherein the mass fraction of the polysilicone cyclophosphazene flame retardant added to the modified epoxy resin is 4%-16%.

[0027] Example 2

[0028] This embodiment is substantially the same as embodiment 1, except that the substitution reaction described in this embodiment is as follows: p-hydroxybenzaldehyde and anhydrous potassium carbonate are added to tetrahydrofuran solvent respectively, wherein the molar ratio of p-hydroxybenzaldehyde to anhydrous potassium carbonate is 1:1-1:1.5, 100 mL of tetrahydrofuran solvent is required to dissolve every 0.01-0.02 mol of p-hydroxybenzaldehyde, and stirring is continued for 1-2 hours; hexachlorotriphosphazene is added to tetrahydrofuran, 100 mL of tetrahydrofuran is required to dissolve every 0.06-0.07 mol of hexachlorotriphosphazene, and the mixture is stirred for 1-2 hours. After dissolution, the hexachlorotrimer phosphazene solution is slowly added dropwise to the above-mentioned p-hydroxybenzaldehyde and anhydrous potassium carbonate solution in a molar ratio of hexachlorotrimer phosphazene to p-hydroxybenzaldehyde of 1:6-1:7, heated in an oil bath with continuous stirring, and reacted at 60-66° C. for 20-24 hours; after the reaction is completed, the reaction solution is cooled to room temperature, poured into a large amount of water, the precipitate is filtered, and vacuum dried at 60-70° C. for 10-12 hours, the crude product is recrystallized from ethyl acetate, allowed to stand and cool, filtered, and vacuum dried at 70-85° C. for 10-12 hours to obtain intermediate 1 as a light yellow solid.

[0029] Example 3

[0030] This embodiment is basically the same as embodiment 2, except that the dehydration condensation reaction described in this embodiment is as follows: intermediate 1 and p-aminobenzoic acid are added to a dioxane solvent in a molar ratio of 1:6 to 1:7, wherein 100 mL of 1,4-dioxane is required to dissolve every 0.008 to 0.009 mol of intermediate 1, vacuumize and pass nitrogen, heat in an oil bath and stir continuously, react at 90 to 101° C. for 20 to 24 h, cool to room temperature after the reaction is completed, pour the reaction solution into an ethanol diluent, filter the precipitate, wash twice with ethanol, and vacuum dry at 60 to 70° C. for 10 to 12 h to obtain intermediate 2 as a white solid.

[0031] Example 4

[0032] This example is basically the same as Example 3, except that the addition reaction described in this example is as follows: intermediate 2, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 1,4-dioxane are added to a three-necked flask, wherein the molar ratio of intermediate 2 to DOPO is 1:6-1:7, 1,4-dioxane is used as a solvent, and 100 mL of 1,4-dioxane is required to dissolve every 0.0006-0.0007 mol of intermediate 2; under nitrogen protection, oil bath heating and continuous stirring are performed, the reaction is carried out at 90-101° C. for 20-24 h, the reaction is completed and cooled to room temperature, the reaction solution is poured into an ethanol diluent, the precipitate is filtered, washed twice with hot water and anhydrous ethanol, respectively, and vacuum dried at 60-70° C. for 10-12 h to obtain intermediate 3 as a white solid.

[0033] Example 5

[0034] This embodiment is basically the same as embodiment 5, except that the method for preparing a polysilicone cyclophosphazene modified epoxy resin described in this embodiment is characterized in that the esterification reaction is as follows: in a three-necked flask, the intermediate 3 and 1-hydroxybenzotriazole (HOBT) are dissolved in DMSO The mixture was stirred for 1-2 hours until dissolved. 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDCI) and diphenylsilanediol were dissolved in DMSO. The molar ratios of intermediate 3 to HOBT, EDCI and diphenylsilanediol were 10:1, 1:3-1:4 and 1:1, respectively. In addition, 100 mL of DMSO was required to dissolve every 0.0009-0.001 mol of intermediate 3. After complete dissolution, the EDCI solution and diphenylsilanediol solution were slowly added dropwise to the three-necked flask, heated in an oil bath and stirred continuously. The mixture was reacted at 115-125°C for 20-24 hours. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into a large amount of water. The precipitate was filtered, washed with ethanol twice, and dried under vacuum at 60-70°C for 10-12 hours to obtain a polysilicon cyclophosphazene flame retardant.

[0035] Example 6

[0036] This embodiment is basically the same as Embodiment 5, except that the curing agent 2 in this embodiment is m-phenylenediamine, and the mass fraction of the polysilicone cyclophosphazene flame retardant added to the modified epoxy resin is 4% or 8% or 12% or 16%, respectively. Among them, the sample in which the addition amount of the polysilicone cyclophosphazene flame retardant in the modified epoxy resin is 4% is marked as EP-1; the sample in which the addition amount of the polysilicone cyclophosphazene flame retardant in the modified epoxy resin is 8% is marked as EP-2; the sample in which the addition amount of the polysilicone cyclophosphazene flame retardant in the modified epoxy resin is 12% is marked as EP-3; the sample in which the addition amount of the polysilicone cyclophosphazene flame retardant in the modified epoxy resin is 16% is marked as EP-4; and the sample of the epoxy resin without adding the flame retardant as the reference sample is marked as EP.

[0037] The structure of the polysilicone cyclophosphazene flame retardant prepared in Example 5 was characterized by infrared spectroscopy, nuclear magnetic resonance hydrogen spectrum and phosphorus spectrum. The test spectrum is shown in FIG. Figures 1 to 3 The flame retardant and mechanical properties of the polysilicone cyclophosphazene modified epoxy resin were studied by conducting vertical combustion (UL-94), limiting oxygen index (LOI), and tensile properties tests on the samples prepared in Example 6, and using the adhesive T peel strength test method. The relevant experimental data records are shown in Table 1, and the video screenshots of the modified epoxy resin during the vertical combustion test are shown in Figure 4 The corresponding stress-strain curve and peel strength test results are shown in Figure 5 , Figure 6 The vertical burning, limiting oxygen index, tensile properties, and peel strength were determined in accordance with the following standards: Vertical burning (UL-94) test: GB / T 2408-2021; Limiting oxygen index (LOI) test: GB / T 2406.2-2009; Tensile properties test: GB / T 1040.2-2006; Peel strength test: GB / T 2791-1995.

[0038] Table 1 Flame retardant properties, breaking strength and bonding properties of samples in various embodiments

[0039] From Table 1 and Figure 4It can be seen that the LOI value of pure epoxy resin is only 21.0%. It continues to burn in the UL-94 test, and dripping occurs at the 33rd second of the combustion process, failing the UL-94 test. The addition of polysilicone cyclophosphazene flame retardant increases the LOI value of the epoxy resin. The UL-94 test results also show that polysilicone cyclophosphazene-modified epoxy resins are self-extinguishing within a certain time range and have excellent flame retardancy. Among them, the polysilicone cyclophosphazene-modified epoxy resins EP-2 and EP-3 obtained in Example 6 have the best flame retardant properties, with LOI values ​​of 32.3% and 30.4%, respectively, both reaching the UL-94 test V-0 level. In addition, from Table 1, Figure 5 and Figure 6 It can be seen that compared with the polysilicone cyclophosphazene modified epoxy resins EP-1 and EP-2 obtained from pure epoxy resin EP and Example 6, the tensile properties and adhesive properties of the polysilicone cyclophosphazene modified epoxy resin are improved, that is, at the corresponding addition amount of this embodiment, the polysilicone cyclophosphazene modified epoxy resin has excellent mechanical properties.

Claims

1. A method for preparing a polysilicone cyclophosphazene modified epoxy resin, the preparation steps of the resin are: Step 1: p-Hydroxybenzaldehyde and hexachlorotriphosphazene undergo substitution reaction to obtain intermediate 1; Step 2: intermediate 1 undergoes a dehydration condensation reaction with p-aminobenzoic acid to generate intermediate 2 containing a Schiff base structure; Step 3: Use DOPO to react with intermediate 2 to obtain intermediate 3; Step 4: Esterification reaction is carried out between diphenylsilanediol and intermediate 3, and due to the presence of two symmetrically located -OH reaction sites in diphenylsilanediol, polysilicone cyclophosphazene flame retardant 4 is obtained; Step 5: Heat the E-51 epoxy resin to 100-120°C, add the polysilicone cyclophosphazene flame retardant 4, mix well, then cool to 60-80°C, add the curing agent, mix well and perform vacuum degassing, then pour into a preheated mold and cure at 60-80°C in a vacuum drying oven for 1.5-2h, then cure at 130-150°C for 1.5-2h, and cool to room temperature to obtain a polysilicone cyclophosphazene modified epoxy resin, wherein: The mass fractions of polysilicone cyclophosphazene flame retardant added to the modified epoxy resin are 4%~16%.

2. The method for preparing a polysilicone cyclophosphazene modified epoxy resin according to claim 1, characterized in that The substitution reaction described in step 1 is as follows: p-hydroxybenzaldehyde and anhydrous potassium carbonate are added to a tetrahydrofuran solvent, wherein the molar ratio of p-hydroxybenzaldehyde to anhydrous potassium carbonate is 1:1-1:1.5, 100 mL of tetrahydrofuran solvent is required to dissolve every 0.01-0.02 mol of p-hydroxybenzaldehyde, and stirring is continued for 1-2 hours; hexachlorotripolyphosphazene is added to tetrahydrofuran, 100 mL of tetrahydrofuran is required to dissolve every 0.06-0.07 mol of hexachlorotripolyphosphazene, and after complete dissolution, the mixture is stirred according to the following steps: The molar ratio of chlorotriphosphazene to p-hydroxybenzaldehyde is 1:6-1:

7. The hexachlorotriphosphazene solution is slowly added dropwise to the p-hydroxybenzaldehyde and anhydrous potassium carbonate solution, heated in an oil bath with continuous stirring, and reacted at 60-66°C for 20-24 hours. After the reaction is completed, the reaction solution is cooled to room temperature, poured into a large amount of water, the precipitate is filtered, and vacuum dried at 60-70°C for 10-12 hours. The crude product is recrystallized from ethyl acetate, allowed to stand and cool, filtered, and vacuum dried at 70-85°C for 10-12 hours to obtain intermediate 1.

3. A method for preparing a polysilicone cyclophosphazene modified epoxy resin as claimed in claim 2, characterized in that The dehydration condensation reaction in step 2 is as follows: intermediate 1 and p-aminobenzoic acid are added to a dioxane solvent in a molar ratio of 1:6 to 1:7, wherein 100 mL of 1,4-dioxane is required to dissolve every 0.008 to 0.009 mol of intermediate 1, vacuumize and pass nitrogen, heat in an oil bath and stir continuously, react at 90 to 101° C. for 20 to 24 hours, cool to room temperature after the reaction is completed, pour the reaction solution into an ethanol diluent, filter the precipitate, wash twice with ethanol, and vacuum dry at 60 to 70° C. for 10 to 12 hours to obtain intermediate 2.

4. A method for preparing a polysilicone cyclophosphazene modified epoxy resin as claimed in claim 3, characterized in that The addition reaction in step 3 is as follows: add intermediate 2, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 1,4-dioxane into a three-necked flask, wherein the molar ratio of intermediate 2 to DOPO is 1:6-1:7, and 1,4-dioxane is used as a solvent, and 100 mL of 1,4-dioxane is required to dissolve every 0.0006-0.0007 mol of intermediate 2; under nitrogen protection, heat in an oil bath and stir continuously, react at 90-101° C. for 20-24 hours, cool to room temperature after the reaction is completed, pour the reaction solution into an ethanol diluent, filter the precipitate, wash twice with hot water and anhydrous ethanol respectively, and vacuum dry at 60-70° C. for 10-12 hours to obtain intermediate 3.

5. A method for preparing a polyorganosilicon cyclophosphazene modified epoxy resin as claimed in claim 4, characterized in that The esterification reaction in step 4 is as follows: In a three-necked flask, the intermediate 3 and 1-hydroxybenzotriazole (HOBT) are dissolved in DMSO The mixture was stirred for 1-2 hours until dissolved. 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDCI) and diphenylsilanediol were dissolved in DMSO. The molar ratios of intermediate 3 to HOBT, EDCI and diphenylsilanediol were 10:1, 1:3-1:4 and 1:1, respectively. In addition, 100 mL of DMSO was required to dissolve every 0.0009-0.001 mol of intermediate 3. After complete dissolution, the EDCI solution and diphenylsilanediol solution were slowly added dropwise to the three-necked flask, heated in an oil bath and stirred continuously. The mixture was reacted at 115-125°C for 20-24 hours. After the reaction was completed, the mixture was cooled to room temperature, and the reaction solution was poured into a large amount of water. The precipitate was filtered, washed with ethanol twice, and dried under vacuum at 60-70°C for 10-12 hours to obtain a polysilicon cyclophosphazene flame retardant.

6. A method for preparing a polyorganosilicon cyclophosphazene modified epoxy resin as claimed in claim 5, characterized in that The curing agent 2 is m-phenylenediamine, and the mass fraction of the polysilicone cyclophosphazene flame retardant added to the modified epoxy resin is 4%, 8%, 12% or 16% respectively.

7. A polyorganosilicon cyclophosphazene modified epoxy resin prepared by the method for preparing a polyorganosilicon cyclophosphazene modified epoxy resin according to claim 6, wherein the flame retardant contains N, P, and Si flame retardant elements, characterized in that The flame retardant uses hexachlorotripolyphosphazene as the core skeleton. The reactive anchor points participating in the curing reaction during the epoxy resin curing process are evenly distributed on the six branches of the six-membered ring, and DOPO groups are introduced into the six branches.

8. A polyorganosilicon cyclophosphazene modified epoxy resin as claimed in claim 7, characterized in that The structural formula of polysilicone cyclophosphazene flame retardant is:

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