Phosphorus-nitrogen-silicon intumescent flame retardant as well as synthesis method and application thereof

Abstract

The invention relates to a phosphorus-nitrogen-silicon intumescent flame retardant and a synthesis method and application thereof, the phosphorus-nitrogen-silicon intumescent flame retardant is synthesized from an acid source, piperazine and siloxane, the acid source is selected from one of orthophosphoric acid, phosphonic acid or phenylphosphonic acid, and the piperazine is selected from one of nitrogen, nitrogen and silicon. The siloxane is selected from one of chloromethyl pentamethyldisiloxane or 2-chloromethyl heptamethyltrisiloxane. The invention also discloses a synthesis method of the siloxane. The flame retardant disclosed by the invention not only has an excellent flame retardant effect, but also shows a certain smoke suppression effect in a combustion process. The siloxane structure contained in the structure of the flame retardant can effectively improve the compatibility between the flame retardant and a high polymer material matrix, so that the effect of the flame retardant is more fully played, the internal defects of the system are reduced, the negative influence of the flame retardant on the mechanical properties of the high polymer material is reduced, and the flame retardant disclosed by the invention is single in component, halogen-free, environment-friendly and suitable for industrial production. The synthesis process is simple, mild in condition and suitable for industrial production.

Description

Technical Field

[0001] The invention relates to the field of flame retardants, and in particular to a phosphorus-nitrogen-silicon intumescent flame retardant and a synthesis method and application thereof. Background Art

[0002] With the development of modern industry, polymer materials have been widely used in various fields, such as construction, transportation, electronic appliances, etc. However, most polymer materials are extremely flammable and often produce a large amount of toxic gases and smoke when burning, which is harmful to personnel safety and the environment. Therefore, improving the flame retardant properties of polymer materials has become a technical problem that needs to be solved urgently. Adding flame retardants is one of the effective methods to improve the flame retardant properties of polymer materials. Flame retardants are mainly divided into two categories: halogen flame retardants and halogen-free flame retardants. Although halogen flame retardants have good flame retardant effects, they will produce toxic hydrogen halide gas during combustion, which is harmful to the environment and human health. In contrast, halogen-free flame retardants have gradually become one of the research hotspots in the field of flame retardants due to their non-toxic, halogen-free, low-smoke and environmentally friendly advantages.

[0003] Intumescent flame retardant (IFR) is an environmentally friendly halogen-free flame retardant, which is composed of three elements: acid source, carbon source and gas source. When heated, IFR will foam and expand to form a heat-insulating and oxygen-insulating carbon foam layer, which significantly improves the flame retardant properties of the material. Its flame retardant mechanism involves the dehydration of the acid source, the carbonization reaction of the carbon source and the foaming effect of the gas source, which work together to achieve high-efficiency flame retardancy. Compared with traditional flame retardants, intumescent flame retardants have the advantages of low smoke, low toxicity and environmental friendliness. They are widely used in flame retardant modification fields such as fibers, plastics, rubber, polyurethane, wood and paper, and have broad prospects. However, with the increase in the amount of flame retardant added. It often leads to serious deterioration of the mechanical properties of polymer materials, thereby affecting the use of polymer materials. CN 111621021B discloses a piperazine polyphosphate composite flame retardant, which is obtained by synthesis and then coated with a silane coupling agent as a coating material, thereby improving the water resistance of the material and increasing the compatibility. However, the piperazine polyphosphate has a large molecular structure and is prone to agglomeration. It has poor dispersibility in the material matrix, which has a significant adverse effect on the mechanical properties of the material.

[0004] Based on the above background, the applicant has conducted research on intumescent flame retardants with the intention of providing an intumescent flame retardant that has less negative impact on the mechanical properties of polymer materials while improving the flame retardancy of polymer materials. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a phosphorus-nitrogen-silicon intumescent flame retardant and a synthesis method and application thereof.

[0006] To solve the above problems, the technical solution adopted by the present invention is: Technical Theme 1 A method for synthesizing a phosphorus-nitrogen-silicon intumescent flame retardant comprises the following steps: S1: dissolving an acid source in solvent I to obtain solution A, and dissolving piperazine in solvent I to obtain solution B; S2: Under stirring at room temperature, solution A is added dropwise to solution B for sufficient reaction. After the reaction is completed, the solution is cooled to room temperature, filtered, and the filter cake is washed and dried to obtain intermediate C; S3: adding intermediate C into DMF and dissolving it to obtain solution D, and adding siloxane into DMF and dissolving it to obtain solution E; S4: Under stirring conditions at 100-140° C., solution E is added dropwise into solution D for sufficient reaction. After the reaction is completed, the reaction solution is cooled to room temperature, filtered, and the solvent is evaporated from the filtrate to obtain a phosphorus-nitrogen-silicon intumescent flame retardant.

[0007] The acid source is selected from one of orthophosphoric acid, phosphonic acid or phenylphosphonic acid.

[0008] The siloxane is selected from one of chloromethylpentamethyldisiloxane and 2-chloromethylheptamethyltrisiloxane.

[0009] As a further improvement of the present invention, when the acid source is orthophosphoric acid, the molar ratio of the acid source to piperazine in S2 is 1:3.0-3.9; when the acid source is phosphonic acid or phenylphosphonic acid, the molar ratio of the acid source to piperazine in S2 is 1:2.0-2.6.

[0010] As a further improvement of the present invention, when the acid source is orthophosphoric acid, the molar ratio of the acid source to piperazine in S2 is 1:3.3.

[0011] When the acid source is phosphonic acid or phenylphosphonic acid, the molar ratio of the acid source to piperazine in S2 is 1:2.2.

[0012] As a further improvement of the present invention, when the acid source is orthophosphoric acid or phosphonic acid, the molar ratio of the intermediate C to the siloxane in S4 is 1:3.

[0013] When the acid source is phenylphosphonic acid, the molar ratio of intermediate C to siloxane in S4 is 1:2.

[0014] As a further improvement of the present invention, the solvent I is anhydrous ethanol or water.

[0015] As a further improvement of the present invention, the stirring rate in S2 is 300-800 rpm, and the reaction time is 6-10 hours.

[0016] As a further improvement of the present invention, the dosage relationship between the acid source and the solvent I in S1 is 0.01 mol: 12-30 mL, and the dosage relationship between piperazine and the solvent I is 0.01 mol: 8-20 mL; the dosage relationship between the intermediate C and DMF in S3 is 0.01 mol: 10-25 mL, and the dosage relationship between the siloxane and DMF is 0.01 mol: 10-30 mL.

[0017] As a further improvement of the present invention, the stirring rate in S4 is 200-500 rpm, and the reaction time is 10-14 hours.

[0018] Technical Theme 2 A phosphorus-nitrogen-silicon intumescent flame retardant obtained by the synthesis method described in technical subject one.

[0019] Technical Theme 3 An application of the phosphorus-nitrogen-silicon intumescent flame retardant as described in technical theme 2 as a flame retardant for polymer materials.

[0020] Preferably, the polymer material is polyolefin or polyurethane.

[0021] The beneficial effects of adopting the above technical solution are: 1. The present invention synthesizes a new type of phosphorus-nitrogen-silicon intumescent flame retardant based on the synergistic flame retardant effect between elements. The flame retardant not only has excellent flame retardant effect, but also can show a certain smoke suppression effect during the combustion process. The three elements of phosphorus, nitrogen and silicon have a synergistic effect in the flame retardant process. When they act together on the polymer material matrix, the phosphorus and nitrogen elements can promote the rapid dehydration and carbonization of the material surface, thereby forming an expanded carbonized layer, and the silicon element can further enhance the stability and durability of the carbonized layer. The flame retardant disclosed in the present invention can significantly improve the flame retardant effect of polymer materials and effectively prevent the spread of flames and the transfer of oxygen.

[0022] 2. The siloxane structure contained in the flame retardant structure can effectively improve the compatibility between the flame retardant and the polymer material matrix, thereby fully exerting the role of the flame retardant, reducing defects within the system, and reducing the negative impact of the flame retardant on the mechanical properties of the polymer material.

[0023] 3. The flame retardant disclosed in the present application has a single component, high performance, halogen-free and environmentally friendly, a simple synthesis process, mild conditions, and is suitable for industrial production. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention is clearly and completely described below in conjunction with specific embodiments.

[0025] Example 1 0.01 mol of orthophosphoric acid was dissolved in 20 mL of anhydrous ethanol to obtain solution A, and 0.033 mol of piperazine was dissolved in 45 mL of anhydrous ethanol to obtain solution B.

[0026] At room temperature, solution A was added dropwise into solution B stirred at 500 r / min for 8 h. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The solid obtained by filtration was rinsed with anhydrous ethanol three times, dried, ground, and passed through a 500-mesh sieve to obtain piperazine phosphate intermediate C1.

[0027] 0.01 mol of the intermediate C1 obtained by the method described in Example 1 was fully dissolved in 15 mL of DMF to obtain solution D, and 0.03 mol of chloromethylpentamethyldisiloxane was fully dissolved in 60 mL of DMF to obtain solution E.

[0028] At 120°C, solution E was added dropwise into solution D stirred at 300 r / min for 12 hours. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was rotary evaporated to remove the solvent to obtain phosphorus-nitrogen-silicon intumescent flame retardant 1.

[0029] Example 2 0.01 mol of phosphonic acid was dissolved in 20 mL of anhydrous ethanol to obtain solution A, and 0.022 mol of piperazine was dissolved in 30 mL of anhydrous ethanol to obtain solution B.

[0030] At room temperature, solution A was added dropwise into solution B stirred at 500 r / min for 8 hours. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The solid obtained by filtration was rinsed with anhydrous ethanol three times, dried, ground, and passed through a 500-mesh sieve to obtain piperazine phosphate intermediate C2.

[0031] 0.01 mol of the intermediate C2 obtained by the method described in Example 2 was fully dissolved in 15 mL of DMF to obtain solution D, and 0.03 mol of chloromethylpentamethyldisiloxane was fully dissolved in 60 mL of DMF to obtain solution E.

[0032] At 120°C, solution E was added dropwise into solution D stirred at 300 r / min for 12 hours. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was rotary evaporated to remove the solvent to obtain phosphorus-nitrogen-silicon intumescent flame retardant 2.

[0033] Example 3 0.01 mol of phenylphosphonic acid was dissolved in 20 mL of anhydrous ethanol to obtain solution A, and 0.022 mol of piperazine was dissolved in 30 mL of anhydrous ethanol to obtain solution B.

[0034] At room temperature, solution A was added dropwise into solution B stirred at 500 r / min for 8 h. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The solid obtained by filtration was rinsed with anhydrous ethanol three times, dried, ground, and passed through a 500-mesh sieve to obtain piperazine phosphate intermediate C3.

[0035] 0.01 mol of the intermediate C3 obtained by the method described in Example 3 was fully dissolved in 15 mL of DMF to obtain solution D, and 0.02 mol of 2-chloromethylheptamethyltrisiloxane was fully dissolved in 40 mL of DMF to obtain solution E.

[0036] At 120°C, solution E was added dropwise into solution D stirred at 300 r / min for 12 hours. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was rotary evaporated to remove the solvent to obtain phosphorus-nitrogen-silicon intumescent flame retardant 3.

[0037] Example 4 0.01 mol of orthophosphoric acid was dissolved in 12 mL of anhydrous ethanol to obtain solution A, and 0.03 mol of piperazine was dissolved in 60 mL of anhydrous ethanol to obtain solution B.

[0038] At room temperature, solution A was added dropwise into solution B stirred at 300 r / min for 10 h. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The solid obtained by filtration was rinsed with anhydrous ethanol three times, dried, ground, and passed through a 500-mesh sieve to obtain piperazine phosphate intermediate C1.

[0039] 0.01 mol of the piperazine phosphate intermediate obtained by the method described in Example 4 was fully dissolved in 10 mL of DMF to obtain solution D, and 0.03 mol of chloromethylpentamethyldisiloxane was fully dissolved in 90 mL of DMF to obtain solution E.

[0040] At 140°C, solution E was added dropwise into solution D stirred at 200 r / min for 10 hours. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was rotary evaporated to remove the solvent to obtain phosphorus-nitrogen-silicon intumescent flame retardant 4.

[0041] Example 5 0.01 mol of orthophosphoric acid was dissolved in 30 mL of anhydrous ethanol to obtain solution A, and 0.039 mol of piperazine was dissolved in 31.2 mL of anhydrous ethanol to obtain solution B.

[0042] At room temperature, solution A was added dropwise into solution B stirred at 800 r / min for 6 h. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The solid obtained by filtration was rinsed with anhydrous ethanol three times, dried, ground, and passed through a 500-mesh sieve to obtain piperazine phosphate intermediate C1.

[0043] 0.01 mol of the piperazine phosphate intermediate obtained by the method described in Example 5 was fully dissolved in 25 mL of DMF to obtain solution D, and 0.03 mol of chloromethylpentamethyldisiloxane was fully dissolved in 30 mL of DMF to obtain solution E.

[0044] At 120°C, solution E was added dropwise into solution D stirred at 300 r / min for 12 hours. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was rotary evaporated to remove the solvent to obtain phosphorus-nitrogen-silicon intumescent flame retardant 5.

[0045] Example 6 0.01 mol of phosphonic acid was dissolved in 20 mL of anhydrous ethanol to obtain solution A, and 0.02 mol of piperazine was dissolved in 25 mL of anhydrous ethanol to obtain solution B.

[0046] At room temperature, solution A was added dropwise into solution B stirred at 500 r / min for 8 hours. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The solid obtained by filtration was rinsed with anhydrous ethanol three times, dried, ground, and passed through a 500-mesh sieve to obtain piperazine phosphate intermediate C2.

[0047] 0.01 mol of the piperazine phosphate intermediate obtained by the method described in Example 6 was fully dissolved in 15 mL of DMF to obtain solution D, and 0.03 mol of chloromethylpentamethyldisiloxane was fully dissolved in 60 mL of DMF to obtain solution E.

[0048] At 100°C, solution E was added dropwise into solution D stirred at 500 r / min for 14 hours. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was rotary evaporated to remove the solvent to obtain phosphorus-nitrogen-silicon intumescent flame retardant 6.

[0049] Example 7 Solution A was obtained by dissolving 0.01 mol of phosphonic acid in 20 mL of deionized water, and solution B was obtained by dissolving 0.026 mol of piperazine in 35 mL of deionized water.

[0050] At room temperature, solution A was added dropwise into solution B stirred at 500 r / min for 8 hours. After the reaction was completed, the reaction solution was cooled to room temperature and filtered. The solid obtained by filtration was rinsed with deionized water three times, dried, ground, and passed through a 500-mesh sieve to obtain piperazine phosphate intermediate C2.

[0051] 0.01 mol of the piperazine phosphate intermediate obtained by the method described in Example 7 was fully dissolved in 15 mL of DMF to obtain solution D, and 0.03 mol of chloromethylpentamethyldisiloxane was fully dissolved in 60 mL of DMF to obtain solution E.

[0052] At 120°C, solution E was added dropwise into solution D stirred at 300 r / min for 12 hours. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was rotary evaporated to remove the solvent to obtain phosphorus-nitrogen-silicon intumescent flame retardant 7.

[0053] Comparative Example 1 The intermediate C1 obtained by the method described in Example 1 was used as a comparative sample.

[0054] Comparative Example 2 0.01 mol of the intermediate C1 obtained by the method described in Example 1 was mechanically mixed with 0.03 mol of chloromethylpentamethyldisiloxane to obtain a comparative sample.

[0055] Comparative Example 3 0.01 mol of the intermediate C1 obtained by the method described in Example 1 was mechanically mixed with 0.03 mol of vinyltriethoxysilane to obtain a comparative sample.

[0056] Comparative Example 4 0.01 mol of the intermediate C1 obtained by the method described in Example 1 was fully dissolved in 15 mL of DMF to obtain solution D, and 0.02 mol of chloromethylpentamethyldisiloxane was fully dissolved in 40 mL of DMF to obtain solution E.

[0057] At 120°C, solution E was added dropwise into solution D stirred at 300 r / min for 12 hours. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was rotary evaporated to remove the solvent to obtain a comparative sample.

[0058] Preparation and testing of test samples 1. Sample Preparation (1) The samples obtained in Examples 1-3, the comparative samples obtained in Comparative Examples 1-4 or the commercially available flame retardant (ammonium polyphosphate) are mixed with the modified raw materials (EVA or PE or PP) in a high-speed mixer according to the weight percentage in Table 1-3, and the mixture is fed into an extruder. The mixture is melt-mixed on the screw extruder, extruded by the extruder, cooled in a water tank, and pelletized by a cutting machine for use. The specific process conditions are as follows: The stirring speed of the high-speed mixer is 2000 r / min, and the stirring time is 10 min.

[0059] Extrusion granulation process: The temperature control of each zone of the EVA material screw extruder is: 135±10℃, 140±10℃, 145±10℃, 145±10℃, 150±10℃, 155±10℃, 155±10℃, 155±10℃; head temperature control: 165±10℃; vacuum degree: ≤-0.06MPa; water tank temperature: ≤50℃; The temperature control of each zone of the PE material screw extruder is: 175±10℃, 180±10℃, 185±10℃, 185±10℃, 190±10℃, 185±10℃, 185±10℃, 185±10℃; head temperature control: 185±10℃; vacuum degree: ≤-0.06MPa; water tank temperature: ≤50℃; The temperature control of each zone of the PP material screw extruder is: 175±10℃, 180±10℃, 185±10℃, 185±10℃, 190±10℃, 190±10℃, 190±10℃, 190±10℃; head temperature control: 190±10℃; vacuum degree: ≤-0.06MPa; water tank temperature: ≤50℃.

[0060] (2) The flame retardant modified particles are injection molded to obtain corresponding test specimens.

[0061] Injection molding machine process: Temperature control of each zone of EVA material injection molding machine: 160±10℃, 155±10℃, 150±10℃, 145±10℃; Temperature control of each zone of PE material injection molding machine: 180±10℃, 175±10℃, 170±10℃, 165±10℃; Temperature control of each zone of PP material injection molding machine: 185±10℃, 180±10℃, 175±10℃, 170±10℃.

[0062] Performance data of each raw material: The EVA is V6020M produced by Jiangsu Sailbon, with a VA content of 28% and a density of 0.937 g / cm 3, the melt flow rate (190℃ / 2.16kg) is 5.5 g / 10min, the tensile fracture stress is 19MPa, and the tensile fracture strain is 750%.

[0063] The PE is 2018CA produced by Exxon, and its density is 0.918g / cm 3 , the melt flow rate (190℃ / 2.16kg) is 2.0g / 10min, the tensile fracture stress is 24MPa, and the tensile fracture strain is 750%.

[0064] The PP is 7032E3 produced by ExxonMobil, and its density is 0.900g / cm 3 , the melt flow rate (190℃ / 2.16kg) is ≤4.0g / 10min, the tensile fracture stress is 25MPa, and the tensile fracture strain is 750%.

[0065] (3) The sample obtained in Example 1 or a commercially available flame retardant (ammonium polyphosphate) was mixed with polyurethane in the weight percentages according to Table 4, and the mixture was poured into a mold and subjected to constant temperature aging at 80° C. for 6 minutes to prepare a polyurethane pad.

[0066] The polyurethane comprises a polyol component and an isocyanate component in a mass ratio of 100:100; Calculated by mass fraction, the polyol component is 65 parts of polyether polyol, 10 parts of chain extender, 0.7 parts of water, 1.2 parts of foam stabilizer, and 0.6 parts of catalyst.

[0067] The polyether polyol is PTMEG 3000 produced by BASF, and the hydroxyl value is 36.2-57.5 mg KOH / g.

[0068] The chain extender is 1,4-butanediol produced by Shandong Jiatai Petrochemical, with a purity of ≥99.5%.

[0069] The foam stabilizer is AK-8871 produced by Jiangsu Meside Chemical.

[0070] The catalyst is PC CAT NMI (N-methylimidazole) produced by German Nitroil Company.

[0071] The isocyanate component is CDMDI-100L (carbodiimide modified diphenylmethane diisocyanate) produced by Wanhua Chemical Group Co., Ltd.

[0072] Table 1 EVA material group Table 2 PE material group Table 3 PP material group Table 4 PU material group 2. Sample testing The samples obtained above were subjected to performance testing, and the standards for each test item are as follows (1) Tensile fracture stress and tensile fracture strain: GB / T 1040.1-2018; (2) Oxygen index: GB / T 2406-2009; (3) Vertical burning grade: GB / T 2408-2008; (4) Smoke density: GB / T 8627-2007; (5) Tensile strength and elongation at break: GB / T 10654-2001.

[0073] 3. Test results The test results are shown in Table 5-8: Table 5 Test results of EVA material group Table 6 Test results of PE material group Table 7 Test results of PP material group Table 8 Test results of PU material group Experiments have shown that the novel phosphorus-nitrogen-silicon intumescent flame retardant provided by the present invention can effectively improve the compatibility with the polymer material matrix, improve the flame retardant performance, and at the same time can effectively reduce the negative impact on the mechanical properties of the polymer material.

[0074] Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art may still modify the technical solutions described in the aforementioned embodiments, or make equivalent substitutions for some of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for synthesizing a phosphorus-nitrogen-silicon intumescent flame retardant, characterized in that: It includes the following steps: S1: dissolving an acid source in solvent I to obtain solution A, and dissolving piperazine in solvent I to obtain solution B; S2: Under stirring at room temperature, solution A is added dropwise to solution B for sufficient reaction. After the reaction is completed, the solution is cooled to room temperature, filtered, and the filter cake is washed and dried to obtain intermediate C; S3: adding intermediate C into DMF and dissolving it to obtain solution D, and adding siloxane into DMF and dissolving it to obtain solution E; S4: under stirring conditions at 100-140° C., solution E is added dropwise to solution D for sufficient reaction. After the reaction is completed, the reaction solution is cooled to room temperature, filtered, and the filtrate is evaporated to remove the solvent to obtain a phosphorus-nitrogen-silicon intumescent flame retardant; The acid source is selected from one of orthophosphoric acid, phosphonic acid or phenylphosphonic acid; The siloxane is selected from one of chloromethylpentamethyldisiloxane and 2-chloromethylheptamethyltrisiloxane.

2. The method for synthesizing a phosphorus-nitrogen-silicon intumescent flame retardant according to claim 1, characterized in that: When the acid source is orthophosphoric acid, the molar ratio of the acid source to piperazine in S2 is 1:3.0-3.9; when the acid source is phosphonic acid or phenylphosphonic acid, the molar ratio of the acid source to piperazine in S2 is 1:2.0-2.

6.

3. The method for synthesizing a phosphorus-nitrogen-silicon intumescent flame retardant according to claim 1, characterized in that: When the acid source is orthophosphoric acid, the molar ratio of the acid source to piperazine in S2 is 1:3.3; when the acid source is phosphonic acid or phenylphosphonic acid, the molar ratio of the acid source to piperazine in S2 is 1:2.

2.

4. The method for synthesizing a phosphorus-nitrogen-silicon intumescent flame retardant according to claim 1, characterized in that: When the acid source is orthophosphoric acid or phosphonic acid, the molar ratio of intermediate C to siloxane in S4 is 1:3; When the acid source is phenylphosphonic acid, the molar ratio of intermediate C to siloxane in S4 is 1:

2.

5. The method for synthesizing a phosphorus-nitrogen-silicon intumescent flame retardant according to claim 1, characterized in that: The solvent I is anhydrous ethanol or water.

6. The method for synthesizing a phosphorus-nitrogen-silicon intumescent flame retardant according to claim 1, characterized in that: The stirring rate in S2 is 300-800 rpm, and the reaction time is 6-10 hours.

7. The method for synthesizing a phosphorus-nitrogen-silicon intumescent flame retardant according to claim 1, characterized in that: In S1, the dosage relationship between the acid source and solvent I is 0.01mol:12-30mL, and the dosage relationship between piperazine and solvent I is 0.01mol:8-20mL; in S3, the dosage relationship between intermediate C and DMF is 0.01mol:10-25mL, and the dosage relationship between siloxane and DMF is 0.01moL:10-30mL.

8. The method for synthesizing a phosphorus-nitrogen-silicon intumescent flame retardant according to claim 1, characterized in that: S4: The stirring rate is 200-500 rpm, and the reaction time is 10-14 hours.

9. A phosphorus-nitrogen-silicon intumescent flame retardant obtained by the synthesis method according to any one of claims 1 to 8.

10. Use of the phosphorus-nitrogen-silicon intumescent flame retardant as claimed in claim 9 as a flame retardant for polymer materials.

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