Flame-retardant polyurethane foam and method for producing the same

Abstract

The application relates to the technical field of chemical materials, and discloses a flame-retardant polyurethane foam and a preparation method thereof. The polyurethane foam comprises component A and component B; the component A is diisocyanate; the component B comprises the following raw materials in percentage by mass: polyether dihydric alcohol 80-90%, hyperbranched polyester polyol 1-5%, flame-retardant chain extender 2.5-6.5%, propylene glycol 0.5-3%, organic tin catalyst 1-2.5%, foaming agent 2-6%, and surfactant 0.3-1%; after the flame-retardant chain extender and the hyperbranched polyester polyol are introduced into the matrix, the synergistic effect of the two can improve the flame-retardant property and the rebound property of the polyurethane foam.

Description

Technical Field

[0001] This invention relates to the field of chemical materials technology, specifically to a flame-retardant polyurethane foam and its preparation method. Background Technology

[0002] Polyurethane foam is a porous polymer material formed by the chemical reaction of polyols and isocyanates. It possesses excellent properties such as lightweight, high elasticity, thermal insulation, sound insulation, and energy absorption. Its open-cell or closed-cell structure can be controlled according to the synthesis process, and it is widely used in building insulation, furniture filling, automotive interiors, electronic device packaging, aerospace, and other fields. However, the molecular structure of traditional polyurethane foam is mainly composed of carbon, hydrogen, and oxygen, with a limiting oxygen index (LOI) typically below 18%, making it a highly flammable material. When burned, it releases large amounts of toxic fumes (such as HCN and CO) and molten droplets, posing a serious fire hazard.

[0003] With increasing global emphasis on fire safety, regulations in various countries have imposed mandatory requirements on the flame-retardant properties of materials. For example, building insulation materials must meet a B1 rating (flame-retardant grade), and interior materials for vehicles must pass flame-retardant tests such as FMVSS 302. Traditional polyurethane foam, due to its flammability, cannot meet these standards and urgently needs flame-retardant modification to improve its fire safety, while also considering mechanical properties, environmental friendliness, and cost control. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a flame-retardant polyurethane foam and its preparation method.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A flame-retardant polyurethane foam comprises component A and component B, wherein component A and component B are reacted after being fed in a mass ratio of 55-75:100.

[0007] Component A is a diisocyanate;

[0008] Component B comprises the following raw materials by mass percentage: 80%-90% polyether diol, 1%-5% hyperbranched polyester polyol, 2.5%-6.5% flame retardant chain extender, 0.5%-3% propylene glycol, 1%-2.5% organotin catalyst, 2%-6% foaming agent, and 0.3%-1% surfactant;

[0009] Further, the diisocyanate is a mixture of diphenylmethane diisocyanate and toluene diisocyanate, wherein the mass ratio of diphenylmethane diisocyanate to toluene diisocyanate is 3:7;

[0010] Furthermore, the polyether diol is a mixture of polyethylene glycol and polypropylene glycol in a mass ratio of 4-7:2-8, wherein the number average molecular weight of polyethylene glycol is 2700-3300 and the number average molecular weight of polypropylene glycol is 3000-5000.

[0011] Furthermore, the organotin catalyst is a mixture of dibutyltin dilaurate and stannous octoate, wherein the weight ratio of dibutyltin dilaurate to stannous octoate is 0.5-2:3-4.5;

[0012] Furthermore, the foaming agent is water, and the surfactant is organosilicon L-6863;

[0013] The flame-retardant chain extender is prepared by the following steps:

[0014] Step A1: Mix 3,5-dinitrobenzic acid, 5-hydroxy-3-pyridinecarboxaldehyde and N,N-dimethylformamide evenly, heat to 100°C, introduce nitrogen gas, add cyclohexane and p-toluenesulfonic acid and react for 1-2 hours, then stop introducing nitrogen gas and react under vacuum for 2-3 hours. Distill under reduced pressure, purify and dry to obtain the intermediate product.

[0015] Further, in step A1, the ratio of 3,5-dinitrobenzoic acid, 5-hydroxy-3-pyridinecarboxaldehyde, N,N-dimethylformamide, cyclohexane, and p-toluenesulfonic acid is 0.01-0.03 mol: 0.01-0.03 mol: 100 mL: 4-8 mL: 0.008-0.02 g;

[0016] Step A2: Stir furfurylamine and water at 45°C until homogeneous, then heat to 75°C, add intermediate product aqueous solution, stir and react for 5-7 hours, then add DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) aqueous solution and stir and react for 12 hours, rotary evaporate and dry to obtain flame retardant precursor;

[0017] Furthermore, in step A2, the ratio of furfurylamine, water, intermediate product aqueous solution, and DOPO aqueous solution is 0.01-0.03 mol: 100 mL: 50 mL: 50 mL;

[0018] Further, in step A2, the intermediate product aqueous solution is prepared by mixing and stirring the intermediate product and water at a ratio of 0.01-0.03 mol: 50 mL;

[0019] Further, in step A2, the DOPO aqueous solution is prepared by mixing and stirring DOPO and water at a ratio of 0.01-0.03 mol: 50 mL;

[0020] Step A3: Mix the flame retardant precursor, Pd / C and ethanol evenly, slowly add hydrazine hydrate, and reflux at 80°C for 5-7 hours. Filter, add water to precipitate, filter again, dry, and recrystallize to obtain the flame retardant chain extender.

[0021] Furthermore, in step A3, the ratio of the flame retardant precursor, Pd / C, ethanol, hydrazine hydrate, and water is 3-5g:0.25-0.5g:50mL:3.5-5.5g:100mL.

[0022] The hyperbranched polyester polyol is prepared by the following steps:

[0023] Step B1: Mix propylene glycol and boric acid, add toluene and concentrated sulfuric acid, stir until homogeneous, heat to 100-110℃, reflux for 7-9 hours, distill and purify to obtain borate ester derivatives.

[0024] Further, in step B1, the ratio of propylene glycol, boric acid, toluene, and concentrated sulfuric acid is 0.3-0.9 mol: 0.1-0.3 mol: 200 mL: 0.05-0.15 mL;

[0025] Step B2: Under nitrogen protection, 1 / 3 mole of 2,2-dimethylolpropionic acid, borate ester derivative and 1 / 6 mole of p-toluenesulfonic acid are mixed and stirred evenly, and the mixture is heated to 140°C and refluxed for 3 hours. Then the remaining 2,2-dimethylolpropionic acid and the remaining p-toluenesulfonic acid are added, and the temperature is maintained and the reaction is continued for 3-4 hours. The mixture is dehydrated under reduced pressure, cooled to room temperature, acetone is added and stirred evenly, recrystallized, filtered and dried to obtain hyperbranched polyester polyol.

[0026] Further, in step B2, the ratio of 2,2-dimethylolpropionic acid, borate ester derivative, p-toluenesulfonic acid and acetone is 0.1-0.3 mol: 0.005-0.015 mol: 0.096-0.288 g: 100 mL.

[0027] A method for preparing flame-retardant polyurethane foam includes the following steps:

[0028] Step S1: Weigh the raw materials according to the mass percentage, and mix the polyether diol, hyperbranched polyester polyol, flame retardant chain extender, propylene glycol, organotin catalyst, foaming agent and surfactant evenly to obtain the B component mixture.

[0029] Step S2: Mix component B and component A diisocyanate using a high-pressure foaming machine and inject the mixture into a mold at a temperature of 55-65℃. After cooling and curing, flame-retardant polyurethane foam is obtained.

[0030] The beneficial effects of this invention are:

[0031] The polyurethane foam of this invention comprises component A and component B. Component B contains a flame retardant chain extender and a hyperbranched polyester polyol. The two work synergistically to improve the flame retardant performance and resilience of the polyurethane foam.

[0032] The flame-retardant chain extender prepared in this invention is introduced into the polyurethane molecular chain as a functional chain extender, significantly improving the flame retardancy of the polyurethane matrix. This is based on the flame-retardant effect produced by the PN synergistic effect, carbonization synergistic effect, and free radical synergistic capture effect among the phosphate ester structure, furan ring, and pyridine ring structure in the chain extender. Among them, the phosphate ester structure decomposes during combustion to generate phosphorus-containing free radicals, which capture the active free radicals generated during combustion, inhibit flame propagation, and promote the carbonization of the polyurethane matrix to form a dense carbon layer, which isolates heat and oxygen and reduces the release of combustible gases. The high-temperature stability and oxygen-containing characteristics of the furan ring can promote the cross-linking and carbonization of the matrix, further enhancing the continuity and density of the carbon layer structure and forming a physical barrier. The nitrogen element contained in the pyridine ring can decompose at high temperature to generate inert gases such as NH3 and N2, which dilute combustible gases and reduce their concentration, thus achieving flame retardancy in the gas phase.

[0033] The hyperbranched polyester polyol prepared by this invention not only acts as a chain extender in the polyurethane matrix, but also has an auxiliary flame retardant effect. The ends of the hyperbranched polyester polyol contain a large number of active hydroxyl groups, which can participate in the reaction to form a denser cross-linked network, improving the compression resilience of the foam. At the same time, the hyperbranched structure also helps to form a more uniform cell structure, reducing the cell collapse or cracking problems caused by uneven molecular entanglement in traditional linear polyols. In addition, the introduced borate ester structure can also synergistically work with the N and P elements in the flame retardant chain extender to further improve the flame retardant performance. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1: The flame retardant chain extender was prepared by the following steps:

[0036] Step A1: Mix 0.01 mol 3,5-dinitrobenzic acid, 0.01 mol 5-hydroxy-3-pyridinecarboxaldehyde and 100 mL N,N-dimethylformamide until homogeneous, heat to 100°C, introduce nitrogen gas, add 4 mL cyclohexane and 0.008 g p-toluenesulfonic acid, react for 1 h, then stop introducing nitrogen gas, react under vacuum for 2 h, distill under reduced pressure, purify, and dry to obtain the intermediate product;

[0037] Step A2: 0.01 mol of furfurylamine and 100 mL of water are stirred evenly at 45°C, then the temperature is raised to 75°C, 50 mL of intermediate product aqueous solution is added, and the mixture is stirred and reacted for 5 h. Then, 50 mL of DOPO aqueous solution is added and the mixture is stirred and reacted for 12 h. The mixture is then rotary evaporated and dried to obtain the flame retardant precursor. The intermediate product aqueous solution is prepared by mixing the intermediate product and water at a ratio of 0.01 mol: 50 mL. The DOPO aqueous solution is prepared by mixing DOPO and water at a ratio of 0.01 mol: 50 mL.

[0038] Step A3: Mix 3g of flame retardant precursor, 0.25g of Pd / C and 50mL of ethanol and stir until homogeneous. Slowly add 3.5g of hydrazine hydrate and heat to 80℃ and reflux for 5 hours. Filter, add 100mL of water to precipitate, filter again, dry and recrystallize to obtain the flame retardant chain extender.

[0039] Hyperbranched polyester polyols are prepared by the following steps:

[0040] Step B1: Mix 0.3 mol propylene glycol and 0.1 mol boric acid, add 200 mL toluene and 0.05 mL concentrated sulfuric acid, mix and stir evenly, heat to 100℃, reflux for 7 h, distill and purify to obtain borate ester derivative.

[0041] Step B2: Under nitrogen protection, 0.035 mol of 2,2-dimethylolpropionic acid, 0.005 mol of borate ester derivative and 0.016 g of p-toluenesulfonic acid were mixed and stirred evenly, and the mixture was heated to 140 °C and refluxed for 3 h. Then, 0.07 mol of 2,2-dimethylolpropionic acid and 0.08 g of p-toluenesulfonic acid were added, and the reaction was continued for 3 h while maintaining the temperature. The mixture was dehydrated under reduced pressure, cooled to room temperature, and 100 mL of acetone was added and stirred evenly. The mixture was recrystallized, filtered, and dried to obtain hyperbranched polyester polyol.

[0042] Example 2: The flame retardant chain extender was prepared by the following steps:

[0043] Step A1: Mix 0.02 mol 3,5-dinitrobenzic acid, 0.02 mol 5-hydroxy-3-pyridinecarboxaldehyde and 100 mL N,N-dimethylformamide until homogeneous, heat to 100 °C, introduce nitrogen gas, add 6 mL cyclohexane and 0.015 g p-toluenesulfonic acid, react for 1.5 h, then stop introducing nitrogen gas, react under vacuum for 2.5 h, distill under reduced pressure, purify, and dry to obtain the intermediate product;

[0044] Step A2: 0.02 mol of furfurylamine and 100 mL of water are stirred evenly at 45°C, then the temperature is raised to 75°C, 50 mL of intermediate product aqueous solution is added, and the mixture is stirred and reacted for 6 hours. Then, 50 mL of DOPO aqueous solution is added and the mixture is stirred and reacted for 12 hours. The mixture is then rotary evaporated and dried to obtain the flame retardant precursor. The intermediate product aqueous solution is prepared by mixing the intermediate product and water at a ratio of 0.02 mol: 50 mL. The DOPO aqueous solution is prepared by mixing DOPO and water at a ratio of 0.02 mol: 50 mL.

[0045] Step A3: Mix 4g of flame retardant precursor, 0.35g of Pd / C and 50mL of ethanol and stir until homogeneous. Slowly add 4.5g of hydrazine hydrate and heat to 80℃ and reflux for 6 hours. Filter, add 100mL of water to precipitate, filter again, dry and recrystallize to obtain the flame retardant chain extender.

[0046] Hyperbranched polyester polyols are prepared by the following steps:

[0047] Step B1: Mix 0.6 mol propylene glycol and 0.2 mol boric acid, add 200 mL toluene and 0.1 mL concentrated sulfuric acid, mix and stir evenly, heat to 105 °C, reflux for 8 h, distill and purify to obtain borate ester derivative.

[0048] Step B2: Under nitrogen protection, 0.07 mol of 2,2-dimethylolpropionic acid, 0.01 mol of borate ester derivative and 0.032 g of p-toluenesulfonic acid were mixed and stirred evenly, and the mixture was heated to 140 °C and refluxed for 3 h. Then, 0.14 mol of 2,2-dimethylolpropionic acid and 0.16 g of p-toluenesulfonic acid were added, and the reaction was continued for 3.5 h while maintaining the temperature. The mixture was dehydrated under reduced pressure, cooled to room temperature, and 100 mL of acetone was added and stirred evenly. The mixture was recrystallized, filtered, and dried to obtain hyperbranched polyester polyol.

[0049] Example 3: The flame retardant chain extender was prepared by the following steps:

[0050] Step A1: Mix 0.01 mol 3,5-dinitrobenzic acid, 0.01 mol 5-hydroxy-3-pyridinecarboxaldehyde and 100 mL N,N-dimethylformamide until homogeneous, heat to 100°C, introduce nitrogen gas, add 4 mL cyclohexane and 0.008 g p-toluenesulfonic acid, react for 1 h, then stop introducing nitrogen gas, react under vacuum for 2 h, distill under reduced pressure, purify, and dry to obtain the intermediate product;

[0051] Step A2: 0.01 mol of furfurylamine and 100 mL of water are stirred evenly at 45°C, then the temperature is raised to 75°C, 50 mL of intermediate product aqueous solution is added, and the mixture is stirred and reacted for 5 h. Then, 50 mL of DOPO aqueous solution is added and the mixture is stirred and reacted for 12 h. The mixture is then rotary evaporated and dried to obtain the flame retardant precursor. The intermediate product aqueous solution is prepared by mixing the intermediate product and water at a ratio of 0.01 mol: 50 mL. The DOPO aqueous solution is prepared by mixing DOPO and water at a ratio of 0.01 mol: 50 mL.

[0052] Step A3: Mix 3g of flame retardant precursor, 0.25g of Pd / C and 50mL of ethanol and stir until homogeneous. Slowly add 3.5g of hydrazine hydrate and heat to 80℃ and reflux for 5 hours. Filter, add 100mL of water to precipitate, filter again, dry and recrystallize to obtain the flame retardant chain extender.

[0053] Hyperbranched polyester polyols are prepared by the following steps:

[0054] Step B1: Mix 0.9 mol propylene glycol and 0.3 mol boric acid, add 200 mL toluene and 0.15 mL concentrated sulfuric acid, mix and stir evenly, heat to 110 °C, reflux for 9 h, distill and purify to obtain borate ester derivative.

[0055] Step B2: Under nitrogen protection, 0.105 mol of 2,2-dimethylolpropionic acid, 0.015 mol of borate ester derivative and 0.048 g of p-toluenesulfonic acid were mixed and stirred evenly, and the mixture was heated to 140 °C and refluxed for 3 h. Then, 0.21 mol of 2,2-dimethylolpropionic acid and 0.24 g of p-toluenesulfonic acid were added, and the reaction was continued for 4 h while maintaining the temperature. The mixture was dehydrated under reduced pressure, cooled to room temperature, and 100 mL of acetone was added and stirred evenly. The mixture was recrystallized, filtered, and dried to obtain hyperbranched polyester polyol.

[0056] Example 4: A method for preparing flame-retardant polyurethane foam includes the following steps:

[0057] Step S1: Weigh the raw materials according to the mass percentage, and mix 90% polyether diol, 1% hyperbranched polyester polyol prepared in Example 1, 2.5% flame retardant chain extender prepared in Example 1, 1% propylene glycol, 1% organotin catalyst, 4% water and 0.5% organosilicon L-6863 evenly to obtain component B mixture; wherein, the polyether diol is a mixture of polyethylene glycol and polypropylene glycol in a mass ratio of 4:6, the number average molecular weight of polyethylene glycol is 2700 and the number average molecular weight of polypropylene glycol is 5000; the organotin catalyst is a mixture of dibutyltin dilaurate and stannous octoate, the weight ratio of dibutyltin dilaurate and stannous octoate is 2:3;

[0058] Step S2: Mix diphenylmethane diisocyanate and toluene diisocyanate at a mass ratio of 3:7 to obtain component A diisocyanate. Then, mix component B and component A diisocyanate at a mass ratio of 100:55 using a high-pressure foaming machine and inject the mixture into a mold at a temperature of 55°C. After cooling and curing, flame-retardant polyurethane foam is obtained.

[0059] Example 5: A method for preparing flame-retardant polyurethane foam includes the following steps:

[0060] Step S1: Weigh the raw materials according to the mass percentage, and mix 83.4% polyether diol, 3% hyperbranched polyester polyol prepared in Example 2, 4.5% flame retardant chain extender prepared in Example 2, 2% propylene glycol, 1.5% organotin catalyst, 5% water and 0.6% organosilicon L-6863 evenly to obtain component B mixture; wherein, the polyether diol is a mixture of polyethylene glycol and polypropylene glycol in a mass ratio of 5:5, the number average molecular weight of polyethylene glycol is 3000 and the number average molecular weight of polypropylene glycol is 4000; the organotin catalyst is a mixture of dibutyltin dilaurate and stannous octoate, the weight ratio of dibutyltin dilaurate and stannous octoate is 1:4;

[0061] Step S2: Mix diphenylmethane diisocyanate and toluene diisocyanate at a mass ratio of 3:7 to obtain component A diisocyanate. Then, mix component B and component A diisocyanate at a mass ratio of 100:65 using a high-pressure foaming machine and inject the mixture into a mold at a temperature of 60°C. After cooling and curing, flame-retardant polyurethane foam is obtained.

[0062] Example 6: A method for preparing flame-retardant polyurethane foam includes the following steps:

[0063] Step S1: Weigh the raw materials according to the mass percentage, and mix 80% polyether diol, 5% hyperbranched polyester polyol prepared in Example 3, 6.5% flame retardant chain extender prepared in Example 3, 0.5% propylene glycol, 2% organotin catalyst, 5% water and 1% organosilicon L-6863 evenly to obtain component B mixture; wherein, the polyether diol is a mixture of polyethylene glycol and polypropylene glycol in a mass ratio of 7:3, the number average molecular weight of polyethylene glycol is 3300 and the number average molecular weight of polypropylene glycol is 3000; the organotin catalyst is a mixture of dibutyltin dilaurate and stannous octoate, the weight ratio of dibutyltin dilaurate to stannous octoate is 0.5:4.5;

[0064] Step S2: Mix diphenylmethane diisocyanate and toluene diisocyanate at a mass ratio of 3:7 to obtain component A diisocyanate. Then, mix component B and component A diisocyanate at a mass ratio of 100:75 using a high-pressure foaming machine and inject the mixture into a mold at a temperature of 65°C. After cooling and curing, flame-retardant polyurethane foam is obtained.

[0065] Comparative Example 1: This comparative example is a polyurethane foam. The difference between this example and Example 6 is that a commercially available hyperbranched polyester polyol (Basonol HPE 1170 B) is used instead of the hyperbranched polyester polyol prepared in Example 3. All other aspects are the same.

[0066] Comparative Example 2: This comparative example is a polyurethane foam. The difference between this example and Example 6 is that 1,4-butanediol is used instead of the flame retardant chain extender prepared in Example 3. All other aspects are the same.

[0067] Comparative Example 3: This comparative example is a polyurethane foam. The difference between this example and Example 6 is that commercially available hyperbranched polyester polyol is used instead of the hyperbranched polyester polyol prepared in Example 3, and 1,4-butanediol is used instead of the flame retardant chain extender prepared in Example 3. All other aspects are the same.

[0068] The polyurethane foams prepared in Examples 4-6 and Comparative Examples 1-3 were subjected to performance tests:

[0069] Limiting oxygen index test: The limiting oxygen index was determined using an oxygen index meter in accordance with the standard GB / T 2406.1-2008.

[0070] UL94 rating test: The flammability rating is determined using a horizontal flammability tester, in accordance with the GB / T 8332-2008 standard.

[0071] Rebound performance test: The test shall be conducted in accordance with the standard GB / T 6670-2008;

[0072] The test results are shown in Table 1:

[0073] Table 1: Performance Test Results

[0074]

[0075] As can be seen from Table 1, after the limiting oxygen index test, UL94 rating test and resilience test, the polyurethane foam prepared by the present invention has a limiting oxygen index in the range of (33.4-34.3)%, a UL94 rating of HF-1, and a resilience of (59-63)%, indicating that the polyurethane foam material has excellent flame retardant properties and good resilience performance.

[0076] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the scope defined by the inventive concept, they should all fall within the protection scope of the present invention.

Claims

1. A flame-retardant polyurethane foam, characterized in that, It includes component A and component B, which are reacted after being fed in a mass ratio of 55-75:

100. Component A is a diisocyanate; Component B comprises the following raw materials by mass percentage: 80%-90% polyether diol, 1%-5% hyperbranched polyester polyol, 2.5%-6.5% flame retardant chain extender, 0.5%-3% propylene glycol, 1%-2.5% organotin catalyst, 2%-6% foaming agent, and 0.3%-1% surfactant; The flame retardant chain extender is prepared by reducing a flame retardant precursor with hydrazine hydrate. The flame retardant precursor is prepared by reacting furfurylamine, an intermediate product and DOPO. The intermediate product is prepared by reacting 3,5-dinitrobenzoic acid and 5-hydroxy-3-pyridinecarboxaldehyde. The hyperbranched polyester polyol is prepared by reacting 2,2-dimethylolpropionic acid with a borate ester derivative, which is prepared by reacting propylene glycol with boric acid.

2. The flame-retardant polyurethane foam according to claim 1, characterized in that, The flame-retardant chain extender is prepared by the following steps: Step A1: Mix 3,5-dinitrobenzic acid, 5-hydroxy-3-pyridinecarboxaldehyde and N,N-dimethylformamide evenly, heat to 100°C, introduce nitrogen gas, add cyclohexane and p-toluenesulfonic acid and react for 1-2 hours, then stop introducing nitrogen gas and react under vacuum for 2-3 hours. Distill under reduced pressure, purify and dry to obtain the intermediate product. Step A2: Stir furfurylamine and water at 45°C until homogeneous, then heat to 75°C, add intermediate product aqueous solution, stir and react for 5-7 hours, then add DOPO aqueous solution and stir and react for 12 hours, rotary evaporate and dry to obtain flame retardant precursor. Step A3: Mix the flame retardant precursor, Pd / C and ethanol evenly, slowly add hydrazine hydrate, and reflux at 80°C for 5-7 hours. Filter, add water to precipitate, filter again, dry, and recrystallize to obtain the flame retardant chain extender.

3. The flame-retardant polyurethane foam according to claim 2, characterized in that, In step A1, the ratio of 3,5-dinitrobenzoic acid, 5-hydroxy-3-pyridinecarboxaldehyde, N,N-dimethylformamide, cyclohexane and p-toluenesulfonic acid is 0.01-0.03 mol: 0.01-0.03 mol: 100 mL: 4-8 mL: 0.008-0.02 g.

4. The flame-retardant polyurethane foam according to claim 2, characterized in that, In step A2, the ratio of furfurylamine, water, intermediate product aqueous solution, and DOPO aqueous solution is 0.01-0.03 mol: 100 mL: 50 mL: 50 mL. The intermediate product aqueous solution is prepared by mixing and stirring the intermediate product and water at a ratio of 0.01-0.03 mol: 50 mL. The DOPO aqueous solution is prepared by mixing and stirring DOPO and water at a ratio of 0.01-0.03 mol: 50 mL.

5. The flame-retardant polyurethane foam according to claim 2, characterized in that, In step A3, the ratio of flame retardant precursor, Pd / C, ethanol, hydrazine hydrate and water is 3-5g:0.25-0.5g:50mL:3.5-5.5g:100mL.

6. The flame-retardant polyurethane foam according to claim 1, characterized in that, The hyperbranched polyester polyol is prepared by the following steps: Step B1: Mix propylene glycol and boric acid, then add toluene and concentrated sulfuric acid, stir until homogeneous, and heat to 100-110℃. Reflux for 7-9 hours, then distill and purify to obtain the borate ester derivative. The ratio of propylene glycol, boric acid, toluene, and concentrated sulfuric acid is 0.3-0.9 mol: 0.1-0.3 mol: 200 mL: 0.05-0.15 mL. Step B2: Under nitrogen protection, mix 1 / 3 mole of 2,2-dimethylolpropionic acid, borate ester derivative, and 1 / 6 mole of p-toluenesulfonic acid and stir until homogeneous. Reflux at 140°C for 3 hours. Then add the remaining 2,2-dimethylolpropionic acid and p-toluenesulfonic acid, maintain the temperature, and continue the reaction for 3-4 hours. Remove water under reduced pressure, cool to room temperature, add acetone, stir until homogeneous, recrystallize, filter, and dry to obtain hyperbranched polyester polyol. The ratio of 2,2-dimethylolpropionic acid, borate ester derivative, p-toluenesulfonic acid, and acetone is 0.1-0.3 mol: 0.005-0.015 mol: 0.096-0.288 g: 100 mL.

7. The flame-retardant polyurethane foam according to claim 1, characterized in that, The diisocyanate is a mixture of diphenylmethane diisocyanate and toluene diisocyanate, wherein the mass ratio of diphenylmethane diisocyanate to toluene diisocyanate is 3:

7.

8. The flame-retardant polyurethane foam according to claim 1, characterized in that, The polyether diol is a mixture of polyethylene glycol and polypropylene glycol in a mass ratio of 4-7:2-8, wherein the number average molecular weight of polyethylene glycol is 2700-3300 and the number average molecular weight of polypropylene glycol is 3000-5000.

9. The flame-retardant polyurethane foam according to claim 1, characterized in that, The organotin catalyst is a mixture of dibutyltin dilaurate and stannous octoate, wherein the weight ratio of dibutyltin dilaurate to stannous octoate is 0.5-2:3-4.

5.

10. A method for preparing flame-retardant polyurethane foam according to any one of claims 1-9, characterized in that, Includes the following steps: Step S1: Weigh the raw materials according to the mass percentage, and mix the polyether diol, hyperbranched polyester polyol, flame retardant chain extender, propylene glycol, organotin catalyst, foaming agent and surfactant evenly to obtain the B component mixture. Step S2: Mix component B and component A diisocyanate using a high-pressure foaming machine and inject the mixture into a mold at a temperature of 55-65℃. After cooling and curing, flame-retardant polyurethane foam is obtained.

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