Preparation method and application of flame retardant polymer polyol

Abstract

The present invention relates to a method for preparing a flame-retardant polymer polyol and its application. The method comprises the following steps: 1) adding sulfonyl chloride and an acid-binding agent to an organic boric acid solution, allowing the mixture to react fully, and filtering to obtain polyhydroxyborane; further adding the acid-binding agent and a hexachlorocyclotriphosphazene solution, allowing the mixture to react fully, and filtering to obtain a phosphazene compound containing multiple hydroxyl groups; and 2) thoroughly mixing a base polyether polyol and the phosphazene compound, adding a polyisocyanate to the mixture under high-shear mixing conditions, and allowing the mixture to react fully to obtain the flame-retardant polymer polyol. The flame-retardant polymer polyol synthesized by the method has the characteristics of high flame retardancy, high solid content, low viscosity, and low aldehyde content, and can be used in the synthesis of flexible polyurethane foams.

Description

Technical Field

[0001] The invention belongs to the field of polyurethane synthetic materials, and particularly relates to a preparation method of a flame retardant polymer polyol and application thereof in polyurethane foam synthesis. Background Art

[0002] Polyisocyanate polyol (PIPA) refers to a product produced by the polyaddition reaction of polyisocyanate and polyol in a base polyether polyol. The dispersed polymer phase is polyurethane or polyurethane-urea polymer. The polyurethane products synthesized in this way have excellent mechanical properties and good low-temperature compliance.

[0003] However, polyurethane foam has the defects of low oxygen index and easy combustion. When burning, it releases a large amount of toxic smoke, which brings great harm to people's life and property safety. In order to improve the oxygen index of polyurethane foam, the commonly used method in industry is to add flame retardants when synthesizing polyurethane foam. This method is simple and convenient, with low cost, but it has the problem of large usage and easy migration and loss. Another method is to introduce flame retardant elements into polyols, so that the flame retardant elements are evenly distributed in the polyurethane foam and are not easy to migrate out. When the amount used is small, it has a better flame retardant effect. The flame retardant elements commonly used in industry currently include halogens, nitrogen, phosphorus, etc. Among them, halogens will release toxic gases such as hydrogen halide when burning, causing suffocation and death. The two elements of phosphorus and nitrogen do not have the above problems. At the same time, the two elements of phosphorus and nitrogen have a synergistic effect. The combination of the two elements has higher flame retardant efficiency and is the main development direction in the field of flame retardancy in the future.

[0004] Currently, existing technologies disclose methods for preparing polyisocyanate-added polyols, but there is no evidence of their application in flame retardancy. For example, CN1353728A discloses a method for preparing PIPA polyols, which involves reacting a compound containing multiple hydroxyl groups, primary and / or secondary amine groups with an isocyanate-reactive compound in a polyol to produce a polyol containing 30-80 wt% dispersed particulate matter. The PIPA polyol synthesized by this method exhibits excellent performance, but the polymer solids contain a low nitrogen content and lack flame retardancy.

[0005] The inventor's earlier patent, CN 113061257 A, disclosed a method for preparing and applying a phosphorus-nitrogen synergistic flame-retardant polymer polyol. The method involves polymerizing a phosphazene compound of a polyamine with a polyaldehyde in a polyether polyol to produce a uniform and stable polymer polyol with excellent flame retardancy. However, since the raw materials include polyaldehydes, the aldehyde content in the product remains above 100 ppm after high-temperature stripping. Furthermore, the polymer chain segments are unstable, and a large amount of small aldehyde molecules is released during the foaming process of the polyether polyol, resulting in aldehyde contents exceeding 5000 ppm in polyurethane foams. This limits its application in the polyurethane industry.

[0006] Therefore, in order to solve the above problems, it is still necessary to develop a flame retardant polymer polyol with high flame retardancy and low aldehyde content. Summary of the Invention

[0007] The purpose of the present invention is to provide a preparation method and application of a flame retardant polymer polyol. The polyol has the characteristics of high flame retardancy, high solid content, low viscosity and low aldehyde content, and can be used for the synthesis of soft polyurethane foam.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A method for preparing a flame retardant polymer polyol comprises the following steps:

[0010] 1) adding sulfonyl chloride and an acid binding agent to an organic boric acid solution, allowing the mixture to react fully and then filtering to obtain polyhydroxy borane; continuing to add the acid binding agent and a hexachlorocyclotriphosphazene solution, allowing the mixture to react fully and then filtering to obtain a phosphazene compound containing multiple hydroxyl groups;

[0011] 2) The base polyether polyol and the phosphazene compound are fully mixed, and polyisocyanate is added to the mixture under high shear mixing conditions, and the mixture is fully reacted to obtain a flame retardant polymer polyol.

[0012] In a specific embodiment, the organic borane solution in step 1) is a solution formed by dissolving organic boronic acid in a solvent; the solvent is selected from at least any one of ethers, alkanes, aromatic hydrocarbons or halogenated aromatic hydrocarbons; preferably, an ether or cyclic ether containing 2 to 6 carbon atoms, an alkane containing 6 to 10 carbon atoms, an aromatic hydrocarbon or halogenated aromatic hydrocarbon containing 6 to 8 carbon atoms; more preferably, one or more of n-propyl ether, benzene, toluene and chlorobenzene.

[0013] In a specific embodiment, the general structural formula of the organic boronic acid is as follows:

[0014]

[0015] Among them, R is any one of a C1-C8 alkyl group, a cycloalkyl group, or a C6-C8 phenyl group, and is preferably a methyl group or a phenyl group.

[0016] In a specific embodiment, the acid binding agent is selected from one or more of sodium carbonate, triethylamine, pyridine, and trimethylamine.

[0017] In a specific embodiment, the molar ratio of organic boronic acid to sulfonyl chloride in preparing polyhydroxyborane is 2:1-2.1:1, the molar ratio of acid binding agent to sulfonyl chloride is 2:1-2.1:1, and the mass ratio of solvent to organic boronic acid is 3:1-10:1.

[0018] In a specific embodiment, the reaction temperature is maintained at 60-130° C. and the reaction time is 2-5 h during the preparation of polyhydroxy borane. Further preferably, the general structural formula of the polyhydroxy borane is as follows:

[0019]

[0020] Among them, R is any one of a C1-C8 alkyl group, a cycloalkyl group, or a C6-C8 phenyl group, and is preferably a methyl group or a phenyl group.

[0021] In a specific embodiment, the molar ratio of polyhydroxyborane to hexachlorocyclotriphosphazene in the preparation of the polyhydroxyphosphazene compound is 6:1-6.1-1, and the molar ratio of the acid binding agent to hexachlorocyclotriphosphazene is 6:1-6.1-1; preferably, the reaction temperature is maintained at -80-10°C, preferably -20-0°C, and after the addition is complete, the temperature is raised to 50-150°C and the reaction is continued for 5-20 hours, preferably at 80-120°C and the reaction is continued for 8-15 hours.

[0022] In a specific embodiment, the general structural formula of the polyhydroxyphosphazene compound is as follows:

[0023]

[0024] Wherein, R1 is a structure in which the hydrogen in one of the hydroxyl groups in polyhydroxy borane is replaced, and the specific structure is as shown in formula (IV):

[0025]

[0026] Among them, R is any one of a C1-C8 alkyl group, a cycloalkyl group, or a C6-C8 phenyl group, and is preferably a methyl group or a phenyl group.

[0027] In a specific embodiment, the base polyether polyol is selected from one or more of polyethylene oxide polyol and polypropylene oxide polyol; preferably, the base polyether polyol has a hydroxyl value of 20 to 60, a functionality of 2 to 6, and a molecular weight of 2000 to 8000; preferably, the polyisocyanate is toluene diisocyanate or diphenylmethane diisocyanate.

[0028] In a specific embodiment, the molar ratio of the phosphazene compound to the polyisocyanate is 0.37-0.67, and the mass ratio of the total mass of the phosphazene compound and the polyisocyanate to the polyether polyol is 0.25-1.

[0029] In a specific embodiment, the reaction temperature in step 2) is 60-130° C., the reaction time is 1-3 h, and the high shear mixing condition is a stirring speed of 1000 rpm or more, preferably 2000 rpm or more.

[0030] On the other hand, the flame retardant polymer polyol prepared by the above preparation method is used in the synthesis of flexible polyurethane foam.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] 1) The polymer polyol prepared by the present invention contains four flame retardant elements, namely phosphorus, nitrogen, boron and sulfur. Each flame retardant element has a synergistic effect. The oxygen index of the polyurethane foam prepared by the present invention reaches about 35%, overcoming the problem that traditional PIPA polyol has no flame retardant ability.

[0033] 2) The total aldehyde content of the polymer polyol prepared by the present invention is within 10 ppm.

[0034] 2) The polymer polyol prepared by the present invention has the characteristics of high solid content and low viscosity. The solid content can be as high as 50 wt%, while the viscosity is as low as 8241 mP·s / 25°C.

[0035] 4) The polymer polyol prepared by the present invention does not contain halogen, and the polyurethane foam plastic prepared therefrom does not release a large amount of toxic gas when burned. DETAILED DESCRIPTION

[0036] In order to better understand the technical solution of the present invention, the following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0037] A method for preparing a flame retardant polymer polyol comprises the following steps: firstly synthesizing a polyhydroxyphosphazene compound containing multiple flame retardant elements such as P, N, B and S, and then reacting the polyhydroxyphosphazene compound with a basic polyether polyol and polyisocyanate to obtain the polymer polyol.

[0038] The steps for synthesizing a polyhydroxyphosphazene compound containing multiple flame retardant elements including P, N, B, and S are as follows:

[0039] Dissolve the organic boronic acid in a solvent and add an acid binding agent, slowly add sulfonyl chloride, maintain the reaction temperature at 60-130°C, filter and remove the solid after the reaction to obtain polyhydroxy borane. Continue to add the acid binding agent and slowly add the hexachlorocyclotriphosphazene solution, maintain the reaction temperature at -80-10°C, preferably -20-0°C, raise the temperature to 50-150°C after the addition, and continue the reaction for 5-20 hours, preferably at 80-120°C, and continue the reaction for 8-15 hours. After the reaction, filter and obtain a polyhydroxy phosphazene compound solution.

[0040] Since the reaction is exothermic, a too fast addition rate may cause the temperature to exceed the upper limit of the reaction temperature, so a slow addition is preferred. It will be appreciated by those skilled in the art that if heat exchange is good and the reaction temperature can be maintained within the target range, there is no restriction on the addition rate.

[0041] A method for preparing a flame retardant polymer polyol comprises the following steps: fully mixing a basic polyether polyol and a phosphazene compound, maintaining the material temperature at 60-130°C, adding polyisocyanate to the mixture under high shear mixing conditions, and distilling off the solvent after sufficient reaction to obtain the flame retardant polymer polyol.

[0042] The high shear mixing condition refers to a stirring speed of 1000 rpm or more, preferably 2000 rpm or more. Under such shear conditions, the reaction is more complete.

[0043] Wherein, the organic boronic acid structure is as shown in formula (I):

[0044]

[0045] Wherein R is any one of C1~C8 alkyl, cycloalkyl or C6~C8 phenyl, for example, alkyl such as methyl, ethyl, propyl, butyl, cycloalkyl such as cyclopentyl, cyclohexyl, phenyl, methylphenyl and other benzene ring-containing groups, preferably methyl or phenyl.

[0046] The polyhydroxy borane structure is as shown in formula (II):

[0047]

[0048] wherein R is any one of a C1-C8 alkyl group, a cycloalkyl group, or a C6-C8 phenyl group, for example, an alkyl group such as methyl, ethyl, propyl, or butyl, a cycloalkyl group such as cyclopentyl or cyclohexyl, or a benzene ring-containing group such as phenyl or methylphenyl, preferably a methyl or phenyl group. Specifically, the selection of the R group is consistent with that in formula (I).

[0049] The structure of the polyhydroxyphosphazene compound prepared in the first step is as shown in formula (III):

[0050]

[0051] Wherein R1 is a structure in which the hydrogen in one of the hydroxyl groups in polyhydroxy borane is replaced, and the specific structure is as shown in formula (IV):

[0052]

[0053] wherein R is any one of a C1-C8 alkyl group, a cycloalkyl group, or a C6-C8 phenyl group, for example, an alkyl group such as methyl, ethyl, propyl, or butyl, a cycloalkyl group such as cyclopentyl or cyclohexyl, or a benzene ring-containing group such as phenyl or methylphenyl, preferably a methyl or phenyl group. Specifically, the selection of the R group is consistent with that in formula (I).

[0054] The organic solvent is selected from ethers, alkanes, aromatic hydrocarbons, halogenated aromatic hydrocarbons, and the like; preferably, ethers or cyclic ethers containing 2 to 6 carbon atoms, alkanes containing 6 to 10 carbon atoms, aromatic hydrocarbons or halogenated aromatic hydrocarbons containing 6 to 8 carbon atoms; more preferably, one or more of n-propyl ether, benzene, toluene, and chlorobenzene. The acid-binding agent is selected from one or more of sodium carbonate, triethylamine, pyridine, and trimethylamine. In the preparation of polyhydroxyborane, the molar ratio of organic boronic acid to sulfonyl chloride is 2:1 to 2.1:1, the molar ratio of acid-binding agent to sulfonyl chloride is 2:1 to 2.1:1, and the mass ratio of solvent to organic boronic acid is 3:1 to 10:1. In the preparation of polyhydroxyphosphazene compounds, the molar ratio of polyhydroxyborane to hexachlorocyclotriphosphazene is 6:1 to 6.1-1, and the molar ratio of acid-binding agent to hexachlorocyclotriphosphazene is 6:1 to 6.1-1.

[0055] The base polyether polyol is one or more of polyethylene oxide polyol and polypropylene oxide polyol. Preferably, the base polyether polyol has a hydroxyl value of 20-60, a functionality of 2-6, and a molecular weight of 2000-8000. Specifically, for example, the base polyether polyol is a commercially available product from Wanhua Chemical, with specific grades such as F3156, F3135, and F3128.

[0056] The polyisocyanate is toluene diisocyanate or diphenylmethane diisocyanate. The molar ratio of the phosphazene compound to the polyisocyanate is 0.37 to 0.67. The mass ratio of the total mass of the phosphazene compound and the polyisocyanate to the polyether polyol is 0.25 to 1, including but not limited to 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, and 1.

[0057] In another aspect of the present invention, the flame retardant polymer polyol prepared by the above method has the characteristics of high flame retardancy, high solid content, low viscosity and low aldehyde content, and can be used for the synthesis of soft polyurethane foam.

[0058] The present invention is further illustrated below with reference to the examples, but is not intended to be limiting.

[0059] The organic boric acid, sulfonyl chloride, hexachlorocyclotriphosphazene, organic solvent, acid-binding agent, isocyanate, polyether polyol, etc. used in the examples are all commercially available reagents and are of analytical grade.

[0060] The polyether polyols used in the embodiments are as follows:

[0061] Polyether polyol 1: a glycerol-initiated propylene oxide / ethylene oxide polyether polyol with a number average molecular weight of 3000, a hydroxyl value of 56 KOH / g, and a viscosity of 350-500 mP·s / 25°C.

[0062] Polyether polyol 2: a propylene oxide / ethylene oxide polyether polyol initiated with glycerol having a number average molecular weight of 4800, a hydroxyl value of 35 KOH / g, and a viscosity of 500-700 mP·s / 25°C.

[0063] Polyether polyol 3: a propylene oxide / ethylene oxide polyether polyol initiated with propylene glycol, having a number average molecular weight of 3500, a hydroxyl value of 32 KOH / g, and a viscosity of 400-550 mP·s / 25°C.

[0064] Polyether polyol 4: a propylene oxide / ethylene oxide polyether polyol initiated with pentaerythritol having a number average molecular weight of 6400, a hydroxyl value of 35 KOH / g, and a viscosity of 850-1000 mP·s / 25°C.

[0065] The specifications of the reagents used in the synthesis of polyurethane foam are as follows:

[0066] POP2140: A commercial product of Wanhua Chemical, a polyether polyol with a copolymer of styrene and acrylonitrile as an organic filler, also known as a polymer polyol.

[0067] F3135: A commercially available product of Wanhua Chemical, a propylene oxide / ethylene oxide polyether polyol initiated with glycerol, with a number average molecular weight of 4800, a hydroxyl value of 35 KOH / g, and a viscosity of 500-550 mP·s / 25°C.

[0068] The organic silicon surfactant, 33% triethylenediamine in diethylene glycol solvent catalyst, 70% solution of bis(xylylethyl)ether, diethanolamine, TM20, etc. used are all commercially available reagents.

[0069] The test method is as follows:

[0070] Oxygen index: GB / T2046.2-2009 Plastics use oxygen index method to determine combustion behavior.

[0071] Smoke density: GB / T20286-2006 Single combustion test of building materials or products.

[0072] Aldehyde content: GBT37196-2018 Determination of aldehyde and ketone content of plastic polyether polyols / polymer polyols.

[0073] Example 1

[0074] Under a nitrogen atmosphere, dissolve 305g of methylboric acid in 915g of n-propyl ether, add 514g of triethylamine, raise the temperature to 90°C, and slowly add 425g of sulfuryl chloride. After addition, continue the reaction for 1 hour, and filter to remove the solid. Add 257g of triethylamine, maintain the reaction temperature at -20°C, dissolve 147g of hexachlorocyclotriphosphazene in 344g of n-propyl ether, and then slowly add it to the polyhydroxy borane solution. After addition, raise the temperature to 80°C, continue the reaction for 15 hours, and filter to obtain a polyhydroxy phosphazene compound solution.

[0075] 599 g of the phosphazene compound and 1200 g of polyether polyol 1 were thoroughly mixed, the temperature was raised to 60° C., the stirring speed was set to 2000 rpm, and 201 g of toluene diisocyanate was added dropwise to the mixture. After the addition was completed, the reaction was continued for 8 hours. The solvent was removed by distillation under reduced pressure to obtain a flame retardant polymer polyol with a solid content of 40%, a viscosity of 5870 mP·s / 25° C., and a total aldehyde content of 8.7 ppm.

[0076] Example 2

[0077] Under a nitrogen atmosphere, dissolve 487g of phenylboronic acid in 1949g of benzene, add 315g of pyridine, raise the temperature to 100°C, and slowly add 318g of sulfuryl chloride. Continue the reaction for 1 hour after addition, and filter to remove the solid. Add 150g of pyridine, maintain the reaction temperature at 0°C, dissolve 108g of hexachlorocyclotriphosphazene in 252g of benzene, and then slowly add this to the polyhydroxyborane solution. After addition, raise the temperature to 120°C, continue the reaction for 8 hours, and filter to obtain a polyhydroxyphosphazene compound solution.

[0078] 683 g of the phosphazene compound and 1200 g of polyether polyol 2 were thoroughly mixed, the temperature was raised to 130° C., the stirring speed was set to 2500 rpm, and 117 g of diphenylmethane diisocyanate was added dropwise to the mixture. After the addition was completed, the reaction was continued for 1 hour, and the solvent was removed by distillation under reduced pressure to obtain a flame retardant polymer polyol with a solid content of 40%, a viscosity of 5943 mP·s / 25° C., and a total aldehyde content of 6.9 ppm.

[0079] Example 3

[0080] Under a nitrogen atmosphere, dissolve 226g of methylboric acid in 1129g of toluene, add 297g of pyridine, raise the temperature to 110°C, and slowly add 314g of sulfonyl chloride. Continue the reaction for 1 hour after addition, and filter to remove the solid. Add 149g of pyridine, maintain the reaction temperature at 0°C, dissolve 109g of hexachlorocyclotriphosphazene in 253g of toluene, and then slowly add this to the polyhydroxyborane solution. After addition, raise the temperature to 100°C, continue the reaction for 10 hours, and filter to obtain a polyhydroxyphosphazene compound solution.

[0081] 443 g of the phosphazene compound was thoroughly mixed with 1400 g of polyether polyol 3, the temperature was raised to 90° C., the stirring speed was set to 2500 rpm, and 157 g of diphenylmethane diisocyanate was added dropwise to the mixture. After the addition was completed, the reaction was continued for 4 hours, and the solvent was removed by distillation under reduced pressure to obtain a flame retardant polymer polyol with a solid content of 30%, a viscosity of 3520 mP·s / 25° C., and a total aldehyde content of 9.2 ppm.

[0082] Example 4

[0083] Under a nitrogen atmosphere, dissolve 592g of cyclohexylboronic acid in 5920g of chlorobenzene, add 467g of triethylamine, raise the temperature to 130°C, slowly add 377g of sulfonyl chloride, continue the reaction for 1h after addition, and filter to remove the solid. Add 228g of triethylamine, maintain the reaction temperature at 10°C, dissolve 130g of hexachlorocyclotriphosphazene in 303g of toluene, and then slowly add the solution to the polyhydroxyborane solution. After addition, raise the temperature to 150°C, continue the reaction for 4h, and filter to obtain a polyhydroxyphosphazene solution.

[0084] 838 g of the phosphazene compound and 1000 g of polyether polyol 4 were thoroughly mixed, the temperature was raised to 110° C., the stirring speed was set to 3000 rpm, and 162 g of toluene diisocyanate was added dropwise to the mixture. After the addition was completed, the reaction was continued for 2 h. The solvent was removed by distillation under reduced pressure to obtain a flame retardant polymer polyol with a solid content of 50%, a viscosity of 8241 mP·s / 25° C., and a total aldehyde content of 5.8 ppm.

[0085] Comparative Example

[0086] Under a nitrogen atmosphere, 245.5 g of hexachlorocyclotriphosphazene was dissolved in 1227 g of acetone, and 427.5 g of triethylamine and 127 g of dimethylamine were added to the above solution, and the mixture was reacted at -10°C for 4 h; then 124 g of butanediamine was added to the solution, and the mixture was reacted at 50°C for 10 h. Finally, a colorless and transparent solution was obtained by filtration, and the phosphazene compound was obtained as a white solid by distillation at high temperature.

[0087] 485 g of a phosphazene compound and 70 g of glutaraldehyde were added to a polyether polyol and reacted at 50° C. for 10 hours. Residual monomers were then removed by vacuum extraction at a pressure of -0.098 MPa to -0.08 MPa and a temperature of 120° C. to obtain a flame-retardant polymer polyol having a solid content of 40%, a viscosity of 5830 mP·s / 25° C., and a total aldehyde content of 139 ppm.

[0088] Polyurethane foam formula:

[0089] F3135: 50 servings

[0090] Example 1-4 or Comparative Example 1 or Comparative Example 2 (POP2140): 50 parts

[0091] Silicone surfactant: 1.0 part

[0092] Triethylenediamine 33% diethylene glycol solvent catalyst: 0.4 parts

[0093] 70% solution of bis(xylylethyl) ether: 0.06 parts

[0094] Diethanolamine: 1.0 part

[0095] Water: 2.8 parts

[0096] TM20: 36.2 copies

[0097] Polyurethane foam synthesis: Select a TDI / MDI blend with a reaction index of 1.05, mix at high speed, inject into a 250*250*150 stainless steel mold, foam at room temperature, and mature at 50℃±5℃. After demolding, place the foam at room temperature for 7 days before testing the physical properties.

[0098] The flame retardant properties of the prepared polyurethane foam were tested, and the test results are shown in Table 1.

[0099] Table 1 Flame retardant performance test results

[0100]

[0101]

[0102] As can be seen from Table 1, the polyurethane foam prepared by the present invention can increase the oxygen index of ordinary polyurethane foam from 18.3% to about 36%, and the smoke density during combustion is also greatly reduced. Compared with the technology in patent CN 113061257A (Comparative Example 1), the polymer polyol aldehyde content prepared by the present invention is greatly reduced, and the flame retardant performance of the prepared polyurethane foam is improved from 34% to about 36%.

[0103] Although the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description is not intended to limit the present invention. Those skilled in the art will appreciate that, based on the teachings of this specification, modifications or adjustments may be made to the present invention. Such modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing a flame retardant polymer polyol, characterized in that: The steps include: 1) adding sulfonyl chloride and an acid binding agent to an organic boric acid solution, allowing the mixture to react fully and then filtering to obtain polyhydroxy borane; continuing to add the acid binding agent and a hexachlorocyclotriphosphazene solution, allowing the mixture to react fully and then filtering to obtain a phosphazene compound containing multiple hydroxyl groups; 2) The base polyether polyol and the phosphazene compound containing multiple hydroxyl groups are fully mixed, and polyisocyanate is added to the mixture under high shear mixing conditions, and the mixture is fully reacted to obtain a flame retardant polymer polyol.

2. The preparation method according to claim 1, characterized in that The organic boronic acid solution in step 1) is a solution formed by dissolving organic boronic acid in a solvent; the solvent is selected from at least one of ether, alkane, aromatic hydrocarbon or halogenated aromatic hydrocarbon.

3. The preparation method according to claim 2, characterized in that The solvent is an ether or cyclic ether containing 2 to 6 carbon atoms, an alkane containing 6 to 10 carbon atoms, an aromatic hydrocarbon containing 6 to 8 carbon atoms, or a halogenated aromatic hydrocarbon.

4. The preparation method according to claim 3, characterized in that The solvent is one or more of n-propyl ether, benzene, toluene and chlorobenzene.

5. The preparation method according to claim 1 or 2, characterized in that The general structural formula of the organic boronic acid is as follows: Wherein R is any one of a C1-C8 alkyl group, a cycloalkyl group or a C6-C8 phenyl-containing group.

6. The preparation method according to claim 5, characterized in that In formula (I), R is a methyl group or a phenyl group.

7. The preparation method according to any one of claims 1 to 4, characterized in that The acid binding agent is selected from one or more of sodium carbonate, triethylamine, pyridine and trimethylamine.

8. The preparation method according to claim 7, characterized in that In the preparation of polyhydroxyborane, the molar ratio of organic boronic acid to sulfonyl chloride is 2:1-2.1:1, the molar ratio of acid binding agent to sulfonyl chloride is 2:1-2.1:1, and the mass ratio of solvent to organic boronic acid is 3:1-10:

1.

9. The preparation method according to claim 8, characterized in that In the preparation of polyhydroxyborane, the reaction temperature is maintained at 60-130° C. and the reaction time is 2-5 hours.

10. The preparation method according to claim 9, characterized in that The general structural formula of the polyhydroxyborane is as follows: Wherein R is any one of a C1-C8 alkyl group, a cycloalkyl group or a C6-C8 phenyl-containing group.

11. The preparation method according to claim 10, characterized in that: In formula (II), R is a methyl group or a phenyl group.

12. The preparation method according to any one of claims 1 to 4, characterized in that: In the preparation of the phosphazene compound containing multiple hydroxyl groups, the molar ratio of polyhydroxy borane to hexachlorocyclotriphosphazene is 6:1-6.1-1, and the molar ratio of the acid binding agent to hexachlorocyclotriphosphazene is 6:1-6.1-1.

13. The preparation method according to claim 12, characterized in that Maintain the reaction temperature at -80-10°C. After the addition is complete, raise the temperature to 50-150°C and continue the reaction for 5-20 hours.

14. The preparation method according to claim 12, characterized in that Maintain the reaction temperature at -20 to 0°C. After the addition is complete, raise the temperature to 80 to 120°C and continue the reaction for 8 to 15 hours.

15. The preparation method according to claim 1, characterized in that The general structural formula of the phosphazene compound containing multiple hydroxyl groups is as follows: Wherein R1 is a structure in which the hydrogen in one of the hydroxyl groups in polyhydroxy borane is replaced, and the specific structure is as shown in formula (IV): Wherein R is any one of a C1-C8 alkyl group, a cycloalkyl group or a C6-C8 phenyl-containing group.

16. The preparation method according to claim 15, characterized in that In formula (IV), R is a methyl group or a phenyl group.

17. The preparation method according to any one of claims 1 to 4, characterized in that: The base polyether polyol is selected from one or more of polyethylene oxide polyol and polypropylene oxide polyol.

18. The preparation method according to claim 17, characterized in that: The basic polyether polyol has a hydroxyl value of 20 to 60, a functionality of 2 to 6, and a molecular weight of 2000 to 8000.

19. The preparation method according to claim 17, characterized in that The polyisocyanate is toluene diisocyanate or diphenylmethane diisocyanate.

20. The preparation method according to claim 17, characterized in that The molar ratio of the phosphazene compound containing multiple hydroxyl groups to the polyisocyanate is 0.37-0.67, and the mass ratio of the total mass of the phosphazene compound containing multiple hydroxyl groups and the polyisocyanate to the base polyether polyol is 0.25-1.

21. The preparation method according to any one of claims 1 to 4, characterized in that: In the step 2), the reaction temperature is 60-130° C., the reaction time is 1-3 hours, and the high shear mixing condition is a stirring speed of 1000 rpm or more.

22. The preparation method according to claim 21, characterized in that The high shear mixing condition is a stirring speed of 2000 rpm or more.

23. Use of the flame retardant polymer polyol prepared by the preparation method according to any one of claims 1 to 22 in the synthesis of flexible polyurethane foam.

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