A phosphorus-containing polyol flame retardant and its preparation method

Abstract

The present invention discloses a phosphorus-containing polyol flame retardant and a preparation method thereof. The phosphorus-containing polyol has the following structural formula, wherein R1 is any one of -H, -CH3, -C2H5, -Ph, R2 is epoxy vegetable oil, aliphatic alkoxy group, halogenated aliphatic alkoxy group, and n1, n2, n3, and n4 are all positive integers of ≥1, and n1 + n2 + n3 + n4 ≤ 12. The phosphorus-containing polyol provided by the present invention has high quality, good color, controllable phosphorus content, and low acid value. For polyurethane foam, it not only has good compatibility, but also can provide flame retardant performance and enhance the mechanical properties of polyurethane foam. The preparation method of the phosphorus-containing polyol flame retardant of the present invention has a moderate reaction temperature, does not use a catalyst, has no by-products, and the excessive epoxide (small molecule) after the reaction can be recycled and reused, which reflects the "atom economy" and meets the requirements of green chemistry. #imgabs0#

Description

Technical Field

[0001] The present invention belongs to the field of synthesis of flame retardants, and particularly relates to a novel phosphorus-containing polyol flame retardant and a preparation method thereof. Background Art

[0002] Polyurethane (PU) refers to a polymer having repeating urethane groups (-NHCOO-) in the polymer main chain structure. PU is formed by the addition polymerization of polyester or polyether polyols and polyisocyanates in the presence of a catalyst. Due to its excellent properties, it has been highly praised by the academic and industrial circles and is considered the "fifth most commonly used plastic" after polyethylene, polyvinyl chloride, polypropylene, and polystyrene. Currently, PU has been widely used in leather processing, textiles, building materials, coatings, medicine, automobiles, national defense, and aerospace and other fields. However, since PU is a combustible or flammable material, it will release highly toxic gases and smoke such as HCN, CO, and NO2 during combustion, which is not only a serious safety hazard but also constantly threatens people's lives, property, and safety. Therefore, it is crucial to improve the heat resistance and flame retardancy of polyurethane materials.

[0003] Currently, the methods for improving the flame retardancy of polyurethane include adding flame retardants and using flame-retardant polyether polyols. Halogen-containing flame retardants have been gradually phased out because they produce a large amount of toxic gases such as hydrogen halide and dioxin during combustion; Additive phosphate flame retardants such as triethyl phosphate, triphenyl phosphate, and dimethyl methylphosphonate have a small molecular weight and are prone to migration in the foam over time, reducing the flame retardancy of the foam and also affecting the mechanical properties of the material; Flame-retardant polyether polyols will cause the formaldehyde content in polyurethane foam to seriously exceed the standard. Traditional additive flame retardants in the form of physical blending are prone to defects such as precipitation and migration of the flame retardant during the use of polyurethane products. Summary of the Invention

[0004] Object of the Invention: Aiming at the problems existing in the existing flame retardants, the present invention provides a novel phosphorus-containing polyol flame retardant to solve the problems such as easy precipitation, poor compatibility with materials, and partial hydrolysis of additive phosphate flame retardants. The novel flame retardant provided by the present invention contains hydroxyl functional groups, so it can react with high-molecular monomers such as isocyanates. When synthesizing polyurethane, the phosphorus-containing polyol flame retardant of the present invention is added as a raw material, and the flame retardant unit will be incorporated into the main chain or side chain of polyurethane in the form of embedding, crosslinking, etc., thereby endowing polyurethane with permanent flame retardancy and effectively overcoming the disadvantages such as easy precipitation and migration of additive flame retardants.

[0005] The present invention also provides a preparation method of the novel phosphorus-containing polyol flame retardant.

[0006] Technical Solution: To achieve the above object, the present invention provides a phosphorus-containing polyol, and the structural formula of the phosphorus-containing polyol is as follows:

[0007]

[0008] Wherein R1 is any one of -H, -CH3, -C2H5, -Ph; R2 is an epoxy vegetable oil, an aliphatic alkoxy group or a halogenated aliphatic alkoxy group; n1, n2, n3, and n4 are all positive integers greater than or equal to 1, and n1 + n2 + n3 + n4 ≤ 12 (n1, n2, n3, n4 are the numbers of R2 substituents).

[0009] Preferably, when R2 is an aliphatic alkoxy group or a halogenated aliphatic alkoxy group, n1, n2, n3, and n4 are all positive integers greater than or equal to 1, and n1 + n2 + n3 + n4 ≤ 12, and the aliphatic alkoxy group or the halogenated aliphatic alkoxy group is any one of the following groups:

[0010]

[0011] When R2 is an epoxy vegetable oil, n1, n2, n3, and n4 are all 1, and the epoxy vegetable oil is any one of the following:

[0012] Epoxidized soybean oil, epoxidized castor oil, epoxidized corn oil, epoxidized linseed oil, epoxidized rapeseed oil, epoxidized tung oil, epoxidized soybean oil methyl ester. When R2 is an epoxy vegetable oil, because the epoxy vegetable oil has a relatively large molecular weight, each molecule contains 3 carbon chains, each carbon chain contains 17 or 18 carbons, and there may be only 1 epoxy group on each carbon chain, so the possibility of its polymerization is relatively small, so n1, n2, n3, and n4 are all 1.

[0013] Preferably, an organic solvent can also be added when adding the epoxy vegetable oil. Using an organic solvent can reduce the viscosity of the reactants, make the reaction uniform, and improve the yield. Products with low viscosity may not require a solvent, which has basically no impact on the yield.

[0014] Furthermore, the solvent is 1,4-dioxane, isopropanol, tert-butanol, toluene, ethyl acetate, tetrahydrofuran. After the reaction is completed, the excess solvent is distilled off under reduced pressure to obtain the phosphorus-containing polyol.

[0015] Preferably, the structural formula of the phosphorus-containing polyol is any one of the following:

[0016]

[0017]

[0018] The preparation method of the phosphorus-containing polyol described in the present invention includes the following steps: Add polyphosphonic acid to a reaction device, then dropwise add an epoxide. After the addition of the epoxide is completed, start the heat preservation reaction. The reaction temperature is 55-95 °C, and the reaction time is 3-9 h; When the dropped epoxide is epoxy vegetable oil, an organic solvent needs to be added to reduce the viscosity and improve the reaction rate at the same time.

[0019] Among them, the polyphosphonic acid is hydroxyethane diphosphonic acid.

[0020] Among them, the epoxide is any one or several of ethylene oxide, propylene oxide, epichlorohydrin, epibromohydrin, 1,1-dimethylethylene oxide, glycidol, and epoxy vegetable oil.

[0021] Among them, the molar ratio of the polyphosphonic acid to the epoxide is 1:(4-14).

[0022] Among them, the solvent is any one or several of 1,4-dioxane, isopropanol, tert-butanol, toluene, ethyl acetate, and tetrahydrofuran.

[0023] Among them, the reaction device is an atmospheric pressure reaction device or a high-pressure reaction device. If a high-pressure reaction device is used, nitrogen is filled into the kettle until the pressure in the kettle is 0.2-1 MPa.

[0024] Furthermore, after the reaction, the excess epoxide (small molecule) is recovered to obtain a reactive phosphorus-containing polyol with an acid value of less than 2 mg KOH / g and a hydroxyl value of 150-420 mg KOH / g.

[0025] The application of the phosphorus-containing polyol described in the present invention as a flame retardant in the preparation of highly flame-retardant polyurethane foam plastics.

[0026] The present invention uses the common scale treatment agent hydroxyethane diphosphonic acid as a raw material to design and synthesize a phosphorus-containing polyol. This polyol can be used as a reactive flame retardant for the flame retardancy of polyurethane, overcoming the disadvantage of easy migration of additive flame retardants. The present invention uses hydroxyethane diphosphonic acid as a raw material to synthesize a new type of phosphorus-containing polyol. Under the self-catalysis of hydroxyethane diphosphonic acid, it catalyzes the ring-opening polymerization of epoxides, effectively realizing the self-catalysis reaction.

[0027] The present invention designs a phosphorus-containing polyol with a brand-new structure, mainly using hydroxyethane diphosphonic acid as the raw material. It has a novel structure and good thermal stability. Its decomposition temperature matches the decomposition temperature of polyurethane, making it suitable for use as a flame retardant for polyurethane foam. At the same time, the synthesis method of the present invention is simple and efficient, and the product has specific hydroxyl value and functionality. When preparing rigid polyurethane foam, the flame retardant prepared by the present invention is gradually increased. The addition of the flame retardant effectively improves the flame retardant effect. At the same time, the addition of a certain amount of flame retardant will not only not affect the mechanical properties, but instead has a certain promoting effect.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0029] (1) The phosphorus-containing polyol provided by the present invention has the following advantages: high quality, good color, controllable phosphorus content, low acid value. For polyurethane foam, it not only has good compatibility, but also can provide flame retardancy and enhance the mechanical properties of polyurethane foam.

[0030] (2) The phosphorus-containing polyol prepared by the present invention can achieve good flame retardancy and improve mechanical strength at the same time.

[0031] (2) The present invention provides a synthesis method of a phosphorus-containing polyol flame retardant with low acid value. The reaction temperature is moderate, no catalyst is used, no by-products are generated, and the excess epoxide (small molecule) after the reaction can be recycled by recovery, which reflects "atom economy" and meets the requirements of green chemistry. Description of the drawings

[0032] Figure 1 It is the appearance diagram of the product, where (a) is the product of Example 1 and (b) is the product of Example 6;

[0033] Figure 2 It is the 1H NMR spectrum of hydroxyethylidene diphosphonic acid and the product phosphorus-containing polyol in Example 1;

[0034] Figure 3 It is the infrared spectrum of hydroxyethylidene diphosphonic acid and the product phosphorus-containing polyol in Example 1;

[0035] Figure 4 It is the thermogravimetric analysis diagram of the product phosphorus-containing polyol in Example 1. Detailed implementation manners

[0036] The following makes a detailed description of the present invention in combination with specific embodiments.

[0037] In the embodiments, if not otherwise specified, the experimental methods are all conventional methods; the reagents and materials, if not otherwise specified, can all be obtained from commercial channels.

[0038] Method for measuring acid value

[0039] Weigh a certain amount of sample, 3 g, in a conical flask using an analytical balance, add about 50 mL of absolute ethanol, shake the conical flask vigorously to completely dissolve the sample. If necessary, heating can also be carried out. Then add 5 drops of self-made phenolphthalein indicator, shake well, and titrate it with a 0.02 mol / L KOH-CH3CH2OH standard titration solution until it turns pink and remains unchanged for 30 s. At the same time, a blank test is carried out.

[0040] Calculation formula:

[0041]

[0042] AV: Acid value, mg KOH / g;

[0043] V1: Volume of potassium hydroxide - C2H5OH standard solution consumed in titrating the sample, mL;

[0044] V2: Volume of potassium hydroxide - C2H5OH standard solution consumed in titrating the blank, mL;

[0045] c: Concentration of potassium hydroxide - C2H5OH standard solution, mol / L;

[0046] m: Mass of the sample, g;

[0047] 56.1: Molar mass of KOH, g / mol;

[0048] Hydroxyl value determination method

[0049] Determination is carried out according to "HG / T 2709-95 Determination of Hydroxyl Value in Polyester Polyol". The hydroxyl groups in the sample react with acetic anhydride in the acetylation reagent. The remaining acetic anhydride is decomposed by adding water, and the acetic acid generated is titrated with 0.5mol / L potassium hydroxide - ethanol standard titration solution. At the same time, a blank test is carried out, and the hydroxyl value of the sample is calculated from the difference.

[0050] Calculation formula

[0051]

[0052] OHV: Hydroxyl value of the sample, mg KOH / g;

[0053] V A : Volume of sodium hydroxide standard solution consumed in the blank experiment, mL;

[0054] V B : Volume of sodium hydroxide standard solution consumed by the sample, mL;

[0055] c: Molar concentration of sodium hydroxide standard solution, mol / L;

[0056] m: Sample mass, g;

[0057] 56.1: Molar mass of KOH, g / mol;

[0058] AV: Acid value of the sample, mg KOH / g.

[0059] Example 1

[0060] Add 10.30 g (0.05 mol) of hydroxyethylidene diphosphonic acid into a 100 mL four-necked flask equipped with a constant pressure dropping funnel, a magnetic stirrer, a thermometer and a reflux condenser. Then, dropwise add 34.85 g (0.60 mol) of propylene oxide, and keep the temperature at 55 °C under normal pressure for 6 h. Wait for the reaction to end, and remove the excess propylene oxide by vacuum pumping with an oil pump to obtain a colorless, transparent and viscous liquid with an acid value of 0.80 mg KOH / g and a hydroxyl value of 420 mg KOH / g. The physical picture of the product of this Example 1 is as shown in Figure 1 (a), which proves that the prepared phosphorus-containing polyol has high quality and good color.

[0061] The 1H NMR spectrum and infrared spectrum of the product are as shown in Figure 2 and 3 .

[0062] The structure of the phosphorus-containing polyol prepared in this Example is as follows:

[0063]

[0064] n1, n2, n3, and n4 are all positive integers ≥ 1, and n1 + n2 + n3 + n4 ≤ 12.

[0065] Figure 2 (a) is the 1H NMR spectrum of hydroxyethylidene diphosphonic acid. The multiplet at 1.45 ppm in the figure is the absorption peak of the methyl group.

[0066] Figure 2 (b) is the 1H NMR spectrum of the phosphorus-containing polyol prepared in Example 1 of the present invention. The multiplet a at 1.12 ppm in the figure is the H of the methyl group in the repeating unit, the singlet b near 1.35 ppm belongs to the H of the methyl group in the main chain structure, the multiplet near 3.47 ppm belongs to the H of the methine group in the repeating structural unit, the multiplet near 3.96 ppm belongs to the H of the methylene group in the repeating structural unit, and the singlet near 4.19 ppm belongs to the active hydrogen of the hydroxyl group.

[0067] By comparing the 1H NMR spectrum and infrared spectrum, it can be proved that the phosphorus-containing polyol prepared in Example 1 has been successfully synthesized.

[0068] The thermogravimetric analysis diagram of the phosphorus-containing polyol synthesized in this Example is as shown in Figure 4 . Figure 4 It shows that the decomposition temperature of this phosphorus-containing polyol matches the decomposition temperature of polyurethane and is suitable for use as a flame retardant for polyurethane foam.

[0069] Example 2

[0070] Add 10.30 g (0.05 mol) of hydroxyethane diphosphonic acid into a high-pressure reactor, then add 22.03 g (0.50 mol) of ethylene oxide. Open the inlet valve of the reactor and adjust the nitrogen pressure reducing valve to control the pressure at 0.5 MPa. Set the temperature at 70 °C and react for 5 h. After the reaction ends, pump out the excess ethylene oxide to obtain a colorless, transparent and viscous liquid with an acid value of 0.88 mg KOH / g and a hydroxyl value of 390 mg KOH / g.

[0071] The phosphorus-containing polyol prepared in this example has the following structure:

[0072]

[0073] n1, n2, n3, and n4 are all positive integers greater than or equal to 1, and n1 + n2 + n3 + n4 ≤ 12.

[0074] Example 3

[0075] Add 10.30 g (0.05 mol) of hydroxyethane diphosphonic acid into a 100 mL four-necked flask equipped with a constant-pressure dropping funnel, magnetic stirrer, thermometer and reflux condenser. Then dropwise add 37.01 g (0.40 mol) of epichlorohydrin and keep it at 95 °C under normal pressure for 7 h. After the reaction ends, pump out the excess epichlorohydrin by vacuum pumping with an oil pump to obtain a slightly yellow, transparent and viscous liquid with an acid value of 1.76 mg KOH / g and a hydroxyl value of 420 mg KOH / g.

[0076] The phosphorus-containing polyol prepared in this example has the following structure:

[0077]

[0078] Example 4

[0079] Add 10.30 g (0.05 mol) of hydroxyethane diphosphonic acid into a 100 mL four-necked flask equipped with a constant-pressure dropping funnel, magnetic stirrer, thermometer and reflux condenser. Dropwise add 41.09 g (0.30 mol) of epibromohydrin. After the addition is completed, keep it at 95 °C under normal pressure for 8 h. After the reaction ends, raise the temperature and pump out the excess epibromohydrin by vacuum pumping with an oil pump to obtain a colorless, transparent and viscous liquid with an acid value of 1.00 mg KOH / g and a hydroxyl value of 385 mg KOH / g.

[0080] Example 5

[0081] Add 10.30 g (0.05 mol) of hydroxyethane diphosphonic acid into a 100 mL four-necked flask equipped with a constant-pressure dropping funnel, a magnetic stirrer, a thermometer and a reflux condenser. Dropwise add 36.089 g (0.50 mol) of 1,1-dimethyloxirane. After the addition is completed, keep it warm at 55 °C under normal pressure for 6 h. Wait for the reaction to end, raise the temperature, and use an oil pump to reduce the pressure to remove the excess 1,1-dimethyloxirane to obtain a light yellow transparent viscous liquid with an acid value of 0.35 mg KOH / g and a hydroxyl value of 370 mg KOH / g.

[0082] The phosphorus-containing polyol prepared in this example has the following structure

[0083]

[0084] Example 6

[0085] Add a mixed solution of 2.5 g (0.012 mol) of hydroxyethane diphosphonic acid and 20 g of 1,4-dioxane into a 100 mL four-necked flask equipped with a thermometer, a condenser, a mechanical stirring device and a dropping funnel. Raise the liquid temperature to 95 °C. After the reaction system refluxes for 20 min, start to dropwise add 21 g (0.084 mol epoxy group) of epoxidized soybean oil. After the addition is completed, keep it warm at 95 °C under normal pressure for 9 h. Wait for the reaction to end, and distill off the solvent under reduced pressure at 80 °C to obtain a viscous liquid with an acid value of 2.00 mg KOH / g and a hydroxyl value of 203 mg KOH / g. The physical picture of the product of this Example 6 is as shown in Figure 1 shown in (b).

[0086] Example 7

[0087] Add a mixed solution of 2.00 g (0.01 mol) of hydroxyethane diphosphonic acid and 20 g of toluene into a 100 mL four-necked flask equipped with a thermometer, a condenser, a mechanical stirring device and a dropping funnel. Raise the liquid temperature to 90 °C. After the reaction system refluxes for 20 min, start to dropwise add 18.30 g (0.07 mol epoxy group) of epoxidized cottonseed oil. After the addition is completed, keep it warm at 90 °C under normal pressure for 8 h. Wait for the reaction to end, and distill off the solvent under reduced pressure at 80 °C to obtain a light yellow viscous liquid with an acid value of 1.59 mg KOH / g and a hydroxyl value of 170 mg KOH / g.

[0088] Example 8

[0089] Add a mixed solution of 1.50 g (0.007 mol) of hydroxyethane diphosphonic acid and 15 g of isopropanol into a 100 mL four-necked flask equipped with a thermometer, a condenser, a mechanical stirring device and a dropping funnel. Raise the liquid temperature to 80 °C. After the reaction system refluxes for 20 min, start to dropwise add 25 g (0.049 mol epoxy group) of epoxy castor oil. After the dropping is completed, keep the reaction at 80 °C under normal pressure for 9 h. After the reaction ends, distill off the solvent under reduced pressure at 80 °C to obtain a light yellow viscous liquid with an acid value of 1.08 mg KOH / g and a hydroxyl value of 157 mg KOH / g.

[0090] Example 9

[0091] Add a mixed solution of 2.00 g (0.01 mol) of hydroxyethane diphosphonic acid and 20 g of isopropanol into a 100 mL four-necked flask equipped with a thermometer, a condenser, a mechanical stirring device and a dropping funnel. Raise the liquid temperature to 80 °C. After the reaction system refluxes for 20 min, start to dropwise add 22 g (0.07 mol epoxy group) of epoxy tung oil. After the dropping is completed, keep the reaction at 85 °C under normal pressure for 9 h. After the reaction ends, distill off the solvent under reduced pressure at 80 °C to obtain a light yellow viscous liquid with an acid value of 0.78 mg KOH / g and a hydroxyl value of 175 mg KOH / g.

[0092] Comparative Example 1

[0093] Add 10.30 g (0.05 mol) of hydroxyethane diphosphonic acid into a 100 mL four-necked flask equipped with a constant pressure dropping funnel, a magnetic stirrer, a thermometer and a reflux condenser, and then dropwise add 23.23 g (0.40 mol) of propylene oxide. Keep the reaction at 10 °C under normal pressure for 6 h. After the reaction ends, use an oil pump to reduce the pressure to remove the excess propylene oxide to obtain a colorless transparent viscous liquid containing a large amount of undissolved solids with an acid value of 61.37 mg KOH / g.

[0094] It can be seen from Comparative Example 1 and Example 1 that when the reaction of hydroxyethane diphosphonic acid and propylene oxide is carried out at low temperature, the acid value of the product is too large and the reaction is incomplete.

[0095] Example 10

[0096] Application of reactive phosphorus-containing polyol flame retardant in polyurethane foam

[0097] Take 0 - 50 parts by weight of the flame retardant (HEDP-PO) in Example 1, and the formulations in Table 1 (all represent parts by weight).

[0098] Table 1 Polyurethane foam formulation

[0099]

[0100]

[0101] Wherein R represents the isocyanate index, which is the ratio of the equivalent number of isocyanate to polyol.

[0102] All foams were prepared according to the same procedure. Table 1 gives the formulation of the foam raw materials. The foams prepared according to the HEDP-PO content in the blended polyol being 0, 10, 20, 30, 40, and 50 parts by weight were named PUF-0, PUF-1, PUF-2, PUF-3, PUF-4, and PUF-5 respectively. As shown in Table 1, rigid polyurethane foam (RPUF) was prepared by the one-step free-rise method. At room temperature, polyether polyol 4110, the flame retardant in Example 1, catalyst DBTDL, distilled water, and foam stabilizer AK8805 were premixed to obtain a homogeneous polyol blend, and then the calculated amount of isocyanate was added to the polyol blend (the addition amount was calculated according to R). After stirring for 10 s, the obtained blend was poured into an open mold for foaming and left for one week to complete curing. Finally, the foam was cut into specific sizes for characterization. The foams were tested, and the results are shown in Table 2 and Table 3.

[0103] The limiting oxygen index (LOI) refers to the minimum oxygen concentration required for a material to burn in a mixed flow of oxygen and nitrogen under specific conditions, and is used to judge the ease of combustion of the material in air. The higher the oxygen index of the material, the less likely it is to burn. Generally, LOI < 22% belongs to flammable, LOI between 22 - 27% belongs to combustible, and LOI > 27% belongs to flame-retardant.

[0104] The vertical burning test (UL-94) refers to a test method in which a flame is applied to a specimen of a certain specification placed vertically under specified conditions, and then classified according to the combustion phenomenon. The UL-94 flame retardant level can generally be divided into V-0, V-1, and V-2 grades, among which the combustion level of V-0 is the highest.

[0105] (1) The limiting oxygen index (LOI) was measured using a JF-3 oxygen index measuring instrument produced by Nanjing Jiangning Analytical Instrument Factory according to the GB / T 2406-1993 standard. The size requirement for the foam was 130 mm × 6.5 mm × 3.0 mm.

[0106] (2) Vertical burning (UL-94) was measured using a CZF-5 type horizontal and vertical burning tester according to the GB / T 2408-2008 standard. The size requirement for the foam was 130 mm × 13.0 mm × 3.0 mm.

[0107] (3) The apparent density of the foam was tested according to the method of GB / T 6343-2009.

[0108] (4) The compressive strength was tested according to GB / T 8813-2008. The sample size was 5 cm × 5 cm × 5 cm. A CMT4000 microcomputer-controlled electronic universal testing machine was used, with a testing speed of 10 mm / min and a compressive deformation of 10%.

[0109] Table 2 Flame retardant properties of polyurethane foam

[0110]

[0111]

[0112] As can be seen from Table 2, as the amount of flame retardant added increases, the phosphorus content in the system increases, and the limiting oxygen index of the material also gradually increases. When the amount of flame retardant added is 30 parts (PUF-3), the limiting oxygen index reaches 25%, and the foam passes the UL-94 vertical burning test at V-0 level; when the addition amount reaches 50 parts, the limiting oxygen index reaches 28%, and the burning grade is V-0 grade, indicating that the flame retardant has good flame retardant properties.

[0113] Table 3 Mechanical properties of polyurethane foam

[0114] Sample PUF-0 PUF-1 PUF-2 PUF-3 PUF-4 PUF-5 <![CDATA[Apparent density (kg / m 3 )]]> 47.0 48.1 49.0 51.1 50.7 49.6 Compressive strength (MPa) 0.167 0.172 0.191 0.215 0.220 0.212

[0115] Compared with the polyurethane foam without adding flame retardant (PUF-0), after adding the flame retardant prepared in Example 1, the mechanical properties of the rigid polyurethane foam are greatly improved. This is because the flame retardant prepared in Example 1 has specific hydroxyl value and functionality, resulting in an increase in the crosslinking density of the prepared polyurethane foam, thus gradually increasing the compressive strength of the polyurethane foam. Another possible reason is that the phosphate group belongs to a flexible group and can play a plasticizing role in polyurethane. In fact, adding flame retardant to polyurethane foam will affect the mechanical properties of polyurethane foam, and the more the amount of flame retardant added, the greater the impact on the mechanical properties. In the prior art, the addition of many reactive flame retardants will lead to a decrease in the mechanical properties (such as compressive strength) of polyurethane foam (see Table 4 for details). However, the polyester foams such as PUF-3 and PUF-4 prepared with the specific flame retardant prepared by the present invention not only do not affect the mechanical properties of the polyester foam, but instead improve its mechanical properties, and the flame retardant level can reach V-0 level, with very significant effects. For PUF-5 in the present invention, due to the relatively high amount of flame retardant added, the mechanical properties are slightly lower than those of PUF-4, but still better than those without adding the flame retardant of the present invention, and the flame retardant level can also reach V-0 level. Table 4 shows that using HEDP-PO polyol as a flame retardant exhibits better performance compared with the previous flame retardants.

[0116] Table 4 Influence of adding flame retardants in the prior art on the mechanical properties of polyurethane foam.

[0117]

[0118]

[0119] Literature 1: Preparation and Properties of Flame-Retardant Soybean Oil-Based Rigid Polyurethane Foams, Huang Shizhao, Master's Thesis of Hubei University, May 2019.

[0120] Literature 2: Synthesis of Polyols Containing Triazine Ring Structure and Their Application in Polyurethanes, Xu Shaoshuai, Master's Thesis of Hubei University, May 2020.

[0121] Literature 3: Research on Flame-Retardant Rigid Polyurethane Foams, Feng Yuelan, Chemical Propellants & Polymeric Materials, Vol. 14, No. 4, 2016.

[0122] Literature 4: Preparation and Properties of Flame-Retardant Rigid Polyurethane Foams, Liu Fengjiao, Master's Thesis of Beijing University of Chemical Technology, June 2014.

Claims

1. Application of a phosphorus-containing polyol as a flame retardant, characterized in that, The structural formula of the phosphorus-containing polyol is as follows: Wherein, R1 is any one of -H, -CH3, -C2H5, -Ph; when R2 is epoxy vegetable oil, n1, n2, n3, and n4 are all 1, and it is any one of the following epoxy vegetable oils: epoxy soybean oil, epoxy castor oil, epoxy corn oil, epoxy linseed oil, epoxy rapeseed oil, epoxy tung oil, epoxy soybean oil methyl ester; Alternatively, R1 is any one of -H, -CH3, -C2H5, -Ph; when R2 is an aliphatic alkoxy group or a halogenated aliphatic alkoxy group, n1, n2, n3, and n4 are all positive integers ≥ 1, and n1 + n2 + n3 + n4 ≤ 12. The aliphatic alkoxy group or halogenated aliphatic alkoxy group is any one of the following groups, X is a halogen, and the following n represents n1, n2, n3, or n4 at different substitution positions of R2:

2. The application according to claim 1, characterized in that The structural formula of the phosphorus-containing polyol is any one of the following: Wherein n1, n2, n3, and n4 are all positive integers ≥ 1, and n1 + n2 + n3 + n4 ≤ 12.

3. The application according to claim 1, wherein The preparation method of the phosphorus-containing polyol described above includes the following steps: Add hydroxyethylidene diphosphonic acid to the reaction device, and then dropwise add the epoxide. After the dropping is completed, start the heat preservation reaction. The reaction temperature is 55 - 95 °C, and the reaction time is 3 - 9 h; the epoxide is any one of ethylene oxide, propylene oxide, epichlorohydrin, epibromohydrin, 1,1-dimethylethylene oxide, glycidol, epoxy vegetable oil; when the dropped epoxide is epoxy vegetable oil, an organic solvent needs to be added.

4. The application according to claim 3, characterized in that, The solvent is any one or several of 1,4-dioxane, isopropanol, tert-butanol, toluene, ethyl acetate, and tetrahydrofuran.

5. The application according to claim 3, wherein The molar ratio of the hydroxyethylidene diphosphonic acid to the epoxide is 1:(4 - 14).

6. The application according to claim 3, wherein, The reaction device is an atmospheric pressure reaction device or a high-pressure reaction device. If a high-pressure reaction device is used, nitrogen is filled into the kettle until the pressure in the kettle is 0.2 - 1 MPa.

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