Phosphonate flame retardant as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of flame-retardant material preparation, and particularly discloses a phosphonate flame retardant as well as a preparation method and application thereof. The preparation method of the phosphonate flame retardant provided by the invention comprises the following steps: under the catalytic action of concentrated sulfuric acid and sulfonate, carrying out esterification reaction on diethyl methylphosphonite rectification by-products and low-boiling-point alcohol compounds, introducing oxygen-containing mixed gas, carrying out oxidation reaction, and carrying out reduced pressure distillation to obtain the phosphonate flame retardant. The preparation method of the phosphonate flame retardant provided by the invention has the advantages of simple process, low raw material cost, easiness in industrial implementation and the like, realizes comprehensive recycling of diethyl methylphosphonite rectification byproduct resources, and has important economic benefits and environmental benefits. The flame retardant composed of diethyl ethyl phosphonate and ethyl methyl ethyl phosphonate prepared by the invention has excellent flame retardant property, and can be used in the fields of plastics, textiles, rubber or building materials and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of flame retardant material preparation, and relates to a phosphonate flame retardant and a preparation method and application thereof. Background Art

[0002] Glufosinate is the second most widely used lethal herbicide in the world, and diethyl methylphosphite is a key intermediate in the synthesis of glufosinate. At present, the aluminum process and the gas phase process are the mainstream routes for the industrial synthesis of diethyl methylphosphite. Both the aluminum process and the gas phase process require the product after the esterification reaction to be distilled to obtain high-purity diethyl methylphosphite. During the distillation process of diethyl methylphosphite, phosphonate distillation by-products are produced, which mainly include triethyl phosphite, ethyl methyl ethylphosphonate, diethyl phosphonate and ethyl methylphosphonate, and the main component structure is as shown in the figure below: .

[0003] Since the diethyl methylphosphite distillation byproduct contains a small amount of diethyl methylphosphite that is prone to redox reaction, phosphorus oxides and low-valent organic phosphorus compounds will be produced during storage or utilization, resulting in poor stability of the distillation byproducts, and the risk of moisture absorption and oxidation exothermic spontaneous combustion. At present, the diethyl methylphosphite distillation byproducts are mainly disposed as hazardous waste, resulting in waste of resources and increased processing costs. Therefore, the resource recycling of diethyl methylphosphite distillation byproducts can not only realize the comprehensive recycling of industrial waste, but also realize the large-scale consumption and transformation of the distillation byproducts, turning waste into treasure, and reducing the adverse effects of the distillation byproducts on the ecological environment from the source. Summary of the invention

[0004] Aiming at the current situation of waste of diethyl methylphosphite distillation by-product resources in the prior art, the present invention provides a method for preparing a phosphonate flame retardant with excellent flame retardant performance by using the diethyl methylphosphite distillation by-product as the main raw material, which has important economic and environmental benefits.

[0005] In order to achieve the above-mentioned object of the invention, the embodiment of the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a phosphonate flame retardant, the preparation method comprising the following steps: S1. In the presence of a catalyst, the diethyl methylphosphite distillation byproduct and the low-boiling alcohol compound are uniformly mixed, and an esterification reaction is carried out in a closed container at 140°C to 180°C to obtain a reaction solution I; S2. After the reaction solution Ⅰ recovers ethanol, it is subjected to oxidation reaction with a mixed gas containing oxygen, and after the reaction is completed, it is distilled under reduced pressure to obtain a phosphonate flame retardant; Wherein, the catalyst comprises concentrated sulfuric acid and sulfonic acid ester.

[0006] The present invention esterifies the diethyl methylphosphite distillation byproduct under the catalytic action of concentrated sulfuric acid and sulfonic acid ester to carry out esterification reaction; the esterified product is then subjected to oxidation reaction to obtain a phosphonate flame retardant. Through the above esterification reaction and oxidation reaction, triethyl phosphite and diethyl phosphonate in the diethyl methylphosphite distillation byproduct are converted into diethyl ethylphosphonate with good flame retardancy, and diethyl methylphosphite and ethyl methylphosphonate in the distillation byproduct are converted into ethyl methylethylphosphonate, thereby improving the flame retardancy of the obtained flame retardant. In addition, through the oxidation reaction, phosphorus oxides and low-valent organic phosphorus in the distillation byproduct are oxidized to high-valent states, thereby greatly improving the stability and safety of the byproducts, and the residual solids after distillation no longer spontaneously combust, and are easy to handle and store.

[0007] The preparation method of the phosphonate flame retardant provided by the invention has the advantages of simple process, low raw material cost and easy industrial implementation, and realizes the comprehensive recovery and utilization of diethyl methylphosphite distillation by-product resources, which has important economic and environmental benefits.

[0008] The phosphonate flame retardant prepared by the invention has excellent flame retardant performance. When a proper amount of the flame retardant is used in polyurethane foam plastics, a product with a fire resistance grade of V-0 can be obtained. The flame retardant has broad application prospects.

[0009] Preferably, the diethyl methylphosphite distillation by-product comprises the following components in mass percentage: 20%-35% of triethyl phosphite, 5%-10% of diethyl phosphonate, 2%-8% of ethyl methylphosphonate, 1%-3% of diethyl methylphosphite, 32%-45% of ethyl methylethylphosphonate, and 7%-15% of other components.

[0010] The diethyl methylphosphite rectification by-product selected in the present invention is prepared by a gas phase process, specifically: methane, phosphorus trichloride and carbon tetrachloride are used as raw materials, methylphosphonic acid dichloride is obtained through high temperature reaction and rectification; the methylphosphonic acid dichloride prepared above is esterified with ethanol and liquid ammonia and distilled to obtain diethyl methylphosphite. The by-product generated in the diethyl methylphosphite rectification process is the raw material selected in the present invention--diethyl methylphosphite rectification by-product, and its specific components are as described above.

[0011] Preferably, the low boiling point alcohol compound comprises ethanol; The oxygen-containing mixed gas includes air; The sulfonate is methyl benzenesulfonate, ethyl p-toluenesulfonate or a low-chain alkyl sulfonate; The lower chain alkyl sulfonate esters include methyl sulfonate esters or ethyl sulfonate esters.

[0012] In the preparation method of the phosphonate flame retardant provided by the present invention, air, which is abundant in resources and low in price, can meet the demand for an oxidant during the oxidation reaction.

[0013] Preferably, the esterification reaction time is 5h~10h; The oxidation reaction time is 5h~10h; The pressure of the reduced pressure distillation is 1400Pa~1500Pa, and the temperature is 80℃~83℃.

[0014] Preferably, the mass ratio of the concentrated sulfuric acid to the diethyl methylphosphite distillation by-product is 1:100 to 3:100; The mass ratio of the sulfonate to the diethyl methylphosphite distillation byproduct is 0.1:100 to 1:100; The mass ratio of the low boiling point alcohol compound to the distillation by-product of diethyl methylphosphite is 5:100-10:100.

[0015] Preferably, the mass concentration of the concentrated sulfuric acid is 92% to 98%; The ethanol is anhydrous ethanol.

[0016] Preferably, after the esterification reaction is completed, the reaction liquid I is cooled to 100°C~120°C, ethanol is recovered through a condenser, and a mixed gas containing oxygen is passed under the liquid surface of the reaction liquid for oxidation reaction, wherein the amount of the mixed gas containing oxygen introduced is 0.5vvm~1vvm; when the content of triethyl phosphonate in the system is ≤0.20%, the oxidation reaction is terminated.

[0017] In a second aspect, the present invention provides a phosphonate flame retardant, which is prepared by the preparation method of the phosphonate flame retardant provided in the first aspect.

[0018] Preferably, the sum of the mass proportions of diethyl ethylphosphonate and ethyl methyl ethylphosphonate in the phosphonate flame retardant is ≥ 95%.

[0019] The phosphonate flame retardant provided by the present invention can achieve a flame retardant effect equivalent to that of the commercially available conventional flame retardant diethyl ethylphosphonate. Within the experimental range of the present invention, the limiting oxygen index of the polyurethane foam plastic prepared by using the phosphonate flame retardant provided by the present invention is 26.6% to 26.9%, and the flame retardant grade can reach V-0 level.

[0020] In a third aspect, the present invention also provides the use of the above-mentioned phosphonate flame retardant in plastics, textiles, rubber or building materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 is a gas chromatogram of reaction solution II in Example 1 of the present invention; Figure 2 is a gas chromatogram of the phosphonate flame retardant in Example 1 of the present invention; DETAILED DESCRIPTION In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] The raw materials and reagents used in the present invention, unless otherwise specified, are conventional commercially available products; the methods used in the present invention, unless otherwise specified, are conventional methods in the art.

[0024] The contents of the components in the distillation byproduct of diethyl methylphosphite and the phosphonate flame retardant were determined by Agilent 6820 gas chromatography. The specific determination conditions are as follows: Chromatographic column: DM-62430m*0.53mm, 3.0μm; detection wavelength: 250nm; temperature program setting: 70℃ for 1min, increase to 230℃ at a heating rate of 15℃ / min and hold for 20min; injection volume: 3μL.

[0025] Example 1 This embodiment provides a method for preparing a phosphonate flame retardant, the preparation method comprising the following steps: S1. Add 1000 g (1.02 L) of diethyl methylphosphite distillation byproduct to a 2 L autoclave, add 50 g of anhydrous ethanol, 1 g of ethyl p-toluenesulfonate and 10 g of 98% concentrated sulfuric acid, heat to 140 ° C, react for 10 h, and obtain reaction solution I; Among them, the diethyl methylphosphite distillation by-product selected in this embodiment contains the following components in mass percentage: 32.4% triethyl phosphite, 8.3% diethyl phosphonate, 5.2% ethyl methylphosphonate, 3.0% diethyl methylphosphite, 39.2% ethyl methylethylphosphonate and 11.9% other components.

[0026] S2. The reaction solution I is cooled to 100°C, the vent valve is opened, and the tail gas is passed through a condenser to recover ethanol. Air is introduced into the autoclave through an air pipe below the liquid surface of the reaction solution, and the air flow rate is controlled to be 0.51 L / min. The reaction solution obtained after 10 hours of reaction is recorded as reaction solution II. The content of triethyl phosphonate in reaction solution II is 0.10% by gas chromatography; wherein, the gas chromatogram of reaction solution II is as follows Figure 1 shown.

[0027] The reaction solution II was distilled under reduced pressure at a pressure of 1500 Pa, and the fraction at 80°C to 83°C was collected to obtain 873 g of phosphonate flame retardant.

[0028] The phosphonate flame retardant prepared in this embodiment was measured by gas chromatography, and its gas chromatogram is as follows: Figure 2 It was determined that the mass proportion of ethyl methyl ethyl phosphonate in the phosphonate flame retardant prepared in this embodiment was 53.5%, the mass proportion of diethyl ethyl phosphonate was 44.3%, and the total mass proportion of ethyl methyl ethyl phosphonate and diethyl ethyl phosphonate was 97.8%.

[0029] Example 2 This embodiment provides a method for preparing a phosphonate flame retardant, the preparation method comprising the following steps: S1. 1000 g of diethyl methylphosphite distillation byproduct was added to a 2L autoclave, 100 g of anhydrous ethanol, 10 g of ethyl p-toluenesulfonate and 30 g of 92% concentrated sulfuric acid were added, the temperature was raised to 160 ° C, and the reaction was carried out for 8 h to obtain a reaction solution Ⅰ; Among them, the diethyl methylphosphite distillation by-product selected in this embodiment contains the following components in mass percentage: 29.4% triethyl phosphite, 9.9% diethyl phosphonate, 2.1% ethyl methylphosphonate, 1.6% diethyl methylphosphite, 44.8% ethyl methylethylphosphonate and 12.2% other components.

[0030] S2. The reaction liquid I was cooled to 120°C, the vent valve was opened, ethanol was recovered from the tail gas through a condenser, air was introduced into the autoclave through an air pipe below the reaction liquid surface, and the air flow rate was controlled to be 0.51 L / min. The reaction liquid obtained after 10 hours of reaction was recorded as reaction liquid II. The content of triethyl phosphonate in reaction liquid II was detected by gas chromatography and was 0.12%.

[0031] The reaction liquid II was distilled under reduced pressure at a pressure of 1450 Pa, and the fraction at 80°C to 83°C was collected to obtain 882 g of phosphonate flame retardant.

[0032] The phosphonate flame retardant prepared in this embodiment was measured by gas chromatography. According to the measurement, the mass proportion of ethyl methyl ethyl phosphonate in the phosphonate flame retardant prepared in this embodiment was 54.3%, the mass proportion of diethyl ethyl phosphonate was 43.1%, and the total mass proportion of ethyl methyl ethyl phosphonate and diethyl ethyl phosphonate was 97.4%.

[0033] Example 3 This embodiment provides a method for preparing a phosphonate flame retardant, the preparation method comprising the following steps: S1. 1000 g of diethyl methylphosphite distillation byproduct was added to a 2L autoclave, 50 g of anhydrous ethanol, 5 g of ethyl p-methylsulfonate and 20 g of 92% concentrated sulfuric acid were added, the temperature was raised to 180 ° C, and the reaction was carried out for 5 h to obtain a reaction solution Ⅰ; Among them, the diethyl methylphosphite distillation by-product selected in this embodiment contains the following components in mass percentage: 34.8% triethyl phosphite, 6.3% diethyl phosphonate, 7.8% ethyl methylphosphonate, 2.6% diethyl methylphosphite, 36.4% ethyl methylethylphosphonate and 12.1% other components.

[0034] S2. The reaction liquid I was cooled to 100°C, the vent valve was opened, ethanol was recovered from the tail gas through a condenser, air was introduced into the autoclave through an air pipe below the liquid surface of the reaction liquid, and the air flow rate was controlled to be 1L / min. The reaction liquid obtained after 5 hours of reaction was recorded as reaction liquid II. The content of triethyl phosphonate in reaction liquid II was detected by gas chromatography and was 0.11%.

[0035] The reaction solution II was distilled under reduced pressure at a pressure of 1500 Pa, and the fraction at 80°C to 83°C was collected to obtain 851 g of phosphonate flame retardant.

[0036] The phosphonate flame retardant prepared in this embodiment was measured by gas chromatography. According to the measurement, the mass proportion of ethyl methyl ethyl phosphonate in the phosphonate flame retardant prepared in this embodiment was 52.7%, the mass proportion of diethyl ethyl phosphonate was 45.2%, and the total mass proportion of ethyl methyl ethyl phosphonate and diethyl ethyl phosphonate was 97.9%.

[0037] Example 4 This embodiment provides a method for preparing a phosphonate flame retardant, the preparation method comprising the following steps: S1. 1000g of diethyl methylphosphite distillation byproduct was added to a 2L autoclave, 75g of anhydrous ethanol, 5g of methyl p-toluenesulfonate and 15g of 96% concentrated sulfuric acid were added, the temperature was raised to 160°C, and the reaction was carried out for 10h to obtain a reaction solution Ⅰ; Among them, the diethyl methylphosphite distillation by-product selected in this embodiment contains the following components in mass percentage: 32.3% triethyl phosphite, 5.1% diethyl phosphonate, 4.6% ethyl methylphosphonate, 1.2% diethyl methylphosphite, 41.6% ethyl methylethylphosphonate and 14.3% other components.

[0038] S2. The reaction liquid I was cooled to 100°C, the vent valve was opened, ethanol was recovered from the tail gas through a condenser, air was introduced into the autoclave through an air pipe below the reaction liquid surface, and the air flow rate was controlled to be 0.8 L / min. The reaction liquid obtained after 8 hours of reaction was recorded as reaction liquid II. The content of triethyl phosphonate in reaction liquid II was detected by gas chromatography and was 0.09%.

[0039] The reaction solution II was distilled under reduced pressure at a pressure of 1500 Pa, and the fraction at 80°C to 83°C was collected to obtain 860 g of phosphonate flame retardant.

[0040] The phosphonate flame retardant prepared in this embodiment was measured by gas chromatography. According to the measurement, the mass proportion of ethyl methyl ethyl phosphonate in the phosphonate flame retardant prepared in this embodiment was 53.7%, the mass proportion of diethyl ethyl phosphonate was 43.1%, and the total mass proportion of ethyl methyl ethyl phosphonate and diethyl ethyl phosphonate was 96.8%.

[0041] Comparative Example 1 This comparative example provides a preparation method of a phosphonate flame retardant. The preparation method provided in this comparative example is basically the same as that in Example 3, except that concentrated sulfuric acid is not added in step S1, and the remaining reaction raw materials and their condition parameters are the same as those in Example 3, which will not be repeated.

[0042] According to the method provided in this comparative example, 791g of phosphonate flame retardant was prepared. According to the measurement, the mass proportion of ethyl methyl ethyl phosphonate in the phosphonate flame retardant prepared in this comparative example was 41.8%, the mass proportion of diethyl ethyl phosphonate was 44.9%, and the total mass proportion of ethyl methyl ethyl phosphonate and diethyl ethyl phosphonate was 86.7%.

[0043] Diethyl phosphonate, ethyl methylphosphonate, diethyl methylphosphite and the like in the reaction solution are not converted into ethyl methylethylphosphonate and diethyl ethylphosphonate, resulting in a significant reduction in the yield of the flame retardant and an increase in residual impurities.

[0044] Comparative Example 2 This comparative example provides a method for preparing a phosphonate flame retardant. The preparation method provided in this comparative example is basically the same as that in Example 3, except that ethyl p-toluenesulfonate and concentrated sulfuric acid are not added in step S1 (i.e., no catalyst is added), and the remaining reaction raw materials and condition parameters are consistent with those in Example 3, specifically: S1. 1000 g of diethyl methylphosphite distillation byproduct was added to a 2L autoclave, 50 g of anhydrous ethanol was added, the temperature was raised to 180 ° C, and the reaction was carried out for 5 h to obtain a reaction solution Ⅰ; S2. The reaction solution I was cooled to 100°C, the vent valve was opened, ethanol was recovered from the tail gas through a condenser, and air was introduced into the autoclave through an air pipe below the liquid surface of the reaction solution. The air flow rate was controlled to be 1 L / min. After 5 hours of reaction, the content of triethyl phosphonate in the reaction solution II was 29.5%.

[0045] The reaction solution II was distilled under reduced pressure at a pressure of 1500 Pa, and the fraction at 80°C to 83°C was collected to obtain 421 g of phosphonate flame retardant.

[0046] It was determined that the mass proportion of ethyl methyl ethyl phosphonate in the phosphonate flame retardant prepared in this comparative example was 81.2%, and diethyl ethyl phosphonate was not detected. The reason may be that triethyl phosphite did not undergo a transposition reaction, and part of triethyl phosphite underwent an oxidation reaction to produce triethyl phosphonate.

[0047] Effect example In order to investigate the flame retardant properties of the phosphonate flame retardants prepared in Examples 1 to 4 and Comparative Examples 1 to 2, the present invention applies them and the commercially available conventional flame retardant diethyl ethylphosphonate to prepare polyurethane foam plastics with flame retardant properties, and evaluates the flame retardant effects of the polyurethane foam plastics prepared by adding different flame retardants.

[0048] The preparation method of polyurethane foam plastics with flame retardant properties is as follows: To 20g of sucrose polyether polyol, 3g of cyclopentane, 1g of silicone polyether stabilizer, 1g of dimethylcyclohexylamine and 12g of flame retardant are added in sequence, and a uniform milky white viscous liquid mixture is obtained by mixing with a high-speed disperser, 40g of polymethylene polyphenyl polyisocyanate is quickly poured into the mixture, and mixed and stirred evenly. When bubbles emerge and the mixture turns white, the mixture is immediately poured into a mold with a mold temperature of 45°C for foaming molding. After demolding, the foam is placed in an oven at 85°C for drying and maturation to obtain a polyurethane foam with flame retardant properties. Wherein, the flame retardant is the phosphonate flame retardant prepared in Examples 1 to 4 or the phosphonate flame retardant prepared in Comparative Examples 1 to 2 or diethyl ethylphosphonate.

[0049] The flame retardant properties of polyurethane foam plastics with flame retardant properties prepared by adding different flame retardants were tested, and their limiting oxygen index and UL94 flame retardant grade were determined. The test results are shown in Table 1 below.

[0050] Table 1 Flame retardant properties of polyurethane foams with flame retardant properties prepared by adding different flame retardants

[0051] As can be seen from Table 1, the mixed flame retardant containing ethyl methyl ethyl phosphonate and diethyl ethyl phosphonate prepared by adding the mixed flame retardant containing ethyl methyl ethyl phosphonate and diethyl ethyl phosphonate prepared by adding the same amount of commercially available conventional diethyl ethyl phosphonate has a similar limiting oxygen index to the polyurethane foam plastic, and the UL94 flame retardant grade of the flame retardant products obtained is the same, both of which are V-0 grade. However, the mass proportion of diethyl ethyl phosphonate in the flame retardant obtained in Comparative Example 1 is reduced, and there are more impurities; the flame retardant obtained in Comparative Example 2 does not contain diethyl ethyl phosphonate. It can be seen that the flame retardant performance of the flame retardant products obtained in Comparative Examples 1-2 is significantly weaker than that of the flame retardants provided in Examples 1-4 of the present invention.

[0052] In summary, the phosphonate flame retardants obtained by the preparation methods provided in Examples 1 to 4 have excellent flame retardant properties and can be used in the fields of plastics, textiles, rubber or building materials to prepare related materials with flame retardant properties.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a phosphonate flame retardant, characterized in that: The preparation method comprises the following steps: S1. In the presence of a catalyst, the diethyl methylphosphite distillation byproduct and the low-boiling alcohol compound are uniformly mixed, and an esterification reaction is carried out in a closed container at 140°C to 180°C to obtain a reaction solution I; S2. The reaction solution Ⅰ is subjected to an oxidation reaction with a mixed gas containing oxygen, and after completion of the reaction, the reaction is distilled under reduced pressure to obtain a phosphonate flame retardant; Wherein, the catalyst comprises concentrated sulfuric acid and sulfonic acid ester.

2. The method for preparing a phosphonate flame retardant according to claim 1, wherein: The diethyl methylphosphite distillation by-product comprises the following components in percentage by mass: 20%-35% of triethyl phosphite, 5%-10% of diethyl phosphonate, 2%-8% of ethyl methylphosphonate, 1%-3% of diethyl methylphosphite and 32%-45% of ethyl methylethylphosphonate.

3. The method for preparing a phosphonate flame retardant according to claim 1, wherein: The low boiling point alcohol compound includes ethanol; and / or The oxygen-containing mixed gas comprises air; and / or The sulfonate is methyl benzenesulfonate, ethyl p-toluenesulfonate or a low-chain alkyl sulfonate.

4. The method for preparing a phosphonate flame retardant according to claim 1, wherein: The esterification reaction time is 5h~10h; and / or The oxidation reaction time is 5h~10h; and / or The pressure of the reduced pressure distillation is 1400Pa~1500Pa, and the temperature is 80℃~83℃.

5. The method for preparing a phosphonate flame retardant according to claim 1, wherein: The mass ratio of the concentrated sulfuric acid to the diethyl methylphosphite distillation by-product is 1:100 to 3:100; and / or The mass ratio of the sulfonic acid ester to the diethyl methylphosphite rectification by-product is 0.1:100 to 1:100; and / or The mass ratio of the low boiling point alcohol compound to the distillation by-product of diethyl methylphosphite is 5:100-10:

100.

6. The method for preparing a phosphonate flame retardant according to claim 1 or 5, characterized in that: The mass concentration of the concentrated sulfuric acid is 92% to 98%.

7. The method for preparing a phosphonate flame retardant according to claim 1 or 3, characterized in that: The amount of oxygen-containing mixed gas introduced is 0.5vvm~1vvm.

8. A phosphonate flame retardant, characterized in that: The phosphonate flame retardant is prepared by the preparation method of the phosphonate flame retardant according to any one of claims 1 to 7.

9. The phosphonate flame retardant according to claim 8, characterized in that: The sum of the mass proportions of diethyl ethylphosphonate and ethyl methyl ethylphosphonate in the phosphonate flame retardant is ≥95%.

10. Use of the phosphonate flame retardant according to claim 8 or 9 in plastics, textiles, rubber or building materials.

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