High performance low cost phosphazene flame retardant and method of making same

Abstract

The application relates to the technical field of phosphazene flame retardants, and particularly discloses a high-performance low-cost phosphazene flame retardant and a preparation method thereof. The method comprises the following steps: first, purifying an industrial by-product mixed sodium phenate to obtain anhydrous mixed sodium phenate; then, under the action of a nucleophilic substitution promoter composed of an alkaline compound and a polar aprotic solvent, step-by-step nucleophilic substitution reaction is carried out by controlling feeding sequence, reaction temperature and other conditions; after the reaction is completed, high-purity phosphazene flame retardant products are obtained through vacuum concentration and water washing precipitation; meanwhile, unreacted sodium phenate and solvents are recycled and reused; and a complete green closed-loop production process is constructed. Through the unique promoter system and process design, the application effectively coordinates the reaction activities of different components in the mixed sodium phenate, inhibits side reactions, significantly reduces the cost of raw materials, ensures excellent thermal stability and flame retardant efficiency of the products, realizes near-zero emission and maximization of resource utilization, and has an outstanding industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of phosphazene flame retardant technology, and in particular to a high-performance, low-cost phosphazene flame retardant and its preparation method. Background Technology

[0002] Phosphazene flame retardants, as a class of highly efficient and environmentally friendly flame retardant materials containing both phosphorus and nitrogen as flame retardant elements, are widely used in various fields such as plastics, rubber, textiles, building materials, and electronics due to their excellent thermal stability, flame retardant efficiency, and environmental compatibility. Among them, phenoxy-substituted phosphazene flame retardants have become a research hotspot and industrial focus in the field of phosphazene flame retardants because they combine good compatibility and flame retardant durability. Their core preparation routes are mostly achieved through nucleophilic substitution reactions between halogenated cyclophosphinitrogen (such as hexachlorocyclotriphosphazene) and sodium phenolate compounds.

[0003] Currently, the sodium phenolate raw materials used in the industrial preparation of phosphazene flame retardants generally rely on high-purity single sodium phenolate (such as sodium phenolate). This type of high-purity sodium phenolate is typically prepared by a directed reaction of refined phenol with metallic sodium, sodium hydride, or high-purity sodium hydroxide. Subsequent complex dehydration and purification processes are required to remove moisture and impurities from the system, ensuring reactivity and product purity. However, high-purity phenol is expensive, and alkaline reagents such as metallic sodium and sodium hydride are not only costly but also pose safety hazards during storage and use, resulting in high overall raw material costs and hindering the large-scale application of this type of flame retardant.

[0004] Neutral sodium phenolate aqueous solution, produced from the alkaline washing of coal tar fractions in chemical production, is a widely available and inexpensive industrial byproduct and a potential low-cost source of sodium phenolate raw materials. This neutral sodium phenolate aqueous solution is mainly obtained by washing tar fractions with a 10%–15% sodium hydroxide aqueous solution to extract phenolic compounds, with a phenol content of approximately 20%–25%. Using this type of mixed sodium phenolate as a raw material to prepare phosphazene flame retardants can not only significantly reduce raw material costs but also realize the resource utilization of industrial byproducts, aligning with the development direction of green chemistry.

[0005] However, mixed sodium phenolates derived from industrial byproducts typically contain sodium salts of various phenolic derivatives such as phenol, sodium methylphenolate, and sodium dimethylphenolate. The varying reactivity of these components leads to uneven nucleophilic substitution reaction rates with halocyclophosphinitriles, easily generating partially substituted phosphinitriles, polysubstituted isomers, and other intermediate byproducts. Simultaneously, impurities in the system may undergo coupling, hydrolysis, and other side reactions with halocyclophosphinitriles, generating non-target heterocyclic compounds. This results in complex product composition, difficulty in controlling purity, and ultimately affects the thermal stability and flame-retardant effect of phosphinitrile flame retardants.

[0006] Therefore, developing a method for preparing phosphazene flame retardants that can utilize industrial byproducts such as mixed sodium phenolate for low-cost preparation, while also addressing the challenges of controlling its reactivity and side reactions and ensuring high product performance, has become a key technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0007] To address the problems of high cost and low industrialization efficiency caused by the reliance on high-purity raw materials in the preparation of phosphazene flame retardants in existing technologies, this invention provides a high-performance, low-cost phosphazene flame retardant and its preparation method. This method uses industrial byproducts, mixed sodium phenolate and phosphazene compounds, as raw materials. Under the action of a nucleophilic substitution promoter, the phosphazene flame retardant is prepared via a nucleophilic substitution reaction. The introduction of the nucleophilic substitution promoter effectively enhances the reactivity of the mixed sodium phenolate, promotes the full progress of the substitution reaction, and inhibits various side reactions caused by impurities. This achieves the goal of ensuring high flame retardancy of the phosphazene flame retardant while reducing raw material costs, providing a feasible path for the large-scale green production of phosphazene flame retardants.

[0008] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a high-performance, low-cost phosphazene flame retardant, comprising the following steps: S1, purify the industrial by-product mixed sodium phenolate raw material to obtain anhydrous mixed sodium phenolate; S2, the anhydrous mixed sodium phenolate, nucleophilic substitution promoter and chlorinated phosphazene compound are subjected to a nucleophilic substitution reaction in an organic solvent to obtain phosphazene flame retardant.

[0009] The nucleophilic substitution promoter comprises a basic compound and a polar aprotic solvent; the basic compound comprises at least one of potassium carbonate, sodium carbonate, potassium bicarbonate, sodium bicarbonate, or sodium ethoxide; and the polar aprotic solvent comprises at least one of N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide.

[0010] Compared to existing technologies, this invention directly uses sodium phenolate, a widely available and inexpensive industrial byproduct, as the main raw material, significantly reducing production costs from the source. By employing a specific nucleophilic substitution promoter system, namely a combination of basic compounds and polar aprotic solvents, the invention ensures efficient and complete reaction, resulting in phosphazene flame retardant products with excellent thermal stability and flame retardant properties. This overcomes the technical problem that traditionally, the use of inexpensive raw materials often leads to a decline in product performance, ensuring the consistency and reliability of phosphazene flame retardant product performance between different batches. It provides an effective technical path for the high-value utilization of various phenol-containing industrial wastes, with significant environmental and social benefits, aligning with the concepts of green chemistry and sustainable development.

[0011] Among them, the specific basic compounds can specifically enhance the nucleophilic activity of phenoxide anions in the mixed sodium phenolate, making up for the defect that the reactivity of the mixed sodium phenolate is lower than that of high-purity sodium phenolate; the specific polar aprotic solvent can promote the interaction between the basic compounds and the mixed sodium phenolate, while inhibiting side reactions such as hydrolysis and coupling of halocyclophosphonitriles, solving the problems of complex reaction components and many by-products in the mixed sodium phenolate system, and ensuring that the substitution reaction is sufficient and directional.

[0012] In summary, this invention, by adding a specific reaction-promoting system, successfully solves the key technical bottleneck in the preparation of high-performance phosphazene flame retardants using industrial mixed sodium phenolate, while significantly reducing raw material costs. The prepared product has superior performance, the process is economical and environmentally friendly, and it has outstanding industrial application value.

[0013] It should be noted that the mixed sodium phenolate raw material, an industrial byproduct, described in this invention is a neutral sodium phenolate aqueous solution. This raw material is widely available and inexpensive, which is key to achieving the low-cost objective of this invention.

[0014] Neutral sodium phenolate aqueous solution can be derived from the coal chemical industry, coking industry, petrochemical industry, pharmaceutical industry, fine chemical industry, dye industry, pesticide industry, wood processing and adhesive industry, etc., and the sources include but are not limited to the above-mentioned industries.

[0015] The neutral sodium phenolate aqueous solution includes sodium salts corresponding to various phenolic derivatives such as sodium phenolate, sodium methylphenolate, and sodium dimethylphenolate. Specifically, it includes at least one of sodium phenolate, sodium 2-methylphenolate, sodium 3-methylphenolate, sodium 4-methylphenolate, sodium 2,3-dimethylphenolate, sodium 2,4-dimethylphenolate, sodium 2,5-dimethylphenolate, sodium 2,6-dimethylphenolate, sodium 3,4-dimethylphenolate, or sodium 3,5-dimethylphenolate.

[0016] As a specific embodiment of the present invention, the preparation method of the high-performance, low-cost phosphazene flame retardant specifically includes the following steps: S1, purify the industrial by-product mixed sodium phenolate raw material to obtain anhydrous mixed sodium phenolate; The anhydrous mixed sodium phenolate and phosphazene compound were dissolved in organic solvents to obtain mixed sodium phenolate solution and phosphazene compound solution, respectively. S2, under conditions of -20℃ to 20℃, the mixed sodium phenolate solution is added dropwise to the chlorinated phosphazene compound solution. After the dropwise addition is completed, the alkaline compound is added. After the temperature is raised to 50℃ to 150℃ and the reaction is carried out for a first preset time, the polar aprotic solvent is added, and the reaction is continued at the temperature for a second preset time. The mixture is then concentrated under reduced pressure to obtain the phosphazene flame retardant.

[0017] In the above preparation method, low-temperature dropwise addition at -20℃ to 20℃ effectively slows down the hydrolysis rate of chlorinated phosphazenes and avoids the generation of isomerization byproducts due to violent local reactions during the dropwise addition process, significantly reducing the incidence of side reactions. After the dropwise addition is completed, an alkaline compound is added to activate the nucleophilic activity of phenoxy anions and to allow the more active components in the mixed sodium phenolate to react preferentially. After a period of reaction, a polar aprotic solvent is added. Its strong dissolving and activating effects can significantly improve the reactivity and diffusion rate of the remaining phenoxy anions (especially the less active components), ensuring that all phenolic components can fully participate in the reaction, thereby achieving efficient and uniform substitution of the mixed sodium phenolate. This effectively avoids the problems of incomplete substitution or uneven product composition caused by differences in reactivity, thus ensuring the high performance and high quality of the phosphazene flame retardant product.

[0018] Furthermore, the mass ratio of the alkaline compound to the chlorinated phosphazene compound is 1:(10~20); the volume ratio of the polar aprotic solvent to the total amount of organic solvent is 1:(15~35).

[0019] By controlling the proportion of alkaline compounds within the above-mentioned range, it is possible to ensure that the alkaline compounds fully activate the nucleophilic activity of phenoxide anions in the mixed sodium phenolate, thus compensating for the insufficient reactivity of the mixed sodium phenolate, while avoiding the occurrence of side reactions such as hydrolysis and self-polymerization of chlorinated phosphazenes caused by excessive alkaline compounds.

[0020] By controlling the proportion of polar aprotic solvents within the above range, it is possible to ensure sufficient activation of sodium phenolate with low activity, without diluting the raw material concentration or reducing the reaction rate due to an excessively high proportion of polar solvents.

[0021] Further, the organic solvent is at least one of tetrahydrofuran, 1,4-dioxane, dichloromethane, chloroform, chlorobenzene, dichlorobenzene, xylene, or acetonitrile; preferably tetrahydrofuran.

[0022] Specifically, in S1, the ratio of anhydrous mixed sodium phenolate to organic solvent is 1g:5mL to 1g:7mL, and the ratio of phosphazene compound to organic solvent is 1g:2mL to 1g:4mL.

[0023] It should be noted that the purification methods used in S1 of this invention include, but are not limited to, at least one of filtration, precipitation, evaporation crystallization, freeze crystallization, acid precipitation, solvent extraction, adsorption, and membrane permeation, in order to obtain a mixed sodium phenolate solid with low water content and few impurities.

[0024] Specifically, in S1, the purification method is evaporation crystallization, and the evaporation temperature is 70℃~90℃.

[0025] Furthermore, the chlorinated phosphazene compound is at least one of cyclic or linear chlorinated phosphazenes with a polymer degree of 3 to 20,000.

[0026] It should be noted that the aforementioned chlorinated phosphazene compound can be selected from hexachlorocyclotriphosphazene or polydichlorophosphazene. The aforementioned polydichlorophosphazene can be prepared using conventional bulk melt polymerization or solution polymerization methods in the art, as detailed in the polymerization method reported in CN110643046B. The polydichlorophosphazene (PDCP) obtained from the polymerization reaction is dissolved in an organic solvent to obtain a PDCP solution, which is then reacted with a mixed sodium phenolate solution.

[0027] Furthermore, the molar ratio of Cl in the chlorinated phosphazene compound to Na in the anhydrous sodium phenolate mixture is 1:(1~4).

[0028] Furthermore, in S2, the first preset time is 3h~10h; the second preset time is 7h~20h.

[0029] It should be noted that in S2, the post-concentration process after vacuum concentration also includes a purification process: the concentrated solution after vacuum concentration is washed with deionized water, allowed to stand and separate into layers, the upper washing liquid is poured off, and the lower product is collected. The above steps are repeated, and the lower product is washed and allowed to stand and separate into layers multiple times in deionized water to finally obtain a high-purity phosphazene flame retardant product.

[0030] The washing liquid is separated into sodium phenolate, solvent and water through evaporation crystallization and distillation. The obtained sodium phenolate and neutral sodium phenolate aqueous solution are used as raw materials for purification and then participate in nucleophilic substitution reaction. The solvent distilled under reduced pressure and the solvent separated from the washing liquid can be returned to the purification step or the reaction step and reused as solvent.

[0031] This invention recycles incompletely reacted sodium phenolate raw materials and reaction solvents, combining this with a front-end process design that utilizes mixed sodium phenolate as an industrial byproduct, thus constructing a complete green closed-loop production process. This closed-loop system not only achieves resource utilization of waste liquid and solvent recycling, but also effectively solves the conversion rate limitation problem caused by the difference in reactivity of mixed sodium phenolate, thereby significantly improving the overall raw material utilization rate and reaction economy. This design makes the entire preparation process nearly waste-free, significantly enhancing the process's economy, environmental friendliness, and sustainability, and possessing outstanding value for industrialization and promotion.

[0032] Secondly, the present invention provides a high-performance, low-cost phosphazene flame retardant, which is prepared by the above-mentioned method for preparing high-performance, low-cost phosphazene flame retardants.

[0033] In summary, this invention provides a method for preparing high-performance phosphazene flame retardants using industrial byproducts, mixed sodium phenolate and chlorinated phosphazene compounds, as raw materials. The method first purifies the mixed sodium phenolate to obtain anhydrous mixed sodium phenolate. Then, under the action of a nucleophilic substitution promoter composed of a basic compound and a polar aprotic solvent, a stepwise nucleophilic substitution reaction is carried out by controlling the feeding sequence and reaction temperature. After the reaction, the product is concentrated under reduced pressure and washed with water to obtain a high-purity phosphazene flame retardant. Simultaneously, unreacted sodium phenolate and the solvent are recovered and reused, constructing a complete green closed-loop production process. This invention, through a unique promoter system and process design, effectively coordinates the reactivity of different components in the mixed sodium phenolate, suppresses side reactions, significantly reduces raw material costs while ensuring excellent thermal stability and flame retardant efficiency of the product, and achieves near-zero emissions and maximizes resource utilization. It provides a practical technical solution for the large-scale, low-cost, and green production of phosphazene flame retardants, and has outstanding prospects for industrial application. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] Unless otherwise specified, all reagents used in the following embodiments are commercially available analytical grade reagents, and all experimental and detection methods used in the following embodiments are existing experimental and detection methods.

[0036] To better illustrate the present invention, further examples are provided below.

[0037] The preparation methods of the anhydrous mixed sodium phenolate solids used in the following examples and comparative examples include the following steps: The neutral sodium phenolate aqueous solution, a byproduct of coal tar alkaline washing, was filtered to remove solid residue. It was then transferred to a rotary evaporator and continuously evaporated at 80°C until a crystalline film or a large number of crystals precipitated on the solution surface. Heating was then stopped, and the solution was dried in a vacuum drying oven for 5 hours to obtain anhydrous mixed sodium phenolate.

[0038] The polydichlorophosphazene (PDCP) used in the following examples and comparative examples was prepared according to the polymerization method reported in CN110643046B. The specific steps are as follows: 120g of hexachlorocyclotriphosphazene monomer and 1g of PDCP with 80% phenoxy substitution were added to a 1000mL four-necked flask. 720mL of chloronaphthalene solvent was added and preheated with stirring to dissolve. The system was refluxed with a condenser. Then, 780mg of boron trifluoride catalyst and 960mg of calcium sulfate dihydrate co-catalyst were added. The system was heated to 200℃ and maintained at this temperature. The reaction time was started when the system temperature reached the reaction temperature. After 3 hours of reaction, 300mL of benzyl ether and sulfolane (1:1) solvent was added to the reaction system. The reaction was then continued at a constant temperature. As the reaction proceeded, the viscosity of the system increased. The reaction was stopped after 30 hours. The synthesized PDCP was finally precipitated in an organic solvent through post-treatment to obtain PDCP.

[0039] Example 1 This embodiment provides a method for preparing a high-performance, low-cost phosphazene flame retardant, which specifically includes the following steps: Weigh 80g of the purified anhydrous sodium phenolate solid and dissolve it in 500mL of tetrahydrofuran to remove water, thus obtaining an anhydrous sodium phenolate solution. 100g of hexachlorocyclotriphosphazene and 200mL of tetrahydrofuran were added to a container under a nitrogen atmosphere and stirred thoroughly to obtain a hexachlorocyclotriphosphazene solution. The above anhydrous mixed sodium phenolate solution was added dropwise to the hexachlorocyclotriphosphazene solution. A reflux condenser was added to the system, and the temperature was controlled at -20~-10℃ during the dropwise addition stage. The molar ratio of Na in the anhydrous mixed sodium phenolate solution to Cl in the hexachlorocyclotriphosphazene solution was 2:1. After the dropwise addition was completed, 6g of potassium carbonate was added. The system was then heated to 65℃ and reacted for 3h. Then 20mL of N,N-dimethylformamide was added, and the reaction temperature was maintained at 65℃. The reaction was continued for 7h. The reaction solution was concentrated under reduced pressure until the solvent no longer distilled off to obtain a crude product solution. The crude product solution was washed in deionized water and allowed to stand to separate into layers. The upper washing liquid was poured off and the lower product was collected. The lower product was washed in deionized water multiple times and allowed to stand to separate into layers. The final lower product was dried in an oven to constant weight to obtain phosphazene flame retardant. The yield was calculated to be 97%.

[0040] The washing liquid is separated into sodium phenolate, solvent and water by evaporation crystallization and distillation. The obtained sodium phenolate and neutral sodium phenolate aqueous solution are used as raw materials for purification and then participate in nucleophilic substitution reaction. The solvent separated from the washing liquid by vacuum concentration can be returned to the purification step or the reaction step and reused as solvent.

[0041] Vertical burning tests were conducted according to UL 94 standards, with V-0 rating in polycarbonate (PC) used as the evaluation of flame retardancy efficiency. When added to PC, the required addition amount to achieve V-0 rating is 0.4%, which is lower than the 0.7% addition amount required by the conventional phosphazene SPB-100 flame retardant.

[0042] Example 2 This embodiment provides a method for preparing a high-performance, low-cost phosphazene flame retardant, which specifically includes the following steps: Weigh 80g of the purified anhydrous sodium phenolate solid and dissolve it in 400mL of tetrahydrofuran to remove water, thus obtaining an anhydrous sodium phenolate solution. 100g of the prepared PDCP and 400mL of tetrahydrofuran were added to a container under a nitrogen atmosphere and stirred thoroughly to obtain a hexachlorocyclotriphosphazene solution. The anhydrous sodium phenolate solution was added dropwise to the hexachlorocyclotriphosphazene solution. A reflux condenser was used to condense the system. The temperature was controlled at 10~20℃ during the dropwise addition, and the molar ratio of Na in the anhydrous sodium phenolate solution to Cl in the hexachlorocyclotriphosphazene solution was 4:1. After the dropwise addition was completed, 10g of sodium bicarbonate was added. The system was then heated to 80℃ and reacted for 5h. Then 48mL of dimethyl sulfoxide was added, and the temperature was further raised to 150℃ and reacted for another 10h. The reaction solution was concentrated under reduced pressure until the solvent no longer distilled off to obtain a crude product solution. The crude product solution was washed in deionized water and allowed to stand for separation. The upper washing liquid was poured off and the lower product was collected. The lower product was washed in deionized water multiple times and allowed to stand for separation. The final lower product was dried in an oven to constant weight to obtain phosphazene flame retardant. The yield was calculated to be 96%.

[0043] The washing liquid is separated into sodium phenolate, solvent and water by evaporation crystallization and distillation. The obtained sodium phenolate and neutral sodium phenolate aqueous solution are used as raw materials for purification and then participate in nucleophilic substitution reaction. The solvent separated from the washing liquid by vacuum concentration can be returned to the purification step or the reaction step and reused as solvent.

[0044] Vertical burning tests were conducted according to UL 94 standards, with V-0 rating in polycarbonate (PC) used as the evaluation of flame retardancy efficiency. When added to PC, the required addition amount to achieve V-0 rating is 0.5%, which is lower than the 0.7% addition amount required by the conventional phosphazene SPB-100 flame retardant.

[0045] Example 3 This embodiment provides a method for preparing a high-performance, low-cost phosphazene flame retardant, which specifically includes the following steps: Weigh 80g of the purified anhydrous sodium phenolate solid and dissolve it in 560mL of tetrahydrofuran to remove water, thus obtaining an anhydrous sodium phenolate solution. 100g of hexachlorocyclotriphosphazene and 300mL of tetrahydrofuran were added to a container under a nitrogen atmosphere and stirred thoroughly to obtain a hexachlorocyclotriphosphazene solution. The above anhydrous mixed sodium phenolate solution was added dropwise to the hexachlorocyclotriphosphazene solution. A reflux condenser was added to the system, and the temperature was controlled at -10℃ to 0℃ during the dropwise addition. The molar ratio of Na in the anhydrous mixed sodium phenolate solution to Cl in the hexachlorocyclotriphosphazene solution was 1:1. After the dropwise addition was completed, 5g of sodium ethoxide was added. The system was then heated to 50℃ and reacted for 10h. Then, 45mL of N,N-dimethylacetamide was added, the temperature was raised to 80℃, and the reaction was continued for 20h. The reaction solution was concentrated under reduced pressure until the solvent no longer distilled off to obtain a crude product solution. The crude product solution was washed in deionized water and allowed to stand for separation. The upper washing liquid was poured off and the lower product was collected. The lower product was washed in deionized water multiple times and allowed to stand for separation. The final lower product was dried in an oven to constant weight to obtain phosphazene flame retardant. The yield was calculated to be 94%.

[0046] The washing liquid is separated into sodium phenolate, solvent and water by evaporation crystallization and distillation. The obtained sodium phenolate and neutral sodium phenolate aqueous solution are used as raw materials for purification and then participate in nucleophilic substitution reaction. The solvent separated from the washing liquid by vacuum concentration can be returned to the purification step or the reaction step and reused as solvent.

[0047] Vertical burning tests were conducted according to UL 94 standards, with V-0 rating in polycarbonate (PC) used as the evaluation of flame retardancy efficiency. When added to PC, the required addition amount to achieve V-0 rating is 0.65%, which is lower than the 0.7% addition amount required by the conventional phosphazene SPB-100 flame retardant.

[0048] Comparative Example 1 This comparative example provides a method for preparing a phosphazene flame retardant, which differs from Example 1 only in that potassium carbonate is not added; otherwise, the methods are identical. The specific steps are as follows: Weigh 80g of the purified anhydrous sodium phenolate solid and dissolve it in 500mL of tetrahydrofuran to remove water, thus obtaining an anhydrous sodium phenolate solution. 100 g of hexachlorocyclotriphosphazene and 200 mL of tetrahydrofuran were added to a container under a nitrogen atmosphere and stirred thoroughly to obtain a hexachlorocyclotriphosphazene solution. The above anhydrous mixed sodium phenolate solution was added dropwise to the hexachlorocyclotriphosphazene solution. A reflux condenser was added to the system, and the temperature was controlled at -20 to -10 °C during the dropwise addition. The molar ratio of Na in the anhydrous mixed sodium phenolate solution to Cl in the hexachlorocyclotriphosphazene solution was 2:1. After the dropwise addition was completed, the system was heated to 65 °C and reacted for 3 h. Then, 20 mL of N,N-dimethylformamide was added, and the reaction temperature was maintained at 65 °C. The reaction was continued for 7 h. The reaction solution was concentrated under reduced pressure until the solvent no longer distilled off to obtain a crude product solution. The crude product solution was washed in deionized water and allowed to stand to separate into layers. The upper washing liquid was poured off and the lower product was collected. The lower product was washed in deionized water multiple times and allowed to stand to separate into layers. The final lower product was dried in an oven to constant weight to obtain phosphazene flame retardant. The yield was calculated to be 86%.

[0049] Vertical burning tests were conducted according to UL 94 standards, with V-0 rating in polycarbonate (PC) used as the evaluation of flame retardancy efficiency. When added to PC, the required addition amount to achieve V-0 rating is 1.0%, which is higher than the 0.7% addition amount required by the conventional phosphazene SPB-100 flame retardant.

[0050] Comparative Example 2 This comparative example provides a method for preparing a phosphazene flame retardant, which differs from Example 1 only in that N,N-dimethylformamide is not added; otherwise, the methods are identical. The specific steps are as follows: Weigh 80g of the purified anhydrous sodium phenolate solid and dissolve it in 500mL of tetrahydrofuran to remove water, thus obtaining an anhydrous sodium phenolate solution. 100g of hexachlorocyclotriphosphazene and 200mL of tetrahydrofuran were added to a container under a nitrogen atmosphere and stirred thoroughly to obtain a hexachlorocyclotriphosphazene solution. The above anhydrous mixed sodium phenolate solution was added dropwise to the hexachlorocyclotriphosphazene solution. A reflux condenser was added to the system, and the temperature was controlled at -20~-10℃ during the dropwise addition stage. The molar ratio of Na in the anhydrous mixed sodium phenolate solution to Cl in the hexachlorocyclotriphosphazene solution was 2:1. After the dropwise addition was completed, 6g of potassium carbonate was added. The system was then heated to 65℃ and reacted for 10h. The reaction solution was concentrated under reduced pressure until the solvent no longer distilled off to obtain a crude product solution. The crude product solution was washed in deionized water and allowed to stand to separate into layers. The upper washing liquid was poured off and the lower product was collected. The lower product was washed in deionized water multiple times and allowed to stand to separate into layers. The final lower product was dried in an oven to constant weight to obtain phosphazene flame retardant. The yield was calculated to be 89%.

[0051] Vertical burning tests were conducted according to UL 94 standards, with V-0 rating in polycarbonate (PC) used as the evaluation of flame retardancy efficiency. When added to PC, the required addition amount to achieve V-0 rating is 0.9%, which is higher than the 0.7% addition amount required by the conventional phosphazene SPB-100 flame retardant.

[0052] Comparative Example 3 This comparative example provides a method for preparing a phosphazene flame retardant, which differs from Example 1 only in that potassium carbonate is replaced with an equal amount of sodium hydride; the rest are identical. The specific steps are as follows: Weigh 80g of the purified anhydrous sodium phenolate solid and dissolve it in 500mL of tetrahydrofuran to remove water, thus obtaining an anhydrous sodium phenolate solution. 100g of hexachlorocyclotriphosphazene and 200mL of tetrahydrofuran were added to a container under a nitrogen atmosphere and stirred thoroughly to obtain a hexachlorocyclotriphosphazene solution. The above anhydrous mixed sodium phenolate solution was added dropwise to the hexachlorocyclotriphosphazene solution. A reflux condenser was added to the system, and the temperature was controlled at -20~-10℃ during the dropwise addition stage. The molar ratio of Na in the anhydrous mixed sodium phenolate solution to Cl in the hexachlorocyclotriphosphazene solution was 2:1. After the dropwise addition was completed, 6g of sodium hydride was added. The system was then heated to 65℃ and reacted for 3h. Then 20mL of N,N-dimethylformamide was added, and the reaction temperature was maintained at 65℃. The reaction was continued for 7h. The reaction solution was concentrated under reduced pressure until the solvent no longer distilled off to obtain a crude product solution. The crude product solution was washed in deionized water and allowed to stand for separation. The upper washing liquid was poured off and the lower product was collected. The lower product was washed in deionized water multiple times and allowed to stand for separation. The final lower product was dried in an oven to constant weight to obtain phosphazene flame retardant. The yield was calculated to be 91%.

[0053] Vertical burning tests were conducted according to UL 94 standards, with V-0 rating in polycarbonate (PC) used as the evaluation of flame retardancy efficiency. When adding to PC, the required addition amount to achieve V-0 rating is 0.8%, which is slightly higher than the 0.7% addition amount required by the conventional phosphazene SPB-100 flame retardant.

[0054] Comparative Example 4 This comparative example provides a method for preparing a phosphazene flame retardant, which differs from Example 1 only in that N,N-dimethylformamide is replaced with an equal amount of acetone; the rest are identical. The specific steps are as follows: Weigh 80g of the purified anhydrous sodium phenolate solid and dissolve it in 500mL of tetrahydrofuran to remove water, thus obtaining an anhydrous sodium phenolate solution. 100g of hexachlorocyclotriphosphazene and 200mL of tetrahydrofuran were added to a container under a nitrogen atmosphere and stirred thoroughly to obtain a hexachlorocyclotriphosphazene solution. The above anhydrous mixed sodium phenolate solution was added dropwise to the hexachlorocyclotriphosphazene solution. A reflux condenser was added to the system, and the temperature was controlled at -20~-10℃ during the dropwise addition stage. The molar ratio of Na in the anhydrous mixed sodium phenolate solution to Cl in the hexachlorocyclotriphosphazene solution was 2:1. After the dropwise addition was completed, 6g of potassium carbonate was added. The system was then heated to 65℃ and reacted for 3h. Then 20mL of acetone was added, and the reaction temperature was maintained at 65℃. The reaction was continued for 7h. The reaction solution was concentrated under reduced pressure until the solvent no longer distilled off to obtain a crude product solution. The crude product solution was washed in deionized water and allowed to stand for separation. The upper washing liquid was poured off and the lower product was collected. The lower product was washed in deionized water multiple times and allowed to stand for separation. The final lower product was dried in an oven to constant weight to obtain phosphazene flame retardant. The yield was calculated to be 93%.

[0055] Vertical burning tests were conducted according to UL 94 standards, with V-0 rating in polycarbonate (PC) used as the evaluation of flame retardancy efficiency. When adding to PC, the required addition amount to achieve V-0 rating is 0.75%, which is slightly higher than the 0.7% addition amount required by the conventional phosphazene SPB-100 flame retardant.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a high-performance, low-cost phosphazene flame retardant, characterized in that, Includes the following steps: S1, purify the industrial by-product mixed sodium phenolate raw material to obtain anhydrous mixed sodium phenolate; S2, the anhydrous mixed sodium phenolate, nucleophilic substitution promoter and chlorinated phosphazene compound are subjected to nucleophilic substitution reaction in an organic solvent to obtain phosphazene flame retardant; The nucleophilic substitution promoter comprises a basic compound and a polar aprotic solvent; the basic compound comprises at least one of potassium carbonate, sodium carbonate, potassium bicarbonate, sodium bicarbonate, or sodium ethoxide; and the polar aprotic solvent comprises at least one of N,N-dimethylformamide, N,N-dimethylacetamide, or dimethyl sulfoxide.

2. The preparation method of the high-performance, low-cost phosphazene flame retardant as described in claim 1, characterized in that, Specifically, the steps include the following: S1, purify the industrial by-product mixed sodium phenolate raw material to obtain anhydrous mixed sodium phenolate; The anhydrous mixed sodium phenolate and phosphazene compound were dissolved in organic solvents to obtain mixed sodium phenolate solution and phosphazene compound solution, respectively. S2, under conditions of -20℃ to 20℃, the mixed sodium phenolate solution is added dropwise to the chlorinated phosphazene compound solution. After the dropwise addition is completed, the alkaline compound is added. After the temperature is raised to 50℃ to 150℃ and the reaction is carried out for a first preset time, the polar aprotic solvent is added, and the reaction is continued at the temperature for a second preset time. The mixture is then concentrated under reduced pressure to obtain the phosphazene flame retardant.

3. The method for preparing the high-performance, low-cost phosphazene flame retardant as described in claim 1 or 2, characterized in that, The industrial byproduct mixed sodium phenolate raw material is a neutral sodium phenolate aqueous solution.

4. The preparation method of the high-performance, low-cost phosphazene flame retardant as described in claim 1 or 2, characterized in that, The mass ratio of the basic compound to the chlorinated phosphazene compound is 1:(10~20); the volume ratio of the polar aprotic solvent to the total amount of organic solvent is 1:(15~35).

5. The method for preparing the high-performance, low-cost phosphazene flame retardant as described in claim 1 or 2, characterized in that, The organic solvent is at least one of tetrahydrofuran, 1,4-dioxane, dichloromethane, chloroform, chlorobenzene, dichlorobenzene, xylene, or acetonitrile.

6. The method for preparing the high-performance, low-cost phosphazene flame retardant as described in claim 1 or 2, characterized in that, The chlorinated phosphazene compound is at least one of cyclic or linear chlorinated phosphazenes with a polymer degree of 3 to 20,000.

7. The method for preparing the high-performance, low-cost phosphazene flame retardant as described in claim 1 or 2, characterized in that, The molar ratio of Cl in the chlorinated phosphazene compound to Na in the anhydrous sodium phenolate mixture is 1:(1~4).

8. The method for preparing the high-performance, low-cost phosphazene flame retardant as described in claim 1 or 2, characterized in that, In S2, the first preset time is 3h~10h; the second preset time is 7h~20h.

9. A high-performance, low-cost phosphazene flame retardant, characterized in that, It is prepared by the method of any one of claims 1 to 8 for the preparation of high-performance, low-cost phosphazene flame retardants.