A dialkyl hypophosphite-alkyl phosphite complex salt flame retardant and a synthesis method thereof

Abstract

The application discloses a kind of dialkyl hypophosphite-alkyl phosphinic acid composite salt flame retardant and synthesis method thereof, it is related to organic phosphorus compound technical field, scheme is: the composite salt flame retardant is composed of dialkyl hypophosphite, alkyl phosphinic acid root and 2-4 valence metal ions;Its synthesis method includes that phosphine is added with gaseous or liquid olefin to occur radical addition, and the obtained addition product is oxidized, pH is adjusted and is salted with 2-4 valence metal salt, obtains target composite salt flame retardant.The beneficial effect of the application is: by controlling reaction ratio and subsequent conversion process, realizes the structure directional control from single salt to composite salt, so that the obtained product simultaneously has dialkyl hypophosphite and alkyl phosphinic acid root coexistence characteristics, while maintaining high conversion level, has stable preparation and good flame retardant application value.

Description

Technical Field

[0001] This invention relates to the field of organophosphorus compound technology, and in particular to a dialkylphosphonic acid-alkylphosphine composite salt flame retardant and its synthesis method. Background Technology

[0002] With the widespread application of polymer materials in electronics, rail transportation, automotive parts, building decoration, and industrial structural components, flame retardancy has become an important technological direction in polymer modification. Among various flame retardant systems, phosphorus-containing flame retardants have gradually become an important component of halogen-free flame retardant systems due to their high flame retardant efficiency, low smoke density, and good environmental friendliness. Among these, metal salt-type phosphorus-containing flame retardants, represented by organophosphonates, possess both organophosphorus and metal ion structural units. They typically exhibit a significant condensed-phase char-forming effect during the thermal decomposition of materials and, under certain conditions, also provide gas-phase flame suppression. Therefore, they have received considerable attention in engineering plastics, thermoplastic resins, and some thermosetting materials. Existing technologies for this type of flame retardant mainly focus on two directions: one is to improve the synthesis process of specific phosphorus-containing structural units, aiming to enhance the reaction conversion degree, product purity, and preparation stability; the other is to introduce existing phosphorus-containing metal salts as flame retardant components into polymer systems, focusing on their impact on flame retardancy rating, thermal stability, and processing adaptability. Overall, existing technologies have demonstrated the application value of these phosphorus-containing metal salts in the flame retardant field, and a relatively mature technical approach of "addition-oxidation-salt formation" or "precursor construction-subsequent salt formation" has been established. However, from the perspective of the current state of technological development, most related research and applications still focus on obtaining phosphorus-containing salt products with a single structural type. That is, the target is usually set as a specific organophosphonate metal salt, and process optimization and performance evaluation are carried out around this. In other words, although existing technologies have made some progress in the preparation and application of single phosphorus-containing salt flame retardants, research and publication on composite flame retardant systems containing different phosphorus components, where these phosphorus components can coexist stably in the same final salt system and form a clear structural boundary, remains relatively insufficient.

[0003] The main shortcoming of existing technologies lies not in whether a certain type of phosphorus-containing flame retardant can be produced, but in their long-term focus on a single product, resulting in a relatively fixed structure of the final product and making it difficult to further achieve the controllable preparation, stable coexistence, and structural characterization of different phosphorus components in the same system. Specifically, existing technologies typically focus on improving the yield, purity, or reaction completion of a single phosphorus salt in the optimization of the reaction system, and the process design tends to push the reaction system towards the concentrated conversion of a single target phosphorus species as much as possible. While this technical approach is beneficial for process simplification and clear product boundaries, its direct result is that existing technologies face significant difficulties when it is desired to introduce the synergistic presence of different phosphorus components into the final product. This is because multi-phosphorus component systems are not a simple "mixing" problem, but involve multiple continuous processes, such as the formation of addition intermediates, the differentiation of subsequent oxidation pathways, the relative retention of different phosphorus species, the selective coordination of the salt formation stage, and the structural stability of the final solid product. These processes are coupled with each other, and any deviation in any stage may cause the system to slide back towards a single salt structure, or produce a complex by-product system with unclear boundaries, component drift, and insufficient reproducibility. Therefore, while existing technologies can improve reaction efficiency to a certain extent through conventional parameter adjustments, they struggle to reliably address the deeper technical challenge of "how different phosphorus components can coexist in a recognizable, controllable, and repeatable manner in the final flame retardant." Furthermore, attempts to introduce multi-component phosphorus structures in existing technologies face two significant difficulties: first, the phosphorus environment changes during the intermediate stage are difficult to control directly, leading to the final product composition being easily influenced by the coupling effects of feed ratios, reaction endpoints, oxidation levels, and salt formation conditions, making it difficult to form a target product with stable structural characteristics; second, even if systems containing different phosphorus components can be obtained in certain situations, it is often difficult to prove that such systems are not accidental byproducts or incompletely reacted products, but rather truly target flame retardants with clear structural significance and technical value. In other words, the main deficiency of existing technologies lies in their focus on "whether a single salt can be produced, whether the yield is sufficient, and whether the process is simplified," rather than truly solving the technical challenge of "how, at higher reaction conversion levels, the system can be shifted from a single salt formation path to a composite salt formation path with clear compositional boundaries through the control of key reaction conditions." Therefore, in this field, it is technically challenging and practically necessary to avoid both system loss of control and eventual degradation back into a single product, while also ensuring that the resulting composite structure has clear characterization results and subsequent application significance.

[0004] Based on the aforementioned state of the prior art, the urgent technical problem to be solved in this field is to provide a new phosphorus-containing flame retardant and its preparation method, so that the final product is no longer limited to the single organophosphonate structure commonly found in the prior art, but can form a composite phosphorus-containing salt system with a clear compositional relationship and a stable existence state; at the same time, the formation of this system should not come at the cost of significantly sacrificing the reaction conversion level, repeatability, or adaptability to subsequent applications, but should be achieved under the premise of ensuring that the reaction process is controllable and the product boundaries are relatively clear. Furthermore, the key issues to be addressed include: how to adjust the key conditions in the reaction system so that the intermediates are not entirely converted into a single phosphorus component along a single path during subsequent conversion, but are retained and evolved into multiple phosphorus components participating in the final salt formation; how to ensure that this multi-phosphorus component coexistence system remains relatively stable in the final solid product, rather than merely exhibiting an incomplete reaction or a state of impurity contamination; and how to ensure that this type of composite phosphorus-containing salt not only differs structurally from existing single-salt systems, but also has clear technical significance in subsequent flame-retardant applications. In other words, the present invention does not aim to solve the problem of "obtaining a flame retardant" or "improving the yield of a certain step" in the general sense, but rather to solve the technical contradictions that have long existed in the prior art, such as the single structural type, the difficulty in the stable coexistence of different phosphorus components, and the difficulty in balancing structural regulation and reaction efficiency. This provides a new technical path for constructing composite phosphorus-containing flame retardants with clear structural characteristics and application value. Summary of the Invention

[0005] To achieve the aforementioned objectives and address the aforementioned technical problems, this invention provides a dialkyl hypophosphite-alkyl phosphite composite salt flame retardant. The composite salt flame retardant is composed of dialkyl phosphonium ions, alkyl phosphonium ions, and 2- to 4-valent metal ions. Wherein, the dialkylphosphinate and the alkylphosphite form a complex salt structure with the divalent to tetravalent metal ions; The organic groups in the dialkylphosphonate and the organic groups in the alkylphosphonate are hydrocarbon groups corresponding to the olefins used.

[0006] Preferably, The composite salt flame retardant has the following structural relationship:

[0007] Wherein, R1, R2, and R3 are hydrocarbon group structures corresponding to the olefins used, and the number of carbon atoms in R1, R2, and R3 is the same as the number of carbon atoms in the corresponding olefins, x+2y=m; M is any one of aluminum ions, zinc ions, magnesium ions, calcium ions, iron ions, or zirconium ions.

[0008] This application also provides a method for synthesizing the above-mentioned dialkylphosphine-alkylphosphine composite salt flame retardant, comprising the following steps: S1: In a pressure-resistant reactor purged with inert gas, phosphine is used as the starting phosphorus-containing raw material. Under the action of a photoinitiator or a free radical initiator, phosphine undergoes a free radical addition reaction with gaseous or liquid olefins to obtain organophosphorus addition products. S2: The organophosphorus addition product obtained in step S1 is added to an aqueous solution containing an oxidant for oxidation reaction, and ammonia or alkali metal hydroxide is added to adjust the pH of the system to 6-8, so that dialkylphosphonic acid component and alkylphosphonic acid component are formed in the system. S3: Add a 2-4 valent metal salt solution to the system obtained in step S2 to carry out a salt formation reaction. After separation, washing and drying, the dialkylphosphine-alkylphosphine composite salt flame retardant is obtained.

[0009] Preferably, step S1 includes: Phosphine is introduced into a pressure-resistant reactor that has been purged with an inert gas. After controlling the partial pressure of phosphine in the reactor to be 0.05-10 MPa, a photoinitiator is added to the reactor, and gaseous olefins and phosphine are continuously introduced while the temperature is increased. At the same time, ultraviolet light is applied to induce a free radical addition reaction between phosphine and the gaseous olefins. After reacting for 0.1–48 h, the phosphine gas was turned off, and olefin gas was continued to be introduced. The reaction was terminated when the number of moles of olefin consumed was 1.01–1.99 times the number of moles of phosphine.

[0010] Preferably, step S1 includes: Phosphine is introduced into a pressure-resistant reactor containing solvent and purged with an inert gas. A photoinitiator is added to the reactor, and gaseous olefins are continuously introduced while the temperature is increased. Simultaneously, ultraviolet light is applied to induce a free radical addition reaction between phosphine and the gaseous olefins. The criterion for terminating the reaction was that the number of moles of gaseous olefins consumed was 1.01 to 1.99 times the number of moles of phosphine introduced.

[0011] Preferably, step S1 includes: Phosphine is introduced into a pressure-resistant reactor containing solvent and free radical initiator, which has been replaced with an inert gas, and gaseous olefins are continuously introduced and heated to allow phosphine to undergo a free radical addition reaction with the gaseous olefins. The criterion for terminating the reaction was that the number of moles of gaseous olefins consumed was 1.01 to 1.99 times the number of moles of phosphine introduced.

[0012] Preferably, step S1 includes: Liquid olefins and free radical initiators are added to a pressure-resistant reactor purged with inert gas, and phosphine is introduced. When the number of moles of phosphine introduced reaches 0.505 to 0.995 of the number of moles of liquid olefins, the introduction of phosphine is stopped. The temperature is then increased to allow phosphine to undergo a free radical addition reaction with the liquid olefin. The reaction ends when the phosphine content in the reactor is less than 100 ppm.

[0013] Preferably, the reaction temperature in step S1 is 10–200°C; More preferably, the reaction temperature in step S1 is 50–150°C.

[0014] Preferably, the salt formation reaction temperature in step S3 is 10–100°C; More preferably, the salt formation reaction temperature in step S3 is 30–80°C.

[0015] Preferably, The gaseous olefin is any one of ethylene, propylene, butene, and isobutene; More preferably, the gaseous olefin is at least one of ethylene and butene.

[0016] The liquid olefin is any one of C5-C18 aliphatic olefins, C8-C18 aromatic olefins, or C4-C18 cyclic olefins; More preferably, the liquid olefin is at least one of styrene, octene, and pentene.

[0017] Preferably, the photoinitiator is a free radical photoinitiator; More preferably, the photoinitiator is at least one of acetone, acetophenone, photoinitiator 1173, and photoinitiator 183.

[0018] Preferably, the free radical initiator is at least one of a peroxide or an azo compound; More preferably, the free radical initiator is at least one of ammonium persulfate, sodium persulfate, peracetic acid, perphenylacetic acid, and azobisisobutyronitrile.

[0019] The amount of the initiator added is 0.1‰ to 10% of the molar amount of phosphine.

[0020] More preferably, the amount of the initiator added is 1‰ to 10% of the molar amount of phosphine.

[0021] The oxidant is selected from at least one of hydrogen peroxide, hypochlorous acid, sodium hypochlorite, perchloric acid, sodium perchlorate, potassium permanganate, potassium dichromate, chromic acid, peracetic acid, perpropionic acid, perbutyric acid, sodium percarbonate, perbenzoic acid, osmium tetroxide, and ozone. More preferably, the oxidant is at least one of hydrogen peroxide, peroxybenzoic acid, and sodium percarbonate.

[0022] The metal ions in the divalent to tetravalent metal salt solution are selected from any one of aluminum ions, zinc ions, magnesium ions, calcium ions, iron ions, or zirconium ions.

[0023] Preferably, the solvent is at least one selected from water, methanol, ethanol, ethyl acetate, toluene, and benzene.

[0024] This application also provides an application of a dialkyl hypophosphite-alkyl phosphite composite salt flame retardant, which can synergistically retard flame alone or in combination with a halogen-free flame retardant.

[0025] Preferably, the halogen-free flame retardant includes: melamine cyanurate (MCA), melamine polyphosphate (MPP), zinc borate, spirophosphate (pentaerythritol dimethylphosphonate, CU), dimethyl methylphosphonate (DMMP), diethyl ethyl phosphate (DEEP), resorcinol bis(diphenyl phosphate) (RDP), bisphenol A bis(diphenyl phosphate) (BDP), phosphazene flame retardants, zinc diethylphosphinate (ZDP), aluminum diisobutylphosphinate, aluminum hydroxide, magnesium hydroxide, aluminum phosphite, and zinc borate.

[0026] This application also provides the application of a dialkyl hypophosphite-alkyl phosphite composite salt flame retardant in polymers, wherein the flame retardant can improve the flame retardant properties of polymers.

[0027] Preferably, the polymer includes: polyethylene (PE), polypropylene (PP), polyisobutylene (PIB), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), acrylonitrile-butadiene-styrene terpolymer (ABS), nylon (PA), polyurethane (PU), and thermoplastic elastomer (TPE).

[0028] The beneficial effects of the technical solution provided by this invention are as follows: 1. This invention controls the reaction ratio of phosphine to olefins within a specific range, especially making the reaction ratio of phosphine to ethylene less than 1:2, thereby enabling the system to form a complex salt structure in which dialkylphosphinate and alkylphosphite coexist during subsequent oxidation and salt formation. Compared with the single dialkylphosphinate structure that is more easily formed when the ratio reaches 1:2, this invention achieves directional control over the structure type of the final product.

[0029] 2. While achieving the above-mentioned composite salt structure, the present invention can still maintain a high and stable organophosphorus generation efficiency, indicating that the technical solution does not obtain a special structure at the expense of the reaction conversion level, but achieves the stable preparation of the composite salt system while ensuring the smooth progress of the addition, oxidation and salt formation processes.

[0030] 3. The composite salt flame retardant obtained by this invention not only exhibits structural characteristics different from those of single dialkylphosphine salts in NMR phosphorus spectrum and infrared spectrum, but also shows good flame retardant effect when used in polymer systems, indicating that the composite salt structure constructed by this invention has clear technical significance and practical application value. Attached Figure Description

[0031] Figure 1 This is a 31P NMR spectrum of Embodiment 1 of the present invention; Figure 2 This is the infrared spectrum of Embodiment 1 of the present invention; Figure 3 This is the 31P NMR spectrum of Comparative Example 1 of the present invention; Figure 4 This is the infrared spectrum of Comparative Example 1 of the present invention. Detailed Implementation

[0032] 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. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0033] Example 1 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen. After controlling the partial pressure of phosphine in the reactor to be 0.05–1 MPa, 0.001 mol of acetone was added. Ethylene and phosphine were then continuously introduced, and a high-pressure mercury lamp was turned on to catalyze the reaction. After 0.1 hours of reaction, the phosphine gas was turned off, and ethylene was continued to be introduced until the amount of ethylene consumed was 1.1 times the amount of phosphine added, at which point the reaction was terminated. Subsequently, a slightly excess of hydrogen peroxide solution was added to the reaction product to carry out the oxidation reaction. After the reaction was completed, sodium hydroxide was added dropwise to dissolve the product and bring the pH of the system to 6-8.

[0034] The system temperature was then controlled at 30°C, and an aqueous solution of aluminum sulfate, with a total aluminum ion content of 0.63 times the molar amount of phosphine consumed, was added dropwise over 48 hours. After the addition was completed, the reaction continued for another 48 hours. After separation, washing, pulverizing, and drying, a diethylphosphine-ethylphosphite composite salt flame retardant was obtained with a yield of approximately 93%. Nuclear magnetic resonance testing showed that the molar ratio of diethylphosphine to ethylphosphite was approximately 1:9.

[0035] Example 2 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen, and the partial pressure of phosphine was controlled at 9-10 MPa. Then, 0.01 mol of acetone was added, and propylene gas and phosphine gas were introduced simultaneously. The high-pressure mercury lamp was then turned on to catalyze the reaction. After 10 hours of reaction, the phosphine gas was turned off. After turning off the phosphine gas, propylene gas was introduced again until the total amount of propylene consumed was 1.5 times, at which point the reaction ended.

[0036] Subsequently, a hydrogen peroxide solution containing a slight excess of hydrogen peroxide was added to the reaction product to carry out an oxidation reaction. After the reaction was completed, sodium hydroxide was added dropwise to dissolve the product and bring the pH of the system to 6-8. The system temperature was controlled at 30℃. An aqueous solution of aluminum sulfate, with a total aluminum ion content of 0.67 times the number of moles of phosphine consumed, was added dropwise over 0.1 h. After the addition was completed, the reaction continued for another 0.1 h. After separation, washing, pulverizing, and drying, a dipropylphosphonic acid-propylphosphonite composite salt flame retardant was obtained with a yield of approximately 88%. Nuclear magnetic resonance testing showed that the molar ratio of dipropylphosphonate to propylphosphonite was approximately 1:1.

[0037] Example 3 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen and contained 0.01 mol of acetone and 100 ml of toluene. Butene and phosphine gas were introduced simultaneously. Then, a high-pressure mercury lamp was turned on to catalyze the reaction. When the amount of phosphine gas used reached 1 mol, the phosphine gas was turned off, and butene gas was continued to be introduced until the amount of butene consumed reached 1.99 mol, at which point the reaction ended.

[0038] An aqueous solution containing 2.2 mol of hydrogen peroxide was added to the reaction product to carry out an oxidation reaction. After the reaction was completed, sodium hydroxide was added dropwise to dissolve the product, bringing the pH of the system to 6-8. Toluene was then distilled off. The system temperature was controlled at 80℃, and an aqueous solution of aluminum sulfate with a total aluminum ion content of 0.34 mol was added dropwise over 12 hours. After the addition was completed, the reaction continued for 8 hours. After separation, washing, crushing, and drying, a dibutylphosphonic acid-butylphosphonic acid composite salt flame retardant was obtained with a yield of about 95%. According to NMR testing, the molar ratio of dibutylphosphonate to butylphosphonate was about 9.9:0.1.

[0039] Example 4 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen and contained 0.1 mol of azobisisobutyronitrile, 500 ml of ethanol, and 1.2 mol of 1-octene. When the amount of phosphine gas added reached 1 mol, the phosphine gas was turned off, and the temperature was raised to 60°C. The reaction was stopped when the phosphine content in the reactor was ≤100 ppm.

[0040] An aqueous solution containing 2 mol of hydrogen peroxide was added to the reaction product for oxidation. After the reaction was completed, sodium hydroxide was added dropwise to dissolve the product and adjust the pH of the system to 6-8. The ethanol was then distilled off. The system temperature was then controlled at 80°C. An aqueous solution containing 1 / 3 mol of aluminum ions was added dropwise over 12 hours. After the addition was completed, the reaction was continued for 4 hours. After separation, washing, pulverization, and drying, a dioctylphosphine-octylphosphonate composite salt flame retardant was obtained with a yield of approximately 91%. Nuclear magnetic resonance (NMR) analysis showed that the molar ratio of dioctylphosphine ions to octylphosphonate ions was approximately 4:1.

[0041] Example 5 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen and contained 0.1 mol of azobisisobutyronitrile and 2 mol of styrene. When the amount of phosphine gas added reached 1.7 mol, the phosphine gas was turned off, the temperature was raised to 60°C and held for 24 hours to stop the reaction.

[0042] Subsequently, an aqueous solution containing 2 mol of hydrogen peroxide was added to the reaction product for oxidation. After the reaction was completed, sodium hydroxide was added dropwise to dissolve the product and bring the pH of the system to 6-8. At the same time, the system temperature was controlled at 80℃. An aqueous solution containing 1 / 3 mol of aluminum ions was added dropwise over 12 hours. After the addition was completed, the reaction continued for 4 hours. After separation, washing, pulverization, and drying, a bis(2-phenylethyl)phosphonic acid-(2-phenylethyl)phosphonite aluminum composite salt flame retardant was obtained with a yield of about 90%. According to NMR testing, the molar ratio of bis(2-phenylethyl)phosphonate to bis(2-phenylethyl)phosphonite was about 7:3.

[0043] Example 6 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen and contained 0.05 mol of peracetic acid and 2 mol of 1-hexene. When the amount of phosphine gas added reached 1.2 mol, the phosphine gas was turned off, the temperature was raised to 60°C and held for 8 hours.

[0044] Subsequently, excess osmium tetroxide was added to the reaction product for oxidation. After the reaction was complete, the mixture was filtered, and the resulting solution was returned to the reaction vessel. Sodium hydroxide was then added dropwise to dissolve the solution, bringing the pH of the system to 6-8. Meanwhile, the system temperature was controlled at 80℃, and an aqueous solution of aluminum sulfate with a total aluminum ion content of 1 / 3 mol was added dropwise over 12 hours. After the addition was completed, the reaction continued for 36 hours. After separation, washing, crushing, and drying, a dihexylphosphonic acid-hexylphosphonite aluminum composite salt flame retardant was obtained with a yield of about 89%. According to NMR testing, the molar ratio of dihexylphosphonate to hexylphosphonite was about 1:4.

[0045] Example 7 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen and contained 0.05 mol of peracetic acid and 500 ml of toluene. The temperature was raised to 60°C and phosphine and propylene were introduced. When 1 mol of phosphine was consumed, the introduction of phosphine was stopped, and propylene was continued to be introduced until 1.5 mol of propylene was consumed, at which point the reaction was stopped.

[0046] Subsequently, excess osmium tetroxide was added to the reaction product for oxidation. After the reaction was complete, the mixture was filtered, and the resulting solution was returned to the reaction vessel. Sodium hydroxide was then added dropwise to dissolve the solution, bringing the pH of the system to 6-8. Meanwhile, the system temperature was controlled at 80℃, and an aqueous solution of aluminum sulfate with a total aluminum ion content of 1 / 3 mol was added dropwise over 12 hours. After the addition was completed, the reaction continued for 36 hours. After separation, washing, crushing, and drying, a dipropylphosphonic acid-propylphosphonite aluminum composite salt flame retardant was obtained with a yield of about 94%. According to NMR testing, the molar ratio of dipropylphosphonate to propylphosphonite was about 1:1.

[0047] Example 8 The flame retardant from Example 6 was granulated in a twin-screw extruder with PBT resin and glass fiber in a ratio of 20:30:50. After drying the particles, they were injection molded into flame retardant strips and placed at 25±3℃ and 50% humidity for 24 hours. Then, vertical burning was tested. The flame retardancy of the obtained PBT composite material met the UL94-V0 flame retardancy rating.

[0048] Comparative Example 1 Phosphine gas was introduced into a pressure-resistant reactor that had been pre-purified with high-purity nitrogen and contained 0.05 mol of sodium persulfate and 500 ml of ethanol / water (ethanol = 20 wt%). When the amount of phosphine gas added reached 1.2 mol, the phosphine gas was turned off, the temperature was raised to 60°C, and ethylene was continuously introduced until 2 mol of ethylene was consumed, at which point the reaction was stopped.

[0049] Subsequently, excess osmium tetroxide was added to the reaction product for oxidation. After the reaction was complete, the mixture was filtered, and the resulting solution was returned to the reaction vessel. Sodium hydroxide was then added dropwise to dissolve the solution, bringing the pH of the system to 6-8. Meanwhile, the system temperature was controlled at 80℃, and an aqueous solution of aluminum sulfate with a total aluminum ion content of 0.4 mol was added dropwise over 12 hours. After the addition was completed, the reaction continued for 36 hours. After separation, washing, crushing, and drying, aluminum diethylphosphinate flame retardant was obtained with a yield of about 90%, which was confirmed by nuclear magnetic resonance (NMR) testing.

[0050] Experimental test: 1. Phosphorus NMR spectroscopy test: Dissolve 1 g of the product in 10 g of 5 mol / L hydrochloric acid and transfer 50 mg of the solution to an NMR tube. Then add heavy water and test in a 400 MHz NMR spectrometer.31 P. 2. Infrared spectroscopy test: The dried sample was placed on the ATR test head of the infrared spectroscopy instrument, compacted with the indenter, and the infrared spectrum of the sample was measured using total reflectance mode at a test range of 400 cm⁻¹. -1 -4500cm -1 .

[0051] Table 1. Example Data

[0052] As can be seen from Example 1, Comparative Example 1, and their test results, the reaction ratio of phosphine to ethylene is the key factor determining the structural type of the final product. In Example 1 of this invention, the ratio of phosphine to ethylene was controlled to be less than 1:2. The resulting product, as shown by NMR testing, exhibited the coexistence of diethylphosphineate and ethylphosphite, indicating that the system formed a diethylphosphine-ethylphosphite complex salt. In Comparative Example 1, when the ratio of phosphine to ethylene reached 1:2, although a high yield of organophosphine product was also obtained, NMR testing showed that it ultimately transformed into a single diethylphosphine aluminum structure, instead of forming the complex salt system described in this invention. Further analysis using the corresponding 31P NMR and infrared spectra further illustrates that the phosphorus environment of the intermediate and the structural characteristics of the final product changed significantly under both conditions. This indicates that the difference was not caused by ordinary process fluctuations or simple yield changes, but rather by a substantial change in the oxidation pathway and salt formation result directly caused by the change in the reaction ratio. Table 1 also shows that all embodiments of the present invention exhibit high and stable organophosphine generation efficiency, indicating that the present invention does not sacrifice reaction efficiency to obtain a special structure, but rather achieves targeted control of the final product structure at a high conversion level. The principle is that when the ethylene ratio is controlled to be less than 1:2, the system after the addition of phosphine and ethylene is more likely to retain some phosphonite components during subsequent oxidation, thus forming a complex salt with coexisting diethylphosphonate and ethylphosphonite in the salt formation stage. However, when the ethylene ratio reaches 1:2, the system tends to convert towards a single diethylphosphonate. Therefore, the essential inventive point of this invention lies in controlling the reaction ratio of phosphine and ethylene within a range of less than 1:2 to achieve structural control from a single salt to a complex salt. This is the fundamental reason why the present invention differs from the comparative examples and results in a difference in technical effect.

[0053] 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, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dialkylphosphonic acid-alkylphosphonic acid composite salt flame retardant, characterized in that, The composite salt flame retardant is composed of dialkyl hypophosphite, alkyl phosphite, and 2- to 4-valent metal ions. Wherein, the dialkylphosphinate and the alkylphosphite form a complex salt structure with the divalent to tetravalent metal ions; The organic groups in the dialkylphosphonate and the organic groups in the alkylphosphonate are hydrocarbon groups corresponding to the olefins used.

2. The dialkylphosphonic acid-alkylphosphonic acid composite salt flame retardant according to claim 1, characterized in that, The composite salt flame retardant has the following structural relationship: Wherein, R1, R2, and R3 are hydrocarbon group structures corresponding to the olefins used, and the number of carbon atoms in R1, R2, and R3 is the same as the number of carbon atoms in the corresponding olefins, x+2y=m; M is any one of aluminum ions, zinc ions, magnesium ions, calcium ions, iron ions, or zirconium ions.

3. A method for synthesizing the dialkylphosphonic acid-alkylphosphonic acid composite salt flame retardant according to any one of claims 1 to 2, characterized in that, The steps include the following: S1: In a pressure-resistant reactor purged with inert gas, phosphine is used as the starting phosphorus-containing raw material. Under the action of a photoinitiator or a free radical initiator, phosphine undergoes a free radical addition reaction with gaseous or liquid olefins to obtain organophosphorus addition products. S2: The organophosphorus addition product obtained in step S1 is added to an aqueous solution containing an oxidant for oxidation reaction, and ammonia or alkali metal hydroxide is added to adjust the pH of the system to 6-8, so that dialkylphosphonic acid component and alkylphosphonic acid component are formed in the system. S3: Add a 2-4 valent metal salt solution to the system obtained in step S2 to carry out a salt formation reaction. After separation, washing and drying, the dialkylphosphine-alkylphosphine composite salt flame retardant is obtained.

4. The synthesis method according to claim 3, characterized in that, Step S1 includes: Phosphine is introduced into a pressure-resistant reactor that has been purged with an inert gas. After controlling the partial pressure of phosphine in the reactor to be 0.05-10 MPa, a photoinitiator is added to the reactor, and gaseous olefins and phosphine are continuously introduced while the temperature is increased. At the same time, ultraviolet light is applied to induce a free radical addition reaction between phosphine and the gaseous olefins. After reacting for 0.1–48 h, the phosphine gas was turned off, and olefin gas was continued to be introduced. The reaction was terminated when the number of moles of olefin consumed was 1.01–1.99 times the number of moles of phosphine.

5. The synthesis method according to claim 3, characterized in that, Step S1 includes: Phosphine is introduced into a pressure-resistant reactor containing solvent and purged with an inert gas. A photoinitiator is added to the reactor, and gaseous olefins are continuously introduced while the temperature is increased. Simultaneously, ultraviolet light is applied to induce a free radical addition reaction between phosphine and the gaseous olefins. The criterion for terminating the reaction was that the number of moles of gaseous olefins consumed was 1.01 to 1.99 times the number of moles of phosphine introduced.

6. The synthesis method according to claim 3, characterized in that, Step S1 includes: Phosphine is introduced into a pressure-resistant reactor containing solvent and free radical initiator, which has been replaced with an inert gas, and gaseous olefins are continuously introduced and heated to allow phosphine to undergo a free radical addition reaction with the gaseous olefins. The criterion for terminating the reaction was that the number of moles of gaseous olefins consumed was 1.01 to 1.99 times the number of moles of phosphine introduced.

7. The synthesis method according to claim 3, characterized in that, Step S1 includes: Liquid olefins and free radical initiators are added to a pressure-resistant reactor purged with inert gas, and phosphine is introduced. When the number of moles of phosphine introduced reaches 0.505 to 0.995 of the number of moles of liquid olefins, the introduction of phosphine is stopped. The temperature is then increased to allow phosphine to undergo a free radical addition reaction with the liquid olefin. The reaction ends when the phosphine content in the reactor is less than 100 ppm.

8. The synthesis method according to any one of claims 3 to 7, characterized in that, The reaction temperature in step S1 is 10–200°C; The salt formation reaction temperature in step S3 is 10–100°C.

9. The synthesis method according to any one of claims 3 to 7, characterized in that, The gaseous olefin is any one of ethylene, propylene, butene, and isobutene; The liquid olefin is any one of C5-C18 aliphatic olefins, C8-C18 aromatic olefins, or C4-C18 cyclic olefins; The photoinitiator is a free radical type photoinitiator; The free radical initiator is at least one of peroxide or azo compound; The amount of the initiator added is 0.1‰ to 10% of the molar amount of phosphine. The oxidant is selected from at least one of hydrogen peroxide, hypochlorous acid, sodium hypochlorite, perchloric acid, sodium perchlorate, potassium permanganate, potassium dichromate, chromic acid, peracetic acid, perpropionic acid, perbutyric acid, sodium percarbonate, perbenzoic acid, osmium tetroxide, and ozone. The metal ions in the divalent to tetravalent metal salt solution are selected from any one of aluminum ions, zinc ions, magnesium ions, calcium ions, iron ions, or zirconium ions.

10. The synthesis method according to any one of claims 5 or 6, characterized in that, The solvent is at least one selected from water, methanol, ethanol, ethyl acetate, toluene, and benzene.

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