High-temperature-resistant phosphorus-nitrogen-containing flame retardant, synthesis method and application thereof

Abstract

The application provides a high-temperature-resistant phosphorus-nitrogen-containing flame retardant and a synthesis method and application thereof, and belongs to the technical field of flame retardant development. The application successfully prepares a flame retardant with excellent intrinsic thermal stability, which can withstand a high-temperature environment exceeding the decomposition temperature of conventional phosphorus-nitrogen-containing flame retardants, does not decompose or volatilize in advance during the processing process, thereby ensuring the persistent flame-retardant function in the final material; meanwhile, the flame retardant exhibits high-efficiency flame-retardant performance in an epoxy resin matrix and the like, and can significantly improve the fireproof grade of the material. The far-reaching significance lies in that the technology provides a reliable flame-retardant solution for high-temperature engineering plastics necessary for the fields of aerospace, new energy vehicles, high-end electronic appliances and the like, breaks through the key bottleneck of safe application, enables the material to work safely and stably in a more harsh thermal environment, and powerfully promotes the lightweight and performance improvement of high-end equipment.

Description

Technical Field

[0001] This invention relates to the field of flame retardant development technology, and in particular to a high-temperature resistant phosphorus-nitrogen flame retardant, its synthesis method, and its application. Background Technology

[0002] Flame retardants are functional additives that impart flame-retardant properties to flammable materials, playing a crucial role in fire prevention and protecting life and property. With increasingly stringent environmental regulations and heightened public safety awareness, traditional halogenated flame retardants are limited due to the toxic and corrosive fumes they produce during combustion, leading to a market shift towards halogen-free flame retardant systems. Among numerous halogen-free flame retardants, phosphorus-nitrogen synergistic flame retardant systems have become a hot topic in current research and development due to their ability to exert flame-retardant effects in both the gas and condensed phases, offering advantages such as high efficiency, low smoke, low toxicity, and environmental friendliness. These flame retardants typically achieve flame retardancy by using phosphorus-containing components to promote char layer formation and nitrogen-containing components to foam and expand, jointly constructing a thermal and oxygen-barrier barrier.

[0003] On the other hand, modern industry's requirements for material performance are constantly evolving towards higher temperatures and higher strengths, leading to the emergence of a series of high-temperature engineering plastics such as polyamide 46 (PA46), polyamide 4T (PA4T), and polyamide 6T (PA6T). These materials typically have melting points and processing temperatures exceeding 300°C or even 400°C, and their application environments are extremely demanding. However, a common challenge when applying flame retardants to such high-temperature materials is that the thermal stability of the flame retardant must match the processing temperature of the base resin. If the thermal decomposition temperature of the flame retardant is lower than the processing temperature, it will decompose, degrade, or volatilize during compounding, injection molding, and other processing. This not only directly results in the loss of flame-retardant components, leaving the material unprotected against fire in actual use, but may also severely degrade the material's mechanical properties, electrical insulation, and appearance quality due to the decomposition products catalyzing resin degradation or generating bubbles. Therefore, developing novel flame retardants that combine high-efficiency flame retardancy with excellent thermal stability to meet the processing and application needs of high-temperature engineering plastics has become a clear and urgent technological development direction in the field of flame-retardant materials. Summary of the Invention

[0004] The purpose of this invention is to provide a high-temperature resistant phosphorus-nitrogen flame retardant, its synthesis method, and its application. This invention solves the technical problem that existing phosphorus-nitrogen flame retardants are unable to maintain structural stability and flame retardant performance during the high-temperature processing of high-temperature engineering plastics (such as nylon PA46, PA6T, etc.) due to insufficient thermal stability, which leads to the failure of the flame retardant performance and the deterioration of the overall performance of the material.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a high-temperature resistant phosphorus-nitrogen-containing flame retardant, comprising the following steps: S1. Under inert gas protection, bis(p-chlorophenyl)phosphoyl chloride, solvent A and piperazine are reacted at 0℃~5℃ in the presence of a catalyst to generate the first intermediate product; S2. The first intermediate product obtained in step S1 is subjected to a first solid-liquid separation and a first washing to obtain a first filter cake; S3. Dissolve the first filter cake obtained in step S2 in water to obtain a first solution, and adjust the pH value of the first solution to 6.5~8.0 with an alkaline substance; S4. Add an aqueous solution of a water-soluble salt containing magnesium ions to the solution obtained in step S3, and react at 70℃~90℃ for 3~8 hours to generate a second intermediate product containing the high-temperature resistant phosphorus-nitrogen flame retardant. S5. The second intermediate product obtained in step S4 is subjected to a second solid-liquid separation and a second washing to obtain a second filter cake. S6. The second filter cake obtained in step S5 is dried to obtain the high-temperature resistant phosphorus-nitrogen flame retardant.

[0006] Preferably, the molar ratio of bis(p-chlorophenyl)phosphoryl chloride to piperazine is 1.1 to 2.0:1, and the molar ratio of the catalyst to piperazine is 2 to 3:1.

[0007] Preferably, the catalyst is selected from one or more of isophorone diamine, 4,4'-diaminodicyclohexylmethane, bis(3-aminophenyl)methylphosphine oxide, tris-(2-aminoethyl)amine, N-methylmorpholine, N,N-diisopropylethylamine and diisopropylethylamine.

[0008] Preferably, solvent A in step S1 is tetrahydrofuran.

[0009] Preferably, in step S1, the piperazine is added dropwise to the reaction system containing the bis(p-chlorophenyl)phosphochloride in the form of a mixed solution of piperazine and solvent A.

[0010] Preferably, in step S2, the first washing is performed using solvent A; The alkaline substance mentioned in step S3 is ammonia water; In step S4, the molar ratio of the water-soluble salt containing magnesium ions to the bis(p-chlorophenyl)phosphochloride in step S1 is 1.0:1 to 1.2:1; the water-soluble salt containing magnesium ions is magnesium sulfate. The drying temperature in step S6 is 80℃~120℃, and the drying time is 8 hours~24 hours.

[0011] The present invention also provides a high-temperature resistant phosphorus-nitrogen flame retardant prepared by the above preparation method.

[0012] This invention also provides the application of the above-mentioned high-temperature resistant phosphorus-nitrogen flame retardant in the preparation of high-temperature engineering plastics.

[0013] The present invention also provides a flame retardant material comprising a polymer matrix and the above-mentioned high-temperature resistant phosphorus-nitrogen flame retardant.

[0014] Preferably, the amount of the high-temperature resistant phosphorus-nitrogen flame retardant added to the flame retardant material is 1.0wt% to 10.0wt% of the total weight of the flame retardant material.

[0015] The relevant terms used in this invention are as follows: Bis(4-chlorophenyl)phosphoryl chloride, commonly abbreviated as DCPP, is an important organophosphoryl chloride compound. Its conventional use is as a key raw material in the synthesis of phosphorus-containing flame retardants, organophosphorus ligands, and pesticide intermediates. In this invention, it serves as the core phosphorus source for the synthesis of high-temperature resistant phosphorus-nitrogen-containing flame retardants.

[0016] Tetrahydrofuran (THF) is a common cyclic ether organic solvent with excellent solubility and a moderate boiling point. It is widely used in Grignard reactions, polymerization reactions, and as a chromatographic mobile phase. In this invention, it is used as the reaction solvent in step S1.

[0017] Piperazine is a nitrogen-containing heterocyclic compound with two secondary amine groups. Its conventional uses include as a pharmaceutical intermediate (such as an anthelmintic), an epoxy resin curing agent, and a polymer modifier. In this invention, it serves as a key nitrogen source for the reaction with phosphoric acid chloride, participating in the construction of a phosphorus-nitrogen synergistic flame-retardant structure.

[0018] Ammonium polyphosphate (APP) is a highly efficient halogen-free intumescent flame retardant widely used in the flame retardancy of polymer materials such as polyolefins, epoxy resins, and polyurethanes. In this invention, it is used as a flame retardant synergist in combination with the aforementioned high-temperature resistant phosphorus-nitrogen flame retardant.

[0019] Water-soluble salts containing magnesium ions: These are salts that can dissociate into magnesium ions (Mg²⁺) in water. Their conventional uses include as chemical raw materials, refractory materials, and desiccants. In a preferred embodiment of this invention, the water-soluble salt containing magnesium ions is magnesium sulfate (MgSO4), which is used to combine with the phosphorus groups of the intermediate to further form a final flame retardant structure with high thermal stability.

[0020] The beneficial effects of this invention are: The high-temperature resistant phosphorus-nitrogen flame retardant, its synthesis method, and its application provided by this invention have the following beneficial effects: Directly, a flame retardant with excellent intrinsic thermal stability is successfully prepared. It can withstand high-temperature environments exceeding the decomposition temperature of conventional phosphorus-nitrogen flame retardants and does not undergo premature decomposition or volatilization during processing, thus ensuring its long-lasting flame-retardant function in the final material. Simultaneously, this flame retardant exhibits highly efficient flame-retardant properties in matrices such as epoxy resins, significantly improving the fire resistance rating of the material. Its profound significance lies in the fact that this technology provides a reliable flame-retardant solution for high-temperature engineering plastics essential for aerospace, new energy vehicles, and high-end electronics, breaking through key bottlenecks in their safe application. This enables materials to work safely and stably in harsher thermal environments, powerfully promoting the lightweighting and performance improvement of high-end equipment. Attached Figure Description

[0021] Figure 1 Infrared spectrum of a novel high-temperature resistant phosphorus-nitrogen flame retardant; Figure 2 Thermogravimetric analysis diagram of a novel high-temperature resistant phosphorus-nitrogen flame retardant. Detailed Implementation

[0022] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0023] Example 1 High-temperature resistant phosphorus-nitrogen flame retardants were prepared by a two-step synthesis method: The specific steps are as follows: DCPP and THF were added to a three-necked round-bottom flask under a nitrogen atmosphere and stirred. After stirring at 0-5 °C for several minutes, a mixed solution of piperazine, catalyst, and THF was added dropwise to the flask through a constant-pressure dropping funnel, with a DCPP:piperazine:catalyst ratio of 1.1:1:2. During the dropwise addition, a large amount of white solid gradually appeared in the system. After the addition was complete, the temperature was raised to a certain level and the reaction was carried out for several hours. After the reaction was completed, the system was cooled and filtered, and the filter cake was collected. The filter cake was washed several times with THF to obtain a white powder solid, which was then dried in a vacuum oven at 80 °C for 12 h. Subsequently, the filter cake was dissolved in deionized water, and the temperature was raised to 80 °C to dissolve the filter cake and form a mixture. Ammonia was added dropwise to adjust the pH to 7.26. Anhydrous magnesium sulfate was dissolved in an appropriate amount of deionized water, with an anhydrous magnesium sulfate:DCPP ratio of 1:1, and slowly poured into the mixture. The reaction was then carried out at 80 °C for 5 h. After the reaction was completed, the system was cooled and filtered, the filter cake was collected, and the filter cake was washed several times with water to obtain a white powder solid. It was dried in a forced-air oven at 100 ℃ for 12 h, weighed, and the yield was calculated. The product was subsequently designated as high-temperature resistant phosphorus and nitrogen flame retardant PN-Mg.

[0024] The selected catalyst was isophorone diamine.

[0025] Table 1. PN-Mg Index Test Data Sample pH Whiteness D50 (µm) PN-Mg 8.18 95.15 44 ~ 45 Example 2 The only difference from Example 1 is that the catalyst is replaced with 4,4'-diaminodicyclohexylmethane and the ratio of anhydrous magnesium sulfate to DCPP is 1.2:1.

[0026] Example 3 The only difference from Example 1 is that the catalyst is replaced with bis(3-aminophenyl), methylphosphine oxide, and the ratio of DCPP:piperazine:catalyst is 2:1:3.

[0027] Example 4 The only difference from Example 1 is that the catalyst is replaced with tri-(2-aminoethyl)amine.

[0028] Example 5 The only difference from Example 1 is that the catalyst is replaced with N-methylmorpholine.

[0029] Example 6 The only difference from Example 1 is that the catalyst is replaced with N,N-diisopropylethylamine.

[0030] Example 7 The only difference from Example 1 is that the catalyst is replaced with diisopropylethylamine.

[0031] Experimental Example FT-IR spectroscopy analysis To demonstrate the successful synthesis of the high-temperature resistant phosphorus-nitrogen flame retardant PN-Mg in Example 1, the product PN-Mg was characterized by FT-IR, and the FT-IR spectrum is shown below. Figure 1 As shown. Between 3025 and 3059 cm, 746 cm -1 The absorption peak at 1604 cm⁻¹ corresponds to the stretching vibration of the CH group on the benzene ring. -1 and 1488 cm -1 The absorption peak at 1436 cm⁻¹ represents the skeletal vibration of the benzene ring. -1 and 1141 cm -1 The absorption peaks at 1103 cm⁻¹ represent the stretching vibrations of PC and P=O, respectively; furthermore, the absorption peak at 1103 cm⁻¹... -1 and 723 cm -1 The absorption peak at this point corresponds to the stretching vibration of PNC. In summary, this indicates that the PN-Mg flame retardant has been successfully synthesized.

[0032] Thermogravimetric analysis To meet the processing requirements of plastics, flame retardants must possess good thermal stability. The thermal stability of the modified composite was evaluated using thermogravimetric analysis. Figure 2It can be seen that when the temperature is raised to 400 ℃, the thermal weight loss is less than 0.5%. With continuous heating, the temperature is 494.8 ℃ when the weight loss of the composite is 1.0% and 529.3 ℃ when the weight loss of the composite is 2.0%. The initial decomposition temperature of the composite is 546.2 ℃, indicating that the flame retardant has good thermal stability and can be applied to a variety of high-temperature engineering plastics, significantly improving safety.

[0033] XRF Analysis of Novel High-Temperature Phosphorus-Nitrogen Flame Retardant The chemical composition of the novel high-temperature resistant phosphorus-nitrogen flame retardant was analyzed by XRF and is shown in Table 2.

[0034] Table 2 Elemental Analysis Analyte Result Proc-Cala Line Net Int. BG Int. <![CDATA[P2O5]]> 67.6758% Quant.-FP P Ka 2097.693 27.152 MgO 29.7858% Quant.-FP Mg Ka 241.290 1.001 <![CDATA[SO3]]> 1.1365% Quant.-FP S Ka 19.134 0.515 <![CDATA[Al2O3]]> 0.3887% Quant.-FP Al Ka 4.381 0.253 <![CDATA[SiO2]]> 0.3645% Quant.-FP Si Ka 5.304 0.632 CaO 0.3413% Quant.-FP Ca Ka 16.704 1.060 Cl 0.2030% Quant.-FP Cl Ka 3.428 0.914 MnO 0.0544% Quant.-FP Mn Ka 4.170 1.095 NiO 0.0249% Quant.-FP Ni Ka 5.216 2.621 <![CDATA[Fe2O3]]> 0.0174% Quant.-FP Fe Ka 1.749 1.611 CuO 0.0077% Quant.-FP Cu Ka 1.726 3.467 XRF analysis revealed that the main components of the sample were P and Mg, consistent with our expected product. Since XRF cannot determine elements such as N, C, H, and O, only P and Mg could be preliminarily identified. The table shows SO3 (1.14%), a significant minor component, indicating the presence of a small amount of magnesium sulfate impurity. Other oxides (Al2O3, SiO2, CaO, etc., all <0.4%) are trace impurities, totaling less than 1.5%. These likely originate from impurities in the raw materials or small amounts of silicates, aluminates, and calcium salts introduced during production and storage. Trace elements (Cl, MnO, NiO, Fe2O3, CuO) are also present, but their content is extremely low. It should be noted that for NiO, Fe2O3, and CuO, their NetInt. (net intensity) and BG Int. (background intensity) values ​​are close to or even lower (e.g., CuO's Net Int. is 1.726, and BG Int. is 3.467). This means that the measurement signals for these elements are very weak, and the results have high uncertainty, and may only be used as a reference. Combined with infrared spectroscopy analysis, it can be confirmed that the novel high-temperature resistant phosphorus-nitrogen flame retardant PN-Mg has been synthesized.

[0035] Note: In this invention, the obtained high-temperature resistant phosphorus-nitrogen flame retardant is a solid composite insoluble in common organic solvents and water. Due to these physicochemical properties, it is impossible to use methods such as NMR spectroscopy or mass spectrometry, which rely on solubility, for precise molecular structure analysis and molecular weight determination. Therefore, this invention uses Fourier transform infrared spectroscopy and X-ray fluorescence spectroscopy to confirm the existence of its key functional groups and main elemental composition, and directly verifies its core thermal stability and flame retardant efficacy through thermogravimetric analysis and flame retardant performance tests as described below.

[0036] 5. Preparation of a novel high-temperature resistant phosphorus-nitrogen flame retardant PN-Mg / epoxy resin (EP-44) To further verify the flame retardancy of the high-temperature resistant phosphorus-nitrogen flame retardant PN-Mg, epoxy resin (EP-44), APP, and the novel high-temperature resistant phosphorus-nitrogen flame retardant were mixed in a certain proportion. The APP content was 2.0 wt%, and the PN-Mg content was 3.0 wt%. The mixture was vacuum-dried in a vacuum oven (70–80 °C) for 5 min, then 21.8 wt% of curing agent was added and mixed thoroughly. The mixture was then vacuum-dried again (70–80 °C, 5 min). The mixture was poured into a 3.2 mm vertical combustion mold and cured under certain conditions (100 °C, 2 h; 150 °C, 2 h). The flame retardancy of the epoxy resin samples was determined according to the UL-94 standard.

[0037] The curing agent can be selected from one or more of ethylenediamine, diethylenetriamine, triethylenetetramine, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, phthalic anhydride, m-phenylenediamine, diaminodiphenylmethane, and diaminodiphenyl sulfone. Ethylenediamine was selected in this experiment.

[0038] Table 3. Test data on the flame retardant properties of EP-44 and its composite materials.

[0039] As shown in Table 3, in the EP-44 system, the epoxy resin is non-flame retardant without a flame retardant. When ammonium polyphosphate is used alone as a flame retardant, the combustion result is V-2. With the addition of 3.0 wt% of the flame retardant PN-Mg, the combustion result is V0, indicating that the novel high-temperature resistant phosphorus-nitrogen flame retardant PN-Mg has a certain flame retardant property. This demonstrates that the novel high-temperature resistant phosphorus-nitrogen flame retardant PN-Mg does indeed play a flame-retardant role in the flame-retardant system.

[0040] As demonstrated by the above embodiments, this invention provides an efficient synthesis method for a high-temperature resistant phosphorus-nitrogen flame retardant. The method has a clear process route, mild and controllable reaction conditions, and can successfully prepare the target flame retardant. Infrared spectroscopy and elemental analysis confirmed that the obtained product possesses the expected molecular structure and chemical composition. Thermogravimetric analysis results show that the flame retardant has a significantly higher initial decomposition temperature and excellent thermal stability than conventional phosphorus-nitrogen flame retardants, meeting the requirements of high-temperature processing environments. Further flame retardant application tests show that applying the synthesized flame retardant to an epoxy resin system significantly improves the flame retardant rating of the composite material, proving its effective flame retardant function. In summary, this invention successfully obtains a novel phosphorus-nitrogen flame retardant with good thermal stability and high flame retardant performance, along with its feasible preparation process.

[0041] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant phosphorus-nitrogen-containing flame retardant, characterized in that, Includes the following steps: S1. Under inert gas protection, bis(p-chlorophenyl)phosphoyl chloride, solvent A and piperazine are reacted at 0℃~5℃ in the presence of a catalyst to generate the first intermediate product; S2. The first intermediate product obtained in step S1 is subjected to first solid-liquid separation and first washing to obtain the first filter cake; S3. Dissolve the first filter cake obtained in step S2 in water to obtain a first solution, and adjust the pH value of the first solution to 6.5~8.0 with an alkaline substance; S4. Add an aqueous solution of a water-soluble salt containing magnesium ions to the solution obtained in step S3, and react at 70℃~90℃ for 3~8 hours to generate a second intermediate product containing the high-temperature resistant phosphorus-nitrogen flame retardant. S5. The second intermediate product obtained in step S4 is subjected to a second solid-liquid separation and a second washing to obtain a second filter cake. S6. The second filter cake obtained in step S5 is dried to obtain the high-temperature resistant phosphorus-nitrogen flame retardant.

2. The preparation method according to claim 1, characterized in that, The molar ratio of bis(p-chlorophenyl)phosphoryl chloride to piperazine is 1.1~2.0:1, and the molar ratio of the catalyst to piperazine is 2~3:

1.

3. The preparation method according to claim 1, characterized in that, The catalyst is selected from one or more of isophorone diamine, 4,4'-diaminodicyclohexylmethane, bis(3-aminophenyl)methylphosphine oxide, tris-(2-aminoethyl)amine, N-methylmorpholine, N,N-diisopropylethylamine and diisopropylethylamine.

4. The preparation method according to claim 1, characterized in that, Solvent A in step S1 is tetrahydrofuran.

5. The preparation method according to claim 1, characterized in that, In step S1, the piperazine is added dropwise to the reaction system containing the bis(p-chlorophenyl)phosphochloride in the form of a mixed solution of piperazine and solvent A.

6. The preparation method according to claim 1, characterized in that, In step S2, the first washing is performed using solvent A; The alkaline substance mentioned in step S3 is ammonia water; In step S4, the molar ratio of the water-soluble salt containing magnesium ions to the bis(p-chlorophenyl)phosphochloride in step S1 is 1.0:1 to 1.2:1; the water-soluble salt containing magnesium ions is magnesium sulfate. The drying temperature in step S6 is 80℃~120℃, and the drying time is 8 hours~24 hours.

7. A high-temperature resistant phosphorus-nitrogen flame retardant prepared by the preparation method according to any one of claims 1 to 6.

8. The application of the high-temperature resistant phosphorus-nitrogen flame retardant according to claim 7 in the preparation of high-temperature engineering plastics.

9. A flame-retardant material, characterized in that, It comprises a polymer matrix and the high-temperature resistant phosphorus-nitrogen flame retardant as described in claim 7.

10. The flame-retardant material according to claim 9, characterized in that, The amount of the high-temperature resistant phosphorus-nitrogen flame retardant added to the flame retardant material is 1.0wt% to 10.0wt% of the total weight of the flame retardant material.

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