Preparation method and application of novel phosphorus-containing nitrogen oxide flame retardant

Abstract

The invention relates to the field of phosphorus-nitrogen flame retardants, and discloses a preparation method and application of a novel phosphorus-containing nitrogen oxide flame retardant, the preparation method comprises the following steps: S1, under the protection of nitrogen, dissolving diphenylphosphinyl hydroxylamine and triethylamine in a tetrahydrofuran solvent to prepare a reaction substrate solution; s2, slowly dropwise adding a diphenylphosphinyl chloride solution into the solution, and then sufficiently carrying out the reaction in a staged heating and heating reflux mode; s3, cooling and filtering to remove solid byproducts generated by reaction, and concentrating filtrate to obtain a crude product solid; and S4, recrystallizing and purifying the crude product by using ethyl acetate, and finally heating and drying the obtained crystal under a vacuum condition to obtain the product. An N-O group is innovatively introduced into the molecular structure of the flame retardant, so that the effect of efficiently capturing gas-phase free radicals in cooperation with a phosphorus-containing group is achieved, and the substantive technical progress that the material can be endowed with excellent flame retardant property with extremely low addition amount is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of phosphorus-nitrogen type flame retardants, in particular to a preparation method of a novel phosphorus-nitrogen oxide-containing flame retardant and application thereof. BACKGROUND

[0002] Thermoplastic polyurethane (TPU) is widely used in electronic devices, new energy vehicles and smart wear due to its unique soft-hard segment microphase separation structure, high elasticity, wear resistance and processing flexibility. To meet the increasing safety standards in these fields, flame-retardant modification of TPU is a key link for its application and development. Among various technical routes, halogen-free flame-retardant modification has become an industry consensus. Additive flame retardants are the mainstream technology for halogen-free flame-retardant modification of TPU due to their simple process, wide application range, and easy-to-control modification effect. Among various halogen-free flame retardants, phosphorus-nitrogen type flame retardants have shown good application prospects in the flame-retardant application of TPU due to their ability to simultaneously play a synergistic flame-retardant role in the gas phase and condensed phase. The existing systems mainly include phosphate, hypophosphite and phosphate ester flame retardants.

[0003] However, in practical applications, the existing technology still needs to be further improved. Studies have shown that, in order to make TPU materials achieve a high flame-retardant grade, conventional phosphorus-nitrogen type flame retardants usually require a high addition amount. Such a high addition amount may interfere with the intermolecular forces within the TPU material, thereby affecting the original excellent mechanical properties of the material. From the flame-retardant mechanism, TPU materials will generate a large amount of high-activity free radicals during combustion decomposition, and the condensed-phase catalytic carbonization effect of traditional phosphorus-nitrogen flame retardants still has room for improvement in inhibiting gas-phase combustion. In recent years, in the research of other polymer systems, it has been confirmed that the nitroxide structure can effectively capture active radicals in the gas phase by generating nitroxide radicals during thermal decomposition. Therefore, exploring how to introduce more efficient gas-phase inhibition groups into the structure of traditional phosphorus-nitrogen flame retardants, in order to achieve excellent flame-retardant effect at a lower addition amount while maintaining the comprehensive performance of the material, has become a technical direction worthy of attention in the field of high-performance flame-retardant TPU materials. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a preparation method of a novel phosphorus-nitrogen oxide-containing flame retardant and application thereof, which solves the problem of serious deterioration of the mechanical properties of TPU composite materials caused by the insufficient flame-retardant efficiency and high amount of addition of traditional phosphorus-nitrogen flame retardants.

[0005] To achieve the above purpose, the present application is implemented by the following technical solutions: a novel phosphorus-nitrogen oxide-containing flame retardant, the synthesis process and structure of the novel phosphorus-nitrogen oxide-containing flame retardant are as follows: .

[0006] A method for preparing a novel phosphorus-containing nitrogen oxide flame retardant includes the following steps: S1. Under nitrogen protection, add diphenylphosphonic hydroxylamine, tetrahydrofuran and triethylamine to a four-necked flask equipped with a thermometer, stirrer, condenser and constant pressure dropping funnel, and stir until completely dissolved. S2. Slowly add a certain amount of diphenylphosphine chloride solution through a constant pressure dropping funnel. After the addition is complete, gradually raise the temperature to 40-50℃ and react for 1.5-2.5h. Then raise the temperature to 70-80℃ and reflux for 7.5-8.5h. S3. After the reaction is complete, cool to room temperature, filter the reaction solution to remove the byproduct triethylamine hydrochloride, and then concentrate the solution obtained by vacuum evaporation to obtain a solid product. S4. The obtained solid product is recrystallized with ethyl acetate and dried in a vacuum oven at 75-85℃ for 7.5-8.5h to obtain a novel phosphorus-containing nitrogen oxide flame retardant N-[(diphenylphosphino)oxy]-P,P-diphenylphosphineamide.

[0007] Preferably, the molar ratio of diphenylphosphonohydroxylamine, diphenylphosphonyl chloride and triethylamine is 1:1:1.1.

[0008] Preferably, in step S2, the heating reflux treatment refers to carrying out the heating reaction at the boiling point temperature of tetrahydrofuran, which is used as a solvent.

[0009] Preferably, in step S3, the byproduct triethylamine hydrochloride removed by the filtered reaction solution is in solid form.

[0010] A novel phosphorus-containing nitrogen oxide flame retardant is used in the preparation of flame-retardant thermoplastic polyurethane composite materials.

[0011] This invention provides a novel method for preparing a phosphorus-containing nitrogen oxide flame retardant and its application. It has the following beneficial effects: 1. This invention innovatively introduces NO groups into the molecular structure of flame retardants, achieving the effect of synergistically capturing gaseous free radicals with phosphorus-containing groups. This solves the technical problems of low flame retardant efficiency and the need for large amounts of traditional phosphorus and nitrogen flame retardants, and realizes a substantial technological advancement of imparting excellent flame retardant properties to materials with extremely low addition amounts.

[0012] 2. This invention achieves good compatibility with TPU matrix and maintains the original properties of the material by realizing extremely low effective addition amount and utilizing the aromatic ring structure in flame retardant molecules. It solves the key problem of serious decline in the mechanical properties of composite materials caused by large addition amount and poor compatibility of traditional flame retardants. This gives flame retardant composite materials a significant advantage in mechanical properties that are basically equivalent to pure TPU.

[0013] 3. This invention achieves high-yield synthesis through a one-pot nucleophilic substitution reaction process, overcoming the industrialization obstacles of cumbersome synthesis routes, harsh reaction conditions, and low yields of some flame retardants. This results in a substantial improvement in process simplicity, mild conditions, safety and controllability, and solvent recyclability, making the industrial production of this flame retardant possible.

[0014] 4. This invention achieves excellent thermal stability and fixed melting point characteristics far exceeding the polymer processing temperature by designing and synthesizing solid powder flame retardants with specific chemical structures. It solves the process problems of insufficient thermal stability, easy decomposition at polymer processing temperature, and difficulty in precise addition and uneven dispersion of some traditional flame retardants, ensuring excellent processing stability and ease of operation, so as to achieve reliable performance of the final product. Attached Figure Description

[0015] Figure 1 This is a synthetic route diagram for the N-[(diphenylphosphino)oxy]-P,P-diphenylphosphine amide of the present invention; Figure 2 Thermogravimetric analysis curve of NDPA, the product of this invention; Figure 3 This is a DSC curve of the product NDPA of the present invention; Figure 4 The FTIR spectra of the raw materials diphenylphosphine chloride, diphenylphosphine hydroxylamine, and the product NDPA of this invention are shown below. Figure 5 The product of this invention, NDPA 1 H NMR spectrum; Figure 6 The product of this invention, NDPA 31 P NMR spectrum. Detailed Implementation

[0016] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example: Please see the appendix Figure 1 -Appendix Figure 6 This invention provides a novel phosphorus-containing nitrogen oxide flame retardant, and the synthesis process and structure of the novel phosphorus-containing nitrogen oxide flame retardant are shown below: .

[0018] Specifically, the phosphorus-nitrogen oxide flame retardant, chemically named N-[(diphenylphosphoyl)oxy]-P,P-diphenylphosphineamide (NDPA), aims to address the key issues of low flame retardant efficiency, poor compatibility with the polymer matrix, and severe degradation of mechanical properties found in commonly used phosphorus-nitrogen flame retardants in current TPU materials.

[0019] This flame retardant product is a white powder. Its physical and chemical properties were characterized by the following tests: according to Figure 2 The thermogravimetric analysis (TGA) curve of the product NDPA is shown. The initial thermal decomposition temperature of this flame retardant is 278℃, indicating that it has excellent thermal stability and can meet the processing temperature requirements of most polymer materials such as thermoplastic polyurethane. At 800℃, the char residue of flame retardant NDPA is only 1.7wt%, indicating that its condensed phase charring ability is limited. It mainly achieves its high-efficiency flame retardancy by generating nitrogen and oxygen free radicals through the NO structure and capturing active free radicals in the gas phase.

[0020] according to Figure 3 The DSC curve of the product NDPA is shown. The melting point of pure NDPA is 191℃. This melting point characteristic differs from that of traditional liquid phosphate flame retardants. Because it has a fixed melting point, it is easier to add during processing and helps it to achieve good dispersion in TPU material matrix.

[0021] To confirm that the synthesized product is indeed the target structure of NDPA, the present invention conducted the following structural characterization analysis: Fourier transform infrared spectroscopy analysis: its such Figure 4 The image shows the infrared spectra of the raw materials diphenylphosphine chloride (DPPC), diphenylphosphine hydroxylamine (DPPH), and the product NDPA. The image shows the infrared spectrum at 3056 cm⁻¹. -1 The absorption peak at 1438 cm⁻¹ corresponds to the stretching vibration of the CH group on the benzene ring. -1 and 1190cm -1 The vibrations were attributed to stretching vibrations of Ph-P and P=O bonds, respectively, at 547 cm⁻¹. -1 The characteristic peaks at 1590 and 1480 cm⁻¹ originate from the stretching vibrations of P-Cl. -1 This is due to vibrations in the benzene ring skeleton. Analysis of the infrared spectrum of the raw material DPPH revealed a value at 3256 cm⁻¹. -1 This corresponds to the stretching vibration of NH. The reaction proceeds via DPPC and DPPH, and the infrared spectrum of the product NDPA shows a peak at 547 cm⁻¹. -1 The characteristic peak of P-Cl at 962 cm⁻¹ disappeared significantly, while the peak at 962 cm⁻¹ disappeared at 962 cm⁻¹. -1 The formation of new PN bonds indicates that the target product, flame retardant NDPA, has been successfully synthesized.

[0022] 1H NMR spectrum ( 1 HNMR analysis: such as Figure 5 As shown, this is the product NDPA. 1 The 1H NMR spectrum shows that the peaks at 7.45 to 7.75 ppm are attributed to the chemical shifts of the H atoms on the benzene ring in the structure, and the peak at 1.61 ppm corresponds to the chemical shift of the H atoms on the NH atom in the diphenylphosphohydroxylamine structure, further confirming that a nucleophilic substitution reaction occurred between DPPC and DPPH.

[0023] Nuclear magnetic resonance phosphorus spectrum ( 31 PNMR analysis: such as Figure 6 As shown, this is the product NDPA. 31 PNMR spectrum. Two phosphorus signal peaks can be observed at 23.35 ppm and 23.33 ppm, which are attributed to two different chemical environments where the P atom is bonded to nitrogen and oxygen, respectively.

[0024] Based on the above FTIR, 1 HNMR and 31 Analysis of the PNMR spectrum shows that the synthesized product is consistent with the expected target structure.

[0025] A method for preparing a novel phosphorus-containing nitrogen oxide flame retardant includes the following steps: S1. Under nitrogen protection, add diphenylphosphonic hydroxylamine, tetrahydrofuran and triethylamine to a four-necked flask equipped with a thermometer, stirrer, condenser and constant pressure dropping funnel, and stir until completely dissolved. S2. Slowly add a certain amount of diphenylphosphine chloride solution through a constant pressure dropping funnel. After the addition is complete, gradually raise the temperature to 40-50℃ and react for 1.5-2.5h. Then raise the temperature to 70-80℃ and reflux for 7.5-8.5h. S3. After the reaction is complete, cool to room temperature, filter the reaction solution to remove the byproduct triethylamine hydrochloride, and then concentrate the solution obtained by vacuum evaporation to obtain a solid product. S4. The obtained solid product was recrystallized with ethyl acetate and dried in a vacuum oven at 75-85℃ for 7.5-8.5h to obtain a novel phosphorus-containing nitrogen oxide flame retardant N-[(diphenylphosphino)oxy]-P,P-diphenylphosphineamide. The molar ratio of diphenylphosphonohydroxylamine, diphenylphosphinochloride, and triethylamine is 1:1:1.1; In step S2, the heating reflux treatment refers to heating the reaction at the boiling point temperature of tetrahydrofuran, which is used as a solvent. In step S3, the byproduct triethylamine hydrochloride removed by the filtered reaction solution is in solid form.

[0026] Specifically, the preparation method of the novel phosphorus-containing nitrogen oxide flame retardant is as follows: A thermometer, mechanical stirrer, nitrogen protection device, reflux condenser, and constant-pressure dropping funnel are installed on a 500mL dry four-necked flask. The reactor is purged multiple times with dry nitrogen to ensure an anhydrous and oxygen-free reaction environment. 23.32g of diphenylphosphine hydroxylamine, 160g of tetrahydrofuran, and 10.12g of triethylamine are added to the four-necked flask and stirred thoroughly at room temperature until completely dissolved. 23.66g of diphenylphosphine chloride is placed in the constant-pressure dropping funnel and slowly added dropwise to the reaction system; a white solid is formed during the addition. After the addition is complete, the temperature is raised to 40-50℃ and the reaction is carried out for 2 hours, followed by continued reflux for 8 hours. After the reaction was completed, the mixture was cooled to room temperature and the reaction solution was filtered to remove the byproduct triethylamine hydrochloride. The solution obtained by vacuum evaporation was concentrated and the crude solid product was recrystallized with ethyl acetate. Then it was dried in a vacuum oven at 80°C for 8 hours to obtain the novel phosphorus-containing nitrogen oxide flame retardant N-[(diphenylphosphoyl)oxy]-P,P-diphenylphosphineamide (NDPA).

[0027] A novel phosphorus-containing nitrogen oxide flame retardant is used in the preparation of flame-retardant thermoplastic polyurethane composite materials.

[0028] Test experiment: Performance Analysis of Flame-Retardant TPU Materials Sample preparation: The synthesized product N-[(diphenylphosphino)oxy]-P,P-diphenylphosphineamide (NDPA) was dried and then melt-blended with thermoplastic polyurethane (TPU) in a torque rheometer at a specific mass ratio for 10 min. The temperature of each heating zone was 185℃, and the rotation speed was 60 r / min. After the flame-retardant TPU composite material was uniformly mixed in the chamber, it was transferred to a flat vulcanizing machine and hot-pressed at 185℃ and 10 MPa. The molded material was then cut into standard test strips for subsequent performance testing.

[0029] Flame retardant performance test of TPU composite material: Test steps: The flame retardant properties of TPU materials were evaluated using vertical burning (UL-94) and limiting oxygen index (LOI) testing methods (see Table 1 for data details).

[0030] Pure TPU is highly flammable, producing a large amount of flammable droplets during combustion, with an LOI value of only 19.8% and no vertical burning rating. The introduction of the flame retardant NDPA significantly improves the flame retardant properties of TPU flame-retardant composites.

[0031] When the addition of NDPA reached 1wt%, the TPU / NDPA1 composite material passed the UL-94V-2 standard, and the LOI value increased to 29.8%. When the NDPA content was increased to 2wt%, the TPU / NDPA2 composite material successfully passed the UL-94V-0 level with an LOI value as high as 30.1%.

[0032] The above-mentioned performance is mainly due to the introduction of the NO structure, which enhances the gas-phase inhibition effect of traditional phosphorus-nitrogen flame retardants. Therefore, NDPA exhibits excellent flame-retardant efficiency in thermoplastic polyurethane materials. Furthermore, the tensile strength and elongation at break of pure TPU are 29.3 MPa and 1077.2%, respectively. When the NDPA content reaches 2 wt%, the tensile strength and elongation at break of TPU / NDPA2 are 26.9 MPa and 1016.8%, respectively, with mechanical properties essentially equivalent to pure TPU while maintaining good transparency. This provides an effective approach for developing flame-retardant TPU composite materials with excellent comprehensive performance.

[0033] Table 1: Vertical burning and limiting oxygen index test data of TPU / NDPA composite materials

[0034] Summarize: Compared with traditional phosphorus-nitrogen type flame retardants, the synthesized novel phosphorus-nitrogen oxide flame retardant NDPA has the following significant advantages in TPU composites: NDPA is synthesized using a one-pot method, which is simple, allows for solvent recycling, has high yield, and is environmentally friendly, making it suitable for industrial production. The decomposition temperature of NDPA is significantly higher than that of TPU, which is beneficial to processing stability. NDPA contains both PC and NO groups. During combustion, the NO group releases nitrogen oxide free radicals, which, together with the phosphorus-containing free radicals generated by the PC bond, can effectively quench highly reactive free radicals such as H·, O·, and HO· generated during TPU combustion, thus playing an excellent gas-phase inhibition role. NDPA contains PO bonds in its molecular structure, which produce phosphoric acid compounds during combustion. These compounds promote the dehydration and carbonization of TPU materials, forming a dense and expanded carbon layer that acts as a barrier for thermal and oxygen insulation in the condensed phase. High flame-retardant efficiency NDPA significantly reduces the need for large-scale introduction of flame retardants, minimizing the negative impact on the mechanical properties of the TPU matrix. Furthermore, its aromatic ring structure endows it with good compatibility with TPU materials, better balancing the flame-retardant and mechanical properties of TPU composites while maintaining good transparency. In summary, the structural design of the phosphorus-nitrogen oxide flame retardant NDPA provides an effective new strategy for obtaining high-performance flame-retardant TPU composites.

Claims

1. A novel phosphorus-containing nitrogen oxide flame retardant, characterized in that, The synthesis process and structure of a novel phosphorus-containing nitrogen oxide flame retardant are shown below: 。 2. A method for preparing a novel phosphorus-containing nitrogen oxide flame retardant as described in claim 1, characterized in that, Includes the following steps: S1. Under nitrogen protection, add diphenylphosphonic hydroxylamine, tetrahydrofuran and triethylamine to a four-necked flask equipped with a thermometer, stirrer, condenser and constant pressure dropping funnel, and stir until completely dissolved. S2. Slowly add a certain amount of diphenylphosphine chloride solution through a constant pressure dropping funnel. After the addition is complete, gradually raise the temperature to 40-50℃ and react for 1.5-2.5h. Then raise the temperature to 70-80℃ and reflux for 7.5-8.5h. S3. After the reaction is complete, cool to room temperature, filter the reaction solution to remove the byproduct triethylamine hydrochloride, and then concentrate the solution obtained by vacuum evaporation to obtain a solid product. S4. The obtained solid product is recrystallized with ethyl acetate and dried in a vacuum oven at 75-85℃ for 7.5-8.5h to obtain a novel phosphorus-containing nitrogen oxide flame retardant N-[(diphenylphosphino)oxy]-P,P-diphenylphosphineamide.

3. The method for preparing a novel phosphorus-containing nitrogen oxide flame retardant according to claim 2, characterized in that, The molar ratio of diphenylphosphonohydroxylamine, diphenylphosphonyl chloride and triethylamine is 1:1:1.

1.

4. The method for preparing a novel phosphorus-containing nitrogen oxide flame retardant according to claim 2, characterized in that, In step S2, the heating reflux treatment refers to heating the reaction at the boiling point temperature of tetrahydrofuran, which is used as a solvent.

5. The preparation method of a novel phosphorus-containing nitrogen oxide flame retardant according to claim 2, characterized in that, In step S3, the byproduct triethylamine hydrochloride removed by the filtered reaction solution is in solid form.

6. A novel phosphorus-containing nitrogen oxide flame retardant according to claim 1, characterized in that, It is used in the preparation of flame-retardant thermoplastic polyurethane composite materials.

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