A phosphorus-nitrogen type polyionic liquid flame retardant, its preparation method and application

Abstract

This invention belongs to the field of flame retardant synthesis technology, specifically relating to a phosphorus-nitrogen type polyionic liquid flame retardant, its preparation method, and its application. This invention utilizes the free radical copolymerization of olefin-based phosphonic acid, hydroxyl-terminated acrylate, and acryloyloxybenzophenone. On one hand, it introduces abundant terminal hydroxyl groups into the polyionic liquid backbone. These hydroxyl groups can form strong hydrogen bonds with the urethane groups or ether bonds of TPU, significantly improving the dispersion stability of the flame retardant in the matrix and completely solving the problem of easy migration and precipitation of traditional ionic liquid flame retardants. On the other hand, by controlling the feed ratio of olefin-based phosphonic acid and hydroxyl-terminated acrylate monomers, the alkyl imidazole chain length, and the neutralization degree of phosphate groups, the phosphorus-nitrogen ratio of the flame retardant can be precisely adjusted, optimizing the balance between char formation and inert gas release during combustion. This allows the material to achieve a UL-94 vertical flammability rating of V-2 while increasing the limiting oxygen index by more than 20%, and with optimal optimization, it can reach V-0.

Description

Technical Field

[0001] This invention belongs to the field of flame retardant synthesis technology, specifically relating to a phosphorus-nitrogen type polyionic liquid flame retardant, its preparation method, and its application. Background Technology

[0002] Thermoplastic polyurethane (TPU), a special polymer material that combines the excellent elasticity of rubber with the superior processing performance of plastics, has deeply penetrated into many high-end manufacturing fields such as wire and cable sheathing, automotive interior components, electronic device packaging, and medical and health care, thanks to its wear resistance, oil resistance, high toughness, and recyclability. It has become an indispensable key basic material in the modern industrial system. However, the inherent chemical structural defects of TPU materials cause its limiting oxygen index (LOI) to hover only in the low range of 18% to 20%. This means that it is very easy to ignite when exposed to a fire source. This inherent flammability makes it difficult to meet the stringent flame retardant safety standards of aerospace, rail transportation, and high-end electronic equipment scenarios, thus limiting its broader application prospects.

[0003] Faced with this challenge, existing flame retardant modification technologies all have significant limitations: traditional halogenated flame retardants, although highly efficient, release large amounts of toxic fumes and corrosive gases during combustion and have been gradually phased out; while phosphorus-nitrogen flame retardants, which have attracted much attention, theoretically possess a synergistic effect of dual flame retardancy in both the gas and condensed phases, in practical applications, the molar ratio of phosphorus and nitrogen elements is difficult to precisely control, resulting in insufficient density and thermal insulation of the char layer. Furthermore, these inorganic or low-molecular-weight organic flame retardants have poor compatibility with the polar TPU matrix, easily forming stress concentration points within the matrix, causing a precipitous drop in the material's mechanical properties. This presents a trade-off between "increased flame retardant efficiency and deteriorated mechanical properties," seriously affecting the long-term durability and reliability of the products.

[0004] While ionic liquid flame retardants, which have emerged in recent years, are considered a new direction due to their extremely low volatility, high structural designability, and potential for high-efficiency flame retardancy, they generally suffer from insufficient thermal stability and are prone to migration and precipitation during high-temperature processing or use, significantly compromising the long-term reliability of the materials. Even more problematic is that most flame retardant strategies fall into the "dosage paradox": high dosages, while barely achieving flame retardant ratings, severely deteriorate the melt flowability and processing window of TPU, even leading to material embrittlement; while low dosages, while maintaining processing performance, fail to provide sufficient fire protection. Therefore, the current core bottleneck lies in how to break through traditional thinking and, under the premise of strictly maintaining the high strength, high toughness, and excellent processing performance of TPU, develop a novel phosphorus-nitrogen synergistic flame retardant system through molecular structure design that combines high-efficiency flame retardancy, excellent matrix compatibility, low smoke and non-toxicity, and long-term thermal stability. This not only requires solving the problem of precise matching of phosphorus and nitrogen ratio and optimization of char quality, but also overcoming the interfacial compatibility problem between flame retardant and polymer matrix, so as to achieve simultaneous improvement of flame retardant performance and mechanical properties. This has become a key scientific problem and technical barrier restricting high-performance TPU materials from moving towards the next generation of high-end applications, and it is also a strategic high ground that needs to be overcome in the future field of polymer flame retardancy.

[0005] Chinese patent application (CN119751500A) discloses a phosphorus-nitrogen synergistic ionic liquid flame retardant, its preparation method, and its application. However, its preparation process involves high reaction temperatures (130-150℃) and reliance on toxic organic solvents such as carbon tetrachloride and chloroform, resulting in high energy consumption and an environmentally unfriendly process. In terms of product performance, the resulting small-molecule flame retardant is prone to migration and precipitation, the unadjustable phosphorus-nitrogen ratio limits the optimization of flame retardant performance, and its poor interfacial compatibility with the polymer matrix not only affects the mechanical properties of the product but also lacks consideration for environmental durability. Summary of the Invention

[0006] The purpose of this invention is to address the above-mentioned problems by providing a phosphorus-nitrogen type polyionic liquid flame retardant, which solves the technical problems of traditional ionic liquid flame retardants such as easy migration and precipitation, poor thermal stability, poor compatibility with TPU polyurethane matrix, and the inability of existing flame retardants to meet the stringent requirements of thermoplastic polyurethane materials for UV resistance, stability and comprehensive performance in high-end applications.

[0007] The above-mentioned objective of the present invention is achieved by the following scheme:

[0008] A phosphorus-nitrogen type polyionic liquid flame retardant, said polyionic liquid flame retardant comprising a structure as shown in Formula I or Formula II:

[0009] ;

[0010] (I)

[0011] .

[0012] (II)

[0013] Among them, R1, R2, and R3 are independently selected from hydrogen, methyl, and ethyl; R4 is selected from hydrogen, methyl, and phenyl; R5 is selected from hydrogen and methyl; R6 is an alkane group with ≤4 carbon atoms; x:y:z = (2-3):(4-12):1.

[0014] This invention introduces a benzophenone group with a specific structure into the main chain of a flame retardant molecule via covalent bonding. This benzophenone group acts as a highly efficient light stabilizer, its mechanism of action being the strong absorption of ultraviolet light with wavelengths of 290–400 nm. Through the rapid and reversible opening and closing of intramolecular hydrogen bonds, the absorbed light energy is converted into harmless heat energy dissipation, effectively blocking the attack of ultraviolet light on the TPU polymer main chain, preventing photo-oxidative degradation, chain breakage, and yellowing. This endows the TPU composite material with durable and stable resistance to ultraviolet aging. Furthermore, the benzophenone group itself possesses high thermal stability and aromatic ring rigidity; its introduction may help increase the thermal decomposition temperature of the copolymer, thereby providing stronger thermal stability during TPU processing and use, complementing the flame retardant effect of the phosphorus / nitrogen flame retardant system in both the gas and condensed phases.

[0015] The present invention also provides a method for preparing the above-mentioned phosphorus-nitrogen type polyionic liquid flame retardant, the method comprising the following steps:

[0016] S1. Dissolve olefinic phosphonic acid, hydroxyl-terminated acrylate, and acryloyloxybenzophenone in solvents to obtain phosphonic acid solution, acrylate solution, and benzophenone solution, respectively.

[0017] S2. Then, the acrylate solution and benzophenone solution are added to the phosphonic acid solution, and an initiator is added to carry out a copolymerization reaction to obtain the copolymer product;

[0018] S3. Redissolve the copolymer in a solvent to obtain a copolymer solution; dissolve the alkylimidazolium in a solvent to obtain an alkylimidazolium solution;

[0019] S4. Add the alkylimidazolium solution dropwise to the copolymer product solution to carry out the ionization reaction and obtain the polyionic liquid flame retardant product.

[0020] In the above-mentioned method for preparing a phosphorus-nitrogen type polyionic liquid flame retardant, in step S1, the olefinic phosphonic acid is at least one of vinylphosphonic acid, 1-styrylphosphonic acid and 1-methylvinylphosphonic acid;

[0021] And / or the hydroxyl-terminated acrylate is at least one of hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, 1-(hydroxymethyl)propyl acrylate, 2-hydroxyisopropyl acrylate and 2-hydroxypropyl acrylate;

[0022] And / or acryloyloxybenzophenone is at least one of 2-hydroxy-4-(methacryloyloxy)benzophenone and 2-hydroxy-4-(acryloyloxy)benzophenone.

[0023] In the above-mentioned method for preparing a phosphorus-nitrogen type polyionic liquid flame retardant, in step S1, the molar ratio of terminal hydroxyl acrylate, olefinic phosphonic acid and acryloyloxybenzophenone is (2-3):(4-12):1.

[0024] Preferably, the initiator includes at least one of azobisisobutyronitrile (AIBN), azobisisoheptanenitrile (ABVN), benzoyl peroxide (BPO), tert-butyl peroxypentanoate (BPP), and di-tert-butyl peroxide (DTBP).

[0025] Preferably, the solvent includes at least one of ethanol, isopropanol, and n-propanol.

[0026] In the above-mentioned method for preparing a phosphorus-nitrogen type polyionic liquid flame retardant, in step S2, the copolymerization reaction temperature is 60-80℃ and the time is 6-10h.

[0027] In the above-mentioned method for preparing a phosphorus-nitrogen type polyionic liquid flame retardant, in step S3, the alkyl imidazole is at least one of N-butylimidazolium, N-propylimidazolium, and N-ethylimidazolium.

[0028] In the above-mentioned method for preparing a phosphorus-nitrogen type polyionic liquid flame retardant, in step S4, the molar ratio of alkylimidazolium to phosphate groups in the copolymer is 1:(0.5-5).

[0029] Preferably, in step S4, the amount of alkylimidazolium added is determined by the degree of neutralization n of the phosphate groups in the copolymer, where n is 1 or 2. A degree of neutralization of 1 indicates that one of the phosphate groups participates in the ionization salt formation reaction with the N atom in the alkylimidazolium; a degree of neutralization of 2 indicates that both phosphate groups participate in the ionization salt formation reaction with the N atom in the alkylimidazolium.

[0030] In the above-mentioned method for preparing a phosphorus-nitrogen type polyionic liquid flame retardant, in step S4, the reaction temperature of the ionization reaction is 40-60℃, and the reaction time is 3-6h.

[0031] The present invention also provides a TPU polyurethane flame retardant material, wherein the TPU polyurethane flame retardant material comprises the above-mentioned phosphorus-nitrogen type polyionic liquid flame retardant or the phosphorus-nitrogen type polyionic liquid flame retardant prepared by the above method.

[0032] Preferably, the TPU flame retardant material contains 5-15 wt% of the above-mentioned phosphorus-nitrogen type polyionic liquid flame retardant.

[0033] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0034] 1. The preparation method of the phosphorus-nitrogen type polyionic liquid flame retardant of this invention, through the innovative use of a "polymerization followed by salt formation" synthesis route, not only achieves flexible control of the phosphorus / nitrogen ratio in the polyionic liquid structure (the degree of neutralization n can be precisely adjusted in the range of 1 to 2), but also achieves simultaneous optimization of the interfacial compatibility between the flame retardant and the TPU matrix and improvement of UV resistance and weather resistance. This design has the benefit of "killing three birds with one stone": enhancing the synergistic flame retardant efficiency of the flame retardant system on the TPU matrix in both the gas and condensed phases while improving its environmental weather resistance, and maintaining the original mechanical strength and toughness of the thermoplastic polyurethane material.

[0035] 2. This invention utilizes the free radical copolymerization of olefinic phosphonic acid, hydroxyl-terminated acrylate, and acryloyloxybenzophenone. On one hand, it introduces abundant terminal hydroxyl groups into the polyionic liquid backbone. These hydroxyl groups can form strong hydrogen bonds with the urethane groups (-NHCOO-) or ether bonds (-O-) of TPU, significantly improving the dispersion stability of the flame retardant in the matrix and completely solving the problem of easy migration and precipitation of traditional ionic liquid flame retardants. On the other hand, by controlling the feed ratio of olefinic phosphonic acid and hydroxyl-terminated acrylate monomers, the alkyl imidazole chain length, and the neutralization degree of phosphate groups (n=1 or 2), the phosphorus-nitrogen ratio of the flame retardant can be precisely adjusted, optimizing the balance between char formation and inert gas release during combustion. This results in a material with a limiting oxygen index (LOI) increase of over 20% while achieving a UL-94 vertical flammability rating of V-2, and with optimal optimization, a V-0 rating. Furthermore, the phosphorus-nitrogen type polyionic liquid flame retardant of this invention significantly improves the UV resistance of TPU materials by introducing benzophenone groups, enhancing their environmental weather resistance.

[0036] 3. The synthesis process of this invention is green and environmentally friendly, with mild reaction conditions (copolymerization at 60-80℃, ionization at 40-60℃). The resulting polyionic liquid flame retardant has excellent thermal stability, with a char residue rate of over 33.2% at 600℃. It also has good processability when blended with TPU (5-15wt% addition). While significantly improving flame retardant performance, the tensile strength and elongation at break decrease by less than 20%, and after optimization, the decrease is less than 10%. Attached Figure Description

[0037] Figure 1The infrared characteristic peaks of the flame retardant products prepared in Examples 1 and 2 are shown. Example 1: VHEHA-1; Example 2: VHEHA-2.

[0038] Figure 2 Thermal weight loss behavior of the flame retardant products prepared in Examples 1 and 2 in a nitrogen atmosphere; Example 1: VHEHA-1; Example 2: VHEHA-2. Detailed Implementation

[0039] The technical solution of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the present invention. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art.

[0040] Example 1:

[0041] The preparation method of the phosphorus-nitrogen type polyionic liquid flame retardant in this embodiment includes the following steps:

[0042] S1: Take 0.04 mol of vinylphosphonic acid (VPA) in a 100 ml flask and dissolve it in 30 ml of ethanol to obtain a VPA solution;

[0043] S2. Take 0.01 mol of hydroxyethyl methacrylate (HEMA) and 0.005 mol of 2-hydroxy-4-(acryloyloxy)benzophenone (HABP), and dissolve them in 30 ml of ethanol;

[0044] S3. Then, the mixed solution of HEMA and HABP is slowly added to the VPA solution to obtain a mixed solution.

[0045] S4. Prepare a 2wt% concentration (relative to the total amount of VPA, HEMA, and HABP monomers) azobisisobutyronitrile (AIBN) ethanol solution, and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80℃ and react for 10 hours under a nitrogen atmosphere.

[0046] S5. After the reaction is complete, the product is poured into a large amount of petroleum ether to settle. After filtration and washing several times, it is dried under vacuum at 45°C to constant weight to obtain the ternary copolymer (number average molecular weight of 15000 g / mol).

[0047] S6: Dissolve approximately 0.024 mol of the ternary copolymer product with phosphate groups in ethanol to obtain a copolymer product solution; then dissolve 0.024 mol of N-ethylimidazole in ethanol to obtain an N-ethylimidazole solution; slowly add the N-ethylimidazole solution dropwise to the copolymer product solution through a constant pressure dropping funnel. After the addition is complete, heat to 60℃ and stir the reaction for 6 hours.

[0048] The polyionic liquid flame retardant product was obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0049] ;

[0050] Where R1 and R2 are hydrogen, R3 is methyl, R4 is hydrogen, R5 is hydrogen, and R6 is ethyl; x:y:z = (2:8:1).

[0051] Example 2:

[0052] The preparation method of the phosphorus-nitrogen type polyionic liquid flame retardant in this embodiment includes the following steps:

[0053] S1: Take 0.04 mol of vinylphosphonic acid (VPA) in a 100 ml flask and dissolve it in 30 ml of ethanol to obtain a VPA solution;

[0054] S2. Take 0.01 mol of hydroxyethyl methacrylate (HEMA) and 0.005 mol of 2-hydroxy-4-(acryloyloxy)benzophenone (HABP), and dissolve them in 30 ml of ethanol;

[0055] S3. Then, the mixed solution of HEMA and HABP is slowly added to the VPA solution to obtain a mixed solution.

[0056] S4. Prepare a 2wt% concentration (relative to the total amount of VPA, HEMA, and HABP monomers) AIBN ethanol solution, and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80℃ and react for 10 hours under a nitrogen atmosphere.

[0057] S5. After the reaction is complete, the product is poured into a large amount of petroleum ether to settle. After filtration and washing several times, it is dried under vacuum at 45°C to constant weight to obtain the ternary copolymer (number average molecular weight of 15000 g / mol).

[0058] S6: Dissolve approximately 0.024 mol of the ternary copolymer product with phosphate groups in ethanol to obtain a copolymer product solution; then dissolve 0.012 mol of N-ethylimidazole in ethanol to obtain an N-ethylimidazole solution; slowly add the N-ethylimidazole solution dropwise to the copolymer product solution through a constant pressure dropping funnel. After the addition is complete, heat to 60°C and stir the reaction for 6 hours.

[0059] The polyionic liquid flame retardant product was obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0060] ;

[0061] Where R1 and R2 are hydrogen, R3 is methyl, R4 is hydrogen, R5 is hydrogen, and R6 is ethyl; x:y:z = (2:8:1).

[0062] Example 3:

[0063] S1: Take 0.02 mol of vinylphosphonic acid (VPA) in a 100 ml flask and dissolve it in 30 ml of ethanol to obtain a VPA solution;

[0064] S2. Take 0.01 mol of hydroxyethyl methacrylate (HEMA) and 0.005 mol of 2-hydroxy-4-(acryloyloxy)benzophenone (HABP), and dissolve them in 30 ml of ethanol;

[0065] S3. Then, the mixed solution of HEMA and HABP is slowly added to the VPA solution to obtain a mixed solution.

[0066] S4. Prepare a 2wt% concentration (relative to the total amount of VPA, HEMA, and HABP monomers) AIBN ethanol solution, and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80℃ and react for 10 hours under a nitrogen atmosphere.

[0067] S5. After the reaction is complete, the product is poured into a large amount of petroleum ether to settle. After filtration and washing several times, it is dried under vacuum at 45°C to constant weight to obtain the ternary copolymer (number average molecular weight of 12000 g / mol).

[0068] S6: Dissolve approximately 0.016 mol of the ternary copolymer with phosphate groups in ethanol to obtain a copolymer solution; then dissolve 0.016 mol of N-ethylimidazole in ethanol to obtain an N-ethylimidazole solution; slowly add the N-ethylimidazole solution dropwise to the copolymer solution through a constant pressure dropping funnel. After the addition is complete, heat to 60°C and stir the reaction for 6 hours.

[0069] The polyionic liquid flame retardant product was obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0070] ;

[0071] Where R1 and R2 are hydrogen, R3 is methyl, R4 is hydrogen, R5 is hydrogen, and R6 is ethyl; x:y:z = (2:4:1).

[0072] Example 4:

[0073] S1: Take 0.06 mol of vinylphosphonic acid (VPA) in a 100 ml flask and dissolve it in 30 ml of ethanol to obtain a VPA solution;

[0074] S2. Take 0.015 mol of hydroxyethyl methacrylate (HEMA) and 0.005 mol of 2-hydroxy-4-(acryloyloxy)benzophenone (HABP), and dissolve them in 30 ml of ethanol;

[0075] S3. Then, the mixed solution of HEMA and HABP is slowly added to the VPA solution to obtain a mixed solution.

[0076] S4. Prepare a 2wt% concentration (relative to the total amount of VPA, HEMA, and HABP monomers) AIBN ethanol solution, and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80℃ and react for 10 hours under a nitrogen atmosphere.

[0077] S5. After the reaction is complete, the product is poured into a large amount of petroleum ether to settle. After filtration and washing several times, it is dried under vacuum at 45°C to constant weight to obtain the ternary copolymer (number average molecular weight of 18000 g / mol).

[0078] S6. Dissolve approximately 0.024 mol of the ternary copolymer product with phosphate groups in ethanol to obtain a copolymer product solution; then dissolve 0.024 mol of N-ethylimidazole in ethanol to obtain an N-ethylimidazole solution. Slowly add the N-ethylimidazole solution dropwise to the copolymer product solution through a constant pressure dropping funnel. After the addition is complete, heat to 60°C and stir the reaction for 6 hours.

[0079] The polyionic liquid flame retardant product was obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0080] ;

[0081] Where R1 and R2 are hydrogen, R3 is methyl, R4 is hydrogen, R5 is hydrogen, and R6 is ethyl; x:y:z = (3:12:1).

[0082] Example 5:

[0083] S1: Take 0.02 mol of vinylphosphonic acid (VPA) in a 100 ml flask and dissolve it in 30 ml of ethanol to obtain a VPA solution;

[0084] S2. Take 0.01 mol of hydroxyethyl methacrylate (HEMA) and 0.005 mol of 2-hydroxy-4-(acryloyloxy)benzophenone (HABP), and dissolve them in 30 ml of ethanol;

[0085] S3. Then, the mixed solution of HEMA and HABP is slowly added to the VPA solution to obtain a mixed solution.

[0086] S4. Prepare a 2wt% concentration (relative to the total amount of VPA, HEMA, and HABP monomers) AIBN ethanol solution, and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80℃ and react for 10 hours under a nitrogen atmosphere.

[0087] S5. After the reaction is complete, the product is poured into a large amount of petroleum ether to settle. After filtration and washing several times, it is dried under vacuum at 45°C to constant weight to obtain the ternary copolymer (number average molecular weight of 12000 g / mol).

[0088] S6: Dissolve approximately 0.016 mol of the ternary copolymer product with phosphate groups in ethanol to obtain a copolymer product solution; then dissolve 0.008 mol of N-ethylimidazole in ethanol to obtain an N-ethylimidazole solution; slowly add the N-ethylimidazole solution dropwise to the copolymer product solution through a constant pressure dropping funnel. After the addition is complete, heat to 60°C and stir the reaction for 6 hours.

[0089] The polyionic liquid flame retardant product was obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0090] ;

[0091] Where R1 and R2 are hydrogen, R3 is methyl, R4 is hydrogen, R5 is hydrogen, and R6 is ethyl; x:y:z = (2:4:1).

[0092] Example 6:

[0093] S1: Take 0.06 mol of vinylphosphonic acid (VPA) in a 100 ml flask and dissolve it in 30 ml of ethanol to obtain a VPA solution;

[0094] S2. Take 0.015 mol of hydroxyethyl methacrylate (HEMA) and 0.005 mol of 2-hydroxy-4-(acryloyloxy)benzophenone (HABP), and dissolve them in 30 ml of ethanol;

[0095] S3. Then, the mixed solution of HEMA and HABP is slowly added to the VPA solution to obtain a mixed solution.

[0096] S4. Prepare a 2wt% concentration (relative to the total amount of VPA, HEMA, and HABP monomers) AIBN ethanol solution, and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80℃ and react for 10 hours under a nitrogen atmosphere.

[0097] S5. After the reaction is complete, the product is poured into a large amount of petroleum ether to settle. After filtration and washing several times, it is dried under vacuum at 45°C to constant weight to obtain the ternary copolymer (number average molecular weight of 18000 g / mol).

[0098] S6: Dissolve approximately 0.024 mol of the ternary copolymer product with phosphate groups in ethanol to obtain a copolymer product solution; then dissolve 0.012 mol of N-ethylimidazole in ethanol to obtain an N-ethylimidazole solution; slowly add the N-ethylimidazole solution dropwise to the copolymer product solution through a constant pressure dropping funnel. After the addition is complete, heat to 60°C and stir the reaction for 6 hours.

[0099] The polyionic liquid flame retardant product was obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0100] ;

[0101] Where R1 and R2 are hydrogen, R3 is methyl, R4 is hydrogen, R5 is hydrogen, and R6 is ethyl; x:y:z = (3:12:1).

[0102] Example 7:

[0103] S1: Take 0.04 mol of vinylphosphonic acid (VPA) in a 100 ml flask and dissolve it in 30 ml of ethanol to obtain a VPA solution;

[0104] S2. Take 0.01 mol of hydroxypropyl methacrylate (HPMA) and 0.005 mol of 2-hydroxy-4-(acryloyloxy)benzophenone (HABP), and dissolve them in 30 ml of ethanol;

[0105] S3. Then slowly add the mixed solution of HPMA and HABP to the VPA solution;

[0106] S4. Prepare a 2wt% concentration (relative to the total amount of VPA, HPMA, and HABP monomers) AIBN ethanol solution, and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80℃ and react for 10 hours under a nitrogen atmosphere.

[0107] S5. After the reaction is complete, the product is poured into a large amount of petroleum ether to settle. After filtration and washing several times, it is dried under vacuum at 45°C to constant weight to obtain the ternary copolymer (number average molecular weight of 15000 g / mol).

[0108] S6: Dissolve approximately 0.022 mol of the ternary copolymer product with phosphate groups in ethanol to obtain a copolymer product solution; then dissolve 0.022 mol of N-ethylimidazole in ethanol to obtain an N-ethylimidazole solution; slowly add the N-ethylimidazole solution dropwise to the copolymer product solution through a constant pressure dropping funnel. After the addition is complete, heat to 60℃ and stir the reaction for 6 hours.

[0109] The polyionic liquid flame retardant product was obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0110] ;

[0111] Wherein, R1 is hydrogen, R2 and R3 are methyl, R4 is hydrogen, R5 is hydrogen, and R6 is ethyl; x:y:z = (2:8:1).

[0112] Example 8:

[0113] S1: Take 0.04 mol of 1-methylvinylphosphonic acid (MVPA) in a 100 ml flask and dissolve it in 30 ml of ethanol to obtain an MVPA solution;

[0114] S2. Take 0.01 mol of hydroxyethyl methacrylate (HEMA) and 0.005 mol of 2-hydroxy-4-(acryloyloxy)benzophenone (HABP), and dissolve them in 30 ml of ethanol;

[0115] S3. Then, the mixed solution of HEMA and HABP is slowly added to the MVPA solution to obtain a mixed solution.

[0116] S4. Prepare a 2wt% concentration (relative to the total amount of MVPA, HEMA, and HABP monomers) AIBN ethanol solution, and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80℃ and react for 10 hours under a nitrogen atmosphere.

[0117] S5. After the reaction is complete, the product is poured into a large amount of petroleum ether to settle. After filtration and washing several times, it is dried under vacuum at 45°C to constant weight to obtain the ternary copolymer (number average molecular weight of 15000 g / mol).

[0118] S6: Dissolve approximately 0.022 mol of the ternary copolymer product with phosphate groups in ethanol to obtain a copolymer product solution; then dissolve 0.022 mol of N-ethylimidazole in ethanol to obtain an N-ethylimidazole solution; slowly add the N-ethylimidazole solution dropwise to the copolymer product solution through a constant pressure dropping funnel. After the addition is complete, heat to 60℃ and stir the reaction for 6 hours.

[0119] The polyionic liquid flame retardant product was obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0120] ;

[0121] Where R1 and R2 are hydrogen, R3 is methyl, R4 is methyl, R5 is hydrogen, and R6 is ethyl; x:y:z = (2:8:1).

[0122] Example 9:

[0123] S1: Take 0.04 mol of 1-methylvinylphosphonic acid (MVPA) in a 100 ml flask and dissolve it in 30 ml of ethanol to obtain an MVPA solution;

[0124] S2. Take 0.01 mol of hydroxyethyl methacrylate (HEMA) and 0.005 mol of 2-hydroxy-4-(methacryloyloxy)benzophenone (HMABP) and dissolve them in 30 ml of ethanol;

[0125] S3. Then, the mixed solution of HEMA and HMABP is slowly added to the MVPA solution to obtain a mixed solution;

[0126] S4. Prepare a 2wt% concentration (relative to the total amount of MVPA, HEMA, and HMABP monomers) AIBN ethanol solution, and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80℃ and react for 10 hours under a nitrogen atmosphere.

[0127] S5. After the reaction is complete, the product is poured into a large amount of petroleum ether to settle. After filtration and washing several times, it is dried under vacuum at 45°C to constant weight to obtain the ternary copolymer (number average molecular weight of 15000 g / mol).

[0128] S6: Dissolve approximately 0.022 mol of the ternary copolymer product with phosphate groups in ethanol to obtain a copolymer product solution; then dissolve 0.022 mol of N-ethylimidazole in ethanol to obtain an N-ethylimidazole solution; slowly add the N-ethylimidazole solution dropwise to the copolymer product solution through a constant pressure dropping funnel. After the addition is complete, heat to 60℃ and stir the reaction for 6 hours.

[0129] The polyionic liquid flame retardant product was obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0130] ;

[0131] Where R1 and R2 are hydrogen, R3 is methyl, R4 is hydrogen, R5 is methyl, and R6 is ethyl; x:y:z = (2:8:1).

[0132] Example 10:

[0133] S1: Take 0.04 mol of vinylphosphonic acid (VPA) in a 100 ml flask and dissolve it in 30 ml of ethanol to obtain a VPA solution;

[0134] S2. Take 0.01 mol of hydroxyethyl methacrylate (HEMA) and 0.005 mol of 2-hydroxy-4-(acryloyloxy)benzophenone (HABP), and dissolve them in 30 ml of ethanol;

[0135] S3. Then, the mixed solution of HEMA and HABP is slowly added to the VPA solution to obtain a mixed solution.

[0136] S4. Prepare a 2wt% AIBN ethanol solution (relative to the total amount of VPA, HEMA, and HABP monomers), and slowly add it dropwise to the above mixed solution using a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80℃ and react for 10 hours under a nitrogen atmosphere.

[0137] S5. After the reaction is complete, the product is poured into a large amount of petroleum ether to settle. After filtration and washing several times, it is dried under vacuum at 45°C to constant weight to obtain the ternary copolymer (number average molecular weight of 15000 g / mol).

[0138] S6: Dissolve approximately 0.022 mol of the ternary copolymer product with phosphate groups in ethanol to obtain a copolymer product solution; then dissolve 0.022 mol of N-butylimidazole in ethanol to obtain an N-butylimidazole solution; slowly add the N-butylimidazole solution dropwise to the copolymer product solution through a constant pressure dropping funnel. After the addition is complete, heat to 60℃ and stir the reaction for 6 hours.

[0139] The polyionic liquid flame retardant product was obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0140] ;

[0141] Where R1 and R2 are hydrogen, R3 is methyl, R4 is methyl, R5 is hydrogen, and R6 is butyl; x:y:z = (2:8:1).

[0142] Comparative Example 1:

[0143] S1: Dissolve 0.04 mol of vinylphosphonic acid (VPA) in 30 mL of ethanol in a 100 mL flask. Dissolve 0.01 mol of hydroxyethyl methacrylate (HEMA) in 30 mL of ethanol, and then slowly add the HEMA solution to the VPA solution. Prepare a 2 wt% AIBN ethanol solution (relative to the total amount of VPA and HEMA monomers) and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80 °C and react under a nitrogen atmosphere for 10 h. After petroleum ether precipitation, filtration, washing, and vacuum drying, the copolymer of VPA and HEMA (number average molecular weight 13000 g / mol) is obtained.

[0144] S2: Approximately 0.028 mol of the copolymer product with acid groups was redissolved in ethanol. 0.028 mol of N-butylimidazole was dissolved in ethanol. The N-butylimidazole solution was slowly added dropwise to the copolymer product solution through a constant-pressure dropping funnel. After the addition was complete, the mixture was heated to 60°C and stirred for 6 hours. The product was then obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0145] .

[0146] Comparative Example 2:

[0147] S1: Dissolve 0.04 mol of vinylphosphonic acid (VPA) in 30 mL of ethanol in a 100 mL flask. Dissolve 0.01 mol of hydroxyethyl methacrylate (HEMA) in 30 mL of ethanol, and then slowly add the HEMA solution to the VPA solution. Prepare a 2 wt% AIBN ethanol solution (relative to the total amount of VPA and HEMA monomers) and slowly add it dropwise to the above mixed solution through a constant pressure dropping funnel. After the addition is complete, raise the temperature to 80 °C and react under a nitrogen atmosphere for 10 h. After precipitation with petroleum ether, filtration, washing, and vacuum drying, the copolymer of VPA and HEMA (number average molecular weight 13000 g / mol) is obtained.

[0148] S2: Approximately 0.028 mol of the copolymer with phosphate groups was redissolved in ethanol. 0.014 mol of N-butylimidazole was dissolved in ethanol. The N-butylimidazole solution was slowly added dropwise to the copolymer solution through a constant-pressure dropping funnel. After the addition was complete, the mixture was heated to 60°C and stirred for 6 hours. The product was then obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0149] .

[0150] Comparative Example 3:

[0151] S1: Dissolve 0.04 mol of vinylphosphonic acid (VPA) in 30 mL of ethanol in a 100 mL flask. Prepare a 2 wt% (relative to VPA monomer) AIBN ethanol solution and slowly add it dropwise to the vinylphosphonic acid solution using a constant pressure dropping funnel. After the addition is complete, heat to 80 °C and react under a nitrogen atmosphere for 10 h. After precipitation with petroleum ether, filtration, washing, and vacuum drying, polyvinylphosphonic acid (number average molecular weight 10000 g / mol) is obtained.

[0152] S2: Approximately 0.037 mol of the copolymer with phosphate groups was redissolved in ethanol. 0.037 mol of N-ethylimidazole was dissolved in ethanol. The N-ethylimidazole solution was slowly added dropwise to the polyvinylphosphonic acid solution through a constant-pressure dropping funnel. After the addition was complete, the mixture was heated to 60°C and stirred for 6 hours. The product was then obtained by rotary evaporation and vacuum drying, with the following structural formula:

[0153] .

[0154] Comparative Example 4:

[0155] The only difference from Example 1 is that the preparation method of Comparative Example 4 only performs steps S1 to S5 to obtain the ternary copolymer product, and does not include step S6.

[0156] According to the mass fractions: 10 parts of the flame retardant prepared in Examples 1-10 and Comparative Examples 1-4 and 90 parts of TPU particles (8795A model purchased from Bayer AG, Germany) were thoroughly mixed, and then extruded and blended (feed section temperature 120°C, mixing section temperature 200°C) and injection molded (210°C) to obtain test strips of different sizes, and LOI, UL-94 vertical burning, tensile and ultraviolet transmittance tests were performed respectively (the TPU particles were prepared as test strips separately for reference).

[0157] Figure 1 The infrared characteristic peaks of the flame retardant products (VHEHA-1 and VHEHA-2) from Examples 1 and 2 are shown. In the infrared absorption peak of product VHEHA-1, some characteristic peaks of the phosphate group and N-ethylimidazole are observed, such as the C=N peak on the imidazole ring (1510 cm⁻¹). -1 P=O (1279cm) -1 However, the PO disappears, and a new PO is generated. - and NH + The absorption peaks are located at 912 and 3030 cm⁻¹, respectively. -1 This indicates that the ionic liquid portion was successfully synthesized; simultaneously, the carbonyl C=O group of the HEMA unit portion reaches 1628 cm⁻¹. -1The presence of these peaks indicates that the monomers participate in the reaction via copolymerization, ultimately forming a polyionic liquid copolymer. In contrast, VHEHA-2 still contains unneutralized phosphate groups, therefore its infrared spectrum retains the characteristic peak of PO (1076 cm⁻¹). -1 ).

[0158] Figure 2 The thermogravimetric behavior of the products (VHEHA-1 and VHEHA-2) in Examples 1 and 2 under a nitrogen atmosphere is shown. Both products VHEHA-1 and VHEHA-2 exhibit good thermal stability, especially VHEHA-1, which has a 33.2 wt% char residue at 600°C, indicating that it has excellent char-forming properties and is expected to promote char formation in the polymer matrix during combustion, significantly improving the flame retardant properties of the matrix material.

[0159] Table 1: Performance test results of TPU polyurethane flame-retardant materials prepared with flame retardants from Examples 1-10 and Comparative Examples 1-4

[0160]

[0161] As shown in Table 1, the repeating unit structure of the phosphorus-nitrogen type polyionic liquid of this invention has a significant impact on the overall performance of TPU materials. At the same phosphorus-nitrogen ratio, the higher the proportion of vinylphosphonic acid monomer in the terpolymer, the better the flame retardant performance of the TPU material. For example, the LOI of Example 4 reached 26.2%, which is superior to Examples 1 and 3. In Example 3, the copolymer had the highest proportion of hydroxyethyl methacrylate, resulting in the TPU sample with the best mechanical properties, a tensile strength of 42 MPa, and an elongation at break of 530%, demonstrating that the introduction of acrylate monomers is beneficial for enhancing the interfacial compatibility between the flame retardant and the matrix. Furthermore, the higher the content of benzophenones in the copolymer, the better the UV shielding performance of the prepared TPU material. For example, the TPU material of Example 3 had a transmittance of only 5% for ultraviolet light (at 350 nm), exhibiting excellent resistance to UV absorption. Changing the type of monomers (changing the R group, such as in Examples 1 and 7-10) has a relatively small impact on the flame retardant, mechanical, and UV shielding properties of the TPU material. Analysis of the data from Examples 5 and 6 shows that adjusting the proportion of intermediate monomer (y) within a certain range has little impact on the overall performance of the TPU composite material. In Example 5, by reducing the proportion of intermediate monomer (y), tensile strength and elongation at break were improved with only a slight decrease in limiting oxygen index (LOI) (26.1%) and a decrease in UV transmittance, indicating that the material maintained high overall performance. In contrast, in Example 6, although the LOI value remained basically the same after increasing the proportion of intermediate monomer (y), both tensile strength and UV shielding performance showed a slight decline. Comparing the results of the two examples, it can be seen that appropriately adjusting the proportion of intermediate monomer (y) can optimize the mechanical properties and UV shielding effect of the material.

[0162] In summary, to highlight the UV shielding effect of the benzophenone group and the interfacial compatibilizing effect of acrylate compounds on flame-retardant composite materials, this invention prepared flame retardants without benzophenone segments (Comparative Examples 1 and 2) and a single polyphosphonic acid / pyrazole polyionic liquid (Comparative Example 3) for comparison. Comparison with the examples revealed that, due to the inability of the preparation processes of Comparative Examples 1-3 to leverage the synergistic effect of the aforementioned key groups, their overall performance was inferior to that of Examples 1-2. Therefore, the polyionic liquid flame retardant prepared by this invention enables TPU to meet flame retardant requirements while also possessing excellent UV shielding and mechanical properties, ultimately achieving the preparation of high-performance TPU composite materials.

[0163] Finally, it should be noted that the specific embodiments described herein are merely illustrative of the spirit of the invention and are not intended to limit the implementation of the invention. Those skilled in the art can make various modifications or additions to the described embodiments or use similar methods to replace them; it is neither necessary nor possible to exemplify all embodiments here. However, these obvious variations or modifications derived from the essential spirit of the invention still fall within the scope of protection of the invention, and interpreting them as any additional limitation would contradict the spirit of the invention.

Claims

1. A phosphorus-nitrogen type polyionic liquid flame retardant, characterized in that, The polyionic liquid flame retardant comprises a structure as shown in Formula I or Formula II: ； （I） ； (II) Among them, R1, R2, and R3 are independently selected from hydrogen, methyl, and ethyl; R4 is selected from hydrogen, methyl, and phenyl; R5 is selected from hydrogen and methyl; R6 is an alkane group with ≤4 carbon atoms; x:y:z = (2-3):(4-12):

1.

2. A method for preparing the phosphorus-nitrogen type polyionic liquid flame retardant as described in claim 1, characterized in that, The method includes the following steps: S1. Dissolve olefinic phosphonic acid, hydroxyl-terminated acrylate, and acryloyloxybenzophenone in solvents to obtain phosphonic acid solution, acrylate solution, and benzophenone solution, respectively. S2. Then, the acrylate solution and benzophenone solution are added to the phosphonic acid solution, and an initiator is added to carry out a copolymerization reaction to obtain the copolymer product; S3. Redissolve the copolymer in a solvent to obtain a copolymer solution; dissolve the alkylimidazolium in a solvent to obtain an alkylimidazolium solution; S4. Add the alkylimidazolium solution dropwise to the copolymer product solution to carry out the ionization reaction and obtain the polyionic liquid flame retardant product.

3. The preparation method of the phosphorus-nitrogen type polyionic liquid flame retardant according to claim 2, characterized in that, In step S1, the olefinic phosphonic acid is at least one of vinylphosphonic acid, 1-styrylphosphonic acid, and 1-methylvinylphosphonic acid; And / or the hydroxyl-terminated acrylate is at least one of hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxyethyl acrylate, and hydroxypropyl acrylate; And / or acryloyloxybenzophenone is at least one of 2-hydroxy-4-(methacryloyloxy)benzophenone and 2-hydroxy-4-(acryloyloxy)benzophenone.

4. The preparation method of the phosphorus-nitrogen type polyionic liquid flame retardant according to claim 2, characterized in that, In step S1, the molar ratio of terminal hydroxyl acrylate, olefinic phosphonic acid and acryloyloxybenzophenone is (2-3):(4-12):

1.

5. The method for preparing the phosphorus-nitrogen type polyionic liquid flame retardant according to claim 2, characterized in that, In step S2, the initiator includes at least one of azobisisobutyronitrile, azobisisoheptanenitrile, benzoyl peroxide, tert-butyl peroxypentanoate, and di-tert-butyl peroxide.

6. The method for preparing the phosphorus-nitrogen type polyionic liquid flame retardant according to claim 2, characterized in that, In step S2, the copolymerization reaction temperature is 60–80°C and the time is 6–10 h.

7. The method for preparing the phosphorus-nitrogen type polyionic liquid flame retardant according to claim 2, characterized in that, In step S3, the alkyl imidazole is at least one of N-butylimidazolium, N-propylimidazolium, and N-ethylimidazolium.

8. The method for preparing the phosphorus-nitrogen type polyionic liquid flame retardant according to claim 2, characterized in that, In step S4, the molar ratio of alkylimidazolium to phosphate groups in the copolymer is 1:(0.5-5).

9. The method for preparing the phosphorus-nitrogen type polyionic liquid flame retardant according to claim 2, characterized in that, In step S4, the ionization reaction is carried out at a temperature of 40–60 °C for 3–6 h.

10. A TPU polyurethane flame-retardant material, characterized in that, The TPU polyurethane flame retardant material includes the phosphorus-nitrogen type polyionic liquid flame retardant of claim 1 or the phosphorus-nitrogen type polyionic liquid flame retardant prepared by any one of claims 2 to 9.

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