Phosphorus-nitrogen-containing synergistic ionic liquid flame retardant as well as preparation method and application thereof

Abstract

The invention relates to the technical field of design synthesis and application of flame retardants, in particular to a phosphorus-nitrogen-containing synergistic ionic liquid flame retardant as well as a preparation method and application thereof. The phosphorus-nitrogen-containing synergistic ionic liquid flame retardant has a structure as shown in a formula I; wherein R1 is selected from a straight chain alkyl group of C1 to C18, a branched chain alkyl group of C1 to C18 or a cycloalkyl group of C3 to C18; r < 2 > and R < 3 > are independently selected from a straight chain alkyl group of C1 to C18, a branched chain alkyl group of C1 to C18, a cycloalkyl group of C3 to C18 or an aryl group of C6 to C24; and R4 is selected from an alkyl group of C1 to C18, an alkenyl group of C2 to C18 or an aryl group of C6 to C24. The phosphorus-nitrogen-containing synergistic ionic liquid flame retardant provided by the invention has the advantages of high flame retardant efficiency, simple production process, realization of industrialization, almost no influence on mechanical properties of high polymer materials and the like. The flame-retardant polymer material prepared from the flame retardant has very high commercial application value.

Description

Technical Field

[0001] The present invention relates to the technical field of design, synthesis and application of flame retardants, and in particular to a phosphorus-nitrogen synergistic ionic liquid flame retardant, a preparation method and application thereof. Background Art

[0002] In recent decades, fields such as construction, transportation and national defense have gradually put forward higher requirements for the flame retardant properties of polymer materials, resulting in the development of a large number of flame retardants. Among them, ionic liquids have become the focus of research in the field of flame retardancy due to their advantages such as high thermal stability, designability and environmental protection. At present, most common ionic liquids contain halogen, boron, silicon, phosphorus, nitrogen and other elements. Considering the green and low-carbon environmental protection concept and the cost of flame retardants, halogen, boron and silicon-containing ionic liquid flame retardants are gradually eliminated by the market. Phosphorus or nitrogen-containing ionic liquids have gradually become the focus of development. However, with the deepening of research on ionic liquid flame retardancy, some researchers have begun to notice that when a single phosphorus or nitrogen-containing ionic liquid is used as a flame retardant, the flame retardant effect of most systems is poor due to the limited and single content of the flame retardant element it contains. Therefore, it is of great research significance to develop ionic liquids containing multiple flame retardant elements.

[0003] Patent application document 202010133301.7 discloses a method for preparing a waterborne epoxy resin modified with a phosphate-based imidazole ionic liquid, and prepares a phosphorus- and nitrogen-containing ionic liquid flame retardant. When the phosphorus- and nitrogen-containing ionic liquid flame retardant is added in an amount of 6wt%, the epoxy resin has good flame retardancy and impact resistance, but there is still a lot of room for improvement in achieving efficient flame retardancy. Patent application document 202310966443.5 discloses a phosphorus- and nitrogen-containing ionic liquid / epoxy resin composite material and a preparation method thereof. When 1 part of phosphorus- and nitrogen-containing ionic liquid is added to every 100 parts of epoxy resin, the epoxy resin has a good flame retardant effect, but the impact performance is significantly reduced. Patent application document 201711445944.X discloses a high-efficiency halogen-free inorganic-organic hybrid ionic liquid flame retardant and its preparation and application. The halogen-free inorganic-organic hybrid ionic liquid prepared by this patent has a high flame retardant efficiency, but the process is complicated and it is difficult to achieve industrial production.

[0004] Therefore, how to prepare a flame retardant with high flame retardancy and almost no effect on the mechanical properties of polymer materials through a simple process has become a technical problem that needs to be solved urgently in this field. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a phosphorus-nitrogen synergistic ionic liquid flame retardant, a preparation method and application thereof. The phosphorus-nitrogen synergistic ionic liquid flame retardant provided by the present invention has the advantages of high flame retardant efficiency, simple production process capable of industrialization, and almost no effect on the mechanical properties of polymer materials. The flame-retardant polymer material prepared using the phosphorus-nitrogen synergistic ionic liquid flame retardant has high commercial application value.

[0006] The present invention provides a phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in Formula I;

[0007]

[0008] Wherein, R1 is selected from C1-C18 straight chain alkyl, C1-C18 branched chain alkyl or C3-C18 cycloalkyl. Preferably, R1 is selected from C1-C10 straight chain alkyl or C1-C10 branched chain alkyl; such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl. More preferably, R1 is selected from methyl or ethyl.

[0009] R2 and R3 are independently selected from C1-C18 straight chain alkyl, C1-C18 branched chain alkyl, C3-C18 cycloalkyl or C6-C24 aromatic group. Preferably, R2 and R3 are independently selected from C1-C10 straight chain alkyl, C1-C10 branched chain alkyl or C6-C10 aromatic group; such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl or phenyl. More preferably, R2 and R3 are both ethyl.

[0010] R4 is selected from C1-C18 alkyl, C2-C18 alkenyl or C6-C24 aromatic. Preferably, R4 is selected from C1-C10 linear alkyl, C1-C10 branched alkyl, C2-C5 alkenyl or C6-C10 aromatic; such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, vinyl, propenyl, butenyl, phenyl, methylphenyl or dimethylphenyl. More preferably, R4 is methyl.

[0011] In some embodiments of the present invention, the phosphorus-nitrogen synergistic ionic liquid flame retardant has structures shown in formula (1) to formula (4);

[0012]

[0013]

[0014] The present invention also provides a method for preparing a phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in Formula I, comprising the following steps:

[0015] A dihydrocarbyl phosphinate alkyl ester having a structure shown in formula II and an imidazole compound having a structure shown in formula III are reacted to obtain a phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in formula I;

[0016]

[0017] Among them, the selection of R1, R2, R3 and R4 is the same as above and will not be repeated here.

[0018] In some embodiments of the present invention, the dihydrocarbyl phosphinate alkyl ester having the structure shown in Formula II is selected from at least one of methyl dimethylphosphinate, methyl diethylphosphinate, methyl dipropylphosphinate, methyl ethylpropylphosphinate, methyl diphenylphosphinate, ethyl dimethylphosphinate, ethyl diethylphosphinate, ethyl dipropylphosphinate, ethyl ethylpropylphosphinate, propyl dimethylphosphinate, propyl diethylphosphinate, propyl dipropylphosphinate, propyl ethylpropylphosphinate, methyl phenylphosphinate and methyl diphenylphosphinate.

[0019] In some embodiments of the present invention, the imidazole compound having the structure shown in Formula III is selected from at least one of 1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, 1-butylimidazole, 1-pentylimidazole, 1-hexylimidazole, 1-heptylimidazole, 1-vinylimidazole, 1-allylimidazole, 1-butylimidazole, 1-allylimidazole, 1-allylimidazole, 1-allylimidazole, 1-allylimidazole, 1-allylimidazole, 1-hexylimidazole, 1-heptylimidazole and 1-phenylimidazole.

[0020] In some embodiments of the present invention, the reaction is carried out under protective gas conditions. The protective gas is an inert gas, such as nitrogen. The reaction is carried out in a flask equipped with a thermometer, a serpentine condenser and a magnetic stirrer.

[0021] In some embodiments of the present invention, the reaction is carried out under normal pressure, positive pressure or negative pressure.

[0022] In some embodiments of the present invention, the molar ratio of the dialkyl phosphinate having the structure shown in formula II to the imidazole compound having the structure shown in formula III is 1.0-5.0:1.0. Preferably, the molar ratio of the dialkyl phosphinate having the structure shown in formula II to the imidazole compound having the structure shown in formula III is 1.0-1.3:1.0.

[0023] When the molar ratio of the dialkyl phosphinate having the structure shown in formula II to the imidazole compound having the structure shown in formula III is too high, the dialkyl phosphinate compound needs to be recovered; when it is too low, the yield of the ionic liquid decreases and the production cost increases.

[0024] In some embodiments of the present invention, the reaction temperature is 0 to 200° C., preferably 150 to 180° C. The reaction time is 1 to 20 hours, preferably 5 to 8 hours.

[0025] In some embodiments of the present invention, after the reaction, the process further comprises: cooling, extracting with a solvent, and subjecting the extracted crude product to rotary evaporation to obtain a phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in Formula I.

[0026] The cooling may be natural cooling to room temperature.

[0027] The solvent is selected from ether, toluene, xylene, dichloromethane, chloroform, carbon tetrachloride, n-butanol, ethyl acetate, hexane or cyclohexane. Preferably, ether is selected. Unreacted dialkylphosphinate and imidazole compounds can be removed by solvent extraction.

[0028] The temperature of the rotary evaporation is 0-200°C, preferably 80-120°C.

[0029] The rotary evaporation time is 1 to 10 hours, preferably 2 to 4 hours.

[0030] The volatile impurities in the crude product after extraction can be removed by rotary evaporation.

[0031] In the present invention, when the polymer material burns, the phosphorus-nitrogen synergistic ionic liquid flame retardant having the structure shown in Formula I produces phosphorus oxygen free radicals and nitrogen in the gas phase to quench the flame, and forms a carbonized layer in the condensed phase to inhibit or prevent combustion, thereby significantly improving the flame retardant properties of the polymer material.

[0032] The present invention also provides a flame-retardant polymer material, comprising a flame retardant and a polymer material, wherein the flame retardant is a phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in Formula I; or the flame retardant is a phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in Formula I obtained by the preparation method described above.

[0033] In some embodiments of the present invention, the polymer material is selected from at least one of vinyl polyphenylene ether resin, epoxy resin, cyanate resin, BT resin, bismaleimide resin, phenolic resin, polyurethane resin, thermosetting polyimide, unsaturated polyester resin, vinyl resin, benzoxazine resin, arylacetylene resin, polybutadiene, polyamide, polyester, polyphenylene ether, acrylonitrile-butadiene-styrene copolymer, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyimide, polyphenylene sulfide and polyetheretherketone. Preferably, the polymer material is epoxy resin.

[0034] In some embodiments of the present invention, in the flame retardant polymer material, the content of the flame retardant is 0-10wt%, and is not 0; preferably 1.6wt%-5.0wt%, such as 1.6wt% or 2wt%.

[0035] In some embodiments of the present invention, the flame retardant polymer material further comprises a curing agent. The curing agent may be diaminodiphenyl sulfone (DDS). In the flame retardant polymer material, the content of the curing agent is 15.0 wt% to 25.0 wt%.

[0036] In some embodiments of the present invention, the method for preparing the flame retardant polymer material comprises the following steps:

[0037] The heated polymer material, flame retardant and curing agent are mixed evenly, placed in a mold, and cured under vacuum conditions to obtain a flame retardant polymer material.

[0038] Specifically, they include:

[0039] Put the polymer material into a four-necked flask, heat it in an oil bath, add the flame retardant and stir evenly, then add the curing agent and stir evenly, pour it into a mold, put it into a vacuum oven and evacuate it, then heat it up and cure it, and after curing, a flame retardant epoxy resin material is obtained.

[0040] The temperature of the heated polymer material is 125-135°C, such as 130°C.

[0041] The present invention successfully introduces two flame retardant elements, nitrogen and phosphorus, by functionalizing the constituent elements of the anions and cations of the ionic liquid to synthesize a synergistic ionic liquid flame retardant with high flame retardant efficiency, free of halogen elements, and environmentally friendly.

[0042] The production process provided by the invention is simple, easy to operate, has a wide source of raw materials, high economic benefits, and is suitable for large-scale industrial production.

[0043] The phosphorus-nitrogen synergistic ionic liquid flame retardant prepared by the invention can impart excellent flame retardancy to polymer materials and has almost no influence on the mechanical properties of the polymer materials. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] In the following examples, the yield is calculated as follows: (product weight / product theoretical weight)×100%.

[0046] Example 1

[0047] 136.13g (1.00mol) of methyl diethylphosphinate and 80.46 (0.98mol) of 1-methylimidazole were added to a flask equipped with a thermometer, a serpentine condenser and a magnetic stirrer, and N2 gas was passed through. After heating in an oil bath at 150°C for 8 hours, the mixture was naturally cooled to room temperature, and unreacted methyl diethylphosphinate and 1-methylimidazole were extracted with ether. The crude product after extraction was subjected to rotary evaporation at 100°C for 3 hours to remove volatile impurities, thereby obtaining a product (flame retardant 1) with a yield of 99.0%. The flame retardant 1 has a structure shown in formula (1).

[0048]

[0049] Example 2

[0050] 136.13g (1.00mol) of methyl diethylphosphinate and 80.46g (0.98mol) of 1-methylimidazole were added to a flask equipped with a thermometer, a serpentine condenser and a magnetic stirrer, and N2 gas was passed through. After heating in an oil bath at 140°C for 8h, the mixture was naturally cooled to room temperature, and unreacted methyl diethylphosphinate and 1-methylimidazole were extracted with ether. The crude product after extraction was subjected to rotary evaporation at 100°C for 3h to remove volatile impurities, thereby obtaining a product (flame retardant 1) with a yield of 98.5%. The flame retardant 1 has a structure shown in formula (1).

[0051] Example 3

[0052] 136.13g (1.00mol) of methyl diethylphosphinate and 80.46g (0.98mol) of 1-methylimidazole were added to a flask equipped with a thermometer, a serpentine condenser and a magnetic stirrer, and N2 gas was passed through. After heating in an oil bath at 130°C for 8h, the mixture was naturally cooled to room temperature, and unreacted methyl diethylphosphinate and 1-methylimidazole were extracted with ether. The crude product after extraction was subjected to rotary evaporation at 100°C for 3h to remove volatile impurities, thereby obtaining a product (flame retardant 1) with a yield of 97.2%. The flame retardant 1 has a structure shown in formula (1).

[0053] Example 4

[0054] 136.13g (1.00mol) of methyl diethylphosphinate and 80.46g (0.98mol) of 1-methylimidazole were added to a flask equipped with a thermometer, a serpentine condenser and a magnetic stirrer, and N2 gas was passed through. After heating in an oil bath at 150°C for 6 hours, the mixture was naturally cooled to room temperature, and unreacted methyl diethylphosphinate and 1-methylimidazole were extracted with ether. The crude product after extraction was subjected to rotary evaporation at 100°C for 3 hours to remove volatile impurities, thereby obtaining a product (flame retardant 1) with a yield of 95.6%. The flame retardant 1 has a structure shown in formula (1).

[0055] Example 5

[0056] 136.13g (1.00mol) of methyl diethylphosphinate and 92.23g (0.98mol) of 1-vinylimidazole were added to a flask equipped with a thermometer, a serpentine condenser and a magnetic stirrer, and N2 gas was passed through. After heating in an oil bath at 150°C for 8h, the mixture was naturally cooled to room temperature, and unreacted methyl diethylphosphinate and 1-vinylimidazole were extracted with ether. The crude product after extraction was subjected to rotary evaporation at 100°C for 3h to remove volatile impurities, thereby obtaining a product (flame retardant 2) with a yield of 98.3%. The flame retardant 2 has a structure shown in formula (2).

[0057]

[0058] Example 6

[0059] 170.15 g (1.00 mol) of methylphenylphosphinate and 80.46 g (0.98 mol) of 1-methylimidazole were added to a flask equipped with a thermometer, a serpentine condenser and a magnetic stirrer, and N2 gas was passed through. After heating in an oil bath at 150° C. for 8 h, the mixture was naturally cooled to room temperature, and unreacted methylphenylphosphinate and 1-methylimidazole were extracted with ether. The crude product after extraction was subjected to rotary evaporation at 100° C. for 3 h to remove volatile impurities, thereby obtaining a product (flame retardant 3) with a yield of 98.6%. The flame retardant 3 has a structure shown in formula (3).

[0060]

[0061] Example 7

[0062] 170.15 g (1.00 mol) of methylphenylphosphinate and 92.23 g (0.98 mol) of 1-vinylimidazole were added to a flask equipped with a thermometer, a serpentine condenser and a magnetic stirrer, and N2 gas was passed through. After heating in an oil bath at 150° C. for 8 h, the mixture was naturally cooled to room temperature, and unreacted methylphenylphosphinate and 1-vinylimidazole were extracted with ether. The crude product was subjected to rotary evaporation at 100° C. for 3 h to remove volatile impurities, thereby obtaining a product (flame retardant 4) with a yield of 98.4%. The flame retardant 4 has a structure shown in formula (4).

[0063]

[0064] Application Example 1

[0065] 39.36g of epoxy resin E-51 was weighed and put into a four-necked flask, and the oil bath was heated to 130°C, 0.80g of the flame retardant 1 synthesized in Example 1 was added thereto and stirred evenly, and then 9.84g of curing agent DDS was added thereto, stirred evenly, poured into a mold, put into a vacuum oven and evacuated, and then heated to 150°C and cured for 4h. After the curing was completed, a flame retardant epoxy resin material was obtained. The content of the flame retardant in the flame retardant epoxy resin material was 1.6wt%.

[0066] Application Example 2

[0067] 39.20g of epoxy resin E-51 was weighed and put into a four-necked flask, and the oil bath was heated to 130°C, 1.0g of the flame retardant 1 synthesized in Example 1 was added thereto and stirred evenly, and then 9.80g of curing agent DDS was added thereto, stirred evenly, poured into a mold, put into a vacuum oven and evacuated, and then heated to 150°C and cured for 4h. After the curing was completed, a flame retardant epoxy resin material was obtained. The content of the flame retardant in the flame retardant epoxy resin material was 2wt%.

[0068] Application Example 3

[0069] 39.36g of epoxy resin E-51 was weighed and put into a four-necked flask, and the oil bath was heated to 130°C, 0.80g of the flame retardant 2 synthesized in Example 5 was added thereto and stirred evenly, and then 9.84g of curing agent DDS was added thereto, stirred evenly, poured into a mold, put into a vacuum oven and evacuated, and then heated to 150°C and cured for 4h. After the curing was completed, a flame retardant epoxy resin material was obtained. The content of the flame retardant in the flame retardant epoxy resin material was 1.6wt%.

[0070] Application Example 4

[0071] 39.36g of epoxy resin E-51 was weighed and put into a four-necked flask, and the oil bath was heated to 130°C, 0.80g of the flame retardant 3 synthesized in Example 6 was added thereto and stirred evenly, and then 9.84g of curing agent DDS was added thereto, stirred evenly, poured into a mold, put into a vacuum oven and evacuated, and then heated to 150°C and cured for 4h. After the curing was completed, a flame retardant epoxy resin material was obtained. The content of the flame retardant in the flame retardant epoxy resin material was 1.6wt%.

[0072] Application Example 5

[0073] 39.36g of epoxy resin E-51 was weighed and put into a four-necked flask, and the oil bath was heated to 130°C, 0.80g of the flame retardant 4 synthesized in Example 7 was added thereto and stirred evenly, and then 9.84g of curing agent DDS was added thereto, stirred evenly, poured into a mold, put into a vacuum oven and evacuated, and then heated to 150°C and cured for 4h. After the curing was completed, a flame retardant epoxy resin material was obtained. The content of the flame retardant in the flame retardant epoxy resin material was 1.6wt%.

[0074] Comparative Example 1

[0075] Weigh 40.0g of epoxy resin E-51 into a four-necked flask, heat it to 130°C in an oil bath, add 10.0g of curing agent DDS, stir evenly and pour it into a mold, put it into a vacuum oven and evacuate it, then heat it to 150°C and cure it for 4h. After curing, a flame retardant epoxy resin material is obtained.

[0076] Comparative Example 2

[0077] 39.52g of epoxy resin E-51 was weighed and put into a four-necked flask, and the oil bath was heated to 130°C, 0.60g of the flame retardant 1 synthesized in Example 1 was added thereto and stirred evenly, and then 9.88g of curing agent DDS was added thereto, stirred evenly, poured into a mold, put into a vacuum oven and evacuated, and then heated to 150°C and cured for 4h. After the curing was completed, a flame retardant epoxy resin material was obtained. The content of the flame retardant in the flame retardant epoxy resin material was 1.2wt%.

[0078] Comparative Example 3

[0079] 3-Methylimidazole and trimethyl phosphate were added to a three-necked flask in a molar ratio of 1:1, heated to 120°C in an oil bath, cooled naturally to room temperature, and ether was used as an extractant to remove unreacted 3-methylimidazole and trimethyl phosphate. The crude product was extracted and volatile impurities were removed by rotary evaporation at room temperature to obtain a flame retardant. 39.36g of epoxy resin E-51 was weighed and placed in a four-necked flask, heated to 130°C in an oil bath, 0.80g of the flame retardant was added thereto and stirred evenly, and then 9.84g of curing agent DDS was added thereto, stirred evenly and poured into a mold, placed in a vacuum oven and evacuated, then heated to 150°C and cured for 4h. After curing, a flame retardant epoxy resin material was obtained. The content of the flame retardant in the flame retardant epoxy resin material is 1.6wt%.

[0080] The properties of the flame retardant epoxy resin materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were tested, and the results are shown in Table 1. Among them, the UL-94 grade was tested according to the national standard GB / T 2408-2008 test standard by CZF-3 horizontal vertical combustion tester, and the sample size was 130×13×4mm. The limiting oxygen index LOI was tested according to the national standard GB / T 2406.2-2009 test standard by JB-3 oxygen index instrument, and the sample size was 100×6.5×3mm. The tensile strength was tested using the high and low temperature double column tester model 5966 of Instron Company of the United States, according to GB / T1040.2-2006, the tensile rate was 5mm / min, and the sample size was 75mm×40mm×3mm.

[0081] Table 1 Properties of flame retardant epoxy resin materials prepared in Application Examples 1 to 5 and Comparative Examples 1 to 3

[0082]

[0083] It can be seen from the test results of the above embodiments and comparative examples that when the content of the phosphorus-nitrogen synergistic ionic liquid flame retardant in the flame-retardant epoxy resin material is not less than 1.6wt%, the vertical combustion grade of the epoxy resin can reach V-0, and the limiting oxygen index is not less than 29.5%; when the content of the phosphorus-nitrogen synergistic ionic liquid flame retardant 4 in the flame-retardant epoxy resin material is 1.6wt%, the vertical combustion grade of the epoxy resin can reach V-0, and the limiting oxygen index is increased by 32.5%, so that the epoxy resin has excellent flame retardant properties, which proves that the flame retardant effect of the flame retardant is highly efficient. At the same time, the mechanical properties of the epoxy resin are almost unaffected. The phosphorus-nitrogen synergistic ionic liquid flame retardant prepared by the present invention not only has the advantages of high flame retardant efficiency, simple production process that can be industrialized, and almost no effect on the mechanical properties of polymer materials, but also the prepared flame retardant epoxy resin has commercial application value.

[0084] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in formula I; in, R1 is selected from a C1-C18 straight chain alkyl group, a C1-C18 branched chain alkyl group or a C3-C18 cycloalkyl group; R2 and R3 are independently selected from C1-C18 straight chain alkyl, C1-C18 branched chain alkyl, C3-C18 cycloalkyl or C6-C24 aromatic group; R4 is selected from C1-C18 alkyl, C2-C18 alkenyl or C6-C24 aromatic.

2. The phosphorus-nitrogen synergistic ionic liquid flame retardant according to claim 1, characterized in that: R1 is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl; R2 and R3 are independently selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl or phenyl; R4 is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, vinyl, propenyl, butenyl, phenyl, methylphenyl or dimethylphenyl.

3. The phosphorus-nitrogen synergistic ionic liquid flame retardant according to claim 1, characterized in that: The phosphorus-nitrogen synergistic ionic liquid flame retardant has structures shown in formula (1) to formula (4); 4. A method for preparing a phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in Formula I, comprising the following steps: A dihydrocarbyl phosphinate alkyl ester having a structure shown in formula II and an imidazole compound having a structure shown in formula III are reacted to obtain a phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in formula I; Wherein, R1 is selected from a C1-C18 straight chain alkyl group, a C1-C18 branched chain alkyl group or a C3-C18 cycloalkyl group; R2 and R3 are independently selected from C1-C18 straight chain alkyl, C1-C18 branched chain alkyl, C3-C18 cycloalkyl or C6-C24 aromatic group; R4 is selected from C1-C18 alkyl, C2-C18 alkenyl or C6-C24 aromatic.

5. The preparation method according to claim 4, characterized in that: The dihydrocarbyl phosphinate alkyl ester having the structure shown in formula II includes at least one of methyl dimethylphosphinate, methyl diethylphosphinate, methyl dipropylphosphinate, methyl ethylpropylphosphinate, methyl diphenylphosphinate, ethyl dimethylphosphinate, ethyl diethylphosphinate, ethyl dipropylphosphinate, ethyl ethylpropylphosphinate, propyl dimethylphosphinate, propyl diethylphosphinate, propyl dipropylphosphinate, propyl ethylpropylphosphinate, methyl phenylphosphinate and methyl diphenylphosphinate.

6. The preparation method according to claim 4, characterized in that: The imidazole compound having the structure shown in formula III includes at least one of 1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, 1-butylimidazole, 1-pentylimidazole, 1-hexylimidazole, 1-heptylimidazole, 1-vinylimidazole, 1-allylimidazole, 1-butylimidazole, 1-allylimidazole, 1-allylimidazole, 1-allylimidazole, 1-allylimidazole, 1-hexylimidazole, 1-heptylimidazole and 1-phenylimidazole.

7. The preparation method according to claim 4, characterized in that: The molar ratio of the dihydrocarbyl phosphinate alkyl ester having a structure shown in formula II to the imidazole compound having a structure shown in formula III is 1.0-5.0:1.

0.

8. The preparation method according to claim 4, characterized in that: The reaction is carried out under the condition of protective gas; The reaction temperature is 0 to 200°C and the reaction time is 1 to 20 hours; After the reaction, the method further comprises: cooling, extracting with a solvent, and rotary evaporating the crude product after extraction to obtain a phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in Formula I; The solvent includes ether, toluene, xylene, dichloromethane, chloroform, carbon tetrachloride, n-butanol, ethyl acetate, hexane or cyclohexane; The temperature of the rotary evaporation is 0-200° C., and the time is 1-10 hours.

9. A flame retardant polymer material, comprising a flame retardant and a polymer material, wherein the flame retardant is a phosphorus-nitrogen synergistic ionic liquid flame retardant having a structure shown in Formula I.

10. The flame retardant polymer material according to claim 9, characterized in that: The polymer material includes at least one of vinyl polyphenylene ether resin, epoxy resin, cyanate resin, BT resin, bismaleimide resin, phenolic resin, polyurethane resin, thermosetting polyimide, unsaturated polyester resin, vinyl resin, benzoxazine resin, arylacetylene resin, polybutadiene, polyamide, polyester, polyphenylene ether, acrylonitrile-butadiene-styrene copolymer, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyimide, polyphenylene sulfide and polyetheretherketone; In the flame retardant polymer material, the content of the flame retardant is 0-10wt% and is not zero.

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