Maleimide type flame retardant and preparation method thereof

Abstract

The invention relates to the field of flame retardants, and particularly discloses a maleimide type flame retardant and a preparation method thereof. The structural formula of the maleimide type flame retardant is # imgabs0. The preparation method comprises the following steps: reacting chloroethylamine with maleic anhydride to prepare chloroethyl maleimide acid; then, the chloroethyl maleimide acid and diethyl phosphine oxide phosphate are subjected to a reaction, and diethyl phosphine oxide maleimide acid is prepared; and finally, carrying out dehydration cyclization reaction on the diethylphosphine oxide maleimide acid to prepare the maleimide type flame retardant. The maleimide type nitrogen-phosphorus composite flame retardant disclosed by the invention is simple in group, more in active sites, relatively high in nitrogen and phosphorus element content and relatively strong in flame-retardant effect. The maleimide type nitrogen-phosphorus composite flame retardant prepared by the preparation method disclosed by the invention is relatively high in purity and yield, and has the characteristics of wide raw material source, low cost, simple and convenient synthesis operation and mild reaction conditions.

Description

Technical Field

[0001] The present application relates to the field of flame retardants, specifically, to the field of nitrogen-phosphorus composite flame retardants, and more specifically, it relates to a maleimide-type flame retardant and a preparation method thereof. Background Art

[0002] Flame retardants are functional additives that can reduce the flammability, self-extinguishing properties, and smoke properties of flammable or combustible materials and improve the flame retardancy of materials. They have broad market prospects in various fields such as chemical building materials, food, clothing, housing, transportation, and electronic appliances. There are many varieties of flame retardants. Generally, based on the method of treating the flame retardant and the substrate, they can be divided into additive flame retardants and reactive flame retardants. Among them, additive flame retardants will not chemically react with other components in the substrate during the flame retardant finishing of the substrate. They only enter the substrate in the form of physical blending or disperse on the surface of the substrate to make it flame retardant. During the processing of this type of flame retardant, the process is relatively simple, but the requirements for the flame retardant itself are high. For example, in terms of the degree of micronization, the smaller the particles, the more uniform the blending of the flame retardant and the substrate, and the better the flame retardant effect. In addition, there is usually a certain degree of incompatibility between additive flame retardants and substrates, and precipitation and separation will occur during the processing, thereby affecting the mechanical properties of the material.

[0003] During the flame retardant finishing process, reactive flame retardants mainly rely on their own polymerization or polycondensation reaction with the substrate and bind to the molecular chain of the polymer to play a flame retardant role. Usually, they have little effect on the mechanical properties of the material, so they have been more widely used. Reactive flame retardants can be divided into two categories according to their chemical composition: inorganic reactive flame retardants and organic reactive flame retardants. Representative flame retardants are halogen flame retardants, intumescent flame retardants, phosphorus flame retardants, nitrogen flame retardants and inorganic hydroxide flame retardants. There are many types of flame retardants, and the application scenarios are also different. But in general, nitrogen flame retardants and phosphorus flame retardants have received more extensive attention from scholars in the chemical industry due to their low toxicity, low smoke density, high modification upper limit and low environmental pollution. They are used in flame retardant scenarios in many fields such as aerospace, machinery, electronics, and textiles. They are currently one of the most valuable types of flame retardants.

[0004] The nitrogen heterocycle and conjugated structure of maleimide (MI) itself make the resin containing MI group have excellent radiation resistance, friction resistance and flame retardant properties. When burning, it releases nitrogen-containing non-combustible gas under heat. These gases will dilute the flammable gas and oxygen concentration in the air and play a flame retardant role. MI is a thermosetting polyimide with considerable double bond activity. It can be used as an amino resin monomer. Its low toxicity, high flame retardant efficiency and weak corrosiveness make MI widely used in reactive nitrogen flame retardants. The construction of active groups containing phosphorus atoms such as phosphine oxide and phosphate is a type of modification method widely used in the field of flame retardant materials. Phosphorus atoms have certain activity. When burning, phosphorus compounds decompose to form a non-flammable liquid film of phosphoric acid, and its boiling point can reach 300°C. At the same time, phosphoric acid is further dehydrated to form metaphosphoric acid, which is further polymerized to form polymetaphosphoric acid. In this process, not only does the covering layer generated by phosphoric acid have a covering effect, but the generated polymetaphosphoric acid is also a strong acid and a very strong dehydrating agent, which can dehydrate and carbonize the polymer, changing the pattern of the polymer combustion process and forming a carbon film on its surface to isolate the air, thereby exerting a stronger flame retardant effect.

[0005] Although nitrogen-based flame retardants and phosphorus-based flame retardants have their own flame retardant methods and effects, according to actual applications, the flame retardant properties of flame retardants containing only nitrogen or only phosphorus cannot reach the best. Since nitrogen has a good synergistic effect, it is often used in combination with other flame retardants, especially in combination with phosphorus flame retardants, which can maximize the synergistic effect. This is because phosphorus can form a stable phosphorus-containing carbonized layer in condensed phase flame retardancy, and nitrogen can form nitrogen-containing flame retardant gases in gas phase flame retardants. These gases also act as foaming agents for the carbon layer to form an expanded porous carbon layer, which further limits the volatile combustibles of the material from entering the gas phase combustion.

[0006] According to current reports, the existing nitrogen-phosphorus composite flame retardants often have low flame retardant efficiency due to the complex groups and low nitrogen and phosphorus content. In addition, amino / maleic anhydride is often used as the substrate for constructing MI, and halogen / phosphite is used as the basis for the Arbuzov reaction to graft phosphorus-containing groups. During this reaction, amino and halogen are very likely to conflict with the push-pull electron effect, resulting in poor reactivity between the raw materials, affecting the flame retardant effect of the flame retardant. Summary of the invention

[0007] In order to solve the above technical problems, the present application provides a maleimide flame retardant with a high phosphorus content and a preparation method thereof. The maleimide flame retardant has the characteristics of multiple active sites, high nitrogen and phosphorus content, high purity and good flame retardant effect.

[0008] In the first aspect, the present application provides a maleimide flame retardant, which adopts the following technical solution: A maleimide flame retardant, the structural formula of the maleimide flame retardant is:

[0009] By adopting the above technical solution, the maleimide flame retardant of the present application is diethylphosphine oxide maleimide, which is a maleimide nitrogen-phosphorus composite flame retardant. As can be seen from the structural formula, the maleimide flame retardant of the present application has a simple group, more active sites, higher nitrogen and phosphorus content, and stronger flame retardant effect.

[0010] In the second aspect, the present application provides a method for preparing a maleimide flame retardant, which adopts the following technical solution: A method for preparing a maleimide flame retardant comprises the following steps: S1. Under the protection of inert gas, chloroethylamine and maleic anhydride are reacted at a temperature of 25-50° C. for 0.5-3.0 hours, and then post-treated to obtain chloroethylmaleimide acid; the reaction formula is as follows: S2, reacting chloroethyl maleimide acid and diethyl phosphine oxide phosphate under the action of a phase transfer catalyst for 0.5-5.0 hours, and then post-treating to obtain diethyl phosphine oxide maleimide acid; the reaction formula is as follows: S3. Under the protection of an inert gas, diethylphosphine oxide maleimide acid is subjected to a dehydration cyclization reaction at a temperature of 120-160° C. The reaction is stopped when no more water is evaporated from the system, and then post-processed to obtain diethylphosphine oxide maleimide; the reaction formula is as follows:

[0011] By adopting the above technical scheme, the present application selects chloroethylamine as the skeleton, uses maleic anhydride and the amino group of chloroethylamine to carry out a ring-opening reaction, amidates the skeleton, and obtains chloroethylmaleimide acid with a purity greater than 95%. At this time, the introduction of the maleimide acid carboxyl group in the chloroethylmaleimide acid can improve the nucleophilic reaction activity of the chlorine atom; then, the Michaelis-Becker reaction is used to carry out nucleophilic substitution between diethylphosphine oxide and the chlorine end of chloroethylmaleimide acid to obtain diethylphosphine oxide maleimide acid; finally, the diethylphosphine oxide maleimide acid is refluxed to separate water, so that a molecule of water is removed from one side of the maleimide acid in the diethylphosphine oxide maleimide acid to generate maleimide, and a maleimide-type nitrogen-phosphorus composite flame retardant with a purity greater than 99% is obtained.

[0012] The present application optimizes the synthesis route of maleimide-type nitrogen-phosphorus composite flame retardant. Compared with the existing synthesis route, the raw materials used in each step of the preparation method of the present application can fully react with each other, fewer by-products are produced during the reaction, and the purity and yield of the obtained product are high. In addition, the flame retardant obtained by the preparation method of the present application has a simple group, high nitrogen and phosphorus content, and good flame retardant effect. In addition, the preparation method of the present application also has the characteristics of wide raw material sources, low cost, simple synthesis operation, and mild reaction conditions.

[0013] In the above preparation method, in step S1, the mixing method of chloroethylamine and maleic anhydride is: under the condition of ice bath and inert gas protection, maleic anhydride dissolved in dichloromethane is added dropwise to chloroethylamine dissolved in dichloromethane, and the dropping rate is controlled to be (66±1) mL / h. After the dropping is completed, the temperature is raised to react.

[0014] Wherein, in step S1, chloroethylamine is obtained by removing hydrochloric acid from chloroethylamine hydrochloride. Specifically, chloroethylamine hydrochloride is dissolved in dichloromethane, and then an equivalent amount of triethylamine is added, stirred thoroughly, and then the hydrochloric acid is removed.

[0015] Optionally, in step S1, the molar ratio of chloroethylamine to maleic anhydride is 1:(0.8-1.3). Further, the molar ratio of chloroethylamine to maleic anhydride is 1:(0.9-1.3). Further, the molar ratio of chloroethylamine to maleic anhydride is 1:(1.0-1.3).

[0016] Furthermore, in the step S1, the reaction temperature of chloroethylamine and maleic anhydride is 25-45° C. Furthermore, in the step S1, the reaction temperature of chloroethylamine and maleic anhydride is 25-40° C.

[0017] Furthermore, in the step S1, the reaction time of chloroethylamine and maleic anhydride is 1-3 hours. Furthermore, in the step S1, the reaction time of chloroethylamine and maleic anhydride is 1.5-3 hours.

[0018] In the above preparation method, in step S1, the post-treatment is specifically as follows: after the reaction is completed, ice water is used to quench the excess maleic anhydride, and then the pH value of the reaction solution is adjusted to acidic, water is added and shaken to obtain the organic phase, and then the organic phase is dehydrated, filtered and dried.

[0019] Optionally, in step S1, the pH value of the reaction solution is adjusted to 3.2-5.2.

[0020] By adopting the above technical scheme, after the reaction is completed, the present application slowly drips an appropriate amount of ice water to quench the excess maleic anhydride to convert it into maleic acid, and then uses a dilute hydrochloric acid solution to adjust the pH value of the reaction solution to be acidic, so that the unreacted chloroethylamine and triethylamine are converted into salt precipitation as much as possible, and then the reaction solution is poured into a separatory funnel, water is added and shaken to obtain an organic phase, anhydrous sodium sulfate is added to remove water, and then suction is filtered and spin-dried to obtain chloroethylmaleimide acid with a purity greater than 95%. This post-treatment process has a good removal effect on the unreacted raw materials, and can make the purity and yield of the product obtained in this step of the reaction higher.

[0021] Furthermore, in the step S1, the pH value of the reaction solution is adjusted to 3.2-4.8. Furthermore, in the step S1, the pH value of the reaction solution is adjusted to 3.2-4.4.

[0022] In the above preparation method, in step S2, the molar ratio of chloroethylmaleimide acid to diethylphosphine oxide phosphate is 1:(0.8-1.2).

[0023] Further, in the step S2, the molar ratio of chloroethylmaleimide acid to diethylphosphine oxide phosphate is 1:(0.9-1.2). Further, in the step S2, the molar ratio of chloroethylmaleimide acid to diethylphosphine oxide phosphate is 1:(0.95-1.1).

[0024] In the above preparation method, in step S2, diethylphosphine oxide phosphate is prepared by dissolving diethylphosphine oxide in a solvent and reacting with sodium hydroxide by stirring; the reaction formula is as follows:

[0025] Optionally, the solvent is selected from one of toluene, benzene, dichloromethane, ethyl acetate, N,N-dimethylformamide, dioxane, and acetone.

[0026] Preferably, the solvent is selected from one of dichloromethane, ethyl acetate, N,N-dimethylformamide, dioxane and acetone.

[0027] Through the above technical scheme, compared with toluene and benzene, the present application further selects one of dichloromethane, ethyl acetate, N,N-dimethylformamide, dioxane, and acetone as the solvent of diethyl phosphine oxide, which can increase the minimum yield of the prepared diethyl phosphine oxide maleimide acid by 46.15-61.70%, and significantly improves the conversion rate of this step reaction.

[0028] Furthermore, in the step S3, the water separation reflux temperature during the dehydration cyclization reaction is 130-160° C. Furthermore, in the step S3, the water separation reflux temperature during the dehydration cyclization reaction is 150-160° C.

[0029] In summary, this application has the following beneficial technical effects: 1. The maleimide-type nitrogen-phosphorus composite flame retardant of the present application has a simple group, more active sites, higher nitrogen and phosphorus content, and stronger flame retardant effect; 2. This application obtains a high-purity, high-yield maleimide-type nitrogen-phosphorus composite flame retardant by optimizing the synthesis route and ingenious post-treatment method; 3. The preparation method of the present application has the characteristics of wide source of raw materials, low cost, simple synthesis operation and mild reaction conditions. DETAILED DESCRIPTION

[0030] The present application is further described in detail below in conjunction with examples and data analysis.

[0031] The raw materials used in this application are all commercially available products.

[0032] Example 1.1 A method for preparing a maleimide flame retardant comprises the following steps: S1. Add 1 mol of chloroethylamine hydrochloride to a reaction vessel and take an appropriate amount of dichloromethane to dissolve it. The amount of dichloromethane used is sufficient to dissolve the chloroethylamine hydrochloride. Then, add 1 mol of triethylamine and stir thoroughly for 1 hour to remove the hydrochloric acid; dissolve 0.8 mol of maleic anhydride in 200 mL of dichloromethane and pour it into a dropping funnel; introduce nitrogen into the reaction vessel, and use an ice-water bath to lower the solution temperature to 0-4°C before starting to drip. The dripping time is controlled to 3 hours, that is, the dripping rate is (6 6±1) mL / h, after the dripping is completed, the reaction is continued with stirring at a temperature of 25°C for 3 hours. After the reaction is completed, the excess maleic anhydride is quenched with ice water, and then an appropriate amount of a 3 mol / L dilute hydrochloric acid solution is added dropwise, the pH value of the reaction solution is adjusted to 3.6, and then 10 times the volume of dichloromethane is added. The organic phase is taken, and then dehydrated, filtered and spin-dried to obtain chloroethylmaleimide acid with a purity greater than 95%, and the yield of chloroethylmaleimide acid is 42.5%; S2, dissolving diethylphosphine oxide in dioxane, adding sodium hydroxide in an ice-water bath and stirring for 1 hour, filtering out the solid to obtain diethylphosphine oxide phosphate; dissolving 1 mol of chloroethyl maleimide acid in dichloromethane, adding a phase transfer catalyst benzyltriethylammonium chloride (BTEAC) and stirring evenly, then adding 0.8 mol of diethylphosphine oxide phosphate to react for 4 hours, extracting after the reaction, taking the organic phase, and draining the solvent with a vacuum pump to obtain diethylphosphine oxide maleimide acid, the yield of diethylphosphine oxide maleimide acid is 71.4%; S3, diethylphosphine oxide maleimide acid is dissolved in toluene, and inhibitor p-hydroxyanisole (MEHQ) is added for magnetic stirring, after nitrogen is introduced, the temperature is raised to 120 ℃ for water separation and reflux, when the volume of water in the water separator is no longer increased, the reaction is stopped and toluene is removed by vacuum rotary evaporation, and the remaining reaction solution is extracted with ethyl acetate / water system, the volume ratio of ethyl acetate to water is 1:4, and then the organic phase is taken, and ethyl acetate is removed by rotary evaporation to obtain diethylphosphine oxide maleimide with a purity greater than 99%, and the yield of diethylphosphine oxide maleimide is 71.6%.

[0033] Example 1.2 A method for preparing a maleimide flame retardant, which is different from that of Example 1.1 in that: in step S1, the molar ratio of chloroethylamine to maleic anhydride is 1:0.9, that is, the amount of chloroethylamine hydrochloride is 1 mol, and the amount of maleic anhydride is 0.9 mol, and the rest is the same as that of Example 1.1, and the purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 54.8%.

[0034] Example 1.3 A method for preparing a maleimide flame retardant, which is different from that of Example 1.1 in that: in step S1, the molar ratio of chloroethylamine to maleic anhydride is 1:1.0, that is, the amount of chloroethylamine hydrochloride is 1 mol, and the amount of maleic anhydride is 1.0 mol, and the rest is the same as that of Example 1.1, and the purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 61.6%.

[0035] Example 1.4 A method for preparing a maleimide flame retardant, which is different from that of Example 1.1 in that: in step S1, the molar ratio of chloroethylamine to maleic anhydride is 1:1.1, that is, the amount of chloroethylamine hydrochloride is 1 mol, and the amount of maleic anhydride is 1.1 mol, and the rest is the same as in Example 1.1, and the obtained chloroethylmaleimide acid has a purity greater than 95% and a yield of 64.3%.

[0036] Example 1.5 A method for preparing a maleimide flame retardant, which is different from that of Example 1.1 in that: in step S1, the molar ratio of chloroethylamine to maleic anhydride is 1:1.2, that is, the amount of chloroethylamine hydrochloride is 1 mol, and the amount of maleic anhydride is 1.2 mol, and the rest is the same as that of Example 1.1, and the purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 63.8%.

[0037] Example 1.6 A method for preparing a maleimide flame retardant, which is different from that of Example 1.1 in that: in step S1, the molar ratio of chloroethylamine to maleic anhydride is 1:1.3, that is, the amount of chloroethylamine hydrochloride is 1 mol, and the amount of maleic anhydride is 1.3 mol, and the rest is the same as that of Example 1.1, and the purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 63.4%.

[0038] Example 2.1 A method for preparing a maleimide flame retardant, which is different from that of Example 1.4 in that: in step S1, after the dripping is completed, the reaction temperature is 30°C, and the rest is the same as that of Example 1.4. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 66.2%.

[0039] Example 2.2 A method for preparing a maleimide flame retardant, which is different from that of Example 1.4 in that: in step S1, after the dripping is completed, the reaction temperature is 35°C, and the rest is the same as that of Example 1.4. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 69.8%.

[0040] Example 2.3 A method for preparing a maleimide flame retardant, which is different from that of Example 1.4 in that: in step S1, after the dripping is completed, the reaction temperature is 40°C, and the rest is the same as that of Example 1.4. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 67.4%.

[0041] Example 2.4 A method for preparing a maleimide flame retardant, which is different from that of Example 1.4 in that: in step S1, after the dripping is completed, the reaction temperature is 45°C, and the rest is the same as that of Example 1.4. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 60.1%.

[0042] Example 2.5 A method for preparing a maleimide flame retardant, which is different from that of Example 1.4 in that: in step S1, after the dripping is completed, the reaction temperature is 50°C, and the rest is the same as that of Example 1.4. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 52.4%.

[0043] Example 3.1 A method for preparing a maleimide flame retardant, which is different from that of Example 2.2 in that: in step S1, after the dripping is completed, the stirring reaction time is continued for 0.5 hours, and the rest is the same as that of Example 2.2. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 48.7%.

[0044] Example 3.2 A method for preparing a maleimide flame retardant, which is different from that of Example 2.2 in that: in step S1, after the dripping is completed, the stirring reaction time is continued for 1.0 hour, and the rest is the same as Example 2.2. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 55.2%.

[0045] Example 3.3 A method for preparing a maleimide flame retardant, which is different from that of Example 2.2 in that: in step S1, after the dripping is completed, the stirring reaction time is continued for 1.5 hours, and the rest is the same as Example 2.2. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 63.3%.

[0046] Example 3.4 A method for preparing a maleimide flame retardant, which is different from that of Example 2.2 in that: in step S1, after the dripping is completed, the stirring reaction time is continued for 2.0 hours, and the rest is the same as Example 2.2. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 69.8%.

[0047] Example 3.5 A method for preparing a maleimide flame retardant, which is different from that of Example 2.2 in that: in step S1, after the dripping is completed, the stirring reaction time is continued for 2.5 hours, and the rest is the same as that of Example 2.2. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 69.2%.

[0048] Example 4.1 A method for preparing a maleimide flame retardant, which is different from Example 3.4 in that: in step S1, the pH value of the reaction solution is adjusted to 5.2, and the rest is the same as Example 3.4. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 61.2%.

[0049] Example 4.2 A method for preparing a maleimide flame retardant, which is different from Example 3.4 in that: in step S1, the pH value of the reaction solution is adjusted to 4.8, and the rest is the same as Example 3.4. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 65.9%.

[0050] Example 4.3 A method for preparing a maleimide flame retardant, which is different from Example 3.4 in that: in step S1, the pH value of the reaction solution is adjusted to 4.4, and the rest is the same as Example 3.4. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 66.1%.

[0051] Example 4.4 A method for preparing a maleimide flame retardant, which is different from Example 3.4 in that: in step S1, the pH value of the reaction solution is adjusted to 4.0, and the rest is the same as Example 3.4. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 67.4%.

[0052] Example 4.5 A method for preparing a maleimide flame retardant, which is different from Example 3.4 in that: in step S1, the pH value of the reaction solution is adjusted to 3.2, and the rest is the same as Example 3.4. The purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is 69.6%.

[0053] Example 5.1 A method for preparing a maleimide flame retardant, which is different from that of Example 1.1 in that: in step S2, the molar ratio of chloroethylmaleimide acid to diethylphosphine oxide phosphate is 1:0.9, that is, the amount of chloroethylmaleimide acid is 1 mol, the amount of diethylphosphine oxide phosphate is 0.9 mol, and the rest is the same as that of Example 1.1, and the yield of the obtained diethylphosphine oxide maleimide acid is 76.3%.

[0054] Example 5.2 A method for preparing a maleimide flame retardant, which is different from that of Example 1.1 in that: in step S2, the molar ratio of chloroethylmaleimide acid to diethylphosphine oxide phosphate is 1:0.95, that is, the amount of chloroethylmaleimide acid is 1 mol, the amount of diethylphosphine oxide phosphate is 0.95 mol, and the rest is the same as that of Example 1.1, and the yield of the obtained diethylphosphine oxide maleimide acid is 78.4%.

[0055] Example 5.3 A method for preparing a maleimide flame retardant, which is different from that of Example 1.1 in that: in step S2, the molar ratio of chloroethylmaleimide acid to diethylphosphine oxide phosphate is 1:1.05, that is, the amount of chloroethylmaleimide acid is 1 mol, the amount of diethylphosphine oxide phosphate is 1.05 mol, and the rest is the same as that of Example 1.1, and the yield of the obtained diethylphosphine oxide maleimide acid is 77.6%.

[0056] Example 5.4 A method for preparing a maleimide flame retardant, which is different from that of Example 1.1 in that: in step S2, the molar ratio of chloroethylmaleimide acid to diethylphosphine oxide phosphate is 1:1.1, that is, the amount of chloroethylmaleimide acid is 1 mol, the amount of diethylphosphine oxide phosphate is 1.1 mol, and the rest is the same as that of Example 1.1, and the yield of the obtained diethylphosphine oxide maleimide acid is 77.3%.

[0057] Example 5.5 A method for preparing a maleimide flame retardant, which is different from that of Example 1.1 in that: in step S2, the molar ratio of chloroethylmaleimide acid to diethylphosphine oxide phosphate is 1:1.2, that is, the amount of chloroethylmaleimide acid is 1 mol, the amount of diethylphosphine oxide phosphate is 1.2 mol, and the rest is the same as that of Example 1.1, and the yield of the obtained diethylphosphine oxide maleimide acid is 76.9%.

[0058] Example 6.1 A method for preparing a maleimide flame retardant, which is different from Example 5.2 in that: in step S2, diethyl phosphine oxide is dissolved in toluene, and the rest is the same as Example 5.2, and the yield of the obtained diethyl phosphine oxide maleimide acid is 32.9%.

[0059] Example 6.2 A method for preparing a maleimide flame retardant, which is different from Example 5.2 in that: in step S2, diethyl phosphine oxide is dissolved in benzene, and the rest is the same as Example 5.2, and the yield of the obtained diethyl phosphine oxide maleimide acid is 36.4%.

[0060] Example 6.3 A method for preparing a maleimide flame retardant, which is different from Example 5.2 in that: in step S2, diethylphosphine oxide is dissolved in dichloromethane, and the rest is the same as Example 5.2, and the yield of the obtained diethylphosphine oxide maleimide acid is 53.2%.

[0061] Example 6.4 A method for preparing a maleimide flame retardant, which is different from Example 5.2 in that: in step S2, diethyl phosphine oxide is dissolved in ethyl acetate, and the rest is the same as Example 5.2, and the yield of the obtained diethyl phosphine oxide maleimide acid is 68.1%.

[0062] Example 6.5 A method for preparing a maleimide flame retardant, which is different from Example 5.2 in that: in step S2, diethyl phosphine oxide is dissolved in N,N-dimethylformamide, and the rest is the same as Example 5.2, and the yield of the obtained diethyl phosphine oxide maleimide acid is 62.4%.

[0063] Example 6.6 A method for preparing a maleimide flame retardant, which is different from Example 5.2 in that: in step S2, diethyl phosphine oxide is dissolved in acetone, and the rest is the same as Example 5.2, and the yield of the obtained diethyl phosphine oxide maleimide acid is 57.5%.

[0064] Example 7.1 A method for preparing a maleimide flame retardant, which is different from Example 5.2 in that: in step S2, the reaction time is 0.5 hours, and the rest is the same as Example 5.2, and the yield of the obtained diethylphosphine oxide maleimide acid is 24.1%.

[0065] Example 7.2 A method for preparing a maleimide flame retardant, which is different from Example 5.2 in that: in step S2, the reaction time is 1.0 hour, and the rest is the same as Example 5.2, and the yield of the obtained diethylphosphine oxide maleimide acid is 32.6%.

[0066] Example 7.3 A method for preparing a maleimide flame retardant, which is different from that of Example 5.2 in that: in step S2, the reaction time is 1.5 hours, and the rest is the same as that of Example 5.2, and the yield of the obtained diethylphosphine oxide maleimide acid is 46.4%.

[0067] Example 7.4 A method for preparing a maleimide flame retardant, which is different from Example 5.2 in that: in step S2, the reaction time is 2.0 hours, and the rest is the same as Example 5.2, and the yield of the obtained diethylphosphine oxide maleimide acid is 57.2%.

[0068] Example 7.5 A method for preparing a maleimide flame retardant, which is different from Example 5.2 in that: in step S2, the reaction time is 3.0 hours, and the rest is the same as Example 5.2, and the yield of the obtained diethylphosphine oxide maleimide acid is 66.1%.

[0069] Example 7.6 A method for preparing a maleimide flame retardant, which is different from that of Example 5.2 in that: in step S2, the reaction time is 5.0 hours, and the rest is the same as that of Example 5.2, and the yield of the obtained diethylphosphine oxide maleimide acid is 77.1%.

[0070] Example 8.1 A method for preparing a maleimide flame retardant, which is different from Example 1.1 in that: in step S3, the temperature of water reflux is 130° C., and the rest is the same as Example 1.1. The purity of the obtained diethylphosphine oxide maleimide is greater than 99%, and the yield is 76.3%.

[0071] Example 8.2 A method for preparing a maleimide flame retardant, which is different from Example 1.1 in that: in step S3, the temperature of water reflux is 140°C, and the rest is the same as Example 1.1. The purity of the obtained diethylphosphine oxide maleimide is greater than 99%, and the yield is 79.4%.

[0072] Example 8.3 A method for preparing a maleimide flame retardant, which is different from Example 1.1 in that: in step S3, the temperature of water reflux is 150° C., and the rest is the same as Example 1.1. The purity of the obtained diethylphosphine oxide maleimide is greater than 99%, and the yield is 83.9%.

[0073] Example 8.4 A method for preparing a maleimide flame retardant, which is different from Example 1.1 in that: in step S3, the temperature of water reflux is 160°C, and the rest is the same as Example 1.1. The purity of the obtained diethylphosphine oxide maleimide is greater than 99%, and the yield is 83.1%.

[0074] Data analysis According to the data of Examples 1-8, it can be seen that the present application has obtained a maleimide-type nitrogen-phosphorus composite flame retardant with high purity and yield by optimizing the synthesis route, controlling the reaction conditions, and combining the post-treatment process. The flame retardant has a simple group, more active sites, higher nitrogen and phosphorus content, and has a better flame retardant effect. In addition, the preparation method of the present application also has the characteristics of wide raw material sources, low cost, simple synthesis operation, and mild reaction conditions.

[0075] In the above numerous embodiments, the difference between embodiments 1.1-1.6 is only that the molar ratio of chloroethylamine and maleic anhydride in step S1 is different. From the data, it can be seen that when the molar ratio of chloroethylamine and maleic anhydride is 1:(0.8-1.3), the purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is in the range of 42.5-64.3%. Experimental data show that the different proportions of chloroethylamine and maleic anhydride will affect the conversion rate of the step reaction, thereby affecting the yield of chloroethylmaleimide acid. Wherein, when the molar ratio of chloroethylamine and maleic anhydride is 1:1.1, the yield of the obtained chloroethylmaleimide acid is the highest, which is 64.3%.

[0076] In the above numerous embodiments, the difference between embodiment 1.1 and embodiment 2.1-2.5 is only that the reaction temperature after the dripping in step S1 is different. It can be seen from the data that when the reaction temperature is 25-50°C, the purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is in the range of 52.4-69.8%. Experimental data show that the reaction temperatures of chloroethylamine and maleic anhydride are different, which will affect the conversion rate of the step reaction, thereby affecting the yield of chloroethylmaleimide acid. Among them, when the reaction temperature of the two is 35°C, the yield of the obtained chloroethylmaleimide acid is the highest, which is 69.8%.

[0077] In the above numerous embodiments, the difference between embodiment 2.2 and embodiment 3.1-3.5 is only that the reaction time after the dripping in step S1 is different. It can be seen from the data that when the reaction time is 0.5-3.0 hours, the purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is in the range of 48.7-69.8%. The experimental data show that the different reaction times of chloroethylamine and maleic anhydride will affect the conversion rate of the reaction step, thereby affecting the yield of chloroethylmaleimide acid.

[0078] In the above numerous embodiments, the difference between embodiment 3.4 and embodiment 4.1-4.5 is that the pH value of the reaction solution is adjusted during post-treatment in step S1. It can be seen from the data that when the pH value of the reaction solution is adjusted to 3.2-5.2, the purity of the obtained chloroethylmaleimide acid is greater than 95%, and the yield is in the range of 61.2-69.8%. Experimental data show that the pH value of the reaction solution is adjusted to different values ​​during post-treatment, which will affect the conversion rate of the step reaction, thereby affecting the yield of chloroethylmaleimide acid. Wherein, when the pH value of the reaction solution is 3.6, the yield of the obtained chloroethylmaleimide acid is the highest, which is 69.8%.

[0079] In the above numerous embodiments, the difference between embodiment 1.1 and embodiment 5.1-5.5 is only that the molar ratio of chloroethyl maleimide acid and diethyl phosphine oxide phosphate is different in step S2. From the data, it can be seen that when the molar ratio of chloroethyl maleimide acid and diethyl phosphine oxide phosphate is 1:(0.8-1.2), the yield of diethyl phosphine oxide maleimide acid is in the range of 71.4-78.4%. Experimental data show that the ratio of 1-chloroethyl maleimide acid and diethyl phosphine oxide phosphate is different, which will affect the conversion rate of the step reaction, thereby affecting the yield of diethyl phosphine oxide maleimide acid. Wherein, when the molar ratio of chloroethyl maleimide acid and diethyl phosphine oxide phosphate is 1:0.95, the yield of diethyl phosphine oxide maleimide acid is the highest, which is 78.4%.

[0080] In the above-mentioned numerous embodiments, the difference between embodiment 5.2 and embodiment 6.1-6.6 is only that the solvent used for dissolving diethyl phosphine oxide in step S2 is different. It can be seen from the data that the different solvents used for dissolving diethyl phosphine oxide will significantly affect the yield of diethyl phosphine oxide maleimide acid. When the solvent is toluene and benzene, the yield of diethyl phosphine oxide maleimide acid is 32.9-36.4%, and when the solvent is one of dichloromethane, ethyl acetate, N, N-dimethylformamide, dioxane, and acetone, the yield of diethyl phosphine oxide maleimide acid is 53.2-78.4%. Among them, when dioxane is used as the solvent, the yield of diethyl phosphine oxide maleimide acid is the highest, which is 78.4%.

[0081] In the above numerous embodiments, the difference between embodiment 5.2 and embodiment 7.1-7.6 is only that the reaction time of chloroethyl maleimide acid and diethyl phosphine oxide phosphate is different in step S2. As can be seen from the data, when the reaction time of the two is 0.5-5 hours, the yield of diethyl phosphine oxide maleimide acid is in the range of 24.1-78.4%. Experimental data show that the reaction time of chloroethyl maleimide acid and diethyl phosphine oxide phosphate is different, which will affect the conversion rate of the step reaction, thereby affecting the yield of diethyl phosphine oxide maleimide acid. Wherein, when the reaction time of chloroethyl maleimide acid and diethyl phosphine oxide phosphate is 4 hours, the yield of diethyl phosphine oxide maleimide acid is the highest, which is 78.4%.

[0082] In the above numerous embodiments, the difference between embodiment 1.1 and embodiment 8.1-8.4 is only that the temperature of water separation and reflux in step S3 is different. It can be seen from the data that when the water separation and reflux temperature is 120-160°C, the purity of the obtained diethylphosphine oxide maleimide is greater than 99%, and the yield is in the range of 71.6-83.9%. Experimental data show that the water separation and reflux temperature of diethylphosphine oxide maleimide acid is different, which will affect the conversion rate of the reaction step, thereby affecting the yield of diethylphosphine oxide maleimide. Among them, when the water separation and reflux temperature of diethylphosphine oxide maleimide is 150°C, the yield of the obtained diethylphosphine oxide maleimide is the highest, which is 83.9%.

[0083] The embodiments of this specific implementation method are all preferred embodiments of the present application, and are not intended to limit the protection scope of the present application. Therefore, all equivalent changes made based on the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A maleimide flame retardant, characterized in that: The structural formula of the maleimide flame retardant is:

2. A method for preparing the maleimide flame retardant according to claim 1, characterized in that: The following steps are involved: S1. Under the protection of inert gas, chloroethylamine and maleic anhydride are reacted at a temperature of 25-50° C. for 0.5-3.0 hours, and then post-treated to obtain chloroethylmaleimide acid; the reaction formula is as follows: S2, reacting chloroethyl maleimide acid and diethyl phosphine oxide phosphate under the action of a phase transfer catalyst for 0.5-5.0 hours, and then post-treating to obtain diethyl phosphine oxide maleimide acid; the reaction formula is as follows: S3. Under the protection of an inert gas, diethylphosphine oxide maleimide acid is subjected to a dehydration cyclization reaction at a temperature of 120-160° C. The reaction is stopped when no more water is evaporated from the system, and then post-processed to obtain diethylphosphine oxide maleimide; the reaction formula is as follows:

3. The method for preparing a maleimide flame retardant according to claim 2, characterized in that: In the step S1, the molar ratio of chloroethylamine to maleic anhydride is 1:(0.8-1.3).

4. The method for preparing a maleimide flame retardant according to claim 2, characterized in that: In step S1, the post-treatment is specifically as follows: after the reaction is completed, ice water is used to quench the excess maleic anhydride, and then the pH value of the reaction solution is adjusted to acidic, water is added and shaken to obtain the organic phase, and then the organic phase is dehydrated, filtered and dried.

5. The method for preparing a maleimide flame retardant according to claim 4, characterized in that: In the step S1, the pH value of the reaction solution is adjusted to 3.2-5.

2.

6. The method for preparing a maleimide flame retardant according to claim 2, characterized in that: In the step S2, the molar ratio of chloroethylmaleimide acid to diethylphosphine oxide phosphate is 1:(0.8-1.2).

7. The method for preparing a maleimide flame retardant according to claim 2, characterized in that: In step S2, diethylphosphine oxide phosphate is prepared by dissolving diethylphosphine oxide in a solvent and reacting with sodium hydroxide with stirring; the reaction formula is as follows:

8. The method for preparing a maleimide flame retardant according to claim 7, characterized in that: The solvent is selected from one of toluene, benzene, dichloromethane, ethyl acetate, N,N-dimethylformamide, dioxane and acetone.

9. The method for preparing a maleimide flame retardant according to claim 8, characterized in that: The solvent is selected from one of dichloromethane, ethyl acetate, N,N-dimethylformamide, dioxane and acetone.

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