Preparation method of maleimide compound

Abstract

The invention provides a preparation method of a maleimide compound, which comprises the following steps: carrying out solid-phase grinding on raw materials comprising an aniline compound and maleic anhydride to prepare a maleamic acid intermediate product, and carrying out ring-closure reaction to prepare the maleimide compound. The process method is simple and easy to implement, an intermediate product can be stably prepared, then the intermediate product is subjected to a closing reaction, the raw material conversion rate and the product yield can be greatly improved, the synthesis process is controllable, no dehydrating agent is used, the reaction time is short, the process is simple and easy to operate, and the obtained maleimide is stable in property and wide in applicability.

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing a maleimide compound. Background Art

[0002] Compounds with imide rings as functional groups primarily include maleimides, polymaleimides, and polyimides. Maleimides and polymaleimides are materials with five-membered ring structures containing double bonds. They are typically white or yellow powders and possess highly reactive carbon-carbon double bonds. As industrial products with promising market prospects, they have numerous potential applications in rubber modifiers, marine antifouling agents, heat stabilizers for high-performance plastics, and heat-resistant additives (such as heat-resistant ABS resin, heat-resistant PP, and weather-resistant, high-strength PVC).

[0003] Currently, there are no clear reports on solid solvent ring closure methods for maleimide rings. There are two main methods for synthesizing maleimides: the first is a one-step method, in which an amine monomer and maleic anhydride are added to a solvent for reaction. This method requires a long reaction time and high reaction temperature; the second is a two-step method, in which an amic acid intermediate is first prepared in a low-boiling point solvent and then subjected to a ring closure reaction.

[0004] There are currently four methods for ring-closing amic acid intermediates: acetic anhydride dehydration, azeotropic dehydration, microwave-assisted dehydration, and ionic liquid dehydration. The acetic anhydride dehydration method involves mixing maleimidic acid with acetic anhydride in a homogeneous system using N,N-dimethylformamide (DMF) as a solvent. The acetic anhydride-assisted dehydration process closes the ring, producing two small acetic acid byproducts. This method is the predominant method for industrial synthesis of maleimide resins, but the recovery of DMF and the processing of acetic acid consume significant energy. Acetic anhydride can also form a heterogeneous system with maleimidic acid in acetone as a solvent for dehydration. However, the high biotoxicity of acetone, coupled with the large amount of acetone used, has certain environmental impacts. The azeotropic dehydration method involves adding a low-boiling azeotrope with water to the system and continuously heating it to remove the water produced by the cyclization reaction, achieving ring closure. However, the azeotropic method suffers from the continuous energy consumption required.

[0005] Microwave-assisted dehydration cyclization utilizes the dual properties of microwaves, which have both electric and magnetic fields and strong penetrating power. Under the dual action of microwaves on the reactants, the reaction efficiency is greatly improved, and reactions that cannot be activated under conventional conditions can occur. Li Peng et al. (Research on the synthesis of new bisphenol A diphenyl ether type bismaleimide by microwave method [J]. Fiberglass / Composite Materials, 2013, (04): 13-6.) used a microwave reactor to prepare new bisphenol A diphenyl ether type bismaleimide. Although the yield was slightly lower than that of the normal system reaction within 0.5 hours, the reaction time was greatly shortened, resulting in improved efficiency. Le et al. (Organic Reactions in Ionic Liquids: Ionic Liquid-Promoted Efficient Synthesis of N-Alkyl and N-Arylimides [J]. Synthesis, 2004, 2004 (07): 995-8.) used ionic liquids as a new environmentally friendly reaction medium and promoter to investigate the reaction of cyclic anhydrides with primary amines in ionic liquids. Alpha-amines, heterocyclic amines, and aromatic amines containing various groups, such as methyl, nitro, and chlorine, react rapidly with maleic anhydride or phthalic anhydride in the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [Bmim][PF6] at 140°C, completing the reaction within 20 minutes and affording the corresponding imides in excellent yields. Related ionic liquids [Bmim][BF4] and [Bmim]Cl are also effective. The ionic liquid can typically be recovered by extracting the product and then drying it in a vacuum, and the ionic liquid [Bmim][PF6] exhibits no significant decomposition under these conditions. The recovered solvent can be reused without significant yield loss. Compared to solvent-based methods reported in the literature, the ionic liquid method offers advantages such as high efficiency, versatility, high yield, simplicity, environmental friendliness, and ease of implementation. However, the relatively high cost of ionic liquids increases the process cost.

[0006] The solid solvent method has been reported in the preparation of polyimide materials. Polyimide can be synthesized using a one-step feeding method under benzoic acid conditions at 140°C. However, due to the high reactivity of maleimide monomers and the high reactivity of the product double bond, the one-step feeding method in a solid solvent has a low yield and the product is difficult to separate. No related reports have yet been published.

[0007] In summary, at present, in order to improve the current status of the use of dehydrating agents and solvents in the preparation process of maleimide, it is necessary to further develop the preparation method of maleimide compounds. Summary of the Invention

[0008] In order to solve the above problems, the present invention proposes a method for preparing maleimide based on green chemistry. No solvent is used in the preparation process of amic acid, the solid solvent used in the cyclization process can be recycled, and no dehydrating agent is used. The reaction time is short, the process is simple and easy to operate, and the obtained maleimide has stable properties and wide applicability.

[0009] The object of the present invention is to provide a method for preparing a maleimide compound, wherein the method comprises solid-phase grinding of raw materials including an aniline compound and maleic anhydride to obtain a maleamic acid intermediate product, and then performing a ring-closure reaction to obtain the maleimide compound.

[0010] The aniline compound is selected from one or more of p-alkylaniline, p-cyanoaniline, p-methoxyaniline, p-nitroaniline, p-halogenated aniline, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-methylenebis(2-methyl-6-ethylaniline), bis(4-aminophenoxy)dimethylsilane and polymers containing primary amino groups on benzene rings.

[0011] The maleamic acid intermediate product is a compound in which the primary amino group -NH2 of the aniline compound is converted into the group -NH-CO-CH=CH-CO-OH.

[0012] The ring-closing reaction comprises mixing a maleamic acid intermediate, a polymerization inhibitor, a catalyst and a solid solvent, heating the mixture for reaction, and then performing post-treatment to obtain a maleimide compound.

[0013] The catalyst is selected from one or more of p-toluenesulfonic acid, triethylamine, metal chloride, acidic non-metallic oxide, alkali metal carbonate compounds, and alkali metal bicarbonate compounds.

[0014] The solid solvent is selected from one or more carboxylic acid compounds having a melting point above 30° C., preferably one or more aromatic carboxylic acid compounds, and more preferably benzoic acid.

[0015] The ring-closing reaction temperature is 115-158°C, preferably 120-140°C, and more preferably 125-135°C.

[0016] The present invention has the following beneficial effects:

[0017] (1) The present invention can obtain a stable intermediate product by simply grinding the raw materials including aniline compounds and maleic anhydride. The method is simple and easy and does not require special processes.

[0018] (2) The intermediate product obtained in the present invention undergoes a closing reaction under the action of a catalyst to obtain a maleimide compound. The reaction conditions are mild and controllable, and the reaction yield is high.

[0019] (3) The present invention rationally designs a synthetic route, and the intermediate product can be converted by simple grinding. The reaction is mild, and the subsequent closing reaction does not require a complicated process to obtain the final product. The reaction time is short, the process is simple and easy to operate, and the obtained maleimide has stable properties and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Shown in Example 1 of the present invention p-methylphenylmaleamic acid 1 H NMR spectrum;

[0021] Figure 2 Shown in Example 1 of the present invention p-methylphenylmaleimide 1 H NMR spectrum;

[0022] Figure 3 The infrared spectra of p-methylaniline, p-methylphenylmaleamic acid and p-methylphenylmaleimide in Example 1 are shown;

[0023] Figure 4 The intermediate phenylene bismaleamic acid of Example 3 is shown. 1 H NMR spectrum;

[0024] Figure 5 The intermediate phenylene bismaleimide of Example 3 is shown. 1 H NMR spectrum;

[0025] Figure 6 The infrared spectra of m-phenylenediamine, m-phenylenebismaleamic acid and m-phenylenebismaleimide of Example 3 are shown;

[0026] Figure 7 The infrared spectra of the polyphenyl polyaminomethane, polyamic acid polymer and polymaleimide polymer of Example 5 are shown. DETAILED DESCRIPTION

[0027] The present invention will be described in detail below through specific embodiments, and the features and advantages of the present invention will become clearer and more distinct with these descriptions.

[0028] The invention provides a method for preparing a maleimide compound. The method comprises solid-phase grinding of raw materials including an aniline compound and maleic anhydride to obtain a maleamic acid intermediate product, and then performing a ring-closure reaction to obtain the maleimide compound.

[0029] The aniline compound is selected from one or more of p-alkylaniline, p-cyanoaniline, p-methoxyaniline, p-nitroaniline, p-halogenated aniline, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-methylenebis(2-methyl-6-ethylaniline), bis(4-aminophenoxy)dimethylsilane and polymers containing primary amino groups on benzene rings, and is preferably selected from one or more of p-methylaniline, p-ethylaniline, p-isopropylaniline, p-tert-butylaniline, p-phenylenediamine, m-phenylenediamine and polymers containing primary amino groups on benzene rings.

[0030] More preferably, the aniline compound is one of the following compounds:

[0031] The repeating unit is polyamine polymers.

[0032] The maleamic acid intermediate product is a compound in which the primary amino group -NH2 of the aniline compound is converted into the group -NH-CO-CH=CH-CO-OH.

[0033] Preferably, the maleamic acid intermediate is:

[0034] The repeating unit is polyamide acid polymers.

[0035] The molar ratio of the aniline compound to maleic anhydride is 30:(16-52), preferably 30:(20-45), and more preferably 30:(24-38). Maleic anhydride is one of the reaction raw materials, contains anhydride functional groups, and reacts with amino functional groups to form amic acid groups. Insufficient anhydride content will result in a low conversion rate of the amino group. Although excessive anhydride content can increase the conversion rate of the amino group, it will make the separation of amic acid difficult. In the reaction under solid phase grinding, increasing the amount of maleic anhydride can only slightly increase the amic acid yield.

[0036] The grinding temperature is 15-40° C., preferably 20-32° C., more preferably 22-28° C. The grinding time is 0.25-2 h, preferably 0.25-1.5 h, more preferably 0.5-1 h.

[0037] After grinding, the reaction mixture is added to an anhydrous alcohol solvent for precipitation, and the resulting insoluble matter is filtered and dried to obtain a maleamic acid intermediate. The alcohol solvent is selected from one or more alkyl alcohols, preferably one or more of methanol, propanol, isopropanol and butanol, more preferably methanol.

[0038] The ring-closing reaction comprises mixing a maleamic acid intermediate, a polymerization inhibitor, a catalyst and a solid solvent, heating the mixture for reaction, and then performing post-treatment to obtain a maleimide compound.

[0039] The polymerization inhibitor is selected from one or more of phenolic polymerization inhibitors and quinone polymerization inhibitors, preferably one or more of p-methoxyphenol and / or p-benzoquinone, more preferably p-methoxyphenol.

[0040] The molar ratio of the polymerization inhibitor to the maleamic acid intermediate is (0.2-0.8):(7-8), preferably (0.3-0.7):(7-8), and more preferably (0.4-0.6):(7-8). Maleimide contains double bonds, which may be triggered to undergo crosslinking reactions under high temperature conditions. The optimal content of the polymerization inhibitor is 1% of the system weight. Excessive polymerization inhibitor will increase the difficulty of post-processing.

[0041] The catalyst is selected from one or more of p-toluenesulfonic acid, triethylamine, metal chloride, acidic non-metallic oxide, alkali metal carbonate compound, and alkali metal bicarbonate compound, preferably selected from one or more of p-toluenesulfonic acid and acidic non-metallic oxide, more preferably p-toluenesulfonic acid. The catalysts such as p-toluenesulfonic acid, triethylamine, and metal chloride can all catalyze the conversion of amic acid into imide. P-toluenesulfonic acid is an acidic catalyst with a better catalytic effect. Compared with other alkaline catalysts and neutral catalysts, p-toluenesulfonic acid has better water solubility, so that p-toluenesulfonic acid can be directly separated in the washing step of separating benzoic acid without the need for separate separation treatment. The catalytic effect of other types of catalysts is not as good as p-toluenesulfonic acid. Metal chlorides and the like are poorly removed by washing during post-treatment and may remain. The amount of catalyst is controlled within 10% of the system mass. Excessive catalyst will reduce the purity of the subsequent recovery of benzoic acid.

[0042] The molar ratio of the catalyst to the maleamic acid intermediate is (1-6):(7-8), preferably (1-5):(7-8), and more preferably (2-4):(7-8).

[0043] The solid solvent is selected from one or more carboxylic acid compounds and acetylcholine with a melting point above 30° C., preferably one or more aromatic carboxylic acid compounds and acetylcholine, more preferably benzoic acid, acetylcholine or salicylic acid.

[0044] The molar ratio of the solid solvent to the maleamic acid intermediate is (20-50): (7-8), preferably (25-45): (7-8), and more preferably (30-40): (7-8). The water solubility of a solid solvent such as benzoic acid (melting point 124°C) varies greatly with temperature. The solubility of benzoic acid at room temperature is 0.17g / 100g water, and the solubility at 95°C is 6.8g / 100g water. Under molten conditions, the acidic conditions of the solid solvent can promote the ring-closure reaction of amic acid to imide. Benzoic acid and acetylcholine can form a deep eutectic solvent and can also be used as a solvent for the reaction; salicylic acid has similar properties to benzoic acid, and its melting point is 158°C. It can be used as a reaction solvent. The reaction temperature is at least 158, but the reaction temperature is high and the conversion rate is relatively low. During the reaction, part of the solid solvent will sublime to the top of the Schlink tube, so the amount of solid solvent is preferably controlled within the above range. The molar ratio of solid solvent to maleamic acid intermediate is (30-40): (7-8) is optimal. Too much solid solvent will increase the post-processing steps and make it more complicated, with more hot water and increased costs. Too little solid solvent will result in incomplete reaction, and the residual solid reactant is difficult to separate. The closed-loop reaction temperature is 115-158°C, preferably 120-140°C, more preferably 125-135°C; the reaction time is 0.5-3h, preferably 0.5-2.5h, more preferably 1-2h. The optimal temperature for the benzoic acid system is 125-135°C, and the optimal reaction time is 0.5-1h. To obtain a sufficient conversion rate below the temperature range, the reaction time needs to be extended. Too long a reaction time increases the possibility of double bond polymerization, and too high a reaction temperature will cause the product to cross-link. When salicylic acid is used as a solid solvent, the minimum reaction temperature is 158°C, and salicylic acid is required for dissolution, but too high a reaction temperature will lead to a decrease in yield.

[0045] After the reaction is completed, post-treatment is performed, which includes washing, filtering, and recovering the solid solvent. The reaction mixture is cooled to room temperature, placed in hot water above 65°C for washing and precipitation, and filtered while hot to obtain a solid, which is then dried to obtain a maleimide compound. The filtered filtrate is cooled to room temperature and filtered to obtain a recovered benzoic acid solid.

[0046] The maleimide compound is one of the following compounds:

[0047]

[0048] Contains groups A polymer wherein R1 is an alkyl group, -OCH3, -CN, -NO2 or a halide group, and R2 is -CH2- or -O-, preferably

[0049]

[0050] Contains groups The polymer, wherein R1 is methyl, ethyl, isopropyl, tert-butyl, -OCH3, -CN, -NO2, more preferably

[0051] Or the repeating unit is of polymers.

[0052] Example

[0053] Example 1

[0054] In a 200ml stainless steel mortar, 3.21g (about 30.00mmol) of p-methylaniline and 2.94g (about 30.00mmol) of maleic anhydride were added to the mortar and ground at 25°C for 0.5h to stop the reaction. The reaction mixture was added to anhydrous methanol for precipitation, and the resulting yellow insoluble matter was further obtained by suction filtration and the filter cake was washed with anhydrous methanol. Finally, the product was dried in a vacuum oven at 50°C for 24h. p-Toluenemaleamic acid was obtained as a light yellow solid powder with a mass yield of 91%.

[0055]

[0056] p-Toluenemaleamic acid 1 H NMR spectrum Figure 1 The infrared spectra of p-methylaniline and p-methylphenylmaleamic acid are shown in Figure 3 As shown, the infrared characteristic peak of p-methylphenylmaleamic acid is at 1705 cm -1 The absorption peak of -C=O of amidic acid is generated, 1535 cm -1 and 1404cm -1 It is the absorption peak of secondary amide -NH and -CN-.

[0057] 4.50g (about 36.9mmol) benzoic acid, 1.50g (about 7.31mmol) p-methylphenylmaleamic acid, 0.50g (about 2.90mmol) p-methylbenzenesulfonic acid and 0.065g (about 0.52mmol) p-methoxyphenol are added to a 25mL round-bottom flask and stirred at reflux for 1h at 130°C to stop the reaction. The reaction mixture is cooled to room temperature, put into hot water for washing and precipitating, and filtered while hot to obtain a yellow solid, which is washed with a small amount of saturated sodium bicarbonate solution. The filtered filtrate is cooled to room temperature and filtered to obtain a recovered benzoic acid solid. Finally, the product is dried in a vacuum oven at 80°C for 24h. P-methylphenylmaleimide is obtained as a yellow solid powder with a mass yield of 85%.

[0058]

[0059] p-Toluenemaleimide 1 H NMR spectrum Figure 2 As shown, the infrared spectrum is as Figure 3 As shown. Infrared spectrum at 3093cm -1 The absorption at 1712 cm represents the double bond -CH stretching vibration absorption peak. -1 The corresponding absorption peak is C=O on the imide ring, at 1153 cm -1 The absorption peak corresponding to CNC, imide ring, 686cm -1 The corresponding bending vibration absorption peak of C=CH on the imide ring is at 833 cm -1 The absorption peak of the disubstituted benzene ring CH.

[0060] Example 2

[0061] p-Toluenemaleamic acid was prepared according to the method of Example 1. The amount of p-toluidine, the amount of maleic anhydride, the grinding time and the yield are shown in Table 1.

[0062] Table 1

[0063] Serial number p-Toluidine (g) Maleic anhydride (g) Grinding time (h) Yield (%) Remark 1 3.21 2.94 0.5 91 Example 1 2 3.21 3.23 0.5 91 Example 2 3 3.21 3.53 1 92 Example 2

[0064] From the data in Table 1, it can be seen that, under the same other conditions, increasing the amount of maleic anhydride and the grinding time at the same time is conducive to further improving the yield.

[0065] p-Toluenemaleimide was prepared according to the method of Example 1. The amount of p-Toluenemaleamic acid, the amount of benzoic acid, the reaction temperature, the reaction time and the yield are shown in Table 2.

[0066] Table 2

[0067]

[0068] Example 3

[0069] In a 200ml stainless steel mortar, 3.24g (about 30.00mmol) of m-phenylenediamine and 5.88g (about 60.00mmol) of maleic anhydride were added to the mortar and ground at 25°C for 0.5h to stop the reaction. The reaction mixture was added to anhydrous methanol for precipitation, and the resulting yellow insoluble matter was further obtained by suction filtration and the filter cake was washed with anhydrous methanol. Finally, the product was dried in a vacuum oven at 50°C for 24h. Metaphenylene bismaleamic acid was obtained as a light yellow solid powder with a yield of 82%.

[0070]

[0071] m-phenylene bismaleamic acid 1H NMR spectrum Figure 4 In its infrared spectrum, the infrared characteristic peak is at 1712cm -1 The absorption peak of C=O of amide acid is 1554 cm -1 and 1404cm -1 It is the absorption peak of secondary amide -NH and -CN- (see Figure 6 ).

[0072] 4.50g (about 36.8mmol) of benzoic acid, 1.50g (about 4.93mmol) of m-phenylene bismaleamic acid, 0.50g (about 2.90mmol) of p-toluenesulfonic acid and 0.065g (about 0.52mmol) of p-methoxyphenol were added to a 25mL round-bottom flask and stirred at 130°C for 1h to stop the reaction. The reaction mixture was cooled to room temperature, put into hot water for washing and precipitation, and filtered while hot to obtain a yellow solid, which was washed with a small amount of saturated sodium bicarbonate solution. The filtered filtrate was cooled to room temperature and filtered to obtain a recovered benzoic acid solid. Finally, the product was dried in a vacuum oven at 80°C for 24h. Metaphenylenediamine maleimide was obtained as a yellow solid powder with a mass yield of 91%.

[0073]

[0074] m-phenylene bismaleimide 1 H NMR spectrum Figure 5 As shown. In its infrared spectrum, the infrared spectrum at 3105cm -1 The absorption at 1720 cm represents the double bond -CH stretching vibration absorption peak. -1 The corresponding absorption peak is C=O on the imide ring, at 1149 cm -1 The absorption peak corresponding to CNC, imide ring, 689cm -1 The corresponding bending vibration absorption peak of C=CH on the imide ring is at 825cm -1 The absorption peak of the meta-disubstituted benzene ring CH (see Figure 6 ).

[0075] Example 4

[0076] Metaphenylene bismaleamic acid was prepared according to the method of Example 3. The amount of metaphenylenediamine, the amount of maleic anhydride, the grinding time and the yield are shown in Table 3.

[0077] Table 3

[0078] Serial number m-Phenylenediamine(g) Maleic anhydride (g) Grinding time (h) Yield (%) Remark 1 3.24 5.88 0.5 82 Example 3 2 3.24 6.47 0.5 83 Example 4 3 3.24 7.06 1 90 Example 4

[0079] Meta-phenylene bismaleimide was prepared according to the method of Example 3. The amount of meta-phenylene bismaleamic acid, the amount of benzoic acid, the reaction temperature, the reaction time and the yield are shown in Table 4.

[0080] Table 4

[0081]

[0082]

[0083] Too high a reaction temperature will result in a decrease in yield.

[0084] Example 5

[0085] In a 200ml stainless steel mortar, 4.05g (39.90mmol-NH2) polyphenyl polyaminomethane (Wanhua, average molecular weight of 135g / mol, average functionality of 1.33, according to the ratio of amino group to anhydride) and 3.91g (about 39.90mmol) maleic anhydride were added to the mortar and ground at 25°C for 0.5h to stop the reaction. The reaction mixture was added to anhydrous methanol for precipitation, and the resulting yellow insoluble matter was further obtained by suction filtration and the filter cake was washed with anhydrous methanol. Finally, the product was dried in a vacuum oven at 50°C for 24h to obtain a polyamide acid polymer as a golden solid powder with a yield of 85%.

[0086]

[0087] The infrared spectrum of polyamide acid polymer is shown in Figure 7 As shown, the infrared characteristic peak is at 1708cm -1 The absorption peak of -C=O of amide acid is generated, 1546 cm -1 and 1406cm -1 It is the absorption peak of secondary amide -NH and -CN-.

[0088] 4.50g (about 36.8mmol) of benzoic acid, 1.50g of polyamide acid polymer, 0.50g (about 2.90mmol) of p-toluenesulfonic acid and 0.065g (about 0.52mmol) of p-methoxyphenol were added to a 25mL round-bottom flask and stirred at 130°C for 1h to stop the reaction. The reaction mixture was cooled to room temperature, put into hot water for washing and precipitation, and filtered while hot to obtain a yellow solid, which was washed with a small amount of saturated sodium bicarbonate solution. The filtered filtrate was cooled to room temperature and filtered to obtain a recovered benzoic acid solid. Finally, the product was dried in a vacuum oven at 80°C for 24h. A multi-maleimide polymer was obtained as a yellow solid with a yield of 93%.

[0089]

[0090] The infrared spectrum showed that at 1712 cm -1 The corresponding absorption peak is C=O on the imide ring, at 1145 cm -1 The absorption peak corresponding to CNC, imide ring, 690cm -1 The corresponding absorption peak is the bending vibration of C=CH on the imide ring.

[0091] Example 6

[0092] Polyamic acid polymer was prepared according to the method of Example 5. The amount of polyamine polymer, amount of maleic anhydride, grinding time and yield are shown in Table 5.

[0093] Table 5

[0094] Serial number Polyamine polymer (g) Maleic anhydride (g) Grinding time (h) Yield (%) Remark 1 4.05 3.91 0.5 85 Example 5 2 4.05 4.30 0.5 89 Example 6 3 4.05 4.69 1 85 Example 6

[0095] Polymaleimide polymer was prepared according to the method of Example 5. The amount of polyamic acid polymer, the amount of benzoic acid, the reaction temperature, the reaction time and the yield are shown in Table 6.

[0096] Table 6

[0097]

[0098] Too high a reaction temperature will result in a decrease in yield.

[0099] Comparative Example

[0100] 4.50 g (36.8 mmol) of benzoic acid, 0.78 g (7.29 mmol) of p-methylaniline, 0.72 g (7.30 mmol) of maleic anhydride, 0.50 g (2.90 mmol) of p-methylbenzenesulfonic acid, and 0.065 g (0.52 mmol) of p-methoxyphenol were added to a 25 mL round-bottom flask and stirred at 130°C for 1 hour. The reaction mixture was cooled to room temperature, washed and precipitated in hot water, and filtered while hot to obtain a yellow solid. The target product was obtained by column chromatography. The filtered filtrate was cooled to room temperature and filtered to obtain recovered benzoic acid solid. Finally, the product was dried in a vacuum oven at 80°C for 24 hours. p-methylphenylmaleimide was obtained as a yellow solid powder with a mass yield of 14%.

[0101]

[0102] The present invention has been described in detail above with reference to specific embodiments and / or exemplary examples and the accompanying drawings. However, these descriptions should not be construed as limiting the present invention. Those skilled in the art will appreciate that various equivalent substitutions, modifications, or improvements may be made to the technical solutions and implementations of the present invention without departing from the spirit and scope of the present invention, all of which fall within the scope of the present invention. The scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a maleimide compound, wherein the method comprises solid-phase grinding of raw materials including an aniline compound and maleic anhydride to obtain a maleamic acid intermediate product, and then performing a ring-closure reaction to obtain the maleimide compound.

2. The method according to claim 1, characterized in that The aniline compound is selected from one or more of p-alkylaniline, p-cyanoaniline, p-methoxyaniline, p-nitroaniline, p-halogenated aniline, m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, 4,4'-methylenebis(2-methyl-6-ethylaniline), bis(4-aminophenoxy)dimethylsilane and polymers containing primary amino groups on benzene rings, and is preferably selected from one or more of p-methylaniline, p-ethylaniline, p-isopropylaniline, p-tert-butylaniline, p-phenylenediamine, m-phenylenediamine and polymers containing primary amino groups on benzene rings.

3. The method according to claim 1, characterized in that The maleamic acid intermediate product is a compound in which the primary amino group -NH2 of the aniline compound is converted into the group -NH-CO-CH=CH-CO-OH.

4. The method according to claim 1, wherein The grinding temperature is 15-40°C, preferably 20-32°C, and the grinding time is 0.25-2h, preferably 0.25-1.5h.

5. The method according to claim 1, wherein The ring-closing reaction comprises mixing a maleamic acid intermediate, a polymerization inhibitor, a catalyst and a solid solvent, heating the mixture for reaction, and then performing post-treatment to obtain a maleimide compound.

6. The method according to claim 5, characterized in that The polymerization inhibitor is selected from one or more of phenolic polymerization inhibitors and quinone polymerization inhibitors, preferably one or more of p-methoxyphenol and / or p-benzoquinone.

7. The method according to claim 5, characterized in that The catalyst is selected from one or more of p-toluenesulfonic acid, triethylamine, metal chloride, acidic non-metallic oxide, alkali metal carbonate compound, and alkali metal bicarbonate compound, preferably selected from one or more of p-toluenesulfonic acid and acidic non-metallic oxide.

8. The method according to claim 5, characterized in that The solid solvent is selected from one or more carboxylic acid compounds having a melting point above 30°C, preferably one or more aromatic carboxylic acid compounds. The molar ratio of the solid solvent to the maleamic acid intermediate is (20-50):(7-8), preferably (25-45):(7-8).

9. The method according to claim 5, characterized in that The ring-closing reaction temperature is 115-158°C, preferably 120-140°C, and more preferably 125-135°C.

10. The method according to any one of claims 1 to 9, characterized in that The maleimide compound is one of the following compounds: Contains groups A polymer, wherein R1 is an alkyl group, -OCH3, -CN, -NO2 or a halide group, and R2 is -CH2- or -O-, preferably: Contains groups A polymer, wherein R1 is methyl, ethyl, isopropyl, tert-butyl, -OCH3, -CN, -NO2, more preferably Or the repeating unit is of polymers.

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