Imidazole epoxy resin curing agent, preparation method and application thereof

Abstract

The present application relates to the technical field of organic synthesis, and particularly relates to an imidazole epoxy resin curing agent and a preparation method and application thereof. The imidazole epoxy resin curing agent is prepared from the following components in parts by weight: 82-144 parts of alkyl imidazole, 108-198 parts of quinone compound and 229-342 parts of solvent. The present application connects a phenolic compound to an imidazole ring, that is, the alkyl imidazole and the quinone compound are subjected to a Michael addition reaction to generate the alkyl imidazole connected with the phenolic compound. The alkyl imidazole curing agent containing a phenolic hydroxyl group fundamentally solves the separation problem of the imidazole curing agent and the phenolic polymerization inhibitor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic synthesis, in particular to an imidazole epoxy resin curing agent and a preparation method and application thereof. BACKGROUND

[0002] Imidazole compounds belong to heat-curable epoxy resin curing agents, and the cured product has excellent heat resistance and insulation, and is widely used in the fields of electronics, electrical appliances and composites. The disadvantage is that the service life after mixing with epoxy resin is relatively short, generally not more than eight hours at room temperature, which greatly limits the use of imidazole curing agents. CN114230767A uses a microcapsule method to coat the imidazole curing agent, and then disperses it into the epoxy resin for heat curing. However, it can only be used in pure epoxy resin systems, and cannot be used in systems containing diluents (or solvents), because the diluent or solvent will dissolve the capsule wall in the microcapsule, release the imidazole curing agent, and still have the problem of service life.

[0003] JP58-13623 uses alkyl imidazole addition with epoxy resin, and the product is dispersed into epoxy resin after being crushed, which can prolong the service life of alkyl imidazole curing agent. The principle is to use alkyl imidazole-epoxy resin adducts that are insoluble in epoxy resin to prolong the service life. However, such imidazole adduct curing agents still cannot be used in systems containing diluents or solvents, because once the adduct is dissolved, the imidazole ring is exposed, which can react with epoxy resin, thereby losing the latent property, which is equivalent to the service life of conventional alkyl imidazole.

[0004] The phenolic hydroxyl group has the function of prolonging the service life of imidazole curing agent, and the principle is that the phenolic hydroxyl group can absorb imidazole negative ion bonds and interrupt the chain reaction, prompting the epoxy resin to stop the curing reaction, thereby prolonging the service life. JP52-3828 uses a method of directly adding a phenolic compound to the alkyl imidazole-epoxy resin adduct to prepare a curing agent with a longer service life. Such curing agents can be dissolved in formulations containing diluents or solvents, and the imidazole curing agent and the phenolic compound are in a separate state, the imidazole curing agent can directly cure the epoxy resin, and the phenolic compound loses the polymerization inhibition function, but this method still cannot solve the problem of short service life in the presence of diluents or solvents. SUMMARY

[0005] In order to solve the above problems, the present application provides an imidazole epoxy resin curing agent and a preparation method and application thereof, which connects a phenolic compound to the imidazole ring, i.e. the alkyl imidazole is reacted with a quinone compound by Michael addition to generate an alkyl imidazole connected with a phenolic compound. Such alkyl imidazole curing agent containing phenolic hydroxyl group fundamentally solves the separation problem of imidazole curing agent and phenolic polymerization inhibitor.

[0006] In order to achieve the above purpose, the present application provides the following technical scheme:

[0007] The present application provides an imidazole epoxy resin curing agent, which is prepared from the following components by weight:

[0008] alkyl imidazole 82-144 parts, quinone compound 108-198 parts and solvent 229-342 parts.

[0009] Preferably, the imidazole epoxy resin curing agent is prepared from the following components by weight:

[0010] alkyl imidazole 110 parts, quinone compound 119-175 parts and solvent 235-357 parts.

[0011] Preferably, the alkyl imidazole comprises 2-methyl imidazole and / or 2-ethyl-4-methyl imidazole.

[0012] Preferably, the quinone compound comprises one or more of p-benzoquinone, o-benzoquinone, 1,4-naphthoquinone and 1,2-naphthoquinone.

[0013] Preferably, the solvent comprises one or more of tetrahydrofuran, dioxane, N,N-dimethylformamide, N,N-dimethylacetamide and hexamethylphosphoric triamide.

[0014] The present application also provides a preparation method of the imidazole epoxy resin curing agent as described in the above technical solution, which comprises the following steps: mixing the alkyl imidazole, quinone compound and solvent under nitrogen protection, addition reaction at 80-120℃ for 5-8h, removing the solvent to obtain the imidazole epoxy resin curing agent.

[0015] The present application also provides the application of the imidazole epoxy resin curing agent as described in the above technical solution in curing epoxy resin.

[0016] Preferably, the application comprises the following steps: mixing the imidazole epoxy resin curing agent with a good solvent and epoxy resin and then curing.

[0017] Preferably, the mass ratio of the imidazole epoxy resin curing agent, good solvent and epoxy resin is 8.8-14.6:50:100.

[0018] Preferably, the good solvent comprises N,N-dimethylformamide.

[0019] The curing conditions comprise a temperature of 100℃ and a time of 2h.

[0020] Beneficial effects:

[0021] The present application generates a phenolic hydroxyl imidazole compound curing agent by carrying out Michael addition reaction of alkyl imidazole and quinone compound in solvent environment. After mixing with epoxy resin, the tertiary nitrogen atom on imidazole ring attacks epoxy group to form oxyanion, and the phenolic hydroxyl group prevents chain reaction of oxyanion, thereby delaying etherification crosslinking reaction of epoxy resin, and finally showing prolonged service life at room temperature from macroscopic level. When heated, the oxyanion kinetic energy becomes large and can complete etherification reaction, so it can be normally cured. The present application utilizes the polymerization inhibition function of phenolic hydroxyl group to prepare phenolic imidazole curing agent with long service life at room temperature. DETAILED DESCRIPTION

[0022] The present application provides an imidazole epoxy resin curing agent prepared from the following components by weight: 82-144 parts of alkyl imidazole, 108-198 parts of quinone compound and 229-342 parts of solvent. In the present application, the imidazole epoxy resin curing agent is preferably prepared from the following components by weight: 110 parts of alkyl imidazole, 119-175 parts of quinone compound and 235-357 parts of solvent. In the present application, the alkyl imidazole preferably includes 2-methyl imidazole and / or 2-ethyl-4-methyl imidazole. In the present application, the quinone compound preferably includes one or more of p-benzoquinone, o-benzoquinone, 1,4-naphthoquinone and 1,2-naphthoquinone. In the present application, the solvent preferably includes one or more of tetrahydrofuran, dioxane, N,N-dimethylformamide, N,N-dimethylacetamide and hexamethylphosphoric triamide. The present application does not have special limitation on the source of the above-mentioned reagents, and conventional commercially available reagents can be used.

[0023] The present application also provides a preparation method of the imidazole epoxy resin curing agent described in the above technical solution, which comprises the following steps: mixing the alkyl imidazole, quinone compound and solvent under nitrogen protection, carrying out addition reaction at 80-120℃ for 5-8h, removing the solvent to obtain the imidazole epoxy resin curing agent.

[0024] The present application also provides the application of the imidazole epoxy resin curing agent described in the above technical solution in curing epoxy resin. In the present application, the application preferably comprises the following steps: mixing the imidazole epoxy resin curing agent with good solvent and epoxy resin and then curing. In the present application, the mass ratio of the imidazole epoxy resin curing agent to good solvent and epoxy resin is preferably 8.8-14.6:50:100. In the present application, the good solvent preferably includes N,N-dimethylformamide. In the present application, the curing conditions preferably include temperature of 100℃ and time of 2h.

[0025] In order to further illustrate the present application, the present application is described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.

[0026] Example 1

[0027] Under nitrogen protection, 82 g of 2-methylimidazole and 108 g of p-benzoquinone were dissolved in 190 g of tetrahydrofuran, and heated to reflux for 8 hours. The tetrahydrofuran solvent was evaporated under reduced pressure to obtain 190 g of brown solid (imidazole epoxy resin curing agent).

[0028] Example 2

[0029] Under nitrogen protection, 110 g of 2-ethyl-4-methylimidazole and 119 g of p-benzoquinone were dissolved in 229 g of dioxane, and reacted at 100°C for 5 hours. The dioxane solvent was evaporated under reduced pressure. The residue was extracted with 200 g of xylene to remove unreacted materials. The residue was evaporated to dryness to obtain 206 g of brown solid (imidazole epoxy resin curing agent).

[0030] Example 3

[0031] Under nitrogen protection, 110 g of 2-ethyl-4-methylimidazole and 125 g of o-benzoquinone were dissolved in 235 g of N,N-dimethylformamide, and heated to 80°C for 8 hours. The N,N-dimethylformamide solvent was evaporated under vacuum. The residue was extracted with 200 g of xylene to remove unreacted materials. The residue was evaporated to dryness to obtain 182 g of light brown solid (imidazole epoxy resin curing agent).

[0032] Example 4

[0033] Under nitrogen protection, 82 g of 2-methylimidazole and 175 g of 1,4-naphthoquinone were dissolved in 257 g of N,N-dimethylformamide, and reacted at 100°C for 8 hours. The N,N-dimethylformamide solvent was evaporated under reduced pressure. The residue was extracted with 200 g of xylene to remove unreacted materials. The residue was evaporated to dryness to obtain 186 g of dark brown solid (imidazole epoxy resin curing agent).

[0034] Example 5

[0035] Under nitrogen protection, 144 g of 2-phenylimidazole and 198 g of 1,2-naphthoquinone were dissolved in 342 g of N,N-dimethylacetamide, and reacted at 120°C for 8 hours. The N,N-dimethylacetamide solvent was evaporated under reduced pressure. Unreacted materials were extracted with 300 g of xylene, and the residue was evaporated to dryness to obtain 233 g of light brown solid (imidazole epoxy resin curing agent).

[0036] Example 6

[0037] Under nitrogen protection, 144 g of 2-phenylimidazole and 125 g of o-benzoquinone were dissolved in 235 g of hexamethylphosphoramide, and reacted at 120°C for 8 hours. Hexamethylphosphoramide solvent was evaporated under reduced pressure. Unreacted substances were extracted with 200 g of dimethylbenzene, and the residue was evaporated to dryness to obtain 212 g of light brown solid (imidazole epoxy resin curing agent).

[0038] Example 7

[0039] The products of Examples 1 to 6 were dissolved in N,N-dimethylformamide (DMF), and an epoxy resin was mixed with the solution, which was used in an amount corresponding to 5% of alkyl imidazole. The epoxy resin was a liquid bisphenol A type epoxy resin with EEW of 190 (128). The formulations were as follows:

[0040] A. Mass ratio of 128 / Example 1 / DMF = 100 / 11.6 / 50;

[0041] B. Mass ratio of 128 / Example 2 / DMF = 100 / 9.9 / 50;

[0042] C. Mass ratio of 128 / Example 3 / DMF = 100 / 9.9 / 50;

[0043] D. Mass ratio of 128 / Example 4 / DMF = 100 / 14.6 / 50;

[0044] E. Mass ratio of 128 / Example 5 / DMF = 100 / 10.5 / 50;

[0045] F. Mass ratio of 128 / Example 6 / DMF = 100 / 8.8 / 50.

[0046] The curing method was to mix the epoxy resin, imidazole epoxy resin curing agent and N,N-dimethylformamide, and then cure at 100°C for 2 hours.

[0047] The evaluation criteria were that the curing was based on the criterion that the needle did not penetrate, and the needle was a blunt needle on the market; the storage period was based on the criterion that the viscosity doubled.

[0048] The results of the examples are shown in Table 1.

[0049] Table 1 Curing results

[0050] No. A B C D E F Storage period 25°C / days 24 35 30 23 18 16 Curing 100°C / 2 hours Curing Curing Curing Curing Curing Curing

[0051] Comparative Example 1

[0052] The formulations were as follows, and the mass ratios were as follows:

[0053] G. Mass ratio of 128 / 2-methylimidazole / DMF = 100 / 5 / 50;

[0054] H.128 / 2-ethyl-4-methylimidazole / DMF = 100 / 5 / 50;

[0055] I.128 / 2-phenylimidazole / DMF = 100 / 5 / 50.

[0056] 128 is a liquid bisphenol A type epoxy resin with EEW 190, cured by the same method and evaluated as in Example 7.

[0057] The results of the comparative examples are shown in Table 2.

[0058] Curing results

[0059] No. G H I Storage period 25°C / days <1 <1 <1 Curing 100°C / 2 hours Curing Curing Curing

[0060] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, not all the embodiments, and people can also obtain other embodiments according to the present embodiments without creativity, which all belong to the protection scope of the present application.

Claims

1. Application of imidazole epoxy resin curing agents in curing epoxy resins; The preparation method of the imidazole epoxy resin curing agent is as follows: under nitrogen protection, 110g of 2-ethyl-4-methylimidazolium and 119g of p-benzoquinone are dissolved in 229g of dioxane, reacted at 100℃ for 5 hours, the dioxane solvent is evaporated under reduced pressure, the residue is extracted with 200g of xylene to remove unreacted substances, and the residue is then heated to dryness to obtain 206g of imidazole epoxy resin curing agent; The application involves the following steps: mixing the imidazole epoxy resin curing agent with a good solvent and epoxy resin, followed by curing. The mass ratio of the imidazole epoxy resin curing agent to the good solvent and epoxy resin is 9.9:50:

100. The good solvent is N,N-dimethylformamide; the curing conditions are: temperature 100℃, time 2h.