Epoxy resin with high reprocessability and preparation method thereof

Abstract

The invention discloses an epoxy resin with high reprocessability and a preparation method thereof, the epoxy resin contains ester bonds, and raw materials for preparing the epoxy resin comprise an epoxy monomer, a curing agent, an accelerant and a liquid ester exchange catalyst; wherein the liquid transesterification catalyst is obtained by carrying out addition reaction on an imidazole derivative and fumarate. The epoxy resin comprises a liquid ester exchange catalyst obtained by addition reaction of an imidazole derivative and fumarate, and the catalyst has high-temperature stability, can maintain a stable structure in a high-temperature curing process, a high-temperature processing process and a service temperature, and avoids high-temperature decomposition and volatilization; besides, the catalyst is in a liquid state, has good compatibility with epoxy resin, can be uniformly dispersed in the epoxy resin, and is beneficial to catalysis of an exchange reaction of dynamic covalent bonds in a high-temperature reprocessing process, so that the epoxy resin is endowed with excellent reprocessing performance, and heat recovery and thermal remodeling of the epoxy resin are realized.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to an epoxy resin with high reprocessability and a preparation method thereof. Background Art

[0002] Anhydride epoxy resin is a cross-linked polymer material containing ester bonds that is widely used in industry and life. The introduction of transesterification reaction allows it to maintain the cross-linked structure while obtaining excellent reprocessing performance. This type of material is named glass-like polymer, which can achieve network topology rearrangement through dynamic covalent bond exchange reaction, thereby achieving reprocessing of the cross-linked network. In order to improve the reprocessing performance of epoxy resin, it is often necessary to add an esterification catalyst.

[0003] Commonly used transesterification catalysts include metal salt catalysts, organic molecular catalysts, and organic salt catalysts. However, due to their solid state and high melting point, metal salt catalysts present serious heterogeneous dispersion problems in resins, which complicates their presence in epoxy monomers. Similarly, organic salt catalysts also face dispersibility problems when in solid state, usually requiring solvents to assist dispersion, and may decompose during high-temperature curing when preparing epoxy resins. Organic catalysts such as imidazole and the most widely used 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) also need to be heated above the melting point to disperse; TBD and its derivatives also have the problem of easy thermal decomposition at higher processing temperatures or service temperatures. Therefore, the reprocessing performance of existing epoxy resins cannot reach a satisfactory level and still needs to be further improved. Summary of the invention

[0004] The present invention aims to solve one of the problems existing in the background technology at least to a certain extent. To this end, one object of the present invention is to provide an epoxy resin with high reprocessing performance.

[0005] Specifically, the present invention provides an epoxy resin with high reprocessability, wherein the epoxy resin contains an ester bond, and the raw materials for preparing the epoxy resin include: an epoxy monomer, a curing agent, an accelerator and a liquid transesterification catalyst; wherein the liquid transesterification catalyst is obtained by an addition reaction between an imidazole derivative and a fumaric acid ester.

[0006] The epoxy resin of the present invention comprises a liquid ester exchange catalyst obtained by an addition reaction of an imidazole derivative and a fumarate ester. The catalyst has high-temperature stability and can maintain a stable structure during a high-temperature curing process, a high-temperature processing process and a service temperature to avoid high-temperature decomposition and volatilization. In addition, the catalyst is liquid and has good compatibility with the epoxy resin. It can be evenly dispersed in the epoxy resin and is beneficial for catalyzing the exchange reaction of dynamic covalent bonds during high-temperature reprocessing, thereby giving the epoxy resin excellent reprocessing performance and realizing thermal recovery and thermal reshaping of the epoxy resin.

[0007] According to some embodiments of the present invention, the imidazole derivative includes an aryl imidazole; preferably, the aryl imidazole includes at least one of 4-phenyl imidazole, 4-biphenyl imidazole, and 4-naphthyl imidazole. The aromatic group on the aryl imidazole can provide steric hindrance, reduce the catalytic performance of the catalyst at the service temperature, and do not affect the catalytic activity of the catalyst at high temperature.

[0008] According to some embodiments of the present invention, the fumarate comprises at least one of bis(2-ethylhexyl)fumarate, dibutyl fumarate, and bis(2-isopropyl-5-methylhexyl)fumarate. The long-chain alkyl in the fumarate can provide steric hindrance, reduce the catalytic performance of the catalyst at the service temperature, and do not affect the catalytic activity of the catalyst at high temperature.

[0009] According to some embodiments of the present invention, the liquid transesterification catalyst comprises Optimizing the type of liquid transesterification catalyst is beneficial to improving the dispersibility and high temperature stability of the catalyst.

[0010] According to some embodiments of the present invention, the mass proportion of the liquid transesterification catalyst in the raw material is 4%-6%. Optimizing the amount of the transesterification catalyst is beneficial to improving the reprocessability of the epoxy resin containing ester bonds.

[0011] According to some embodiments of the present invention, the epoxy resin comprises anhydride epoxy resin.

[0012] The second aspect of the present invention provides a method for preparing the epoxy resin with high reprocessability according to the first aspect of the present invention, comprising the following steps:

[0013] The epoxy monomer, curing agent, accelerator and liquid transesterification catalyst are mixed under heating and cured to obtain epoxy resin;

[0014] Wherein, at least one of the epoxy monomer, curing agent and accelerator contains an ester bond; and the liquid transesterification catalyst is obtained by an addition reaction between an imidazole derivative and a fumaric acid ester.

[0015] The method of the invention has a simple process flow, does not require additional steps, has good reproducibility, and is suitable for large-scale industrial production applications.

[0016] According to some embodiments of the present invention, the heating temperature is 50-70° C. and the heating time is 20-40 min. Mixing the raw materials at a certain heating temperature is conducive to uniform dispersion of the transesterification catalyst in the entire reaction system, thereby facilitating the reprocessability of the epoxy resin containing ester bonds at high temperatures.

[0017] According to some embodiments of the present invention, the curing temperature is 130-150° C. and the curing time is 10-14 hours. Optimizing the curing temperature is conducive to obtaining an epoxy resin with stable mechanical properties at the service temperature.

[0018] According to some embodiments of the present invention, after mixing and before curing, the method further comprises: degassing at 70-90°C under vacuum, and pre-curing at 70-90°C; preferably, the pre-curing time is 3-5 hours. Degassing before curing can ensure that the physical properties and appearance quality of the resin will not be affected by the presence of bubbles during the curing process, thereby improving the overall quality of the final product, improving the curing effect, reducing the stress concentration caused by bubbles, and thus extending the service life of the resin.

[0019] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a photograph of the epoxy resin sample prepared in Example 1.

[0021] Figure 2 It is a TGA (thermal gravimetric analysis) curve of the epoxy resin prepared in Example 1.

[0022] Figure 3 This is a photo of the epoxy resin prepared in Example 1 after reprocessing.

[0023] Figure 4 is the calculation of the activation energy of the epoxy resin transesterification reaction prepared in Example 1, Figure 4 a: Epoxy resin shear stress relaxation test (the horizontal axis is time, and the vertical axis is normalized stress); Figure 4 b: Arrhenius relationship fitting line (the horizontal axis is the inverse of the temperature multiplied by 1000, unit (K -1 ), the ordinate is ln (characteristic relaxation temperature), where the characteristic relaxation temperature is given by Figure 4 a, which is the time (in s) for the normalized stress of the curve corresponding to each temperature to drop to 1 / e. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the present application is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present application belongs. In the embodiments, unless otherwise specified, the raw materials used are commercially available, and the methods used in the following embodiments are conventional methods in the art unless otherwise specified.

[0025] In a first aspect, the present invention provides an epoxy resin with high reprocessability, wherein the epoxy resin contains an ester bond, and the raw materials for preparing the epoxy resin include: an epoxy monomer, a curing agent, an accelerator and a liquid transesterification catalyst; wherein the liquid transesterification catalyst is obtained by an addition reaction between an imidazole derivative and a fumaric acid ester.

[0026] The epoxy resin of the present invention comprises a liquid ester exchange catalyst obtained by an addition reaction of an imidazole derivative and a fumarate ester. The catalyst has high-temperature stability and can maintain a stable structure during a high-temperature curing process, a high-temperature processing process and a service temperature to avoid high-temperature decomposition and volatilization. In addition, the catalyst is liquid and has good compatibility with the epoxy resin. It can be evenly dispersed in the epoxy resin and is beneficial for catalyzing the exchange reaction of dynamic covalent bonds during high-temperature reprocessing, thereby giving the epoxy resin excellent reprocessing performance and realizing thermal recovery and thermal reshaping of the epoxy resin.

[0027] In addition, the catalyst has a special molecular structure that can reduce the catalytic performance at the service temperature through the steric effect, so that the epoxy resin maintains mechanical stability at the service temperature; when the epoxy resin is heated to a high temperature, the catalyst exhibits a catalytic effect and can catalyze the transesterification reaction to achieve thermal recovery and thermal reshaping of the epoxy resin. However, the existing metal salt catalysts, organic molecular catalysts, and organic salt catalysts all have high catalytic performance at the service temperature, which leads to the problem of mechanical instability of the epoxy resin at the service temperature.

[0028] In some embodiments, the imidazole derivative includes aryl imidazole. The aryl group on the aryl imidazole can provide steric hindrance, reduce the catalytic performance of the catalyst at the service temperature, and does not affect the catalytic activity of the catalyst at high temperature.

[0029] In some specific embodiments, the aryl imidazole includes at least one of 4-phenylimidazole, 4-biphenylimidazole, and 4-naphthyl imidazole.

[0030] In some embodiments, the fumarate comprises at least one of bis(2-ethylhexyl)fumarate, dibutyl fumarate, and bis(2-isopropyl-5-methylhexyl)fumarate. The long-chain alkyl in the fumarate can provide steric hindrance, reduce the catalytic performance of the catalyst at the service temperature, and do not affect the catalytic activity of the catalyst at high temperature.

[0031] In some embodiments, the liquid transesterification catalyst comprises Optimizing the type of liquid transesterification catalyst is beneficial to improving the dispersibility and high temperature stability of the catalyst.

[0032] In some specific embodiments, the liquid transesterification catalyst is

[0033] In some embodiments, the mass proportion of the liquid transesterification catalyst in the raw material is 4%-6%. Optimizing the amount of the transesterification catalyst is beneficial to improving the reprocessability of the epoxy resin containing ester bonds.

[0034] In some specific embodiments, the mass proportion of the liquid transesterification catalyst in the raw material is 4%, 4.5%, 5%, 5.5% or 6%.

[0035] In some embodiments, the epoxy resin comprises an anhydride epoxy resin.

[0036] In some embodiments, the curing agent includes at least one of an anhydride and a diacid. The anhydride may include methyltetrahydrophthalic anhydride.

[0037] In some embodiments, the promoter includes at least one of 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, triethylamine, triethanolamine, o-hydroxybenzyldimethylamine, N-(2-hydroxyphenyl)-N',N'-dimethylurea, N-(2-hydroxy-4-nitrobenzene)-N',N'-dimethylurea, N-(5-chloro-2-hydroxybenzene)-N',N'-dimethylurea, N-(4-chlorophenyl)-N',N'-dimethylurea, N-(4-chloro-2-hydroxybenzene)-N',N'-dimethylurea, and a boron trifluoride complex.

[0038] The second aspect of the present invention provides a method for preparing the epoxy resin with high reprocessability according to the first aspect of the present invention, comprising the following steps:

[0039] The epoxy monomer, curing agent, accelerator and liquid transesterification catalyst are mixed under heating and cured to obtain epoxy resin;

[0040] Wherein, at least one of the epoxy monomer, curing agent and accelerator contains an ester bond; and the liquid transesterification catalyst is obtained by an addition reaction between an imidazole derivative and a fumaric acid ester.

[0041] The method of the invention has a simple process flow, does not require additional steps, has good reproducibility, and is suitable for large-scale industrial production applications.

[0042] In some embodiments, the heating temperature may be 50-70° C. and the heating time may be 20-40 min. Mixing the raw materials at a certain heating temperature is conducive to uniform dispersion of the transesterification catalyst in the entire reaction system, thereby facilitating the reprocessability of the epoxy resin containing ester bonds at high temperatures.

[0043] In some specific embodiments, the heating temperature may be 50°C, 55°C, 60°C, 65°C or 70°C.

[0044] In some specific embodiments, the heating time may be 20 min, 25 min, 30 min, 35 min or 40 min.

[0045] In some embodiments, the curing temperature may be 130-150° C. and the curing time may be 10-14 hours. Optimizing the curing temperature is conducive to obtaining an epoxy resin with stable mechanical properties at the service temperature.

[0046] In some specific embodiments, the curing temperature can be 130°C, 135°C, 140°C, 145°C, or 150°C.

[0047] In some specific embodiments, the curing time may be 10 h, 11 h, 12 h, 13 h or 14 h.

[0048] In some embodiments, after mixing and before curing, the method further comprises: degassing at 70-90° C. in a vacuum state, and pre-curing at 70-90° C.; preferably, the pre-curing time is 3-5 hours. Degassing before curing can ensure that the physical properties and appearance quality of the resin will not be affected by the presence of bubbles during the curing process, thereby improving the overall quality of the final product, improving the curing effect, reducing the stress concentration caused by bubbles, and thus extending the service life of the resin.

[0049] In some embodiments, the degassing temperature may be 70°C, 75°C, 80°C, 85°C, or 90°C.

[0050] In some embodiments, the pre-curing temperature may be 70°C, 75°C, 80°C, 85°C, or 90°C.

[0051] In some embodiments, the pre-curing time may be 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours.

[0052] In some embodiments, the preparation of the liquid transesterification catalyst comprises: mixing an imidazole derivative, a fumarate, and a catalyst, and reacting the mixture to obtain the liquid transesterification catalyst.

[0053] In some specific embodiments, the molar ratio of the imidazole derivative to the fumarate is (0.8-1.2):1, such as 0.8:1, 0.9:1, 1:1, 1.1:1 or 1.2:1.

[0054] In some embodiments, the reaction temperature is below 100°C, such as 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C.

[0055] In some specific embodiments, the reaction time can be 6.5 h-12 h, for example 6.5 h, 7 h, 8 h, 9 h, 10 h, 11 h or 12 h.

[0056] In some specific embodiments, the imidazole derivative, the fumarate, and the catalyst may be mixed in a solvent, and the solvent may be at least one of acetonitrile, dichloromethane, chloroform, and tetrahydrofuran.

[0057] In some embodiments, the catalyst can include 1,8-diazabicycloundec-7-ene.

[0058] The present invention is described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0059] Example 1

[0060] (1) Preparation of liquid transesterification catalyst:

[0061] First, 10 mmol of bis(2-ethylhexyl) fumarate and 10 mmol of 4-phenylimidazole were dissolved in 10 mL of acetonitrile and stirred evenly at room temperature; then, 4 mmol of 1,8-diazabicycloundec-7-ene (DBU) was added to the above mixture, and stirring was continued at room temperature for 12 hours; then, the acetonitrile was removed by a rotary evaporator, and the product was dissolved in ethyl acetate, washed three times with saturated brine, and dried with anhydrous magnesium sulfate powder; finally, the product was separated and purified by column chromatography, and the eluent was n-hexane / ethyl acetate with a volume ratio of 4:1. The obtained product was a brown-yellow liquid, and the synthesis route was as follows.

[0062]

[0063] (2) Preparation of epoxy resin:

[0064] First, take 2.225g of methyltetrahydrophthalic anhydride (MTHPA), 0.035g of N,N-dimethylbenzylamine (BDMA) and 2.5g of 331 resin (DER331 resin purchased from Minnesota Mining and Machinery Manufacturing Company, epoxy equivalent 182-192, as shown in Formula 1), add them into a 50mL round-bottom flask, and stir at 60°C to fully mix the ingredients; then, add the liquid ester exchange catalyst (0.238g) prepared in step 1 (the mass proportion of the liquid ester exchange catalyst in the raw material is 5%), and continue to stir at 60°C for 30 minutes to ensure that the catalyst is fully dispersed; then pour the above mixture into a rectangular mold while hot, put it into a vacuum drying oven at 80°C, vacuum and degas, and heat it for 4 hours to perform a pre-curing reaction; finally, increase the temperature to 140°C, continue to cure for 12 hours, and the target epoxy resin material can be obtained after demolding, such as Figure 1 The DSC curve of the epoxy resin is shown in Figure 2 As shown, the thermal stability is up to 230°C.

[0065]

[0066] Reprocessing performance test

[0067] (1) Cut a small piece of the epoxy resin sample prepared in Example 1, place a steel wire on top of it, apply pressure to both, and heat to 160°C. The stress-bearing part of the sample surface deforms, causing the steel wire to be slightly embedded in the surface. After heating for 2 hours, cool to room temperature, remove the steel wire, and an indentation is generated on the sample surface. Put the sample into a 160°C heating jacket again to anneal it. After annealing, the indentation does not disappear (such as Figure 3 ), indicating that the stress-bearing site undergoes reshaping, further proving the occurrence of transesterification.

[0068] (2) Relaxation stress test

[0069] The stress relaxation test was carried out using a rheometer with an 8 mm contact axis. The epoxy resin sample prepared in Example 1 was balanced at the corresponding temperature for 2 minutes, and then a constant strain of 1% and a normal force of 10 N were applied to ensure good contact. The test results are shown in FIG. Figure 4 As shown, Figure 4 a shows that in the temperature range of 190-220 °C, the sample can relax stress to 1 / e (normalized) through transesterification reaction. Figure 4 b shows that the inverse of the characteristic relaxation time and temperature conforms to the Arrhenius law. Through linear fitting, it can be calculated that the activation energy of the transesterification reaction under the catalysis of the liquid transesterification catalyst is 216.0 kJ mol -1 .

[0070] In summary, the present invention provides an epoxy resin with high reprocessability, wherein the epoxy resin comprises a liquid ester exchange catalyst obtained by an addition reaction of an imidazole derivative and a fumarate ester, wherein the catalyst has high temperature stability, and can maintain a stable structure during a high temperature curing process, a high temperature processing process, and a service temperature to avoid high temperature decomposition; in addition, the catalyst is in a liquid state, has good compatibility with the epoxy resin, can be evenly dispersed in the epoxy resin, and is beneficial to catalyzing the exchange reaction of dynamic covalent bonds during high temperature reprocessing, thereby giving the epoxy resin excellent reprocessability and realizing thermal recovery and thermal reshaping of the epoxy resin.

[0071] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0072] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. An epoxy resin with high reprocessability, characterized in that The epoxy resin contains ester bonds, and the raw materials for preparing the epoxy resin include: epoxy monomer, curing agent, accelerator and liquid transesterification catalyst; wherein the liquid transesterification catalyst is obtained by addition reaction of imidazole derivative and fumaric acid ester.

2. The epoxy resin according to claim 1, characterized in that The imidazole derivatives include aryl imidazoles; Preferably, the aryl imidazole includes at least one of 4-phenylimidazole, 4-biphenylimidazole and 4-naphthylimidazole.

3. The epoxy resin according to claim 1 or 2, characterized in that The fumaric acid ester includes at least one of bis(2-ethylhexyl) fumarate, dibutyl fumarate, and bis(2-isopropyl-5-methylhexyl) fumarate.

4. The epoxy resin according to claim 2, characterized in that The liquid transesterification catalyst comprises At least one of .

5. The epoxy resin according to claim 1 or 2, characterized in that The mass proportion of the liquid transesterification catalyst in the raw material is 4%-6%.

6. The epoxy resin according to claim 1 or 2, characterized in that The epoxy resin includes anhydride epoxy resin.

7. A method for preparing the epoxy resin with high reprocessability according to any one of claims 1 to 6, characterized in that: The following steps are involved: The epoxy monomer, curing agent, accelerator and liquid transesterification catalyst are mixed under heating and cured to obtain epoxy resin; Wherein, at least one of the epoxy monomer, curing agent and accelerator contains an ester bond; and the liquid transesterification catalyst is obtained by an addition reaction between an imidazole derivative and a fumaric acid ester.

8. The method according to claim 7, characterized in that The heating temperature is 50-70° C., and the heating time is 20-40 minutes.

9. The method according to claim 7 or 8, characterized in that: The curing temperature is 130-150° C. and the curing time is 10-14 hours.

10. The method according to claim 7 or 8, characterized in that: After mixing and before curing, the method further comprises: degassing at 70-90° C. in a vacuum state, and pre-curing at 70-90° C.; preferably, the pre-curing time is 3-5 hours.

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