Epoxy resin having high reworkability and method for producing the same

Abstract

The application discloses an epoxy resin with high reworkability and a preparation method thereof. The epoxy resin comprises an ester bond, and raw materials for preparing the epoxy resin comprise an epoxy monomer, a curing agent, an accelerator and a liquid transesterification catalyst. The liquid transesterification catalyst is obtained by an addition reaction of an imidazole derivative and a fumarate. The epoxy resin of the application comprises the liquid transesterification catalyst obtained by the addition reaction of the imidazole derivative and the fumarate. 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. In addition, the catalyst is in a liquid state, has good compatibility with the epoxy resin, can be uniformly dispersed in the epoxy resin, is beneficial to a catalytic exchange reaction of a dynamic covalent bond in a high-temperature reprocessing process, and thus excellent reworkability is given to the epoxy resin, and heat recovery and heat reshaping of the epoxy resin are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high polymer materials, and particularly relates to an epoxy resin with high reworkability and a preparation method thereof. BACKGROUND

[0002] Anhydride epoxy resin is a cross-linked polymer material containing ester bonds, which is widely used in industry and life. The introduction of ester exchange reaction enables the material to maintain cross-linked structure while obtaining excellent reworkability. This kind of material is named as glass-like polymer, which can realize rework of cross-linked network through exchange reaction of dynamic covalent bond to rearrange network topology. In order to improve the reworkability of epoxy resin, an ester exchange catalyst is often added.

[0003] The commonly used ester exchange catalysts include metal salt catalysts, organic molecule catalysts and organic salt catalysts. However, the metal salt catalysts have serious heterogeneous dispersion problems in the resin due to their solid state and high melting point, which makes the existence of the metal salt catalysts in the epoxy monomer complex. Similarly, the organic salt catalysts also face dispersion problems in the solid state, and usually need a solvent to assist dispersion, and may be decomposed in the high-temperature curing process when preparing the epoxy resin. 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 be dispersed; the TBD and its derivatives also have the problem of easy thermal decomposition at a relatively high processing temperature or service temperature. Therefore, the reworkability of the existing epoxy resin cannot reach a satisfactory degree, and still needs to be further improved. SUMMARY

[0004] The present application aims to at least partially solve one of the problems in the background art. To this end, one object of the present application is to provide an epoxy resin with high reworkability.

[0005] Specifically, the present application provides an epoxy resin with high reworkability, which contains ester bonds, and raw materials for preparing the epoxy resin include: an epoxy monomer, a curing agent, an accelerator and a liquid ester exchange catalyst; wherein the liquid ester exchange catalyst is obtained by addition reaction of an imidazole derivative and a fumarate ester.

[0006] The epoxy resin of the present application comprises a liquid transesterification catalyst obtained by addition reaction of an imidazole derivative and a fumarate, which has high temperature stability and can maintain stable structure at high temperature curing process, high temperature processing process and service temperature, avoiding high temperature decomposition and volatilization; in addition, the catalyst is liquid, has good compatibility with the epoxy resin, can be uniformly dispersed in the epoxy resin, and is beneficial to the exchange reaction of the catalytic dynamic covalent bond in the high temperature reprocessing process, thereby imparting excellent reprocessing performance to the epoxy resin, realizing heat recovery and heat reshaping of the epoxy resin.

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

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

[0009] According to some embodiments of the present application, the liquid transesterification catalyst comprises at least one of 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 application, the mass fraction 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 bond.

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

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

[0013] mixing, under heating, an epoxy monomer, a curing agent, an accelerator and a liquid transesterification catalyst, and curing to obtain an epoxy resin;

[0014] wherein at least one of the epoxy monomer, the curing agent and the accelerator comprises an ester bond; and the liquid transesterification catalyst is obtained by addition reaction of an imidazole derivative and a fumarate.

[0015] The method has simple process flow, does not need to increase additional steps, has good reproducibility, and is suitable for large-scale industrial production application.

[0016] According to some embodiments of the present application, the heating temperature is 50-70℃, and the heating time is 20-40min. Mixing raw materials at a certain heating temperature is favorable for uniformly dispersing the transesterification catalyst in the whole reaction system, thereby favoring the improvement of the reworkability of the epoxy resin containing ester bonds at high temperature.

[0017] According to some embodiments of the present application, the curing temperature is 130-150℃, and the curing time is 10-14h. Optimizing the curing temperature is favorable for obtaining the epoxy resin with stable mechanical properties at service temperature.

[0018] According to some embodiments of the present application, after mixing and before curing, the method further comprises: degassing under vacuum at 70-90℃, and pre-curing at 70-90℃; preferably, the pre-curing time is 3-5h. Degassing before curing can ensure that the resin will not affect its physical properties and appearance quality due to the existence of bubbles during the curing process, thereby improving the overall quality of the final product, improving the curing effect, reducing stress concentration caused by bubbles, and thereby prolonging the service life of the resin.

[0019] Additional aspects and advantages of the present application will be partially given in the following description, partially will become obvious from the following description, or will be understood by the practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

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

[0021] Figure 2 is a TGA (Thermogravimetric Analysis) curve of the epoxy resin prepared in Example 1.

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

[0023] Figure 4 is the calculation of the activation energy of the transesterification reaction of the epoxy resin prepared in Example 1, Figure 4 a: Shear stress relaxation test of the epoxy resin (the abscissa is time, and the ordinate is normalized stress); Figure 4 b: Arrhenius relationship fitting line (the abscissa is the reciprocal of temperature multiplied by 1000, unit (K -1 ), and the ordinate is ln(characteristic relaxation temperature), wherein the characteristic relaxation temperature is obtained in a, which is the time (unit s) corresponding to the normalized stress drop of each temperature curve to 1 / e). Figure 4 DETAILED DESCRIPTION​

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

[0025] In a first aspect, the present application provides an epoxy resin with high reworkability, the epoxy resin comprising an ester bond, and raw materials for preparing the epoxy resin comprising: an epoxy monomer, a curing agent, an accelerator, and a liquid transesterification catalyst; wherein the liquid transesterification catalyst is obtained by an addition reaction of an imidazole derivative and a fumarate ester.

[0026] The epoxy resin of the present application comprises a liquid transesterification catalyst obtained by an addition reaction of an imidazole derivative and a fumarate ester, which has high temperature stability and can maintain a stable structure at high temperature curing process, high temperature processing process and service temperature, avoiding high temperature decomposition and volatilization. In addition, the catalyst is in liquid state, has good compatibility with the epoxy resin, and can be uniformly dispersed in the epoxy resin, which is beneficial to the exchange reaction of the catalytic dynamic covalent bond during high temperature reprocessing, thereby endowing the epoxy resin with excellent reworkability, realizing heat recycling and heat reshaping of the epoxy resin.

[0027] In addition, the catalyst has a special molecular structure, which can reduce the catalytic performance at the service temperature through steric hindrance effect, so as to make the epoxy resin maintain mechanical stability at the service temperature; while the epoxy resin is heated to high temperature, the catalyst shows catalytic effect and can catalyze the transesterification reaction, realizing heat recycling and heat 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 unstable mechanical structure of the epoxy resin at the service temperature.

[0028] In some embodiments, the imidazole derivative comprises an arylimidazole. The aryl group on the arylimidazole can provide steric hindrance to reduce the catalytic performance of the catalyst at the service temperature, while not affecting the catalytic activity of the catalyst at high temperature.

[0029] In some specific embodiments, the arylimidazole comprises at least one of 4-phenylimidazole, 4-biphenyl imidazole, and 4-naphthyl imidazole.

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

[0031] In some embodiments, the liquid transesterification catalyst includes at least one of Optimizing the type of liquid transesterification catalyst can facilitate 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 fraction of the liquid transesterification catalyst in the raw material is 4%-6%. Optimizing the amount of the transesterification catalyst can facilitate improving the reworkability of the epoxy resin containing ester bonds.

[0034] In some specific embodiments, the mass fraction 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 includes an acid anhydride epoxy resin.

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

[0037] In some embodiments, the accelerator includes at least one of 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, triethylamine, triethanolamine, o-hydroxybenzyl dimethylamine, N-(2-hydroxyphenyl)-N',N'-dimethylurea, N-(2-hydroxy-4-nitrophenyl)-N',N'-dimethylurea, N-(5-chloro-2-hydroxyphenyl)-N',N'-dimethylurea, N-(4-chlorophenyl)-N',N'-dimethylurea, N-(4-chloro-2-hydroxyphenyl)-N',N'-dimethylurea, boron trifluoride complex.

[0038] A second aspect of the present application provides a method for preparing the epoxy resin with high reworkability of the first aspect of the present application, including the following steps:

[0039] Mixing the epoxy monomer, the curing agent, the accelerator, and the liquid transesterification catalyst under heating, curing to obtain the epoxy resin;

[0040] The at least one of the epoxy monomer, the curing agent and the accelerator comprises an ester bond; and the liquid transesterification catalyst is obtained by an addition reaction of an imidazole derivative and a fumarate ester.

[0041] The method has a simple process flow, does not need to add additional steps, has good reproducibility, and is suitable for large-scale industrial production application.

[0042] In some embodiments, the heating temperature can be 50-70 DEG C, and the heating time can be 20-40 min. Mixing the raw materials at a certain heating temperature is beneficial to uniformly dispersing the transesterification catalyst in the entire reaction system, thereby being beneficial to improving the reworkability of the epoxy resin containing an ester bond at high temperature.

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

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

[0045] In some embodiments, the curing temperature can be 130-150 DEG C, and the curing time can be 10-14 h. Optimizing the curing temperature is beneficial to obtaining the epoxy resin with stable mechanical properties at a service temperature.

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

[0047] In some specific embodiments, the curing time can 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 DEG C under vacuum, and pre-curing at 70-90 DEG C; preferably, the pre-curing time is 3-5 h. Degassing before curing can ensure that the resin does not affect its physical properties and appearance quality due to the existence of bubbles during the curing process, thereby improving the overall quality of the final product, improving the curing effect, reducing stress concentration caused by bubbles, and thereby prolonging the service life of the resin.

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

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

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

[0052] In some embodiments, the preparation of the liquid transesterification catalyst comprises: mixing the imidazole derivative, the fumarate, and the catalyst, and obtaining the liquid transesterification catalyst after reaction.

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

[0054] In some specific embodiments, the reaction temperature is below 100°C, for example 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 6.5h-12h, for example 6.5h, 7h, 8h, 9h, 10h, 11h, or 12h.

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

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

[0058] The present application is described below with reference to specific embodiments, which are merely illustrative and not in any way limit the present application.

[0059] Example 1

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

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

[0062]

[0063] (2) Preparation of the epoxy resin:

[0064] First, 2.225 g of methyltetrahydrophthalic anhydride (MTHPA), 0.035 g of N,N-dimethylbenzylamine (BDMA), and 2.5 g of 331 resin (D.E.R. 331 resin, purchased from Minnesota Mining and Manufacturing Company, epoxy equivalent weight 182-192, as shown in Formula 1) were added into a 50 mL round-bottom flask, and stirred at 60°C to mix and homogenize the ingredients; then, the liquid transesterification catalyst prepared in Step 1 (0.238 g) was added (the mass ratio of the liquid transesterification catalyst in the raw materials was 5%), and the stirring was continued at 60°C for 30 minutes to ensure that the catalyst was fully dispersed; after that, the mixture was poured into a rectangular mold while hot, and placed in a vacuum drying oven at 80°C to remove bubbles under vacuum, and then heated for 4 hours to perform a pre-curing reaction; finally, the temperature was increased to 140°C, and the curing was continued for 12 hours, after which the epoxy resin material was obtained after demolding, as shown in Figure 1 The DSC curve of the epoxy resin is shown in Figure 2 , and the thermal stability is as high as 230°C.

[0065]

[0066] Post-processing performance test

[0067] (1) A small sample of the epoxy resin prepared in Example 1 was cut, a steel wire was placed above it, pressure was applied to both, and heated to 160°C, and the sample surface at the stressed site was deformed, so that the steel wire was slightly embedded in the surface. After heating for 2 hours, the sample was cooled to room temperature, the steel wire was removed, and a pressure mark was generated on the surface of the sample. The sample was placed again in a heating jacket at 160°C to anneal, and the pressure mark did not disappear after annealing (as shown in Figure 3 ), indicating that the stressed site was reshaped, which further proved the occurrence of transesterification reaction.

[0068] (2) Relaxation stress test

[0069] The rheometer was used to perform the stress relaxation test, and the 8 mm contact shaft was used. The sample of the epoxy resin prepared in Example 1 was equilibrated 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 Figure 4 Figure 4 a indicates that the sample can well relax the stress to 1 / e (after normalization) through the transesterification reaction in the temperature range of 190-220°C, Figure 4 b indicates that the characteristic relaxation time and the inverse of the temperature comply with the Arrhenius law, and through linear fitting, the activation energy of the transesterification reaction under the catalysis of the liquid transesterification catalyst is calculated to be 216.0 kJ mol -1 .

[0070] ​In summary, the present application provides an epoxy resin with high reworkability, which comprises a liquid transesterification catalyst obtained by addition reaction of an imidazole derivative and a fumarate ester, the catalyst having high temperature stability, maintaining stable structure during high temperature curing process, high temperature processing process and service temperature, avoiding high temperature decomposition; in addition, the catalyst is liquid, having good compatibility with the epoxy resin, being able to be uniformly dispersed in the epoxy resin, being beneficial to the exchange reaction of the catalytic dynamic covalent bond during high temperature reprocessing process, thereby endowing the epoxy resin with excellent reworkability, realizing heat recycling and heat reshaping of the epoxy resin.

[0071] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and modified by those skilled in the art without contradiction, if possible.

[0072] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

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 monomers, curing agents, accelerators, and liquid transesterification catalysts; the epoxy resin includes anhydride epoxy resins. The liquid transesterification catalyst is obtained by an addition reaction between an imidazole derivative and a fumarate ester. The imidazole derivative includes aryl imidazole, wherein the aryl imidazole is 4-phenylimidazolium; the fumarate includes at least one selected from bis(2-ethylhexyl) fumarate, dibutyl fumarate, and bis(2-isopropyl-5-methylhexyl) fumarate. The liquid transesterification catalyst includes , , At least one of the following; the liquid transesterification catalyst accounts for 4%-6% of the mass of the raw material.

2. A method for preparing the highly reprocessable epoxy resin according to claim 1, characterized in that, Includes the following steps: Epoxy monomers, curing agents, accelerators, and liquid transesterification catalysts are mixed under heating and then cured to obtain epoxy resin; the heating temperature is 50-70℃, the heating time is 20-40 min; the curing temperature is 130-150℃; and the curing time is 10-14 h. After mixing and before curing, the mixture is degassed under vacuum at 70-90°C and pre-cured at 70-90°C; the pre-curing time is 3-5 hours. Wherein, at least one of the epoxy monomer, curing agent, and accelerator contains an ester bond; the liquid transesterification catalyst is obtained by an addition reaction between an imidazole derivative and a fumarate ester. The imidazole derivative includes aryl imidazole, wherein the aryl imidazole is 4-phenylimidazolium; the fumarate includes at least one of bis(2-ethylhexyl) fumarate, dibutyl fumarate, and bis(2-isopropyl-5-methylhexyl) fumarate.

Images