Epoxy resin curing indicator compound and preparation method and composition

Abstract

This application belongs to the technical field of electrical insulation materials, and particularly relates to an epoxy resin curing indicator compound, its preparation method, and composition. The epoxy resin curing indicator compound provided in this application can cause the color of the cured epoxy resin to gradually change from colorless to red, and then to dark red, as the curing reaction proceeds. This allows people to visually observe the color of the object and judge the degree of curing of the epoxy resin through visual effects. Furthermore, by using a pre-established linear relationship between curing time and absorbance, the curing time of the epoxy resin can be judged more accurately, solving the technical problem of lacking a direct way to judge the degree of curing of epoxy resin in the prior art.

Description

Technical Field

[0001] This application belongs to the field of electrical insulation materials technology, and in particular relates to an epoxy resin curing indicator compound, its preparation method, and composition. Background Technology

[0002] Epoxy resin is a general term for a class of polymers containing two or more epoxy groups. It is a high-molecular-weight thermosetting polymer. Due to the chemical reactivity of epoxy groups, it can be ring-opened, cured, and cross-linked to form a network structure using various curing agents containing active hydrogen. Alkaline curing agents, acidic curing agents, addition-type curing agents, catalytic curing agents, and susceptible curing agents can all cross-link and cure epoxy resin. Cross-linked and cured epoxy resin has advantages such as high insulation performance, high structural strength, and good sealing performance. As an electrical engineering insulation material, it is widely used in high and low voltage electrical appliances, motors, electronic components, and other fields.

[0003] The curing of epoxy resin significantly affects its performance. Therefore, researchers employ various methods to determine the degree of curing. Differential scanning calorimetry (DSC) can be used to study the degree of curing. Since the curing reaction of epoxy resin is exothermic, the degree of curing can be obtained by comparing the residual heat of reaction with the heat of complete curing. In addition to DSC, the degree of curing also affects the mechanical properties of epoxy resin. Mechanical property testing methods, such as impact testing to measure the toughness of epoxy resin samples, hardness testing to measure the hardness of epoxy resin samples, and bending testing to measure the flexural strength and flexural modulus of epoxy resin samples, can also reflect the degree of curing based on mechanical properties.

[0004] However, testing methods such as differential scanning calorimetry, toughness, hardness, flexural strength, and flexural modulus all require additional instruments and equipment. The degree of curing of epoxy resin can only be determined based on the test results of the instruments and equipment. Currently, there is a lack of intuitive methods to determine the degree of curing of epoxy resin. The color of an object is an intuitive feature. People can intuitively observe the color of an object through the visual effect of the eye without damaging the epoxy resin. Summary of the Invention

[0005] In view of this, this application provides an epoxy resin curing indicator compound, its preparation method, and a composition to solve the technical problem of lacking a direct way to judge the degree of curing of epoxy resin in the prior art.

[0006] The first aspect of this application provides an epoxy resin curing indicator compound, the chemical structure of which is shown in Formula I.

[0007] Formula I.

[0008] In Formula I, Et is selected from alkyl groups.

[0009] Preferably, the alkyl group is selected from any one of methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, and hexyl.

[0010] The second aspect of this application provides a method for preparing an epoxy resin curing indicator compound, which can prepare the epoxy resin curing indicator compound described in the first aspect. The preparation method includes the following steps:

[0011] Step S1: 1-{[(2-methylprop-2-yl)oxy]carbonyl}hexahydropyridine-4-carboxylic acid, 2-(ethyl{4-[(1Z)-(4-nitrophenyl)ethazenoyl]phenyl}amino)ethyl-1-ol) are reacted at room temperature to give hexahydropyridine-4-carboxylic acid-2-(ethyl{4-[(1Z)-(4-nitrophenyl)ethazenoyl]phenyl}amino)ethyl ester;

[0012] Step S2: 2-(ethyl{4-[(1Z)-(4-nitrophenyl)ethazinyl]phenyl}amino)ethyl ester and 2-(4-{[dimethyl(2-methylprop-2-yl)silyl]oxy}phenyl)-2-hydroxyacetic acid are reacted at room temperature to give 2-(4-{[dimethyl(2-methylprop-2-yl)silyl]oxy}phenyl)-1-[4-({[2-(ethyl{4-[(4-nitrophenyl)ethazinyl]phenyl}amino)ethyl]dioxy}thio)hexahydropyridin-1-yl]-2-hydroxyethyl-1-one;

[0013] Step S3: 2-(4-{[dimethyl(2-methylprop-2-yl)silyl]oxy}phenyl)-1-[4-({[2-(ethyl{4-[(4-nitrophenyl)ethazenoyl]phenyl}amino)ethyl]dioxy}thio)hexahydropyridin-1-yl]-2-hydroxyethyl-1-one and p-nitrophenyl chloroformate are reacted at room temperature to obtain the epoxy resin curing indicator compound shown in Formula I.

[0014] Preferably, in step S1, the reaction process includes reacting in a mixed reaction system of 4-dimethylaminopyridine, dichloromethane, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide for 6 to 18 hours.

[0015] Preferably, in step S2, the reaction process includes reacting in a mixed reaction system of diisopropylethylamine, benzotriazole-N,N,N',N'-tetramethylurea hexafluorophosphate and N,N-dimethylformamide for 4-8 hours.

[0016] Preferably, in step S3, the reaction process includes reacting in a mixed reaction system of 2,6-dimethylpyridine and dichloromethane for 6 to 18 hours.

[0017] A third aspect of this application provides an epoxy resin curing indicator composition comprising: a colorless and transparent epoxy resin, a colorless and transparent epoxy resin curing agent, and an epoxy resin curing indicator compound.

[0018] Preferably, in the epoxy resin curing indicator composition, the colorless and transparent epoxy resin is selected from bisphenol A type epoxy resin, and the colorless and transparent epoxy resin curing agent is selected from polypropylene glycol triamine.

[0019] Preferably, in the epoxy resin curing indicator composition, the volume ratio of bisphenol A type epoxy resin to polypropylene glycol triamine is 100:30~60.

[0020] Preferably, in the epoxy resin curing indicator composition, the doping amount of the compound shown in Formula I is 0.005%~0.015% (V / V).

[0021] Preferably, the epoxy resin curing indicator composition further includes: butanediol diglycidyl ether, C13-C15-glycidyl ether, and benzyl alcohol.

[0022] The fourth aspect of this application provides the use of an epoxy resin curing indicator composition in determining epoxy resin curing.

[0023] Preferably, the application specifically includes the following steps:

[0024] Step S1: Curing the epoxy resin curing indicator composition and recording the epoxy resin absorbance at different curing times;

[0025] Step S2: Establish a linear relationship between the absorbance of epoxy resin and curing time based on the absorbance of epoxy resin at different curing times;

[0026] Step S3: Substitute the absorbance of the epoxy resin curing indicator composition to be tested, which has the same formulation as the epoxy resin curing indicator composition, into the linear relationship between the absorbance of epoxy resin and curing time to obtain the curing time of the epoxy resin curing indicator composition to be tested.

[0027] Preferably, in step S1, the recording of the absorbance of epoxy resin at different curing times specifically refers to:

[0028] The absorbance of epoxy resin at curing times of 10 min, 20 min, 30 min, 40 min, and 60 min was recorded using a UV-Vis-NIR spectrometer.

[0029] Preferably, in step S2, the linear relationship between the absorbance of the epoxy resin and the curing time is y = 0.0275x - 0.165, R 2 =0.9494, where y is the absorbance and x is the curing time.

[0030] In summary, this application provides an epoxy resin curing indicator compound, its preparation method, and a composition. The epoxy resin curing indicator compound provided in this application, after being used as a chromophore in the three-dimensional cross-linked network of cured epoxy resin (such as bisphenol A type epoxy resin and colorless transparent epoxy resin curing agents such as polypropylene glycol triamine), can be introduced into the epoxy resin cross-linked network as a chromophore. As the epoxy resin curing reaction proceeds, the network structure of the cured epoxy resin contains more and more chromophores. Therefore, as the epoxy resin curing reaction proceeds and the network structure is formed, the color of the epoxy resin will gradually change from colorless to light red, red, and dark red. The color change of the epoxy resin can be directly observed with the eye without damaging the epoxy resin. The redder the epoxy resin appears, the greater the degree of curing, thus solving the technical problem of lacking a direct way to judge the degree of curing of epoxy resin in the prior art. Attached Figure Description

[0031] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0032] Figure 1 This is a schematic diagram of the preparation method of the epoxy resin curing indicator compound described in Example 1 of this application;

[0033] Figure 2 The nuclear magnetic resonance spectrum of the epoxy resin curing indicator compound described in Example 1 of this application;

[0034] Figure 3 This is a schematic diagram showing the absorbance of epoxy resin at different curing times (10 min, 20 min, 30 min, 40 min, 60 min) as described in Example 3 of this application.

[0035] Figure 4 This is a graph showing the fitting results of the absorbance of epoxy resin at different curing times (10 min, 20 min, 30 min, 40 min, 60 min) as described in Example 4 of this application. Detailed Implementation

[0036] This application provides an epoxy resin curing indicator compound, its preparation method, and a composition to solve the technical problem of lacking a direct way to judge the degree of curing of epoxy resin in the prior art.

[0037] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] Given the current lack of a direct way to judge the degree of curing of epoxy resin, this application provides an epoxy resin curing indicator compound, the structure of which is shown in Formula I. Under the action of a curing agent, the epoxy resin undergoes a curing reaction. In the resulting three-dimensional cross-linked network of cured epoxy resin, the epoxy resin curing indicator compound can be introduced as a chromophore into the cross-linked network. A chromophore is a light source that absorbs a certain wavelength of light while not absorbing other wavelengths, thus causing the cured epoxy resin containing the chromophore to display the color corresponding to the absorbed wavelength. As the curing reaction of the epoxy resin proceeds, more and more chromophores are introduced into the cured epoxy resin, resulting in a darker color. People can directly observe the color of the cured epoxy resin to judge its degree of curing. A lighter color indicates a lower degree of curing, while a darker color indicates a higher degree of curing. This method also avoids the problems of requiring additional instruments and equipment and damaging epoxy resin samples for performance tests such as differential scanning calorimetry, toughness, hardness, flexural strength, and flexural modulus, thus overcoming the lack of a direct way to judge the degree of curing of epoxy resin.

[0039] Preferably, this application also provides an epoxy resin curing indicator composition, which is obtained by mixing an epoxy resin curing indicator compound, a colorless and transparent epoxy resin, and a colorless and transparent epoxy resin curing agent.

[0040] Preferably, in the epoxy resin curing indicator composition provided in this application, the colorless and transparent epoxy resin is selected from bisphenol A type epoxy resin, and the colorless and transparent epoxy resin curing agent is selected from polypropylene glycol triamine. The compound shown in Formula I combines with the groups (amine or alcohol) generated in the crosslinking network after the bisphenol A type epoxy resin is cured to produce a wavelength color that can absorb about 650nm, corresponding to the wavelength of red light, thereby causing the cured epoxy resin to gradually change from colorless to light red, light red to red, and then to dark red.

[0041] Preferably, in the epoxy resin curing indicator composition provided in this application, the doping amount of the epoxy resin curing indicator compound is 0.005%~0.015% (V / V). That is, 0.005~0.015 ml of epoxy resin curing indicator compound is doped into every 100 ml of epoxy resin curing indicator composition.

[0042] Preferably, in the epoxy resin curing indicator composition provided in this application, the volume ratio of colorless transparent epoxy resin to colorless transparent epoxy resin curing agent is 100:30~60; and diluent components such as butylene glycol diglycidyl ether, C13-C15-glycidyl ether and benzyl alcohol are also added.

[0043] Preferably, this application also utilizes the relationship between the curing degree and color change of the epoxy resin curing indicator composition to establish a quantitative method for the curing degree of epoxy resin; considering that the curing time has a significant impact on the curing of epoxy resin, the quantitative relationship between the curing time and color change in the curing degree of epoxy resin established in this application is specifically to determine the curing time of epoxy resin based on the color of epoxy resin.

[0044] The following will describe in detail, with reference to embodiments and experimental examples, an epoxy resin curing indicator composition and a method for determining it, provided in this application.

[0045] Example 1

[0046] Example 1 of this application provides a method for preparing an epoxy resin curing indicator compound, the process of which is as follows: Figure 1 As shown, the steps include:

[0047] A mixture of 1.15 g of 1-{[(2-methylprop-2-yl)oxy]carbonyl}hexahydropyridine-4-carboxylic acid (5.0 mmol), 61.3 mg of DMAP (0.50 mmol), 20 ml of CH2Cl2, and 1.15 g of EDC (6.0 mmol) was allowed to stand at 0 °C for 10 minutes. Then, 1.74 g of 2-(ethyl{4-[(1Z)-(4-nitrophenyl)ethazenyl]phenyl}amino)ethyl-1-ol (5.5 mmol) was added to the above solution. After stirring and mixing at room temperature for 12 h, the mixture was given to obtain hexahydropyridine-4-carboxylic acid-2-(ethyl{4-[(1Z)-(4-nitrophenyl)ethazenyl]phenyl}amino)ethyl ester.

[0048] 1.824 g of 2-(ethyl{4-[(1Z)-(4-nitrophenyl)ethazinyl]phenyl}amino)ethyl ester (4.29 mmol) and 1.104 g of 2-(4-{[dimethyl(2-methylprop-2-yl)silyl]oxy}phenyl)-2-hydroxyacetic acid (3.89 mmol) were dissolved in 50 mL of DMF with stirring. 2.13 mL of DIEA (1.06 mmol) and 0.597 g of HBTU (3.89 mmol) were added, and the mixture was reacted at room temperature for 6 h to give 2-(4-{[dimethyl(2-methylprop-2-yl)silyl]oxy}phenyl)-1-[4-({[2-(ethyl{4-[(4-nitrophenyl)ethazinyl]phenyl}amino)ethyl]dioxy}thio)hexahydropyridin-1-yl]-2-hydroxyethyl-1-one;

[0049] An epoxy resin curing indicator compound was obtained by adding 0.100 g of 2-(4-{[dimethyl(2-methylprop-2-yl)silyl]oxy}phenyl)-1-[4-({[2-(ethyl{4-[(4-nitrophenyl)ethazenoyl]phenyl}amino)ethyl]dioxy}thio)hexahydropyridin-1-yl]-2-hydroxyethyl-1-one (0.1451 mmol) to 5 mL of CH2Cl2, 100 µL of 2,6-dimethylpyridine (0.87 mmol), and 0.110 g of p-nitrobenzene chloroformate (0.58 mmol) and reacting for 12 h. The 1H NMR spectrum of the epoxy resin curing indicator compound is shown below. Figure 2 As shown.

[0050] Example 2

[0051] Example 2 of this application provides a method for preparing an epoxy resin curing indicator composition, the steps of which include:

[0052] An epoxy resin curing indicator composition was prepared by mixing 80 ml of bisphenol A type epoxy resin, 15 ml of butanediol diglycidyl ether, 5 ml of C13-C15-glycidyl ether, 2 ml of benzyl alcohol, 45 ml of polyoxypropylene glycol triamine, and 0.01 ml of the epoxy resin curing indicator compound provided in Example 1. The epoxy resin curing indicator composition of this formulation was initially colorless.

[0053] Example 3

[0054] Example 3 of this application provides a method for testing the curing performance of an epoxy resin curing indicator composition.

[0055] The epoxy resin curing indicator composition was placed in the sample oven of a UV-Vis-NIR spectrometer and cured at a fixed temperature of 80°C. The absorption spectra of the epoxy resin curing indicator composition were recorded at 10 min, 20 min, 30 min, 40 min, and 60 min of curing. The absorption spectrum results are shown below. Figure 3 As shown in Table 1, the curing time and absorbance are as follows.

[0056]

[0057] Table 1. Absorption rate (%) of epoxy resin cured products at 650 nm wavelength

[0058] from Figure 3 It can be seen that within 10-30 minutes, the absorption peak of the absorption spectrum undergoes a red shift. At 30, 40, and 60 minutes, the absorption peak of the epoxy resin is around 650 nm, indicating that the epoxy resin is red after curing for 30-60 minutes. Furthermore, the absorption peak of the epoxy resin after curing for 60 minutes is higher, and the absorption of wavelengths around 650 nm is stronger, indicating a deeper red. Further, referring to Table 1, it can be seen that as the curing time of the epoxy resin curing indicator composition increases, the absorbance at 650 nm gradually increases, indicating that the red gradually becomes darker. This shows that the compound shown in Formula I in the epoxy resin curing indicator composition provided in this application combines with the groups (amines or alcohols) generated in the crosslinking network after curing of bisphenol A type epoxy resin to produce a color that can absorb wavelengths around 650 nm, corresponding to the wavelength of red light, thereby causing the cured epoxy resin to gradually change from colorless to light red, light red to red, and then to dark red.

[0059] In Table 1, the absorbance is calculated using Equation II;

[0060] Formula II;

[0061] In Equation II, y is the absorbance.

[0062] I0 is the initial light intensity emitted by the light source (650nm).

[0063] I represents the current light intensity monitored by the spectrometer (650 nm).

[0064] Example 4

[0065] Example 4 of this application provides an application of an epoxy resin curing indicator composition.

[0066] The application process first involves fitting the curing time and absorbance in Table 1, and the results are as follows: Figure 4 As shown, the obtained linear relationship is: y = 0.0275x - 0.165, R0 2 =0.9494.

[0067] When an epoxy resin curing indicator composition with the same formulation as in Example 2 is cured in an 80°C oven for a certain period of time, the absorbance of this epoxy resin curing indicator composition can be measured using a UV-Vis-NIR spectrometer. Then, based on the formula y=0.0275x-0.165, the approximate curing time of the epoxy resin curing indicator composition can be determined. In this example, the curing time of the epoxy resin can be determined more accurately by using a pre-established linear relationship between curing time and absorbance.

[0068] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An epoxy resin curing indicator compound, characterized in that, The chemical structure is shown in Formula I; Formula I; In Formula I, Et is selected from alkyl groups.

2. The epoxy resin curing indicator compound according to claim 1, characterized in that, The alkyl group is selected from any one of methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, and hexyl.

3. A method for preparing an epoxy resin curing indicator compound according to any one of claims 1-2, characterized in that, Including the following steps: Step S1: 1-{[(2-methylprop-2-yl)oxy]carbonyl}hexahydropyridine-4-carboxylic acid, 2-(ethyl{4-[(1Z)-(4-nitrophenyl)diazeninyl]phenyl}amino)ethyl alcohol are reacted at room temperature to give hexahydropyridine-4-carboxylic acid-2-(ethyl{4-[(1Z)-(4-nitrophenyl)diazeninyl]phenyl}amino)ethyl ester; Step S2: 2-(ethyl{4-[(1Z)-(4-nitrophenyl)diazeninyl]phenyl}amino)ethyl ester and 2-(4-{[dimethyl(2-methylprop-2-yl)silyl]oxy}phenyl)-2-hydroxyacetic acid are reacted at room temperature to give 2-(4-{[dimethyl(2-methylprop-2-yl)silyl]oxy}phenyl)-1-[4-({[2-(ethyl{4-[(4-nitrophenyl)diazeninyl]phenyl}amino)ethyl]dioxy}thio)hexahydropyridin-1-yl]-2-hydroxyethyl-1-one; Step S3: 2-(4-{[dimethyl(2-methylprop-2-yl)silyl]oxy}phenyl)-1-[4-({[2-(ethyl{4-[(4-nitrophenyl)diazeninyl]phenyl}amino)ethyl]dioxy}thio)hexahydropyridin-1-yl]-2-hydroxyethyl-1-one and p-nitrophenyl chloroformate are reacted at room temperature to obtain the epoxy resin curing indicator compound shown in Formula I.

4. The method for preparing an epoxy resin curing indicator compound according to claim 3, characterized in that, In step S1, the reaction process includes reacting in a mixed reaction system of 4-dimethylaminopyridine, dichloromethane, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide for 6 to 18 hours.

5. The method for preparing an epoxy resin curing indicator compound according to claim 3, characterized in that, In step S2, the reaction process includes reacting for 4-8 hours in a mixed reaction system of diisopropylethylamine, benzotriazole-N,N,N',N'-tetramethylurea hexafluorophosphate and N,N-dimethylformamide.

6. The method for preparing an epoxy resin curing indicator compound according to claim 3, It is characterized in that In step S3, the reaction process includes reacting in a mixed reaction system of 2,6-dimethylpyridine and dichloromethane for 6 to 18 hours.

7. An epoxy resin curing indicator composition, characterized in that, include: Colorless and transparent epoxy resin, colorless and transparent epoxy resin curing agent, and epoxy resin curing indicator compound according to any one of claims 1-2.

8. The epoxy resin curing indicator composition according to claim 7, characterized in that, In the epoxy resin curing indicator composition, the doping amount of the epoxy resin curing indicator compound according to any one of claims 1-2 is 0.005~0.015%V / V.

9. The epoxy resin curing indicator composition according to claim 7, characterized in that, In the epoxy resin curing indicator composition, the colorless and transparent epoxy resin is selected from bisphenol A type epoxy resin, and the colorless and transparent epoxy resin curing agent is selected from polypropylene glycol triamine.

10. The use of the epoxy resin curing indicator composition according to any one of claims 7-9 in determining epoxy resin curing.

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