O-hydroxyl cinnamamide derivative, synthetic method thereof and application of derivative as epoxy resin latent photo-thermal curing agent

Abstract

The invention discloses an o-hydroxyl cinnamamide derivative, a synthesis method thereof and application of the o-hydroxyl cinnamamide derivative as an epoxy resin latent photo-thermal curing agent. The latent photo-thermal curing agent has good optical performance and latency, and can fully respond to 365 nm LED light, so that a coumarin skeleton in the structure is subjected to cis-trans-configuration inversion, amine is released, and no gas is generated. The latent photo-thermal curing agent is mixed with epoxy resin E-51, the mixture is irradiated by a 365 nm LED lamp and heated, a cast column body with the thickness of 2 mm is obtained, the static mechanical property of the cast body is good, no gas is generated in the process, and large-scale industrial application is expected to be carried out.

Description

Technical Field

[0001] The present invention relates to the technical field of epoxy resin curing agents, and particularly relates to an o-hydroxycinnamide derivative, a synthesis method thereof, and an application as a latent photo-thermal curing agent for epoxy resins. Background Art

[0002] Epoxy resins refer to compounds containing two or more epoxy groups in the molecule. According to the molecular structure classification, they can be divided into five categories: glycidyl esters, glycidyl ethers, glycidyl amines, linear aliphatics, and alicyclics. Among them, bisphenol A epoxy resin (E-51) belonging to the glycidyl ether type has a very high cost performance and is currently the one with the largest production scale and the widest use. A curing agent is a compound containing certain specific groups, and under certain conditions such as a certain temperature, humidity, and light, it can carry out an addition polymerization reaction or a catalytic polymerization reaction with the epoxy group of the epoxy resin to form a cured product with a three-dimensional network structure (also known as a three-dimensional network structure).

[0003] In recent years, the photopolymerization technology has been widely used in the fields of photocurable coatings, photocurable inks, stereolithography, 3D printing, etc. due to its "5E" characteristics, namely: energy saving, economy, environmental protection, high efficiency, and wide adaptability. Currently, the commonly used photoinitiators (PIs) in the photopolymerization system are divided into free radical PIs, cationic PIs (photoacid-generating curing agents), and anionic PIs (photo-base-generating curing agents), which are respectively used in free radical photopolymerization systems, cationic photopolymerization systems, and anionic photopolymerization systems. Free radical photopolymerization systems usually use acrylates as oligomers and are widely used in many advanced fields, but their cured product shrinkage rate is high and there is oxygen inhibition, which limits their application. In contrast, the cationic photopolymerization system does not have these problems and can polymerize epoxy resins, but the currently most commonly polymerized alicyclic epoxy resins in the cationic photopolymerization system, and most of the currently used photoacid-generating curing agents have poor solubility, and the super strong acids generated will corrode the metal substrate. Photo-base-generating curing agents usually generate organic bases, can cure epoxy resins, and will not corrode the metal substrate, but most of the currently used photo-base-generating curing agents generally produce gas by-products during photolysis, resulting in voids and bubbles in the cured product, affecting the morphology and performance of the cured product, and most of the products applied to the curing of epoxy resins are thin films.

[0004] Amine compounds are the most common curing agents for epoxy resin E-51. One of their disadvantages is high reactivity and no latency period. Curing starts immediately after mixing, and the initiation cannot be controlled. Therefore, amine compounds usually form a two-component system when used with epoxy resin E-51. The two-component system must be prepared and used immediately, which is cumbersome in manual operation and has high transportation costs. Thermal curing technology is the most commonly used technology for curing epoxy resin E-51 with amine compounds. The cured products obtained by thermal curing technology have the advantages of high strength, heat resistance, chemical corrosion resistance, strong process controllability, and the ability to optimize performance by adjusting parameters.

[0005] Therefore, from both the economic perspective and the perspective of the properties of the cured products, it is very meaningful to develop a latent photo-thermal curing agent that can form a single-component system with epoxy resin E-51 and prepare a casting body. Summary of the Invention

[0006] The purpose of the present invention is to provide an o-hydroxycinnamamide derivative, its synthesis method, and its application as a latent photo-thermal curing agent for epoxy resin. The epoxy resin system formed by the latent photo-thermal curing agent of the present invention as an epoxy resin curing agent has good room-temperature storage stability, can apply green light source LED lamps to epoxy resin curing, has no side reactions and gas by-products generated during the curing process, the curing can proceed normally, and is expected to be applied in large-scale industrialization.

[0007] The purpose of the present invention is achieved through the following technical solutions.

[0008] An o-hydroxycinnamamide derivative, the structural formula is as follows:

[0009]

[0010] X is one of H, -NO2, -SO3H, preferably H or -NO2;

[0011] R is

[0012] One of them, where n = 1 to 8; preferably

[0013] Further preferably, the o-hydroxycinnamamide derivative is

[0014] The preparation method of the above-mentioned o-hydroxycinnamamide derivative includes the following steps:

[0015] Put React with an amine under the action of a condensing agent and a catalyst at 0°C to 25°C for 5h to 12h to obtain an o-hydroxycinnamide derivative;

[0016] Or React with an amine under the action of a condensing agent and a catalyst at 90°C to 120°C for 6h to 8h to obtain an o-hydroxycinnamide derivative;

[0017] The X is one of H, -NO2, -SO3H;

[0018] The amine is

[0019] One of them, where n = 1 to 8.

[0020] Preferably, the molar ratio of the to the amine is 1.1 to 2.2:1; the condensing agent used is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI), and the molar ratio of the condensing agent to the amine is 1.1 to 2.2:1.

[0021] Preferably, the molar ratio of the to the amine is 1:8 to 10; the condensing agent used is 1,3-dicyclohexylcarbodiimide (DCC), and the molar ratio of the condensing agent to the is 1.0 to 1.2:1.

[0022] Preferably, 4-dimethylaminopyridine (DMAP) is used as the catalyst for the amidation reaction.

[0023] Preferably, the amidation reaction is carried out in a solvent system, and the solvent is at least one of N,N-dimethylformamide, anhydrous tetrahydrofuran, triethylamine, and pyridine.

[0024] More preferably, amidation reaction occurs with the amine, and the solvent is at least one of N,N-dimethylformamide and anhydrous tetrahydrofuran.

[0025] More preferably, amidation reaction occurs with the amine, and the solvent is at least one of N,N-dimethylformamide, triethylamine, and pyridine.

[0026] An epoxy resin curing agent contains the o-hydroxycinnamide derivative described in any one of the above, which can photodecompose under 365nm LED light to release primary or secondary amine compounds, thereby curing epoxy resin.

[0027] An epoxy resin casting body, comprising epoxy resin E-51 and the o-hydroxycinnamide derivative described in any one of the above.

[0028] Preferably, the mass ratio of the epoxy resin E-51 to the o-hydroxycinnamide derivative is 100:11-90.

[0029] A preparation method of the epoxy resin casting body as described above comprises the following steps:

[0030] Mix the epoxy resin E-51 and the latent photo-thermal curing agent evenly at room temperature. Stir the mixture under the irradiation of a 365 nm LED lamp. After the latent photo-thermal curing agent is completely photolyzed, then pour the flowing system into a mold coated with dimethyl silicone oil. Preheat and evacuate to remove air bubbles. Then heat up to the specified curing temperature for curing to obtain an epoxy resin casting body (dumbbell-shaped) with a thickness of 2 mm.

[0031] In the present invention, the amine curing agent is modified into a latent photo-thermal curing agent, which can effectively inhibit the activity of the amine curing agent. It is combined with the epoxy resin E-51 to form a single-component system. After light irradiation, the activity of the amine compound is restored, and then heated for curing to prepare the casting body. There are no gas by-products generated during the process, and it also solves the problems such as the amine curing agent having no latent period and high product transportation cost, meeting the current actual application requirements.

[0032] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0033] 1) The latent photo-thermal curing agent of the present invention significantly improves the shortcoming that the amine compound has no latent period. By introducing the coumarin ring structure, this type of photo-thermal curing agent can respond to a 365 nm LED lamp and can form a single-component system with the epoxy resin. Its room-temperature storage stability is effectively improved, and there are no side reactions or gas by-products generated during the photolysis curing process. The static mechanical properties and morphology of the cured casting body are good.

[0034] 2) The preparation method of the latent photo-thermal curing agent of the present invention is simple and safe, with low production cost, and is suitable for large-scale industrial applications. Description of the Drawings

[0035] Figure 1 UV-visible absorption spectra of the latent photo-thermal curing agents of Examples 1 to 4 dissolved in methanol with a concentration of 30 μM in the range of 200 nm to 500 nm.

[0036] Figure 2 GC-MS result diagram of the latent photo-thermal curing agent of Example 1 after being irradiated by a 365 nm LED lamp for 2 h.

[0037] Figure 3GC-MS result chart of the latent photo-thermal curing agent in Example 3 after being irradiated by a 465 nm LED lamp for 2 h.

[0038] Figure 4a 、 Figure 4b 1H NMR and 1 1H NMR and 13 13C NMR spectra of the latent photo-thermal curing agent in Example 1.

[0039] Figure 5a 、 Figure 5b 1H NMR and 1 1H NMR and 13 13C NMR spectra of the latent photo-thermal curing agent in Example 2.

[0040] Figure 6a 、 Figure 6b 1H NMR and 1 1H NMR and 13 13C NMR spectra of the latent photo-thermal curing agent in Example 3.

[0041] Figure 7a 、 Figure 7b 1H NMR and 1 1H NMR and 13 13C NMR spectra of the latent photo-thermal curing agent in Example 4. Detailed implementation mode

[0042] The following further illustrates the specific implementation of the present invention in combination with examples and drawings, but the implementation mode of the present invention is not limited thereto.

[0043] Example 1

[0044] A kind of latent photo-thermal curing agent, and its preparation method is as follows:

[0045] Dissolve 18.04 g (11 mmol) of o-hydroxycinnamic acid in tetrahydrofuran. After cooling the solution to 0 °C in an ice bath, add 21.01 g (11 mmol) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI). After 10 minutes, add 12.52 g (10 mmol) of 1-(3-aminopropyl)imidazole and 0.24 g (0.2 mmol) of 4-dimethylaminopyridine (DMAP). Stir and react at room temperature for 7 h. Cool the reaction solution in an ice bath, filter, and concentrate under reduced pressure. Wash the solid 3 times with saturated sodium bicarbonate solution and 3 times with 10% hydrochloric acid solution. After filtration and drying, the latent photo-thermal curing agent (E)-N-(3-(1H-imidazol-1-yl)propyl)-3-(2-hydroxyphenyl)acrylamide (yellow powder, yield 56%) is obtained;

[0046] The latent photo-thermal curing agent of this example1 1H NMR and 13 13C NMR nuclear magnetic data are as follows:

[0047] 1 1H NMR (400 MHz, DMSO-d6) δ 10.27 (s, 1H), 8.23 (s, 1H), 7.67 (d, J = 18.1 Hz, 2H), 7.43 (d, J = 7.7 Hz, 1H), 7.20 (d, J = 15.6 Hz, 2H), 7.01–6.62 (m, 4H), 4.01 (t, J = 7.1 Hz, 2H), 3.15 (s, 2H), 2.04–1.76 (m, 2H).

[0048] 13 13C NMR (101 MHz, DMSO-d6) δ 166.33, 157.19, 135.38, 130.90, 128.94, 128.93, 128.91, 122.16, 121.93, 119.57, 119.57, 116.66, 44.22, 36.36, 31.35.

[0049] For the specific NMR spectra, see Figure 4a and Figure 4b .

[0050] In summary, the structural formula of the latent photo-thermal curing agent in this example is as follows:

[0051]

[0052] Example 2

[0053] A latent photo-thermal curing agent, and its preparation method is as follows:

[0054] Dissolve 3.28 g (2.2 mmol) of o-hydroxycinnamic acid in tetrahydrofuran. After cooling the solution to 0 °C in an ice bath, add 3.82 g (2.2 mmol) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI). After 10 minutes, add 1.70 g (1.0 mmol) of isophorone diamine and 0.24 g (0.2 mmol) of 4-dimethylaminopyridine (DMAP), stir at room temperature for 12 h, cool the reaction solution in an ice bath, filter, and concentrate under reduced pressure. Wash the solid 3 times with saturated sodium bicarbonate solution and 3 times with 10% hydrochloric acid solution. After filtration and drying, the latent photo-thermal curing agent (E)-3-(2-hydroxyphenyl)-N-((5-((E)-3-(2-hydroxyphenyl)acrylamido)-1,3,3-trimethylcyclohexyl)methyl)acrylamide (white powder, yield 30%) is obtained.

[0055] The latent photo-thermal curing agent of this embodiment 1 H NMR and 13 C NMR nuclear magnetic data are as follows:

[0056] 1 H NMR(500MHz,DMSO-d6)δ10.10(s,2H,-OH),8.12-7.97(m,2H),7.64(t,J=14.7Hz,2H),7.40(dd,J=14.5,7.7Hz,2H),7.16(d,J=7.9Hz,2H),6.94(d,J=8.7Hz,2H),6.80(d,J=6.1Hz,2H),6.68(dd,J=15.9,9.2Hz,1H),4.05(q,J=11.6,11.1Hz,1H),3.34-3.21(m,1H),3.12-2.88(m,3H),2.66(d,J=16.4Hz,1H),1.65-1.49(m,2H),1.19(d,J=13.8Hz,1H),1.10(d,J=13.9Hz,1H),1.03(s,3H),1.01-0.97(m,3H),0.91(d,J=6.3Hz,3H).

[0057] 13 C NMR(126MHz,DMSO-d6)δ166.54,165.17,156.67(d,J=3.1Hz),135.11,134.82,130.83,128.55,122.90-121.83(m),120.02,119.79,116.54(d,J=3.2Hz),52.88,47.41,36.82,35.32(d,J=38.8Hz),32.03-31.62(m),28.00,27.60(d,J=20.2Hz),23.88,23.71.

[0058] See the specific nuclear magnetic spectra in Figure 5a 、 Figure 5b 。

[0059] In summary, the structural formula of the latent photo-thermal curing agent of this embodiment is as follows:

[0060]

[0061] Example 3

[0062] A latent photo-thermal curing agent, and its preparation method is as follows:

[0063] 0.60 g (3.15 mmol) of 6-nitrocoumarin, 2.8 g (28 mmol) of 1-methylpiperazine, 0.95 g (9.45 mmol) of triethylamine, 0.78 g (3.78 mmol) of 1,3-dicyclohexylcarbodiimide (DCC), 0.24 g (0.2 mmol) of 4-dimethylaminopyridine (DMAP), reflux and stir at 120 °C for 6 h; after the reaction solution is cooled to room temperature, add 10 ml of chloroform, adjust the pH value of the reaction solution to about 1 with 10% hydrochloric acid solution, and let it stand until the solid completely precipitates; the solid obtained by suction filtration is washed with water and ethyl acetate for many times and then filtered, and after vacuum drying, the latent photothermal curing agent (E)-3-(2-hydroxy-5-nitrophenyl)-1-(4-methylpiperazin-1-yl)acrylamide (light yellow powder, yield 72%) is obtained.

[0064] The latent photothermal curing agent of this example 1 H NMR and 13 C NMR nuclear magnetic data are as follows:

[0065] 1 H NMR (400 MHz, DMSO-d6) δ 11.48 (s, 1H, -OH), 8.66 (d, J = 2.9 Hz, 1H), 8.12 (dd, J = 9.1, 2.8 Hz, 1H), 7.81 (d, J = 15.6 Hz, 1H), 7.42 (d, J = 15.5 Hz, 1H), 7.18 (d, J = 9.1 Hz, 1H), 4.52 (br, s, 2H), 3.39 (br, s, 6H), 2.78 (s, 3H).

[0066] 13 C NMR (101 MHz, DMSO-d6) δ 165.07, 162.65, 140.29, 135.87, 126.83, 124.08, 122.76, 119.36, 116.94, 42.43.

[0067] The specific NMR spectra are shown in Figure 6a 、 Figure 6b 。

[0068] In summary, the structural formula of the latent photothermal curing agent of this example is as follows:

[0069]

[0070] Example 4

[0071] A latent photothermal curing agent, and its preparation method is as follows:

[0072] Dissolve 1.80 g (1.1 mmol) of o-hydroxycinnamic acid in tetrahydrofuran. After cooling the solution to 0 °C in an ice bath, add 2.10 g (1.1 mmol) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI). After 10 minutes, add 1.00 g (1 mmol) of 1-methylpiperazine and 0.24 g (0.2 mmol) of 4-dimethylaminopyridine (DMAP). Stir the reaction at room temperature for 5 h. Cool the reaction solution in an ice bath, filter, and concentrate under reduced pressure. Wash the solid three times with saturated sodium bicarbonate solution and three times with 10% hydrochloric acid solution. After filtration and drying, the latent photo-thermal curing agent (E)-3-(2-hydroxyphenyl)-1-(4-methylpiperazin-1-yl)acrylamide (white powder, yield 75%) is obtained;

[0073] The 1H NMR and 13C NMR data of the latent photo-thermal curing agent in this example are as follows:

[0074] 1 1H NMR (400 MHz, DMSO-d6) δ 10.03 (s, 1H, -OH), 7.80 (d, J = 15.5 Hz, 1H), 7.68 (d, J = 7.8 Hz, 1H), 7.22 - 7.13 (m, 2H), 6.90 (d, J = 8.2 Hz, 1H), 6.81 (t, J = 7.6 Hz, 1H), 3.61 (d, J = 31.1 Hz, 4H), 2.31 (s, 4H), 2.19 (s, 3H).

[0075] 13 13C NMR (101 MHz, DMSO-d6) δ 165.41, 156.64, 137.44, 131.12, 128.56, 122.36, 119.66, 117.31, 54.86, 46.07, 45.40, 41.98.

[0076] For the specific NMR spectra, see Figure 7a and Figure 7b .

[0077] In summary, the structural formula of the latent photo-thermal curing agent in this example is as follows:

[0078]

[0079] Photolysis tests of Examples 1 - 4

[0080] Ultraviolet spectrum test: Prepare solutions with a concentration of 30 μM from the products prepared in Examples 1 - 4 respectively, and test them with HITACHI-U3900H. The scanning range is 200 - 500 nm, and the scanning speed is 300 nm / min. The ultraviolet spectra of Examples 1 - 4 obtained are asFigure 1 as shown

[0081] Dissolve 0.5 mmol of the latent photo-thermal curing agents of Examples 1 to 4 in 70 ml of methanol respectively, add 0.5 ml of glacial acetic acid for catalysis, stir under irradiation of a 365 nm LED lamp for 2 h, monitor the reaction according to thin layer chromatography. After the light irradiation ends, take 0.1 ml of the reaction solution from the reaction systems of the latent photo-thermal curing agents of Examples 1 to 4 into 5-ml centrifuge tubes respectively, dilute the samples to 3 ml, and then take 1.5 ml into sample vials for GC-MS testing to verify the photolysis results. The photolysis result of the latent photo-thermal curing agent of Example 1 is as Figure 2 shown. The photolysis results of Examples 2 to 4 are similar and will not be shown. Dissolve 0.5 mmol of the latent photo-thermal curing agents of Examples 1 to 4 in 70 ml of methanol respectively, add 0.5 ml of glacial acetic acid for catalysis, stir under irradiation of a 465 nm LED lamp for 2 h, use thin layer chromatography to monitor the reaction, and repeat the above sampling operation for GC-MS testing to verify the photolysis results after the light irradiation ends. The results are as Figure 3 shown

[0082] Dissolve 0.5 mmol of the latent photo-thermal curing agents of Examples 1 to 4 in 70 ml of methanol respectively, add 0.5 mmol of dodecane as an internal standard, add 0.5 ml of glacial acetic acid for catalysis, stir under irradiation of a 365 nm LED lamp, and take 0.1 ml of the reaction solution into a 5-ml centrifuge tube every 10 minutes with a dropper, dilute the sample to 3 ml, and then take 1.5 ml into a sample vial for GC-MS testing. Calculate by the internal standard method according to the test results, and determine the photolysis efficiency of the latent photo-thermal curing agent by the release efficiency of coumarin / 6-nitro-coumarin. The results are shown in Table 1

[0083] Table 1 Results of calculating the photolysis efficiency of the latent photo-thermal curing agent by the internal standard method

[0084]

[0085]

[0086] From Figure 1 and Figure 2 and Figure 3 Table 1, it can be seen that

[0087] The ultraviolet spectra of the latent photo-thermal curing agents of Examples 1 to 4 ( Figure 1)It is shown that they all have obvious absorption in the range of 250 - 365 nm, which provides evidence that they can respond to the irradiation of 365 nm LED light and cause cis-trans configuration inversion on the coumarin skeleton and release amines. In addition, Example 3 with a nitro group in its structure has obvious absorption at 400 - 500 nm. It can be speculated that the introduction of the nitro group causes a red shift in the response wavelength of this type of latent photo-thermal curing agent.

[0088] Taking the GC-MS results of the latent photo-thermal curing agent of Example 1 ( Figure 2 ) as an example, from left to right are 1-(3-aminopropyl)imidazole and coumarin. The amine is successfully released by photolysis, and the product is correct. The GC-MS results of the latent photo-thermal curing agents of other Examples 2 - 4 are similar, and the photolysis products are correct. When the light source is changed to a 465 nm LED lamp, only the latent photo-thermal curing agent of Example 3 with a nitro group in its structure undergoes photolysis, and the photolysis product is correct ( Figure 3 ), while the latent photo-thermal curing agents of other examples do not undergo photolysis, which verifies the results of the ultraviolet spectra of the latent photo-thermal curing agents of the above Examples 1 - 4.

[0089] The amine release efficiency, that is, the photolysis efficiency, of the latent photo-thermal curing agents of Examples 1 - 4 is all 100%. In addition, the illumination time required for the latent photo-thermal curing agents of Examples 1 - 4 to reach a photolysis efficiency of 100% is concentrated in 60 - 70 min. The latent photo-thermal curing agent of Example 3 with a nitro group in its structure does not have a decisive impact on the illumination time. Therefore, the photolysis time of this type of latent photo-thermal curing agent may be jointly determined by the structures of the amine and the coumarin derivative.

[0090] Latency tests of Examples 1 - 4

[0091] Epoxy resin E-51 and the latent photo-thermal curing agents of Examples 1 - 4 are respectively mixed at a mass ratio of 100:11, 100:90, 100:30, and 100:25, and stirred evenly at room temperature to form mixtures. Referring to "GB / T7123.2 - 2002 Determination of the storage life of adhesives", the storage life of the mixtures of epoxy resin E-51 and the latent photo-thermal curing agents is determined. The specific operation is as follows: Put the prepared mixtures of epoxy resin E-51 and the latent photo-thermal curing agents into a constant temperature control box, keep the temperature at 25 °C, and determine the maximum storage time for which the mixtures can maintain their operating performance. The viscosities and pot lives of the one-component systems composed of the latent photo-thermal curing agents and epoxy resin E-51 are shown in the following table

[0092] Table 2 Viscosities and pot lives of the one-component systems of the latent photo-thermal curing agents and epoxy resin E-51

[0093]

[0094] As can be seen from Table 2, the photo-thermal curing agents in Examples 1 to 4, when combined with epoxy resin E-51 to form a one-component system, all have a certain latency. Among them, the storage periods of the E-51 / Examples 1 to 3 systems are greater than 90 days, while the E-51 /

[0095] Example 4 system is only 24 days. By comparing the structures of the two latent photo-thermal curing agents in Example 3 and Example 4, it can be seen that the difference between the latent photo-thermal curing agents in Example 3 and Example 4 is that a nitro group is introduced in the structure. The introduction of this nitro group not only increases the response wavelength range of the photo-thermal curing agent, but also increases its steric hindrance, reducing its reactivity with epoxy resin E-51 at room temperature. As a result, the latent photo-thermal curing agent in Example 4 with an original storage period of 24 days becomes the latent photo-thermal curing agent in Example 3 with a storage period greater than 90 days after the introduction of the nitro group. Therefore, this type of latent photo-thermal curing agent has a good storage period, and the introduction of the nitro group may extend the storage period of this type of photo-thermal curing agent. Among them, Example 1 of imidazole class cures epoxy resin E-51 by a catalytic mechanism, has a small addition amount, high solubility, and has good industrial application prospects.

[0096] Example 5

[0097] An epoxy resin casting body, and its preparation method is as follows:

[0098] Epoxy resin E-51 and the latent photo-thermal curing agent of Example 1 are mixed at room temperature according to a mass ratio of 100:11. The mixture is stirred under 365 nm light irradiation. After the latent photo-thermal curing agent is completely photolyzed, the flowing system is then poured into a mold coated with dimethyl silicone oil. The mold is placed in a vacuum drying oven, heated to 50 °C, and intermittently evacuated to remove air bubbles. The mixture is baked and cured at 100 °C for 2 hours. After curing, the mold is cooled to room temperature and then demolded to obtain an epoxy resin casting body (dumbbell-shaped) with a thickness of 2 mm.

[0099] Performance test

[0100] Epoxy resin E-51 was mixed with the latent photo-thermal curing agent of Example 1 at a ratio of 100:11. The curing agent 1-(3-aminopropyl)imidazole (3-APYI) had a mass fraction of 5% after complete photolysis in Example 1. After irradiation with a 365 nm LED lamp, the flowing system was poured into a mold and baked at 100 °C to obtain an E-51 / epoxy resin casting of Example 1 with a thickness of 2 mm. Referring to "GB / T 1040.2-2022 Plastics - Determination of tensile properties - Part 2: Test conditions for moulded and extruded plastics", the static mechanical properties of the epoxy resin casting of Example 1 were tested using an INSTRON tensile machine. In addition, the coumarin released during photolysis may affect the static mechanical properties of the thermoset plastic. Therefore, the epoxy resin casting of the prototype 1-(3-aminopropyl)imidazole (mass fraction of 5%) without coumarin obtained under the same conditions was tested for static mechanical properties according to the same standard. The above test results are shown in Table 3.

[0101] Table 3 Static mechanical properties of epoxy resin castings of Example 1 and 1-(3-aminopropyl)imidazole

[0102]

[0103]

[0104] As can be seen from Table 3, the difference between E-51 / Example 1 and its prototype E-51 / 1-(3-aminopropyl)imidazole is that after photolysis is completed, 1-(3-aminopropyl)imidazole and coumarin are released in the former. The presence of coumarin does change the tensile strength and elongation at break of the casting, but the data difference is not large. Therefore, it can be considered that the coumarin released by the photolysis of the latent photo-thermal curing agent in Example 1 does not affect the static mechanical properties of the casting, which indicates that the curing process can proceed normally, no gas is generated during the photolysis curing process, the morphology of the cured product casting is complete, making this type of latent photo-thermal curing agent more promising in industry.

[0105] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. An o-hydroxycinnamide derivative, characterized in that, The structural formula is as follows: X is one of H, -NO2, -SO3H; R is one of, where n = 1 to 8.

2. The o-hydroxycinnamide derivative according to claim 1, characterized in that, The o-hydroxycinnamamide derivative is 3. A method for preparing an o-hydroxycinnamamide derivative according to claim 1 or 2, characterized in that, It includes the following steps: React with an amine under the action of a condensing agent and a catalyst at 0 °C to 25 °C for 5 h to 12 h to obtain an o-hydroxycinnamamide derivative; Or react with amine under the action of a condensing agent and a catalyst at 90 °C to 120 °C for 6 h to 8 h to obtain an o-hydroxycinnamamide derivative; The said X is one of H, -NO2, -SO3H; The amine is one of them, where n = 1 to 8.

4. The preparation method of an o-hydroxycinnamamide derivative according to claim 3, characterized in that, The The molar ratio with the amine is 1.1 to 2.2:1; the condensing agent used is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and the molar ratio of the condensing agent to the amine is 1.1 to 2.2:

1.

5. The preparation method of an o-hydroxycinnamamide derivative according to claim 3, characterized in that, The has a molar ratio with the amine of 1:8 to 10; the condensing agent used is 1,3-dicyclohexylcarbodiimide, and the molar ratio of the condensing agent to is 1.0 to 1.2:

1.

6. The preparation method of an o-hydroxycinnamamide derivative according to claim 3, characterized in that, 4-Dimethylaminopyridine is used as the catalyst for the amidation reaction.

7. The preparation method of an o-hydroxycinnamamide derivative according to claim 3, characterized in that, The said amidation reaction is carried out in a solvent system, and the solvent is at least one of N,N-dimethylformamide, anhydrous tetrahydrofuran, triethylamine, and pyridine.

8. An epoxy resin curing agent, characterized in that, It contains the o-hydroxycinnamide derivative described in any one of claims 1 to 2.

9. An epoxy resin casting body, characterized in that, It contains epoxy resin E-51 and the o-hydroxycinnamide derivative described in any one of claims 1 to 2.

10. An epoxy resin casting according to claim 9, characterized in that, The mass ratio of the said epoxy resin E-51 to the o-hydroxycinnamide derivative is 100:11 - 90.

Images