High-toughness long-chain mercaptan compound and epoxy adhesive, and preparation method and application thereof

Abstract

The application belongs to the technical field of organic synthesis, and particularly relates to a high-toughness long-chain mercaptan compound and a preparation method and application thereof. The long-chain dithiol compound has a structure shown in formula (1). The long-chain dithiol compound provided by the application can effectively improve the long-term toughness of an epoxy adhesive as a curing agent of the epoxy adhesive. In addition, the preparation method of the long-chain dithiol compound provided by the application can efficiently obtain the long-chain dithiol compound through only two-step reactions, is beneficial to the improvement of the total yield, and thus realizes the efficient synthesis of the long-chain dithiol compound without sulfur odor.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of organic synthesis, and particularly relates to a long-chain mercaptan compound with high toughness, an epoxy adhesive, and a preparation method and application thereof. BACKGROUND

[0002] Epoxy adhesives have excellent bonding strength, electrical properties, heat resistance, and chemical resistance, and are widely used as base resins for paints, electrical and electronic insulating materials, adhesives, and the like. Among them, an epoxy adhesive often adopts an epoxy resin-mercaptan system, which can meet the requirements of curing at a relatively low temperature of the adhesive and having sufficient bonding strength.

[0003] Toughened epoxy resin adhesives are a kind of epoxy adhesives with good toughness, which have good resistance to deformation and fracture when subjected to external force, so as to still maintain good bonding stability when subjected to external force. Toughened epoxy resin adhesives are widely used in the fields of aerospace, automobile manufacturing industry, and electronic industry, etc. At present, toughened epoxy resin adhesives are usually obtained by adding toughening agents (such as rubber particles, etc.) to epoxy resin adhesives, which can absorb and disperse external force during the curing process, thereby enhancing the impact resistance of the epoxy adhesive. However, although the introduction of toughening agents into the epoxy resin adhesive can improve the toughness at the initial stage of the bonding of the article, as the bonding time of the article prolongs, stress concentration phenomenon occurs at the position where the toughening agent exists in the epoxy adhesive, resulting in fatigue cracks in the cured epoxy adhesive layer, and thus the epoxy adhesive cannot continue to provide good toughness. SUMMARY

[0004] A first object of the present application is to provide a long-chain dithiol compound capable of effectively improving the long-term toughness of an epoxy adhesive.

[0005] A second object of the present application is to provide a preparation method of the above-mentioned long-chain dithiol compound.

[0006] A third object of the present application is to provide the application of the above-mentioned long-chain dithiol compound in adhesives.

[0007] A fourth object of the present application is to provide an epoxy adhesive.

[0008] Specifically, the long-chain dithiol compound provided by the present application has a structure shown in formula (1):

[0009]

[0010] In formula (1), R1, R2, R3, R4, R5, R6, R7, and R8 are independently H or C1-C5 alkyl, and m is an integer of 5-10.

[0011] The preparation method of the long-chain dithiol compound provided by the application comprises the following steps:

[0012] S1. performing a substitution reaction on the biphenyl diol shown in formula (2) and the long-chain halogenated sulfonate compound shown in formula (3) in the presence of a base I and a catalyst to obtain an intermediate-containing product;

[0013] S2. performing a hydrolysis reaction on the intermediate-containing product in the presence of a base II to obtain a long-chain dithiol compound-containing product;

[0014]

[0015] In formula (2), R1, R2, R3, R4, R5, R6, R7 and R8 are independently H or C1-C5 alkyl; in formula (3), n is an integer of 5-10, and X is halogen.

[0016] The epoxy adhesive provided by the application comprises an epoxy resin and a curing agent, and the curing agent is the long-chain dithiol compound.

[0017] The inventors of the application have conducted in-depth and extensive research on the epoxy adhesive, and tried to adjust from the aspects of modification of the epoxy resin itself, types and amounts of toughening agents and the like, but all failed to improve the long-term toughness of the epoxy adhesive well. The inventors of the application surprisingly found that the long-chain dithiol compound having the structure shown in formula (1) can effectively improve the long-term toughness of the epoxy adhesive as the curing agent of the epoxy adhesive.

[0018] In addition, the biphenyl diol and the long-chain halogenated sulfonate compound are used as starting materials in the application, and both the biphenyl diol and the long-chain halogenated sulfonate compound have active reaction types and good structural stability. After the substitution reaction of the biphenyl diol and the long-chain halogenated sulfonate compound, the hydrolysis reaction is performed, which can ensure the full play of the reaction activity and the stability of the reaction process. The long-chain dithiol compound can be efficiently obtained by only two steps, which is conducive to the improvement of the total yield, thereby realizing the efficient synthesis of the long-chain dithiol compound without sulfur odor. In addition, the preparation system of the long-chain dithiol compound provided by the application is simple and easy to operate, the reaction conditions are mild, and the whole reaction system is economical and efficient. DETAILED DESCRIPTION

[0019] The long-chain dithiol compound provided by the application has the structure shown in formula (1):

[0020]

[0021] In formula (1), R1, R2, R3, R4, R5, R6, R7 and R8 are independently H or C1-C5 alkyl, preferably all are H. n is an integer of 5-10, preferably an integer of 5-7. Specific examples of the C1-C5 alkyl include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl or neopentyl. n can be 5, 6, 7, 8, 9 or 10.

[0022] The method for preparing the long-chain dithiol compound provided by the present application comprises the following steps:

[0023] S1. performing substitution reaction on the diphenylol with the long-chain halogenated thioester compound in the presence of base I and a catalyst to obtain a product containing an intermediate;

[0024] S2. performing hydrolysis reaction on the product containing the intermediate in the presence of base II to obtain the long-chain dithiol compound.

[0025] The reaction equation of the preparation process of the long-chain dithiol compound provided by the present application is as follows:

[0026]

[0027] In the present application, the diphenylol has the structure shown in formula (2):

[0028]

[0029] In formula (2), R1, R2, R3, R4, R5, R6, R7 and R8 are independently H or C1-C5 alkyl, preferably all are H. Specific examples of the C1-C5 alkyl include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl or neopentyl.

[0030] In the present application, the long-chain halogenated thioester compound has the structure shown in formula (3):

[0031]

[0032] In formula (3), n is an integer of 5-10, preferably an integer of 5-7; X is halogen. n can be 5, 6, 7, 8, 9 or 10. X can be bromine or chlorine.

[0033] In the present application, the molar ratio of the diphenylol to the long-chain halogenated thioester compound is preferably 1:(1.9-2.1), such as 1:1.9, 1:1.92, 1:1.94, 1:1.96, 1:1.98, 1:2, 1:2.02, 1:2.04, 1:2.06, 1:2.08, 1:2.1 or any value therebetween.

[0034] In a preferred embodiment, in step S1, the step of substitution reaction comprises dissolving the biphenyl diol in organic solvent I, adding a base to provide alkaline conditions, adding a catalyst, heating to the temperature of substitution reaction under inert gas protection and stirring, then adding the long-chain halogenated thioester compound to perform the substitution reaction, removing the solvent by distillation under reduced pressure after the reaction is completed, washing the crude product with water and drying to obtain the product containing the intermediate.

[0035] In a preferred embodiment, in step S2, the product containing the intermediate is dissolved in organic solvent II, a base is added to provide alkaline conditions, and then heated to the temperature of substitution reaction to perform the substitution reaction, and the solvent is removed by distillation under reduced pressure after the reaction is completed to obtain the product containing the long-chain dithiol compound.

[0036] The preparation method of the long-chain dithiol compound provided by the present application preferably further comprises purifying and separating the long-chain dithiol compound from the product containing the long-chain dithiol compound, and the purification method comprises washing the product containing the long-chain dithiol compound to neutral, then extracting with ethyl acetate, drying the organic phase with anhydrous sodium sulfate, and then removing the solvent by distillation under reduced pressure to obtain the long-chain dithiol compound. After this purification treatment, the purity of the long-chain dithiol compound can be significantly improved.

[0037] In the present application, the conditions of the substitution reaction preferably include a temperature of 50-90℃, such as 50℃, 52℃, 55℃, 58℃, 60℃, 62℃, 65℃, 68℃, 70℃, 72℃, 75℃, 78℃, 80℃, 82℃, 85℃, 88℃, 90℃, or any value between them; and a time of 8-14h, such as 8h, 10h, 12h, 14h, or any value between them.

[0038] In the present application, the conditions of the hydrolysis reaction preferably include a temperature of 50-100℃, such as 50℃, 52℃, 55℃, 58℃, 60℃, 62℃, 65℃, 68℃, 70℃, 72℃, 75℃, 78℃, 80℃, 82℃, 85℃, 88℃, 90℃, 92℃, 95℃, 98℃, 100℃, or any value between them; and a time of 8-14h, such as 8h, 10h, 12h, 14h, or any value between them.

[0039] In the present application, the base I and base II can be independently selected from at least one of potassium carbonate, sodium carbonate, potassium hydroxide, sodium hydroxide and ammonia. In a preferred embodiment, the base I is potassium carbonate and / or sodium carbonate, and the base II is potassium hydroxide and / or sodium hydroxide, which can make the compatibility between different reactions better, thus promoting the reaction and further improving the reaction yield. In addition, the molar ratio of the base I to the diphenylol is preferably (1-5):1, such as 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1 or any value between them. The base II is used in the form of an aqueous solution, and the concentration of the base II aqueous solution is generally 30-60%, such as 30%, 35%, 40%, 45%, 50%, 55%, 60% or any value between them. The amount ratio of the base II aqueous solution to the diphenylol is preferably (200-500)mL:1mol, such as 200mL:1mol, 250mL:1mol, 300mL:1mol, 350mL:1mol, 400mL:1mol, 450mL:1mol, 500mL:1mol or any value between them. The terms "I" and "II" are only used to distinguish the bases used in different steps for the purpose of description, and have no other special meanings.

[0040] In the present application, the organic solvent I and the organic solvent II can be various inert liquid substances that can be used as reaction media, and can be at least one of alcohol solvents, ester solvents, ether solvents, hydrocarbon solvents, ketone solvents, etc. In a preferred embodiment, the organic solvent I is acetonitrile, and the organic solvent II is ethanol, which is more conducive to improving the compatibility between different reactions, and thus is more conducive to improving the reaction yield. The terms "I" and "II" are only used to distinguish the organic solvents used in different steps for the purpose of description, and have no other special meanings.

[0041] The present application does not have a particular limitation on the type of catalyst, which can be various substances that can improve the reaction rate, and can be at least one of 18-crown-6, benzyltriethylammonium chloride, tetrabutylammonium chloride and tetrabutylammonium bromide, and is particularly preferably tetrabutylammonium chloride. When the catalyst is selected as tetrabutylammonium chloride, it is more conducive to improving the yield of long-chain dithiol compounds.

[0042] The present application also provides the use of the above-mentioned long-chain dithiol compound in adhesives.

[0043] The epoxy adhesive provided by the present application comprises an epoxy resin and a curing agent, and the curing agent is the above-mentioned long-chain dithiol compound.

[0044] The present application will be further described below with reference to examples.

[0045] Preparation Example 1

[0046] S1. 2,2'-diphenol 186 g (1 mol, 1 eq) was dissolved in 10 L of a reaction kettle with 2.5 L of acetonitrile, then potassium carbonate 468 g (3.38 mol, 3.38 eq) and tetrabutylammonium 27.9 g (0.1 mol, 0.1 eq) were added, and the reaction was stirred at 85°C for 10 min under inert gas protection, then 6-bromo-1-hexylthioacetate 550 g (having the structure shown in formula (3), X is bromine, n is 5, 2.3 mol, 2.3 eq) was slowly added and reacted for 12 h, then the solvent was recovered by distillation under reduced pressure, washed with water and dried to obtain an intermediate-containing product.

[0047] S2. The intermediate-containing product obtained in step S1 was dissolved in the original reaction kettle with 3.2 L of ethanol, then 330 mL of 50% potassium hydroxide aqueous solution was added, and the reaction was hydrolyzed at 90°C for 12 h, after the reaction was completed, dilute hydrochloric acid was added to adjust the pH value to 7, the solvent was recovered by distillation under reduced pressure, extracted with ethyl acetate, washed with water and dried to obtain 360 g of a long-chain dithiol compound in the form of a light yellow viscous liquid.

[0048] The total yield of the two-step reaction was 71.1%, and the long-chain dithiol compound had basically no sulfur odor.

[0049] The nuclear magnetic resonance data and characteristic data of the long-chain dithiol compound are as follows: 1 H NMR (400 MHz, CDCl3) δ 7.44-7.15 (m, 4H), 7.08-6.84 (m, 4H), 3.93 (t, J = 6.3 Hz, 4H), 2.48 (dd, J = 14.7, 7.5 Hz, 3H), 1.75-1.41 (m, 9H), 1.41-1.21 (m, 10H).

[0050] Preparation Example 2

[0051] S1. 2,2'-diphenol 186 g (1 mol, 1 eq) was dissolved in 10 L of a reaction kettle with 2.5 L of acetonitrile, then potassium carbonate 468 g (3.38 mol, 3.38 eq) and tetrabutylammonium 27.9 g (0.1 mol, 0.1 eq) were added, and the reaction was stirred at 85°C for 10 min under inert gas protection, then 6-bromo-1-hexylthioacetate 550 g (having the structure shown in formula (3), X is bromine, n is 5, 2.3 mol, 2.3 eq) was slowly added and reacted for 12 h, then the solvent was recovered by distillation under reduced pressure, washed with water and dried to obtain an intermediate-containing product.

[0052] S2. The intermediate-containing product obtained in step S1 was dissolved in 30 L of ethanol in the original reaction kettle, then 50% potassium hydroxide aqueous solution 3.33 mL was added, and the hydrolysis reaction was carried out at 50°C for 14 h. After the reaction was completed, dilute hydrochloric acid was added to adjust the pH value to 7, the solvent was recovered by distillation under reduced pressure, extracted with ethyl acetate, washed with water, and dried to obtain 4.1 kg of long-chain dithiol compound in the form of a yellowish sticky liquid.

[0053] The total yield of the two-step reaction was 81%, and the long-chain dithiol compound had substantially no sulfur odor.

[0054] The nuclear magnetic resonance data and characteristic data of the long-chain dithiol compound are as follows:

[0055] 1 H NMR (400 MHz, CDC13) δ 7.44-7.15 (m, 4H), 7.08-6.84 (m, 4H), 3.93 (t, J = 6.3 Hz, 4H), 2.48 (dd, J = 14.7, 7.5 Hz, 3H), 1.75-1.41 (m, 9H), 1.41-1.21 (m, 10H).

[0056] Preparation Example 3

[0057] S1. 2,2'-Biphenol 186 g (1 mmol, 1 eq) was dissolved in 2.5 L of acetonitrile in a 100 L reaction kettle, then potassium carbonate 468 g (3.38 mol, 3.384 eq) and tetrabutylammonium chloride 27.6 g (0.1 mol, 0.1 eq) were added, and the reaction was stirred at 70°C for 10 min under inert gas protection, then 7-bromo-1-heptanethioacetate 541 g (having the structure shown in formula (3), X is bromine, n is 6, 2.14 mol, 2.14 eq) was slowly added, and the reaction was carried out for 10 h. The solvent was recovered by distillation under reduced pressure, washed with water, and dried to obtain an intermediate-containing product.

[0058] S2. The intermediate-containing product obtained in step S1 was dissolved in 3.2 L of ethanol in the original reaction kettle, then 50% potassium hydroxide aqueous solution 330 mL was added, and the hydrolysis reaction was carried out at 70°C for 10 h. After the reaction was completed, dilute hydrochloric acid was added to adjust the pH value to 7, the solvent was recovered by distillation under reduced pressure, extracted with ethyl acetate, washed with water, and dried to obtain 350 g of long-chain dithiol compound in the form of a yellowish sticky liquid.

[0059] The total yield of the two-step reaction was 70.1%, and the long-chain dithiol compound had substantially no sulfur odor.

[0060] The nuclear magnetic resonance data and characteristic data of the long-chain dithiol compound are as follows: 1H NMR (400 MHz, CDC13) δ 7.30 (dd, J = 14.9, 7.5 Hz, 4H), 6.99 (dd, J = 19.2, 7.8 Hz, 4H), 3.93 (t, J = 6.3 Hz, 4H), 2.54 (dq, J = 14.7, 7.4 Hz, 4H), 1.59 (ddd, J = 26.1, 16.1, 9.0 Hz, 8H), 1.40 - 1.19 (m, 14H).

[0061] Preparation Example 4

[0062] S1. 2,2'-diphenol 1.86 kg (10 mol, 1 eq) was dissolved in 50 L of a reaction kettle with 20 L of acetonitrile, then potassium carbonate 4.68 kg (33.8 mol, 3.38 eq) and tetrabutylammonium chloride 276 g (1 mol, 0.1 eq) were added, and the reaction was stirred at 85°C for 10 min under inert gas protection, then 7-bromo-1-heptyl acetate 5.41 kg (having the structure shown in formula (3), X is bromine, n is 6, 21.4 mol, 2.14 eq) was added and reacted for 12 h, then the solvent was recovered by distillation under reduced pressure, washed with water and dried to obtain an intermediate-containing product.

[0063] S2. The intermediate-containing product obtained in step 1 was dissolved in 30 L of ethanol in the original reaction kettle, then 3.33 L of 50% potassium hydroxide aqueous solution was added, and the reaction was hydrolyzed at 90°C for 12 h. After the reaction was completed, dilute hydrochloric acid was added to adjust the pH value to 7, the solvent was recovered by distillation under reduced pressure, extracted with ethyl acetate, washed with water, and dried to obtain 3.48 kg of a long-chain dithiol compound in the form of a yellowish viscous liquid.

[0064] The total yield of the two-step reaction was 78%, and the long-chain dithiol compound had basically no sulfur odor.

[0065] The nuclear magnetic resonance data and characteristic data of the long-chain dithiol compound are as follows:

[0066] 1 H NMR (400 MHz, CDC13) δ 7.30 (dd, J = 14.9, 7.5 Hz, 4H), 6.99 (dd, J = 19.2, 7.8 Hz, 4H), 3.93 (t, J = 6.3 Hz, 4H), 2.54 (dq, J = 14.7, 7.4 Hz, 4H), 1.59 (ddd, J = 26.1, 16.1, 9.0 Hz, 8H), 1.40 - 1.19 (m, 14H).

[0067] Preparation Example 5

[0068] S1. 2,2'-diphenol 186 g (1 mol, 1 eq) was dissolved in 10 L of a reaction kettle with 2.5 L of acetonitrile, then potassium carbonate 468 g (3.38 mol, 3.38 eq) and tetrabutylammonium chloride 27.6 g (0.1 mol, 0.1 eq) were added, and the reaction was stirred at 85°C for 10 min under inert gas protection, then 8-bromo-1-octylthioacetate 571 g (having the structure shown in formula (3), X is bromine, n is 7, 2.14 mol, 2.14 eq) was slowly added and reacted for 12 h, then the solvent was recovered by distillation under reduced pressure, washed with water and dried to obtain an intermediate-containing product.

[0069] S2. The intermediate-containing product obtained in step S1 was dissolved in 3.2 L of ethanol in the original reaction kettle, then 330 mL of 50% potassium hydroxide aqueous solution was added, and the reaction was hydrolyzed at 90°C for 12 h. After the reaction was completed, dilute hydrochloric acid was added to adjust the pH value to 7, the solvent was recovered by distillation under reduced pressure, extracted with ethyl acetate, washed with water, and dried to obtain 450 g of a long-chain dithiol compound in the form of a yellowish viscous liquid.

[0070] The total yield of the two-step reaction was 86%, and the long-chain dithiol compound had basically no sulfur odor.

[0071] The nuclear magnetic resonance data and characteristic data of the long-chain dithiol compound are as follows: 1 H NMR (400 MHz, CDCl3) δ 7.29 (dd, J = 13.8, 7.1 Hz, 4H), 6.98 (dd, J = 17.7, 7.9 Hz, 4H), 3.92 (t, J = 6.4 Hz, 4H), 2.54 (q, J = 7.4 Hz, 4H), 1.73-1.53 (m, 9H), 1.43-1.14 (m, 19H).

[0072] Preparation Example 6

[0073] S1. 2,2'-diphenol 186 g (1 mol, 1 eq) was dissolved in 10 L of a reaction kettle with 2.5 L of acetonitrile, then potassium carbonate 468 g (3.38 mol, 3.38 eq) and tetrabutylammonium chloride 27.6 g (0.1 mol, 0.1 eq) were added, and the reaction was stirred at 85°C for 10 min under inert gas protection, then 8-bromo-1-octylthioacetate 571 g (having the structure shown in formula (3), X is bromine, n is 7, 2.14 mol, 2.14 eq) was slowly added and reacted for 12 h, then the solvent was recovered by distillation under reduced pressure, washed with water and dried to obtain an intermediate-containing product.

[0074] S2. The intermediate-containing product obtained in step 1 was dissolved in 30 L of ethanol in the original reaction kettle, followed by the addition of 50% potassium hydroxide aqueous solution 3.33 L, and the hydrolysis reaction was carried out at 90°C for 12 h. After the reaction was completed, dilute hydrochloric acid was added to adjust the pH value to 7, the solvent was recovered by distillation under reduced pressure, extracted with ethyl acetate, washed with water, and dried to obtain 4.65 kg of long-chain dithiol compound in the form of a yellowish viscous liquid.

[0075] The total yield of the two-step reaction was 89%, and the long-chain dithiol compound had substantially no sulfur odor.

[0076] The nuclear magnetic resonance data and characteristic data of the long-chain dithiol compound are as follows:

[0077] 1 H NMR (400 MHz, CDCl3) δ 7.29 (dd, J = 13.8, 7.1 Hz, 4H), 6.98 (dd, J = 17.7, 7.9 Hz, 4H), 3.92 (t, J = 6.4 Hz, 4H), 2.54 (q, J = 7.4 Hz, 4H), 1.73-1.53 (m, 9H), 1.43-1.14 (m, 19H).

[0078] Comparative Preparation Example 1

[0079] The dithiol compound was prepared according to the method of Preparation Example 1, except that 6-bromo-1-hexyl thioacetate was replaced by the same molar amount of 3-bromo-1-propyl thioacetate, and the other conditions were the same as those of Preparation Example 1, to obtain the dithiol compound.

[0080] The total yield of the two-step reaction was 72.3%, and the dithiol compound had substantially no sulfur odor.

[0081] The nuclear magnetic resonance data and characteristic data of the dithiol compound are as follows: 1 H NMR (500 MHz, CDCl3) δ 7.43-7.17 (m, 4H), 7.10-6.88 (m, 4H), 4.05 (t, J = 5.8 Hz, 4H), 2.49 (dd, J = 15.1, 6.9 Hz, 4H), 2.02-1.85 (m, 4H), 1.34-1.16 (m, 2H).

[0082] Comparative Preparation Example 2

[0083] The dithiol compound was prepared according to the method of Preparation Example 1, except that 2,2'-diphenol was replaced by the same molar amount of p-phenol, and the other conditions were the same as those of Preparation Example 1, to obtain the dithiol compound.

[0084] The total yield of the two-step reaction was 73.5%, and the dithiol compound had substantially no sulfur odor.

[0085] The nuclear magnetic resonance data and characteristic data of the dithiol compound are as follows: 1 H NMR (500 MHz, CDC13) δ 7.17 (s, 4H), 4.11-4.08 (m, 4H), 2.59-2.53 (m, 4H), 1.82-1.76 (m, 4H), 1.52-1.28 (m, 14H).

[0086] Example 1

[0087] After 60 parts by weight of a bisphenol A type epoxy resin (jER-828EL from Mitsubishi Chemical Corporation), 5 parts by weight of a hydrogenated bisphenol A type epoxy resin (Epalloy 5000 from CVC Thermoset Specialties, USA), 20 parts by weight of the long chain dithiol compound obtained from Preparation Example 1, and 3 parts by weight of a latent curing accelerator (AJICURE PN-23 from Ajinomoto Fine-Techno Co., Inc.) were uniformly mixed, the mixture was subjected to a defoaming treatment, and the obtained epoxy resin adhesive was discharged and packaged.

[0088] Example 2

[0089] The epoxy adhesive was prepared according to the method of Example 1, except that the long chain dithiol compound obtained from Preparation Example 1 was replaced with the same parts by weight of the long chain dithiol compound obtained from Preparation Example 2, and the remaining conditions were the same as in Example 1, to obtain an epoxy resin adhesive.

[0090] Example 3

[0091] The epoxy adhesive was prepared according to the method of Example 1, except that the long chain dithiol compound obtained from Preparation Example 1 was replaced with the same parts by weight of the long chain dithiol compound obtained from Preparation Example 3, and the remaining conditions were the same as in Example 1, to obtain an epoxy resin adhesive.

[0092] Example 4

[0093] The epoxy adhesive was prepared according to the method of Example 1, except that the long chain dithiol compound obtained from Preparation Example 1 was replaced with the same parts by weight of the long chain dithiol compound obtained from Preparation Example 4, and the remaining conditions were the same as in Example 1, to obtain an epoxy resin adhesive.

[0094] Example 5

[0095] The epoxy adhesive was prepared according to the method of Example 1, except that the long chain dithiol compound obtained from Preparation Example 1 was replaced with the same parts by weight of the long chain dithiol compound obtained from Preparation Example 5, and the remaining conditions were the same as in Example 1, to obtain an epoxy resin adhesive.

[0096] Example 6

[0097] The epoxy adhesive was prepared according to the method of Example 1, except that the long-chain dithiol compound obtained from Preparation Example 1 was replaced with the same weight part of the dithiol compound obtained from Comparative Preparation Example 1, and the other conditions were the same as those of Example 1, to obtain an epoxy resin adhesive.

[0098] Comparative Example 1

[0099] The epoxy adhesive was prepared according to the method of Example 1, except that the long-chain dithiol compound obtained from Preparation Example 1 was replaced with the same weight part of the dithiol compound obtained from Comparative Preparation Example 1, and the other conditions were the same as those of Example 1, to obtain an epoxy resin adhesive.

[0100] Comparative Example 2

[0101] The epoxy adhesive was prepared according to the method of Example 1, except that the long-chain dithiol compound obtained from Preparation Example 1 was replaced with the same weight part of the dithiol compound obtained from Comparative Preparation Example 2, and the other conditions were the same as those of Example 1, to obtain an epoxy resin adhesive.

[0102] Test Example

[0103] (1) Initial toughness: The epoxy adhesive obtained in each of the above examples and comparative examples was prepared into a sample according to the method specified in GB / T6328-2021, and the impact resistance was tested, and the obtained result was the initial toughness.

[0104] (2) Long-term toughness: The epoxy adhesive obtained in each of the above examples and comparative examples was prepared into a sample according to the method specified in GB / T6328-2021, and was aged at 25°C for 6 months, and the impact resistance was measured according to the method specified in GB / T6328-2021, and the obtained result was the long-term toughness.

[0105] The specific results are shown in Table 1.

[0106] Table 1

[0107] Item Initial toughness (KJ / m 2 ) Long-term toughness (KJ / m 2 ) Example 1 46.13 45.55 Example 2 44.56 42.33 Example 3 44.87 42.45 Example 4 45.62 43.61 Example 5 45.98 43.45 Example 6 44.96 42.16 Comparative Example 1 34.87 21.54 Comparative Example 2 32.54 20.12

[0108] As can be seen from the results in Table 1, using the long-chain dithiol compound provided by the present application as the curing agent of the epoxy adhesive can effectively improve the long-term toughness of the epoxy adhesive.

[0109] Although the embodiments of the present application have been shown and described above, it should be understood that the above 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 embodiments without departing from the principles and spirit of the present application within the scope of the present application.

Claims

1. A long-chain dithiol compound, characterized in that, The long-chain dithiol compound has the structure shown in formula (1): Equation (1), In equation (1), R1, R2, R3, R4, R5, R6, R7 and R8 are H, and n is an integer from 5 to 10.

2. The long-chain dithiol compound according to claim 1, characterized in that, In equation (1), n ​​is an integer from 5 to 7.

3. The method for preparing the long-chain dithiol compound according to claim 1 or 2, characterized in that, The method includes the following steps: S1. The biphenyl ester shown in formula (2) and the long-chain halothioester compound shown in formula (3) are subjected to a substitution reaction in the presence of base I and a catalyst to obtain a product containing an intermediate; S2. The product containing the intermediate is hydrolyzed in the presence of base II to obtain a product containing a long-chain dithiol compound; Equation (2), Equation (3), In equation (2), R1, R2, R3, R4, R5, R6, R7 and R8 are H; in equation (3), n is an integer from 5 to 10, and X is a halogen.

4. The method for preparing the long-chain dithiol compound according to claim 3, characterized in that, In step S1, the substitution reaction includes dissolving biphenyl hydroquinone in organic solvent I, adding base I to provide alkaline conditions, adding a catalyst, heating to the substitution reaction temperature under inert gas protection and stirring, adding a long-chain halothioester compound to carry out the substitution reaction, removing the solvent by vacuum distillation after the reaction is complete, washing the crude product with water and drying it to obtain a product containing the intermediate.

5. The method for preparing the long-chain dithiol compound according to claim 4, characterized in that, In step S2, the product containing the intermediate is dissolved in organic solvent II, base II is added to provide alkaline conditions, and then the temperature is raised to the hydrolysis reaction temperature to carry out the hydrolysis reaction. After the reaction is completed, the solvent is removed under reduced pressure to obtain the product containing the long-chain dithiol compound.

6. The method for preparing the long-chain dithiol compound according to claim 5, characterized in that, The method further includes purifying and isolating the long-chain dithiol compound from the product containing the long-chain dithiol compound. The purification method includes washing the product containing the long-chain dithiol compound with acid until neutral, then extracting it with ethyl acetate, collecting the organic phase, drying it with anhydrous sodium sulfate, and removing the solvent by vacuum distillation to obtain the long-chain dithiol compound.

7. The method for preparing the long-chain dithiol compound according to any one of claims 3 to 6, characterized in that, The conditions for the substitution reaction include a temperature of 50℃~90℃ and a time of 8~14h; the conditions for the hydrolysis reaction include a temperature of 50℃~100℃ and a time of 8~14h.

8. The method for preparing the long-chain dithiol compound according to any one of claims 3 to 6, characterized in that, The base I is potassium carbonate and / or sodium carbonate; the base II is potassium hydroxide and / or sodium hydroxide.

9. The method for preparing the long-chain dithiol compound according to any one of claims 3 to 6, characterized in that, The catalyst is tetrabutylammonium chloride.

10. The use of the long-chain dithiol compound of claim 1 or 2 in adhesives.

11. An epoxy adhesive, characterized in that, The epoxy adhesive comprises epoxy resin and a curing agent, wherein the curing agent is a long-chain dithiol compound as described in claim 1 or 2.

Images