High-toughness long-chain thiol compound and epoxy adhesive as well as preparation method and application of high-toughness long-chain thiol compound and epoxy adhesive

Abstract

The invention belongs to the technical field of organic synthesis, and particularly relates to a high-toughness long-chain thiol compound as well as a preparation method and application thereof. The long-chain dithiol compound has a structure as shown in a formula (1). The long-chain dithiol compound provided by the invention is used as a curing agent of an epoxy adhesive, and can effectively improve the long-term toughness of the epoxy adhesive. Besides, according to the preparation method of the long-chain dithiol compound provided by the invention, the long-chain dithiol compound can be efficiently obtained only through two-step reaction, and the improvement of the total yield is facilitated, so that efficient synthesis of the sulfur-free odor long-chain dithiol compound is realized. # imgabs0 #

Description

Technical Field

[0001] The invention belongs to the technical field of organic synthesis, and specifically relates to a high-toughness long-chain thiol compound and an epoxy adhesive, and a preparation method and application thereof. Background Art

[0002] Epoxy adhesives have excellent bonding strength, electrical properties, heat resistance, and chemical resistance, and are widely used as base resins for coatings, electrical and electronic insulation materials, adhesives, etc. Among them, epoxy adhesives often use epoxy resin-thiol systems, which can meet the requirements of curing at a lower temperature and having sufficient bonding strength.

[0003] Toughened epoxy resin adhesive is a kind of epoxy adhesive with good toughness, which has good resistance to deformation and fracture when subjected to external force, so that it can still maintain good bonding stability when subjected to external force. Toughened epoxy resin adhesive is widely used in aerospace field, automobile manufacturing industry and electronic industry, etc. At present, toughened epoxy resin adhesive is usually obtained by adding toughening agent (such as rubber particles, etc.) to epoxy resin adhesive, and these toughening agents can absorb and disperse external force during curing, thereby enhancing the impact resistance of epoxy adhesive. However, although the method of introducing toughening agent into epoxy resin adhesive can improve toughness in the initial stage of article bonding, as the article bonding time is extended, the position where the toughening agent exists in the epoxy adhesive will have stress concentration phenomenon and cause fatigue cracks in the cured epoxy adhesive layer, so it is impossible to continue to provide good toughness. Summary of the invention

[0004] The first object of the present invention is to provide a long-chain dithiol compound that can effectively improve the long-term toughness of epoxy adhesives.

[0005] The second object of the present invention is to provide a method for preparing the long-chain dithiol compound.

[0006] The third object of the present invention is to provide use of the long-chain dithiol compound in an adhesive.

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

[0008] Specifically, the long-chain dithiol compound provided by the present invention 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 a C1-C5 alkyl group, and m is an integer of 5-10.

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

[0012] S1. performing a substitution reaction between the biphenol represented by formula (2) and the long-chain halogenated thioester compound represented by formula (3) in the presence of a base I and a catalyst to obtain a product containing an intermediate;

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

[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 a halogen.

[0016] The epoxy adhesive provided by the present invention comprises epoxy resin and a curing agent, wherein the curing agent is the above-mentioned long-chain dithiol compound.

[0017] The inventors of the present invention have conducted in-depth and extensive research on epoxy adhesives, and have tried to adjust the properties of epoxy resins, the types and amounts of toughening agents, etc., but have not been able to improve the long-term toughness of epoxy adhesives. The inventors of the present invention were pleasantly surprised to find that using a long-chain dithiol compound having a structure shown in formula (1) as a curing agent for epoxy adhesives can effectively improve the long-term toughness of epoxy adhesives.

[0018] In addition, the present invention uses biphenol and long-chain halogenated thioester compounds as starting materials, and both biphenol and long-chain halogenated thioester compounds have active reaction types and good structural stability. Biphenol and long-chain halogenated thioester compounds are subjected to a substitution reaction and then subjected to a hydrolysis reaction, which can ensure that the reaction activity is fully exerted and the stability of the reaction process is guaranteed. Only two steps of reaction are required to efficiently obtain a long-chain dithiol compound, which is conducive to the improvement of the total yield, thereby realizing the efficient synthesis of a sulfur-free long-chain dithiol compound. In addition, the preparation system of the long-chain dithiol compound provided by the present invention is simple, easy to operate, mild reaction conditions, and the entire reaction system is economical and efficient. DETAILED DESCRIPTION

[0019] The long-chain dithiol compound provided by the present invention has a 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 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 preparation method of the long-chain dithiol compound provided by the present invention comprises the following steps:

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

[0024] S2. The product containing the intermediate is subjected to a hydrolysis reaction in the presence of a base II to obtain a long-chain dithiol compound.

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

[0026]

[0027] In the present invention, the biphenol has a 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 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 invention, the long-chain halogenated thioester compound has a structure shown in formula (3):

[0031]

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

[0033] In the present invention, the molar ratio of the biphenol 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 substitution reaction step comprises dissolving biphenol in an organic solvent I, adding a base to provide alkaline conditions, then adding a catalyst, heating to the substitution reaction temperature under the protection of an inert gas and under stirring conditions, then adding a long-chain halogenated thioester compound to carry out a substitution reaction, and after the reaction is completed, removing the solvent by distillation under reduced pressure, washing the crude product with water and drying it to obtain a product containing an intermediate.

[0035] In a preferred embodiment, in step S2, the product containing the intermediate is dissolved in an organic solvent II, a base is added to provide alkaline conditions, and then the temperature is raised to a substitution reaction temperature to carry out a substitution reaction. After the reaction is completed, the solvent is removed under reduced pressure to obtain a product containing a long-chain dithiol compound.

[0036] The preparation method of the long-chain dithiol compound provided by the present invention preferably also includes purifying and separating the long-chain dithiol compound from the product containing the long-chain dithiol compound. The purification method includes acid washing the product containing the long-chain dithiol compound to neutrality, then extracting it with ethyl acetate, collecting the organic phase and drying it with anhydrous sodium sulfate, and removing the solvent by reduced pressure distillation 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 invention, the conditions for the substitution reaction preferably include a temperature of 50°C to 90°C, such as 50°C, 52°C, 55°C, 58°C, 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, 82°C, 85°C, 88°C, 90°C or any value therebetween; and a time of 8 to 14h, such as 8h, 10h, 12h, 14h or any value therebetween.

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

[0039] In the present invention, the base I and the 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 different reactions have better compatibility, thereby promoting the reaction and further improving the reaction yield. In addition, the molar ratio of the base I to biphenol 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 therebetween. 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 therebetween. The amount ratio of the aqueous solution of alkali II to biphenol is preferably (200-500) mL:1 mol, such as 200 mL:1 mol, 250 mL:1 mol, 300 mL:1 mol, 350 mL:1 mol, 400 mL:1 mol, 450 mL:1 mol, 500 mL:1 mol or any value therebetween. The terms "Ⅰ" and "Ⅱ" are only used to distinguish the alkali used in different steps for ease of description and have no other special meanings.

[0040] In the present invention, the organic solvent I and the organic solvent II can be various existing 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 further 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 convenience of description and have no other special meanings.

[0041] The present invention has no particular limitation on the type of catalyst, and can be any existing substance that can improve the reaction rate, such as at least one of 18-crown ether-6, benzyltriethylammonium chloride, tetrabutylammonium chloride and tetrabutylammonium bromide, and tetrabutylammonium chloride is particularly preferred. When tetrabutylammonium chloride is selected as the catalyst, it is more conducive to improving the yield of the long-chain dithiol compound.

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

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

[0044] The present invention will be further described below in conjunction with embodiments.

[0045] Preparation Example 1

[0046] S1. 186 g (1 mol, 1 eq) of 2,2'-biphenyldiphenol was dissolved in 2.5 L of acetonitrile in a 10 L reactor, followed by the addition of 468 g (3.38 mol, 3.38 eq) of potassium carbonate and 27.9 g (0.1 mol, 0.1 eq) of tetrabutylammonium. The mixture was heated to 85° C. under inert gas protection and stirred for 10 min. Then, 550 g of 6-bromo-1-acetic acid hexylthioester (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. The solvent was then recovered by distillation under reduced pressure, washed with water, and dried to obtain a product containing an intermediate.

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

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

[0049] The NMR data and characteristic data of the long-chain dithiol compound are as follows: 1 H NMR (400MHz, CDCl3) δ7.44-7.15(m,4H),7.08-6.84(m,4H),3.93(t,J=6.3H z,4H),2.48(dd,J=14.7,7.5Hz,3H),1.75-1.41(m,9H),1.41-1.21(m,10H).

[0050] Preparation Example 2

[0051] S1. 1.86 kg (10 mol, 1 eq) of 2,2'-biphenyldiphenol was dissolved in 20 L of acetonitrile in a 50 L reactor, followed by the addition of 4.68 kg (33.8 mol, 3.38 eq) of potassium carbonate and 277.9 g (1 mol, 0.1 eq) of tetrabutylammonium chloride. The mixture was heated to 50° C. under inert gas protection and stirred for 10 min. Then, 5.5 kg of 6-bromo-1-acetic acid hexylthioester (having the structure shown in formula (3), X is bromine, n is 5, 23 mol, 2.3 eq) was slowly added and reacted for 14 h. The solvent was then recovered by distillation under reduced pressure, washed with water, and dried to obtain a product containing an intermediate.

[0052] S2. The intermediate-containing product obtained in step S1 was dissolved in 30 L of ethanol in the original reactor, and then 3.33 mL of 50% potassium hydroxide aqueous solution was added, and the temperature was raised to 50°C for hydrolysis reaction for 14 h. After the reaction was completed, dilute hydrochloric acid was added to adjust the pH value to 7, and the solvent was recovered by vacuum distillation. The product was extracted with ethyl acetate, washed with water, and dried to obtain 4.1 kg of a long-chain dithiol compound in the form of a light yellow viscous 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 NMR data and characteristic data of the long-chain dithiol compound are as follows:

[0055] 1 H NMR (400MHz, CDCl3) δ7.44-7.15(m,4H),7.08-6.84(m,4H),3.93(t,J=6.3H z,4H),2.48(dd,J=14.7,7.5Hz,3H),1.75-1.41(m,9H),1.41-1.21(m,10H).

[0056] Preparation Example 3

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

[0058] S2. The intermediate-containing product obtained in step S1 was dissolved in 3.2 L of ethanol in the original reactor, and then 330 mL of 50% potassium hydroxide aqueous solution was added, and the temperature was raised to 70°C for hydrolysis reaction for 10 hours. After the reaction was completed, dilute hydrochloric acid was added to adjust the pH value to 7, and the solvent was recovered by vacuum distillation. The product was extracted with ethyl acetate, washed with water, and dried to obtain 350 g of a long-chain dithiol compound as a light yellow viscous 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 NMR data and characteristic data of the long-chain dithiol compound are as follows: 1H NMR (400MHz, CDCl3) δ7.30 (dd, J=14.9, 7.5Hz, 4H), 6.99 (dd, J=19.2, 7.8Hz, 4H), 3.93 (t, J=6.3 Hz, 4H), 2.54 (dq, J=14.7, 7.4Hz, 4H), 1.59 (ddd, J=26.1, 16.1, 9.0Hz, 8H), 1.40-1.19 (m, 14H).

[0061] Preparation Example 4

[0062] S1. 1.86 kg (10 mol, 1 eq) of 2,2'-biphenyldiphenol was dissolved in 20 L of acetonitrile in a 50 L reactor, followed by the addition of 4.68 kg (33.8 mol, 3.38 eq) of potassium carbonate and 276 g (1 mol, 0.1 eq) of tetrabutylammonium chloride. The mixture was heated to 85° C. under inert gas protection and stirred for 10 min. Then, 5.41 kg of 7-bromo-1-heptylthioacetate (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. The solvent was then recovered by distillation under reduced pressure, washed with water, and dried to obtain a product containing an intermediate.

[0063] S2. The intermediate-containing product obtained in step 1 was dissolved in 30 L of ethanol in the original reactor, and then 3.33 L of 50% potassium hydroxide aqueous solution was added, and the temperature was raised to 90°C for hydrolysis reaction for 12 hours. After the reaction was completed, dilute hydrochloric acid was added to adjust the pH value to 7, and the solvent was recovered by vacuum distillation. The product was 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 light yellow viscous liquid.

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

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

[0066] 1 H NMR (400MHz, CDCl3) δ7.30 (dd, J=14.9, 7.5Hz, 4H), 6.99 (dd, J=19.2, 7.8Hz, 4H), 3.93 (t, J=6.3 Hz, 4H), 2.54 (dq, J=14.7, 7.4Hz, 4H), 1.59 (ddd, J=26.1, 16.1, 9.0Hz, 8H), 1.40-1.19 (m, 14H).

[0067] Preparation Example 5

[0068] S1. 186 g (1 mol, 1 eq) of 2,2'-biphenyldiphenol was dissolved in 2.5 L of acetonitrile in a 10 L reactor, followed by the addition of 468 g (3.38 mol, 3.38 eq) of potassium carbonate and 27.6 g (0.1 mol, 0.1 eq) of tetrabutylammonium chloride. The mixture was heated to 85° C. under inert gas protection and stirred for 10 min. Then, 571 g of 8-bromo-1-acetic acid octylthioester (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. The solvent was then recovered by distillation under reduced pressure, washed with water, and dried to obtain a product containing an intermediate.

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

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

[0071] The NMR data and characteristic data of the long-chain dithiol compound are as follows: 1 H NMR (400MHz, CDCl3) δ7.29 (dd, J=13.8, 7.1Hz, 4H), 6.98 (dd, J=17.7, 7.9Hz, 4H), 3 .92(t,J=6.4Hz,4H),2.54(q,J=7.4Hz,4H),1.73-1.53(m,9H),1.43-1.14(m,19H).

[0072] Preparation Example 6

[0073] S1. 1.86 kg (10 mol, 1 eq) of 2,2'-biphenyldiphenol was dissolved in 20 L of acetonitrile in a 50 L reactor, followed by the addition of 4.68 kg (33.8 mol, 3.38 eq) of potassium carbonate and 276 g (1 mol, 0.1 eq) of tetrabutylammonium chloride. The mixture was heated to 85°C under inert gas protection and stirred for 10 min. Then, 5.71 kg of 8-bromo-1-acetic acid octylthioester (having the structure shown in formula (3), X is bromine, n is 7, 21.4 mol, 2.14 eq) was slowly added and reacted for 12 h. The solvent was then recovered by distillation under reduced pressure, washed with water, and dried to obtain a product containing an intermediate.

[0074] S2. The intermediate-containing product obtained in step 1 was dissolved in 30 L of ethanol in the original reactor, and then 3.33 L of 50% potassium hydroxide aqueous solution was added, and the temperature was raised to 90°C for hydrolysis reaction for 12 hours. After the reaction was completed, dilute hydrochloric acid was added to adjust the pH value to 7, and the solvent was recovered by vacuum distillation. The product was extracted with ethyl acetate, washed with water, and dried to obtain 4.65 kg of a long-chain dithiol compound in the form of a light yellow viscous liquid.

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

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

[0077] 1 H NMR (400MHz, CDCl3) δ7.29 (dd, J=13.8, 7.1Hz, 4H), 6.98 (dd, J=17.7, 7.9Hz, 4H), 3 .92(t,J=6.4Hz,4H),2.54(q,J=7.4Hz,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-acetic acid hexylthioester was replaced by the same molar amount of 3-bromo-1-acetic acid propylthioester, 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 NMR data and characteristic data of the dithiol compound are as follows: 1 H NMR (500MHz, CDCl3) δ7.43-7.17(m,4H),7.10-6.88(m,4H),4.05(t,J=5.8Hz,4H),2.49(dd,J=15.1,6.9Hz,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'-biphenyldiphenol was replaced by the same molar amount of hydroquinone, 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 NMR data and characteristic data of the dithiol compound are as follows: 1 H NMR (500MHz, CDCl3) δ7.17(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] 60 parts by weight of bisphenol A epoxy resin (jER-828EL from Mitsubishi Chemical Corporation), 5 parts by weight of hydrogenated bisphenol A epoxy resin (Epalloy 5000 from CVC Thermosetting Specialty Materials, Inc., USA), 20 parts by weight of the long-chain dithiol compound obtained in Preparation Example 1, and 3 parts by weight of a latent curing accelerator (AJICURE PN-23 from Ajinomoto Fine Chemicals Co., Ltd.) are mixed evenly and degassed, and the epoxy resin adhesive is obtained after the material is discharged and packaged.

[0088] Example 2

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

[0090] Example 3

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

[0092] Example 4

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

[0094] Example 5

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

[0096] Example 6

[0097] An epoxy adhesive was prepared according to the method of Example 1, except that the long-chain dithiol compound obtained in Preparation Example 1 was replaced by the long-chain dithiol compound obtained in Preparation Example 6 in equal parts by weight, and the remaining conditions were the same as in Example 1 to obtain an epoxy resin adhesive.

[0098] Comparative Example 1

[0099] An epoxy adhesive was prepared according to the method of Example 1, except that the long-chain dithiol compound obtained in Preparation Example 1 was replaced by the dithiol compound obtained in Comparative Preparation Example 1 in equal parts by weight, and the remaining conditions were the same as in Example 1 to obtain an epoxy resin adhesive.

[0100] Comparative Example 2

[0101] An epoxy adhesive was prepared according to the method of Example 1, except that the long-chain dithiol compound obtained in Preparation Example 1 was replaced by the dithiol compound obtained in Comparative Preparation Example 2 in equal parts by weight, and the remaining conditions were the same as in Example 1 to obtain an epoxy resin adhesive.

[0102] Test Case

[0103] (1) Initial toughness: The epoxy adhesives obtained in the above embodiments and comparative examples were prepared into samples according to the method specified in GB / T6328-2021 and the impact resistance was tested. The result obtained was the initial toughness.

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

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

[0106] Table 1

[0107] project <![CDATA[Initial toughness (KJ / m 2 )]]> <![CDATA[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] It can be seen from the results in Table 1 that the use of the long-chain dithiol compound provided by the present invention as a curing agent for epoxy adhesive can effectively improve the long-term toughness of the epoxy adhesive.

[0109] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A long-chain dithiol compound, characterized in that: The long-chain dithiol compound has a structure shown in formula (1): In formula (1), R1, R2, R3, R4, R5, R6, R7 and R8 are independently H or a C1-C5 alkyl group, and n is an integer of 5-10.

2. The long-chain dithiol compound according to claim 1, characterized in that In formula (1), R1, R2, R3, R4, R5, R6, R7 and R8 are all H, and n is an integer of 5 to 7.

3. The method for preparing the long-chain dithiol compound according to claim 1 or 2, characterized in that: The method comprises the following steps: S1. The biphenol represented by formula (2) and the long-chain halogenated thioester compound represented by 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. hydrolyzing the product containing the intermediate in the presence of base II to obtain a product containing a long-chain dithiol compound; 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 a halogen.

4. The method for preparing a long-chain dithiol compound according to claim 3, characterized in that: In step S1, the substitution reaction step includes dissolving biphenol in an organic solvent I, adding a base I to provide alkaline conditions, then adding a catalyst, heating to the substitution reaction temperature under the protection of an inert gas and under stirring conditions, and then adding a long-chain halogenated thioester compound to carry out a substitution reaction. After the reaction is completed, the solvent is removed by distillation under reduced pressure, and the crude product is washed with water and dried to obtain a product containing an intermediate.

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

6. The method for preparing a long-chain dithiol compound according to claim 5, characterized in that: The method also includes purifying and separating the long-chain dithiol compound from the product containing the long-chain dithiol compound. The purification method includes acid washing the product containing the long-chain dithiol compound to neutrality, then extracting it with ethyl acetate, collecting the organic phase and drying it with anhydrous sodium sulfate, and removing the solvent by reduced pressure distillation to obtain the long-chain dithiol compound.

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

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

10. Use of the long-chain dithiol compound according to claim 1 or 2 in an adhesive.

11. An epoxy adhesive, characterized in that: The epoxy adhesive comprises an epoxy resin and a curing agent, and the curing agent is the long-chain dithiol compound according to claim 1 or 2.

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