Curing agents, processes for their preparation and use

Abstract

The application discloses a curing agent and a preparation method and application thereof. The curing agent is obtained by reacting diisocyanate and polyalkylene ether glycol in the presence of a disulfide bond-containing compound and a ketimine compound. The curing agent contains a dynamic covalent bond, and a self-repairing epoxy resin can be prepared by mixing the curing agent with a common epoxy resin.

Description

TECHNICAL FIELD

[0001] The present application relates to a curing agent and a preparation method and use thereof. BACKGROUND

[0002] Epoxy resin is a kind of thermosetting resin, which is widely used in many fields such as transportation, aerospace, electronics, paint anticorrosion, etc. The three-dimensional cross-linked network formed after the curing of epoxy resin makes it difficult to degrade. The introduction of dynamic reversible covalent bonds in the polymer network of epoxy resin can prepare self-repairing epoxy resin which is recyclable, reusable and degradable. At present, the epoxy resin containing dynamic covalent bonds is generally directly synthesized, and the synthesis process is relatively complex. SUMMARY

[0003] Therefore, one object of the present application is to provide a curing agent containing dynamic covalent bonds, which can be used to prepare self-repairing epoxy resin by mixing with epoxy resin.

[0004] Another object of the present application is to provide a preparation method of the curing agent, which can be used to prepare the above-mentioned curing agent.

[0005] Still another object of the present application is to provide a use of the curing agent.

[0006] In one aspect, the present application provides a curing agent, which is obtained by reacting diisocyanate and polyalkylene ether glycol in the presence of a disulfide bond compound and a ketimine compound.

[0007] The present application uses polyalkylene ether glycol and diisocyanate as main raw materials, and the reaction system further includes a disulfide bond compound, a C2-C6 alkyl glycol and a ketimine compound, to obtain a curing agent containing dynamic covalent bonds. The curing agent can be mixed with epoxy resin to obtain self-repairing epoxy resin by heating.

[0008] In the present application, the diisocyanate can be selected from one or more of toluene diisocyanate, isophorone diisocyanate, diphenyl methane diisocyanate, dicyclohexyl methane diisocyanate and hexamethylene diisocyanate; preferably toluene diisocyanate, isophorone diisocyanate or diphenyl methane diisocyanate; more preferably isophorone diisocyanate. The polyalkylene ether glycol can be referred to as polyether glycol, which can be selected from one or more of polyethylene glycol, polypropylene glycol and polybutylene glycol; preferably polypropylene glycol; more preferably polypropylene glycol 2000 or polypropylene glycol 3000. The C2-C6 alkyl glycol can be selected from one or more of ethylene glycol, 1,3-propanediol and 1,4-butanediol, preferably 1,4-butanediol.

[0009] According to the curing agent of the present application, preferably, the diisocyanate is selected from one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate and hexamethylene diisocyanate.

[0010] The polyalkylene ether glycol is selected from one or more of polyethylene glycol, polypropylene glycol and polybutylene glycol.

[0011] According to the curing agent of the present application, preferably, C2-C6 alkyl diol is further included in the reaction system. The C2-C6 alkyl diol of the present application can be selected from one or more of ethylene glycol, 1,3-propanediol and 1,4-butanediol.

[0012] According to the curing agent of the present application, preferably, the disulfide bond-containing compound has a structure shown in formula (I):

[0013]

[0014] wherein R1 and R2 are independently selected from C1-C6 alkylene, and R3 is selected from C6-C18 alkyl.

[0015] In the present application, R1 and R2 can be independently selected from linear or branched C1-C6 alkylene. Preferably, R1 and R2 are independently selected from C2-C4 alkylene. More preferably, R1 and R2 are each ethylene. In the present application, R3 can be selected from C6-C18 alkyl. Preferably, R3 is selected from C10-C18 alkyl. More preferably, R3 is selected from dodecyl, tetradecyl, hexadecyl or octadecyl. This can effectively improve the mechanical properties and self-repairing properties of the epoxy resin.

[0016] According to the curing agent of the present application, preferably, the ketimine compound has a structure shown in formula (II):

[0017]

[0018] wherein R4, R5 and R6 are independently selected from C1-C6 alkylene.

[0019] In the present application, R4, R5 and R6 can be independently selected from linear C1-C6 alkylene. Preferably, R4, R5 and R6 are independently selected from C1-C2 alkylene. More preferably, R4, R5 and R6 are each methylene. Such ketimine compound can better introduce dynamic covalent bond into the curing agent.

[0020] According to the curing agent of the present application, preferably, R4, R5 and R6 are independently selected from C1-C2 alkylene.

[0021] According to the present application, the molar ratio of the polyalkylene ether glycol and the diisocyanate is preferably (1-2):(4-12), the molar ratio of the diisocyanate, the disulfide bond-containing compound and the ketimine compound is (4-12):(1-2):(4-10), and the molar ratio of the polyalkylene ether glycol and the C2-C6 alkyl glycol is (1-2):(1-2).

[0022] In the present application, the molar ratio of the polyalkylene ether glycol and the diisocyanate can be (1-2):(4-12), preferably 1:(4-6). The pre-polymer thus formed is more conducive to the introduction of dynamic covalent bonds. The molar ratio of the polyalkylene ether glycol and the C2-C6 alkyl glycol can be (1-2):(1-2), preferably 1:(1-2). The molar ratio of the diisocyanate, the disulfide bond-containing compound and the ketimine compound can be (4-12):(1-2):(4-10), preferably (4-6):1:(4-6). This helps to reduce by-products and form a curing agent containing dynamic covalent bonds.

[0023] In another aspect, the present application provides a method for preparing the above curing agent, comprising the following steps:

[0024] (1) mixing the polyalkylene ether glycol and the catalyst, and dehydrating under vacuum at 100-130°C to obtain a dehydration product;

[0025] (2) cooling the dehydration product to 80-95°C, adding the diisocyanate, and reacting for 0.5-2h, then adding the C2-C6 alkyl glycol, and reacting for 1-4h;

[0026] (3) cooling to 70-75°C, adding the disulfide bond-containing compound, and reacting for 1-4h;

[0027] (4) cooling to 50-65°C, adding the ketimine compound, and reacting for 1-4h to obtain the curing agent.

[0028] In the present application, the polyalkylene ether glycol and the catalyst are dehydrated under vacuum to obtain a dehydration product. The temperature for vacuum dehydration can be 100-130°C, preferably 110-120°C. The time for vacuum dehydration can be 0.5-3h, preferably 1-2h. This can not only improve the reaction speed, but also prevent side reactions from occurring.

[0029] The dehydrated product is cooled to 80-95℃, preferably 80-85℃. The diisocyanate is added and reacted for 0.5-2h, preferably 1-2h, to obtain a first product. The C2-C6 alkyl diol is added to the first product and reacted for 1-4h, preferably 2-3h, to obtain a second product. The second product is cooled to 70-75℃, preferably 70℃, and then the disulfide bond-containing compound is added and reacted for 1-4h, preferably 2-3h, to obtain a third product. The third product is cooled to 50-65℃, preferably 60℃, and then the ketimine compound is added and reacted for 1-4h, preferably 2-3h, to obtain the curing agent. In this way, the residual isocyanate groups can be better capped, thereby introducing dynamic covalent bonds into the curing agent.

[0030] In the present application, the catalyst can be selected from dibutyltin dilaurate and / or dioctyltin dilaurate, preferably dibutyltin dilaurate. The catalyst can be added in an amount of 0.1-3wt%, preferably 0.5-3wt%, based on the amount of polyalkylene ether glycol.

[0031] According to the preparation method of the present application, preferably, the catalyst is selected from dibutyltin dilaurate and / or dioctyltin dilaurate.

[0032] In another aspect, the present application provides a use of the above-mentioned curing agent for improving the self-repairing performance of epoxy resin.

[0033] The curing agent of the present application is mixed with epoxy resin, and after heating, a self-repairing epoxy resin containing dynamic covalent bonds can be obtained. The mass ratio of the curing agent to the epoxy resin can be calculated according to the ratio of the amino groups in the curing agent to the epoxy groups in the epoxy resin. The ratio of the amino groups in the curing agent to the epoxy groups in the epoxy resin can be 1:1-1.3, preferably 1:1-1.15.

[0034] According to some embodiments of the present application, the above-mentioned curing agent and epoxy resin are mixed, and then reacted at 100-130℃ for 1-5h to obtain an epoxy resin containing dynamic covalent bonds. The resin has good self-repairing performance.

[0035] In the present application, the epoxy resin can be a conventional epoxy resin, such as epoxy resin E-51.

[0036] The curing agent of the present application contains dynamic covalent bonds, and when it is mixed with ordinary epoxy resin and heated, a self-repairing epoxy resin containing dynamic covalent bonds can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The infrared spectrum of the curing agent in Example 1.

[0038] Figure 2 The Raman spectrum of the curing agent in Example 1.

[0039] Figure 3 Microscope image of self-repairing process of self-repairing epoxy resin in application example 1. DETAILED DESCRIPTION

[0040] The application will be further described in conjunction with the specific embodiments, but the protection scope of the application is not limited thereto.

[0041] The test method is introduced as follows:

[0042] (1) Structure determination of curing agent:

[0043] The Fourier infrared spectrometer (TENSOR II, Bruker Optics) was used for structure determination, and the scanning range was 4000-400 cm -1 .

[0044] The Raman spectrometer (HORIBA Scientific LabRAM HR Evolution) was used for structure determination, and the scanning range was 200-4000 cm -1 , and the excitation wavelength was 633 nm.

[0045] (2) Determination of tensile properties of self-repairing epoxy resin:

[0046] The tensile properties of the self-repairing epoxy resin were tested according to the standard BG / T 2567-2008.

[0047] (3) Determination of self-healing rate of self-repairing epoxy resin:

[0048] First, the original tensile strength of the self-repairing epoxy resin was tested. Then, the broken self-repairing epoxy resin was spliced together and placed in a 120℃ oven for self-repairing, and the repair time was 30 min. Finally, the tensile strength of the repaired self-repairing epoxy resin was tested, and the self-healing rate was calculated according to the following formula.

[0049] Self-healing rate (%) = (tensile strength of repaired sample / original tensile strength of sample) x 100%.

[0050] In the preparation examples, examples, and comparative examples of the application, the chemical reagents used were all analytical pure (AR) and were purchased from Shanghai Aldrich Biochemical Technology Co., Ltd.

[0051] In the application examples and comparative examples of the application, the epoxy resin E-51 was purchased from Nantong Xingchen Synthetic Material Co., Ltd.

[0052] Preparation Example 1

[0053] The cystamine dihydrochloride was added to 500 mL of a mixed solution of ethanol and tetrahydrofuran in a mass ratio of 1:1 to obtain an organic solution of the cystamine dihydrochloride. To the organic solution of the cystamine dihydrochloride, 2 mol of triethylamine and 2 mol of stearyl acrylate were added, and the reaction was stirred at 35°C for 12 h, and then the product was washed with deionized water and dried at 50°C under vacuum to obtain the disulfide bond-containing compound.

[0054] The production scale can be expanded to obtain more disulfide bond-containing compounds.

[0055] The reaction equation of Preparation Example 1 is as follows:

[0056]

[0057] Preparation Example 2

[0058] The hexanedione was added to 100 mL of a mixed solution of ethanol and water in a mass ratio of 1:1 to be dissolved to obtain a reaction solution. To the reaction solution, 1 mol of ethanolamine was added, and the reaction was stirred at 25°C for 4 h. Then, 1 mol of ethylenediamine was added, and the reaction was continuously stirred for 4 h to obtain the ketimine compound.

[0059] The production scale can be expanded to obtain more ketimine compounds.

[0060] The reaction equation of Preparation Example 2 is as follows:

[0061]

[0062] Example 1

[0063] (1) 1 mol of polypropylene glycol 2000 was mixed with dibutyltin dilaurate, and dehydrated at 120°C under vacuum for 1 h to obtain a dehydrated product. The amount of dibutyltin dilaurate was 3 wt% of the amount of polypropylene glycol 2000.

[0064] (2) The dehydrated product was cooled to 85°C, 5.6 mol of isophorone diisocyanate was added, and the reaction was performed for 1 h. Then, 1 mol of 1,4-butanediol was added, and the reaction was continuously performed for 2 h.

[0065] (3) The temperature was lowered to 70°C, 1 mol of the disulfide bond-containing compound prepared according to Preparation Example 1 was added, and the reaction was performed for 2 h.

[0066] (4) The temperature was lowered to 60°C, 5 mol of the ketimine compound prepared according to Preparation Example 2 was added, and the reaction was performed for 2 h to obtain the curing agent.

[0067] The structure of the curing agent of Example 1 was tested, and the results are as follows: Figure 1 and Figure 2shown.

[0068] From Figure 1 the infrared spectrum, the characteristic peak at 3330 cm -1 corresponds to the stretching vibration peak of -NH- in urea group and carbamate group, 2920 cm -1 and 2853 cm -1 correspond to the anti-symmetry and symmetry stretching vibration peaks of -CH3 and -CH2- respectively, 1560 cm -1 is attributed to the bending vibration peak of -NH, 1162 cm -1 is attributed to the stretching vibration peak of C-O-C, 1670 cm -1 is the stretching vibration peak of -C=N. As can be seen from the figure, there is an imine bond in the curing agent. In addition, the sample has no peak at 2270 cm -1 , indicating that there is no isocyanate group (NCO) remaining in the curing agent, and the terminal aminization of the curing agent is successful. Since the absorption peak of disulfide bond (S-S) is in the fingerprint region of infrared spectrum, it is difficult to be distinguished and identified. Therefore, Raman spectrum is selected to detect the disulfide bond in the curing agent. From Figure 2 , the characteristic peaks belonging to S-S bond (508 m -1 ) and C-S bond (640 cm -1 ) can be clearly observed, indicating that there is S-S bond in the curing agent. The above results show that the curing agent containing dynamic covalent bond is successfully synthesized.

[0069] Comparative Example 1

[0070] Except that the ketimine compound of Preparation Example 2 added in step (2) is replaced by ethylenediamine, the rest is the same as Example 1.

[0071] Comparative Example 2

[0072] Except that the disulfide-containing compound of Preparation Example 1 added in step (2) is replaced by 2-hydroxyethyl disulfide, the rest is the same as Example 1.

[0073] Application Example 1

[0074] 10 g of the curing agent prepared in Example 1 is mixed with 60 g of epoxy resin E-51, and then cured at 120℃ for 3 h to obtain a self-repairing epoxy resin containing disulfide bond and imine bond.

[0075] The self-repairing epoxy resin prepared in the above step is taken for tensile property and self-healing rate test, and the results are shown in Table 1.

[0076] Application Comparative Example 1

[0077] Except that the curing agent prepared in Example 1 was replaced by the polymer prepared in Comparative Example 1, the rest was the same as in Application Example 1.

[0078] The self-healing epoxy resin prepared in the above steps was tested for tensile properties and self-healing rate. The results are shown in Table 1.

[0079] Application Comparative Example 2

[0080] Except that the curing agent prepared in Example 1 was replaced by the polymer prepared in Comparative Example 2, the rest was the same as in Application Example 1.

[0081] The self-healing epoxy resin prepared in the above steps was tested for tensile properties and self-healing rate. The results are shown in Table 1.

[0082] Table 1

[0083]

[0084] As can be seen from Table 1, the curing agent of the present invention can be directly mixed with ordinary epoxy resin to prepare self-healing epoxy resin, and the self-healing rate of the self-healing epoxy resin is relatively high, reaching more than 90%.

[0085] The self-healing process of self-healing epoxy resin was monitored using a Leica laser confocal industrial microscope. Figure 3 First, the self-healing epoxy resin film is cut into 4mm×4mm square specimens, and the specimen is cut from the middle to ensure that the cut fits tightly, as shown in the figure. Figure 3 (a) As shown; then the sample was placed in a 120℃ oven for self-repair, and the film was taken out of the oven every 5 minutes to observe the changes in the incision, as shown in Figure 3 (b) to (d) are shown. Figure 3 As can be seen in images (b) to (d), the damaged cut on the self-healing epoxy film gradually heals and its appearance gradually shrinks. After 10 minutes of self-healing, the damaged cut on the self-healing epoxy film is essentially healed. After 15 minutes of self-healing, the microscopic appearance of the damaged cut on the self-healing epoxy film is consistent with that of the surrounding undamaged area, demonstrating excellent repair results.

[0086] The present invention is not limited to the above-mentioned embodiments. Any modification, improvement, or substitution that can be conceived by those skilled in the art without departing from the essential content of the present invention shall fall within the scope of the present invention.

Claims

1. A method for producing a curing agent, characterized by, The steps include: (1) mixing polyalkylene ether glycol and a catalyst, and vacuum dehydrating the mixture at 100-130° C. to obtain a dehydrated product; the catalyst is dibutyltin dilaurate and / or dioctyltin dilaurate, and the amount of the catalyst added is 0.1-3 wt % of the amount of the polyalkylene ether glycol added; (2) cooling the dehydrated product to 80-95° C., adding diisocyanate, reacting for 0.5-2 h, and then adding C2-C6 alkyl glycol, reacting for 1-4 h; the molar ratio of the polyalkylene ether glycol to the diisocyanate is (1-2):(4-12); the molar ratio of the polyalkylene ether glycol to the C2-C6 alkyl glycol is (1-2):(1-2); (3) Cooling to 70-75° C., adding a disulfide bond-containing compound, and reacting for 1-4 hours; the disulfide bond-containing compound has a structure shown in formula (I): wherein R1 and R2 are independently selected from C1 to C6 alkylene groups, and R3 is selected from C6 to C18 alkyl groups; (4) cooling to 50-65° C., adding a ketimine compound, and reacting for 1-4 hours to obtain the curing agent; the ketimine compound has a structure shown in formula (II): wherein R4, R5 and R6 are independently selected from C1 to C6 alkylene groups; The molar ratio of the diisocyanate, the disulfide bond-containing compound and the ketimine compound is (4-12):(1-2):(4-10).

2. The production method according to claim 1, characterized by, The diisocyanate is selected from one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate and hexamethylene diisocyanate; The polyalkylene ether glycol is selected from one or more of polyethylene glycol, polypropylene glycol and polybutylene glycol.

3. The preparation method according to claim 1, characterized in that In the structure represented by formula (II), R4, R5 and R6 are each independently selected from C1-C2 alkylene groups.

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