Preparation method of modified polyurethane toughened epoxy resin

Abstract

The present invention relates to the field of polymer technology, and discloses a preparation method of a modified polyurethane toughened epoxy resin. Using 4-(Boc-amino)phenylboronic acid, diethanolamine, 1,3-bis(3-glycidyletheroxypropyl)tetramethyldisiloxane and other raw materials, a borate siloxane chain extender is obtained through a series of chemical reactions and participates in the chain extension of polyurethane. The epoxy resin is modified with the polyurethane prepolymer to obtain a modified polyurethane toughened epoxy resin. The "soft segment" and Si-O structure in the modified polyurethane can also improve the flexibility of the cured network, effectively change the fracture mechanism of the resin, absorb a large amount of energy when the resin fractures, and help improve the toughness of the epoxy resin. On the basis of ensuring the strength of the epoxy resin, the present invention improves the toughness and flame retardancy of the epoxy resin, and can be applied to fields such as composites, coatings and adhesives with high toughness and flame retardancy requirements, and has wide applicability.

Description

Technical Field

[0001] The present invention relates to the field of polymer technology, and specifically to a preparation method of a modified polyurethane toughened epoxy resin. Background Art

[0002] Epoxy resin (EP), as a thermosetting polymer synthetic material, is widely used in the fields of adhesives, coatings, and composite materials due to its good adhesion, corrosion resistance, and high strength characteristics. However, epoxy resin has poor toughness, is brittle, prone to cracking, and has low impact strength, which limits its application in some occasions that require high strength and toughness; in addition, the oxygen index of pure epoxy resin is only 19.8%, belonging to an extremely flammable material. It is often the most easily combustible part of composite materials in fire accidents, and continues to burn and release a large amount of smoke after catching fire, which greatly limits its application in high-temperature environments such as aerospace, integrated circuit packaging, and nuclear reactor systems. Therefore, developing an epoxy resin system with both toughness and flame retardancy has very important industrial value.

[0003] Due to the characteristics of large bonding strength, good flexibility, and high mechanical strength of polyurethane, combining it with epoxy resin can form an interpenetrating polymer network structure, organically combining the high elasticity of polyurethane with the good adhesion of epoxy resin, thus achieving a good toughening effect; however, in traditional polyurethane-modified epoxy resin materials, the compatibility between polyurethane and epoxy resin is not completely ideal, and the addition amount of polyurethane cannot be too high, otherwise the toughening effect will not be ideal; at the same time, using polyurethane to toughen epoxy resin will cause a serious reduction in the tensile strength and shear strength of epoxy resin. In addition, polyurethane has disadvantages such as flammability and poor heat resistance, which is not conducive to improving the flame retardancy of epoxy resin; Patent No. CN114773610A discloses a preparation method of a polyurethane toughened epoxy resin, which uses ferrocene-modified polyisocyanate and polypropylene glycol to synthesize a piperazine-modified polyurethane prepolymer, and then grafts the piperazine-modified polyurethane prepolymer with epoxy resin to prepare a toughened epoxy resin. However, the number of crazes significantly increases when the modified epoxy resin fractures, and it is prone to the phenomenon of ductile fracture, and the problem of poor flame retardancy of epoxy resin is not solved.

[0004] The siloxane chain has excellent flexibility and can be used as a toughening material for resins and their composites. However, the compatibility between silicone and epoxy resin is poor. If simply mixed, due to the large interfacial tension between the two phases, the mixture shows a multiphase separation structure and cannot achieve the modification effect; the borate ester bond is a special dynamic covalent bond with the characteristic of undergoing a bond exchange reaction at room temperature; based on this, the present application aims to utilize the designability of polyurethane to introduce silicone and borate ester into the polyurethane structure and modify epoxy resin, improving the toughness and flame retardancy of epoxy resin while ensuring the mechanical properties of epoxy resin. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the object of the present invention is to provide a preparation method of modified polyurethane toughened epoxy resin, which can improve the toughness and flame retardancy of epoxy resin while ensuring the strength of epoxy resin.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of modified polyurethane toughened epoxy resin comprises the following steps:

[0008] Step (1): Under a nitrogen atmosphere, add 100 parts of polyether polyol by weight to a reaction flask, place it in an environment with a temperature of 100 - 120 °C and a vacuum degree of 0.05 - 0.1 MPa for vacuum dehydration for 1 - 2 h, then stir and mix it with 20 - 30 parts of toluene diisocyanate, heat to 70 - 80 °C, add 0.1 - 0.3 part of tin catalyst and 2 - 10 parts of borate siloxane chain extender. After adding, keep warm for 2 - 6 h, then cool down and discharge, and let it stand to defoam to obtain a modified polyurethane prepolymer.

[0009] Step (2): Under a nitrogen atmosphere, add 100 parts of bisphenol A epoxy resin, 10 - 30 parts of modified polyurethane prepolymer, 6 - 10 parts of curing agent and 1 - 3 parts of active diluent by weight, heat to 60 - 80 °C for mechanical stirring. After mixing evenly, then cure at 100 - 120 °C for 2 - 4 h, 125 - 140 °C for 3 - 5 h, and 160 - 180 °C for 4 - 6 h, and cool to room temperature to obtain modified polyurethane toughened epoxy resin.

[0010] Further, in step (1), the polyether polyol is polytetrahydrofuran ether diol with a molecular weight of 2000.

[0011] Further, in step (2), the tin catalyst is stannous octoate, dibutyltin dilaurate or stannous oleate.

[0012] Further, in step (2), the curing agent is 4,4′ - diaminodiphenylmethane, and the active diluent is ethylene glycol diglycidyl ether.

[0013] Further, the preparation method of the borate siloxane chain extender in step (1) comprises the following steps:

[0014] Step S1: Under a nitrogen atmosphere, add 4-(Boc - amino)phenylboronic acid and N,N - dimethylformamide to a reaction flask, stir evenly, then add diethanolamine, stir and react. After the reaction is completed, recrystallize with petroleum ether, filter and wash to obtain a nitrogen - containing coordinated borate monomer. The preparation reaction formula is as follows:

[0015]

[0016] Step S2: Under a nitrogen atmosphere, add 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and N-methylpyrrolidone to the reaction flask. After stirring evenly, add the nitrogen-containing coordinated borate monomer and potassium carbonate, and stir for reaction. After the reaction is completed, extract with brine and dichloromethane, concentrate the organic phase, add trifluoroacetic acid and dichloromethane, stir at room temperature for 3 - 8 h, filter and concentrate, and obtain the borate siloxane chain extender after drying. The preparation reaction formula is as follows:

[0017]

[0018] Furthermore, the proportional relationship between 4-(Boc-amino)phenylboronic acid and diethanolamine in step S1 is 1 mol : (1.05 - 1.2) mol.

[0019] Furthermore, the reaction temperature in step S1 is 45 - 60 °C, and the reaction time is 2 - 5 h.

[0020] Furthermore, the proportional relationship between 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane, the nitrogen-containing coordinated borate monomer, potassium carbonate, and trifluoroacetic acid in step S2 is 1 mol : (2.1 - 2.3) mol : (2.5 - 2.8) mol : (8 - 10) mol.

[0021] Furthermore, the reaction temperature in step S2 is 65 - 80 °C, and the reaction time is 12 - 24 h.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) An interpenetrating polymer network and hydrogen bonds are formed between the modified polyurethane and the epoxy resin, which is beneficial to resisting deformation and promoting energy absorption under impact force. In addition, the siloxane chain has excellent flexibility, and the "soft segment" in the polyurethane and the Si-O structure can also improve the flexibility of the cured network, effectively changing the fracture mechanism of the resin, absorbing a large amount of energy when the resin fractures, and contributing to improving the toughness of the epoxy resin; at the same time, the amino and hydroxyl groups of the borate siloxane chain extender can not only react with isocyanates but also act as curing agents to promote the combination with the epoxy resin, improve the good compatibility with the epoxy resin, realize the crosslinking modification of the polyurethane and the epoxy resin, and thus play the effect of toughening the epoxy resin.

[0024] (2) The borate bond has good self-healing ability. When the epoxy resin is subjected to external force, the borate bond can quickly respond and rearrange, thereby absorbing and dispersing energy and improving the toughness of the material. When the borate structure is introduced into the epoxy resin, due to the difference in chain segment rigidity and flexibility, a microphase separation structure will be generated in the polymer network, resulting in multiple microphase separation regions inside the material. These regions can serve as stress concentration points or crack initiation points. Under the action of external force, these microphase structures can gradually generate holes and bridge with each other, which helps to absorb a large amount of energy and prevent the rapid propagation of cracks, thereby improving the toughness of the material.

[0025] (3) The hydroxyl and amino groups in the structure of the borate siloxane chain extender can participate in the curing reaction of the epoxy resin to form a three-dimensional branched network structure with intertwined molecular chains, which can effectively improve the density of the cured epoxy resin. In addition, the bond energy of the B-O bond is relatively high. Introducing the B-O bond into the molecular structure of the epoxy resin can greatly improve the heat resistance of the epoxy resin. The rich boron, nitrogen, and silicon elements in the structure of this chain extender can form a dense and expanded carbon layer during the combustion of the cured epoxy resin, which can not only effectively isolate oxygen and heat, but also achieve the effect of locking the generated smoke inside the material during combustion, thereby greatly enhancing the flame retardant performance of the epoxy resin. Detailed implementation manners

[0026] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application clearer and more understandable, the following further details this application in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit this application. Unless otherwise specified, the raw materials and reagents used in this application are commercially available products or can be prepared by known methods.

[0027] 4-(Boc-amino)phenylboronic acid, with the CAS number 380430-49-9.

[0028] Diethanolamine, with the CAS number 111-42-2.

[0029] 1,3-Bis(3-glycidyloxypropyl)tetramethyldisiloxane, with the CAS number 126-80-7. Example 1

[0030] (1) Under a nitrogen atmosphere, 85 mmol of 4-(Boc-amino)phenylboronic acid and 510 mL of N,N-dimethylformamide were added to a reaction flask. After stirring evenly, 95.2 mmol of diethanolamine was added, and the reaction was carried out at 55 °C for 3 h. Recrystallization was carried out with petroleum ether, followed by filtration and washing to obtain a nitrogen-containing coordination borate monomer.

[0031] (2) Under a nitrogen atmosphere, 70 mmol of 1,3-bis(3-glycidylethoxypropyl)tetramethyldisiloxane and 625 mL of N-methylpyrrolidone were added to a reaction flask. After stirring evenly, 155 mmol of a nitrogen-containing coordinated borate monomer and 185.5 mmol of potassium carbonate were added, and the reaction was carried out at 75 °C for 16 h. After extraction with brine and dichloromethane, the organic phase was concentrated. 630 mmol of trifluoroacetic acid and 560 mL of dichloromethane were added, and the mixture was stirred at room temperature for 6 h. After filtration and concentration, a borate siloxane chain extender was obtained after drying.

[0032] (3) Under a nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to a reaction flask. After vacuum dehydration for 2 h in an environment with a temperature of 110 °C and a vacuum degree of 0.08 MPa, it was stirred and mixed with 25 g of toluene diisocyanate, heated to 75 °C, 0.2 g of stannous octoate and 2 g of borate siloxane chain extender were added. After the addition, the temperature was kept for 5 h, then the temperature was lowered and the material was discharged, and it was left standing to defoam to obtain a modified polyurethane prepolymer.

[0033] (4) Under a nitrogen atmosphere, 100 g of bisphenol A epoxy resin, 10 g of modified polyurethane prepolymer, 8 g of 4,4′-diaminodiphenylmethane and 2 g of ethylene glycol diglycidyl ether were heated to 70 °C for mechanical stirring. After mixing evenly, it was then cured at 110 °C for 3 h, 130 °C for 3 h, and 170 °C for 5 h, and then cooled to room temperature to obtain a modified polyurethane toughened epoxy resin. Example 2

[0034] (1) Under a nitrogen atmosphere, 150 mmol of 4-(Boc-amino)phenylboronic acid and 750 mL of N,N-dimethylformamide were added to a reaction flask. After stirring evenly, 157.5 mmol of diethanolamine was added, and the reaction was carried out at 60 °C for 2 h. After recrystallization with petroleum ether, filtration and washing, a nitrogen-containing coordinated borate monomer was obtained.

[0035] (2) Under a nitrogen atmosphere, 135 mmol of 1,3-bis(3-glycidylethoxypropyl)tetramethyldisiloxane and 810 mL of N-methylpyrrolidone were added to a reaction flask. After stirring evenly, 283.5 mmol of nitrogen-containing coordinated borate monomer and 337.5 mmol of potassium carbonate were added, and the reaction was carried out at 80 °C for 12 h. After extraction with brine and dichloromethane, the organic phase was concentrated. 1080 mmol of trifluoroacetic acid and 675 mL of dichloromethane were added, and the mixture was stirred at room temperature for 3 h. After filtration and concentration, a borate siloxane chain extender was obtained after drying.

[0036] (3) Under a nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to a reaction flask. After being placed in an environment with a temperature of 120 °C and a vacuum degree of 0.1 MPa for vacuum dehydration for 1 h, it was stirred and mixed with 20 g of toluene diisocyanate. After heating to 80 °C, 0.1 g of dilauryl and 4 g of borate siloxane chain extender were added. After adding, it was kept warm for 2 h, then cooled and discharged, and left to stand for defoaming to obtain a modified polyurethane prepolymer.

[0037] (4) Under a nitrogen atmosphere, 100 g of bisphenol A epoxy resin, 15 g of modified polyurethane prepolymer, 6 g of 4,4′-diaminodiphenylmethane, and 3 g of ethylene glycol diglycidyl ether were heated to 80 °C for mechanical stirring. After mixing evenly, it was then cured at 120 °C for 2 h, 140 °C for 3 h, and 180 °C for 4 h, and cooled to room temperature to obtain a modified polyurethane toughened epoxy resin. Example 3

[0038] (1) Under a nitrogen atmosphere, 45 mmol of 4-(Boc-amino)phenylboronic acid and 360 mL of N,N-dimethylformamide were added to a reaction flask. After stirring evenly, 54 mmol of diethanolamine was added, and the reaction was carried out at 45 °C for 5 h. It was recrystallized with petroleum ether, filtered and washed to obtain a nitrogen-containing coordinated borate monomer.

[0039] (2) Under a nitrogen atmosphere, 40 mmol of 1,3-bis(3-glycidylethoxypropyl)tetramethyldisiloxane and 400 mL of N-methylpyrrolidone were added to a reaction flask. After stirring evenly, 92 mmol of nitrogen-containing coordinated borate monomer and 112 mmol of potassium carbonate were added, and the reaction was carried out at 65 °C for 24 h. It was extracted with brine and dichloromethane, the organic phase was concentrated, 400 mmol of trifluoroacetic acid and 400 mL of dichloromethane were added, and it was stirred at room temperature for 8 h, filtered and concentrated, and dried to obtain a borate siloxane chain extender.

[0040] (3) Under a nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to a reaction flask. After being placed in an environment with a temperature of 100 °C and a vacuum degree of 0.05 MPa for vacuum dehydration for 2 h, it was stirred and mixed with 30 g of toluene diisocyanate. After heating to 70 °C, 0.3 g of stannous oleate and 6 g of borate siloxane chain extender were added. After adding, it was kept warm for 6 h, then cooled and discharged, and left to stand for defoaming to obtain a modified polyurethane prepolymer.

[0041] (4) Under a nitrogen atmosphere, 100 g of bisphenol A epoxy resin, 20 g of modified polyurethane prepolymer, 10 g of 4,4′-diaminodiphenylmethane, and 1 g of ethylene glycol diglycidyl ether were heated to 60 °C for mechanical stirring. After mixing evenly, it was then cured at 100 °C for 4 h, 125 °C for 5 h, and 160 °C for 6 h, and cooled to room temperature to obtain a modified polyurethane toughened epoxy resin. Example 4

[0042] (1) Under a nitrogen atmosphere, 30 mmol of 4-(Boc-amino)phenylboronic acid and 205 mL of N,N-dimethylformamide were added to a reaction flask. After stirring evenly, 34.5 mmol of diethanolamine was added, and the reaction was carried out at 55 °C for 4 h. Recrystallization was carried out with petroleum ether, followed by filtration and washing to obtain a nitrogen-containing coordinated borate monomer.

[0043] (2) Under a nitrogen atmosphere, 25 mmol of 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane and 215 mL of N-methylpyrrolidone were added to a reaction flask. After stirring evenly, 54 mmol of the nitrogen-containing coordinated borate monomer and 66 mmol of potassium carbonate were added, and the reaction was carried out at 75 °C for 15 h. Extraction was carried out with brine and dichloromethane, the organic phase was concentrated, 210 mmol of trifluoroacetic acid and 235 mL of dichloromethane were added, and the mixture was stirred at room temperature for 6 h. Filtration and concentration were carried out, and after drying, a borate siloxane chain extender was obtained.

[0044] (3) Under a nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to a reaction flask. After being placed in an environment with a temperature of 115 °C and a vacuum degree of 0.08 MPa for vacuum dehydration for 2 h, it was stirred and mixed with 26 g of toluene diisocyanate, heated to 75 °C, 0.25 g of stannous octoate and 8 g of the borate siloxane chain extender were added. After adding, it was kept warm for 5 h, then cooled and discharged, and left standing to defoam to obtain a modified polyurethane prepolymer.

[0045] (4) Under a nitrogen atmosphere, 100 g of bisphenol A epoxy resin, 25 g of the modified polyurethane prepolymer, 9 g of 4,4′-diaminodiphenylmethane and 2.5 g of ethylene glycol diglycidyl ether were heated to 75 °C for mechanical stirring. After mixing evenly, it was then cured at 110 °C for 3 h, 130 °C for 5 h, and 175 °C for 4 h, and cooled to room temperature to obtain a modified polyurethane toughened epoxy resin. Example 5

[0046] (1) Under a nitrogen atmosphere, 52 mmol of 4-(Boc-amino)phenylboronic acid and 390 mL of N,N-dimethylformamide were added to a reaction flask. After stirring evenly, 60 mmol of diethanolamine was added, and the reaction was carried out at 60 °C for 5 h. Recrystallization was carried out with petroleum ether, followed by filtration and washing to obtain a nitrogen-containing coordinated borate monomer.

[0047] (2) Under a nitrogen atmosphere, 45 mmol of 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane and 378 mL of N-methylpyrrolidone were added to a reaction flask. After stirring evenly, 97.2 mmol of a nitrogen-containing coordinated borate monomer and 124.2 mmol of potassium carbonate were added, and the reaction was carried out at 70 °C for 24 h. It was extracted with brine and dichloromethane, the organic phase was concentrated, 396 mmol of trifluoroacetic acid and 306 mL of dichloromethane were added, and it was stirred at room temperature for 6 h, filtered and concentrated, and after drying, a borate siloxane chain extender was obtained.

[0048] (3) Under a nitrogen atmosphere, 100 g of polytetrahydrofuran ether glycol with a molecular weight of 2000 was added to a reaction flask. After being placed in an environment with a temperature of 120 °C and a vacuum degree of 0.05 MPa for vacuum dehydration for 2 h, it was stirred and mixed with 30 g of tolylene diisocyanate, heated to 70 °C, 0.3 g of dibutyltin dilaurate and 10 g of the borate siloxane chain extender were added. After adding, it was kept warm for 5 h, then cooled and discharged, and left standing to defoam to obtain a modified polyurethane prepolymer.

[0049] (4) Under a nitrogen atmosphere, 100 g of bisphenol A epoxy resin, 30 g of the modified polyurethane prepolymer, 8.5 g of 4,4′-diaminodiphenylmethane and 3 g of ethylene glycol diglycidyl ether were heated to 75 °C for mechanical stirring. After mixing evenly, it was then cured at 105 °C for 2 h, 135 °C for 5 h, and 170 °C for 5 h, and cooled to room temperature to obtain a modified polyurethane toughened epoxy resin.

[0050] Comparative Example 1

[0051] (1) Under a nitrogen atmosphere, 70 mmol of ethylene glycol diglycidyl ether (structural formula is , CAS number is 2224-15-9) and 625 mL of N-methylpyrrolidone were added to a reaction flask. After stirring evenly, 155 mmol of a nitrogen-containing coordinated borate monomer (prepared in Example 1) and 185.5 mmol of potassium carbonate were added, and the reaction was carried out at 75 °C for 16 h. It was extracted with brine and dichloromethane, the organic phase was concentrated, 630 mmol of trifluoroacetic acid and 560 mL of dichloromethane were added, and it was stirred at room temperature for 6 h, filtered and concentrated, and after drying, a borate chain extender was obtained.

[0052] (2) Under a nitrogen atmosphere, 100 g of polytetrahydrofuran ether glycol with a molecular weight of 2000 was added to a reaction flask. After being placed in an environment with a temperature of 110 °C and a vacuum degree of 0.08 MPa for vacuum dehydration for 2 h, it was stirred and mixed with 25 g of tolylene diisocyanate, heated to 75 °C, 0.2 g of stannous octoate and 2 g of the borate chain extender were added. After adding, it was kept warm for 5 h, then cooled and discharged, and left standing to defoam to obtain a modified polyurethane prepolymer.

[0053] (3) Under a nitrogen atmosphere, 100 g of bisphenol A epoxy resin, 10 g of modified polyurethane prepolymer, 8 g of 4,4′-diaminodiphenylmethane, and 2 g of ethylene glycol diglycidyl ether were heated to 70 °C and mechanically stirred. After mixing evenly, it was then cured at 110 °C for 3 h, 130 °C for 3 h, and 170 °C for 5 h, and then cooled to room temperature to obtain polyurethane-modified epoxy resin.

[0054] Comparative Example 2

[0055] (1) Under a nitrogen atmosphere, 70 mmol of 1,3-bis(3-glycidoxypropyl)tetramethyldisiloxane and 625 mL of N-methylpyrrolidone were added to a reaction flask. After stirring evenly, 155 mmol of tert-butyl 4-(piperidin-4-yl)phenylcarbamate (structural formula is , CAS No. 887589-58-4) and 185.5 mmol of potassium carbonate were added, and the reaction was carried out at 75 °C for 16 h. It was extracted with brine and dichloromethane, the organic phase was concentrated, 630 mmol of trifluoroacetic acid and 560 mL of dichloromethane were added, and it was stirred at room temperature for 6 h, filtered and concentrated, and dried to obtain a siloxane chain extender.

[0056] (2) Under a nitrogen atmosphere, 100 g of polytetrahydrofuran ether glycol with a molecular weight of 2000 was added to a reaction flask. After vacuum dehydration at 110 °C and a vacuum degree of 0.08 MPa for 2 h, it was stirred and mixed with 25 g of toluene diisocyanate, heated to 75 °C, 0.2 g of stannous octoate and 2 g of siloxane chain extender were added. After adding, it was kept warm for 5 h, then cooled and discharged, and left to stand for defoaming to obtain a modified polyurethane prepolymer.

[0057] (3) Under a nitrogen atmosphere, 100 g of bisphenol A epoxy resin, 10 g of modified polyurethane prepolymer, 8 g of 4,4′-diaminodiphenylmethane, and 2 g of ethylene glycol diglycidyl ether were heated to 70 °C and mechanically stirred. After mixing evenly, it was then cured at 110 °C for 3 h, 130 °C for 3 h, and 170 °C for 5 h, and then cooled to room temperature to obtain polyurethane-modified epoxy resin.

[0058] Comparative Example 3

[0059] (1) Under a nitrogen atmosphere, 100 g of polytetrahydrofuran ether glycol with a molecular weight of 2000 was added to a reaction flask. After vacuum dehydration at 110 °C and a vacuum degree of 0.08 MPa for 2 h, it was stirred and mixed with 25 g of toluene diisocyanate, heated to 75 °C, 0.2 g of stannous octoate and 2 g of 1,4-butanediol chain extender were added. After adding, it was kept warm for 5 h, then cooled and discharged, and left to stand for defoaming to obtain a polyurethane prepolymer.

[0060] (2)Under a nitrogen atmosphere, 100 g of bisphenol A epoxy resin, 10 g of polyurethane prepolymer, 8 g of 4,4′-diaminodiphenylmethane, and 2 g of ethylene glycol diglycidyl ether were heated to 70 °C and mechanically stirred. After mixing evenly, it was then cured at 110 °C for 3 h, 130 °C for 3 h, and 170 °C for 5 h, and then cooled to room temperature to obtain polyurethane-modified epoxy resin.

[0061] Tensile property test: According to the standard of GB / T 2567-2008, the cured epoxy resin specimen was made into a dumbbell shape and tested using a universal testing machine. The tensile rate was 20 mm / min, and the test environment temperature was 25 °C.

[0062] Impact property test: According to the standard of GB / T 2567-2008, the cured epoxy resin specimen was made into a non-notch impact spline and tested on a simply supported beam impact tester.

[0063] Shear strength test: According to the standard of GB / T 7124-2008, a universal electronic testing machine was used to conduct a steel / steel tensile shear strength test, and the tensile rate was 10 mm / min.

[0064]

[0065] It can be seen from the test results in the above table that the tensile strength, elongation at break, impact strength, and shear strength of the epoxy resin prepared in the examples at room temperature are significantly higher than those of the comparative examples, indicating that the present application will not have a negative impact on the strength while toughening and modifying the epoxy resin, and has good mechanical strength and fracture toughness. This is because on the one hand, an interpenetrating polymer network and hydrogen bonds are formed between the modified polyurethane and the epoxy resin, which is beneficial to resisting deformation and promoting energy absorption under impact force. In addition, the siloxane chain has excellent flexibility, and the "soft segment" in the polyurethane and the Si-O structure can also improve the flexibility of the cured network, effectively changing the fracture mechanism of the resin and absorbing a large amount of energy when the resin fractures, which helps to improve the toughness of the epoxy resin. At the same time, the amino and hydroxyl groups of the borate siloxane chain extender can not only react with isocyanates but also act as curing agents to promote the combination with the epoxy resin, improve the good compatibility with the epoxy resin, realize the crosslinking modification of the polyurethane and the epoxy resin, and further enhance the toughness of the epoxy resin. In Comparative Examples 1 and 3, there is no siloxane, and the content of "hard segments" in their cured structures is relatively high, resulting in poor toughness. The present invention can be applied to reinforced composite materials, prepreg matrix materials, and adhesives with relatively high toughness and flame retardancy requirements.

[0066] Self-healing property test: The prepared cured epoxy resin specimen was cut in half from the middle, and then the fracture surfaces were closely fitted. After pressing with fingers for 5 min, it was placed in an oven and repaired at 60 °C for 48 h. The repaired sample was subjected to an impact strength test, and the self-healing efficiency was calculated.

[0067]

[0068] The borate ester bond is a special dynamic covalent bond that can undergo a bond exchange reaction at room temperature. That is, under water or other specific conditions, the borate ester bond can undergo a hydrolysis reaction and break. When the water is removed, the borate ester bond can be regenerated again. This reversible hydrolysis reaction is the basis for the self-healing ability of borate esters. From the test results in the above table, it can be seen that the impact strength of the repaired epoxy resin recovers relatively quickly, and the self-healing efficiency reaches up to 92.5%. This is because when the epoxy resin is subjected to an external force, the borate ester bond can quickly respond and rearrange, thereby absorbing and dispersing energy and improving the toughness of the material. When a borate ester structure is introduced into the epoxy resin, due to the difference in the rigidity and flexibility of the chain segments, a microphase separation structure will be generated in the polymer network, resulting in multiple microphase separation regions inside the material. These regions can serve as stress concentration points or crack initiation points. Under the action of an external force, these microphase structures can gradually generate cavities and bridge with each other, which helps to absorb a large amount of energy and prevent the rapid propagation of cracks, thereby improving the toughness of the material. In Comparative Examples 2 and 3, there is no borate ester structure and they do not have self-healing ability.

[0069] Limiting oxygen index test: According to the standard GB / T 2406.2-2009, the limiting oxygen index test was carried out.

[0070]

[0071] The hydroxyl groups and amino groups in the structure of the borate ester siloxane chain extender can participate in the curing reaction of the epoxy resin to form a three-dimensional branched network structure with intertwined molecular chains, which can effectively improve the density of the epoxy resin cured product. In addition, the bond energy of the B-O bond is relatively high. Introducing the B-O bond into the molecular structure of the epoxy resin can greatly improve the heat resistance of the epoxy resin. The rich boron, nitrogen, and silicon elements in the chain extender structure can form a dense and expanded carbon layer when the epoxy resin cured product burns, which can not only effectively isolate oxygen and heat, but also achieve the effect of locking the generated smoke inside the material during combustion, thereby greatly enhancing the flame retardant performance of the epoxy resin.

[0072] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included within the protection scope of the present application.

Claims

1. A method for preparing a modified polyurethane toughened epoxy resin, characterized in that: The preparation method comprises the following steps: Step (1), under a nitrogen atmosphere, add 100 parts by weight of a polyether polyol into a reaction flask, place it in an environment with a temperature of 100-120° C. and a vacuum degree of 0.05-0.1 MPa for vacuum dehydration for 1-2 hours, stir and mix with 20-30 parts of toluene diisocyanate, heat to 70-80° C., add 0.1-0.3 parts of a tin catalyst and 2-10 parts of a borate siloxane chain extender, after the addition is completed, keep the temperature for 2-6 hours, cool and discharge the material, let it stand for defoaming, and obtain a modified polyurethane prepolymer; Step (2), under a nitrogen atmosphere, heating 100 parts by weight of bisphenol A epoxy resin, 10-30 parts of modified polyurethane prepolymer, 6-10 parts of curing agent and 1-3 parts of reactive diluent to 60-80° C. and mechanically stirring, mixing evenly, then curing at 100-120° C. for 2-4 hours, 125-140° C. for 3-5 hours, and 160-180° C. for 4-6 hours, and cooling to room temperature to obtain a modified polyurethane toughened epoxy resin; The method for preparing the borate siloxane chain extender in step (1) comprises the following steps: Step S1, under a nitrogen atmosphere, add 4-(Boc-amino)phenylboronic acid and N,N-dimethylformamide to a reaction flask, stir evenly, add diethanolamine, stir to react, after the reaction is completed, recrystallize with petroleum ether, filter and wash, to obtain a nitrogen-containing coordinated borate ester monomer; Step S2, under a nitrogen atmosphere, add 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and N-methylpyrrolidone to a reaction flask, stir evenly, add nitrogen-containing coordinated borate monomer and potassium carbonate, stir to react, after the reaction is completed, extract with brine and dichloromethane, concentrate the organic phase, add trifluoroacetic acid and dichloromethane, stir at room temperature for 3-8h, filter and concentrate, and dry to obtain a borate siloxane chain extender.

2. The method for preparing a modified polyurethane toughened epoxy resin according to claim 1, characterized in that: The polyether polyol in step (1) is polytetramethylene ether diol, and the molecular weight is 2000.

3. The method for preparing a modified polyurethane toughened epoxy resin according to claim 1, characterized in that: The tin catalyst in step (1) is stannous octoate, dibutyltin dilaurate or stannous oleate.

4. The method for preparing a modified polyurethane toughened epoxy resin according to claim 1, characterized in that: In the step (2), the curing agent is 4,4′-diaminodiphenylmethane, and the active diluent is ethylene glycol diglycidyl ether.

5. The method for preparing modified polyurethane toughened epoxy resin according to claim 1, characterized in that: In the step S1, the ratio of 4-(Boc-amino)phenylboronic acid to diethanolamine is 1 mol: (1.05-1.2) mol.

6. The method for preparing modified polyurethane toughened epoxy resin according to claim 1, characterized in that: In step S1, the reaction temperature is 45-60° C. and the reaction time is 2-5 h.

7. The method for preparing modified polyurethane toughened epoxy resin according to claim 1, characterized in that: In the step S2, the ratio of 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane, nitrogen-containing coordinated borate monomer, potassium carbonate and trifluoroacetic acid is 1 mol: (2.1-2.3) mol: (2.5-2.8) mol: (8-10) mol.

8. The method for preparing modified polyurethane toughened epoxy resin according to claim 1, characterized in that: In step S2, the reaction temperature is 65-80° C. and the reaction time is 12-24 h.

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