Preparation method of modified polyurethane toughened epoxy resin

Abstract

The invention relates to the technical field of macromolecules, and discloses a preparation method of modified polyurethane toughened epoxy resin, which comprises the following steps: by taking 4-(Boc-amino) phenylboronic acid, diethanol amine, 1, 3-bis (3-glycidyl ether oxypropyl) tetramethyldisiloxane and the like as raw materials, carrying out a series of chemical reactions to obtain a borate siloxane chain extender; the method comprises the following steps: adding a polyurethane prepolymer into the epoxy resin, participating in chain extension of polyurethane, and modifying the epoxy resin by using the polyurethane prepolymer to obtain the modified polyurethane toughened epoxy resin. A'soft segment 'and an Si-O structure in the modified polyurethane can also improve the flexibility of a curing network, effectively change the fracture mechanism of the resin, absorb a large amount of energy when the resin is fractured, and contribute to improving the toughness of the epoxy resin; on the basis of ensuring the strength of the epoxy resin, the toughness and flame retardant property of the epoxy resin are improved, and the epoxy resin can be applied to the fields of composite materials, coatings, adhesives and the like with higher toughness and flame retardant requirements, and has wide applicability.

Description

Technical Field

[0001] The invention relates to the technical field of polymers, in particular to a method for preparing a modified polyurethane toughened epoxy resin. Background Art

[0002] Epoxy resin (EP), as a thermosetting polymer synthetic material, is widely used in adhesives, coatings and composite materials due to its good adhesion, corrosion resistance and high strength. However, epoxy resin has poor toughness, is brittle, easy to crack 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%, which is an extremely flammable material. In a fire accident, it is often the most flammable part of the composite material, and it continues to burn and release a lot of smoke after a fire, which greatly limits its application in high-temperature environments such as aerospace, integrated circuit packaging and nuclear reactor systems. Therefore, the development of epoxy resin systems with both toughness and flame retardancy has very important industrial value.

[0003] Polyurethane has the characteristics of high bonding strength, good flexibility and high mechanical strength. When combined with epoxy resin, it can form an interpenetrating polymer network structure, organically combining the high elasticity of polyurethane with the good adhesion of epoxy resin, thereby achieving a good toughening effect; however, in traditional polyurethane-modified epoxy resin materials, the compatibility of polyurethane and epoxy resin is not completely ideal, and the amount of polyurethane added cannot be too high, otherwise the toughening effect will be unsatisfactory; at the same time, using polyurethane to toughen epoxy resin will cause a serious reduction in the tensile strength and shear strength of the epoxy resin. External polyurethane has the disadvantages of flammability and poor heat resistance, which are not conducive to the improvement of the flame retardant properties of epoxy resin; Patent No. CN114773610A discloses a method for preparing a polyurethane toughened epoxy resin, which uses ferrocene-modified polyisocyanate and polypropylene glycol to synthesize a piperazine-modified polyurethane prepolymer, and then the piperazine-modified polyurethane prepolymer is grafted with an epoxy resin to prepare a toughened epoxy resin. However, the silver streaks of the modified epoxy resin increase significantly when it breaks, and it is easy to produce tough fracture, and the problem of poor flame retardant properties of the epoxy resin is not solved.

[0004] Siloxane chains have excellent flexibility and can be used as toughening materials for resins and their composite materials. However, silicone has poor compatibility with epoxy resin. If it is simply mixed, the mixture will present a multiphase separation structure due to the large interfacial tension between the two phases, and the modification effect cannot be achieved. The borate bond is a special dynamic covalent bond that has the characteristic of undergoing bond exchange reactions at room temperature. Based on this, the present application aims to utilize the designability of polyurethane to introduce silicone and borate into the polyurethane structure and modify the epoxy resin, thereby improving the toughness and flame retardancy of the epoxy resin while ensuring the mechanical properties of the epoxy resin. Summary of the invention

[0005] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a method for preparing a modified polyurethane toughened epoxy resin, which improves the toughness and flame retardant properties of the epoxy resin while ensuring the strength of the epoxy resin.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A method for preparing a modified polyurethane toughened epoxy resin 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.

[0007] Step (2), under a nitrogen atmosphere, heating 100 parts by weight of bisphenol A epoxy resin, 10-30 parts by weight of modified polyurethane prepolymer, 6-10 parts by weight of curing agent and 1-3 parts by weight of reactive diluent to 60-80° C. and mechanically stirring, mixing evenly, then curing at 100-120° C. for 2-4 h, 125-140° C. for 3-5 h, and 160-180° C. for 4-6 h, and cooling to room temperature to obtain a modified polyurethane toughened epoxy resin.

[0008] Furthermore, in step (1), the polyether polyol is polytetramethylene ether diol, and the molecular weight is 2000.

[0009] Furthermore, in step (2), the tin catalyst is stannous octoate, dibutyltin dilaurate or stannous oleate.

[0010] Furthermore, in step (2), the curing agent is 4,4′-diaminodiphenylmethane and the active diluent is ethylene glycol diglycidyl ether.

[0011] Furthermore, the method for preparing the borate siloxane chain extender in step (1) comprises the following steps: Step S1: In a nitrogen atmosphere, add 4-(Boc-amino)phenylboronic acid and N,N-dimethylformamide to a reaction flask, stir evenly, add diethanolamine, stir and react, after the reaction is completed, recrystallize with petroleum ether, filter and wash, and obtain a nitrogen-containing coordinated borate ester monomer. The preparation reaction formula is as follows:

[0012] Step S2: In a nitrogen atmosphere, 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and N-methylpyrrolidone are added to a reaction flask, and after stirring evenly, a nitrogen-containing coordinated borate monomer and potassium carbonate are added, and the reaction is stirred. After the reaction is completed, salt water and dichloromethane are extracted, the organic phase is concentrated, trifluoroacetic acid and dichloromethane are added, and the mixture is stirred at room temperature for 3-8 hours, filtered and concentrated, and dried to obtain a borate siloxane chain extender. The preparation reaction formula is as follows:

[0013] Furthermore, in step S1, the ratio of 4-(Boc-amino)phenylboronic acid to diethanolamine is 1 mol: (1.05-1.2) mol.

[0014] Furthermore, in step S1, the reaction temperature is 45-60° C., and the reaction time is 2-5 h.

[0015] Furthermore, in 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.

[0016] Furthermore, in step S2, the reaction temperature is 65-80° C., and the reaction time is 12-24 h.

[0017] Compared with the prior art, the present invention has the following beneficial effects: (1) Interpenetrating polymer networks and hydrogen bonds are formed between modified polyurethane and epoxy resin, which is beneficial for resisting deformation and promoting energy absorption under impact. In addition, the siloxane chain has excellent flexibility. The "soft segment" and Si-O structure in the polyurethane can also improve the flexibility of the curing network, effectively changing the fracture mechanism of the resin. When the resin breaks, it absorbs a large amount of energy, 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 react with isocyanate and act as a curing agent, promoting the combination with the epoxy resin, improving the good compatibility with the epoxy resin, and realizing the cross-linking modification of the polyurethane and epoxy resin, thereby playing the role of toughening the epoxy resin.

[0018] (2) Borate bonds have good self-healing ability. When epoxy resin is subjected to external force, the borate bonds can respond quickly and rearrange themselves, 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 the rigidity and flexibility of the chain segments, the polymer network will produce a microphase separation structure, resulting in the existence of multi-level 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 produce holes and bridge each other, which helps to absorb a large amount of energy and prevent the rapid expansion of cracks, thereby improving the toughness of the material.

[0019] (3) The hydroxyl and amino groups in the borate siloxane chain extender structure can participate in the curing reaction of epoxy resin, forming a three-dimensional branched network structure in which the molecular chains are intertwined, which can effectively improve the density of epoxy resin cured products. In addition, the bond energy of the BO bond is relatively high. Introducing the BO bond into the molecular structure of epoxy resin can greatly improve the heat resistance of epoxy resin. The boron, nitrogen and silicon elements rich in the chain extender structure can form a dense 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 smoke generated by combustion inside the material, thereby greatly enhancing the flame retardant properties of epoxy resin. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects to be solved in the present application clearer, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Unless otherwise indicated, the raw materials and reagents used in the present application are all commercially available products, or can be prepared by known methods.

[0021] 4-(Boc-amino)phenylboronic acid, CAS number is 380430-49-9.

[0022] Diethanolamine, CAS number is 111-42-2.

[0023] 1,3-Bis(3-glycidyloxypropyl)tetramethyldisiloxane, CAS number is 126-80-7. Example 1

[0024] (1) Under nitrogen atmosphere, add 85 mmol of 4-(Boc-amino)phenylboronic acid and 510 mL of N,N-dimethylformamide into a reaction flask. After stirring evenly, add 95.2 mmol of diethanolamine and react at 55 °C for 3 h. Recrystallize with petroleum ether, filter and wash to obtain a nitrogen-containing coordinated borate ester monomer.

[0025] (2) Under nitrogen atmosphere, add 70 mmol of 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and 625 mL of N-methylpyrrolidone into a reaction flask, stir evenly, then add 155 mmol of nitrogen-containing coordinated borate monomer and 185.5 mmol of potassium carbonate, react at 75 °C for 16 h, extract with brine and dichloromethane, concentrate the organic phase, add 630 mmol of trifluoroacetic acid and 560 mL of dichloromethane, stir at room temperature for 6 h, filter, concentrate, and dry to obtain a borate siloxane chain extender.

[0026] (3) Under nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to the reaction flask, and the mixture was placed in an environment with a temperature of 110°C and a vacuum degree of 0.08 MPa for vacuum dehydration for 2 h. Then, the mixture was stirred and mixed with 25 g of toluene diisocyanate, and the mixture was heated to 75°C. 0.2 g of stannous octoate and 2 g of borate siloxane chain extender were added. After the addition was completed, the mixture was kept warm for 5 h, cooled and discharged, and allowed to stand for defoaming to obtain a modified polyurethane prepolymer.

[0027] (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 and mechanically stirred. After being evenly mixed, the mixture was cured at 110°C for 3 h, 130°C for 3 h, and 170°C for 5 h. The mixture was cooled to room temperature to obtain a modified polyurethane toughened epoxy resin. Example 2

[0028] (1) Under nitrogen atmosphere, add 150 mmol of 4-(Boc-amino)phenylboronic acid and 750 mL of N,N-dimethylformamide into a reaction flask. After stirring evenly, add 157.5 mmol of diethanolamine and react at 60 °C for 2 h. Recrystallize with petroleum ether, filter and wash to obtain a nitrogen-containing coordinated borate ester monomer.

[0029] (2) Under nitrogen atmosphere, 135 mmol of 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and 810 mL of N-methylpyrrolidone were added to the reaction flask. After stirring evenly, 283.5 mmol of nitrogen-containing coordinated borate monomer and 337.5 mmol of potassium carbonate were added. The mixture was reacted at 80 °C for 12 h. The mixture was extracted with brine and dichloromethane. The organic phase was concentrated. 1080 mmol of trifluoroacetic acid and 675 mL of dichloromethane were added. The mixture was stirred at room temperature for 3 h. The mixture was filtered, concentrated and dried to obtain a borate siloxane chain extender.

[0030] (3) Under nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to the reaction flask, and the mixture was placed in an environment with a temperature of 120°C and a vacuum degree of 0.1 MPa for vacuum dehydration for 1 h. Then, the mixture was stirred and mixed with 20 g of toluene diisocyanate, and the mixture was heated to 80°C. 0.1 g of dilaurylamide and 4 g of borate siloxane chain extender were added. After the addition was completed, the mixture was kept warm for 2 h, cooled and discharged, and allowed to stand for defoaming to obtain a modified polyurethane prepolymer.

[0031] (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 and mechanically stirred. After being evenly mixed, the mixture was cured at 120°C for 2 h, 140°C for 3 h, and 180°C for 4 h. The mixture was cooled to room temperature to obtain a modified polyurethane toughened epoxy resin. Example 3

[0032] (1) Under 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, 54 mmol of diethanolamine was added and the mixture was reacted at 45 °C for 5 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain a nitrogen-coordinated borate ester monomer.

[0033] (2) Under nitrogen atmosphere, add 40 mmol of 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and 400 mL of N-methylpyrrolidone into a reaction flask, stir evenly, then add 92 mmol of nitrogen-containing coordinated borate monomer and 112 mmol of potassium carbonate, react at 65 °C for 24 h, extract with brine and dichloromethane, concentrate the organic phase, add 400 mmol of trifluoroacetic acid and 400 mL of dichloromethane, stir at room temperature for 8 h, filter, concentrate, and dry to obtain a borate siloxane chain extender.

[0034] (3) Under nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to the reaction flask, and the mixture was placed in an environment with a temperature of 100°C and a vacuum degree of 0.05 MPa for vacuum dehydration for 2 h. Then, the mixture was stirred and mixed with 30 g of toluene diisocyanate, and the mixture was heated to 70°C. 0.3 g of stannous oleate and 6 g of borate siloxane chain extender were added. After the addition was completed, the mixture was kept warm for 6 h, cooled and discharged, and allowed to stand for defoaming to obtain a modified polyurethane prepolymer.

[0035] (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 and mechanically stirred. After being evenly mixed, the mixture was cured at 100°C for 4 h, 125°C for 5 h, and 160°C for 6 h. The mixture was cooled to room temperature to obtain a modified polyurethane toughened epoxy resin. Example 4

[0036] (1) Under 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, 34.5 mmol of diethanolamine was added and the mixture was reacted at 55 °C for 4 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain a nitrogen-coordinated borate ester monomer.

[0037] (2) Under nitrogen atmosphere, add 25 mmol of 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and 215 mL of N-methylpyrrolidone to a reaction flask. After stirring evenly, add 54 mmol of nitrogen-containing coordinated borate monomer and 66 mmol of potassium carbonate. The reaction is carried out at 75 °C for 15 h. The mixture is extracted with brine and dichloromethane. The organic phase is concentrated. 210 mmol of trifluoroacetic acid and 235 mL of dichloromethane are added. The mixture is stirred at room temperature for 6 h. The mixture is filtered, concentrated, and dried to obtain a borate siloxane chain extender.

[0038] (3) Under nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to the reaction flask, and the mixture was placed in an environment with a temperature of 115°C and a vacuum degree of 0.08 MPa for vacuum dehydration for 2 h. Then, the mixture was stirred and mixed with 26 g of toluene diisocyanate, and the mixture was heated to 75°C. 0.25 g of stannous octoate and 8 g of borate siloxane chain extender were added. After the addition was completed, the mixture was kept warm for 5 h, cooled and discharged, and allowed to stand for defoaming to obtain a modified polyurethane prepolymer.

[0039] (4) Under a nitrogen atmosphere, 100 g of bisphenol A epoxy resin, 25 g of modified polyurethane prepolymer, 9 g of 4,4′-diaminodiphenylmethane and 2.5 g of ethylene glycol diglycidyl ether were heated to 75°C and mechanically stirred. After being evenly mixed, the mixture was cured at 110°C for 3 h, 130°C for 5 h, and 175°C for 4 h. The mixture was cooled to room temperature to obtain a modified polyurethane toughened epoxy resin. Example 5

[0040] (1) Under 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, 60 mmol of diethanolamine was added and the mixture was reacted at 60 °C for 5 h. The mixture was recrystallized from petroleum ether, filtered and washed to obtain a nitrogen-coordinated borate ester monomer.

[0041] (2) Under nitrogen atmosphere, 45 mmol of 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and 378 mL of N-methylpyrrolidone were added to the reaction flask. After stirring evenly, 97.2 mmol of nitrogen-containing coordinated borate monomer and 124.2 mmol of potassium carbonate were added. The mixture was reacted at 70 °C for 24 h. The mixture was extracted with brine and dichloromethane. The organic phase was concentrated. 396 mmol of trifluoroacetic acid and 306 mL of dichloromethane were added. The mixture was stirred at room temperature for 6 h. The mixture was filtered, concentrated and dried to obtain a borate siloxane chain extender.

[0042] (3) Under nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to the reaction flask, and the mixture was placed in an environment with a temperature of 120°C and a vacuum degree of 0.05 MPa for vacuum dehydration for 2 h. Then, the mixture was stirred and mixed with 30 g of toluene diisocyanate, and the mixture was heated to 70°C. 0.3 g of dibutyltin dilaurate and 10 g of borate siloxane chain extender were added. After the addition was completed, the mixture was kept warm for 5 h, cooled, discharged, and allowed to stand for defoaming to obtain a modified polyurethane prepolymer.

[0043] (4) Under a nitrogen atmosphere, 100 g of bisphenol A epoxy resin, 30 g of modified polyurethane prepolymer, 8.5 g of 4,4′-diaminodiphenylmethane and 3 g of ethylene glycol diglycidyl ether were heated to 75°C and mechanically stirred. After being evenly mixed, the mixture was cured at 105°C for 2 h, 135°C for 5 h and 170°C for 5 h. The mixture was cooled to room temperature to obtain a modified polyurethane toughened epoxy resin.

[0044] Comparative Example 1 (1) Under nitrogen atmosphere, add 70 mmol of ethylene glycol diglycidyl ether (structural formula: , CAS No. 2224-15-9) and 625 mL of N-methylpyrrolidone, after stirring evenly, add 155 mmol of nitrogen-containing coordinated borate monomer (prepared in Example 1) and 185.5 mmol of potassium carbonate, react at 75°C for 16 h, extract with brine and dichloromethane, concentrate the organic phase, add 630 mmol of trifluoroacetic acid and 560 mL of dichloromethane, stir at room temperature for 6 h, filter, concentrate, and dry to obtain a borate chain extender.

[0045] (2) Under nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to a reaction flask, and the mixture was placed in an environment with a temperature of 110°C and a vacuum degree of 0.08 MPa for vacuum dehydration for 2 h. The mixture was then stirred and mixed with 25 g of toluene diisocyanate, heated to 75°C, and 0.2 g of stannous octoate and 2 g of borate chain extender were added. After the addition was completed, the mixture was kept warm for 5 h, cooled and discharged, and allowed to stand for defoaming to obtain a modified polyurethane prepolymer.

[0046] (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 being evenly mixed, the mixture was cured at 110°C for 3 h, 130°C for 3 h, and 170°C for 5 h. The mixture was cooled to room temperature to obtain a polyurethane modified epoxy resin.

[0047] Comparative Example 2 (1) Under nitrogen atmosphere, add 70 mmol of 1,3-bis(3-glycidyloxypropyl)tetramethyldisiloxane and 625 mL of N-methylpyrrolidone to a reaction flask, stir evenly, and then add 155 mmol of tert-butyl 4-piperidin-4-yl-phenyl)-carbamate (structural formula: , CAS No. 887589-58-4) and 185.5mmol potassium carbonate, react at 75℃ for 16h, extract with brine and dichloromethane, concentrate the organic phase, add 630mmol trifluoroacetic acid and 560mL dichloromethane, stir at room temperature for 6h, filter and concentrate, and dry to obtain a siloxane chain extender.

[0048] (2) Under nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to a reaction flask, and the mixture was placed in an environment with a temperature of 110°C and a vacuum degree of 0.08 MPa for vacuum dehydration for 2 h. The mixture was then stirred and mixed with 25 g of toluene diisocyanate and heated to 75°C. 0.2 g of stannous octoate and 2 g of a siloxane chain extender were added. After the addition was completed, the mixture was kept warm for 5 h, cooled and discharged, and allowed to stand for defoaming to obtain a modified polyurethane prepolymer.

[0049] (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 being evenly mixed, the mixture was cured at 110°C for 3 h, 130°C for 3 h, and 170°C for 5 h. The mixture was cooled to room temperature to obtain a polyurethane modified epoxy resin.

[0050] Comparative Example 3 (1) Under nitrogen atmosphere, 100 g of polytetrahydrofuran ether diol with a molecular weight of 2000 was added to a reaction flask, and the mixture was placed in an environment with a temperature of 110°C and a vacuum degree of 0.08 MPa for vacuum dehydration for 2 h. The mixture was then stirred and mixed with 25 g of toluene diisocyanate, heated to 75°C, and 0.2 g of stannous octoate and 2 g of 1,4-butanediol chain extender were added. After the addition was completed, the mixture was kept warm for 5 h, cooled, discharged, and allowed to stand for defoaming to obtain a polyurethane prepolymer.

[0051] (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 being evenly mixed, they were cured at 110°C for 3 h, 130°C for 3 h, and 170°C for 5 h. The mixture was cooled to room temperature to obtain a polyurethane-modified epoxy resin.

[0052] Tensile performance test: According to GB / T 2567-2008 standard, the cured epoxy resin sample was made into a dumbbell shape and tested using a universal testing machine with a tensile rate of 20 mm / min and a test environment temperature of 25°C.

[0053] Impact performance test: According to GB / T 2567-2008 standard, the cured epoxy resin sample is made into a non-notched impact specimen and tested on a simply supported beam impact tester.

[0054] Shear strength test: According to GB / T 7124-2008 standard, a universal electronic testing machine was used to conduct steel / steel tensile shear strength test at a tensile rate of 10 mm / min.

[0055]

[0056] As can be seen from the test results in the above table, the tensile strength, elongation at break, impact strength and shear strength of the epoxy resin prepared in the embodiment at room temperature are significantly higher than those of the comparative example, indicating that the present application will not have a negative impact on the strength of the epoxy resin while toughening and modifying it, 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 conducive to resisting deformation and promoting energy absorption under impact force. In addition, the siloxane chain has excellent flexibility, and the "soft segment" and Si-O structure in the polyurethane can also improve the flexibility of the cured network, effectively change the fracture mechanism of the resin, and absorb a large amount of energy when the resin breaks, 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 react with isocyanate and act as a curing agent to promote the combination with the epoxy resin, improve the good compatibility with the epoxy resin, and realize the cross-linking modification of polyurethane and epoxy resin, thereby improving the toughness of the epoxy resin. Comparative Examples 1 and 3 do not contain siloxane, and the "hard segment" content in its cured structure is high, and the toughness is poor. The invention can be applied to reinforced composite materials, prepreg matrix materials and adhesives with higher toughness and flame retardancy requirements.

[0057] Self-healing performance test: The prepared epoxy resin cured product sample was cut in the middle, and then the broken part was tightly fitted. After pressing with fingers for 5 minutes, it was placed in an oven and repaired at 60°C for 48 hours. The repaired sample was subjected to an impact strength test, and the self-healing efficiency was calculated.

[0058]

[0059] Boric acid ester bond is a special dynamic covalent bond, and bond exchange reaction can occur at room temperature, that is, under water or other specific conditions, boric acid ester bond can undergo hydrolysis reaction and break, and when water is removed, boric acid ester bond can be regenerated, and this reversible hydrolysis reaction is the basis for boric acid ester to have self-healing ability. It can be seen from the test results in the above table that the impact strength of the repaired epoxy resin recovers faster, and the self-healing efficiency reaches up to 92.5%. This is because when the epoxy resin is subjected to external force, the boric acid ester bond can respond quickly and rearrange, thereby absorbing and dispersing energy, and improving the toughness of the material; when the boric acid ester structure is introduced into the epoxy resin, due to the difference in rigidity and flexibility of the chain segment, the polymer network will produce a microphase separation structure, so that there are multi-level microphase separation areas inside the material, which can be used as stress concentration points or crack initiation points. Under the action of external force, these microphase structures can gradually produce holes and bridge each other, which helps to absorb a large amount of energy and prevent the rapid expansion of cracks, thereby improving the toughness of the material. Comparative Examples 2 and 3 do not contain boric acid ester structure and do not have self-healing ability.

[0060] Limiting oxygen index test: According to standard GB / T 2406.2-2009, the limiting oxygen index test is carried out.

[0061]

[0062] The hydroxyl and amino groups in the borate siloxane chain extender structure can participate in the curing reaction of epoxy resin to form a three-dimensional branched network structure in which the molecular chains are intertwined, which can effectively improve the density of epoxy resin cured products. In addition, the bond energy of the BO bond is relatively high. Introducing the BO bond into the molecular structure of epoxy resin can greatly improve the heat resistance of epoxy resin. The rich boron, nitrogen and silicon elements in the chain extender structure can form a dense 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 smoke generated by combustion inside the material, thereby greatly enhancing the flame retardant properties of epoxy resin.

[0063] The embodiments described above 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 aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in 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 (2) 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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