Preparation method of bismaleimide resin system with high impact toughness

Abstract

The invention relates to the technical field of thermosetting resin, in particular to a preparation method of a bismaleimide resin system with high impact toughness, which specifically comprises the following steps: mixing and prepolymerizing diamine and bisphenol A diphenyl ether type bismaleimide; and adding the prepolymer into a diphenylmethane bismaleimide / diallyl bisphenol A resin system, blending, then prepolymerizing again, and defoaming and curing a prepolymerization product to obtain the bismaleimide resin system with high impact toughness. According to the invention, a diphenylmethane type bismaleimide / diallyl bisphenol A resin system is used as a resin matrix, and bisphenol A diphenyl ether type bismaleimide subjected to chain extension by a small amount of diamine is used as a modifier, so that the toughness of the bismaleimide resin system is further remarkably improved while good thermal stability and manufacturability are maintained.

Description

Technical Field

[0001] The invention relates to the technical field of thermosetting resins, and in particular to a method for preparing a bismaleimide resin system with high impact toughness. Background Art

[0002] Advanced resin composites (APC) have the characteristics of light weight, high strength, and high modulus. When used as structural materials for aircraft, they can greatly reduce the weight of the aircraft, and the reduction in aircraft weight can greatly increase the range of the aircraft. Therefore, the amount of APC used has become an important indicator of the advancement of aircraft. At present, the main APC resin matrices include epoxy resin, polyimide resin, bismaleimide resin, benzoxazine resin, etc.

[0003] Bismaleimide resin (BMI) is a very important APC resin matrix. Bismaleimide resin usually contains a large number of rigid structures and has a short molecular chain, which makes the cross-linking density of the bismaleimide resin high after curing. This molecular structure gives the bismaleimide resin good high temperature resistance, but also makes the bismaleimide resin brittle. This shortcoming has become the biggest obstacle to the further application of bismaleimide resin. On the basis of ensuring other excellent properties of bismaleimide resin, toughening bismaleimide resin has become a major research hotspot of bismaleimide resin.

[0004] At present, the toughening methods of bismaleimide resin mainly include diamine compound toughening, allyl compound toughening, thermoplastic resin toughening and inorganic nanoparticle toughening. Diamine compound toughening is to extend the molecular chain of bismaleimide by Michael addition reaction between active hydrogen in diamine and bismaleimide resin, thereby reducing the crosslinking density after curing, but the processability of bismaleimide resin after diamine modification is generally poor; allyl compound modified bismaleimide resin is the most popular modification method at present, among which diallyl bisphenol A is the most common type of allyl compound modifier. The bismaleimide resin modified with diallyl bisphenol A not only has good impact toughness, but also has good processing and forming properties, but the degree of toughness improvement after modification with allyl compound alone is not ideal. Therefore, there is an urgent need for a bismaleimide resin system and its preparation method that have both processability, thermal stability and toughness. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention firstly prepolymerizes diamine and bisphenol A diphenyl ether type bismaleimide to obtain prepolymer A; adds prepolymer A with different mass fractions into a prepared diphenylmethane type bismaleimide / diallyl bisphenol A resin system, stirs at a specific temperature so that the blend becomes a uniform blend system, and obtains prepolymer B; and cures prepolymer B at a high temperature to obtain a modified bismaleimide resin system cured product having both heat resistance and impact toughness.

[0006] The above scheme uses a diphenylmethane bismaleimide / diallyl bisphenol A resin system as a resin matrix, and uses a small amount of diamine-extended bisphenol A diphenyl ether bismaleimide as a modifier, while maintaining good thermal stability and processability, further significantly improving the toughness of the bismaleimide resin system.

[0007] The specific technical solutions provided by the present invention are as follows: A method for preparing a bismaleimide resin system with high impact toughness, comprising the steps of: (1) Preparation of prepolymer A: diamine and bisphenol A diphenyl ether type bismaleimide are mixed, and the mixture is continuously stirred in a molten state to carry out a prepolymerization reaction to obtain prepolymer A.

[0008] (2) Preparation of diphenylmethane bismaleimide / diallyl bisphenol A resin system: diphenylmethane bismaleimide and diallyl bisphenol A are mixed to prepare a diphenylmethane bismaleimide / diallyl bisphenol A resin system.

[0009] (3) Preparation of prepolymer B: Prepolymer A is added to a diphenylmethane bismaleimide / diallyl bisphenol A resin system to form a blend system, and the mixture is continuously stirred at a specific temperature to perform a prepolymerization reaction to obtain prepolymer B.

[0010] (4) The prepolymer B is vacuum degassed at a certain temperature for a period of time, and then cured under a specific curing process to obtain a bismaleimide resin system with high impact toughness.

[0011] In the present invention, a diphenylmethane bismaleimide / diallyl bisphenol A resin system is used as a bismaleimide-modified matrix, wherein the cost of diphenylmethane bismaleimide is relatively low, while the cost of bisphenol A diphenyl ether bismaleimide is relatively expensive. Using diphenylmethane bismaleimide as a matrix component with a larger specific gravity can ensure that the production cost of the bismaleimide resin system prepared by this process is relatively low.

[0012] There is a competitive relationship between the reaction of diamine toughener and allyl compound with BMI. If they are blended together, unreacted diamine will be present in the product. Therefore, in the present invention, a diphenylmethane type bismaleimide / diallyl bisphenol A resin system and a diamine chain-extended bisphenol A diphenyl ether type bismaleimide are prepared separately, and the latter is used as a modifier of the former to modify the product.

[0013] The structural formulas of the bisphenol A diphenyl ether type bismaleimide and diphenylmethane type bismaleimide are shown in Formula I and Formula II, respectively: Formula I Formula II

[0014] The structural formula of diallyl bisphenol A is shown in Formula III: Formula III

[0015] The diamine is 2,7-bis(4-aminophenoxy)naphthalene or diaminodiphenylmethane, and the molecular structures are shown in Formula IV and Formula V respectively: Formula IV Formula V

[0016] The diamine chain extender reduces the crosslinking density after curing by extending the BMI chain. The flexible ether bond in 2,7-bis(4-aminophenoxy)naphthalene can increase the spin of the molecular chain to further toughen it. Its naphthalene ring has the function of improving heat resistance while toughening. Although diaminodiphenylmethane does not contain a flexible ether bond in its structure, it can also achieve the purpose of extending the BMI chain. However, the toughening effect of 2,7-bis(4-aminophenoxy)naphthalene is better than that of diaminodiphenylmethane.

[0017] The carbon-carbon double bonds of the bismaleimide resin after chain extension by diamine and the carbon-carbon double bonds in diallyl bisphenol A can undergo ene addition reaction to generate an intermediate, which can then undergo Diels-Alder reaction with the bismaleimide group and then be cured and cross-linked, which can significantly improve the process performance of BMI while increasing toughness and prolong the molding time of the bismaleimide resin during curing.

[0018] Preferably, the molar ratio of the diamine to bisphenol A diphenyl ether bismaleimide in step (1) is 1:(1-3), more preferably 1:2. The ratio of the diamine to bisphenol A diphenyl ether bismaleimide resin should be moderate. If the ratio is too large, the heat resistance of the resin system will be excessively lost; if the ratio is too small, the toughening effect will not be obvious.

[0019] Preferably, the prepolymerization temperature of the diamine and bisphenol A diphenyl ether type bismaleimide in step (1) is 140-160°C, more preferably 150°C. The prepolymerization temperature of the diamine and bisphenol A diphenyl ether type bismaleimide should be moderate. If the prepolymerization temperature is too high, the resin curing degree will be too high and the viscosity will be too high; if the prepolymerization temperature is too low, the prepolymerization degree will be insufficient.

[0020] Preferably, the prepolymerization time of the diamine and bisphenol A diphenyl ether type bismaleimide in step (1) is 10 min-30 min, more preferably 20 min. The prepolymerization time of the diamine and bismaleimide should be moderate. If the prepolymerization time is too long, the resin curing degree will be too high and the viscosity will be too high; if the prepolymerization time is too short, the prepolymerization degree will be insufficient.

[0021] Preferably, the stirring rates in step (1) and step (3) are both 1000 r / min-2000 r / min.

[0022] Preferably, in step (2), the molar ratio of diphenylmethane bismaleimide to diallyl bisphenol A is 1:(0.8-1.2), more preferably 1:0.87.

[0023] Preferably, the amount of prepolymer A added in step (3) accounts for 3%-18% of the mass fraction of prepolymer B, more preferably 3%-9%, and most preferably 6%; if the mass fraction of the added prepolymer A is too small, it may not be possible to obtain the ideal impact toughness; if the mass fraction of the added prepolymer A is too large, it may cause the viscosity to increase during the degassing process, which is not conducive to the discharge of bubbles, resulting in defects in the resin solidified material affecting the performance of the resin. Therefore, selecting the above-mentioned appropriate addition range plays an important role in the performance of the final product.

[0024] Preferably, the prepolymerization temperature of the blending system in step (3) is 130-150°C, more preferably 140°C. The prepolymerization temperature of the blending system should be moderate. If the prepolymerization temperature is too high, the degree of curing of the resin will be too high and the viscosity will be too high. If the prepolymerization temperature is too low, the degree of prepolymerization will be insufficient.

[0025] Preferably, the prepolymerization time of the blending system in step (3) is 15-45 min, more preferably 30 min. The prepolymerization time of the blending system should be moderate. If the prepolymerization time is too long, the degree of curing of the resin will be too high and the viscosity will be too high; if the prepolymerization time is too short, the degree of prepolymerization will be insufficient.

[0026] Preferably, the vacuum degassing temperature of the blending system in step (4) is 130-150°C, more preferably 150°C.

[0027] Preferably, the vacuum degassing time of the blended system in step (4) is 0.5-1 h; the curing adopts a step-by-step temperature curing process; The step-by-step temperature rise curing process is 180 ℃ / 2h+210 ℃ / 2h+240 ℃ / 4h+260 ℃ / 2h; through the step-by-step temperature rise curing process, the curing reaction is balanced and the curing is complete.

[0028] The preparation method of the diamine containing a naphthalene ring and an ether bond in the present invention is not limited and can be prepared by using existing techniques, for example, referring to the literature (Polymer Materials Science and Engineering, 2011, 27(11), 1-3). Specifically, it can also be prepared according to the following steps.

[0029] 1) In an appropriate amount of N,N-dimethylformamide, 2,7-dihydroxynaphthalene, p-nitrochlorobenzene and anhydrous potassium carbonate are mixed in a molar ratio of 1:2:2, and reacted at 120-150°C for 6-12 hours. After the reaction is completed, the mixture is filtered while hot, and the filtrate is cooled to room temperature and allowed to stand for more than 8 hours to precipitate a large amount of crystals, which are then filtered and retained. The crystals are washed with water several times and then dried in an oven to obtain a dinitro compound.

[0030] There is no special requirement for the amount of N,N-dimethylformamide used. Preferably, the volume ratio of N,N-dimethylformamide to the mass ratio of 2,7-dihydroxynaphthalene is (15-25) mL:1 g.

[0031] 2) An appropriate amount of dinitro compound is reacted at 75-105°C for 8-10 h in a N2 atmosphere with an appropriate amount of ethylene glycol methyl ether as a solvent, hydrazine hydrate as a reducing agent, activated carbon as an adsorbent, and FeCl3·6H2O as a catalyst. After the reaction is completed, the filtrate is filtered while hot, and the filtrate is cooled to room temperature and subjected to rotary evaporation to obtain a large amount of crystals. The precipitated crystals are washed with alcohol and water for multiple times and then dried to obtain 2,7-bis(4-aminophenoxy)naphthalene.

[0032] Preferably, the reaction temperature in step 1) is 150° C. and the reaction time is 10 h.

[0033] Preferably, the reaction temperature in step 2) is 100° C. and the reaction time is 8 h.

[0034] In step 1), the structural formulas of 2,7-dihydroxynaphthalene, p-nitrochlorobenzene and dinitro compound are shown in Formula VI, Formula VII and Formula VIII respectively: Formula VI Formula VII Formula VIII

[0035] Compared with the prior art, the technical effects of the present invention are: (1) The present invention prepares a diphenylmethane type bismaleimide / diallyl bisphenol A resin system and a diamine-modified bisphenol A diphenyl ether type bismaleimide respectively, and uses the latter as a modifier for the former. The bismaleimide resin system is prepared by this method, and the toughness of the product resin can be further significantly improved on the basis of maintaining low cost, good high temperature resistance and process performance.

[0036] (2) Compared with the conventional diamine modifier of bismaleimide resin, the diamine 2,7-bis(4-aminophenoxy)naphthalene containing ether bonds and naphthalene rings used in some embodiments of the present invention has a longer molecular chain and contains a flexible ether bond, which can increase the spin of the molecular chain and further toughen it. At the same time, the naphthalene ring is a rigid group, which can make up for the reduced heat resistance caused by the longer molecular chain and the introduction of the ether bond. The diamine can undergo a Michael addition reaction with bismaleimide, which can greatly reduce the crosslinking density of bismaleimide after curing and increase the spin of the molecular chain, thereby achieving a toughening effect.

[0037] (3) In the present invention, prepolymer A is obtained by prepolymerizing diamine with bisphenol A diphenyl ether type bismaleimide. The bisphenol A diphenyl ether bismaleimide structure contains two flexible ether bonds, and the molecular chain is longer than that of traditional diphenylmethane type bismaleimide. After prepolymerization with diamine, the molecular chain of prepolymer A is further extended compared with diamine, and prepolymer A contains maleimide groups, which further guarantees the high temperature resistance of the modified resin on the basis of further toughening.

[0038] (4) Since the prepolymer viscosity of the bismaleimide resin modified by diamine is relatively high, the molding time is relatively short, and the processability is poor, the prepolymer of diamine and bismaleimide is used to modify the diphenylmethane type bismaleimide / diallyl bisphenol A resin system in the present invention. Diallyl bisphenol A can act as a toughening agent for the bismaleimide resin and a reactive diluent to improve the processability of the system. Compared with the bismaleimide resin modified by diamine alone, the viscosity of the system is greatly reduced during the preparation of the casting body, and the molding time is greatly extended. Experiments have found that the resin after adding the reactive diluent can maintain a low viscosity state for at least 60 minutes at 150°C. If the reactive diluent is not added, the viscosity at 150°C for 30 minutes has reached a relatively high level. Compared with the modification with only allyl compounds, the introduction of diamines can further improve the impact toughness of the resin on the basis of improving the processability by the modification with allyl compounds.

[0039] (5) Diamine can be reacted with maleic anhydride to synthesize bismaleimide resin. Compared with the synthesis of bismaleimide resin by reacting diamine with maleic anhydride, the present invention directly uses diamine to modify bismaleimide, eliminating the steps of ring-opening reaction and dehydration cyclization of diamine and maleic anhydride, greatly improving the modification efficiency and shortening the process time.

[0040] (6) In order to achieve the simultaneous use of diamine and diallyl bisphenol A, the present invention first prepolymerizes diamine with bisphenol A diphenyl ether type bismaleimide, and then adds the prepolymer to the diphenylmethane type bismaleimide / diallyl bisphenol A resin system, which is equivalent to using diamine to extend bisphenol A diphenyl ether type bismaleimide as a modifier and using the diphenylmethane type bismaleimide / diallyl bisphenol A resin system as the modified body. If all materials are directly blended, the problem of reaction competition may occur, resulting in the presence of unreacted diamine in the system, thereby affecting the resin performance.

[0041] (7) The present invention has good modification effect on bismaleimide resin, simple process and strong practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The dinitro compound prepared in the specific embodiment of the present invention is 1 H-NMR spectrum; Figure 2 The diamine prepared in the specific embodiment of the present invention 1 H-NMR spectrum; Figure 3 1 is a DSC graph of prepolymer B in Examples 1-3 and the prepolymer in Comparative Example 1 prepared by the present invention; Figure 4 It is a graph of the impact strength of the unnotched cantilever beam impact of the experimental samples 1-3 of the present invention and the comparative sample 1. DETAILED DESCRIPTION

[0043] The present invention is further described in detail below through specific embodiments, but this should not be construed as limiting the scope of the present invention to the following examples. Without departing from the above-mentioned method concept of the present invention, various substitutions or changes made according to common technical knowledge and conventional means in the art should be included in the scope of the present invention.

[0044] The 2,7-bis(4-aminophenoxy)naphthalene used in the following examples was prepared by the following method: ① Preparation of dinitro compounds: In 150 mL DMF, 8 g of 2,7-dihydroxynaphthalene, 15.8 g of p-nitrochlorobenzene and 13.8 g of anhydrous potassium carbonate (the molar ratio of 2,7-dihydroxynaphthalene, p-nitrochlorobenzene and anhydrous potassium carbonate is 1:2:2) are reacted at 150°C for 10 hours. After the reaction is completed, the reaction solution is filtered while hot to remove inorganic matter. The filtrate is allowed to stand for more than 8 hours to precipitate. After filtration, the filter residue is retained. The filter residue is washed with water several times and then dried in an oven at 60°C to obtain a dinitro compound.

[0045] like Figure 1 The above dinitro compound 1 H-MNR diagram, there are five different hydrogen proton resonance absorption peaks in the diagram. The peak at δ = 8.28 is the peak of the hydrogen proton at position a on the benzene ring; the peak at δ = 7.22 is the peak of the hydrogen proton at position b on the benzene ring; the peak at δ = 7.68 is the peak of the hydrogen proton at position c on the naphthalene ring; δ = 7.38 is the peak of the hydrogen proton at position d on the naphthalene ring; the peak at δ = 8.18 is the peak of the hydrogen proton at position e on the naphthalene ring.

[0046] ② Preparation of diamine: Weigh 20 g of the prepared dinitro compound, add 25 mL of hydrazine hydrate as a reducing agent, 8 g of activated carbon as an adsorbent, and 1.2 g of FeCl3·6H2O as a catalyst to 100 mL of ethylene glycol methyl ether under N2 atmosphere, and react at 100°C for 8 hours. After the reaction is completed, filter while hot, and perform rotary evaporation on the filtrate at 80°C. After rotary evaporation, pour the concentrated solution into deionized water to precipitate a large amount of solid. The precipitated solid is washed with ethanol several times and then dried in an oven at 60°C to obtain 2,7-bis(4-aminophenoxy)naphthalene.

[0047] like Figure 2 As shown, the above diamine 1 H-MNR diagram, there are six different resonance absorption peaks of hydrogen protons. The peak at δ = 5.00 is the peak of the amino group at a, the peak at δ = 6.61 is the peak of the hydrogen proton at b on the benzene ring, the peak at δ = 6.8 is the peak of the hydrogen proton at c on the benzene ring, and the peaks of the hydrogen protons at d, e, and f in the naphthalene ring appear at δ = 6.96, δ = 7.05, and δ = 7.81, respectively. 1 H-NMR analysis showed that the synthesized product was consistent with the target product.

[0048] Example 1 A method for preparing a bismaleimide resin system with high impact toughness, the specific steps are as follows: (1) 2,7-Bis(4-aminophenoxy)naphthalene and bisphenol A diphenyl ether type bismaleimide were mixed in a molar ratio of 1:2 and melt prepolymerized at a temperature of 150°C and a stirring rate of 1500 r / min for 20 min to obtain prepolymer A.

[0049] (2) Diphenylmethane bismaleimide and diallyl bisphenol A are mixed in a molar ratio of 1:0.87 to obtain a diphenylmethane bismaleimide / diallyl bisphenol A resin system.

[0050] (3) Prepolymer A is added to the diphenylmethane bismaleimide / diallyl bisphenol A resin system obtained in step (2) to prepare a blending system, and the blending system is melt-prepolymerized at a temperature of 140° C. and a stirring rate of 1500 r / min for 30 min to obtain prepolymer B. The amount of prepolymer A added is 3% of the mass of prepolymer B.

[0051] (4) After the prepolymerization, the molten prepolymer B is poured into a mold and vacuum degassed at 150°C for 1 h. After the degassed, a step-by-step temperature rise curing process is adopted. The specific curing process is 180°C / 2h+210°C / 2h+240°C / 4h+260°C / 2h. After the curing, a bismaleimide resin system with high impact toughness is obtained.

[0052] Example 2 A method for preparing a bismaleimide resin system with high impact toughness, the specific steps are as follows: (1) Prepolymer A was prepared by the same method as step (1) of Example 1, except that 2,7-bis(4-aminophenoxy)naphthalene and bisphenol A diphenyl ether type bismaleimide were mixed in a molar ratio of 1:2.5.

[0053] (2) A diphenylmethane bismaleimide / diallyl bisphenol A resin system was obtained in the same manner as in Example 1.

[0054] (3) Prepolymer A is added to the diphenylmethane bismaleimide / diallyl bisphenol A resin system obtained in step (2) to prepare a blending system, and the blending system is melt-prepolymerized at a temperature of 150° C. and a stirring rate of 1000 r / min for 30 min to obtain prepolymer B. The amount of prepolymer A added is 6% of the mass of prepolymer B.

[0055] (4) Prepolymer B was cast and vacuum degassed in the same manner as in Example 1, and then heated for curing to obtain a bismaleimide resin system with high impact toughness.

[0056] Example 3 A method for preparing a bismaleimide resin system with high impact toughness, the specific steps are as follows: (1) Prepolymer A was prepared in the same manner as in Example 1.

[0057] (2) A diphenylmethane bismaleimide / diallyl bisphenol A resin system was obtained in the same manner as in Example 1.

[0058] (3) Prepolymer A is added to the diphenylmethane bismaleimide / diallyl bisphenol A resin system obtained in step (2) to prepare a blending system, and the blending system is melt-prepolymerized at a temperature of 130° C. and a stirring rate of 1500 r / min for 30 min to obtain prepolymer B. The amount of prepolymer A added is 9% of the mass of prepolymer B.

[0059] (4) Prepolymer B was cast and vacuum degassed in the same manner as in Example 1, and then heated for curing to obtain a bismaleimide resin system with high impact toughness.

[0060] Example 4 A method for preparing a bismaleimide resin system with high impact toughness, the specific steps are as follows: (1) Prepolymer A was prepared by the same method as step (1) of Example 1, except that in this example, 2,7-bis(4-aminophenoxy)naphthalene was not added, but an equimolar amount of diaminodiphenylmethane was added.

[0061] (2) A diphenylmethane bismaleimide / diallyl bisphenol A resin system was obtained in the same manner as in Example 1.

[0062] (3) Prepolymer A is added to the diphenylmethane bismaleimide / diallyl bisphenol A resin system obtained in step (2) to prepare a blending system, and the blending system is melt-prepolymerized at a temperature of 130° C. and a stirring rate of 1000 r / min for 30 min to obtain prepolymer B. The amount of prepolymer A added is 6% of the mass of prepolymer B.

[0063] (4) Prepolymer B was cast and vacuum degassed in the same manner as in Example 1, and then heated for curing to obtain a bismaleimide resin system with high impact toughness.

[0064] Comparative Example 1 The bismaleimide resin system was prepared by the following method: (1) A diphenylmethane bismaleimide / diallyl bisphenol A resin system was obtained in the same manner as in Example 1.

[0065] (2) The diphenylmethane bismaleimide / diallyl bisphenol A resin system obtained in step (1) was placed in an oven and prepolymerized at a temperature of 140° C. and a stirring rate of 1000 r / min for 30 min to obtain a prepolymer.

[0066] (3) The prepolymer was cast, vacuum degassed and then heated for curing in the same manner as in Example 1 to obtain a bismaleimide resin system.

[0067] Comparative Example 2 In order to study whether the addition of prepolymer A will definitely improve the mechanical properties of bismaleimide resin, the present invention studies a system in which a large amount of prepolymer A is added as a comparative example.

[0068] That is, the amount of prepolymer A added was changed to 18% of prepolymer B, and other conditions were the same as those in Example 1, to obtain a bismaleimide resin system.

[0069] Comparative Example 3 The bismaleimide resin system was prepared by the following method: (1) 2,7-Bis(4-aminophenoxy)naphthalene and bisphenol A diphenyl ether type bismaleimide were mixed in a molar ratio of 1:2 and melt prepolymerized at a temperature of 180°C and a stirring rate of 1500 r / min for 20 min to obtain prepolymer A.

[0070] (2) After the prepolymerization, prepolymer A was added into diallyl bisphenol A preheated to 140°C, and the ternary blend system was prepolymerized at 140°C and a stirring rate of 1500 r / min for 30 min to obtain prepolymer B. The molar ratio of bisphenol A diphenyl ether type bismaleimide, 2,7-bis(4-aminophenoxy)naphthalene and diallyl bisphenol A in prepolymer B was 2:1:1.

[0071] (3) Place prepolymer B in an oven and perform vacuum degassing at 140 °C for 1 h.

[0072] (4) After degassing, the sample was cured according to the curing process of 150°C / 1 h+180°C / 2 h+220°C / 4 h.

[0073] Experimental example The impact strength, flexural strength and flexural modulus of the samples of the above-mentioned embodiments 1-4 and the samples of comparative examples 1-3 were tested in accordance with GB / T 2567-2021, wherein the sample size for testing the impact strength was 80 mm × 10 mm × 4 mm; the sample size for testing the flexural performance was 80 mm × 15 mm × 4 mm. The number of samples tested in each group of embodiments and comparative examples was not less than 5, and the results were averaged. The results of impact strength, flexural strength and flexural modulus are shown in Table 1.

[0074] Table 1 Test results of impact strength, flexural strength and flexural modulus of bismaleimide resin systems of Examples 1-4 and Comparative Examples 1-3

[0075] From the test results of Examples 1-4 and Comparative Examples 1 and 2 in Table 1, it can be seen that when an appropriate amount of prepolymer A is added to diphenylmethane bismaleimide / diallyl bisphenol A, the bending properties and impact properties of the modified resin can be improved, and the comprehensive mechanical properties of Example 2 are the best.

[0076] It can be seen from Examples 1-4 and Comparative Example 2 that the addition of prepolymer A does not necessarily improve the mechanical properties of the resin system. During the experiment, it was found that when 18% of prepolymer A was added, the viscosity of the resin system increased significantly during the casting process, and defects were easily generated during the processing, resulting in a decrease in bending performance, indicating that the addition of prepolymer A and diphenylmethane bismaleimide / diallyl bisphenol A resin system in any proportion can improve the mechanical properties of the system. In all embodiments, the mechanical properties of the system with a mass fraction of 6% prepolymer A were optimal, and the impact strength was increased by 82% compared to Comparative Example 1.

[0077] It can be seen from Examples 1-3 and Comparative Example 3 that compared with prepolymer A diluted directly with diallyl bisphenol A having a molar ratio of 1:1 with 2,7-bis(4-aminophenoxy)naphthalene, the impact performance and bending performance of the diphenylmethane-type bismaleimide / diallyl bisphenol A system modified with prepolymer A are greatly improved. This is mainly due to the fact that the viscosity of the system modified only with Comparative Example 3 increases rapidly during the degassing process, resulting in incomplete degassing and causing a large number of defects in the cured product, which in turn affects the resin performance. The impact strength of Example 4 is improved compared to that of Comparative Example 3, and the reason is still due to the rapid increase in viscosity in Comparative Example 3, but the impact performance and bending performance of Example 4 are not as good as those of Examples 1-3 due to the influence of the methyl group in diaminodiphenylmethane.

[0078] T of Examples 1-4 and Comparative Examples 1-3 5% , T 10% The residual carbon rate at 800 °C is shown in Table 2. The test method is: take 3-10 mg of sample and put it into the crucible. The test temperature range is 30-800 °C, the heating rate is 10 °C / min, the test atmosphere is N2 atmosphere, and the N2 flow rate is 60 mL / min.

[0079] Table 2 Thermogravimetric temperature and carbon residue rate test results of bismaleimide resin system of Examples 1-4 and Comparative Examples 1-3

[0080] It can be seen from Examples 1-4 and Comparative Example 1 in Table 2 that the T 5% This is mainly due to the presence of long molecular chain structure and some easily decomposable groups in the diamine in the prepolymer, the longer molecular chain and flexible ether bond of bisphenol A diphenyl ether type bismaleimide in some embodiments, which makes T 5% However, all examples have T 5% are all greater than 400°C, and the T 5%All of them are above 410°C, which still have a very high thermal decomposition temperature. The thermal decomposition temperature of Example 2 is basically the same as that of Comparative Example 1. 10% and Y c The T values ​​of Examples 1-3 are slightly higher than those of Comparative Example 1, which is mainly due to the presence of rigid groups such as benzene rings and naphthalene rings in the added prepolymers, and the decomposition temperatures of the rigid groups are relatively high. 5% and T 10% The temperatures are significantly higher than those in Comparative Example 2. This is mainly because a large amount of prepolymer A is added in Comparative Example 2. The large amount of ether bonds and methyl groups in prepolymer A are easily decomposed by heat. 5% The thermal stability of Example 4 is almost no better than that of Comparative Examples 1-3, which is mainly due to the presence of methyl groups in diaminodiphenylmethane due to the addition of diaminodiphenylmethane.

[0081] Figure 3 Shown are the DSC graphs of prepolymer B with three prepolymer A contents in Examples 1-3 of the present invention and the prepolymer in Comparative Example 1. With the addition of prepolymer A, the peak temperature of the blending system did not show obvious changes, and the four systems had similar curing behaviors. The DSC peak temperatures of Comparative Example 1 and Examples 1-3 appeared at 253.6°C, 249.6°C, 250.8°C and 246.5°C, respectively. The starting temperature of the curing reaction was slightly advanced with the addition of prepolymer A. This is mainly because with the addition of prepolymer A, the number of reaction sites in the resin system increased, which increased the probability of collision between active groups.

[0082] Figure 4 The impact strength bar graph of the unnotched cantilever beam impact of Comparative Example 1 (mass fraction of prepolymer A is 0%) and Examples 1-3 of the present invention is shown. It can be seen that the impact strength of the sample of the example first increases and then decreases with the increase of the diamine content. This is because the longer diamine molecular chain reduces the crosslinking density of the cured product, and the diamine contains flexible ether bonds, which improves the spin of the molecular chain, so the impact strength will increase. However, with the increase of the diamine content, the viscosity of the prepolymer increases, which will lead to a large number of defects in the curing process, thereby reducing the impact strength.

[0083] The above embodiments are preferred implementations of the present invention, which mainly demonstrate and describe the main features and basic principles of the present invention. However, the implementation of the present invention is not limited to the above embodiments, and any modification, alteration, substitution, combination, simplification made by any person familiar with the relevant fields and technologies without departing from the spirit and scope of the present invention shall be deemed to be within the scope of the present invention.

Claims

1. A method for preparing a bismaleimide resin system with high impact toughness, characterized in that: The steps include: (1) Preparing prepolymer A: mixing diamine and bisphenol A diphenyl ether type bismaleimide, stirring continuously in a molten state, and performing a prepolymerization reaction to obtain prepolymer A; (2) Preparing a diphenylmethane bismaleimide / diallyl bisphenol A resin system: mixing diphenylmethane bismaleimide and diallyl bisphenol A to prepare a diphenylmethane bismaleimide / diallyl bisphenol A resin system; (3) Preparing prepolymer B: adding prepolymer A to a diphenylmethane bismaleimide / diallyl bisphenol A resin system to form a blending system, and continuously stirring at a specific temperature to perform a prepolymerization reaction to obtain prepolymer B, wherein the amount of prepolymer A added accounts for 3% to 18% of the mass fraction of prepolymer B; (4) The prepolymer B is vacuum degassed at a certain temperature for a period of time, and then cured under a specific curing process to obtain a bismaleimide resin system with high impact toughness.

2. The preparation method according to claim 1, characterized in that: The diamine is 2,7-bis(4-aminophenoxy)naphthalene or diaminodiphenylmethane.

3. The preparation method according to claim 1, characterized in that: The molar ratio of the diamine to bisphenol A diphenyl ether type bismaleimide in step (1) is 1:(1-3), the temperature for prepolymerization of the diamine and bisphenol A diphenyl ether type bismaleimide in step (1) is 140-160° C., the time for prepolymerization of the diamine and bisphenol A diphenyl ether type bismaleimide in step (1) is 10 min-30 min, and the stirring rate is 1000-2000 r / min.

4. The preparation method according to claim 1 or 3, characterized in that: The molar ratio of the diamine to bisphenol A diphenyl ether bismaleimide in step (1) is 1:2, the temperature for prepolymerization of the diamine and bisphenol A diphenyl ether bismaleimide in step (1) is 150° C., and the time for prepolymerization of the diamine and bisphenol A diphenyl ether bismaleimide in step (1) is 20 minutes.

5. The preparation method according to claim 1, characterized in that: In step (2), the molar ratio of diphenylmethane bismaleimide to diallyl bisphenol A is 1:(0.8-1.2).

6. The preparation method according to claim 1 or 5, characterized in that: In step (2), the molar ratio of diphenylmethane bismaleimide to diallyl bisphenol A is 1:0.

87.

7. The preparation method according to claim 1, characterized in that: The amount of prepolymer A added in step (3) accounts for 3%-9% of the mass fraction of prepolymer B, the prepolymerization temperature of the blending system in step (3) is 130-150° C., the prepolymerization time of the blending system in step (3) is 15-45 min, and the stirring rate is 1000-2000 r / min.

8. The preparation method according to claim 1 or 7, characterized in that: The amount of prepolymer A added in step (3) accounts for 6% of the mass fraction of prepolymer B. The prepolymerization temperature of the blending system in step (3) is 140° C. and the prepolymerization time of the blending system in step (3) is 30 min.

9. The preparation method according to claim 1, characterized in that: In step (4), the vacuum degassing temperature of the blended system is 130-150° C., and the vacuum degassing time is 0.5-1 h; the curing adopts a step-by-step temperature rise curing process.

10. The preparation method according to claim 9, characterized in that: In step (4), the step-by-step temperature rise curing process is 180°C / 2h+210°C / 2h+240°C / 4h+260°C / 2h.

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