Preparation method of diamine chain extension toughened bismaleimide resin

Abstract

The invention belongs to the field of new resin materials, and particularly relates to a preparation method of diamine chain extension toughened bismaleimide resin, which comprises the following steps: mixing a diamine chain extender with bismaleimide, heating and melting the mixture, continuously stirring in a molten state, and reacting for a period of time to form a prepolymer A; mixing the prepolymer A and a reactive diluent to form a blending system, heating and melting the blending system, continuously stirring in a molten state, and reacting for a period of time to form a prepolymer B; and defoaming and curing the prepolymer B to obtain the diamine chain extension toughened maleimide resin. According to the preparation method, on the basis of keeping good thermal stability, the manufacturability of the bismaleimide resin in the preparation process is obviously improved, and meanwhile, the toughness of the bismaleimide resin is obviously improved.

Description

Technical Field

[0001] The invention belongs to the field of new resin materials, and specifically relates to a method for preparing a diamine chain-extended toughened bismaleimide resin. Background Art

[0002] Bismaleimide (BMI) resin is a very important thermosetting resin with excellent high temperature resistance. The thermal decomposition temperature of most BMI resins is greater than 450°C. At the same time, bismaleimide resin also has the advantages of low moisture absorption, corrosion resistance, and good processing properties. It is widely used in aerospace, machinery, electronics and other fields.

[0003] Usually, the molecular chain of BMI is relatively short and contains a large number of rigid structures, which leads to a relatively large cross-linking density of BMI resin after curing. This feature gives BMI resin excellent heat resistance, but also makes BMI resin have poor impact toughness after curing, which has become the biggest obstacle to the further application of BMI resin. How to toughen bismaleimide resin while ensuring its excellent heat resistance is the main research direction of BMI resin at present. At present, the main toughening modification methods of BMI resin include diamine compound toughening, allyl compound toughening, thermoplastic resin toughening and inorganic filler toughening.

[0004] The diamine toughening method is an earlier modification method used to toughen BMI resins. The amino group in the diamine can undergo a Michael addition reaction with the carbon-carbon double bond in BMI to extend the BMI chain and reduce the crosslinking density after curing to achieve the purpose of toughening. However, the processability of BMI toughened with diamine is poor. Allyl compound modification is the most common modification method for BMI resins. Liquid allyl compounds can not only effectively improve the toughness of BMI resins, but also act as active diluents, greatly improving the process performance of pure BMI resins. However, it is difficult to obtain ideal toughness for resins modified with allyl compounds alone. Therefore, there is an urgent need for a bismaleimide resin with good processability, thermal stability and toughness and a preparation method thereof. Summary of the invention

[0005] In order to solve the problem of unsatisfactory toughness and processability of bismaleimide in the prior art, the present invention provides a method for preparing a diamine chain-extended toughened bismaleimide resin, specifically, after mixing a diamine chain extender with bismaleimide, heating and melting the mixture, stirring continuously in a molten state, and reacting for a period of time to form a prepolymer A; mixing prepolymer A and an active diluent to form a blending system, heating and melting the blending system, stirring continuously in a molten state, and reacting for a period of time to form a prepolymer B; degassing and curing prepolymer B to obtain a diamine chain-extended toughened maleimide resin. The above-mentioned preparation method significantly improves the processability in the preparation process of bismaleimide resin while maintaining good thermal stability, and significantly improves the toughness of bismaleimide resin.

[0006] To achieve the above purpose, the specific technical solutions provided by the present invention are as follows: A method for preparing a diamine chain-extended toughened bismaleimide resin comprises the following steps: (1) After mixing the diamine chain extender and bismaleimide, the mixture is heated to melt, and the mixture is continuously stirred in a molten state. After a period of reaction, a prepolymer A is formed.

[0007] (2) Prepolymer A and an active diluent are mixed to form a blend system, the blend system is heated to melt, and the blend system is continuously stirred in a molten state, and prepolymer B is formed after a period of reaction.

[0008] (3) Degassing the prepolymer B in a mold and curing it after degassing to obtain a diamine chain-extended and toughened maleimide resin.

[0009] There is a competitive relationship between the reaction of diamine and active diluent with bismaleimide. If the two are mixed at the same time, unreacted diamine may exist in the system. Therefore, in the present invention, the diamine chain extender is first mixed with bismaleimide for reaction, and then mixed with the active diluent for reaction.

[0010] Preferably, the bismaleimide resin in step (1) is diphenylmethane bismaleimide or bisphenol A diphenyl ether bismaleimide, and their structural formulas are shown in Formula I and Formula II respectively: Formula I Formula II

[0011] Diphenylmethane bismaleimide is the most commonly used bismaleimide resin at present. Its thermal decomposition performance is better than that of bisphenol A diphenyl ether bismaleimide. Bisphenol A diphenyl ether bismaleimide has a long molecular chain structure and flexible ether bonds, which will have a beneficial effect on improving toughness.

[0012] Preferably, the diamine chain extender in step (1) is 2,7-bis(4-aminophenoxy)naphthalene or diaminodiphenylmethane, wherein the 2,7-bis(4-aminophenoxy)naphthalene is represented by formula III, and the diaminodiphenylmethane is represented by formula IV: Formula III Formula IV

[0013] 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.

[0014] The carbon-carbon double bonds of the bismaleimide resin after chain extension by diamine and the carbon-carbon double bonds in the active diluent can undergo ene addition reaction to generate an intermediate, which can then undergo Diels-Alder reaction with the bismaleimide group. The subsequent curing and cross-linking can significantly improve the process performance of BMI while toughening it and increase the molding time of the bismaleimide resin during curing.

[0015] Preferably, the molar ratio of the diamine chain extender to bismaleimide in step (1) is 1:(1-3), more preferably 1:2. If the molar ratio of diamine to bismaleimide is too large, it will lead to excessive loss of heat resistance; if the molar ratio of diamine to bismaleimide is too small, the toughening effect will not be obvious. Therefore, it is advisable to control the molar ratio to 1:2.

[0016] Preferably, the prepolymerization temperature in step (1) is 130-180°C, more preferably 150°C; the prepolymerization time is 10-30 min, more preferably 20 min. If the prepolymerization temperature is too high or the time is too long, the resin will solidify too quickly and the viscosity will increase sharply; if the prepolymerization temperature is too low or the time is too short, the prepolymerization degree will be insufficient.

[0017] Preferably, the stirring rate in step (1) is 1000 r / min-2000 r / min.

[0018] Preferably, the active diluent in step (2) is one or more of diallyl bisphenol A, allyl phenol, and bisphenol A diallyl ether.

[0019] Preferably, the molar ratio of the active diluent in step (2) to the diamine chain extender in step (1) is (1-2):1, more preferably 1:1.

[0020] Preferably, the prepolymerization temperature in step (2) is 130-150°C, more preferably 140°C; the prepolymerization time is 0.5-1h, more preferably 0.5h. If the prepolymerization temperature is too high or the time is too long, the resin will solidify too quickly and the viscosity will increase sharply; if the prepolymerization temperature is too low or the time is too short, the prepolymerization degree will be insufficient.

[0021] Preferably, the stirring rate in step (2) is 1000 r / min-2000 r / min.

[0022] Preferably, in step (3), the degassing time of prepolymer B in the mold is 0.5-1 h, and the degassing temperature is 130-150°C.

[0023] Preferably, the curing in step (3) adopts a step-by-step temperature-increasing curing process, and the specific curing process is 150°C / 1 h+180°C / 2 h+220°C / 4 h. Through the step-by-step temperature-increasing curing process, the curing reaction is carried out evenly and the curing is complete.

[0024] The preparation method of 2,7-bis(4-aminophenoxy)naphthalene described in the present invention is not limited and can be prepared by using existing technology, for example, reference can be made to the literature (Polymer Materials Science and Engineering, 2011, 27(11), 1-3). Specifically, it can also be prepared according to the following steps: 1) 2,7-dihydroxynaphthalene, p-nitrochlorobenzene and anhydrous potassium carbonate are mixed in N,N-dimethylformamide 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. The crystals are then filtered and retained, and the crystals are washed with water several times and then dried in an oven to obtain a dinitro compound; 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.

[0025] 2) An appropriate amount of dinitro compound is reacted at 75-105°C for 8-10 h in a N2 atmosphere with ethylene glycol methyl ether as solvent, hydrazine hydrate as reducing agent, activated carbon as adsorbent and FeCl3·6H2O as 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.

[0026] Preferably, the reaction temperature in step 1) is 150° C. and the reaction time is 10 h.

[0027] Preferably, the reaction temperature in step 2) is 100° C. and the reaction time is 8 h.

[0028] In step 1), the structural formulas of 2,7-dihydroxynaphthalene, p-nitrochlorobenzene and dinitro compound are shown in Formula V, Formula VI and Formula VII respectively: Formula V Formula VI Formula VII

[0029] Compared with the prior art, the technical effects of the present invention are: (1) Compared with the conventional diamine toughening agent of bismaleimide resin, the diamine containing naphthalene ring and ether bond used in 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 react with bismaleimide by Michael addition, which can greatly reduce the crosslinking density of bismaleimide after curing and improve the spin of the molecular chain, thereby achieving a toughening effect.

[0030] (2) 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 liquid allyl active diluent introduced in the present invention can not only act as a toughening agent for the bismaleimide resin, but also 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 active diluent can maintain a low viscosity state at 150°C for at least 60 minutes. If no active diluent is added, the viscosity at 150°C for 30 minutes has reached a 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 of the allyl compound modification.

[0031] (3) Diamine can be reacted with maleic anhydride to synthesize bismaleimide resin. Compared with synthesizing bismaleimide resin by reacting diamine with maleic anhydride followed by dehydration cyclization, the present invention directly modifies bismaleimide with diamine, thereby eliminating the steps of ring-opening reaction and dehydration cyclization of diamine with maleic anhydride.

[0032] (4) Prepolymerizing the diamine and bismaleimide and then adding an active diluent can allow the diamine to react with bismaleimide first. If the three are directly blended, there may be a problem of competition between the diamine, allyl bisphenol A and bismaleimide, resulting in the presence of unreacted diamine in the system that affects the resin performance.

[0033] (5) The present invention has a good modification effect on bismaleimide resin, a simple process, and strong practicability. On the basis of maintaining good thermal stability, the processability of the bismaleimide resin preparation process can be significantly improved, and the toughness of the bismaleimide resin can be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The dinitro compound prepared in the specific embodiment of the present invention is 1 H-NMR spectrum; Figure 2 is the diamine prepared in the specific embodiment of the present invention 1 H-NMR spectrum; Figure 3 is the DSC graph of prepolymer A in Examples 1, 2 and 4 prepared in the present invention; Figure 4 1 is the TGA chart of prepolymer A prepared in Examples 1, 2 and 4 of the present invention. DETAILED DESCRIPTION

[0035] 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 embodiments. Various substitutions or changes made according to common technical knowledge and customary means in the art without departing from the above-mentioned method concept of the present invention should be included in the scope of the present invention.

[0036] All materials and reagents used, unless otherwise specified, are commercially available products.

[0037] 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 N,N-dimethylformamide, 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.

[0038] like Figure 1 The above dinitro compound 1H-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.

[0039] 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 and water several times and then dried in an oven at 60°C to obtain 2,7-bis(4-aminophenoxy)naphthalene.

[0040] 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.

[0041] Example 1 A method for preparing a diamine chain-extended and toughened bismaleimide resin, the specific steps are as follows: (1) Preparation of prepolymer A: 2,7-bis(4-aminophenoxy)naphthalene and diphenylmethane bismaleimide were mixed in a molar ratio of 1:2, placed in a three-necked flask, and heated in an oil bath with a magnetic stirring device at a stirring rate of 1000 r / min, a heating temperature of 150°C, and a prepolymerization time of 20 min to obtain prepolymer A.

[0042] (2) Diallyl bisphenol A was heated to 140°C, and then prepolymer A was added to diallyl bisphenol A, and prepolymerized at 140°C and a stirring rate of 1000 r / min for 0.5 h to obtain a uniform blending system, i.e., prepolymer B. The molar ratio of 2,7-bis(4-aminophenoxy)naphthalene, diphenylmethane-type bismaleimide and diallyl bisphenol A in the blending system was 1:2:1.

[0043] (3) The prepolymer B was vacuum degassed at 140°C for 1 h. After the degassed process, the prepolymer was cured according to a curing process of 150°C / 1 h+180°C / 2 h+220°C / 4 h. After the curing process, a sample was obtained.

[0044] Example 2 Preparation method of diamine chain-extended toughened bismaleimide resin, the specific steps are as follows: (1) Preparation of prepolymer A: 2,7-bis(4-aminophenoxy)naphthalene and bisphenol A diphenyl ether type bismaleimide were mixed in a molar ratio of 1:2, placed in a three-necked flask, and heated in an oil bath with a magnetic stirring device at a stirring rate of 1500 r / min, a heating temperature of 180°C, and a prepolymerization time of 20 min to obtain prepolymer A.

[0045] (2) Bisphenol A bisallyl ether was heated to 140°C, and then prepolymer A was added to bisphenol A bisallyl ether, and prepolymerized at 140°C and a stirring rate of 1500 r / min for 0.5 h to obtain a uniform blending system, i.e., prepolymer B. The molar ratio of 2,7-bis(4-aminophenoxy)naphthalene, bisphenol A diphenyl ether type bismaleimide and bisphenol A bisallyl ether in the blending system was 1:2:1.

[0046] (3) The prepolymer B was vacuum degassed at 140°C for 1 h. After the degassed process, the prepolymer was cured according to a curing process of 150°C / 1 h+180°C / 2 h+220°C / 4 h. After the curing process, a sample was obtained.

[0047] Example 3 Preparation method of diamine chain-extended toughened bismaleimide resin, the specific steps are as follows: (1) Preparation of prepolymer A: Diaminodiphenylmethane and diphenylmethane-type bismaleimide were mixed in a molar ratio of 1:2, placed in a three-necked flask, and heated in an oil bath with a magnetic stirring device at a stirring rate of 1500 r / min, a heating temperature of 150°C, and a prepolymerization time of 20 min to obtain prepolymer A.

[0048] (2) Diallyl bisphenol A was heated to 150°C, and then prepolymer A was added to diallyl bisphenol A, and prepolymerized at 150°C and a stirring rate of 1500 r / min for 0.5 h. A uniform blending system, i.e., prepolymer B, was obtained. The molar ratio of diaminodiphenylmethane, diphenylmethane-type bismaleimide and diallyl bisphenol A in the blending system was 1:2:1.

[0049] (3) The prepolymer B was vacuum degassed at 140°C for 1 h. After the degassed process, the prepolymer was cured according to a curing process of 150°C / 1 h+180°C / 2 h+220°C / 4 h. After the curing process, a sample was obtained.

[0050] Example 4 A method for preparing a diamine chain-extended and toughened bismaleimide resin, the specific steps are as follows: (1) Preparation of prepolymer A: 2,7-bis(4-aminophenoxy)naphthalene and diphenylmethane bismaleimide were mixed in a molar ratio of 1:2.5, placed in a three-necked flask, and heated in an oil bath with a magnetic stirring device at a stirring rate of 1500 r / min, a heating temperature of 150°C, and a prepolymerization time of 20 min to obtain prepolymer A.

[0051] (2) Diallyl bisphenol A and allyl phenol were mixed in a molar ratio of 8:2 to obtain a mixed liquid, and then the mixed liquid was heated to 140°C, and then prepolymer A was added to the mixed liquid, and prepolymerized at 140°C and a stirring rate of 1500 r / min for 0.5 h. A uniform blending system, i.e., prepolymer B, was obtained. The molar ratio of 2,7-bis(4-aminophenoxy)naphthalene, diphenylmethane-type bismaleimide, diallyl bisphenol A and allyl phenol in the blending system was 1:2:0.8:0.2.

[0052] (3) The prepolymer B was vacuum degassed at 140°C for 1 h. After the degassed process, the prepolymer was cured according to a curing process of 150°C / 1 h+180°C / 2 h+220°C / 4 h. After the curing process, a sample was obtained.

[0053] Figure 3 The DSC curves of two prepolymers A in Examples 1, 2, and 4 of the present invention at a heating rate of 20°C / min are shown, namely, 2,7-bis(4-aminophenoxy)naphthalene / diphenylmethane type bismaleimide (BD) and 2,7-bis(4-aminophenoxy)naphthalene / bisphenol A diphenyl ether type bismaleimide (PD). BD and PD have similar curing behaviors, with peak temperatures at 267.7°C and 287.1°C, respectively. The main reactions include: Michael addition reaction of double bonds of bismaleimide resin with diamine and self-polymerization of bismaleimide resin. The exothermic peak of PD appears at a higher temperature because the molecular weight of bisphenol A diphenyl ether type bismaleimide is larger, resulting in a larger melt viscosity, which in turn reduces the chance of collision of active groups in the resin system.

[0054] Figure 4 The TG graphs of the two prepolymers A after curing in Examples 1, 2 and 4 of the present invention are shown. It can be seen from the TG graphs that both prepolymers have high thermal decomposition starting temperatures, and the decomposition rate of the PD cured product at high temperature is greater than that of the BD cured product. This is mainly because the PD molecular chain is longer and the flexible ether bonds in the PD will decompose first at high temperature.

[0055] Comparative Example 1 Diphenylmethane bismaleimide and diallyl bisphenol A were added in a molar ratio of 2:1 to prepare a bismaleimide / diallyl bisphenol A binary system. The binary system was prepolymerized at a temperature of 140°C and a stirring rate of 1500 r / min for 1 h to obtain a prepolymer. After the prepolymerization, the prepolymer was vacuum degassed for 1 h. After the degassed, the prepolymer was cured according to the curing process of 150°C / 1 h+180°C / 2 h+220°C / 4 h, and the sample was obtained after the curing.

[0056] Comparative Example 2 Diphenylmethane bismaleimide and diallyl bisphenol A were added in a molar ratio of 2:1 to prepare a bismaleimide / diallyl bisphenol A binary system. The binary system was prepolymerized at 140°C and a stirring rate of 1500 r / min for 0.5 h to obtain a prepolymer. After the prepolymerization, the prepolymer was vacuum degassed for 1 h. After the degassed, the prepolymer was cured according to the curing process of 150°C / 1 h+180°C / 2 h+220°C / 4 h, and the sample was obtained after the curing.

[0057] Comparative Example 3 Diphenylmethane-type bismaleimide and diaminodiphenylmethane were added in a molar ratio of 2:1 to prepare a bismaleimide / diaminodiphenylmethane binary system. The binary system was prepolymerized at 150°C and a stirring rate of 1500 r / min for 20 min to obtain a prepolymer. After the prepolymerization, the prepolymer was vacuum degassed for 30 min. After the degassed, the prepolymer was cured according to the curing process of 150°C / 1 h+180°C / 2 h+220°C / 4 h, and the sample was obtained after the curing.

[0058] 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.

[0059] Table 1 Test results of impact strength, flexural strength and flexural modulus of samples of Examples and Comparative Examples

[0060] From the test results of the samples of Examples 1-4 and Comparative Examples 1-3 in Table 1, it can be seen that when a proper amount of toughening agent is added, the bending properties and impact properties of the modified resin can be improved, and the comprehensive mechanical properties of Example 2 are the best.

[0061] The addition of diamine greatly improves the impact strength of the system. This is mainly because the reaction between diamine and bismaleimide resin will extend the molecular chain of bismaleimide resin and reduce the crosslinking density after curing, thereby achieving the effect of improving impact toughness. It can be seen from Comparative Example 3 and Example 3 that the impact strength, flexural strength and flexural modulus of Comparative Example 3 modified only with diamine are not as good as those of Example 3 modified with diamine and diallyl bisphenol A. This is because diallyl bisphenol A is not added as an active diluent, resulting in excessive viscosity of the resin system composed of diamine and bismaleimide during prepolymerization and degassing. Excessive viscosity will reduce the fluidity of the resin, and bubbles are difficult to remove, resulting in a large number of defects inside. In addition, the addition of active diluents can also enable the diamine and bismaleimide system to maintain a low viscosity for a long time at high temperature during curing, thereby extending the molding time and improving processability.

[0062] It can be seen from Comparative Example 1 and Example 3 that the performance of Comparative Example 1 modified only with an allyl compound is not as good as that of Example 3 modified with a diamine and diallyl bisphenol A. This is because the diamine, as a chain extender, can significantly reduce the crosslinking density after curing.

[0063] The impact strength of Example 2 reaches the maximum value, because the molecular chain of the diamine containing ether bond and naphthalene ring structure is longer than that of diaminodiphenylmethane, and the molecular structure contains two flexible ether bonds, the molecular chain of bisphenol A diphenyl ether type bismaleimide resin is longer than that of diphenylmethane type bismaleimide, and the molecular structure of bisphenol A diphenyl ether type bismaleimide contains two flexible ether bonds. Except for Example 3, the bending strength and modulus of all the samples of the examples are greater than those of the comparative samples, which is due to the effect brought about by the introduction of rigid structures such as naphthalene rings.

[0064] Table 2 shows the weight loss 5% temperature (T 5% )、10% weight loss temperature(T 10% ) and 800℃ residual carbon rate (Y c ), the test method is: take 3-10 mg of sample and put it into the crucible, the test temperature range is 30-800℃, the heating rate is 10℃ / min, the test atmosphere is N2 atmosphere, and the N2 flow rate is 60 mL / min.

[0065] Table 2 Thermal decomposition performance test results of examples and comparative examples

[0066] It can be seen that the embodiment system T with the addition of diamine 5% and T 10%The results are lower than those of Comparative Examples 1 and 2 modified with diallyl bisphenol A only. This is because the influence of some flexible bonds and long chain structures in the diamine will lead to T 5% and T 10% In all embodiments, the thermal decomposition performance is basically maintained at the same level, and still has a high temperature resistance. The T of Example 1 5% , T 10% and Y c It is the highest among all the embodiments. This is because the bismaleimide used in Embodiment 1 is diphenylmethane bismaleimide, and the diamine used is 2,7-bis(4-aminophenoxy)naphthalene. The thermal decomposition performance of diphenylmethane bismaleimide is better than that of bisphenol A diphenyl ether bismaleimide, and the thermal decomposition performance of 2,7-bis(4-aminophenoxy)naphthalene is better than that of diaminodiphenylmethane due to the presence of rigid groups. Therefore, the thermal decomposition performance of Embodiment 1 is the best.

[0067] Y of Example 1-4 c Compared with Comparative Examples 1-3, the Y values ​​of Comparative Examples 1-3 decreased. This is because pure bismaleimide has good thermal stability. In Comparative Examples 1-3, the proportion of bismaleimide is relatively large. In the embodiments, allyl compounds are added. Some groups in the allyl compounds are easily decomposed. Therefore, the Y values ​​of Comparative Examples 1-3 at 800°C are c All of them are higher than Y of Examples 1-4 c。

[0068] The above results show that the bismaleimide resin prepared by the technical solution of the present invention can significantly improve the processability in the preparation process of the bismaleimide resin while maintaining good thermal stability, and at the same time significantly improve the toughness of the bismaleimide resin.

[0069] 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 diamine chain-extended toughened bismaleimide resin, characterized in that: The following steps are involved: (1) After mixing the diamine chain extender and bismaleimide, the mixture is heated to melt, and the mixture is continuously stirred in a molten state, and a prepolymer A is formed after a reaction for a period of time; (2) Prepolymer A and a reactive diluent are mixed to form a blend system, the blend system is heated to melt, and the blend system is continuously stirred in a molten state, and after a period of reaction, prepolymer B is formed; (3) Degassing the prepolymer B in a mold and curing it after degassing to obtain a diamine chain-extended and toughened maleimide resin.

2. The method for preparing the diamine chain-extended toughened bismaleimide resin according to claim 1, characterized in that: The bismaleimide resin in step (1) is diphenylmethane type bismaleimide or bisphenol A diphenyl ether type bismaleimide.

3. The method for preparing the diamine chain-extended toughened bismaleimide resin according to claim 1, characterized in that: The diamine chain extender in step (1) is 2,7-bis(4-aminophenoxy)naphthalene or diaminodiphenylmethane.

4. The method for preparing the diamine chain-extended toughened bismaleimide resin according to claim 1, characterized in that: The molar ratio of the diamine chain extender to bismaleimide in step (1) is 1:(1-3), the prepolymerization temperature is 130-180° C., and the prepolymerization time is 10-30 min.

5. The method for preparing the diamine chain-extended toughened bismaleimide resin according to claim 1 or 4, characterized in that: The molar ratio of the diamine chain extender to bismaleimide in step (1) is 1:2, the prepolymerization temperature is 150° C., and the prepolymerization time is 20 min.

6. The method for preparing the diamine chain-extended toughened bismaleimide resin according to claim 1, characterized in that: The stirring rate in step (1) and step (2) is 1000 r / min-2000 r / min.

7. The method for preparing the diamine chain-extended toughened bismaleimide resin according to claim 1, characterized in that: The active diluent in step (2) is one or more of diallyl bisphenol A, allyl phenol, and bisphenol A diallyl ether.

8. The method for preparing the diamine chain-extended toughened bismaleimide resin according to claim 1, characterized in that: The molar ratio of the active diluent in step (2) to the diamine chain extender in step (1) is (1-2):1, the prepolymerization temperature is 130-150° C., and the prepolymerization time is 0.5-1 h.

9. The method for preparing the diamine chain-extended toughened bismaleimide resin according to claim 1 or 8, characterized in that: The molar ratio of the active diluent in step (2) to the diamine chain extender in step (1) is 1:1; the prepolymerization temperature is 140° C.; and the prepolymerization time is 0.5 h.

10. The method for preparing the diamine chain-extended toughened bismaleimide resin according to claim 1, characterized in that: In step (3), the degassing time of prepolymer B in the mold is 0.5-1 h, and the degassing temperature is 130-150°C; the curing adopts a step-by-step temperature rise curing process, and the specific curing process is 150°C / 1 h+180°C / 2 h+220°C / 4h.

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