A bio-based bismaleimide resin, a preparation method and application thereof

Abstract

The application belongs to the technical field of materials, and provides a bio-based bismaleimide resin and a preparation method and application thereof, the resin being prepared by copolymerization of curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide. The curcumin allyl ether has a beta-diketone conjugated system, and is prepared by nucleophilic substitution reaction of curcumin and allyl bromide in a potassium carbonate acetone system; when prepared, the two are cured in stages at 150-240 DEG C to form a high crosslinking network, and a vacuum degassing and curing process is combined. The bio-based bismaleimide resin provided in the application has a curing peak temperature that is 20-30 DEG C lower than that of a traditional BD resin, a Tg that is nearly 90 DEG C higher than that of the BD resin, a carbon residue rate at 800 DEG C that is greater than or equal to 42%, an LOI that is greater than or equal to 37%, reaches a UL-94 V-0 level, a THR that is as low as 12.4 kJ / g, less flammable volatile matter at high temperatures, and a high degree of carbonization of residual carbon.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of materials, and particularly relates to a bio-based bismaleimide resin and a preparation method and application thereof. BACKGROUND

[0002] Bismaleimide (BMI) resin has become a key basic material in the fields of aerospace composites, printed circuit boards (PCB) and high-temperature electronic packaging materials, etc. due to its excellent thermal stability, mechanical properties and chemical stability, especially in scenarios with strict requirements for material temperature resistance and reliability.

[0003] However, traditional BMI resins (such as resins mainly based on N,N'-4,4'-diphenylmethane bismaleimide (BDM)) have inherent technical defects: on the one hand, they have high brittleness and narrow processing window, and the curing temperature usually needs to be higher than 250℃, resulting in large processing energy consumption, poor process compatibility and difficulty in adapting to low-cost mass production requirements; on the other hand, their flame retardant performance is insufficient, and additional flame retardants need to be added to achieve the required flame retardant grade, which not only increases the material preparation process and cost, but also may have a negative impact on the thermal mechanical properties of the resin.

[0004] To solve the above problems, the existing technology often uses petroleum-based co-monomers (such as 2,2'-diallyl bisphenol A (DABPA)) to modify BMI resins, and improves the processability and toughness by introducing flexible segments. However, DABPA has endocrine disrupting potential, which does not meet the current demand for environmentally friendly and sustainable development in the field of materials, and the glass transition temperature (Tg) of the modified resin is usually lower than 310℃, and the carbon residue rate at 800℃ is less than 31%, so the thermal stability and flame retardant performance are still difficult to meet the dual requirements of high thermal stability and intrinsic flame retardancy in high-end fields such as high-frequency high-speed communication and aerospace.

[0005] Meanwhile, biomass resources have become an important research direction for modifying monomers of BMI resins due to their advantages of being renewable and environmentally compatible. In the prior art, there are schemes for modifying BMI resins by using DBB derived from camphor wood alcohol, AER (allyl resveratrol ether), and ACDE derived from cashew nut shell liquid, and the like. Although some modified resins can achieve Tg of 388℃ and LOI of 37.7%, there are still the following deficiencies: first, the synthesis of some bio-based monomers needs to use high-boiling polar solvents (such as DMF and DMSO) or strong alkali (such as NaH), which may cause metal salts and high-boiling solvents to remain in the monomers, thereby affecting the uniformity of subsequent resin curing and dielectric properties; second, the copolymerization reaction sites of bio-based monomers and BDM are single, and the crosslinked network structure of the cured resin is simple, which is difficult to simultaneously achieve the synergistic improvement of “low curing temperature, high thermal stability, and wide processing window”, and especially in the sub-scenarios of low dielectric loss required for high-frequency and high-speed copper-clad plates and wide temperature range bonding stability required for aviation structural adhesive films, there is still a gap in performance.

[0006] Therefore, the prior art is difficult to simultaneously achieve low curing temperature, wide processing window, and good flame retardancy while maintaining high glass transition temperature. SUMMARY

[0007] The purpose of the embodiments of the present application is to provide a bio-based bismaleimide resin and a preparation method thereof, aiming to solve the problem that the prior art is difficult to simultaneously achieve low curing temperature, wide processing window, and good flame retardancy while maintaining high glass transition temperature.

[0008] The embodiments of the present application provide a bio-based bismaleimide resin, which is copolymerized from curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide; wherein the curcumin allyl ether has a β-diketone conjugated system, is prepared by nucleophilic substitution reaction of curcumin and allyl bromide in a potassium carbonate and acetone solvent system, and has a molecular weight of 488 g / mol; and the N,N'-4,4'-diphenylmethane bismaleimide is formed into a high crosslinking degree network by being segmentedly cured at 150-240℃.

[0009] The embodiments of the present application also provide a preparation method of the bio-based bismaleimide resin, comprising:

[0010] In step S1, curcumin and allyl bromide are reacted in a potassium carbonate and acetone solvent system under the condition of 60℃ and nitrogen protection for 24 h to obtain curcumin allyl ether;

[0011] Step S2, mixing curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide at a molar ratio of imide group to allyl group of 0.6-1.0, melting and stirring at 150°C until a transparent liquid is formed, standing for 30 min to obtain a prepolymer;

[0012] Step S3, degassing the prepolymer under vacuum for 30 min, and then performing staged temperature curing, with a temperature program of 150°C / 2 h→180°C / 2 h→200°C / 2 h→220°C / 2 h→240°C / 4 h, and cooling to obtain the bio-based bismaleimide resin.

[0013] The application also provides an application of the bio-based bismaleimide resin in high-frequency high-speed copper-clad plates, aviation structural adhesive films, or high-temperature electronic packaging materials.

[0014] The application synthesizes curcumin allyl ether with a β-diketone conjugated system by taking curcumin as a raw material, and combines the curcumin allyl ether with N,N'-4,4'-diphenylmethane bismaleimide, a vacuum degassing process, and a staged temperature curing process to form a high-crosslinking-degree network, thereby preparing the bio-based bismaleimide resin, which brings about the following remarkable technical effects:

[0015] In terms of thermal performance and processability, the synergism of low curing temperature (the curing peak temperature is reduced by 20-30°C compared with traditional BD resins, and is as low as about 230°C), high glass transition temperature (Tg≥390°C, and some samples are higher than 400°C, which is increased by nearly 90°C compared with BD resins), and wide processing window is achieved, and the apparent viscosity of the prepolymer is 0.5-2 Pa・s at 120°C, which is suitable for the preparation of prepregs or adhesive films;

[0016] In terms of flame retardation and thermal stability, the carbon residue rate of the resin is ≥42% at 800°C, the limiting oxygen index (LOI) is ≥37%, reaches the UL-94 V-0 level, the total heat release (THR) is as low as 12.4 kJ / g, the flammable volatile products are reduced at high temperatures, and the degree of graphitization of the carbon residue is higher;

[0017] In terms of synthesis and industrialization adaptability, the synthesis of curcumin allyl ether adopts a mild and clean system of acetone / potassium carbonate / allyl bromide, avoids the use of strong alkali and high-boiling solvents, and the residues of the solvents, and the use of hazardous chemicals, the solvent is easy to recover, the post-treatment is simplified, and the impurities are few, which is highly coupled with the subsequent melting prepolymerization and staged curing process, and can support the needs of high-end applications such as high-frequency high-speed copper-clad plates, aviation structural adhesive films, and high-temperature electronic packaging materials in terms of material performance and industrialization. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1The structural characterization of AEC provided for the embodiments of this application includes: (a) the ¹H NMR spectrum of AEC, (b) the Fourier transform infrared spectrum of AEC, and (c) the mass spectrum of AEC.

[0019] Figure 2 Differential scanning calorimetry (DSC) curves of BA(a) and BD(b) resins provided in the embodiments of this application;

[0020] Figure 3 TGA and DTG curves of cured BA(a) and BD(b) resins provided for embodiments of this application;

[0021] Figure 4 The following images are provided for embodiments of this application: (a) the first combustion of BD-0.87 resin flame, (b) the second combustion of BD-0.87 resin flame, (c) the first combustion of BA-0.87 resin flame, and (d) the second combustion of BA-0.87 resin flame.

[0022] Figure 5 SEM images of BA-0.87(a)(b) and BD-0.87(c)(d) resins provided for embodiments of this application at 1 μm and 2 μm, respectively;

[0023] Figure 6 Raman spectra of (a) BA-0.87 resin and (b) BD-0.87 resin provided for embodiments of this application;

[0024] Figure 7 TGA and DTG curves of BA-0.87 and BD-0.87 cured resins provided for embodiments of this application;

[0025] Figure 8 Fourier transform infrared spectra of the pyrolysis products of BA-0.87(a) and BD-0.87(b) resins provided for embodiments of this application at typical temperatures;

[0026] Figure 9 Three-dimensional infrared spectra of the pyrolysis products of BA-0.87(a) and BD-0.87(b) resins provided for embodiments of this application;

[0027] Figure 10 The absorbance versus temperature curves of the pyrolysis products of BA-0.87 and BD-0.87 resins provided for the embodiments of this application are as follows: (a) H2O, (b) hydrocarbons, (c) CO2, (d) NO2, (e) aromatic compounds, and (f) organic nitrogen compounds. Detailed Implementation

[0028] In order to make the purposes, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application.

[0029] The embodiment of the present application provides a kind of bio-based bismaleimide resin, which is made of curcumin allyl ether (AEC) and N,N'-4,4'-diphenylmethane bismaleimide (BDM) copolymerization;Among them, the curcumin allyl ether has β-diketone structure and symmetrical double allyl site, which is prepared by nucleophilic substitution reaction of curcumin and allyl bromide in potassium carbonate and acetone solvent system, and the molecular weight is 488 g / mol, and N,N'-4,4'-diphenylmethane bismaleimide is segmented cured at 150-240 DEG C to form a high cross-linking network.The glass transition temperature of the bio-based bismaleimide resin is greater than or equal to 390 DEG C, the limiting oxygen index is greater than or equal to 37%, the UL-94 flame retardant grade is V-0 level, and the carbon residue rate at 800 DEG C is greater than or equal to 42%.

[0030] The embodiment of the present application provides a kind of bio-based bismaleimide resin preparation method described above, comprising:

[0031] Step S1, under the condition of nitrogen protection at 60 DEG C, curcumin and allyl bromide are reacted in potassium carbonate and acetone solvent system for 24 h to obtain curcumin allyl ether.

[0032] In the synthesis process of curcumin allyl ether, acetone / potassium carbonate / allyl bromide system is used, and double etherification can be completed at 60 DEG C for 24 h;Compared with traditional NaH / DMF strong alkali system (alkaline, high temperature, residual metal / halide salt) or Mitsunobu method (need PPh3 / DEAD dangerous chemicals, by-product salt is difficult to remove), the by-product (self-condensation / oxidation) and metal / phosphine salt residue can be reduced, the product color is lighter, and the dielectric and thermal stability is easier to control.

[0033] acetone solvent selected has medium polarity, low boiling point, easy recovery and low toxicological burden, avoiding the problems of difficulty in removing DMF / DMSO with high boiling and high viscosity, affecting subsequent prepolymerization / curing, facilitating batch recovery and purification and shortening the post-treatment link; low-temperature reaction at 60℃ does not require high-temperature reflux or strong alkali activation, has lower energy consumption and shorter thermal history, can reduce the degradation and coloring risk of curcumin β-diketone conjugated skeleton, and ensure the subsequent flame-retardant charring stability; the selected allyl bromide has higher nucleophilic activity, and can realize etherification at both ends under mild alkali, compared with allyl chloride (which requires stronger alkali / high temperature) or Mitsunobu method (single / double substitution ratio is unstable), the double substitution selectivity and reaction rate are higher, and the by-products are less; the synthesis process is only direct etherification -> cooling -> extraction and purification, without protection-deprotection or oxidation-reduction steps, and does not use metal Lewis acid / phase transfer catalyst, compared with the Mitsunobu method which needs to handle a large amount of by-product salt and the strong alkali / phase transfer process which easily introduces ion residues, the impurity spectrum is simpler, and by 1 H NMR, FT-IR and HRMS triple characterization verify the product structure and purity (hydroxyl peak disappears, 1248 cm -1 ether bond absorption, [M+H] + ≈489.22); the synthesized AEC can directly enter the 150℃ melting prepolymerization and five-stage curing process due to the small amount of residue, which can reduce the curing peak temperature, widen the processing window, reduce the heat / color / impurity risk in the whole process from monomer synthesis to subsequent process, adapt to industrialization and ensure the stable dielectric properties of the final bio-based bismaleimide resin.

[0034] Optionally, step S1 is specifically:

[0035] Dissolve 1 gram of curcumin in 40 milliliters of acetone, add 3.7 grams of potassium carbonate and 14 grams of bromine propylene to the solution. Heat the mixture to 60℃ and keep the temperature under nitrogen for 24 hours, filter the reaction solution, extract, and remove the solvent under reduced pressure to obtain curcumin allyl ether.

[0036] Preferably, in step S1, 0.02-0.05 wt% of a free radical inhibitor MEHQ or BHT can be added to the reaction system to inhibit the allyl side polymerization reaction.

[0037] Step S2, mix curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide at a molar ratio of imide groups to allyl groups of 0.6-1.0, melt and stir at 150℃ until a transparent liquid is formed, and stand for 30 min to obtain a prepolymer.

[0038] Preferably, in step S2, curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide are mixed at a molar ratio of imide groups to allyl groups of 0.87.

[0039] Step S3, degassing the prepolymer under vacuum for 30 min, then performing staged temperature curing, the temperature program is 150℃ / 2 h→180℃ / 2 h→200℃ / 2 h→220℃ / 2 h→240℃ / 4 h, cooling to obtain the bio-based bismaleimide resin.

[0040] The bio-based bismaleimide resin and the preparation method thereof provided by the present application are described in detail below with specific examples, but the protection scope of the present application is not limited to the following examples. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents, etc. used are commercially available unless otherwise specified.

[0041] Raw materials: BDM and DABPA (purity 90%) were provided by Shanghai Hejiu Chemical Co., Ltd. Curcumin (purity 98%) was purchased from Bide Pharmaceutical Technology Co., Ltd. Bromopropylene and potassium carbonate were both analytical grade commercial reagents purchased from Shanghai Aldrin Biochemical Technology Co., Ltd. All other reagents were analytical grade and used without further purification.

[0042] Example 1: Synthesis of allyl curcumin ether (AEC)

[0043] Dissolve 1 gram of curcumin in 40 milliliters of acetone, add 3.7 grams of potassium carbonate and 14 grams of bromopropylene to the solution. Heat the mixture to 60℃ and maintain the temperature for 24 hours under nitrogen. Filter, extract and reduce the pressure to remove the solvent. The target product is a yellow solid weighing 1.04 grams with a total yield of 80%. The synthesis route is as follows:

[0044]

[0045] Example 2: Synthesis of BDM / AEC (BA) bio-based bismaleimide resin

[0046] Mix curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide at a molar ratio of 0.7, 0.87, 1.0 of imide groups to allyl groups, melt and stir at 150℃ until a transparent liquid is formed, and then stand for 30 min to obtain a prepolymer. Degas the prepolymer under vacuum for 30 min, then transfer it into a mold, and then perform staged temperature curing, the temperature program is 150℃ / 2 h→180℃ / 2 h→200℃ / 2 h→220℃ / 2 h→240℃ / 4 h, and then cool and demold to obtain the bio-based bismaleimide resin, which is labeled as BA-0.7, BA-0.87, and BA-1.0, respectively. The synthesis route is as follows:

[0047]

[0048] Synthesis of BDM / DABPA (BD) resin

[0049] 2,2'-diallyl bisphenol A and N,N'-4,4'-diphenylmethane bismaleimide were mixed at 0.7, 0.87, 1.0 molar ratio of imide group to allyl group, respectively, and stirred at 150°C until a transparent liquid was formed. The prepolymers were obtained after 30 min of standing. The prepolymers were degassed under vacuum for 30 min, transferred into a mold, and then cured by stepwise heating at 150°C / 2 h→180°C / 2 h→200°C / 2 h→220°C / 2 h→240°C / 4 h. The BD resins were obtained after cooling and demolding, and were labeled as BD-0.7, BD-0.87, and BD-1.0, respectively. The synthesis route is as follows:

[0050]

[0051] The structure of the allyl curcumin ether (AEC) synthesized in Example 1 above was characterized, as shown in Figure 1 Figure 1 (a) shows the 1H NMR spectrum of AEC, in which characteristic peaks of the allyl ether group can be observed. The characteristic peak of the proton at 7.26 ppm corresponds to CDCl3, and the peaks at 7.68 ppm (Hg, Hg'), 6.91 ppm (He, He'), 6.84 ppm (Hh, Hh'), 6.06 ppm (Hb, Hb', Hb"), and 5.25 ppm (Ha, Ha', Ha") correspond to the protons on the allyl double bond in AEC, and the peaks at 4.65 ppm (Hc, Hc') and 3.93 ppm (Hi, Hi') correspond to the single bond protons thereof. In Figure 1 (b) In the Fourier transform infrared spectrum, the peak at 3400 cm -1 indicates the presence of hydroxyl groups in the raw material curcumin. However, this peak completely disappears in the AEC product. The methylene group is observed at 2964 cm -1 , and the ether bond in AEC is observed at 1248 cm -1 . These observations indicate that curcumin has completely reacted to form the corresponding ether compound. Figure 1 (c) shows that the expected molecular weight of the allyl curcumin ether is confirmed by electrospray ionization Fourier transform mass spectrometry (ESI-FTMS) technology. The fragmentation peak and charge mass ratio signal position of the target ion (M: C30H32O6) are [M+H] + : 489.22483, and the literature value is 489.2287. [M+Na+H2O] + : 529.25587. The molecular weight of AEC is 488. ​

[0052] Further, the curing reactivity of the BD resin provided by the above-mentioned comparative example and the BA resin provided by Example 2 was detected by differential scanning calorimetry. Figure 2 The differential scanning calorimetry curves of the BD and BA resins are shown. Each curve presents a single curing exothermic peak, and the exothermic peak of the BD resin appears at about 250°C, while the curing temperature of the BA resin is lower than that of the BD resin, indicating that the BA resin has a wider processing window. The cause may be attributed to the following three points: the Claisen rearrangement reaction occurring in the AEC structure; the increased crosslinking density caused by the high functional group number of the curcumin allyl ether. In a high crosslinking density system, the limited molecular chain spacing may inhibit the diffusion of reactants and the reaction rate, thereby delaying the release of reaction heat and further reducing the peak curing temperature; there is another possibility: the reaction of BDM and AEC occurs at more positions at the same time, and the reaction heat is dispersed to multiple reaction points instead of being released at a specific temperature point, resulting in a decrease in the peak curing temperature.

[0053] The main indicators for evaluating the heat resistance of thermosetting resins are mainly two key indicators: DMA (dynamic mechanical analysis) and TGA (thermogravimetric analyzer). DMA has been proven to be the most effective method for characterizing polymer materials. TGA is used to evaluate the thermal weight loss characteristics of thermosetting resins. "T d5% " represents the temperature at which the mass loss reaches 5% during thermal decomposition, while "T dmax " refers to the peak temperature of the DTG curve, which is also the temperature of the maximum mass loss rate. "Y 800℃ " refers to the carbon residue rate of the resin at a high temperature of 800°C, i.e., the mass percentage of the remaining solid carbonized material at 800°C after thermal decomposition of the resin relative to the initial sample mass. The glass transition temperature (Tg) is usually defined as the temperature corresponding to the peak of the tangent delta curve. The test results are shown in Figure 3 and Table 1.

[0054] Table 1 Typical parameters of cured BD resin and BA resin in TGA and DMA tests

[0055]

[0056] As shown in Figure 3 , the increase in allyl content leads to a decrease in T d5%The decrease in Tg is associated with a decrease in the glass transition temperature (Tg) and can be attributed to the chain-elongation effect of the allyl group, which has been shown to decrease the crosslinking density of the resin and thus promote higher mobility of the polymer units. Nonetheless, the BA resins exhibit higher Tg values than the BD resins. It is worth noting that the trends in the storage modulus and loss modulus in the figure indicate that the Tg values of the BA-0.7 and BA-0.87 resins exceed 400 °C. The Tg of the cured product of the BA-1.0 resin was measured to be 389.85 °C, which is about 90 °C higher than that of the BD-1.0 resin.

[0057] As can be clearly seen from the DMA results, the Tg values of the cured products of the BA resins reflect their excellent heat resistance - generally, the Tg value represents the maximum use temperature of a cured product of a thermosetting resin.

[0058] The mechanical properties of the BA-0.87 and BD-0.87 resins were the best according to the nanoindentation test, so the BA-0.87 and BD-0.87 resins were selected for the flame retardant test. The test results are shown in Table 2 and Figure 4

[0059] Table 2 Typical indicators of cured resins in the flame retardant test

[0060]

[0061] As can be seen from Table 2, the limiting oxygen index (LOI) of the BA-0.87 resin is higher than that of the BD-0.87 resin, which is consistent with the results of the coke yield of the cured resins at 800 °C in the thermogravimetric analysis. Figure 4 The UL-94 of the BD resins and the BA resins in the flame retardant test was recorded. As Figure 4 shown, the combustion phenomena of the BA and BD resins were investigated by the UL-94 test. The combustion time of the BA-0.87 resin after two ignitions was less than 10 seconds, and no drips were generated. Similarly, the combustion time of the BD-0.87 resin after two ignitions was less than 30 seconds, and no drips were generated. The experiment proves that the BA resins have the easy-to-extinguish feature and exhibit excellent flame retardant performance.

[0062] ​Microscale calorimetry testing (MCC) is a technique that explores the correlation between polymer chemical structure and flammability behavior based on oxygen consumption theory. Key parameters include peak HRR, peak heat release temperature (TPHRR), total heat release (THR), and heat release capacity (HRC). The scientific community generally agrees that HRC is the best predictor of flammability, as a lower value indicates greater flame retardancy. The specific heat capacity of BA resin (291.5 J / (g·K)) is lower than that of BD-0.87 resin (305.6 J / (g·K)). In addition, the total heat release test results show that the total heat release of the cured BA-0.87 resin is only 12.4 kJ / g, which is much lower than that of the cured BD-0.87 resin (20.2 kJ / g). Both the heat release rate and the total heat release data confirm that BA resin is superior to BD resin in terms of suppressing heat release rate and total amount.

[0063] Further, to gain a deeper understanding of the flame retardant mechanism of BA resin cured products, the morphology and structure of the char formed after combustion testing were analyzed. In addition, the volatiles produced during thermal degradation were analyzed. First, the morphological characteristics of the carbon layer remaining on the surface of the samples after LOI testing were characterized by scanning electron microscopy (SEM), as shown in Figure 5 (a), (b), (c), and (d). The scanning electron microscope images show that the residual char structure of BD-0.87 and BA-0.87 resin cured products is highly similar, despite the difference in char yield. Given the significant difference in gas molecule size and pore size, it is reasonable to infer that both structures are conducive to gas permeation. The two samples may have comparable thermal insulation performance, indicating that the flame retardant mechanism of BA resin may not rely on the formation of traditional dense carbon layers. Therefore, Raman spectroscopy was used to analyze the residual carbon to assess the degree of graphitization. The resulting Raman spectra are shown in Figure 6 (a) and (b).

[0064] As shown by the Raman spectroscopy results, there is a significant difference in the degree of graphitization between the residual carbon sample after BA-0.87 resin combustion and the residual carbon sample after BD-0.87 resin combustion, which is mainly measured by the intensity ratio of D peak to G peak. In Raman spectroscopy, the D peak (about 1350 cm -1 ) has been proven to be related to defects or disordered structures in carbon materials, while the G peak (about 1580 cm -1 ) corresponds to ordered graphite structures of sp² hybridized carbon atoms (E2g vibration mode). A lower I D / I G ratio indicates a higher degree of graphitization of the sample, meaning a larger sp² carbon domain and fewer structural defects. As shown by BA-0.87 resin, the I D / I GThe ratio was measured to be 0.72, far below the established threshold of 1. This result indicates a significant increase in graphitization degree - a low ratio (e.g. <0.9) means that the carbon skeleton is mainly composed of sp2 hybridized carbon atoms. Such samples have a low defect density, and their structure is arranged close to the ideal graphite sequence. In contrast, the I D / I G ratio of the BA-0.87 sample was 0.93, still below 1 but significantly higher than that of the BD-0.87 sample. This ratio close to 1 indicates a relatively low degree of graphitization, suggesting the presence of more disordered regions or defects (e.g. grain boundaries, vacancies, or heteroatom doping) in the carbon structure. The increased I D / I G value is typically associated with partially graphitized carbon materials, which are characterized by small sp2 carbon domains or poor domain continuity. Therefore, the improved flame retardancy of the BA-0.87 resin cured material compared to the BD-0.87 resin cured material is mainly due to the increase in the content of carbonized residues and the enhancement of their own stability. This increase in carbonized residues and the enhancement of their stability are mainly due to the characteristics of the internal structure of AEC - this structure not only promotes the formation of carbonized products, but also enhances the degree of graphitization.

[0065] As shown in FIG. 7, the TGA and DTG curves of the BD-0.87 and BA-0.87 resin cured materials obtained by TG-IR test show that the thermal resistance of the BA-0.87 resin cured material is better, not only the Td value (5% residual carbon content) is higher than that of the BD-0.87 resin cured material, but also the residual carbon content at 800°C is as high as 43.06%, which is 16.08% higher than the residual carbon content of 26.98% of the BD-0.87 resin cured material at the same temperature. At the same time, it can be observed from the DTG curve that the thermal decomposition rate of the BA-0.87 resin cured product is significantly lower than that of the BD-0.87 resin cured product; the higher residual carbon content of the BA-0.87 resin cured material indicates that it produces less volatile matter during thermal decomposition, which is due to the fact that more cured products of the material are converted into residual carbon and remain on the surface and inside of the material during thermal decomposition.

[0066] FIG. 8 presents the Fourier transform infrared spectra of the thermal decomposition products of the BA-0.87 and BD-0.87 resin cured materials at a specific temperature, and there are obvious differences in the characteristics of the thermal decomposition products of the two. Among them, the BD-0.87 resin cured product (see Figure 8 (b)) appears a characteristic peak of CO2 (2363, 2330 and 669 cm d5% ) at 428°C (i.e. its T -1This marks the start of thermal decomposition, at which point the intensity of the characteristic peak increases and the characteristic peaks of other decomposition products begin to appear, at 3650, 1374, 1616, 1507, and 1176 cm⁻¹. -1 The peak values ​​at these points correspond to H2O, nitrogen dioxide (NO2), nitrogen oxides (NO2), and organic nitrogen compounds, respectively, up to T. dmax The characteristic peaks of volatile substances reach their most significant state at 479℃, during which combustible decomposition products (such as hydrocarbons) correspond to 3017 and 2971 cm⁻¹. -1 (At its peak) continued to volatilize, while carbonyl compounds at 1717 cm⁻¹... -1 The characteristic spectrum is observed at this location; while BA-0.87 resin-cured material (see...) Figure 8 (a) The reduced number of absorption peaks observed at a specified temperature indicates a decrease in the variety of thermal decomposition products.

[0067] Figure 9 shows BA-0.87 ( Figure 9 a) and BD-0.87 ( Figure 9 b) The three-dimensional infrared spectrum of the resin pyrolysis products, combined with the absorbance curves of the pyrolysis products in Figure 10, shows that during the pyrolysis of BA-0.87 resin cured material, the release of H2O (Figure 10a), CO2 (Figure 10c) and NO2 (Figure 10d) is significantly increased; conversely, the release of various combustible gases shows a decreasing trend, including aromatic compounds shown in Figure 10(e) and nitrogen-containing organic compounds and other hydrocarbon-related substances shown in Figure 10(f).

[0068] It is worth noting that the curing mechanism of the BA resin in this application is that after AEC replaces DABPA, the conjugated system of dielyl and β-diketone in its structure provides abundant reaction sites. The specific curing reaction exhibits a multi-mechanism parallel characteristic, including: ① ene / Michael addition reaction of allyl and maleimide double bond; ② [3,3]-Claisen rearrangement of allyl ether during heating, generating ortho-allyl substituted phenol, which further reacts with BMI double bond; ③ free radical self-polymerization reaction of BMI double bond; ④ allyl free radical coupling and curcumin skeleton condensation-carbonization reaction at high temperature. The above multiple reactions synergistically construct a three-dimensional network structure with high crosslinking density, and this curing mechanism is corroborated by infrared and thermal analysis results: during the curing process, the intensity of C=C absorption peak decreases significantly with increasing temperature, and the position of C=O peak shifts slightly to the red, confirming the gradual consumption of double bond and change of imide environment; while 1248 cm⁻¹ -1The ether bond peak remained stable, indicating that the AEC skeleton structure was not damaged. Compared with the BD system, the curing exothermic peak temperature of the BA system was confirmed to decrease by 20-30°C by DSC test, and the reaction process was more gentle, which was attributed to the more abundant reaction sites, which made the exothermic process uniformly dispersed. In addition, the carbonization behavior of the BA resin is closely related to its flame retardant mechanism: the β-diketone structure in the curcumin skeleton can promote the carbonization and graphitization process at high temperature. The Raman spectrum shows that the I D / I G The ratio (0.72) of the BA-0.87 sample was lower than that of the BD-0.87 (0.93), indicating that the order degree of the carbonized layer was significantly improved; at the same time, the TG-IR test confirmed that the release amount of flammable volatile products of the BA system was reduced. The above results show that the AEC structure not only provides sufficient crosslinking active sites for the resin, but also endows the system with excellent intrinsic flame retardant properties. In summary, the BA resin of the present application realizes the synergistic consideration of low curing temperature, wide processing window, high glass transition temperature, high crosslinking density and excellent heat-resistant and flame-retardant properties. The root of this comprehensive performance advantage lies in the synergistic effect of the reaction activity and carbonization ability formed by the conjugated structure of the double allyl ether and the β-diketone in the AEC structure.

[0069] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of protection of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

[0070] The above only describes the preferred embodiments of the present application, and does not limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A bio-based bismaleimide resin, characterized in that, It is prepared by copolymerization of curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide; wherein, the curcumin allyl ether has a β-diketone conjugated system and is prepared by nucleophilic substitution reaction of curcumin and allyl bromide in potassium carbonate and acetone solvent system, with a molecular weight of 488 g / mol, and is cured in stages with N,N'-4,4'-diphenylmethane bismaleimide at 150-240℃ to form a highly crosslinked network.

2. The bio-based bismaleimide resin according to claim 1, characterized in that, The bio-based bismaleimide resin has a glass transition temperature ≥390℃, a limiting oxygen index ≥37%, a UL-94 flame retardancy rating of V-0, and a char residue rate ≥42% at 800℃.

3. A method for preparing the bio-based bismaleimide resin according to claim 1 or 2, characterized in that, include: Step S1: Curcumin and allyl bromide are reacted in a potassium carbonate and acetone solvent system at 60°C for 24 h to obtain curcumin allyl ether. Step S2: Curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide are mixed at a molar ratio of imide group to allyl group of 0.6-1.0, and stirred at 150°C until a transparent liquid is formed. The mixture is then allowed to stand for 30 min to obtain the prepolymer. Step S3: Degas the prepolymer under vacuum for 30 min, then perform segmented heating and curing. The heating program is 150℃ / 2 h → 180℃ / 2 h → 200℃ / 2 h → 220℃ / 2 h → 240℃ / 4 h. Cool to obtain bio-based bismaleimide resin.

4. The method for preparing the bio-based bismaleimide resin according to claim 3, characterized in that, In step S2, curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide are mixed at a molar ratio of imide group to allyl group of 0.

87.

5. The method for preparing the bio-based bismaleimide resin according to claim 3, characterized in that, Step S1 is as follows: 1 gram of curcumin was dissolved in 40 ml of acetone. 3.7 grams of potassium carbonate and 14 grams of bromopropylene were added to the solution. The mixture was heated to 60 °C and maintained at this temperature for 24 hours under nitrogen. The reaction solution was filtered, extracted, and the solvent was removed under reduced pressure to obtain curcumin allyl ether.

6. The application of a bio-based bismaleimide resin according to claim 1 or 2 in high-frequency high-speed copper-clad laminates, aerospace structural films, or high-temperature electronic packaging materials.

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