Bio-based bismaleimide resin as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of materials, and provides bio-based bismaleimide resin as well as a preparation method and application thereof, and the resin is prepared by copolymerizing curcumin allyl ether and N, N '-4, 4'-diphenylmethane bismaleimide. The curcumin allyl ether has a beta-diketone conjugated system and is prepared by carrying out nucleophilic substitution reaction on curcumin and allyl bromide in a potassium carbonate acetone system; during preparation, the two components are subjected to segmented curing at 150-240 DEG C to form a high-crosslinking network, and vacuum degassing and curing processes are combined. According to the bio-based bismaleimide resin provided by the invention, in thermal performance and processability, the curing peak temperature is reduced by 20-30 DEG C compared with that of traditional BD resin, and Tg is greater than or equal to 390 DEG C and is increased by nearly 90 DEG C compared with that of the BD resin; in flame retardance and thermal stability, the carbon residue rate at 800 DEG C is greater than or equal to 42%, the LOI is greater than or equal to 37% and reaches the UL-94 V-0 level, the THR is as low as 12.4 kJ / g, the high-temperature flammable volatile matter is few, and the carbon residue graphitization degree is high.

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, etc. Although some modified resins can achieve Tg of 388℃ and LOI of 37.7%, there are still the following shortcomings: 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”, especially in the low dielectric loss required by high-frequency high-speed copper-clad plates and the wide temperature range bonding stability required by aviation structural adhesive films, etc., 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: Step S1, reacting curcumin and allyl bromide in a potassium carbonate and acetone solvent system under the condition of 60℃ and nitrogen protection for 24 h to obtain curcumin allyl ether; Step S2, mixing the curcumin allyl ether and the N,N'-4,4'-diphenylmethane bismaleimide according to a molar ratio of imide groups to allyl groups of 0.6-1.0, melt stirring at 150℃ until a transparent liquid is formed, and standing for 30 min to obtain a prepolymer. Step S3, degassing the prepolymer under vacuum for 30 min, and then performing staged temperature curing, with a temperature program of 150℃ / 2 h→180℃ / 2 h→200℃ / 2 h→220℃ / 2 h→240℃ / 4 h, and cooling to obtain the bio-based bismaleimide resin.

[0010] The application also provides a use of the bio-based bismaleimide resin in high-frequency high-speed copper-clad plates, aviation structural adhesive films, or high-temperature electronic packaging materials.

[0011] The application synthesizes curcumin allyl ether with a conjugated β-diketone system by taking curcumin as a raw material, and forms a high-crosslinking network by combining N,N'-4,4'-diphenylmethane bismaleimide, vacuum degassing, and staged temperature curing, thereby preparing a bio-based bismaleimide resin, which brings about the following technical effects: In terms of thermal performance and processability, the synergism of low curing temperature (the curing peak temperature is reduced by 20-30℃ than that of a traditional BD resin, and is as low as about 230℃), high glass transition temperature (Tg≥390℃, and some samples are higher than 400℃, which is increased by nearly 90℃ than that of the BD resin), and wide processing window is achieved, and the apparent viscosity of the prepolymer is 0.5-2 Pa・s at 120℃, which is suitable for the preparation of prepregs or adhesive films; In terms of flame retardation and thermal stability, the resin has a char yield of ≥42% at 800℃, a limiting oxygen index (LOI) of ≥37%, reaches UL-94 V-0 level, a total heat release (THR) as low as 12.4 kJ / g, reduced flammable volatile products at high temperatures, and a higher degree of carbonization of residual carbon; In terms of synthesis and industrialization adaptability, the synthesis of curcumin allyl ether adopts a mild and clean acetone / potassium carbonate / allyl bromide system, avoids the use of strong alkali and high-boiling solvents, and the solvent is easy to recover and 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

[0012] Figure 1 The structure of the AEC provided in the application is characterized by (a) the 1H NMR spectrum of the AEC, (b) the Fourier transform infrared spectrum of the AEC, and (c) the mass spectrum of the AEC; Figure 2 The differential scanning calorimetry curve of the BA (a) and BD (b) resin provided in the application is shown in the following figure; Figure 3TGA and DTG curves of cured BA(a) and BD(b) resins provided for embodiments of this application; 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. 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; Figure 6 Raman spectra of (a) BA-0.87 resin and (b) BD-0.87 resin provided for embodiments of this application; Figure 7 TGA and DTG curves of BA-0.87 and BD-0.87 cured resins provided for embodiments of this application; 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; 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; 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

[0013] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0014] The application embodiment provides a kind of bio-based bismaleimide resin, is made by curcumin allyl ether (AEC) and N,N'-4,4'-diphenylmethane bismaleimide (BDM) copolymerization;Wherein, the curcumin allyl ether has β-diketone structure and symmetrical double allyl site, 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 high crosslinking 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 level is V-0 level, and the carbon residue rate at 800 DEG C is greater than or equal to 42%.

[0015] The application embodiment provides a kind of bio-based bismaleimide resin of above-mentioned preparation method, comprising: Step S1, under the condition of nitrogen protection at 60 DEG C, curcumin is reacted with allyl bromide in potassium carbonate and acetone solvent system for 24 h to obtain curcumin allyl ether.

[0016] 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 base system (strong alkaline, high temperature, residual metal / halide salt) or Mitsunobu method (need PPh3 / DEAD dangerous chemicals, by-product salt is difficult to remove), the by-reaction (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.

[0017] Among them, the selected acetone solvent is medium polarity, low boiling point, easy to recover and low toxicological burden, which avoids the problems of amplification removal difficulty and influence on subsequent prepolymerization / curing caused by high boiling and high viscosity of DMF / DMSO, facilitates batch recovery and shortens the post-treatment link;60 DEG C low temperature reaction does not need high temperature reflux or strong alkali activation, which is lower in energy consumption and shorter in thermal history, can reduce the degradation and coloring risk of curcumin β-diketone conjugated skeleton, and ensure the subsequent flame-retardant charring stability;The nucleophilic activity of the selected allyl bromide is higher, and double-end etherification can be realized under mild base, compared with allyl chloride (need stronger base / high temperature) or Mitsunobu method (single / double substitution ratio is unstable), the double substitution selectivity and reaction rate are higher, and the by-product is less;The synthesis process is only direct etherification→cooling→extraction and purification, without protection-deprotection or oxidation-reduction steps, without using metal Lewis acid / phase transfer catalyst, compared with Mitsunobu method which needs to handle a large amount of by-product salt and strong alkali / phase transfer process which easily introduces ion residues, the impurity spectrum is simpler, and the product purity is higher through 1 H NMR, FT-IR, HRMS triple characterization verifies the product structure and purity (hydroxyl peak disappears, 1248 cm -1ether linkage absorption, [M+H] + ≈489.22); the synthesized AEC has less residue, can directly enter the 150℃ melt prepolymerization and five-stage curing process, can reduce the curing peak temperature and broaden the processing window, can reduce the risk of heat / color / impurity from monomer synthesis to subsequent process whole process, is suitable for industrialization and guarantees the stable dielectric properties of the final bio-based bismaleimide resin.

[0018] Optionally, step S1 is specifically: 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 condition, filter the reaction solution, extract, and remove the solvent under reduced pressure to obtain curcumin allyl ether.

[0019] 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.

[0020] Step S2, mix curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide at an imide group to allyl group molar ratio 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.

[0021] Preferably, in step S2, curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide are mixed at an imide group to allyl group molar ratio of 0.87.

[0022] Step S3, degas the prepolymer under vacuum condition for 30 min, and then perform staged temperature rising curing with a temperature rising program of 150℃ / 2 h→180℃ / 2 h→200℃ / 2 h→220℃ / 2 h→240℃ / 4 h, and cool to obtain a bio-based bismaleimide resin.

[0023] The bio-based bismaleimide resin and the preparation method thereof provided in the present application are described in detail in the following 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.

[0024] Raw materials: BDM and DABPA (purity 90%) were provided by Shanghai Hejiu Chemical Co., Ltd. Curcumin (purity 98%) was purchased from Bid Pharmaceutical Technology Co., Ltd. Bromopropylene and potassium carbonate were both analytical grade commercial reagents purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. All other reagents were analytical grade and used without further purification.

[0025] Example 1: Synthesis of allyl curcumin ether (AEC) Dissolve 1 gram of curcumin in 40 milliliters of acetone, add 3.7 grams of potassium carbonate and 14 grams of bromoallyl to the solution. Heat the mixture to 60°C and maintain the temperature for 24 hours under nitrogen, filter the reaction solution, extract, and remove the solvent under reduced pressure. The target product is a yellow solid weighing 1.04 grams, with a total yield of 80%. The synthesis route is as follows:

[0026] Example 2: Synthesis of BDM / AEC (BA) bio-based bismaleimide resin Mix curcumin allyl ether and N,N'-4,4'-diphenylmethane bismaleimide at a molar ratio of 0.7, 0.87, and 1.0 of imide groups to allyl groups, respectively, melt and stir at 150°C until a transparent liquid is formed, and then let stand for 30 min to obtain a prepolymer. Degas the prepolymer under vacuum for 30 min, transfer it to a mold, and then perform 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. Cool and demold to obtain a bio-based bismaleimide resin, labeled as BA-0.7, BA-0.87, and BA-1.0, respectively. The synthesis route is as follows:

[0027] Comparative Example: Synthesis of BDM / DABPA (BD) resin Mix 2,2'-diallyl bisphenol A and N,N'-4,4'-diphenylmethane bismaleimide at a molar ratio of 0.7, 0.87, and 1.0 of imide groups to allyl groups, respectively, melt and stir at 150°C until a transparent liquid is formed, and then let stand for 30 min to obtain a prepolymer. Degas the prepolymer under vacuum for 30 min, transfer it to a mold, and then perform 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. Cool and demold to obtain a BD resin, labeled as BD-0.7, BD-0.87, and BD-1.0, respectively. The synthesis route is as follows:

[0028] Structural characterization of the curcumin allyl ether (AEC) synthesized in the above Example 1 is shown in Figure 1 . Figure 1(a) shows the 1H NMR spectrum of AEC, in which the characteristic peaks of allyl ether group can be observed. The characteristic peak of proton at 7.26 ppm corresponds to CDCl3, 7.68 ppm (Hg, Hg'), 6.91 ppm (He, He'), 6.84 ppm (Hh, Hh'), 6.06 ppm (Hb, Hb', Hb"), 5.25 ppm (Ha, Ha', Ha") correspond to the protons on the double bond of allyl group in AEC, 4.65 ppm (Hc, Hc'), 3.93 ppm (Hi, Hi') are 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 group in the raw material curcumin. However, the peak disappears completely in the AEC product. The methylene group can be seen at 2964 cm -1 , while the ether bond in AEC appears at 1248 cm -1 . These observations indicate that curcumin has been completely reacted and the corresponding ether compound has been formed. Figure 1 (c) shows that the expected molecular weight of curcumin allyl ether is confirmed by electrospray ionization Fourier transform mass spectrometry (ESI-FTMS) technique. The fragmentation peak and charge mass ratio signal position of the target ion (M: C30H32O6) are [M+H] + : 489.22483, while the literature value is 489.2287. [M+Na+H2O] + : 529.25587. The molecular weight of AEC is 488.

[0029] Further, the curing reactivity of the BD resin provided by the above-mentioned comparative example and the BA resin provided by Example 2 is detected by differential scanning calorimetry. Figure 2 The differential scanning calorimetry curves of BD and BA resins are shown. Each curve presents a single curing exothermic peak, the exothermic peak of BD resin appears at about 250°C, while the curing temperature of BA resin is lower than that of BD resin, indicating that BA resin has a wider processing window. The cause may be attributed to the following three points: the Claisen rearrangement reaction occurring in the structure of AEC; the increase in crosslinking density caused by the high functional group number of 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 thus reducing the peak curing temperature; there is another possibility: the reaction of BDM and AEC occurs simultaneously at more positions, and the reaction heat is dispersed to multiple reaction points rather than concentrated at a specific temperature point, resulting in a lower peak curing temperature.

[0030] Two key indicators are used to evaluate the heat resistance of thermoset resins: DMA (Dynamic Mechanical Analysis) and TGA (Thermogravimetric Analysis). DMA has been proven to be the most effective method to characterize polymer materials. TGA is used to evaluate the thermal weight loss characteristics of thermoset resins. "T d5% " represents the temperature at which 5% of mass loss occurs 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 800°C, which is the percentage of the mass of the solid carbonized product remaining at 800°C after thermal decomposition of the initial sample. 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.

[0031] Table 1 Typical parameters of cured BD resin and BA resin in TGA and DMA tests

[0032] As shown in Figure 3 , the increase in allyl content leads to a decrease in T d5% , which is associated with a decrease in the glass transition temperature (Tg), which can be attributed to the chain extension effect of allyl groups, which studies have shown to reduce the crosslinking density of the resin, thus promoting higher mobility of the polymer units. However, the BA resin cured system still shows a higher Tg value than the BD resin. It is worth noting that the trends of storage modulus and loss modulus in the figure show that the Tg values of BA-0.7 and BA-0.87 resins both exceed 400°C. The Tg of the cured product of BA-1.0 resin is measured to be 389.85°C, which is about 90°C higher than that of BD-1.0 resin.

[0033] As can be clearly seen from the DMA results, the Tg value of the cured product of BA resin reflects its excellent heat resistance - generally, the Tg value represents the highest use temperature of the cured product of thermoset resin.

[0034] After nano-indentation testing, BA-0.87 and BD-0.87 have the best mechanical properties, so BA-0.87 and BD-0.87 are selected for flame retardant testing. The test results are shown in Table 2 and Figure 4 . Table 2 Typical indicators of cured resins in flame retardant tests

[0035] As can be seen from Table 2, the oxygen index (LOI) of BA-0.87 resin is higher than that of BD-0.87, which is consistent with the results of the carbon yield of the cured resins at 800°C in the thermogravimetric analysis. Figure 4The UL-94 results for the BD and BA resins are reported in Table 1. As shown in Table 1, the BA resins passed the UL-94 test at 0.87 wt% loading, while the BD resins failed the UL-94 test at 0.87 wt% loading. Figure 4 The combustion behavior of the BA and BD resins was investigated by UL-94 testing. As shown in Table 1, the BA-0.87 resin passed the UL-94 test with both ignitions having a burn time of less than 10 seconds and no drips. Similarly, the BD-0.87 resin failed the UL-94 test with both ignitions having a burn time of less than 30 seconds and no drips. The experiments confirmed that the BA resins have an easy-to-extinguish characteristic, demonstrating excellent flame retardant properties.

[0036] Microscale calorimetry testing (MCC) is a technique that correlates the chemical structure of polymers with their 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 of a material, with lower values indicating greater flame retardancy. The BA resins have a lower heat capacity (291.5 J / (g K)) than the BD-0.87 resin (305.6 J / (g K)). In addition, the total heat release testing results show that the BA-0.87 resin after curing has a total heat release of only 12.4 kJ / g, which is much lower than the cured BD-0.87 resin (20.2 kJ / g). Both the heat release rate and total heat release data confirm that the BA resins are superior to the BD resins in terms of suppressing heat release rate and total amount.

[0037] Further, to gain a deeper understanding of the flame retardant mechanism of the BA resin cured product, the morphology and structure of the char formed after the combustion test were analyzed. In addition, the volatiles produced during thermal degradation were analyzed. First, the morphology of the carbon layer remaining on the surface of the sample after the LOI test was characterized by scanning electron microscopy (SEM), as shown in FIGS. 1(a), 1(b), 1(c), and 1(d). Figure 5 The SEM images show that the residual char structure of the 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 can be reasonably inferred that both structures are conducive to gas permeation. The heat insulation performance of the two samples can be comparable, indicating that the flame retardant mechanism of the BA resin can not rely on the formation of a traditional dense carbon layer. Therefore, the residual carbon was analyzed by Raman spectroscopy to assess the degree of graphitization. The Raman spectra obtained are shown in FIGS. 2(a) and 2(b). Figure 6

[0038] As shown in the Raman spectroscopy analysis results, there is a significant difference in the degree of graphitization between the residual carbon sample after combustion of the BA-0.87 resin and the residual carbon sample after combustion of the BD-0.87 resin, which is mainly measured by the intensity ratio of the D peak and the G peak. In Raman spectroscopy, the D peak (about 1350 cm -1 ​) has been confirmed 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, meaning a larger sp2 carbon domain and fewer structural defects. As shown in the BA-0.87 resin, its I D / I G ratio is measured to be 0.72, far below the established threshold of 1. This result indicates a significant improvement in the degree of graphitization - a low ratio (such as <0.9) means that the carbon skeleton is mainly composed of sp2 hybridized carbon atoms. Such a sample has a lower defect density, and its structural arrangement is close to the ideal graphite sequence. In contrast, the I D / I G ratio of the BD-0.87 sample is 0.93, which is still lower than 1, but significantly higher than that of the BA-0.87. This ratio close to 1 indicates a relatively low degree of graphitization, suggesting the presence of more disordered regions or defects (such as grain boundaries, vacancies, or heteroatom doping) in the carbon structure. The increased I D / I G value is usually associated with partially graphitized carbon materials, which are characterized by a small sp2 carbon domain 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 its own stability. This increase in carbonized residues and the enhancement of its stability are mainly due to the characteristics of the internal structure of the AEC - this structure not only promotes the formation of carbonized products, but also enhances the degree of graphitization.

[0039] As shown in Figure 7, the TGA and DTG curves of the BD-0.87 and BA-0.87 resin cured materials obtained by TG-IR testing show that the BA-0.87 resin cured material has better heat resistance. Not only is its Td value (5% residual carbon content) higher than that of the BD-0.87 resin cured material, but its residual carbon content at 800°C is as high as 43.06%, which is 16.08% higher than the 26.98% residual carbon content 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 fewer volatile substances during thermal decomposition, which is due to the fact that more cured products are converted into residual carbon and remain on the surface and inside of the material during thermal decomposition.

[0040] Figure 8 shows the Fourier transform infrared spectra of the thermal decomposition products of BA-0.87 and BD-0.87 resins at specific temperatures. The characteristics of the thermal decomposition products of the two resins are significantly different. Specifically, the BD-0.87 resin cured product (see...) Figure 8 (b) at 428℃ (i.e., its T) d5% The characteristic peaks of CO2 (2363, 2330 and 669 cm⁻¹) appear at this time. -1 This 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 the 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.

[0041] 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).

[0042] 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 -1 The stable ether bond peak indicates that the AEC framework structure remained intact. Compared to the BD system, the curing exothermic peak temperature of the BA system decreased by 20-30℃ as confirmed by DSC testing, and the reaction process became more gradual. This phenomenon is attributed to its richer reaction sites, resulting in a more uniformly dispersed exothermic process. Furthermore, the charring behavior of the BA resin is closely related to its flame retardant mechanism: the β-diketone structure in the curcumin framework can promote charring and graphitization at high temperatures. Raman spectroscopy shows that the Ig of the BA-0.87 sample... D / I G The ratio (0.72) is lower than BD-0.87 (0.93), indicating a significant improvement in the orderliness of its charred layer; simultaneously, TG-IR testing confirms a reduction in the release of flammable volatile products from the BA system. These results demonstrate that the AEC structure not only provides ample crosslinking active sites for the resin but also endows the system with excellent intrinsic flame-retardant properties. In summary, the BA resin of this application achieves a synergistic balance between low curing temperature, wide processing window, high glass transition temperature, high crosslinking density, and excellent heat resistance and flame retardancy. The root of this comprehensive performance advantage lies in the synergistic effect of the reactivity and char-forming ability formed by the conjugated structure of diallyl ether and β-diketone in the AEC structure.

[0043] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

[0044] The above only describes preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should 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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