Bifunctional vanillin active ester, flame-retardant low-dielectric bio-based thermosetting epoxy resin as well as preparation method and application of flame-retardant low-dielectric bio-based thermosetting epoxy resin

Abstract

The invention belongs to the field of bio-based new materials, and discloses a bifunctional vanillin active ester, a flame-retardant low-dielectric bio-based thermosetting epoxy resin, and a preparation method and an application of the flame-retardant low-dielectric bio-based thermosetting epoxy resin. The preparation method comprises the following steps: dissolving acetyl vanillin and 4, 4 '-diaminodiphenylmethane in a solvent, carrying out a reflux reaction to obtain a vanillin derivative containing a Schiff base structure, uniformly mixing the vanillin derivative with 9, 10-dihydro-9-oxa-10-phosphaphenanthrene oxide and a solvent, and carrying out a reflux reaction to obtain the bifunctional vanillin active ester. The preparation method comprises the following steps: dissolving vanillin active ester, tri (m-toluoyl) resveratrol active ester, epoxy resin and a catalyst in a solvent to form a uniform solution, and curing after the solvent is volatilized to obtain the flame-retardant low-dielectric bio-based thermosetting epoxy resin. The difunctional biomass vanillin active ester curing agent can significantly improve the dielectric property and hydrophobic property of the epoxy resin, and greatly improve the flame retardant property of the epoxy resin.

Description

Technical Field

[0001] The present invention belongs to the field of bio-based new materials, and particularly relates to a bifunctional vanillin active ester, a flame-retardant and low-dielectric bio-based thermosetting epoxy resin, and a preparation method and application thereof. Background Art

[0002] Artificial intelligence, smartphones, automobiles, and the industrial Internet of Things are triggering major changes and driving the microelectronics industry into a period of rapid development. The resistance-capacitance effect, crosstalk noise, and power consumption brought about by the integration and miniaturization of electronic devices will cause signal delay, damage, and heat accumulation. Epoxy resin has good adhesiveness, dimensional stability, and mechanical properties, and has strong application potential in the field of printed circuit boards. However, due to reasons such as disordered polymer entanglement, large group polarity, and carbon-rich structure, traditional epoxy resin materials have disadvantages such as high dielectric constant, large dielectric loss, and flammability, and it is difficult to meet the development needs of next-generation communications. To solve these problems, it is necessary to develop low-dielectric and flame-retardant insulating materials as interlayer dielectrics or encapsulation materials.

[0003] Polymers with low dielectric constants can be mainly achieved in two ways: one is to use groups with less polarizability to replace high-polar groups such as -OH to reduce molar polarization; the other is to increase the porosity and free volume of the polymer. Zhou Jiefeng et al. cured dicyclopentadiene phenol epoxy monomer (DCPD) with bisphenol A active ester (H7070), and the dielectric constant and dielectric loss of the prepared H7070 / DCPD cured product were 3.41 and 0.0163 (1 MHz), respectively (Zhou Jiefeng, Huang Jie, Zhou You, et al. Study on the curing kinetics and properties of bisphenol A active ester / dicyclopentadiene epoxy resin system [J]. Insulating Materials, 2019, 52(09): 25-29.). However, although the problem of high dielectric properties of epoxy resin caused by secondary hydroxyl groups has been solved by using an active ester curing agent, the flame-retardant performance of epoxy resin has not been improved.

[0004] At present, the vast majority of commercial epoxy resins are derived from non-renewable petrochemical raw materials. The deep development and use of fossil energy by human society have caused the depletion of petrochemical energy and the prominent environmental problems. Therefore, in order to meet the social needs and the requirements of sustainable development, it is urgent to develop a sustainable development flame-retardant and low-dielectric bio-based thermosetting epoxy resin that is easy to prepare and has excellent performance. Summary of the Invention

[0005] In order to overcome the disadvantages and deficiencies of the prior art, the primary object of the present invention is to provide a bifunctional vanillin active ester.

[0006] Another object of the present invention is to provide a preparation method of a bifunctional vanillin active ester.

[0007] Another object of the present invention is to provide a preparation method of a flame-retardant and low-dielectric bio-based thermosetting epoxy resin; this method is to prepare a bifunctional biomass vanillin active ester curing agent containing phosphorus and nitrogen elements from renewable acetyl vanillin, and use this vanillin active ester curing agent and tris(m-toluoyl) resveratrol active ester curing agent to co-cure dicyclopentadiene phenol epoxy resin to obtain a bio-based thermosetting epoxy resin, achieving the flame-retardant and low-dielectric properties, sustainable development, and good hydrophobic properties of the epoxy resin.

[0008] Another object of the present invention is to provide a flame-retardant and low-dielectric bio-based thermosetting epoxy resin prepared by the above preparation method.

[0009] Another object of the present invention is to provide the application of the above flame-retardant and low-dielectric bio-based thermosetting epoxy resin.

[0010] The object of the present invention is achieved by the following technical solutions:

[0011] A bifunctional vanillin active ester, the structural formula is shown in formula (I):

[0012]

[0013] A preparation method of a bifunctional vanillin active ester, comprising the following steps:

[0014] (1) Under an inert atmosphere, acetyl vanillin and 4,4'-diaminodiphenylmethane are dissolved in solvent 1 and refluxed. After the reaction is completed, the reaction product is post-treated to obtain a vanillin derivative containing a Schiff base structure;

[0015] (2) The vanillin derivative containing a Schiff base structure obtained in step (1), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and solvent 2 are mixed evenly and refluxed. After the reaction is completed, the reaction product is washed and dried to obtain a bifunctional vanillin active ester.

[0016] Preferably, the molar ratio of acetyl vanillin to 4,4'-diaminodiphenylmethane in step (1) is (2 - 2.5):1;

[0017] The reflux reaction temperature in step (1) is 50 - 65 °C, and the reaction time is 4 - 10 h.

[0018] Preferably, the molar ratio of the vanillin derivative containing a Schiff base structure to 9,10-dihydro-9-oxa-10-phosphaphenanthrene in step (2) is 1:(2 - 3.5);

[0019] The reflux reaction temperature in step (2) is 50 - 65 °C, and the reaction time is 12 - 48 h.

[0020] Preferably, the solvent 1 is at least one of anhydrous ethanol, methanol, and dichloromethane;

[0021] The solvent 2 is at least one of anhydrous ethanol, N,N-dimethylacetamide, methanol, and N,N-dimethylformamide;

[0022] The organic solvent for washing in step (2) is at least one of dichloromethane, chloroform, tetrahydrofuran, acetone, N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylacetamide, and anhydrous ethanol.

[0023] Preferably, the inert atmosphere is any one of nitrogen, argon, and helium.

[0024] A preparation method of a flame-retardant and low-dielectric bio-based thermosetting epoxy resin includes the following steps: dissolving the above-mentioned bifunctional vanillin active ester, tris(m-toluoyl) resveratrol active ester, epoxy resin, and catalyst in a solvent to form a homogeneous viscous solution, pouring it into a mold, and curing after the solvent volatilizes, thereby obtaining the flame-retardant and low-dielectric bio-based thermosetting epoxy resin;

[0025] The bifunctional vanillin active ester and tris(m-toluoyl) resveratrol active ester are curing agents for co-curing the epoxy resin.

[0026] Preferably, the molar ratio of the total active ester functional groups of the curing agent to the epoxy groups of the epoxy resin is 1 - 1.25:1, more preferably 1:1;

[0027] The mass ratio of the bifunctional vanillin active ester, tris(m-toluoyl) resveratrol active ester, and epoxy resin is (0 - 23):(0 - 9.09):10, preferably (0 - 18.4):(0 - 7.27):10; the mass ratio of the epoxy resin to the catalyst is 1:0.005 - 0.02;

[0028] The solid content of the system is 25% - 50%, and the solid content is the proportion of the mass of the remaining part after the solvent volatilizes to the total mass of the system.

[0029] Preferably, the epoxy resin is at least one of dicyclopentadiene phenol epoxy resin, bisphenol A epoxy resin, bisphenol F epoxy resin, biphenyl epoxy resin, naphthalene epoxy resin, alicyclic epoxy resin, resorcinol epoxy resin, polyethylene glycol epoxy resin, brominated epoxy resin, and phenolic epoxy resin;

[0030] The solvent is at least one of N,N-dimethylacetamide, tetrahydrofuran, toluene, xylene, N-methylpyrrolidone, and N-ethylpyrrolidone; the catalyst is at least one of 4-dimethylaminopyridine, triphenylphosphine, and 2-methylimidazole;

[0031] The specific steps of curing are as follows: First, pre-cure at 80 - 120 °C for 2 - 4 hours, then cure at 120 - 160 °C for 2 - 4 hours, and then cure at 160 - 200 °C for 1 - 2 hours.

[0032] A flame-retardant and low-dielectric bio-based thermosetting epoxy resin is prepared by the above method.

[0033] Preferably, the dielectric constant of the flame-retardant and low-dielectric bio-based thermosetting epoxy resin is 2.5 - 3.3, and the dielectric loss is 0.0045 - 0.0073;

[0034] The vertical burning grade of the flame-retardant and low-dielectric bio-based thermosetting epoxy resin is V-0 or V-1, and the limiting oxygen index (LOI) is greater than 31%.

[0035] The application of the above-mentioned flame-retardant and low-dielectric bio-based thermosetting epoxy resin in electronic packaging materials.

[0036] Preferably, the application of the above-mentioned flame-retardant and low-dielectric bio-based thermosetting epoxy resin in high-frequency and high-speed electronic packaging materials.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] (1) The present invention uses resveratrol and vanillin derivatives that are renewable and have a significant abundance. Through simple chemical modification, they are used to cure dicyclopentadiene phenol epoxy resin. It is environmentally friendly, does not involve cumbersome processing techniques, and can reduce the use of petroleum resources and environmental hazards during the production of flame-retardant and low-dielectric thermosetting epoxy resins.

[0039] (2) The bifunctional biomass vanillin active ester curing agent obtained in the present invention can form a three-dimensional network structure that does not contain high-polarity hydroxyl groups with dicyclopentadiene phenol epoxy resin. Compared with traditional active hydrogen curing agents, it can improve the dielectric properties and hydrophobic properties of epoxy resins; compared with dicyclopentadiene phenol epoxy resin, the dielectric loss is reduced by 23 - 52%, and compared with traditional epoxy resins, the dielectric loss is reduced by about 65 - 78%. Moreover, by introducing phosphorus and nitrogen elements into the thermosetting epoxy resin, the flame-retardant performance of the epoxy resin can be greatly improved, and both can reach above the UL-94V1 grade, and the limiting oxygen index is greater than 31%.

[0040] (3) The present invention first proposes to co-cure dicyclopentadiene phenol epoxy resin using biomass vanillin and resveratrol derivatives. This method can not only efficiently convert natural products into high-value-added products, but also significantly improve the comprehensive performance of epoxy resins, providing a new method for the high-value utilization of renewable resources and the sustainable substitution of petrochemical materials. Description of the Drawings

[0041] Figure 1 Schematic diagram of the synthesis route of the bifunctional biomass vanillin active ester curing agent containing phosphorus and nitrogen elements and the tri(m-toluoyl)resveratrol biomass active ester curing agent prepared in Example 1 of the present invention.

[0042] Figure 2 1H NMR spectrum of the biomass vanillin derivative containing Schiff base structure prepared in Example 1 of the present invention.

[0043] Figure 3 1H NMR spectrum of the bifunctional biomass vanillin active ester curing agent containing phosphorus and nitrogen elements prepared in Example 1 of the present invention.

[0044] Figure 4 FT-IR spectra of the flame-retardant and low-dielectric bio-based thermosetting epoxy resins prepared in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention. Detailed Description of the Invention

[0045] The present invention will be further described in detail below with reference to specific embodiments. However, the embodiments of the present invention are not limited thereto. For process parameters not specifically mentioned, conventional techniques can be referred to.

[0046] The schematic diagram of the synthesis route of the bifunctional biomass vanillin active ester curing agent containing phosphorus and nitrogen elements and the tri(m-toluoyl)resveratrol biomass active ester curing agent prepared in the examples is as Figure 1 shown.

[0047] The tri(m-toluoyl)resveratrol biomass active ester (AES) was prepared with reference to the literature Yang H, Yuan G, Jiao E, et al. Resveratrol-Derived Liquid Crystal Epoxy Resin with Low-Dielectric Properties and Excellent Mechanical Strength and Toughness[J].

[0048] Example 1:

[0049] Under a nitrogen atmosphere, 4.96 g (0.025 mol) of 4,4'-diaminodiphenylmethane and 9.71 g (0.05 mol) of acetyl vanillin were added to 100 mL of absolute ethanol. The mixture was heated to 60 °C and stirred under reflux for 4 hours. Then, the mixture cooled to room temperature was filtered, and the filtrate was washed several times with absolute ethanol. It was dried overnight in a vacuum oven at 60 °C to obtain a yellow crystalline product, which was a biomass vanillin derivative containing a Schiff base structure, named AEVA. 5.51 g (0.01 mol) of AEVA, 4.33 g (0.02 mol) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 80 mL of absolute ethanol were fully mixed and reacted at 60 °C for 24 h. After the reaction, the mixture was dissolved in dichloromethane, and then poured into a large amount of absolute ethanol for washing. After filtration, it was dried in a vacuum oven at 60 °C for 24 hours to obtain a white powdery product, namely a bifunctional biomass vanillin active ester curing agent containing phosphorus and nitrogen elements, named AEPVA. 10 g of dicyclopentadiene phenol epoxy resin (DCPD), 6.54 g of AES, 1.84 g of AEPVA, and 0.1 g of 4-dimethylaminopyridine (DMAP) were dissolved in 10.48 g of N-methylpyrrolidone. After the solution became uniformly transparent, it was slowly poured into a mold. After the solvent evaporated overnight, it was first pre-cured at 110 °C for 2 hours, then cured at 150 °C for 2 hours, and then cured at 180 °C for 2 hours to obtain a bio-based epoxy thermosetting resin, named AEP1.

[0050] Example 2:

[0051] Under a nitrogen atmosphere, 4.96 g (0.025 mol) of 4,4'-diaminodiphenylmethane and 9.71 g (0.05 mol) of acetyl vanillin were added to 100 mL of absolute ethanol. The mixture was heated to 60 °C and stirred under reflux for 4 hours. Then, the mixture cooled to room temperature was filtered, and the filtrate was washed several times with absolute ethanol. It was dried overnight in a vacuum oven at 60 °C to obtain a yellow crystalline product, a biomass vanillin derivative containing a Schiff base structure, named AEVA. 5.51 g (0.01 mol) of AEVA, 4.33 g (0.02 mol) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 80 mL of absolute ethanol were fully mixed and reacted at 60 °C for 24 h. After the reaction, the mixture was dissolved in dichloromethane, and then poured into a large amount of absolute ethanol for washing. After filtration, it was dried in a vacuum oven at 60 °C for 24 hours to obtain a white powdery product, namely a bifunctional biomass vanillin active ester curing agent containing phosphorus and nitrogen elements, named AEPVA. 10 g of DCPD, 5.81 g of AES, 3.68 g of AEPVA, and 0.1 g of DMAP were dissolved in 19.59 g of N-methylpyrrolidone. After the solution became uniformly transparent, it was slowly poured into a mold. After the solvent evaporated overnight, it was first pre-cured at 110 °C for 2 hours, then cured at 150 °C for 2 hours, and then cured at 180 °C for 2 hours to obtain a bio-based epoxy thermosetting resin, named AEP2.

[0052] Example 3:

[0053] Under a nitrogen atmosphere, 4.96 g (0.025 mol) of 4,4'-diaminodiphenylmethane and 9.71 g (0.05 mol) of acetyl vanillin were added to 100 mL of absolute ethanol. The mixture was heated to 60 °C and stirred under reflux for 4 hours. Then, the mixture cooled to room temperature was filtered, and the filtrate was washed several times with absolute ethanol. It was dried overnight in a vacuum oven at 60 °C to obtain a yellow crystalline product, a biomass vanillin derivative containing a Schiff base structure, named AEVA. 5.51 g (0.01 mol) of AEVA, 4.33 g (0.02 mol) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and 80 mL of absolute ethanol were thoroughly mixed and reacted at 60 °C for 24 h. After the reaction, the mixture was dissolved in dichloromethane, and then poured into a large amount of absolute ethanol for washing. After filtration, it was dried in a vacuum oven at 60 °C for 24 hours to obtain a white powdery product, a bifunctional biomass vanillin active ester curing agent containing phosphorus and nitrogen elements, named AEPVA. 10 g of DCPD, 5.09 g of AES, 5.52 g of AEPVA, and 0.1 g of DMAP were dissolved in 20.71 g of N-methylpyrrolidone. After the solution became uniformly transparent, it was slowly poured into a mold. After the solvent evaporated overnight, it was first pre-cured at 110 °C for 2 hours, then cured at 150 °C for 2 hours, and then cured at 180 °C for 2 hours to obtain a bio-based epoxy thermosetting resin, named AEP3.

[0054] Example 4:

[0055] Under a nitrogen atmosphere, 4.96 g (0.025 mol) of 4,4'-diaminodiphenylmethane and 9.71 g (0.05 mol) of acetylvanillin were added to 100 mL of absolute ethanol. The mixture was heated to 60 °C and stirred under reflux for 4 hours. Then, the mixture cooled to room temperature was filtered, and the filtrate was washed several times with absolute ethanol. It was dried overnight in a vacuum oven at 60 °C to obtain a yellow crystalline product, a biomass vanillin derivative containing a Schiff base structure, named AEVA. 5.51 g (0.01 mol) of AEVA, 4.33 g (0.02 mol) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 80 mL of absolute ethanol were thoroughly mixed and reacted at 60 °C for 24 h. After the reaction, the mixture was dissolved in dichloromethane, and then poured into a large amount of absolute ethanol for washing. After filtration, it was dried in a vacuum oven at 60 °C for 24 hours to obtain a white powdery product, a bifunctional biomass vanillin active ester curing agent containing phosphorus and nitrogen elements, named AEPVA. 10 g of DCPD, 4.36 g of AES, 7.37 g of AEPVA, and 0.1 g of DMAP were dissolved in 21.83 g of N-methylpyrrolidone. After the solution became uniformly transparent, it was slowly poured into a mold. After the solvent evaporated overnight, it was first pre-cured at 110 °C for 2 hours, then cured at 150 °C for 2 hours, and then cured at 180 °C for 2 hours to obtain a bio-based epoxy thermosetting resin, named AEP4.

[0056] Example 5:

[0057] Under a nitrogen atmosphere, 4.96 g (0.025 mol) of 4,4'-diaminodiphenylmethane and 9.71 g (0.05 mol) of acetylvanillin were added to 100 mL of absolute ethanol. The mixture was heated to 60 °C and stirred under reflux for 4 hours. Then, the mixture cooled to room temperature was filtered, and the filtrate was washed several times with absolute ethanol. It was dried overnight in a vacuum oven at 60 °C to obtain a yellow crystalline product, which was a biomass vanillin derivative containing a Schiff base structure, named AEVA. 5.51 g (0.01 mol) of AEVA, 4.33 g (0.02 mol) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 80 mL of absolute ethanol were thoroughly mixed and reacted at 60 °C for 24 h. After the reaction, the mixture was dissolved in dichloromethane, and then poured into a large amount of absolute ethanol for washing. After filtration, it was dried in a vacuum oven at 60 °C for 24 hours to obtain a white powdery product, namely a bifunctional biomass vanillin active ester curing agent containing phosphorus and nitrogen elements, named AEPVA. 10 g of DCPD, 3.63 g of AES, 9.21 g of AEPVA, and 0.1 g of DMAP were dissolved in 22.94 g of N-methylpyrrolidone. After the solution became uniformly transparent, it was slowly poured into a mold. After the solvent evaporated overnight, it was first pre-cured at 110 °C for 2 hours, then cured at 150 °C for 2 hours, and then cured at 180 °C for 2 hours to obtain a bio-based epoxy thermosetting resin, named AEP5.

[0058] Example 6:

[0059] Under a nitrogen atmosphere, 4.96 g (0.025 mol) of 4,4'-diaminodiphenylmethane and 9.71 g (0.05 mol) of acetylvanillin were added to 100 mL of absolute ethanol. The mixture was heated to 60 °C and stirred under reflux for 4 hours. Then, the mixture cooled to room temperature was filtered, and the filtrate was washed several times with absolute ethanol. It was dried overnight in a vacuum oven at 60 °C to obtain a yellow crystalline product, a biomass vanillin derivative containing a Schiff base structure, named AEVA. 5.51 g (0.01 mol) of AEVA, 4.33 g (0.02 mol) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 80 mL of absolute ethanol were thoroughly mixed and reacted at 60 °C for 24 h. After the reaction, the mixture was dissolved in dichloromethane, and then poured into a large amount of absolute ethanol for washing. After filtration, it was dried in a vacuum oven at 60 °C for 24 hours to obtain a white powdery product, namely a bifunctional biomass vanillin active ester curing agent containing phosphorus and nitrogen elements, named AEPVA. 10 g of DCPD, 2.91 g of AES, 11 g of AEPVA, and 0.1 g of DMAP were dissolved in 24.01 g of N-methylpyrrolidone. After the solution became uniformly transparent, it was slowly poured into a mold. After the solvent evaporated overnight, it was first pre-cured at 110 °C for 2 hours, then cured at 150 °C for 2 hours, and then cured at 180 °C for 2 hours to obtain a bio-based epoxy thermosetting resin, named AEP5.

[0060] Comparative Example 1:

[0061] 10 g of DCPD, 2.91 g of AES, and 0.1 g of DMAP were dissolved in 13.01 g of N-methylpyrrolidone. After the solution became uniformly transparent, it was slowly poured into a mold. After the solvent evaporated overnight, it was first pre-cured at 110 °C for 2 hours, then cured at 150 °C for 2 hours, and then cured at 180 °C for 2 hours to obtain a bio-based epoxy thermosetting resin, named AE.

[0062] Comparative Example 2:

[0063] 10 g of DCPD, 0.56 g of 4,4'-diaminodiphenylmethane, 5.09 g of AES, and 0.1 g of DMAP were dissolved in 15.75 g of N-methylpyrrolidone. After the solution became uniformly transparent, it was slowly poured into a mold. After the solvent evaporated overnight, it was first pre-cured at 110 °C for 2 hours, then cured at 150 °C for 2 hours, and then cured at 180 °C for 2 hours to obtain an epoxy thermosetting resin.

[0064] Comparative Example 3:

[0065] Dissolve 10 g of DCPD, 11 g of AEPVA, and 0.1 g of DMAP in 21.1 g of N-methylpyrrolidone. After the solution becomes uniformly transparent, slowly pour it into a mold. After the solvent evaporates, cure it, but it is not easy to cure and form.

[0066] Test Example 1:

[0067] The structures of AEVA and AEPVA prepared in Example 1 were analyzed in detail using a nuclear magnetic resonance spectrometer. As Figure 2 shown, in the proton nuclear magnetic resonance spectrum of AEVA, a characteristic signal of -N=CH- appears at 8.47 ppm, and no corresponding signal of the aldehyde group (near 9.87 ppm) is detected. This result fully proves that the aldehyde group has been completely consumed and a Schiff base structure has been introduced into the vanillin derivative. As Figure 3 shown, in the proton nuclear magnetic resonance spectrum of AEPVA, a significant increase in the number of protons belonging to the benzene ring is clearly observed in the range of 8.0 - 6.30 ppm. Signals belonging to -NH- are recorded at 4.73 and 4.81 ppm, indicating that 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide has reacted with the Schiff base. These chemical signals and shifts are in complete agreement with the predicted structure, proving the successful preparation of AEVA and AEPVA. Fourier transform infrared spectroscopy was used to confirm the structures of the flame-retardant low-dielectric bio-based thermosetting epoxy resins prepared in Example 1, Example 2, Example 3, and Comparative Example 1. As Figure 4 shown, in the infrared spectra of the epoxy thermosetting resins prepared in Example 1, Example 2, Example 3, and Comparative Example 1, the peak appearing at 1721 cm -1 is the characteristic absorption peak of the ester carbonyl group, while in the infrared spectrum of AEPVA, the peak of the ester carbonyl group appears at 1758 cm -1 . The red shift of the carbonyl absorption peak indicates that the ester group has changed from an aromatic ester to a fatty ester group. None of the epoxy thermosetting resins prepared in Example 1, Example 2, Example 3, and Comparative Example 1 show a characteristic peak of the epoxy group near 911 cm -1 , indicating that the epoxy groups of the dicyclopentadiene phenol epoxy resin have fully reacted.

[0068] Test Example 2:

[0069] Characterize the dielectric properties, hydrophobic properties, and flame-retardant properties of traditional epoxy resins, dicyclopentadiene phenol epoxy resins, Comparative Examples 1 and 2, and the products prepared in Examples 1, 2, and 3. The characterization methods and results are as follows:

[0070] I. Dielectric Properties

[0071] The dielectric properties were measured by an Agilent 4294A dielectric device at room temperature at a frequency of 100 MHz, and the dielectric constant and dielectric loss were obtained using the broadband dielectric test mode, as shown in Table 1:

[0072] Table 1

[0073]

[0074] As can be seen from Table 1, since the traditional epoxy resin cured by active hydrogen contains highly polar hydroxyl groups, it has a high dielectric constant and dielectric loss. After curing epoxy with active esters, no highly polar hydroxyl groups are generated, but ester groups and ether bonds are formed. Therefore, both the examples and Comparative Example 1 have reduced dielectric constant and dielectric loss. Compared with AE resins prepared in Comparative Examples 1 and 2 without adding the bifunctional biomass vanillin active ester curing agent AEPVA containing phosphorus and nitrogen elements, the bio-based epoxy resin added with AEPVA prepared in the present invention has reduced dielectric constant and dielectric loss. Compared with dicyclopentadiene phenol epoxy resin, the dielectric loss is reduced by 23-52%, and compared with traditional epoxy resin, the dielectric loss is reduced by about 65-78%. Moreover, as the amount of AEPVA increases, the dielectric constant and dielectric loss of the obtained product decrease successively.

[0075] II. Hydrophobic property

[0076] The hydrophobic property was determined by soaking the bio-based thermosetting epoxy resin in deionized water for 1 week, and the water absorption rate was calculated based on the weight change before and after soaking, as shown in Table 2:

[0077] Table 2

[0078]

[0079] As can be seen from Table 2, since no highly polar hydroxyl groups are generated after curing epoxy with active esters, the bio-based epoxy resin added with AEPVA prepared in the present invention has more excellent hydrophobic properties than traditional epoxy resins.

[0080] III. Flame retardant property

[0081] According to the ASTM D3801-2010 standard, a vertical burning test (UL-94 test) was carried out using a CFZ-2 instrument (Jiangning Analytical Instrument Co., Ltd., China). The specimen size was 120 mm × 12.5 mm × 3 mm, and each specimen was tested in parallel 5 times.

[0082] According to the ASTM D2863-2008 standard, the limiting oxygen index (LOI) was measured using an HC-2 oxygen index instrument (Jiangning Analytical Instrument Co., Ltd., China). The specimen size was 100 mm × 6.5 mm × 3 mm.

[0083] The UL-94 test and LOI were used to evaluate the flame retardancy of the specimens, as shown in Table 3:

[0084] Table 3

[0085]

[0086] As can be seen from Table 3, traditional epoxy resins cannot pass any grade of UL-94, and the limiting oxygen index is less than 21%, indicating that they are highly flammable. Compared with the thermosetting resins prepared in Comparative Examples 1 and 2 without adding the bifunctional biomass vanillin active ester curing agent AEPVA containing phosphorus and nitrogen elements, the bio-based epoxy resins obtained in the examples can all reach above the UL-94 V1 grade, and the limiting oxygen index is greater than 31%, indicating that the bio-based epoxy resins added with AEPVA prepared in the present invention have significantly improved flame retardancy, can all reach above the UL-94 V1 grade, and with the increase of the amount of AEPVA, the flame retardancy increases in turn. The flame retardancy grade of the comparative examples and dicyclopentadiene phenol epoxy resin is HB, which is the lowest flame retardancy grade, indicating that the material is flammable and does not have flame retardancy.

[0087] The above embodiments are the preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A bifunctional vanillin active ester, characterized in that: The structural formula is shown in formula (I):

2. The method for preparing the bifunctional vanillin active ester according to claim 1, characterized in that: The steps include: (1) Under an inert atmosphere, acetyl vanillin and 4,4'-diaminodiphenylmethane are dissolved in solvent 1 and subjected to reflux reaction, and after the reaction, the reaction product is post-treated to obtain a vanillin derivative containing a Schiff base structure; (2) The vanillin derivative containing a Schiff base structure obtained in step (1), 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, and solvent 2 are uniformly mixed and subjected to reflux reaction. After the reaction is completed, the reaction product is washed and dried to obtain a bifunctional vanillin active ester.

3. The method for preparing the bifunctional vanillin active ester according to claim 2, characterized in that: The molar ratio of acetyl vanillin and 4,4'-diaminodiphenylmethane in step (1) is (2-2.5):1; The temperature of the reflux reaction in step (1) is 50-65° C., and the reaction time is 4-10 h.

4. The method for preparing a bifunctional vanillin active ester according to claim 2, characterized in that: In step (2), the molar ratio of the vanillin derivative containing a Schiff base structure to 9,10-dihydro-9-oxa-10-phosphaphenanthrene is 1:(2-3.5); The reflux reaction temperature in step (2) is 50-65° C., and the reaction time is 12-48 h.

5. The method for preparing bifunctional vanillin active ester according to claim 2, characterized in that: The solvent 1 is at least one of anhydrous ethanol, methanol and dichloromethane; The solvent 2 is at least one of anhydrous ethanol, N,N-dimethylacetamide, methanol, and N,N-dimethylformamide; The organic solvent for washing in step (2) is at least one of dichloromethane, chloroform, tetrahydrofuran, acetone, N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylacetamide and anhydrous ethanol.

6. A method for preparing a flame retardant, low dielectric bio-based thermosetting epoxy resin, characterized in that: The method comprises the following steps: dissolving the bifunctional vanillin active ester and tri(m-toluoyl)resveratrol active ester, epoxy resin and catalyst in a solvent to form a uniform viscous solution, pouring the solution into a mold, and curing the solution after the solvent evaporates to obtain a flame retardant low dielectric bio-based thermosetting epoxy resin; The bifunctional vanillin active ester and tri(m-toluoyl)resveratrol active ester are curing agents.

7. The method for preparing the flame-retardant low-dielectric bio-based thermosetting epoxy resin according to claim 6, characterized in that: The molar ratio of the total active ester functional groups of the curing agent to the epoxy groups of the epoxy resin is 1-1.25:1; the mass ratio of the bifunctional vanillin active ester to the tri(m-toluoyl)resveratrol active ester and the epoxy resin is (0-23):(0-9.09):10; the mass ratio of the epoxy resin to the catalyst is 1:0.005-0.02; and the solid content of the system is 25%-50%.

8. The method for preparing the flame retardant low dielectric bio-based thermosetting epoxy resin according to claim 6, characterized in that: The epoxy resin is at least one of dicyclopentadiene phenol epoxy resin, bisphenol A epoxy resin, bisphenol F epoxy resin, biphenyl epoxy resin, naphthalene epoxy resin, alicyclic epoxy resin, resorcinol epoxy resin, polyethylene glycol epoxy resin, brominated epoxy resin, and phenolic epoxy resin; The solvent is at least one of N,N-dimethylacetamide, tetrahydrofuran, toluene, xylene, N-methylpyrrolidone, and N-ethylpyrrolidone; the catalyst is at least one of 4-dimethylaminopyridine, triphenylphosphine, and 2-methylimidazole; The specific steps of the curing are: firstly pre-curing at 80-120°C for 2-4 hours, then curing at 120-160°C for 2-4 hours, and then curing at 160-200°C for 1-2 hours.

9. A flame retardant low dielectric bio-based thermosetting epoxy resin, characterized in that: Prepared by the method described in claim 7 or 8.

10. Use of the flame-retardant, low-dielectric bio-based thermosetting epoxy resin according to claim 9 in electronic packaging materials.

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