A bio-based benzoxazine monomer, its preparation method and application

Abstract

This invention relates to a bio-based benzoxazine monomer, its preparation method, and its applications. The bio-based benzoxazine monomer is obtained by reacting 5,5'-methylenedifurfuralamine, vanillin, and paraformaldehyde. This monomer has a high biomass content, and the resin obtained by its melt curing exhibits good heat resistance, high strength, and good toughness. More importantly, the monomer has a large difference between its melting and curing temperatures, allowing it to copolymerize with Schiff base phenolic monomers obtained by reacting vanillin and tyramine to prepare high-biomass-content and biodegradable benzoxazine copolymer resins. These copolymers possess outstanding heat resistance, flame retardancy, and mechanical properties, solving the problems of low biomass content and low heat resistance in existing biodegradable biomass benzoxazine resins. This invention shows promising application prospects in adhesives, coatings, and other fields.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a bio-based benzoxazine monomer, its preparation method, and its application. Background Technology

[0002] Benzoxazine resins, as a novel type of thermosetting phenolic resin, have attracted widespread attention due to their lack of small molecule release during ring-opening polymerization, near-zero volume shrinkage, excellent mechanical properties, high heat resistance, and outstanding flame retardant properties. Traditional benzoxazine resins are typically synthesized from petroleum-based raw materials (such as phenol, bisphenol A, and amine compounds), forming a highly cross-linked, dense network structure after curing. While this largely endows the material with high strength and heat resistance, it also makes it difficult to degrade under natural or specific conditions, contradicting the requirements of environmental sustainability.

[0003] To address environmental challenges, researchers have begun exploring the use of renewable biomass resources (such as cashew nut shell extract, eugenol, and furfurylamine) to partially or completely replace petroleum-based feedstocks in the development of biodegradable biomass benzoxazine resins. This type of research aims to reduce dependence on fossil resources and endow materials with environmentally friendly properties. In previous work, Gu Aijuan et al. have achieved certain research results in the preparation of biomass benzoxazine resins. For example:

[0004] The patent CN2021109042086 discloses a recyclable and degradable biomass benzoxazine resin, which is obtained by copolymerizing benzoxazine monomers prepared from decanediamine, formaldehyde compounds, and isoeugenol with Schiff base monomers prepared from vanillin and diaminodiphenyl ether. This first endowed the resin with the characteristics of being recyclable and degradable. However, the resin has insufficient heat resistance, with a glass transition temperature of only 129 °C, which greatly limits the application of this type of resin.

[0005] In addition, patent CN2021109042086 discloses a bio-based flame-retardant benzoxazine resin. It uses bio-based vanillin and erythritol as raw materials, obtaining an intermediate through a condensation reaction, which is then reacted with furfurylamine upon heating to obtain a bio-based benzoxazine monomer. The cured benzoxazine resin exhibits outstanding heat resistance, with a glass transition temperature as high as 280 °C. However, this type of resin cannot be directly degraded, and because the melting point and curing temperature of the resin monomer are too close (melting point 210 °C, curing temperature 235 °C), the monomer polymerizes while melting, thus lacking melt flowability. This makes it impossible to prepare biodegradable resins by melt blending this monomer with other monomers.

[0006] Therefore, there is an urgent need for a bio-based benzoxazine monomer that can overcome the bottlenecks of existing technologies and be used to prepare benzoxazine resins, achieving a balance of high biomass content, biodegradability, excellent heat resistance (especially higher glass transition temperature), high strength, and good toughness, in order to meet the growing demand for high-performance and environmentally friendly materials. Summary of the Invention

[0007] To address the issues of low biomass content and the inability to simultaneously achieve biodegradability, heat resistance, and mechanical properties in existing benzoxazine resins, this invention provides a bio-based benzoxazine monomer, its preparation method, and its applications. This monomer not only boasts a high biomass content but also produces a resin with excellent heat resistance, high strength, and good toughness after melt curing. Crucially, the monomer exhibits a large difference between its melting and curing temperatures, allowing it to be melt-blended with Schiff base phenolic monomers obtained from the reaction of vanillin and tyramine at relatively low temperatures. This results in a high-biomass-content and biodegradable benzoxazine copolymer resin, which combines outstanding heat resistance and mechanical properties, showing promising application prospects in adhesives, composite matrix, and coatings.

[0008] Specifically, the following technical solutions are provided:

[0009] The first aspect of this invention provides a bio-based benzoxazine monomer, the structure of which is as follows:

[0010] .

[0011] A second aspect of this invention provides a method for preparing the bio-based benzoxazine monomer described in the first aspect, comprising the following steps:

[0012] 5,5'-methylenedifurfuralamine was reacted with vanillin and paraformaldehyde by heating to obtain the bio-based benzoxazine monomer;

[0013] The structure of the 5,5'-methylenedifurfural is shown below:

[0014] .

[0015] Furthermore, the preferred molar ratio of 5,5'-methylenedifurfural to vanillin and paraformaldehyde is 1:2:(3-5), such as 1:2:3, 1:2:4, 1:2:5, etc., including but not limited to the molar ratios listed above.

[0016] Furthermore, the degree of polymerization of the paraformaldehyde is preferably 8-10.

[0017] Furthermore, the heating reaction temperature is preferably 130-150 °C, and the time is preferably 3-6 h.

[0018] Further, the preparation method of the 5,5'-methylenedifurfural is as follows: furfurylamine is reacted with formaldehyde in the presence of an acid reagent and an organic solvent. After the reaction is complete, an alkaline reagent is added to adjust the pH to alkaline. After extraction and rotary evaporation to remove the solvent, the 5,5'-methylenedifurfural is obtained.

[0019] Furthermore, the acid reagent includes, but is not limited to, hydrochloric acid, and the base reagent includes, but is not limited to, sodium hydroxide.

[0020] Furthermore, the organic solvent is formaldehyde.

[0021] Further, an alkaline reagent is added to adjust the pH to 10.

[0022] Furthermore, the solvent used in the extraction is chloroform.

[0023] In some preferred embodiments of the present invention, hydrochloric acid is first slowly added dropwise to a three-necked flask containing furfurylamine under an ice-water bath. Then, the reaction solution is brought to room temperature (25 °C), and 37% formaldehyde solution is added dropwise to the reaction solution. The reaction is carried out at room temperature for 6 h. After the reaction is completed, the solution is neutralized with sodium hydroxide solution. When the pH of the reaction solution reaches 10, it is extracted with chloroform, the lower organic phase is removed, and the chloroform is removed by rotary evaporation to obtain the 5,5'-methylenedifurfurylamine.

[0024] A third aspect of the present invention provides a bio-based benzoxazine resin, which is obtained by self-curing of the bio-based benzoxazine monomer described in the first aspect.

[0025] Furthermore, the self-curing temperature is preferably 160-220 ℃, and the time is preferably 7-10 h; more preferably, the self-curing is a stepped heating method, with the holding time at each step temperature not less than 1 h, and the temperature difference between adjacent steps not exceeding 30 ℃, for example, self-curing is carried out according to the procedure of 160 ℃ / 2 h + 180 ℃ / 2 h + 200 ℃ / 2 h + 220 ℃ / 2 h.

[0026] A fourth aspect of this invention provides a biodegradable bio-based benzoxazine copolymer resin, obtained by melt mixing and curing the bio-based benzoxazine monomer described in the first aspect with a phenolic monomer containing a Schiff base structure as shown in formula (I); the structure shown in formula (I) is as follows:

[0027] .

[0028] Furthermore, the preferred molar ratio of the bio-based benzoxazine monomer to the phenolic monomer containing the Schiff base structure shown in formula (I) is (1-2):1, for example, 1:1, 1.5:1, 2:1, etc., including but not limited to the molar ratios listed above.

[0029] Furthermore, the melting and mixing temperature is preferably 120-160 °C, and the time is preferably 10-30 min, for example, melting and mixing at 140 °C for 15 min.

[0030] Further, the curing temperature is preferably 160-200 ℃, and the curing time is preferably 6-8 h. More preferably, the curing is carried out by a stepped heating method, with the holding time at each step temperature not less than 1 h, and the temperature difference between adjacent steps not exceeding 30 ℃, for example, self-curing is carried out according to the procedure of 160 ℃ / 2 h + 180 ℃ / 2 h + 200 ℃ / 2 h.

[0031] Furthermore, the phenolic monomer containing the Schiff base structure is prepared by condensation reaction of vanillin and tyramine; preferably, the molar ratio of vanillin to tyramine is 1:(1-1.5), the temperature of the condensation reaction is 60-80 °C, and the time is 5-8 h.

[0032] Furthermore, the reaction is carried out in the presence of a solvent, preferably ethanol.

[0033] The fifth aspect of the present invention provides the use of the bio-based benzoxazine resin described in the third aspect or the biodegradable bio-based benzoxazine copolymer resin described in the fourth aspect in the preparation of adhesives, composite matrix or coatings.

[0034] In this invention, biomass content refers to the percentage of bio-based raw materials. Specifically, the biomass content of benzoxazine monomer is calculated as {[Mr(vanillyl)×2+Mr(furfurylamine)×2] / Mr(bio-based benzoxazine monomer)}×100%={[154.16×2+97.12×2] / 562.24}×100%=89.3%; the biomass content of biodegradable bio-based benzoxazine copolymer resin is calculated as {[Mr(tyramine)+Mr(vanillin)+Mr(vanillyl)×2+Mr(furfurylamine)×2] / [Mr(phenolic monomer containing Schiff base structure)+Mr(bio-based benzoxazine monomer)]}×100%={[137.14+152.15+154.16×2+97.12×2] / [271.27+562.24]}×100%=95.0%. It should be noted that, due to disagreements in the academic community regarding whether paraformaldehyde is a biomass, paraformaldehyde is not considered a biomass in this invention.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] 1. This invention provides a bio-based benzoxazine monomer with a biomass content as high as 89.3%. The bio-based benzoxazine resin prepared by its self-curing exhibits good heat resistance, with a glass transition temperature as high as 330 ℃ and an initial thermal decomposition temperature as high as 360 ℃, which is beneficial for expanding the application window of this type of material at high temperatures. In addition, the above-mentioned bio-based benzoxazine resin can combine excellent mechanical strength and good toughness, with a storage modulus of 3.39 GPa. The tensile strength, tensile modulus and elongation at break at room temperature are 43.2 MPa, 1.72 GPa and 2.67%, respectively, overcoming the high brittleness of traditional benzoxazine resins.

[0037] 2. The bio-based benzoxazine monomer provided by this invention has a low melting temperature and a large difference between its melting and curing temperatures. It can be melt-blended with a fully biomass Schiff base phenolic monomer obtained from the reaction of vanillin and tyramine at a relatively low temperature to prepare a biodegradable bio-based benzoxazine copolymer resin. The curing temperature for preparing the above copolymer is lower than the self-curing temperature of a single bio-based benzoxazine monomer, requiring only 200 °C. This is because the introduced specific Schiff base phenolic monomer contains phenolic hydroxyl groups, which, through hydrogen bonding and proton transfer, effectively reduce the activation energy required for ring-opening of benzoxazine, thereby effectively catalyzing the ring-opening reaction of the benzoxazine monomer. The lower curing temperature helps reduce the thermal stress generated during the curing process, thus contributing to the superior overall performance of the cured resin.

[0038] 3. The biodegradable bio-based benzoxazine copolymer resin prepared by this invention not only possesses biodegradability and high biomass characteristics, but also exhibits outstanding heat resistance and mechanical properties. The high heat resistance of the copolymer stems from the combined effect of highly rigid and strongly polar groups in its crosslinked structure. Specifically, the molecular chain is rich in rigid units such as furan rings and benzene rings, significantly restricting chain segment movement. Furthermore, the introduction of the side group -OH enhances intermolecular forces, further hindering chain segment movement. In addition, the copolymer structure not only contains rigid units such as furan rings and benzene rings, but also has a suitable crosslinking density, thus enabling the copolymer to possess both good mechanical strength and toughness. Furthermore, the overall properties of the copolymer can be adjusted by changing the copolymer ratio. For example, when the molar ratio of bio-based benzoxazine monomer to phenolic monomer containing Schiff base structure is (1-2):1, the glass transition temperature of the prepared benzoxazine copolymer resin is 314-325 ℃, the initial thermal decomposition temperature is 347-354 ℃, the storage modulus is 2.44 GPa-2.89 GPa, the tensile strength is 31.4 MPa-37.7 MPa, the tensile modulus is 1.22 GPa-1.65 GPa, and the elongation at break is 1.54%-3.10%. The mechanical strength is not significantly reduced compared to the resin prepared from a single bio-based benzoxazine monomer, and the toughness is improved, with the elongation at break increasing to 3.10%.

[0039] 4. The bio-based benzoxazine resin and the biodegradable bio-based benzoxazine copolymer resin prepared by this invention have good thermal stability and high carbonization ability. They are both non-flammable materials and have good flame retardant effects.

[0040] 5. The biodegradable bio-based benzoxazine copolymer resin prepared by this invention has good degradation performance and can be degraded in a 1 M HCl aqueous solution containing dimethyl sulfoxide at 80°C. Attached Figure Description

[0041] Figure 1 The 1H NMR spectra of 5,5'-methylenedifurfural (DFDA) and bio-based benzoxazine monomer (VA-dfda) in Example 1 of this invention are shown. 1 H NMR);

[0042] Figure 2 The carbon NMR spectra of 5,5'-methylenedifurfural (DFDA) and bio-based benzoxazine monomer (VA-dfda) in Example 1 of this invention are shown. 13 (C NMR).

[0043] Figure 3 The Fourier transform infrared (FTIR) spectra of 5,5'-methylenedifurfural (DFDA) and bio-based benzoxazine monomer (VA-dfda) in Example 1 of this invention are shown.

[0044] Figure 4 This is the high-resolution mass spectrometry (HRMS) of 5,5'-methylenedifurfuralamine (DFDA) and bio-based benzoxazine monomer (VA-dfda) in Example 1 of this invention.

[0045] Figure 5 The synthesis reaction formula and chemical structural formula of 5,5'-methylenedifurfural (DFDA) and bio-based benzoxazine monomer (VA-dfda) synthesized in Example 1 of this invention are shown.

[0046] Figure 6 The images show the differential scanning calorimetry (DSC) curves of the uncured resins of the bio-based benzoxazine monomer VA-dfda (a) prepared in Example 2 of this invention; and the uncured resins of the benzoxazine copolymer prepared in Example 3, namely 1-VA-dfda / VT (b), 1.5-VA-dfda / VT (c) and 2-VA-dfda / VT (d), under a nitrogen atmosphere in the range of 25 ℃-300 ℃, with heating rates of 5 ℃ / min, 10 ℃ / min, 15 ℃ / min and 20 ℃ / min, respectively.

[0047] Figure 7The thermogravimetric analysis (TGA) curves of the bio-based benzoxazine resin (poly(VA-dfda)) prepared in Example 2 and the biodegradable bio-based benzoxazine copolymer resins (poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), poly(2-VA-dfda / VT)) prepared in Example 3 under a nitrogen atmosphere at 25 ℃-800 ℃, with a heating rate of 10 ℃ / min;

[0048] Figure 8 The tanδ-temperature curves of the bio-based benzoxazine resin (poly(VA-dfda)) prepared in Example 2 and the biodegradable bio-based benzoxazine copolymer resin (poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), poly(2-VA-dfda / VT)) prepared in Example 3 in the range of 25 ℃-350 ℃ with a heating rate of 3 ℃ / min are shown.

[0049] Figure 9 The storage modulus-temperature curves of the bio-based benzoxazine resin (poly(VA-dfda)) prepared in Example 2 and the biodegradable bio-based benzoxazine copolymer resins (poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), poly(2-VA-dfda / VT)) prepared in Example 3 are shown. The heating rate is 3 ℃ / min in the range of 25 ℃-350 ℃.

[0050] Figure 10 The tensile stress-strain curves are those of the bio-based benzoxazine resin (poly(VA-dfda)) prepared in Example 2 of this invention and the biodegradable bio-based benzoxazine copolymer resins (poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), poly(2-VA-dfda / VT)) prepared in Example 3.

[0051] Figure 11 The heat release rate (HRR)-temperature curves of the bio-based benzoxazine resin (poly(VA-dfda)) prepared in Example 2 and the biodegradable bio-based benzoxazine copolymer resins (poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), poly(2-VA-dfda / VT)) prepared in Example 3 are shown.

[0052] Figure 12 The synthesis reaction formula and chemical structural formula of the phenolic compound (VT) containing a Schiff base structure synthesized in Example 3 of this invention are shown.

[0053] Figure 13 These are digital photos of the degradation of the bio-based benzoxazine resin (poly(VA-dfda)) prepared in Example 2 of this invention and the biodegradable bio-based benzoxazine copolymer resin (poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), poly(2-VA-dfda / VT)) prepared in Example 3. From left to right, they are poly(VA-dfda), poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), and poly(2-VA-dfda / VT). Detailed Implementation

[0054] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0055] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The terms “comprising” or “including” used in this invention may also be replaced with the closed form “is” or “consisting of”.

[0056] All raw materials used in the following examples are commercially available, and the specific preparation operations and testing methods involved are conventional methods in the art. Specifically:

[0057] Tested using a nuclear magnetic resonance spectrometer (Bruker 400-600 MHz, Germany). 1 H NMR and 13 C10 NMR, solvent: CDCl3.

[0058] The 600 cm⁻¹ infrared spectrometer (Bruker Vertex 70, Germany) was used to measure the infrared spectrometer. -1 Up to 4000 cm -1 Fourier transform infrared (FTIR) spectra of the region.

[0059] High-resolution time-of-flight (HRMS) mass spectrometry was performed using a high-resolution mass spectrometer (MICRO TOF-Q Ⅲ, Germany) in ASAP mode.

[0060] Differential scanning calorimetry (DSC) curves in the range of 25 °C–300 °C under nitrogen atmosphere were tested using a TA Instrument (Q200, USA) at a heating rate of 10 °C / min.

[0061] Thermogravimetric analysis (TGA) curves were tested under a nitrogen atmosphere from 25 °C to 800 °C using a thermogravimetric analyzer (TA Instrument (Discovery), USA). The heating rate was 10 °C / min, and the temperature at which 5% weight loss occurred was T. di .

[0062] Dynamic mechanical analysis (DMA) was performed using a dynamic mechanical analyzer (TA DMA Q800, USA) at a rate of 3℃ / min in the range of 25℃-350℃. The size of each sample was (30±0.5)mm×(5±0.2)mm×(1±0.1)mm.

[0063] Tensile mechanical properties were tested using a universal testing machine (MTS CMT-4104, China). The tensile test standard was based on the American material testing standard ASTM-D882. The dimensions of each sample were (100±0.2) mm × (10±0.2) mm × (1±0.2) mm, and the samples were measured five times.

[0064] Microcalorimetry (MCC) tests were conducted in a mixed atmosphere (79% nitrogen + 21% oxygen) at a heating rate of 1 °C / s within the range of 75 °C to 750 °C using a microcalorimeter (FTT0001, UK). Example 1

[0065] This embodiment relates to the preparation of bio-based benzoxazine monomers, as detailed below:

[0066] (1) Preparation of 5,5'-methylenedifurfural (DFDA)

[0067] Under ice-water bath conditions, furfurylamine (19.497 g, 0.201 mol) was added to a three-necked flask, followed by the dropwise addition of 120 mL of 6 mol / L hydrochloric acid solution. After the hydrochloric acid solution was completely added, the reaction solution was allowed to reach room temperature (25 °C). Formaldehyde solution (37%, 8.120 g, 0.1 mol) was then added dropwise to the reaction solution, and the reaction was carried out at room temperature (25 °C) for 6 h. After the reaction was complete, the solution was neutralized with 120 mL of 6 mol / L sodium hydroxide solution until the pH reached 10. The solution was then extracted with 100 mL of chloroform. The lower organic phase was collected, washed three times with 500 mL of deionized water, and the chloroform was removed by rotary evaporation to obtain 5,5'-methylenedifurfuralamine, denoted as DFDA.

[0068] The proton NMR spectrum of the prepared product DFDA ( 1 H NMR, carbon nuclear magnetic resonance (NMR) 13 C NMR, FTIR, and high-resolution mass spectrometry (HRMS) are shown in the figures below. Figure 1 , Figure 2 , Figure 3 and Figure 4 .

[0069] (2) Preparation of bio-based benzoxazine monomer (VA-dfda)

[0070] DFDA (9.721 g, 0.0472 mol) and paraformaldehyde (5.664 g, 0.189 mol, degree of polymerization 8-10) were added to a 250 mL three-necked flask and stirred at 75 °C for 1 h. Then, vanillin (16.538 g, 0.107 mol) was added, and the temperature was raised to 140 °C for 3 h. After the reaction was complete, a reddish-brown solid was obtained. After cooling, 100 mL of chloroform was added to dissolve the product, and the solution was washed three times each with 1 mol / L NaOH solution and deionized water. The chloroform was removed by rotary evaporation, and the product was recrystallized in ethyl acetate. After drying the crystals, a reddish-brown solid was obtained, denoted as VA-dfda. The synthetic reaction formula for VA-dfda is shown in [reference needed]. Figure 5 Its mechanism is the Mannich condensation reaction of phenolic derivatives, primary amines and formaldehyde.

[0071] The proton nuclear magnetic resonance spectrum of the prepared product VA-dfda ( 1 H NMR, carbon nuclear magnetic resonance (NMR) 13 C NMR, FTIR, and high-resolution mass spectrometry (HRMS) are shown in the figures below. Figure 1 , Figure 2 , Figure 3 and Figure 4 .

[0072] Figure 1 The 1H NMR spectra of DFDA and VA-dfda ( 1 In the DFDA spectrum (H NMR), 6.05 ppm (H1) and 5.99 ppm (H2) represent hydrogen atoms on the furan ring, 3.94 ppm (H3) represents hydrogen atoms on the methylene group attached to the amino group, 3.77 ppm (H4) represents hydrogen atoms on the methylene group connecting the two furan rings, and 1.62 ppm (H5) represents hydrogen atoms on the amino group. In the VA-dfda spectrum, 6.79 ppm (H1) and 6.57 ppm (H2) represent hydrogen on the benzene ring, 6.15 ppm (H3) and 6.01 ppm (H4) represent hydrogen on the furan ring, 4.97 ppm (H5) and 4.01 ppm (H7) represent hydrogen on the methylene group of the oxazine ring, 4.58 ppm (H6) represents hydrogen on the methylene group attached to the hydroxyl group, 3.93 ppm (H8) represents hydrogen on the methylene group attached to the oxazine ring, 3.89 ppm (H9) represents hydrogen on the methylene group connecting two furan rings, and 3.84 ppm (H... 10) represents the hydrogen atom on the methoxy group, 1.87 ppm (H 11 ) represents the hydrogen atom on the hydroxyl group of an alcohol.

[0073] Figure 2 These are the carbon NMR spectra of DFDA and VA-dfda. 13 In the DFDA NMR spectrum, C1 at 155.65 ppm, C2 at 150.67 ppm, C3 at 107.00 ppm, and C4 at 105.90 ppm represent carbon atoms on the furan ring, C5 at 39.37 ppm represents a carbon atom on the -CH2-NH2 group, and C6 at 27.55 ppm represents a carbon atom on the methylene group connecting the two furan rings. In the VA-dfda spectrum, 150.41 ppm (C2), 147.77 ppm (C3), 142.62 ppm (C5), 132.89 ppm (C6), 119.89 ppm (C7), and 118.07 ppm (C8) represent carbons on the benzene ring, and 151.68 ppm (C1), 146.53 ppm (C4), 112.21 ppm (C9), and 107.18 ppm (C6) represent carbons on the benzene ring. 10 The number at () represents the carbon on the furan ring, 82.18 ppm (C 11 ) and 56.14 ppm (C 13 The value at () represents the C on the oxazine ring, 65.31 ppm (C 12 ) represents C on -CH2-OH-, 55.86 ppm (C 14 ) represents the C on the methoxy group, 48.31 ppm (C 15 ) represents the C on the methylene group attached to the oxazine ring, 27.69 ppm (C 16 ) represents the C on the methylene group that connects the two furan rings.

[0074] Figure 3 These are the FTIR spectra of DFDA and VA-dfda. In the FTIR spectrum of VA-dfda, no characteristic absorption peak for amine groups (3406 cm⁻¹) was observed. -1 and 3293 cm -1 A skeletal vibrational peak belonging to the oxazine ring (931 cm⁻¹) appeared. -1 ) and the asymmetric vibration peak (1224 cm⁻¹) belonging to the -COC- group of the oxazine ring moiety. -1 ) and symmetrical stretching vibration peak (1020 cm) -1 This provides preliminary evidence of the successful synthesis of benzoxazine. Furthermore, the FTIR spectrum of VA-dfda revealed an asymmetric stretching vibration (2920 cm⁻¹) belonging to the methylene group (-CH₂-). -1) and symmetrical stretching vibration (2852 cm) -1 ), proving that the two furan rings are connected by -CH2-; and 3417 cm -1 The broad peak at that point is a characteristic absorption peak of the alcohol hydroxyl group.

[0075] Figure 4 High-resolution mass spectrometry (HRMS) of DFDA and VA-dfda shows that the mass-to-charge ratios are respectively ([C 11 H 14 N2O2H] + :206.1128) and ([C 31 H 34 N2O8H] + The values ​​are approximately 562.2395, almost equal to their theoretical values. The above spectra prove that DFDA and VA-dfda have been successfully synthesized.

[0076] In addition, VA-dfda can be prepared by changing the molar ratio of 5,5'-methylenedifuramine to vanillin and paraformaldehyde to 1:2:3 or 1:2:5, or by changing the reaction temperature after adding vanillin in step (2) to 130 ℃ or 150 ℃. Example 2

[0077] This embodiment relates to the preparation of bio-based benzoxazine resin, as detailed below:

[0078] The VA-dfda prepared in Example 1 was heated from room temperature to 60 °C and held at that temperature for 20 min to ensure complete melting of the monomer. The molten monomer was then added to a preheated mold and cured according to the procedure of 160 °C / 2 h + 180 °C / 2 h + 200 °C / 2 h + 220 °C / 2 h to obtain a bio-based benzoxazine resin, denoted as poly(VA-dfda).

[0079] Figure 6 (a) in the figure is the differential scanning calorimetry (DSC) curve of VA-dfda. The curve of VA-dfda shows a sharp endothermic peak and a symmetrical exothermic peak, which represent its melting peak and curing peak, respectively. As can be seen from the figure, the melting temperature of VA-dfda is low and the difference between the melting temperature and the curing temperature is large.

[0080] The thermogravimetric analysis (TGA) curve of the bio-based benzoxazine resin prepared in this embodiment is as follows: Figure 7 As shown, the initial thermal decomposition temperature (T) of the resin is... di The residual carbon rate Y at 360 ℃ and 800 ℃ is... c It has a purity of 61.6%, indicating good flame retardant properties.

[0081] The tanδ-temperature curve of the bio-based benzoxazine resin prepared in this embodiment is as follows: Figure 8 As shown in the figure, the glass transition temperature (T) of this resin is... g The DMA (330 °C) value is 330 °C.

[0082] The storage modulus-temperature curve and tensile stress-strain curve of the bio-based benzoxazine resin prepared in this embodiment are shown in the figures below. Figure 9 , 10 As shown in the figure, the storage modulus (E') of the resin is 3.39 GPa, the tensile strength at room temperature is 43.2 MPa, the tensile modulus is 1.72 GPa, and the elongation at break is 2.67%, exhibiting both excellent mechanical strength and toughness.

[0083] The heat release rate (HRR)-temperature curve of the bio-based benzoxazine resin prepared in this embodiment is shown below. Figure 11 As shown, the heat release capacity (HRC) of this resin, which characterizes its flame retardant properties, is 97.0 J / (g·k), and the total heat release (THR) is 7.3 kJ / g, classifying it as a non-flammable material. Example 3

[0084] This embodiment relates to the preparation of a biodegradable bio-based benzoxazine copolymer resin, as detailed below:

[0085] (1) Preparation of phenolic monomers (VT) containing Schiff base structure

[0086] Vanillin (15.215 g, 0.1 mol) and tyramine (13.723 g, 0.1 mol) were dissolved in 150 mL of ethanol and refluxed at 60 °C with stirring for 5 h. After the reaction was complete, the mixture was filtered, washed three times with ethanol, and dried to obtain a yellow solid product, denoted as VT. Figure 12 It is its synthetic reaction formula, and its mechanism is the dehydration condensation reaction between the amine group and the aldehyde group.

[0087] (2) Preparation of biodegradable bio-based benzoxazine copolymer resin poly(1-VA-dfda / VT)

[0088] The VA-dfda prepared in Example 1 and the VT prepared in step (1) were melt-blended at 140 °C for 15 min at a molar ratio of 1:1 to obtain the prepolymer 1-VA-dfda / VT;

[0089] Then, it was cured according to the procedure of 160 ℃ / 2 h + 180 ℃ / 2 h + 200 ℃ / 2 h, and the resulting copolymer resin was denoted as poly(1-VA-dfda / VT).

[0090] (3) Preparation of biodegradable bio-based benzoxazine copolymer resin poly(1.5-VA-dfda / VT)

[0091] The VA-dfda prepared in Example 1 and the VT prepared in step (1) were melt-blended at 140 °C for 15 min at a molar ratio of 1.5:1 to obtain the prepolymer 1.5-VA-dfda / VT;

[0092] Then, it was cured according to the procedure of 160 ℃ / 2 h + 180 ℃ / 2 h + 200 ℃ / 2 h, and the resulting copolymer resin was denoted as poly(1.5-VA-dfda / VT).

[0093] (4) Preparation of biodegradable bio-based benzoxazine copolymer resin poly(2-VA-dfda / VT)

[0094] The VA-dfda prepared in Example 1 and the VT prepared in step (1) were melt-blended at 140 °C for 15 min at a molar ratio of 2:1 to obtain the prepolymer 2-VA-dfda / VT;

[0095] Then, it was cured according to the procedure of 160℃ / 2 h + 180℃ / 2 h + 200℃ / 2 h, and the resulting copolymer resin was denoted as poly(2-VA-dfda / VT).

[0096] The differential scanning calorimetry (DSC) curves of the prepolymers 1-VA-dfda / VT, 1.5-VA-dfda / VT, and 2-VA-dfda / VT prepared in this embodiment are shown below. Figure 6 As shown in (b), (c), and (d) of the figure, it can be seen that the curves of the prepolymers all show only one exothermic peak, and they all shift to higher temperatures as the VT content decreases. This indicates that as the VT content decreases, the curing reaction of the prepolymer will take place at a higher temperature.

[0097] The thermogravimetric analysis (TGA) curves of the various biodegradable bio-based benzoxazine copolymer resins prepared in this embodiment are shown below. Figure 7 As shown in the figure, the initial thermal decomposition temperatures (T0) of the copolymer resins poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), and poly(2-VA-dfda / VT) are as follows: di The T values ​​were 347 °C, 350 °C, and 354 °C, respectively, which are higher than the T values ​​of biomass-degradable benzoxazine resins reported in the SCI database. di Value (265-309℃), and char residue Y at 800℃ c The values ​​are 57.9%, 58.4%, and 59.2% respectively, indicating good flame retardant properties.

[0098] The tanδ-temperature curves of the various biodegradable bio-based benzoxazine copolymer resins prepared in this embodiment are as follows: Figure 8 As shown in the figure, the glass transition temperatures (T0) of the copolymer resins poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), and poly(2-VA-dfda / VT) are as follows: g The DMA values ​​were 314 °C, 320 °C, and 325 °C, respectively, far exceeding the T values ​​of biomass-degradable benzoxazine resins included in the SCI database. g (68-287 ℃).

[0099] The storage modulus-temperature curves and tensile stress-strain curves of the various biodegradable bio-based benzoxazine copolymer resins prepared in this embodiment are shown below. Figure 9 , 10 As shown in the figure, the storage modulus (E') of the copolymer resins poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), and poly(2-VA-dfda / VT) are 2.89 GPa, 3.09 GPa, and 2.44 GPa, respectively, which are higher than the storage modulus (1.0 GPa-2.5 GPa) of biomass-degradable benzoxazine resins reported in the SCI database. Moreover, the tensile strengths at room temperature are 31.4 MPa, 35.6 MPa, and 37.7 MPa, respectively, the tensile modulus is 1.65 GPa, 1.46 GPa, and 122 GPa, and the elongation at break is 1.54%, 2.53%, and 3.10%, respectively, exhibiting excellent mechanical strength and toughness.

[0100] In addition, the heat release rate (HRR)-temperature curves of each biodegradable bio-based benzoxazine copolymer resin prepared in this embodiment are as follows: Figure 11 As shown, the heat release capacity (HRC) of the copolymer resins poly(1-VA-dfda / VT), poly(1.5-VA-dfda / VT), and poly(2-VA-dfda / VT) for characterizing flame retardancy are 60.7 J / (g·k), 62.4 J / (g·k), and 66.9 J / (g·k), respectively, and the total heat release (THR) are 3.0 kJ / g, 4.0 kJ / g, and 5.3 kJ / g, respectively, which are classified as non-combustible materials. Example 4

[0101] The bio-based benzoxazine resin prepared in Example 2 and the biodegradable bio-based benzoxazine copolymer resins prepared in Example 3 were placed in 1 M HCl solution (the solvent was a mixed solvent obtained by mixing dimethyl sulfoxide and water at a volume ratio of 9:1) and allowed to stand at 80 °C.

[0102] The results are as follows Figure 13 As shown, the bio-based benzoxazine resin is non-degradable, while the biodegradable bio-based benzoxazine copolymer resins prepared in Example 3 are all degradable under these conditions.

[0103] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. A bio-based benzoxazine monomer, characterized in that, The structure of the bio-based benzoxazine monomer is as follows: 。 2. A method for preparing the bio-based benzoxazine monomer according to claim 1, characterized in that, Includes the following steps: 5,5'-methylenedifurfuralamine was reacted with vanillin and paraformaldehyde by heating to obtain the bio-based benzoxazine monomer; The structure of the 5,5'-methylenedifurfural is shown below: 。 3. The preparation method according to claim 2, characterized in that, The molar ratio of 5,5'-methylenedifurfural to vanillin and paraformaldehyde is 1:2:(3-5). The heating reaction is carried out at a temperature of 130-150 °C for 3-6 h.

4. The preparation method according to claim 2, characterized in that, The preparation method of the 5,5'-methylenedifurfural is as follows: Furfural is reacted with formaldehyde in the presence of an acid reagent and an organic solvent. After the reaction is complete, an alkaline reagent is added to adjust the pH to alkaline. After extraction and rotary evaporation to remove the solvent, the 5,5'-methylenedifurfural is obtained.

5. A bio-based benzoxazine resin, characterized in that, It is obtained by self-curing of the bio-based benzoxazine monomer as described in claim 1.

6. The bio-based benzoxazine resin according to claim 5, characterized in that, The self-curing temperature is 160-220 ℃, and the time is 7-10 h.

7. A biodegradable bio-based benzoxazine copolymer resin, characterized in that, It is obtained by melting and mixing the bio-based benzoxazine monomer of claim 1 with a phenolic monomer containing a Schiff base structure as shown in formula (I) and then solidifying it; the structure shown in formula (I) is as follows: 。 8. The biodegradable bio-based benzoxazine copolymer resin according to claim 7, characterized in that, The molar ratio of the bio-based benzoxazine monomer to the phenolic monomer containing the Schiff base structure shown in formula (I) is (1-2):1; The melting and mixing temperature is 120-160 ℃, and the time is 10-30 min; The curing temperature is 160-200 ℃, and the time is 6-8 h.

9. The use of a bio-based benzoxazine resin according to claim 5 or 6, or a biodegradable bio-based benzoxazine copolymer resin according to claim 7 or 8, in the preparation of adhesives, composite matrixes, or coatings.

Images