Bio-based benzoxazine monomers, resins, and methods of making the same

Abstract

This invention relates to a bio-based benzoxazine monomer, resin, and its preparation method, belonging to the field of polymer materials technology. The structural formula of the bio-based benzoxazine monomer of this invention is shown in formula (I): wherein R1 is H or methyl; R2 is H or methoxy; and R3 is methyl, ethyl, phenethyl, or furanylmethyl. Compared with existing technologies, the resin system synthesized by this invention is more environmentally friendly and possesses higher heat resistance and excellent mechanical properties. The bio-based photocurable 3D printing benzoxazine resin prepared by this invention has good prospects for industrial application and commercial economic value. The method of this invention achieves high yield and successfully synthesizes the monomer.

Description

Technical Field

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

[0002] 3D printing is a technology that uses digital model files as a basis to form complex objects layer by layer. It has many advantages over traditional manufacturing methods and has been widely used in many fields such as biomedicine, science and research, aerospace, automotive, model verification, and structural engineering. Among them, photopolymerization technology has advantages over other molding technologies, such as fast molding speed, high precision, energy saving, and being green and pollution-free.

[0003] With the widespread application of 3D printing technology in various fields, the performance requirements for photopolymer 3D printed products are becoming increasingly stringent. Among these requirements, the photosensitive resin system is one of the most important factors affecting the quality of 3D printed products. Currently, commonly used photosensitive resin systems include epoxy resin and acrylate resin. While these resins can be used to create complex structures, they are insufficient in terms of heat resistance and mechanical properties, failing to meet the requirements of fields such as aerospace and rail transportation. Therefore, developing novel, high-performance photosensitive resin materials has become a key to breakthroughs in photochemical polymerization technology.

[0004] To improve the heat resistance and mechanical properties of photocurable 3D printed products, common measures include developing new resins, adjusting formulations, and adding nano-inorganic fillers. Among these, functionalizing existing resin systems with high heat resistance and excellent mechanical properties through photocuring (i.e., developing new resin systems) allows for extensive research. For example, patent CN 112646085 B discloses a photosensitive resin composition based on bismaleimide resin and its application in 405nm 3D printing. The synthesized photocurable bismaleimide resin system achieves a glass transition temperature of 133.4℃, a flexural strength of 117.5MPa, and a tensile strength of 72.9MPa after photocuring. Patent CN 114478914 B discloses a benzoxazine resin for photocurable 3D printing and its application. The synthesized photocurable benzoxazine resin system, after photocurable 3D printing and thermal curing, achieves a mechanical strength of 95.3MPa and a glass transition temperature of 267℃. The literature “High-performance cyanate ester resins with interpenetration networks for 3D printing” (Zhou ZX, Li Y, Zhong J, et al. ACS applied materials & interfaces, 2020, 12(34): 38682-38689.) uses trifunctional acrylates and low-viscosity cyanate esters to blend. After photopolymerization 3D printing and thermopolymerization, the glass transition temperature of the cured product can reach 240-245℃ and the decomposition temperature can reach 362-381℃. The literature "Heat-resistant phthalonitrile-based resins for 3D printing via VAT photopolymerization" (Nechausov S, Aleksanova A, Morozov O, et al. ACS Applied Polymer Materials, 2022, 4(10): 6958-6968.) prepared a photocurable phthalonitrile resin system. After photocuring 3D printing and thermal curing, the glass transition temperature of the cured product reached 354℃, and the decomposition temperature was 365℃. Existing technologies demonstrate that photocuring functionalizes existing high-performance resin systems can effectively improve their heat resistance and mechanical properties. However, the raw materials used are all derived from petroleum-based compounds. Therefore, introducing bio-based raw materials into the photocurable resin system through chemical reactions to prepare a bio-based high-performance resin system suitable for photocurable 3D printing is one of the directions of 3D printing research.

[0005] Benzoxazine is a novel thermosetting resin developed based on phenolic resin. It not only inherits the excellent heat resistance and thermal stability of phenolic resin, but also features low volume shrinkage after curing, does not require strong acid or alkali catalysis during curing (ring-opening polymerization can be completed solely by heat), and exhibits good dimensional stability. Simultaneously, polybenzoxazine resin also possesses excellent mechanical and dielectric properties, making it increasingly important in the electronics, aerospace, and other industrial fields. However, the high curing temperature (180–250℃) of benzoxazine resin leads to poor processability, limiting processing to sheets, coatings, rods, and fiber composites. Therefore, it is crucial to leverage the advantages of 3D printing manufacturing technology to develop high-performance photosensitive resins that can achieve miniaturization, high precision, high complexity, and on-demand design, which holds promising industrial application prospects and commercial economic value. Summary of the Invention

[0006] The first objective of this invention is to provide a novel bio-based benzoxazine monomer.

[0007] To achieve the first objective of this invention, the structural formula of the bio-based benzoxazine monomer is shown in formula (I) below:

[0008]

[0009] Wherein, R1 is H or methyl; R2 is H or methoxy; R3 is methyl, ethyl, phenylethyl, or furanmethyl.

[0010] In one specific embodiment, the method for preparing the bio-based benzoxazine monomer includes:

[0011]

[0012] The compound shown in formula (II) was dissolved in solvent C, and an acid-binding agent was added. The mixture was stirred and cooled to -20°C to -5°C. Compound A was added dropwise at a rate of 1 to 10 mL / min under an inert atmosphere and light-shielding conditions, while controlling the reaction temperature to -5 to 0°C. After the addition was completed, the temperature was raised to room temperature at a rate of 5 to 10°C / min and stirred for 12 to 24 h. After the reaction was completed, the bio-based benzoxazine monomer was obtained by purification. The compound A is at least one of acryloyl chloride or methacryloyl chloride.

[0013] The reaction equation for the preparation of bio-based benzoxazine monomers is as follows:

[0014]

[0015] In one specific embodiment, the solvent C includes at least one of chloroform, dichloromethane, xylene, dioxane, DMF, N,N-dimethylacetamide, or N-methylpyrrolidone;

[0016] The acid-binding agent includes at least one of triethylamine, pyridine, and N,N-diisopropylethylamine;

[0017] The preferred molar ratio of the compound shown in formula (II), compound A, and acid-binding agent is 1:1 to 1.2:1 to 1.2.

[0018] In one specific embodiment, the preparation method of the compound represented by formula (II) includes: mixing phenol source, amine source, paraformaldehyde and solvent A, raising the temperature to 60-120°C at a rate of 10-30°C / min, stirring the reaction for 5-48 hours, and purifying to obtain the compound represented by formula (II);

[0019] The phenolic source includes at least one of tyrosol and homovanillin;

[0020] The amine source includes at least one of methylamine, ethylamine, 2-phenylethylamine, and furfurylamine;

[0021] Solvent A preferably includes at least one of chloroform, toluene, xylene, ethanol, dioxane, DMF, DMAc, or NMP.

[0022] The reaction equation for the compound represented by formula (II) is as follows:

[0023]

[0024] Paraformaldehyde can be an aqueous solution of formaldehyde, paraformaldehyde, tyrosol (p-hydroxyphenylethanol), and homovanillin (4-hydroxy-3-methoxyphenylethanol).

[0025] In one specific embodiment, the molar ratio of the phenolic source, amine source, and paraformaldehyde is 1:1:2 to 2.4. The molar amount of formaldehyde compound in the molar ratio of phenolic source, amine source, and paraformaldehyde is calculated in formaldehyde equivalents.

[0026] In one specific embodiment, the method for purifying to obtain the bio-based benzoxazine monomer includes:

[0027] After the reaction is complete, the mixture is filtered to remove the precipitated acid-binding agent hydrochloride. Solvent B is added for dilution, and the organic phase is washed with alkali 2 to 6 times, then washed with water until neutral. The phase is dried, filtered, and the solvent is removed by rotary evaporation to obtain the bio-based benzoxazine monomer. The preferred method for removing the solvent by rotary evaporation is to add 0.005 wt.% to 0.02 wt.% of a polymerization inhibitor to the bio-based benzoxazine monomer before rotary evaporation.

[0028] The polymerization inhibitor preferably includes at least one of hydroquinone, 4-methoxyphenol, p-tert-butylcatechol, and 2,6-di-tert-butyl-p-methylphenol.

[0029] The method for purifying the compound represented by formula (II) includes: after the reaction is completed, cooling to room temperature, adding solvent B for dilution, washing with alkali 2 to 6 times, washing with water until neutral, and drying to obtain the compound represented by formula (II); the alkali washing is preferably done with 0.5 to 4 mol / L NaOH solution;

[0030] Solvent B preferably includes at least one of chloroform or dichloroform.

[0031] A second objective of this invention is to provide a bio-based benzoxazine resin.

[0032] To achieve the second objective of this invention, the bio-based benzoxazine resin is obtained by curing the aforementioned bio-based benzoxazine monomer; preferably, the curing includes photocuring and thermal curing; more preferably, the curing is as follows: mixing the bio-based benzoxazine monomer with an active diluent and a photocuring aid to obtain a mixture, subjecting the mixture to ultraviolet 3D printing and thermal curing treatment to obtain the bio-based benzoxazine resin, wherein the mass ratio of the bio-based benzoxazine monomer to the active diluent is 50wt.% to 80wt.%: 20wt.% to 50wt.%, and the photocuring aid is preferably at least one of a UV photoradical initiator or an ultraviolet absorber; the ultraviolet absorber is preferably at least one of benzophenones and benzotriazoles.

[0033] In one specific embodiment, the reactive diluent includes at least one of the following: isoborneol acrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, dimethylolpropane tetraacrylate, dipropylene glycol diacrylate, 3-glycidyl ether oxypropyltrimethoxysilane, polyethylene glycol diacrylate, cyclotrimethylolpropane methyl acetal acrylate, N-vinylpyrrolidone, acrylmorpholine, hydroxyethyl methacrylate, tetrahydrofuran acrylate, and lauryl methacrylate.

[0034] The UV photoradical initiator includes at least one selected from benzoin dimethyl ether, benzophenone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 2-isopropylthioxanthone, ethyl 2,46-trimethylbenzoylphenylphosphonate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and 1-hydroxycyclohexylbenzophenone; the amount of UV photoradical initiator added is preferably 2 wt.% to 5 wt.% of the total resin mass.

[0035] In one specific embodiment, the wavelength of the ultraviolet curing is 355-405nm, the exposure time is 5-45s / layer, and the layer thickness is 20-60μm;

[0036] The thermosetting process preferably includes: heating to 120°C and holding for 1-2 hours, then heating to 140°C and holding for 1-2 hours, then heating to 160°C and holding for 1-2 hours, then heating to 180°C and holding for 1-2 hours, then heating to 200°C and holding for 1-2 hours, and then heating to 220°C and holding for 2-4 hours.

[0037] A third objective of this invention is to provide a method for preparing a bio-based benzoxazine monomer.

[0038] To achieve the third objective of this invention, the method for preparing the bio-based benzoxazine monomer includes:

[0039]

[0040] The compound shown in formula (II) was dissolved in solvent C, and an acid-binding agent was added. The mixture was stirred and cooled to -20°C to -5°C. Compound A was added dropwise at a rate of 1 to 10 mL / min under an inert atmosphere and light-shielding conditions, while controlling the reaction temperature to -5 to 0°C. After the addition was completed, the temperature was raised to room temperature at a rate of 5 to 10°C / min and stirred for 12 to 24 h. After the reaction was completed, the mixture was purified to obtain a bio-based benzoxazine monomer. The compound A is at least one of acryloyl chloride or methacryloyl chloride.

[0041] The solvent C preferably includes at least one of chloroform, dichloromethane, xylene, dioxane, DMF, N,N-dimethylacetamide, or N-methylpyrrolidone;

[0042] The acid-binding agent includes at least one of triethylamine, pyridine, and N,N-diisopropylethylamine;

[0043] The preferred molar ratio of the compound shown in formula (II), compound A, and acid-binding agent is 1:1 to 1.2:1 to 1.2.

[0044] Beneficial effects:

[0045] 1. Based on its flexible molecular design capabilities, this invention utilizes bio-based phenolic and amine sources to prepare photocurable bio-based benzoxazine resins through a two-step reaction. Through formulation design, a high-performance bio-based benzoxazine resin system is prepared via photocuring 3D printing and thermosetting. Compared to existing technologies, the resin system synthesized in this invention is more environmentally friendly and possesses higher heat resistance and superior mechanical properties.

[0046] 2. The bio-based photopolymerizable 3D printing benzoxazine resin prepared by this invention endows benzoxazine monomers with photosensitive groups, thereby giving them photosensitivity. This is expected to fill the gap in high-performance photosensitive resins and broaden the application fields of benzoxazine resins. By combining 3D printing technology, miniaturized, high-precision, highly complex, and customizable high-performance photosensitive resins can be achieved, demonstrating good prospects for industrial application and commercial economic value.

[0047] 3. The esterification reaction of the compound shown in formula (II) is difficult. If the synthesis conditions are not suitable, the yield of the product is low and the product separation is difficult. The method of the present invention has a high yield and successfully synthesizes the monomer. Attached Figure Description

[0048] Figure 1 The image shows the Fourier transform infrared (FT-IR) spectra of the hydroxyl-containing bio-based benzoxazine resin and its acrylate compounds in Example 3.

[0049] Figure 2 The 1H NMR spectrum of the hydroxyl-containing bio-based benzoxazine resin and its acrylate compound in Example 3 ( 1 H-NMR).

[0050] Figure 3 The carbon NMR spectra of the hydroxyl-containing bio-based benzoxazine resin and its acrylate compounds in Example 3 are shown. 13 C-NMR).

[0051] Figure 4 The product is the product obtained by photopolymerization 3D printing and thermopolymerization of the hydroxyl-containing bio-based benzoxazine acrylate composition in Example 3.

[0052] Figure 5 The thermomechanical dynamic curves of the hydroxyl-containing bio-based benzoxazine acrylate composition in Example 3 after photocuring 3D printing and thermal curing are shown. T-fa-MA-UV represents the photocured sample, and T-fa-MA-UV represents the thermally cured sample. Detailed Implementation

[0053] To achieve the first objective of this invention, the structural formula of the bio-based benzoxazine monomer is shown in formula (I) below:

[0054]

[0055] Wherein, R1 is H or methyl; R2 is H or methoxy; R3 is methyl, ethyl, phenylethyl, or furanmethyl.

[0056] In one specific embodiment, the method for preparing the bio-based benzoxazine monomer includes:

[0057]

[0058] The compound shown in formula (II) was dissolved in solvent C, and an acid-binding agent was added. The mixture was stirred and cooled to -20°C to -5°C. Compound A was added dropwise at a rate of 1 to 10 mL / min under an inert atmosphere and light-shielding conditions, while controlling the reaction temperature to -5 to 0°C. After the addition was completed, the temperature was raised to room temperature at a rate of 5 to 10°C / min and stirred for 12 to 24 h. After the reaction was completed, the bio-based benzoxazine monomer was obtained by purification. The compound A is at least one of acryloyl chloride or methacryloyl chloride.

[0059] The reaction equation for the preparation of bio-based benzoxazine monomers is as follows:

[0060]

[0061] In one specific embodiment, the solvent C includes at least one of chloroform, dichloromethane, xylene, dioxane, DMF, N,N-dimethylacetamide, or N-methylpyrrolidone;

[0062] The acid-binding agent includes at least one of triethylamine, pyridine, and N,N-diisopropylethylamine;

[0063] The preferred molar ratio of the compound shown in formula (II), compound A, and acid-binding agent is 1:1 to 1.2:1 to 1.2.

[0064] In one specific embodiment, the preparation method of the compound represented by formula (II) includes: mixing phenol source, amine source, paraformaldehyde and solvent A, raising the temperature to 60-120°C at a rate of 10-30°C / min, stirring the reaction for 5-48 hours, and purifying to obtain the compound represented by formula (II);

[0065] The phenolic source includes at least one of tyrosol and homovanillin;

[0066] The amine source includes at least one of methylamine, ethylamine, 2-phenylethylamine, and furfurylamine;

[0067] Solvent A preferably includes at least one of chloroform, toluene, xylene, ethanol, dioxane, DMF, DMAc, or NMP.

[0068] The reaction equation for the compound represented by formula (II) is as follows:

[0069]

[0070] Paraformaldehyde can be an aqueous solution of formaldehyde, paraformaldehyde, tyrosol (p-hydroxyphenylethanol), and homovanillin (4-hydroxy-3-methoxyphenylethanol).

[0071] In one specific embodiment, the molar ratio of the phenolic source, amine source, and formaldehyde compound is 1:1:2 to 2.4. The molar amount of formaldehyde compound in the molar ratio of phenolic source, amine source, and paraformaldehyde is calculated in formaldehyde equivalents.

[0072] In one specific embodiment, the method for purifying to obtain the bio-based benzoxazine monomer includes:

[0073] After the reaction is complete, the mixture is filtered to remove the precipitated acid-binding agent hydrochloride. Solvent B is added for dilution, and the organic phase is washed with alkali 2 to 6 times, then washed with water until neutral. The phase is dried, filtered, and the solvent is removed by rotary evaporation to obtain the bio-based benzoxazine monomer. The preferred method for removing the solvent by rotary evaporation is to add 0.005 wt.% to 0.02 wt.% of a polymerization inhibitor to the bio-based benzoxazine monomer before rotary evaporation.

[0074] The polymerization inhibitor preferably includes at least one of hydroquinone, 4-methoxyphenol, p-tert-butylcatechol, and 2,6-di-tert-butyl-p-methylphenol.

[0075] The method for purifying the compound represented by formula (II) includes: after the reaction is completed, cooling to room temperature, adding solvent B for dilution, washing with alkali 2 to 6 times, washing with water until neutral, and drying to obtain the compound represented by formula (II); the alkali washing is preferably done with 0.5 to 4 mol / L NaOH solution;

[0076] Solvent B preferably includes at least one of chloroform or dichloroform.

[0077] To achieve the second objective of this invention, the bio-based benzoxazine resin is obtained by curing the aforementioned bio-based benzoxazine monomer; preferably, the curing includes photocuring and thermal curing; more preferably, the curing is as follows: mixing the bio-based benzoxazine monomer with an active diluent and a photocuring aid to obtain a mixture, subjecting the mixture to ultraviolet 3D printing and thermal curing treatment to obtain the bio-based benzoxazine resin, wherein the mass ratio of the bio-based benzoxazine monomer to the active diluent is 50wt.% to 80wt.%: 20wt.% to 50wt.%, and the photocuring aid is preferably at least one of a UV photoradical initiator or an ultraviolet absorber; the ultraviolet absorber is preferably at least one of benzophenones and benzotriazoles.

[0078] In one specific embodiment, the reactive diluent includes at least one of the following: isoborneol acrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, dimethylolpropane tetraacrylate, dipropylene glycol diacrylate, 3-glycidyl ether oxypropyltrimethoxysilane, polyethylene glycol diacrylate, cyclotrimethylolpropane methyl acetal acrylate, N-vinylpyrrolidone, acrylmorpholine, hydroxyethyl methacrylate, tetrahydrofuran acrylate, and lauryl methacrylate.

[0079] The UV photoradical initiator includes at least one selected from benzoin dimethyl ether, benzophenone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 2-isopropylthioxanthone, ethyl 2,46-trimethylbenzoylphenylphosphonate, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and 1-hydroxycyclohexylbenzophenone; the amount of UV photoradical initiator added is preferably 2 wt.% to 5 wt.% of the total resin mass.

[0080] In one specific embodiment, the wavelength of the ultraviolet curing is 355-405nm, the exposure time is 5-45s / layer, and the layer thickness is 20-60μm;

[0081] The thermosetting process preferably includes: heating to 120°C and holding for 1-2 hours, then heating to 140°C and holding for 1-2 hours, then heating to 160°C and holding for 1-2 hours, then heating to 180°C and holding for 1-2 hours, then heating to 200°C and holding for 1-2 hours, and then heating to 220°C and holding for 2-4 hours.

[0082] To achieve the third objective of this invention, the method for preparing the bio-based benzoxazine monomer includes:

[0083]

[0084] The compound shown in formula (II) was dissolved in solvent C, and an acid-binding agent was added. The mixture was stirred and cooled to -20°C to -5°C. Compound A was added dropwise at a rate of 1 to 10 mL / min under an inert atmosphere and light-shielding conditions, while controlling the reaction temperature to -5 to 0°C. After the addition was completed, the temperature was raised to room temperature at a rate of 5 to 10°C / min and stirred for 12 to 24 h. After the reaction was completed, the mixture was purified to obtain a bio-based benzoxazine monomer. The compound A is at least one of acryloyl chloride or methacryloyl chloride.

[0085] The solvent C preferably includes at least one of chloroform, dichloromethane, xylene, dioxane, DMF, N,N-dimethylacetamide, or N-methylpyrrolidone;

[0086] The acid-binding agent includes at least one of triethylamine, pyridine, and N,N-diisopropylethylamine;

[0087] The preferred molar ratio of the compound shown in formula (II), compound A, and acid-binding agent is 1:1 to 1.2:1 to 1.2.

[0088] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0089] Example 1

[0090] (1) In a 500 mL reactor equipped with a mechanical stirrer, thermometer, and condenser, 69.0 g (0.5 mol) of 4-hydroxyphenylethanol, 15.5 g (0.5 mol) of methylamine, 98.0 g (1.2 mol) of 37 wt.% formaldehyde aqueous solution, and 180 g of chloroform were added. The temperature was slowly increased to 60 °C at a rate of 10 °C / min and reacted for 24 h. After the reaction was completed, the mixture was cooled to room temperature, diluted with 100 mL of dichloromethane, and then washed twice with 200 mL of 1 mol / L NaOH solution, followed by washing with water until neutral. After washing with water, the organic layer was dried with anhydrous magnesium sulfate, and the solvent was removed by rotary evaporation to obtain a hydroxyl-containing bio-based benzoxazine.

[0091] (2) Weigh 96.5 g (0.5 mol) of the above-mentioned hydroxyl-containing bio-based benzoxazine and dissolve it in 600 mL of dichloromethane. Add 50.5 g (0.5 mol) of triethylamine as an acid-binding agent, then stir and cool the mixture to -10 °C. Under an inert atmosphere and in the absence of light, slowly add 45 g (0.5 mol) of acryloyl chloride at a rate of 4 mL / min, controlling the reaction temperature within the range of -5 to 0 °C. After the addition is complete, slowly raise the temperature to room temperature at a rate of 5 °C / min and stir the reaction for 24 h. After the reaction is complete, filter to remove the precipitated triethylamine hydrochloride. Wash the organic phase twice with 300 mL of 1 mol / L NaOH solution, and then wash with water until neutral. After drying the organic phase with anhydrous magnesium sulfate, filter to obtain a propylene ester-functionalized benzoxazine solution. The solid content of the propylene ester-functionalized benzoxazine solution was tested to be 20%. 0.02 wt.% of the polymerization inhibitor p-tert-butylcatechol was added to the solution, and then the solvent was removed by rotary evaporation to obtain 105 g of esterified propylene ester-functionalized benzoxazine.

[0092] (3) A benzoxazine resin composition suitable for photocuring 3D printing was prepared by adding propylene ester-functionalized benzoxazine as the main component (60 wt.), reactive diluent trimethylolpropane triacrylate (15 wt.%), isoborneol acrylate (25 wt.%), and 2 wt.% photoinitiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide. The resin composition was photocured using DLP (Digital Laser Processing) with a UV curing wavelength of 405 nm, an exposure time of 25 s / layer, and a layer thickness of 20 μm. After printing, the sample was thermocured using a process of slowly heating to 120 °C and holding for 2 h, then heating to 140 °C and holding for 2 h, then heating to 160 °C and holding for 2 h, then heating to 180 °C and holding for 2 h, then heating to 200 °C and holding for 2 h, and finally heating to 220 °C and holding for 4 h. This process resulted in a 3D printed product based on a bio-based benzoxazine resin photosensitive resin composition.

[0093] This invention enables the rapid preparation of high-performance bio-based benzoxazine resin products through a dual photo-thermal curing reaction. The performance of the product after thermal curing is detailed in Table 1.

[0094] Table 1 Product performance after thermosetting

[0095]

[0096] Example 2

[0097] (1) In a 500 mL reactor equipped with a mechanical stirrer, thermometer, and condenser, 69.0 g (0.5 mol) of 4-hydroxyphenylethanol, 22.5 g (0.5 mol) of ethylamine, 30.0 g (1.0 mol) of trioxane, and 180 g of toluene were added. The temperature was slowly increased to 120 °C at a rate of 10 °C / min and reacted for 5 h. After the reaction was completed, the mixture was cooled to room temperature, diluted with 100 mL of dichloromethane, and then washed twice with 100 mL of 1 mol / L NaOH solution, followed by washing with water until neutral. After washing with water, the organic layer was dried with anhydrous magnesium sulfate, and the solvent was removed by rotary evaporation to obtain a hydroxyl-containing bio-based benzoxazine.

[0098] (2) Weigh 103.5 g (0.5 mol) of the above-mentioned hydroxyl-containing bio-based benzoxazine and dissolve it in 650 mL of chloroform. Add 77.4 g (0.6 mol) of the acid-binding agent N,N-diisopropylethylamine, and then stir and cool the mixed solution to -10 °C. Under an inert atmosphere and in the absence of light, slowly add 62.4 g (0.6 mol) of methacryloyl chloride at a rate of 2 mL / min, controlling the reaction temperature within the range of -5 to 0 °C. After the addition is complete, slowly raise the temperature to room temperature at a rate of 5 °C / min and stir the reaction for 12 h. After the reaction is complete, filter to remove the precipitated N,N-diisopropylethylamine hydrochloride. Wash the organic phase twice with 200 mL of 1 mol / L NaOH solution, and then wash with water until neutral. After drying the organic phase with anhydrous magnesium sulfate, filter to obtain a methacrylic acid-functionalized benzoxazine solution. The solid content of the methacrylate-functionalized benzoxazine solution was tested to be 18%. 0.01 wt.% of the polymerization inhibitor 4-methoxyphenol was added to the solution, and then the solvent was removed by rotary evaporation to obtain 110 g of esterified methacrylate-functionalized benzoxazine.

[0099] (3) A benzoxazine resin composition suitable for photocuring 3D printing was prepared by adding 25 wt.% of reactive diluents tripropylene glycol diacrylate, 25 wt.% of 1,6-hexanediol diacrylate, and 2 wt.% of photoinitiator 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone as the main component of propylene ester-functionalized benzoxazine. The resin composition was photocured using DLP for 3D printing. The UV curing wavelength was 405nm, the exposure time was 30s / layer, and the layer thickness was 50μm. After printing, the sample was thermocured. The thermocuring procedure was as follows: slowly raise the temperature to 120℃ and hold for 2h, then raise the temperature to 140℃ and hold for 2h, then raise the temperature to 160℃ and hold for 2h, then raise the temperature to 180℃ and hold for 2h, then raise the temperature to 200℃ and hold for 2h, and finally raise the temperature to 220℃ and hold for 4h. Finally, a 3D printed product based on a bio-based benzoxazine resin photosensitive resin composition was obtained.

[0100] Example 3

[0101] (1) In a 500 mL reactor equipped with a mechanical stirrer, thermometer, and condenser, 69.0 g (0.5 mol) of 4-hydroxyphenylethanol, 48.6 g (0.5 mol) of furfurylamine, 36.0 g (1.2 mol) of paraformaldehyde, and 200 g of chloroform were added. The temperature was slowly increased to 65 °C at a rate of 10 °C / min and reacted for 24 h. After the reaction was completed, the mixture was cooled to room temperature, diluted with 200 mL of dichloromethane, and then washed twice with 150 mL of 1 mol / L NaOH solution, followed by washing with water until neutral. After washing with water, the organic layer was dried with anhydrous magnesium sulfate, and the solvent was removed by rotary evaporation to obtain a hydroxyl-containing bio-based benzoxazine.

[0102] (2) Weigh 129.5 g (0.5 mol) of the above-mentioned hydroxyl-containing bio-based benzoxazine and dissolve it in 500 mL of dichloromethane. Add 60.6 g (0.6 mol) of triethylamine as an acid-binding agent, then stir and cool the mixture to -10 °C. Under an inert atmosphere and in the absence of light, slowly add 54 g (0.6 mol) of acryloyl chloride at a rate of 5 mL / min, controlling the reaction temperature within the range of -5 to 0 °C. After the addition is complete, slowly raise the temperature to room temperature at a rate of 10 °C / min and stir the reaction for 24 h. After the reaction is complete, filter to remove the precipitated triethylamine hydrochloride. Wash the organic phase twice with 200 mL of 1 mol / L NaOH solution, and then wash with water until neutral. After drying the organic phase with anhydrous magnesium sulfate, filter to obtain a propylene ester-functionalized benzoxazine solution. The solid content of the propylene ester-functionalized benzoxazine solution was tested to be 18%. 0.005 wt.% of the polymerization inhibitor 2,6-di-tert-butyl-p-methylphenol was added to the solution, followed by rotary evaporation to remove the solvent, yielding 130 g of esterified propylene ester-functionalized benzoxazine.

[0103] The infrared spectra of the hydroxyl-containing bio-based benzoxazine and its acrylate compounds prepared in this embodiment are shown below. Figure 1 The figure shows 3383cm. -1 The corresponding structure contains the hydroxyl group -OH of hydroxybenzoxazine; 1724 cm -1 The characteristic peak corresponding to the carbon-oxygen double bond (C=O) in the acrylate structure; 1620 cm⁻¹ -1 The characteristic peak corresponding to the carbon-carbon double bond (C=C) in the acrylate structure; 1500 cm⁻¹ -1 The characteristic peaks of furfurylamine in the corresponding structure; 1227 and 1016 cm⁻¹ -1 The characteristic peak of Ar-O-CH2 in the benzoxazine structure corresponds to 937 cm⁻¹. -1 Characteristic peaks corresponding to the oxazine ring structure. The 1H and 1C NMR spectra of the hydroxyl-containing bio-based benzoxazine and its acrylate compounds prepared in this example are shown below. Figure 2 and Figure 3 In the 1H N2 spectrum, the Ar-CH2-N and O-CH2-N on the oxazine ring correspond to H N2. 1 H 2 The position; the two methylene characteristic carbon resonance peaks of Ar-CH2-N and O-CH2-N on the oxazine ring in the carbon spectrum correspond to C 6 C 7 The positions of the remaining hydrogen and carbon atoms in the structure also correspond to those in the figure, and the number of hydrogen atoms corresponds to the same integral area in the figure. As shown in the figure, the preparation of hydroxybenzoxazine and bio-based benzoxazine acrylate in this embodiment was successful.

[0104] (3) A benzoxazine resin composition suitable for photocuring 3D printing was prepared by adding 1,6-hexanediol diacrylate (30 wt.%) as an active diluent and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (5 wt.%) as a photoinitiator. The resin composition was photocured using DLP with a wavelength of 405 nm, an exposure time of 45 s / layer, and a layer thickness of 50 μm. After printing, the sample was thermocured. The thermocuring procedure was as follows: slowly raise the temperature to 120 °C and hold for 1 h, then raise the temperature to 140 °C and hold for 1 h, then raise the temperature to 160 °C and hold for 1 h, then raise the temperature to 180 °C and hold for 1 h, then raise the temperature to 200 °C and hold for 1 h, and then raise the temperature to 220 °C and hold for 4 h. Finally, a 3D printed product based on a bio-based benzoxazine resin photosensitive resin composition was obtained. Dynamic thermomechanical analysis of the samples showed that the glass transition temperature of the 3D printed product was 61.9℃ and the thermal decomposition temperature was 249.5℃. After further thermosetting, the glass transition temperature of the sample was 229.0℃ and the thermal decomposition temperature was 339.2℃.

[0105] Example 4

[0106] (1) In a 500 mL reactor equipped with a mechanical stirrer, thermometer, and condenser, 84.0 g (0.5 mol) of 4-hydroxy-3-methoxyphenylethanol, 60.5 g (0.5 mol) of 2-phenylethylamine, 36.0 g (1.2 mol) of paraformaldehyde, and 300 g of xylene were added. The temperature was slowly increased to 120 °C at a rate of 10 °C / min and reacted for 8 h. After the reaction was completed, the mixture was cooled to room temperature, diluted with 200 mL of dichloromethane, and then washed twice with 200 mL of 1 mol / L NaOH solution, followed by washing with water until neutral. After washing with water, the organic layer was dried with anhydrous magnesium sulfate, and the solvent was removed by rotary evaporation to obtain a hydroxyl-containing bio-based benzoxazine.

[0107] (2) Weigh 156.5 g (0.5 mol) of the above-mentioned hydroxyl-containing bio-based benzoxazine and dissolve it in 600 mL of dichloromethane. Add 47.4 g (0.6 mol) of pyridine as an acid-binding agent, and then stir and cool the mixture to -10 °C. Under an inert atmosphere and in the absence of light, slowly add 62.4 g (0.6 mol) of methacryloyl chloride at a rate of 5 mL / min, controlling the reaction temperature within the range of -5 to 0 °C. After the addition is complete, slowly raise the temperature to room temperature at a rate of 10 °C / min and stir the reaction for 24 h. After the reaction is complete, filter to remove the precipitated pyridine hydrochloride. Wash the organic phase twice with 200 mL of 1 mol / L NaOH solution, and then wash with water until neutral. After drying the organic phase with anhydrous magnesium sulfate, filter to obtain a methacrylic acid-functionalized benzoxazine solution. The solid content of the propylene ester-functionalized benzoxazine solution was tested to be 17.5%. 0.01 wt.% of the polymerization inhibitor hydroquinone was added to the solution, and then the solvent was removed by rotary evaporation to obtain 150 g of esterified methpropylene ester-functionalized benzoxazine.

[0108] (3) A benzoxazine resin composition suitable for photocuring 3D printing was prepared by adding dimethylolpropane tetraacrylate (20wt.%), cyclotrimethylolpropane methyl acetal acrylate (10wt.%), methylolpropane methyl acetal acrylate (3wt.%), ethyl 2,4,6-trimethylbenzoylphenylphosphonate and 1-hydroxycyclohexyl phenyl ketone as photoinitiators. The resin composition was photocured using DLP (Digital Laser Processing) with a UV curing wavelength of 405 nm, an exposure time of 45 s / layer, and a layer thickness of 60 μm. After printing, the sample was thermocured using a process of slowly heating to 120 °C and holding for 1 h, then heating to 140 °C and holding for 1 h, then heating to 160 °C and holding for 1 h, then heating to 180 °C and holding for 1 h, then heating to 200 °C and holding for 2 h, and finally heating to 220 °C and holding for 4 h. The result was a 3D printed product based on a bio-based benzoxazine resin photosensitive resin composition.

[0109] Example 5

[0110] (1) In a 500 mL reactor equipped with a mechanical stirrer, thermometer, and condenser, 84.0 g (0.5 mol) of 4-hydroxy-3-methoxyphenylethanol, 22.5 g (0.5 mol) of ethylamine, 30.0 g (1.0 mol) of trioxane, and 300 g of dioxane were added. The temperature was slowly increased to 100 °C at a rate of 20 °C / min and reacted for 12 h. After the reaction was completed, the mixture was cooled to room temperature, diluted with 200 mL of chloroform, and then washed twice with 200 mL of 1 mol / L NaOH solution, followed by washing with water until neutral. After washing with water, the organic layer was dried with anhydrous magnesium sulfate, and the solvent was removed by rotary evaporation to obtain a hydroxyl-containing bio-based benzoxazine.

[0111] (2) Weigh 118.5 g (0.5 mol) of the above-mentioned hydroxyl-containing bio-based benzoxazine and dissolve it in 600 mL of dichloromethane. Add 77.4 g (0.6 mol) of the acid-binding agent N,N-diisopropylethylamine, and then stir and cool the mixed solution to -10 °C. Under an inert atmosphere and light-shielding conditions, slowly add 54.0 g (0.6 mol) of acryloyl chloride at a rate of 5 mL / min, controlling the reaction temperature within the range of -5 to 0 °C. After the addition is complete, slowly raise the temperature to room temperature at a rate of 8 °C / min and stir the reaction for 24 h. After the reaction is complete, filter to remove the precipitated pyridine hydrochloride. Wash the organic phase twice with 200 mL of 1 mol / L NaOH solution, and then wash with water until neutral. After drying the organic phase with anhydrous magnesium sulfate, filter to obtain a propylene ester-functionalized benzoxazine solution. The solid content of the propylene ester-functionalized benzoxazine solution was tested to be 18.5%. 0.02 wt.% of the polymerization inhibitor 2,6-di-tert-butyl-p-methylphenol was added to the solution, and then the solvent was removed by rotary evaporation to obtain 123 g of esterified propylene ester-functionalized benzoxazine.

[0112] (3) A benzoxazine resin composition suitable for photocuring 3D printing was prepared by adding dipropylene glycol diacrylate (25wt.%), acryloylmorpholine (10wt.%), ethyl 2,4,6-trimethylbenzoylphenylphosphonate and benzoin dimethyl ether as the main components of propylene ester-functionalized benzoxazine (65wt.%). The resin composition was photocured using DLP (Digital Laser Processing) with a UV curing wavelength of 405 nm, an exposure time of 25 s / layer, and a layer thickness of 40 μm. After printing, the sample was thermocured using a process of slowly heating to 120 °C and holding for 1 h, then heating to 140 °C and holding for 1 h, then heating to 160 °C and holding for 2 h, then heating to 180 °C and holding for 2 h, then heating to 200 °C and holding for 2 h, and finally heating to 220 °C and holding for 4 h. This process resulted in a 3D printed product based on a bio-based benzoxazine resin photosensitive resin composition.

[0113] Example 6

[0114] (1) In a 500 mL reactor equipped with a mechanical stirrer, thermometer, and condenser, 84.0 g (0.5 mol) of 4-hydroxy-3-methoxyphenylethanol, 48.5 g (0.5 mol) of furfurylamine, 36.0 g (1.2 mol) of paraformaldehyde, and 300 g of DMF were added. The temperature was slowly increased to 100 °C at a rate of 20 °C / min and reacted for 18 h. After the reaction was completed, the mixture was cooled to room temperature, diluted with 500 mL of dichloromethane, and then washed twice with 200 mL of 1 mol / L NaOH solution, followed by washing with water until neutral. After washing with water, the organic layer was dried with anhydrous magnesium sulfate, and the solvent was removed by rotary evaporation to obtain a hydroxyl-containing bio-based benzoxazine.

[0115] (2) Weigh 144.5 g (0.5 mol) of the above-mentioned hydroxyl-containing bio-based benzoxazine and dissolve it in 550 mL of dichloromethane. Add 60.6 g (0.6 mol) of triethylamine as an acid-binding agent, then stir and cool the mixture to -10 °C. Under an inert atmosphere and in the absence of light, slowly add 62.4 g (0.6 mol) of methacryloyl chloride at a rate of 5 mL / min, controlling the reaction temperature within the range of -5 to 0 °C. After the addition is complete, slowly raise the temperature to room temperature at a rate of 8 °C / min and stir the reaction for 24 h. After the reaction is complete, filter to remove the precipitated pyridine hydrochloride. Wash the organic phase twice with 200 mL of 1 mol / L NaOH solution, and then wash with water until neutral. After drying the organic phase with anhydrous magnesium sulfate, filter to obtain a methacrylic acid-functionalized benzoxazine solution. The solid content of the methacrylate-functionalized benzoxazine solution was tested to be 17.8%. 0.01 wt.% of the polymerization inhibitor hydroquinone was added to the solution, and then the solvent was removed by rotary evaporation to obtain 134 g of esterified methacrylate-functionalized benzoxazine.

[0116] (3) A benzoxazine resin composition suitable for photocuring 3D printing was prepared by adding propylene ester-functionalized benzoxazine as the main component (50 wt.), reactive diluents tripropylene glycol diacrylate (20 wt.%), N-vinylpyrrolidone (30 wt.%), photoinitiator 3 wt.% ethyl 2,4,6-trimethylbenzoylphenylphosphonate and 2 wt.% benzophenone. The resin composition was photocured using DLP (Digital Laser Processing) with a UV curing wavelength of 405 nm, an exposure time of 30 s / layer, and a layer thickness of 40 μm. After printing, the sample was thermocured using a process of slowly heating to 120 °C and holding for 2 h, then heating to 140 °C and holding for 2 h, then heating to 160 °C and holding for 2 h, then heating to 180 °C and holding for 2 h, then heating to 200 °C and holding for 2 h, and finally heating to 220 °C and holding for 4 h. The result was a 3D printed product based on a bio-based benzoxazine resin photosensitive resin composition.

[0117] Example 7

[0118] (1) Weigh 129.5 g (0.5 mol) of the hydroxyl-containing bio-based benzoxazine from Example 3 and dissolve it in 500 mL of dichloromethane. Add 60.6 g (0.6 mol) of triethylamine as an acid-binding agent. Then, stir and cool the mixture to -10 °C. Under an inert atmosphere and in the absence of light, slowly add 54 g (0.6 mol) of methacryloyl chloride at a rate of 5 mL / min, controlling the reaction temperature within the range of -5 to 0 °C. After the addition is complete, slowly raise the temperature to room temperature at a rate of 8 °C / min and stir the reaction for 24 h. After the reaction is complete, filter to remove the precipitated triethylamine hydrochloride. Wash the organic phase twice with 200 mL of 1 mol / L NaOH solution, and then wash with water until neutral. After drying the organic phase with anhydrous magnesium sulfate, filter to obtain a methacrylic acid-functionalized benzoxazine solution. The solid content of the methacrylate-functionalized benzoxazine solution was tested to be 18.5%. 0.01 wt.% of the polymerization inhibitor 2,6-di-tert-butyl-p-methylphenol was added to the solution, and then the solvent was removed by rotary evaporation to obtain 139 g of esterified methacrylate-functionalized benzoxazine.

[0119] (2) A benzoxazine resin composition suitable for photocuring 3D printing was prepared by adding 1,6-hexanediol diacrylate (20wt.%) and hydroxyethyl methacrylate (10wt.%) as reactive diluents and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide as photoinitiator. The resin composition was photocured using DLP (Digital Laser Processing) with a UV curing wavelength of 405 nm, an exposure time of 25 s / layer, and a layer thickness of 45 μm. After printing, the sample was thermocured using a process of slowly heating to 120 °C and holding for 2 h, then heating to 140 °C and holding for 2 h, then heating to 160 °C and holding for 2 h, then heating to 180 °C and holding for 2 h, then heating to 200 °C and holding for 2 h, and finally heating to 220 °C and holding for 4 h. This process resulted in a 3D printed product based on a bio-based benzoxazine resin photosensitive resin composition.

[0120] Comparative Example 1

[0121] The second-step esterification reaction is not carried out under nitrogen protection and light-blocking treatment, resulting in products that are difficult to separate.

Claims

1. A bio-based benzoxazine monomer, characterized in that, The structural formula of the bio-based benzoxazine monomer is shown in formula (I) below: Formula (I) Wherein, R1 is H or methyl; R2 is H; R3 is methyl or ethyl; The method for preparing the bio-based benzoxazine monomer includes: Equation (II) The compound shown in formula (II) was dissolved in solvent C, and after adding an acid-binding agent, the mixture was stirred and cooled to -20°C to -5°C. Compound A was then added dropwise at a rate of 1–10 mL / min under an inert atmosphere and light-shielding conditions, with the reaction temperature controlled between -5°C and 0°C. o C. After the addition is complete, the temperature is raised to room temperature at a rate of 5-10℃ / min, and the reaction is stirred for 12-24 h. After the reaction is complete, the bio-based benzoxazine monomer is obtained by purification. The compound A is at least one of acryloyl chloride or methacryloyl chloride. The molar ratio of the compound shown in formula (II), compound A, and acid-binding agent is 1:1 to 1.2:1 to 1.2; The preparation method of the compound represented by formula (II) includes: mixing a phenolic source, an amine source, paraformaldehyde, and solvent A, and heating the mixture to 60-120 °C at a rate of 10-30 °C / min. o C, the reaction was stirred for 5–48 h, and the compound represented by formula (II) was obtained after purification; The phenol source is tyrosol; The amine source includes at least one of methylamine and ethylamine; The molar ratio of the phenolic source, amine source and paraformaldehyde is 1:1:2 to 2.

4.

2. The bio-based benzoxazine monomer according to claim 1, characterized in that, The solvent C includes at least one of chloroform, dichloromethane, xylene, dioxane, DMF, N,N-dimethylacetamide, or N-methylpyrrolidone; The acid-binding agent includes at least one of triethylamine, pyridine, and N,N-diisopropylethylamine.

3. The bio-based benzoxazine monomer according to claim 1 or 2, characterized in that, Solvent A includes at least one of chloroform, toluene, xylene, ethanol, dioxane, DMF, DMAc, or NMP.

4. The bio-based benzoxazine monomer according to claim 1, characterized in that, Methods for purifying bio-based benzoxazine monomers include: After the reaction is complete, the mixture is filtered to remove the precipitated acid-binding agent hydrochloride. Solvent B is added for dilution, and the organic phase is washed with alkali 2 to 6 times, then washed with water until neutral. The phase is dried, filtered, and the solvent is removed by rotary evaporation to obtain the bio-based benzoxazine monomer. The solvent removal by rotary evaporation involves adding 0.005 wt.% to 0.02 wt.% of a polymerization inhibitor to the bio-based benzoxazine monomer before rotary evaporation. The method for purifying the compound represented by formula (II) includes: after the reaction is completed, cooling to room temperature, adding solvent B for dilution, washing with alkali 2 to 6 times, washing with water until neutral, and drying to obtain the compound represented by formula (II).

5. The bio-based benzoxazine monomer according to claim 4, characterized in that, The polymerization inhibitor includes at least one of hydroquinone, 4-methoxyphenol, p-tert-butylcatechol, and 2,6-di-tert-butyl-p-methylphenol.

6. The bio-based benzoxazine monomer according to claim 4, characterized in that, The alkaline washing uses a 0.5–4 mol / L NaOH solution.

7. The bio-based benzoxazine monomer according to claim 4, characterized in that, Solvent B includes at least one of trichloromethane or dichloromethane.

8. A bio-based benzoxazine resin, characterized in that, The bio-based benzoxazine resin is obtained by curing the bio-based benzoxazine monomer according to any one of claims 1 to 7.

9. The bio-based benzoxazine resin according to claim 8, characterized in that, The curing process includes photocuring and thermal curing.

10. The bio-based benzoxazine resin according to claim 9, characterized in that, The curing process involves mixing a bio-based benzoxazine monomer with an active diluent and a photocuring agent to obtain a mixture, and then subjecting the mixture to UV 3D printing and thermosetting to obtain a bio-based benzoxazine resin. The mass ratio of the bio-based benzoxazine monomer to the active diluent is 50 wt.%–80 wt.%: 20 wt.%–50 wt.%.

11. The bio-based benzoxazine resin according to claim 10, characterized in that, The photocuring aid is at least one of a UV photoradical initiator or an ultraviolet absorber.

12. The bio-based benzoxazine resin according to claim 11, characterized in that, The ultraviolet absorber is at least one of benzophenone and benzotriazole.

13. The bio-based benzoxazine resin according to claim 11, characterized in that, The active diluent includes at least one of the following: isoborneol acrylate, tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, dimethylolpropane tetraacrylate, dipropylene glycol diacrylate, 3-glycidyl ether oxypropyltrimethoxysilane, polyethylene glycol diacrylate, cyclotrimethylolpropane methyl acetal acrylate, N-vinylpyrrolidone, acrylmorpholine, hydroxyethyl methacrylate, tetrahydrofuran acrylate, and lauryl methacrylate. The UV photoradical initiator includes at least one of benzoin dimethyl ether, benzophenone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 2-isopropylthioxanthone, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, and 1-hydroxycyclohexylbenzophenone.

14. The bio-based benzoxazine resin according to claim 13, characterized in that, The amount of UV photoradical initiator added is 2 wt.% to 5 wt.% of the total resin mass.

15. The bio-based benzoxazine resin according to claim 9, characterized in that, The wavelength of the photocuring is 355–405 nm, the exposure time is 5–45 s / layer, and the layer thickness is 20–60 μm.

16. The bio-based benzoxazine resin according to claim 9, characterized in that, The thermosetting process includes: heating to 120℃ and holding for 1-2 hours, then heating to 140℃ and holding for 1-2 hours, then heating to 160℃ and holding for 1-2 hours, then heating to 180℃ and holding for 1-2 hours, then heating to 200℃ and holding for 1-2 hours, and then heating to 220℃ and holding for 2-4 hours.

17. The method for preparing the bio-based benzoxazine monomer according to any one of claims 1 to 7, characterized in that, The method includes: Equation (II) The compound shown in formula (II) was dissolved in solvent C, and after adding an acid-binding agent, the mixture was stirred and cooled to -20°C to -5°C. Compound A was then added dropwise at a rate of 1–10 mL / min under an inert atmosphere and light-shielding conditions, with the reaction temperature controlled between -5°C and 0°C. o C. After the addition is complete, the temperature is raised to room temperature at a rate of 5-10℃ / min, and the reaction is stirred for 12-24 h. After the reaction is complete, the bio-based benzoxazine monomer is obtained by purification. The compound A is at least one of acryloyl chloride or methacryloyl chloride. The molar ratio of the compound shown in formula (II), compound A and the acid-binding agent is 1:1 to 1.2:1 to 1.

2.

18. The method for preparing the bio-based benzoxazine monomer as described in claim 17, characterized in that, The solvent C includes at least one of chloroform, dichloromethane, xylene, dioxane, DMF, N,N-dimethylacetamide, or N-methylpyrrolidone; The acid-binding agent includes at least one of triethylamine, pyridine, and N,N-diisopropylethylamine.

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