Benzoxazine resin based on protocatechuic acid and synthesis and application thereof

Abstract

The invention discloses benzoxazine resin based on protocatechuic acid and synthesis and application thereof.The protocatechuic acid serves as a raw material, amidation is conducted through furfuryl amine, and then a protocatechuic acid-based benzoxazine monomer (NDBA-fa) is synthesized with furfuryl amine and paraformaldehyde through a one-pot method; the resin monomer can be independently cured to form the protocatechuic acid benzoxazine resin. When the mass content of the NDBA-fa enhanced bisphenol A-aniline benzoxazine (BA-a) is 7.5%, the glass transition temperature Tg, the thermal decomposition temperature Td5% and the thermal decomposition temperature Td10% of the cured resin are respectively improved by 21 DEG C, 14 DEG C, 23 DEG C and 16.8%, and the heat release capacity HRC is reduced by 76.3 Jg <-1 > K <-1 >. The protocatechuic acid-based benzoxazine monomer provided by the invention can be used as a novel modifier, and can effectively improve the thermal stability and flame retardant property of BA-a. The application range of biological resources is also widened. # imgabs0 #

Description

Technical Field

[0001] The invention relates to the technical field of a bio-based thermosetting resin and a preparation thereof, and in particular to a protocatechuic acid-based benzoxazine resin and a synthesis and application thereof. Background Art

[0002] Benzoxazine (BOZ) monomers synthesized from phenolic compounds, primary amine compounds, and formaldehyde through the Mannich reaction can undergo a ring-opening self-polymerization reaction under heating conditions to generate BOZ resins. BOZ resins have the characteristics of good heat resistance, excellent thermal oxidation stability, high electrical insulation properties, high dimensional stability, etc., and are widely used in coatings, electronic packaging, ablative materials and other fields.

[0003] There are a variety of natural phenolic compounds with unique chemical structures in nature, so the development of new sustainable BOZ resins using bio-based phenolic compounds has become one of the hot topics in this field. However, the BOZ resins synthesized using monooxazine rings such as cardanol and guaiacol have low thermal stability due to low crosslinking density. Therefore, the design and preparation of monomers with polyoxazine ring structures to improve the performance of bio-based BOZ resins has attracted increasing attention.

[0004] 3, 4-dihydroxybenzoic acid (protocatechuic acid, PCA) is a new type of bio-based chemical. In recent years, the biosynthesis technology of protocatechuic acid has made breakthroughs, and its cost has been greatly reduced, making it economical for the development of thermosetting materials. Research on protocatechuic acid in epoxy resin has been carried out, but there are only sporadic reports in the BOZ field, and there is still a huge gap in its application scenarios. Summary of the invention

[0005] The first object of the present invention is to provide a novel benzoxazine resin monomer (II) based on biomass protocatechuic acid in view of the deficiencies of the prior art.

[0006] The present invention adopts the following technical solutions: A benzoxazine resin monomer based on protocatechuic acid, the structural formula of which is shown in formula (II): (II) The second object of the present invention is to provide a method for preparing the above-mentioned protocatechuic acid-based benzoxazine resin monomer, and a method for preparing the benzoxazine resin monomer from protocatechuic acid.

[0007] Step (1), Preparation of N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (NDBA) (I) Dissolving protocatechuic acid, furfurylamine and a catalyst in a solvent to carry out an amidation reaction; removing excess solvent after the reaction is completed to obtain N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (I); (I) Preferably, the catalyst is selected from one or more combinations of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI), 1-hydroxybenzotriazole (HOBT), N,N'-diisopropylcarbodiimide (DIC), N,N-dicyclohexylcarbodiimide (DCC), and 4-dimethylaminopyridine (DMAP). More preferably, the catalyst is a combination of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1-hydroxybenzotriazole, which serves as a condensation agent in the reaction.

[0008] Preferably, the solvent is selected from acetone, dioxane, tetrahydrofuran and dimethylformamide, more preferably dimethylformamide.

[0009] Preferably, the reaction temperature is 25-50°C, more preferably room temperature; the reaction time is 2-5h, more preferably 4h.

[0010] Step (2): Preparation of protocatechuic acid-based benzoxazine resin monomer (NDBA-fa) (II) NDBA, furfurylamine and paraformaldehyde are dissolved in a solvent, heated under reflux and stirred for reaction, and after the reaction is completed, the solvent is removed to obtain a crude product; the crude product is dissolved in dichloromethane, washed to neutrality, and then the solvent is removed and dried to obtain the protocatechuic acid-based benzoxazine resin monomer (II).

[0011] The name of the protocatechuic acid-based benzoxazine resin monomer is: N, 3, 8-tris(furan-2-ylmethyl)-2, 3, 4, 7, 8, 9-hexahydrobenzo[1, 2-e: 4, 3-e']bis([1, 3]oxazine)-5-carboxamide (NDBA-fa); Preferably, the solvent is selected from toluene, dioxane, ethanol, chloroform and butanone, more preferably ethanol; the molar ratio of compound (I) NDBA, furfurylamine and paraformaldehyde is 1:2:3-5, more preferably 1:2:3.5-4.5.

[0012] Preferably, the reaction temperature is 70-120° C., more preferably reflux temperature, and the reaction time is 6-12 h, more preferably 10 h.

[0013] The third object of the present invention is to provide the use of the above-mentioned protocatechuic acid-based benzoxazine resin monomer in the preparation of highly functional heat-resistant and flame-retardant materials.

[0014] The bi-oxazine ring structure brought by the two phenolic hydroxyl groups of the protocatechuic acid of the present invention and the carboxyl group of the protocatechuic acid introduce more additional cross-linking points brought by other groups through amidation reaction, which can form a more compact three-dimensional network cross-linking structure after curing, thereby improving the thermal stability of the protocatechuic acid-based benzoxazine resin poly (NDBA-fa). On the other hand, the amide bond in the protocatechuic acid derivative has better thermal stability than the carboxyl group and the carbon-carbon single bond. In addition, the two phenolic hydroxyl groups of protocatechuic acid are on the same benzene ring, which results in only one vacancy on the benzene ring of the protocatechuic acid-based benzoxazine monomer for electrophilic reaction, so that the protocatechuic acid-based benzoxazine monomer will form more thermally stable amine Mannich structures in the curing stage, which can effectively inhibit degradation.

[0015] The preparation method of the protocatechuic acid-based benzoxazine resin poly(NDBA-fa) is specifically prepared by thermally curing the protocatechuic acid-based benzoxazine monomer (II).

[0016] Preferably, the curing method is carried out by a process selected from the following group: mixing, molding, and curing in three stages, specifically, adding the protocatechuic acid benzoxazine monomer (II) into a dissolving container, pouring it into a mold after evenly dissolving, and reacting at 180°C, 200°C, and 220°C for 1 hour each.

[0017] The fourth object of the present invention is to provide a use of a benzoxazine monomer based on biomass protocatechuic acid in heat-resistant and flame-retardant modifiers.

[0018] Specifically, protocatechuic acid-based benzoxazine (NDBA-fa) and bisphenol A-aniline benzoxazine (BA-a) are mixed in different proportions (NDBA-fa mass percentage is 0-10%) and the modified benzoxazine resin is prepared by thermal curing.

[0019] Preferably, the curing method is carried out by a process selected from the following group: mixing, molding, and curing in three stages, specifically, protocatechuic acid benzoxazine monomer (II) and bisphenol A-aniline benzoxazine (BA-a) are added to the reactor in different proportions, mixed evenly, and poured into the mold, and reacted at 180°C, 200°C, 220°C, and 240°C for 1 hour each.

[0020] More preferably, a method for preparing a protocatechuic acid epoxy resin comprises the following steps: (i) mixing protocatechuic acid benzoxazine monomer (II) and bisphenol A-aniline benzoxazine (BA-a); (ii) dissolving the mixture obtained in step (i) by ultrasonic or stirring to form a uniform transparent solution; or dissolving the mixture in step (i) in an organic solvent to form a uniform transparent solution; Preferably, the solvent is selected from one or more combinations of cyclohexanone, dichloromethane, chloroform and acetone.

[0021] (iii) pouring the mixture into a polytetrafluoroethylene mold under an inert atmosphere and heating it to cure; (iv) curing the residue obtained in the step (iii) by heating to obtain the desired protocatechuic acid-based benzoxazine-modified bisphenol A-aniline benzoxazine.

[0022] Compared with the prior art, the main advantages of the present invention include: (1) The method provided by the present invention belongs to the deep processing and utilization of biomass. The two phenolic hydroxyl groups of protocatechuic acid are used to synthesize benzoxazine with a bi-oxazine ring structure, which broadens the application of protocatechuic acid and enriches the types of bio-based benzoxazine. New applications of biomass resources are developed, sustainable development is achieved, the demand pressure of chemical energy is reduced, and the development of green economy is promoted.

[0023] (2) The protocatechuic acid-based benzoxazine synthesized by the present invention has good thermal stability and flame retardancy, and can be used as a modifier to improve the thermal stability and flame retardancy of commercial bisphenol A-aniline benzoxazine (universal benzoxazine). BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the NMR spectrum of protocatechuic acid-based benzoxazine monomer NDBA-fa, wherein A is the hydrogen NMR spectrum and B is the carbon NMR spectrum; Figure 2 The thermogravimetric curve and HRR (heat release rate) and temperature relationship curve of protocatechuic acid benzoxazine resin poly(NDBA-fa), where A is the thermogravimetric curve and B is the HRR and temperature relationship curve; Figure 3 The thermogravimetric curves of benzoxazine resins with different protocatechuic acid-based benzoxazine NDBA-fa contents; Figure 4 The HRR and temperature curves of benzoxazine resins with different protocatechuic acid-benzoxazine NDBA-fa contents. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples without specifying specific conditions are usually based on conventional conditions or the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are calculated by weight.

[0026] Example 1-1 Synthesis of N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (NDBA) Under nitrogen protection, protocatechuic acid (7.7 g, 0.05 mol), 1-hydroxybenzotriazole (8.11 g, 0.06 mol), and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (11.5 g, 0.06 mol) were mixed in 30 mL DMF in an ice bath. Furfurylamine (5.10 g, 0.0525 mol) was added to the mixture and the mixture was returned to room temperature and stirred for 4 hours. After the reaction was completed, the reaction mixture was poured into 300 mL of sodium bicarbonate aqueous solution and stirred vigorously, and then centrifuged to obtain the supernatant. The supernatant was extracted several times with ethyl acetate. The collected organic layer was washed once with sodium bicarbonate and 3 times with deionized water. Finally, the solvent was removed by rotary evaporation and dried in a vacuum drying oven for 24 h to obtain 6.1 g of white solid N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (NDBA).

[0027] Example 1-2 Synthesis of N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (NDBA) The experimental method was the same as that of Example 1-1, except that the condensing agents 1-hydroxybenzotriazole and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride were replaced with N,N-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP), and the other reaction conditions remained unchanged, to obtain 5.2 g of the target monomer.

[0028] Example 1-3 Synthesis of N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (NDBA) The experimental method was the same as that of Example 1-1, except that the solvent DMF was changed to tetrahydrofuran and other reaction conditions remained unchanged, to obtain 5.6 g of the target monomer.

[0029] Example 2-1 Synthesis of Protocatechuic Acid-Based Benzoxazine Monomer NDBA-fa NDBA (1.165 g, 0.005 mol), furfurylamine (0.971 g, 0.010 mol), paraformaldehyde (0.660 g, 0.022 mol) and 90 ml ethanol obtained in Example 1-1 were added to a 250 ml round-bottom flask. The whole system was stirred at room temperature for 1 hour, and then heated to reflux and stirred for 12 h. After cooling to room temperature, the organic solvent ethanol was removed by rotary evaporator to obtain a crude benzoxazine product. The crude benzoxazine product was dissolved in dichloromethane, washed with 1 M NaOH aqueous solution 3 times, and then washed with a large amount of water until neutral, and finally the solvent was removed by rotary evaporation and dried in a vacuum drying oven for 24 h to obtain 0.97 g of white solid protocatechuic acid-based benzoxazine monomer (NDBA-fa).

[0030] Example 2-2 Synthesis of Protocatechuic Acid-Based Benzoxazine Monomer NDBA-fa The experimental method was the same as that of Example 2-1, except that the organic solvent ethanol was changed to toluene and other reaction conditions remained unchanged, to obtain 0.82 g of the target monomer.

[0031] Example 2-3 Synthesis of Protocatechuic Acid-Based Benzoxazine Monomer NDBA-fa The experimental method was the same as that of Example 2-1, except that paraformaldehyde (0.660 g, 0.022 mol) was replaced with paraformaldehyde (0.540 g, 0.018 mol), and other reaction conditions remained unchanged, yielding 0.75 g of the target monomer.

[0032] The NMR spectrum of protocatechuic acid-based benzoxazine monomer NDBA-fa is shown in Figure 1 As shown, its specific attribution is: 1 H NMR (400MHz, DMSO-d6): δ8.64(t, 1H, C-NH-CH2), δ7.57(d, 1H, Ar), δ7.33(d, 1H, Ar), δ7.25(dd, 1H, Ar), δ6.78(d, 1H, Ar), δ6.40(dd, 1H, Ar), δ6.24(d, 1H,Ar), δ4.43(d, 1H, NH-CH2-Ar); 13 C NMR (400MHz, DMSO-d6): δ=166.81, 153.63, 149.27, 145.64, 142.62, 126.17, 119.88, 115.98, 115.65, 111.25, 107.41, 36.75.

[0033] Example 3 Curing of Protocatechuic Acid Benzoxazine Resin The protocatechuic acid benzoxazine monomer (II) was evenly poured into the mold and reacted at 180°C, 200°C, and 220°C for 1 h each to obtain the cured protocatechuic acid benzoxazine resin poly(NDBA-fa).

[0034] In order to evaluate the thermal stability of poly(NDBA-fa), the thermogravimetric analysis (TGA) technique was used for testing. The temperature was raised from 100°C to 800°C at a heating rate of 10°C / min in a nitrogen atmosphere. Figure 2 This test provides a deeper understanding of the thermal stability and decomposition behavior of poly(NDBA-fa) at different temperatures. The T d5 and T d10 363℃ and 403℃ respectively.

[0035] The flame retardant properties of polybenzoxazine were tested using a micro combustion calorimeter. The sample was heated from 100°C to 700°C at a constant heating rate of 1°C / s in a nitrogen flow of 80 mL / min. The thermal degradation products of the sample in a nitrogen atmosphere were then mixed with an oxygen flow of 20 mL / min and entered a combustion furnace at 900°C. Figure 2 The graph shows the heat release rate as the temperature changes. From the data in the graph, it can be calculated that the HRC (Heat Release Capacity) of poly(NDBA-fa) is only 15.8 Jg -1 K -1 , which indicates that the material has a relatively low heat release capacity during thermal combustion and because its HRC is less than 100 Jg -1 K -1 , is a flame retardant material.

[0036] Example 4-1 Protocatechuic acid-based benzoxazine-modified general-purpose benzoxazine (bisphenol A-aniline benzoxazine) Without adding NDBA-fa, universal benzoxazine (BA-a) was poured into the mold and reacted at 180°C, 200°C, 220°C, and 240°C for 1 h each to obtain universal benzoxazine poly (BA-a).

[0037] Example 4-2 Protocatechuic acid-based benzoxazine modified general-purpose benzoxazine Protocatechuic acid benzoxazine monomer (NDBA-fa) and general benzoxazine (BA-a) were added into the reactor according to the NDBA-fa content of 2.5%, mixed evenly and poured into the mold, and reacted at 180℃, 200℃, 220℃ and 240℃ for 1h each to obtain protocatechuic acid benzoxazine modified general benzoxazine poly (NDBA-fa 2.5wt% / BA-a).

[0038] Example 4-3 Protocatechuic acid-based benzoxazine modified general-purpose benzoxazine The experimental method was the same as that of Example 4-2, except that the NDBA-fa content was changed to 5%, and the other reaction conditions remained unchanged. 5wt% / BA-a).

[0039] Example 4-4 Protocatechuic acid-based benzoxazine modified general-purpose benzoxazine The experimental method was the same as that of Example 4-2, except that the NDBA-fa content was changed to 7.5%, and the other reaction conditions remained unchanged. 7.5wt% / BA-a).

[0040] Example 4-5 General-purpose benzoxazine modified with protocatechuic acid-based benzoxazine The experimental method was the same as that of Example 4-2, except that the NDBA-fa content was changed to 10%, and the other reaction conditions remained unchanged. 10wt% / BA-a).

[0041] The performance test results of the modified benzoxazine resins prepared in Examples 4-1 to 4-5 are shown in Table 1.

[0042] Table 1 Thermal properties and flame retardant properties (HRC) of benzoxazine resins with different NDBA-fa contents Example <![CDATA[T d5 (℃)]]> <![CDATA[T d10 (℃)]]> Carbon Residue Rate Heat release rate (HRC) 4-1（0%） 325.89 354.38 35.16 232.99 4-2（2.5%） 327.92 359.95 44.75 213.32 4-3（5%） 334.50 364.33 45.33 165.74 4-4（7.5%） 339.48 377.34 51.92 156.55 4-5（10%） 348.08 369.59 39.28 224.39 From the data in Table 1, it can be seen that within the range of 0-10%, the addition of NDBA-fa can increase the T d5 、T d10 , residual carbon rate and HRC, the optimal addition amount of NDBA-fa is 7.5%, at which point its T d5 、T d10 , residual carbon rate and HRC were 339.48℃, 377.34℃, 51.92%, 156.55Jg respectively -1 K -1 .

[0043] The thermal gravimetric curves of the modified benzoxazine resins prepared in Examples 4-1 to 4-5 are as follows: Figure 3 As shown, the relationship curve between HRR and temperature is as follows Figure 4 shown.

[0044] In summary, the protocatechuic acid-based benzoxazine monomer NDBA-fa synthesized in the present invention has good thermal stability and flame retardancy after curing; and NDBA-fa, as a modifier, can effectively improve the thermal stability and flame retardancy of the general-purpose benzoxazine BA-a.

[0045] All documents mentioned in the present invention are cited as references in this application, just as each document is cited as references separately. In addition, it should be understood that after reading the above teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present invention.

Claims

1. A benzoxazine resin monomer based on protocatechuic acid, characterized in that: The chemical structure is shown in formula (II): (II).

2. A method for preparing a protocatechuic acid-based benzoxazine resin monomer according to claim 1, characterized in that: The preparation method comprises the following steps: Step (1), Preparation of N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide NDBA Dissolving protocatechuic acid, furfurylamine and a catalyst in a solvent to carry out an amidation reaction; removing excess solvent after the reaction is completed to obtain N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide NDBA, the structural formula of which is shown in formula (I); （I） Step (2): Preparation of benzoxazine resin monomer NDBA-fa based on protocatechuic acid NDBA, furfurylamine and polyformaldehyde are dissolved in a solvent, heated under reflux and stirred for reaction, and after the reaction is completed, the solvent is removed to obtain a crude product; the crude product is dissolved in dichloromethane, washed to neutrality, and then the solvent is removed and dried to obtain a protocatechuic acid-based benzoxazine resin monomer with a chemical structure as shown in formula (II).

3. The preparation method according to claim 2, characterized in that: The catalyst in step (1) is selected from one or more of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride EDCI, 1-hydroxybenzotriazole HOBT, N,N'-diisopropylcarbodiimide DIC, N,N-dicyclohexylcarbodiimide DCC, and 4-dimethylaminopyridine DMAP.

4. The preparation method according to claim 2, characterized in that: The solvent in step (1) is selected from the group consisting of acetone, dioxane, tetrahydrofuran and dimethylformamide.

5. The preparation method according to claim 2, characterized in that: The solvent in step (2) is selected from toluene, dioxane, ethanol, chloroform and butanone.

6. The preparation method according to claim 2, characterized in that: The molar ratio of NDBA, furfurylamine and paraformaldehyde in step (2) is 1:2:3-5.

7. The preparation method according to claim 2, characterized in that: The reaction temperature of step (1) is 25-50°C and the reaction time is 2-5h; the reaction temperature of step (2) is 70-120°C and the reaction time is 6-12h.

8. A protocatechuic acid-based benzoxazine resin, characterized in that: The benzoxazine resin is obtained by thermal curing the protocatechuic acid-based benzoxazine resin monomer according to claim 1.

9. Use of the protocatechuic acid-based benzoxazine resin monomer according to claim 1 in the preparation of heat-resistant and flame-retardant materials.

10. Use of the protocatechuic acid-based benzoxazine resin monomer as claimed in claim 1 as a heat-resistant and flame-retardant modifier.

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