A proto-catechuic acid-based benzoxazine resin and synthesis and application thereof

Abstract

The application discloses a kind of benzoxazine resin based on protocatechuic acid and synthesis and application thereof, with protocatechuic acid as raw material, first with furfurylamine to carry out amidation, then with furfurylamine and paraformaldehyde one-pot synthesis protocatechuic acid-based benzoxazine monomer (NDBA-fa);The resin monomer can be cured to form protocatechuic acid benzoxazine resin alone.Use NDBA-fa to enhance the mass content of bisphenol A-aniline benzoxazine (BA-a) is 7.5%, and the glass transition temperature of the cured resin T g , thermal decomposition temperature T d5% 、T d10% , carbon residue rate is increased by 21 ℃, 14 ℃, 23 ℃, 16.8%, and the heat release capacity HRC is decreased by 76.3 Jg ‑1 K ‑1 The protocatechuic acid-based benzoxazine monomer provided by the application can be used as a new modifier, which can effectively improve the thermal stability and flame retardant property of BA-a. The application range of biological resources is also widened.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bio-based thermosetting resin and its preparation, in particular to a benzoxazine resin based on protocatechuic acid and its synthesis and application. BACKGROUND

[0002] Benzoxazine (BOZ) monomers synthesized by Mannich reaction of phenolic compounds, primary amine compounds and formaldehyde can undergo ring-opening self-polymerization reaction under heating conditions to generate BOZ resin. BOZ resin has good heat resistance, excellent thermal oxidative stability, high electrical insulation performance, high dimensional stability and other characteristics, and is widely used in coating, electronic packaging, ablation materials and other fields.

[0003] Natural phenolic compounds are rich in nature and have unique chemical structures, so developing new sustainable BOZ resin using bio-based phenolic compounds has become one of the hotspots in the field. However, the monooxazine ring synthesized by using cashew phenol and guaiacol has low crosslinking density, resulting in low thermal stability of BOZ resin, so designing and preparing monomers with polyoxazine ring structure to improve the performance of bio-based BOZ resin has been increasingly concerned.

[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 been broken through, and its cost has been greatly reduced, which has economic feasibility for the development of thermosetting materials. The research on protocatechuic acid in epoxy resin has been carried out, but there are only sporadic reports in the field of BOZ, and there is still a great gap in its application scenarios. SUMMARY

[0005] The first object of the present application is to provide a new type of benzoxazine resin monomer (II) based on biomass protocatechuic acid to overcome the shortcomings of the prior art.

[0006] The present application adopts the following technical solutions:

[0007] A benzoxazine resin monomer based on protocatechuic acid, the structural formula of which is shown as formula (II):

[0008]

[0009] (II)

[0010] The second object of the present application is to provide a preparation method of the above-mentioned benzoxazine resin monomer based on protocatechuic acid, which is a method for preparing benzoxazine resin monomers from protocatechuic acid.

[0011] Step (1), preparation of N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (NDBA) (I)

[0012] The original catechin, furanamine and catalyst are dissolved in a solvent to carry out an amidation reaction; after the reaction is completed, the excess solvent is removed to obtain N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (I);

[0013]

[0014] (I)

[0015] As a preference, the catalyst is selected from one or a combination of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDCI), 1-hydroxybenzotriazole (HOBT), N,N'-diisopropyl carbodiimide (DIC), N,N-dicyclohexyl carbodiimide (DCC), 4-dimethylaminopyridine (DMAP), and more preferably, the catalyst is a combination of 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride and 1-hydroxybenzotriazole, which acts as a condensing agent in the reaction.

[0016] As a preference, the solvent is selected from one of acetone, dioxane, tetrahydrofuran, dimethylformamide, and more preferably, dimethylformamide.

[0017] As a preference, the reaction temperature is 25-50°C, and more preferably, room temperature; the reaction time is 2-5h, and more preferably, 4h.

[0018] Step (2), preparation of a benzo-oxazine resin monomer based on original catechin (NDBA-fa) (II)

[0019] The NDBA, furanamine and paraformaldehyde are dissolved in a solvent, heated to reflux and stirred to react, and after the reaction is completed, the solvent is removed to obtain a crude product; the crude product is dissolved in dichloromethane, washed to neutral, and then the solvent is removed and dried to obtain the benzo-oxazine resin monomer based on original catechin (II).

[0020] The name of the benzo-oxazine resin monomer based on original catechin is: N, 3, 8-tri(furan-2-ylmethyl)-2, 3, 4, 7, 8, 9-hexahydrobenzo[1, 2-e: 4, 3-e']bis([1, 3]oxazine)-5-formamide (NDBA-fa);

[0021] As a preference, the solvent is selected from one of toluene, dioxane, ethanol, chloroform, butanone, and more preferably, ethanol; the molar ratio of the compound (I) NDBA, furanamine and paraformaldehyde is 1:2:3-5, and more preferably, the molar ratio is 1:2:3.5-4.5.

[0022] As preferred, the reaction temperature is 70-120℃, more preferably reflux temperature, and the reaction time is 6-12h, more preferably 10h.

[0023] A third object of the present application is to provide the use of the above-mentioned benzoxazine monomer based on protocatechuic acid in the preparation of high-functionality heat-resistant and flame-retardant materials.

[0024] The double benzoxazine ring structure brought by the two phenolic hydroxyl groups of protocatechuic acid and the additional crosslinking points brought by the introduction of other groups through amidation reaction of the carboxyl group of protocatechuic acid can make the protocatechuic acid-based benzoxazine resin poly(NDBA-fa) form a more compact three-dimensional network 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 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 more thermally stable Mannich structures are formed during the curing stage of the protocatechuic acid-based benzoxazine monomer, which can effectively inhibit degradation.

[0025] The above-mentioned preparation method of the protocatechuic acid-based benzoxazine resin poly(NDBA-fa) is prepared by thermal curing of the protocatechuic acid-based benzoxazine monomer (II).

[0026] As preferred, the curing method is carried out by selecting the following processes: mixing, mold filling, and three stages of curing, specifically adding the protocatechuic acid-based benzoxazine monomer (II) into a dissolving container, pouring into a mold after uniform mixing, and reacting at 180℃, 200℃, and 220℃ for 1h each.

[0027] A fourth object of the present application is to provide the use of a benzoxazine monomer based on biomass protocatechuic acid as a heat-resistant and flame-retardant modifier.

[0028] Specifically, the protocatechuic acid-based benzoxazine (NDBA-fa) and the bisphenol A-aniline benzoxazine (BA-a) are mixed in different proportions (NDBA-fa mass percentage content is 0-10%), and a modified benzoxazine resin is prepared by thermal curing.

[0029] As preferred, the curing method is carried out by selecting the following processes: mixing, mold filling, and three stages of curing, specifically adding the protocatechuic acid-based benzoxazine monomer (II) and the bisphenol A-aniline benzoxazine (BA-a) into a reactor in different proportions, pouring into a mold after uniform mixing, and reacting at 180℃, 200℃, 220℃, and 240℃ for 1h each.

[0030] More preferably, a preparation method of a protocatechuic acid-based epoxy resin comprises the following steps:

[0031] (i) mixing of protocatechuic acid benzoxazine monomer (II) and bisphenol A-aniline benzoxazine (BA-a);

[0032] (ii) forming a uniform transparent solution by dissolving the mixture obtained in step (i) through ultrasonic or stirring; or dissolving the mixture of step (i) in an organic solvent to make the mixture into a uniform transparent solution;

[0033] As a preferred, the solvent is selected from one or more combinations of cyclohexanone, dichloromethane, trichloromethane, acetone.

[0034] (iii) pouring the mixture into a polytetrafluoroethylene mold under an inert atmosphere, and heating for solidification;

[0035] (iv) heating and solidifying the residue obtained in step (iii) to obtain the desired protocatechuic acid-based benzoxazine modified bisphenol A-aniline benzoxazine.

[0036] Compared with the prior art, the main advantages of the present application include:

[0037] (1) The method provided by the present application belongs to deep processing and utilization of biomass, and a benzoxazine with a double oxazine ring structure is synthesized by using two phenolic hydroxyl groups of protocatechuic acid, which widens the application of protocatechuic acid and enriches the types of bio-based benzoxazines. New application of biomass resources is developed, sustainable development is realized, the demand pressure of chemical energy is reduced, and green economic development is promoted.

[0038] (2) The protocatechuic acid-based benzoxazine synthesized by the present application has good thermal stability and flame retardant performance, and can be used as a modifier to improve the thermal stability and flame retardant performance of commercial bisphenol A-aniline benzoxazine (general type benzoxazine). BRIEF DESCRIPTION OF DRAWINGS

[0039] Figure 1 The figure is the nuclear magnetic resonance spectrum of protocatechuic acid-based benzoxazine monomer NDBA-fa, wherein A is nuclear magnetic resonance hydrogen spectrum, and B is nuclear magnetic resonance carbon spectrum;

[0040] Figure 2 The figure is the thermogravimetric curve and the HRR (Heat release rate) and temperature relationship curve of protocatechuic acid benzoxazine resin poly (NDBA-fa), wherein A is the thermogravimetric curve, and B is the HRR and temperature relationship curve;

[0041] Figure 3 The figure is the thermogravimetric curve of benzoxazine resin with different contents of protocatechuic acid-based benzoxazine NDBA-fa;

[0042] Figure 4HRR vs. temperature curves of the benzoxazine resins with different contents of protocatechuic acid-based benzoxazine NDBA-fa. DETAILED DESCRIPTION

[0043] The application will be further described in conjunction with specific examples. It should be understood that these examples are only used to illustrate the application and not intended to limit the scope of the application. The experimental methods in the following examples, if not otherwise specified, are usually carried out under conventional conditions or under the conditions recommended by the manufacturers. Unless otherwise specified, percentages and parts are by weight.

[0044] Example 1-1 Synthesis of N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (NDBA)

[0045] Under nitrogen gas 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 sequentially mixed into 30 mL DMF under ice bath conditions. After the addition of furfurylamine (5.10 g, 0.0525 mol) into the mixture, the mixture was stirred at room temperature for 4 hours. After the reaction was completed, the reaction mixture was poured into 300 mL of sodium bicarbonate aqueous solution and stirred vigorously, followed by centrifugation to obtain the supernatant. The supernatant was extracted with ethyl acetate for multiple times. The collected organic layer was washed with sodium bicarbonate once and deionized water three times. 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).

[0046] Example 1-2 Synthesis of N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (NDBA)

[0047] The experimental method was the same as that in Example 1-1, except that the condensing agent 1-hydroxybenzotriazole and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride were replaced by N,N-dicyclohexyl carbodiimide (DCC) and 4-dimethylaminopyridine (DMAP), and other reaction conditions were unchanged, to obtain 5.2 g of the target monomer.

[0048] Example 1-3 Synthesis of N-(furan-2-ylmethyl)-3,4-dihydroxybenzamide (NDBA)

[0049] The experimental method was the same as that in Example 1-1, except that the solvent DMF was replaced by tetrahydrofuran, and other reaction conditions were unchanged, to obtain 5.6 g of the target monomer.

[0050] Example 2-1 Synthesis of protocatechuic acid-based benzoxazine monomer NDBA-fa

[0051] 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 were added into a 250 ml round bottom flask. After the whole system was stirred at room temperature for 1 h, the reaction was heated to reflux and stirred for 12 h. After cooling to room temperature, the organic solvent ethanol was removed by a rotary evaporator to obtain the crude product of benzoxazine. The crude product of benzoxazine was dissolved in dichloromethane and washed with 1 M NaOH aqueous solution for 3 times, then washed with a large amount of water until neutral, 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 of protocatechuic acid-based benzoxazine monomer (NDBA-fa).

[0052] Example 2-2 Synthesis of protocatechuic acid-based benzoxazine monomer NDBA-fa

[0053] The experimental method was the same as that of Example 2-1, the organic solvent ethanol was replaced by toluene, and other reaction conditions were unchanged, to obtain 0.82 g of the target monomer.

[0054] Example 2-3 Synthesis of protocatechuic acid-based benzoxazine monomer NDBA-fa

[0055] The experimental method was the same as that of Example 2-1, paraformaldehyde (0.660 g, 0.022 mol) was replaced by paraformaldehyde (0.540 g, 0.018 mol), and other reaction conditions were unchanged, to obtain 0.75 g of the target monomer.

[0056] The nuclear magnetic resonance spectrum of protocatechuic acid-based benzoxazine monomer NDBA-fa is shown in Figure 1 , which is specifically attributed to:

[0057] 1 H NMR (400 MHz, DMSO-d6): δ 8.64 (t, 1H, C-NH-CH2), δ 7.57 (d, 1H, Ar), δ 7.33 (d, 1H, Ar), δ 7.25 (dd, 1H, Ar), δ 6.78 (d, 1H, Ar), δ 6.40 (dd, 1H, Ar), δ 6.24 (d, 1H, Ar), δ 4.43 (d, 1H, NH-CH2-Ar);

[0058] 13C NMR (400 MHz, 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.

[0059] Example 3 Curing of Protocatechuic Acid Benzoxazine Resin

[0060] The protocatechuic acid benzoxazine monomer (II) was poured into the mold uniformly, and reacted at 180°C, 200°C, and 220°C for 1 h each. The cured protocatechuic acid benzoxazine resin poly(NDBA-fa) was obtained.

[0061] To evaluate the thermal stability of poly(NDBA-fa), Thermogravimetric Analysis (TGA) technique was used for testing. The temperature was raised from 100°C to 800°C at a rate of 10°C / min under nitrogen atmosphere. Details are shown in Figure 2 . Through this test, the thermal stability and decomposition behavior of poly(NDBA-fa) at different temperatures can be further understood. From the thermogravimetric curve, the T d5 and T d10 of poly(NDBA-fa) were measured to be 363°C and 403°C, respectively.

[0062] Micro-combustion calorimeter was used to test the flame retardant performance of polybenzoxazine. The sample was heated from 100°C to 700°C at a constant heating rate of 1°C / s under a nitrogen flow of 80 mL / min. Subsequently, the thermal degradation products of the sample under nitrogen atmosphere were mixed with an oxygen flow of 20 mL / min and then entered the combustion furnace at 900°C. Figure 2 The graph showing the heat release rate as a function of temperature is shown. From the data in the graph, the HRC (Heat Release Capacity) of poly(NDBA-fa) was calculated to be only 15.8 Jg -1 K -1 , which indicates that the material has a relatively low heat release capacity during thermal combustion, and since its HRC is less than 100 Jg -1 K -1 , it is a flame retardant material.

[0063] Example 4-1 Protocatechuic Acid Benzoxazine Modified General Type Benzoxazine (Bisphenol A-Aniline Benzoxazine)

[0064] Without adding NDBA-fa, pour the general benzoxazine (BA-a) into the mold, and react at 180°C, 200°C, 220°C, and 240°C for 1 h respectively. The general benzoxazine poly(BA-a) is obtained.

[0065] Example 4-2: Protocatechuic acid-based benzoxazine modified general benzoxazine

[0066] Add the protocatechuic acid benzoxazine monomer (NDBA-fa) and the general benzoxazine (BA-a) into the reactor according to the NDBA-fa content of 2.5%, mix uniformly, and then pour into the mold. React at 180°C, 200°C, 220°C, and 240°C for 1 h respectively to obtain the protocatechuic acid-based benzoxazine modified general benzoxazine poly(NDBA-fa / BA-a). 2.5wt%

[0067] Example 4-3: Protocatechuic acid-based benzoxazine modified general benzoxazine

[0068] The experimental method is the same as that in Example 4-2, the NDBA-fa content is changed to 5%, and other reaction conditions remain unchanged. The protocatechuic acid-based benzoxazine modified general benzoxazine poly(NDBA-fa / BA-a) is obtained. 5wt%

[0069] Example 4-4: Protocatechuic acid-based benzoxazine modified general benzoxazine

[0070] The experimental method is the same as that in Example 4-2, the NDBA-fa content is changed to 7.5%, and other reaction conditions remain unchanged. The protocatechuic acid-based benzoxazine modified general benzoxazine poly(NDBA-fa / BA-a) is obtained. 7.5wt%

[0071] Example 4-5: Protocatechuic acid-based benzoxazine modified general benzoxazine

[0072] The experimental method is the same as that in Example 4-2, the NDBA-fa content is changed to 10%, and other reaction conditions remain unchanged. The protocatechuic acid-based benzoxazine modified general benzoxazine poly(NDBA-fa / BA-a) is obtained. 10wt%

[0073] The performance test results of the modified benzoxazine resins prepared in Examples 4-1 to 4-5 are shown in Table 1.

[0074] Table 1: Thermal and flame retardant properties (HRC) of benzoxazine resins with different NDBA-fa contents

[0075] Example T d5 (°C) T d10 (°C) Residual carbon 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

[0076] ​​​​As can be seen from the data in Table 1, in the range of 0-10%, the addition of NDBA-fa can improve the T d5 , T d10 , carbon residue rate and HRC of BA-a, and the optimal addition amount of NDBA-fa is 7.5%, at which the T d5 , T d10 , carbon residue rate and HRC are 339.48℃, 377.34℃, 51.92% and 156.55Jg -1 K -1 , respectively.

[0077] The thermal gravimetric curves of the modified benzoxazine resins prepared in Example 4-1 to Example 4-5 are shown in Figure 3 , and the HRR-temperature relationship curves are shown in Figure 4 .

[0078] In summary, the synthesized protocatechuic acid-based benzoxazine monomer NDBA-fa has good thermal stability and flame retardant performance after curing; and NDBA-fa as a modifier can effectively improve the thermal stability and flame retardant performance of the general benzoxazine BA-a.

[0079] All the documents mentioned in the present application are incorporated herein by reference as if each document were individually incorporated by reference. In addition, it should be understood that various modifications and changes can be made to the present application by those skilled in the art reading the above teachings of the present application, and such equivalent forms are also within the scope of the appended claims of the present application.

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 Protocatechuic acid, furfurylamine, and a catalyst are dissolved in a solvent to carry out an amidation reaction; after the reaction is completed, excess solvent is removed 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 protocatechuic acid-based benzoxazine resin monomer NDBA-fa NDBA, furfurylamine, and paraformaldehyde are dissolved in a solvent, heated under reflux and stirred to react, and after the reaction, 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 one 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 one of 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 2-5 hours; the reaction temperature of step (2) is 70-120°C, and the reaction time is 6-12 hours.

8. A protocatechuic acid-based benzoxazine resin, characterized in that The benzoxazine resin is obtained by thermally 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 according to claim 1 as a heat-resistant and flame-retardant modifier.

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