A kind of multifunctional benzoxazine resin and preparation method thereof

Abstract

The invention belongs to the technical field of thermosetting resins, and relates to a kind of multi-functional benzoxazine resin and preparation method thereof, specifically a tri-functional benzoxazine containing phenolic hydroxyl group, alcoholic hydroxyl group and intramolecular hydrogen bond and preparation method thereof, and specific preparation method: quercetin, amine compounds, and paraformaldehyde are mixed, added to a low-polarity solvent for reaction, reacted at 70-130 DEG C for 2-10h, then the organic solvent is removed by rotary evaporation, and the product is dried to obtain. The advantage of the present invention is that quercetin is used as the phenol source of benzoxazine resin, and the synthesized benzoxazine resin has a multi-functional structure, and contains phenolic hydroxyl group and alcoholic hydroxyl group in the molecule, which can give the resin effective storage and low-temperature curing characteristics, while having excellent thermodynamic properties. The present invention has simple synthesis steps, and the benzoxazine resin after curing has excellent thermal and mechanical properties, has low requirements for production equipment, and is suitable for large-scale production.

Description

Technical Field

[0001] The present invention is applicable to the technical field of thermosetting resins, and in particular relates to a multifunctional benzoxazine resin and a preparation method thereof. Background Art

[0002] Benzoxazine is a class of compounds synthesized from phenols, aldehydes and primary amines. It is a high-performance thermosetting resin with good thermal stability, low water absorption, high residual carbon rate, easy processing and zero volume shrinkage after curing. Benzoxazine resin has been widely used in aerospace, automotive, electronics and defense industries.

[0003] At present, the global economic and social development is facing two prominent problems: shortage of oil resources and environmental pollution. In response to this situation, a global research boom has been launched to use bio-renewable resources to replace petroleum raw materials to prepare polymer materials. As humans gradually pay more attention to the living environment, replacing petroleum-based polymer materials with bio-based polymer materials is an inevitable path for green and sustainable development.

[0004] In order to improve the thermomechanical properties of benzoxazines, petroleum-based groups such as acetylene, allyl, nitrile and maleimide can be incorporated into the benzoxazines structure, but the environmental problems caused by petroleum raw materials are still unavoidable. Compared with traditional petroleum-based benzoxazines, benzoxazines produced from bio-based raw materials have become an effective way to achieve sustainable development. However, the curing temperature of bio-based benzoxazines is generally higher, which increases the difficulty of resin processing.

[0005] In view of the above problems, the present invention designs a quercetin-based bio-based benzoxazine resin and a preparation method thereof. Quercetin is rich in hydroxyl groups, and one of the phenolic hydroxyl groups protected by the adjacent keto group does not participate in the oxazine ring-forming reaction due to the formation of intramolecular hydrogen bonds. The unreacted phenolic hydroxyl group can catalyze the oxazine ring opening reaction only after breaking the hydrogen bond. On the other hand, the alcoholic hydroxyl group on the other side of the keto group can weaken the strength of the intramolecular hydrogen bond, break the hydrogen bond at low temperature, release the activity of the phenolic hydroxyl group, and make the resin have low-temperature curing characteristics. Summary of the invention

[0006] In view of the environmental and performance defects of current benzoxazine resins, the present invention uses bio-based quercetin as a phenol source. Not only is the raw material environmentally friendly, but quercetin can also be used to synthesize a bio-based benzoxazine resin that is easy to store and has low-temperature curing properties. The trifunctional resin structure can also promote the formation of a highly cross-linked dense structure after curing. Compared with other reported benzoxazine resins, the quercetin-based bio-based benzoxazine resin of the present invention has lower curing temperature, high temperature resistance and other characteristics.

[0007] One of the purposes of the present invention is to provide a multifunctional benzoxazine resin, the molecular chemical structure of which is shown below:

[0008]

[0009] in, One of the following structures:

[0010]

[0011] The second object of the present invention is to provide a method for preparing a multifunctional bio-based benzoxazine resin using quercetin as a phenol source.

[0012] Using quercetin, amine compounds and paraformaldehyde as raw materials, benzoxazine is prepared. The chemical reaction equation is as follows:

[0013]

[0014] The structural formula of the amine compound is R-NH2, which is one of the following structures:

[0015]

[0016] The specific steps include:

[0017] The quercetin, amine compounds and polyformaldehyde are mixed and added to a reaction flask, and an organic solvent is added, and the mixture is reacted at 70-130° C. for 2-10 hours. After the reaction is stopped, the solvent is removed by rotary evaporation, and the product is dried to obtain a solid product, which is a quercetin-based bio-based benzoxazine resin. The molar ratio of the quercetin, amine compounds and polyformaldehyde is 1:3:6-1:3:8.

[0018] Furthermore, the optimal molar ratio of quercetin, amine compounds and paraformaldehyde is 1:3:6.5.

[0019] The organic solvent is one of dioxane, toluene and xylene or a mixture of several of them.

[0020] Compared with the prior art, the advantages of the present invention are:

[0021] Using bio-based quercetin as a phenol source, a trifunctional benzoxazine resin containing phenolic hydroxyl and alcoholic hydroxyl is synthesized. A phenolic hydroxyl protected by an adjacent keto group in the resin structure does not participate in the oxazine ring-forming reaction due to the formation of intramolecular hydrogen bonds. The unreacted phenolic hydroxyl group can catalyze the oxazine ring opening reaction only after breaking the hydrogen bond. On the other hand, the alcoholic hydroxyl group on the other side of the keto group can weaken the strength of the intramolecular hydrogen bond, break the hydrogen bond at low temperature, release the activity of the phenolic hydroxyl group, and make the resin have low-temperature curing characteristics. This benzoxazine has a very low curing temperature and excellent thermal and mechanical properties. The peak curing temperature is 150-210°C, the glass transition temperature is 250-400°C, and the residual carbon rate is 60-80% at 800°C in an inert gas atmosphere; the synthesis process is simple, the yield is high, the equipment requirements are low, and it is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the hydrogen nuclear magnetic resonance spectrum of the benzoxazine resin obtained in Example 1;

[0023] Figure 2 is the infrared spectrum of the benzoxazine resin obtained in Example 1;

[0024] Figure 3 is the DSC spectrum of the benzoxazine resin obtained in Example 1;

[0025] Figure 4 This is the TGA spectrum of the benzoxazine resin obtained in Example 1 after curing. DETAILED DESCRIPTION

[0026] The following provides a specific embodiment of a multifunctional benzoxazine resin and a preparation method thereof of the present invention. It is necessary to point out that the following examples are only used to explain the present invention in more detail, rather than to narrow the scope of protection of the present invention. After reading the present invention, improvements and adjustments made by professionals in this technical field without departing from the concept of the present invention are within the scope of protection claimed by the present invention.

[0027] Embodiment 1:

[0028] Example 1

[0029] 2-Furfurylamine was used as the amine source. 1g (0.0033mol) of quercetin, 0.974g (0.0101mol) of 2-Furfurylamine, and 0.656g (0.0218mol) of paraformaldehyde were added to a flask, and 50ml of toluene solution was added. A condenser was connected, and the mixture was stirred and reacted at 110°C for 8h. After the reaction was stopped, the solvent was removed by rotary evaporation, and the mixture was dried in a vacuum drying oven at 50°C for one day to obtain 1.63g of benzoxazine monomer with a yield of 75%. The chemical reaction equation is as follows:

[0030]

[0031] In this embodiment, the structure of the obtained oxazine product is:

[0032]

[0033] The H NMR spectrum, FTIR spectrum, DSC curve and thermogravimetric curve of the product are shown in the attached Figure 1 , Attachment Figure 2 , Attachment Figure 3 and attached Figure 4 .

[0034] Attached Figure 1 H NMR spectrum. The chemical shifts of 5.09, 5.06, 4.97 ppm and 4.25, 4.11, 4.07 ppm are the characteristic peaks of methylene on the oxazine ring. Figure 2 Infrared spectrum, 929cm -1 and 1241cm -1 The absorption peak at is the characteristic absorption peak of benzoxazine ring. Figure 3 The DSC curve shows that the peak temperature of the benzoxazine monomer curing exothermic reaction is 189°C. Figure 4 The TGA curve of the cured resin material shows that the temperature at which the benzoxazine resin loses 5% of its thermal weight is 371°C, the carbon residue rate under 800°C inert gas is 66%, and the glass transition temperature of the cured resin material is 321°C.

[0035] Example 2

[0036] The amine source compound 2-furanmethylamine in Example 1 was replaced by aniline. The other steps were the same as those in Example 1.

[0037] The specific chemical structural formula of aniline is: The amount of reactants was changed to: weigh 1 g (0.0033 mol) of quercetin, 0.9244 g (0.0099 mol) of aniline, and 0.6551 g (0.0218 mol) of paraformaldehyde. The yield was 81%.

[0038]

[0039] The polyfunctional benzoxazine resin monomer obtained in this embodiment has a curing exothermic peak temperature of 172°C. After further curing and cross-linking, the temperature of the polybenzoxazine resin is 366°C when the thermal weight loss is 5%, the residual carbon rate is 60% at 800°C in an inert gas atmosphere, and the glass transition temperature is 295°C.

[0040] Example 3

[0041] The amine source compound 2-furylmethylamine in Example 1 was replaced by 4-methylaniline. The other steps were the same as those in Example 1.

[0042] The specific chemical structural formula of 4-methylaniline is: The amount of reactants was changed to: weigh quercetin 1g (0.0033mol), 4-methylaniline 1.0637g (0.0099mol), paraformaldehyde 0.6551g (0.0218mol). The yield was 83%.

[0043]

[0044] The polyfunctional benzoxazine resin monomer obtained in this embodiment has a curing exothermic peak temperature of 167°C. After further curing and cross-linking, the temperature of the polybenzoxazine resin is 358°C when the thermal weight loss is 5%, the residual carbon rate is 61% at 800°C in an inert gas atmosphere, and the glass transition temperature is 281°C.

[0045] Example 4

[0046] The amine source compound 2-furanmethylamine in Example 1 was replaced by 3-alkynylaniline. The other steps were the same as those in Example 1.

[0047] The specific chemical structural formula of 3-alkynylaniline is: The amount of reactants was changed to: weigh quercetin 1g (0.0033mol), 3-alkynylaniline 1.1628g (0.0109mol), paraformaldehyde 0.6551g (0.0218mol). The yield was 76%.

[0048]

[0049] The polyfunctional benzoxazine resin monomer obtained in this embodiment has a curing exothermic peak temperature of 162°C. After further curing and cross-linking, the temperature of the polybenzoxazine resin is 410°C when the thermal weight loss is 5%, the residual carbon rate is 72% at 800°C in an inert gas atmosphere, and the glass transition temperature is 385°C.

[0050] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A polyfunctional benzoxazine resin having the following molecular formula: in, One of the following structures: ； The peak curing temperature is 150-210°C. The multifunctional benzoxazine resin is further cured and cross-linked to obtain a polybenzoxazine resin, the glass transition temperature is 250-400°C, and the residual carbon rate is 60-80% under an inert gas atmosphere at 800°C. The preparation method of the multifunctional benzoxazine resin comprises the following steps: Quercetin, amine compounds and paraformaldehyde are mixed, an organic solvent is added, and the mixture is reacted at 70-130° C. for 2-10 hours. After the reaction is stopped, the solvent is removed by rotary evaporation, and the product is dried to obtain a solid product, which is a multifunctional bio-based benzoxazine resin.

2. The method for preparing a polyfunctional benzoxazine resin according to claim 1, characterized in that: The amine compound has a structural formula of R-NH2, which is one of the following structures:

3. The method for preparing a polyfunctional benzoxazine resin according to claim 1, characterized in that: The molar ratio of the quercetin, the amine compound and the paraformaldehyde is 1:3:6-1:3:

8.

4. The method for preparing a polyfunctional benzoxazine resin according to claim 3, characterized in that: The optimal molar ratio of the quercetin, the amine compound and the paraformaldehyde is 1:3:6.

5.

5. The method for preparing a polyfunctional benzoxazine resin according to claim 1, wherein: The organic solvent is one of dioxane, toluene and xylene or a mixture of several of them.

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