A bio-based flame-retardant benzoxazine resin monomer and a preparation method thereof

Abstract

This invention belongs to the field of thermosetting resin technology and relates to a bio-based flame-retardant benzoxazine resin monomer and its preparation method. The invention employs a one-pot method, with the following specific steps: salicylaldehyde and an amine compound from biomass are added to an appropriate amount of ethanol and reacted at approximately 50°C for 2-3 hours; 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is added to the mixture, and the temperature is raised to 70°C for 8-12 hours; benzaldehyde is added to the mixture, and the reaction continues for 8-12 hours; after the reaction is complete, the product is obtained by rotary evaporation and drying. The difference between this invention and traditional benzoxazine resins lies in the following: this preparation uses bio-based benzaldehyde instead of traditional formaldehyde to synthesize benzoxazine resin, and utilizes a large amount of biomass raw materials, striving for sustainable development while also obtaining benzoxazine resin with extremely excellent flame-retardant properties; furthermore, the synthesis process of this invention is simple, economical, and environmentally friendly, suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of thermosetting resin technology, and specifically relates to a bio-based flame-retardant benzoxazine resin monomer and its preparation method. Background Technology

[0002] Benzoxazine resin is a high-performance thermosetting resin that has emerged in the last thirty years. It is a compound with a benzo[a]heterocyclic structure, prepared by the Mannich condensation reaction of phenolic compounds, primary amine compounds, and aldehydes (formaldehyde or paraformaldehyde), and capable of ring-opening polymerization under heating or catalysis. Compared with other conventional thermosetting resins, the cured product of benzo[a]hexazine resin, polybenzo[a]hexazine resin, exhibits superior overall performance: near-zero curing yield, extremely low water absorption, excellent mechanical properties, higher glass transition temperature, excellent dielectric properties, excellent thermal stability, and flame retardant properties. Therefore, benzo[a]hexazine resin is widely used in aerospace, composite materials, ablation-resistant materials, electronic packaging, and other fields.

[0003] Although benzoxazine resins have become an ideal alternative to many traditional thermosetting resins, they also face the same challenges as other polymers in terms of raw material supply. In the last century, the abuse of petroleum has had a continuous negative impact on daily life. Therefore, much effort has been made to develop sustainable bio-based polymer materials to replace their petroleum-based counterparts. Sustainable synthesis of polymers using natural renewable resources has received extensive investment and will become an inevitable choice for the polymer industry.

[0004] All current patent reports on benzoxazine use formaldehyde for synthesis (e.g., CN 112341584A, CN107573334B). Based on this research status, this invention innovatively uses biomass raw materials salicylaldehyde and benzaldehyde instead of formaldehyde and employs the green solvent ethanol for the preparation of benzoxazine. Furthermore, DOPO is introduced into the molecule, achieving both sustainable development and obtaining benzoxazine resins with extremely excellent flame-retardant properties. All obtained polybenzoxazine thermosetting resins achieved a V-0 rating in vertical burning tests. The synthesis process is simple, economical, and environmentally friendly, suitable for large-scale production. Summary of the Invention

[0005] The purpose of this invention is to improve the flame retardant properties of benzoxazine resin while making the most use of biomass raw materials, and to provide a bio-based flame retardant benzoxazine resin monomer and its preparation method.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] One objective of this invention is to provide a bio-based flame-retardant benzoxazine resin monomer with the following molecular formula:

[0008]

[0009] in, One of the following:

[0010]

[0011] The second objective of this invention is to provide a method for preparing a bio-based flame-retardant benzoxazine resin monomer, the specific steps of which are as follows:

[0012] First, salicylaldehyde and amine compounds from biomass are added to an appropriate amount of ethanol and reacted at 45–55°C for 2–3 hours. Then, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is added to the mixture, and the temperature is raised to 65–75°C for 8–12 hours. Finally, benzaldehyde is added to the mixture, and the reaction is continued for another 8–12 hours. After the reaction is complete, the product is obtained by rotary evaporation and drying. The chemical reaction equation is as follows:

[0013]

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

[0015]

[0016] The molar ratio of salicylaldehyde, amine compounds, DOPO and benzaldehyde is 1:1:1:1 to 1:1:1:1.5.

[0017] The optimal molar ratio of salicylaldehyde, amine compounds, DOPO and benzaldehyde is 1:1:1:1 to 1:1:1:1.12.

[0018] Beneficial technical effects

[0019] Compared with existing technologies, the advantages of this invention are that it uses biomass materials such as salicylaldehyde and benzaldehyde instead of formaldehyde, and employs a one-pot reaction with the green solvent ethanol. The synthesis steps are simple, the yield is high, and the cured benzoxazine resin exhibits excellent flame retardant properties, achieving a UL94-V0 rating. In contrast, existing commercially available benzoxazine resins require petroleum-based raw materials for synthesis, which cannot meet the needs of sustainable development. While the cured benzoxazine resin material has excellent thermal stability, it lacks self-extinguishing characteristics and does not reach the flame retardant rating of the bio-based benzoxazine resin proposed in this invention. Furthermore, the synthesis process of this invention is simple, economical, and environmentally friendly, making it suitable for large-scale production. Attached Figure Description

[0020] Figure 1 The 1H NMR spectrum of the benzoxazole resin obtained in Example 1;

[0021] Figure 2 Infrared spectrum of the benzoxazole resin obtained in Example 1;

[0022] Figure 3 DSC spectrum of the benzoxazine resin obtained in Example 1;

[0023] Figure 4 TGA spectrum of the cured benzoxazine resin obtained in Example 1. Detailed Implementation

[0024] The following provides specific embodiments of a bio-based flame-retardant benzoxazine resin monomer and its preparation method according to the present invention. It should be noted that the following examples are only for illustrating the present invention in more detail, and not for narrowing the scope of protection of the present invention. Improvements and adjustments made by those skilled in the art after reading this invention without departing from the concept of the present invention are all within the scope of protection claimed by the present invention.

[0025] Example 1

[0026] A bio-based flame-retardant benzoxazine resin monomer and its preparation method, the specific steps of which are as follows:

[0027] 1.22 g (10 mmol) of salicylaldehyde and 0.97 g (10 mmol) of furfural were added to a reaction flask equipped with a stir bar and a condenser. Ethanol was added, and the mixture was heated to 50 °C with stirring. After reacting for 3 h, 2.16 g (10 mmol) of DOPO was added to the reaction flask, the temperature was raised to 70 °C, and the reaction was continued with stirring for 10 h. Immediately afterwards, 1.17 g (11 mmol) of benzaldehyde was added, and the reaction was continued for 12 h. After the reaction was completed, the product was recrystallized in ethanol solution, and after filtration, 3.84 g of white product was obtained, with a yield of 76%.

[0028]

[0029] In this embodiment, the structure of the obtained oxazine product is as follows:

[0030]

[0031] The proton NMR spectrum, Fourier transform infrared spectrum, DSC curve, and thermogravimetric analysis curve of the product are attached. Figure 1 Appendix Figure 2 Appendix Figure 3 and attached Figure 4 .

[0032] Appendix Figure 1The proton NMR spectrum shows chemical shifts of 6.54 ppm and 4.29 ppm, which are characteristic peaks of the methylene group on the oxazine ring. Figure 2 This is an infrared spectrum, where 923 and 1232 cm⁻¹ are... -1 The peak at this location is a characteristic absorption peak of the benzoxazine ring. (See attached image) Figure 3 The attached DSC curve shows that the peak exothermic temperature during the curing of this benzoxazine monomer is 232℃. Figure 3 It can be seen that the polybenzoxazine resin has a thermal weight loss of 5% at a temperature of 291°C, and a char rate of 36% at 800°C. Furthermore, the benzoxazine resin obtained in this embodiment achieved a V-0 rating in a vertical combustion test after curing.

[0033] Example 2

[0034] The furfural in Example 1 was replaced with aniline, and the other steps were the same as in Example 1.

[0035] The specific chemical structure of aniline is as follows:

[0036] In the reaction step, the amount of reactant was changed to: 0.93 g (10 mmol) of aniline was weighed.

[0037] The structural formula of the obtained benzoxazine is:

[0038]

[0039] The yield of the bisbenzoxazine monomer obtained in this embodiment was 74%. After further curing and crosslinking, the polybenzoxazine resin had a char rate of 35% at 286°C when it lost 5% of its weight at thermal stress and at 800°C in an inert gas atmosphere. The vertical combustion test yielded a V-0 rating.

[0040] Example 3

[0041] The furfurylamine in Example 1 was replaced with 3-methylaniline, and the other steps were the same as in Example 1.

[0042] The specific chemical structure of 3-methylaniline is as follows:

[0043] In the reaction step, the amount of reactant was changed to: 1.07 g (10 mmol) of 3-methylaniline was weighed.

[0044] The structural formula of the obtained benzoxazine is:

[0045]

[0046] The yield of the bisbenzoxazine monomer obtained in this embodiment was 76%. After further curing and crosslinking, the polybenzoxazine resin had a char rate of 36% at 289°C when it lost 5% of its weight at thermal stress and at 800°C in an inert gas atmosphere. The vertical combustion test yielded a V-0 rating.

[0047] Example 4

[0048] The furfural in Example 1 was replaced with 3-aminobenzonitrile, and the other steps were the same as in Example 1.

[0049] The specific chemical structure of 3-aminobenzonitrile is as follows:

[0050] In the reaction step, the amount of reactant was changed to: 1.18 g (10 mmol) of 3-aminobenzonitrile was weighed.

[0051] The structural formula of the obtained benzoxazine is:

[0052]

[0053] The bisbenzoxazine monomer yield obtained in this embodiment is 69%. After further curing and crosslinking, the polybenzoxazine resin has a char rate of 39% at 296°C when the thermal weight loss is 5% and at 800°C in an inert gas atmosphere. The vertical combustion test obtained a V-0 rating.

[0054] Example 5

[0055] The furfural in Example 1 was replaced with 3-ethynylaniline, and the other steps were the same as in Example 1.

[0056] The specific chemical structure of 3-ethynylaniline is as follows:

[0057] In the reaction step, the amount of reactant was changed to: 1.17 g (10 mmol) of 3-ethynylaniline was weighed.

[0058] The structural formula of the obtained benzoxazine is:

[0059]

[0060] The bisbenzoxazine monomer yield obtained in this embodiment was 75%. After further curing and crosslinking, the polybenzoxazine resin had a char rate of 40% at 299°C when it lost 5% of its weight at thermal stress and at 800°C in an inert gas atmosphere. The vertical combustion test obtained a V-0 rating.

[0061] The above description is merely a preferred embodiment of the present invention and does not impose any limitation on the present invention. Although the present invention is described above as a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A bio-based flame-retardant benzoxazine resin monomer, characterized in that, The molecular formula is as follows: in, One of the following: The preparation method of the bio-based flame-retardant benzoxazine resin monomer includes the following specific steps: First, salicylaldehyde and amine compounds from biomass are added to an appropriate amount of ethanol and reacted at 45–55°C for 2–3 hours. Then, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) is added to the mixture, and the temperature is raised to 65–75°C for 8–12 hours. Finally, benzaldehyde is added to the mixture and reacted for another 8–12 hours. After the reaction is completed, the product is obtained by rotary evaporation and drying.

2. The bio-based flame-retardant benzoxazine resin monomer according to claim 1, characterized in that, After further curing and crosslinking, the polybenzoxazine resin exhibits a char rate of 35-55% at 250-400℃ when it loses 5% of its weight due to heat, and at 800℃ in an inert gas atmosphere. The polybenzoxazine resin also achieves a V-0 rating in vertical combustion tests.

3. The bio-based flame-retardant benzoxazine resin monomer according to claim 1, characterized in that, The amine compound has the structural formula R-NH2, which is one of the following structures:

4. The bio-based flame-retardant benzoxazine resin monomer as described in claim 1, characterized in that, The molar ratio of salicylaldehyde, amine compounds, DOPO and benzaldehyde is 1:1:1:1 to 1:1:1:1.

5.

5. The bio-based flame-retardant benzoxazine resin monomer as described in claim 1, characterized in that, The optimal molar ratio of salicylaldehyde, amine compounds, DOPO and benzaldehyde is 1:1:1:1 to 1:1:1:1.12.

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