WO2021037273A1

WO2021037273A1 - Covalent organic frame flame retardant having schiff base-containing vanillin group, and preparation method therefor

Info

Publication number: WO2021037273A1
Application number: PCT/CN2020/112714
Authority: WO
Inventors: 戴李宗; 彭超华; 陈婷; 陈国荣; 袁丛辉; 许一婷; 曾碧榕; 申应军; 罗伟昂
Original assignee: 厦门大学; 金旸（厦门）新材料科技有限公司
Priority date: 2019-08-30
Filing date: 2020-08-31
Publication date: 2021-03-04
Also published as: CN110698620B; CN110698620A

Abstract

Disclosed in the present invention are a covalent organic frame flame retardant having a Schiff base-containing vanillin group, and a preparation method therefor. In the present invention, the covalent organic frame flame retardant is prepared by performing a Schiff base amine aldehyde condensation reaction on a tridentate aldehyde compound containing R2 and a bidentate amine compound containing R1. A bio-based feedstock used in the present invention is environmentally friendly, a Schiff base structure contained in a molecular structure has high thermal stability and uses an amine aldehyde condensation reaction to make a reaction condition be mild, and the formation of a covalent organic structure that is rich in a benzene ring structure can significantly improve the thermal stability of the flame retardant and increasing the amount of formed carbon.

Description

Vanillin-based covalent organic frame flame retardant containing Schiff base and preparation method thereof

Technical field

The invention belongs to the technical field of polymer flame retardants, and specifically relates to a vanillin-based covalent organic frame flame retardant containing Schiff base and a preparation method thereof.

Background technique

Covalent organic framework materials are a new class of porous materials. Since Yaghi et al. prepared covalent organic framework materials in 2005, they have shown great application potential in gas storage and separation, catalysis, and energy storage. However, the monomers involved in the current covalent organic framework materials are often difficult to synthesize and expensive, which greatly limits their large-scale preparation and practical application. Due to the existence of C=N in the Schiff base structure, the nitrogen lone pair of electrons can neutralize free radicals and inhibit thermal degradation of the polymer during the pyrolysis process. At the same time, the Schiff base structure will eventually form a six-membered nitrogen heterocyclic structure when heated, which can significantly improve Thermal stability of carbon residue. As people's awareness of environmental protection has increased, people have also realized that halogen-free flame retardants containing phosphorus and nitrogen are more environmentally friendly than halogen-containing flame retardants. The current phosphorus-containing small molecules or linear polymers have a low decomposition temperature that does not meet the processing requirements of some high-molecular materials, and at the same time, there is a phenomenon that the flame retardant fails due to migration during long-term use. As a renewable resource, the application of bio-based raw materials can not only alleviate the pressure of dependence on petroleum, but also alleviate the pollution in the production of petroleum raw materials. Vanillin, as a compound produced on a platform of aromatic radicals derived from lignin, has shown good potential in the field of polymers.

Summary of the invention

The purpose of the present invention is to overcome the defects of the prior art and provide a vanillin-based covalent organic frame flame retardant containing Schiff base.

Another object of the present invention is to provide a method for preparing the above-mentioned covalent organic frame flame retardant.

The technical scheme of the present invention is as follows:

A vanillin-based covalent organic frame flame retardant containing Schiff base, its structural formula is:

Where R ₁ is

R ₂ is

Method for preparing the flame retardant covalent organic frameworks, comprising: a compound containing an aldehyde R ₂ tridentate and bidentate amine compound containing as R ₁ amine-aldehyde Schiff base via condensation reaction of;

The structural formula of the above trichloro compound is:

The structural formula of the above bidentate amine compound is:

In a preferred embodiment of the present invention, the following steps are included:

(1) Dissolving the bidentate amine compound in a first organic solvent;

(2) Dissolving the tridentate aldehyde compound in a second organic solvent;

(3) Under a nitrogen atmosphere, add the material obtained in step (2) to the material obtained in step (1), then add an appropriate amount of acetic acid, and stir for 2-4 hours at 75-85°C;

(4) Filter the material obtained in step (3) to obtain a solid, wash the solid with a third solvent, and dry in vacuum to obtain the covalent organic frame flame retardant.

Further preferably, the first organic solvent is at least one of acetonitrile, tetrahydrofuran, N,N-dimethylformamide, methanol, dimethyl sulfoxide, trimethylbenzene and dioxane.

Further preferably, the second organic solvent is at least one of acetonitrile, tetrahydrofuran, N,N-dimethylformamide, methanol, dimethyl sulfoxide, trimethylbenzene and dioxane.

Further preferably, the third organic solvent is at least one of tetrahydrofuran, N,N-dimethylformamide and acetone.

Further preferably, the molar ratio of the bidentate amine compound to the tridentate aldehyde compound is 3-4:2.

Further preferably, the ratio of the bidentate amine compound to the first organic solvent is 1 g: 10-25 mL.

Further preferably, the ratio of the tridentate aldehyde compound to the second organic solvent is 1 g: 10-25 mL.

Further preferably, the added amount of the acetic acid is 0.25-1% of the total volume of the material obtained in step (1) and the material obtained in step (2).

In a preferred embodiment of the present invention, the synthesis steps of the bidentate amine compound are as follows:

(1) The molar ratio of 1:1:1-3 was added to a three-necked flask with phosphorus-containing compounds, aminoacetophenone and aniline (0.36mmol), and then p-toluenesulfonic acid (4wt%, based on phosphorus-containing compounds). ) Stir and mix at 80°C-180°C under nitrogen. Lasts for 12-24h. After that, the reaction mixture is poured into an excess precipitating agent to precipitate the resulting product bidentate amine compound. Finally, dry the bidentate amine compound in an oven at 60°C-80°C for 6-12h;

Wherein the precipitating agent is tetrahydrofuran, ethyl acetate or a mixture of both; the phosphorus-containing compound is

In a preferred embodiment of the present invention, the method for synthesizing the tridentate aldehyde compound is: weighing vanillin, sodium hydroxide and trichloride _{containing R 2 in a molar ratio of 3-3.5:3-3.5:1,} First dissolve vanillin in the mixed solution, add hydroxide under ice bath conditions, and magnetically stir for 30min-60min. Slowly add the trichloride solution dissolved in an organic solvent dropwise, continue to stir for 1-3h, and then reflux for 2-4h at 60℃-100℃, and cool naturally. Pour the reacted solution into an appropriate amount of distilled water to form a large amount of white solid. After filtering, the solid powder is washed 2-3 times with 10% sodium carbonate solution and dried in vacuum.

The above-mentioned mixed solution may be a mixed solution composed of acetone/tetrahydrofuran and water in a volume ratio of 1-2:1-2; the above-mentioned organic solvent may be acetone or tetrahydrofuran or any mixed solvent of the two. The above-mentioned trichloride is cyanuric chloride or 1,3,5-trichloro-1,3,5-triazine-2,4,6-trione.

The beneficial effects of the present invention are:

1. Compared with the traditional preparation of covalent organic framework materials, the raw materials used are difficult to synthesize and expensive. The present invention is inexpensive, simple and easy to obtain, and at the same time uses green and environmentally friendly vanillin.

2. In the present invention, a high molecular weight flame retardant is prepared through mild amine-aldehyde condensation reaction, which avoids the migration and failure of the flame retardant, and can significantly increase the amount of residual carbon. At the same time, the introduction of the Schiff base structure can give the material potential The optical and chemical properties, and the six-membered nitrogen heterocyclic structure eventually formed by heating, can significantly improve the thermal stability of the carbon residue.

3. The covalent organic frame flame retardant prepared by the present invention has high molecular weight and is rich in benzene rings, which can exhibit good thermal stability, making it suitable for processing and using various polymers.

Description of the drawings

Figure 1 is an infrared image of the bidentate amine compound, tridentate aldehyde compound and covalent organic frame flame retardant obtained in Example 1 of the present invention.

2 is a thermogravimetric diagram of the covalent organic frame flame retardant obtained in Example 1 of the present invention under a nitrogen atmosphere.

Fig. 3 is a test heat release curve of the epoxy nanocomposite micro-calorimeter prepared in Example 5 of the present invention.

Figure 4 is the thermogravimetric curve of the epoxy resin nanocomposite prepared in Example 5 of the present invention in a nitrogen atmosphere.

detailed description

The technical solutions of the present invention will be further illustrated and described below through specific implementations.

Example 1:

1) 28.08g diphenylphosphonate (0.12mol), 16.46g 4-aminoacetophenone (0.12mol), 167.5g aniline (0.36mmol) and 1.123g p-toluenesulfonic acid (4wt%, based on Diphenylphosphonate) was stirred and mixed at 130°C under nitrogen for 24h. After that, the reaction mixture was poured into an excess of THF to obtain a precipitate, and then the precipitate was dried in an oven at 60° C. for 12 hours to obtain a bidentate amine compound as shown in FIG. 1 (in this example, 2-(4-amino) Phenyl)-1-(6-oxo-6H-dibenzo<c,e><1,2>]oxaphosphin-6-yl)ethane bidentate amine).

2) Weigh 9.27 g (61.0 mmol) of vanillin and dissolve it in 100 mL of _{a mixed solution of acetone and H 2} O (1/1, v/v), add 2.48 g of sodium hydroxide under ice bath conditions, and magnetically stir for 30 min. Slowly add 50 mL of acetone-dissolved cyanuric chloride (3.7 g, 20.0 mmol) solution dropwise, continue stirring for 1 h, and then stir and reflux at 80° C. for 2 h, and cool naturally. The reaction solution was poured into 300 mL of distilled water, and a large amount of white solid was formed. After filtering, the solid powder is washed 2-3 times with a 10% sodium carbonate solution, and dried under vacuum to obtain the tridentate aldehyde compound as shown in FIG. 1.

3) Weigh out 0.3mmol 2-(4-aminophenyl)-1-(6-oxo-6H-dibenzo<c,e><1,2>]oxaphosphene-6- Ethane bidentate amine, put it into a 10 mL glass pressure bottle, and then add 1 mL of mesitylene/dioxane (1:1, v/v) mixed solvent to form a uniform dispersion. Then weigh the above tridentate aldehyde compound (0.2 mmol) into another 10 mL glass bottle, and add 1 mL of mesitylene/dioxane (1:1, v/v) mixed solvent to form a uniform dispersion. Transfer the formed tridentate aldehyde compound dispersion to the pressure bottle where the above bidentate amine compound dispersion is located, mix it evenly, and then repeatedly fill with protective gas (nitrogen) to exhaust the air, and then slowly add acetic acid (0.2 mL), sealed, and stirred at 80°C for 4h. A powdery solid product precipitated. The product was washed alternately with acetone, DMF and tetrahydrofuran. Until the washing liquid becomes colorless, the solid product is vacuum dried at 50°C for 24 hours to obtain the covalent organic frame flame retardant in the form of a light yellow solid powder (infrared image and thermogravimetric image are shown in Figure 1 and Figure 2 respectively) ).

Example 2:

1) 25.94g DOPO (0.12mol), 16.46g 4-aminoacetophenone (0.12mol), 167.5g aniline (0.36mmol) and 1.038g p-toluenesulfonic acid (4wt%, based on DOPO) under nitrogen Stir and mix at 130°C for 24h. After that, the reaction mixture was poured into excess THF to obtain a precipitate, and then the precipitate was dried in an oven at 60° C. for 12 h to obtain a bidentate amine compound (2-(4-aminophenyl)-1-in this example). (6-oxo-6H-dibenzo<c,e><1,2>]oxaphosphin-6-yl)ethane bidentate amine).

2) Weigh 9.27 g (61.0 mmol) of vanillin and dissolve it in 100 mL of _{a mixed solution of acetone and H 2} O (1/1, v/v), add 2.48 g of sodium hydroxide under ice bath conditions, and magnetically stir for 30 min. Slowly add 50 mL of acetone-dissolved cyanuric chloride (3.7 g, 20.0 mmol) solution dropwise, continue stirring for 1 h, and then stir and reflux at 80° C. for 2 h, and cool naturally. The reacted solution was poured into 300 mL of distilled water, and a large amount of white solid was formed. After filtering, the solid powder is washed 2-3 times with a 10% sodium carbonate solution, and dried in a vacuum to obtain a tridentate aldehyde compound.

3) Weigh out 0.3mmol 2-(4-aminophenyl)-1-(6-oxo-6H-dibenzo<c,e><1,2>]oxaphosphene-6- Ethane bidentate amine, put it into a 10 mL glass pressure bottle, and then add 1 mL of mesitylene/dioxane (1:1, v/v) mixed solvent to form a uniform dispersion. Then weigh the monomer tridentate aldehyde compound (0.2 mmol) and place it in another 10 mL glass bottle, while adding 1 mL of mesitylene/dioxane (1:1, v/v) mixed solvent to form a uniform dispersion. Transfer the formed tridentate aldehyde compound dispersion to the pressure bottle where the above bidentate amine compound dispersion is located, mix it evenly, and then repeatedly fill with protective gas (nitrogen) to exhaust the air, and then slowly add acetic acid (0.2 mL), sealed, and stirred at 80°C for 4h, a powdery solid product precipitated. The product was washed alternately with acetone, DMF and tetrahydrofuran. Until the washing liquid becomes colorless, the solid product is vacuum-dried at 50° C. for 24 hours to obtain the covalent organic frame flame retardant as a light yellow solid powder.

Example 3:

1) 28.08g diphenylphosphonate (0.12mol), 16.46g 4-aminoacetophenone (0.12mol), 167.5g aniline (0.36mmol) and 1.123g p-toluenesulfonic acid (4wt%, based on Diphenylphosphonate) was stirred and mixed at 130°C under nitrogen for 24h. After that, the reaction mixture was poured into excess THF to obtain a precipitate, and then the precipitate was dried in an oven at 60° C. for 12 h to obtain a bidentate amine compound (2-(4-aminophenyl)-1-in this example). (6-oxo-6H-dibenzo<c,e><1,2>]oxaphosphin-6-yl)ethane bidentate amine).

2) Weigh 9.27 g (61.0 mmol) of vanillin and dissolve it in 100 mL of _{a mixed solution of acetone and H 2} O (1/1, v/v), add 2.48 g of sodium hydroxide under ice bath conditions, and magnetically stir for 30 min. Slowly add 50 mL of acetone-dissolved 1,3,5-trichloro-1,3,5-triazine-2,4,6-trione (4.6g, 20.0mmol) solution, continue to stir for 1h, and then make it in Stir and reflux for 2h at 80°C and cool naturally. The reaction solution was poured into 300 mL of distilled water, and a large amount of white solid was formed. After filtering, the solid powder is washed 2-3 times with a 10% sodium carbonate solution, and dried in a vacuum to obtain a tridentate aldehyde compound.

Example 4:

1) 25.94g DOPO (0.12mol), 16.46g 4-aminoacetophenone (0.12mol), 167.5g aniline (0.36mmol) and 1.038g p-toluenesulfonic acid (4wt%, based on DOPO) under nitrogen Stir and mix at 130°C. Lasts for 24h. After that, the reaction mixture was poured into excess THF to obtain a precipitate, and then the precipitate was dried in an oven at 60° C. for 12 h to obtain a bidentate amine compound (2-(4-aminophenyl)-1-in this example). (6-oxo-6H-dibenzo<c,e><1,2>]oxaphosphin-6-yl)ethane bidentate amine).

2) Weigh 9.27 g (61.0 mmol) of vanillin and dissolve it in 100 mL of a mixed solution of acetone and H2O (1/1, v/v), add 2.48 g of sodium hydroxide under ice bath conditions, and magnetically stir for 30 min. Slowly add 50 mL of acetone-dissolved 1,3,5-trichloro-1,3,5-triazine-2,4,6-trione (4.6g, 20.0mmol) solution, continue to stir for 1h, and then make it in Stir and reflux for 2h at 80°C and cool naturally. The reacted solution was poured into 300 mL of distilled water, and a large amount of white solid was formed. After filtering, the solid powder is washed 2-3 times with a 10% sodium carbonate solution, and dried in a vacuum to obtain a tridentate aldehyde compound.

3) Weigh 0.3mmol of 2-(4-aminophenyl)-1-(6-oxo-6H-dibenzo<c,e><1,2>]oxaphosphin-6- Ethane bidentate amine, put it into a 10 mL glass pressure bottle, and then add 1 mL of mesitylene/dioxane (1:1, v/v) mixed solvent to form a uniform dispersion. Then weigh the monomer tridentate aldehyde compound (0.2 mmol) and place it in another 10 mL glass bottle, while adding 1 mL of mesitylene/dioxane (1:1, v/v) mixed solvent to form a uniform dispersion. Transfer the formed tridentate aldehyde compound dispersion to the pressure bottle where the above bidentate amine compound dispersion is located, mix it evenly, and then repeatedly fill with protective gas (nitrogen) to exhaust the air, and then slowly add acetic acid (0.2 mL), sealed, and stirred at 80°C for 4h. A powdery solid product precipitated. The product was washed alternately with acetone, DMF and tetrahydrofuran. Until the washing liquid becomes colorless, the solid product is vacuum dried at °C for h to obtain the covalent organic frame flame retardant as a light yellow solid powder.

Example 5:

The application of the covalent organic frame flame retardant prepared in Example 1 as the flame retardant additive of epoxy resin is as follows: Weigh 2g of covalent organic frame flame retardant, 38.4g epoxy resin, stir at 90°C for 3h, and vacuum Remove the water, then cool down to 80°C, add 9.6g of diaminodiphenylmethane, cure at 120°C for two hours, and cure at 180°C for 2 hours. The prepared epoxy resin nanocomposite was subjected to micro-calorimeter test and thermogravimetric test to study its flame-retardant behavior. Figure 3 shows the heat release curve of the epoxy nanocomposite micro-calorimeter test. Compared with pure epoxy, 4% organic frame flame retardant is added, and the peak heat release rate drops significantly. Figure 4 shows the thermogravimetric curve of the prepared epoxy nanocomposite under nitrogen atmosphere. At 750°C, the carbon residue rate has increased from 12wt% of pure epoxy to 21wt%.

Example 6:

The application of the covalent organic frame flame retardant prepared in Example 3 as a flame retardant additive of polylactic acid is as follows: weigh 48 g of polylactic acid, weigh 2 g of the covalent organic frame flame retardant prepared in Example 3, and use a mixer Mix at 180°C for 5 minutes with a rotor speed of 60 rpm to obtain a composite material. Then, the obtained composite material was hot pressed at 180° C. under a pressure of 10 MPa for 5 minutes to form a sheet, and then quickly cooled to room temperature. The prepared polylactic acid nanocomposite was tested by a miniature calorimeter, and it was found that compared with the pure polylactic acid prepared under the same conditions, the peak heat release rate of the polylactic acid nanocomposite decreased by nearly 21%.

The above are only the preferred embodiments of the present invention, so the scope of implementation of the present invention cannot be limited accordingly. That is, equivalent changes and modifications made according to the scope of the patent of the present invention and the contents of the specification should still be covered by the present invention. In the range.

Industrial applicability

The present invention discloses a frame retardant covalent organic herbs and a preparation method of the aldehyde-containing Schiff bases, according to the present invention is a compound containing an aldehyde R ₂ tridentate and bidentate amine-containing compound R ₁ through Schiff base Amine-aldehyde condensation reaction system. The invention uses bio-based raw materials to be green and environmentally friendly. The Schiff base structure contained in the molecular structure has high thermal stability and uses amine-aldehyde condensation reaction to make the reaction conditions mild. At the same time, the formation of covalent organic structures rich in benzene ring structures can be significantly improved The thermal stability and carbon content of flame retardants have industrial applicability.

Claims

A vanillin-based covalent organic frame flame retardant containing Schiff base, which is characterized in that its structural formula is:

Where R 1 is
R 2 is
The method for preparing a covalent organic frame flame retardant according to claim 1, characterized in that it comprises: reacting vanillin, a trichloro compound containing R 2 and sodium hydroxide to form a tridentate aldehyde compound, and then reacting with a tridentate aldehyde compound containing R 1 The bidentate amine compound is prepared by Schiff base amine aldehyde condensation reaction;

The structural formula of the above trichloro compound is:

The structural formula of the above bidentate amine compound is:
3. The preparation method according to claim 2, characterized in that it comprises the following steps:

(1) Dissolving the bidentate amine compound in a first organic solvent;

(2) Dissolving the tridentate aldehyde compound in a second organic solvent;

(3) Under a nitrogen atmosphere, add the material obtained in step (2) to the material obtained in step (1), then add an appropriate amount of acetic acid, and stir for 2-4 hours at 75-85°C;

(4) Filter the material obtained in step (3) to obtain a solid, wash the solid with a third solvent, and dry in vacuum to obtain the covalent organic frame flame retardant.
The preparation method according to claim 3, wherein the first organic solvent is acetonitrile, tetrahydrofuran, N,N-dimethylformamide, methanol, dimethyl sulfoxide, trimethylbenzene and dioxane At least one of them.
The preparation method according to claim 3, wherein the second organic solvent is acetonitrile, tetrahydrofuran, N,N-dimethylformamide, methanol, dimethyl sulfoxide, trimethylbenzene and dioxane At least one of them.
The preparation method according to claim 3, wherein the third organic solvent is at least one of tetrahydrofuran, N,N-dimethylformamide and acetone.
The preparation method according to claim 3, wherein the molar ratio of the bidentate amine compound to the tridentate aldehyde compound is 3-4:2.
The preparation method according to claim 3, wherein the ratio of the bidentate amine compound to the first organic solvent is 1 g: 10-25 mL.
8. The preparation method of claim 3, wherein the ratio of the tridentate aldehyde compound to the second organic solvent is 1 g: 10-25 mL.
The preparation method according to claim 1, wherein the added amount of the acetic acid is 0.25-1% of the total volume of the material obtained in step (1) and the material obtained in step (2).