CN114573842B - High temperature resistant, reprocessable benzoxazine thermosetting resin and its synthesis method and application - Google Patents

Abstract

The present invention relates to high temperature resistant and reprocessable benzoxazine thermosetting resin and its synthesis method and application. First, allylamine, phenolic compounds and formaldehyde are used as raw materials to synthesize a double-bonded benzoxazine monomer through Mannich reaction; then, a double-bonded benzoxazine oligomer is prepared through a heating ring-opening reaction. things. Finally, the "thiol-ene" click chemical reaction between thiols and double bonds containing borate ester bonds was used to prepare reprocessable benzoxazine resin cross-linked with borate ester bonds. The benzoxazine resin synthesized by the invention has excellent reprocessability, mechanical properties and heat resistance. After three reprocessings, the recovery rate of tensile strength can still reach 84%, _Tg can reach 227°C, and the tensile strength Reach 31MPa.

Description

High temperature resistant, reprocessable benzoxazine thermosetting resin and its synthesis method and application

Technical field

The invention relates to the preparation of high-temperature-resistant and reprocessable benzoxazine thermosetting resin by cross-linking benzoxazine oligomers containing double bonds through borate ester bonds, and belongs to the field of high-temperature-resistant thermosetting resins.

Background technique

Thermosetting polymers have been widely used in structural materials and insulation materials due to their properties such as high temperature resistance, solvent resistance, dimensional stability and excellent insulation properties. However, traditional thermosetting polymers contain irreversible covalently cross-linked structures, making them insoluble and infusible after solidification, and cannot be reprocessed and recycled, resulting in resource waste and environmental pollution. In recent years, the introduction of dynamic covalent bonds in polymer networks has been a breakthrough in solving the above problems. Dynamic covalent bonds refer to covalent bonds that can be reversibly broken and formed under certain conditions. By introducing dynamic covalent bonds at the main chain position or cross-linking bond position of the polymer network, the response to stimulation can be achieved (such as thermally induced response, etc.), thereby achieving repeatable processing performance.

Generally, dynamic covalent bonds can be divided into two types: dissociation type and association type according to different exchange mechanisms. In the former, the bond is broken first and then reorganized, such as the Diels-Alder addition reaction; in the latter, the bond is broken and reorganized at the same time, such as boronic acid ester bond, disulfide bond, acylhydrazone bond, etc. The borate ester bond is an associative dynamic covalent bond with a very high bond energy (515kJ/mol). The cross-linking density remains almost constant during the bond exchange process, which is beneficial to the preparation of high-temperature resistant and reprocessable thermosetting materials. Ideal crosslinks for resins.

As a new type of thermosetting resin, polybenzoxazine has attracted much attention due to its good heat resistance, excellent flame retardancy and high hydrophobicity. Like traditional thermosetting resins, the inherent cross-linked structure prevents them from being recycled.

In addition, CN113292691A discloses a cardanol-based benzoxazine resin and its preparation method and application. The preparation method used is to solidify the benzoxazine monomer containing borate ester bonds at high temperature, and the final product forms dynamic boron Dual network of acid-ester bond cross-linking and benzoxazine self-cross-linking. However, the cardanol-based benzoxazine resin will greatly reduce the mechanical strength recovery rate after reprocessing because the benzoxazine self-crosslinked network does not contain dynamic covalent bonds.

Contents of the invention

In view of the shortcomings of the existing technology, especially the low mechanical strength recovery rate of the current reprocessable benzoxazine resin after reprocessing, the present invention provides a borate ester bond cross-linked, reversible "purity" High temperature resistance, reprocessable benzoxazine thermosetting resin to achieve high heat resistance and high mechanical strength recovery rate of the resin after reprocessing.

Specifically, allylamine, formaldehyde and phenolic compounds are used as raw materials to synthesize benzoxazine monomers, and then ring-opening polymerization is performed to prepare benzoxazine oligomers containing double bonds. The thiol-containing borate ester cross-linking agent is used to perform a "thiol-ene" click chemical reaction with double bonds to prepare a highly reversible cross-linked network with only dynamic borate ester bond cross-linking. The benzoxazine resin has excellent thermal properties and high mechanical strength recovery rate.

Summary of the invention:

The invention first uses allylamine, phenolic compounds and formaldehyde to synthesize benzoxazine monomers through Mannich reaction; prepares benzoxazine oligomers containing double bonds through heating ring-opening reaction; and uses thiol-containing boric acid to Esters are used as cross-linking agents. Through the "thiol-ene" click chemical reaction, a cross-linked structure with dynamic borate ester bonds is produced, which has excellent heat resistance and high mechanical strength recovery rate and can be added with benzene. Oxazine resin.

Detailed description of the invention:

The technical solution of the present invention is as follows:

A new high-temperature-resistant, reprocessable benzoxazine resin cross-linked with borate ester bonds has the following structure:

in,

R ₁ =-CH ₃ , -C(CH ₃ ) ₃ , -CH ₂ -CH＝CH ₂ ;

n=2-100.

According to the present invention, the preparation method of the above-mentioned borate ester bond cross-linked high temperature resistant and reprocessable benzoxazine resin includes the following steps:

First, allylamine, formaldehyde and phenolic compounds are used as raw materials to synthesize benzoxazine monomers, and then heated to ring-opening polymerization to prepare benzoxazine oligomers containing double bonds; finally, thiol-containing borate esters are used to synthesize benzoxazine monomers. As a cross-linking agent, through the "thiol-ene" click chemical reaction, a high-temperature-resistant and reprocessable benzoxazine resin cross-linked by borate ester bonds is obtained. The benzoxazine resin cross-linked structure is a dynamic borate ester bond, with excellent heat resistance and high mechanical strength recovery rate.

According to the present invention, preferably, the preparation method of the borate ester bond cross-linked high temperature resistant and reprocessable benzoxazine resin includes the following steps:

(1) Mix allylamine, phenolic compounds, formaldehyde and solvent, stir evenly, react at a temperature of 80-100°C, remove the solvent after the reaction, and dry under vacuum to obtain a double bond-containing benzoxazine monomer;

(2) Add p-tert-butylphenol to the benzoxazine monomer, mix evenly, and heat for ring-opening polymerization to obtain a benzoxazine oligomer containing double bonds;

(3) Mix terephthalic diboric acid and 3-thiol-1,2-propanediol in ethanol evenly, react at room temperature for 14-28 hours, remove the solvent after the reaction, and dry under vacuum to obtain diboron ester dithiol;

(4) Mix the products in steps (2) and (3) evenly in the solvent, and use the thiol-containing borate ester and the double bond to perform a "thiol-ene" click chemical reaction to prepare the borate ester bond Cross-linked, reprocessable benzoxazine resin.

According to the present invention, preferably, the phenolic compound described in step (1) is any one of phenol, p-cresol, p-tert-butylphenol, cardanol, and p-allylphenol.

According to the present invention, preferably, the formaldehyde described in step (1) is paraformaldehyde or a formaldehyde aqueous solution.

According to the present invention, preferably, the molar ratio of allylamine, phenolic compounds, and formaldehyde in step (1) is 1:1:(2-2.5).

According to the present invention, preferably, the temperature at which the ring-opening polymerization reaction is heated in step (2) is 140-150°C.

According to the present invention, preferably, the molar ratio of the double bonds in the diborane dithiol and benzoxazine oligomer added in step (4) is 1:(2-3).

According to the present invention, preferably, the thermally initiated polymerization reaction temperature of the "thiol-ene" click chemical reaction in step (4) is 75°C, the reaction time is 6 hours, and then the temperature is gradually raised to 100, 120, and 140°C for 2 hours each.

According to the present invention, the application of the above-mentioned borate ester cross-linked, high temperature resistant, reprocessable novel benzoxazine resin in reprocessed resin;

Preferably, the reprocessing steps are as follows: Grind the damaged, reprocessable benzoxazine resin into powder, hot-press at a temperature of 140-160°C, a pressure of 16-20MPa, and a hot-pressing time of 2-5 hours.

The synthesis route of the borate ester cross-linked, high temperature resistant, and reprocessable novel benzoxazine resin prepared by the present invention is as follows:

The beneficial effects of the present invention are as follows:

1. In terms of synthesis, the present invention designs benzoxazine oligomers to be cross-linked with borate ester bonds, so that the cross-linked structures in the cross-linked network are all dynamic borate ester bonds and do not contain other non-reversible cross-linked structures. , the reversible "purity" of the network is high.

2. In terms of performance, since the benzoxazine resin synthesized in the present invention has a high "purity" reversible cross-linked network, it has excellent reprocessability, and the recovery rate of tensile strength after three reprocessings can still reach 84 %.

3. In terms of performance, since the benzoxazine resin synthesized in the present invention uses dynamic borate ester bonds with high bond energy, it has excellent heat resistance, and _Tg can reach 227°C.

4. Since the benzoxazine resin synthesized in the present invention has a high cross-linking density, the product has high mechanical strength, which can reach 31MPa.

Description of the drawings

Figure 1 is a ¹ HNMR (Proton Nuclear Magnetic Spectrum) chart of cardanol, allylamine, benzoxazine monomers and oligomers based on allylamine and cardanol in Example 1.

Figure 2 shows the thiol-containing borate ester bond cross-linking agent, the benzoxazine monomer based on allylamine and cardanol, and the borate ester bond cross-linking agent based on allylamine and cardanol in Example 1. FT-IR (Fourier Transform Infrared Spectroscopy) pattern of reprocessable benzoxazine resin.

Figure 3 is an SEC (gel permeation chromatography) chart of benzoxazine monomers and oligomers based on allylamine and cardanol in Example 1.

Figure 4 is a ¹ HNMR (hydrogen nuclear magnetic spectrum) chart of the thiol-containing borate ester bond cross-linking agent in Example 1.

Figure 5 is a ¹ H NMR (Proton Nuclear Magnetic Spectrum) chart of benzoxazine monomers and oligomers based on allylamine and p-cresol in Example 2.

Figure 6 is the tensile strength and elongation at break of the initial and third reprocessing of the reprocessable benzoxazine resin based on allylamine and cardanol cross-linked by borate ester bonds in the test example.

Figure 7 is a DMA (dynamic thermomechanical analysis) diagram of the initial and third reprocessing of the reprocessable benzoxazine resin based on allylamine and cardanol cross-linked by borate ester bonds in the test example.

Figure 8 is a TGA (thermogravimetric analysis) diagram of the initial and third reprocessing of the reprocessable benzoxazine resin based on allylamine and cardanol cross-linked by borate ester bonds in the test example.

Detailed ways

The present invention will be further described below through specific examples, but it is not limited thereto.

The reagents used in the examples are all conventional commercial products.

Example 1: Reprocessable benzoxazine resin based on allylamine and cardanol

(1) Add allylamine (8.55g, 150mmol), paraformaldehyde (9.47g, 300mmol), triethylamine (5mL) and toluene (300mL) into a 500mL three-necked flask, and stir at room temperature for 0.5h. Cardanol (46.61g, 150mmol) was added dropwise to the above mixture. The reaction was stirred under reflux for 12 h. The benzoxazine monomer (BZ) was obtained by vacuum drying at 60°C with a yield of 83%.

Test the ¹ HNMR data of the benzoxazine monomer obtained in this example, as follows:

¹ H NMR (400MHz, CDCl ₃ , ppm): 6.90-6.60 (3H, Ar-H), 5.84-5.76 (1H,-CH ₂ -CH＝CH ₂ ), 4.85 (2H, O-CH ₂ -N) ,5.28-5.15(2H,CH ₂ =CH-),3.96(2H,Ar-CH ₂ -N),3.41-3.35(2H,N-CH ₂ -CH-),2.57-2.48(2H,Ar-CH ₂ -),1.64-1.51(2H,Ar-CH ₂ -CH ₂ -CH ₂ -). The chart is shown in Figure 1.

Test the FT-IR data of the benzoxazine monomer obtained in this example, as follows:

FT-IR (KBr, cm ^-1 ): 2926 and 2854 (CH ₂ of the oxazine ring and the side chain alkyl group of cardanol), 1640 (C=C of the allyl group), 1505 (C= on the benzene ring) C), 1242 (COC on oxazine ring), 968 (oxazine ring). The chart is shown in Figure 2.

SEC spectrum, as shown in Figure 3.

(2) Add p-tert-butylphenol (1.5g) to benzoxazine monomer (15g), stir at 100°C for 5 minutes until completely mixed, polymerize the resulting mixture at 150°C for 10h, and cool to room temperature A wine red solid was obtained. Dissolve the obtained crude product in n-hexane, pour it into 500 mL of methanol, filter and collect the solid, and dry it under vacuum at 50°C to obtain benzoxazine oligomer (OBZ) with a yield of 70%. ¹ HNMR spectrum, as shown in Figure 1; FT-IR spectrum, as shown in Figure 2;

SEC spectrum, as shown in Figure 3.

(3) Dissolve 1,4-phenylenediboronic acid (3.03g, 18.1mmol) and 3-thiol-1,2-propanediol (4.12g, 36.2mmol) in ethanol (65mL), stir at room temperature for 24h, and the reaction is completed Afterwards, ethanol was removed by rotary evaporation under reduced pressure to obtain the target compound as a white solid, which was designated as BDB (6.58g, 92%).

Test the ¹ H NMR data of the benzoxazine monomer obtained in this example, as follows:

¹ H NMR (400MHz, CDCl ₃ ,ppm): 1.48(2H,-SH), 2.81(4H,HS-CH ₂ -), 4.18 and 4.49(4H,O-CH ₂ -), 4.74(2H,O- CH-(CH ₂ -) ₂ ),7.83(4H,Ar-H). The graph is shown in Figure 4.

The FT-IR spectrum is shown in Figure 2.

(4) Under argon protection, combine the benzoxazine oligomer (3.02g) in step (2) and the thiol-containing borate ester cross-linking agent (1.51g) in step (3) at 75°C Dissolve in anisole respectively, mix the two and cool to room temperature. Add AIBN (0.13g) dissolved in anisole to the above system. After stirring evenly, pour it into an aluminum foil tank and put it into the oven: react at 75℃ for 12h, gradually increase the temperature to 100, 120, and 140℃ for 2h each, and then react at 100℃ After vacuum drying, a wine red transparent film is obtained.

The FT-IR spectrum is shown in Figure 2.

Example 2: Reprocessable benzoxazine resin based on allylamine and p-cresol.

(1) Add allylamine (8.55g, 0.15mol), paraformaldehyde (9.90g, 0.33mol), p-cresol (16.20g, 0.15mol), triethylamine (4mL) and 200mL toluene into 500mL three ports In the flask, stir the reaction under reflux for 4 hours. When the reaction is completed, it is cooled to room temperature and dried under vacuum at 60°C to obtain the benzoxazine monomer with a yield of 70%.

Test the ¹ HNMR data of the benzoxazine monomer obtained in this example, as follows:

¹ H NMR (400MHz, CDCl ₃ , ppm): 6.87-6.61 (3H, Ar-H); 5.89-5.79 (1H,-CH ₂ -CH＝CH ₂ ), 5.18-5.12 (2H,-CH ₂ -CH ＝CH ₂ ),4.77(2H,O-CH ₂ -N),3.89(2H,Ar-CH ₂ -N),3.31(2H,-CH ₂ -CH＝CH ₂ ),2.18(3H,Ar-CH ₃ ). The graph is shown in Figure 5.

(2) Add p-tert-butylphenol (1.5g) to benzoxazine monomer (15g), stir at 100°C for 5 minutes until completely mixed, polymerize the resulting mixture at 150°C for 10h, and cool to room temperature A light yellow solid was obtained. Dissolve the obtained crude product in toluene, pour it into 500 mL of n-hexane, filter and collect the solid, and dry it under vacuum at 50°C to obtain a light yellow benzoxazine oligomer.

Test the ¹ HNMR data of the benzoxazine monomer obtained in this example, as follows:

¹ H NMR (400MHz, CDCl ₃ ,ppm): 6.93–6.69(2H,Ar-H), 5.96(1H,-CH ₂ -CH＝CH ₂ ), 5.20(2H,-CH ₂ -CH＝CH ₂ ) ,3.67(4H,Ar-CH ₂ -N), 3.12(2H,-CH ₂ -CH＝CH ₂ ), 2.21(3H,Ar-CH ₃ ). The graph is shown in Figure 5.

(3) Dissolve 1,4-phenylenediboronic acid (3.03g, 18.1mmol) and 3-thiol-1,2-propanediol (4.12g, 36.2mmol) in ethanol (65mL), stir at room temperature for 24h, and the reaction is completed Afterwards, ethanol was removed by rotary evaporation under reduced pressure to obtain the target compound as a white solid (6.58g, 92%).

(4) Under argon protection, combine the benzoxazine oligomer (4.02g) in step (2) and the thiol-containing borate ester cross-linking agent (2.71g) in step (3) at 75 Dissolve in anisole respectively at ℃, mix the two and cool to room temperature. Add AIBN (0.18g) dissolved in anisole to the above system. After stirring evenly, pour it into an aluminum foil tank and put it into the oven: react at 75°C for 12 hours, gradually increase the temperature to 100, 120, and 140°C for 2 hours each, and then react at 100°C. After vacuum drying, a light yellow transparent film is obtained.

Example 3: Reprocessable benzoxazine resin based on allylamine and p-tert-butylphenol.

(1) Add allylamine (8.55g, 0.15mol), paraformaldehyde (9.90g, 0.33mol), p-tert-butylphenol (22.5g, 0.15mol), triethylamine (4mL) and 250mL chloroform In a 500 mL three-necked flask, stir the reaction under reflux for 4 hours. When the reaction is completed, cool to room temperature and dry under vacuum at 40°C to obtain the benzoxazine monomer.

(2) Add p-tert-butylphenol (1.5g) to benzoxazine monomer (15g), stir at 100°C for 5 minutes until completely mixed, polymerize the resulting mixture at 150°C for 10h, and cool to room temperature A light yellow solid was obtained. Dissolve the obtained crude product in toluene, pour it into 500 mL of n-hexane, collect the solid by suction filtration, and dry it under vacuum at 50°C to obtain benzoxazine oligomers.

(3) Dissolve 1,4-phenylenediboronic acid (3.03g, 18.1mmol) and 3-thiol-1,2-propanediol (4.12g, 36.2mmol) in ethanol (65mL), stir at room temperature for 24h, and the reaction is completed Afterwards, the ethanol was removed by rotary evaporation under reduced pressure to obtain the target compound as a white solid.

(4) Under argon protection, combine the benzoxazine oligomer (3.86g) in step (2) and the thiol-containing borate ester cross-linking agent (2.21g) in step (3) at 75°C Dissolve in anisole respectively, mix the two and cool to room temperature. Add AIBN (0.17g) dissolved in anisole to the above system. After stirring evenly, pour it into an aluminum foil tank and put it into the oven: react at 75°C for 12 hours, gradually increase the temperature to 100, 120, and 140°C for 2 hours each, and then react at 100°C. Vacuum drying gives the final product.

Test example: Reprocessability experiment based on allylamine and cardanol.

The sample prepared in Example 1 was ground into powder, fully filled into a stainless steel mold, and hot-pressed for 2 hours at 16 MPa and 160°C to obtain a reprocessable dumbbell-shaped specimen and test its mechanical properties.

The tensile strength and elongation at break properties of the initial and third reprocessing of the reprocessable benzoxazine resin based on allylamine and cardanol cross-linked with borate ester linkages are shown in Figure 6. It can be seen that the initial tensile strength is 31MPa. After three reprocessing processes, 84% of the tensile strength is still retained, showing good reprocessability.

The DMA diagrams of the initial and third reprocessing of reprocessable benzoxazine resins based on allylamine and cardanol cross-linked by borate ester bonds are shown in Figure 7. It can be seen that the glass transition temperature is higher than 200°C both initially and after the reprocessing process.

The TGA plots of the initial and third reprocessing of the reprocessable benzoxazine resin based on allylamine and cardanol cross-linked by borate ester bonds are shown in Figure 8. It can be seen that the initial thermal decomposition temperature after the initial and reprocessing processes is higher than 260°C, indicating that the material has good heat resistance and thermal stability.

Therefore, the benzoxazine resin synthesized in the present invention exhibits excellent reprocessability and heat resistance, making the recycling of benzoxazine in the field of high temperature resistance a good prospect.

Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, they do not limit the scope of the present invention. On the basis of the technical solutions of the present invention, those skilled in the art can make various modifications without any creative work. Modifications or transformations are still within the scope of the present invention.

Claims (10)

1. Preparation method of high temperature resistant and reprocessable benzoxazine resin cross-linked by borate ester bonds. The benzoxazine resin has the following structure: in, R ₁ =-CH ₃ , -C(CH ₃ ) ₃ , -CH ₂ -CH＝CH ₂ ; n=2-100; The preparation method includes the following steps: (1) Mix allylamine, phenolic compounds, formaldehyde and solvent, stir evenly, react at a temperature of 80-100°C, remove the solvent after the reaction, and dry under vacuum to obtain a double bond-containing benzoxazine monomer; (2) Add p-tert-butylphenol to the benzoxazine monomer, mix evenly, and heat for ring-opening polymerization to obtain a benzoxazine oligomer containing double bonds; (3) Mix terephthalic diboric acid and 3-thiol-1,2-propanediol in ethanol evenly, react at room temperature for 14-28 hours, remove the solvent after the reaction, and dry under vacuum to obtain diboron ester dithiol; (4) Mix the products in steps (2) and (3) evenly in the solvent, and use the thiol-containing borate ester and the double bond to perform a "thiol-ene" click chemical reaction to prepare the borate ester bond Cross-linked, reprocessable benzoxazine resin. 2. The preparation method of borate ester bond cross-linked high temperature resistant reprocessable benzoxazine resin according to claim 1, characterized in that the phenolic compound described in step (1) is phenol, p- Any one of cresol, p-tert-butylphenol, cardanol, and p-allylphenol. 3. The preparation method of borate ester bond cross-linked high temperature resistant reprocessable benzoxazine resin according to claim 1, characterized in that the formaldehyde described in step (1) is paraformaldehyde or formaldehyde aqueous solution. 4. The preparation method of borate ester bond cross-linked high temperature resistant and reprocessable benzoxazine resin according to claim 1, characterized in that in step (1), allylamine, phenolic compounds, formaldehyde The molar ratio is 1:1:(2-2.5). 5. The preparation method of the high-temperature-resistant and reprocessable benzoxazine resin cross-linked by borate ester bonds according to claim 1, characterized in that the temperature of the heated ring-opening polymerization reaction in step (2) is 140-140°C. 150℃. 6. The preparation method of borate ester bond cross-linked high temperature resistant reprocessable benzoxazine resin according to claim 1, characterized in that the diborane dithiol added in step (4) and benzene The molar ratio of double bonds in the oxazine oligomer is 1:(2-3). 7. The preparation method of borate ester bond cross-linked high temperature resistant and reprocessable benzoxazine resin according to claim 1, characterized in that the "thiol-ene" click chemical reaction in step (4) The thermally initiated polymerization reaction temperature was 75°C, the reaction time was 6 h, and then the temperature was gradually raised to 100, 120, and 140°C for 2 h each. 8. A benzoxazine resin prepared by the method for preparing a borate ester bond cross-linked high-temperature reprocessable benzoxazine resin according to any one of claims 1 to 7. 9. Application of the benzoxazine resin according to claim 8 in reprocessed resin. 10. The application according to claim 9, characterized in that the reprocessing step is as follows: Grind the damaged, reprocessable benzoxazine resin into powder, and the hot pressing temperature is 140-160°C and the pressure is 16 -20MPa, hot pressing time 2-5h.