CN116082327A

CN116082327A - Guaiacol-containing bio-based benzoxazine, resin, preparation method and application thereof

Info

Publication number: CN116082327A
Application number: CN202310000971.5A
Authority: CN
Inventors: 郭凯; 李金兰; 何军; 李振江; 孙戒; 颜蕊; 陈恺; 段彤; 黄卫州
Original assignee: Nanjing Tech University
Current assignee: Nanjing Tech University
Priority date: 2023-01-03
Filing date: 2023-01-03
Publication date: 2023-05-09

Abstract

The invention discloses a bio-based benzoxazine containing guaiacol, resin and a preparation method and application thereof. Raw materials of phenol, acid/ester and furfuryl amine are all biological sources, so that fossil resources are saved and the environment is protected; the benzoxazine has low curing temperature and is easy to be applied subsequently; the molecular side chain can be modified to improve the thermal stability of the benzoxazine; the synthesis is carried out by a two-step method, and the process is simple.

Description

Guaiacol-containing bio-based benzoxazine, resin, preparation method and application thereof

Technical Field

The invention belongs to the field of thermosetting resins, and particularly relates to a bio-based benzoxazine and a preparation method thereof.

Background

Benzoxazines are relatively new phenolic thermosetting materials, and have excellent properties, such as nearly zero shrinkage during polymerization, high coke yield, high glass transition temperature, excellent electrical and mechanical properties, and the like. In addition, the curing thereof generally does not require an external catalyst or curing agent, simplifying the use process thereof. Therefore, the benzoxazine has wide application prospect in the fields of aerospace, electronic elements and the like.

In recent years, due to the scarcity of fossil resources and environmental protection requirements, industrially conventional bisphenol a benzoxazines are gradually replaced by bio-based materials. Zhang et al reported guaiacol-containing biobased benzoxazine resins [ European Polymer Journal,131, (2020) 10970]. It uses two molecules of guaiacol and one molecule of furfural to synthesize bis-guaiacol by condensation, then uses Mannich condensation with paraformaldehyde and furfuryl amine to synthesize benzoxazine monomer [ European Polymer Journal,131, (2020) 10970 containing guaiacol]The following reaction scheme is guaiacol-containing bio-based benzoxazine, and the synthetic resin has a glass transition temperature of 290 ℃. However, as shown in the following reaction equation, the benzoxazine monomer synthesized by Zhang has a single structure and no re-modifier. The benzoxazine resin needs to be synthesized by ring opening at a high curing peak temperature of 240 ℃, which is inconvenient for practical application and consumes heat energy. T of the resin _d10％ About 375 c, the thermal stability is not high enough.

Disclosure of Invention

In order to reduce the curing temperature of the guaiacol-containing benzoxazine and improve the thermal stability and the remodification property of the resin, the invention provides the guaiacol-containing bio-based benzoxazine and a preparation method thereof.

The technical scheme of the invention is as follows:

the bio-based benzoxazine resin containing the guaiacol is obtained by curing a benzoxazine monomer shown in a formula I, and the structure of the benzoxazine resin containing the guaiacol is shown in a formula II:

wherein R is H,

wherein R is H,

the benzoxazine shown in the formula I is synthesized by the following method:

respectively dripping organic solution containing bis-guaiacol and furfuryl amine into organic solution of paraformaldehyde, reacting at high temperature of 90-130 ℃ for 6-24 hours, and extracting and purifying to obtain bio-based benzoxazine, wherein the bis-guaiacol is shown as formula III:

wherein R is H,

the benzoxazine resin shown in the formula II is obtained by curing in the following way:

and curing the benzoxazine shown in the formula I at 60-180 ℃ for 2-24 hours to obtain the benzoxazine resin.

The preparation method of the bio-based benzoxazine resin comprises the following steps:

1. synthesis of benzoxazines

Respectively dripping organic solution containing guaiacol and furfuryl amine into organic solution of paraformaldehyde, reacting at high temperature of 90-130 ℃ for 6-24 hours, and extracting and purifying to obtain the bio-based benzoxazine, wherein the reaction equation is as follows:

wherein R is H,

2. preparation of benzoxazine resins

And curing the benzoxazine at 60-180 ℃ for 2-24 hours to obtain the benzoxazine resin.

According to the scheme, the guaiacol in the step one is prepared in the following manner:

heating guaiacol and levulinic acid/ethyl levulinate under the action of a catalyst to react, thereby obtaining the bis-guaiacol. The reaction equation is as follows:

according to the scheme, the mole ratio of the guaiacol to the furfuryl amine in the first step is 1:2-2.5, and most preferably 1:2.2; the molar ratio of the guaiacol to the paraformaldehyde is 1:2-4, and most preferably 1:3;

according to the scheme, the reaction steps of the first step are as follows: at normal temperature, firstly, dissolving paraformaldehyde in an organic solvent, and stirring for 30 minutes; then dripping the organic solution of furfuryl amine into the paraformaldehyde solution at the rate of 1min/mL, and stirring for 30 min; and finally, dripping the organic solution of the guaiacol into the mixture at the rate of 1min/mL, and reacting for 5-24 hours at the high temperature of 80-130 ℃. After the reaction, the solvent was removed by rotary evaporation, followed by three extractions with diethyl ether and deionized water, and finally drying over night with anhydrous sodium sulfate. Filtering and rotary steaming to remove the solution to obtain brown yellow powder, namely the bio-based benzoxazine. Most preferably, the temperature is 110℃and the time is 24 hours.

According to the scheme, the organic solvent in the first step comprises toluene, tetrahydrofuran, dioxane, ethanol and methanol; most preferred is dioxane.

A guaiacol-containing bio-based benzoxazine resin is applied to an adhesive.

The beneficial effects are that:

(1) The invention selects the guaiacol and the levulinic acid/ethyl levulinate which are biological sources as raw materials, is environment-friendly, and synthesizes the bio-based benzoxazine with the furfuryl amine by using a two-step method, and has simple process.

(2) The invention introduces levulinic acid as a side chain, and the benzoxazine can be solidified at a lower temperature because the existence of carboxyl can catalyze the ring opening of the benzoxazine, the solidification peak temperature is only 183 ℃, as shown in figure 4, and the general bisphenol A benzoxazine solidification peak temperature is 240 ℃. The cure peak temperature of the guaiacol benzoxazine synthesized by Zhang et al is also 240 ℃ [ European Polymer Journal,131, (2020) 10970]. Therefore, the bio-based benzoxazine synthesized by the invention can effectively reduce the curing temperature from 240 ℃ to 183 ℃ and reduce the energy consumption.

(3) The furfuryl amine introduced by the invention is not only biological, but also has a structure that the furan ring can participate in the ring-opening solidification of benzoxazine to form a cross-linked structure, as shown in figure 3, 735cm in infrared spectrum ^-1 The furan ring absorption peak is obviously reduced; FIG. 4 shows that the exothermic peak around 220℃in DSC is probably attributed to the furan ring. Furfuryl amine participates in curing and crosslinking to improve the crosslinking density of the prepared benzoxazine resin, so that the benzoxazine resin has better thermal stability and T _d10％ The carbon residue rate is improved to 66% at 386 ℃.

(4) The benzoxazine side chain is levulinic acid, and carboxyl can be subjected to re-modification, such as esterification and amidation, so that the re-modification property and the thermal stability of the benzoxazine resin can be further improved.

Drawings

Fig. 1: guaiacol-containing biobased benzoxazine 4b ¹ H NMR chart;

fig. 2: guaiacol-containing biobased benzoxazines 5b ¹ H NMR chart;

fig. 3: infrared spectra of guaiacol-containing bio-based benzoxazine/resin 4b/2 c;

fig. 4: DSC profile of guaiacol-containing bio-based benzoxazine 4b and bisphenol a benzoxazine 6b.

Detailed Description

The invention will be further illustrated by the following examples, which are intended to illustrate, but not to limit, the invention. It will be understood by those of ordinary skill in the art that these examples are not limiting of the invention in any way and that appropriate modifications and data changes may be made thereto without departing from the spirit and scope of the invention. In the following examples, various processes and methods not described in detail are conventional methods well known in the art, and materials, reagents, devices, instruments, equipment, etc. used in the following examples are commercially available unless otherwise specified.

The nuclear magnetic resonance hydrogen spectrum involved in the examples was measured by Bruker Assend TM-400 nuclear magnetic resonance hydrogen spectrometer (Bruker), the deuterating reagent being deuterated dimethyl sulfoxide (DMSO-d) ₆ )。

The method for testing the curing temperature comprises the following steps: weighing 5-10mg of dry sample in a platinum tray, capping and placing into an instrument.

Heating program: preserving heat for 2 minutes at 0 ℃; heating to 280 ℃ at 10 ℃/min; incubate for 2 minutes.

Example 1a:

preparation of guaiacol 1a:

levulinic acid (5.8 g,0.05mol,1 eq), guaiacol (18.6 g,0.15mol,3 eq), 37% hydrochloric acid solution (18.5 mL,0.5mol,10 eq), and propanethiol (0.31 g,5mmol,0.1 eq) were thoroughly mixed in a 250mL reaction flask under nitrogen protection, reacted at 60 ℃ for 48 hours, extracted and washed with ethyl acetate several times, dried overnight with anhydrous sodium sulfate, and ethyl acetate was removed by rotary evaporation to give a pale yellow solid, i.e., guaiacol 1a in 67% yield.

Example 2a:

preparation of bis-guaifenesin 2a:

ethyl levulinate (7.2 g,0.05mol,1 eq), guaiacol (18.6 g,0.15mol,3 eq), 37% hydrochloric acid solution (18.5 mL,0.5mol,10 eq), and propanethiol (0.31 g,5mmol,0.1 eq) were thoroughly mixed in a 250mL reaction flask under nitrogen protection, reacted at 60℃for 48 hours, extracted and washed with ethyl acetate several times, dried overnight with anhydrous sodium sulfate, and the ethyl acetate was removed by rotary evaporation to give a pale yellow viscous liquid, i.e., bis-guaiacol ethyl 2a, in 63% yield.

Example 3a:

preparation of guaiacol isopropyl ester 3a:

isopropyl levulinate (7.9 g,0.05mol,1 eq), guaiacol (18.6 g,0.15mol,3 eq), 37% hydrochloric acid solution (18.5 mL,0.5mol,10 eq), and propanethiol (0.31 g,5mmol,0.1 eq) were thoroughly mixed in a 250mL reaction flask under nitrogen protection, reacted at 60 ℃ for 48 hours, extracted and washed with ethyl acetate several times, dried overnight with anhydrous sodium sulfate, and the ethyl acetate was removed by rotary evaporation to give pale yellow viscous liquid, i.e. guaiacol isopropyl ester 3a, 60% yield.

Example 4a:

preparation of butyl bis-guaiacol 4a:

butyl levulinate (8.6 g,0.05mol,1 eq), guaiacol (18.6 g,0.15mol,3 eq), 37% hydrochloric acid solution (18.5 mL,0.5mol,10 eq), and propanethiol (0.31 g,5mmol,0.1 eq) were thoroughly mixed in a 250mL reaction flask under nitrogen protection, reacted at 60 ℃ for 48 hours, extracted and washed with ethyl acetate several times, dried overnight with anhydrous sodium sulfate, and the ethyl acetate was removed by rotary evaporation to give a pale yellow viscous liquid, i.e. butyl bis-guaiacolate 4a, 57% yield.

Example 1b:

preparation of biobased benzoxazine 1b:

the guaiacol 1a (1.73 g,5mmol,1 eq) prepared in example 1a was dissolved in methanol (10 mL), and paraformaldehyde (0.9 g,10mmol,2 eq) and methanol (20 mL) were added first to a 100 mL three-necked flask equipped with 2 constant pressure dropping funnels, a straight condenser and a stirrer, and stirred at room temperature for 30 minutes. A solution of furfuryl amine (0.97 g,10mmol,2 eq) in methanol (20 mL) was then added dropwise to the flask via a constant pressure dropping funnel at a rate of 1mL/min and stirred for 30 minutes. Then, the guaiacol solution was added dropwise to the flask at a rate of 1mL/min via a constant pressure dropping funnel, and the temperature was raised to 80℃for reflux reaction for 6 hours. After the reaction was completed, the solution was distilled off to remove the solvent, then extracted three times with diethyl ether and deionized water, and finally dried over anhydrous sodium sulfate overnight. Filtering and rotary evaporating to remove the solvent to obtain brown yellow powder, namely the bio-based benzoxazine 1b. The yield was 72%. The curing temperature was 189 ℃.

Example 2b:

preparation of biobased benzoxazine 2b:

the guaiacol 1a (1.73 g,5mmol,1 eq) prepared in example 1a was dissolved in tetrahydrofuran (10 mL), and paraformaldehyde (1.35 g,15mmol,3 eq) and tetrahydrofuran (20 mL) were added first to a 100 mL three-necked flask equipped with 2 constant pressure dropping funnels, a straight condenser and a stirrer, and stirred at room temperature for 30 minutes. A solution of furfuryl amine (1.067 g,11mmol,2.2 eq) in tetrahydrofuran (20 mL) was then added dropwise to the flask via a constant pressure dropping funnel at a rate of 1mL/min and stirred for 30 minutes. Then, the guaiacol solution was added dropwise to the flask at a rate of 1mL/min via a constant pressure dropping funnel, and the temperature was raised to 80℃for reflux reaction for 9 hours. After the reaction was completed, the solution was distilled off to remove the solvent, then extracted three times with diethyl ether and deionized water, and finally dried over anhydrous sodium sulfate overnight. Filtering and rotary evaporating to remove the solvent to obtain brown yellow powder, namely the bio-based benzoxazine 2b. The yield was 78%. The curing temperature was 188 ℃.

Example 3b:

preparation of biobased benzoxazine 3b:

the guaiacol 1a (1.73 g,5mmol,1 eq) prepared in example 1a was dissolved in dioxane (10 mL), and paraformaldehyde (1.35 g,15mmol,3 eq) and dioxane (20 mL) were added first to a 100 mL three-necked flask equipped with 2 constant pressure dropping funnels, a straight condenser and a stirrer, and stirred at room temperature for 30 minutes. A solution of furfuryl amine (1.067 g,11mmol,2.2 eq) in dioxane (20 mL) was then added dropwise to the flask via a constant pressure dropping funnel at a rate of 1mL/min and stirred for 30 minutes. Then, the guaiacol solution was added dropwise to the flask at a rate of 1mL/min via a constant pressure dropping funnel, and the temperature was raised to 110℃for reflux reaction for 12 hours. After the reaction was completed, the solution was distilled off to remove the solvent, then extracted three times with diethyl ether and deionized water, and finally dried over anhydrous sodium sulfate overnight. Filtering and rotary evaporating to remove the solvent to obtain brown yellow powder, namely the bio-based benzoxazine 3b. The yield was 85%. The curing temperature was 186 ℃.

Example 4b:

preparation of biobased benzoxazine 4b:

the guaiacol 1a (1.73 g,5mmol,1 eq) prepared in example 1a was dissolved in dioxane (10 mL), and paraformaldehyde (1.35 g,15mmol,3 eq) and dioxane (20 mL) were added first to a 100 mL three-necked flask equipped with 2 constant pressure dropping funnels, a straight condenser and a stirrer, and stirred at room temperature for 30 minutes. A solution of furfuryl amine (1.067 g,11mmol,2.2 eq) in dioxane (20 mL) was then added dropwise to the flask via a constant pressure dropping funnel at a rate of 1mL/min and stirred for 30 minutes. Then, the guaiacol solution was added dropwise to the flask at a rate of 1mL/min via a constant pressure dropping funnel, and the temperature was raised to 110℃for reflux reaction for 24 hours. After the reaction was completed, the solution was distilled off to remove the solvent, then extracted three times with diethyl ether and deionized water, and finally dried over anhydrous sodium sulfate overnight. Filtering and rotary evaporating to remove the solvent to obtain brown yellow powder, namely the bio-based benzoxazine 4b. The yield was 88%. The curing temperature was 183 ℃.

Example 5b:

preparation of biobased benzoxazine 5b:

the guaiacol ethyl ester 2a (1.87 g,5mmol,1 eq) prepared in example 2a was dissolved in dioxane (10 mL), and paraformaldehyde (1.35 g,15mmol,3 eq) and dioxane (20 mL) were added first to a 100 mL three-necked flask equipped with 2 constant pressure dropping funnels, a straight condenser and a stirrer, and stirred at room temperature for 30 minutes. A solution of furfuryl amine (1.067 g,11mmol,2.2 eq) in dioxane (20 mL) was then added dropwise to the flask via a constant pressure dropping funnel at a rate of 1mL/min and stirred for 30 minutes. Then, the guaiacol ethyl ester solution was added dropwise to the flask at a rate of 1mL/min via a constant pressure dropping funnel, and the temperature was raised to 110℃for reflux reaction for 24 hours. After the reaction was completed, the solution was distilled off to remove the solvent, then extracted three times with diethyl ether and deionized water, and finally dried over anhydrous sodium sulfate overnight. Filtering and rotary evaporating to remove the solvent to obtain brown yellow viscous liquid, namely the bio-based benzoxazine 5b. The yield was 86%. The curing temperature was 231 ℃.

Comparative example 6b:

preparation of bisphenol a benzoxazine 6b:

50 g of bisphenol A, 30g of paraformaldehyde and 100g of toluene are sequentially added into a 500mL eggplant type bottle, the temperature is raised to 75 ℃, 43g of aniline solution (toluene is used as a solvent) is dropwise added, and the dropwise addition is completed, and the reaction is carried out at 90 ℃ for 2 hours. After the reaction is finished, removing the solvent, preserving the temperature at 120 ℃ for 8 hours, and cooling to room temperature to obtain a reddish brown solid, namely bisphenol A benzoxazine 6b. The curing temperature was 240 ℃.

Fig. 4: DSC of guaiacol-containing biobased benzoxazine 4b and bisphenol A benzoxazine 6b

Fig. 4 is a DSC profile of guaiacol-containing bio-based benzoxazine 4b and bisphenol a benzoxazine 6b. It can be found that the curing peak temperature of the synthesized bio-based benzoxazine 4b is 183 ℃ which is far lower than the curing temperature (240 ℃) of 6b, so that the curing temperature required by subsequent application of the benzoxazine is effectively reduced, and the energy consumption is saved.

Example 1c:

preparation of biobased benzoxazine resin 1c:

the bio-based benzoxazine 1b prepared in the example 1b is filled into a mold, is solidified for 2 hours in a blast oven at 80 ℃, is heated to 120 ℃ and is solidified for 10 hours, and is taken out after being cooled to obtain the bio-based benzoxazine resin 1c.

Example 2c:

preparation of biobased benzoxazine resin 2c:

the bio-based benzoxazine 4b prepared in example 4b was filled into a mold, cured in a forced air oven at 80 ℃ for 2 hours, then heated to 180 ℃ for 22 hours, and taken out after cooling to obtain bio-based benzoxazine resin 2c.

Example 3c:

preparation of biobased benzoxazine resin 3c:

the bio-based benzoxazine 5b (ethylation) prepared in example 5b was charged into a mold, cured in a forced air oven at 80 ℃ for 2 hours, then heated to 180 ℃ for 10 hours, then heated to 220 ℃ for 12 hours, and taken out after cooling to obtain bio-based benzoxazine resin 3c.

Comparative example 4c:

preparation of conventional bisphenol a benzoxazine resin 4c:

filling the bisphenol A benzoxazine 6b prepared in the comparative example 6b into a mold, curing for 2 hours in a blast oven at 80 ℃, then heating to 180 ℃ for curing for 10 hours, heating to 240 ℃ for curing for 12 hours, and taking out after cooling to obtain bisphenol A benzoxazine 4c.

Thermal stability test of benzoxazine resin:

the benzoxazine resins were tested for thermal stability using a thermogravimetric analyzer and the data obtained are set forth below

Table 1.

Compared with bisphenol A benzoxazine resin, the bio-based benzoxazine resin prepared by the invention has better thermal stability and T of 2c _d10％ Up to 386 deg.c, carbon residue at 800 deg.c up to 57%, about 24 deg.c and 24% higher than bisphenol A benzoxazine 4c, respectively. In addition, repair by ethyl esterificationThe thermal stability of the decorated biobased benzoxazine 3c is further improved, T _d10％ And carbon residue rates as high as 399 ℃ and 66%, respectively.

Example 1d:

application of bio-based benzoxazine 1b in adhesive:

the bio-based benzoxazine 1b prepared in example 1b was uniformly knife coated on the surface of a metal block with a glass rod, then the coated surface of the metal block was adhered to another metal block, pressed, put into an 80 ℃ oven for 2 hours, and put into a 120 ℃ oven for 10 hours.

Example 2d:

application of bio-based benzoxazine 4b in adhesive:

the bio-based benzoxazine 4b prepared in example 4b was uniformly knife coated on the surface of a metal block with a glass rod, then the coated surface of the metal block was adhered to another metal block, pressed, put into an 80 ℃ oven for curing for 4 hours, and put into a 180 ℃ oven for curing for 22 hours.

Example 3d:

application of bio-based benzoxazine 5b in adhesive:

the bio-based benzoxazine 5b prepared in example 5b was uniformly knife coated on the surface of a metal block with a glass rod, then the coated surface of the metal block was stuck on another metal block, pressed, put into an 80 ℃ oven for curing for 4 hours, put into a 180 ℃ oven for curing for 10 hours, and then heated to 220 ℃ for curing for 12 hours.

Comparative example 4d:

application of bisphenol A benzoxazine 6b in adhesive:

the bisphenol a benzoxazine 6b prepared in example 6b was uniformly knife coated on the surface of a metal block with a glass rod, then the coated surface of the metal block was stuck on another metal block, pressed, put into an 80 ℃ oven for curing for 4 hours, put into a 180 ℃ oven for curing for 10 hours, and then heated to 240 ℃ for curing for 12 hours.

The metal blocks obtained in the four examples 1d to 4d were tested for tensile strength on a WDW-20 KN universal tester at a test speed of 5mm/min, and the test results are shown in Table 2 below:

as shown in Table 2, the tensile strength and the elongation at break of the bio-based benzoxazines 1 d-3 d are higher than those of bisphenol A benzoxazine 4d, and the highest tensile strength and elongation at break are 8.6MPa and 6.6%, so that the bio-based benzoxazine serving as the adhesive has better tensile property, and the elongation at break is higher, namely the toughness is better, and the comprehensive performance is better than that of the bisphenol A benzoxazine 4d serving as the adhesive. The bio-based benzoxazine disclosed by the invention has the advantages of lower curing temperature, high thermal stability, high tensile strength, remodification, simple synthesis process, environment friendliness and the like by combining DSC, thermogravimetric analysis and tensile test.

Claims

1. A guaiacol-containing bio-based benzoxazine, characterized in that: the structure of the bio-based benzoxazine is shown as a formula I:

wherein R is

2. A guaiacol-containing bio-based benzoxazine for an adhesive, characterized by: the structure of the bio-based benzoxazine is shown as a formula I:

wherein R is

3. A method for preparing bio-based benzoxazine containing guaiacol is characterized in that,

wherein R is

And (3) reacting the organic solution containing the guaiacol and the furfuryl amine shown in the formula III in a paraformaldehyde medium at a high temperature of 80-130 ℃ for 5-24 hours to obtain the bio-based benzoxazine containing the guaiacol shown in the formula I.

4. The preparation method according to claim 3, wherein the molar ratio of the guaiacol to the furfuryl amine is 1:2-2.5, and the molar ratio of the guaiacol to the paraformaldehyde is 1:2-4.

5. The preparation method according to claim 4, wherein the molar ratio of the guaiacol to the furfuryl amine is 1:2.2 the molar ratio of guaiacol to paraformaldehyde as shown in formula III is 1:3.

6. The method of claim 3, wherein the organic solvent comprises toluene, tetrahydrofuran, dioxane, ethanol, or methanol.

7. A guaiacol-containing biobased benzoxazine obtainable according to any one of claims 1-6 for use in an adhesive.

8. A guaiacol-containing bio-based benzoxazine resin, characterized in that: the structure of the guaiacol-containing bio-based benzoxazine resin is shown as a formula II:

wherein R is

9. The method for preparing the bio-based benzoxazine resin shown in formula II as claimed in claim 7, wherein the bio-based benzoxazine resin containing guaiacol shown in formula I is solidified to obtain the benzoxazine resin shown in formula II

The temperature of the curing reaction is 70-220 ℃ and the time is 5-24 h.

10. A guaiacol-containing bio-based benzoxazine resin as claimed in claim 8 or 9 for use in adhesives.