WO2021121426A1 - Synthesis and use of protocatechuic acid-based epoxy resin - Google Patents

Abstract

Synthesis and use of a protocatechuic acid-based epoxy resin. Specifically, a protocatechuic acid epoxidized monomer has a structure as shown in the following formula (I). The monomer can be cured to form a protocatechuic acid epoxy resin, thereby being used for preparing aerospace special materials.

Description

Synthesis and application of an epoxy resin based on protocatechin Technical field

The invention relates to the technical field of high-performance polymer manufacturing, in particular to a method for preparing an epoxy resin with a high glass transition temperature starting from the glucose fermentation product protocatechin.

Background technique

As a thermosetting resin, epoxy resin was first used as a surface coating in 1947 and realized its first commercial application. Due to the wide selection of curing agents, from alkyl amines, alcohols, mercaptans to aromatic amines, phenols, etc., the cured epoxy resin has a wide range of adjustable thermodynamic and mechanical properties. Therefore, it means that epoxy resin has the potential to be used in different application scenarios. Currently, epoxy resins are commonly used as base resins, adhesives, surface coatings, and include aerospace fields. The largest proportion of its applications is still surface coatings. In addition, composite materials made of epoxy resin mixed with inorganic fillers (graphene, etc.) or glass fibers are also a hot field of its current application. According to reports, the amount of fiber-reinforced epoxy resin used in each aircraft of the Air Force and Navy today exceeds 1,000 pounds. Although, currently in the automobile manufacturing industry, the application of epoxy resin has not yet been mass-produced, but once mass-produced in the future, its epoxy resin will again develop rapidly.

Although epoxy resin has a wide range of uses, there are still many problems with its use. For example, commercialized bisphenol A epoxy resins release trace amounts of bisphenol A during use. As a synthetic estrogen, bisphenol A can act like a hormone, which may damage the fragile endocrine system and cause problems in the physical development of adolescents. As early as 2008, Canada became the first country in the world to publicly announce the ban on BPA on all food packaging and containers (including milk bottles). Subsequently, Australia, the United States, and China have successively made the same measures. These problems also suffice to show that there are still many problems in the current commercial epoxy resins. In addition, in addition to safety issues, energy issues are also major issues faced by other fossil energy-based materials (polyethylene, polypropylene, etc.) in addition to epoxy resin. With the decreasing of petroleum energy, all countries are striving to develop sustainable energy, such as solar energy, wind energy, and so on. In the material field, more attention is paid to renewable resources that can be obtained in large quantities, such as anethole, eugenol, lignin, and cellulose, which can be extracted from plants and crops in large quantities. How to convert them into high-performance materials simply and efficiently to gradually replace the existing fossil energy is the top priority of current research.

Summary of the invention

The purpose of the present invention is to provide a new type of epoxy resin with high glass transition temperature based on biomass protocatechin.

The first aspect of the present invention provides a protocatechin epoxy resin, which is prepared by curing with a monomer represented by the following formula I:

In another preferred embodiment, the resin is prepared by curing with an aromatic amine curing agent.

In another preferred embodiment, the epoxy resin is prepared by curing and molding the protocatechuic acid epoxidized monomer as shown in formula I and 4,4'-diaminodiphenylmethane (DDM) .

The second aspect of the present invention provides a method for preparing the epoxy resin as shown in the first aspect of the present invention, including the steps:

(i) Mix the epoxy monomer and DDM as described in the first aspect of the present invention, and heat for 40-60 minutes;

(ii) Dissolving by ultrasonic or organic solvent to make the mixture obtained in step (i) form a uniform and transparent solution;

(iii) Under an inert atmosphere, remove the solvent in the solution;

(iv) The residue obtained in the step (iii) is heated and cured to obtain the epoxy resin according to the first aspect of the present invention.

In another preferred example, the glass transition temperature of the epoxy resin is ≥250°C (tested by DMA method).

In another preferred embodiment, the curing and molding are performed by a molding process selected from the group consisting of injection molding, solution spin coating, or solution drip coating.

In another preferred embodiment, the molding method includes the steps of: mixing the epoxy monomer and DDM as described in the first aspect of the present invention and heating to 40-60°C, ultrasonically melting into a uniform and transparent solution, or dissolving in In the organic solvent, the mixture becomes a uniform and transparent solution, and the solvent is removed by heating under nitrogen. The residue is cured at elevated temperature to obtain a cured resin. The solvent is selected from the following group: cyclohexanone, dichloromethane, chloroform, acetone, or a combination thereof.

In another preferred embodiment, the method further comprises: preparing the monomer of formula I by the following steps:

(1) Under the catalysis of a phase transfer catalyst, protocatechuic acid is reacted with epichlorohydrin to obtain a first reaction mixture;

(2) Adding a strong alkali aqueous solution to the first reaction mixture for reaction to obtain protocatechin epoxidized monomer;

In another preferred example, in the steps (1) and (2), epichlorohydrin is used as the solvent.

In another preferred example, in the step (1), the reaction temperature is 70°C-140°C.

In another preferred example, in the step (2), the reaction temperature is 10°C-40°C.

In another preferred example, the protocatechuic acid used in the step (1) is obtained from glucose fermentation.

In another preferred embodiment, the phase transfer catalyst is selected from the following group: benzyltriethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, cetyltrimethylammonium chloride , Or a combination thereof.

In another preferred example, the total reaction time of the steps (1) and (2) is 1 to 10 hours, preferably 2 to 5 hours.

In another preferred embodiment, the strong alkaline aqueous solution is a strong alkaline aqueous solution selected from the group consisting of potassium hydroxide, sodium hydroxide, or a combination thereof.

In another preferred example, the concentration of the strong alkali aqueous solution is 10-50wt%, preferably 15-25wt%.

The third aspect of the present invention provides a protocatechin epoxy resin, characterized in that the protocatechin epoxy resin includes a copolymer unit represented by the following formula II:

In another preferred embodiment, the copolymer unit is obtained by the preparation method of the second aspect of the present invention.

It should be understood that within the scope of the present invention, the above-mentioned technical features of the present invention and the technical features specifically described in the following (such as the embodiments) can be combined with each other to form a new or preferred technical solution. Due to space limitations, I will not repeat them one by one here.

Description of the drawings

Figure 1 is the CTE curve of DDM curing protocatechin-based epoxy resin and E51 epoxy resin;

Figure 2 shows the DMA curves of DDM cured protocatechin-based epoxy resin and E51 epoxy resin.

Detailed ways

After long-term screening and research on the curing agent, the inventor found that when DDM is used as the curing agent to perform curing and copolymerization with protocatechuic acid epoxide, it can achieve excellent results with high glass transition temperature and high energy storage. Modulus, and low thermal expansion coefficient of protocatechin epoxy resin. Based on the above findings, the inventor completed the present invention.

Protocatechin epoxy compound monomer

Protocatechuic acid, also known as 3,4-dihydroxybenzoic acid, is a compound containing two hydroxyl groups and one carboxyl group, which is very suitable for preparing epoxy resins. However, the currently commercialized protocatechuic acid all come from chemical synthesis processes. Due to the long synthetic route, unsatisfactory yield and purity, this chemical is expensive. On the other hand, protocatechuic acid is almost always used as a pharmaceutical intermediate or fine chemical, and there are few examples of its application in materials. In recent years, through biological fermentation technology, starting from cheap glucose, it is possible to obtain satisfactory protocatechuic acid. In view of the price advantage of protocatechuic acid derived from glucose, the development of new uses will definitely bring greater economic benefits to biomass protocatechuic acid. The present invention uses the protocatechuic acid obtained by biological fermentation to prepare a novel epoxy resin.

The present invention provides a protocatechin epoxide monomer, which has a structure shown in the following formula:

The shown protocatechin epoxide monomer can be prepared by the following method:

Protocatechin is reacted with epichlorohydrin under the catalysis of a phase transfer catalyst, and then the ring is closed under the action of alkaline water, and then separated by simple column chromatography to obtain the target protocatechin epoxy compound. body.

Wherein, the phase transfer catalyst includes benzyl triethyl ammonium chloride, tetrabutyl ammonium chloride, tetrabutyl ammonium bromide, and cetyl trimethyl ammonium chloride. The alkaline aqueous solution includes potassium hydroxide and sodium hydroxide, and its mass concentration is 10% to 50%, preferably 20%.

The raw material protocatechin used in the protocatechuic acid epoxide monomer of the present invention is produced by bio-based fermentation, thereby broadening the application range of biological resources, and the cured product can be used as a material in the fields of aerospace and electronics , Has great application value.

Protocatechin epoxy resin

The invention belongs to the field of deep processing and utilization of biomass, and specifically relates to a method for preparing epoxy resin by using protocatechuic acid obtained by glucose fermentation, and the performance and application of the epoxy resin prepared by the method as a high-performance polymer. Specifically, the protocatechin-based epoxy resin is synthesized in a one-pot method using protocatechin as the raw material and epichlorohydrin as the solvent. The resin is cured with the universal curing agent diaminodiphenylmethane (DDM), and the glass transition temperature of the cured product is greater than 250°C (DMA method test), and under the same conditions, the commercial bisphenol A epoxy resin (E51) is cured The product shows a glass transition temperature below 190°C. In addition, the cured product of protocatechin-based epoxy resin also exhibits a high storage modulus and a low linear thermal expansion coefficient. The synthesis method provided by the present invention has mild reaction conditions and high yield, and has great application prospects in the fields of aerospace and electronics. The invention also broadens the application range of biological resources.

The protocatechin epoxy compound monomer can be directly used for curing with the curing agent DDM, and is characterized in that the protocatechin epoxy compound monomer and DDM are mixed and heated 40-60 ultrasonically to melt into a uniform and transparent solution , Or dissolved in an organic solvent to make the mixture a uniform and transparent solution, and remove the solvent by heating under nitrogen. The residue is heated and cured to obtain a cured resin. The solvent is selected from the group consisting of ethyl acetate, dichloromethane, chloroform, or a combination thereof.

Compared with the prior art, the main advantages of the present invention include:

(1) The method provided by the present invention belongs to the deep processing and utilization of biomass, develops new applications of biomass resources, realizes sustainable development, reduces the demand pressure of chemical energy, and promotes the development of green economy.

(2) The present invention has simple synthesis steps, mild process conditions and high yield, and can be used for industrialized large-scale production.

The present invention will be further explained below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods that do not indicate specific conditions in the following examples usually follow the conventional conditions or the conditions recommended by the manufacturer. Unless otherwise stated, percentages and parts are calculated by weight.

Example 1 Synthesis of protocatechin epoxy monomer

Under the protection of nitrogen gas, add magneton, 100mmol protocatechuic acid and 94mL epichlorohydrin to a 250ml dry three-necked flask. Then 5mmol of triethylbenzylammonium chloride was added, the temperature was raised to 100°C, and the reaction was carried out for 2 hours, then cooled to room temperature, and 120mL of 20wt% sodium hydroxide aqueous solution was added. The reaction was carried out at room temperature for 2 hours. Water sodium sulfate drying, concentration, column chromatography to obtain the target colorless oily epoxy compound monomer 6.4g.

¹ H NMR(400MHz,DMSO-d ₆ )δ7.62(dd,J=8.4,2.0Hz,1H), 7.52(d,J=2.1Hz,1H), 7.14(d,J=8.6Hz,1H) ,4.61(dd,J＝12.4,2.7Hz,1H),4.50–4.39(m,2H),4.06(dd,J＝12.4,6.4Hz,1H),3.92(dddd,J＝21.9,11.4,6.6, 1.8Hz, 2H), 3.39 (dqd, J = 7.9, 4.0, 2.2 Hz, 3H), 2.90-2.81 (m, 3H), 2.74 (ddt, J = 7.3, 5.0, 2.7 Hz, 3H). ¹³ C NMR (101MHz, CDCl ₃ ) δ165.71, 152.74, 148.00, 124.53, 122.87, 115.26, 112.91, 70.14 (d, J = 6.8 Hz), 69.74 (d, J = 6.8 Hz), 65.36, 49.98 (d, J = 7.4 Hz ),49.49,44.63(d,J=7.5Hz).

Example 2 Synthesis of protocatechin epoxy monomer

The experimental method is the same as in Example 1, except that tetraethyl ammonium chloride is used instead of triethyl benzyl ammonium chloride, and 5.2 g of target monomer is obtained by column chromatography.

Example 3 Synthesis of protocatechin epoxy monomer

The experimental method is the same as in Example 1, except that tetrabutylammonium chloride is used instead of triethylbenzylammonium chloride, and 5.1 g of the target monomer is obtained by column chromatography.

Example 4 Synthesis of protocatechin epoxy monomer

The experimental method is basically the same as in Example 1, except that tetrabutylammonium bromide is used instead of triethylbenzylammonium chloride, and 4.5g of the target monomer is obtained by column chromatography.

Example 5 Synthesis of protocatechin epoxy monomer

The experimental method is basically the same as that in Example 1, except that potassium hydroxide aqueous solution is used instead of sodium hydroxide aqueous solution, and 3.9 g of target monomer is obtained by column chromatography.

Example 6 Curing of protocatechin epoxy resin

Take the target protocatechin epoxy compound monomer obtained in Example 1 and DDM, heat it to 40-60℃ ultrasonically to melt into a uniform and transparent solution, or dissolve it in an organic solvent to make the mixture a uniform and transparent solution. Lower the temperature to remove the solvent. The solvent is selected from the group consisting of ethyl acetate, dichloromethane, chloroform or a combination thereof. The residue was heated to 100°C to cure for 1 hour, and at 130°C for 3 hours to cool to obtain a cured resin.

The TGA test of the obtained resin showed that its 5% thermal weight loss temperature was 321°C, and the residual carbon rate was 27.7%.

Comparative Example 1 Curing of E51 epoxy resin

E51 is a commercially available bisphenol A epoxy resin, and its structure is shown in Figure (a) below. Its epoxy value is between 0.48-0.54.

Mix E51 epoxy resin with DDM, and the mixing steps are the same as those in Example 6. The residue was heated to 170° C. and solidified for 3 hours after cooling to obtain a solidified resin.

Test example Study on thermomechanical properties of cured resin

The resin samples prepared in Example 6 and Example 7 were tested for CTE and DMA, respectively. The test conditions are under nitrogen, from room temperature to 250°C, and the heating rate is 3°C/min. The thermal expansion coefficient, glass transition temperature and storage modulus of the epoxy resin obtained in the present invention and commercial E51 epoxy resin were compared, and the results are shown in Figs. 1 and 2.

It can be seen from Figure 1 that the thermal expansion coefficient of the cured product of E51 epoxy resin is 72 ppm/°C. The T _g is 176°C; the thermal expansion coefficient of the cured product of protocatechin epoxy resin is 66ppm/°C, and the glass transition temperature is greater than 200°C, up to 221°C.

It can be seen from Figure 2 that the T _g of the cured product of E51 epoxy resin is 189°C, while the cured product of protocatechin epoxy resin has no obvious glass transition temperature within 250°C. In addition, the storage modulus of the cured product of protocatechin epoxy resin is 1.9 GPa, which is higher than the 1.6 GPa of the cured product of E51 epoxy resin.

All documents mentioned in the present invention are cited as references in this application, as if each document was individually cited as a reference. In addition, it should be understood that after reading the above teaching content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

Claims (10)

1. A protocatechin epoxy resin, characterized in that, the protocatechin epoxy resin is prepared by curing with a monomer represented by the following formula I:

   
2. The protocatechuic acid epoxy resin according to claim 1, wherein the epoxy resin is a protocatechuic acid epoxidized monomer as shown in formula I and 4,4'-diamino Diphenylmethane (DDM) is prepared by curing and molding.
3. The method for preparing epoxy resin according to claim 1, characterized in that it comprises the steps of:

   (i) Mix the epoxy monomer according to claim 1 and DDM, and heat for 40-60 minutes;

   (ii) Dissolving by ultrasonic or organic solvent to make the mixture obtained in step (i) form a uniform and transparent solution;

   (iii) Under an inert atmosphere, remove the solvent in the solution;

   (iv) The residue obtained in the step (iii) is heated and cured to obtain the epoxy resin according to claim 1.
4. The preparation method according to claim 3, wherein the method further comprises: preparing the monomer of formula I by the following steps:

   (1) Under the catalysis of a phase transfer catalyst, protocatechuic acid is reacted with epichlorohydrin to obtain a first reaction mixture;

   (2) Adding a strong alkali aqueous solution to the first reaction mixture for reaction to obtain protocatechin epoxidized monomer;

   
5. The method according to claim 1, characterized in that, in the steps (1) and (2), epichlorohydrin is used as a solvent.
6. The method according to claim 1, wherein in the step (1), the reaction temperature is 70°C-140°C.
7. The method according to claim 1, wherein in the step (2), the reaction temperature is 10°C-40°C.
8. The preparation method according to claim 1, wherein the phase transfer catalyst is selected from the group consisting of benzyltriethylammonium chloride, tetrabutylammonium chloride, tetrabutylammonium bromide, hexadecane Trimethylammonium chloride, or a combination thereof.
9. The preparation method according to claim 1, wherein the strong alkaline aqueous solution is a strong alkaline aqueous solution selected from the group consisting of potassium hydroxide, sodium hydroxide, or a combination thereof.
10. A protocatechin epoxy resin, characterized in that the protocatechin epoxy resin comprises a copolymer unit represented by the following formula II:

    

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