阅读说明：本技术 一种化学稳定型主链苯并噁嗪前驱体及其制备方法 (Chemically stable main chain benzoxazine precursor and preparation method thereof ) 是由 胡永琪 谢富平 张侃 于 2021-07-29 设计创作，主要内容包括：本发明公开了一种化学稳定型主链苯并噁嗪前驱体及其制备方法,先通过降冰片烯二酸酐和氨基苯酚合成降冰片烯官能化酚；再利用降冰片烯官能化酚、2-呋喃甲胺、多聚甲醛为原料,合成主链型苯并噁嗪前驱体。化学稳定型主链苯并噁嗪前驱体中的降冰片烯和呋喃基团仅在外界催化剂的作用下发生Diels-Alder反应,进行可控聚合生成主链型苯并噁嗪,再经升温固化形成树脂材料,这种独特的机理使该树脂具有优异的综合性能。该前驱体制备的主链型苯并噁嗪固化后材料表现出出色的热性能,材料在800℃时残炭率高于50％,T-(d5)高于390℃,T-(d10)高于420℃,介电常数值在2-3之间；本发明的主链型苯并噁嗪前驱体所获得的材料具有优异的热、力、电学性能与良好的可加工性,生产成本低。(The invention discloses a chemically stable main chain benzoxazine precursor and a preparation method thereof, which comprises the steps of firstly synthesizing norbornene functionalized phenol by using nadic anhydride and aminophenol; and then synthesizing a main chain type benzoxazine precursor by using norbornene functionalized phenol, 2-furanmethanamine and paraformaldehyde as raw materials. Norbornene and furan groups in the chemically stable main chain benzoxazine precursor are subjected to Diels-Alder reaction only under the action of an external catalyst, controllable polymerization is carried out to generate main chain benzoxazine, and the main chain benzoxazine is heated and cured to form a resin material. The cured main chain benzoxazine material prepared by the precursor shows excellent thermal performance, the carbon residue rate of the material is higher than 50% at 800 ℃, and T is d5 Above 390 ℃ C, T d10 Above 420 ℃, the dielectric constant value is between 2 and 3; the material obtained by the main chain type benzoxazine precursor of the inventionThe material has excellent heat, force and electric properties, good processability and low production cost.)

1. A chemically stable main chain benzoxazine precursor is characterized in that the molecular structural formula is as follows:

wherein the content of the first and second substances,in the presence of oxygenOrtho, meta or para to the atom;

the precursor has high chemical stability, can not independently perform Diels-Alder reaction in an organic solvent or heating and melting process, can perform linear polymerization to form main chain type benzoxazine only under the external catalytic action, has a carbon residue rate higher than 50% at 800 ℃, and has a T-shaped carbon residue rate higher than 50% after being cured_d5Above 390 ℃ C, T_d10Above 420 ℃ and a dielectric constant between 2 and 3.

2. A method of making a chemically stabilized backbone benzoxazine precursor according to claim 1 comprising the steps of:

(1) synthesis of norbornene imide phenol:

mixing nadic anhydride and aminophenol in proportion, adding a solvent, reacting, pouring a reaction solution into a large amount of water, filtering a precipitated solid by suction, and drying to obtain norbornene functionalized phenol;

(2) synthesizing a chemically stable main chain benzoxazine precursor:

mixing the norbornene functionalized phenol prepared in the step (1), 2-furanmethanamine and paraformaldehyde, adding the mixture into a flask, adding a low-polarity solvent, stirring and reacting in an oil bath kettle, slowly raising the temperature from room temperature to 140 ℃, reacting for 5-8h, removing the solvent by suspension evaporation after the reaction is finished, and performing vacuum drying to obtain a chemically stable main chain benzoxazine precursor;

3. the method for preparing a chemically stabilized backbone benzoxazine precursor according to claim 2 wherein in step (1) the molar ratio of nadic anhydride and aminophenol is 1:1, preferably 1.05: 1.

4. The method for preparing a chemically stable backbone benzoxazine precursor according to claim 2 wherein in step (1), the solvent is one or more of glacial acetic acid, N dimethylformamide, N dimethylacetamide.

5. The method for preparing a chemically stable backbone benzoxazine precursor according to claim 2 wherein in step (1), the reaction temperature is 120 ℃ and the reaction time is 8 hours.

6. The method of preparing a chemically stable backbone benzoxazine precursor according to claim 2 wherein in step (2), the low polarity solvent is one or more of toluene, xylene or 1, 4-dioxane.

7. A method of preparing a chemically stable backbone benzoxazine precursor according to claim 2 wherein the norbornene functionalized phenol, 2-furanmethanamine, paraformaldehyde are in a molar ratio of 1:1:2 to 1:1:2.4, preferably in a ratio of 1:1: 2.24.

Technical Field

The invention relates to the technical field of high-performance thermosetting resin, in particular to a chemically stable main chain benzoxazine precursor; the invention also relates to a preparation method of the stable main chain type benzoxazine precursor.

Background

As a novel thermosetting resin material, benzoxazine has many advantages, such as good molecular design, processability, volume shrinkage rate in a curing process is almost zero, high carbon residue rate, low water absorption rate, low dielectric property, excellent tolerance performance and the like, and the excellent performance enables a polymer of the benzoxazine to have certain application in the fields of composite materials, fuel cells, resin transfer molding, transportation and the like. However, benzoxazine has the defects of high curing temperature, low crosslinking density, high brittleness and the like, and the main chain type benzoxazine makes up part of the defects of benzoxazine by utilizing the advantages of molecular design.

Patent No. (CN107573334B) discloses a monofunctional benzoxazine containing alicyclic hydrocarbon imide group, which has high yield and easy preparation method, but needs to have improved thermal properties. A bio-based benzoxazine resin containing a furan amide structure disclosed in patent No. (CN112341584A) has excellent thermal properties, but the preparation process is complicated, and the disadvantage of high brittleness of the benzoxazine resin still exists. With the increasing demand of people for high-performance materials, the performance of benzoxazine can be further improved through molecular design, for example, main chain type benzoxazine is prepared to overcome the defects, so that the benzoxazine can be used in some extreme environments. Patent No. (CN109776518A) discloses an AB-type benzoxazine monomer, but the maleimide and furan in the structure undergo a Diels-Alder reaction in a molten state, and the polymerization cannot be effectively controlled, so further molecular design is required.

Disclosure of Invention

The invention mainly aims to provide a preparation method of a chemically stable main chain benzoxazine precursor by utilizing molecular design and considering the defect that the polymerization of Diels-Alder monomers can not be effectively controlled in the past.

In order to achieve the purpose, the invention provides the following technical scheme:

a chemically stable main chain benzoxazine precursor has the following molecular structural formula:

wherein the content of the first and second substances,in the ortho, meta or para position to the oxygen atom;

the precursor has high chemical stability, can not independently perform Diels-Alder reaction in an organic solvent or a heating and melting process, and can perform linear polymerization to form the main chain type benzoxazine only under the external catalytic action. The carbon residue rate of the main chain type benzoxazine cured material prepared by the precursor is higher than 50% at 800 ℃, and T is_d5Above 390 ℃ C, T_d10Above 420 ℃ and a dielectric constant between 2 and 3.

A preparation method of a chemically stable main chain benzoxazine precursor comprises the following steps:

(1) synthesis of norbornene imide phenol:

mixing nadic anhydride and aminophenol in proportion, adding a solvent, reacting, pouring a reaction solution into a large amount of water, filtering a precipitated solid by suction, and drying to obtain norbornene functionalized phenol;

(2) synthesizing a chemically stable main chain benzoxazine precursor:

mixing the norbornene functionalized phenol prepared in the step (1), 2-furanmethanamine and paraformaldehyde, adding the mixture into a flask, adding a low-polarity solvent, stirring and reacting in an oil bath kettle, slowly raising the temperature from room temperature to 140 ℃, reacting for 5-8h, removing the solvent by suspension evaporation after the reaction is finished, and performing vacuum drying to obtain a chemically stable main chain benzoxazine precursor;

as a preferable technical scheme, in the step (1), the molar ratio of the norbornene dianhydride to the aminophenol is 1:1, and the preferable ratio is 1.05: 1.

In a preferable technical scheme, in the step (1), the solvent is one or more of glacial acetic acid, N-dimethylformamide and N, N-dimethylacetamide.

As a preferable embodiment, in the step (1), the reaction temperature is 120 ℃ and the reaction time is 8 hours.

In a preferable embodiment, in step (2), the low-polarity solvent is one or more of toluene, xylene, and 1, 4-dioxane.

As a preferable technical scheme, the molar ratio of the norbornene functionalized phenol to the 2-furanmethanamine to the paraformaldehyde is 1:1:2 to 1:1:2.4, and the preferable ratio is 1:1: 2.24.

In summary, due to the adoption of the technology, the invention has the beneficial effects that:

the invention aims to overcome the brittleness defect of benzoxazine resin, norbornene groups and furan groups are introduced into benzoxazine monomers through molecular design, linear backbone benzoxazine can be formed through Diels-Alder reaction between the two groups, and Diels-Alder reaction can be triggered to cause polymerization only under the action of external catalysts such as anhydrous aluminum oxide and the like, so that the controllability of the reaction process is realized;

the precursor resin prepared by the invention is verified by methods such as nuclear magnetic resonance, infrared, differential scanning calorimetry, comprehensive thermal analysis and the like, and after the main chain type benzoxazine precursor synthesized by the method is polymerized and cured, the carbon residue rate of the material at 800 ℃ is higher than 50 percent, and the T is_d5Above 390 ℃ C, T_d10Above 420 ℃ and a dielectric constant between 2 and 3.

Drawings

FIG. 1 is an infrared spectrum of a chemically stabilized main chain benzoxazine precursor according to the present invention;

FIG. 2 is a nuclear magnetic resonance hydrogen spectrogram of the chemically stabilized main chain benzoxazine precursor according to the present invention;

FIG. 3 is a DSC spectrum of the chemically stabilized main chain benzoxazine precursor according to the present invention;

FIG. 4 is a TGA spectrum of a main chain type benzoxazine cured material prepared from the main chain benzoxazine precursor according to the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings of the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention. Thus, the following detailed description of the embodiments of the present invention, presented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

The first embodiment is as follows:

the first step is as follows: 4g of nadic anhydride and 2.663g of o-aminophenol were mixed, 50ml of glacial acetic acid was added, and then reaction was carried out at 120 ℃ for 8 hours, the reaction solution was poured into a large amount of water, and the precipitated solid was suction-filtered and dried to obtain 5.6g of 2-norbornene-functionalized phenol. The reaction equation is as follows:

the second step is that: 2g of norbornene functionalized phenol obtained by the first step of reaction, 0.761g of 2-furanmethanamine and 0.527g of paraformaldehyde are added into a flask, 50ml of toluene solution is added, stirring and reaction are carried out in an oil bath kettle, the temperature is slowly increased to 120 ℃ from room temperature, reaction is carried out for 6h, substances in the reaction solution are purified, and drying is carried out in a 50 ℃ vacuum drying oven for 48h, so that 2.499g of chemically stable benzoxazine precursor is obtained, and the yield is 76%. The reaction equation is as follows:

FIG. 1 shows the IR spectra of chemically stabilized main chain benzoxazine precursors, wherein 924 and 1222cm^-1The position is a characteristic peak of oxazine ring;

as shown in a nuclear magnetic resonance hydrogen spectrogram of a chemically stable main chain benzoxazine precursor in figure 2, doublets with chemical shifts of about 4.8ppm and 3.9ppm are characteristic peaks of methylene on an oxazine ring.

As shown in the DSC graph of fig. 3, the curing exothermic peak temperature of the benzoxazine monomer is 231.6 ℃.

As shown in the TGA graph of the resin material after polymerization and curing of the main chain benzoxazine precursor in fig. 4, it can be seen that the temperature of the benzoxazine resin thermal material at 10% weight loss is 430 ℃, and the carbon residue rate at 800 ℃ is 56%.

The dielectric constant of the cured resin material is as low as 2.8 at 1 MHz.

Example two:

the first step is the same as in example 1.

The second step is that: 2g of norbornene functionalized phenol 2g, 0.761g of 2-furanmethanamine 0.527g of paraformaldehyde are added into a flask, 50ml of toluene solution is added, stirring and reaction are carried out in an oil bath kettle, the temperature is slowly increased to 140 ℃ from room temperature, reaction is carried out for 5h, substances in the reaction liquid are purified, and drying is carried out in a 50 ℃ vacuum drying oven for 48h, so that 2.377g of chemically stable benzoxazine precursor is obtained, and the yield is 72.3%.

Example three:

the first step is to mix 4g of nadic anhydride and 2.663g of p-aminophenol, add 30mL of N, N-dimethylformamide, then react for 8h at 120 ℃, pour the reaction solution into a large amount of water, filter the precipitated solid by suction, and dry to obtain 5.6g of norbornene functionalized phenol. The reaction equation is as follows:

the second step is that: adding 1g of norbornene functionalized phenol, 0.380g of 2-furanmethanamine and 0.264g of paraformaldehyde into a flask, adding 50ml of 1, 4-dioxane solution, stirring and reacting in an oil bath kettle, slowly raising the temperature from room temperature to 100 ℃, reacting for 8 hours, purifying substances in the reaction solution, and drying in a 50 ℃ vacuum drying oven for 48 hours to obtain 1.172g of chemically stable benzoxazine precursor with the yield of 71.3%. The reaction equation is as follows:

the above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.