CN112538053B

CN112538053B - Method for synthesizing nitroquinoxaline or derivative thereof and aminoquinoxaline or derivative thereof

Info

Publication number: CN112538053B
Application number: CN202010678948.8A
Authority: CN
Inventors: 路庆华; 刘团青
Original assignee: Tongji University
Current assignee: Tongji University
Priority date: 2019-10-12
Filing date: 2020-07-15
Publication date: 2022-09-02
Anticipated expiration: 2040-07-15
Also published as: CN112538053A

Abstract

The present application relates to a method for synthesizing a nitroquinoxaline or a derivative thereof, which comprises reacting a mononitro-substituted o-phenylenediamine or a derivative thereof with a mononitro-substituted benzil or a derivative thereof in a solvent in the presence of a catalyst, a solvent, and a solvent for a predetermined period of time to obtain the nitroquinoxaline or the derivative thereof. The present application also provides a method of synthesizing aminoquinoxaline or a derivative thereof. The present application also provides a polyimide prepared by the aminoquinoxaline as described above and a preparation method thereof. The synthesis process has low cost and high yield, and is favorable for realizing large-scale preparation of the nitroquinoxaline or the derivative thereof and the aminoquinoxaline or the derivative thereof. The polyimide film described herein has excellent heat resistance, mechanical properties, and electrical properties.

Description

Method for synthesizing nitroquinoxaline or derivative thereof and aminoquinoxaline or derivative thereof

Technical Field

The application relates to the technical field of organic synthesis, in particular to a method for synthesizing nitroquinoxaline or derivatives thereof and aminoquinoxaline or derivatives thereof.

Background

Quinoxaline is a benzopyrazine compound having excellent biological activity and thermal stability, and has been widely studied because it exists in various compounds and is expected to be used in the fields of dyes, organic semiconductors, electroluminescent materials, anion receptors, and the like. Similarly, quinoxaline derivatives are potentially applicable in many fields. Therefore, many methods have been developed in the art for synthesizing quinoxaline derivatives, for example, reacting a monomer containing an o-phenylenediamine structure with an α -hydroxyketone or an epoxide, etc.

Aminoquinoxaline has a higher chemical bond energy, a larger molar volume and a weaker polarity, which endows a polymer prepared from the aminoquinoxaline with excellent heat resistance and oxidation resistance, higher environmental stability, a low dielectric constant, dielectric loss and higher plasticity. The aminoquinoxaline can be dissolved in an organic solvent and has good processing performance.

The mixture of 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline is a novel aminoquinoxaline diamine monomer. Polymers such as quinoxaline polyimide, polyether, polyester and the like synthesized by the mixture have good thermal stability, chemical stability, excellent conductivity, good air permeability and toughness. In addition, the mixture has good solubility in organic solvents, low crystallinity and a wider processing window.

Chinese patent publication CN105153144A discloses a main chain diamine type quinoxalinyl benzoxazine and a preparation method thereof, wherein 4-nitrophenyl benzil, 4-nitro-o-phenylenediamine and glacial acetic acid are used as starting materials, a mixture of 2- (4-nitrophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-nitrophenyl) -2-phenyl-6-aminoquinoxaline is synthesized firstly, and the yield is 81 percent. Then, the mixture of 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline is obtained by hydrazine hydrate reduction. The process disclosed in the patent document has disadvantages that the yield of the mixture of nitroquinoxalines is not high, and the starting material 4-nitrobenzoyl is expensive and not easily available, resulting in high production cost and unsuitability for industrial production.

Chinese invention patent publication CN107089954A discloses a method for synthesizing a mixture of 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline, which comprises (1) obtaining 4-nitrophenylacetyl chloride by chlorination reaction with 4-nitrophenylacetic acid as a starting material; (2) reacting 4-nitrophenylacetyl chloride with benzene to obtain 2- (4-nitrophenyl) -1-acetophenone; (3) reacting 2- (4-nitrophenyl) -1-acetophenone with 4-nitro-o-phenylenediamine to obtain a mixture of 2- (4-nitrophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-nitrophenyl) -2-phenyl-6-aminoquinoxaline; and (4) carrying out catalytic hydrogenation on the nitroquinoxaline mixture in the step (3) to obtain a mixture of 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline. The synthesis method disclosed in the patent document does not use 4-nitrobenzoyl, and reduces the production cost to a certain extent. However, step (3) of the process needs to be carried out at a relatively high temperature of 70-80 ℃ in the presence of a gaseous oxidant and a basic catalyst, with a yield between 90.1% and 95.0%.

For this reason, there is a continuous need in the art to develop a low-cost, high-yield method for synthesizing nitroquinoxaline or a derivative thereof and aminoquinoxaline or a derivative thereof.

Disclosure of Invention

The present application aims to provide a method for synthesizing nitroquinoxaline or a derivative thereof at a low cost and a high yield, thereby solving the above-mentioned technical problems in the prior art. Specifically, 4-nitro iodobenzene and phenylacetylene are used as starting materials to economically and efficiently synthesize 4-nitro benzil. Then, a mixture of 2- (4-nitrophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-nitrophenyl) -2-phenyl-6-aminoquinoxaline is prepared by reacting 4-nitrophenyl benzil with 4-nitrophthalimide at normal temperature and pressure in a yield of up to 98% using o-benzoylsulfonylimide (also called saccharin) as a specific catalyst. Finally, the mixture of 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline is prepared by a catalytic hydrogenation process.

It is also an object of the present application to provide a nitroquinoxaline or a derivative thereof prepared by the process as described above.

It is also an object of the present application to provide a method for synthesizing aminoquinoxaline or a derivative thereof.

It is also an object of the present application to provide a method for preparing polyimide using the aminoquinoxaline or the derivative thereof as described above.

It is also an object of the present application to provide a polyimide prepared by the method as described above.

The application also aims to provide an application of the o-benzoylsulfonyl imide as a catalyst in the preparation of nitroquinoxaline or derivatives thereof.

It is also an object of the present application to provide a process for the preparation of 4-nitrobenzoyl.

In order to solve the above technical problem, the present application provides the following technical solutions:

in a first aspect, the present application provides a method for synthesizing nitroquinoxaline or a derivative thereof, characterized in that the method comprises the steps of: reacting a mono-nitro substituted o-phenylenediamine or a derivative thereof with a mono-nitro substituted benzil or a derivative thereof in a solvent in the presence of a catalyst, o-benzoylsulfimide, for a predetermined period of time to obtain the nitroquinoxaline or the derivative thereof;

wherein the mononitro-substituted o-phenylenediamine or derivative thereof has a structure represented by the following general formula (I):

in the general formula (I), the groups R1, R2, R3 and R4 are each independently selected from H, C1-C10 alkyl or nitro, and one and only one of the groups R1, R2, R3 and R4 is nitro;

wherein the mononitro-substituted benzil has a structure represented by the following general formula (II):

in general formula (II), the groups R5, R6, R7, R8, R9, R10, R11, R12, R13 and R14 are each independently selected from H, C1-C10 alkyl or nitro, and one and only one of the groups R5, R6, R7, R8, R9, R10, R11, R12, R13 and R14 is nitro;

wherein the nitroquinoxaline or the derivative thereof has a structure represented by the following general formula (III):

in formula (III), the groups R21, R22, R23 and R24 are each independently selected from H, C1-C10 alkyl or nitro, and one and only one of the groups R21, R22, R23 and R24 is nitro; in formula (III), the radicals R31, R32, R33, R34, R35, R41, R42, R43, R44 and R45 are each independently selected from H, C1-C10 alkyl or nitro, and one and only one of the radicals R31, R32, R33, R34, R35, R41, R42, R43, R44 and R45 is nitro.

In one embodiment of the first aspect, the mononitro-substituted benzil or derivative thereof comprises 4-nitrobenzoyl, 3-nitrobenzoyl, 2-methyl-4-nitrobenzoyl, 3-methyl-4-nitrobenzoyl, 2, 3-dimethyl-4-nitrobenzoyl, 2,3, 5-trimethyl-4-nitrobenzoyl;

and/or the mononitro-substituted o-phenylenediamine or the derivative thereof is 3-nitrophthalenediamine, 4-nitrophthalenediamine, 5-nitrophthalenediamine, 6-nitrophthalenediamine, 3-methyl-4-nitrophthalenediamine, 5-methyl-4-nitrophthalenediamine, 3, 5-dimethyl-4-nitrophthalenediamine or 3,5, 6-trimethyl-4-nitrophthalenediamine;

and/or the solvent is one or more of glacial acetic acid, methanol, N N-dimethylformamide or acetonitrile.

In one embodiment of the first aspect, the catalyst is present in an amount of less than or equal to 5% o/f on a molar basis of the benzoylsulfonimide and the mononitro-substituted benzil.

In one embodiment of the first aspect, the nitroquinoxaline or derivative thereof comprises a mixture of 2- (4-nitrophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-nitrophenyl) -2-phenyl-6-aminoquinoxaline.

In one embodiment of the first aspect, the 4-nitrobenzoyl is prepared by the following process:

(1) reacting nitrohalogenated benzene with phenylacetylene to obtain 1-nitro-4-phenylacetylene; and

(2) reacting 1-nitro-4-phenylacetylene with an oxidant in the presence of a metal catalyst to obtain the 4-nitrobenzoyl.

In one embodiment of the first aspect, the nitrohalobenzene is 4-nitroiodobenzene, 4-nitrobromobenzene or 4-nitrochlorobenzene;

and/or the metal catalyst is palladium dichloride or a mixture of equimolar amounts of aluminum chloride and palladium acetate;

and/or the oxidizing agent is dimethyl sulfoxide.

In a second aspect, the present application provides a nitroquinoxaline or a derivative thereof synthesized by the method of the first aspect.

In a third aspect, the present application provides a method for synthesizing an aminoquinoxaline or a derivative thereof, characterized in that the method comprises reducing a nitro group corresponding to a nitroquinoxaline or a derivative thereof prepared by the method for synthesizing a nitroquinoxaline or a derivative thereof according to claim 1 to an amino group to obtain the aminoquinoxaline or the derivative thereof.

In one embodiment of the third aspect, the aminoquinoxaline or derivative thereof is a mixture of 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline.

In a fourth aspect, the present application provides a method of preparing a polyimide, the method comprising the steps of: s1: reacting the aminoquinoxaline or the derivative thereof according to the third aspect with an acid anhydride to obtain a polyamic acid; and

s2: the polyamic acid was thermally imidized to obtain a polyimide.

In a fifth aspect, the present application provides a polyimide prepared by the method as described in the fourth aspect.

In a sixth aspect, the present application provides the use of a phthalimide as a catalyst in the synthesis of nitroquinoxaline or a derivative thereof.

In a seventh aspect, the present application provides a process for preparing 4-nitrobenzoyl comprising the steps of:

Compared with the prior art, the method has the beneficial effects that the synthesis process is low in cost and high in yield, and is beneficial to large-scale preparation of the nitroquinoxaline or the derivative thereof and the aminoquinoxaline or the derivative thereof. Polyimides prepared using the aminoquinoxalines described herein have excellent heat resistance, mechanical properties, and electrical properties.

Drawings

FIG. 1 shows a hydrogen nuclear magnetic resonance spectrum of 1-nitro-4-phenylacetylene benzene.

FIG. 2 shows a hydrogen nuclear magnetic resonance spectrum of 4-nitrobenzoyl.

FIG. 3 shows the hydrogen nuclear magnetic resonance spectra of a mixture of two isomers, 2- (4-nitrophenyl) -3-phenyl-6-nitroquinoxaline and 3- (4-nitrophenyl) -2-phenyl-6-nitroquinoxaline, according to example 1, in a molar ratio of 1: 1.

FIG. 4 shows the NMR spectra of a mixture of two isomers, 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline, in a molar ratio 1:1 according to example 1.

FIG. 5 shows total reflection infrared spectra of polyimide films according to examples 3 to 6. In FIG. 5, the abscissa is the wave number (cm) ^-1 ) The ordinate represents transmittance.

FIG. 6 shows ultraviolet absorption spectra of polyimide films according to examples 3 to 6. In fig. 6, the abscissa represents wavelength (nm) and the ordinate represents transmittance.

FIG. 7 shows thermogravimetric analysis (TGA) profiles of polyimide films according to examples 3-6. In FIG. 7, the abscissa represents temperature (. degree. C.) and the ordinate represents weight (%).

Fig. 8 shows dynamic thermo-mechanical analysis (DMA) patterns of polyimide films according to examples 3-6. In FIG. 8, the abscissa is temperature (. degree. C.) and the ordinate is tan. delta.

Fig. 9 shows thermomechanical analysis (TMA) patterns of polyimide films according to examples 3-6. In fig. 9, the abscissa is temperature (° c), and the ordinate is dimensional change (micrometers).

FIG. 10 shows dielectric constant patterns of polyimide films according to examples 3 to 6. In fig. 10, the abscissa is frequency (Hz) and the ordinate is dielectric constant.

FIG. 11 shows dielectric loss spectra of polyimide films according to examples 3-6. In fig. 11, the abscissa is frequency (Hz) and the ordinate is dielectric loss.

In FIGS. 5-11, a solid square represents example 3, a solid circle represents example 4, a solid regular triangle (with the triangle pointed upward) represents example 5, and a solid inverted triangle (with the triangle pointed downward) represents example 6.

Detailed Description

The aminoquinoxaline or the derivative thereof is a novel diamine monomer, and the polyimide, polyether, polyester and other polymers synthesized by utilizing the aminoquinoxaline have excellent thermal stability and chemical stability. Nitroquinoxaline or a derivative thereof is a precursor compound for synthesizing aminoquinoxaline or a derivative thereof, and a process for converting a nitro group into an amino group, such as catalytic hydrogenation reduction, hydrazine hydrate reduction and the like, is well established in the industry. However, the process for synthesizing nitroquinoline or derivatives thereof in the prior art has high cost, low reaction yield and harsh reaction conditions. Therefore, there is a continuing need in the art to develop a low-cost, high-yield method for synthesizing nitroquinoxaline or a derivative thereof.

The application provides a method for synthesizing nitroquinoxaline or a derivative thereof, which is characterized by comprising the following steps: reacting a mononitro-substituted o-phenylenediamine or derivative thereof with a mononitro-substituted benzil or derivative thereof in a solvent in the presence of a catalyst, o-benzoylsulfimide, for a predetermined period of time to obtain said nitroquinoxaline or derivative thereof;

in formula (I), the groups R1, R2, R3 and R4 are each independently selected from H, C1-C10 alkyl or nitro, and only one and one of the groups R1, R2, R3 and R4 is nitro;

In one embodiment, the arrow in the formula (III) indicates the simultaneous presence of two isomers, specifically a mixture of isomers composed of the interchanging of substituents at the 2-and 3-positions on the nitrogen-containing six-membered ring of quinoxaline.

As used herein, the term "C1-C10 alkyl" refers to a straight or branched chain alkyl group having from 1 to 10 carbon atoms. In one embodiment, the C1-C10 alkyl group includes methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, or decyl, and the like.

In a particularly preferred embodiment, the nitroquinoline or derivative thereof is a mixture of 2- (4-nitrophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-nitrophenyl) -2-phenyl-6-aminoquinoxaline.

In a particularly preferred embodiment, the aminoquinoline or derivative thereof is a mixture of 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline.

In another embodiment, the inventors of the present application have surprisingly found that the yield of the reaction between mononitrosubstituted benzil and mononitrosubstituted o-phenylenediamine is significantly increased with very low amounts of phthalimide (also known as saccharin), which is commonly used as a sweetener.

The application also provides a method for economically and efficiently synthesizing the 4-nitrobenzoyl. The method may comprise the steps of: (1) reacting nitrohalogenated benzene with phenylacetylene to obtain 1-nitro-4-phenylacetylene; and (2) reacting 1-nitro-4-phenylacetylene with an oxidant in the presence of a metal catalyst to obtain the 4-nitrobenzoyl.

In one embodiment, the palladium chloride is replaced by equimolar amounts of aluminum chloride and palladium acetate in the preparation of benzil, but the yields of aluminum chloride and palladium acetate as catalyst are low (around 40%).

In one embodiment, higher yields can be achieved without the use of a catalyst at different temperatures and durations: the glacial acetic acid is taken as a solvent to react for 12h at normal temperature, and the yield can reach 98%; the yield can reach 98 percent after the reaction is carried out for 12 hours at the temperature of 64 ℃ by taking methanol as a solvent under heating and refluxing; the yield can be more than 80% after 36h reaction at 90 ℃ by using DMF as a solvent, and the yield can be more than 60% after 36h reaction at 90 ℃ by using acetonitrile as a solvent. The reaction time can be shortened to 1h by using saccharin as a catalyst in the presence of 5% of glacial acetic acid as a solvent.

Examples

The present application will now be described and illustrated in further detail with reference to the following examples. All chemical raw materials can be purchased from the market unless otherwise specified. Those skilled in the art will appreciate that the following embodiments are exemplary only.

In the following examples, the characterization methods are as follows.

Nuclear magnetic resonance hydrogen/carbon spectrum ( ¹ H NMR、 ¹³ C NMR)：

Nuclear magnetic resonance spectrum of reaction product and intermediate ( ¹ H NMR and ¹³ c NMR) spectra were obtained on brueck AVANCE III HD 400/500, germany. The sample preparation method comprises the following steps: in a clean and dry glass magnetic tube, about 10mg of the sample was completely dissolved in about 0.5mL of deuterated reagent. The better soluble product was deuterated chloroform as solvent (CDCl) ₃ ) The product is dissolved at room temperature, the product with poor solubility takes deuterated dimethyl sulfoxide (DMSO-d6) as a solvent, DMSO-d6 is easy to solidify at low room temperature, and blowing is needed before loading. Tetramethylsilane (TMS) was used as an internal standard for the test at room temperature, and the chemical shift was 0 ppm.

Fourier Infrared transform Spectroscopy (FT-IR):

in a dry environment, a proper amount of sample is mixed with potassium bromide powder, fully and uniformly ground, and a transparent sheet is prepared on a tablet press. The model of the infrared spectrometer is Nicolet 6700, and the scanning range is 4000-650cm ^-1 Resolution was set to 2cm ^-1 The number of scans was set to 32, and the average was automatically taken.

Gel Permeation Chromatography (GPC):

the Hitachi gel permeation chromatograph (GPC LC-20AD) was adjusted with polystyrene standards and used to measure the molecular weight (M) of the polyamic acid solution _n And M _w ) And molecular weight distribution (PDI). Samples were taken and diluted to 1mg/mL by calculating the solids content of the polyamic acid, supplemented with chromatographically pure DMAc, and filtered repeatedly until needed. After the sample injector is rinsed for many times, 100 mul of sample solution is loaded, and is rinsed by chromatographic pure DMAc, the flow rate is set to be 0.6mL/min, the testing time is 15min, and the column temperature is set to be 40 ℃.

Total reflectance Infrared Spectroscopy (ATR-FTIR):

the structural characteristics of the polyimide film are tested by adopting a total reflection accessory on a Nicolet 6700 infrared spectrometer, and the resolution ratio is 4cm ^-1 The scanning range is set to 4000-650cm ^-1 The number of scans was set to 32.

Ultraviolet visible spectrum (UV-Vis):

the optical transmittance of the polyimide film was analyzed by a Shimadzu UV-1800 spectrophotometer, and the scanning range was set at 200-800cm ^-1 And 32 scans at room temperature.

Thermal performance analysis (TGA & DMA & TMA):

the thermal weight loss behavior of the polyimide film is performed on a TA Discovery 550 thermogravimetric analyzer (TGA) under the protection of nitrogen, the gas flow is 50mL/min, the temperature is increased from room temperature to 120 ℃ at 20 ℃/min and stays for 15min, and then the temperature is increased from 50 ℃ to 800 ℃ at 10 ℃/min.

Glass transition temperature (T) _g ) The process was carried out on a TA Q800 dynamic thermomechanical analyzer (DMA), cutting the polyimide film into rectangular strips of uniform width, setting the loading frequency at 1Hz, increasing from 30 ℃ to 500 ℃ at a rate of 5 ℃/min, and protecting with nitrogen.

The thermal dimensional stability of the polyimide film was analyzed by a TA Q400 thermomechanical analyzer (TMA) in tensile mode to determine the change in the dimensions of the bars with increasing temperature. The polyimide film is prepared into a long and thin strip shape with uniform width, the static load is 0.05N, the heating rate is 5 ℃/min, the heating range is from room temperature to 400 ℃, and the nitrogen flow is 50 mL/min. The temperature programming step is divided into two parts, the temperature is raised at the same speed in the first step and then reduced to eliminate the residual internal stress of the film in the thermal imidization, and curve data of the second step of heating to 400 ℃ is recorded.

Mechanical property analysis:

the mechanical property of the polyimide film is measured by a Sagitaijie SUST CMT1104 universal tensile testing machine, a sample is cut into a rectangular strip, the traction rate is 10mm/min, and the average value of the multiple effective test results is taken.

And (3) dielectric property analysis:

the dielectric properties of the polyimide films were measured by Novocontrol Concept 40 broadband dielectric impedance spectrometer, GermanyMeasuring, preparing a square sample with side length larger than 2cm, drying at 80 deg.C for two hours, covering copper on the front and back surfaces of the sample by vacuum electrodeposition in a drying chamber, measuring the thickness of the film by a thickness gauge, and testing the electrical properties of the sample by a parallel plate capacitance method with a test frequency of 10 ² ～10 ⁶ Hz。

High performance Liquid Chromatography (LCMS):

a small amount of diamine powder was dissolved in high purity acetonitrile, and a trace of insoluble matter was removed with a needle filter. The eluent ratio was 20mmol/L ammonium formate aqueous solution (40%) and chromatographically pure acetonitrile (60%) eluting at 250. mu.L/min flow rate for 30min, and the column temperature was maintained at 35 ℃.

Example 1

The synthetic route of this example is as follows:

hereinafter, the nuclear magnetic resonance spectrometer used is a bruker 500M nuclear magnetic resonance spectrometer.

In the nuclear magnetic data described below, it is, ¹ H NMR(CDCl ₃ 400MHz) represents the hydrogen nuclear magnetic resonance spectrum at 400MHz using deuterated chloroform as a solvent. ¹ H NMR (DMSO-d6,500MHz) represents a hydrogen nuclear magnetic resonance spectrum at 500MHz using deuterated DMSO as a solvent.

Step 1: synthesis of 1-nitro-4-phenylacetylene benzene

12.5g (50mmol) of 4-nitroiodobenzene, 6.5mL (60mmol) of phenylacetylene, 112.3mg (0.5mmol) of palladium acetate, 95.3mg (0.5mmol) of iodone iodide, Xantphos (289.3mg (0.5mmol) of CAS:161265-03-8), and 32.6g (100mmol) of cesium carbonate were dissolved in 200mL of N, N-dimethylformamide. Heated to 60 ℃ and stirred for 16 h. The reaction was terminated by Thin Layer Chromatography (TLC) and quenched by adding 200mL of distilled water to the system. Ethyl acetate (200mL × 2) was extracted, and the organic phase was washed with saturated brine (200mL × 2). The mixture was dried over anhydrous magnesium sulfate, rotary evaporated to dryness and separated by column chromatography to give 10.47g (yield 94%) of a yellow solid powder. Performing hydrogen nuclear magnetic resonance characterization on the product, wherein the spectrogram is shown in figure 1, and the nuclear magnetic peak data is as follows:

¹ H NMR(CDCl ₃ ,400MHz):δ8.23(d,J＝8.84Hz,2H),7.67(d,J＝8.88Hz,2H),7.58-7.55(m,2H),7.40-7.39(m,3H)。

step 2: synthesis of 4-nitrobenzoyl

8.9g (40mmol) of 1-nitro-4-phenylacetylene benzene was uniformly dissolved in 250mL of dimethyl sulfoxide, and 709.3mg (4mmol) of palladium dichloride was further added. Heated to 145 ℃ and stirred for 4 h. The reaction was terminated by Thin Layer Chromatography (TLC) and quenched by adding 250mL of distilled water to the system. Ethyl acetate (150ml x 2) was extracted and the organic phase was washed with saturated brine (100ml x 2). The extract was dried over anhydrous magnesium sulfate, rotary evaporated to dryness and separated by column chromatography to give 8.78g (yield: 86%) of a yellow solid powder. And (3) performing hydrogen nuclear magnetic resonance characterization on the product, wherein the spectrogram is shown in figure 2, and the nuclear magnetic peak data is as follows:

¹ H NMR(CDCl ₃ ,400MHz):δ8.36(d,J＝8.28Hz,2H),8.17(d,J＝7.72Hz,2H),7.99(d,J＝7.28Hz,2H),7.73-7.70(m,1H),7.58-7.54(m,2H)。

and step 3: synthesis of 2- (4-nitrophenyl) -3-phenyl-6-nitroquinoxaline and 3- (4-nitrophenyl) -2-phenyl-6-nitroquinoxaline mixtures

6.7g (26mmol) of 4-nitrobenzoyl, 4.0g (26mmol) of 4-nitrophthalimide and 241mg (1.3mmol) of saccharin were dissolved uniformly in 250mL of glacial acetic acid at ordinary temperature and pressure. Stir at room temperature for 1 h. The reaction was terminated by Thin Layer Chromatography (TLC) and quenched by adding 250mL of distilled water to the system. Filtration, washing with distilled water three times, and drying gave 9.49g (yield 98%) of a yellow solid powder. The product was characterized by hydrogen nuclear magnetic resonance (including a mixture of two isomers) as shown in fig. 3, and the nuclear magnetic peak data were as follows:

¹ H NMR(CDCl ₃ ,400MHz):δ9.10(1H),8.59-8.56(1H),8.34-8.32(1H),8.24-8.22(2H),7.78-7.75(2H),7.54-7.39(5H)。

and 4, step 4: synthesis of 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline and 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline mixtures

9g (24mmol) of the nitro mixture was dissolved homogeneously in 250mL of methanol and 0.9g of 5% palladium on carbon was added. The solution was placed in a hydrogen bag to replace hydrogen three times and stirred at room temperature under one atmosphere for 12 hours. The reaction was monitored by Thin Layer Chromatography (TLC) for completion, filtered through celite, and the palladium on carbon was recovered. The filtrate was concentrated and recrystallized from methanol to obtain 5.85g (yield: 78%) of a yellow solid powder. The product was characterized by hydrogen nuclear magnetic resonance (including a mixture of two isomers) as shown in fig. 4, and the nuclear magnetic peak data were as follows:

¹ H NMR(DMSO-d6,500MHz):δ7.74-7.71(1H),7.45-7.41(2H),7.37-7.33(3H),7.23-7.16(1H),7.12-7.06(2H),6.94-6.92(1H),6.47-6.44(2H),6.02-5.98(2H),5.36-5.27(2H)。

example 2

This example relates to the separation of 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline (p-QBDA) and 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline.

In the LCMS spectrum, 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline (p-QBDA) and 2- (4-aminophenyl) -3-phenyl-6-aminoquinoxaline mixed in QBDA can be seen to correspond to two fluorescence peaks. The abscissa of the first fluorescence peak was 12.131 minutes, and the peak area was 6833991. The abscissa of the second fluorescence peak is 21.514 minutes, and the peak area is 1357890.

p-QBDA with lower polarity can be judged as the upper point by thin-layer chromatography (petroleum ether: ethyl acetate: 1:2), and p-QBDA with diamine in para position is obtained by a large amount of column chromatography. The chemical structure of p-QBDA is characterized by nuclear magnetism, and the specific data is as follows: ¹ H NMR(DMSO-d ₆ ,500MHz)：δ7.78-7.76(1H)，7.48-7.47(2H)，7.40-7.38(3H)，7.26-7.24(1H)，7.11-7.09(2H)，6.97-6.97(1H)，6.49-6.47(2H)，6.02(2H)，5.32(2H)。 ¹³ C NMR(DMSO-d ₆ 125 MHz): δ 152.57, 150.47, 149.12, 148.24, 142.77, 140.78, 135.20, 130.94, 129.86, 129.47, 128.53, 128.37, 126.79, 122.80, 113.55105.40. Chemical shifts are consistent with those described previously for QBDA.

Example 3

Examples 3-6 relate to the preparation of polyimides using QBDA prepared according to example 1.

Under the protection of nitrogen and an ice-water bath, 50mmol of QBDA powder is uniformly dissolved in DMAc, 10.91g (50mmol) of 1,2,4, 5-pyromellitic anhydride (PMDA) is added into 2-3 batches, and the mixture is stirred for about 12 hours at room temperature to obtain uniform polyamic acid glue solution. Removing bubbles involved in the glue solution in the reaction by a centrifugal defoaming machine. Uniformly scraping PAA glue solution on the surface of a dried glass plate by using a scraper with the gap width of 250 mu m, removing bubbles in the polyamide acid film again by a vacuumizing mode, and performing hot imidization in a muffle furnace by using a fixed temperature-rising program (115 ℃/15min, 140 ℃/15min, 200 ℃/30min, 250 ℃/5min and 380 ℃/90min) to obtain the polyimide film. After cooling to room temperature, the polyimide film was immersed in hot water, peeled from the glass substrate, and dried at 80 ℃ for 2 hours. A polyimide film according to example 4 was obtained.

Example 4

The acid anhydride in example 3 was replaced with 14.71g (50mmol) of 4, 4' -biphenyltetracarboxylic dianhydride (BPDA), yielding a polyimide film according to example 4.

Example 5

The acid anhydride in example 3 was replaced with 16.11g (50mmol) of 3,3 ', 4, 4' -benzophenonetetracarboxylic dianhydride (BTDA), yielding a polyimide film according to example 5.

Example 6

The anhydride in example 3 was replaced by 15.5g (50mmol) of 3,3 ', 4, 4' -diphenylmethylether tetracarboxylic dianhydride (OTDA).

The molecular structure of the polyimide film is characterized by a characteristic peak of total reflection infrared detection, and the characterization result is shown in figure 5. 1604/1601cm ^-1 Infrared absorption peak (C ═ N stretching vibration) at (b) confirmed that the quinoxaline ring structure was successfully introduced into the PI backbone. Amide groups at 1550 and 1660cm ^-1 The absorption peak at (A) disappeared and the imide ring was observed at 1776/1778cm ^-1 (asymmetric stretching vibration of C ═ O), 1708/1713cm ^-1 (C-O symmetric stretching vibration) 1357/1356cm ^-1 (stretching vibration of C-N-C) and 725cm ^-1 Characteristic absorption peaks at positions (C ═ O bending vibration) and the like indicate that the polyamic acid has been successfully cyclized to polyimide.

The molecular weights of the polyamic acids according to examples 3 to 6 and the poly(s) according to examples 3 to 6 were characterized respectivelyOptical, thermal, mechanical and electrical properties of the imide film. The results are shown in FIGS. 6-11 and the following tables. In Table 2, T _d ^5％ Denotes the thermal decomposition temperature at 5% weight loss, T _d ^10％ Thermal decomposition temperature, R, representing 10% weight loss _w Represents the char yield after firing to 800 ℃. In Table 3,. sigma. _max Denotes the tensile strength, E denotes the initial modulus,. epsilon _b Represents elongation at break and ε _r Indicating the dielectric constant.

Table 1 molecular weights of polyimide acids according to examples 3 to 6 and optical properties of polyimide films.

Table 2 thermal properties of the polyimide films according to examples 3 to 6.

Table 3 mechanical and electrical properties of the polyimide films according to examples 3 to 6.

Example numbering	σ _max (MPa)	ε _b (％)	E(GPa)	ε _r	tanδ(×10 ^-3 )
						Example 3	127±4	4.5±0.5	3.7±0.5	3.3	2.8
Example 4	138±5	12.8±0.6	2.3±0.1	3.6	2.1
						Example 5	109±4	5.2±0.5	2.6±0.2	3.7	3.8
Example 6	145±4	11.8±1.8	2.6±0.2	3.7	3.2

Example 7

This example relates to the preparation of polyimide membranes using 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline (p-QBDA) isolated according to example 2.

The QBDA in example 3 was replaced with 50mmol of p-QBDA to obtain a polyimide film according to example 7.

Example 8

The acid anhydride in example 7 was replaced with 14.71g (50mmol) of 4, 4' -biphenyltetracarboxylic dianhydride (BPDA), to give a polyimide film according to example 8.

The molecular weights of the polyamic acids according to examples 7 and 8, and the optical, thermal, mechanical, and electrical properties of the polyimide films according to examples 7 and 8, respectively, were characterized. The thermal properties of the polyimide films according to examples 7 and 8 are shown in table 4 below.

Table 4 thermal properties of the polyimide films according to example 7 and example 8.

TGA curves and thermal decomposition behavior parameters (T) of two series of polyimide films due to the same chemical composition and average bond energy of QBDA and p-QBDA _d ^5％、T _d ^10％、R _w ) The difference is not so large, that is, the configuration is hardly so large as to the heat resistance of the polyimide film. The p-QBDA lacks another kinking structure relative to QBDA, the reduction of the mutual kinking degree among molecular chains leads to the reduction of molecular rotation energy which needs to be overcome by the motion of high molecular chain segments, so the T of the p-QBDA-m _g The value is reduced by 27 ℃ relative to QBDA-m, and the value of p-QBDA-b is also reduced by 34 ℃ relative to QBDA-b. The para-configuration shows better linearity in two configurations of QBDA, so that the in-plane linear expansion coefficient of p-QBDA-PIs is remarkably lower than that of QBDA-PIs, wherein p-QBDA-m obtained by homopolymerizing p-QBDA and dianhydride PMDA with the best linearity still keeps the same size at 350 ℃, namely the CTE value is 0. T of p-QBDA-b _g Values below 350 ℃ are thus only detectable with a CTE value of 24ppm/K at 300 ℃.

The embodiments described above are intended to facilitate the understanding and appreciation of the application by those skilled in the art. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present application is not limited to the embodiments herein, and those skilled in the art who have the benefit of this disclosure will appreciate that many modifications and variations are possible within the scope of the present application without departing from the scope and spirit of the present application.

Claims

1. A method of preparing a polyimide, comprising the steps of:

s1: reacting aminoquinoxaline or a derivative thereof with an acid anhydride to obtain polyamic acid; and

s2: performing thermal imidization on the polyamide acid to obtain polyimide;

wherein the aminoquinoxaline or the derivative thereof is 3- (4-aminophenyl) -2-phenyl-6-aminoquinoxaline;

wherein the acid anhydride is 1,2,4, 5-pyromellitic anhydride.

2. A polyimide prepared by the method of claim 1.