Polyamic acid solution, chiral polyimide porous material and preparation method of chiral polyimide porous material

Abstract

The invention belongs to the technical field of high polymer materials, and discloses a polyamide acid solution, a chiral polyimide porous material and a preparation method of the chiral polyimide porous material. The preparation method of the polyamide acid solution comprises the following steps: S1, under the protection of nitrogen, taking 3, 5-dinitrobenzoyl chloride and (R)-(+)-alpha-methylbenzylamine as raw materials, and sequentially carrying out ice bath reaction for 2 hours and room temperature reaction for 6 hours to prepare (R)-(+)-N-(3, 5-dinitrobenzoyl)-alpha-methylbenzylamine; the (R)-(+)-N-(3, 5-dinitrobenzoyl)-alpha-methylbenzylamine is reduced by adopting excessive SnCl2. 2H2O, and a diamine monomer of the (R)-(+)-N-(3, 5-diaminobenzoyl)-alpha-methylbenzylamine is obtained; s2, under the protection of nitrogen, respectively dissolving benzenehexanoic acid trianhydride and the diamine monomer through an organic solvent to obtain an anhydride solution and a diamine monomer solution; wherein the molar ratio of the benzenehexacarboxylic acid trianhydride to the diamine monomer is 2: 3; and slowly dropwise adding the anhydride solution into the diamine monomer solution, reacting in an ice bath for 4 hours, and reacting at room temperature for 12 hours to obtain a polyamide acid solution with the solid content of 10wt%.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a polyamic acid solution, a chiral polyimide porous material, and a method for preparing the same. Background Technology

[0002] Currently, several types of chiral porous composite membrane materials have been explored in the field of chiral solid membrane separation, including chiral metal-organic frameworks (CMOF), chiral covalent organic frameworks (CCOF), molecularly imprinted polymers (MIP), and chiral mesoporous silica (CMS). Chiral porous composite membrane materials have rich pore structures and large specific surface areas, and can separate enantiomers by recognizing chiral recognition sites. However, most existing chiral porous composite membrane materials have high preparation costs, many harmful byproducts, complex preparation processes, high energy consumption, and poor reusability. Summary of the Invention

[0003] One objective of this invention is to provide a method for preparing a solution of polyamic acid as a precursor for polyimide. The polyamic acid prepared by this method exhibits good stability, providing favorable prerequisites for subsequently obtaining polyimide with a high relative molecular weight.

[0004] The specific technical solution is as follows:

[0005] A method for preparing a polyamic acid solution, comprising:

[0006] S1. Preparation of diamine monomers

[0007] Under nitrogen protection, 3,5-dinitrobenzoyl chloride was added to dichloromethane and dissolved by stirring in an ice bath. Then, (R)-(+)-α-methylbenzylamine, propylene oxide, and triethylamine were added sequentially. The reaction was carried out in an ice bath for 2 hours and then at room temperature for 6 hours. The solid in the reaction product was precipitated out using deionized water, filtered, dried for 12 hours, recrystallized from anhydrous ethanol, and dried for 24 hours to obtain (R)-(+)-N-(3,5-dinitrobenzoyl)-α-methylbenzylamine.

[0008] The (R)-(+)-N-(3,5-dinitrobenzoyl)-α-methylbenzylamine was reduced with excess SnCl2·2H2O to obtain the diamine monomer of (R)-(+)-N-(3,5-diaminobenzoyl)-α-methylbenzylamine;

[0009] S2. Preparation of polyamic acid solution

[0010] Under nitrogen protection, benzohexacarboxylic acid trianic anhydride and the diamine monomer are dissolved in an organic solvent to obtain an anhydride solution and a diamine monomer solution; wherein the molar ratio of benzohexacarboxylic acid trianic anhydride to the diamine monomer is 2:3;

[0011] The acid anhydride solution was slowly added dropwise to the diamine monomer solution, and the reaction was carried out in an ice bath for 4 hours and then at room temperature for 12 hours to obtain a polyamic acid solution with a solid content of 10 wt%.

[0012] Preferably, the molar ratio of 3,5-dinitrobenzoyl chloride to (R)-(+)-α-methylbenzylamine is 1:1 to 1.5; and the volume ratio of (R)-(+)-α-methylbenzylamine, propylene oxide and triethylamine is 80 to 85:1:85.

[0013] Preferably, the reduction reaction comprises: mixing excess SnCl2·2H2O with the (R)-(+)-N-(3,5-dinitrobenzoyl)-α-methylbenzylamine to obtain a mixture; dissolving the mixture in ethanol under nitrogen protection and refluxing vigorously at 78°C for 10 h; purifying the reaction solution in deionized water and alkalizing it with saturated sodium bicarbonate solution; allowing it to stand and refrigerate for 12 h; extracting the organic phase with ethyl acetate, drying with anhydrous MgSO4, filtering, and rotary evaporating to obtain a crude product; dissolving the crude product in ethyl acetate and precipitating it with n-hexane, filtering, washing with n-hexane, and drying to obtain the diamine monomer.

[0014] Preferably, the organic solvent is any one of N,N-dimethylacetamide, N-methylpyrrolidone, or N,N-dimethylformamide.

[0015] Another objective of this invention is to provide a novel structure of highly stable, highly heat-resistant, and highly strong polyimide and chiral polyimide porous materials and their preparation methods, in order to address the shortcomings of existing chiral porous composite membrane materials with poor reusability.

[0016] The specific technical solution is as follows:

[0017] A polyimide, using polyamic acid prepared by the above method as a precursor.

[0018] A chiral polyimide porous material comprising the aforementioned polyimide.

[0019] The method for preparing the chiral polyimide porous material includes the following steps:

[0020] (1) The polyamic acid solution was cast onto a porous substrate and continuously vacuum dried at 50°C, 85°C and 100°C for 1.5 h to remove the solvent and obtain a polyimide precursor.

[0021] (2) The polyimide precursor obtained in step (1) is subjected to high-temperature thermal imidization:

[0022] Under normal pressure, the samples were continuously heat-treated at 145℃, 165℃, 185℃, 205℃, 225℃, 245℃ and 265℃ for 1 hour, and then cooled to room temperature.

[0023] The material is washed with detergent and dried to obtain the chiral polyimide porous material.

[0024] Preferably, the porous substrate includes the following processing steps:

[0025] At room temperature, the SiO2 substrate was immersed in hydrochloric acid aqueous solution for ultrasonic activation treatment for 1.5 h, washed with ethanol, and dried to obtain an activated porous substrate.

[0026] Under nitrogen protection, the activated porous substrate and 3-aminopropyltriethoxysilane were placed in toluene solvent and reacted at 80°C for 12 h. The substrate was then washed with ethanol and dried under vacuum for 12 h to obtain the functionalized porous substrate.

[0027] Preferably, in step (2), the detergent washing includes: mixing methanol and tetrahydrofuran in a 1:1 ratio to prepare a detergent; and performing washing with the detergent at 40-45°C.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] This invention provides a method for preparing chiral polyimide porous materials that exhibit strong chemical stability, resistance to acids, alkalis, and organic solvents, high temperature resistance, high mechanical strength, large specific surface area, abundant permanent pore structure, high mass transfer efficiency, fast separation speed, good repeatability, low cost, and simple preparation. This method aligns with the principles of green chemistry and has significant research implications and scientific value in the field of chiral separation.

[0030] Specifically, in the method for preparing polyamic acid, a polyimide precursor, the purity of the diamine monomer is ensured to reach over 95% by recrystallization from anhydrous ethanol. The diamine monomer is (R)-(+)-N-(3,5-diaminobenzoyl)-α-methylbenzylamine, which is a non-chiral site. It successfully polymerizes by overcoming steric hindrance and the anhydride group, while exposing the chiral site of the 1-position amide, which can effectively enhance the chiral recognition function. In addition, it is preferred to limit the copolymerization-condensation process to a molar ratio of benzohexacarboxylic acid trianic anhydride to the diamine monomer of 2:3 and a solid content of 10wt%, which effectively ensures the excellent stability of the prepared polyamic acid, a polyimide precursor. Attached Figure Description

[0031] Figure 1 The infrared spectrum of the chiral polyimide porous material prepared in this invention;

[0032] Figure 2 The electron microscope images show the surface and cross-section of the chiral polyimide porous material prepared in this invention. Detailed Implementation

[0033] To further understand the content of this invention, a detailed description of the invention is provided in conjunction with the accompanying drawings and embodiments. The structures, proportions, sizes, etc., depicted in the accompanying drawings are merely for illustrative purposes and to aid those skilled in the art, and are not intended to limit the implementation conditions of the invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effects and objectives of the invention, should still fall within the scope of the technical content disclosed in this invention. Furthermore, terms such as "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity and not intended to limit the scope of implementation. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention. It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein.

[0034] Example 1

[0035] Firstly, the preparation method of the polyamic acid solution includes:

[0036] (1) Preparation of diamine monomers

[0037] Under nitrogen protection, 2.31 g (10 mmol) of 3,5-dinitrobenzoyl chloride and 50 mL of dichloromethane were injected into a 250 mL three-necked flask and dissolved by stirring in an ice bath. Then, (R)-(+)-α-methylbenzylamine (1.65 mL, 13 mmol), propylene oxide (0.02 mL), and triethylamine (1.70 mL) were added sequentially. The reaction was carried out in an ice bath for 2 h, then at room temperature for 6 h. 700 mL of deionized water was added to the three-necked flask to precipitate the solid from the reaction product. The product was filtered, dried under vacuum for 12 h, and recrystallized from anhydrous ethanol (a white solid precipitated). The solid was then dried under vacuum for 24 h to obtain (R)-(+)-N-(3,5-dinitrobenzoyl)-α-methylbenzylamine. Purity: 98%, Yield: 85%.

[0038] The (R)-(+)-N-(3,5-dinitrobenzoyl)-α-methylbenzylamine (2.08 g, 6.60 mmol) and excess SnCl2·2H2O (14.2 g, 63.0 mmol) were injected into a 500 mL three-necked flask. Under nitrogen protection, ethanol (100 mL) was added to the flask, and the mixture was refluxed vigorously at 78 °C for 10 h to obtain a light yellow reaction solution. The reaction solution was purified in 1200 mL of deionized water and then purified using saturated sodium bicarbonate solution (20 g, 2... The solution was alkalized to an alkaline pH (0.00 mL); after standing and refrigerating for 12 h, the organic phase was extracted with ethyl acetate (specifically, five extractions were performed, and the organic phases from the five extractions were mixed), dried over anhydrous MgSO4, filtered, and rotary evaporated to obtain the crude product; the crude product was dissolved in 10 mL of ethyl acetate and then precipitated by passing it through 1200 mL of n-hexane, filtered, washed with n-hexane, and dried under vacuum at 35 °C for 8 h to obtain a light pink (R)-(+)-N-(3,5-diaminobenzoyl)-α-methylbenzylamine, i.e., the diamine monomer. The purity was 95% and the yield was 70%.

[0039] (2) Preparation of polyamic acid solution

[0040] Benzene hexacarboxylic acid trihydride (0.144 g, 0.500 mmol) and the diamine monomer (0.191 g, 0.750 mmol) were injected into different two-necked flasks, and then 1.44 mL and 1.91 mL of N,N-dimethylformamide (DMF) were injected respectively to dissolve the Benzene hexacarboxylic acid trihydride and the diamine monomer, respectively, to obtain anhydride solution and diamine monomer solution;

[0041] Under nitrogen protection, the acid anhydride solution was slowly added dropwise to the diamine monomer solution, and the reaction was carried out in an ice bath for 4 hours and then at room temperature for 12 hours to obtain a polyamic acid solution (PAA) with a solid content of 10 wt%.

[0042] In summary, the chemical formula for preparing the polyamic acid is as follows: .

[0043] Secondly, the preparation method of the chiral polyimide porous material includes:

[0044] (1) Provide a SiO2 substrate (SS) with a diameter of 25.0 mm and a thickness of 2.50 mm. Polish it with sandpaper (400-1000 mesh) until the surface is flat and smooth. At room temperature, immerse the SiO2 substrate in hydrochloric acid aqueous solution (1M, 50 mL) and ultrasonically activate it for 1.5 h to activate the hydroxyl groups on the surface of the SiO2 substrate. Wash with ethanol and vacuum dry for 3 h to obtain activated porous substrate (SS-OH).

[0045] (3) Under nitrogen protection, the activated porous substrate and 3-aminopropyltriethoxysilane (0.873 mL) were placed in toluene solvent (12 mL), reacted at 80 °C for 12 h, washed repeatedly with 100 mL of ethanol, and dried under vacuum for 12 h to obtain the functionalized porous substrate (SS-NH2).

[0046] (4) 1.0 mL of the polyamic acid solution was cast onto a functionalized porous substrate and continuously vacuum-dried at 50°C, 85°C, and 100°C for 1.5 h to remove the solvent, thus obtaining a polyimide precursor. Under normal pressure, the precursor was continuously heat-treated at 145°C, 165°C, 185°C, 205°C, 225°C, 245°C, and 265°C for 1 h to thermally imidize the polyamic acid. After cooling to room temperature, a detergent was prepared by mixing methanol and tetrahydrofuran in a 1:1 ratio, and the substrate was washed three times with the detergent at 40-45°C for 20 min each time. The substrate was then vacuum-dried at 100°C for 6 h to obtain a blackish-brown chiral polyimide porous material (CO-PI-1 / SS) with a transparent luster.

[0047] In summary, the chemical formula for preparing the chiral polyimide porous material is as follows:

[0048] .

[0049] Figure 1 The image shows the infrared spectrum of the chiral polyimide porous material prepared in this invention. As can be seen from the image, the Si-O-Si absorption peak in SS appears at 1073 cm⁻¹. -1 The absorption peaks of Si-O-CH2 and Si-O-Si in SS-NH2 appear at 1090 cm⁻¹. -1 and 1030cm -1 At 750cm -1 The out-of-plane deformation vibration peak of NH appeared at 1647 cm⁻¹. -1 An in-plane deformation vibration peak of NH2 was observed; the Si-O-CH2 and Si-O-Si absorption peaks in CO-PI-1 / SS appeared at 1100 cm⁻¹, respectively. -1 and 1010cm -1 At 3426cm -1 The stretching vibration peak of NH appeared at 1723 cm⁻¹. -1 and 1777 cm -1 A C=O stretching vibration peak appears at 1377 cm⁻¹. -1 A CNC stretching vibration peak appeared at the location.

[0050] Figure 2The images show electron microscope (EM) surface and cross-sectional views of the chiral polyimide porous material prepared according to the present invention. Specifically, the left image is a surface view, and the right image is a cross-sectional view; as can be seen from the images, the chiral polyimide porous material has a large specific surface area and abundant porous structure.

[0051] In summary, this demonstrates the successful preparation of chiral polyimide porous materials. Furthermore, these chiral polyimide porous materials possess a permanent porous structure and a large specific surface area, thereby increasing the number of polymer growth sites and resulting in a significant improvement in resolution performance.

[0052] In the description of this invention, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0053] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for preparing a polyamide acid solution, characterized by, Comprising: S1. Preparing a diamine monomer Under nitrogen protection, 3,5-dinitrobenzoyl chloride is added into dichloromethane, stirred and dissolved in an ice bath, then (R)-(+)-a-methylbenzylamine, propylene oxide and triethylamine are added in sequence, reacted in an ice bath for 2h and at room temperature for 6h; the solid in the reaction product is precipitated out using deionized water, filtered, dried for 12h, recrystallized in anhydrous ethanol and dried for 24h to obtain (R)-(+)-N-(3,5-dinitrobenzoyl)-a-methylbenzylamine; The (R)-(+)-N-(3,5-dinitrobenzoyl)-a-methylbenzylamine is reduced by an excess of SnCl2·2H2O to obtain a diamine monomer of (R)-(+)-N-(3,5-diamino benzoyl)-a-methylbenzylamine; S2. Preparing a polyamic acid solution Under nitrogen protection, phthalic anhydride and the diamine monomer are respectively dissolved in an organic solvent to obtain an anhydride solution and a diamine monomer solution; wherein the molar ratio of the phthalic anhydride to the diamine monomer is 2:3; The anhydride solution is slowly added into the diamine monomer solution, reacted in an ice bath for 4h and at room temperature for 12h to obtain a polyamic acid solution with a solid content of 10wt%.

2. The method for preparing a polyamic acid solution according to claim 1, characterized in that: The molar ratio of the 3,5-dinitrobenzoyl chloride to the (R)-(+)-a-methylbenzylamine is 1:1-1.5; the volume ratio of the (R)-(+)-a-methylbenzylamine, propylene oxide and triethylamine is 80-85:1:

85.

3. The method for preparing a polyamic acid solution according to claim 1, characterized in that, The reduction reaction comprises: mixing an excess of SnCl2·2H2O with the (R)-(+)-N-(3,5-dinitrobenzoyl)-a-methylbenzylamine to obtain a mixture; under nitrogen protection, the mixture is dissolved in ethanol and refluxed at 78℃ for 10h; the reaction liquid is purified in deionized water and treated by alkalization using a saturated sodium bicarbonate solution; after being placed in a cold storage for 12h, the organic phase is extracted by ethyl acetate, dried by anhydrous MgSO4, filtered, rotary evaporated to obtain a crude product; the crude product is dissolved in ethyl acetate and precipitated by n-hexane, filtered, washed by n-hexane and dried to obtain the diamine monomer.

4. The method for preparing a polyamic acid solution according to claim 1, characterized in that: The organic solvent is any one of N,N-dimethylacetamide, N-methylpyrrolidone or N,N-dimethylformamide.

5. A polyamic acid solution prepared by the preparation method in any one of claims 1-4.

6. A polyimide, taking the polyamic acid prepared by the preparation method in any one of claims 1-4 as a precursor.

7. A chiral polyimide porous material comprising the polyimide in claim 6.

8. The method for preparing the chiral polyimide porous material as described in claim 7, characterized in that, Comprising the following steps: (1) the polyamic acid solution is cast on a porous substrate, continuously vacuum dried at 50℃, 85℃ and 100℃ for 1.5h respectively to remove the solvent and obtain a polyimide precursor; (2) the polyimide precursor obtained in step (1) is subjected to high-temperature thermal imidization: under atmospheric pressure, continuously heat-treated at 145℃, 165℃, 185℃, 205℃, 225℃, 245℃ and 265℃ for 1h respectively and then cooled to room temperature; Detergent washing, drying at 140℃ for 6h, to obtain the chiral polyimide porous material.

9. The method for preparing the chiral polyimide porous material according to claim 8, characterized in that, The porous substrate comprises the following processing steps: The SiO2 substrate is immersed in an aqueous hydrochloric acid solution under ultrasonic activation at room temperature for 1.5h, washed with ethanol, and dried to obtain an activated porous substrate; The activated porous substrate is placed in toluene solvent with 3-aminopropyl triethoxysilane under nitrogen protection, and reacted at 80℃ for 12h, washed with ethanol, and vacuum dried for 12h to obtain a functionalized porous substrate.

10. The method for preparing the chiral polyimide porous material according to claim 8, characterized in that, In step (2), the detergent washing comprises: preparing a detergent by mixing methanol and tetrahydrofuran at a ratio of 1:1; and performing washing by using the detergent at a temperature of 40-45℃.

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