Polyimide compound, preparation method therefor and use thereof

Abstract

Disclosed in the present invention are a polyimide compound, a preparation method therefor, and a use thereof. The compound has the following structural formula: Formula I, wherein the value ranges of m and n are independently selected from 50-500. In the solution of the present invention, the compound with the structure can be prepared into a polymer-based colorimetric chemical sensor, and the polymer-based colorimetric chemical sensor can be used for fluorine ion and trace water detection and can realize detection even by means of naked eyes. The polymer-based colorimetric chemical sensor has high detection sensitivity and a high response speed and can also be directly used in situ, without the need for a precision instrument, thereby achieving simple and convenient operation. The present invention has good industrial application prospects.

Description

A polyimide compound and its preparation method and application Technical Field

[0001] The present invention relates to the technical field related to polymer materials, and in particular to a polyimide compound and a preparation method and application thereof. Background Art

[0002] Fluoride ions, as an essential micronutrient for the human body, can effectively prevent tooth decay and help treat osteoporosis. However, excessive fluoride ions may harm human health and, to a certain extent, damage the ecological environment. Currently, chemical sensors based on hydrogen bonding are one of the important means of detecting fluoride ions, as fluoride ions can act as hydrogen bond receptors. However, most reported fluoride ion chemical sensors based on hydrogen bond donor compounds are designed based on small molecules and have several drawbacks during detection, such as being limited to solution detection, poor thermal and photostability, and poor practicality.

[0003] Water is essential to our daily lives, but water molecules often exist as impurities in organic solvents. The presence of water can lead to side reactions, catalytic deactivation, or impure products. Therefore, it is necessary to detect trace amounts of water in chemical reactions and industry. Most chemical sensors for water sensing are based on small organic molecules, which often have poor photostability and struggle to detect trace amounts of water.

[0004] Colorimetric chemical sensors have been widely used in many fields due to their advantages such as visual detection, high sensitivity, fast response speed, convenient in-situ use, and no need for precision instruments. This type of sensor plays an important role in analytical chemistry, environmental monitoring, medical diagnosis, etc. However, there is no suitable colorimetric chemical sensor suitable for fluoride ion and trace water detection. Chinese invention patent ZL201910025624.1 discloses a fluoride ion colorimetric sensing polyimide film. The polyimide film is immersed in the solution to be tested. However, it needs to be immersed in the fluoride ion solution for 20-60 minutes before a significant color change can be observed. Although colorimetric sensing and determination of fluoride ions can be achieved, the material has a long response time to fluoride ions, which is not conducive to rapid detection and is not suitable for water detection. Therefore, there is an urgent need to develop a new material that can simply and quickly detect fluoride ions and trace water in organic solvents.

[0005] Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a polyimide compound that can be used to prepare a fluoride ion and water detection reagent.

[0007] According to one aspect of the present invention, a polyimide compound is provided, having the following structural formula:

[0008] Wherein, m and n represent the average number of repeating structural units, and the value range is independently selected from 50-500.

[0009] According to a preferred embodiment of the present invention, at least the following beneficial effects are achieved: the structural compound of the present invention can be prepared into a polymer-based colorimetric chemical sensor, which can be used for the detection of fluoride ions and trace water, and can be detected by the naked eye. It not only has high detection sensitivity and fast response speed, but can also be used directly in situ without the need for precision instruments, is easy to operate, and has good industrial application prospects.

[0010] m and n represent the average number of repeating structural units, and the values ​​can be controlled to be less than 400, less than 300, less than 200 or less than 100, and can be controlled as needed.

[0011] According to another aspect of the present invention, a method for preparing the above-mentioned polyimide compound is provided, comprising the following steps:

[0012] Under a protective atmosphere (such as nitrogen or other inert gases), diamine monomer 1, diamine monomer 2 and 4,4'-oxydiphthalic anhydride are reacted in a strongly polar aprotic organic solvent, first undergoing a preliminary reaction, and then heating to 100-200° C. to continue the reaction to obtain the polyimide compound;

[0013] Wherein, the structural formulas of the diamine monomer 1 and diamine monomer 2 are as follows:

[0014] The preparation method according to a preferred embodiment of the present invention has at least the following beneficial effects: the solution of the present invention does not require separation of intermediate products, and the target product can be prepared in one pot, which is simple to operate.

[0015] In some embodiments of the present invention, the reaction conditions of the preliminary reaction include at least one of the following conditions:

[0016] (1) The reaction time is 6 hours or longer; preferably 24 hours or shorter; more preferably 12 hours; and / or

[0017] (2) The reaction temperature is 20-30°C.

[0018] The initial reaction is carried out at room temperature to save energy. The initial reaction time can be 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, etc. The reaction temperature can be 20°C, 25°C, 30°C, etc.

[0019] In some embodiments of the present invention, the reaction time is 2 hours or longer. Preferably, the reaction time is 36 hours or shorter, for example, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, 28 hours, 30 hours, 32 hours, etc.

[0020] In some embodiments of the present invention, the temperature of the continued reaction is below 180°C.

[0021] In some embodiments of the present invention, the reaction is carried out under the catalysis of a catalyst, and the catalyst is at least one of isoquinoline, acetic anhydride, triethylamine and pyridine.

[0022] In some embodiments of the present invention, the amount of the catalyst is 0.01-0.1 times the mole of the diamine monomer.

[0023] In some embodiments of the present invention, the molar ratio of the diamine monomer 1, the diamine monomer 2 and the 4,4'-oxydiphthalic anhydride is controlled to be 0.9-1.1:0.9-1.1:2.

[0024] In some embodiments of the present invention, the highly polar aprotic organic solvent includes at least one of a phenol solvent, a ketone solvent, an amide solvent, or a sulfoxide organic solvent.

[0025] In some embodiments of the present invention, the highly polar aprotic organic solvent is selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylacetamide and m-cresol.

[0026] According to another aspect of the present invention, a nanofiber membrane is provided. The nanofiber membrane is obtained by electrostatic spinning of a fibrous polyimide compound, and the fibrous polyimide compound is obtained by converting the above-mentioned polyimide compound.

[0027] According to a preferred embodiment of the present invention, the nanofiber membrane has at least the following beneficial effects: the nanofiber film prepared by electrospinning technology has a high specific surface area, and can effectively improve the sensitivity of the interaction between the film and the analyte in the colorimetric detection of fluoride ions and water molecules in organic solvents, and has good application prospects.

[0028] In some embodiments of the present invention, the fibrous polyimide compound is obtained by converting the above-mentioned polyimide compound through treatment with a polar organic solvent, and the polar organic solvent includes an alcohol solvent.

[0029] In some embodiments of the present invention, the alcohol solvent includes methanol and ethanol.

[0030] In some embodiments of the present invention, the polyimide compound is added to a polar organic solvent to generate a fibrous precipitate, which is allowed to stand and filtered, the solvent is removed, and the precipitate is dried to obtain a fibrous polyimide polymer.

[0031] In some embodiments of the present invention, the polyimide compound is directly added to the polar organic solvent in the form of a prepared reaction solution, and the mass ratio of the reaction solution to the polar organic solvent is 1:10-20.

[0032] In some embodiments of the present invention, the mass ratio of the reaction solution to the polar organic solvent is 1:15-20.

[0033] In some embodiments of the present invention, the precipitation drying treatment temperature is 80-100° C.; and / or the time is 8-12 hours.

[0034] In some embodiments of the present invention, the precipitate is dried by vacuum drying.

[0035] In some embodiments of the present invention, the preparation process of the electrospinning solution used in the electrospinning is as follows:

[0036] The fibrous polyimide compound is mixed with the organic solvent I, and the mass proportion of the fibrous polyimide compound is controlled to be 8-18% of the electrospinning solution.

[0037] In some embodiments of the present invention, the organic solvent I includes at least one of a ketone solvent, an amide solvent, or a sulfoxide solvent.

[0038] In some embodiments of the present invention, the organic solvent I includes N,N-dimethylformamide, N,N-diethylformamide, N-methylpyrrolidone, N-ethylpyrrolidone, dimethyl sulfoxide, diethyl sulfoxide and N,N-dimethylacetamide.

[0039] In some embodiments of the present invention, the electrospinning solution is stirred for 3-8 hours before starting electrospinning. The solution is stirred sufficiently to allow the polymer to form fibers better.

[0040] In some embodiments of the present invention, the electrospinning parameters include at least one of the following conditions:

[0041] 1) Voltage 15kV-22kV;

[0042] 2) Infusion rate 0.5 mL / h-1.5 mL / h;

[0043] 3) The receiving distance during spinning is 12cm-20cm;

[0044] 4) The spinning temperature is 20°C-40°C;

[0045] 5) The relative humidity during spinning is 30%-70%;

[0046] 6) The spinning time is 6-15h.

[0047] In some embodiments of the present invention, the nanofiber membrane is dried after electrospinning and then used for later use.

[0048] In some embodiments of the present invention, the drying process is vacuum drying.

[0049] In some embodiments of the present invention, the drying treatment temperature is 100-120° C.; and / or the drying treatment time is 1-3 hours.

[0050] According to another aspect of the present invention, a detection reagent, a sensor or a detection kit is provided, comprising the above-mentioned polyimide compound or the above-mentioned nanofiber membrane.

[0051] According to another aspect of the present invention, a method for detecting fluoride ions or water is provided, comprising the following steps:

[0052] Take the test liquid and soak the nanofiber membrane in the test liquid for more than 1 minute;

[0053] If it is a fluoride ion detection method, the test liquid contains organic solvent II and does not contain water;

[0054] If it is a water detection method, the liquid to be tested contains water, organic solvent II and fluoride ions.

[0055] According to a preferred embodiment of the present invention, the detection method has at least the following beneficial effects: a relatively obvious color difference can be seen in 1 minute, which enables rapid detection, requires only immersion, and is easy to operate. In an anhydrous fluoride ion organic solution, the hydroxyl and imino groups on the surface of the polyimide nanofiber film form hydrogen bonds with the fluoride ions, causing the film to change color, and the color change takes a short time; in an aqueous fluoride ion organic solution, water can interfere with the hydroxyl and imino groups on the surface of the polyimide nanofiber film and the fluoride ions, and the color of the film does not change. Therefore, the technical solution of the present invention can directly detect fluoride ions and trace water in organic solvents by colorimetric comparison.

[0056] In some embodiments of the present invention, the polyimide nanofiber membrane is cut into 1×1 cm squares for testing.

[0057] In some embodiments of the present invention, the soaking time is less than 60 minutes. Controlling the soaking time within 1 hour is more conducive to improving efficiency, and can be specifically 2 minutes, 5 minutes, 10 minutes, 30 minutes, 45 minutes, 50 minutes, etc., which can be set as needed.

[0058] In some embodiments of the present invention, the organic solvent II includes at least one of an alcohol solvent, a nitrile solvent, and a ketone solvent.

[0059] In some embodiments of the present invention, the organic solvent II includes methanol, ethanol, acetonitrile and acetone.

[0060] In some embodiments of the present invention, the detection method is qualitative detection or quantitative detection, that is, qualitative detection can be achieved by naked eye observation, or quantitative or semi-quantitative detection can be achieved by colorimetry or instrumentation.

[0061] In some embodiments of the present invention, when detecting fluoride ions, the nanofiber membrane is immersed in a test solution for 1-60 minutes, then removed and observed for color changes. Only when immersed in a solution containing fluoride ions does the polyimide nanofiber membrane change from light yellow to green, a color change that can be visually identified. The polyimide nanofiber membrane exhibits significant colorimetric detection performance for fluoride ions. As the immersion concentration increases, the color of the membrane gradually changes from light yellow to green, and the color change of the membrane depends on the fluoride ion concentration in the test solution.

[0062] In some embodiments of the present invention, if the test liquid is a fluoride ion detection test liquid, the concentration of fluoride ions is 10 -6 -0.1mol / L. The material of the present invention has high sensitivity and can detect trace fluoride ions even at concentrations as low as 10 -6 Detection can also be achieved in the mol / L range.

[0063] In some embodiments of the present invention, if the test liquid is a fluoride ion detection test liquid, the concentration of fluoride ions is 10 -5 mol / L, 10 -4 mol / L, 10 -3 mol / L, 10 -2 mol / L, etc.

[0064] In some embodiments of the present invention, if the test liquid is a fluoride ion detection test liquid, the concentration of fluoride ions is 10 -4 -0.1mol / L. When fluoride ion 10 -4 When the concentration is above 1 mol / L, the color change is more obvious.

[0065] In some embodiments of the present invention, if the test liquid is water, the concentration of fluoride ions is 0.01-0.1 mol / L.

[0066] In some embodiments of the present invention, when detecting water, the nanofiber film is immersed in the test liquid and the color of the fiber film is observed. If the color of the fiber film does not change, it indicates that the test liquid contains water; if the color of the fiber film changes from light yellow to green, it indicates that the test liquid does not contain water. The degree of color change of the film depends on the water content of the organic solvent. As the water content increases, the degree of color change of the film gradually decreases. By visually observing the degree of color change of the film, the corresponding water content can be estimated. As the water content of the test liquid decreases, the color of the film gradually changes from light yellow to green.

[0067] In some embodiments of the present invention, if the test liquid is water test liquid, the water content is below 10%.

[0068] In some embodiments of the present invention, if the test liquid is water, the water content is 0.05%-10%, such as 0.1%, 0.2%, 0.5%, 1%, 5%, etc.

[0069] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which:

[0071] FIG1 is an infrared spectrum of the fibrous polyimide compound prepared in Example 2 of the present invention;

[0072] FIG2 is a graph showing the effect of the nanofiber membrane prepared in Example 2 of the present invention after being exposed to fluoride ions at the same concentration and for different time periods;

[0073] FIG3 is a diagram showing the effects of the nanofiber membrane prepared in Example 2 of the present invention after being reacted with fluoride ions at different concentrations;

[0074] FIG4 is a graph showing the selectivity effect of the nanofiber membrane prepared in Example 2 of the present invention;

[0075] FIG5 is a diagram showing the effect of the nanofiber membrane prepared in Example 2 of the present invention when detecting different water contents. DETAILED DESCRIPTION

[0076] The following will clearly and completely describe the concept of the present invention and the technical effects produced in conjunction with the embodiments, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. Unless otherwise specified, the test methods used in the embodiments are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, are reagents and materials obtained from commercial channels. Unless otherwise specified, the same parameter in each embodiment has the same value. The embodiments described below are exemplary and are only used to explain the present invention, and are not to be understood as limitations of the present invention.

[0077] In the description of the present invention, if I and II are described, they are only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0078] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0079] The room temperature in the embodiment is specifically 25±5°C.

[0080] Example 1

[0081] In this example, a polyimide compound was prepared. The specific process is as follows:

[0082] (1) Synthesis of diamine monomer 1

[0083] S1. Weigh 0.05 mol of 2,7-dihydroxy-9-fluorenone into a 500 mL single-necked flask, add 0.4 mol of 2,6-dimethylaniline, and then dropwise add 0.025 mol of methanesulfonic acid (CH3SO3H) as a catalyst. Under nitrogen, heat to 150°C and react for 15 hours. After the reaction, cool the reaction mixture to 110°C, add 200 mL of triethylamine, and continue to reflux at 110°C for 20 minutes.

[0084] S2. After stopping the reaction, cool to room temperature, add an appropriate amount of ethanol to precipitate a black viscous solid, let it stand and filter to obtain a crude product, wash the black viscous solid with ethanol several times to a light yellow powder solid, filter and take a solid sample, and dry it in a vacuum drying oven at 110°C for 12 hours to finally obtain 15.81g of pure diamine monomer 1.

[0085] (2) Synthesis of polyimide polymers

[0086] S1. Place 4 mmol of 4,4'-oxydiphthalic anhydride, 2 mmol of diamine monomer 1, and 2 mmol of diamine monomer 2 in a three-necked flask. Pour 14.06 mL of N-methylpyrrolidone solvent into the flask, and finally add 4-5 drops of isoquinoline. Mix thoroughly with magnetic stirring. Under nitrogen, react at room temperature for 24 hours. Then, heat the reactants to 120°C and maintain the temperature for one hour. Then, continue heating to 180°C and maintain the temperature for at least three hours to terminate the reaction.

[0087] Example 2

[0088] In this example, a nanofiber membrane was prepared. The specific process was as follows:

[0089] S1. The reaction solution obtained after the reaction in Example 1 was directly added dropwise to 300 mL of ethanol to produce a fibrous precipitate. After the addition was completed, the precipitate was allowed to stand and filtered; the precipitate was vacuum-dried at 80° C. for 8 hours to obtain a fibrous polyimide polymer.

[0090] S2. After drying, take about 30 mL of N,N-dimethylformamide and stir and dissolve the dried sample. Repeat S2 and dry again to obtain fibrous ODPA-DMOH-BNH resin.

[0091] S3. Preparation of polyimide spinning solution: The fibrous ODPA-DMOH-BNH resin treated in step S2 was dissolved in DMSO to a solid content of 9 wt %, and stirred for more than 3 hours to form a uniform viscous yellow liquid.

[0092] S4. Preparation of polyimide nanofiber membrane

[0093] The mixed spinning solution prepared above was placed in a 10mL syringe and installed on an electrospinning device. Appropriate spinning parameters were adjusted, including a spinning solution applied voltage of 18kV, a liquid infusion rate of 0.55mL / h, a receiving distance of 12cm during spinning, a spinning temperature of 30-35°C, a humidity of 40-50%, a roller receiving method, glossy paper as the receiving substrate, a roller speed of 240r / min, and the preparation was completed in 10 hours. The film was vacuum dried at 100°C for 1 hour to obtain a light yellow polyimide nanofiber membrane.

[0094] Test Case

[0095] This test example tests the structure of the resin prepared in the example and the performance of the nanofiber membrane.

[0096] 1) Structural test:

[0097] The IR spectrum of the product after step S2 in Example 2 is shown in FIG1 . As can be seen from the figure, the IR spectrum at 3000 cm -1 -3600cm -1 The characteristic absorption broad peaks of hydroxyl and imino groups appeared at 2800 cm -1 -3000cm -1 (saturated CH stretching vibration), at 1784 cm -1 and 1718cm -1 The asymmetric stretching vibration absorption peak and the symmetric stretching vibration absorption peak of C=O appeared on the left and right, respectively, at 1367cm -1 The C-N bond stretching vibration absorption peak of the imide ring appeared around 10. It was dissolved in DMF and the number average molecular weight was measured by GPC method to be 7.32×10 4 , PDI = 1.54, the average number of repeating structural units is 58; it can be inferred from the above that the molecular structure of the obtained polyimide is consistent with the theoretical speculation, that is:

[0098] 2) Performance testing:

[0099] i) Response time test of polyimide nanofiber membrane for fluoride ion colorimetric detection

[0100] The nanofiber membrane prepared in Example 2 was cut into 1×1 cm squares and immersed in a solution containing 10 -2 The color change of the fiber membrane was observed at different times in acetonitrile solution with 10 M fluoride ion concentration. -2 In an acetonitrile solution with a fluoride ion concentration of 4,000,000, the color of the fiber membrane varied over time, changing from light yellow to dark green as time progressed (Figure 2). As can be seen from the figure, a clear yellow-green color shift can be observed even within 1 minute, demonstrating that the resulting polyimide nanofiber membrane is capable of rapid colorimetric detection of fluoride ions.

[0101] ii) Sensitivity test of polyimide nanofiber membrane for colorimetric detection of fluoride ions

[0102] The polyimide nanofiber membrane prepared in Example 2 was cut into 1×1 cm squares, and tetrabutylammonium fluoride was dissolved in acetonitrile to prepare fluoride ion concentrations of 10 -6 , 10 -5 , 10 -4 , 10-3 , 10 -2 The polyimide nanofiber membrane was immersed in 0.1M and 0.2M solutions for 10 minutes respectively, and the color change of the fiber membrane was observed. The results showed that with the increase of fluoride ion concentration, the color of the fiber membrane changed from light yellow to dark green (as shown in Figure 3). Even if the polyimide nanofiber membrane was added with fluoride ion concentration as low as 10 -6 M solution, it can be observed that the color of the fiber membrane changes obviously to yellow-green, indicating that the obtained polyimide nanofiber membrane has high sensitivity for colorimetric detection of fluoride ions.

[0103] iii) Selective testing of polyimide nanofiber membranes for fluoride ion detection

[0104] The polyimide nanofiber membrane prepared in Example 2 was cut into 1×1 cm squares and immersed in 10 -2 M's F - 、AcO - 、BF4 - Br - 、Cl - 、ClO4 - 、CN - 、H2PO4 - 、HSO4 - , I - 、NO3 - and PF6 - The color of the polyimide nanofiber membrane changed significantly from light yellow to green with the addition of fluoride ions, while the color of the polyimide nanofiber membrane changed significantly with the addition of AcO - 、BF4 - Br - 、Cl - 、ClO4 - 、CN - 、H2PO4 - 、HSO4 - , I - 、NO3 - and PF6 - , the color of the polyimide nanofiber membrane hardly changed (as shown in FIG4 ), indicating that the obtained polyimide nanofiber membrane has high selectivity for the colorimetric visualization detection of fluoride ions.

[0105] iv) Test of the water colorimetric detection effect of polyimide nanofiber membrane

[0106] Take 8 portions containing 10 -2The acetonitrile solution with a fluorine ion concentration of 1.5 M was then added with a trace amount of water to form a test solution. The water content (v / v) of the test solution was 0%, 0.05%, 0.1%, 0.2%, 0.5%, 1.0%, 5.0%, and 10.0%. Eight portions of the polyimide nanofiber membranes prepared in Example 2 were immersed in the test solution prepared above and the color change of the fiber membranes was observed. The results showed that as the water content of the solution increased, the color of the fiber membrane gradually changed from green to light yellow-green (as shown in Figure 5). As can be seen from the figure, even when the water content was as low as 0.1%, a significant change in the color of the fiber membrane was observed. The resulting polyimide nanofiber membrane has a more sensitive colorimetric sensing effect for the visual detection of water content in acetonitrile.

[0107] The polyimide nanofiber membrane provided by the present invention is prepared from the above-mentioned polyimide polymer using electrospinning technology. This polyimide nanofiber membrane is used to detect fluoride ions in organic solvents. Fluoride ions form strong hydrogen bonds with hydroxyl and imino groups on the surface of the polyimide nanofiber membrane. When fluoride ions are in excess, the hydroxyl and imino groups deprotonate to form oxygen anion species, thereby enhancing the charge transfer effect within the polyimide molecular chain, causing the fiber membrane color to change from light yellow to green. In addition, trace water can interfere with the interaction between fluoride ions and the hydroxyl and imino groups in the polyimide molecular chain, but the color of the nanofiber membrane remains unchanged, remaining light yellow. Therefore, the technical solution of the present invention can directly visually detect fluoride ions and trace water in organic solvents. As shown by the above test results, the polyimide nanofiber membrane of the present invention can be directly cut into sheets and used as a sensor device. It is very convenient to manufacture and is used for colorimetric detection of fluoride ions with a short response time, high sensitivity, and high selectivity. After detecting fluoride ions, the fiber membrane can further detect trace water, which has great application value.

[0108] The embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the scope of the present invention.

Claims

1. A polyimide compound, characterized in that: It has the following structural formula: Wherein, m and n represent the average number of repeating structural units, and the value range is independently selected from 50-500.

2. The method for preparing a polyimide compound according to claim 1, wherein: The steps include: Under a protective atmosphere, diamine monomer 1, diamine monomer 2 and 4,4'-oxydiphthalic anhydride are reacted in a strongly polar aprotic organic solvent, first undergoing a preliminary reaction, and then heating to 100-200° C. to continue the reaction to obtain the polyimide compound; Wherein, the structural formulas of the diamine monomer 1 and diamine monomer 2 are as follows:

3. The method for preparing a polyimide compound according to claim 2, wherein: The preparation method includes at least one of the following conditions: 1) The initial reaction time is 6 hours or longer; preferably 24 hours or shorter; more preferably 12 hours; 2) the initial reaction temperature is 20-30°C; 3) The reaction is continued for more than 2 hours; preferably, the reaction is continued for less than 36 hours; 4) the temperature of the continued reaction is below 180° C.; 5) the reaction is carried out under the catalysis of a catalyst, wherein the catalyst is at least one of isoquinoline, acetic anhydride, triethylamine and pyridine; preferably, the amount of the catalyst is 0.01-0.1 times the mole of the diamine monomer; 6) the molar ratio of the diamine monomer 1, the diamine monomer 2 and the 4,4'-oxydiphthalic anhydride is controlled to be 0.9-1.1:0.9-1.1:2; and 7) The highly polar aprotic organic solvent includes at least one of a phenolic solvent, a ketone solvent, an amide solvent or a sulfoxide organic solvent; preferably, the highly polar aprotic organic solvent is selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylacetamide and meta-cresol.

4. A nanofiber membrane, characterized in that: The nanofiber membrane is obtained by electrostatic spinning of a fibrous polyimide compound, and the fibrous polyimide compound is converted from the polyimide compound according to claim 1 or the polyimide compound prepared by the preparation method according to claim 2 or 3.

5. The nanofiber membrane according to claim 4, characterized in that: The fibrous polyimide compound is obtained by dropwise adding the polyimide compound solution obtained by the above reaction into an alcohol solvent; preferably, the polyimide compound solution is added to ethanol to produce a fibrous precipitate, which is allowed to stand and filtered to remove the solvent, and the precipitate is dried to obtain a fibrous polyimide polymer.

6. The nanofiber membrane according to claim 4, characterized in that: The electrospinning process is as follows: The fibrous polyimide compound is mixed with an organic solvent I, and the mass proportion of the fibrous polyimide compound in the electrospinning solution is controlled to be 8-18%; preferably, the organic solvent I includes at least one of a ketone solvent, an amide solvent or a sulfoxide solvent; preferably, the electrospinning solution is stirred for 3-8 hours before starting electrospinning.

7. The nanofiber membrane according to claim 4, characterized in that: The electrospinning parameters include at least one of the following conditions: 1) Voltage 15kV-22kV; 2) Infusion rate 0.5 mL / h-1.5 mL / h; 3) The receiving distance during spinning is 12cm-20cm; 4) The spinning temperature is 20°C-40°C; 5) The relative humidity during spinning is 30%-70%; and 6) Spinning time is 6-15h.

8. A detection reagent, sensor or detection kit, characterized in that: It comprises the polyimide compound according to claim 1 or the nanofiber membrane according to any one of claims 4 to 7.

9. A method for detecting fluoride ions or water, characterized in that: The steps include: Taking a test liquid, and immersing the nanofiber membrane according to any one of claims 4 to 7 in the test liquid for more than 1 minute; If it is a fluoride ion detection method, the test liquid contains organic solvent II and does not contain water; If it is a water detection method, the liquid to be tested contains water, organic solvent II and fluoride ions; Preferably, the organic solvent II includes at least one of an alcohol solvent, a nitrile solvent, and a ketone solvent.

10. The detection method according to claim 9, characterized in that: If the test liquid is a fluoride ion test liquid, the concentration of fluoride ions is 10 -6 -0.1mol / L; if the test liquid is water test liquid, the concentration of fluoride ions is 0.01-0.1mol / L; preferably, if the test liquid is water test liquid, the water content is below 10%.

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