Fluorine-containing meta-copolymerized polyimide, membrane material thereof and preparation method of membrane material

Abstract

The invention relates to fluorine-containing meta-position copolyimide, a membrane material thereof and a preparation method of the membrane material, the structural formula of the copolyimide is # imgabs0 #, x is 1, 2, 3..., and y is 1, 2, 3.... According to the invention, the fluorine-containing meta-copolymerized polyimide polymer has good film-forming property, toughness and gas separation property. The modified polyimide film has excellent toughness, processability and gas separation property of the modified polyimide film, and also can combine the advantages of the inorganic filler, so that a more efficient gas separation effect is realized. According to the preparation method of the fluorine-containing meta-position copolymerized polyimide film material, the copolymerized polyimide polymer can be directly obtained through one-step solution polycondensation, polyamide acid does not need to be converted into polyimide, and the synthesis preparation process is simple and easy to industrialize.

Description

Technical Field

[0001] The invention relates to the technical field of gas separation membranes, and in particular to a fluorine-containing meta-copolymer polyimide and a membrane material thereof, and a method for preparing the membrane material. Background Art

[0002] Mixed matrix composite membranes are composed of nanofillers as dispersed phases and polymers as continuous phases. They can effectively combine the advantages of the two and break through the performance limit of traditional polymer membranes. In the study of polymer continuous phase matrices, it was found that aromatic polyimide (PI) as a widely used special engineering polymer has inherent development advantages. It was originally developed for the aerospace industry. PI's excellent physical and chemical properties, high design, good mechanical properties, and easy processing make it also regarded as an ideal gas separation membrane material. Faced with the country's increasing demand for clean energy, PI modified separation membranes have gradually emerged in the field of gas separation such as CO2 / N2 and CO2 / CH4. However, the gas permeability and selectivity of most PI membranes are limited by the trade-off of Robeson's upper limit and cannot be improved at the same time. The rigid main chain of PI glassy polymer has a screening effect on different molecules and has high separation performance for gases such as CO2 / CH4 and CO2 / N2.

[0003] However, the biggest drawback of PI as a membrane material is its poor permeability, so people improve the chain structure of PI through modification, prevent the close stacking of chain segments inside PI, weaken or eliminate the mutual attraction between chains, increase solubility, and improve permeability and separation. Summary of the invention

[0004] The main purpose of the present invention is to overcome the defects of the existing fluorinated meta-copolymer polyimide and to provide a new fluorinated meta-copolymer polyimide and its membrane material and a method for preparing the membrane material, which can at least solve the biggest defect of PI as a membrane material, which is poor permeability. Therefore, people improve the chain structure of PI through modification, prevent the close stacking of the internal chain segments of PI, weaken or eliminate the mutual attraction between the chains, increase solubility, and improve the permeability and separation. Technical problems.

[0005] The purpose of the present invention and the solution to the technical problem are achieved by adopting the following technical solutions.

[0006] On the one hand, a fluorine-containing meta-copolymer polyimide is provided, and the structural formula of the copolymer polyimide is:

[0007]

[0008] Among them, x is 1, 2, 3..., and y is 1, 2, 3...

[0009] In an optional embodiment, the glass transition temperature range of the fluorinated meta-copolymer polyimide is 265°C to 293°C, and the 10% thermal weight loss temperature ranges in air and nitrogen are 543°C to 557°C and 575°C to 592°C, respectively; the tensile strength is 74MPa to 93MPa, the elastic modulus is 1.7GPa-1.9GPa, and the elongation at break is 9.9%-12.4%.

[0010] In an optional embodiment, the permeability coefficients of the fluorinated meta-copolymer polyimide to CO2, CH4, and N2 are above 91.7, 4.8, and 6.7 barrer, respectively;

[0011] The separation coefficients of the fluorinated meta-copolymer polyimide for CO2 / CH4 and CO2 / N2 are between 11.1 and 14.6 and 9.3 and 12.1, respectively.

[0012] On the other hand, a method for preparing a fluorine-containing meta-copolymerized polyimide film material is provided, the method comprising:

[0013] Under a nitrogen atmosphere, a fluorine-containing asymmetric diamine monomer, a methyl-containing diamine monomer, an aromatic dianhydride monomer and an organic solvent in a preset ratio are mixed to obtain a mixture;

[0014] Stirring at 80° C. to 100° C. to dissolve the solid raw material in the mixture in the organic solvent, adding a catalyst after the reaction system becomes homogeneous, and continuing to heat to 180° C. to 200° C. to react for 5 h to 8 h to obtain a viscous polymer solution;

[0015] The polymer solution is added into ethanol for sedimentation, and then filtered, washed and dried to obtain a fibrous fluorine-containing copolymer polyimide polymer;

[0016] The fluorine-containing copolymer polyimide polymer is added into an organic solvent to prepare a 5wt% to 10wt% solution, filtered, coated, and dried to obtain the fluorine-containing meta-copolymer polyimide.

[0017] In an optional embodiment, the fluorine-containing asymmetric diamine monomer is 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene, and the methyl-containing diamine monomer is 2,6-diaminotoluene;

[0018] The chemical structural formula of the 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene is:

[0019]

[0020] The chemical structural formula of the methyl diamine monomer 2,6-diaminotoluene is:

[0021]

[0022] In an optional embodiment, the aromatic dianhydride monomer is diphenyl ether tetraacid dianhydride.

[0023] In an optional embodiment, the organic solvent is m-cresol or N-methylpyrrolidone.

[0024] In an optional embodiment, the catalyst is isoquinoline, and the amount of the isoquinoline used is 1% to 3% of the amount of the fluorine-containing asymmetric diamine monomer.

[0025] In an optional embodiment, the preset ratio of the fluorine-containing asymmetric diamine monomer, the methyl-containing diamine monomer, the aromatic dianhydride monomer and the organic solvent is a molar ratio of 1:1-2:2-5.

[0026] In an optional embodiment, in the mixture, the mass percentage of the fluorine-containing asymmetric diamine monomer, the methyl-containing diamine monomer and the aromatic dianhydride monomer in the organic solvent is 5% to 20%.

[0027] On the other hand, an embodiment of the present invention provides a fluorine-containing meta-copolymerized polyimide film material, and the fluorine-containing meta-copolymerized polyimide film material is prepared by the above method.

[0028] By means of the above technical scheme, the method for preparing the fluorinated meta-copolymerized polyimide and its membrane material of the present invention has at least the following advantages:

[0029] (1) The preparation method of the fluorinated meta-copolymerized polyimide and its membrane material of the present invention, by introducing asymmetric bistrifluoromethylbenzene large side groups, methyl side groups, flexible ether bonds and meta-structures into the polymer molecular structure through copolymerization, improves the looseness of the polymer molecular chain, establishes more chain activity space, and makes the fluorinated meta-copolymerized polyimide polymer have good film-forming properties, toughness and gas separation properties. The prepared fluorinated meta-copolymerized polyimide film can be used as a continuous phase in a mixed matrix membrane in the future. Through the organic combination with different inorganic fillers, the mixed matrix membrane not only has the excellent toughness, processability and gas separation properties of the modified polyimide membrane, but also can combine the advantages of inorganic fillers, thereby achieving a more efficient gas separation effect.

[0030] (2) The preparation method of the fluorinated meta-copolymer polyimide film material of the present invention can directly obtain the copolymer polyimide polymer by one-step solution polycondensation without converting the polyamic acid into polyimide. The synthesis preparation process is simple and easy to industrialize.

[0031] In summary, the special fluorinated meta-copolymerized polyimide and its membrane material preparation method of the present invention can at least solve the biggest defect of PI as a membrane material, which is poor permeability. Therefore, people improve the chain structure of PI by modification, prevent the close stacking of the internal chain segments of PI, weaken or eliminate the mutual attraction between chains to increase solubility, and improve the technical problem of permeability and separation. It has many advantages and practical value mentioned above, and no similar design has been published or used in the preparation method of similar fluorinated meta-copolymerized polyimide and its membrane material, so it is indeed innovative. It has great improvements in both the preparation method and function of fluorinated meta-copolymerized polyimide and its membrane material, and has great progress in technology, and has produced good and practical effects. It has multiple enhanced functions compared with the existing preparation method of fluorinated meta-copolymerized polyimide and its membrane material, so it is more suitable for practical use and has wide industrial utilization value. It is truly a novel, progressive and practical new design.

[0032] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention in conjunction with the accompanying drawings.

[0033] The specific preparation method of the fluorinated meta-copolymer polyimide and its membrane material of the present invention is given in detail by the following examples and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the infrared spectrum of the fluorinated meta-copolymer polyimides CPI-1 to CPI-4 in Example 1.

[0035] Figure 2 This is the thermal gravimetric loss curve of the fluorinated meta-copolymer polyimide CPI-1 to CPI-4 prepared in Example 2 under N2.

[0036] Figure 3 This is the thermogravimetric curve of the fluorinated meta-copolymer polyimide CPI-1 to CPI-4 prepared in Example 2 under air.

[0037] Figure 4 It is the DSC curve diagram of the fluorinated meta-copolymer polyimide CPI-1 to CPI-4 prepared in the examples. DETAILED DESCRIPTION

[0038] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the fluorinated meta-copolymer polyimide and the preparation method of the membrane material thereof proposed by the present invention in combination with the accompanying drawings and preferred embodiments.

[0039] On the one hand, an embodiment of the present invention provides a fluorine-containing meta-copolymer polyimide, the structural formula of the copolymer polyimide is:

[0040]

[0041] Among them, x is 1, 2, 3..., and y is 1, 2, 3...

[0042] In an optional embodiment, the glass transition temperature of the fluorinated meta-copolymer polyimide is in the range of 265°C to 293°C. The 10% thermal weight loss temperature in air and nitrogen is in the range of 543°C to 557°C and 575°C to 592°C, respectively. The tensile strength is 74MPa to 93MPa. The elastic modulus is 1.7GPa to 1.9GPa. The elongation at break is 9.9% to 12.4%.

[0043] Exemplarily, the glass transition temperature range of the fluorinated meta-copolymer polyimide may be 265°C, 267°C, 269°C, 270°C, 271°C, 275°C, 277°C, 279°C, 280°C, 281°C, 285°C, 283°C, 293°C, etc. The 10% thermal weight loss temperature range under air is 543°C to 557°C. Exemplarily, the 10% thermal weight loss temperature range under air may be 543°C, 545°C, 547°C, 548°C, 549°C, 553°C, 555°C or 547°C, etc. The tensile strength may be 74MPa, 75MPa, 77MPa, 79MPa, 84MPa, 88MPa, 89MPa, 90MPa, 91MPa, 92MPa or 90MPa, etc. The elastic modulus may be 1.7 GPa, 1.8 GPa or 1.9 GPa, etc. The elongation at break may be 9.9%, 10.0%, 10.4%, 10.8%, 10.9%, 11.2%, 11.5%, 11.7%, 11.9%, 12.0%, 12.3% or 12.4%, etc.

[0044] In an optional embodiment, the permeability coefficients of the fluorinated meta-copolymer polyimide to CO2, CH4, and N2 are above 91.7, 4.8, and 6.7 barrer, respectively.

[0045] Among them, Barrer is the unit used to evaluate gas permeability. -10 cm 3 cm / (cm 2 ·s·cmHg).

[0046] The separation coefficients of fluorinated meta-copolymer polyimide for CO2 / CH4 and CO2 / N2 are between 11.1 and 14.6 and 9.3 and 12.1, respectively.

[0047] For example, the separation coefficient of the fluorinated meta-copolymer polyimide for CO2 / CH4 can be 11.1, 11.2, 12.1, 12.3, 12.6, 12.8, 13.1, 13.4, 13.6, 13.7, 14.2, 14.5 or 14.6, etc. The separation coefficient of the fluorinated meta-copolymer polyimide for CO2 / N2 can be 9.3, 9.6, 10.8, 10.1, 10.4, 10.6, 10.7, 10.2, 10.5, 11.1, 11.2, 12.1, etc.

[0048] On the other hand, a method for preparing a fluorine-containing meta-copolymer polyimide film material is provided, the method comprising: mixing a preset proportion of a fluorine-containing asymmetric diamine monomer, a methyl diamine monomer and an aromatic dianhydride monomer and an organic solvent under a nitrogen atmosphere to obtain a mixture.

[0049] The solid raw materials in the mixture are dissolved in the organic solvent by stirring at 80°C to 100°C, and the catalyst is added after the reaction system becomes homogeneous. The temperature is continued to rise to 180°C to 200°C and the reaction is carried out for 5h to 8h to obtain a viscous polymer solution.

[0050] The polymer solution is added into ethanol for sedimentation, and then filtered, washed and dried to obtain a fibrous fluorine-containing copolymer polyimide polymer.

[0051] The fibrous fluorine-containing copolymer polyimide polymer is added into an organic solvent to prepare a 5wt% to 10wt% solution, filtered, coated, and dried to obtain a fluorine-containing meta-copolymer polyimide membrane material.

[0052] In an optional embodiment, the fluorine-containing asymmetric diamine monomer is 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene, and the methyl-containing diamine monomer is 2,6-diaminotoluene.

[0053] The chemical structure of 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene is:

[0054]

[0055] The chemical formula of methyl diamine monomer 2,6-diaminotoluene is:

[0056] In an optional embodiment, the aromatic dianhydride monomer is diphenyl ether tetracarboxylic dianhydride.

[0057] In an optional embodiment, the organic solvent is m-cresol or N-methylpyrrolidone.

[0058] In an optional embodiment, the catalyst is isoquinoline, and the amount of isoquinoline used is 1% to 3% of the amount of the fluorine-containing asymmetric diamine monomer.

[0059] In an optional embodiment, the preset ratio of the fluorine-containing asymmetric diamine monomer, the methyl-containing diamine monomer, the aromatic dianhydride monomer and the organic solvent is a molar ratio of 1:1-2:2-5.

[0060] In an optional embodiment, in the mixture, the mass percentage of the fluorine-containing asymmetric diamine monomer, the methyl-containing diamine monomer and the aromatic dianhydride monomer in the organic solvent is 5% to 20%.

[0061] Illustratively, in the mixture, the mass percentage of the fluorine-containing asymmetric diamine monomer, the methyl diamine monomer and the aromatic dianhydride monomer in the organic solvent can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 15%, 16%, 17%, 18%, 19% or 20%.

[0062] The preferred embodiments of the present invention will be described in more detail below in conjunction with specific examples.

[0063] The following are the raw materials and medicines used in the examples:

[0064] 3,5-Bis(trifluoromethyl)phenyl-2,4-diaminobenzene: purity 99%. 2,6-Diaminotoluene: purity 99%. Diphenyl ether tetraacid dianhydride: purity 99%. Metacresol: purity 99%. Isoquinoline: purity 99%. N-Methylpyrrolidone: purity 99%. N,N-Dimethylacetamide: purity 99%.

[0065] Example 1

[0066] This embodiment provides a method for preparing a fluorine-containing meta-copolymerized polyimide film material, the steps of which are as follows:

[0067] (1) In a 100 mL dry three-necked flask equipped with nitrogen protection and a condenser, 2.5618 g (8 mmol) of diamine monomer 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene, 0.2443 g of 2,6-diaminotoluene (2 mmol) and 3.1021 g (10 mmol) of diphenyl ether tetracarboxylic dianhydride were added respectively, and then 29 mL of m-cresol (solid content of the system was 20%) and 0.10 mmol of isoquinoline were added in sequence. The mixture was stirred at 80° C. for half an hour until the monomers were completely dissolved, and then the temperature was continued to rise to 180° C. for reaction for 10 hours to obtain a viscous polymer solution. The reaction was terminated, and the polymer solution was poured into ethanol for sedimentation, and further filtered, washed and dried to obtain a fibrous copolymer polyimide polymer containing bis(trifluoromethyl)benzene and methyl asymmetric meta-structure, which was recorded as CPI-1 with a yield of 99%.

[0068] (2) Add the polyimide polymer prepared in step (1) to an appropriate amount of N-methylpyrrolidone to prepare a 10 wt% solution, filter and coat, and further vacuum dry at 90° C. for 12 h to obtain the corresponding asymmetric meta-structure copolymer polyimide film containing bistrifluoromethylbenzene and methyl side groups.

[0069] Example 2

[0070] This embodiment provides a method for preparing a fluorine-containing meta-copolymer polyimide film, the steps are as follows:

[0071] (1) 1.6012 g (5 mmol) of diamine monomer 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene, 0.6109 g of 2,6-diaminotoluene (5 mmol) and 3.1021 g (10 mmol) of diphenyl ether tetracarboxylic dianhydride were added respectively, and then 25 mL of N-methylpyrrolidone (solid content of the system was 10%) and 0.12 mmol of isoquinoline were added in sequence. The mixture was stirred at 90° C. for half an hour until the monomers were completely dissolved, and then the temperature was raised to 190° C. for reaction for 6 hours. The reaction was terminated, and the polymer solution was poured into ethanol for precipitation, and further filtered, washed and dried to obtain a fibrous fluorine-containing meta-copolymer polyimide containing bis(trifluoromethyl)benzene and a methyl asymmetric meta-structure, which was recorded as CPI-2 with a yield of 98%.

[0072] (2) Add the fluorinated meta-copolymer polyimide to an appropriate amount of N-methylpyrrolidone to prepare a 5 wt% solution, filter and coat the solution, and further vacuum dry at 70°C for 24 hours to obtain the corresponding fluorinated meta-copolymer polyimide film containing bistrifluoromethylbenzene and methyl side groups with an asymmetric meta-structure.

[0073] Example 3

[0074] This embodiment provides a method for preparing a fluorine-containing meta-copolymer polyimide film, the steps are as follows:

[0075] (1) In a 100 mL dry three-necked flask equipped with nitrogen protection and a condenser, 2.5619 g (8 mmol) of diamine monomer 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene, 0.2444 g of 2,6-diaminotoluene (2 mmol) and 3.1021 g (10 mmol) of diphenyl ether tetracarboxylic dianhydride were added respectively, and then 25 mL of m-cresol (solid content of the system was 10%) and 0.12 mmol of isoquinoline were added in sequence. The mixture was stirred at 100° C. for half an hour, and after the monomers were completely dissolved, the temperature was continued to rise to 195° C. and reacted for 10 hours to obtain a viscous polymer solution. The reaction was terminated, and the polymer solution was poured into ethanol for sedimentation, and further filtered, washed and dried to obtain a fibrous fluorine-containing meta-copolymer polyimide containing bis(trifluoromethyl)benzene and methyl asymmetric, which was recorded as CPI-3 with a yield of 99%.

[0076] (2) Add the fluorinated meta-copolymer polyimide to an appropriate amount of N,N-dimethylacetamide to prepare a 10 wt% solution, filter and coat the solution, and further vacuum dry at 90°C for 12 h to obtain the corresponding fluorinated meta-copolymer polyimide film containing bistrifluoromethylbenzene and methyl side groups with an asymmetric meta-structure.

[0077] The infrared spectra FT-IR of the fluorinated meta-copolymer polyimides CPI-1 to CPI-4 prepared from diamine monomers 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene, 2,6-diaminotoluene and diphenyl ether tetracarboxylic dianhydride are as follows: Figure 1 As shown, the thermal weight loss curves of copolymer polyimide CPI-1 to CPI-4 under N2 and air are as follows Figure 2 and Figure 3 As shown, the DSC curves of copolymerized polyimide CPI-1 to CPI-4 are shown in Figure 4 Its intrinsic viscosity in DMAc, Mw, Mn value and polydispersity index (PDI) when dissolved in DMF (N,N-dimethylformamide) are shown in Table 1, its solubility properties are shown in Table 2, its mechanical properties are shown in Table 3, and its gas separation performance is shown in Table 4.

[0078] Comparative Example 1

[0079] A method for preparing a fluorine-containing meta-copolymer polyimide film, comprising the following steps:

[0080] (1) A 100 mL three-necked round-bottom flask with mechanical stirring and nitrogen inlet and outlet was placed in a constant temperature ice water bath, 0.0025 mol of DETDA was dissolved in 17.6235 g of N-methylpyrrolidone (NMP), the solid content of the reaction system was 25%, after the dissolution was completed, 0.01 mol of 6FDA was added and continued to stir, and 0.0075 mol of MPD was added after 0.5 h to 1 h. The solution was reacted in an ice water bath under nitrogen protection for 24 hours to form a viscous polyamic acid solution.

[0081] (2) Add 0.05 mol of acetic anhydride and 0.025 mol of anhydrous pyridine to the obtained polyamic acid solution for chemical imidization. After reacting at room temperature for 24 hours, the polymer is precipitated in methanol, washed with methanol, placed in a vacuum oven, and dried to remove the residual solvent to obtain a dry copolymerized polyimide powder. The copolymerized polyimide powder is dissolved, the solid content of the casting solution is 5.0 wt%, and filtered with a 0.45 μm polytetrafluoroethylene filter membrane.

[0082] (3) Take 0.70g of the dried copolymerized polyimide powder and dissolve it in N,N-dimethylformamide (DMF), stir until it is completely dissolved, and the solid content of the casting liquid is 5.0wt%. Filter it with a 0.45μm polytetrafluoroethylene filter membrane, inject the filtered solution into a flat glass culture dish, and then put it into a vacuum oven and dry it to obtain a polyimide gas separation membrane.

[0083] Table 1. Intrinsic viscosity of fluorinated meta-copolymer polyimide and Mw (molecular weight), Mn value and polydispersity index (PDI) dissolved in DMF

[0084]

[0085] In Table 1, TFDB is 4,4'-diamino-2,2'-bis(trifluoromethyl)biphenyl, TDA is 2,4-toluenediamine or 2,6-toluenediamine, ODPA is 4,4'-oxydiphthalic anhydride, and GPC is the molar content.

[0086] Table 2. Solubility properties of copolymerized polyimide

[0087]

[0088] Note: ++, 0.1g sampledissolved in 1mL solvent (10wt%); +, soluble at 5wt%; Δ, solube at high temperature; s, swell at room temperature; --, insoluble at room temperature.

[0089] Table 3. Mechanical properties of copolymerized polyimide

[0090]

[0091] Table 4. Gas permeability coefficient (P) and selectivity (α) of copolymerized polyimide

[0092]

[0093] It can be seen from Tables 1 to 4 that the various properties of the fluorinated meta-copolymer polyimide provided in the embodiments of the present invention are better than those of the copolymer polyimide provided in Comparative Example 1. In addition, the fluorinated meta-copolymer polyimide provided in the embodiments of the present invention can improve the gas separation performance of polyimide, so that it has significant advantages when used as a material for the continuous phase of the polymer of the mixed matrix membrane, thereby further breaking through the upper limit of the gas separation performance of the mixed matrix membrane. The fluorinated meta-copolymer polyimide membrane material prepared by the method for preparing the fluorinated meta-copolymer polyimide membrane material provided in the embodiments of the present invention provides more reference value for the selection of the continuous phase of the polymer of the mixed matrix membrane. The gas permeability and selectivity of polyimide membranes are greatly affected by the chemical structure of diamines. Through systematic modification and optimization, on the basis of not reducing the rigidity of the diamine structural unit, a more convenient synthetic process route is used to introduce flexible ether bonds, asymmetric bistrifluoromethylbenzene large side groups, methyl side groups and meta structures into the polyimide molecular structure, and the structure of the polymer repeating unit is adjusted by copolymerization to prepare a fluorinated meta copolymer polyimide, which effectively improves its tight rigid molecular skeleton spatial stacking. On the one hand, increasing the flexibility of the polymer chain improves the film-forming property and gas separation performance of the polyimide, and on the other hand, it maintains the original excellent thermal and mechanical properties of the polyimide. The combination of these modification methods makes the fluorinated meta copolymer polyimide polymer show higher film-forming property, mechanical properties and gas separation performance. This type of fluorinated meta copolymer polyimide has important potential application value in the field of mixed matrix membrane gas separation.

[0094] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes by using the methods and technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A fluorinated meta-copolymer polyimide, characterized in that: The structural formula of the copolymerized polyimide is: Among them, x is 1, 2, 3..., and y is 1, 2, 3...

2. The fluorinated meta-copolymer polyimide according to claim 1, characterized in that: The glass transition temperature of the fluorinated meta-copolymer polyimide is in the range of 265°C to 293°C, and the 10% thermal weight loss temperature in air and nitrogen is in the range of 543°C to 557°C and 575°C to 592°C respectively; the tensile strength is 74MPa to 93MPa, the elastic modulus is 1.7GPa to 1.9GPa, and the elongation at break is 9.9% to 12.4%.

3. The fluorinated meta-copolymer polyimide according to claim 1, characterized in that: The permeability coefficients of the fluorinated meta-copolymer polyimide to CO2, CH4, and N2 are above 91.7, 4.8, and 6.7 barrer, respectively; The separation coefficients of the fluorinated meta-copolymer polyimide for CO2 / CH4 and CO2 / N2 are between 11.1 and 14.6 and 9.3 and 12.1, respectively.

4. A method for preparing a fluorinated meta-copolymerized polyimide film material, characterized in that: The method comprises: Under a nitrogen atmosphere, a fluorine-containing asymmetric diamine monomer, a methyl-containing diamine monomer, an aromatic dianhydride monomer and an organic solvent in a preset ratio are mixed to obtain a mixture; Stirring at 80° C. to 100° C. to dissolve the solid raw material in the mixture in the organic solvent, adding a catalyst after the reaction system becomes homogeneous, and continuing to heat to 180° C. to 200° C. to react for 5 h to 8 h to obtain a viscous polymer solution; The polymer solution is added into ethanol for sedimentation, and then filtered, washed and dried to obtain the fluorine-containing copolymer polyimide polymer according to any one of claims 1 to 3; The fibrous fluorine-containing copolymer polyimide polymer is added into an organic solvent to prepare a 5wt% to 10wt% solution, filtered and coated, and dried to obtain a fluorine-containing meta-copolymer polyimide membrane material.

5. The method for preparing the fluorine-containing meta-copolymer polyimide film material according to claim 4, characterized in that: The fluorine-containing asymmetric diamine monomer is 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene, and the methyl-containing diamine monomer is 2,6-diaminotoluene; The chemical structural formula of the 3,5-bis(trifluoromethyl)phenyl-2,4-diaminobenzene is: The chemical structural formula of the methyl diamine monomer 2,6-diaminotoluene is:

6. The method for preparing the fluorine-containing meta-copolymer polyimide film material according to claim 4, characterized in that: The aromatic dianhydride monomer is diphenyl ether tetraacid dianhydride.

7. The method for preparing the fluorine-containing meta-copolymer polyimide film material according to claim 4, characterized in that: The organic solvent is m-cresol or N-methylpyrrolidone.

8. The method for preparing the fluorine-containing meta-copolymer polyimide film material according to claim 4, characterized in that: The catalyst is isoquinoline, and the amount of the isoquinoline used is 1% to 3% of the amount of the fluorine-containing asymmetric diamine monomer.

9. The method for preparing the fluorine-containing meta-copolymer polyimide film material according to claim 4, characterized in that: The preset ratio of the fluorine-containing asymmetric diamine monomer, the methyl-containing diamine monomer, the aromatic dianhydride monomer and the organic solvent is a molar ratio of 1:1-2:2-5.

10. The method for preparing the fluorine-containing meta-copolymer polyimide film material according to claim 4, characterized in that: In the mixture, the mass percentage of the fluorine-containing asymmetric diamine monomer, the methyl-containing diamine monomer and the aromatic dianhydride monomer in the organic solvent is 5% to 20%.

11. A fluorine-containing meta-copolymer polyimide film material, characterized in that: The fluorinated meta-copolymer polyimide membrane material is prepared by the method described in any one of claims 4-9.

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