A copolyimide film, its preparation method and application

Abstract

This invention discloses a copolymerized polyimide film, its preparation method, and its application, belonging to the field of polymer materials, and is used in gas separation. The copolymerized microporous polymer membrane is prepared by introducing two diamine monomers with significantly different spatial configurations: a three-dimensional rigid cage-like triterpenoid diamine and a brominated fluorenyl diamine with a twisted non-planar structure, which are polycondensed with aromatic dianhydrides and then subjected to thermal imidization. The resulting copolymerized microporous polyimide membrane is mainly used for gas separation. The copolymerized microporous polyimide (COPI) membrane proposed in this invention effectively inhibits the tight stacking of molecular chains through the special spatial structures of the two diamine monomers, significantly increasing the free volume of the membrane material and overcoming the trade-off between permeability and selectivity. Furthermore, the introduction of bromine substitution as a structural control site restricts bond rotation through steric hindrance, thereby stabilizing the structure, slowing the release of free volume, delaying micropore collapse, and thus synergistically improving separation performance (selectivity and permeability) and anti-aging ability.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a copolyimide film, its preparation method, and its application. Background Technology

[0002] Highly efficient gas separation technology has become a key approach to promoting energy structure optimization and industrial emission reduction. Traditional separation methods are energy-intensive and require complex equipment, making it difficult to meet the demands of green and low-carbon development. In contrast, membrane separation technology, with its advantages of low energy consumption, high efficiency, and modularity, has shown great potential in areas such as carbon dioxide capture, natural gas purification, and biogas upgrading.

[0003] Traditional polyimide molecules are tightly packed, and gas permeation depends on the instantaneous gaps formed by chain segment movement. Its performance follows a "trade-off effect" of high selectivity but corresponding to low permeability, and physical aging is significant. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a copolyimide film, its preparation method, and its application.

[0005] In a first aspect, the present invention provides a copolyimide film comprising the following structure: , Where m and n are both in the range of 1 to 10, and the sum of m and n is 10; specifically, m:n is 9:1; 8:2; 7:3; 6:4:5:5, 4:6; 3:7, 2:8; 1:9.

[0006] Preferably, the ratio of m:n is 7:3, 5:5, or 3:7.

[0007] A more preferred m:n ratio is 5:5.

[0008] A includes any of the following: .

[0009] B includes any of the following: .

[0010] C includes any of the following: .

[0011] Secondly, the present invention provides a method for preparing the above-mentioned copolyimide film, comprising the following steps: In a protective atmosphere, the dianhydride compound, the first diamine monomer, and the second diamine monomer are fully dissolved in an organic solvent and reacted in the presence of a catalyst to obtain a reaction solution. The reaction solution was treated by solvent precipitation and then dried to obtain the copolyimide. The copolyimide was dissolved in a volatile solvent and then cultured to obtain a copolyimide film.

[0012] Furthermore, the molar ratio of the total diamine monomer, the dianhydride compound, and the catalyst is 1:1:(0.1-2).

[0013] Furthermore, the dianhydride compound includes One of them.

[0014] Furthermore, the first diamine monomer includes At least one of them.

[0015] Furthermore, the second diamine monomer includes At least one of them.

[0016] Furthermore, the organic solvent includes at least one selected from m-cresol, tetrahydrofuran, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, 1,4-dioxane, and chloroform.

[0017] Furthermore, the catalyst includes a basic catalyst or an acidic catalyst.

[0018] Furthermore, the alkaline catalyst includes at least one of isoquinoline and triethylamine.

[0019] Furthermore, the acidic catalyst includes at least one of benzoic acid and p-hydroxybenzoic acid.

[0020] Furthermore, the volatile solvent includes at least one of tetrahydrofuran, 1,4-dioxane, chloroform, and dichloromethane.

[0021] Furthermore, the reaction temperature is 100-160℃, and the reaction time is 6-12h.

[0022] Furthermore, the solvent precipitation method specifically includes: adding the reaction solution to a mixed solution of ethanol and water, stirring to precipitate the polyimide, and then filtering to obtain the copolyimide.

[0023] Furthermore, the drying temperature is 80-120℃, and the drying time is 10-20 h.

[0024] This invention limits the drying temperature to 80-120℃ and the time to 10-20 h, which can fully remove residual solvent and inhibit excessive relaxation of molecular chains and micropore collapse. If the temperature is too low or the time is insufficient, solvent residue will easily remain, crowding out free volume and reducing permeability. If the temperature is too high or the time is too long, it will aggravate chain rearrangement, destroy the microporous structure, and deteriorate gas separation performance and anti-aging stability. Thirdly, the present invention also provides an application of the copolyimide film described above and the copolyimide film prepared by the preparation method in gas separation.

[0025] Furthermore, the gas separation includes at least one of separating CO2 from a CO2 / CH4 gas mixture, separating O2 from an O2 / N2 gas mixture, separating H2 from an H2 / CH4 gas mixture, or separating CO2 from a CO2 / N2 gas mixture.

[0026] Compared with the prior art, the present invention has the following beneficial effects: (1) The copolyimide (COPI) film proposed in this invention effectively inhibits the tight stacking of molecular chains through the special spatial structure of two diamine monomers, significantly increases the free volume of the membrane material, effectively breaks through the trade-off between permeation and selectivity, and introduces bromine substitution as a structural regulation site to restrict bond rotation through steric hindrance, thereby stabilizing the structure, slowing down the release of free volume and delaying micropore collapse, thus synergistically improving separation performance (selectivity, permeability) and anti-aging ability. Attached Figure Description

[0027] Figure 1 These are the infrared spectra of the thin films obtained in Examples 1-3 and Comparative Example 1 of the present invention; Figure 2 These are the 1H NMR spectra of the thin films obtained in Examples 1-3 and Comparative Example 1 of this invention; Figure 3 These are thermogravimetric analysis diagrams of the thin films obtained in Examples 1-3 and Comparative Example 1 of the present invention; Figure 4 The glass transition temperature diagrams are for the thin films obtained in Examples 1-3 and Comparative Example 1 of this invention. Figure 5 These are rotational energy barriers and dihedral angle analysis diagrams of the thin films obtained in Examples 1-3 and Comparative Example 1 of the present invention; Figure 6 These are gas separation performance diagrams of gas separation membranes in Embodiment 1 of the present invention, Comparative Examples 1-2, and the prior art. Detailed Implementation

[0028] Hereinafter, embodiments of the present invention will be described in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0029] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" means that all real numbers between "0~5" have been listed in this article, and "0-5" is just a shortened representation of these numerical combinations. In addition, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0031] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0032] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0033] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0034] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0035] Unless otherwise specified, in this application, the terms "first," "second," "third," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0036] In this application, the terms "multiple", "various", etc., refer to two or more kinds.

[0037] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0038] Unless otherwise stated, for any experimental steps or conditions not specified in this invention, the conventional experimental steps or conditions described in the literature in this field can be followed; the raw materials or instruments used are all commercially available conventional products, including but not limited to the raw materials or instruments used in the embodiments of this application; the values ​​of each parameter mentioned in this application can be determined by various commonly used testing methods in this field, for example, they can be determined according to the testing methods given in the embodiments of this application.

[0039] I. Raw materials used in this invention 1,2,6-Diaminotriptene, abbreviated as DATRI The DATRI used in this invention was prepared according to the method described in the reference (Cho, YJ and Park, HB (2011), HighPerformance Polyimide with High Internal Free Volume Elements. Macromol. Rapid Commun., 32: 579-586.): Nitration: 30 g of triptene and 27 g of potassium nitrate were added to 500 mL of acetonitrile, and then trifluoroacetic anhydride (60 mL) was added dropwise. The reaction mixture was placed at room temperature and stirred overnight. The solid was filtered, washed twice with methanol, dried in an oven at 100 °C for 12 h, and slurried three times with dichloromethane (200 mL × 3). The remaining white solid was pure 2,6-diaminotriptene.

[0040] Reduction: Reflux reaction. 10 g of dinitrotriptene was weighed into a 500 mL single-necked flask under argon protection. 250 mL of anhydrous ethanol was added as a solvent, and stirring was initiated. 10 mL of hydrazine hydrate was added, followed by 2 g of palladium on carbon as a catalyst under argon protection. The temperature was raised to 50 °C, and after the reaction stabilized, the temperature was further increased to 120 °C. After two hours of reaction, a homogeneous solution was obtained. The palladium on carbon catalyst was removed with diatomaceous earth, and half of the solvent was removed by rotary evaporation. The precipitate was poured into deionized water, filtered to obtain the solid, and dried in a vacuum oven at 80 °C for 12 hours to obtain DATRI.

[0041] The synthetic route for DATRI is as follows: ; 2,9,9-Bis(3-bromo-4-aminophenyl)fluorene The 9,9-bis(3-bromo-4-aminophenyl)fluorene used in this invention was prepared according to the method described in the literature (Wei Zhao, Simultaneously enhanced gas separation and anti-aging performance of intrinsic microporous polyimide by dibromo substitution, Journal of Membrane Science, Volume 687, 2023, 122081, ISSN 0376-7388). 0.2 mol of 9,9-bis(4-aminophenyl)fluorene (FDA: 69.6 g) and 0.4 mol of N-bromosuccinimide (NBS: 71.2 g) were dissolved separately in 1000 mL of dichloromethane. After thorough stirring and dissolution, the NBS solution was added dropwise to the FDA solution while stirring continuously for 0.5 h. After the reaction was complete, the solution changed from transparent to brown. The resulting mixed solution was rotary evaporated and dried under vacuum at 80 °C to obtain a mixture containing the target product.

[0042] Purification: First, dissolve the mixture in an appropriate amount of ethyl acetate, allowing the crude sample to precipitate slightly. Pour the solution into a heating mantle equipped with a mechanical stirrer, heat and stir at 30-35 °C. After slurrying for 2 hours, centrifuge the mixture. Wash the solid product obtained by centrifugation with an organic solvent to obtain the target product. Rotary evaporate the remaining ethyl acetate phase solution after centrifugation, repeating the above steps. Dry the resulting white solid in a vacuum oven at 80 °C for 12 hours to obtain high-purity 9,9-bis(3-bromo,4-aminophenyl)fluorene.

[0043] 3. In this invention, each abbreviation represents the following raw materials: 6FDA: 4,4'-(hexafluoroisopropylidene) phthalic anhydride; BAFL-NH2: 9,9-bis(3-bromo-4-aminophenyl)fluorene; TDA-NH2: 2,6-Diaminotriptene; BTDA: 3,3',4,4'-benzophenone tetracarboxylic dianhydride; 6FCDA: 4,4'-(hexafluoroisopropylidene)dioxophthalic anhydride; TMSBI-DA: 4,4'-(9,9-dimethylfluorene-2,7-diyl)phthalic anhydride; DSDA: 3,3',4,4'-Diphenylsulfone tetracarboxylic dianhydride.

[0044] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings.

[0045] Example 1 The copolyimide (COPI) film synthesized in this embodiment (denoted as COPI B / T-6FDA (5:5)) has the following chemical structural formula: , Among them, the diamine monomer containing the bromofluorene group is BAFL-NH2, and the diamine monomer of tripterene is TDA-NH2, with m:n=5:5.

[0046] A method for preparing a copolyimide film specifically includes the following steps: Under a nitrogen atmosphere, 9,9-bis(3-bromo-4-aminophenyl)fluorene (BAFL-NH2) (0.5035 g, 1 mmol) and 2,6-diaminotriptene (TDA-NH2) (0.284 g, 1 mmol) monomers in a 5:5 molar ratio were added to a polymerization tube equipped with a magnetic stir bar. 6 mL of m-cresol organic solvent was added, and stirring was started. 0.8884 g of 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) (2 mmol) was weighed out. The total molar amount of the two diamine monomers was equal to the molar amount of 6FDA monomer. 6FDA was poured into the polymerization tube, followed by 0.2 mL of isoquinoline catalyst. The temperature was gradually heated to 160 °C. After complete dissolution, the reaction proceeded until the magnetic stir bar could no longer rotate (viscosity approximately 10 w cps), yielding a viscous reaction solution.

[0047] The resulting viscous reaction solution was slowly poured into a mixed solution of ethanol and water (volume ratio 1:1), and after standing, the precipitate was formed. After repeating this process three times, the mixture was dried in a vacuum oven at 90 °C for 2 days to obtain a copolyimide polymer, which was used for film laying. 0.2 g of copolyimide polymer was dissolved in 10 ml of tetrahydrofuran (THF). The solution was stirred thoroughly for 24 h to dissolve the solute. The solution was then sonicated for 30 min and filtered through a 0.45 μm PTFE filter into a smooth petri dish. After solvent evaporation, an isotropic film was obtained. After complete solvent evaporation, a transparent film with a thickness of 60 μm was obtained. The film was dried in a vacuum oven at 100 °C for 12 h and then further heated in a tube furnace under N2 atmosphere at 230 °C for 2 h to ensure complete removal of residual solvent, thus obtaining the COPI film.

[0048] NMR structural characterization of COPI thin films: COPI (B / T=5:5): ¹H NMR (400 MHz, DMSO-d6): δ 8.29 (s, 1.0H), 8.16 (s,0.5H), 8.07 (s, 1.0H), 7.98 (s, 0.5H), 7.77 (s, 1.0H), 7.22–7.14 (m, 2.0H), 6.55 (d, J = 8.2 Hz, 0.5H), 6.46 (s, 2.5H), 2.20 (s, 0.5H), 1.35 (d, J = 22.3Hz, 13.0H).

[0049] Performance testing of COPI films: The pure gas permeation performance of the obtained membrane was measured using a constant volume / swing pressure method. To remove any contaminants from the permeation system and membrane, the system with the masked membrane within the sealed permeation unit was degassed for 24 hours. The pure gas permeabilities of He, H2, N2, O2, CH4, and CO2 were measured at 2 bar and 35 °C. The gas permeabilities were determined as follows:

[0050] In the formula, the permeability coefficient P is expressed in terms of barrer (1 barrer = 10). -10 cm 3 (STP)·cm cm -2 ·s -1 ·cm Hg -1 Or 7.5×10 -18 m 3 (STP)·mm -2 ·s -1 ·Pa -1 Units are: Pup (cmHg), T (K), and Vd (cm³). 3 ); dp / dt represents the change in osmotic pressure (cm Hg·s). -1 A is the effective area of ​​the membrane (cm²). 2 ); l is the thickness (cm); R is the gas constant, equal to 0.278cm. 3 cm Hg cm -3 (STP)·K -1 Pure gas selectivity AB is calculated as follows:

[0051] In this study, the permeability coefficients of gases A and B are denoted as PA and PB, respectively, and DA, DB, SA, and SB are the diffusion coefficients and solubility coefficients of A and B, respectively. Each polymer membrane was tested three times, and the deviations in permeability and selectivity were within 5%. Specific results are as follows:

[0052] The permeability coefficients are as follows: hydrogen 422.15 Barrer, oxygen 57.84 Barrer, nitrogen 10.97 Barrer, carbon dioxide 338.97 Barrer, and methane 8.00 Barrer. The selectivity coefficients for carbon dioxide / methane are 42.37, for hydrogen / methane 52.77, for oxygen / nitrogen 5.27, and for carbon dioxide / nitrogen 30.89.

[0053] Example 2 Unlike Example 1, the copolyimide (COPI) film synthesized in this example (denoted as COPI B / T-6FDA (7:3)) has the following chemical structural formula: , Among them, the diamine monomer containing the bromofluorene group is BAFL-NH2, and the diamine monomer of tripterene is TDA-NH2, with m:n=7:3.

[0054] A method for preparing a copolyimide film specifically includes the following steps: Under a nitrogen atmosphere, 9,9-bis(3-bromo-4-aminophenyl)fluorene (BAFL-NH2) (1.762 g, 3.5 mmol) and 2,6-diaminotriptene (TDA-NH2) (0.426 g, 1.5 mmol) monomers in a molar ratio of 7:3 were added to a polymerization tube equipped with a magnetic stir bar. 6 mL of m-cresol organic solvent was added, and stirring was started. 2.221 g of 4,4'-(hexafluoroisopropylidene) phthalic anhydride (6FDA) (5 mmol) was weighed. The total molar amount of the two diamine monomers was equal to the molar amount of 6FDA monomer. 6FDA was poured into the polymerization tube, followed by 0.2 mL of isoquinoline catalyst. The temperature was gradually heated to 160 °C. After complete dissolution, the reaction proceeded until the magnetic stir bar could no longer rotate (viscosity approximately 10 w cps), yielding a viscous reaction solution.

[0055] The resulting viscous reaction solution was slowly poured into a mixed solution of ethanol and water (volume ratio 1:1), and after standing, the precipitate was formed. After repeating this process three times, the mixture was dried in a vacuum oven at 90 °C for 2 days to obtain a copolyimide polymer, which was used for film laying. 0.2 g of copolyimide polymer was dissolved in 10 ml of tetrahydrofuran (THF) and stirred thoroughly for 24 h to dissolve the solute. The solution was then sonicated for 30 min and filtered through a 0.45 μm PTFE filter into a smooth petri dish. After solvent evaporation, an isotropic film was obtained. After complete solvent evaporation, a transparent film with a thickness of 60 μm was obtained. The film was dried in a vacuum oven at 100 °C for 12 h and then further heated at 230 °C for 2 h in a tube furnace under N2 atmosphere to ensure complete removal of residual solvent, thus obtaining the COPI film.

[0056] NMR structural characterization of COPI thin films: COPI (B / T=7:3): ¹H NMR (400 MHz, DMSO-d6): δ 8.28 (s, 1.4H), 8.16 (s,0.7H), 8.07 (s, 1.4H), 7.98 (s, 0.7H), 7.77 (s, 1.4H), 7.22–7.14 (m, 2.8H), 6.55 (d, J = 8.2 Hz, 0.7H), 6.46 (s, 3.5H), 2.20 (s, 0.7H), 1.35 (d, J = 22.3Hz, 18.2H).

[0057] Performance testing of COPI films: The method is the same as in Example 1, and the specific results are as follows: COPI (B / T=7:3) membrane gas separation test: hydrogen permeability coefficient is 225.76 Barrer, oxygen permeability coefficient is 29.81 Barrer, nitrogen permeability coefficient is 5.53 Barrer, carbon dioxide permeability coefficient is 160.16 Barrer, and methane permeability coefficient is 4.21 Barrer. The selectivity coefficients for carbon dioxide / methane are 38.02, hydrogen / methane are 53.59, oxygen / nitrogen are 5.39, and carbon dioxide / nitrogen are 28.96.

[0058] Example 3 Unlike Example 1, the copolyimide (COPI) film synthesized in this example (denoted as COPI B / T-6FDA (3:7)) has the following chemical structural formula: , Among them, the diamine monomer containing the bromofluorene group is BAFL-NH2, and the diamine monomer of tripterene is TDA-NH2, with m:n=3:7.

[0059] A method for preparing a copolyimide film specifically includes the following steps: Under a nitrogen atmosphere, 9,9-bis(3-bromo-4-aminophenyl)fluorene (BAFL-NH2) (0.755 g, 1.5 mmol) and 2,6-diaminotriptene (TDA-NH2) (0.994 g, 3.5 mmol) monomers in a molar ratio of 3:7 were added to a polymerization tube equipped with a magnetic stir bar. 6 mL of m-cresol solvent was added, and stirring was started. 4,4'-(hexafluoroisopropylidene) phthalic anhydride and (6FDA) (2.221 g, 5 mmol) were weighed out, with the total molar amount of the two diamine monomers equal to the molar amount of 6FDA monomer. 6FDA was poured into the polymerization tube, followed by the addition of isoquinoline catalyst (0.2 mL). The temperature was gradually heated to 160°C. After complete dissolution, the reaction proceeded until the magnetic stir bar could no longer rotate (viscosity approximately 10 w cps), yielding a viscous reaction solution. The resulting viscous reaction solution was slowly poured into a mixed solution of ethanol and water (volume ratio 1:1), and after standing, the precipitate was formed. This process was repeated three times, and the mixture was then dried in a vacuum oven at 90 °C for 2 days to obtain a copolyimide polymer, which was used for film laying. 0.2 g of copolyimide polymer was dissolved in 10 ml of tetrahydrofuran (THF). The solution was stirred thoroughly for 24 h to dissolve the solute. The solution was then sonicated for 30 min and filtered through a 0.45 μm PTFE filter into a smooth petri dish. After solvent evaporation, an isotropic film was obtained. After complete solvent evaporation, a transparent film with a thickness of 60 μm was obtained. The film was dried in a vacuum oven at 100 °C for 12 h and then further heated in a tube furnace under N2 atmosphere at 230 °C for 2 h to ensure complete removal of residual solvent, thus obtaining the COPI film.

[0060] NMR structural characterization of COPI thin films: COPI (B / T=3:7): ¹H NMR (400 MHz, DMSO-d6): δ 8.28 (s, 0.6H), 8.16 (s,0.3H), 8.07 (s, 0.6H), 7.98 (s, 0.3H), 7.77 (s, 0.6H), 7.22–7.14 (m, 1.2H), 6.55 (d, J = 8.2 Hz, 0.3H), 6.46 (s, 1.5H), 2.20 (s, 0.3H), 1.35 (d, J = 22.3Hz, 7.8H).

[0061] Performance testing of COPI films: The method is the same as in Example 1, and the specific results are as follows: COPI (B / T=3:7): Thin-film gas separation test, hydrogen permeability coefficient is 523.96 Barrer, oxygen permeability coefficient is 81.13 Barrer, nitrogen permeability coefficient is 15.87 Barrer, carbon dioxide permeability coefficient is 433.08 Barrer, and methane permeability coefficient is 12.41 Barrer; The selectivity coefficients for carbon dioxide / methane are 34.90, hydrogen / methane are 42.22, oxygen / nitrogen are 5.11, and carbon dioxide / nitrogen are 27.28.

[0062] Example 4 Unlike Example 1, the copolyimide (COPI) film synthesized in this example (denoted as COAPI (m:n=1:9)) has the following chemical structural formula: , A method for preparing a copolyimide film specifically includes the following steps: Under a nitrogen atmosphere, 2,2-biphenyl diamine (0.092 g, 0.5 mmol) and 1,3-bis(4-aminophenoxy)benzene (1.314 g, 4.5 mmol) monomers in a molar ratio of 1:9 were added to a polymerization tube equipped with a magnetic stir bar. 6 mL of m-cresol organic solvent was added, and stirring was started. 4,4'-(hexafluoroisopropylidene) phthalic anhydride and (6FDA) (2.221 g, 5 mmol) were weighed, with the total molar amount of the two diamine monomers equal to the molar amount of the 6FDA monomer. The 6FDA was poured into the polymerization tube, followed by the addition of isoquinoline catalyst (0.2 mL). The temperature was gradually heated to 160 °C. After complete dissolution, the reaction proceeded until the magnetic stir bar could no longer rotate (viscosity approximately 10 w cps), yielding a viscous reaction solution. The resulting viscous reaction solution was slowly poured into a mixed solution of ethanol and water (volume ratio 1:1), and after standing, the precipitate was formed. This process was repeated three times, and the mixture was then dried in a vacuum oven at 90 °C for 2 days to obtain a copolyimide polymer, which was used for film laying. 0.2 g of the copolyimide polymer was dissolved in 10 ml of tetrahydrofuran (THF). The solution was stirred thoroughly for 24 h to dissolve the solute. The solution was then sonicated for 30 min and filtered through a 0.45 μm PTFE filter into a smooth petri dish. After solvent evaporation, an isotropic film was obtained. After complete solvent evaporation, a transparent film with a thickness of 60 μm was obtained. The film was dried in a vacuum oven at 100 °C for 12 h and then further heated in a tube furnace under N2 atmosphere at 230 °C for 2 h to ensure complete removal of residual solvent, yielding the COAPI film.

[0063] NMR structural characterization of COAPI thin films: COAPI (m:n=1:9): ¹H NMR (400 MHz, DMSO-d6): δ 8.28 (s, 0.6H), 8.16 (s,0.3H), 8.07 (s, 0.6H), 7.98 (s, 0.3H), 7.84–7.77 (m, 1.2H), 7.53–7.32 (m,1.2H), 7.22–7.13 (m, 1.8H), 6.86–6.80 (m, 1.8H), 6.55 (d, J=8.2 Hz, 0.3H), 6.46 (s, 1.5H), 2.25 (s, 0.9H), 2.20 (s, 0.3H), 1.35 (d, J=22.3 Hz, 7.8H).

[0064] Performance testing of COAPI thin films: The method is the same as in Example 1, and the specific results are as follows: COAPI (m:n=1:9): Thin-film gas separation test, hydrogen permeability coefficient is 192.42 Barrer, oxygen permeability coefficient is 24.54 Barrer, nitrogen permeability coefficient is 4.52 Barrer, carbon dioxide permeability coefficient is 135.29 Barrer, and methane permeability coefficient is 3.57 Barrer; The selectivity coefficients for carbon dioxide / methane are 37.89, hydrogen / methane are 53.89, oxygen / nitrogen are 5.42, and carbon dioxide / nitrogen are 29.93.

[0065] Example 5 Unlike Example 1, the copolyimide (COPI) film synthesized in this example (denoted as COAPI(9:1)-BTDA) has the following chemical structural formula: , The dianhydride monomer is BTDA.

[0066] A method for preparing a copolyimide film specifically includes the following steps: Under a nitrogen atmosphere, 2,2-biphenyl diamine (0.828 g, 4.5 mmol) and 1,3-bis(4-aminophenoxy)benzene (0.147 g, 0.5 mmol) monomers in a molar ratio of 9:1 were added to a polymerization tube equipped with a magnetic stir bar. 6 mL of m-cresol solvent was added, and stirring was started. 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) (1.74 g, 5 mmol) was weighed out, with the total molar amount of the two diamine monomers equal to the molar amount of BTDA monomer. BTDA was poured into the polymerization tube, followed by the addition of isoquinoline catalyst (0.2 mL). The temperature was gradually heated to 160 °C. After complete dissolution, the reaction proceeded until the magnetic stir bar could no longer rotate (viscosity approximately 10 w cps), yielding a viscous reaction solution. The resulting viscous reaction solution was slowly poured into a mixed solution of ethanol and water (volume ratio 1:1), and after standing, the precipitate was formed. This process was repeated three times, and the mixture was then dried in a vacuum oven at 90 °C for 2 days to obtain a copolyimide polymer, which was used for film laying. 0.2 g of the copolyimide polymer was dissolved in 10 ml of tetrahydrofuran (THF). The solution was stirred thoroughly for 24 h to dissolve the solute. The solution was then sonicated for 30 min and filtered through a 0.45 μm PTFE filter into a smooth petri dish. After solvent evaporation, an isotropic film was obtained. After complete solvent evaporation, a transparent film with a thickness of 60 μm was obtained. The film was dried in a vacuum oven at 100 °C for 12 h and then heated in a tube furnace under N2 atmosphere at 230 °C for 2 h to ensure complete removal of residual solvent, yielding a COAPI (9:1)-BTDA film.

[0067] NMR structural characterization of COAPI (9:1)-BTDA thin films: COAPI (9:1)-BTDA: ¹H NMR (400 MHz, DMSO-d6): δ 8.28 (s, 0.6H), 8.16(s, 0.3H), 8.07 (s, 0.6H), 7.98 (s, 0.3H), 7.84–7.77 (m, 1.2H), 7.53–7.32 (m,1.2H), 7.22–7.13 (m, 1.8H), 6.86–6.80 (m, 1.8H), 6.55 (d, J = 8.2 Hz, 0.3H), 6.46 (s, 1.5H), 2.25 (s, 0.9H), 2.20 (s, 0.3H), 1.35 (d, J = 22.3 Hz, 7.8H).

[0068] Performance testing of COAPI (9:1)-BTDA thin films: The method is the same as in Example 1, and the specific results are as follows: COAPI (9:1)-BTDA: Thin-film gas separation test, hydrogen permeability coefficient is 150.25 Barrer, oxygen permeability coefficient is 18.52 Barrer, nitrogen permeability coefficient is 3.58 Barrer, carbon dioxide permeability coefficient is 105.16 Barrer, and methane permeability coefficient is 2.78 Barrer; The selectivity coefficients for carbon dioxide / methane are 37.82, hydrogen / methane are 54.04, oxygen / nitrogen are 5.17, and carbon dioxide / nitrogen are 29.37.

[0069] Example 6 Unlike Example 1, the copolyimide (COPI) film synthesized in this example (denoted as COPI-B / T-6FCDA (5:5)) has the following chemical structural formula: ; Under a nitrogen atmosphere, 9,9-bis(3-bromo,4-aminophenyl)fluorene (BAFL-NH2) (0.5035 g, 1 mmol) and 2,6-diaminotriptene (TDA-NH2) (0.284 g, 1 mmol) monomers in a molar ratio of 5:5 were added to a polymerization tube equipped with a magnetic stir bar. 6 mL of m-cresol solvent was added, and stirring was started. 4,4'-(hexafluoroisopropylidene)dioxophthalic anhydride and (6FCDA) (0.916 g, 2 mmol) were weighed out, with the total molar amount of the two diamine monomers equal to the molar amount of 6FCDA monomer. 6FCDA was poured into the polymerization tube, followed by the addition of isoquinoline catalyst (0.2 mL). The temperature was gradually heated to 160 °C. After complete dissolution, the reaction proceeded until the magnetic stir bar could no longer rotate (viscosity approximately 10 w cps), yielding a viscous reaction solution. The resulting viscous reaction solution was slowly poured into a mixed solution of ethanol and water (volume ratio 1:1), and after standing, the precipitate was formed. This process was repeated three times, and the mixture was then dried in a vacuum oven at 90 °C for 2 days to obtain a copolyimide polymer, which was used for film laying. 0.2 g of copolyimide polymer was dissolved in 10 ml of tetrahydrofuran (THF). The solution was stirred thoroughly for 24 h to dissolve the solute. The solution was then sonicated for 30 min and filtered through a 0.45 μm PTFE filter into a smooth petri dish. After solvent evaporation, an isotropic film was obtained. After complete solvent evaporation, a transparent film with a thickness of 60 μm was obtained. The film was dried in a vacuum oven at 100 °C for 12 h and then further heated in a tube furnace under N2 atmosphere at 230 °C for 2 h to ensure complete removal of residual solvent, thus obtaining the COPI film.

[0070] The NMR structure of the COPI thin film is characterized as follows: COPI-B / T-6FCDA (5:5): ¹H NMR (400 MHz, DMSO-d6) δ 8.27 (s, 2H), 8.14(s, 1H), 7.91 (m, 4H), 7.77 (m, 4H), 7.62 (m, 4H), 7.40 (m, 4H), 7.21 (m,4H), 7.09 (m, 4H), 5.18 (s, 2H), 3.33 (s, H2O), 2.50 (s, DMSO-d6).

[0071] COPI film performance testing The method is the same as in Example 1, and the specific results are as follows: The COPI-B / T-6FCDA(5:5) membrane gas separation test showed that the hydrogen permeability coefficient was 385.23 Barrer, the oxygen permeability coefficient was 59.14 Barrer, the nitrogen permeability coefficient was 9.86 Barrer, the carbon dioxide permeability coefficient was 303.95 Barrer, and the methane permeability coefficient was 7.55 Barrer. The selectivity coefficients for carbon dioxide / methane are 40.25, for hydrogen / methane 51.02, for oxygen / nitrogen 5.99, and for carbon dioxide / nitrogen 30.82.

[0072] Example 7 Unlike Example 1, the copolyimide (COPI) film synthesized in this example (denoted as COPI-M / B-TMSBI-DA (5:5)) has the following chemical structural formula: , Under a nitrogen atmosphere, 4,4'-methylenediphenylamine (0.198 g, 1 mmol) and 4,4'-bis(4-aminophenoxy)diphenyl sulfone (0.432 g, 1 mmol) monomers in a molar ratio of 5:5 were added to a polymerization tube equipped with a magnetic stir bar. 6 mL of m-cresol solvent was added, and stirring was started. 0.996 g of 4,4'-(9,9-dimethylfluorene-2,7-diyl)phthalic anhydride (TMSBI-DA) (2 mmol) was weighed, with the total molar amount of the two diamine monomers equal to the molar amount of TMSBI-DA monomer. TMSBI-DA was poured into the polymerization tube, followed by the addition of isoquinoline catalyst (0.2 mL). The temperature was gradually heated to 160 °C. After complete dissolution, the reaction proceeded until the magnetic stir bar could no longer rotate (viscosity approximately 10 w cps), yielding a viscous reaction solution. The resulting viscous reaction solution was slowly poured into a mixed solution of ethanol and water (volume ratio 1:1), and after standing, the precipitate was formed. This process was repeated three times, and the mixture was then dried in a vacuum oven at 90 °C for 2 days to obtain a copolyimide polymer, which was used for film laying. 0.2 g of copolyimide polymer was dissolved in 10 ml of tetrahydrofuran (THF). The solution was stirred thoroughly for 24 h to dissolve the solute. The solution was then sonicated for 30 min and filtered through a 0.45 μm PTFE filter into a smooth petri dish. After solvent evaporation, an isotropic film was obtained. After complete solvent evaporation, a transparent film with a thickness of 60 μm was obtained. The film was dried in a vacuum oven at 100 °C for 12 h and then further heated in a tube furnace under N2 atmosphere at 230 °C for 2 h to ensure complete removal of residual solvent, thus obtaining the COPI film.

[0073] The NMR structure of the COPI thin film is characterized as follows: COPI-M / B-TMSBI-DA (5:5): ¹H NMR (300 MHz, DMSO-d6) δ 7.86 (m, 4H),7.70 (m, 4H), 7.41 (m, 4H), 7.20 (m, 4H), 7.03 (m, 4H), 4.01 (s, 2H), 3.00 (s, 2H), 2.10 (m, 4H), 3.33 (s, H2O), 2.50 (s, DMSO-d6).

[0074] COPI film performance testing The method is the same as in Example 1, and the specific results are as follows: COPI-M / B-TMSBI-DA (5:5) membrane gas separation test: hydrogen permeability coefficient is 335.15 Barrer, oxygen permeability coefficient is 44.22 Barrer, nitrogen permeability coefficient is 8.28 Barrer, carbon dioxide permeability coefficient is 255.39 Barrer, and methane permeability coefficient is 6.12 Barrer; The selectivity coefficients for carbon dioxide / methane are 41.73, hydrogen / methane are 54.76, oxygen / nitrogen are 5.34, and carbon dioxide / nitrogen are 30.84.

[0075] Example 8 Unlike Example 1, the copolyimide (COPI) film synthesized in this example (denoted as COPI-B / F-DSDA (5:5)) has the following chemical structural formula: , Under a nitrogen atmosphere, 2,4,6-trimethyl-1,3-phenylenediamine (0.150 g, 1 mmol) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (0.518 g, 1 mmol) monomers in a molar ratio of 5:5 were added to a polymerization tube equipped with a magnetic stir bar. 6 mL of m-cresol solvent was added, and stirring was started. 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride and DSDA (0.720 g, 2 mmol) were weighed out. The total molar amount of the two diamine monomers was equal to the molar amount of DSDA monomer. After adding DSDA to the polymerization tube, isoquinoline catalyst (0.2 mL) was added. The temperature was gradually heated to 160 °C. After complete dissolution, the reaction proceeded until the magnetic stir bar could no longer rotate (viscosity approximately 10 w cps), resulting in a viscous reaction solution. The resulting viscous reaction solution was slowly poured into a mixed solution of ethanol and water (volume ratio 1:1), and after standing, the precipitate was formed. This process was repeated three times, and the mixture was then dried in a vacuum oven at 90 °C for 2 days to obtain a copolyimide polymer, which was used for film laying. 0.2 g of copolyimide polymer was dissolved in 10 ml of tetrahydrofuran (THF). The solution was stirred thoroughly for 24 h to dissolve the solute. The solution was then sonicated for 30 min and filtered through a 0.45 μm PTFE filter into a smooth petri dish. After solvent evaporation, an isotropic film was obtained. After complete solvent evaporation, a transparent film with a thickness of 60 μm was obtained. The film was dried in a vacuum oven at 100 °C for 12 h and then further heated in a tube furnace under N2 atmosphere at 230 °C for 2 h to ensure complete removal of residual solvent, thus obtaining the COPI film.

[0076] The NMR structure of the COPI thin film is characterized as follows: COPI-B / F-DSDA (5:5) 6FDA-FDA-TAPA (5%): ¹H NMR (300 MHz, DMSO-d6) δ8.51 (m, 2H), 8.45 (m, 1H), 8.05 (s, 2H), 7.13 (m, 4H), 6.98 (m, 2H), 6.86(m, 4H), 3.05 (s, 3H), 2.25 (s, 3H), 2.12 (m, 2H), 1.95 (m, 2H), 1.75 (m,4H), 1.20 (d, 3H), 3.33 (s, H2O), 2.50 (s, DMSO-d6).

[0077] COPI film performance testing The method is the same as in Example 1, and the specific results are as follows: The COPI-B / F-DSDA (5:5) membrane gas separation test showed that the hydrogen permeability coefficient was 280.41 Barrer, the oxygen permeability coefficient was 36.58 Barrer, the nitrogen permeability coefficient was 6.79 Barrer, the carbon dioxide permeability coefficient was 202.66 Barrer, and the methane permeability coefficient was 5.14 Barrer. The selectivity coefficients for carbon dioxide / methane are 39.42, for hydrogen / methane 54.55, for oxygen / nitrogen 5.38, and for carbon dioxide / nitrogen 29.84.

[0078] Comparative Example 1 Unlike Example 1, the copolyimide (COPI) film synthesized in this example (denoted as PI B / T-6FDA (0:1)) has the following chemical structural formula: , Among them, the trimerene diamine monomer is TDA-NH2, and n is 10.

[0079] A method for preparing a PI thin film specifically includes the following steps: Under a nitrogen atmosphere, 2,6-diaminotriptene (TDA-NH2) (0.284 g, 1 mmol) monomer molar ratio (0:1) was added to a polymerization tube equipped with a magnetic stir bar, and 6 mL of m-cresol solvent was added. Stirring was started. 4,4'-(hexafluoroisopropylidene) phthalic anhydride and (6FDA) (0.4442 g, 1 mmol) were weighed out, wherein the molar number of diamine monomer was equal to the molar number of 6FDA monomer. After 6FDA was poured into the polymerization tube, isoquinoline catalyst (0.2 mL) was added. The temperature was gradually heated to 160 °C. After complete dissolution, the reaction proceeded until the magnetic stir bar could no longer rotate (viscosity was approximately 10 w cps), resulting in a viscous reaction solution. The resulting viscous reaction solution was slowly poured into a mixed solution of ethanol and water (volume ratio 1:1), and after standing, the precipitate was formed. This process was repeated three times, and the mixture was then dried in a vacuum oven at 90 °C for 2 days to obtain a polyimide polymer, which was used for film laying. 0.2 g of polyimide polymer was dissolved in 10 ml of tetrahydrofuran (THF) and stirred thoroughly for 24 h to dissolve the solute. The solution was then sonicated for 30 min and filtered through a 0.45 μm PTFE filter into a smooth petri dish. After solvent evaporation, an isotropic film was obtained. After complete solvent evaporation, a transparent film with a thickness of 60 μm was obtained. The film was dried in a vacuum oven at 100 °C for 12 h and then further heated in a tube furnace under N2 atmosphere at 230 °C for 2 h to ensure complete removal of residual solvent, thus obtaining the PI film.

[0080] NMR structural characterization of PI thin films: COPI (B / T=0:1): ¹H NMR (400 MHz, DMSO-d6): δ 8.15 (s, 1H), 8.06 (s,2H), 7.97 (s, 1H), 7.76 (s, 2H), 7.22–7.14 (m, 4H), 6.45 (s, 5H), 2.19 (s,1H), 1.34 (d, J = 22.3 Hz, 26H) Performance testing of PI films: The method is the same as in Example 1, and the specific results are as follows: PI-6FDA (0:1) membrane gas separation test: hydrogen permeability coefficient is 272.18 Barrer, oxygen permeability coefficient is 42.53 Barrer, nitrogen permeability coefficient is 7.02 Barrer, carbon dioxide permeability coefficient is 212.08 Barrer, and methane permeability coefficient is 5.90 Barrer. The selectivity coefficients for carbon dioxide / methane are 35.94, for hydrogen / methane 46.13, for oxygen / nitrogen 6.05, and for carbon dioxide / nitrogen 30.21.

[0081] Comparative Example 2 Unlike Example 1, the copolyimide (COPI) film synthesized in this example (denoted as COPI-B / T-6FCDA (1:0)) has the following chemical structural formula: , The diamine monomer is 2,2-biphenyldiamine with m = 10, and the dianhydride compound is 6FCDA monomer.

[0082] A method for preparing a copolyimide (COPI) film specifically includes the following steps: Under a nitrogen atmosphere, 2,2-biphenyldiamine (0.184 g, 1 mmol) was added to a polymerization tube equipped with a magnetic stir bar; the monomer molar ratio was (0:1), and 6 mL of m-cresol organic solvent was added, and stirring was started; 4,4'-(hexafluoroisopropylidene)dioxophthalic anhydride (6FCDA) (0.458 g, 1 mmol) was weighed, wherein the total molar amount of the two diamine monomers was equal to the molar amount of 6FCDA monomer. After 6FCDA was poured into the polymerization tube, isoquinoline catalyst (0.2 mL) was added; the temperature was gradually heated to 160 °C, and after complete dissolution, the reaction was continued until the magnetic stir bar could no longer be rotated (viscosity was about 10 w cps), resulting in a viscous reaction solution; The resulting viscous reaction solution was slowly poured into a mixed solution of ethanol and water (volume ratio 1:1), and after standing, the precipitate was formed. This process was repeated three times, and the mixture was then dried in a vacuum oven at 90 °C for 2 days to obtain a copolyimide polymer, which was used for film laying. 0.2 g of copolyimide polymer was dissolved in 10 ml of tetrahydrofuran (THF). The solution was stirred thoroughly for 24 h to dissolve the solute. The solution was then sonicated for 30 min and filtered through a 0.45 μm PTFE filter into a smooth petri dish. After solvent evaporation, an isotropic film was obtained. After complete solvent evaporation, a transparent film with a thickness of 60 μm was obtained. The film was dried in a vacuum oven at 100 °C for 12 h and then further heated in a tube furnace under N2 atmosphere at 230 °C for 2 h to ensure complete removal of residual solvent, thus obtaining the COPI film.

[0083] The NMR structure of the COPI thin film is characterized as follows: COPI-B / T-6FCDA (1:0): ¹H NMR (300 MHz, DMSO-d6) δ 8.22 (m, 2H), 7.98(s, 1H), 7.85 (m, 2H), 7.68 (s, 2H), 7.48 (m, 4H), 7.35 (m, 6H), 3.05 (s,3H), 2.20 (s, 3H), 3.33 (s, H2O), 2.50 (s, DMSO-d6).

[0084] COPI film performance testing The method is the same as in Example 1, and the specific results are as follows: The COPI-B / T-6FCDA(0:1) membrane gas separation test showed that the hydrogen permeability coefficient was 195.83 Barrer, the oxygen permeability coefficient was 20.12 Barrer, the nitrogen permeability coefficient was 5.23 Barrer, the carbon dioxide permeability coefficient was 158.54 Barrer, and the methane permeability coefficient was 4.89 Barrer. The selectivity coefficients for carbon dioxide / methane are 32.42, for hydrogen / methane 40.04, for oxygen / nitrogen 4.88, and for carbon dioxide / nitrogen 30.31.

[0085] Test Example 1 This test case aims to study the infrared spectra of the copolymer microporous polymer membranes prepared in the examples and comparative examples.

[0086] Infrared spectra of B / T-6FDA at different proportions (Examples 1-3 and Comparative Example 1) are shown below. Figure 1As shown in the figure, the FT-IR spectra of all B / T-6FDA polyimide samples exhibit typical polyimide characteristic peaks: the imide C=O stretching vibration peak at 1720–1780 cm⁻¹ and the imide CN stretching vibration peak at 1370 cm⁻¹, confirming the occurrence of complete imidization reaction. The C-Br stretching vibration peaks at 600–700 cm⁻¹ and 400–500 cm⁻¹ are specific characteristics of the BAFL-NH₂ unit, and their intensity gradually weakens and eventually disappears as the molar fraction of BAFL-NH₂ decreases (from 100% to 0%), intuitively reflecting the precise control of the copolymer composition and verifying the stability of the polyimide backbone structure under different copolymerization ratios.

[0087] Test Example 2 This test case aims to study the proton NMR spectra of the copolymer microporous polymer membranes and microporous polymer films prepared in Examples 1-3 and Comparative Example 1.

[0088] The proton NMR spectra of B / T-6FDA at different scales are as follows: Figure 2 As shown in the figure, the ¹H NMR spectra (400 MHz, DMSO-d6) of all B / T-6FDA copolyimides exhibit characteristic signals in the aromatic region (5.8–8.4 ppm). The multiplet at δ 8.2–8.4 ppm (labeled i) is the specific signal of the bromine-substituted ortho-benzene ring hydrogen in the BAFL-NH2 unit, and its intensity gradually decreases with decreasing BAFL-NH2 molar fraction until it disappears completely in B / T (0:1)-6FDA; the multiplet at δ 5.8–7.2 ppm (labeled n / m / k) is the characteristic signal of the TDA-NH2 unit, and its intensity increases with increasing TDA-NH2 molar fraction. The signal in the δ 7.4–8.2 ppm range is attributed to the aromatic hydrogens of the 6FDA dianhydride unit and the two diamines, and it is stable in all copolymerization ratios, confirming the integrity of the polyimide backbone structure. The intensity evolution of characteristic peaks directly reflects the precise controllability of copolymer composition, providing a reliable structural basis for structure-property relationship research.

[0089] Test Example 3 This test case aims to study the thermogravimetric and glass transition temperatures of the copolymer microporous polymer membranes and microporous polymer films prepared in Examples 1-3 and Comparative Example 1.

[0090] Thermogravimetric analysis charts of B / T-6FDA at different scales are shown below. Figure 3 As shown, the glass transition temperature diagram is as follows: Figure 4As shown in the figure, the 5% thermal decomposition temperature of all B / Tx-6FDA copolyimides is approximately 416℃, with no significant mass loss below 400℃, exhibiting excellent thermal stability. The main thermal decomposition peak is located at 560℃, corresponding to the thermal degradation of the polyimide backbone, and the decomposition peak positions are highly consistent across different copolymerization ratios, indicating that the diamine ratio adjustment does not alter the backbone decomposition mechanism. The char residue at 800℃ decreases with increasing BAFL-NH2 (B unit) content, originating from the escape of bromine atoms in small molecule form during pyrolysis. DSC results show that the glass transition temperature (Tg) of the copolymer increases linearly from 382.02℃ to 400.95℃ with increasing TDA-NH2 (T unit) content. This is because the absence of bromine-containing T units enhances interchain interactions, improving chain rigidity and thermal stability, while the introduction of bromine substituents weakens interchain forces, achieving precise adjustment of Tg.

[0091] Test Example 4 This test case aims to study the dihedral angle and rotational energy barrier of the copolymer microporous polymer membranes and microporous polymer films prepared in Examples 1-3 and Comparative Example 1.

[0092] This invention is achieved through Figure 5 The rotational energy barrier comparison data shown indicates that the introduction of bromofluorene-containing units (BAFL) dramatically increases the dihedral rotational energy barrier of the polymer segments from the conventional 10–15 kcal / mol to 400–600 kcal / mol. This order-of-magnitude increase in energy barrier (at least one order of magnitude higher) indicates that the BAFL units form a significant torsional kinetic barrier in the copolymer matrix. This microscopic mechanism endows the copolymer film with significant resistance to physical aging: without relying on chemical crosslinking, through the physical chain-locking effect, it retains the excellent permeability provided by the high free volume while effectively inhibiting the relaxation of non-equilibrium segments towards thermodynamic equilibrium, thus achieving a balance between permeability and stability.

[0093] Test Example 5 This test case aims to evaluate the gas permeation flux (H2, N2, O2, CH4, CO2) and selectivity (CO2 / CH4, H2 / CH4, O2 / N2, CO2 / N2) of high-performance polymer membranes reported in all embodiments, comparative examples, and some existing technologies. The gas separation performance of the membrane materials was tested using the constant volumetric pressure method. The results are shown in Table 1.

[0094] Table 1 Gas separation performance The 6FDA-TMPDA / MOCA in the above membrane sample was synthesized by the method described in the European Polymer Journal, Gastransport properties of 6FDA-TMPDA / MOCA copolyimides, 2008 44(1), 225-232.

[0095] Test Example 6 This test example aims to study the anti-aging performance of the membrane sample prepared above. Specifically, it is characterized by measuring the change in gas permeability of the membrane sample over time. The original membrane was exposed to room temperature (20°C, 1 atm) for 30 days for monitoring. Gas permeability tests were performed on the membranes after 0 and 30 days of aging.

[0096] The results are shown in Table 2.

[0097] Table 2 Anti-aging gas separation performance test Test Example 7 This test example aims to calculate the gas selectivity of different membrane samples after 30 days using the formula provided in Test Example 1: Table 3. Calculation of gas selectivity performance of different membrane samples after 30 days. Combine Tables 1, 2, and 3 with Figure 6 Data analysis shows that Example 1 breaks through the permeability-selectivity tradeoff curve in the initial CO2 / CH4 and H2 / CH4 separation. Its CO2 / CH4 selectivity (42.37) is 17.9% higher than Comparative Example 1, 30.7% higher than Comparative Example 2, and 30.0% higher than the prior art. The H2 / CH4 selectivity (52.77) is 14.4%, 31.8%, and 35.4% higher, respectively. At the same time, the permeability coefficients of H2 and CO2 reach 422.15 Barrer and 338.97 Barrer, respectively, which are significantly higher than all comparative examples and the prior art.

[0098] For the O2 / N2 system, due to the only 0.18 Å difference in kinetic diameter between O2 and N2, the requirement for pore size uniformity is extremely high. The selectivity of Example 1 (5.27) is only slightly lower than that of Comparative Example 1 (6.05). However, this invention has achieved an irreplaceable breakthrough in the separation of CO2 / CH4 and H2 / CH4, which has higher industrial value. At the same time, although Examples 2 and Examples 4-8 are lower than Comparative Example 1 in terms of initial gas permeability, their selectivity after 30 days of aging is significantly higher. After aging, the selectivity of H2 / CH4 and CO2 / CH4 in Example 1 is increased by 16.5% and 16.6% respectively compared with that before aging. The retention rate of Example 2 is as high as 91.7%. Example 4, without bromine After aging for 5 and 8 days, the H2 / CH4 selectivity jumped to over 70%, far exceeding that of Comparative Example 1 (60.54), Comparative Example 2 (49.40), and the existing technology (49.31). This is due to the brominated system and the equivalent steric hindrance units such as biphenyl, methyl, fluorenyl / sulfone rigid non-bromine systems, which effectively delayed the non-selective collapse of micropores. Comparative Example 1, lacking any steric hindrance units, experienced micropore collapse during the 30-day aging test. Comparative Example 2, lacking tripterene expansion, experienced chain segment relaxation and further blockage, resulting in a rapid decline in separation performance. The existing technology, lacking both functional units, suffered a comprehensive performance degradation.

[0099] The above results show that the present invention does not simply pursue the maximization of initial permeation flux, but achieves a synergistic improvement in initial separation performance and long-term stability through the molecular synergy of "rigid expansion of tripterene" and "bromofluorene group / equivalent steric unit". Even if the initial performance of some embodiments is not as good as that of the comparative example, the gas separation effect over a long period of time can still exceed that of the comparative example and the prior art, providing a solution for polyimide gas separation membrane materials that has both high separation efficiency and anti-aging performance.

[0100] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the inventive concept of this invention, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0101] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If such modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A copolyimide film, characterized in that, Includes the following structure: ， Where m and n are both in the range of 1 to 10, and the sum of m and n is 10; A includes any of the following: ， B includes any of the following: ， C includes any of the following: 。 2. A method for preparing the copolyimide film according to claim 1, characterized in that, Includes the following steps: In a protective atmosphere, the dianhydride compound, the first diamine monomer, and the second diamine monomer are fully dissolved in an organic solvent and reacted in the presence of a catalyst to obtain a reaction solution. The reaction solution was treated by solvent precipitation and then dried to obtain the copolyimide. The copolyimide was dissolved in a volatile solvent and then cultured to obtain a copolyimide film.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the total diamine monomer, dianhydride compound, and catalyst is 1:1:(0.1-2).

4. The preparation method according to claim 2, characterized in that, The dianhydride compound includes at least one of 4,4'-(hexafluoroisopropylidene) phthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylidene)dioxadiphthalic anhydride, 4,4'-(9,9-dimethylfluorene-2,7-diyl) phthalic anhydride, and 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride; And / or, the first diamine monomer comprises at least one of 2,2'-diaminobiphenyl, 2,4,6-trimethyl-1,3-phenylenediamine, 1,2-bis(4-aminophenyl)ethane, and 9,9-bis(3-bromo-4-aminophenyl)-9H-fluorene; And / or, the second diamine monomer includes at least one of 4,4'-bis(4-aminophenoxy)diphenyl sulfone, 2,6-diaminotriphenylene, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, and 1,4-bis(4-aminophenoxy)benzene; And / or, the organic solvent includes at least one of m-cresol, tetrahydrofuran, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, 1,4-dioxane, and chloroform; And / or, the catalyst comprises at least one of isoquinoline, triethylamine, benzoic acid, and p-hydroxybenzoic acid; And / or, the volatile solvent includes at least one of tetrahydrofuran, 1,4-dioxane, chloroform, and dichloromethane.

5. The preparation method according to claim 2, characterized in that, The reaction temperature is 100-160℃, and the reaction time is 6-12h.

6. The preparation method according to claim 2, characterized in that, The solvent precipitation method specifically includes: adding the reaction solution to a mixed solution of ethanol and water, stirring to precipitate the polyimide, and then filtering to obtain the copolyimide.

7. The preparation method according to claim 2, characterized in that, The drying temperature is 80-120℃, and the drying time is 10-20 h.

8. The application of the copolyimide film according to claim 1 in gas separation.

9. The application of the copolyimide film according to claim 8 in gas separation, wherein the gas separation includes at least one of separating H2 from an H2 / N2 mixed gas, separating O2 from an O2 / N2 mixed gas, separating CO2 from a CO2 / CH4 mixed gas, separating H2 from an H2 / CH4 mixed gas, or separating CO2 from a CO2 / N2 mixed gas.

Images