A tetrafluorostyrene-containing heat-crosslinkable structural diamine, and a preparation method and application thereof

Abstract

The application belongs to the technical field of functional polymer membrane materials, and particularly relates to a kind of tetrafluoro styrene-containing heat-crosslinkable structure diamine and its preparation method and application.The diamine has a rigid bulky skeleton containing spirocycle, hexafluoroisopropyl, fluorene ring or cyclohexane, and introduces heat-crosslinkable tetrafluoro styrene side groups in the skeleton.The diamine is copolymerized with a specific dianhydride monomer to obtain a polyimide resin, and a gas separation membrane is prepared through a step-by-step process of low-temperature drying and forming first and high-temperature heat-crosslinking later.The membrane combines the ultra-large free volume generated by the rigid skeleton and the three-dimensional network structure formed by heat-crosslinking, and has high gas permeability, high selectivity, excellent anti-aging and anti-plasticization performance, solving the industry problem that traditional polyimide membranes are difficult to balance processability, permeability and long-term operation stability, and being particularly suitable for efficient separation of CO2 and other gases.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer membrane materials technology, specifically relating to a thermally crosslinkable diamine containing tetrafluorostyrene, its preparation method, and its application. Background Technology

[0002] Polymer membrane separation technology, as a key method for gas separation and purification in modern industry, has shown broad application prospects in various fields such as natural gas purification, hydrogen recovery, carbon dioxide capture, and volatile organic compound treatment. Compared with traditional high-energy-consuming low-temperature distillation and absorption processes, membrane separation technology has become a research hotspot in the field of gas separation due to its low energy consumption, ease of operation, and environmental friendliness. However, with increasingly harsh industrial application environments, the performance requirements for gas separation membrane materials are constantly increasing, especially in terms of long-term stability and adaptability to complex operating conditions. The market urgently needs to develop new membrane materials that combine high separation efficiency with excellent durability.

[0003] Currently, research on high-performance gas separation membranes largely focuses on polyimide materials, whose excellent thermal stability, mechanical strength, and tunable molecular structure make them ideal candidate materials. In existing technologies, to improve the separation performance of polyimide membranes, researchers typically employ molecular design by introducing rigid, large-volume structural units such as spirocyclic, tripterene, and fluorene rings to adjust the chain segment stacking pattern and enhance gas permeability and selectivity. These methods have improved the membrane's separation characteristics to some extent, providing a feasible path for the development of high-performance membranes.

[0004] However, existing technologies still have significant limitations. On the one hand, while traditional structural modification methods can improve separation performance, they are insufficient to effectively improve the membrane's resistance to aging during long-term use, especially in high-temperature, high-pressure, or corrosive gas environments, where membrane materials are prone to structural degradation and performance decline. On the other hand, such membranes are susceptible to plasticization under high-pressure gases, leading to decreased separation efficiency and shortened service life. Furthermore, the trade-off between permeability and selectivity also restricts further improvements in the overall performance of membrane materials. Therefore, existing polyimide gas separation membranes still fail to meet the demands of industrial applications in terms of anti-aging, anti-plasticization, and long-term stability.

[0005] Faced with the above challenges, developing a polyimide gas separation membrane that combines high gas separation performance with excellent anti-aging and anti-plasticization properties has become an urgent technological need in this field. Only by fundamentally overcoming the structural and performance limitations of existing materials can gas separation membrane technology be promoted towards greater efficiency and durability, meeting the requirements for long-term stable operation in complex industrial environments. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a thermally crosslinkable diamine containing tetrafluorostyrene and its application in the preparation of high-performance polyimide gas separation membranes. This invention designs and synthesizes a diamine monomer with a specific structure containing tetrafluorostyrene side groups, introduces it into the polyimide backbone, and then induces side group crosslinking through heat treatment. This provides an innovative solution for achieving gas separation membranes with high permeability selectivity, excellent anti-aging properties, and anti-plasticization performance.

[0007] The first objective of this invention is achieved through the following technical solution: A diamine containing a thermocrosslinkable tetrafluorostyrene structure, the diamine having the structure shown in general formula (1), wherein R is any one of structural formula I, structural formula II or structural formula III:

[0008] ;

[0009] .

[0010] Preferably, the diamine has a structure shown in structural formula I or structural formula III.

[0011] The second objective of this invention is achieved through the following technical solution:

[0012] A method for preparing a tetrafluorostyrene-containing thermocrosslinkable diamine as described above includes the following steps:

[0013] The starting compound, 2,3,4,5,6-pentafluorostyrene, was dissolved in an aprotic polar solvent and subjected to the Williamson synthesis reaction in the presence of a basic reagent and a phase transfer catalyst at a temperature of 50-120 °C for a time of 12-48 h.

[0014] Preferably, the starting compound has the structure shown in structural formulas V, VI, and VI:

[0015] .

[0016] Preferably, the polar aprotic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and acetonitrile.

[0017] More preferably, the polar aprotic solvent is N,N-dimethylacetamide.

[0018] Preferably, the alkaline reagent is one or more of sodium hydride, calcium hydride, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate.

[0019] More preferably, the alkaline reagent is calcium hydride.

[0020] Preferably, the phase transfer catalyst is cesium fluoride.

[0021] The reaction temperature can be 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, or any two of these values ​​or a subrange thereof.

[0022] The reaction time can be 12 hours, 14 hours, 16 hours, 18 hours, 24 hours, 30 hours, 36 hours, 42 hours, 48 ​​hours, or any two of these values ​​or a subrange thereof.

[0023] Preferably, the molar ratio of the starting compound to 2,3,4,5,6-pentafluorostyrene is 1:(2-4.0).

[0024] More preferably, the molar ratio of the starting compound to 2,3,4,5,6-pentafluorostyrene is 1:(2-2.2).

[0025] Preferably, the molar ratio of the alkaline reagent to the starting compound is (1.5-5.0):1.

[0026] More preferably, the molar ratio of the alkaline reagent to the starting compound is (3.5-4.5):1.

[0027] Preferably, the molar ratio of the phase transfer catalyst to the starting compound is (0.1-0.5):1.

[0028] More preferably, the molar ratio of the phase transfer catalyst to the starting compound is (0.15-0.25):1.

[0029] Preferably, the amount of the aprotic polar solvent used is 1-100 mL / g based on the mass of the starting compound.

[0030] More preferably, the amount of the aprotic polar solvent used is 8-15 mL / g based on the mass of the starting compound.

[0031] This scheme provides an efficient and convenient synthetic route for preparing the novel diamine monomer. The technical principle lies in utilizing the extremely high reactivity of the fluorine atom at the para-position of the vinyl group in the 2,3,4,5,6-pentafluorostyrene molecule. Under conditions of a strong base (such as calcium hydride) and a phase transfer catalyst (such as cesium fluoride), it undergoes a typical Williamson ether synthesis reaction with the starting compound (a diamine containing a phenolic hydroxyl group). By precisely controlling the reaction temperature between 40-100℃ and the reaction time between 12-48 hours, the efficient connection of the tetrafluorostyrene side group to the rigid diamine core skeleton under mild conditions is successfully achieved. This avoids the problem of low reaction efficiency at low temperatures and suppresses side reactions that may be caused by high temperatures, ensuring the smooth synthesis and purification of the target diamine monomer and providing high-purity raw materials for subsequent polymerization reactions.

[0032] The third objective of this invention is achieved through the following technical solution:

[0033] A polyimide gas separation membrane is prepared by thermal crosslinking of a polyimide resin having the structure shown in general formula (2), wherein the polyimide resin having the structure shown in general formula (2) is prepared using the above-mentioned tetrafluorostyrene-containing thermally crosslinkable diamine as one of the raw materials;

[0034] Where n is 1, m is 1-9, and R2 is any one of structural formula I, structural formula II, and structural formula III.

[0035] Preferably, R1 is one or more of the following structures:

[0036] .

[0037] Preferably, R3 is one or more of the following structures:

[0038] .

[0039] Preferably, the polyimide gas separation membrane has a number-average molecular weight of 30,000-120,000, a weight-average molecular weight of 60,000-240,000, and a molecular weight distribution coefficient of 1.6-2.6.

[0040] More preferably, the number-average molecular weight of the polyimide gas separation membrane can be 40,000, 45,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, or any two of these values, or a sub-range thereof; the molecular weight distribution coefficient of the polyimide gas separation membrane can be 1.6, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.6, or any two of these values, or a sub-range thereof.

[0041] This scheme utilizes the dual effects of a rigid, large-volume structure and thermally crosslinkable side groups in polyimide polymer chains with a specific general formula. On one hand, the inherent and introduced rigid, twisted, non-coplanar large-volume structures of the main chain, such as spirocyclic, hexafluoroisopropyl, fluorene, and cyclohexane rings, generate a significant chain-stacking inhibition effect, preventing the polymer chains from compactly packing. This results in a large number of molecular-level voids (free volumes) with controllable dimensions. These voids provide channels for selective diffusion of gas molecules with different kinetic diameters, forming the physical basis for achieving high gas permeability and ideal selectivity. On the other hand, the tetrafluorostyrene side groups suspended on the polymer main chain undergo thermal crosslinking reactions in the final stage of membrane preparation through high-temperature heat treatment, activating their vinyl double bonds. This crosslinking structure forms a robust covalent network in the polyimide system, acting like a "shackle" on the molecular chains. This significantly restricts the movement and swelling tendency of chain segments under long-term use or harsh conditions (such as high-pressure CO2), thereby significantly improving the dimensional and chemical stability of the membrane. This not only effectively inhibits the physical aging process that leads to performance degradation, but also fundamentally solves the plasticization phenomenon caused by highly plasticizing gases such as high-pressure CO2, enabling the separation membrane to maintain an initial gas permeability of over 95% and excellent selectivity after long-term operation, while maintaining the inherent high heat resistance and mechanical strength of polyimide materials.

[0042] The fourth objective of this invention is achieved through the following technical solution:

[0043] A method for preparing the polyimide gas separation membrane as described above includes the following steps:

[0044] A) Under an inert atmosphere, the dianhydride monomer, the diamine containing the thermocrosslinkable tetrafluorostyrene structure, and the diamine monomer used to form R3 in general formula (2) are reacted in a polar aprotic solvent for 6-24 hours to obtain a polyamic acid solution; wherein the ratio of the total molar number of amino groups in all diamine monomers to the total molar number of anhydride groups in all dianhydride monomers is 1:1 to 1.02:1;

[0045] B) Add an imidizing agent to the polyamic acid solution obtained in step A) to carry out a chemical imidization reaction to obtain polyimide resin;

[0046] C) Dissolve the polyimide resin obtained in step B) in an organic solvent, filter it, and cast it into a membrane. First, evaporate the solvent at 15-30℃ for 20-72h, and then dry it under vacuum at 80-150℃ to obtain an uncrosslinked polyimide gas separation membrane.

[0047] D) Thermal crosslinking: The uncrosslinked polyimide gas separation membrane obtained in step C) is post-baked at 200-260℃ for 0.5-6 hours to obtain a crosslinked polyimide gas separation membrane.

[0048] Preferably, in step A), the polar aprotic solvent is one or more of N,N-dimethylacetamide, N,N-dimethylformamide, or N,N-diethylacetamide.

[0049] More preferably, the polar aprotic solvent is N,N-dimethylacetamide.

[0050] In step A), the reaction time can be 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 15 hours, 16 hours, 18 hours, 20 hours, 22 hours, 24 hours, or any range or subrange between any two of these values.

[0051] Preferably, in step A), the dianhydride monomer includes at least one of 1,2,4,5-pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, 4,4'-biphenyl ether dianhydride, 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride, 9,9-bis(trifluoromethyl)-2,3,6,7-oxanthracene tetracarboxylic acid dianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride, and 2,3,6,7-naphthalenetetracarboxylic acid dianhydride.

[0052] More preferably, the dianhydride monomer is 2,2'-bis(3,4-dicarboxylic acid)hexafluoropropane dianhydride.

[0053] Preferably, in step A), the diamine monomer used to form R3 in general formula (2) is selected from one or more of the following: 1,4-phenylenediamine, 2,5-dimethyl-p-phenylenediamine, tetramethyl-p-phenylenediamine, 4,4'-diaminodiphenyl ether, 4,4-diaminophenyl sulfone, 2,2'-di(trifluoromethyl)diaminobiphenyl, 2,2'-dimethyl-4,4'-diaminobiphenyl, 4,4'-diaminobenzoylaniline, and p-aminophenyl benzoate.

[0054] Preferably, in step A), the diamine containing a thermocrosslinkable tetrafluorostyrene structure accounts for 10%-100% of the total molar number of all diamine monomers.

[0055] More preferably, the tetrafluorostyrene-containing thermally crosslinkable diamine accounts for 20%-60% of the total molar number of all diamine monomers.

[0056] Preferably, in step B), the imidizing agent for the chemical imidization reaction is a mixed solution of acetic anhydride and pyridine.

[0057] More preferably, the molar ratio of the acetic anhydride to the anhydride groups in the dianhydride monomer is (2.0-15.0):1.

[0058] More preferably, the molar ratio of the acetic anhydride to the anhydride group is 4:1, 5:1, 6:1, 8:1, or any two of these values ​​or a subrange thereof.

[0059] Preferably, in step B), the chemical imidization reaction is carried out at 60-140°C.

[0060] More preferably, the chemical imidization reaction is carried out at 80-100°C.

[0061] Preferably, in step B), the chemical imidization reaction takes 6-12 hours.

[0062] More preferably, the chemical imidization reaction takes 6-8 hours.

[0063] Preferably, in step B), the polyimide resin is precipitated, washed, and dried in one or more mixtures of water, methanol, and ethanol.

[0064] Preferably, in step D), the post-drying temperature is 200-260°C.

[0065] More preferably, the post-drying temperature is 200°C, 220°C, 240°C, 260°C, or a range between any two of these values.

[0066] Preferably, in step D), the post-drying time is 1-3 hours.

[0067] More preferably, the post-baking time can be 0.5h, 1h, 2h, 3h, 4h, 5h, 6h, or any two of these values.

[0068] This solution provides a complete and optimized preparation process. Its technical principle lies in the synergistic optimization of the membrane's microstructure and long-term stability through a meticulously designed step-by-step process of pre-forming and then locking. First, a two-step polymerization method ensures the synthesis of high-molecular-weight polyimide, laying the foundation for film formation. In the film formation and curing stages, the core of this invention lies in the step-by-step and independent control of two key processes: solvent evaporation and drying, and thermal crosslinking and curing. In step C, the solvent is first slowly evaporated at room temperature and then vacuum-dried at a lower temperature of 80-150 degrees Celsius. The purpose of this stage is to gently and thoroughly remove residual solvent, avoiding premature glassing of the polymer chains or local crosslinking due to excessively high temperatures, which would hinder the full escape of the solvent and create defects. This process ensures that the polymer chains can fully relax and arrange themselves under solvent-free or minimal conditions to form an initial membrane structure with a loosely packed, large free volume, a prerequisite for achieving high gas permeability. In step D, the completely dried membrane undergoes a post-baking treatment at a higher temperature of 200-260 degrees Celsius. The sole purpose of this stage is to activate the vinyl double bonds in the tetrafluorostyrene side chain groups, causing an intermolecular thermal crosslinking reaction. If drying and crosslinking are combined, the presence of solvent can interfere with the efficiency and uniformity of the crosslinking reaction, and rapid solvent evaporation may lead to internal stress and defects in the membrane. However, this invention performs high-temperature crosslinking after the membrane structure has been finalized, enabling the construction of a uniform and robust three-dimensional covalent network within the polyimide matrix. The synergistic effect of this stepwise process lies in the effective fixation and locking of the loosely stacked chain structure, which facilitates rapid gas permeation, created by the low-temperature drying process, by the three-dimensional network generated by subsequent high-temperature crosslinking. This network significantly restricts the movement and creep of polymer molecular chains, resulting in a qualitative leap in membrane structural stability. This allows the membrane to simultaneously and effectively resist physical aging during long-term use and swelling caused by the intrusion of highly plasticizing gases such as high-pressure carbon dioxide. Ultimately, it successfully combines high permeation selectivity with excellent anti-aging and anti-plasticization properties—two characteristics that are typically difficult to achieve simultaneously—into the final separation membrane product, achieving a breakthrough in overall performance.

[0069] The fifth objective of this invention is achieved through the following technical solution:

[0070] The above describes the application of polyimide gas separation membranes in the field of gas separation.

[0071] Preferably, the polyimide gas separation membrane is used to separate carbon dioxide from the mixed gas.

[0072] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0073] 1. The tetrafluorostyrene-containing thermally crosslinkable diamine monomer provided by the present invention introduces thermally crosslinkable fluorostyrene side groups into its rigid large-volume skeleton, so that the polyimide prepared thereby not only maintains good solubility and processing performance, but also forms a stable crosslinked network through subsequent heat treatment, fundamentally solving the contradiction between the traditional polyimide material's difficulty in balancing processing performance and stability in use.

[0074] 2. The present invention prepares polyimide by copolymerizing the diamine monomer with a specific dianhydride monomer. Due to the steric hindrance effect of the rigid non-coplanar structure in its molecular chain, the close packing of chain segments is effectively suppressed, the free volume of the polymer is increased, and more transport channels are provided for gas molecules. This allows the gas separation membrane to achieve a significantly improved gas permeation rate while maintaining high selectivity.

[0075] 3. This invention introduces tetrafluorostyrene groups into the side chains of polyimide molecules and implements precisely controlled thermal crosslinking treatment, forming a uniform and stable three-dimensional network structure in the membrane. This crosslinking network effectively restricts the mobility and swelling space of the polymer chain segments, enabling the gas separation membrane to exhibit excellent resistance to physical aging and carbon dioxide plasticization, and maintain stable separation performance during long-term use.

[0076] 4. The stepwise preparation process of the present invention, which involves first drying and molding at low temperature and then heat treatment and crosslinking at high temperature, separates the solvent evaporation process from the crosslinking reaction. This ensures that the nascent membrane can form an ideal loose chain stacking structure and avoids the interference of the solvent on the crosslinking reaction, thus ensuring the integrity of the final membrane structure and the reliability of its performance.

[0077] 5. The complete technical solution provided by this invention, from monomer design and polymer synthesis to membrane preparation, has a clear and well-defined process route, precise parameter control, and close connection between each step, providing a practical and feasible industrial path for preparing high-performance gas separation membranes with high separation performance, excellent long-term stability, and good mechanical strength. Attached Figure Description

[0078] Figure 1 The 1H NMR spectrum of the tetrafluorostyrene-containing thermocrosslinkable diamine prepared in Example 1; Figure 2 The carbon NMR spectrum of the tetrafluorostyrene-containing thermocrosslinkable diamine prepared in Example 1; Figure 3 The 1H NMR spectrum of the tetrafluorostyrene-containing thermally crosslinkable diamine prepared in Example 2; Figure 4 The carbon NMR spectrum of the tetrafluorostyrene-containing thermocrosslinkable diamine prepared in Example 2; Figure 5The polyimides containing a thermocrosslinkable tetrafluorostyrene structure prepared in Examples 3-5 and Comparative Examples 1-4; Figure 6 This is a schematic diagram of the synthesis process of diamine monomers of structural formula I and structural formula II of the present invention; Figure 7 This is a schematic diagram of the synthesis process of the III-diamine monomer of the present invention; Figure 8 This diagram illustrates the synthesis process of the thermally crosslinkable polyimide gas separation membrane prepared according to the present invention, as well as the schematic diagram of the polymer thermal crosslinking mechanism. Detailed Implementation

[0079] The following will provide a clear and complete description of the concept, specific structure, and technical effects of the present invention in conjunction with embodiments and accompanying drawings, so as to fully understand the purpose, solution, and effects of the present invention. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0080] Example 1 The 3,3,3',3'-tetramethyl-6,6'-bis(2,3,5,6-tetrafluoro-4-vinylphenoxy)-2,2',3,3'-tetrahydro-1,1'-spirodi[indene]-5,5'-diamine of Example 1 was prepared by the following method: a) Under a nitrogen atmosphere, bisphenol A (100 g, 438.0 mmol) and a magnetic stir bar were added to a 500 mL three-necked flask. Then, methanesulfonic acid (10 mL) was added using a syringe. The reaction system was heated in an oil bath at 135 °C. The solid gradually dissolved, and the solution color changed from yellow to dark brown. After stirring at 135 °C for 5 hours, the reaction progress was monitored by thin-layer chromatography (developing solvent: dichloromethane / petroleum ether volume ratio = 4:1, Rf = 0.25). The disappearance of the starting material spot and the appearance of a new product spot indicated the completion of the reaction. The heated mixture was slowly poured into an ice-water mixture (2000 mL) with mechanical stirring. A dark reddish-brown solid precipitated. The mixture was filtered through a Buchner funnel, and the filter cake was washed six times (500 mL each time) with 80 °C hot water until the filtrate was colorless, yielding a light brown solid. The obtained solid was dried in a vacuum drying oven at 100 °C for 12 hours. The dried crude product was transferred to a 1000 mL single-necked flask, and a mixture of anhydrous ethanol and water in a volume ratio of 10:1 (total 550 mL) was added. The mixture was heated until the solid dissolved, then allowed to stand, slowly cooled to room temperature, and left to stand overnight. White crystals precipitated out, and were filtered to give white flaky crystalline compound 1 (25 g, yield 56%).

[0081] b) In a 250 mL three-necked flask, add compound 1 (3.08 g, 10.0 mmol) and glacial acetic acid (100 mL), and stir in an ice-water bath until completely dissolved. A mixture of nitric acid solution (4.0 mol / L, 5.3 mL, 21.0 mmol) and glacial acetic acid (50 mL) is slowly added dropwise to the reaction flask over 15 minutes, during which a yellow solid gradually precipitates. Remove the ice bath and stir the reaction mixture at room temperature (25 °C) for 12 hours. TLC monitoring (evolving solvent: dichloromethane / petroleum ether volume ratio = 4:1, Rf = 0.25) indicates that the reaction is complete. Filter the reaction mixture to obtain a yellow crude product. Purification was performed by column chromatography (stationary phase: 300-400 mesh silica gel; eluent: petroleum ether / dichloromethane mixed solvent, volume ratio gradually changed from 4:1 to 1:1). The target component was collected, and the solvent was removed by concentration under reduced pressure to obtain yellow solid compound 2 (3.16 g, yield: 80.0%).

[0082] c) Compound 2 (10.0 g, 25.0 mmol) and a 10 wt% palladium-on-carbon catalyst (Pd / C, 0.8 g) were added to a 500 mL three-necked flask. Under nitrogen protection, anhydrous ethanol (200 mL) was added, the mixture was stirred, and heated to 90 °C under reflux. Then, 85% hydrazine hydrate (N2H4·H2O, 20 mL) was slowly added dropwise using a syringe, and the mixture was refluxed at this temperature for 8 hours. The reaction was confirmed to be complete by TLC (electrolyte: ethyl acetate / petroleum ether, volume ratio = 1:2, Rf = 0.5). The reaction system was cooled to room temperature and hot-filtered through a diatomaceous earth-lined sand core funnel to remove the palladium-on-carbon catalyst. The filtrate was poured into 1000 mL of distilled water and stirred, resulting in the precipitation of a white solid. The solid was filtered, collected, and dried in a vacuum oven at 80 °C for 12 hours to obtain a white powder, compound 3 (8.1 g, yield: 96%).

[0083] d) In a 50 mL round-bottom three-necked flask equipped with a mechanical stirrer, a nitrogen inlet tube, and a condenser, compound 3 (1.3538 g, 4.0 mmol), 2,3,4,5,6-pentafluorostyrene (1.5696 g, 8.0 mmol), calcium hydride (CaH2, 0.6848 g, 16.0 mmol), cesium fluoride (CsF, 0.2431 g, 1.6 mmol), and N,N-dimethylacetamide (DMAc, 20 mL) were added sequentially. Under a nitrogen atmosphere, the reaction system was heated to 80 °C and stirred for 24 hours. After the reaction was complete, the mixture was cooled to room temperature and then quenched in 200 mL of deionized water. The solid was collected by suction filtration and washed three times with 50 mL of deionized water each time. The solid was dried to constant weight in a vacuum oven at 60 °C to obtain the crude product. The crude product was purified by column chromatography (stationary phase: silica gel; eluent: petroleum ether / ethyl acetate volume ratio = 2:1). The target component was collected, and the solvent was removed by rotary evaporation to obtain a light yellow solid powder product (containing a diamine compound of structural formula I) with a yield of 82%.

[0084] The 3,3,3',3'-tetramethyl-6,6'-bis(2,3,5,6-tetrafluoro-4-vinylphenoxy)-2,2',3,3'-tetrahydro-1,1'-spirodi[indene]-5,5'-diamine prepared in Example 1 was characterized by 1H NMR, 1C NMR, and FTIR spectra. The FTIR data are as follows: FTIR (KBr, cm⁻¹) -1 ): 3462 3373 (amino: NH), 2954 (CH3), 2866 (CH2), 1631 (C=C), 1318 (CF), 1234 (Ar-O-Ar), 992, 913 (=CH). ¹H and ¹³C NMR spectra are as follows: Figure 1 and 2 As shown, the specific analytical data is as follows: 1 H NMR (DMSO- d 6,600 MHz): δ 6.71 (s, 1H, Ar-H), 6.63-6.69 (m, 2H, CH=C), 6.53 (d, J = 1.2 Hz, 1H, Ar-H), 6.44 (d, J = 0.6 Hz, 1H, Ar-H), 6.33 (s, 1H, Ar-H), 6.09 (dd, J = 18 Hz, 2H, C=CH2), 5.69 (dd, J = 18 Hz, 2H, C=CH2), 4.00 (s, 2H, NH2), 3.48 (s, 2H, NH2), 2.50 (d,J = 12 Hz, 1H, CH2), 2.36 (d, J = 12 Hz, 1H, CH2), 2.24 (d, J = 12 Hz, 1H, CH2), 2.06 (d, J = 12 Hz, 1H, CH2), 1.43 (s, 3H, CH3), 1.38 (s, 3H, CH3), 1.31 (s, 3H, CH3), 1.29 (s, 3H, CH3) ppm. 13 C NMR (DMSO- d6 , 150MHz): δ 149.01, 148.49, 146.02, 145.12, 144.29, 140.78, 140.26, 137.55,136.48, 132.89, 132.65, 123.04, 122.99, 122.93, 122.88, 122.83, 122.01,121.95, 113.80, 112.67, 112.58, 112.50, 112.41, 110.42, 110.34, 109.76,59.79, 56.36, 53.35, 43.19, 42.98, 32.16, 31.75, 29.85, 29.47ppm.

[0085] Example 2

[0086] The 4,4'-(perfluoropropane-2,2-diyl)bis(2-(2,3,5,6-tetrafluoro-4-vinylphenoxy)aniline of Example 2 was prepared by the following method: In a 50 mL round-bottom three-necked flask equipped with a mechanical stirrer, a nitrogen inlet tube, and a condenser, 2,2-bis(3-amino-4-hydroxybenzene)hexafluoropropane (1.464 g, 4.0 mmol), 2,3,4,5,6-pentafluorostyrene (1.5696 g, 8.0 mmol), calcium hydride (CaH2, 0.6848 g, 16.0 mmol), cesium fluoride (CsF, 0.2431 g, 1.6 mmol), and N,N-dimethylacetamide (DMAc, 20 mL) were added sequentially. Under a nitrogen atmosphere, the reaction system was heated to 80 °C and stirred for 24 hours. After the reaction was complete, the mixture was cooled to room temperature and then quenched in 200 mL of deionized water. The solid was collected by suction filtration and washed three times with 50 mL of deionized water each time. The solid was dried to constant weight in a vacuum oven at 60 °C to obtain the crude product. The crude product was purified by column chromatography (stationary phase: silica gel; eluent: petroleum ether / ethyl acetate volume ratio = 2:1). The target component was collected, and the solvent was removed by rotary evaporation to obtain a light yellow solid powder product (containing a diamine compound of structural formula II) with a yield of 82%.

[0087] The 4,4'-(perfluoropropane-2,2-diyl)bis(2-(2,3,5,6-tetrafluoro-4-vinylphenoxy)aniline prepared in Example 2 was characterized by 1H NMR, 1C NMR, and FTIR spectra. The FTIR resolution data are as follows: FTIR (KBr, cm⁻¹) -1 ): 3460, 3371 (amino: NH), 2954 (CH3), 2861 (CH2), 1633 (C=C), 1315 (CF), 1215 (-CF3), 1242 (Ar-O-Ar), 991, 915 (=CH). ¹H and ¹³C NMR spectra are as follows: Figure 3 and 4 As shown, the specific analytical data is as follows: 1 H NMR (DMSO- d 6, 600 MHz): δ 6.73 (s, 2H, CH=C), 6.56-6.61 (m, 4H, Ar-H), 6.03 (d, J = 18 Hz, 2H, C=CH2), 5.63 (d, J = 12 Hz, 2H, C=CH2), 3.94 (s, 4H, NH2) ppm. 13 C NMR (DMSO- d6, 150 MHz): δ 146.00, 144.95, 144.34, 142.38, 142.28, 140.73, 140.62, 135.86, 132.03, 131.94, 131.85, 129.31, 125.12, 123.72, 123.66,121.80, 120.35, 118.43, 113.71, 113.62, 113.53, 113.27, 77.27, 77.06, 76.85ppm.

[0088] Example 3

[0089] The polyimide gas separation membrane in Example 3 was prepared by the following method: In a 100 mL three-necked flask equipped with a mechanical stirrer, a nitrogen inlet tube, and a drying tube, under a continuous nitrogen atmosphere, the following were added sequentially: a thermally crosslinkable diamine containing tetrafluorostyrene (Structural Formula I, 0.892 g, 2.0 mmol), 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB, 0.960 g, 3.0 mmol), and anhydrous N,N-dimethylacetamide (DMAc, 15 mL), prepared in Example 1. The mixture was stirred at room temperature (25 °C) for 30 minutes until the diamine monomer was completely dissolved, yielding a clear solution. While continuously stirring, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6 FDA, 5.0 mmol) was added to the diamine solution in three portions, controlling the addition rate to maintain the system temperature below 35 °C. After all the dianhydride had been added, the reaction was continued at room temperature for 16 hours to obtain a highly viscous polyamic acid solution. The ratio of the total number of moles of amino groups in the diamine monomer to the total number of moles of anhydride groups in the dianhydride monomer is 1:1. A mixture of acetic anhydride (5.0 mL) and pyridine (2.5 mL) was slowly added to the above polyamic acid solution under mechanical stirring. The oil bath temperature of the reaction system was then raised to 120 °C, and the reaction was continued at this temperature with stirring for 6 hours to complete the chemical imidization process, yielding a polyimide resin solution. After the reaction, the mixture was cooled to room temperature and slowly poured into a mixture of 250 mL anhydrous ethanol and 250 mL deionized water under vigorous stirring. A white fibrous solid precipitated. The polymer was collected by filtration through a Buchner funnel, and the filter cake was washed three times with 300 mL of deionized water. The obtained solid was placed in a Soxhlet extractor and continuously extracted with anhydrous ethanol for 24 hours. Finally, the purified polymer was dried in a vacuum drying oven at 120 °C for 12 hours to obtain a white fibrous polyimide resin solid (3.12 g, yield 93%), which has the structure shown in general formula 2. The polyimide resin obtained in step b) was redissolved in anhydrous chloroform at a solid content of 10 wt%. The solution was filtered through a 0.22 μm organic filter membrane to remove impurities. The solution was then poured into a dry, clean glass dish and allowed to slowly evaporate for 3 days in a clean room (25°C, RH < 40%) to ensure complete solvent evaporation, resulting in an uncrosslinked polyimide gas separation membrane. The glass dish containing the separation membrane was then placed in a vacuum oven and sequentially vacuum-dried at 100°C for 1 hour, 200°C for 0.5 hours, and 260°C for 4 hours to complete the thermal crosslinking process, yielding a crosslinked high-performance polyimide gas separation membrane. After cooling to room temperature, the separation membrane was immersed in hot water and peeled off from the glass substrate. Finally, the separation membrane was dried in a conventional oven at 100°C for 1 hour to obtain the final separation membrane. The thickness of the membrane was measured at three different locations using a digital micrometer, and the measured values ​​were 24.8 μm, 25.2 μm, and 25.1 μm, respectively. The membrane thickness is uniform, and the thickness at all measurement points is within the range of 25 μm ± 2 μm.

[0090] Example 4

[0091] In the preparation method of the polyimide gas separation membrane in Example 4, steps b)-c) are the same as in Example 3, except that the tetrafluorostyrene thermally crosslinkable diamine (structural formula I, 0.892 g, 2.0 mmol) prepared in Example 1 in step a) is replaced with the tetrafluorostyrene thermally crosslinkable diamine (structural formula II, 2.0 mmol) prepared in Example 2.

[0092] Example 5

[0093] In the preparation method of the polyimide gas separation membrane in Example 5, steps b)-c) are the same as in Example 3, except that the tetrafluorostyrene thermally crosslinkable diamine (structural formula I, 0.892 g, 2.0 mmol) prepared in Example 1 in step a) is replaced with 4,4'-(cyclohexane-1,1-diyl)bis[2-(2,3,5,6-tetrafluoro-4-vinylphenoxy)aniline] (containing structural formula III, 2.0 mmol).

[0094] Comparative Example 1 In the preparation method of the polyimide gas separation membrane of Comparative Example 1, steps b)-d) are the same as in Example 3, except that the vacuum drying step in step c) is replaced by vacuum drying at 100°C for 1 hour only.

[0095] Comparative Example 2 In the preparation method of the polyimide gas separation membrane of Comparative Example 2, steps b)-d) are the same as in Example 4, except that the vacuum drying step in step c) is replaced by vacuum drying at 100°C for 1 hour only.

[0096] Comparative Example 3 In the preparation method of the polyimide gas separation membrane of Comparative Example 3, steps b)-d) are the same as in Example 3, except that the tetrafluorostyrene thermally crosslinkable diamine (structural formula I, 0.892 g, 2.0 mmol) prepared in Example 1 in step a) is replaced with 2,3,5,6-tetramethyl-1,4-phenylenediamine (TMPD, 2.0 mmol).

[0097] Comparative Example 4 In the preparation method of the polyimide gas separation membrane of Comparative Example 4, steps b)-d) are the same as in Example 3, except that the tetrafluorostyrene thermally crosslinkable diamine (structural formula I, 0.892 g, 2.0 mmol) prepared in Example 1 in step a) is replaced with 4,4'-diaminodiphenyl ether (ODA, 2.0 mmol).

[0098] The polyimide resins and their gas separation membranes prepared in Examples 3-5 and Comparative Examples 1-4 were characterized in a series of ways, and the results are as follows: Figure 1-5 As shown in Table 1-4.

[0099] Table 1. Number-average molecular weight, weight-average molecular weight, and molecular weight distribution of the polyimide resins prepared in the examples and comparative examples.

[0100]

[0101] Table 2. Solubility of polyimide resins prepared in the examples and comparative examples

[0102]

[0103] Note: (++: easy to dissolve; +: soluble; -: insoluble)

[0104] Table 3 Thermal properties of the polyimide separation membranes prepared in the examples and comparative examples

[0105]

[0106] Table 4. Gas separation performance of the polyimide separation membranes prepared in the examples and comparative examples.

[0107]

[0108] Note: Aging data are all test results of membrane samples after being placed at room temperature and pressure for 60 days.

[0109] Figures 1 to 4 The 1H and 1C NMR spectra clearly verified that the chemical structures of the target diamine monomers in Examples 1 and 2 were successfully synthesized, and the chemical shifts of their characteristic functional groups were in complete agreement with expectations, providing a high-purity raw material guarantee for subsequent polymerization reactions.

[0110] As shown in Table 1, all polyimide resins have sufficiently high molecular weights and good molecular weight distributions, which ensures that the polyimides can form flexible gas separation membranes.

[0111] As shown in Table 2, the polyimide resins prepared from the diamine monomers of this invention (Examples 3-5) exhibit excellent solubility, being soluble not only in high-boiling-point polar solvents such as DMAc and NMP, but also readily soluble in low-boiling-point solvents such as dichloromethane and chloroform. This characteristic can be attributed to... Figure 6 and Figure 7 In the synthetic route shown, the large, twisted non-coplanar structures such as spirocyclic, hexafluoroisopropyl, and cyclohexane introduced into the molecular backbone effectively inhibit the close packing of polymer chains and weaken intermolecular interactions, thereby greatly improving the solution processability of the material and solving the problems of poor solubility and difficult processing of traditional polyimides (such as Comparative Examples 3 and 4).

[0112] As shown in Table 3, the polyimide gas separation membranes prepared by the present invention (Examples 3-5) all have excellent thermal stability. Figure 5 The thermogravimetric analysis curves visually demonstrate this point; the initial thermal decomposition temperature (Td) of all membrane materials... 5% All of them are above 500℃, and can still maintain a residual rate of more than 68% at 600℃, indicating that they have excellent thermal stability and are sufficient to meet the application requirements of high-temperature industrial environments.

[0113] As can be seen from the gas separation performance data and aging test results in Table 4, this invention has achieved a breakthrough in overall performance. On the one hand, the rigid non-coplanar large-volume structure creates abundant molecular-level free volume, providing efficient transport channels for gas molecules, resulting in high gas permeability in the membranes of Examples 3-5. On the other hand, the tetrafluorostyrene side chain groups successfully underwent a crosslinking reaction after heat treatment, constructing a stable three-dimensional network in the polymer system. This structure greatly restricts the movement of polymer chain segments, leading to a qualitative leap in the membrane's resistance to physical aging. As shown in Examples 3 and 4, the gas permeability retention rate after 60 days of aging is as high as 95%, significantly better than Comparative Examples 1 and 2 without thermal crosslinking and Comparative Examples 3 and 4 of traditional polyimides without the introduction of crosslinkable side groups.

[0114] The biggest challenge currently facing polymer gas separation membranes in industrial applications is their high gas selectivity but low gas permeability, leading to low separation efficiency. The core reason is the highly dense packing of polymer molecular chains, making it difficult for gas to permeate through the membrane structure. Introducing a "rigid, twisted, large-volume framework" into the polymer can significantly improve the tight packing of polymer chains, creating a large amount of free volume and providing space for gas molecules to pass through the separation membrane. However, excessively increasing the free volume of polymer molecular chains can sacrifice gas selectivity and anti-aging properties to some extent. Therefore, a further innovative approach is to introduce tetrafluorostyrene groups into the "rigid, twisted, large-volume framework," and through intermolecular thermal crosslinking of vinyl groups, such as... Figure 8 As shown, the free volume space of the polymer is synergistically controlled, which can also significantly improve the anti-aging performance of large-volume polymer separation membranes. Therefore, the best gas separation performance in Example 3 is attributed to the innovative synergistic effect of the rigid twisted spirocyclic large-volume structure and the thermally crosslinkable tetrafluorostyrene groups, which solves the problem of achieving high permeability, high selectivity and anti-aging properties simultaneously in the practical application of polymer gas separation membranes.

[0115] In summary, this invention, through the synergistic design of a "rigid large-volume skeleton" and "thermally crosslinkable side groups," as well as a post-drying process, successfully integrates high permeability, high selectivity, and excellent long-term stability into a polyimide gas separation membrane, providing a high-performance membrane material solution with great application prospects.

[0116] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A diamine containing a thermocrosslinkable tetrafluorostyrene structure, characterized in that, The diamine has the structure shown in general formula (1), wherein R is any one of the structures shown in formula I, formula II or formula III: ； 。 2. A method for preparing a tetrafluorostyrene-containing thermally crosslinkable diamine according to claim 1, characterized in that, Includes the following steps: The starting compound, 2,3,4,5,6-pentafluorostyrene, was dissolved in an aprotic polar solvent and subjected to the Williamson synthesis reaction in the presence of a basic reagent and a phase transfer catalyst at a temperature of 50-120 °C for a time of 12-48 h.

3. The preparation method according to claim 2, characterized in that, The starting compound has the structure shown in structural formula IV, V, or VI: 。 4. The preparation method according to claim 3, characterized in that: The polar aprotic solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, and acetonitrile. And / or, the alkaline reagent is one or more of sodium hydride, calcium hydride, sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate; And / or, the phase transfer catalyst is cesium fluoride.

5. A polyimide gas separation membrane, characterized in that, The polyimide gas separation membrane is obtained by thermal crosslinking of a polyimide resin having the structure shown in general formula (2), wherein the polyimide resin having the structure shown in general formula (2) is prepared using the tetrafluorostyrene-containing thermally crosslinkable diamine as described in claim 1 as one of the raw materials: ； Where n is 1, m is 1-9, and R2 is any one of structural formula I, structural formula II, and structural formula III.

6. The polyimide gas separation membrane according to claim 5, characterized in that, R1 can be one or more of the following structures: ； R3 can be one or more of the following structures: 。 7. The polyimide gas separation membrane according to claim 5 or 6, characterized in that, The polyimide gas separation membrane has a number average molecular weight of 30,000-120,000, a weight average molecular weight of 60,000-240,000, and a molecular weight distribution coefficient of 1.6-2.

6.

8. A method for preparing the polyimide gas separation membrane as described in claim 5 or 6, characterized in that, Includes the following steps: A) Under an inert atmosphere, the dianhydride monomer, the diamine containing the thermocrosslinkable tetrafluorostyrene structure, and the diamine monomer used to form R3 in general formula (2) are reacted in a polar aprotic solvent for 6-24 hours to obtain a polyamic acid solution; wherein the ratio of the total molar number of amino groups in all diamine monomers to the total molar number of anhydride groups in all dianhydride monomers is 1:1 to 1.02:1; B) Add an imidizing agent to the polyamic acid solution obtained in step A) to carry out a chemical imidization reaction to obtain polyimide resin; C) Dissolve the polyimide resin obtained in step B) in an organic solvent, filter it, and cast it into a membrane. First, evaporate the solvent at 15-30℃ for 20-72h, and then dry it under vacuum at 80-150℃ to obtain an uncrosslinked polyimide gas separation membrane. D) Thermal crosslinking: The uncrosslinked polyimide gas separation membrane obtained in step C) is post-baked at 200-260℃ for 0.5-6 hours to obtain a crosslinked polyimide gas separation membrane.

9. The preparation method according to claim 8, characterized in that: In step A), the polar aprotic solvent is one or more of N,N-dimethylacetamide, N,N-dimethylformamide, or N,N-diethylacetamide; And / or, in step B), the imidizing agent for the chemical imidization reaction is a mixed solution of acetic anhydride and pyridine; And / or, in step B), the chemical imidization reaction is carried out at 60-140°C; And / or, in step B), the chemical imidization reaction takes 6-12 hours; And / or, in step B), the polyimide resin is precipitated, washed, and dried in an ethanol / water mixture.

10. The application of the polyimide gas separation membrane as described in claim 5 or 6 in the field of gas separation.

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