A triazine-based covalent organic polymer free-standing membrane and a method for preparing the same

Abstract

The application discloses a triazine-based covalent organic polymer self-supporting film and a preparation method thereof, and belongs to the technical field of high polymer materials. The preparation method comprises the following steps: dissolving monomer A (cyanuric chloride) and monomer B (aromatic polyamine) in an organic solvent, forming a homogeneous pre-polymer solution through controlled pre-reaction at room temperature, and then constructing a self-supporting film with a highly cross-linked structure through solution casting and heat treatment to induce in-situ polymerization. Through accurate control of reaction kinetics, the application solves the problem that covalent organic polymers are prone to gelation at high temperatures and are difficult to be processed into films due to high cross-linking, and realizes self-supporting formation of a novel triazine-based covalent organic polymer structure. The obtained film has excellent intrinsic microporous structure and physical and chemical stability, and exhibits excellent permeability and selectivity in CO2 / N2, CO2 / CH4 and other separation systems.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and particularly relates to a triazine-based covalent organic polymer self-supporting membrane and its preparation method. Background Technology

[0002] Covalent organic frameworks (COFs), as a class of crystalline porous materials with high crystallinity and regular pores, have attracted widespread attention in the field of gas separation. For example, Chinese patent CN119857381A discloses a gas separation membrane based on a covalent organic framework and its preparation method, which utilizes crystalline pores to achieve efficient sieving. However, the construction of COFs is mostly based on dynamic covalent chemistry (such as C=N bonds, BO bonds, etc.), and their stability in humid or acidic industrial flue gas environments faces challenges. In addition, due to the extremely high crystallinity of COFs, their intrinsic brittleness is high, making it extremely difficult to prepare macroscopically intact, flexible, self-supporting films without the need for a porous substrate.

[0003] In contrast, covalent organic polymers (COPs), as amorphous counterparts of COFs, typically exhibit better mechanical toughness and chemical stability due to their highly cross-linked random networks. In particular, triazine-based COPs constructed from cyanuric chloride monomers, linked by irreversible CN bonds, demonstrate even superior physicochemical resistance.

[0004] However, the practical application of triazine-based COP in membrane formation faces serious "processing challenges." Due to the extremely high nucleophilic substitution activity and three crosslinking sites of cyanuric chloride, during traditional polycondensation, the monomer often undergoes rapid crosslinking polymerization within a short period. This causes the polymer to quickly gel and precipitate from the solution in the early stages of formation, ultimately yielding only an insoluble amorphous powder. To achieve membrane separation applications, existing technologies often require incorporating the powder filler into the matrix polymer. However, this easily leads to interfacial defects or embedding of active sites, severely affecting the membrane's selectivity.

[0005] Therefore, drawing on the molecular-level design advantages of COFs and utilizing the stability and toughness of COPs, developing a method to regulate polymerization kinetics, solve processing and molding problems, and construct novel high-performance triazine-based COP self-supporting separation membranes in situ is a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a triazine-based covalent organic polymer self-supporting membrane and its preparation method, which features a relatively simple process, ease of in-situ molding, and excellent gas separation performance. This addresses one of the problems encountered by existing cross-linked organic polymers during the preparation process, namely, rapid gelation during the high-temperature polymerization stage due to the high monomer reactivity and high cross-linking density, making them difficult to transfer and process.

[0007] On one hand, embodiments of the present invention provide a method for preparing a triazine-based covalent organic polymer self-supporting membrane, comprising the steps of: S1. Place monomer A and monomer B in a reaction vessel, add organic solvent and stir to dissolve, to obtain a precursor solution; S2. At room temperature, the precursor solution is stirred to carry out a prepolymerization reaction for 0.5-2 hours to obtain a prepolymer solution. S3. Transfer the prepolymer solution into the molding die and allow it to flow naturally to level out. S4. The molding die is heated at 80-160℃ for 8-24 hours to obtain a crude polymer film. S5. The obtained crude film is purified and dried to obtain an organic polymer self-supporting membrane. Among them, monomer A is cyanuric chloride; monomer B is selected from aromatic polyamines.

[0008] Furthermore, in step S1, if monomer B is an aromatic diamine, the molar ratio of monomer A to monomer B is 2:3; if monomer B is an aromatic triamine, the molar ratio of monomer A to monomer B is 1:1. The monomer B is selected from 1,3,5-tris(4-aminophenyl)benzene, 3,3'-dimethylbenzidine, 2,6-diaminotriptene or 2,7-diaminotriptene, 2,6,14-triaminotriptene, 4,4'-diaminodiphenyl ether, p-phenylenediamine, benzidine, 9,9-bis(4-aminophenyl)fluorene, tris(4-aminophenyl)amine, 1,5-diaminonaphthalene or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine.

[0009] Furthermore, in step S1, the organic solvent is selected from polar aprotic solvents; preferably, the organic solvent is selected from N,N-dimethylformamide, dimethyl sulfoxide, and N-methylpyrrolidone; preferably, the organic solvent is selected from N-methylpyrrolidone.

[0010] Furthermore, in step S2, the stirring time is 30-60 min; preferably, the stirring time is 30 min.

[0011] Furthermore, in step S4, the heat treatment temperature is 100-150°C; preferably, the heat treatment temperature is 100°C. The heat treatment time is 12-15 h; preferably, the heat treatment time is 12 h.

[0012] On one hand, embodiments of the present invention provide a thin film prepared by the above preparation method, wherein the thin film is a self-supporting film with an intrinsic microporous network structure, and its crosslinking backbone is formed by triazine ring centers and aromatic amine units connected by covalent bonds.

[0013] On the one hand, embodiments of the present invention provide the application of the above-mentioned thin film in processing separation systems containing CO2 / N2, CO2 / CH4, etc.

[0014] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. Macroscopic continuous film formation was achieved: By utilizing the stepwise reaction characteristics of cyanuric chloride and controlling the degree of crosslinking in the early stage of the system through room temperature prepolymerization, the common problems of easy powdering and difficult processing of crosslinked porous polymers during the synthesis process were solved, and a self-supporting membrane material with complete physical morphology and high flatness was obtained.

[0015] 2. Simplified process and improved purity: The film formation process does not require the addition of external catalysts (such as organic bases), avoiding the pollution of the membrane microporous environment by residual catalysts, and giving the obtained COP membrane more intrinsic pore properties.

[0016] 3. Enhanced structural stability: The strong covalent cross-linked network formed between the triazine ring and the aromatic amine gives the film good mechanical strength and physicochemical resistance, which can meet the requirements of harsh industrial separation environments.

[0017] 4. Flexible design space for separation performance: By changing the geometric configuration of monomer B (such as rigid bridge rings, bifurcated structures, etc.), the free volume and micropore distribution within the membrane can be effectively adjusted to obtain separation performance that combines high permeation flux and gas selectivity. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the triazine-based covalent organic polymer self-supporting membrane COP-TAPB of the present invention; Figure 2 This is a scanning electron microscope image of the surface of the triazine-based covalent organic polymer self-supporting membrane COP-TAPB of the present invention; Figure 3 Solid-state NMR of the triazine-based covalent organic polymer self-supporting film COP-TAPB of this invention 13 C spectrum; Figure 4The infrared spectrum of the triazine-based covalent organic polymer self-supporting membrane COP-TAPB of this invention; Figure 5 This is a schematic diagram of the stress-strain curve of the triazine-based covalent organic polymer self-supporting membrane COP-TAPB of the present invention; Figure 6 The image shows the XRD pattern of the triazine-based covalent organic polymer self-supporting membrane COP-TAPB of this invention. Figure 7 The CO2 adsorption-desorption curves of the triazine-based covalent organic polymer self-supporting membrane COP-TAPB of this invention are shown below. Figure 8 This is a schematic diagram of the thin film product prepared in Comparative Example 1. Detailed Implementation

[0019] The technical solutions in specific embodiments of the present invention will be described in detail and completely below. Obviously, the described embodiments are only some specific implementations of the overall technical solution of the present invention, and not all implementations. Based on the overall concept of the present invention, all other embodiments obtained by those skilled in the art fall within the protection scope of the present invention.

[0020] To provide a clearer and more detailed description of the preparation method of the triazine-based covalent organic polymer self-supporting membrane provided in the embodiments of the present invention, the following description will be based on specific embodiments.

[0021] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Unless otherwise specified, the materials and reagents used in the following examples are commercially available.

[0022] To address the problems of rapid gelation, difficulty in transfer, and molding during the high-temperature polymerization stage of existing crosslinked organic polymers due to the high reactivity and crosslinking density of monomers, this invention provides a method for preparing a self-supporting membrane of a triazine-based covalent organic polymer, comprising the following steps: S1. According to the principle of equimolar balance of monomer active sites, monomer A (cyanuric chloride) and monomer B (aromatic polyamine) are stirred and dissolved in an organic solvent to form a precursor solution. S2. The precursor solution is magnetically stirred at room temperature at a stirring speed of 200 rpm to pre-react, so that the monomer undergoes a preliminary nucleophilic substitution reaction to form a prepolymer solution with a viscosity between 100-1000 cp. S3. Transfer the homogeneous prepolymer solution into a molding mold (circular petri dish) and allow it to level naturally; S4. The molding die is heated at 80-160℃ to drive the rearrangement of polymer chain segments by the continuous evaporation of solvent and simultaneously trigger the deep polymerization of the remaining active sites of monomers to achieve in-situ cross-linking and film formation, thereby obtaining a crude film. S5. The obtained crude film is purified and dried to obtain crude polymer film.

[0023] In step S1, the ratio logic of monomer A and monomer B is as follows: if monomer B is an aromatic diamine, the molar ratio of monomer A to monomer B is 2:3; if monomer B is an aromatic triamine, the molar ratio of monomer A to monomer B is 1:1.

[0024] Wherein, monomer B is selected from one or more of 1,3,5-tris(4-aminophenyl)benzene (TAPB), 3,3'-dimethylbenzidine (DMB), 2,6-diaminotriphenylene (TDA), 2,6,14-triaminotriphenylene (TAT), 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PPD), benzidine (BD), 9,9-bis(4-aminophenyl)fluorene (BAFL), tris(4-aminophenyl)amine (TAPA), 1,5-diaminonaphthalene (DAN), and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA).

[0025] In one possible implementation, monomer B is selected from TAPB.

[0026] In one possible implementation, monomer B is selected from DMB.

[0027] In one possible implementation, monomer B is selected from TDA.

[0028] In one possible implementation, monomer B is selected from TAT.

[0029] In one possible implementation, monomer B is selected from TAT.

[0030] In one possible implementation, monomer B is selected from ODA.

[0031] In one possible implementation, monomer B is selected from PPD.

[0032] In one possible implementation, monomer B is selected from BD.

[0033] In one possible implementation, monomer B is selected from BAFL.

[0034] In one possible implementation, monomer B is selected from TAPA.

[0035] In one possible implementation, monomer B is selected from DAN.

[0036] In one possible implementation, monomer B is selected from TTA.

[0037] In S1, the organic solvent is a polar aprotic solvent; preferably, the organic solvent is selected from N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) or N-methylpyrrolidone (NMP); preferably, the organic solvent is selected from NMP.

[0038] In step S2, the stirring time is 0.5-2 h; more preferably, the stirring time is 30-60 min; and more preferably, the stirring time is 30 min. The room temperature is generally 20-30℃, preferably 25℃.

[0039] In step S4, the heat treatment temperature range is 80-160℃, and the heat treatment time is 8-24 h; preferably, the heat treatment temperature is 100-150℃, and the time is 12-15 h.

[0040] In step S5, the purification method is methanol Soxhlet extraction for 8-24 h, the oil bath temperature is set at 70℃, and the drying treatment is vacuum drying at 120℃ for 2 h.

[0041] This invention also provides an application of a triazine-based covalent organic polymer self-supporting membrane.

[0042] Example 1: Preparation of COP-TAPB self-supporting thin films Cyanuric chloride (36.9 mg, 0.2 mmol) and 1,3,5-tris(4-aminophenyl)benzene (TAPB, 70.3 mg, 0.2 mmol) were placed in a reaction vessel; 4 mL of NMP solvent was added and stirred until dissolved; the mixture was magnetically stirred (200 rpm) at room temperature (approximately 25 °C) for 30 min to bring the solution viscosity to between 100 and 1000 cp; then the mixture was poured into round glass petri dishes, allowed to level naturally, and the petri dishes were heat-treated in an oven at 100 °C for 12 h; after Soxhlet extraction with methanol for 8 h (oil bath temperature of 70 °C), the mixture was vacuum dried at 120 °C for 2 h.

[0043] Combination Figure 1 As can be seen from the images, the film prepared by the room temperature prepolymerization and high temperature deep polymerization strategy of this invention is transparent and uniform, and possesses certain toughness and mechanical strength; Figure 2 The surface scanning electron microscope image shows that the prepared thin film is smooth and defect-free; Figure 3 MRI 13As can be seen from C, the resonance peak at 164.5 ppm belongs to the characteristic C of the triazine ring, and the resonance peaks at 138, 128, and 120 ppm belong to the characteristic peaks of the aromatic carbon of the triamine monomer TAPB, thus preliminarily proving the structure of the triazine-based covalent organic polymer film; Figure 4 The infrared spectrum of the thin film shows a value of 3380 cm⁻¹. -1 The characteristic peaks of -NH- at 1562 and 1469 cm⁻¹ -1 The -C=N- and -CN- vibrational peaks further confirm the successful preparation of the triazine-based covalent organic polymer film; Figure 5 The stress-strain curve of the thin film shows that the prepared thin film has a certain mechanical strength, meeting the requirements of a gas separation membrane; Figure 6 Wide-angle X-ray scattering spectra revealed that the film was in a completely amorphous state, with only two broad peaks observed, corresponding to average chain distances of [missing information]. and ;analyze Figure 7 The CO2 adsorption / desorption curves of the thin film were obtained, and its specific surface area was found to be as high as 513 m², calculated by nonlocal density functional theory. 2 g -1 This is attributed to the introduction of rigid monomers with large-volume spatial steric hindrance.

[0044] Example 2: Preparation of COP-DMB self-supporting thin films The difference from Example 1 is that the monomers are: cyanuric chloride (36.9 mg, 0.2 mmol) and 3,3'-dimethylbenzidine (DMB, 63.7 mg, 0.3 mmol). The finished membrane was prepared using the same steps as in Example 1.

[0045] Example 3: Preparation of COP-TDA self-supporting thin films The difference from Example 1 is that the monomers are: cyanuric chloride (36.9 mg, 0.2 mmol) and 2,6-diaminotriptene (TDA, 85.3 mg, 0.3 mmol). The finished membrane was prepared using the same steps as in Example 1.

[0046] Example 4: Preparation of COP-TAT self-supporting thin films The difference from Example 1 is that the monomers are: cyanuric chloride (36.9 mg, 0.2 mmol) and 2,6,14-triaminotriptene (TAT, 59.9 mg, 0.2 mmol). The finished membrane was prepared using the same steps as in Example 1.

[0047] Example 5: Preparation of COP-ODA self-supporting thin film The difference from Example 1 is that the monomers are: cyanuric chloride (36.9 mg, 0.2 mmol) and 4,4'-diaminodiphenyl ether (ODA, 60.1 mg, 0.3 mmol). The finished membrane was prepared using the same steps as in Example 1.

[0048] Example 6: Preparation of COP-PPD self-supporting thin films The difference from Example 1 is that the monomers are: cyanuric chloride (36.9 mg, 0.2 mmol) and p-phenylenediamine (PPD, 32.4 mg, 0.3 mmol). The finished membrane was prepared using the same steps as in Example 1.

[0049] Example 7: Preparation of COP-BD self-supporting thin films The difference from Example 1 is that the monomers are: cyanuric chloride (36.9 mg, 0.2 mmol) and benzidine (BD, 55.3 mg, 0.3 mmol). The finished membrane was prepared using the same steps as in Example 1.

[0050] Example 8: Preparation of COP-BAFL self-supporting thin films The difference from Example 1 is that the monomers are: cyanuric chloride (36.9 mg, 0.2 mmol) and 9,9-bis(4-aminophenyl)fluorene (BAFL, 104.5 mg, 0.3 mmol). The finished membrane was prepared using the same steps as in Example 1.

[0051] Example 9: Preparation of COP-TAPA self-supporting thin films The difference from Example 1 is that the monomers are: cyanuric chloride (36.9 mg, 0.2 mmol) and tris(4-aminophenyl)amine (TAPA, 58.1 mg, 0.2 mmol). The finished membrane was prepared using the same steps as in Example 1.

[0052] Example 10: Preparation of COP-DAN self-supporting thin films The difference from Example 1 is that the monomers are: cyanuric chloride (36.9 mg, 0.2 mmol) and 1,5-diaminonaphthalene (DAN, 47.5 mg, 0.3 mmol). The finished membrane was prepared using the same steps as in Example 1.

[0053] Example 11: Preparation of COP-TTA self-supporting thin films The difference from Example 1 is that the monomers are: cyanuric chloride (36.9 mg, 0.2 mmol) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TTA, 70.9 mg, 0.2 mmol). The finished membrane was prepared using the same steps as in Example 1.

[0054] Comparative Example 1: Direct heating treatment without pre-reaction The monomer ratio is the same as in Example 1 (TAPB system). After dissolution, it is not pre-reacted at room temperature, but directly placed at 100°C for treatment.

[0055] Results: The system precipitated fragments and failed to form a continuous self-supporting film, as shown in the attached image. Figure 8 As shown.

[0056] Performance testing 1. Pure gas permeability and selectivity test The encapsulated membrane was placed in the constant volume pressure change test device. After the instrument was evacuated, the gas to be tested was introduced upstream at 0.2 MPa. The change in downstream pressure of the test membrane over time was used to obtain the amount of gas permeation per unit time, thereby obtaining its gas permeability. The test data are shown in Table 1.

[0057] Table 1. Test results of pure gas separation performance Note: The unit for gas permeability of the dense membrane is Barrer. The permeation flux and selectivity were measured at 25°C and 2 bar pressure, where 1 bar = 0.1 MPa.

[0058] Performance evaluation results show that the series of triazine-based covalent organic polymer (COP) membranes prepared using this invention exhibit excellent gas separation performance, especially in CO2 / N2 and CO2 / CH4 systems. Specifically, COP-DMB, due to the strong π-π stacking interaction between the rigid triazine ring and benzidine, results in tightly packed molecular chains, thus exhibiting lower CO2 permeability through enhanced molecular sieving effect, but achieving significantly improved CO2 / N2 and CO2 / CH4 selectivity. In contrast, the introduction of rigid monomers with large steric hindrance (such as TAPB and TDA) significantly increases the free volume within the polymer, resulting in a substantial increase in the permeability of the obtained membrane while maintaining good separation selectivity. Taking COP-TAPB as an example, its CO2 permeability coefficient reaches as high as 1458 Barrer, and its selectivity for CO2 / N2 and CO2 / CH4 remains at 32.5 and 27.5, respectively. The above results confirm that by flexibly designing and controlling the structure of polyamine monomers, the membrane microstructure can be effectively optimized, thereby obtaining a novel triazine-based COP membrane with both high permeability and high selectivity, which has broad application prospects in the field of carbon capture.

[0059] 2. Mixed gas permeability and selectivity test The membrane packaged in Example 2 was installed in a cross-flow constant volume pressure swing test apparatus. First, the entire system was thoroughly evacuated to eliminate interference from residual gas within the system. Then, compressed air with a pressure range of 0.2 ~ 1.5 MPa was introduced upstream of the test apparatus as a gas supply source. The gas permeation rate per unit time was obtained by monitoring the pressure change in the downstream cavity of the membrane. To further determine the composition of the permeated gas, downstream gas samples were collected after stable permeation, and gas chromatography was used for component analysis to obtain the permeation performance of each gas component in the membrane material. The corresponding gas permeability test results are detailed in Table 2.

[0060] Table 2. Gas Separation Performance Test Note: The gas permeability and selectivity were measured at 25℃ and 2-15 bar, where 1 bar = 0.1 MPa. Given that the membrane material prepared in Example 2 exhibited excellent permeability and selectivity in pure gas separation tests, further CO2 / N2 mixed gas separation performance tests were conducted to evaluate its separation capacity and stability under practical application conditions. In the mixed gas permeation test, considering the significant competitive adsorption effect between CO2 and N2, the permeability of both gases decreased to some extent with increasing upstream gas supply pressure.

Claims

1. A method for preparing a triazine-based covalent organic polymer self-supporting membrane, characterized in that, Including the following steps: S1. Place monomer A and monomer B in a reaction vessel, add organic solvent and stir to dissolve, to obtain a precursor solution; S2. At room temperature, the precursor solution is stirred to carry out a prepolymerization reaction for 0.5-2 hours to obtain a prepolymer solution. S3. Transfer the prepolymer solution into the molding die and allow it to flow naturally to level out. S4. The molding die is heated at 80-160℃ for 8-24 hours to obtain a crude polymer film. S5. The obtained crude film is purified and dried to obtain an organic polymer self-supporting membrane. Among them, monomer A is cyanuric chloride; monomer B is selected from aromatic polyamines.

2. The preparation method according to claim 1, characterized in that, In step S1, if monomer B is an aromatic diamine, the molar ratio of monomer A to monomer B is 2:3; if monomer B is an aromatic triamine, the molar ratio of monomer A to monomer B is 1:

1. The monomer B is selected from 1,3,5-tris(4-aminophenyl)benzene, 3,3'-dimethylbenzidine, 2,6-diaminotriptene or 2,7-diaminotriptene, 2,6,14-triaminotriptene, 4,4'-diaminodiphenyl ether, p-phenylenediamine, benzidine, 9,9-bis(4-aminophenyl)fluorene, tris(4-aminophenyl)amine, 1,5-diaminonaphthalene, or 2,4,6-tris(4-aminophenyl)-1,3,5-triazine.

3. The preparation method according to claim 1 or 2, characterized in that, In step S1, the organic solvent is selected from polar aprotic solvents; preferably, the organic solvent is selected from N,N-dimethylformamide, dimethyl sulfoxide, or N-methylpyrrolidone; preferably, the organic solvent is selected from N-methylpyrrolidone.

4. The preparation method according to any one of claims 1-3, characterized in that, In step S2, the stirring time is 30-60 min; preferably, the stirring time is 30 min.

5. The preparation method according to any one of claims 1-4, characterized in that, In step S4, the heat treatment temperature is 100-150℃; preferably, the heat treatment temperature is 100℃. The heat treatment time is 12-15 h; preferably, the heat treatment time is 12 h.

6. The thin film prepared by the method according to any one of claims 1-5, characterized in that, The film is a self-supporting film with an intrinsic microporous network structure, and its cross-linked backbone is formed by triazine ring centers and aromatic amine units connected by covalent bonds.

7. The application of the membrane according to claim 6 in processing separation systems containing CO2 / N2, CO2 / CH4, etc.

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