A method for modifying the surface of an aromatic polyamide composite membrane with a functional isocyanate crosslinking agent

Abstract

The present invention provides a method for modifying the surface of an aromatic polyamide composite membrane with a functional isocyanate crosslinking agent. Specifically, it is a graft crosslinking modification of the surface of the aromatic polyamide composite membrane with an isocyanate crosslinking agent containing disulfobetaine and a polyether chain in its molecular structure. After modification, the surface of the membrane has high hydrophilicity; the intrinsic N-H groups of the aromatic polyamide separation layer are replaced by the newly formed aromatic polyamide N-H groups, and the latter participates in the reaction with residual chlorine or chlorine oxides in seawater, effectively ensuring the long-term stability of the structure of the aromatic polyamide composite membrane.

Description

Technical Field

[0001] The present invention relates to a method for modifying the surface of an aromatic polyamide composite membrane, specifically a method for modifying the surface of an aromatic polyamide composite membrane with a functional isocyanate crosslinking agent containing disulfobetaine and a polyether chain in its molecular structure, which is applied to the seawater desalination process and belongs to the field of functional polymer materials. Technical Background

[0002] Since the invention of the aromatic polyamide reverse osmosis composite membrane by Dow Filmtec in 1987, it has become one of the most effective and economical methods for seawater and brackish water desalination, sewage treatment, reclaimed water reuse, and pure water preparation. The aromatic polyamide reverse osmosis composite membrane is usually composed of a polysulfone ultrafiltration membrane or a polyethersulfone ultrafiltration membrane as a support membrane and a thin aromatic polyamide separation layer. The aromatic polyamide reverse osmosis composite membrane has the advantages of simple preparation technology, high desalination rate, large water flux, and low operating pressure. However, its marine biofouling still restricts its application and development. One of the simple and low-cost improvement measures is to disinfect and sterilize the seawater before reverse osmosis with chlorine to clean the water source and control biological pollution. However, the aromatic polyamide reverse osmosis composite membrane is sensitive to chlorine oxidation, and the residual active chlorine (including chlorine gas or hypochlorite) in seawater will cause chemical damage to the molecular chain structure of the aromatic polyamide separation layer, resulting in a rapid decline in the membrane separation performance and a significant reduction in the service life. Therefore, for decades, people have been continuously investing a huge amount of manpower, financial resources, and material resources in researching and developing aromatic polyamide reverse osmosis composite membranes with high chlorine resistance.

[0003] Professionals are well aware that the structural characteristics of the aromatic polyamide separation layer of the aromatic polyamide reverse osmosis composite membrane determine its surface hydrophilicity, chlorine oxidation resistance, separation efficiency, easy cleaning of dirt, regeneration and reuse, etc., which are all key factors determining the low-cost and high-efficiency operation of seawater desalination. The structure of the aromatic polyamide separation layer has three levels. First, it is the aromatic polyamide polymer chain structure formed by monomer polymerization (referring to polymerization units, repeating units, bonding valence states, chain crosslinking, etc.); second, it is the inter-chain structure determined by polymerization technology and processes (mainly inter-chain entanglement, stacking, hydrogen bonding, etc.); third, it is the membrane surface characteristics (mainly referring to the types of surface groups, charge status, hydrophilic / hydrophobic properties, surface smoothness, adsorption or attachability, etc.). In order to obtain an aromatic polyamide composite membrane with excellent comprehensive properties such as high surface antifouling performance, high anti-chlorine oxidation stability, high surface hydrophilicity, large water permeability, and high desalination and separation performance, the research and development space from the first and second levels of the structure is relatively small. Relatively speaking, modifying its surface is a simple, effective, fast, and flexible method to improve or enhance the comprehensive performance of the membrane.

[0004] In the past four decades, there have been a wide variety of examples of surface modification of related aromatic polyamide reverse osmosis composite membranes, mainly including: (1) surface coating, (2) surface deposition, and (3) surface grafting. Among them, grafting water-soluble substances onto the membrane surface by chemical methods, such as polyethylene glycol, polyacrylic acid, polyacrylamide, quaternary ammonium salts, zwitterionic polymer brushes, betaine, etc., and also grafting thioethers, sulfonamides, chlorohydantoins, polysaccharides, graphene oxide or carbon nanotubes, etc., have all played a positive role in improving their antifouling performance and chlorine resistance stability. However, the uniformity of modifying the membrane surface by the above methods is poor, the density of introduced functional groups is small, the changes in membrane surface characteristics are not significant, and the water flux changes little; some are also extremely prone to causing membrane pore blockage, resulting in a decrease in water permeation ability instead; in addition, during the process of surface graft copolymer modification of the membrane, the waste of monomer raw materials caused by monomer homopolymerization is serious; finally, the prominent defect of these existing surface modification methods and technologies is that the improvement of the performance of aromatic polyamide composite membranes is single. How to comprehensively improve the comprehensive performance of the membrane remains a bottleneck problem in the field of seawater desalination by reverse osmosis membranes.

[0005] Aiming at the defects of the existing surface modification technology and grafting modification method of aromatic polyamide composite membranes, CN103349922B once proposed a method of "planting" a lattice containing quaternary ammonium salt and salicylaldehyde functional groups on the membrane surface through chemical reactions. Its purpose is to utilize the sterilization and biocidal effects of quaternary ammonium salt and salicylaldehyde functional groups with different mechanisms and the selective complexation and adsorption of heavy metal ions in seawater to produce a synergistic and highly efficient anti-marine biofouling function to ensure the cleanliness of the membrane surface; secondly, the salicylaldehyde units on the surface of the aromatic polyamide composite membrane are more sensitive to chemical reactions of chlorine or chlorine oxides and can be used as sacrificial materials to protect the intrinsic structure of the membrane; furthermore, grafting quaternary ammonium salt on the membrane surface can effectively improve the hydrophilicity of the membrane, which is beneficial to ensuring the water flux of the membrane. However, with the extension of the membrane use time, the problem of marine biofouling still exists. In 2015, CN105251372B disclosed a method of modifying a new aromatic polyamide composite membrane with organic polyamine and then carrying out a condensation reaction with N,N,N-trihydroxy-N-(4-hydroxy-3-aldehyde benzyl) ammonium chloride to prepare a method for densely grafting salicylaldehyde Schiff base and quaternary ammonium cations on the membrane surface. The hydrophilicity of the membrane surface has changed and the water flux has increased. However, the process is relatively complex, the modification object is single, and the application prospect is not good. Subsequently, CN201811305536.9 and CN201811011240.6 introduced the surface graft modification of aromatic polyamide composite membranes with terminal isocyanate group polyurethane prepolymers containing quaternary ammonium cations, polyethers and salicylaldehyde units in their molecular structures. However, the intermolecular structure of the aromatic polyamide separation layer is partially damaged, affecting the separation efficiency of the membrane.

[0006] On the basis of drawing on the strengths and advantages of existing technologies and methods, the inventor of the present invention carefully analyzed and accurately determined the defects of existing methods and technologies. Therefore, a surface modification method of an aromatic polyamide composite membrane with a functional isocyanate crosslinking agent containing disulfobetaine and polyether chains in its molecular structure is proposed. The aromatic polyamide composite membrane includes an aromatic polyamide composite membrane (referred to as a nascent membrane for short) produced by completing a polycondensation reaction on a microporous polysulfone support membrane or a polyethersulfone support membrane using m-phenylenediamine and trimesoyl chloride as raw materials; an aromatic polyamide composite membrane after hydrolysis of the nascent membrane, referred to as a commercial membrane for short; an aromatic polyamide composite membrane surface-modified by the nascent membrane or the commercial membrane, referred to as a modified membrane for short; or a used aromatic polyamide composite membrane cleaned by physical or chemical methods, referred to as a regenerated membrane for short). There are already numerous experimental facts indicating that the zwitterions of sulfobetaine have strong hydration and sterilization and antibacterial effects, and excellent anti-protein or microbial surface adhesion performance, and belong to the preferred materials for preventing biological fouling. It can also significantly improve the hydrophilicity of the membrane surface and reduce the membrane water permeation resistance; the flexible packing and hydration effect presented by the polyether chain on the membrane surface also have significant anti-biofouling performance; the aromatic isocyanate crosslinking agent can not only chemically react with the residual intrinsic primary amino group or intrinsic aromatic amide N-H on the surface of the aromatic polyamide composite membrane, eliminate the chemical degradation of the vulnerable parts of the membrane by active chlorine, and improve the chlorine resistance of the membrane; in addition, the newly generated aromatic amide N-H units produced by the reaction of the aromatic isocyanate crosslinking agent with the residual intrinsic primary amino group or intrinsic aromatic amide N-H on the membrane surface can replace the intrinsic aromatic amide N-H of the membrane with higher reactivity to participate in the chemical reaction of active chlorine in water, and also strengthen the intermolecular structure firmness of the separation layer of the aromatic polyamide composite membrane through the crosslinking of the aromatic isocyanate crosslinking agent between the chains of the aromatic polyamide separation layer, ensuring the efficient and long-lasting operation of the aromatic polyamide composite membrane. To sum up, the surface modification of the aromatic polyamide composite membrane with a functional isocyanate crosslinking agent containing disulfobetaine and polyether chains provided by the present invention has the characteristics of a wide range of adaptable modification methods, multiple modification directions, comprehensive improvement of membrane properties, simple process, and adjustable and controllable operation. Summary of the Invention

[0007] The surface modification method of the aromatic polyamide composite membrane with the functional isocyanate crosslinking agent described in the present invention is realized according to the following method: The cleaned and dried aromatic polyamide composite membrane is immersed in the functional isocyanate crosslinking agent solution, or the functional isocyanate crosslinking agent solution is sprayed, brushed or roll-coated on the surface of the aromatic polyamide composite membrane, and then heat-treated at 60-130 °C for 0.2-20 hours, and the organic solvent and diluent are recovered to obtain an aromatic polyamide composite membrane with disulfobetaine and polyether chains grafted on the surface.

[0008] Wherein the aromatic polyamide composite membrane includes one of a nascent membrane, a hydrolyzed membrane, a modified membrane, or a regenerated membrane; the nascent membrane refers to an aromatic polyamide composite membrane directly produced by carrying out a polycondensation reaction on a porous polysulfone support membrane or a porous polyethersulfone support membrane using m-phenylenediamine and trimellitic acid chloride as raw materials; the hydrolyzed membrane refers to an aromatic polyamide composite membrane obtained by hydrolyzing the nascent membrane; the modified membrane refers to an aromatic polyamide composite membrane surface-modified from the nascent membrane, the hydrolyzed membrane, or a commercially available aromatic polyamide composite membrane; the regenerated membrane refers to a used aromatic polyamide composite membrane cleaned by physical or chemical methods.

[0009] The mass percentage concentration of the functional isocyanate crosslinking agent in the functional isocyanate crosslinking agent solution is 0.5 - 50%; the functional isocyanate crosslinking agent solution is 5 - 50% of the mass of the aromatic polyamide composite membrane.

[0010] The functional isocyanate crosslinking agent has the structure shown in the general formula (A):

[0011]

[0012] Wherein R1 and R2 in the general formula (A) are each independently selected from substituted or unsubstituted C1 - C 18 hydrocarbyl groups, n is a natural number selected from 1 to 2000, and is selected from C1 - C 18 alkylene groups, and is selected from C1 - C 18 alkylene groups or one of them, where p is a natural number selected from 1 to 2000.

[0013] In the present invention, there are three types of functional groups in the molecular structure of the functional isocyanate crosslinking agent. First, the isocyanate group (-NCO), which is a group that chemically reacts with the residual NH2 or the intrinsic aromatic amide N-H on the surface of the aromatic polyamide composite membrane; the newly generated aromatic amide N-H produced thereafter can replace the intrinsic aromatic amide N-H on the surface of the aromatic polyamide composite membrane for the chloro-oxygen reaction. Secondly, the disulfobetaine and polyether chain, which have hydrophilicity, conductivity, antibacterial properties, antifogging, antifouling, or anticoagulant properties, can generate a hydration layer, a bactericidal and antibacterial layer, and a soft elastic layer on the membrane surface, all of which will produce the effect of preventing marine biofouling. Furthermore, the functional isocyanate crosslinking agent of the present invention can chemically crosslink the intrinsic N-H in the membrane chain structure to improve the physical, chemical, or mechanical stability.

[0014] The specific preparation process of the functional isocyanate crosslinking agent of general formula (A) according to the present invention is as follows: At room temperature, dissolve general formula (B) in an organic solvent, start stirring and slowly add polyethylene glycol monoacrylate, and the dosage of polyethylene glycol monoacrylate is 2.0 - 2.5 times the molar amount of general formula (B); after the feeding of polyethylene glycol monoacrylate is completed, raise the reaction temperature to 50 - 70 °C, continue the reaction for 4 - 40 hours, and then end the Michael addition reaction process; keep the reaction temperature, add γ - propiolactone to the reaction system, and the dosage of γ - propiolactone is 1.8 - 2.2 times the molar amount of general formula (B), after reacting for 2 - 6 hours, end the ring - opening reaction process; add the catalyst, diluent and general formula (D) into the reaction system in sequence, continue stirring and keep the temperature for reaction, after detecting that the NCO content in the materials in the reactor is consistent with the predetermined value, lower the temperature of the reaction product system to room temperature, end the addition reaction process, and obtain the functional isocyanate crosslinking agent solution with the structure shown in general formula (A) for standby.

[0015] Among them, general formula (B) has the following structure:

[0016]

[0017] Among them, R1 and R2 in general formula (B) are respectively selected from substituted or unsubstituted hydrocarbon groups, and the is selected from C1 - C 18 alkylene or one of them, and p therein is a natural number selected from 1 - 2000.

[0018] The polyethylene glycol monoacrylate has the structure shown in general formula (C):

[0019]

[0020] Among them, R in general formula (C) is selected from H or methyl, and n therein is a natural number selected from 1 - 2000.

[0021] The organic solvent refers to one or more of tetrahydrofuran, 1,4 - dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, chlorobenzene, chloroform, 1,2 - dichloroethane, hexane, cyclohexane, toluene, xylene, decalin, ethyl acetate, N - methylpyrrolidone, acetone, butanone, cyclohexanone, N,N - dimethylaniline, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, N,N - dimethylformamide, N,N - dimethylacetamide or dimethyl sulfoxide; the dosage of the organic solvent is 1 - 10 times the mass of general formula (B).

[0022] The catalyst refers to a complex of organotin and organic amine; wherein the organotin refers to one of dibutyltin dilaurate, stannous octoate, stannous oxalate, dibutyltin dimaleate, bis(dodecylthio)dibutyltin or dibutyltin diacetate; the organic amine refers to one of triethylamine, p-dimethylaminopyridine, N,N-dimethylformamide, triethylenediamine, 1,4-dialkylpiperazine, 1-alkylimidazole, 1,8-diazabicyclo[5.4.0]undec-7-ene, triethylenediamine carboxylate, 1,4-dialkylpiperazine carboxylate or 1-alkylimidazole carboxylate; the mass ratio of the organotin to the organic amine is 1:0 to 1.5; the dosage of the catalyst is 0.01 to 5% of the mass of the polyisocyanate of the general formula (D).

[0023] The general formula (D) refers to a polyisocyanate having the structure shown by the general formula (D):

[0024]

[0025] wherein q in the general formula (D) is selected from positive integers from 1 to 5, and the is selected from C1-C 18 alkylene;

[0026] The dosage of the polyisocyanate is 2.02 to 2.25 times the molar amount of the general formula (B).

[0027] The diluent refers to one or more of acetone, butanone, cyclohexanone, methyl acetate, ethyl acetate, ether, tetrahydrofuran, 1,4-dioxane, toluene, xylene or dimethyl sulfoxide; the dosage of the diluent is 1 to 10 times the mass of the general formula (B).

[0028] Compared with the prior art, the modified aromatic polyamide composite film prepared by the present invention has the following advantages:

[0029] ① After the functional isocyanate crosslinking agent of the general formula (A) provided by the present invention is applied to the surface modification of the aromatic polyamide composite film, the surface of the obtained modified polyaromatic amide composite film has superhydrophilicity and high anti-fouling and chlorine resistance performance.

[0030] ② The post-chemical modification of the aromatic polyamide composite film by using the functional isocyanate crosslinking agent of the general formula (A) provided by the present invention is simple and easy to operate and is easy to industrialize. Detailed implementation mode

[0031] Example 1 Application of the functional isocyanate crosslinking agent of formula (A1) to the modification of the aromatic polyamide composite film Preparation of the functional isocyanate crosslinking agent of formula (A1)

[0032] Dissolve 25 g of N,N'-dibenzylethylenediamine in 80 g of 1,4-dioxane and put it into the reaction kettle. Start stirring, and slowly add 30 g of 2-hydroxyethyl methacrylate at room temperature. After the addition of 2-hydroxyethyl methacrylate is complete, raise the reaction temperature to 55 - 60 °C and continue the reaction for 4 hours to obtain the intermediate of formula (1a); maintain the temperature of the reactants in the reaction kettle, add 26 g of γ-propane sultone to the reaction kettle, and after reacting for 6 hours, obtain the intermediate of formula (1b); put 0.22 g of dibutyltin dilaurate, 0.15 g of triethylenediamine, 120 g of acetone and 40 g of toluene diisocyanate into the reaction kettle, continue stirring and reacting while maintaining the temperature. When the NCO value in the reaction product system is detected to be 3.78%, lower the temperature of the reaction product system to room temperature to obtain a solution of the functional isocyanate crosslinking agent of formula (A1) for standby.

[0033]

[0034] Surface modification of the newly formed aromatic polyamide composite membrane

[0035] According to the methods and steps disclosed in Journal Membrane Science 428 (2013) 403–409 or Journal Membrane Science 457 (2014) 88–97, CN103349922B or CN105251372B, using m-phenylenediamine and trimesoyl chloride as monomers, through interfacial polymerization on the surface of a porous polysulfone support membrane, a newly formed aromatic polyamide composite membrane with an area of 1*1 cm and containing acyl chloride groups on the surface is prepared. Immerse the newly formed aromatic polyamide composite membrane in a solution of the functional isocyanate crosslinking agent of formula (1) with a mass percentage concentration of 4 - 6%, then take out the membrane and place it in a pressing plate at 120 °C for heat treatment for 3 minutes, and then cool down and wash it with deionized water until neutral to obtain the modified membrane (A1-1) of the newly formed aromatic polyamide composite membrane modified with the functional isocyanate crosslinking agent of formula A(1).

[0036] Surface modification of the commercially available aromatic polyamide composite membrane

[0037] Cut the commercially available aromatic polyamide composite membrane (BW-30, DuPont FilmTec RO membrane of the United States) into 1*1 cm sample membranes, and use the above-mentioned modification procedures and processes of the newly formed aromatic polyamide composite membrane to treat the sample membranes with the solution of the functional isocyanate crosslinking agent of formula (A1) to obtain the modified membrane (A1-2) of the commercially available BW-30, DuPont FilmTec RO membrane modified with the functional isocyanate crosslinking agent of formula (A1).

[0038] Example 2 Application of the functional isocyanate crosslinking agent of formula (A2) to the modification of the aromatic polyamide composite membrane

[0039] According to the method and operation steps of Example 1, change the hydroxyethyl methacrylate in Example 1 to polyethylene glycol-600 monomethacrylate, and change the toluene diisocyanate to diphenylmethane diisocyanate to prepare a solution of the functional isocyanate crosslinking agent of formula (A2) for standby.

[0040]

[0041] According to the method and operation steps of Example 1, use the solution of the functional isocyanate crosslinking agent of formula (A2) to perform surface modification treatment on the fresh membrane and the commercially available membrane respectively, and prepare the modified fresh modified membrane (A2-1) and BW-30 modified membrane (A2-2) respectively.

[0042] Example 3 Application of the functional isocyanate crosslinking agent of formula (A3) to the modification of aromatic polyamide composite membranes

[0043] According to the method and operation steps of Example 1, change the N,N'-dibenzylethylenediamine in Example 1 to N,N'-didodecylhexanediamine, change the hydroxyethyl methacrylate to polyethylene glycol-600 monomethacrylate, and change the toluene diisocyanate to diphenylmethane diisocyanate to prepare a solution of the functional isocyanate crosslinking agent of formula (A3) for standby.

[0044]

[0045] According to the method and operation steps of Example 1, use the solution of the functional isocyanate crosslinking agent of formula (A3) to perform surface modification treatment on the fresh membrane and the commercially available membrane respectively, and prepare the modified fresh modified membrane (A3-1) and BW-30 modified membrane (A3-2) respectively.

[0046] Example 4 Application of the functional isocyanate crosslinking agent of formula (A4) to the modification of aromatic polyamide composite membranes

[0047] According to the method and operation steps of Example 1, change the N,N'-dibenzylethylenediamine in Example 1 to α,ω-bis(benzylamino)polyether-200, and change the hydroxyethyl methacrylate to polyethylene glycol-600 monomethacrylate to prepare a solution of the functional isocyanate crosslinking agent of formula (A4) for standby.

[0048]

[0049] According to the method and operation steps of Example 1, use the solution of the functional isocyanate crosslinking agent of formula (A4) to perform surface modification treatment on the fresh aromatic polyamide composite membrane and the commercially available BW-30 aromatic polyamide composite membrane respectively, and prepare the modified fresh modified membrane (A4-1) and BW-30 modified membrane (A4-2) respectively.

[0050] Surface characteristics before and after membrane modification in Example 5

[0051] Take the freshly prepared modified membranes, BW-30 commercial membranes and modified BW-30 membranes in Examples 1 to 4, and observe the water contact angles of these membranes respectively according to the methods disclosed in Journal of Membrane Science 428(2013)403–409 or Journal of Membrane Science 457(2014)88–97, CN103349922B or CN105251372B. The results are shown in Table 1.

[0052] Table 1 Surface characteristics of aromatic polyamide composite membranes

[0053]

[0054] The experimental results in Table 1 clearly show that whether it is a newly prepared aromatic polyamide composite membrane or a commercially available aromatic polyamide composite membrane, after being treated with the functional isocyanate crosslinking agent described in the present invention, its surface hydrophilicity is greatly improved, and a water-wetting phenomenon appears. This indicates that disulfobetaine and polyether chains are grafted onto the surface of the aromatic polyamide composite membrane. Because only when disulfobetaine and polyether chains with strong hydration effects are successfully grafted onto the surface of the aromatic polyamide composite membrane can its surface hydrophilicity be effectively improved.

Claims

1. A method for modifying the surface of an aromatic polyamide composite membrane with a functional isocyanate crosslinking agent, characterized in that It includes the following steps: The aromatic polyamide composite membrane after being cleaned, purified and dried on the surface is impregnated in a functional isocyanate cross-linking agent solution, or the functional isocyanate cross-linking agent solution is sprayed, brushed or roll-coated on the surface of the aromatic polyamide composite membrane. Subsequently, after heat treatment at 60-130 °C for 0.2-20 hours, an aromatic polyamide composite membrane grafted with disulfobetaine and polyether chain on the surface is obtained; Wherein the functional isocyanate cross-linking agent has the structure shown in general formula (A): Among them, R1 and R2 in the general formula (A) are respectively selected from substituted or unsubstituted C1-C 18 hydrocarbyl groups, n is selected from natural numbers between 1 and 15, and the is selected from C1-C 18 alkylene groups, and the is selected from C1-C 18 alkylene groups or one of them, where p is 5; The mass percentage concentration of the functional isocyanate cross-linking agent in the functional isocyanate cross-linking agent solution is 0.5-50%; the functional isocyanate cross-linking agent solution is 5-50% of the mass of the aromatic polyamide composite membrane.

2. The surface modification method of the aromatic polyamide composite membrane with a functional isocyanate crosslinking agent according to claim 1, characterized in that The aromatic polyamide composite membrane includes one of a nascent membrane, a hydrolyzed membrane, a modified membrane or a regenerated membrane; Wherein the nascent membrane refers to an aromatic polyamide composite membrane produced by carrying out a polycondensation reaction on a porous polysulfone support membrane or a porous polyethersulfone support membrane using m-phenylenediamine and trimesoyl chloride as raw materials; the hydrolyzed membrane refers to an aromatic polyamide composite membrane obtained by hydrolyzing the nascent membrane; the modified membrane refers to an aromatic polyamide composite membrane obtained by surface modification of the nascent membrane, the hydrolyzed membrane or a commercially available aromatic polyamide composite membrane; the regenerated membrane refers to a used aromatic polyamide composite membrane cleaned by physical or chemical methods.

3. The method for modifying the surface of an aromatic polyamide composite membrane with a functional isocyanate crosslinking agent according to claim 1, characterized in that Wherein the specific preparation process of the functional isocyanate cross-linking agent of general formula (A) is as follows: At room temperature, dissolve general formula (B) in an organic solvent, start stirring and slowly add polyethylene glycol monoacrylate. The dosage of polyethylene glycol monoacrylate is 2.0-2.5 times the molar amount of general formula (B). After the addition of polyethylene glycol monoacrylate is completed, raise the reaction temperature to 50-70 °C and continue the reaction for 4-40 hours. Then, while maintaining the reaction temperature, add γ-propanesultone to the reaction system. The dosage of γ-propanesultone is 1.8-2.2 times the molar amount of general formula (B). After reacting for 2-6 hours, end the ring-opening reaction process; Add the catalyst, diluent and general formula (D) to the reaction system in sequence, continue stirring and keep the reaction at a constant temperature. After detecting that the NCO content in the reactor material is consistent with the predetermined value, lower the temperature of the reaction product system to room temperature and end the addition reaction process to obtain a solution of the functional isocyanate cross-linking agent with the structure shown in general formula (A) for standby; Wherein general formula (B) has the following structure: wherein R1 and R2 in the general formula (B) are each independently selected from substituted or unsubstituted hydrocarbon groups, and the selected from C1-C 18 alkylene group or one of them, wherein p is a natural number between 1 and 2000; The polyethylene glycol monoacrylate has the structure shown in general formula (C): Wherein R in general formula (C) is selected from H or methyl, and n is selected from natural numbers between 1 and 2000; General formula (D) refers to a polyisocyanate and has the structure shown in general formula (D): wherein q in the general formula (D) is selected from positive integers of 1 to 5, and said is selected from C1 to C 18 alkylene; The dosage of the polyisocyanate is 2.02-2.25 times the molar amount of general formula (B).

4. The method for modifying the surface of an aromatic polyamide composite membrane with a functional isocyanate crosslinking agent according to claim 3, characterized in that The organic solvent is selected from one or more of tetrahydrofuran, 1,4-dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, chlorobenzene, chloroform, 1,2-dichloroethane, hexane, cyclohexane, toluene, xylene, decalin, ethyl acetate, N-methylpyrrolidone, N,N-dimethylaniline, dimethyl phthalate, diethyl phthalate, dibutyl phthalate, N,N-dimethylformamide, N,N-dimethylacetamide or dimethyl sulfoxide; the amount of the organic solvent used is 1 to 10 times the mass of the general formula (B).

5. The method for modifying the surface of an aromatic polyamide composite membrane with a functional isocyanate crosslinking agent according to claim 3, characterized in that The catalyst refers to a complex of organotin and organic amine; wherein the organotin refers to one of dibutyltin dilaurate, stannous octoate, stannous oxalate, dibutyltin dimaleate, bis(dodecylthio)dibutyltin or dibutyltin diacetate; the organic amine refers to one of triethylamine, p-dimethylaminopyridine, N,N-dimethylformamide, triethylenediamine, 1,4-dialkylpiperazine, 1-alkylimidazole, 1,8-diazabicyclo[5.4.0]undec-7-ene, triethylenediamine carboxylate, 1,4-dialkylpiperazine carboxylate or 1-alkylimidazole carboxylate; the mass ratio of the organotin to the organic amine is 1:0 to 1.5; the amount of the catalyst used is 0.01 to 5% of the mass of the polyisocyanate of the general formula (D).

6. The surface modification method of an aromatic polyamide composite film by a functional isocyanate crosslinking agent according to claim 3, characterized in that The diluent refers to one or more of acetone, butanone, cyclohexanone, methyl acetate, ethyl acetate, ether, tetrahydrofuran, 1,4-dioxane, toluene, xylene or dimethyl sulfoxide; the amount of the diluent used is 1 to 10 times the mass of the general formula (B).

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