Cyano-terminated modified polysulfone and preparation method thereof

Abstract

The invention discloses cyano-terminated modified polysulfone and a preparation method thereof. The terminal cyano group is selected from at least one of the following groups: n, m, p, q and r are independently 0 or 1; r1, R2, R3 and R4 are respectively and independently selected from any one of H, methyl, trifluoromethyl and cyano. Through molecular structure design, a polar group (cyano) with large dipole moment is introduced into the end group of polysulfone to prepare the cyano-terminated modified polysulfone and the film thereof. According to the polysulfone provided by the invention, the cyano group at the chain end has a relatively large degree of freedom, and when the cyano group is subjected to sub-Tg polarization, the steric hindrance is relatively small. Therefore, the cyano-terminated modified polysulfone can maintain relatively low dielectric loss and high Tg while increasing the dielectric constant.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer film capacitors, and in particular to a cyano-terminated modified polysulfone and a preparation method thereof. Background Art

[0002] Polysulfone resin is an amorphous thermoplastic special engineering plastic with good heat resistance, chemical corrosion resistance, mechanical strength and electrical insulation properties. It is widely used in chemical industry, aerospace, electronic appliances and other fields. Polysulfone has a high glass transition temperature (T g ), so it is considered as an important candidate material for high temperature resistant polymer medium. Although polysulfone has excellent mechanical properties, heat resistance and high breakdown strength (E b ), but the relative dielectric constant (ε r ) is only 3.2~3.4, which greatly limits its use in the field of high temperature capacitor energy storage. r The polysulfone material has important practical significance.

[0003] In the existing technology, there are five main methods to improve the dielectric energy storage performance of high temperature resistant materials:

[0004] 1. Towards high T g Highly polar inorganic fillers are added to polymer matrices. The basic principle of this approach is to utilize the high dielectric constant of inorganic nanoparticles to increase the apparent dielectric constant of ceramic / polymer composites. However, in industrial production, organic-inorganic composites obtained by adding inorganic fillers cannot solve the problems of uniform dispersion of inorganic particles and interface problems. In particular, space charge polarization at high temperatures often leads to severe performance degradation. Furthermore, the inclusion of large amounts of fillers can lead to poor mechanical properties of dielectric films, resulting in brittle texture, reduced processability, and reduced reliability.

[0005] Second, modify the surface morphology of dielectric polymer films or construct a multilayer structure to suppress charge injection from the electrode, thereby improving the electrical breakdown strength of the dielectric composite film and, in turn, the dielectric energy storage performance;

[0006] 3. Increase the degree of cross-linking of polymers. By increasing the degree of cross-linking, the movement and relaxation of polymer chain segments are restricted, dielectric loss is reduced, and the modulus and dielectric breakdown strength of the material are increased, thereby improving energy storage performance. However, in order to increase the degree of cross-linking, external cross-linking agents are usually required, which will produce small molecular byproducts or require too high a reaction temperature.

[0007] Fourth, blending with other polymers: The polymers after blending can form either a homogeneous mixture or a multiphase structure. By rationally designing and adjusting the structure of the blend, superior performance can be achieved. In comparison, the preparation process of polymer blends is simple and cost-effective, but the improvement in dielectric properties is relatively small. In addition, to achieve optimal performance, the amount of the two polymers in the blend film often needs to be large, sometimes even reaching a 1:1 ratio. This places more stringent requirements on the compatibility between the different polymers, limiting its further application.

[0008] 5. In polymer molecular engineering, polar groups are introduced into the polymer molecular chain in the form of covalent bonds through chemical reactions to improve the energy storage performance of the material. r and tanδ (dielectric loss) are also large. However, using dipolar glassy polymer sub-T g Directed polarization can effectively alleviate this contradiction, because the conduction of space charges (electrons and impurity ions) can be suppressed in the glassy state, and the resistance to rotational polarization of the flexible segments of the main chain or the flexible side chains in the free volume is low, and the resulting losses are relatively low. There are two specific modification methods: one is the main chain block modification, which regulates the flexibility of the segments by adjusting the main chain skeleton structure, thereby reducing the dipole polarization resistance and improving the dielectric properties. However, if the group introduced on the main chain is a high polar group, a polymer with a low glass transition temperature must be used or a flexible segment must be introduced at the same time. The reason is that the dipole orientation of the polymer in the glassy state is largely frozen as the main chain moves, which is not conducive to high temperature applications. The second is side chain grafting modification, which introduces large dipole moment polar groups into the molecular side chains. The polar groups on the side chains are highly active, which is beneficial in improving ε r While maintaining the good thermal and mechanical properties of the polymer film. In the side chain modification, the polarization of the polar group is sub-T g Relaxation increases the dielectric constant by directional polarization of branched dipoles below the glass transition temperature while minimizing the dielectric loss associated with glass transition relaxation. However, this modification method is complicated to operate and often requires design and synthesis starting from monomers, which is costly. Summary of the Invention

[0009] In order to solve the above technical problems, the present invention provides a cyano-terminated polysulfone and its preparation method. The present invention utilizes polymer molecular engineering to graft large dipole moment groups (cyano, -CN) at the chain ends of polysulfone molecules to improve the ε r , while maintaining the high glass transition temperature (T g ) and low tan δ. Furthermore, the cyano-containing end-capping agent eliminates the terminal hydroxyl groups of the polysulfone, improving the thermal stability and thermal processing properties of the polymer.

[0010] To achieve the above object, the technical solution adopted by the present invention is:

[0011] In one aspect, the present invention provides a polysulfone modified with a terminal cyano group, wherein the terminal cyano group is selected from at least one of the following:

[0012] wherein n, m, p, q and r are each independently 0 or 1; and R1, R2, R3 and R4 are each independently selected from any one of H, methyl, trifluoromethyl and cyano.

[0013] As a preferred embodiment, the terminal cyano group is selected from at least one of the following:

[0014]

[0015] As a preferred embodiment, the cyano-terminated polysulfone is obtained by polymerization of a diphenol monomer and a difluoro monomer, and then capped with a capping agent containing a cyano terminal group.

[0016] Preferably, at least one of the diphenol monomer and the difluoro monomer contains a sulfone group (-SO2-);

[0017] Preferably, the capping agent is a halide containing the terminal cyano group;

[0018] In the technical solution of the present invention, the end-capping agent may be a halide of the terminal cyano group.

[0019] In the technical solution of the present invention, the general structural formula of the cyano-terminated polysulfone is shown in formula (1):

[0020]

[0021] In formula (1):

[0022] X1 is derived from a diphenol monomer, specifically a residue after the hydroxyl group is removed from the diphenol monomer; X2 is derived from a difluoro monomer, specifically a residue after the fluorine substituent is removed from the difluoro monomer; at least one of X1 and X2 contains a sulfone group (-SO2-); X3 is the terminal cyano group, derived from the capping agent;

[0023] Preferably, the molecular weight of the cyano-terminated polysulfone is 10,000 to 1,000,000.

[0024] As a preferred embodiment, the diphenol monomer is selected from at least one of 4,4'-dihydroxydiphenyl sulfone, bisphenol A, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenylmethane, 2,5-dihydroxytoluene, 2,7-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 2,7-dihydroxyfluorene, 1,4-dihydroxybenzene and 1,4-bis(3-hydroxyphenoxy)benzene;

[0025] Preferably, the difluoromonomer is selected from at least one of 4,4'-difluorodiphenyl sulfone, 1,3-difluorobenzene, 1,4-difluorobenzene, 4,4'-difluorodiphenylmethane and 4,4'-difluorodiphenyl ether;

[0026] Preferably, the end-capping agent is selected from at least one of p-fluorobenzonitrile, 3,5-dicyanofluorobenzene, 6-chloro-3-cyanopyridine, 3-cyanobenzyl chloride, p-cyanobenzyl chloride, 3-fluorobenzonitrile, 3-chlorophenylacetonitrile, o-chlorophenylacetonitrile, 1,4-dicyano-3-fluorobenzene, 3-chloro-5-(trifluoromethyl)benzonitrile, 2-bromo-4-(trifluoromethoxy)benzonitrile and 5-chloro-2-methylbenzonitrile.

[0027] In another aspect, the present invention provides a method for preparing the above-mentioned cyano-terminated polysulfone, comprising the following steps:

[0028] (1) subjecting diphenol monomer and difluoro monomer to polymerization reaction under the action of water-carrying agent and alkali;

[0029] (2) adding a capping agent and continuing the polymerization reaction to obtain the cyano-terminated polysulfone.

[0030] The principle of the above preparation method is: under alkaline conditions, solution polycondensation (step-by-step polymerization) occurs through the nucleophilic substitution reaction of diphenol monomer and difluoro monomer, and a capping agent is added in the middle and late stages of the polymerization reaction to introduce cyano groups into the chain ends of the polysulfone through the nucleophilic substitution of the capping agent.

[0031] As a preferred embodiment, in step (1), the polymerization reaction is carried out in a solvent; the solvent is preferably a high-polarity, high-boiling-point solvent; the high-polarity, high-boiling-point solvent can be exemplified by N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), etc., and the above-mentioned solvents can be used alone or in combination;

[0032] Preferably, the water-carrying agent is toluene;

[0033] Preferably, the base is selected from one or more of potassium carbonate, cesium carbonate, sodium carbonate, sodium bicarbonate and potassium bicarbonate.

[0034] As a preferred embodiment, in step (1), the molar ratio of the diphenol monomer to the difluoro monomer is (1-1.1):1, preferably 1.025:1;

[0035] Preferably, the mass ratio of the solvent to the water-carrying agent is (3-9):1, more preferably 3:1;

[0036] Preferably, the solid content of the polymerization reaction system is 10% to 50%, more preferably 20% to 30%. In the technical solution of the present invention, the solid content can be calculated as (mass of diphenol monomer + mass of difluoro monomer) / (mass of diphenol monomer + mass of difluoro monomer + mass of solvent + mass of water-carrying agent) * 100%.

[0037] Preferably, the molar ratio of the difluoromonomer to the base is 1:(1-1.4), more preferably 1:1.2;

[0038] Preferably, the polymerization reaction temperature is 160-170°C;

[0039] Preferably, the polymerization reaction time is 1 to 5 hours, more preferably 2.5 hours;

[0040] In certain specific embodiments, the specific operation of step (1) is as follows: dissolving the diphenol monomer and the difluoro monomer in a mixed solution of a solvent and a water-carrying agent under nitrogen elution and heating at 30 to 60° C.; after sufficient dissolution, adding alkali, and azeotropic dehydration under heating conditions, and after the water-carrying agent is completely evaporated, heating to 160 to 170° C. and heating for polymerization reaction for 1 to 5 hours; the temperature of azeotropic dehydration under the heating conditions is 145 to 155° C.

[0041] As a preferred embodiment, in step (2), the molar ratio of the end-capping agent to the difluoromonomer is (0.03-0.08):1, more preferably 0.04-0.06:1;

[0042] Preferably, the polymerization reaction temperature is 160-170°C;

[0043] Preferably, the polymerization reaction time is 1 to 5 hours;

[0044] In certain specific embodiments, the specific operation of step (2) is: adding a capping agent to the reaction system obtained in step (1) and continuing the reaction at 160-170° C. for 1-5 hours.

[0045] In some specific embodiments, post-treatment is further included; the post-treatment is to dilute the reaction solution with a solvent when the system is cooled to 100°C, and then pour it into deionized water for cooling and precipitation; the precipitate is filtered, washed, dried, and crushed, and then boiled in 90°C deionized water for 8 hours, filtered and washed, and the boiling is repeated 7 to 10 times until the pH of the filtrate is 7; and the final polysulfone is obtained after drying.

[0046] In another aspect, the present invention provides a modified polysulfone membrane prepared from the above-mentioned cyano-terminated polysulfone.

[0047] As a preferred embodiment, the modified polysulfone film is prepared by coating the cyano-terminated polysulfone solution on a substrate, and obtaining the modified polysulfone film after the solvent evaporates;

[0048] Preferably, in the polysulfone solution, the solid content of the cyano-terminated polysulfone is 15% to 25%;

[0049] Preferably, the solvent of the polysulfone solution is selected from one or more of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO);

[0050] Preferably, the solvent volatilization is carried out under heating conditions; the heating is preferably carried out by drying at 45-65°C for 7-12 hours, then keeping warm at 80-120°C for 3-5 hours, and continuing to keep warm at 170-200°C for 3-5 hours.

[0051] In certain specific embodiments, the method for preparing the polysulfone solution comprises: dissolving the cyano-terminated polysulfone in a solvent under heating and stirring conditions; the heating temperature is 50-100°C, preferably 80°C.

[0052] In some specific embodiments, the coating is performed by blade coating or spin coating.

[0053] In the technical solution of the present invention, after water is dripped onto the edge of the thin film formed on the substrate, the thin film can automatically separate from the substrate, and after further drying the water, a peeled modified polysulfone film can be obtained.

[0054] The above technical solution has the following advantages or beneficial effects:

[0055] The present invention introduces a polar group (cyano group) with a large dipole moment into the end group of polysulfone through molecular structure design to prepare a cyano-terminated polysulfone and its film. The polysulfone provided by the present invention has a large degree of freedom at the end of the chain. g When polarized, the steric hindrance is small. Therefore, the end-cyano modified polysulfone can maintain low dielectric loss and high T while improving the dielectric constant. g .

[0056] Compared with the prior art, the present invention has the following advantages:

[0057] (1) The present invention improves the dielectric constant of polysulfone by introducing terminal cyano groups into polysulfone, thereby reducing the adverse effects of modification on the thermodynamic properties of the polymer bulk and maintaining the high glass transition temperature (T g ) and low dielectric loss (tanδ);

[0058] (2) Compared with the method of improving dielectric properties by preparing organic / inorganic composite materials, the polymer intrinsic modification method adopted in the present invention not only avoids the interface problems that may exist in the composite materials, but also retains the excellent mechanical properties of polysulfone itself to the greatest extent;

[0059] (3) The present invention eliminates the terminal hydroxyl groups of the polysulfone molecular chain through end group modification, thereby improving the thermal stability and thermal processability of the polysulfone. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a synthetic route for the cyano-terminated polysulfone in Example 1 of the present invention. DETAILED DESCRIPTION

[0061] The following embodiments are merely some of the embodiments of the present invention, rather than all of them. Therefore, the detailed description of the embodiments of the present invention provided below is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by those skilled in the art based on the embodiments of the present invention without creative effort are intended to fall within the scope of protection of the present invention.

[0062] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0063] Example 1

[0064] This embodiment provides a cyano-terminated polysulfone, the synthesis route of which is as follows: Figure 1 As shown, the following steps are included:

[0065] (1) 4,4'-difluorodiphenyl sulfone (DOD, 0.05 mol), bisphenol A (0.05125 mol), N,N-dimethylacetamide (DMAC, 45 g), and toluene (MB, 15 g) were added to a three-necked flask in sequence and stirred to dissolve at 40°C while rinsing with nitrogen. After sufficient dissolution, anhydrous potassium carbonate (0.06 mol) was added. The temperature was raised to 150°C for azeotropic dehydration for 4 h, and the distillate was released. After all the toluene was removed, the temperature was raised to 170°C for polymerization reaction for 2.5 h.

[0066] (2) Add 3-fluorobenzonitrile (0.0025 mol) and continue the polymerization reaction at 170°C for 2.5 h;

[0067] (3) After the reaction is completed, heating is stopped. When the temperature drops to 100°C, DMAC is added to dilute the reaction solution; the diluted reaction solution is poured into deionized water and cooled to precipitate a strip-like solid; the precipitated strip-like solid is filtered, washed, and dried to obtain a light yellow solid; the light yellow solid is crushed and boiled in 90°C deionized water for 8 hours and then filtered. The boiling and filtering are repeated 7-10 times until the pH of the filtrate is 7, and the polysulfone powder PSF-1 is obtained after drying.

[0068] The molecular weight of the cyano-terminated polysulfone prepared in this example is 41,800.

[0069] This example also prepared a PSF-1 modified film, and the process was as follows:

[0070] PSF-1 (10 g) was added to DMAC (50 g) and stirred at 80°C until completely dissolved to obtain a polysulfone solution. The cooled polysulfone solution was then spread on a glass plate. The glass plate was transferred to a vacuum oven, dried at 55°C for 10 hours, kept at 100°C for 4 hours, and cured at 180°C for 4 hours to obtain a PSF-1 modified film.

[0071] Example 2

[0072] This embodiment provides a cyano-terminated polysulfone, the preparation method of which comprises the following steps:

[0073] (1) 4,4'-difluorodiphenyl sulfone (DOD, 0.05 mol), bisphenol A (0.05125 mol), DMAC (45 g), and MB (15 g) were added to a three-necked flask in sequence and stirred to dissolve at 40°C while rinsing with nitrogen. After sufficient dissolution, anhydrous potassium carbonate (0.06 mol) was added. The temperature was raised to 150°C for azeotropic dehydration for 4 h, and the distillate was released. After all the toluene was removed, the temperature was raised to 170°C for polymerization reaction for 2.5 h.

[0074] (2) Add 3,5-dicyanofluorobenzene (0.0025 mol) and continue the polymerization reaction at 170°C for 2.5 h;

[0075] (3) After the reaction is completed, heating is stopped and DMAC is added to dilute the reaction solution when the temperature drops to 100°C; the diluted reaction solution is poured into deionized water and cooled to precipitate a strip-like solid; the precipitated strip-like solid is filtered, washed, and dried to obtain a light yellow solid; the light yellow solid is crushed and boiled in 90°C deionized water for 8 hours and then filtered, and the boiling and filtering are repeated 7-10 times until the pH of the filtrate is 7, and the polysulfone powder PSF-2 is obtained after drying.

[0076] The molecular weight of the cyano-terminated polysulfone prepared in this example is 46,300.

[0077] This example also prepared a PSF-2 modified film, and the process was as follows:

[0078] PSF-2 (10 g) was added to DMAC (50 g) and stirred at 80°C until completely dissolved to obtain a polysulfone solution. The cooled polysulfone solution was then spread on a glass plate. The glass plate was transferred to a vacuum oven, dried at 55°C for 10 hours, kept at 100°C for 4 hours, and cured at 180°C for 4 hours to obtain a PSF-2 modified film.

[0079] Comparative Example 1

[0080] (1) 4,4'-difluorodiphenyl sulfone (DOD, 0.05 mol), bisphenol A (0.05125 mol), DMAC (45 g), and MB (15 g) were added to a three-necked flask in sequence and stirred to dissolve at 40°C while rinsing with nitrogen. After sufficient dissolution, anhydrous potassium carbonate (0.06 mol) was added. The temperature was raised to 150°C for azeotropic dehydration for 4 h, and the distillate was released. After all the toluene was removed, the temperature was raised to 170°C for polymerization reaction for 5 h.

[0081] (2) After the polymerization reaction is completed, heating is stopped and DMAC is added to dilute the reaction solution when the temperature drops to 100°C; the diluted reaction solution is poured into deionized water and cooled to precipitate a strip-like solid; the precipitated strip-like solid is filtered, washed, and dried to obtain a light yellow solid; the light yellow solid is crushed and boiled in 90°C deionized water for 8 hours and then filtered, and the boiling and filtering are repeated 7-10 times until the pH of the filtrate is 7, and the polysulfone powder PSF is obtained after drying.

[0082] This comparative example also prepared a PSF film, and the process was as follows:

[0083] PSF (10 g) was added to DMAC (50 g) and stirred at 80°C until completely dissolved to obtain a polysulfone solution. The cooled polysulfone solution was then spread on a glass plate. The glass plate was transferred to a vacuum oven, dried at 55°C for 10 hours, kept at 100°C for 4 hours, and cured at 180°C for 4 hours to obtain a PSF film.

[0084] Table 1 shows the performance test data of the films prepared in the above examples and comparative examples. As can be seen from Table 1, the cyano-terminated modified polysulfone films prepared by the present invention have an improved dielectric constant compared to the unterminated polysulfone films in the comparative examples, while maintaining lower dielectric loss and a higher glass transition temperature, while also maintaining the excellent mechanical properties of the polysulfone. Therefore, the modified polysulfone films provided by the present invention have excellent mechanical properties and thermodynamic stability.

[0085] Table 1

[0086]

[0087]

[0088] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A cyano-terminated polysulfone, characterized in that: The terminal cyano group is selected from at least one of the following: wherein n, m, p, q and r are each independently 0 or 1; and R1, R2, R3 and R4 are each independently selected from any one of H, methyl, trifluoromethyl and cyano.

2. The cyano-terminated polysulfone according to claim 1, characterized in that The terminal cyano group is selected from at least one of the following:

3. The cyano-terminated polysulfone according to claim 1, characterized in that The terminal cyano-modified polysulfone is obtained by polymerization of a diphenol monomer and a difluoro monomer, and then capped with a capping agent containing a terminal cyano group. Preferably, at least one of the diphenol monomer and the difluoro monomer contains a sulfone group; Preferably, the capping agent is a halide containing the terminal cyano group; Preferably, the molecular weight of the cyano-terminated polysulfone is 10,000 to 1,000,000.

4. The cyano-terminated polysulfone according to claim 3, characterized in that The diphenol monomer is selected from at least one of 4,4'-dihydroxydiphenyl sulfone, bisphenol A, 4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxybiphenyl, 4,4'-dihydroxydiphenylmethane, 2,5-dihydroxytoluene, 2,7-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, 2,7-dihydroxyfluorene, 1,4-dihydroxybenzene and 1,4-bis(3-hydroxyphenoxy)benzene; and / or, the difluoromonomer is at least one selected from 4,4'-difluorodiphenyl sulfone, 1,3-difluorobenzene, 1,4-difluorobenzene, 4,4'-difluorodiphenylmethane and 4,4'-difluorodiphenyl ether; And / or, the end-capping agent is selected from at least one of p-fluorobenzonitrile, 3,5-dicyanofluorobenzene, 6-chloro-3-cyanopyridine, 3-cyanobenzyl chloride, p-cyanobenzyl chloride, 3-fluorobenzonitrile, 3-chlorophenylacetonitrile, o-chlorophenylacetonitrile, 1,4-dicyano-3-fluorobenzene, 3-chloro-5-(trifluoromethyl)benzonitrile, 2-bromo-4-(trifluoromethoxy)benzonitrile and 5-chloro-2-methylbenzonitrile.

5. The method for preparing the cyano-terminated polysulfone according to any one of claims 1 to 4, characterized in that: The following steps are involved: (1) subjecting diphenol monomer and difluoro monomer to polymerization reaction under the action of water-carrying agent and alkali; (2) adding a capping agent and continuing the polymerization reaction to obtain the cyano-terminated polysulfone.

6. The preparation method according to claim 5, characterized in that In step (1), the polymerization reaction is carried out in a solvent; Preferably, the solvent is selected from one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide; Preferably, the water-carrying agent is toluene; Preferably, the base is selected from one or more of potassium carbonate, cesium carbonate, sodium carbonate, sodium bicarbonate and potassium bicarbonate.

7. The preparation method according to claim 6, characterized in that In step (1), the molar ratio of the diphenol monomer to the difluoro monomer is (1-1.1):1, preferably 1.025:1; Preferably, the mass ratio of the solvent to the water-carrying agent is (3-9):1, more preferably 3:1; Preferably, the solid content of the polymerization reaction system is 10% to 50%, more preferably 20% to 30%; Preferably, the molar ratio of the difluoromonomer to the base is 1:(1-1.4), more preferably 1:1.2; Preferably, in step (1), the polymerization reaction temperature is 160-170°C; Preferably, in step (1), the polymerization reaction time is 1 to 5 hours, more preferably 2.5 hours.

8. The preparation method according to claim 5, characterized in that In step (2), the molar ratio of the end-capping agent to the difluoromonomer is (0.03-0.08):1, more preferably (0.04-0.06):1; Preferably, in step (2), the polymerization reaction temperature is 160-170°C; Preferably, in step (2), the polymerization reaction time is 1 to 5 hours.

9. A modified polysulfone membrane, characterized in that: The polysulfone is prepared from the cyano-terminated polysulfone described in any one of claims 1 to 4.

10. The modified polysulfone membrane according to claim 9, characterized in that The modified polysulfone film is prepared by coating the cyano-terminated polysulfone solution on a substrate, and obtaining the modified polysulfone film after the solvent evaporates; Preferably, in the polysulfone solution, the solid content of the cyano-terminated polysulfone is 15% to 25%; Preferably, the solvent of the polysulfone solution is selected from one or more of N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide; Preferably, the solvent volatilization is carried out under heating conditions; the heating is preferably drying at 45-65°C for 7-12 hours, then keeping warm at 80-120°C for 3-5 hours, and continuing to keep warm at 170-200°C for 3-5 hours.

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