Graft polymer brush polyimide film and method of making same

Abstract

The application relates to the field of preparation of polymer brushes, and discloses a grafted polymer brush polyimide film and a preparation method thereof, which comprises the following steps: preparing polyimide powder by carrying out polycondensation reaction on diamine monomers and acid anhydride monomers, washing, and drying; carrying out grafting reaction on the polyimide powder and initiator 2-bromoisobutyryl bromide in a pyridine solvent, washing, and drying to obtain polyimide powder grafted with initiators; dissolving the polyimide powder grafted with initiators in an N-methylpyrrolidone solvent, preparing into a film casting solution, coating, and preparing polyimide film; and carrying out reaction on the polyimide film in an oxygen-free atmosphere by immersing the polyimide film in an aqueous solution containing the polymer brush monomers, and adding copper bromide, 2,2'-dipyridyl and ascorbic acid to obtain the grafted polymer brush polyimide film. The initiator 2-bromoisobutyryl bromide is grafted on the polyimide main chain, so that the grafting thickness of the polymer brush reaches the micron level.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of polymer brush preparation, and in particular to a grafted polyimide film of polymer brush and a preparation method thereof. BACKGROUND

[0002] Polyimide (PI) is a high-performance polymer material that is widely used in the fields of aviation, electronics, and materials science due to its excellent thermal stability, mechanical properties, and electrical insulation properties. However, traditional PI film preparation methods have certain limitations, such as unstable, easily falling off and uneven surface modification layers, which limit the performance of PI films in specific applications. To solve these problems, in recent years, researchers have proposed methods to improve the surface properties of polyimide films through grafting technology.

[0003] Document [Zeng Y, **e L, Chi F, et al. Controlled Growth of Ultra-Thick Polymer Brushes via Surface-Initiated Atom Transfer Radical Polymerization with Active Polymers as Initiators [J]. Macromolecular Rapid Communications, 2019, 40(13): 1900078.] mentions that polymer brushes are applied to responsive surfaces, non-biological fouling surfaces, cell adhesion surfaces, protein binding and fixation, chromatography support, membrane applications, antibacterial coatings, and low-friction surfaces. However, these applications usually require polymer brushes to have the desired thickness, which affects the performance and effectiveness of the application. Document [Jeong, Jaehoon, et al. "Formation of antifouling brushes on various substrates using a melanin-inspired initiator film." Langmuir 39.22 (2023): 7598-7604.] synthesized a tyrosine-bound bromide initiator to form an initiator film on the substrate, and used an air-resistant activator film for the atom transfer radical polymerization of zwitterionic carboxybetaine to form an antifouling polymer brush. The monomer of the polymer brush in this document is 3-[(3-acrylamidopropyl)dimethylammonio]propanoate, and the prepared polymer brush has a thickness of nanometers. Although existing technologies have made significant progress in controlling the thickness of polymer brushes, it is still a challenge to prepare ultra-thick polymer brushes. SUMMARY

[0004] Based on the above polyimide film application technical problems, the application provides a new polyimide film preparation method. The core of the method is to prepare polyimide powder by selecting a diamine monomer containing a hydroxyl group and an acid anhydride monomer for condensation reaction; on this basis, the polyimide powder and an initiator are subjected to grafting reaction in a pyridine solvent to form polyimide powder linked to the initiator; a casting solution is prepared through an N-methyl pyrrolidone solvent, and a polyimide film is prepared through a doctor blade coating, casting or spin coating method; finally, the polyimide film containing the initiator is soaked in a monomer-containing solution for grafting polymerization to form a polymer brush, so as to obtain a modified polyimide film with excellent surface performance and high grafting density.

[0005] To achieve the above-mentioned purpose, in one aspect, the application provides a preparation method of a grafted polymer brush polyimide film, comprising the following steps:

[0006] S1, selecting a diamine monomer as 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol, and subjecting the diamine monomer and an acid anhydride monomer to condensation reaction, washing, and drying to prepare polyimide powder:

[0007] Alternatively, selecting a diamine monomer as 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, and subjecting the diamine monomer and an acid anhydride monomer to condensation reaction, then to chemical imidization treatment, washing, and drying to prepare polyimide powder;

[0008] The structural formula of the diamine monomer is shown in the following formula (1)-(2):

[0009]

[0010] S2, subjecting the polyimide powder obtained in step S1 to grafting reaction with an initiator 2-bromoisobutyryl bromide in a pyridine solvent, washing, and drying to obtain polyimide powder linked to the initiator;

[0011] The structural formula of the 2-bromoisobutyryl bromide is shown in the following formula (3):

[0012]

[0013] S3, dissolving the polyimide powder obtained in step S2 in an N-methyl pyrrolidone solvent to prepare a casting solution, and coating to prepare a polyimide film.

[0014] S4, selecting the polymer brush monomer as 3-[(3-acrylamidopropyl)dimethylammonium] propionate or polyethylene glycol methacrylate, immersing the polyimide film obtained in step S3 in an aqueous solution containing the polymer brush monomer, and adding copper bromide, 2,2'-bipyridine and ascorbic acid, or adding copper bromide, cuprous bromide and pentamethyldiethylenetriamine to react, to obtain a grafted polymer brush polyimide film;

[0015] wherein the polymer brush monomer has the structural formula as shown in the following formula (4) and (5):

[0016]

[0017] As a further preferred technical solution of the present application, in step S1, the anhydride monomer is selected from at least one of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 5-aminosalicylic acid and pyromellitic anhydride.

[0018] As a further preferred technical solution of the present application, in step S1, when the diamine monomer is 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, after the completion of the polycondensation reaction, a chemical imidization method is used, a dehydrating agent and a dehydration catalyst are added to the polyamic acid solution obtained by polycondensation of the diamine monomer and the anhydride monomer, and the mixture is stirred and reacted at room temperature to 150°C, to obtain a polyimide solution, and the polyimide solution is washed and dried to obtain a polyimide powder.

[0019] wherein the dehydrating agent is at least one of acetic anhydride, propionic anhydride, butyric anhydride and sodium acetate, and the dehydration catalyst is at least one of triethylamine, isoquinoline, pyridine and N-methylpyridine.

[0020] The present application selects pyridine as the solvent, which has good solubility and good catalytic effect on the reaction, promoting the grafting reaction between the initiator and the polyimide main chain. As a further preferred technical solution of the present application, in step S2, the mass ratio of the polyimide powder, the initiator and the pyridine solvent is 1:2:30-1:5:50.

[0021] As a further preferred technical solution of the present application, steps S1 and S2 are carried out in a protective atmosphere, and the protective atmosphere is nitrogen or inert gas.

[0022] The present application controls the solid content of the casting solution to obtain good mechanical properties and optical transparency while forming the film. As a further preferred technical solution of the present application, in step S3, the solid content of the casting solution is 20-30wt%.

[0023] As a further preferred technical solution of the present application, in step S3, the coating is performed by means of blade coating, casting or spin coating, and after coating, the coated product is dried at 60-70°C for 2-3h, and then dried at 130-150°C for 4-5h.

[0024] As a further preferred technical solution of the present application, in step S4, after the polyimide film is immersed in the reaction solution, the polyimide film is repeatedly washed with PBS and deionized water, and then dried under nitrogen gas flow to obtain the dried polyimide film with grafted polymer brushes.

[0025] As a further preferred technical solution of the present application, in step S4, the solvent used is deionized water.

[0026] According to another aspect of the present application, the present application also provides a polyimide film with grafted polymer brushes, which is prepared by the above method, and the thickness of the polymer brushes is in the micron level.

[0027] Compared with the prior art, the present application can achieve the following beneficial effects:

[0028] 1) In the present application, the initiator 2-bromoisobutyryl bromide is grafted onto the polyimide backbone, so that the initiator is directly introduced into the polyimide during film formation, which not only solves the problems of non-uniformity and easy peeling of the traditional initiator layer, but also has good initiation effect, so that the thickness of the grafted polymer brushes reaches the micron level, thereby facilitating the expansion of the application of the polyimide film.

[0029] 2) The polyimide film with grafted polymer brushes prepared in the present application can be used as an antifouling film, and the thickness of the grafted polymer brushes reaches the micron level, which can greatly improve the antifouling effect. In addition, the surface of the polyimide film is coated with glue for bonding with copper foil or the surface of the polyimide film is deposited with copper, silver or other metal materials by electroplating or sputtering for the manufacture of flexible copper-clad plate. The surface roughness of the polyimide film can be improved by grafting polymer brushes, thereby effectively improving the adhesion between the polyimide film and the metal material, and increasing the peel strength. BRIEF DESCRIPTION OF DRAWINGS

[0030] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0031] Figure 1 Structure diagram of the polyimide film with grafted polymer brushes for the initiator-grafted polyimide film of Example 1.

[0032] Figure 2 NMR hydrogen spectrum of the polyimide powder and the initiator-grafted polyimide powder of Example 1.

[0033] Figure 3 Thickness diagram of the grafted polymer brushes for the initiator-grafted polyimide film of Example 1.

[0034] Figure 4 Scanning electron microscope images of polyimide film grafted with polymer brushes of example 1 before and after main chain grafting initiator, wherein (a) is before grafting polymer brushes, (b) is after grafting polymer brushes.

[0035] The purposes, functional features and advantages of the present application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0036] The specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely intended to illustrate and explain the present application, and are not intended to limit the present application.

[0037] Unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which the present application pertains. The experimental reagents used in the following examples are all conventional biochemical reagents, unless otherwise specified. The experimental methods described, unless otherwise specified, are conventional methods.

[0038] Example 1

[0039] The diamine monomer is 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (AHHFP), the acid anhydride monomer is 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, the initiator is 2-bromoisobutyryl bromide, and the polymer brush monomer is 3-[(3-acrylamidopropyl)dimethylammonio]propanesulfonate (CB).

[0040] The preparation method of the polyimide film grafted with the polymer brush provided in the present embodiment is as follows:

[0041] 1) Preparation of polyimide

[0042] Under nitrogen protection, 0.7222 g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane was dissolved in 10 mL of super dry N-methyl pyrrolidone solvent to form a clear transparent liquid under stirring at room temperature. The reaction bottle was placed near 0°C, and 0.888 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride was slowly added into the N-methyl pyrrolidone solvent containing 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane in batches under stirring while maintaining nitrogen protection. The reaction was stirred at 0°C for 12 hours to obtain a light yellow PAA solution. The PAA solution was placed at room temperature, and 4 mL of acetic anhydride and 2 mL of pyridine solution were measured for imidization under stirring. After the dropwise addition was completed, the reaction bottle was continuously reacted at 110°C for 6 h to obtain a brown polyimide solution. Then, the polyimide solution was slowly dropped into deionized water under stirring, and brown solid was precipitated. The precipitate was filtered, washed with water and methanol repeatedly, and dried at 50°C under vacuum to obtain white polyimide powder.

[0043] 2) Grafting of initiator

[0044] The polyimide powder 600 mg was dissolved in 20 mL of pyridine solution to form a clear solution. Under nitrogen protection, 1.3 g of 2-bromoisobutyryl bromide was slowly dropped into the pyridine solution containing the polyimide powder, and the reaction was carried out at 0°C for 1.5 h and then at room temperature for 12 h. After the reaction was completed, the solution was filtered, and the filtrate was treated with methanol by sedimentation, and then filtered, washed with methanol repeatedly, and dried at room temperature under vacuum to obtain white polyimide powder containing the main chain grafting initiator.

[0045] 3) Preparation of polyimide film

[0046] The polyimide powder 200 mg containing the main chain grafting initiator was dissolved in 0.8 mL of N-methyl pyrrolidone to form a casting solution with a solid content of 20 wt%, and a polyimide film was prepared by using a doctor blade method. The film was dried at 70°C for 3 h and then at 150°C for 5 h to obtain a polyimide film with a surface exposed to the initiator.

[0047] 4) Grafting of polymer brush

[0048] 6.7 mg of CuBr2and 28.1 mg of 2,2'-bipyridine were dissolved in 20 mL of deionized water, 264 mg of ascorbic acid was dissolved in 20 mL of deionized water, and 684.9 mg of 3-[(3-acrylamidopropyl)dimethylammonio]propanoate was dissolved in 4.6 mL of deionized water.

[0049] Under nitrogen protection, 1 cm2of the initiator-exposed polyimide film was placed in a reaction vessel, and 0.5 mL of the above prepared solution containing the initiator was dropped onto the film under stirring. The reaction was carried out at room temperature for 24 h to obtain a polymer brush grafted polyimide film. 2The polyimide film of the naked leak initiator was added with an aqueous solution of 3-[(3-acrylamidopropyl)dimethylammonium] propionate, vacuumed, filled with nitrogen, and then an aqueous solution of 0.2 mL of CuBr2 and 2,2'-dipyridyl was added into the reaction container, and deoxygenated by ultrasonic for 10 min, and then 0.2 mL of an aqueous solution of ascorbic acid was added, and deoxygenated by ultrasonic for another 10 min, and reacted at room temperature for 3 h. After the reaction was completed, the polyimide film was taken out, and washed repeatedly with PBS and deionized water, and dried under a nitrogen stream to obtain a polyimide film grafted with a polymer brush, and the thickness of the polymer brush was 40 μm.

[0050] Figure 1 A schematic diagram of the structure of the polyimide film grafted with a polymer brush using the main chain graft initiator provided in Example 1, Figure 1 wherein: 1 is the polyimide film of the main chain graft initiator; and 2 is the grafted polymer brush.

[0051] Figure 2 The 1H NMR spectrum of the polyimide powder and the polyimide powder of the main chain graft initiator in Example 1 showed a characteristic peak of a methyl group at 1.84 ppm, proving that the polyimide main chain was successfully grafted with the initiator.

[0052] The polyimide film sample grafted with a polymer brush in Example 1 was subjected to three-dimensional imaging under a bright field mode by a three-dimensional digital microscope instrument, and the height difference of the surface of the sample was characterized by measuring the horizontal height of the surface profile, and the test data were derived as shown in Table 1. Figure 3 As can be seen from the figure, the thickness of the grafted polymer brush was about 40 μm.

[0053] Referring to Figure 4 The scanning electron microscope images of the polyimide film grafted with a polymer brush before and after Example 1 were compared, and it can be clearly seen from the figure that the polymer brush grafted on the surface of the polyimide film was uniformly distributed.

[0054] Example 2

[0055] The diamine monomer was aniline and 2,7-dihydroxy-9-fluorenequinone monomer to prepare 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (AHF), the acid anhydride monomer was 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, the initiator was 2-bromoisobutyryl bromide, and the polymer brush monomer was 3-[(3-acrylamidopropyl)dimethylammonium] propionate.

[0056] The specific preparation method is as follows:

[0057] 1) Preparation of polyimide

[0058] Under nitrogen protection, 10.54 g of aniline, 4.0 g of 2,7-dihydroxy-9-fluorenone and 0.9 g of methanesulfonic acid were weighed into a 100 mL three-necked flask, the mixture was refluxed at 150°C for 14 h, then the reaction was cooled to 110°C, triethylamine was added, and stirred at 110°C for 40 min. After the reaction was completed, the reaction was cooled to room temperature, and poured into excess ethanol, and washed repeatedly with ethanol and water until the filtrate was colorless. After drying under vacuum at room temperature, 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (AHF) was obtained as a light purple solid.

[0059] 1.0 g of 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol, 1.1674 g of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, 6 g of isoquinoline and 26.3 mL of m-cresol were weighed into a 250 mL reaction flask, and the mixture was stirred at 80°C for 10 h, at 110°C for 10 h, at 150°C for 10 h, and at 180°C for 10 h under nitrogen protection. After the reaction was completed, the reaction was cooled to room temperature, and slowly poured into excess ethanol, and filtered, and washed repeatedly with ethanol, and dried under vacuum at room temperature to obtain polyimide powder.

[0060] 2) Grafting of initiator

[0061] 600 mg of polyimide powder was dissolved in 20 mL of pyridine solution to completely dissolve. Under nitrogen protection, 1.3 g of 2-bromoisobutyryl bromide was slowly added dropwise to the pyridine solution containing the polyimide powder, and reacted at 0°C for 1.5 h, and then at room temperature for 12 h. After the reaction was completed, the reaction was filtered, and the filtrate was treated with methanol, and filtered, and washed repeatedly with methanol, and dried under vacuum at room temperature to obtain the polyimide powder with main chain grafting initiator.

[0062] 3) Preparation of polyimide film

[0063] 200 mg of the polyimide powder with main chain grafting initiator was dissolved in 0.8 mL of N-methylpyrrolidone solvent to prepare a casting solution with a solid content of 20 wt%, and a polyimide film was prepared by spin coating, and dried at 70°C for 3 h, and then at 150°C for 5 h to obtain a polyimide film with a surface exposed initiator.

[0064] 4) Grafting of polymer brush

[0065] 6.7 mg of CuBr2 and 28.1 mg of 2,2'-bipyridine were dissolved in 20 mL of deionized water, 264 mg of ascorbic acid was dissolved in 20 mL of deionized water, and 684.9 mg of 3-[(3-acrylamidopropyl)dimethylammonio]propanoate was dissolved in 4.6 mL of deionized water.

[0066] Into a reaction vessel, 1 cm 2 The polyimide film with bare initiator was placed in a reaction vessel, 3-[(3-acrylamidopropyl)dimethylammonium] propionate aqueous solution was added, vacuumed, filled with nitrogen, and then 0.2 mL of CuBr2 and 2,2'-bipyridine mixed aqueous solution was measured and added into the reaction vessel, and oxygen was removed by ultrasonic for 10 min. Then 0.2 mL of ascorbic acid aqueous solution was added, and oxygen was removed by ultrasonic for 10 min. The reaction was carried out at room temperature for 3 h. After the reaction was completed, the polyimide film was taken out, washed repeatedly with PBS and deionized water, and dried under nitrogen flow to obtain a polyimide film with grafted polymer brushes. The thickness of the polymer brush was 32 μm.

[0067] Comparative Example 1

[0068] As a control experiment of Example 1, the difference is that the diamino monomer is replaced by 4,4'-tetraminodiphenyl ether.

[0069] The diamino monomer is 4,4'-tetraminodiphenyl ether (TADE), the anhydride monomer is 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, the initiator is 2-bromoisobutyryl bromide, and the polymer brush monomer is 3-[(3-acrylamidopropyl)dimethylammonium] propionate.

[0070] The specific preparation method is as follows:

[0071] 1) Preparation of polyimide

[0072] Under nitrogen protection, 460.54 mg of 4,4'-tetraminodiphenyl ether, 976.72 mg of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, and 32 g of polyphosphoric acid were added into a 500 mL reaction bottle, stirred at 190℃ for 1.5 h, then heated to 290℃ and stirred for 7 h. After the reaction was completed, the reaction was poured into 250 mL of deionized water, filtered, and dried. The dried solid was placed in a 5% NaHCO3 aqueous solution and stirred for 5 h, filtered, washed with deionized water until neutral, and then the product was dried in an oven at 80℃ for 17 h to obtain polyimide powder.

[0073] 2) Grafting of initiator

[0074] Polyimide powder 600 mg was dissolved in 20 mL of pyridine solution to completely dissolve. Under nitrogen protection, 1.3 g of 2-bromoisobutyryl bromide was slowly added to the pyridine solution containing the polyimide powder, reacted at 0℃ for 1.5 h, and then reacted at room temperature for 12 h. After the reaction was completed, it was filtered, the filtrate was treated with methanol, filtered, washed with methanol repeatedly, and vacuum dried at room temperature to obtain white main chain grafted initiator polyimide powder.

[0075] 3) Preparation of polyimide film

[0076] 200 mg of polyimide powder containing the main chain grafting initiator was weighed and dissolved in 0.8 mL of N-methylpyrrolidone solvent to prepare a casting solution with a solid content of 20 wt%. A polyimide film was prepared by doctor blading. The film was dried at 70 ° C for 3 h and then at 150 ° C for 5 h to obtain a polyimide film with a surface exposed to the initiator.

[0077] 4) Grafting of polymer brushes

[0078] Weigh 6.7 mg of CuBr2 and 28.1 mg of 2,2'-bipyridine and dissolve them in 20 mL of deionized water. Weigh 264 mg of ascorbic acid and dissolve it in 20 mL of deionized water. Weigh 684.9 mg of 3-[(3-acrylamidopropyl)dimethylammonium]propionate and dissolve it in 4.6 mL of deionized water.

[0079] Under nitrogen protection, a 1cm 2 To the polyimide film with bare initiator, add 3-[(3-acrylamidopropyl)dimethylammonium]propionate aqueous solution, evacuate and fill with nitrogen, then add 0.2mL of CuBr2 and 2,2'-bipyridine mixed aqueous solution into the reaction vessel, ultrasonically deoxygenate for 10 minutes, then add 0.2mL of ascorbic acid aqueous solution, ultrasonically deoxygenate for another 10 minutes, and react at room temperature for 3 hours. After the reaction is completed, take out the polyimide film, rinse it repeatedly with PBS and deionized water, and dry it under nitrogen flow to obtain a polyimide film grafted with polymer brushes. The thickness of the polymer brushes is 15μm.

[0080] Example 3

[0081] The diamine monomer is selected as 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, the anhydride monomer is 4,4'-(hexafluoroisopropylene) diphthalic anhydride, the initiator is 2-bromoisobutyl bromide, and the polymer brush monomer is polyethylene glycol methacrylate (EGMA).

[0082] The specific preparation method is as follows:

[0083] 1) Preparation of polyimide

[0084] Under nitrogen protection, 0.7222 g of 2,2-bis(3-amino-4-hydroxyphenyl)- hexafluoropropane was dissolved in 10 mL of super dry N-methyl pyrrolidone solvent to form a clear transparent liquid. The reaction bottle was placed near 0°C, 0.888 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride was slowly added into the N-methyl pyrrolidone solvent containing 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, stirring while adding, and nitrogen protection was maintained, stirring at 0°C for 12 hours to obtain a light yellow PAA solution. The PAA solution was placed at room temperature, 4 mL of acetic anhydride and 2 mL of pyridine solution were measured for imidization, and stirring was performed while adding. After the dropwise addition was completed, the reaction bottle was kept at 110°C for 6h to obtain a brown polyimide solution. Then cooled to room temperature, the polyimide solution was slowly added to deionized water, stirring while adding, and brown solid precipitated, filtered, washed with water and methanol repeatedly, and dried at 50°C under vacuum to obtain white polyimide powder.

[0085] 2) Grafting of initiator

[0086] Polyimide powder 600 mg was weighed and dissolved in 20 mL of pyridine solution to completely dissolve. Under nitrogen protection, 1.3 g of 2-bromoisobutyryl bromide was slowly added to the pyridine solution containing the polyimide powder, reacted at 0°C for 1.5 h, and then at room temperature for 12 h. After the reaction was completed, the filtrate was filtered, settled with methanol, suction filtered, washed with methanol repeatedly, and dried at room temperature under vacuum to obtain white polyimide powder with main chain grafting initiator.

[0087] 3) Preparation of polyimide film

[0088] Polyimide powder 200 mg with main chain grafting initiator was weighed and dissolved in 0.8 mL of N-methyl pyrrolidone solvent to prepare a casting solution with a solid content of 20 wt%, and a polyimide film was prepared by using a doctor blade method, dried at 70°C for 3 h, and then at 150°C for 5 h to obtain a polyimide film with initiator exposed on the surface.

[0089] 4) Grafting of polymer brush

[0090] CuBr2 7.460 mg, CuBr 23.972 mg, polyethylene glycol methacrylate 8.8 g, pentamethyldiethylenetriamine 43.412 mg were placed in a 50 mL reaction bottle, 16 mL of deionized water was added, vacuumed, and nitrogen was filled. Under nitrogen protection, 2,2-bis(3-aminophenyl)-hexafluoropropane 0.7222 g was added to the reaction bottle, and the reaction bottle was placed near 0°C. 4,4'-(hexafluoroisopropylidene)diphthalic anhydride 0.888 g was slowly added into the N-methyl pyrrolidone solvent containing 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, stirring while adding, and nitrogen protection was maintained, stirring at 0°C for 12 hours to obtain a light yellow PAA solution. The PAA solution was placed at room temperature, 4 mL of acetic anhydride and 2 mL of pyridine solution were measured for imidization, and stirring was performed while adding. After the dropwise addition was completed, the reaction bottle was kept at 110°C for 6h to obtain a brown polyimide solution. Then cooled to room temperature, the polyimide solution was slowly added to deionized water, stirring while adding, and brown solid precipitated, filtered, washed with water and methanol repeatedly, and dried at 50°C under vacuum to obtain white polyimide powder. 2The polyimide film with the naked initiator is immersed in the solution, the system is sealed, vacuumed, filled with nitrogen, and the operation is repeated three times. After 10 hours of reaction at room temperature, the polyimide film is taken out, washed repeatedly with deionized water, and dried under a nitrogen stream to obtain a polyimide film with grafted polymer brushes. The thickness of the polymer brush is 35 μm.

[0091] Example 4

[0092] The diamine monomer is 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (AHF), the acid anhydride monomer is 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, the initiator is 2-bromoisobutyryl bromide, and the polymer brush monomer is polyethylene glycol methacrylate.

[0093] The specific preparation method is as follows:

[0094] 1) Preparation of polyimide

[0095] Under the protection of nitrogen, 10.54 g of aniline, 4.0 g of 2,7-dihydroxy-9-fluorenone, and 0.9 g of methyl sulfonic acid are weighed into a 100 mL three-necked bottle, and the mixture is refluxed at 150°C for 14 h. Then the reaction is cooled to 110°C, triethylamine is added, and stirred at 110°C for 40 min. After the reaction is completed, the reaction is cooled to room temperature, poured into excess ethanol, washed repeatedly with ethanol and water until the filtrate is colorless, and vacuum dried at room temperature to obtain 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol in light purple.

[0096] 1.0 g of a solid diamine monomer containing a hydroxyl group, 1.1674 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 6 g of isoquinoline, and 26.3 mL of m-cresol are weighed into a 250 mL reaction bottle. Under the protection of nitrogen, the mixture is stirred at 80°C for 10 h, at 110°C for 10 h, at 150°C for 10 h, and at 180°C for 10 h. After the reaction is completed, it is cooled to room temperature, slowly poured into excess ethanol, filtered, washed repeatedly with ethanol, and vacuum dried at room temperature to obtain polyimide powder.

[0097] 2) Grafting of initiator

[0098] 600 mg of polyimide powder is dissolved in 20 mL of pyridine solution to completely dissolve it. Under the protection of nitrogen, 1.3 g of 2-bromoisobutyryl bromide is slowly added to the pyridine solution containing the polyimide powder, and reacted at 0°C for 1.5 h and at room temperature for 12 h. After the reaction is completed, it is filtered, treated with methanol, filtered, washed repeatedly with methanol, and vacuum dried at room temperature to obtain polyimide powder grafted with an initiator.

[0099] 3) Preparation of polyimide film

[0100] The 200 mg of main chain branched initiator polyimide powder was weighed into 0.8 mL of N-methylpyrrolidone solvent to prepare a casting solution with a solid content of 20 wt%, and a polyimide film was prepared by using a doctor blade or spin coating method. The polyimide film was dried at 70°C for 3 h and then at 150°C for 5 h to obtain a polyimide film with a surface exposed to the initiator.

[0101] 4) Grafting of polymer brushes

[0102] 7.460 mg of CuBr2, 23.972 mg of CuBr, 8.8 g of polyethylene glycol methacrylate, and 43.412 mg of pentamethyldiethylenetriamine were weighed into a 50 mL reaction bottle, 16 mL of deionized water was added, vacuumed, and filled with nitrogen. Under nitrogen protection, 1 cm2of 1 cm x 1 cm x 0.1 cm size initiator was placed in the reaction bottle, and the reaction bottle was sealed. The reaction bottle was vacuumed and filled with nitrogen, and the operation was repeated three times. The initiator was immersed in the reaction bottle, and the reaction was carried out at room temperature for 10 h. After the reaction was completed, the initiator was taken out, washed with deionized water repeatedly, and dried under a nitrogen stream to obtain a polyimide film with a polymer brush grafted thereon, and the thickness of the polymer brush was 28 μm. 2 The initiator-exposed polyimide film was immersed in the reaction bottle, the system was sealed, vacuumed, and filled with nitrogen, and the operation was repeated three times. The reaction was carried out at room temperature for 10 h. After the reaction was completed, the polyimide film was taken out, washed with deionized water repeatedly, and dried under a nitrogen stream to obtain a polyimide film with a polymer brush grafted thereon, and the thickness of the polymer brush was 28 μm.

[0103] Comparative Example 2

[0104] As a control experiment of Example 3, the difference is that the diamino monomer is replaced by 4,4'-tetraminodiphenyl ether.

[0105] The diamino monomer is 4,4'-tetraminodiphenyl ether, the anhydride monomer is 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, the initiator is 2-bromoisobutyryl bromide, and the polymer brush monomer is polyethylene glycol methacrylate.

[0106] The specific preparation method is as follows:

[0107] 1) Preparation of polyimide

[0108] Under nitrogen protection, 460.54 mg of 4,4'-tetraminodiphenyl ether, 976.72 mg of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride, and 32 g of polyphosphoric acid were weighed into a 500 mL reaction bottle, stirred at 190°C for 1.5 h, then heated to 290°C and stirred for 7 h. After the reaction was completed, the reaction was poured into 250 mL of deionized water, filtered, and dried. The dried solid was stirred in 5% NaHCO3 aqueous solution for 5 h, filtered, washed with deionized water until neutral, and then dried in an oven at 80°C for 17 h to obtain polyimide powder.

[0109] 2) Grafting of initiator

[0110] The polyimide powder 600 mg was weighed and dissolved in 20 mL of pyridine solution to make it completely dissolved. Under nitrogen protection, 1.3 g of 2-bromoisobutyryl bromide was slowly added to the pyridine solution containing the polyimide powder, and reacted at 0°C for 1.5 h and then at room temperature for 12 h. After the reaction was completed, the solution was filtered, precipitated with methanol, and washed with methanol repeatedly. The white polyimide powder of the main chain branched initiator was obtained by vacuum drying at room temperature.

[0111] 3) Preparation of polyimide film

[0112] The polyimide powder 200 mg of the main chain branched initiator was weighed and dissolved in 0.8 mL of N-methylpyrrolidone solvent to prepare a casting solution with a solid content of 20 wt%. The polyimide film was prepared by using a doctor blade method, dried at 70°C for 3 h, and then dried at 150°C for 5 h to obtain the polyimide film with the surface exposed initiator.

[0113] 4) Grafting of polymer brush

[0114] The CuBr2 7.460 mg, CuBr 23.972 mg, polyethylene glycol methacrylate 8.8 g, and pentamethyldiethylenetriamine 43.412 mg were placed in a 50 mL reaction bottle, 16 mL of deionized water was added, vacuumed, and filled with nitrogen. Under nitrogen protection, the reaction bottle was placed in a 1 cm 2 The polyimide film with the surface exposed initiator was immersed in the system, the system was sealed, vacuumed, and filled with nitrogen. The operation was repeated three times, and the reaction was carried out at room temperature for 10 h. After the reaction was completed, the polyimide film was taken out, washed with deionized water repeatedly, and dried under nitrogen flow to obtain the polyimide film grafted with the polymer brush, and the thickness of the polymer brush was 9 μm.

[0115] Example 5

[0116] The diamine monomer was 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, the acid anhydride monomer was 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, the initiator was 2-bromoisobutyryl bromide, and the polymer brush monomer was 3-[(3-acrylamidopropyl)dimethylammonio] propionate.

[0117] The preparation method of the polyimide film grafted with the polymer brush provided in the embodiment is as follows:

[0118] 1) Preparation of polyimide

[0119] Under nitrogen protection, 0.7222 g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane was dissolved in 10 mL of super dry N-methyl pyrrolidone solvent, and stirred to dissolve at room temperature until a clear transparent liquid was obtained. The reaction bottle was placed near 0°C, and 0.888 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride was slowly added into the N-methyl pyrrolidone solvent containing 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, while stirring and maintaining nitrogen protection, and stirred at 0°C for 12 hours to obtain a light yellow PAA solution. The PAA solution was placed at room temperature, and 4 mL of acetic anhydride and 2 mL of pyridine solution were measured for imidization, while stirring. After the dropwise addition was completed, the reaction bottle was continuously reacted at 110°C for 6 h to obtain a brown polyimide solution. Then cooled to room temperature, the polyimide solution was slowly added into deionized water, while stirring, and brown solid precipitated, filtered, washed with water and methanol repeatedly, and vacuum dried at 50°C to obtain white polyimide powder.

[0120] 2) Grafting of initiator

[0121] The polyimide powder 600 mg was dissolved in 20 mL of pyridine solution, and completely dissolved. Under nitrogen protection, 0.8 g of 2-bromoisobutyryl bromide was slowly added into the pyridine solution containing the polyimide powder, and reacted at 0°C for 1.5 h, and then at room temperature for 12 h. After the reaction was completed, filtered, the filtrate was treated with methanol, and filtered, washed with methanol repeatedly, and vacuum dried at room temperature to obtain white polyimide powder of main chain grafting initiator.

[0122] 3) Preparation of polyimide film

[0123] The polyimide powder 200 mg of main chain grafting initiator was dissolved in 0.8 mL of N-methyl pyrrolidone solvent, and a casting solution with a solid content of 20 wt% was prepared, and a polyimide film was prepared by using a doctor blade method, dried at 70°C for 3 h, and then at 150°C for 5 h to obtain a polyimide film with surface exposed initiator.

[0124] 4) Grafting of polymer brush

[0125] 6.7 mg of CuBr2and 28.1 mg of 2,2'-bipyridine were dissolved in 20 mL of deionized water, 264 mg of ascorbic acid was dissolved in 20 mL of deionized water, and 684.9 mg of 3-[(3-acrylamidopropyl)dimethylammonio]propanoate was dissolved in 4.6 mL of deionized water.

[0126] Under nitrogen protection, 1 cm2 2The polyimide film is prepared by nakedly exposing the initiator. Then, 3-[(3-acrylamidopropyl)dimethylammonium] propionate aqueous solution is added. Vacuum is applied, and nitrogen is filled. Then, 0.2 mL of CuBr2 and 2,2'-bipyridine mixed aqueous solution is added into the reaction container. Oxygen is removed by ultrasonic for 10 min. Then, 0.2 mL of ascorbic acid aqueous solution is added. Oxygen is removed by ultrasonic for another 10 min. The reaction is carried out at room temperature for 3 h. After the reaction is completed, the polyimide film is taken out and washed repeatedly with PBS and deionized water. The polyimide film grafted with polymer brushes is obtained by drying under nitrogen flow. The thickness of the polymer brush is 30 μm.

[0127] Example 6

[0128] The diamine monomer is 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol prepared by using aniline and 2,7-dihydroxy-9-fluorenone monomer. The anhydride monomer is 4,4'-(hexafluoroisopropylidene)diphthalic anhydride. The initiator is 2-bromoisobutyryl bromide. The polymer brush monomer is 3-[(3-acrylamidopropyl)dimethylammonium] propionate.

[0129] The specific preparation method is as follows:

[0130] 1) Preparation of polyimide

[0131] Under the protection of nitrogen, 10.54 g of aniline, 4.0 g of 2,7-dihydroxy-9-fluorenone, and 0.9 g of methyl sulfonic acid are weighed into a 100 mL three-necked bottle. The mixture is refluxed at 150 °C for 14 h. Then, the reaction is cooled to 110 °C, and triethylamine is added. The mixture is stirred at 110 °C for 40 min. After the reaction is completed, the reaction is cooled to room temperature. The reaction is poured into excess ethanol. The mixture is washed repeatedly with ethanol and water until the filtrate is colorless. The mixture is dried under vacuum at room temperature to obtain 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (AHF) in light purple.

[0132] 1.0 g of 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol solid, 1.1674 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 6 g of isoquinoline, and 26.3 mL of m-cresol are weighed into a 250 mL reaction bottle. The mixture is stirred at 80 °C for 10 h, at 110 °C for 10 h, at 150 °C for 10 h, and at 180 °C for 10 h under the protection of nitrogen. After the reaction is completed, the mixture is cooled to room temperature. The mixture is slowly poured into excess ethanol. The mixture is filtered and washed repeatedly with ethanol. The mixture is dried under vacuum at room temperature to obtain polyimide powder.

[0133] 2) Grafting of initiator

[0134] Weigh 600 mg of polyimide powder and dissolve it completely in 20 mL of pyridine solution. Under nitrogen, slowly add 0.8 g of 2-bromoisobutyric acid bromide dropwise to the pyridine solution containing the polyimide powder. Allow to react at 0°C for 1.5 hours, then at room temperature for 12 hours. After the reaction, filter the mixture, and settle the filtrate with methanol. Filter the mixture, wash it repeatedly with methanol, and dry it in a vacuum oven at room temperature to obtain the polyimide powder containing the backbone grafting initiator.

[0135] 3) Preparation of polyimide film

[0136] 200 mg of polyimide powder containing the main chain grafting initiator was weighed and dissolved in 0.8 mL of N-methylpyrrolidone solvent to prepare a casting solution with a solid content of 20 wt%. A polyimide film was prepared by spin coating and dried at 70 ° C for 3 h and then at 150 ° C for 5 h to obtain a polyimide film with a surface exposed to the initiator.

[0137] 4) Grafting of polymer brushes

[0138] Weigh 6.7 mg of CuBr2 and 28.1 mg of 2,2'-bipyridine and dissolve them in 20 mL of deionized water. Weigh 264 mg of ascorbic acid and dissolve it in 20 mL of deionized water. Weigh 684.9 mg of 3-[(3-acrylamidopropyl)dimethylammonium]propionate and dissolve it in 4.6 mL of deionized water.

[0139] Under nitrogen protection, a 1cm 2 To the polyimide film with bare initiator, add 3-[(3-acrylamidopropyl)dimethylammonium]propionate aqueous solution, evacuate and fill with nitrogen, then add 0.2mL of CuBr2 and 2,2'-bipyridine mixed aqueous solution into the reaction vessel, ultrasonically deoxygenate for 10 minutes, then add 0.2mL of ascorbic acid aqueous solution, ultrasonically deoxygenate for 10 minutes, and react at room temperature for 3 hours. After the reaction is completed, take out the polyimide film, rinse repeatedly with PBS and deionized water, and dry under nitrogen flow to obtain a polyimide film grafted with polymer brushes. The thickness of the polymer brushes is 25μm.

[0140] The thickness data of the polyimide films grafted with polymer brushes prepared using different materials and processes in Examples 1-6 and Comparative Examples 1-2 are summarized in Table 1.

[0141] Table 1

[0142] Serial number Diaminomonomer Amount of initiator (g) Thickness (pm) Example 1 AHHFP CB Example 2 1.3 40 AHF CB Comparative Example 1 1.3 32 TADE CB Example 3 1.3 0 AHHFP EGMA Example 4 1.3 35 AHF EGMA Comparative Example 2 1.3 28 TADE EGMA Example 5 1.3 0 AHHFP CB Example 6 0.8 30 AHF CB ​ 0.8 25

[0143] It can be seen from Table 1 that the thickness of the main chain grafted polyimide film grafted polymer brushes of Examples 1-6 can all reach micrometer level.

[0144] From the comparison of Example 1 and 5 and Example 2 and 6, it can be seen that the amount of polyimide main chain initiator also affects the thickness of the polymer brush, because when the initiator is not excessive, the hydroxyl group on the polyimide main chain is difficult to completely react, resulting in low grafting rate of the initiator, and in the later grafting polymer brush process, the initiator density is low, thereby affecting the grafting polymer brush density to reduce, and further affecting the brush thickness to reduce. The effect is best when the mass ratio of polyimide to initiator is 0.6:1.3.

[0145] From the comparison of Example 1 and 2, there is a difference in grafting thickness, mainly because after the reaction of the polyimide main chain formed by the diamine monomer and the acid anhydride monomer in Example 2 and the initiator, the steric hindrance of the polymer chain is larger, thereby affecting the initiation effect of the initiator, and further affecting the grafting density, so that the thickness is lower. The effect of the polyimide grafted polymer brush prepared by the diamine monomer AHHFP is best.

[0146] From the comparison of Example 1 and 3, and Comparative Examples 1 and 2, respectively, because the diamine monomer and the acid anhydride monomer in the comparative examples do not have hydroxyl groups, the polyimide main chain formed does not have exposed hydroxyl groups to react with the initiator, so the grafting of the initiator is almost zero, making the prepared polyimide film almost no grafting in the reaction of grafting polymer brush, so the polymer brush thickness is zero. The polyimide film prepared by the two diamine monomers containing hydroxyl groups selected by the present application has obvious advantages compared with ordinary polyimide film without hydroxyl groups for grafting high-thickness polymer brush.

[0147] Although the specific embodiments of the present application are described above, those skilled in the art should understand that these are only illustrative, and various changes or modifications can be made to the present embodiments without departing from the principles and essence of the present application, and the protection scope of the present application is only limited by the appended claims.

Claims

1. A method for producing a grafted polyimide film of a polymeric brush, characterized by, The method comprises the following steps: S1, selecting 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol as a diamino monomer, and performing a polycondensation reaction on the diamino monomer and an anhydride monomer, washing, and drying to obtain a polyimide powder; Alternatively, selecting 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane as a diamino monomer, performing a polycondensation reaction on the diamino monomer and an anhydride monomer, and then performing a chemical imidization treatment, washing, and drying to obtain a polyimide powder; S2, performing a grafting reaction on the polyimide powder obtained in step S1 and an initiator 2-bromoisobutyryl bromide in a pyridine solvent, washing, and drying to obtain a polyimide powder grafted with an initiator; S3, dissolving the polyimide powder obtained in step S2 in an N-methylpyrrolidone solvent to configure a casting solution, and performing coating to obtain a polyimide film; S4, selecting 3-[(3-acrylamidopropyl)dimethylammonium] propionate or polyethylene glycol methacrylate as a polymer brush monomer, immersing the polyimide film obtained in step S3 in an aqueous solution containing the polymer brush monomer in an oxygen-free atmosphere, and adding copper bromide, 2,2'-bipyridine, and ascorbic acid, or adding copper bromide, cuprous bromide, and pentamethyldiethylenetriamine to perform a reaction, to obtain a polyimide film grafted with a polymer brush.

2. The method for producing a grafted polyimide film of a polymeric brush according to claim 1, characterized by, In step S1, the anhydride monomer is selected from at least one of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 5-aminosalicylic acid and pyromellitic anhydride.

3. The method of claim 1, wherein the polyimide film is prepared by grafting a polyimide film with a polymeric brush. In step S1, when the diamino monomer is 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol, after the polycondensation reaction is completed, a polyamide acid solution obtained by polycondensation reaction of the diamino monomer and the anhydride monomer is added with a dehydrating agent and a dehydration catalyst, and stirring is performed at room temperature to 150 DEG C to obtain a polyimide solution, and the polyimide solution is washed and dried to obtain a polyimide powder. The dehydrating agent is at least one of acetic anhydride, propionic anhydride, butyric anhydride, and sodium acetate, and the dehydration catalyst is at least one of triethylamine, isoquinoline, pyridine, and N-methylpyridine.

4. The method of claim 1, wherein the polyimide film is prepared by grafting a polyimide film with a polymeric brush. Steps S1 and S2 are both performed in a protective atmosphere, and the protective atmosphere is an inert gas.

5. The method of claim 1, wherein the polyimide film is prepared by grafting a polyimide film with a polymeric brush. In step S3, the solid content of the casting solution is 20-30 wt%.

6. The method of claim 1, wherein the polyimide film is prepared by grafting a polyimide film with a polymeric brush. In step S3, the coating is performed by means of blade coating, casting, or spin coating, and after coating, drying is first performed at 60-70 DEG C for 2-3 h, and then drying is performed at 130-150 DEG C for 4-5 h.

7. The method for preparing a polyimide film of a grafted polymer brush according to claim 1, wherein: In step S4, after the immersion reaction of the polyimide film is completed, PBS and deionized water are repeatedly rinsed, and then drying is performed under a nitrogen gas stream to obtain a dried polyimide film grafted with a polymer brush.

8. The method of claim 1, wherein the polyimide film is prepared by grafting a polyimide film with a polymeric brush. In step S4, the solvent used is deionized water.

9. A polyimide film grafted with a polymer brush, characterized by, The method is prepared by any one of claims 1-8, and the thickness of the polymer brush is microns.

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