Polyimide film grafted with polymer brush and preparation method of polyimide film

Abstract

The invention relates to the field of preparation of polymer brushes, and discloses a polyimide film grafted with a polymer brush and a preparation method thereof, and the method comprises the following steps: carrying out polycondensation reaction on a diamine monomer and an anhydride monomer, washing, and drying to obtain the polyimide film grafted with the polymer brush. Performing grafting reaction on the polyimide powder and an initiator 2-bromoisotolyl bromide in a pyridine solvent, washing and drying to obtain polyimide powder of which the main chain is grafted with the initiator; dissolving the initiator grafted polyimide powder in an N-methyl pyrrolidone solvent to prepare a film casting solution, and coating to prepare a polyimide film; in a deoxidizing atmosphere, a polyimide film is soaked in an aqueous solution in which the polymer brush monomer is dissolved, and copper bromide, 2, 2 '-dipyridyl and ascorbic acid are added for reaction to obtain the polyimide film grafted with the polymer brush. According to the preparation method, the initiator 2-bromoisotolyl bromide is grafted on a polyimide main chain, so that the grafting thickness of a polymer brush reaches a micron level.

Description

Technical Field

[0001] The invention relates to the field of preparation of polymer brushes, and in particular to a polyimide film grafted with a polymer brush and a preparation method thereof. Background Art

[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, the traditional method for preparing PI films has certain limitations, such as unstable, easy-to-fall-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 a method to improve the surface properties of polyimide films by grafting technology.

[0003] The literature [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 immobilization, chromatographic supports, membrane applications, antibacterial coatings and low-friction surfaces. However, these applications usually require the polymer brushes to have the required thickness, and its thickness affects the application performance and effect. The literature [Jeong, Jaehoon, et al. "Formation of antifouling brushes on various substrates using a melanin-inspired initiator film." Langmuir 39.22(2023):7598-7604.] synthesizes a tyrosine-bound bromide initiator to form an initiator film on a substrate, and uses an electron transfer-regenerated air-resistant activator to carry out atom transfer radical polymerization of zwitterionic carboxybetaine to form an antifouling polymer brush. The polymer brush monomer of this literature is 3-[(3-acrylamidopropyl)dimethylammonium] propionate, and the thickness of the prepared polymer brush is nanometer-scale. Although the prior art has made significant progress in controlling the thickness of polymer brushes, the preparation of ultra-thick polymer brushes remains a challenge. Summary of the invention

[0004] Based on the above application technology problems of polyimide film, the present invention provides a new method for preparing polyimide film. The core of the method is to select diamine monomers containing hydroxyl groups and anhydride monomers for polycondensation reaction to prepare polyimide powder; on this basis, the polyimide powder and the initiator are grafted in a pyridine solvent to form a polyimide powder with a main chain grafted with the initiator; the casting solution is prepared by N-methylpyrrolidone solvent, and the polyimide film is prepared by blade coating, casting or spin coating; finally, the polyimide film containing the initiator is immersed in a solution containing monomers for graft polymerization to form a polymer brush, so as to obtain a modified polyimide film with excellent surface properties and high grafting density.

[0005] To achieve the above object, on the one hand, the present invention provides a method for preparing a polyimide film grafted with a polymer brush, which comprises the following steps:

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

[0007] Alternatively, the diamine monomer is selected as 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, the diamine monomer and the acid anhydride monomer are subjected to a condensation reaction, and then subjected to a chemical imidization treatment, washed, and dried to prepare a polyimide powder;

[0008] The structural formulas of the diamine monomers are shown in the following formulas (1)-(2):

[0009]

[0010] S2, carrying out a grafting reaction between the polyimide powder obtained in step S1 and the initiator 2-bromoisobutyl bromide in a pyridine solvent, washing, and drying to obtain a polyimide powder with a main chain grafted with the initiator;

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

[0012]

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

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

[0015] The structural formula of the polymer brush monomer is shown in the following formulas (4) and (5):

[0016]

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

[0018] As a further preferred technical solution of the present invention, in step S1, when the diamine monomer is 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, after the polycondensation reaction is completed, a chemical imidization method is used to polycondense the diamine monomer and the acid anhydride monomer to obtain a polyamic acid solution, a dehydrating agent and a dehydration catalyst are added to the polyamic acid solution, and the reaction is stirred 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] The dehydrating agent is at least one of acetic anhydride, propionic anhydride, butyric anhydride and sodium acetate, and the dehydrating catalyst is at least one of triethylamine, isoquinoline, pyridine and N-methylpyridine.

[0020] The present invention selects pyridine as a solvent, which has good solubility and good catalytic effect on the reaction, and promotes the grafting reaction between the initiator and the polyimide main chain. As a further preferred technical solution of the present invention, 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 invention, steps S1 and S2 are both performed under a protective atmosphere, and the protective atmosphere is nitrogen or an inert gas.

[0022] The present invention 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 invention, in step S3, the solid content of the casting solution is 20-30wt%.

[0023] As a further preferred technical solution of the present invention, in step S3, coating is performed by scraping, casting or spin coating. After coating, the coating is first dried at 60-70° C. for 2-3 hours, and then dried at 130-150° C. for 4-5 hours.

[0024] As a further preferred technical solution of the present invention, in step S4, after the immersion reaction of the polyimide film is completed, it is repeatedly rinsed with PBS and deionized water, and then dried under a nitrogen flow to obtain a dried polyimide film of the grafted polymer brush.

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

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

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

[0028] 1) The present invention grafts the initiator 2-bromoisobutyl bromide onto the main chain of polyimide, so that the initiator is directly introduced into the polyimide during the film-forming process, which not only solves the problems of unevenness and easy falling off of the traditional initiator layer, but also has a good initiation effect, so that the polymer brush grafting thickness reaches the micron level, which is conducive to expanding the application of polyimide films.

[0029] 2) The polyimide film grafted with a polymer brush prepared by the present invention can be used as an antifouling film. The thickness of the polymer brush grafting reaches the micron level, which can greatly improve the antifouling effect. In addition, the manufacture of flexible copper-clad laminates requires that the surface of the polyimide film be coated with glue and then bonded to the copper foil or that metal materials such as copper and silver be deposited on the surface of the polyimide film by electroplating or sputtering. The surface of the polyimide film can be grafted with a polymer brush to improve the surface roughness, thereby effectively improving its bonding performance with metal materials and making the peeling strength higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0031] Figure 1 This is a schematic diagram of the structure of the polyimide film grafted polymer brush with the main chain grafted initiator in Example 1.

[0032] Figure 2 This is the H-NMR spectrum of the polyimide powder of Example 1 and the polyimide powder grafted with the main chain initiator.

[0033] Figure 3 This is the thickness diagram of the polyimide film grafted polymerization brush of the main chain grafting initiator in Example 1.

[0034] Figure 4 The scanning electron microscope images of the polyimide film with the main chain grafted initiator before and after the grafting of the polymer brush in Example 1, wherein (a) is before the grafting of the polymer brush, and (b) is after the grafting of the polymer brush.

[0035] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0036] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

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

[0038] Example 1

[0039] The diamine monomer was selected as 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane (AHHFP), the anhydride monomer was 4,4'-(hexafluoroisopropylene) diphthalic anhydride, the initiator was 2-bromoisobutyl bromide, and the polymer brush monomer was 3-[(3-acrylamidopropyl)dimethylammonium] propionate (CB).

[0040] The method for preparing the polyimide film of the grafted polymer brush provided in this embodiment is as follows:

[0041] 1) Preparation of polyimide

[0042] Under nitrogen protection, weigh 0.7222g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and dissolve it in 10mL of ultra-dry N-methylpyrrolidone solvent, and stir and dissolve it at room temperature until it becomes a clear transparent liquid. Place the reaction bottle near 0°C, weigh 0.888g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, and slowly add it in batches to the N-methylpyrrolidone solvent containing 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, stirring while adding, while maintaining nitrogen protection, stirring and reacting at 0°C for 12 hours to obtain a light yellow PAA solution. Place the PAA solution at room temperature, measure 4mL of acetic anhydride and 2mL of pyridine solution for imidization, stirring while adding. After the addition is completed, allow the reaction bottle to react for 6h at 110°C to obtain a brown polyimide solution. Then the mixture was cooled to room temperature, and the polyimide solution was slowly added dropwise to deionized water while stirring. A brown solid precipitate appeared, which was filtered, repeatedly washed with water and methanol, and vacuum dried at 50° C. to obtain a white polyimide powder.

[0043] 2) Grafting of initiator

[0044] Weigh 600 mg of polyimide powder and dissolve it in 20 mL of pyridine solution to make it completely dissolved. Under nitrogen protection, slowly drop 1.3 g of 2-bromoisobutyl bromide into the pyridine solution containing the polyimide powder, react at 0°C for 1.5 hours, and then react at room temperature for 12 hours. After the reaction is completed, filter, use methanol to precipitate the filtrate, filter, wash repeatedly with methanol, and vacuum dry at room temperature to obtain white polyimide powder with main chain grafting initiator.

[0045] 3) Preparation of polyimide film

[0046] 200 mg of polyimide powder with 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 blade coating. 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 bare initiator on the surface.

[0047] 4) Grafting of polymer brushes

[0048] Weigh 6.7 mg of CuBr2 and 28.1 mg of 2,2'-bipyridine and dissolve them in 20 mL of deionized water for later use; weigh 264 mg of ascorbic acid and dissolve it in 20 mL of deionized water for later use; weigh 684.9 mg of 3-[(3-acrylamidopropyl)dimethylammonium]propionate and dissolve it in 4.6 mL of deionized water for later use.

[0049] Under nitrogen protection, a 1cm 2To the polyimide film with bare initiator, add 3-[(3-acrylamidopropyl)dimethylammonium] propionate aqueous solution, evacuate, fill with nitrogen, then add 0.2mL of CuBr2 and 2,2'-bipyridine mixed aqueous solution into the reaction container, ultrasonically deoxygenate for 10 minutes, then add 0.2mL of ascorbic acid aqueous solution, ultrasonically deoxygenate for 10 minutes, and then react at room temperature for 3 hours. After the reaction, take out the polyimide film, rinse it repeatedly with PBS and deionized water, and dry it under nitrogen flow to obtain the polyimide film grafted with polymer brushes, and the thickness of the polymer brushes is 40μm.

[0050] Figure 1 This is a schematic diagram of the structure of the polyimide film grafted polymer brush with the main chain grafted initiator provided in Example 1, Figure 1 Middle: 1 is the polyimide film with grafted initiator on the main chain; 2 is the grafted polymer brush.

[0051] Figure 2 This is the H-NMR spectrum of the polyimide powder grafted with the main chain of the polyimide powder in Example 1. The characteristic peak of methyl group appears at 1.84 ppm, which proves that the polyimide main chain is successfully grafted with the initiator.

[0052] The polyimide film sample grafted with polymer brushes in Example 1 was imaged in three dimensions using a three-dimensional digital microscope in bright field mode. The height difference of the sample surface was characterized by measuring the horizontal height of the surface profile. The test data was derived as follows: Figure 3 As shown, it can be seen from the figure that the thickness of the grafted polymer brush is about 40 μm.

[0053] See also Figure 4 , the scanning electron microscope images before and after the polyimide film was grafted with the polymer brush in Example 1 were compared. It can be clearly seen from the images that the polymer brush grafted on the surface of the polyimide film is evenly distributed.

[0054] Example 2

[0055] The diamine monomer selected was 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (AHF) prepared from aniline and 2,7-dihydroxy-9-fluorenequinone monomers, the anhydride monomer was 4,4'-(hexafluoroisopropylene) diphthalic anhydride, the initiator was 2-bromoisopropyl 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-fluorenequinone and 0.9 g of methanesulfonic acid were weighed into a 100 mL three-necked flask, and the mixture was refluxed at 150° C. for 14 h. The reactant was then cooled to 110° C., triethylamine was added, and the mixture was stirred at 110° C. for 40 min. After the reaction was completed, the mixture was cooled to room temperature, poured into excess ethanol, and washed repeatedly with ethanol and water until the filtrate was colorless. The mixture was dried in vacuo at room temperature to obtain light purple 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (AHF).

[0059] Weigh 1.0 g of 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol solid, 1.1674 g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 6 g of isoquinoline and 26.3 mL of m-cresol into a 250 mL reaction bottle. Under nitrogen protection, stir the mixture at 80° C. for 10 h, 110° C. for 10 h, 150° C. for 10 h, and 180° C. for 10 h. After the reaction is completed, cool to room temperature, slowly pour into excess ethanol, filter, repeatedly wash with ethanol, and vacuum dry at room temperature to obtain polyimide powder.

[0060] 2) Grafting of initiator

[0061] Weigh 600 mg of polyimide powder and dissolve it in 20 mL of pyridine solution to make it completely dissolved. Under nitrogen protection, slowly drop 1.3 g of 2-bromoisobutyl bromide into the pyridine solution containing the polyimide powder, react at 0°C for 1.5 hours, and then react at room temperature for 12 hours. After the reaction is completed, filter, use methanol to precipitate the filtrate, filter, wash repeatedly with methanol, and vacuum dry at room temperature to obtain the polyimide powder of the main chain grafting initiator.

[0062] 3) Preparation of polyimide film

[0063] 200 mg of polyimide powder with 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 bare initiator on the surface.

[0064] 4) Grafting of polymer brushes

[0065] Weigh 6.7 mg of CuBr2 and 28.1 mg of 2,2'-bipyridine and dissolve them in 20 mL of deionized water for later use; weigh 264 mg of ascorbic acid and dissolve it in 20 mL of deionized water for later use; weigh 684.9 mg of 3-[(3-acrylamidopropyl)dimethylammonium]propionate and dissolve it in 4.6 mL of deionized water for later use.

[0066] Under nitrogen protection, a 1cm 2 To the polyimide film with bare initiator, add 3-[(3-acrylamidopropyl)dimethylammonium] propionate aqueous solution, evacuate, fill with nitrogen, then add 0.2mL of CuBr2 and 2,2'-bipyridine mixed aqueous solution into the reaction container, ultrasonically deoxygenate for 10 minutes, then add 0.2mL of ascorbic acid aqueous solution, ultrasonically deoxygenate for 10 minutes, 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 32μm.

[0067] Comparative Example 1

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

[0069] The diamine monomer is selected as 4,4'-tetraaminodiphenyl ether (TADE), the anhydride monomer is selected as 4,4'-(hexafluoroisopropylene) diphthalic anhydride, the initiator is selected as 2-bromoisobutyl bromide, and the polymer brush monomer is selected as 3-[(3-acrylamidopropyl) dimethylammonium] propionate.

[0070] The specific preparation method is as follows:

[0071] 1) Preparation of polyimide

[0072] Under nitrogen protection, weigh 460.54 mg of 4,4'-tetraaminodiphenyl ether, 976.72 mg of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, and 32 g of polyphosphoric acid into a 500 mL reaction bottle, stir at 190 ° C for 1.5 hours, then heat to 290 ° C and stir for 7 hours. After the reaction is completed, pour the reactant into 250 mL of deionized water, filter, and dry. Place the dried solid in a 5% NaHCO3 aqueous solution and stir for 5 hours, filter, wash with deionized water until neutral, and then dry the product in an oven at 80 ° C for 17 hours to obtain polyimide powder.

[0073] 2) Grafting of initiator

[0074] Weigh 600 mg of polyimide powder and dissolve it in 20 mL of pyridine solution to make it completely dissolved. Under nitrogen protection, slowly drop 1.3 g of 2-bromoisobutyl bromide into the pyridine solution containing the polyimide powder, react at 0°C for 1.5 hours, and then react at room temperature for 12 hours. After the reaction is completed, filter, use methanol to precipitate the filtrate, filter, wash repeatedly with methanol, and vacuum dry at room temperature to obtain white polyimide powder with main chain grafting initiator.

[0075] 3) Preparation of polyimide film

[0076] 200 mg of polyimide powder with 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 blade coating. 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 bare initiator on the surface.

[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 for later use; weigh 264 mg of ascorbic acid and dissolve it in 20 mL of deionized water for later use; weigh 684.9 mg of 3-[(3-acrylamidopropyl)dimethylammonium]propionate and dissolve it in 4.6 mL of deionized water for later use.

[0079] Under nitrogen protection, a 1cm 2 To the polyimide film with bare initiator, add 3-[(3-acrylamidopropyl)dimethylammonium] propionate aqueous solution, evacuate, fill with nitrogen, then add 0.2mL of CuBr2 and 2,2'-bipyridine mixed aqueous solution into the reaction container, ultrasonically deoxygenate for 10 minutes, then add 0.2mL of ascorbic acid aqueous solution, ultrasonically deoxygenate for 10 minutes, and then react at room temperature for 3 hours. After the reaction, take out the polyimide film, rinse it repeatedly with PBS and deionized water, and dry it under nitrogen flow to obtain the polyimide film grafted with polymer brushes, and 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, weigh 0.7222g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and dissolve it in 10mL of ultra-dry N-methylpyrrolidone solvent, and stir and dissolve it at room temperature until it becomes a clear transparent liquid. Place the reaction bottle near 0°C, weigh 0.888g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, and slowly add it in batches to the N-methylpyrrolidone solvent containing 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, stirring while adding, while maintaining nitrogen protection, stirring and reacting at 0°C for 12 hours to obtain a light yellow PAA solution. Place the PAA solution at room temperature, measure 4mL of acetic anhydride and 2mL of pyridine solution for imidization, stirring while adding. After the addition is completed, allow the reaction bottle to react for 6h at 110°C to obtain a brown polyimide solution. Then the mixture was cooled to room temperature, and the polyimide solution was slowly added dropwise to deionized water while stirring. A brown solid precipitate appeared, which was filtered, repeatedly washed with water and methanol, and vacuum dried at 50° C. to obtain a white polyimide powder.

[0085] 2) Grafting of initiator

[0086] Weigh 600 mg of polyimide powder and dissolve it in 20 mL of pyridine solution to make it completely dissolved. Under nitrogen protection, slowly drop 1.3 g of 2-bromoisobutyl bromide into the pyridine solution containing the polyimide powder, react at 0°C for 1.5 hours, and then react at room temperature for 12 hours. After the reaction is completed, filter, use methanol to precipitate the filtrate, filter, wash repeatedly with methanol, and vacuum dry at room temperature to obtain white polyimide powder with main chain grafting initiator.

[0087] 3) Preparation of polyimide film

[0088] Weigh 200 mg of polyimide powder with main chain grafting initiator and dissolve it in 0.8 mL of N-methylpyrrolidone solvent to prepare a casting solution with a solid content of 20 wt%. Prepare a polyimide film by blade coating, dry it at 70°C for 3 h, and then dry it at 150°C for 5 h to obtain a polyimide film with a bare initiator on the surface.

[0089] 4) Grafting of polymer brushes

[0090] Weigh 7.460 mg CuBr2, 23.972 mg CuBr, 8.8 g polyethylene glycol methacrylate, and 43.412 mg pentamethyldiethylenetriamine, place in a 50 mL reaction bottle, add 16 mL deionized water, evacuate, and fill with nitrogen. Under nitrogen protection, place a 1 cm 2The polyimide film with bare initiator is immersed in it, the system is sealed, evacuated, and filled with nitrogen, and the operation is repeated three times. The reaction is allowed to proceed at room temperature for 10 hours. After the reaction is completed, the polyimide film is taken out, repeatedly rinsed with deionized water, and dried under a nitrogen flow to obtain a polyimide film grafted with a polymer brush. The thickness of the polymer brush is 35 μm.

[0091] Example 4

[0092] The diamine monomer is selected as 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol (AHF), the anhydride monomer is 4,4'-(hexafluoroisopropylene) diphthalic anhydride, the initiator is 2-bromoisobutyl 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 nitrogen protection, 10.54 g of aniline, 4.0 g of 2,7-dihydroxy-9-fluorenequinone and 0.9 g of methanesulfonic acid were weighed into a 100 mL three-necked flask, and the mixture was refluxed at 150 ° C for 14 h, then the reactant was cooled to 110 ° C, triethylamine was added, and stirred at 110 ° C for 40 min. After the reaction was completed, it was cooled to room temperature, poured into excess ethanol, and washed repeatedly with ethanol and water until the filtrate was colorless, and dried in vacuo at room temperature to obtain light purple 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol.

[0096] Weigh 1.0 g of a hydroxyl-containing diamine monomer solid, 1.1674 g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 6 g of isoquinoline and 26.3 mL of m-cresol into a 250 mL reaction bottle. Under nitrogen protection, stir the mixture at 80°C for 10 h, 110°C for 10 h, 150°C for 10 h, and 180°C for 10 h. After the reaction is completed, cool to room temperature, slowly pour into excess ethanol, filter, repeatedly wash with ethanol, and vacuum dry at room temperature to obtain polyimide powder.

[0097] 2) Grafting of initiator

[0098] Weigh 600 mg of polyimide powder and dissolve it in 20 mL of pyridine solution to make it completely dissolved. Under nitrogen protection, slowly drop 1.3 g of 2-bromoisobutyl bromide into the pyridine solution containing the polyimide powder, react at 0°C for 1.5 hours, and then react at room temperature for 12 hours. After the reaction is completed, filter, use methanol to precipitate the filtrate, filter, wash repeatedly with methanol, and vacuum dry at room temperature to obtain the polyimide powder of the main chain grafting initiator.

[0099] 3) Preparation of polyimide film

[0100] Weigh 200 mg of polyimide powder with main chain grafting initiator and dissolve it in 0.8 mL of N-methylpyrrolidone solvent to prepare a casting solution with a solid content of 20 wt%. Prepare a polyimide film by blade coating or spin coating, dry it at 70 ° C for 3 h, and then dry it at 150 ° C for 5 h to obtain a polyimide film with a bare initiator on the surface.

[0101] 4) Grafting of polymer brushes

[0102] Weigh 7.460 mg CuBr2, 23.972 mg CuBr, 8.8 g polyethylene glycol methacrylate, and 43.412 mg pentamethyldiethylenetriamine, place in a 50 mL reaction bottle, add 16 mL deionized water, evacuate, and fill with nitrogen. Under nitrogen protection, place a 1 cm 2 The polyimide film with bare initiator is immersed in it, the system is sealed, evacuated, and filled with nitrogen, and the operation is repeated three times. The reaction is allowed to proceed at room temperature for 10 hours. After the reaction is completed, the polyimide film is taken out, repeatedly rinsed with deionized water, and dried under a nitrogen flow to obtain a polyimide film grafted with a polymer brush. The thickness of the polymer brush is 28 μm.

[0103] Comparative Example 2

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

[0105] The diamine monomer is selected as 4,4'-tetraaminodiphenyl ether, the anhydride monomer is selected as 4,4'-(hexafluoroisopropylene) diphthalic anhydride, the initiator is selected as 2-bromoisobutyl bromide, and the polymer brush monomer is selected as polyethylene glycol methacrylate.

[0106] The specific preparation method is as follows:

[0107] 1) Preparation of polyimide

[0108] Under nitrogen protection, weigh 460.54 mg of 4,4'-tetraaminodiphenyl ether, 976.72 mg of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, and 32 g of polyphosphoric acid into a 500 mL reaction bottle, stir at 190 ° C for 1.5 hours, then heat to 290 ° C and stir for 7 hours. After the reaction is completed, pour the reactant into 250 mL of deionized water, filter, and dry. Place the dried solid in a 5% NaHCO3 aqueous solution and stir for 5 hours, filter, wash with deionized water until neutral, and then dry the product in an oven at 80 ° C for 17 hours to obtain polyimide powder.

[0109] 2) Grafting of initiator

[0110] Weigh 600 mg of polyimide powder and dissolve it in 20 mL of pyridine solution to make it completely dissolved. Under nitrogen protection, slowly drop 1.3 g of 2-bromoisobutyl bromide into the pyridine solution containing the polyimide powder, react at 0°C for 1.5 hours, and then react at room temperature for 12 hours. After the reaction is completed, filter, use methanol to precipitate the filtrate, filter, wash repeatedly with methanol, and vacuum dry at room temperature to obtain white polyimide powder with main chain grafting initiator.

[0111] 3) Preparation of polyimide film

[0112] Weigh 200 mg of polyimide powder with main chain grafting initiator and dissolve it in 0.8 mL of N-methylpyrrolidone solvent to prepare a casting solution with a solid content of 20 wt%. Prepare a polyimide film by blade coating, dry it at 70°C for 3 h, and then dry it at 150°C for 5 h to obtain a polyimide film with a bare initiator on the surface.

[0113] 4) Grafting of polymer brushes

[0114] Weigh 7.460 mg CuBr2, 23.972 mg CuBr, 8.8 g polyethylene glycol methacrylate, and 43.412 mg pentamethyldiethylenetriamine, place in a 50 mL reaction bottle, add 16 mL deionized water, evacuate, and fill with nitrogen. Under nitrogen protection, place a 1 cm 2 The polyimide film with bare initiator is immersed in it, the system is sealed, evacuated, and filled with nitrogen, and the operation is repeated three times. The reaction is allowed to proceed at room temperature for 10 hours. After the reaction is completed, the polyimide film is taken out, repeatedly rinsed with deionized water, and dried under a nitrogen flow to obtain a polyimide film grafted with a polymer brush. The thickness of the polymer brush is 9 μm.

[0115] Example 5

[0116] 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 3-[(3-acrylamidopropyl)dimethylammonium] propionate.

[0117] The method for preparing the polyimide film of the grafted polymer brush provided in this embodiment is as follows:

[0118] 1) Preparation of polyimide

[0119] Under nitrogen protection, weigh 0.7222g of 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane and dissolve it in 10mL of ultra-dry N-methylpyrrolidone solvent, and stir and dissolve it at room temperature until it becomes a clear transparent liquid. Place the reaction bottle near 0°C, weigh 0.888g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, and slowly add it in batches to the N-methylpyrrolidone solvent containing 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, stirring while adding, while maintaining nitrogen protection, stirring and reacting at 0°C for 12 hours to obtain a light yellow PAA solution. Place the PAA solution at room temperature, measure 4mL of acetic anhydride and 2mL of pyridine solution for imidization, stirring while adding. After the addition is completed, allow the reaction bottle to react for 6h at 110°C to obtain a brown polyimide solution. Then the mixture was cooled to room temperature, and the polyimide solution was slowly added dropwise to deionized water while stirring. A brown solid precipitate appeared, which was filtered, repeatedly washed with water and methanol, and vacuum dried at 50° C. to obtain a white polyimide powder.

[0120] 2) Grafting of initiator

[0121] Weigh 600 mg of polyimide powder and dissolve it in 20 mL of pyridine solution to make it completely dissolved. Under nitrogen protection, slowly drop 0.8 g of 2-bromoisobutyl bromide into the pyridine solution containing the polyimide powder, react at 0°C for 1.5 hours, and then react at room temperature for 12 hours. After the reaction is completed, filter, use methanol to precipitate the filtrate, filter, wash repeatedly with methanol, and vacuum dry at room temperature to obtain white polyimide powder with main chain grafting initiator.

[0122] 3) Preparation of polyimide film

[0123] 200 mg of polyimide powder with 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 blade coating. 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 bare initiator on the surface.

[0124] 4) Grafting of polymer brushes

[0125] Weigh 6.7 mg of CuBr2 and 28.1 mg of 2,2'-bipyridine and dissolve them in 20 mL of deionized water for later use; weigh 264 mg of ascorbic acid and dissolve it in 20 mL of deionized water for later use; weigh 684.9 mg of 3-[(3-acrylamidopropyl)dimethylammonium]propionate and dissolve it in 4.6 mL of deionized water for later use.

[0126] Under nitrogen protection, a 1cm 2To the polyimide film with bare initiator, add 3-[(3-acrylamidopropyl)dimethylammonium] propionate aqueous solution, evacuate, fill with nitrogen, then add 0.2mL of CuBr2 and 2,2'-bipyridine mixed aqueous solution into the reaction container, ultrasonically deoxygenate for 10 minutes, then add 0.2mL of ascorbic acid aqueous solution, ultrasonically deoxygenate for 10 minutes, and then react at room temperature for 3 hours. After the reaction, take out the polyimide film, rinse it repeatedly with PBS and deionized water, and dry it under nitrogen flow to obtain the polyimide film grafted with polymer brushes, and the thickness of the polymer brushes is 30μm.

[0127] Example 6

[0128] The diamine monomer selected was 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol prepared from aniline and 2,7-dihydroxy-9-fluorenequinone monomers, the anhydride monomer was 4,4'-(hexafluoroisopropylene) diphthalic anhydride, the initiator was 2-bromoisopropyl bromide, and the polymer brush monomer was 3-[(3-acrylamidopropyl)dimethylammonium] propionate.

[0129] The specific preparation method is as follows:

[0130] 1) Preparation of polyimide

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

[0132] Weigh 1.0 g of 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol solid, 1.1674 g of 4,4'-(hexafluoroisopropylene) diphthalic anhydride, 6 g of isoquinoline and 26.3 mL of m-cresol into a 250 mL reaction bottle. Under nitrogen protection, stir the mixture at 80° C. for 10 h, 110° C. for 10 h, 150° C. for 10 h, and 180° C. for 10 h. After the reaction is completed, cool to room temperature, slowly pour into excess ethanol, filter, repeatedly wash with ethanol, and vacuum dry at room temperature to obtain polyimide powder.

[0133] 2) Grafting of initiator

[0134] Weigh 600 mg of polyimide powder and dissolve it in 20 mL of pyridine solution to make it completely dissolved. Under nitrogen protection, slowly drop 0.8 g of 2-bromoisobutyl bromide into the pyridine solution containing the polyimide powder, react at 0°C for 1.5 hours, and then react at room temperature for 12 hours. After the reaction is completed, filter, use methanol to precipitate the filtrate, filter, wash repeatedly with methanol, and vacuum dry at room temperature to obtain the polyimide powder of the main chain grafting initiator.

[0135] 3) Preparation of polyimide film

[0136] 200 mg of polyimide powder with 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 bare initiator on the surface.

[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 for later use; weigh 264 mg of ascorbic acid and dissolve it in 20 mL of deionized water for later use; weigh 684.9 mg of 3-[(3-acrylamidopropyl)dimethylammonium]propionate and dissolve it in 4.6 mL of deionized water for later use.

[0139] Under nitrogen protection, a 1cm 2 To the polyimide film with bare initiator, add 3-[(3-acrylamidopropyl)dimethylammonium] propionate aqueous solution, evacuate, fill with nitrogen, then add 0.2mL of CuBr2 and 2,2'-bipyridine mixed aqueous solution into the reaction container, ultrasonically deoxygenate for 10 minutes, then add 0.2mL of ascorbic acid aqueous solution, ultrasonically deoxygenate for 10 minutes, 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 polymer brushes of the polyimide films grafted with polymer brushes prepared by different materials and processes in the above Examples 1-6 and Comparative Examples 1-2 are summarized in Table 1.

[0141] Table 1

[0142] Serial number Diamine monomer Brush unit Amount of initiator (g) Thickness(μm) Example 1 AHHFP CB 1.3 40 Example 2 AHF CB 1.3 32 Comparative Example 1 TADE CB 1.3 0 Example 3 AHHFP EGMA 1.3 35 Example 4 AHF EGMA 1.3 28 Comparative Example 2 TADE EGMA 1.3 0 Example 5 AHHFP CB 0.8 30 Example 6 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 reach micrometer level.

[0144] From the comparison between Examples 1 and 5 and Examples 2 and 6, it can be seen that the amount of the grafted initiator on the polyimide main chain will also affect the thickness of the polymer brush. This is because when the initiator is not excessive, the hydroxyl groups on the polyimide main chain are difficult to react completely, resulting in a low initiator grafting rate. In the later grafting polymer brush process, the initiator density is low, which will affect the reduction of the grafted polymer brush density and further affect the reduction of the brush thickness. The present invention has the best effect when the mass ratio of polyimide to initiator is 0.6:1.3.

[0145] Comparing Examples 1 and 2, there is a difference in the grafting thickness, mainly because after the polyimide main chain formed by the reaction of the diamine monomer and the anhydride monomer in Example 2 reacts with the initiator, the steric hindrance of the polymer chain is greater, thereby affecting the initiation effect of the initiator, and then affecting the grafting density, resulting in a lower thickness. The polyimide grafted polymer brush prepared with the diamine monomer AHHFP of the present invention has the best effect.

[0146] By comparing Examples 1 and 3 with Comparative Examples 1 and 2, since the diamine monomer and the anhydride monomer in the comparative examples do not have hydroxyl groups, the formed polyimide main chain has no exposed hydroxyl groups to react with the initiator, so the grafting of the initiator is almost zero, so that the prepared polyimide film has almost no grafting in the reaction of grafting the polymer brush, so the thickness of the polymer brush is zero. The polyimide film prepared by the diamine monomer containing hydroxyl groups selected by the present invention has obvious advantages over ordinary polyimide films without hydroxyl groups for grafting high-thickness polymer brushes.

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

Claims

1. A method for preparing a polyimide film grafted with a polymer brush, characterized in that: The following steps are involved: S1. Selecting a diamine monomer as 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol, subjecting the diamine monomer to a polycondensation reaction with an acid anhydride monomer, washing, and drying to prepare a polyimide powder: Alternatively, the diamine monomer is selected as 2,2-bis(3-amino-4-hydroxyphenyl)-hexafluoropropane, the diamine monomer and the acid anhydride monomer are subjected to a condensation reaction, and then subjected to a chemical imidization treatment, washed, and dried to prepare a polyimide powder; S2, carrying out a grafting reaction between the polyimide powder obtained in step S1 and the initiator 2-bromoisobutyl bromide in a pyridine solvent, washing, and drying to obtain a polyimide powder with a main chain grafted with the initiator; S3, dissolving the polyimide powder obtained in step S2 in N-methylpyrrolidone solvent to prepare a casting solution, and coating to prepare a polyimide film; S4. Select 3-[(3-acrylamidopropyl)dimethylammonium] propionate or polyethylene glycol methacrylate as the polymer brush monomer. In a deoxygenated atmosphere, immerse the polyimide film obtained in step S3 in an aqueous solution containing the polymer brush monomer, and add copper bromide, 2,2'-bipyridine and ascorbic acid, or add copper bromide, cuprous bromide and pentamethyldiethylenetriamine to react to obtain a polyimide film grafted with a polymer brush.

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

3. The method for preparing a polyimide film of a grafted polymer brush according to claim 1, characterized in that: In step S1, when the diamine monomer is 9,9-bis(4-aminophenyl)-9H-fluorene-2,7-diol, after the polycondensation reaction is completed, a chemical imidization method is used to polycondense the diamine monomer and the acid anhydride monomer to obtain a polyamic acid solution, a dehydrating agent and a dehydration catalyst are added to the polyamic acid solution, and the reaction is stirred at room temperature to 150° 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 dehydrating catalyst is at least one of triethylamine, isoquinoline, pyridine and N-methylpyridine.

4. The method for preparing a polyimide film of a grafted polymer brush according to claim 1, characterized in that: In step S2, the mass ratio of the polyimide powder, the initiator and the pyridine solvent is 1:2:30-1:5:

50.

5. The method for preparing a polyimide film of a grafted polymer brush according to claim 1, characterized in that: Steps S1 and S2 are both performed under a protective atmosphere, which is nitrogen or an inert gas.

6. The method for preparing a polyimide film of a grafted polymer brush according to claim 1, characterized in that: In step S3, the solid content of the casting solution is 20-30 wt%.

7. The method for preparing a polyimide film of a grafted polymer brush according to claim 1, characterized in that: In step S3, coating is performed by blade coating, casting or spin coating. After coating, the coating is first dried at 60-70° C. for 2-3 hours, and then dried at 130-150° C. for 4-5 hours.

8. The method for preparing a polyimide film of a grafted polymer brush according to claim 1, characterized in that: In step S4, after the immersion reaction of the polyimide film is completed, it is repeatedly rinsed with PBS and deionized water, and then dried under a nitrogen flow to obtain a dried polyimide film with a grafted polymer brush.

9. The method for preparing a polyimide film of a grafted polymer brush according to claim 1, characterized in that: In step S4, the solvent used is deionized water.

10. A polyimide film grafted with a polymer brush, characterized in that: The polymer brush is prepared by the method described in any one of claims 1 to 9, and has a thickness of micrometer level.

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