Polyimide and preparation method thereof, optical transparent film and flexible electronic device

Abstract

The invention relates to polyimide and a preparation method thereof, an optical transparent film and a flexible electronic device. The polyimide is prepared from the following raw materials: a dianhydride monomer and a diamine monomer, wherein the dianhydride monomer is selected from one or more # imgabs0 # of compounds with structural characteristics shown in a formula (I). The diamine monomer is selected from one or more # imgabs 1 # of compounds with the structural characteristics shown in the formula (II). According to the polyimide disclosed by the invention, specific diamine monomers and dianhydride monomers are selected, so that the polymerization temperature of the polyimide can be effectively reduced, and a polyimide material with relatively low glass transition temperature can be obtained.

Description

Technical Field

[0001] The present application belongs to the technical field of polyimide materials, and specifically relates to a polyimide and a preparation method thereof, an optically transparent film and a flexible electronic device. Background Art

[0002] With the development of polymers, polyimide (PI) has begun to attract attention. PI is a type of high molecular polymer containing cyclic imide groups in the molecular chain. It has excellent heat resistance and bendability, as well as high optical transmittance. The excellent properties of PI make it widely used in the manufacture of OLED flexible substrates.

[0003] Traditional polyimide materials usually have a high glass transition temperature, so their softening temperature is usually high. At this time, the processing of polyimide requires a higher reaction temperature (300℃~425℃). Processing thermoplastic polyimide at this temperature requires a large production cost and has many safety hazards. The most critical thing is that within this temperature, a slight cross-linking occurs in the polyimide molecular chain, so it is also called "pseudo-thermoplastic" polyimide. Therefore, polyimide with a higher glass transition temperature or a higher processing temperature will prematurely become brittle, harden, lose elasticity and other problems. Summary of the invention

[0004] Based on this, the present application provides a polyimide and a preparation method thereof, an optically transparent film and a flexible electronic device. The polyimide of the present application has a lower glass transition temperature and a lower processing temperature.

[0005] In a first aspect of the present application, a polyimide is provided, wherein the raw materials for preparing the polyimide include a dianhydride monomer and a diamine monomer, wherein the dianhydride monomer is selected from one or more compounds having the structural characteristics shown in formula (I):

[0006]

[0007] Among them, X 1 and X 2 are each independently selected from -O- or -S-; A is selected from C 2 ~C 6 Alkylene or C 2 ~C 10 Haloalkylene; n is a positive integer between 2 and 20;

[0008] The diamine monomer is selected from one or more compounds having the structural characteristics shown in formula (II):

[0009]

[0010] Wherein Ar is selected from a single bond, 1Substituted or unsubstituted phenylene, or R 1 Substituted or unsubstituted C 6 ~C 24 A fused cyclic group;

[0011] L 1 , L 2 are each independently selected from H, halogen, C 1 ~C 10 Alkyl, C 1 ~C 10 Haloalkyl, R 1 Substituted or unsubstituted phenyl, R 1 Substituted or unsubstituted biphenyl, R 1 Substituted or unsubstituted phenoxy, R 1 Substituted or unsubstituted C 3 ~C 10 Heteroaryl, or R 1 Substituted or unsubstituted C 6 ~C 24 Fused ring group; R 1 Each occurrence is independently halogen, C 1 ~C 3 Alkyl or C 1 ~C 3 Halogenated alkyl.

[0012] In one embodiment, the polyimide has one or more of the following characteristics:

[0013] (1) X 1 and X 2 are each independently selected from -O-; A is selected from C 2 ~C 4 Alkyl or C 2 ~C 4 Halogenated alkyl; n is a positive integer between 2 and 10;

[0014] (2) Ar is selected from a single bond, 1 Substituted or unsubstituted phenyl, or R 1 Substituted or unsubstituted C 6 ~C 18 Condensed ring group; L 1 , L 2 are each independently selected from H, halogen, C 1 ~C 5 Alkyl, C 1 ~C 5 Haloalkyl, R 1 Substituted or unsubstituted phenyl, R 1 Substituted or unsubstituted biphenyl, R 1 Substituted or unsubstituted phenoxy, R1 Substituted or unsubstituted C 3 ~C 6 Heteroaryl, or R 1 Substituted or unsubstituted C 6 ~C 18 Fused ring group; R 1 Each occurrence is independently halogen, -CH 3 CF 3 、-CH 2 CH 3 or -CF 2 CF 3 .

[0015] In one embodiment, the polyimide has one or more of the following characteristics:

[0016] (1) X 1 and X 2 are each independently selected from -O-; A is selected from -CH(CH 3 )-、-CH 2 CH 2 -、-CH(CH 2 CH 3 )-、-CH 2 CH(CH 3 )-、-CH 2 CH 2 CH 2 -or-CH 2 CH 2 CH 2 CH 2 -, n is a positive integer between 2 and 10;

[0017] (2) Ar is selected from a single bond, , , , or ;

[0018] L 1 , L 2 are each independently selected from H, halogen, -CH 3 , -CF 3 , , , , , , , or .

[0019] In one embodiment, the polyimide has one or more of the following characteristics:

[0020] (1) The dianhydride monomer includes and One or more of; n1 is a positive integer between 2 and 10;

[0021] (2) The diamine monomer includes , , , , , , , , , , , , , and One or more of .

[0022] In one embodiment, the molar ratio of the dianhydride monomer to the diamine monomer is 1:(0.9-1.2).

[0023] In a second aspect of the present application, a method for preparing a polyimide is provided, comprising the following steps: mixing the dianhydride monomer and the diamine monomer in a solvent to prepare a polyimide slurry;

[0024] The polyimide slurry is subjected to a thermal imidization reaction to prepare the polyimide.

[0025] In one embodiment, the solvent includes one or more of N-methylpyrrolidone, m-cresol, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, cyclohexanone and N,N-dimethylformamide.

[0026] In one embodiment, the process parameters of the thermal imidization reaction include: a first heat treatment at a temperature of 90°C to 110°C, a second heat treatment at a temperature of 190°C to 210°C, and a third heat treatment at a temperature of 220°C to 240°C.

[0027] The third aspect of the present application provides an optically transparent film, comprising the polyimide described in any one of the first aspects of the present application.

[0028] A fourth aspect of the present application provides a flexible electronic device, comprising the optically transparent film described in the third aspect of the present application.

[0029] This application has at least the following beneficial effects:

[0030] The polyimide of the present application is prepared by diamine monomer and dianhydride monomer of specific structure. Wherein, the presence of ether bond or thioether bond in polyether or polysulfide dianhydride monomer can increase the reactivity of monomer, improve polymerization degree, and the alkyl, cycloalkyl and alkyl halide connected with ether bond or thioether bond can distort the spatial structure of polyimide molecular chain, make the structure stacking become scattered, and then cause the glass transition temperature and processing temperature of polyimide to reduce. In addition, the diamine monomer coordinated with dianhydride monomer has a polyaromatic ring structure, which can increase the rigidity of polyimide molecular chain, and enhance the interaction between molecules by π-π stacking effect, and this force helps to improve the cohesion and strength of polyimide, to ensure that polyimide has good mechanical properties.

[0031] In summary, the polyimide of the present application uses specific diamine monomers and dianhydride monomers, which can effectively reduce the polymerization temperature of the polyimide and obtain a polyimide material with a lower glass transition temperature. DETAILED DESCRIPTION

[0032] The polyimide and preparation method, optical transparent film and flexible electronic device of the present application are further described in detail below in conjunction with specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive. Of course, they are merely examples and are not intended to limit the present application.

[0033] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. Unless otherwise specified or there is a contradiction, the terms or phrases used herein have the following meanings:

[0035] In the present application, "plurality", "multiple", "multiple times", "plurality", etc., unless otherwise specified, refer to a number greater than 2 or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0036] In this application, in the "first aspect", "second aspect", "third aspect", "fourth aspect", etc., the terms "first", "second", "third", "fourth", etc. are used only for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third", "fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0037] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0038] In the present application, references to “combinations thereof”, “any combination thereof”, “any combination thereof”, etc. include all suitable combinations of any two or more of the listed items.

[0039] In this application, the “suitable” mentioned in “suitable combination”, “suitable method”, “any suitable method”, etc. shall be based on the ability to implement the technical solution of this application, solve the technical problems of this application, and achieve the expected technical effects of this application.

[0040] In the present application, the terms “preferred”, “better”, “more preferred” and “suitable” are only used to describe implementation methods or examples with better effects, and it should be understood that they do not constitute limitations on the scope of protection of the present application.

[0041] In the present application, the terms “further”, “furthermore”, “particularly”, etc. are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of the present application.

[0042] In this application, "optionally", "optional" and "optional" refer to optional, that is, to any one of the two parallel schemes of "yes" or "no". If multiple "options" appear in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "optional" is independent.

[0043] In the present application, when it comes to numerical intervals (i.e., numerical ranges), unless otherwise specified, the optional numerical distribution is considered continuous within the above numerical interval, and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical range, and each numerical value between the two numerical endpoints. Unless otherwise specified, when the numerical interval only refers to the integers within the numerical interval, it includes the two endpoint integers of the numerical range, and each integer between the two endpoints. In this article, it is equivalent to directly listing each integer, such as t is an integer selected from 1 to 10, indicating that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. In addition, when multiple ranges are provided to describe features or characteristics, these ranges can be combined. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges included therein.

[0044] The temperature parameters in this application, unless otherwise specified, are allowed to be either constant temperature treatment or to vary within a certain temperature range. It should be understood that the constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument. Fluctuations within the range of ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are allowed.

[0045] In the present application, the percentage content, unless otherwise specified, refers to mass percentage for solid-liquid mixing and solid-solid mixing, and volume percentage for liquid-liquid mixing.

[0046] In this application, when it comes to percentage concentration, unless otherwise specified, it refers to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of the component.

[0047] In this application, "alkyl" refers to a saturated hydrocarbon group containing primary (normal) carbon atoms, or secondary carbon atoms, or tertiary carbon atoms, or quaternary carbon atoms, or a combination thereof. Phrases containing this term, for example, "C1-C6 alkyl" refers to an alkyl group containing 1 to 10 carbon atoms, and each occurrence can be independently C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, C6 alkyl. Suitable examples include, but are not limited to, methyl (Me, -CH 3 ), ethyl (Et, -CH 2 CH 3 ), 1-propyl (n-propyl, n-Pr, n-propyl, -CH 2 CH 2 CH 3 ), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-butyl, n-Bu, n-butyl, -CH 2 CH 2 CH 2 CH 3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH 2 CH(CH 3 ) 2 ), 2-butyl (s-Bu, s-butyl, -CH (CH 3 )CH 2 CH 3 ), tert-butyl (1,1-dimethylethyl, 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH 3 ) 3 ), 1-pentyl (n-pentyl, n-pentyl, -CH 2 CH 2 CH 2 CH 2 CH 3 ), 2-pentyl (-CH(CH 3 )CH 2 CH 2 CH 3 ), 3-pentyl (-CH(CH 2 CH 3 ) 2 )、2-methyl-2-butyl(-C(CH3) 2 CH 2 CH 3 ), 3-methyl-2-butyl (-CH(CH 3 )CH(CH 3 ) 2 ), 3-methyl-1-butyl (-CH 2 CH 2 CH(CH 3 ) 2 ), 2-methyl-1-butyl (-CH 2 CH(CH 3 )CH 2 CH 3 ), 1-hexyl (n-hexyl, -CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 ), 2-hexyl (-CH(CH 3 )CH 2 CH 2 CH 2 CH 3 )、3-hexyl(-CH(CH 2 CH 3 )(CH 2 CH 2 CH 3 ))、2-methyl-2-pentyl (-C(CH3 ) 2 CH 2 CH 2 CH 3 ), 3-methyl-2-pentyl (-CH(CH 3 )CH(CH 3 )CH 2 CH 3 ), 4-methyl-2-pentyl (-CH(CH 3 )CH 2 CH(CH 3 ) 2 ), 3-methyl-3-pentyl (-C(CH 3 )(CH 2 CH 3 ) 2 ) and 2-methyl-3-pentyl (-CH(CH 2 CH 3 )CH(CH 3 ) 2 ).

[0048] "Alkylene" refers to a hydrocarbon group with two monovalent radical centers derived from an alkyl group by removing a hydrogen atom, which can be a saturated branched alkyl group or a saturated straight chain alkyl group. For example, "C1-C6 alkylene" means that the alkyl part contains 1 to 6 carbon atoms, and each occurrence can be independently C1 alkylene, C4 alkylene, C5 alkylene, C6 alkylene. Suitable examples include, but are not limited to: methylene (-CH 2 -), 1,1-ethyl (-CH(CH 3 )-), 1,2-ethyl (-CH 2 CH 2 -), 1,1-propyl (-CH(CH 2 CH 3 )-), 1,2-propyl (-CH 2 CH(CH 3 )-), 1,3-propyl (-CH 2 CH 2 CH 2 -) and 1,4-butyl (-CH 2 CH 2 CH 2 CH 2 -).

[0049] "Haloalkylene" means that on the basis of "alkylene", halogen atoms are substituted for hydrogen atoms in the alkylene. It is understood that the number of fluorine atoms substituted is ≤ the number of hydrogen atoms in the alkylene.

[0050] In this application, "phenyl" refers to In this application, "biphenyl" refers to In this application, "phenoxy" refers to In the present application, "phenylene" is a group derived from "phenyl" by removing a hydrogen atom.

[0051] In the present application, "condensed ring group" refers to a group derived from a condensed ring aromatic hydrocarbon by removing a hydrogen atom. Condensed ring aromatic hydrocarbon refers to an aromatic hydrocarbon containing two or more benzene rings in the molecule, which are fused by sharing two adjacent carbon atoms. In the present application, "sub-condensed ring group" refers to a group derived from a condensed ring group by removing a hydrogen atom.

[0052] In the present application, "heteroaryl" means that at least one carbon atom on the basis of aryl or cyclopentadienyl is replaced by a non-carbon atom, and the non-carbon atom can be a N atom, an O atom, a S atom, etc. For example, "C 3 ~C 10 "Heteroaryl" refers to a heteroaryl group containing 3 to 10 carbon atoms, each occurrence of which can be independently C 3 Heteroaryl, C 4 Heteroaryl, C 5 Heteroaryl, C 6 Heteroaryl, C 7 Heteroaryl, C 8 Heteroaryl. Suitable examples include, but are not limited to, furan, benzofuran, thiophene, benzothiophene, pyrrole, pyrazole, triazole, imidazole, oxazole, oxadiazole, thiazole, tetrazole, indole, carbazole, pyrroloimidazole, pyrrolopyrrole, thienopyrrole, thienothiophene, furopyrrole, furofuran, thienofuran, benzisoxazole, benzisothiazole, benzimidazole, pyridine, pyrazine, pyridazine, pyrimidine, triazine, quinoline, isoquinoline, o-naphthyridine, quinoxaline, phenanthridine, primary idine, quinazoline, and quinazolinone.

[0053] At present, polyimide generally has a high glass transition temperature, which means that it is necessary to achieve the transition of polyimide from a glassy state to a highly elastic state at a higher temperature. The processing of polyimide generally requires preparation steps such as melt processing, and the preparation temperature at this time needs to be heated to above the glass transition temperature, that is, polyimide with a higher glass transition temperature also requires a higher processing temperature.

[0054] Based on this, the first aspect of the present application provides a polyimide, wherein the raw materials for preparing the polyimide include a dianhydride monomer and a diamine monomer, and the dianhydride monomer is selected from one or more compounds having the structural characteristics shown in formula (I):

[0055]

[0056] The diamine monomer is selected from one or more compounds having the structural characteristics shown in formula (II):

[0057] .

[0058] Among them, X 1 and X 2 Each is independently selected from -O- or -S-.

[0059] Furthermore, X 1 and X 2 are each independently selected from -O-.

[0060] Among them, A is selected from C 2 ~C 6 Alkylene or C 2 ~C 10 A haloalkylene group.

[0061] Furthermore, A is selected from C 2 ~C 4 Alkyl or C 2 ~C 4 Halogenated alkyl.

[0062] Furthermore, A is selected from -CH(CH 3 )-、-CH 2 CH 2 -、-CH(CH 2 CH 3 )-、-CH 2 CH(CH 3 )-、-CH 2 CH 2 CH 2 -or-CH 2 CH 2 CH 2 CH 2 -.

[0063] Wherein, n is a positive integer between 2 and 20. It is understood that the value of n includes but is not limited to 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20.

[0064] Furthermore, n is a positive integer between 2 and 10.

[0065] Wherein Ar is selected from a single bond, 1 Substituted or unsubstituted phenylene, or R 1 Substituted or unsubstituted C 6 ~C 24 A fused cyclic group.

[0066] Further, Ar is selected from a single bond,1 Substituted or unsubstituted phenylene, or R 1 Substituted or unsubstituted C 6 ~C 18 A fused cyclic group.

[0067] Furthermore, Ar is selected from a single bond, , , , or .

[0068] Among them, L 1 , L 2 are each independently selected from H, halogen, C 1 ~C 10 Alkyl, C 1 ~C 10 Haloalkyl, R 1 Substituted or unsubstituted phenyl, R 1 Substituted or unsubstituted biphenyl, R 1 Substituted or unsubstituted phenoxy, R 1 Substituted or unsubstituted C 3 ~C 10 Heteroaryl, or R 1 Substituted or unsubstituted C 6 ~C 24 Fused ring group; R 1 Each occurrence is independently halogen, C 1 ~C 3 Alkyl or C 1 ~C 3 Halogenated alkyl.

[0069] Furthermore, L 1 , L 2 are each independently selected from H, halogen, C 1 ~C 5 Alkyl, C 1 ~C 5 Haloalkyl, R 1 Substituted or unsubstituted phenyl, R 1 Substituted or unsubstituted biphenyl, R 1 Substituted or unsubstituted phenoxy, R 1 Substituted or unsubstituted C 3 ~C 6 Heteroaryl, or R 1 Substituted or unsubstituted C 6 ~C 18 Fused ring group; R 1 Each occurrence is independently halogen, -CH 3 CF 3 、-CH2 CH 3 or -CF 2 CF 3 .

[0070] Furthermore, L 1 , L 2 are each independently selected from H, halogen, -CH 3 , -CF 3 , , , , , , , or .

[0071] In one example, the dianhydride monomer includes and One or more of .

[0072] In one example, the diamine monomer includes , , , , , , , , , , , , , and One or more of .

[0073] Furthermore, the diamine monomer includes , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , and One or more of .

[0074] In one example, the molar ratio of the dianhydride monomer to the diamine monomer is 1:(0.9~1.2). The molar ratio of the dianhydride monomer to the diamine monomer plays an important role in the structural change of the polyimide. The present application defines the molar ratio of the dianhydride monomer to the diamine monomer, which can ensure that the polyimide has a lower glass transition temperature; and the dianhydride monomer and the diamine monomer in the above molar ratio are conducive to ensuring their solubility in the solvent, and are suitable for preparing polyimide films by solution processing. It can be understood that the molar ratio of the dianhydride monomer to the diamine monomer can be selected from any value between 1:(0.9~1.2). Further, the molar ratio of the dianhydride monomer to the diamine monomer includes but is not limited to 1:0.9, 1:0.92, 1:0.94, 1:0.96, 1:0.98, 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8 or 1:2.

[0075] In one example, the polyimide has a structure shown in formula (III): ;

[0076] Among them, Y is ; m is a positive integer ≥1.

[0077] The amino group (-NH 2 ) has strong nucleophilicity, while the anhydride group (-CO-O-CO-) in the dianhydride monomer has certain electrophilicity. Under low temperature conditions, the dianhydride monomer and the diamine monomer are added to the solvent, and the amino group of the diamine monomer will attack the anhydride group of the dianhydride monomer with nucleophilicity, resulting in a nucleophilic addition reaction. After one amino group reacts with the anhydride group, an amide bond (-CONH-) and a carboxyl group (-COOH) are formed, while the other anhydride group remains. The carboxyl group on the generated intermediate product will continue to react with the amino group of other diamine monomers, and the nucleophilic addition reaction and chain growth process will be repeated continuously, so that the molecular chain will continue to extend, and finally form the intermediate product polyamic acid. A dehydration reaction will occur between the carboxyl group and the amide bond on the polyamic acid molecular chain, and the hydroxyl group (-OH) in the carboxyl group and the hydrogen atom in the amide bond will combine to form a water molecule and remove, while forming an imide ring. As the dehydration reaction proceeds, the polyamic acid is gradually converted into polyimide. Therefore, it can be understood that the X appearing in the polyimide structure 1 , X 2 , A, L1 , L 2 and Ar are defined as in the above-mentioned dianhydride monomer and diamine monomer.

[0078] For example, X 1 and X 2 Each is independently selected from -O- or -S-.

[0079] Furthermore, X 1 and X 2 are each independently selected from -O-.

[0080] Among them, A is selected from C 2 ~C 6 Alkylene or C 2 ~C 10 A haloalkylene group.

[0081] Furthermore, A is selected from C 2 ~C 4 Alkyl or C 2 ~C 4 Halogenated alkyl.

[0082] Furthermore, A is selected from -CH(CH 3 )-、-CH 2 CH 2 -、-CH(CH 2 CH 3 )-、-CH 2 CH(CH 3 )-、-CH 2 CH 2 CH 2 -or-CH 2 CH 2 CH 2 CH 2 -.

[0083] Wherein, n is a positive integer between 2 and 20. It is understood that the value of n includes but is not limited to 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20.

[0084] Furthermore, n is a positive integer between 2 and 10.

[0085] Wherein Ar is selected from a single bond, 1 Substituted or unsubstituted phenyl, or R 1 Substituted or unsubstituted C 6 ~C 24 Condensed ring group.

[0086] Further, Ar is selected from a single bond, 1 Substituted or unsubstituted phenyl, or R1 Substituted or unsubstituted C 6 ~C 18 Condensed ring group.

[0087] Furthermore, Ar is selected from a single bond, , , , or .

[0088] Among them, L 1 , L 2 are each independently selected from H, halogen, C 1 ~C 10 Alkyl, C 1 ~C 10 Haloalkyl, R 1 Substituted or unsubstituted phenyl, R 1 Substituted or unsubstituted biphenyl, R 1 Substituted or unsubstituted phenoxy, R 1 Substituted or unsubstituted C 3 ~C 10 Heteroaryl, or R 1 Substituted or unsubstituted C 6 ~C 24 Fused ring group; R 1 Each occurrence is independently halogen, C 1 ~C 3 Alkyl or C 1 ~C 3 Halogenated alkyl.

[0089] Furthermore, L 1 , L 2 are each independently selected from H, halogen, C 1 ~C 5 Alkyl, C 1 ~C 5 Haloalkyl, R 1 Substituted or unsubstituted phenyl, R 1 Substituted or unsubstituted biphenyl, R 1 Substituted or unsubstituted phenoxy, R 1 Substituted or unsubstituted C 3 ~C 6 Heteroaryl, or R 1 Substituted or unsubstituted C 6 ~C 18 Fused ring group; R 1 Each occurrence is independently halogen, -CH 3 CF 3 、-CH 2 CH 3or -CF 2 CF 3 .

[0090] Furthermore, L 1 , L 2 are each independently selected from H, halogen, -CH 3 , -CF 3 , , , , , , , or .

[0091] The polyimide of the present application includes a polyether bond or a polysulfide bond and an alkyl group or the like connected to the polyether bond or the polysulfide bond, which reduces the structural regularity, giving the polyimide more flexibility, allowing it to move at a lower temperature; in addition, the polyether bond or the polysulfide bond has a lower polarity, which can weaken the intermolecular forces such as van der Waals force and hydrogen bond, thereby effectively reducing the formation temperature and glass transition temperature of the polyimide. To complement the polyether bond or the polysulfide bond, the polyimide also contains a polyaromatic ring structure, whose higher bond energy and stable structure make the molecular chain less likely to deform, thereby giving the polyimide good mechanical properties.

[0092] A second aspect of the present application provides a method for preparing a polyimide, comprising the following steps:

[0093] S10, mixing the dianhydride monomer and the diamine monomer in a solvent to prepare a polyimide slurry;

[0094] S20, subjecting the polyimide slurry to a thermal imidization reaction to prepare the polyimide.

[0095] In one example, in step S10, in the step of mixing the dianhydride monomer and the diamine monomer in a solvent, the solvent includes N-methylpyrrolidone (NMP, )、m-cresol( )、N,N-dimethylacetamide( )、Dimethyl sulfoxide( ), γ-butyrolactone ( )、Cyclohexanone( ) and N,N-dimethylformamide ( )

[0096] Furthermore, the preparation steps of the polyimide slurry include:

[0097] a. performing a first mixing of the diamine monomer in a solvent to prepare an intermediate solution containing the diamine monomer;

[0098] b. Adding dianhydride monomer to the intermediate solution containing diamine monomer for second mixing to prepare polyimide slurry.

[0099] Specifically, in step a, the mass ratio of the diamine monomer to the solvent is 1:(10-21). Specifically, the mass ratio of the diamine monomer to the solvent includes but is not limited to 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:16.5, 1:16.6, 1:16.7, 1:17, 1:17.5, 1:17.6, 1:18.2, 1:18.3, 1:19, 1:20.5, 1:20.6 or 1:21.

[0100] Further, in step a, the temperature for the first mixing is 40° C. to 80° C. The temperature for the first mixing includes but is not limited to 40° C., 42° C., 45° C., 48° C., 50° C., 52° C., 55° C., 58° C., 60° C., 65° C., 70° C., 75° C. or 80° C.

[0101] In step b, the temperature for the second mixing is 10° C. to 60° C. Specifically, the temperature for the second mixing includes but is not limited to 10° C., 12° C., 14° C., 15° C., 16° C., 17° C., 18° C., 20° C., 25° C., 30° C., 35° C., 40° C., 45° C., 50° C., 55° C. or 60° C. Further, in step b, the time for the second mixing is 12 h to 36 h.

[0102] The first mixing and the second mixing are performed in sequence, and the mixing temperature and the time of the second mixing are limited. At this time, the amino group of the diamine monomer undergoes a nucleophilic addition reaction with the anhydride group of the dianhydride monomer to generate an amide (-CONH-) and a carboxyl group (-COOH); the generated carboxyl group will continue to react with the amino group of other diamine monomers, and the nucleophilic addition reaction and chain growth process will be continuously repeated, so that the molecular chain is continuously extended, and finally a polyimide slurry containing the intermediate product polyamic acid is formed.

[0103] In one example, in step S20, the process parameters of the thermal imidization reaction include: a first heat treatment at a temperature of 90°C to 110°C, a second heat treatment at a temperature of 190°C to 210°C, and a third heat treatment at a temperature of 220°C to 240°C.

[0104] Further, the temperature for the first heat treatment includes but is not limited to 90°C, 95°C, 98°C, 100°C, 102°C, 105°C, 108°C or 110°C. The temperature for the second heat treatment includes but is not limited to 190°C, 192°C, 195°C, 198°C, 200°C, 202°C, 205°C, 208°C or 210°C. The temperature for the third heat treatment includes but is not limited to 220°C, 222°C, 225°C, 227°C, 230°C, 232°C, 235°C, 238°C or 240°C.

[0105] Specifically, the first heating treatment and the second heating treatment are each independently performed for 10 minutes to 20 minutes, and the third heating treatment is performed for 25 minutes to 35 minutes.

[0106] The present application also provides a method for preparing a polyimide film, comprising the following steps:

[0107] The polyimide slurry is coated on a substrate, and a polymerization reaction is performed. After the solvent in the polyimide slurry is removed, the polyimide film is formed on the substrate.

[0108] Specifically, the material of the substrate includes but is not limited to ceramic, glass, silicon, metal, plastic, etc. For example, the ceramic may be alumina ceramic, and the metal may be stainless steel, aluminum, copper, etc. The plastic may be a polyimide film. Preferably, the substrate is glass, and further, the substrate is polished glass.

[0109] The third aspect of the present application provides an optically transparent film, comprising the polyimide described in any one of the first aspects of the present application.

[0110] A fourth aspect of the present application provides a flexible electronic device, comprising the optically transparent film described in the third aspect of the present application.

[0111] In order to make the purpose and advantages of the present invention clearer, the polyimide film of the present invention and its effects are further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and shall not be used to limit the present invention. The following embodiments do not include other components except inevitable impurities unless otherwise specified. The drugs and instruments used in the embodiments are conventionally selected in the art unless otherwise specified. The experimental methods for which specific conditions are not specified in the embodiments are implemented according to conventional conditions, such as the conditions described in the literature, books, or the methods recommended by the manufacturer.

[0112] [Diamine monomer]

[0113] A1: 4,4'-diaminoterphenyl, , commercially available;

[0114] A2: 9,10-bis(p-diaminophenyl)anthracene, ;

[0115] A2 is synthesized by following the steps below: .

[0116] A3: ;

[0117] A3 is synthesized by referring to the following steps:

[0118] .

[0119] A4: 4,4'-diamino-2,2'-dimethylbiphenyl , commercially available;

[0120] A5: ; A5 is synthesized by referring to the following steps:

[0121] .

[0122] A6: ; A6 is synthesized by referring to the following steps:

[0123] .

[0124] A7: Nonanediamine, , commercially available.

[0125] [Dianhydride monomer]

[0126] B1: ;

[0127] B2: ;

[0128] B3: 2,3,3',4'-biphenyltetracarboxylic dianhydride, .

[0129] Example 1

[0130] Adjust the reaction apparatus to be airtight and introduce N 2 The air was replaced. At 50°C, 2.9645g of diamine monomer 4,4'-diaminoterphenyl (A1) was dissolved in 42.5g of solvent N-methylpyrrolidone. After the diamine monomer was completely dissolved, 4.5355g of dianhydride monomer (B1) was added. After conversion, the molar ratio of the dianhydride monomer to the diamine monomer was about 1:0.96. Then, the mixture was stirred at 15°C for 24h to prepare a polyimide slurry.

[0131] Place a clean glass plate on the platform of the automatic coating machine, select a 100μm scraper and place it on the glass plate, use a plastic dropper to evenly cover the polyimide slurry prepared by the above method between the scraper and the glass plate, set the scraping length to 30cm, and start coating. After the coating is completed, place the glass plate in an oven for thermal imidization, and heat it at 100℃ for 15min, 200℃ for 15min, and 230℃ for 30min in a gradient heating process to evaporate the solvent. After the thermal imidization reaction is completed, take it out after natural cooling, cut the transparent polyimide film on the smoother part of the film surface with a blade, soak it in deionized water, peel off the transparent polyimide film, wipe the surface moisture of the transparent polyimide film with a dust-free cloth, and store it well to obtain a polyimide film.

[0132] Example 2

[0133] Adjust the reaction apparatus to be airtight and introduce N 2 The air was replaced. At 50°C, 3.5629g of diamine monomer 9,10-di(p-diaminophenyl)anthracene (A2) was dissolved in 42.5g of solvent N-methylpyrrolidone. After the diamine monomer was completely dissolved, 3.9371g of dianhydride monomer (B1) was added. After conversion, the molar ratio of the dianhydride monomer to the diamine monomer was about 1:1. The mixture was then stirred at 15°C for 24h to prepare a polyimide slurry.

[0134] Place a clean glass plate on the platform of the automatic coating machine, select a 100μm scraper and place it on the glass plate, use a plastic dropper to evenly cover the polyimide slurry prepared by the above method between the scraper and the glass plate, set the scraping length to 30cm, and start coating. After the coating is completed, place the glass plate in an oven for thermal imidization, and heat it at 100℃ for 15min, 200℃ for 15min, and 230℃ for 30min in a gradient heating process to evaporate the solvent. After the thermal imidization reaction is completed, take it out after natural cooling, cut the transparent polyimide film on the smoother part of the film surface with a blade, soak it in deionized water, peel off the transparent polyimide film, wipe the surface moisture of the transparent polyimide film with a dust-free cloth, and store it well to obtain a polyimide film.

[0135] Example 3

[0136] Adjust the reaction apparatus to be airtight and introduce N 2 The air was replaced. At 50°C, 2.7610 g of diamine monomer 4,4'-diaminoterphenyl (A1) was dissolved in 42.5 g of solvent N-methylpyrrolidone. After the diamine monomer was completely dissolved, 4.7390 g of dianhydride monomer (B2) was added. After conversion, the molar ratio of dianhydride monomer to diamine monomer was about 1:0.95. Then, the mixture was stirred at 15°C for 24 hours to prepare a polyimide slurry.

[0137] Place a clean glass plate on the platform of the automatic coating machine, select a 100μm scraper and place it on the glass plate, use a plastic dropper to evenly cover the polyimide slurry prepared by the above method between the scraper and the glass plate, set the scraping length to 30cm, and start coating. After the coating is completed, place the glass plate in an oven for thermal imidization, and heat it at 100℃ for 15min, 200℃ for 15min, and 230℃ for 30min in a gradient heating process to evaporate the solvent. After the thermal imidization reaction is completed, take it out after natural cooling, cut the transparent polyimide film on the smoother part of the film surface with a blade, soak it in deionized water, peel off the transparent polyimide film, wipe the surface moisture of the transparent polyimide film with a dust-free cloth, and store it well to obtain a polyimide film.

[0138] Example 4

[0139] Adjust the reaction apparatus to be airtight and introduce N 2 The air was replaced. At 50°C, 3.3487g of diamine monomer 9,10-di(p-diaminophenyl)anthracene (A2) was dissolved in 42.5g of solvent N-methylpyrrolidone. After the diamine monomer was completely dissolved, 4.1513g of dianhydride monomer (B2) was added. After conversion, the molar ratio of dianhydride monomer to diamine monomer was about 1:0.99. Then, the mixture was stirred at 15°C for 24h to prepare polyimide slurry.

[0140] Place a clean glass plate on the platform of the automatic coating machine, select a 100μm scraper and place it on the glass plate, use a plastic dropper to evenly cover the polyimide slurry prepared by the above method between the scraper and the glass plate, set the scraping length to 30cm, and start coating. After the coating is completed, place the glass plate in an oven for thermal imidization, and heat it at 100℃ for 15min, 200℃ for 15min, and 230℃ for 30min in a gradient heating process to evaporate the solvent. After the thermal imidization reaction is completed, take it out after natural cooling, cut the transparent polyimide film on the smoother part of the film surface with a blade, soak it in deionized water, peel off the transparent polyimide film, wipe the surface moisture of the transparent polyimide film with a dust-free cloth, and store it well to obtain a polyimide film.

[0141] Example 5

[0142] Adjust the reaction apparatus to be airtight and introduce N 2 The air was replaced. At 50°C, 3.1255 g of diamine monomer (A3) was dissolved in 42.5 g of solvent N-methylpyrrolidone. After the diamine monomer was completely dissolved, 4.1513 g of dianhydride monomer (B2) was added. After conversion, the molar ratio of dianhydride monomer to diamine monomer was about 1:0.99. Then, the mixture was stirred at 15°C for 24 hours to prepare a polyimide slurry.

[0143] Place a clean glass plate on the platform of the automatic coating machine, select a 100μm scraper and place it on the glass plate, use a plastic dropper to evenly cover the polyimide slurry prepared by the above method between the scraper and the glass plate, set the scraping length to 30cm, and start coating. After the coating is completed, place the glass plate in an oven for thermal imidization, and heat it at 100℃ for 15min, 200℃ for 15min, and 230℃ for 30min in a gradient heating process to evaporate the solvent. After the thermal imidization reaction is completed, take it out after natural cooling, cut the transparent polyimide film on the smoother part of the film surface with a blade, soak it in deionized water, peel off the transparent polyimide film, wipe the surface moisture of the transparent polyimide film with a dust-free cloth, and store it well to obtain a polyimide film.

[0144] Example 6

[0145] Adjust the reaction apparatus to be airtight and introduce N 2 The air was replaced. At 50°C, 3.4228 g of diamine monomer (A4) was dissolved in 42.5 g of solvent N-methylpyrrolidone. After the diamine monomer was completely dissolved, 4.1513 g of dianhydride monomer (B2) was added. After conversion, the molar ratio of dianhydride monomer to diamine monomer was about 1:0.99. Then, the mixture was stirred at 15°C for 24 hours to prepare a polyimide slurry.

[0146] Place a clean glass plate on the platform of the automatic coating machine, select a 100μm scraper and place it on the glass plate, use a plastic dropper to evenly cover the polyimide slurry prepared by the above method between the scraper and the glass plate, set the scraping length to 30cm, and start coating. After the coating is completed, place the glass plate in an oven for thermal imidization, and heat it at 100℃ for 15min, 200℃ for 15min, and 230℃ for 30min in a gradient heating process to evaporate the solvent. After the thermal imidization reaction is completed, take it out after natural cooling, cut the transparent polyimide film on the smoother part of the film surface with a blade, soak it in deionized water, peel off the transparent polyimide film, wipe the surface moisture of the transparent polyimide film with a dust-free cloth, and store it well to obtain a polyimide film.

[0147] Example 7

[0148] Adjust the reaction apparatus to be airtight and introduce N 2 The air was replaced. At 50°C, 2.9390 g of diamine monomer (A5) was dissolved in 42.5 g of solvent N-methylpyrrolidone. After the diamine monomer was completely dissolved, 4.1513 g of dianhydride monomer (B2) was added. After conversion, the molar ratio of dianhydride monomer to diamine monomer was about 1:0.99. Then, the mixture was stirred at 15°C for 24 hours to prepare a polyimide slurry.

[0149] Place a clean glass plate on the platform of the automatic coating machine, select a 100μm scraper and place it on the glass plate, use a plastic dropper to evenly cover the polyimide slurry prepared by the above method between the scraper and the glass plate, set the scraping length to 30cm, and start coating. After the coating is completed, place the glass plate in an oven for thermal imidization, and heat it at 100℃ for 15min, 200℃ for 15min, and 230℃ for 30min in a gradient heating process to evaporate the solvent. After the thermal imidization reaction is completed, take it out after natural cooling, cut the transparent polyimide film on the smoother part of the film surface with a blade, soak it in deionized water, peel off the transparent polyimide film, wipe the surface moisture of the transparent polyimide film with a dust-free cloth, and store it well to obtain a polyimide film.

[0150] Example 8

[0151] Adjust the reaction apparatus to be airtight and introduce N 2 The air was replaced. At 50°C, 4.0557 g of diamine monomer (A6) was dissolved in 42.5 g of solvent N-methylpyrrolidone. After the diamine monomer was completely dissolved, 4.1513 g of dianhydride monomer (B2) was added. After conversion, the molar ratio of dianhydride monomer to diamine monomer was about 1:0.99. Then, the mixture was stirred at 15°C for 24 hours to prepare a polyimide slurry.

[0152] Place a clean glass plate on the platform of the automatic coating machine, select a 100μm scraper and place it on the glass plate, use a plastic dropper to evenly cover the polyimide slurry prepared by the above method between the scraper and the glass plate, set the scraping length to 30cm, and start coating. After the coating is completed, place the glass plate in an oven for thermal imidization, and heat it at 100℃ for 15min, 200℃ for 15min, and 230℃ for 30min in a gradient heating process to evaporate the solvent. After the thermal imidization reaction is completed, take it out after natural cooling, cut the transparent polyimide film on the smoother part of the film surface with a blade, soak it in deionized water, peel off the transparent polyimide film, wipe the surface moisture of the transparent polyimide film with a dust-free cloth, and store it well to obtain a polyimide film.

[0153] Comparative Example 1

[0154] Adjust the reaction apparatus to be airtight and introduce N 2 The air was replaced. At 50°C, 3.3487g of diamine monomer 9,10-di(p-diaminophenyl)anthracene (A2) was dissolved in 42.5g of solvent N-methylpyrrolidone. After the diamine monomer was completely dissolved, 2.7610g of dianhydride monomer (B3) was added. After conversion, the molar ratio of dianhydride monomer to diamine monomer was about 1:0.99. Then, the mixture was stirred at 15°C for 24h to prepare polyimide slurry.

[0155] Place a clean glass plate on the platform of the automatic coating machine, select a 100μm scraper and place it on the glass plate, use a plastic dropper to evenly cover the polyimide slurry prepared by the above method between the scraper and the glass plate, set the scraping length to 30cm, and start coating. After the coating is completed, place the glass plate in an oven for thermal imidization, and heat it at 100℃ for 15min, 200℃ for 15min, and 230℃ for 30min in a gradient heating process to evaporate the solvent. After the thermal imidization reaction is completed, take it out after natural cooling, cut the transparent polyimide film on the smoother part of the film surface with a blade, soak it in deionized water, peel off the transparent polyimide film, wipe the surface moisture of the transparent polyimide film with a dust-free cloth, and store it well to obtain a polyimide film.

[0156] Comparative Example 2

[0157] Adjust the reaction apparatus to be airtight and introduce N 2 The air was replaced. At 50°C, 1.4705 g of diamine monomer (A7) was dissolved in 42.5 g of solvent N-methylpyrrolidone. After the diamine monomer was completely dissolved, 4.1513 g of dianhydride monomer (B2) was added. After conversion, the molar ratio of dianhydride monomer to diamine monomer was about 1:0.99. The mixture was then stirred at 15°C for 24 hours to prepare a polyimide slurry.

[0158] Place a clean glass plate on the platform of the automatic coating machine, select a 100μm scraper and place it on the glass plate, use a plastic dropper to evenly cover the polyimide slurry prepared by the above method between the scraper and the glass plate, set the scraping length to 30cm, and start coating. After the coating is completed, place the glass plate in an oven for thermal imidization, and heat it at 100℃ for 15min, 200℃ for 15min, and 230℃ for 30min in a gradient heating process to evaporate the solvent. After the thermal imidization reaction is completed, take it out after natural cooling, cut the transparent polyimide film on the smoother part of the film surface with a blade, soak it in deionized water, peel off the transparent polyimide film, wipe the surface moisture of the transparent polyimide film with a dust-free cloth, and store it well to obtain a polyimide film.

[0159] The viscosity and other data of the polyimide slurry of each embodiment and comparative example are recorded in Table 1.

[0160] The obtained results of the viscosity of the polyimide solutions prepared in the above examples and comparative examples, the film thickness, tensile strength and glass transition temperature Tg of the polyimide film samples are recorded in Table 1.

[0161] Table 1

[0162]

[0163] As can be seen from the data in Table 1, the selection of dianhydride monomer B3 in Comparative Example 1 leads to an increase in the glass transition temperature of the polyimide film prepared therefrom. In Comparative Example 2, the selection of diamine monomer A7, although its glass transition temperature is effectively reduced, the mechanical properties such as tensile strength of the polyimide film are greatly reduced.

[0164] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0165] The above-described embodiments only express several implementation methods of the present application, which is convenient for understanding the technical solution of the present application in detail, but it cannot be understood as limiting the scope of protection of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all belong to the protection scope of the present application. It should be understood that the technical solutions obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the technical solutions provided in the present application are all within the protection scope of the claims attached to the present application. Therefore, the scope of protection of the patent of this application shall be based on the content of the attached claims, and the description can be used to interpret the content of the claims.

Claims

1. A polyimide, characterized in that: The raw materials for preparing the polyimide include dianhydride monomers and diamine monomers, and the dianhydride monomers are selected from one or more compounds having the structural characteristics shown in formula (I): Wherein, X1 and X2 are each independently selected from -O- or -S-; A is selected from C2~C6 alkylene or C2~C 10 Haloalkylene; n is a positive integer between 2 and 20; The diamine monomer is selected from one or more compounds having the structural characteristics shown in formula (II): Wherein, Ar is selected from a single bond, a phenylene group substituted or unsubstituted by R1, or a C6~C 24 A fused cyclic group; L1 and L2 are each independently selected from H, halogen, C1~C 10 Alkyl, C1~C 10 haloalkyl, phenyl substituted or unsubstituted by R1, biphenyl substituted or unsubstituted by R1, phenoxy substituted or unsubstituted by R1, C3~C 10 Heteroaryl, or C6~C 24 Condensed ring group; R1, when it appears each time, is independently halogen, C1~C3 alkyl or C1~C3 haloalkyl.

2. The polyimide according to claim 1, characterized in that The polyimide has one or more of the following characteristics: (1) X1 and X2 are each independently selected from -O-; A is selected from C2~C4 alkyl or C2~C4 haloalkyl; n is a positive integer between 2 and 10; (2) Ar is selected from a single bond, a phenyl group substituted or unsubstituted by R1, or a C6~C 18 The fused ring group; L1 and L2 are each independently selected from H, halogen, C1~C5 alkyl, C1~C5 haloalkyl, phenyl substituted or unsubstituted by R1, biphenyl substituted or unsubstituted by R1, phenoxy substituted or unsubstituted by R1, C3~C6 heteroaryl substituted or unsubstituted by R1, or C6~C 18 Fused cyclic group; R1 each time appears, each is independently halogen, -CH3, CF3, -CH2CH3 or -CF2CF3.

3. The polyimide according to claim 1, characterized in that The polyimide has one or more of the following characteristics: (1) X1 and X2 are each independently selected from -O-; A is selected from -CH(CH3)-, -CH2CH2-, -CH(CH2CH3)-, -CH2CH(CH3)-, -CH2CH2CH2- or -CH2CH2CH2CH2-, and n is a positive integer between 2 and 10; (2) Ar is selected from a single bond, , , , or ; L1, L2 are each independently selected from H, halogen, -CH3, -CF3, , , , , , , or .

4. The polyimide according to any one of claims 1 to 3, characterized in that The polyimide has one or more of the following characteristics: (1) The dianhydride monomer includes and One or more of; n1 is a positive integer between 2 and 10; (2) The diamine monomer includes , , , , , , , , , , , , , and One or more of .

5. The polyimide according to claim 4, characterized in that The molar ratio of the dianhydride monomer to the diamine monomer is 1:(0.9-1.2).

6. A method for preparing a polyimide according to any one of claims 1 to 5, characterized in that: The following steps are involved: The dianhydride monomer and the diamine monomer are mixed in a solvent to prepare a polyimide slurry; The polyimide slurry is subjected to a thermal imidization reaction to prepare the polyimide.

7. The method for preparing a polyimide according to claim 6, characterized in that: The solvent includes one or more of N-methylpyrrolidone, m-cresol, N,N-dimethylacetamide, dimethyl sulfoxide, γ-butyrolactone, cyclohexanone and N,N-dimethylformamide.

8. The method for preparing a polyimide according to claim 6 or 7, characterized in that: The process parameters of the thermal imidization reaction include: a first heating treatment at a temperature of 90°C to 110°C, a second heating treatment at a temperature of 190°C to 210°C, and a third heating treatment at a temperature of 220°C to 240°C.

9. An optically transparent film, characterized in that: The invention comprises the polyimide according to any one of claims 1 to 5.

10. A flexible electronic device, characterized in that: The optically transparent film according to claim 9 is included.

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