Polyimide, preparation method and optical transparent film

Abstract

The invention belongs to the technical field of polyimide materials, and particularly relates to polypolyimide, a preparation method and an optical transparent film. 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 of compounds with structural characteristics as shown in a formula (I); the diamine monomer comprises a main diamine monomer and an auxiliary diamine monomer, and in the diamine monomer, the molar fraction of the main diamine monomer is 50%-90%, and the molar fraction of the auxiliary diamine monomer is 10%-50%; the main diamine monomer is selected from one or more of compounds with structural characteristics as shown in a formula (II); the auxiliary diamine monomer comprises one or more of an aromatic ring-containing diamine monomer and an aliphatic ring-containing diamine monomer. The polyimide provided by the invention has a relatively low glass transition temperature and a relatively low curing temperature.

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, and an optically transparent film. Background Art

[0002] Polyimide (PI) is a type of high molecular polymer containing cyclic imide groups in the molecular chain. Among them, flexible transparent polyimide can not only maintain the high heat resistance and high bendability of polyimide itself, but also has a high optical transmittance, which makes it more widely used in many high-tech fields. For example, in flexible OLED displays, transparent polyimide (CPI) will be used as an optically transparent film for transparent flexible substrates, touch substrates, under-screen camera covers, and mobile phone covers.

[0003] Traditional polyimide materials usually have a high glass transition temperature, so their softening temperature is usually high, and their processing temperature is usually as high as 370℃~425℃. When processed and molded at this temperature, the aromatic rings inside the polyimide molecules will be dehydrogenated to form free radicals, and cross-linking may also occur between the aromatic rings with free radicals, which may cause the polyimide to become brittle, harden, and lose elasticity prematurely. Summary of the invention

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

[0005] In a first aspect of the present application, a polyimide is provided, wherein raw materials for preparing the polyimide include a dianhydride monomer and a diamine monomer.

[0006] The dianhydride monomer is selected from one or more compounds having the structural characteristics shown in formula (I): ; wherein R1 is independently a single bond, -O-, an ester group, an alkylene group having 1 to 6 carbon atoms, a fluoroalkylene group having 1 to 6 carbon atoms, an arylene group having 6 to 12 carbon atoms, , or ; L1, L2 and L3 are each independently an arylene group having 6 to 12 carbon atoms;

[0007] The diamine monomers include a main diamine monomer and an auxiliary diamine monomer. In terms of mole fraction, the mole fraction of the main diamine monomer is 50% to 90%, and the mole fraction of the auxiliary diamine monomer is 10% to 50%;

[0008] The main diamine monomer is selected from one or more compounds having the structural characteristics shown in formula (II): ; wherein R2 is selected from an alkylene group having 1 to 300 carbon atoms or a fluoroalkylene group having 1 to 300 carbon atoms;

[0009] The auxiliary diamine monomer includes one or more of an aromatic cyclic diamine monomer and an aliphatic cyclic diamine monomer.

[0010] In one embodiment, R2 is selected from the following groups: , wherein n1, n2, n3, n4 and n5 are each independently selected from positive integers between 0 and 20, and 6≤n1+n2+n3+n4+n5≤20; R 21 , R 22 , R 23 , R 24 , R 25 and R 26 Each is independently selected from hydrogen, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl, 2-butyl, 2-methyl-2-propyl, 2-pentyl, 3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 3-methyl-1-butyl, 2-methyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, trifluoromethyl or fluorine.

[0011] In one embodiment, R 21 , R 22 , R 23 , R 24 , R 25 and R 26 Each is independently selected from hydrogen, methyl, ethyl, 1-propyl, and 2-propyl.

[0012] In one embodiment, the main diamine monomer comprises , , , , , , , , and One or more of .

[0013] In one embodiment, the aromatic cyclic diamine monomer is selected from one or more compounds having the structural characteristics shown in formula (III):

[0014] ; wherein R3 is independently -O-, -S-, , , , , an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms;

[0015] The aliphatic cyclic diamine monomer is selected from one or more compounds having structural characteristics shown in formula (IV-1) to formula (IV-2): , ; wherein R4 is independently -O-, -S-, , , , , an alkylene group having 1 to 6 carbon atoms, or a fluorinated alkylene group having 1 to 6 carbon atoms.

[0016] In one embodiment, the molar ratio of the diamine monomer to the dianhydride monomer is (0.8-1.2):1.

[0017] In a second aspect of the present application, there is provided a method for preparing the polyimide according to any one of the embodiments of the first aspect of the present application, comprising the following steps:

[0018] The dianhydride monomer and the diamine monomer are mixed in a solvent to prepare a polyimide slurry; and the polyimide slurry is polymerized to prepare the polyimide.

[0019] 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.

[0020] In one embodiment, the process parameters of the polymerization 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.

[0021] A third aspect of the present application provides an optically transparent film, comprising the polyimide described in any one of the embodiments of the first aspect of the present application.

[0022] This application has at least the following beneficial effects:

[0023] The polyimide of the present application is prepared by diamine monomers and dianhydride monomers of specific structures. Among them, the diamine monomers include a fatty chain main diamine monomer containing an alkylene group, and an aromatic ring-containing or aliphatic ring-containing auxiliary diamine monomer, the two of which cooperate with each other, and the presence of a flexible segment in the main diamine monomer can provide better freedom of movement between molecules to improve the flexibility of the polyimide, reduce the glass transition temperature, and make the polyimide have better flexibility and processability at a lower temperature. Further supplemented with an aromatic ring-containing or aliphatic ring-containing auxiliary diamine monomer and a dianhydride monomer of a specific structure, it can optimize the thermal stability and mechanical strength of the polyimide and reduce the brittleness of the polyimide.

[0024] 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

[0025] The polyimide and preparation method and optical transparent film 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 the purpose is not to limit the present application.

[0026] 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.

[0027] 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:

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] In the present application, "alkyl" refers to a saturated hydrocarbon group containing a primary (normal) carbon atom, or a secondary carbon atom, or a tertiary carbon atom, or a quaternary carbon atom, or a combination thereof. Phrases containing this term, for example, "C1~C6 alkyl" refers to an alkyl group containing 1 to 6 carbon atoms, and each time it appears, it 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, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-propyl, n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-butyl, n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2 -butyl (s-Bu, s-butyl, -CH(CH3)CH2CH3), tert-butyl (1,1-dimethylethyl, 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH3)3), 1-pentyl (n-pentyl, n-pentyl, -CH2CH2CH2CH2CH3), 2-pentyl (-CH(CH3)CH2CH2CH3), 3-pentyl (-CH(CH2CH3)2), 2-methyl-2-butyl (-C(CH3) 2CH2CH3), 3-methyl-2-butyl (-CH(CH3)CH(CH3)2), 3-methyl-1-butyl (-CH2CH2CH(CH3)2), 2-methyl-1-butyl (-CH2CH(CH3)CH2CH3), 1-hexyl (n-hexyl, -CH2CH2CH2CH2CH2CH3), 2-hexyl (-CH(CH3)CH2CH2CH2CH3), 3-hexyl (-CH(CH2CH3 )(CH2CH2CH3)), 2-methyl-2-pentyl (-C(CH3)2CH2CH2CH3), 3-methyl-2-pentyl (-CH(CH3)CH(CH3)CH2CH3), 4-methyl-2-pentyl (-CH(CH3)CH2CH(CH3)2), 3-methyl-3-pentyl (-C(CH3)(CH2CH3)2) and 2-methyl-3-pentyl (-CH(CH2CH3)CH(CH3)2).

[0041] "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 time it appears, it can be independently C1 alkylene, C4 alkylene, C5 alkylene, C6 alkylene. Suitable examples include, but are not limited to: methylene (-CH2-), 1,1-ethyl (-CH(CH3)-), 1,2-ethyl (-CH2CH2-), 1,1-propyl (-CH(CH2CH3)-), 1,2-propyl (-CH2CH(CH3)-), 1,3-propyl (-CH2CH2CH2-) and 1,4-butyl (-CH2CH2CH2CH2-).

[0042] "Fluorinated alkylene" means that fluorine atoms replace hydrogen atoms in the alkylene group. It is understood that the number of fluorine atoms substituted is ≤ the number of hydrogen atoms in the alkylene group.

[0043] In the present application, "aryl" refers to an aromatic hydrocarbon group derived from an aromatic ring compound by removing a hydrogen atom, which can be a monocyclic aromatic group, a condensed aromatic group, or a polycyclic aromatic group. For polycyclic rings, at least one is an aromatic ring system. Phrases containing this term, for example, "aryl having 6 to 12 carbon atoms" refers to an aromatic group containing 6 to 12 atoms, and each occurrence can be independently a C6 aromatic group or a C10 aromatic group. Suitable examples include, but are not limited to, benzene and naphthalene. "Arylene" refers to an aromatic hydrocarbon group derived from an "aryl" group by removing a hydrogen atom.

[0044] At present, the preparation method of polyimide is mainly a two-step method: first prepare a synthetic polyimide slurry, then evaporate the solvent through thermal imidization or chemical imidization, and dehydrate to form polyimide. Traditionally prepared polyimides usually have excellent heat resistance, and their glass transition temperature is relatively high, generally above 200°C. However, imidization must be carried out at a temperature at which the molecular chain can move, that is, it should be above the glass transition temperature to completely occur. Therefore, as the cyclization reaction proceeds, the rigidity of the polymer molecular chain becomes higher and higher, and the temperature required to continue imidization also increases. Therefore, in the traditional process, in the process of preparing polyimide with a higher glass transition temperature, it is usually necessary to carry out imidization at a heating temperature exceeding 300°C, which makes the gradient heating and imidization in the entire process take a long time, which limits the wider application of polyimide.

[0045] In a first aspect of the present application, a polyimide is provided, wherein raw materials for preparing the polyimide include a dianhydride monomer and a diamine monomer.

[0046] The dianhydride monomer is selected from one or more compounds having the structural characteristics shown in formula (I): ; wherein R1 is independently a single bond, -O-, an ester group, an alkylene group having 1 to 6 carbon atoms, a fluoroalkylene group having 1 to 6 carbon atoms, an arylene group having 6 to 12 carbon atoms, , or ; L1, L2 and L3 are each independently an arylene group having 6 to 12 carbon atoms;

[0047] The diamine monomers include a main diamine monomer and an auxiliary diamine monomer. In terms of mole fraction, the mole fraction of the main diamine monomer is 50% to 90%, and the mole fraction of the auxiliary diamine monomer is 10% to 50%;

[0048] The main diamine monomer is selected from one or more compounds having the structural characteristics shown in formula (II): ; wherein R2 is selected from an alkylene group having 1 to 300 carbon atoms or a fluoroalkylene group having 1 to 300 carbon atoms;

[0049] The auxiliary diamine monomer includes one or more of an aromatic cyclic diamine monomer and an aliphatic cyclic diamine monomer.

[0050] The diamine monomers include a main diamine monomer and an auxiliary diamine monomer. In terms of mole fraction, in the diamine monomers, the mole fraction of the main diamine monomer is 50% to 90%, and the mole fraction of the auxiliary diamine monomer is 10% to 50%.

[0051] It is understood that in the diamine monomer, the mole fraction of the main diamine monomer can be selected from any value between 50% and 90%. Specifically, the mole fraction of the main diamine monomer includes but is not limited to 50%, 53%, 55%, 58%, 60%, 62%, 65%, 67%, 69%, 70%, 73%, 75%, 78%, 80%, 82%, 85%, 87%, 88% or 90%. The mole fraction of the auxiliary diamine monomer includes but is not limited to 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 42%, 45%, 48% or 50%.

[0052] The polyimide of the present application is prepared by diamine monomers and dianhydride monomers of specific structures. Among them, the diamine monomers include a fatty chain main diamine monomer containing an alkylene group, and an aromatic ring-containing or aliphatic ring-containing auxiliary diamine monomer, the two of which cooperate with each other, and the presence of a flexible segment in the main diamine monomer can provide better freedom of movement between molecules to improve the flexibility of the polyimide, reduce the glass transition temperature, and make the polyimide have better flexibility and processability at a lower temperature. Further supplemented with an aromatic ring-containing or aliphatic ring-containing auxiliary diamine monomer and a dianhydride monomer of a specific structure, it can optimize the thermal stability and mechanical strength of the polyimide and reduce the brittleness of the polyimide.

[0053] 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.

[0054] Furthermore, the dianhydride monomer comprises , , , , , and One or more of .

[0055] Furthermore, the dianhydride monomer comprises The structural symmetry of 2,3,3',4'-biphenyltetracarboxylic dianhydride can improve the stability of the polyimide chain, thereby increasing its mechanical strength; further, the selection of the dianhydride monomer can also reduce the glass transition temperature of the polyimide, so that it can still maintain good processability at a lower temperature.

[0056] In one example, R2 is selected from the group shown below: , wherein n1, n2, n3, n4 and n5 are each independently selected from positive integers between 0 and 20, and 6≤n1+n2+n3+n4+n5≤20; R 21 , R 22 , R 23 , R 24 , R 25 and R 26Each is independently selected from hydrogen, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl, 2-butyl, 2-methyl-2-propyl, 2-pentyl, 3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 3-methyl-1-butyl, 2-methyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, trifluoromethyl or fluorine. It is understood that n1, n2, n3, n4 and n5 are each independently selected from 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 or 20.

[0057] Furthermore, R 21 , R 22 , R 23 , R 24 , R 25 and R 26 Each is independently selected from hydrogen, methyl, ethyl, 1-propyl, and 2-propyl.

[0058] Furthermore, the main diamine monomer includes , , , , , , , , and One or more of .

[0059] Furthermore, the main diamine monomer includes , , , , , , , and One or more of .

[0060] Furthermore, the main diamine monomer includes 1,16-hexadecanediamine, 1,15-pentadecanediamine, 1,14-tetradecanediamine, 1,13-tridecanediamine, 1,12-dodecanediamine, 1,11-undecanediamine, 1,10-decanediamine, 1,9-nonanediamine, 1,8-octanediamine, 1,7-heptanediamine, 1,6-hexanediamine, 3,4-dimethyl-1,6-hexanediamine, 3,4-dimethyl-1,7 -heptanediamine, 3,4-dimethyl-1,8-octanediamine, 3,4-dimethyl-1,9-nonanediamine, 3,4-dimethyl-1,10-decanediamine, 4,5-dimethyl-1,10-decanediamine, 5,6-dimethyl-1,10-decanediamine, 3,4-diethyl-1,6-hexanediamine, 3,4-diethyl-1,7-heptanediamine, 3,4-diethyl-1,8-octanediamine, 3,4-diethyl-1,9-nonanediamine Amine, 3,4-diethyl-1,10-decanediamine, 4,5-diethyl-1,10-decanediamine, 5,6-diethyl-1,10-decanediamine, 2,3,4,5-tetramethyl-1,6-hexanediamine, 2,3,4,5,6-pentamethyl-1,7-heptanediamine, 2,3,4,5,6,7-hexamethyl-1,8-octanediamine, 2,3,4,5,6,7,8-heptamethyl-1,9-nonanediamine, 2,3,4 ,5,6,7,8,9-octamethyl-1,10-decanediamine, 2,3,4,5-tetraethyl-1,6-hexanediamine, 2,3,4,5,6-pentaethyl-1,7-heptanediamine, 2,3,4,5,6,7-hexaethyl-1,8-octanediamine, 2,3,4,5,6,7,8-heptaethyl-1,9-nonanediamine and one or more of 2,3,4,5,6,7,8,9-octaethyl-1,10-decanediamine.

[0061] R 21 , R 22 , R 23 , R 24 , R 25 and R 26 When at least one of the carbon substituents is replaced by a methyl group or an ethyl group, the carbon substituent introduces more branches or steric hindrances, which reduces the close arrangement and interaction between chains, thereby reducing the glass transition temperature of the material. More preferably, R 21 , R 22 , R 23 , R 24 , R 25 and R 26 At least one of them is substituted with an ethyl group.

[0062] In one example, the aromatic cyclic diamine monomer is selected from one or more compounds having the structural characteristics shown in formula (III):

[0063] ; wherein R3 is independently -O-, -S-, , , , , an alkylene group having 1 to 6 carbon atoms, or a fluorinated alkylene group having 1 to 6 carbon atoms.

[0064] Furthermore, the aromatic cyclic diamine monomer includes , and One or more of .

[0065] The combination of aromatic cyclic diamine monomers and main diamine monomers can improve the mechanical strength of polyimide and reduce its glass transition temperature: since the aromatic cyclic diamine provides higher thermal stability and strength, and the main diamine monomer introduces the flexibility of the chain segment, the two work synergistically to improve the mechanical strength of polyimide and reduce its glass transition temperature.

[0066] In one example, the aliphatic cyclic diamine monomer is selected from one or more compounds having structural features shown in formula (IV-1) to formula (IV-2): , ; wherein R4 is independently -O-, -S-, , , , , an alkylene group having 1 to 6 carbon atoms, or a fluorinated alkylene group having 1 to 6 carbon atoms.

[0067] In one example, the aliphatic cyclic diamine monomer includes , , and One or more of .

[0068] In one example, the molar ratio of the diamine monomer to the dianhydride monomer is (0.8-1.2): 1. It is understandable that the molar ratio of the diamine monomer to the dianhydride monomer can be selected from any value between (0.8-1.2): 1. Specifically, the molar ratio of the diamine monomer to the dianhydride monomer includes but is not limited to 0.8: 1, 0.83: 1, 0.85: 1, 0.88: 1, 0.9: 1, 0.93: 1, 0.95: 1, 0.98: 1, 1: 1, 1.01: 1, 1.03: 1, 1.05: 1, 1.08: 1, 1.1: 1, 1.12: 1, 1.15: 1, 1.18: 1 or 1.2: 1.

[0069] In a second aspect of the present application, there is provided a method for preparing the polyimide described in any example of the first aspect of the present application, comprising the following steps:

[0070] The dianhydride monomer and the diamine monomer are mixed in a solvent to prepare a polyimide slurry; and the polyimide slurry is polymerized to prepare the polyimide.

[0071] In one example, the solvent includes N-methylpyrrolidone (NMP, )、m-cresol( )、N,N-dimethylacetamide( )、Dimethyl sulfoxide( ), γ-butyrolactone ( )、Cyclohexanone( ) and N,N-dimethylformamide ( )

[0072] Furthermore, the preparation steps of the polyimide slurry include:

[0073] S10, dissolving the diamine monomer in a solvent for initial mixing to prepare an intermediate solution containing the diamine monomer;

[0074] S20, adding dianhydride monomer to the intermediate solution containing diamine monomer for secondary mixing to prepare polyimide slurry.

[0075] Specifically, in step S10, 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.

[0076] Further, in step S10, the temperature for the initial mixing is 40° C. to 80° C. Specifically, the temperature for the initial 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.

[0077] In step S20, the temperature for secondary mixing is 10° C. to 60° C. Specifically, the temperature for secondary 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.

[0078] In one example, the process parameters of the polymerization 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.

[0079] Specifically, 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.

[0080] 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.

[0081] The present application also provides a method for preparing a polyimide film, comprising the following steps:

[0082] 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.

[0083] 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.

[0084] According to a third aspect of the present application, an optically transparent film is provided, comprising the polyimide described in any one of the examples of the first aspect of the present application.

[0085] The present application also provides a flexible electronic device, comprising the polyimide described in the present application.

[0086] 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 methods recommended by the manufacturer. For example, the book may be "Polyimide-Monomer Synthesis, Polymerization Methods and Materials".

[0087] [Diamine monomer]

[0088] [Main diamine monomer]

[0089] A1: 1,12-dodecanediamine;

[0090] A2: 2,3,4,5,6,7-hexamethyl-1,8-octanediamine;

[0091] A3: 3,6-diethyl-1,9-nonanediamine;

[0092] A4: 4,5-dimethyl-1,10-decanediamine;

[0093] [Auxiliary diamine monomer]

[0094] B1: , 4,4'-diaminodiphenyl ether (ODA);

[0095] B2: , 4,4'-diaminodiphenyl sulfone (DDS);

[0096] B3: , 4,4'-diaminodicyclohexylmethane (PACM);

[0097] [Dianhydride monomer]

[0098] C1: 2,3,3',4'-biphenyltetracarboxylic dianhydride .

[0099] C2: Cyclobutanetetracarboxylic dianhydride .

[0100] Example 1

[0101] The reaction device was adjusted to be airtight, and N2 was introduced into it to replace the air. At 50°C, 3.0206g of the main diamine monomer 1,12-dodecanediamine (A1) and 3.0187g of the auxiliary diamine monomer ODA (B1) were dissolved in 85g of the solvent N,N-dimethylacetamide. After the diamine monomer was completely dissolved, 8.9607g of the dianhydride monomer BPDA (C1) was added. After conversion, the molar ratio of the diamine monomer to the dianhydride monomer was about 1:1; in the diamine monomer, the molar fraction of the main diamine monomer was about 50%, and the molar fraction of the auxiliary diamine monomer was about 50%. Then, the mixture was stirred at 15°C for 24h to prepare a polyimide slurry.

[0102] 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 polymerization 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 to obtain a polyimide film.

[0103] Example 2

[0104] The reaction device was adjusted to be airtight, and N2 was introduced into it to replace the air. At 50°C, 3.1988g of the main diamine monomer 2,3,4,5,6,7-hexamethyl-1,8-octanediamine (A2) and 3.4773g of the auxiliary diamine monomer DDS (B2) were dissolved in 85g of the solvent N,N-dimethylacetamide. After the diamine monomer was completely dissolved, 8.3239g of the dianhydride monomer BPDA (C1) was added. After conversion, the molar ratio of the diamine monomer to the dianhydride monomer was about 0.99:1; in the diamine monomer, the molar fraction of the main diamine monomer was about 50%, and the molar fraction of the auxiliary diamine monomer was about 50%. Then, the mixture was stirred at 15°C for 24h to prepare a polyimide slurry.

[0105] 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 polymerization 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 to obtain a polyimide film.

[0106] Example 3

[0107] The reaction apparatus was adjusted to be airtight, and N2 was introduced into it to replace the air. At 50°C, 3.1868g of the main diamine monomer 3,6-diethyl-1,9-nonanediamine (A3) and 2.9769g of the auxiliary diamine monomer ODA (B1) were dissolved in 85g of the solvent N,N-dimethylacetamide. After the diamine monomer was completely dissolved, 8.8364g of the dianhydride monomer BPDA (C1) was added. After conversion, the molar ratio of the diamine monomer to the dianhydride monomer was about 0.99:1; in the diamine monomer, the molar fraction of the main diamine monomer was about 50%, and the molar fraction of the auxiliary diamine monomer was about 50%. Then, the mixture was stirred at 15°C for 24h to prepare a polyimide slurry.

[0108] 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 polymerization 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 to obtain a polyimide film.

[0109] Example 4

[0110] The reaction device was adjusted to be airtight, and N2 was introduced into it to replace the air. At 50°C, 2.9901g of the main diamine monomer 4,5-dimethyl-1,10-decanediamine (A4) and 3.1395g of the auxiliary diamine monomer PACM (B3) were dissolved in 85g of the solvent N,N-dimethylacetamide. After the diamine monomer was completely dissolved, 8.88704g of the dianhydride monomer BPDA (C1) was added. After conversion, the molar ratio of the diamine monomer to the dianhydride monomer was about 0.99:1; in the diamine monomer, the molar fraction of the main diamine monomer was about 50%, and the molar fraction of the auxiliary diamine monomer was about 50%. Then, the mixture was stirred at 15°C for 24h to prepare a polyimide slurry.

[0111] 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 polymerization 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 to obtain a polyimide film.

[0112] Example 5

[0113] The reaction device was adjusted to be airtight, and N2 was introduced into it to replace the air. At 50°C, 2.9901g of the main diamine monomer 4,5-dimethyl-1,10-decanediamine (A4) and 3.7057g of the auxiliary diamine monomer DDS (B2) were dissolved in 85g of the solvent N,N-dimethylacetamide. After the diamine monomer was completely dissolved, 8.88704g of the dianhydride monomer BPDA (C1) was added. After conversion, the molar ratio of the diamine monomer to the dianhydride monomer was about 0.99:1; in the diamine monomer, the molar fraction of the main diamine monomer was about 50%, and the molar fraction of the auxiliary diamine monomer was about 50%. Then, the mixture was stirred at 15°C for 24h to prepare a polyimide slurry.

[0114] 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 polymerization 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 to obtain a polyimide film.

[0115] Comparative Example 1

[0116] The reaction device was adjusted to be airtight, and N2 was introduced into it to replace the air. At 50°C, 3.0206g of the main diamine monomer 1,12-dodecanediamine (A1) and 3.0187g of the auxiliary diamine monomer ODA (B1) were dissolved in 85g of the solvent N,N-dimethylacetamide. After the diamine monomer was completely dissolved, 5.9727g of the dianhydride monomer cyclobutanetetracarboxylic dianhydride (C2) was added. After conversion, the molar ratio of the diamine monomer to the dianhydride monomer was about 1:1; in the diamine monomer, the molar fraction of the main diamine monomer was about 50%, and the molar fraction of the auxiliary diamine monomer was about 50%. Then, the mixture was stirred at 15°C for 24h to prepare a polyimide slurry.

[0117] Place a clean glass plate on the platform of an 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 according to the gradient temperature treatment to volatilize the solvent. After the polymerization reaction is completed, a polyimide film is obtained.

[0118] In Comparative Example 1, the dianhydride monomer cyclobutanetetracarboxylic dianhydride (C2) was selected, which had poor reactivity with the diamine monomer and the obtained slurry had low viscosity. The film obtained after the polymerization reaction was fragile and had poor mechanical properties, so relevant performance tests could not be performed.

[0119] Comparative Example 2

[0120] The reaction device was adjusted to be airtight, and N2 was introduced into it to replace the air. At 50°C, 6.0411g of diamine monomer 1,12-dodecanediamine (A1) was dissolved in 85g of solvent N,N-dimethylacetamide. After the diamine monomer was completely dissolved, 8.9607g of dianhydride monomer BPDA (C1) was added. After conversion, the molar ratio of diamine monomer to dianhydride monomer was about 1:1; then stirred at 15°C for 24h to prepare polyimide slurry.

[0121] 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 polymerization 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 to obtain a polyimide film.

[0122] Comparative Example 3

[0123] The reaction device was adjusted to be airtight, and N2 was introduced into it to replace the air. At 50°C, 1.8123g of diamine monomer 1,12-dodecanediamine (A1) and 4.2262g of diamine monomer ODA (B1) were dissolved in 85g of solvent N,N-dimethylacetamide. After the diamine monomer was completely dissolved, 8.9607g of dianhydride monomer BPDA (C1) was added. After conversion, the molar ratio of the diamine monomer to the dianhydride monomer was about 1:1; in the diamine monomer, the molar fraction of the diamine monomer 1,12-dodecanediamine (A1) was about 30%, and the molar fraction of the diamine monomer ODA (B1) was about 70%. Then, the mixture was stirred at 15°C for 24h to prepare a polyimide slurry.

[0124] 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 polymerization 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 to obtain a polyimide film.

[0125] The viscosity and other data of the polyimide slurry of each embodiment and comparative example are recorded in Table 1.

[0126] The obtained results of the film thickness, glass transition temperature Tg, 5% weight loss temperature, tensile strength, Young's modulus and elongation at break of the transparent polyimide film samples prepared in the above examples and comparative examples are recorded in Table 1.

[0127] Table 1

[0128]

[0129] It can be seen from Examples 1 to 5 that the polyimide film provided in the present application has a lower glass transition temperature and excellent mechanical properties. In Comparative Example 1, cyclobutanetetracarboxylic dianhydride (C2) is selected as the dianhydride monomer, and its reactivity with the diamine monomer is poor. The prepared polyimide film is fragile, so performance testing cannot be performed. In Comparative Example 2, only the diamine monomer 1,12-dodecanediamine (A1) is selected. Although it can reduce the glass transition temperature of the polyimide, its mechanical properties are poor. In Comparative Example 3, the molar fraction of 1,12-dodecanediamine is lower than the molar fraction of ODA (B1), resulting in an increase in its glass transition temperature.

[0130] 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.

[0131] 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. The dianhydride monomer is selected from one or more compounds having the structural characteristics shown in formula (I): ; wherein R1 is independently a single bond, -O-, an ester group, an alkylene group having 1 to 6 carbon atoms, a fluoroalkylene group having 1 to 6 carbon atoms, an arylene group having 6 to 12 carbon atoms, , or ; L1, L2 and L3 are each independently an arylene group having 6 to 12 carbon atoms; The diamine monomers include a main diamine monomer and an auxiliary diamine monomer. In terms of mole fraction, the mole fraction of the main diamine monomer is 50% to 90%, and the mole fraction of the auxiliary diamine monomer is 10% to 50%; The main diamine monomer is selected from one or more compounds having the structural characteristics shown in formula (II): ; wherein R2 is selected from an alkylene group having 1 to 300 carbon atoms or a fluoroalkylene group having 1 to 300 carbon atoms; The auxiliary diamine monomer includes one or more of an aromatic cyclic diamine monomer and an aliphatic cyclic diamine monomer.

2. The polyimide according to claim 1, characterized in that R2 is selected from the following groups: , wherein n1, n2, n3, n4 and n5 are each independently selected from positive integers between 0 and 20, and 6≤n1+n2+n3+n4+n5≤20; R 21 , R 22 , R 23 , R 24 , R 25 and R 26 Each is independently selected from hydrogen, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-methyl-1-propyl, 2-butyl, 2-methyl-2-propyl, 2-pentyl, 3-pentyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 3-methyl-1-butyl, 2-methyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, trifluoromethyl or fluorine.

3. The polyimide according to claim 2, characterized in that R 21 , R 22 , R 23 , R 24 , R 25 and R 26 Each is independently selected from hydrogen, methyl, ethyl, 1-propyl, and 2-propyl.

4. The polyimide according to any one of claims 2 or 3, characterized in that The main diamine monomer includes , , , , , , , , and One or more of .

5. The polyimide according to any one of claims 1 to 4, characterized in that The aromatic cyclic diamine monomer is selected from one or more compounds having the structural characteristics shown in formula (III): ; wherein R3 is independently -O-, -S-, , , , , an alkylene group having 1 to 6 carbon atoms or a fluoroalkylene group having 1 to 6 carbon atoms; The aliphatic cyclic diamine monomer is selected from one or more compounds having structural characteristics shown in formula (IV-1) to formula (IV-2): , ; wherein R4 is independently -O-, -S-, , , , , an alkylene group having 1 to 6 carbon atoms, or a fluoroalkylene group having 1 to 6 carbon atoms.

6. The polyimide according to claim 5, characterized in that The molar ratio of the diamine monomer to the dianhydride monomer is (0.8-1.2):

1.

7. A method for preparing a polyimide according to any one of claims 1 to 6, 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 polymerization reaction to prepare the polyimide.

8. The method for preparing a polyimide according to claim 7, 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.

9. The method for preparing a polyimide according to claim 7 or 8, characterized in that: The process parameters of the polymerization 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.

10. An optically transparent film, characterized in that: The invention comprises the polyimide according to any one of claims 1 to 6.

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