Diamine compounds, polyimides, polyimide films, and methods of making the same

Abstract

The application discloses a diamine compound shown in formula (I) or formula (II), a polyimide, a polyimide film and a preparation method thereof, and relates to the field of high polymer materials. The application introduces a benzoxazole structure and an aliphatic ring structure into the structure of the diamine compound, can balance the rigidity and flexibility of the molecular chain and charge transfer interaction, and the polyimide film prepared by using the diamine compound as raw material has excellent heat resistance and transparency, and can be applied to the fields of photoelectric display and solar energy substrate. Experimental results show that the polyimide film prepared by using the diamine compound provided by the application has heat resistance and transparency, and has good comprehensive performance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials, and more particularly to diamine compounds, polyimides, polyimide films, and methods for their preparation. Background Technology

[0002] Polyimide is a class of polymer materials obtained by polymerizing dianhydrides and diamines. It possesses excellent high and low temperature resistance, mechanical properties, and radiation resistance, and has the advantage of tunable molecular structure, making it widely used in defense, military, and civilian high-tech fields. Traditional aromatic polyimide films are yellow or dark brown in color, which limits their application in transparent flexible substrates and transparent circuit boards. Therefore, improving the transparency of polyimide while maintaining its excellent heat resistance has become a research hotspot in related fields.

[0003] Numerous studies have shown that there is a charge transfer (CT) effect between electron donor diamine and electron acceptor dianhydride in polyimide molecules, which mainly affects the color of the film; the weaker the CT effect, the lighter the color. In order to reduce the CT effect in polyimide molecules, the following strategies can be adopted from the perspective of molecular structure design: (1) Introduce alicyclic structures into the molecular backbone, such as cyclobutane, cyclohexane and other structures (CN116574260A, CN116425976A, CN116178388A); (2) Introduce fluorine-containing groups, such as structures containing -CF3 and -F (CN116478402A, CN116253879A, CN115894258A); (3) Introduce large side groups or non-coplanar structures (CN116535411A, CN104119532A, CN115557848A). Fluorinated groups can effectively suppress the Coulomb-Coulomb (CT) interaction in polyimides, improving the optical transparency of the film. However, fluorinated monomers are generally expensive, increasing the cost of commercializing polyimides. The introduction of fluorinated groups also degrades the thermal and mechanical properties of the film. Introducing alicyclic structures into the polyimide molecular chain can also weaken the CT interaction, thereby improving the optical transparency of the polyimide film. However, the alicyclic structure lacks thermal stability, leading to a decrease in the film's thermal properties. Achieving high optical transmittance and high temperature resistance in polyimide films simultaneously is often difficult; therefore, achieving a good balance between optical and thermodynamic properties has become a design challenge. Furthermore, the heat resistance of polyimide films is related to factors such as molecular chain rigidity and interchain interactions. The key to developing high-performance polyimide films is to design a reasonable molecular structure to balance the overall performance of the film. Summary of the Invention

[0004] In view of this, the present invention provides a diamine compound, polyimide, polyimide film and a method for preparing the same. The polyimide film prepared using the diamine compound provided by the present invention as a raw material has both heat resistance and transparency, and has good overall performance.

[0005] This invention provides a diamine compound with the structure of formula (I) or formula (II):

[0006]

[0007] Where X is selected from 0 or NH; n is selected from integers from 1 to 5.

[0008] In some specific implementations, n is 1, 2, 3, 4 or 5, preferably n is 1, 2 or 3, and more preferably n is 1.

[0009] This application introduces benzoazole (e.g., benzoxazole or benzimidazole) and aliphatic ring (e.g., cyclohexane) structures into the structure of diamine compounds, which can balance the rigidity and flexibility of molecular chains and charge transfer interactions. Polyimide films made from these materials have excellent heat resistance and transparency, and can be applied to optoelectronic displays and solar energy substrates.

[0010] In some specific implementations, the diamine compound with structure (I) has structures of formulas (I-1) and (I-2):

[0011]

[0012] Diamine compounds with the (I-1) and (I-2) structures have cis-trans structures, which can enhance intermolecular forces and improve the stability of the compounds.

[0013] In some specific implementations, equation (I-1) has the structures of (I-1a) and (I-1b):

[0014]

[0015]

[0016] Diamine compounds with structures of formula (I-1a) and (I-1b) have benzoxazole or benzimidazole structures, which can enhance the strength of intramolecular hydrogen bonds, thereby increasing molecular rigidity.

[0017] In some specific implementations, equation (I-1a) has the structures (I-1a-1) and (I-1a-2):

[0018]

[0019] In diamine compounds with the structure of formula (I-1a-1), the substitution positions of benzoxazole and cyclohexane are para-positions, which can reduce the steric hindrance effect between substituents and improve the reaction yield; in diamine compounds with the structure of formula (I-1a-2), the substitution positions of benzoxazole and cyclohexane are meta-positions, which can improve the reactivity of diamine compounds and shorten the polymerization time.

[0020] In some specific implementations, equation (I-1b) has the structures (I-1b-1) and (I-1b-2):

[0021]

[0022] In diamine compounds with the structure of formula (I-1b-1), the substitution positions of benzimidazole and cyclohexane are para-positions, which can reduce the steric hindrance effect between substituents and improve the reaction yield; in diamine compounds with the structure of formula (I-1b-2), the substitution positions of benzimidazole and cyclohexane are meta-positions, which can improve the reactivity of diamine compounds and shorten the polymerization time.

[0023] In some specific implementations, equation (I-2) has the structures of (I-2a) and (I-2b):

[0024]

[0025] Diamine compounds with the structures (I-2a) and (I-2b) have benzoxazole or benzimidazole structures, which can enhance the strength of intramolecular hydrogen bonds, thereby increasing molecular rigidity.

[0026] In some specific implementations, equation (I-2a) has the structures (I-2a-1) and (I-2a-2):

[0027]

[0028] In diamine compounds with the structure of formula (I-2a-1), the substitution positions of benzoxazole and cyclohexane are para-positions, which can reduce the steric hindrance effect between substituents and improve the reaction yield; in diamine compounds with the structure of formula (I-2a-2), the substitution positions of benzoxazole and cyclohexane are meta-positions, which can improve the reactivity of diamine compounds and shorten the polymerization time.

[0029] In some specific implementations, equation (I-2b) has the structures (I-2b-1) and (I-2b-2):

[0030]

[0031] In diamine compounds with the structure of formula (I-2b-1), the substitution positions of benzimidazole and cyclohexane are para-positions, which can reduce the steric hindrance effect between substituents and improve the reaction yield; in diamine compounds with the structure of formula (I-2b-2), the substitution positions of benzimidazole and cyclohexane are meta-positions, which can improve the reactivity of diamine compounds and shorten the polymerization time.

[0032] In some specific implementations, the diamine compound with structure (II) has structures of formula (II-1) and (II-2):

[0033]

[0034] Diamine compounds with formulas (II-1) and (II-2) have cis-trans structures, which can enhance intermolecular forces and improve the stability of the compounds.

[0035] In some specific implementations, equation (II-1) has the structures of (II-1a) and (II-1b):

[0036]

[0037] Diamine compounds with structures of formula (II-1a) and (II-1b) have benzoxazole or benzimidazole structures, which can enhance the strength of intramolecular hydrogen bonds, thereby increasing molecular rigidity.

[0038] In some specific implementations, equation (II-1a) has the structures (II-1a-1) and (II-1a-2):

[0039]

[0040] In diamine compounds with the structure of formula (II-1a-1), the substitution positions of benzoxazole and cyclohexane are para-positions, which can reduce the steric hindrance effect between substituents and improve the reaction yield; in diamine compounds with the structure of formula (II-1a-2), the substitution positions of benzoxazole and cyclohexane are meta-positions, which can improve the reactivity of diamine compounds and shorten the polymerization time.

[0041] In some specific implementations, equation (II-1b) has the structures (II-1b-1) and (II-1b-2):

[0042]

[0043] In diamine compounds with the structure of formula (II-1b-1), the substitution positions of benzimidazole and cyclohexane are para-positions, which can reduce the steric hindrance effect between substituents and improve the reaction yield; in diamine compounds with the structure of formula (II-1b-2), the substitution positions of benzimidazole and cyclohexane are meta-positions, which can improve the reactivity of diamine compounds and shorten the polymerization time.

[0044] In some specific implementations, equation (II-2) has the structures of (II-2a) and (II-2b):

[0045]

[0046]

[0047] Diamine compounds with structures of formula (II-2a) and (II-2b) have benzoxazole or benzimidazole structures, which can enhance the strength of intramolecular hydrogen bonds, thereby increasing molecular rigidity.

[0048] In some specific implementations, equation (II-2a) has the structures of (II-2a-1) and (II-2a-2):

[0049]

[0050] In diamine compounds with the structure of formula (II-2a-1), the substitution positions of benzoxazole and cyclohexane are para-positions, which can reduce the steric hindrance effect between substituents and improve the reaction yield; in diamine compounds with the structure of formula (II-2a-2), the substitution positions of benzoxazole and cyclohexane are meta-positions, which can improve the reactivity of diamine compounds and shorten the polymerization time.

[0051] In some specific implementations, equation (II-2b) has the structures of (II-2b-1) and (II-2b-2):

[0052]

[0053] In diamine compounds with the structure of formula (II-2b-1), the substitution positions of benzimidazole and cyclohexane are para-positions, which can reduce the steric hindrance effect between substituents and improve the reaction yield; in diamine compounds with the structure of formula (II-2b-2), the substitution positions of benzimidazole and cyclohexane are meta-positions, which can improve the reactivity of diamine compounds and shorten the polymerization time.

[0054] This invention also provides a method for preparing a diamine compound, comprising:

[0055] A cycloalkane compound having the structure of formula (III), an aniline compound having the structure of formula (IV) or (V), and a reducing agent undergo a first reaction in an inert atmosphere, followed by a second reaction with a dehydrating agent to obtain a diamine compound as shown in formula (I) or (II).

[0056]

[0057] Wherein, R3 is a hydroxyl group, and R1 and R2 are independently acyl chloride, carboxyl group or amino group; or R3 is an amino group, and R1 and R2 are independently acyl chloride, carboxyl group or hydroxyl group;

[0058] X is selected from O or NH;

[0059] n is an integer selected from 1 to 5.

[0060] This invention uses cycloalkane compounds with the structure of formula (III) and aniline compounds with the structure of formula (IV) or (V) as raw materials. Under a reducing agent and an inert atmosphere, a first reaction occurs, activating the reactants. Then, a dehydrating agent is added to initiate a second reaction, during which the amino group and R3 in the aniline compound condense with R1 or R2 in the cycloalkane compound to form a ring, yielding a diamine compound. Specifically, the diamine compound with the structure of formula (I) or (II) can be synthesized according to the following route:

[0061]

[0062] In formula (IV) or (V), R3 is selected from hydroxyl or amino groups; correspondingly, in formula (III), R1 or R2 is selected from groups capable of undergoing condensation ring formation reactions with hydroxyl or amino groups, such as acyl chloride, carboxyl, amino, or hydroxyl groups. Specifically, R3 is a hydroxyl group, and R1 and R2 are independently acyl chloride, carboxyl, or amino groups; or R3 is an amino group, and R1 and R2 are independently acyl chloride, carboxyl, or hydroxyl groups. In formula (III), n is an integer from 1 to 5, for example, it can be 1, 2, 3, 4, or 5.

[0063] The above reaction is carried out in a solvent, which includes, but is not limited to, one or more of boric acid, concentrated sulfuric acid, and polyphosphoric acid, preferably polyphosphoric acid. In this invention, the solvent is first heated, then a cycloalkane compound and a reducing agent are added. An aniline compound is then added in batches under an inert atmosphere. After the addition is complete, the mixture is continuously stirred to complete the first reaction.

[0064] In some specific implementations, the solvent is first heated to 40–80°C, preferably 45–75°C, more preferably 50–70°C, and then the reactants and catalyst are added to carry out the reaction. In some specific implementations, the mass ratio of the solvent to the cycloalkane compound is 15–30:1, preferably 20–30:1. In some specific implementations, the molar ratio of the cycloalkane compound to the aniline compound is 1:0.5–2, preferably 1:1–2. In some specific implementations, the reducing agent includes, but is not limited to, tin powder and stannous chloride, preferably stannous chloride, and the molar ratio of the reducing agent to the cycloalkane compound is 1–10:100, preferably 3–8:100. In some specific implementations, the first reaction time is 5–10 hours, preferably 6–9 hours, more preferably 7–8 hours. In some specific implementations, the inert atmosphere is preferably nitrogen or argon, more preferably nitrogen.

[0065] After the first reaction is completed, a dehydrating agent is added to the reaction system to carry out a second reaction. After the reaction is complete, a diamine compound is obtained.

[0066] In some specific implementations, the dehydrating agent includes, but is not limited to, phosphorus pentoxide, and the molar ratio of the dehydrating agent to the cycloalkane compound is 0.5–2:1, preferably 0.6–1.5:1, and more preferably 0.75–1.25:1. In some specific implementations, the temperature of the second reaction is 170–220°C, preferably 180–210°C, and more preferably 190–200°C. In some specific implementations, the time for the second reaction is 5–16 hours, preferably 7–14 hours, and more preferably 8–10 hours.

[0067] In some specific implementations, the process of obtaining the diamine compound further includes post-processing, which includes cooling, adjusting the pH of the solution, removing impurities, and drying.

[0068] In some specific implementations, the cooling temperature is preferably room temperature. In some specific implementations, the solution pH is preferably adjusted to 7-10, more preferably 8-9. In some specific implementations, the reagent used to adjust the solution pH is a saturated sodium carbonate solution. In some specific implementations, the impurity removal method includes, but is not limited to, filtration and washing. In some specific implementations, the solvent used for washing can be water or ethanol, and washing is performed 1-5 times, preferably 2-4 times. This product does not have any special limitations on the methods of filtration, washing, and drying.

[0069] This application utilizes a multi-level molecular design to simultaneously prepare high-performance transparent polyimide (CPI) films. A series of diamines containing benzoazole and aliphatic ring structures were synthesized. Firstly, the introduction of benzoazole structures increases the rigidity and linearity of the molecular chain, endowing the film with excellent heat resistance. Secondly, the introduction of aliphatic ring structures suppresses CT (transient catalytic cracking) in the molecular chain, improving the film's optical properties. This application combines the advantages of each monomer through copolymerization, controlling the overall performance of the film. The resulting high-performance CPI films have broad application prospects in flexible electronics and spacecraft thermal management.

[0070] The present invention also provides a polyimide having a structure of formula (VI) or formula (VII):

[0071]

[0072] Where k is the repeating unit in the polymer molecule. The proportion, 0≤k≤0.5;

[0073] X is selected from O or NH;

[0074] n is an integer selected from 1 to 5;

[0075] The Ar1 is selected from C6 to C6. 30 Aromatic groups, substituted C6-C 30 Aromatic groups, C4-C 30 cycloalkyl, substituted C4-C 30 cycloalkyl, C6-C 30 heteroaryl or substituted C6-C 30 heteroaryl groups;

[0076] The Ar2 is selected from C6~C6. 30 Aromatic groups, substituted C6-C 30 Aromatic groups, C4-C 30 cycloalkyl or substituted C4-C 30 cycloalkyl, C6-C 30 heteroaryl or substituted C6-C 30 Mixed aromatic compounds.

[0077] In some specific implementations, n is 1, 2, 3, 4 or 5, preferably n is 1, 2 or 3, and more preferably n is 1.

[0078] In some specific implementations, the aromatic group refers to a compound having a benzene ring structure, including but not limited to monophenyl aromatic groups and polyphenyl aromatic groups. In some specific implementations, the cycloalkyl group includes but is not limited to monocyclic and polycyclic structures. In some specific implementations, the heteroaryl group includes but is not limited to monosubstituted monoaromatic rings, monosubstituted polyaromatic rings, polysubstituted polyaromatic rings, and polysubstituted polyaromatic rings.

[0079] Specifically, the polyimide structure can be the following:

[0080]

[0081] This application uses diamine compounds containing both benzoazole and aliphatic ring structures as raw materials to prepare polyimides, which improves the mechanical properties, thermodynamic properties and oxidative stability of the polyimide molecular chain, while increasing the free volume between molecular chains and reducing intramolecular and intermolecular charge transfer interactions.

[0082] In some specific implementations, the Ar1 is preferably structured as follows:

[0083]

[0084] More preferably, the following structure is preferred:

[0085]

[0086] In some specific implementations, the Ar2 is preferably structured as follows:

[0087]

[0088] Wherein, Y is selected from O, S, SO2, CO, or

[0089] m is an integer from 1 to 4, preferably an integer from 1 to 3, and more preferably 1;

[0090] R1 and R2 are selected from H, C1-C6 alkyl groups, halogen-substituted C1-C6 alkyl groups, preferably H, fluorine-substituted C1-C6 alkyl groups, and more preferably trifluoromethyl.

[0091] Z is selected from O, N, or S.

[0092] This invention provides a method for preparing polyimide, comprising:

[0093] a) A diamine compound of formula (I) or formula (II), an optional diamine compound of formula (a) and a dianhydride compound of formula (b) are subjected to a polymerization reaction to obtain polyamic acid;

[0094] b) The polyamic acid is subjected to an imidization reaction to obtain a polyimide;

[0095]

[0096] The diamine compounds represented by formulas (I) and (II) have the same selection range as those represented by formulas (I) and (II) above, and will not be repeated here;

[0097] In the diamine compound shown in formula (a), the selection range of Ar2 is the same as that of the compounds with the structure shown in formula (VI) or formula (VII) above, and will not be repeated here;

[0098] In the diamine compound shown in formula (b), the selection range of Ar1 is the same as that of the compounds with the structures shown in formula (VI) or (VII) above, and will not be repeated here.

[0099] In some specific implementations, the diamine compound represented by formula (a) is preferably selected from the following structures:

[0100]

[0101] Wherein, Y is selected from O, S, SO2, CO, or

[0102] m is an integer from 1 to 4, preferably an integer from 1 to 3, and more preferably 1;

[0103] R1 and R2 are selected from H, C1-C6 alkyl groups, halogen-substituted C1-C6 alkyl groups, preferably H, fluorine-substituted C1-C6 alkyl groups, and more preferably trifluoromethyl.

[0104] Z is selected from O, N, or S.

[0105] In some specific implementations, the dianhydride compound represented by formula (b) preferably has the following structure:

[0106]

[0107] More preferably, the following structure is preferred:

[0108]

[0109] In this invention, a diamine compound of formula (I) or formula (II), optionally a diamine compound of formula (a), and a dianhydride compound of formula (b) are dissolved in a solvent and stirred continuously in an inert atmosphere. The amino group in the diamine compound reacts with the anhydride in the dianhydride compound to produce polyamic acid. The polyamic acid undergoes an imidization reaction under the action of an imidizing agent, followed by dehydration and cyclization, to produce polyimide.

[0110] The polymerization reaction described in this invention is carried out in a solvent, which is a polar aprotic solvent, including but not limited to one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone, preferably N,N-dimethylacetamide. In this invention, the total amount of a diamine compound, i.e., the diamine compound shown in formula (I) or (II) and the diamine compound shown in formula (a), and a dianhydride compound are dissolved in a solvent under an inert atmosphere. The mixture is continuously stirred, causing the amino group in the diamine compound to dehydrate and condense with the anhydride in the dianhydride compound, resulting in a polyamic acid solution.

[0111] In some specific implementations, the molar ratio of the diamine compound to the dianhydride compound in the polymerization reaction is 0.9:1 to 1:0.9, preferably 0.95:1 to 1:0.95. In some specific implementations, the molar ratio of the diamine compound represented by formula (I) or formula (II) to the diamine compound represented by formula (a) is preferably 1 to 2:0 to 1, more preferably 1 to 2:1. In some specific implementations, the temperature of the polymerization reaction is 0 to 30°C, preferably 0 to 25°C, more preferably 0 to 20°C. In some specific implementations, the time of the polymerization reaction is 6 to 108 h, preferably 10 to 100 h, more preferably 20 to 80 h.

[0112] After obtaining the polyamic acid solution, it is imidized. Specifically, an imidizing agent can be added to the obtained polyamic acid solution, and the mixture can be stirred continuously for 6 to 24 hours, preferably 7 to 20 hours, and more preferably 8 to 15 hours, to imidize the polyamic acid into polyimide.

[0113] In some specific implementations, the reagents for the imidization reaction are acetic anhydride and pyridine, and the molar ratio of the acetic anhydride to the pyridine is 1:1 to 10, preferably 1:1 to 5, and more preferably 1:1 to 3. In some specific implementations, the molar ratio of the reagents for the imidization reaction to the total amount of the diamine compound, i.e., the diamine compound represented by formula (I) or (II) and the diamine compound represented by formula (a), is 0.5 to 3:1, preferably 0.8 to 2.5:1, and more preferably 1 to 2:1.

[0114] In some specific implementations, the obtained polyimide is further subjected to post-processing, which includes precipitation, impurity removal, and drying.

[0115] In some specific implementations, the precipitation includes immersing the polyimide solution in a polar solvent to precipitate a solid. In some specific implementations, the polar solvent includes, but is not limited to, methanol. In some specific implementations, the impurity removal includes, but is not limited to, filtration and washing. This product does not have any particular limitations on the methods of precipitation, impurity removal, and drying.

[0116] In some specific implementations, this application can also prepare polyimide in a one-step process, the specific process of which is as follows:

[0117] Polyimide is obtained by polymerizing dianhydride and diamine in a phenolic solvent under an inert gas atmosphere.

[0118] In some specific implementations, the dianhydride and diamine are as described above, and will not be repeated here. The phenolic solvent includes, but is not limited to, m-cresol or m-chlorophenol, the polymerization temperature is 180–210°C, and the polymerization time is 6–72 h.

[0119] This invention provides a polyimide film prepared from polyimides having the structure of formula (VI) or formula (VII). The benzoxazole structure in the polyimide with the structure of formula (VI) or formula (VII) can improve the rigidity and linearity of the molecular chain, giving the film excellent heat resistance; the alicyclic structure can suppress the CT effect in the molecular chain, improving the optical properties of the film.

[0120] This application does not impose any particular restrictions on the preparation method of the polyimide film. For example, the prepared polyimide can be dissolved, cast into a film, and then dried. This application does not impose any particular restrictions on the solvent used to dissolve the polyimide, nor on the temperature during the drying process.

[0121] In some specific implementations, after obtaining the polyimide in this application, the polyimide solution can be directly cast into a film and dried to prepare a polyimide film without post-processing. The specific process is similar to that described above, and will not be repeated here.

[0122] This application introduces benzoazole and aliphatic ring structures into the diamine compound structure, which can balance the rigidity and flexibility of the molecular chain and the charge transfer interaction. The polyimide film prepared using this as a raw material has excellent heat resistance and transparency, and can be applied in optoelectronic displays and solar energy substrates. Experimental results show that the polyimide film prepared by polymerizing the diamine compound provided by this invention has both heat resistance and transparency, and has good overall performance. Attached Figure Description

[0123] Figure 1 The diamine compound in Example 1 of this invention 1 H NMR spectrum;

[0124] Figure 2 The diamine compound in Example 2 of this invention 1 H NMR spectrum;

[0125] Figure 3DMA curves of the polyimide films prepared in Examples 5 and 8 of this invention;

[0126] Figure 4 The ultraviolet-visible light transmittance curves are for the polyimide films prepared in Examples 5 and 8 of this invention. Detailed Implementation

[0127] It should be understood that the expression “one or more of…” individually includes each of the objects described after the expression, as well as various different combinations of two or more of the described objects, unless otherwise understood from the context and usage. The expression “and / or” combined with three or more described objects should be understood to have the same meaning, unless otherwise understood from the context.

[0128] The terms “including,” “having,” or “containing,” including the use of their grammatical synonyms, should generally be understood as open-ended and non-restrictive, for example, not excluding other unstated elements or steps, unless otherwise specifically stated or understood from the context.

[0129] It should be understood that the order of the steps or the order in which certain actions are performed is not important as long as the invention remains operational. Furthermore, two or more steps or actions can be performed simultaneously.

[0130] The use of any and all instances or exemplary language such as “e.g.” or “including” in this document is merely intended to better illustrate the invention and is not intended to limit the scope of the invention unless the claims are made. No language in this specification should be construed as indicating that any unclaimed element is essential to the practice of the invention.

[0131] Furthermore, the numerical ranges and parameters used to define the present invention are approximate values, and the relevant values ​​in the specific embodiments have been presented as precisely as possible. However, any value inevitably contains standard deviations due to individual test methods. Therefore, unless explicitly stated otherwise, it should be understood that all ranges, quantities, values, and percentages used in this disclosure are modified with the word "approximately." Here, "approximately" generally means an actual value within plus or minus 10%, 5%, 1%, or 0.5% of a particular value or range.

[0132] The present invention is further illustrated below with reference to the embodiments. The scope of protection of the present invention is not limited to the following embodiments.

[0133] Example 1

[0134] Under nitrogen protection, polyphosphoric acid (1000 g), trans-1,4-cyclohexanedicarboxylic acid (34.436 g, 0.2 mol), and stannous chloride dihydrate (4.513 g, 0.02 mol) were added to a 3 L three-necked flask equipped with a mechanical stirrer. The mixture was then heated to 60 °C, and 2,4-diaminophenol dihydrochloric acid (78.824 g, 0.4 mol) was added in batches. After the addition was complete, the mixture was stirred for 5–10 hours until HCl gas ceased to volatilize. Phosphorus pentoxide (28.388 g, 0.2 mol) was added to the flask, and stirring continued for 0.5 hours. The temperature was slowly increased to 150 °C and reacted for 3 hours, followed by increasing the temperature to 200 °C and reacting for 10 hours. After the reaction was complete, the solution was cooled to room temperature. The pH of the solution was adjusted to approximately 8 using saturated sodium carbonate solution. The solution was washed three times with water and three times with ethanol, respectively. After filtration and drying, the crude product was obtained. After purification, the diamine monomer I-1a-1 was obtained as a pale yellow solid with a yield of 77%. 1 H NMR spectrum as shown Figure 1 As shown.

[0135]

[0136] The purified product was characterized by nuclear magnetic resonance (NMR), and the 1H NMR spectrum results are as follows: 1 H NMR (500MHz, DMSO-d6) δ = 7.28 (dd, J = 8.6, 7.5, 2H), 6.78 (dd, J = 10.6, 2.2, 2H), 6.58 (ddd, J = 9.7, 8.6, 2.2, 2H), 3.06 (m,2H),2.22(m,2H),2.05(dt,J=13.2,5.7,2H),1.94(ddd,J=11.6,8.0,5.0,2H),1.74(dq,J=13.2,10.5,9.9,2H).

[0137] Example 2

[0138] Under nitrogen protection, polyphosphoric acid (1000 g), cis-1,4-cyclohexanedicarboxylic acid (34.436 g, 0.2 mol), and stannous chloride dihydrate (4.513 g, 0.02 mol) were added to a 3 L three-necked flask equipped with a mechanical stirrer. The mixture was then heated to 60 °C, and 2,4-diaminophenol dihydrochloric acid (78.824 g, 0.4 mol) was added in batches. After the addition was complete, the mixture was stirred for 5–10 hours until HCl gas ceased to volatilize. Then, phosphorus pentoxide (28.388 g, 0.2 mol) was added, and the mixture was stirred for 0.5 hours. The solution was slowly heated to 150 °C and stirred for 3 hours, then heated to 200 °C and reacted for 10 hours. After the reaction was complete, the solution was cooled to room temperature. The pH of the solution was then adjusted to approximately 8 using saturated sodium carbonate solution. The solution was washed three times with water and three times with ethanol, then filtered and dried to obtain the crude product. After purification, the diamine monomer I-2a-1 was obtained as a pale yellow solid with a yield of 79%. 1 H NMR spectrum as shown Figure 2 As shown.

[0139]

[0140] The obtained product was characterized by nuclear magnetic resonance (NMR), and the 1H NMR spectrum results are as follows: 1 H NMR (500MHz, DMSO-d6) δ=7.28(t,J=8.0,2H),6.78(dd,J=10.5,2.2,2H),6.58(td,J=9.7,9.2,2.3,2H),4.99(d,J=8.1,4H),3.19(dq,J=8 .2,4.4,4.0,1H),3.03-2.94(m,1H),2.22(hept,J=4.8,3.7,2H),2.05(dt,J=13.4,5.6,1H),1.98-1.89(m,1H),1.74(td,J=9.2,3.3,2H).

[0141] Example 3

[0142] Under nitrogen protection, 3.554 g (8 mmol) of 4,4'-(hexafluoroisopropylidene) phthalic anhydride 6FDA and 25 g of N,N-dimethylacetamide were added to a 100 mL three-necked flask equipped with a mechanical stirrer. After the dianhydride dissolved, diamine I-1a-1 (2.788 g, 8 mmol) was added, and the reaction was carried out at 0 °C for 72 h. Then, acetic anhydride (0.816 g, 8 mmol) and pyridine (15.8 g, 20 mmol) were added, and stirring was continued for 10 h to obtain crude polyimide. The crude product was transferred to methanol to precipitate, filtered, the cell walls were broken, and dried to obtain polyimide powder. The polyimide powder was redissolved in N,N-dimethylacetamide solvent to achieve a solid content of 15 wt%. A uniform polyimide solution was coated onto a clean, flat glass plate. Residual solvent was removed by drying at 80℃ for 5 hours, 150℃ for 1 hour, 250℃ for 1 hour, and 300℃ for 1 hour in an oven. The dried polyimide was then placed in hot water to allow the film to peel off automatically. The film was then placed in an oven and dried at 100℃ for 5 hours to remove residual moisture. The resulting transparent polyimide film was then obtained.

[0143] Example 4

[0144] Under nitrogen protection, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride H-PMDA (1.793 g, 8 mmol) and N,N-dimethylacetamide (18 g) were added to a 100 mL three-necked flask equipped with a mechanical stirrer. After the dianhydride dissolved, diamine I-1a-1 (2.788 g, 8 mmol) was added, and the reaction was carried out at 0 °C for 72 h. Then, acetic anhydride (0.816 g, 8 mmol) and pyridine (15.8 g, 20 mmol) were added, and stirring was continued for 10 h to obtain crude polyimide. The crude product was transferred to methanol to precipitate, filtered, the cell walls were broken, and dried to obtain polyimide powder. The polyimide powder was redissolved in N,N-dimethylacetamide solvent to achieve a solid content of 15 wt%. A uniform polyimide solution was coated onto a clean, flat glass plate. Residual solvent was removed by drying at 80℃ for 5 hours, 150℃ for 1 hour, 250℃ for 1 hour, and 300℃ for 1 hour in an oven. The dried polyimide was then placed in hot water to allow the film to peel off automatically. The film was then placed in an oven and dried at 100℃ for 5 hours to remove residual moisture. The resulting transparent polyimide film was then obtained.

[0145] Example 5

[0146] Under nitrogen protection, cyclobutanetetracarboxylic acid dianhydride (CBDA) (1.569 g, 8 mmol) and N,N-dimethylacetamide (17 g) were added to a 100 mL three-necked flask equipped with a mechanical stirrer. After the dianhydride dissolved, diamine I-1a-1 (2.788 g, 8 mmol) was added, and the reaction was carried out at 0 °C for 72 h. Then, acetic anhydride (0.816 g, 8 mmol) and pyridine (15.8 g, 20 mmol) were added, and stirring was continued for 10 h to obtain crude polyimide. The crude product was transferred to methanol to precipitate, filtered, the cell walls were broken, and dried to obtain polyimide powder. The polyimide powder was redissolved in N,N-dimethylacetamide solvent to a solid content of 15 wt%. The homogeneous polyimide solution was coated onto a clean and flat glass plate and dried in an oven at 80 °C / 5 h, 150 °C / 1 h, 250 °C / 1 h, and 300 °C / 1 h to remove residual solvent. The dried polyimide is placed in hot water to allow the film to peel off automatically. The film is then placed in an oven and dried at 100°C for 5 hours to remove residual moisture. After removal, a transparent polyimide film is obtained.

[0147] Example 6

[0148] Under nitrogen protection, 3.554 g (8 mmol) of 4,4'-(hexafluoroisopropylidene) phthalic anhydride 6FDA and 25 g of N,N-dimethylacetamide were added to a 100 mL three-necked flask equipped with a mechanical stirrer. After the dianhydride dissolved, diamine I-2a-1 (2.788 g, 8 mmol) was added, and the reaction was carried out at 0 °C for 72 h. Then, acetic anhydride (0.816 g, 8 mmol) and pyridine (15.8 g, 20 mmol) were added, and stirring was continued for 10 h to obtain crude polyimide. The crude product was transferred to methanol to precipitate, filtered, the cell walls were broken, and dried to obtain polyimide powder. The polyimide powder was redissolved in N,N-dimethylacetamide solvent to achieve a solid content of 15 wt%. A uniform polyimide solution was coated onto a clean, flat glass plate. Residual solvent was removed by drying at 80℃ for 5 hours, 150℃ for 1 hour, 250℃ for 1 hour, and 300℃ for 1 hour in an oven. The dried polyimide was then placed in hot water to allow the film to peel off automatically. The film was then placed in an oven and dried at 100℃ for 5 hours to remove residual moisture. The resulting transparent polyimide film was then obtained.

[0149] Example 7

[0150] Under nitrogen protection, 1,2,4,5-cyclohexanetetracarboxylic acid dianhydride H-PMDA (1.793 g, 8 mmol) and N,N-dimethylacetamide (18 g) were added to a 100 mL three-necked flask equipped with a mechanical stirrer. After the dianhydride dissolved, diamine I-2a-1 (2.788 g, 8 mmol) was added, and the reaction was carried out at 0 °C for 72 h. Then, acetic anhydride (0.816 g, 8 mmol) and pyridine (15.8 g, 20 mmol) were added, and stirring was continued for 10 h to obtain crude polyimide. The crude product was transferred to methanol to precipitate, filtered, the cell walls were broken, and dried to obtain polyimide powder. The polyimide powder was redissolved in N,N-dimethylacetamide solvent to achieve a solid content of 15 wt%. A uniform polyimide solution was coated onto a clean, flat glass plate. Residual solvent was removed by drying at 80℃ for 5 hours, 150℃ for 1 hour, 250℃ for 1 hour, and 300℃ for 1 hour in an oven. The dried polyimide was then placed in hot water to allow the film to peel off automatically. The film was then placed in an oven and dried at 100℃ for 5 hours to remove residual moisture. The resulting transparent polyimide film was then obtained.

[0151] Example 8

[0152] Under nitrogen protection, cyclobutanetetracarboxylic acid dianhydride (CBDA) (1.569 g, 8 mmol) and N,N-dimethylacetamide (17 g) were added to a 100 mL three-necked flask equipped with a mechanical stirrer. After the dianhydride dissolved, diamine I-2a-1 (2.788 g, 8 mmol) was added, and the reaction was carried out at 0 °C for 72 h. Then, acetic anhydride (0.816 g, 8 mmol) and pyridine (15.8 g, 20 mmol) were added, and stirring was continued for 10 h to obtain crude polyimide. The crude product was transferred to methanol to precipitate, filtered, the cell walls were broken, and dried to obtain polyimide powder. The polyimide powder was redissolved in N,N-dimethylacetamide solvent to a solid content of 15 wt%. The homogeneous polyimide solution was coated onto a clean and flat glass plate and dried in an oven at 80 °C / 5 h, 150 °C / 1 h, 250 °C / 1 h, and 300 °C / 1 h to remove residual solvent. The dried polyimide is placed in hot water to allow the film to peel off automatically. The film is then placed in an oven and dried at 100°C for 5 hours to remove residual moisture. After removal, a transparent polyimide film is obtained.

[0153] The polyimide films prepared in Examples 5 and 8 were subjected to dynamic mechanical analysis and UV-Vis transmittance analysis, and the results are as follows: Figure 3 and Figure 4 As shown. Figure 3 The two curves in the upper half represent the storage modulus of Examples 5 and 8 at different temperatures, respectively, while the two curves in the lower half represent the loss tangent of Examples 5 and 8 at different temperatures. Figure 4The two curves represent the light transmittance of Examples 5 and 8 under different wavelengths of light, respectively. Figure 3 and Figure 4 It can be seen that the glass transition temperatures of the polyimide films prepared in Examples 5 and 8 are 400℃ and 404℃, respectively, and the transmittance at 450nm is 83.7% and 83.5%, respectively. This indicates that the polyimide films prepared by this method achieve a good balance between heat resistance and transparency, which is beneficial for their application in fields such as transparent flexible substrates and transparent circuit boards.

[0154] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. Polyimides having a structure of formula (VI) or formula (VII): Formula (VI); Equation (VII).

2. A method for preparing the polyimide according to claim 1, characterized in that, include: a) A diamine compound of formula (I-1a-1) or (I-2a-1) and a dianhydride compound of formula (b) are polymerized to obtain polyamic acid; b) The polyamic acid undergoes an imidization reaction to obtain polyimide; ； ； （b）； Ar1 is selected from cyclobutyl.

3. The method for preparing polyimide according to claim 2, characterized in that, In step a), the molar ratio of the diamine compound represented by formula (I-1a-1) or formula (I-2a-1) to the dianhydride compound is 0.9:1 to 1:0.9, the reaction temperature is 0 to 30°C, and the reaction time is 6 to 108 h. The solvent used in the reaction is a polar aprotic solvent; The solid content of the reaction is 5 wt% to 25 wt%. The imidizing reagents in step b) of the imidization reaction are acetic anhydride and pyridine, and the molar ratio of the reagents to the diamine compound shown in formula (I-1a-1) or formula (I-2a-1) is 0.5 to 3:

1. The imidization reaction takes 6 to 24 hours.

4. A polyimide film prepared from the polyimide according to claim 1.

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