Soluble polyimide molecular composite material, preparation method, film preparation method and application

Abstract

The invention relates to a soluble polyimide molecular composite material, a preparation method of the soluble polyimide molecular composite material, a film preparation method and application of the soluble polyimide molecular composite material. The diamine monomer and aromatic diacyl chloride are subjected to in-situ polymerization reaction among polyimide molecular chains to form rigid rod-shaped small-molecule aromatic polyamide, the polyimide molecular composite material with the polyimide molecular chains arranged in order is obtained, the molar ratio of the diamine monomer to the aromatic diacyl chloride meets (x-1) / (x + 1), and x is the theoretical polymerization degree of the aromatic polyamide. Rigid rod-shaped small-molecule polymer molecules are dispersed in a soluble polyimide matrix, so that ordered and directional arrangement among soluble polyimide molecular chains is promoted, and on the basis of keeping excellent optical transparency of soluble polyimide, thermal stability, dielectricity and strength performance are optimized; and the application of the soluble polyamide molecular composite material in the field of flexible display can be expanded.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of polyimide material preparation and application, and particularly relates to a soluble polyimide molecular composite material, a preparation method thereof, a film preparation method and application. BACKGROUND

[0002] Flexible transparent substrate is an important component of flexible transparent electronic devices.

[0003] With the rapid development of flexible display and wearable electronics, the colorless flexible transparent substrate material is required to be lightweight, bendable, high transparent, high thermal stability (glass transition temperature Tg≥200℃), high mechanical strength, excellent dielectric properties, and solution processable.

[0004] However, traditional materials are difficult to meet the above requirements at the same time, for example, inorganic glass lacks flexibility, and PC, PET, PES, PEN, etc. have low glass transition temperature.

[0005] Polyimide (PI) is considered as a high-performance candidate material in extreme environments such as aerospace, optoelectronic devices, and flexible display due to the imide ring in the main chain. However, the performance of PI varies with the structure of the monomer: aliphatic PI has good solubility and high transparency, but weak thermal stability and mechanical properties; aromatic PI has excellent thermal stability, such as high Tg, low CTE, and high decomposition temperature, but the conjugated backbone forms a charge transfer complex (CTC) between the electron-donating diamine and the electron-accepting dianhydride, resulting in absorption in the visible region, presenting yellow-brown color, which limits its application in the display field.

[0006] The common strategies for developing colorless transparent PI include introducing non-coplanar / asymmetric structure, grafting large side groups, containing fluorine or strong electron-withdrawing groups, adding inorganic fillers, etc., to reduce the chain packing density and increase the interchain distance, thereby inhibiting CTC and improving transmittance. However, the above methods significantly weaken the thermal stability of PI due to the expansion of the interchain distance.

[0007] Therefore, it is still a challenge to prepare PI with a balance of "high transparency, low CTE, high strength, high heat resistance, and insulation". SUMMARY

[0008] The present application aims to provide a soluble polyimide molecular composite, a film and a preparation method, by dispersing rigid rod-like small molecule polymer molecules in a soluble polyimide matrix, forming strong intermolecular interaction between the rigid rod-like small molecule polymer and the soluble polyimide matrix, weakening the charge transfer between the soluble polyimide molecular chains, promoting the order and directional arrangement of the soluble polyimide molecular chains, optimizing the thermal stability, dielectric property and strength performance on the basis of maintaining the excellent optical transparency of the soluble polyimide, so that the soluble polyimide molecular composite can expand its application in the flexible display field.

[0009] The preparation method of the soluble polyimide molecular composite provided by the present application comprises the following steps: The diamine monomer and the aromatic dichloride are sequentially added to the soluble polyimide solution, and the diamine monomer and the aromatic dichloride are in-situ polymerized between the polyimide molecular chains to form rigid rod-like small molecule aromatic polyamide, thereby obtaining a polyimide molecular composite with ordered polyimide molecular chains, wherein the molar ratio of the diamine monomer to the aromatic dichloride satisfies (x-1) / (x+1), and x is the theoretical polymerization degree of the aromatic polyamide.

[0010] Further, the value range of x is [10, 25]. The minimum polymerization degree of the aromatic polyamide is limited to 10, otherwise, if the polymerization degree is too low, unreacted monomers may remain as impurities, which will damage the optical transparency and mechanical properties of the soluble polyimide molecular composite.

[0011] Further, the molar ratio of the diamine monomer to the soluble polyimide ranges from 0.11 to 0.43.

[0012] Further, the in-situ polymerization reaction conditions of the diamine monomer and the aromatic dichloride between the polyimide molecular chains are as follows: Sealed environment Reaction temperature: room temperature Reaction time: 4h~6h.

[0013] Further, the preparation method of the soluble polyimide comprises the following steps: Under the protection of nitrogen, the diamine monomer is dissolved in a polar aprotic solvent, the dianhydride monomer is added in batches, then the end-capping agent is added, and the stirring reaction is continued to generate a polyamide acid solution, wherein the molar ratio of the diamine monomer to the total dianhydride monomer satisfies (0.98~1.02):1; An acylation reagent is added to the polyamide acid solution, and the reaction is sealed to generate a polyimide solution; The polyimide solution is slowly poured into excess deionized water to precipitate fibrous soluble polyimide.

[0014] Further, the soluble polyimide fibers are obtained by washing, filtering and vacuum drying the precipitated fibers, and then taking out the soluble polyimide fibers.

[0015] Compared with the prior art, the preparation method of the soluble polyimide molecular composite material provided by the application realizes synchronous improvement of mechanical strength, dimensional stability, heat resistance and electrical insulation without sacrificing optical transparency by in-situ polymerization of rigid rod-like small molecule polyamide PA as a reinforcing phase between the soluble polyimide molecular chains, and by controlling the molecular weight of the polyamide and the loading amount, so that strong molecular interaction is formed between the amide bonds of the rigid rod-like small molecule polyamide PA and the soluble polyimide molecules, the orientation of the soluble polyimide matrix molecules is induced, and the order and directionality of the soluble polyimide molecular chains are further improved. Meanwhile, by precisely controlling the non-stoichiometric monomer feeding ratio of the diamine monomer and the aromatic dichloride for in-situ polymerization, the rigid rod-like small molecule polyamide PA with more end groups is formed, the action of the carbonyl interaction sites of the rigid rod-like small molecule polyamide PA and the soluble polyimide is further strengthened, and the order and directionality of the soluble polyimide molecular chains are further improved.

[0016] Meanwhile, the application provides a soluble polyimide molecular composite material prepared according to the preparation method of the soluble polyimide molecular composite material according to any one of the above, and the structural formula of the soluble polyimide molecular composite material is as follows:

[0017] wherein n and x are positive integers, n represents the polymerization degree of the soluble polyimide, x represents the theoretical polymerization degree of the aromatic polyamide, 50 ≤ n ≤ 200, R1 represents a diamine monomer with an electron donor group, R2 represents a dianhydride monomer with an electron acceptor group, R3 represents a diamine monomer, and R4 represents an aromatic dichloride.

[0018] Compared with the prior art, the soluble polyimide molecular composite material provided by the application has excellent optical transparency, and synchronous improvement of mechanical strength, dimensional stability, heat resistance and electrical insulation.

[0019] Meanwhile, the application provides a preparation method of a soluble polyimide molecular composite material film, and the soluble polyimide molecular composite material is subjected to the following treatment: The solution of the soluble polyimide molecular composite material is vacuum degassed and defoamed for 1 h; Then, the solution is cast on a clean glass plate and pre-baked at 80℃ for 0.5 h; Then, the solution is subjected to stepwise temperature rising in a nitrogen atmosphere: 80℃×1 h → 180℃×1 h → 250℃×1 h → 300℃×1 h → 360℃×1 h; After naturally cooling to room temperature, the soluble polyimide molecular composite film is peeled off from the glass plate to obtain the soluble polyimide molecular composite film.

[0020] Compared with existing technologies, the soluble polyimide molecular composite film proposed in this invention has excellent optical transparency, while simultaneously improving mechanical strength, dimensional stability, heat resistance and electrical insulation.

[0021] Meanwhile, this invention proposes an application of a soluble polyimide molecular composite film, which is applied to flexible electronic devices. Attached Figure Description

[0022] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings.

[0023] Figure 1 This is a schematic diagram of the preparation process of the soluble polyimide molecular composite material of the present invention; Figure 2 This is the skeletal structural formula of the soluble polyimide molecular composite material of the present invention; Figure 3 (a) is a comparison diagram of the nuclear magnetic resonance test of the diamine monomer in Examples 9 to 12 of the present invention, the comparative example, and the diamine monomer; Figure 3 (b) is a comparison diagram of nuclear magnetic resonance tests in Examples 1 to 8 of the present invention, with test conditions of 600 MHz and solvent DMSO-d6; Figure 4 (a) is a comparison chart of transmittance tests of Examples 1 to 4 and the comparative examples of the present invention; Figure 4 (b) is a comparison chart of transmittance tests in Examples 5 to 8 of the present invention; Figure 4 (c) is a comparison chart of transmittance tests in Examples 9 to 12 of the present invention; Figure 4 (d) is the figure in Figure (a) at 1600cm. -1 ~1650cm -1 Enlarged image; Figure 4 (e) Examples 2, 6, 10, and comparative examples were taken at 3200 cm. -1 ~3450cm -1 Transmittance test comparison chart; Figure 4 (f) Examples 1, 5, 9 and comparative examples were measured at 1700 cm. -1 ~1800cm -1 Transmittance test comparison chart; Figure 5 (a) Comparison charts of thermogravimetric tests of Examples 1 to 12 and comparative examples of the present invention; Figure 5 (b) Comparison chart of linear thermal expansion coefficient test results for Examples 1 to 12 and comparative examples of the present invention; Figure 5(c) Comparison diagrams of Young's mod test results of Examples 1 to 12 and comparative examples of the present invention; Figure 5 (d) Comparison charts of glass transition temperature tests of Examples 9 to 12 and comparative examples of the present invention. Detailed Implementation

[0024] To facilitate understanding of the present invention, a more comprehensive and detailed description of the present invention will be provided below, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0025] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention are well known in the art, but do not limit the implementation of this invention. Other reagents and equipment well known in the art can also be applied to the implementation of the following embodiments of this invention.

[0026] Addressing the limitation of existing polyimides in simultaneously achieving "high transparency, low CTE, high strength, high heat resistance, and insulation," this invention investigates a method for preparing soluble polyimide molecular composites. This method involves using non-stoichiometric monomer feeding in a soluble polyimide solution to in-situ polymerize rigid rod-shaped small-molecule polyamide (PA) chains with controllable molecular weight between the soluble polyimide molecular chains, forming a reinforcing phase. This results in an ordered and oriented arrangement of the soluble polyimide molecular chains. Compared to pure soluble polyimide materials, the polyimide molecular composites prepared by this method exhibit molecular-level dispersion of the rigid rod-shaped small-molecule polyamide (PA) chains within the soluble polyimide matrix. This promotes the ordered stacking of soluble polyimide macromolecular chains and introduces rigid units and end groups, improving transparency while optimizing toughness. Consequently, the soluble polyimide molecular composites possess comprehensive properties including colorless transparency, low CTE, high strength, high heat resistance, and insulation.

[0027] The following describes in detail the preparation method of the soluble polyimide molecular composite material with rigid rod-shaped small molecule polyamide PA chains as the reinforcing phase, including the following steps.

[0028] (I) Preparation of polyamic acid Under nitrogen protection, diamine monomer R1 is dissolved in a polar aprotic solvent, dianhydride monomer R2 is added in batches, and then a capping agent is added. The reaction is stirred continuously to generate a polyamic acid solution.

[0029] The polar aprotic solvent is selected from: N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, γ-butyrolactone, etc. The diamine monomer R1 has an electron-donating group and is selected from:

[0030] The R11 in each of the above structural formulas may be the same or different, and each is independently selected from: methyl, trifluoromethyl, fluorine atom, hydrogen atom.

[0031] The dianhydride monomer R2 has an electron acceptor group and is selected from: .

[0032] The capping agent is phthalic anhydride or other capping agents.

[0033] The molar ratio of the diamine monomer R1 to the dianhydride monomer R2 is controlled at (0.98~1.02):1.

[0034] When the diamine monomer R1 and dianhydride monomer R2 are dissolved in a polar aprotic solution, the solid content of the solution is controlled to be between 10% and 20%.

[0035] The reaction time of the diamine monomer R1 and the dianhydride monomer R2 in the polar aprotic solution is controlled to be 18h~24h.

[0036] The molar ratio of the capping agent to diamine monomer R1 or dianhydride monomer R2 is controlled to be (0.003~0.005):1.

[0037] (II) Preparation of soluble polyimide fibers An acylation reagent is added to a polyamic acid solution, and the reaction is sealed to generate a polyimide solution. The polyimide solution is slowly poured into excess deionized water to precipitate fibrous soluble polyimide. After washing with ethanol, filtering, and vacuum drying, soluble polyimide fibers are obtained.

[0038] The acylating agent is selected from commonly used acylating agents, such as acetic anhydride and pyridine.

[0039] The molar ratio of the acylating agent to the polyamic acid is controlled, i.e., the mol[Ac2O] / mol[COOH] value is within ( ).

[0040] The time for the acylation reaction of the acylation reagent to be carried out in a sealed environment is controlled between 24h and 48h.

[0041] The temperature for vacuum drying is controlled between 105℃ and 120℃.

[0042] The vacuum drying time should be controlled between 10 and 12 hours.

[0043] (III) Preparation of soluble polyimide matrix solution Soluble polyimide fibers are dissolved in a polar aprotic solution.

[0044] The solid content of the polyimide solution is controlled to be between 5% and 30%.

[0045] It should be noted that steps (i) and (ii) of this application provide a method for preparing soluble polyimide fibers, which is not a limitation on soluble polyimide fibers. Commercially available soluble polyimide materials prepared by other methods that meet the purity requirements can be used to prepare soluble polyimide matrix solutions.

[0046] (iv) Preparation of soluble polyimide molecular composite material PI-PAx-y Diamine monomer R3 and aromatic diacyl chloride R4 are sequentially added to a soluble polyimide solution. The diamine monomer R3 and aromatic diacyl chloride R4 undergo in-situ polymerization between the polyimide molecular chains to form rigid rod-shaped small-molecule aromatic polyamide PA, yielding a polyimide molecular composite material PI-PAx-y with ordered polyimide molecular chains. Here, x represents the degree of polymerization of the aromatic polyamide, and y represents the number of moles of diamine monomer R3 when the sum of the molar numbers of diamine monomer R3 and soluble polyimide is 10. The structural formula of the polyimide molecular composite material PI-PAx-y is shown below:

[0047] Where n and x are positive integers, n represents the degree of polymerization of soluble polyimide, x represents the theoretical degree of polymerization of aromatic polyamide, 50≤n≤200, and the value range of x is [10,25]. R1 represents a diamine monomer with an electron donor group, R2 represents a dianhydride monomer with an electron acceptor group, R3 represents a diamine monomer, and R4 represents an aromatic diacyl chloride. The molar ratio of diamine monomer R3 to aromatic diacyl chloride R4 satisfies (x-1) / (x+1).

[0048] The value of y ranges from [1, 3], representing the molar number of diamine monomer R3 when the sum of the molar numbers of diamine monomer R3 and soluble polyimide is 10. For example, y = 1 indicates a molar ratio of diamine monomer R3 to soluble polyimide of 1:9; y = 2 indicates a molar ratio of diamine monomer R3 to soluble polyimide of 2:8; and y = 3 indicates a molar ratio of diamine monomer R3 to soluble polyimide of 3:7. Correspondingly, the range of the molar ratio of diamine monomer R3 to soluble polyimide is 0.11 to 0.43.

[0049] For example, taking PI-PA10-1 as an example: x=10, indicating that the molar ratio of diamine monomer R3 to aromatic diacyl chloride R4 is 9:11, and y=1, indicating that the molar ratio of diamine monomer R3 to soluble polyimide is 1:9.

[0050] The diamine monomer R3 is selected from:

[0051] The R12 in each of the above structural formulas may be the same or different, and each is independently selected from: methyl, trifluoromethyl, fluorine atom, hydrogen atom.

[0052] The aromatic diacyl chloride R4 is selected from: .

[0053] (V) Preparation of soluble polyimide molecular composite PI-PAx-y films The polyimide molecular composite material PI-PAx-y was subjected to vacuum degassing and defoaming treatment and cast onto a clean glass plate, and pre-baked at 80℃ for 0.5 h; then, it was heated in a nitrogen atmosphere in a stepwise manner: 80℃×1 h → 180℃×1 h → 250℃×1 h → 300℃×1 h → 360℃×1 h; after natural cooling to room temperature, the soluble polyimide molecular composite film was peeled off from the glass plate to obtain a soluble polyimide molecular composite film with a thickness of 20±5μm.

[0054] The minimum degree of polymerization of the rigid rod-shaped small molecule aromatic polyamide PA of this invention is set to 10, and the maximum baking temperature is not lower than 360°C; otherwise, if the polymerization is too low, unreacted monomers may remain as impurities, which will damage the optical transparency and mechanical properties of the sample.

[0055] The technical solutions and effects of the present invention will be further explained below with reference to embodiments and comparative examples.

[0056] It should be noted that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0057] Example 1 This embodiment prepares a soluble polyimide molecular composite material PI-PA10-1 film.

[0058] Prepare the raw materials, among which, the diamine monomers R1 and R3 are 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB); the dianhydride monomer R2 is hexafluorodianhydride (6FDA); the polar aprotic solvent is N,N-dimethylacetamide (DMAC); the acylating agent is a mixed solution of acetic anhydride and pyridine in a volume ratio of 7:3; and the aromatic diacyl chloride R4 is terephthaloyl chloride (TPC).

[0059] S1: Under nitrogen protection, TFMB (6.4046 g, 20.0 mmol) was dissolved in anhydrous DMAC (65.30 mL), 6FDA (8.8848 g, total 20.0 mmol) was added in portions, followed by the capping agent phthalic anhydride (0.0148 g, 0.1 mmol), and the mixture was stirred continuously for 18 h to generate a polyamic acid solution. S2: Add a mixed solution of acetic anhydride and pyridine (Ac2O 9.39 mL, pyridine 4.02 mL) to a polyamic acid solution, seal and react for 24 h to generate a polyimide solution; slowly pour the polyimide solution into excess deionized water to precipitate fibrous soluble polyimide; wash with ethanol, filter, dry under vacuum at 120℃ for 12 h, and then take out to obtain soluble polyimide fibers; S3: Soluble polyimide fiber PI (10.00 g, 13.73 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.4884 g, 1.53 mmol) and TPC (0.3784 g, 1.87 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA10-1. S4: The polyimide molecular composite material PI-PA10-1 was subjected to vacuum degassing and defoaming treatment for 1 hour, and then cast onto a clean glass plate and pre-baked at 80℃ for 0.5 hours. Subsequently, the temperature was increased in a nitrogen atmosphere in stages: 80℃×1 h → 180℃×1 h → 250℃×1 h → 300℃×1 h → 360℃×1 h. After naturally cooling to room temperature, the soluble polyimide molecular composite material PI-PA10-1 film was peeled off from the glass plate to obtain a soluble polyimide molecular composite material PI-PA10-1 film with a thickness of 20±5μm.

[0060] Example 2 This embodiment prepares a soluble polyimide molecular composite material PI-PA15-1 film.

[0061] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (10.00 g, 13.73 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.4884 g, 1.53 mmol) and TPC (0.3539 g, 1.74 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA15-1.

[0062] Example 3 This embodiment prepares a soluble polyimide molecular composite material PI-PA20-1 film.

[0063] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (10.00 g, 13.73 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.4884 g, 1.53 mmol) and TPC (0.3422 g, 1.69 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA20-1.

[0064] Example 4 This embodiment prepares a soluble polyimide molecular composite material PI-PA25-1 film.

[0065] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (10.00 g, 13.73 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.4884 g, 1.53 mmol) and TPC (0.3354 g, 1.65 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA25-1.

[0066] Example 5 This embodiment prepares a soluble polyimide molecular composite material PI-PA10-2 film.

[0067] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (6.00 g, 8.24 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.6594 g, 2.06 mmol) and TPC (0.5109 g, 2.52 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA10-2.

[0068] Example 6 This embodiment prepares a soluble polyimide molecular composite material PI-PA15-2 film.

[0069] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (6.00 g, 8.24 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.6594 g, 2.06 mmol) and TPC (0.4778 g, 2.35 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA15-2.

[0070] Example 7 This embodiment prepares a soluble polyimide molecular composite material PI-PA20-2 film.

[0071] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (6.00 g, 8.24 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.6594 g, 2.06 mmol) and TPC (0.4620 g, 2.28 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA20-2.

[0072] Example 8 This embodiment prepares a soluble polyimide molecular composite material PI-PA25-2 film.

[0073] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (6.00 g, 8.24 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.6594 g, 2.06 mmol) and TPC (0.4529 g, 2.23 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA25-2.

[0074] Example 9 This embodiment prepares a soluble polyimide molecular composite material PI-PA10-3 film.

[0075] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (3.00 g, 4.12 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.5652 g, 1.77 mmol) and TPC (0.4380 g, 2.16 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA10-3.

[0076] Example 10 This embodiment prepares a soluble polyimide molecular composite material PI-PA15-3 film.

[0077] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (3.00 g, 4.12 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.5652 g, 1.77 mmol) and TPC (0.4095 g, 2.02 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA15-3.

[0078] Example 11 This embodiment prepares a soluble polyimide molecular composite material PI-PA20-3 film.

[0079] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (3.00 g, 4.12 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.5652 g, 1.77 mmol) and TPC (0.3961 g, 1.95 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA20-3.

[0080] Example 12 This embodiment prepares a soluble polyimide molecular composite material PI-PA25-3 film.

[0081] The preparation method in this embodiment is basically the same as that in Example 1, except for step S3, which is as follows: S3: Soluble polyimide fiber PI (3.00 g, 4.12 mmol) was dissolved in anhydrous DMAc (60.50 mL). After complete dissolution, TFMB (0.5652 g, 1.77 mmol) and TPC (0.3882 g, 1.91 mmol) were added sequentially. The mixture was sealed and reacted at room temperature for 5 h to obtain the polyimide molecular composite material PI-PA25-3.

[0082] Comparative Example This comparative example prepares a polyimide (PI) film without introducing rigid rod-shaped small molecule polyamide (PA) as a reinforcing term.

[0083] The preparation method of this comparative example is basically the same as that of Example 1, except for step S3, which is as follows: S3: Dissolve soluble polyimide fiber PI (10.00 g, 13.73 mmol) in anhydrous DMAc (60.50 mL).

[0084] Results Test Analysis The performance of the soluble polyimide molecular composite films prepared in Examples 1 to 12 and the soluble polyimide molecular composite films prepared in the comparative examples were tested and analyzed. The test results are as follows.

[0085] 1. Structural Characterization Please see Figure 3 (a) and Figure 3 (b) Except for the diamine monomer TFMB, no amino proton peak was observed at 5.80 ppm in the comparative example and the examples, indicating that the amino groups had completely reacted regardless of the PA loading amount or degree of polymerization. This helps the soluble polyimide molecular composite film remain colorless and transparent after high-temperature baking; it also ensures that the TFMB and TPC added in the examples will not undergo side reactions with the PI main chain.

[0086] Please see Figure 4 (a) to Figure 4 (c) Confirms that hydrogen bonds are formed between PA and soluble polyimide molecular chains; Figure 4 (d) shows that, affected by hydrogen bonding, the carbonyl stretching vibration peak of the amide group in the PA molecular chain is located at 1620 cm-1, and the intensity of this peak increases with the degree of polymerization of PA, indicating that the number of secondary amide groups generated by in-situ polymerization increases. Figure 4 (e) shows that the NH stretching vibration peak of the secondary amide in the PA molecular chain appears at 3390 cm-1, while this peak is not present in the pure PI of the comparative example. Figure 4 (f) shows that the stretching vibration peak of the carbonyl (C=O) group connected to the imide ring in the PI-PAx-y system appears at 1730 cm-1 and 1780 cm-1, while this peak is not present in the pure PI of the comparative example.

[0087] In the PI-PAx-y system, the protons of the secondary amide on the PA molecular chain form intermolecular hydrogen bonds with the carbonyl group in the PI molecular chain. As the content of PA molecular chain increases, the NH stretching vibration peak in the PA molecular chain gradually shifts to a lower wavenumber, indicating that the intermolecular hydrogen bonds are strengthened. Figure 3 and Figure 4 Together, it was confirmed that different PA contents have been successfully introduced into the PI matrix to form a series of PI-PAx-y molecular composite materials; the hydrogen bonding between the two chains is enhanced with the increase of PA content.

[0088] 2 Optical performance Table 1

[0089] Wherein: T 400 λ is the transmittance of the thin film at 400 nm. cutoff This is the cutoff wavelength.

[0090] As is well known, adding particulate fillers such as SiO2 to PI systems can lead to decreased transmittance and increased haze due to nanoparticle aggregation. Referring to Table 1, even when rigid rod-shaped small-molecule polyamide (PA) fragments are polymerized in situ between soluble polyimide macromolecular chains to enhance the ordered arrangement of the chains, excellent optical performance can still be maintained. This is because the rigid rod-shaped small-molecule polyamide (PA) fragments are inserted between PI molecular chains, expanding the inter-chain spacing and suppressing CTC interactions between chains, thereby maintaining optical performance. Simultaneously, the rigid rod-shaped small-molecule polyamide (PA) fragments are easily and uniformly dispersed in PI, avoiding aggregation that causes significant light scattering and refraction, which is also a reason for the maintenance of optical performance.

[0091] 2. Thermal properties Table 2

[0092] Where: T5% represents the temperature at which 5% weight loss occurs under nitrogen atmosphere; Tg represents the glass transition temperature determined by DMA method; CTE represents the coefficient of thermal expansion determined by TMA method, ranging from 50 to 200 ℃; Mn, Mw, and PDI represent the number-average molecular weight, weight-average molecular weight, and dispersibility index determined by GPC method, respectively.

[0093] Please see Figure 5 (a) to Figure 5 (d) and Table 2.

[0094] Because the unstable end groups of rigid polyamide structures are prone to degradation at high temperatures, their thermal stability is affected. In the configuration of this invention, due to hydrogen bonding interactions and the resonance structure of amide bonds, the 5% weight loss temperature (T5%) of polyamide PA containing an appropriate amount of rigid rod-shaped small molecule PA is still higher than 500°C, indicating that the introduction of rigid rod-shaped small molecule polyamide PA does not impair the thermal stability of the material.

[0095] Furthermore, CTE is a key indicator for measuring the thermal compatibility between the film and its substrate during processing: mismatch can lead to warping or cracking, especially under thermal cycling conditions. The introduction of rigid rod-shaped small molecule polyamide (PA) molecular chain segments promotes more ordered chain stacking and restricts the rotation or deformation of soluble polyimide molecular chains, thereby effectively reducing CTE. In the range of 50℃-200℃, the CTE of PI-PA15-3 decreased significantly from 50 ppm·K-1 of pure PI to 24.8 ppm·K-1, a reduction of 50.4%. For the PI-PA-2 and PI-PA-3 series, the CTE values ​​are between 25.7-36.5 ppm·K-1, which is comparable to traditional materials such as aluminum alloys and glass fiber reinforced nylon, and is within a practically acceptable range. It is worth noting that, at the same addition amount, CTE shows a "decreasing then increasing" trend with the increase of the molecular weight of rigid rod-shaped small molecule polyamide PA: therefore, only chain segments of appropriate length can most effectively reduce the CTE of the film; beyond this optimal value, further growth of chain segments will hinder the orderly arrangement of soluble polyimide molecular chains.

[0096] Figure 5 (d) DMA curves of PI and the PI-PA-3 series with controllable degree of polymerization are given. It can be seen that the introduction of rigid rod-shaped small molecule polyamide PA effectively increases the glass transition temperature (Tg) of the material from 352℃ to 364℃. This indicates that there is an effective interaction between the rigid rod-shaped small molecule polyamide PA and the soluble polyimide molecular chain, which restricts the cooperative movement of the soluble polyimide molecular chain and significantly weakens the energy dissipation capacity of the material during the glass transition process.

[0097] 3. Mechanical and electrical properties Table 3

[0098] Please refer to Table 3. Compared with pure PI, the mechanical properties of the PI-PAx-y series are significantly improved with the increase of rigid rod-shaped small molecule polyamide PA content: Young's modulus increases by 4.2±0.2 GPa (PI-PA15-3), an increase of about 62%; tensile strength reaches 130.2±18 MPa (PI-PA15-3), an increase of 102%; and breakdown strength can reach 724MV·m-1 (PI-PA15-3), an increase of 32%.

[0099] When rigid rod-shaped small molecule polyamide (PA) is introduced into a soluble polyimide matrix, the risk of aggregation of rigid rod-shaped small molecule polyamide (PA) is reduced, while the number of hydrogen bonds is retained to ensure good interfacial compatibility. At the same time, the formation of a large network is avoided, resulting in better stacking of soluble polyimide molecular chains and molecular order, thereby achieving increased strength without sacrificing toughness.

[0100] The above data demonstrate that the soluble polyimide molecular composite film prepared by this invention, while maintaining the unique optical transparency and thermal properties of polyimide molecules, effectively improves the poor dimensional stability, mechanical properties, and electrical properties of polyimide films. The soluble polyimide molecular composite film prepared by the method of this invention exhibits excellent optical transparency, mechanical strength, dimensional stability, heat resistance, and electrical insulation.

[0101] This invention is not limited to the above-described embodiments. If any modifications or variations to this invention do not depart from the spirit and scope of this invention, and if such modifications and variations fall within the scope of the claims and equivalent technologies of this invention, then this invention also intends to include such modifications and variations.

Claims

1. A method for preparing a soluble polyimide molecular composite material, characterized in that: Diamine monomer and aromatic diacyl chloride are added sequentially to a soluble polyimide solution. The diamine monomer and aromatic diacyl chloride undergo in-situ polymerization between the polyimide molecular chains to form rigid rod-shaped small molecule aromatic polyamides, resulting in a polyimide molecular composite material with ordered polyimide molecular chains. The molar ratio of diamine monomer to aromatic diacyl chloride satisfies (x-1) / (x+1), where x is the theoretical degree of polymerization of the aromatic polyamide.

2. The method for preparing the soluble polyimide molecular composite material according to claim 1, characterized in that, The value of x is in the range of [10, 25].

3. The method for preparing the soluble polyimide molecular composite material according to claim 1, characterized in that, The molar ratio of the diamine monomer to the soluble polyimide is in the range of 0.11 to 0.

43.

4. The method for preparing the soluble polyimide molecular composite material according to claim 1, characterized in that, The conditions for the in-situ polymerization reaction of the diamine monomer and aromatic diacyl chloride between the polyimide molecular chains are as follows: Sealed environment; Reaction temperature: room temperature; Reaction time: 4h~6h.

5. The method for preparing the soluble polyimide molecular composite material according to claim 1, characterized in that, The method for preparing the soluble polyimide includes the following steps: Under nitrogen protection, the diamine monomer is dissolved in a polar aprotic solvent, and the dianhydride monomer is added in batches, followed by the addition of a capping agent. The reaction is stirred continuously to generate a polyamic acid solution, wherein the molar ratio of the diamine monomer to the total dianhydride monomer satisfies (0.98~1.02):

1. An acylation reagent is added to a polyamic acid solution, and the reaction is sealed to generate a polyimide solution; Slowly pour the polyimide solution into excess deionized water to precipitate fibrous soluble polyimide.

6. The method for preparing the soluble polyimide molecular composite material according to claim 5, characterized in that, The precipitated fibrous soluble polyimide was washed with ethanol, filtered, and vacuum dried to obtain soluble polyimide fibers.

7. A soluble polyimide molecular composite material, characterized in that: The soluble polyimide molecular composite material is prepared according to any one of claims 1 to 6, and its structural formula is as follows: Where n and x are positive integers, n represents the degree of polymerization of soluble polyimide, x represents the theoretical degree of polymerization of aromatic polyamide, 50≤n≤200, R1 represents a diamine monomer with an electron donor group, R2 represents a dianhydride monomer with an electron acceptor group, R3 represents a diamine monomer, and R4 represents an aromatic diacyl chloride.

8. A method for preparing a soluble polyimide molecular composite film, characterized in that, The soluble polyimide molecular composite material according to claim 8 is subjected to the following treatment: The solution of soluble polyimide molecular composite material was subjected to vacuum degassing and defoaming for 1 h; It was then cast onto a clean glass plate and pre-baked at 80°C for 0.5 h; The temperature was then increased in a nitrogen atmosphere in stages: 80℃×1 h → 180℃×1 h → 250℃×1 h → 300℃×1 h → 360℃×1 h; After naturally cooling to room temperature, the soluble polyimide molecular composite film is peeled off from the glass plate to obtain the soluble polyimide molecular composite film.

9. The method for preparing a soluble polyimide molecular composite film according to claim 8, characterized in that, The thickness of the soluble polyimide molecular composite film is 20 μm ± 5 μm.

10. An application of a soluble polyimide molecular composite film, characterized in that, The soluble polyimide molecular composite film prepared according to claim 9 is applied to flexible electronic devices.

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