A polyamide-polyimide composite and its preparation method and application

Abstract

The present invention relates to a polyamide-polyimide composite and a preparation method and application thereof, wherein a diamine monomer is dissolved in a soluble polyimide solution, and at least one polymer monomer introducing hydrogen bonding is slowly added to the solution to generate an aromatic polyamide molecular chain, wherein the aromatic polyamide molecular chain is chemically blended with a polyimide molecular chain by in-situ polymerization to obtain a double-chain structure formed by an aromatic polyamide molecular chain containing NH-CO- and a soluble polyimide molecular chain, and the double-chain has an interpenetrating hydrogen bond network structure of the polyamide-polyimide composite. By controlling the molar ratio of the aromatic polyamide molecular chain to the polyimide molecular chain, the thermal expansion coefficient, optical properties and mechanical properties of the polyamide-polyimide composite are regulated to meet the personalized needs of different flexible devices for ultra-low thermal expansion coefficient, high light transmittance, high heat resistance and high organic solvent resistance.

Description

Technical Field

[0001] The invention belongs to the field of preparation and application of polyimide materials, and specifically relates to a polyamide-polyimide composite and a preparation method and application thereof. Background Art

[0002] Flexible transparent substrates are an important component of flexible transparent electronic devices. As substrates for flexible transparent displays, they need to meet the following conditions:

[0003] (1) Good heat resistance;

[0004] (2) Good resistance to organic solvents;

[0005] (3) Has good light transmittance.

[0006] Transparent polyimide (PI) is considered to be the most promising substrate material in the field of flexible display due to its advantages such as high thermal stability and high light transmittance. At the same time, compared with inorganic glass, transparent polyimide is more flexible, low-density and easy to process, making it popular in the field of flexible display. In order to obtain colorless and transparent polyimide with high glass transition temperature, low thermal expansion coefficient, high light transmittance and good mechanical properties, the existing mainstream preparation methods include the following:

[0007] 1) Synthesis of polyimide composite system by in-situ polymerization of nanofillers. This method introduces various nanofillers such as TiO2, SiO2, clay, carbon nanotubes, graphene, etc. into polyimide to prepare polyimide composite materials. However, due to the weak interfacial interaction between polyimide and nanofillers, chemical incompatibility and poor dispersibility of polyimide in nanofillers, the polyimide composite materials prepared by this method have poor mechanical properties and high haze.

[0008] 2) Synthesis of polyimide-polyamide system by random copolymerization, in which aromatic polyamide containing hydrogen bonds is randomly copolymerized with polyimide to prepare single-chain polyimide-polyamide polymer; the hydrogen bond arrangement regularity of the polyimide-polyamide polymer prepared by this method is poor, which greatly reduces the effect of hydrogen bonds, resulting in poor overall performance of the prepared polyimide-polyamide film, large thermal expansion coefficient, large yellowness and haze;

[0009] 3) The block copolymerization method is used to synthesize the polyimide-polyamide system. This method involves introducing a hydrogen-bonded polymer monomer into a precursor polyamic acid solution in which a diamine monomer is dissolved to obtain a polyamic acid-polyamide polymer, and then subjecting the polyamic acid-polyamide polymer to an imidization reaction to prepare a single-chain polyimide-polyamide polymer; please refer to Figure 1The hydrogen bonds of the polyimide-polyamide polymer prepared by this method are arranged regularly, but the imide ring density of the polyimide is reduced and the hydrogen bonds between the biphenyl structure and the polyamide chain cannot be fully utilized, thereby weakening the interaction between polyimide and polyamide, resulting in poor thermal performance of the polyimide-polyamide system. Summary of the invention

[0010] The object of the present invention is to provide a method for preparing a polyamide-polyimide composite material by mixing an aromatic polyamide reinforcement phase into a soluble polyimide matrix based on an in-situ polymerization method.

[0011] The method for preparing a polyamide-polyimide composite of the present invention comprises the following steps:

[0012] The diamine monomer is dissolved in a soluble polyimide solution, and at least one polymer monomer introducing hydrogen bonding is slowly added to the solution to generate an aromatic polyamide molecular chain, which is chemically blended with a polyimide molecular chain through in-situ polymerization to obtain an aromatic polyamide-polyimide double-chain blended polymer.

[0013] Compared with the prior art, the method for preparing a polyamide-polyimide composite by mixing an aromatic polyamide reinforcement phase into a soluble polyimide matrix based on an in-situ polymerization method provided by the present invention can prepare a polyamide-polyimide composite with a new structure, wherein the composite contains a double-chain structure and the double-chain chains have an interpenetrating hydrogen bond network structure. At the same time, the preparation method is simple, the raw materials, preparation equipment, etc. used are all well known in the art, and the economic benefit is high.

[0014] At the same time, a polyamide-polyimide composite prepared by the preparation method of the present invention has a double-chain structure formed by an aromatic polyamide molecular chain and a polyimide molecular chain, and the double-chain has an interpenetrating hydrogen bond network structure, and its structural formula is:

[0015]

[0016] Wherein, m and n are positive integers representing the degree of polymerization, 5≤m≤100, 10≤n≤550, R1, R2, R3, R4 are the same or different, and each independently represents a substituted or unsubstituted cycloalkyl, aryl, saturated or unsaturated heterocyclic group, or a skeleton structure formed by a combination thereof.

[0017] Compared with the prior art, the double-chain structure contained in the polyamide-polyimide composite of the present invention can make full use of the effect of ordered hydrogen bonds and imide rings without destroying the structure of polyimide. The interpenetrating hydrogen bond network structure between the double chains greatly weakens the mutual movement ability of the aromatic polyamide molecular chain and the polyimide molecular chain and reduces the chain spacing between the double chains, so that the interaction between the polyimide matrix and the aromatic polyamide reinforcement phase is further enhanced; at the same time, due to the effect of ordered hydrogen bonds and imide rings, the crystallization of polymer chains caused by ordered hydrogen bonds between aromatic polyamide molecules can be effectively avoided, so that a molecularly dispersed rigid polyamide polymer can be formed in the polyimide matrix, and the reinforcing effect of the rigid polyamide macromolecule on the polyimide matrix can be maximized. Therefore, the polyamide-polyimide composite containing double chains and having an interpenetrating hydrogen bond network structure between the chains has a lower thermal expansion coefficient, a higher glass transition temperature and more excellent dimensional thermal stability.

[0018] Furthermore, the polyimide is a soluble polyimide.

[0019] Furthermore, R1 in the aromatic polyamide molecular chain is the same or different and is independently selected from:

[0020]

[0021] In the above structural formulas, R5, R6, R7, R8, R 10 The same or different, each independently is H or selected from:

[0022]

[0023] R9 in the above structural formulas are the same or different and are independently selected from:

[0024]

[0025] Among them, the wavy line represents a connecting bond, and P is a positive integer.

[0026] Furthermore, R2 in the aromatic polyamide molecular chain and R4 in the polyimide molecular chain are the same or different and are independently selected from:

[0027]

[0028] In the above structural formulas, R 11 are the same or different, each independently selected from: methyl, trifluoromethyl, fluorine atom, hydrogen atom,

[0029] The dotted line represents a ring connection.

[0030] Furthermore, R3 in the polyimide molecular chain is the same or different and is independently selected from:

[0031]

[0032] The dotted line represents a ring connection.

[0033] At the same time, the film prepared from the polyamide-polyimide composite of the present invention can be suitable for substrates and cover plates of flexible electronic devices, such as substrates of flexible carbon nanotube transistor devices, flexible oxide semiconductor devices and flexible sensors, etc.; such as cover plates of flexible organic light-emitting diode (OLED) screens, flexible solar cells, etc.

[0034] Compared with the prior art, the film made based on the polyamide-polyimide composite provided by the present invention has a lower thermal expansion coefficient, a higher glass transition temperature, and thus has excellent dimensional thermal stability, so that the film is not easy to curl or peel off during device processing, and does not undergo dimensional changes or even melt when processed in a high-temperature atmosphere.

[0035] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The skeleton structure of polyimide-polyamide synthesized by block copolymerization;

[0037] Figure 2 is the skeleton structural formula of the polyamide-polyimide composite of the present invention;

[0038] Figure 3 Schematic diagram of the double-chain interpenetrating network structure of the polyamide-polyimide composite of the present invention;

[0039] Figure 4 The figure is a synthesis process diagram of the polyamide-polyimide composite of the present invention;

[0040] Figure 5 The heating rate of Examples 1-4 and Comparative Examples in the temperature range of 50-400°C is 10°C·min -1 Measured DMA curve;

[0041] Figure 6 The heating rate of the polyamides of Examples 1 to 4 of the present invention and the comparative example under nitrogen atmosphere is 10°C·min -1 TGA curve measured at ;

[0042] Figure 7 For Examples 1 to 4 of the present invention and the comparative example, the heating rate is 10°C·min -1 TMA curve measured between 50 and 400 °C under the following conditions;

[0043] Figure 8The percentage decrease of the thermal expansion coefficient of Examples 1-4 and the comparative example of the present invention when the data collection temperature range is 50 to 250° C.;

[0044] Fig. 9 The optical transmission spectra of Examples 1-4 of the present invention and the comparative example are shown in the figure. The inset is the optical schematic diagram of the film of Example 5 overlaid on the picture. DETAILED DESCRIPTION

[0045] In order to facilitate the understanding of the present invention, the present invention will be described in more comprehensive and detailed manner below, but the protection scope of the present invention is not limited to the following specific embodiments.

[0046] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0047] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention are well known in the art, but do not limit the implementation of the present invention. Other reagents and equipment well known in the art can be applied to the implementation of the following embodiments of the present invention.

[0048] Aromatic polyamides have excellent thermal stability and mechanical properties. They are usually introduced into polyimide systems as reinforcing phases in the form of polymers through physical blending. However, strong hydrogen bonding interactions cannot be formed between polyamides and polyimides through physical blending, resulting in poor interfacial interactions in such polyimide composites and unsatisfactory thermal performance enhancement effects.

[0049] Therefore, the present invention re-studies a mixing method of introducing an aromatic polyamide with excellent performance into a polyimide system as a reinforcing phase. Based on the strong hydrogen bond interaction between the aromatic polyamide molecular chain and the biphenyl structure, the present invention studies the use of an in-situ polymerization method to add a polymer monomer that introduces hydrogen bonds to a soluble polyimide matrix solution in which a diamine monomer is dissolved to polymerize the reinforcing phase polyamide molecular chain in situ, so that the aromatic polyamide molecular chain generated by polymerization is chemically blended with the polyimide molecular chain to obtain an aromatic polyamide-polyimide double-chain blended polymer. This method can make full use of the effects of ordered hydrogen bonds and imide rings without destroying the structure of polyimide, greatly weaken the mutual movement ability of aromatic polyamide chains and polyimide chains and reduce the chain spacing between double chains, so that the interaction force between the polyimide matrix and the aromatic polyamide reinforcement phase is further enhanced; at the same time, since the effects of ordered hydrogen bonds and imide rings can effectively avoid the crystallization of polymer chains caused by ordered hydrogen bonds between aromatic polyamide molecules, a molecularly dispersed rigid polyamide polymer can be formed in the polyimide matrix, maximizing the reinforcing effect of the rigid polyamide macromolecules on the polyimide matrix.

[0050] The following specifically describes the method for preparing the polyamide-polyimide composite with double-stranded blending of the present application, which includes the following steps.

[0051] (I) Preparation of precursor polyamic acid

[0052] A diamine monomer and a dianhydride monomer are added to a polar aprotic solvent, and the mixture is continuously stirred and reacted in an inert atmosphere at 0° C. to 25° C. to generate a precursor polyamic acid containing repeating units of R3 and R4.

[0053] The polar aprotic solvent is selected from: N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, γ-butyrolactone and the like.

[0054] The R3 is selected from:

[0055]

[0056] The R4 is selected from:

[0057]

[0058] In the above structural formulas, R 11 The same or different, each independently selected from: methyl, trifluoromethyl, fluorine atom, hydrogen atom.

[0059] The molar ratio of the diamine monomer to the dianhydride monomer is controlled to be (1±0.02).

[0060] When the diamine monomer and the dianhydride monomer are dissolved in a polar aprotic solution, the solid content of the solution is controlled to be between 10% and 20%.

[0061] The reaction time of the diamine monomer and the dianhydride monomer in the polar aprotic solution is controlled to be between 12 hours and 24 hours.

[0062] (II) Preparation of soluble polyimide solid

[0063] An acylation agent is added to the precursor polyamic acid to generate a polyimide glue solution, and the polyimide glue solution is placed in ethanol for sedimentation, and the sediment is extracted with ethanol, and vacuum dried to obtain a soluble polyimide solid.

[0064] The acylating agent is selected from commonly used acylating agents, such as acetic anhydride and pyridine.

[0065] Control the molar ratio of the acylating agent to the polyamic acid, i.e., mol [Ac2O] / mol [COOH] The value is (5±0.5).

[0066] The time for adding the acylation agent to the precursor polyamic acid for acylation reaction is controlled to be 24 hours to 48 hours.

[0067] (III) Preparation of polyimide matrix solution

[0068] The soluble polyimide solid is dissolved in a polar aprotic solution to prepare a polyimide solution containing polyimide molecular chains, and a diamine monomer is added to the polyimide solution. After the diamine monomer is completely dissolved, a polyimide matrix solution is obtained.

[0069] The polar aprotic solvent is selected from: N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, γ-butyrolactone and the like.

[0070] The solid content of the polyimide solution is controlled within a range of 5% to 30%.

[0071] It should be noted that step (1) and step (2) of the present application provide a method for preparing a soluble polyimide solid, which is not a limitation on the soluble polyimide solid. Soluble polyimide solids sold on the market or prepared by other preparation methods that meet the purity requirements can be used for the preparation of the polyimide matrix solution.

[0072] (IV) Preparation of polyamide-polyimide double-stranded blend composites

[0073] At least one polymer monomer that introduces hydrogen bonding is slowly added to the polyimide-based body fluid to generate an aromatic polyamide molecular chain containing R1 and R2. The aromatic polyamide molecular chain is chemically blended with the polyimide molecular chain through in-situ polymerization to obtain an aromatic polyamide-polyimide double-chain blended polymer. The structural formula of the aromatic polyamide-polyimide double-chain blended polymer is as follows:

[0074]

[0075] The structure is a double-chain structure formed by an aromatic polyamide molecular chain containing an amide bond (-NH-CO-) and a polyimide molecular chain, and the double-chain has an interpenetrating hydrogen bond network structure. The chain rigidity and linearity of the aromatic polyamide molecular chain containing an amide bond contribute to the orientation of the polyimide molecular chain and the formation of an interpenetrating network structure between the double chains. The chain orientation and the interpenetrating network between the double chains increase the molecular rigidity and reduce the mobility. At the same time, the interpenetrating hydrogen bond network structure formed by the ordered hydrogen bonds of the aromatic polyamide molecular chain and the imide ring of the polyimide molecular chain can effectively avoid the crystallization of the polymer chain caused by the ordered hydrogen bonds between the aromatic polyamide molecules, so that the aromatic polyamide molecular chain presents a rigid polyamide polymer dispersed at the molecular level.

[0076] By controlling the molar ratio of the aromatic polyamide molecular chain containing amide bonds to the polyimide molecular chain, the proportion of the double-chain network structure with interpenetrating hydrogen bonds between the chains can be controlled.

[0077] Specifically, the R1 is selected from:

[0078]

[0079] Among them, R5, R6, R7, R8, R 10 The same or different, each independently is H or selected from:

[0080]

[0081] R9 in each structural formula is the same or different and is independently selected from:

[0082]

[0083] In the above structural formula, the wavy line represents a connecting bond, and P is a positive integer.

[0084] The R2 is selected from:

[0085]

[0086] In the above structural formulas, R 11 The same or different, each independently selected from: methyl, trifluoromethyl, fluorine atom, hydrogen atom.

[0087] (V) Preparation of polyamide-polyimide double-stranded blend film

[0088] The polyamide-polyimide double-chain polymer blend is coated on a substrate and heated and cured to obtain the polyamide-polyimide composite film.

[0089] Specifically, the polyamide-polyimide double-chain polymer blend is uniformly coated on a glass substrate, dried at 60° C. for 1 hour in a forced air oven, and then heated to 360° C. in a vacuum oven using a gradient heating method to remove the polar aprotic solution and hydrochloric acid produced by the reaction, thereby obtaining a polyamide-polyimide composite film with a thickness of 20 to 30 μm.

[0090] The specific heating steps of the gradient heating method are: the first gradient, heating to 80°C and keeping warm for 1 hour; the second gradient, heating to 180°C and keeping warm for 1 hour; the third gradient, heating to 250°C and keeping warm for 1 hour; the fourth gradient, heating to 300°C and keeping warm for 1 hour; the fifth gradient, heating to 360°C and keeping warm for 1 hour. The film prepared by this heating method has good density, uniform thickness and few defects.

[0091] The thermal expansion coefficient, optical properties and mechanical properties of the film prepared from the polyamide-polyimide composite can be regulated by controlling the molar ratio of the aromatic polyamide molecular chain containing amide bonds to the polyimide molecular chain, so as to meet the personalized needs of different flexible devices for ultra-low thermal expansion coefficient, high light transmittance, high heat resistance and high resistance to organic solvents.

[0092] The technical scheme and technical effects of the present invention are further described below in conjunction with embodiments and comparative examples.

[0093] It should be noted that the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0094] Example 1

[0095] In this embodiment, a polyamide-polyimide composite film having a molar ratio of aromatic polyamide to polyimide of 0.11:1 was prepared according to the following method.

[0096] The raw materials were prepared, wherein the diamine monomer was 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB); the dianhydride monomer was hexafluorodianhydride (6FDA); the polar aprotic solvent was N,N-dimethylacetamide (DMAC); the acylating agent was a mixed solution of acetic anhydride and pyridine in a volume ratio of 7:3; and the polymer monomer for introducing hydrogen bonds was terephthaloyl chloride (TC).

[0097] (I) Preparation of precursor polyamic acid

[0098] S11: 0.01 mol of TFMB is placed in a 50 mL three-necked flask protected by nitrogen, and then 43.32 mL of DMAC is added to the three-necked flask to completely dissolve TFMB in DMAC;

[0099] S12: gradually adding 0.01 mol of 6FDA into the three-necked flask to obtain a mixture of 6FDA and TFMB, wherein the solid content of the solution is 15%;

[0100] S13: continuously stirring the mixture in a nitrogen atmosphere at 0°C for 12 hours to obtain a viscous precursor polyamic acid.

[0101] (II) Preparation of soluble polyimide solid

[0102] S21: gradually adding the acylating agent to the precursor polyamic acid at room temperature, and continuously stirring vigorously at room temperature for 24 hours to generate a polyimide glue solution, wherein the amount of the acylating agent is such that the molar ratio of acetic anhydride in the acylating agent to the carboxyl group in the precursor polyamic acid is equal to 5, that is, [Ac2O] / [COOH] PAA =5;

[0103] S22 uses the acylation reagent to dilute the polyimide glue into a homogeneous glue, slowly pours the diluted polyimide glue into a large amount of ethanol and allows it to settle, collects the precipitate and repeatedly washes and filters it with fresh ethanol, and vacuum dries the precipitate extracted with fresh ethanol at 120°C for 12 hours to obtain a soluble polyimide solid.

[0104] (III) Preparation of polyimide matrix solution

[0105] S31 dissolving the soluble polyimide solid in anhydrous DMAC to prepare a polyimide solution containing polyimide molecular chains, wherein the amount of DMAC is such that the solid content of the polyimide solution is 10%;

[0106] S32: adding 0.0011 mol of TFMB into the polyimide solution to completely dissolve TFMB in the polyimide solution to obtain a polyimide-based liquid.

[0107] (IV) Preparation of polyamide-polyimide double-stranded blend composites

[0108] S41: gradually adding 0.0011 mol of TC into the polyimide matrix glue solution, and stirring at 0° C. for 24 hours to obtain a glue solution containing a polyamide-polyimide double-chain blend polymer.

[0109] (V) Preparation of polyamide-polyimide double-stranded blend film

[0110] S51: uniformly coating the polyamide-polyimide double-chain polymer blend glue on a glass substrate, and drying in a forced air oven at 60° C. for 1 h;

[0111] S52 The glass substrate coated with the polyamide-polyimide double-chain blend polymer is heated to 360°C in a vacuum oven using a gradient heating method and then kept warm for 1 hour to remove the polar aprotic solution and the hydrochloric acid produced by the reaction, thereby obtaining a polyamide-polyimide composite film with a thickness of 20 to 30 um and a molar ratio of polyamide to polyimide of 0.11:1.

[0112] Among them, the specific heating steps of the gradient heating method are: the first gradient, heating to 80°C and keeping warm for 1 hour; the second gradient, heating to 180°C and keeping warm for 1 hour; the third gradient, heating to 250°C and keeping warm for 1 hour; the fourth gradient, heating to 300°C and keeping warm for 1 hour; the fifth gradient, heating to 360°C and keeping warm for 1 hour.

[0113] Example 2

[0114] In this embodiment, a polyamide-polyimide composite film having a molar ratio of polyamide to polyimide of 0.25:1 was prepared according to the following method.

[0115] The preparation method of this embodiment is basically the same as that of embodiment 1, except that in steps S32 and S41, the molar amounts of the diamine monomer and the polymer monomer for introducing hydrogen bonds added to the polyimide solution are different, specifically:

[0116] S32: adding 0.0025 mol of TFMB into the polyimide solution to completely dissolve TFMB in the polyimide solution to obtain a polyimide-based liquid.

[0117] S41: gradually adding 0.0025 mol of TC into the polyimide matrix glue solution, and stirring at 0° C. for 24 hours to obtain a glue solution containing a polyamide-polyimide double-chain blend polymer.

[0118] Example 3

[0119] In this embodiment, a polyamide-polyimide composite film having a polyamide to polyimide molar ratio of 0.43:1 was prepared according to the following method.

[0120] The preparation method of this embodiment is basically the same as that of embodiment 1, except that in steps S32 and S41, the molar amounts of the diamine monomer and the polymer monomer for introducing hydrogen bonds added to the polyimide solution are different, specifically:

[0121] S32: adding 0.0043 mol of TFMB into the polyimide solution to completely dissolve TFMB in the polyimide solution to obtain a polyimide-based liquid.

[0122] S41: gradually adding 0.0043 mol of TC into the polyimide matrix glue solution, and stirring at 0° C. for 24 hours to obtain a glue solution containing a polyamide-polyimide double-chain blend polymer.

[0123] Example 4

[0124] In this embodiment, a polyamide-polyimide composite film having a polyamide to polyimide molar ratio of 0.67:1 was prepared according to the following method.

[0125] The preparation method of this embodiment is basically the same as that of embodiment 1, except that in steps S32 and S41, the molar amounts of the diamine monomer and the polymer monomer for introducing hydrogen bonds added to the polyimide solution are different, specifically:

[0126] S32: adding 0.0067 mol of TFMB into the polyimide solution to completely dissolve TFMB in the polyimide solution to obtain a polyimide-based liquid.

[0127] S41: gradually adding 0.0067 mol of TC into the polyimide matrix glue solution, and stirring at 0° C. for 24 hours to obtain a glue solution containing a polyamide-polyimide double-chain blend polymer.

[0128] Comparative Example

[0129] This comparative example is a method for preparing a polyimide film without a mixed reinforcing polyamide, specifically, comprising the following steps:

[0130] The raw materials were prepared, wherein the diamine monomer was 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB); the dianhydride monomer was hexafluorodianhydride (6FDA); the polar aprotic solvent was N,N-dimethylacetamide (DMAC); and the acylating agent was a mixed solution of acetic anhydride and pyridine in a volume ratio of 7:3.

[0131] (I) Preparation of precursor polyamic acid

[0132] S11: 0.01 mol of TFMB is placed in a 50 mL three-necked flask protected by nitrogen, and then 43.32 mL of DMAC is added to the three-necked flask to completely dissolve TFMB in DMAC;

[0133] S12: gradually adding 0.01 mol of 6FDA into the three-necked flask to obtain a mixture of 6FDA and TFMB, wherein the solid content of the solution is 15%;

[0134] S13: continuously stirring the mixture in a nitrogen atmosphere at 0°C for 12 hours to obtain a viscous precursor polyamic acid.

[0135] (II) Preparation of soluble polyimide solid

[0136] S21: gradually adding the acylating agent to the precursor polyamic acid at room temperature, and continuously stirring vigorously at room temperature for 24 hours to generate a polyimide glue solution, wherein the amount of the acylating agent is such that the molar ratio of acetic anhydride in the acylating agent to the carboxyl group in the precursor polyamic acid is equal to 5, that is, [Ac2O] / [COOH] PAA =5;

[0137] S22 uses the acylation reagent to dilute the polyimide glue into a homogeneous glue, slowly pours the diluted polyimide glue into a large amount of ethanol and allows it to settle, collects the precipitate and repeatedly washes and filters it with fresh ethanol, and vacuum dries the precipitate extracted with fresh ethanol at 120°C for 12 hours to obtain a soluble polyimide solid.

[0138] (III) Preparation of polyimide solution

[0139] S31 dissolving the soluble polyimide solid in anhydrous DMAC to prepare a polyimide solution containing polyimide molecular chains, wherein the amount of DMAC is such that the solid content of the polyimide solution is 10%;

[0140] (IV) Preparation of polyimide film

[0141] S41′: uniformly coating the polyimide solution on a glass substrate, and drying in a forced air oven at 60° C. for 1 h;

[0142] S42' then heats the glass substrate coated with the polyimide solution to 360°C in a vacuum oven by a gradient heating method and then keeps the temperature for 1 hour to remove the polar aprotic solution, thereby obtaining a polyimide film with a thickness of 20 to 30 um.

[0143] Among them, the specific heating steps of the gradient heating method are: the first gradient, heating to 80°C and keeping warm for 1 hour; the second gradient, heating to 180°C and keeping warm for 1 hour; the third gradient, heating to 250°C and keeping warm for 1 hour; the fourth gradient, heating to 300°C and keeping warm for 1 hour; the fifth gradient, heating to 360°C and keeping warm for 1 hour.

[0144] Results Test Analysis

[0145] The performance test and analysis were performed on the polyamide-polyimide films prepared in Examples 1 to 4 and the polyimide film prepared in the comparative example.

[0146] Test environment conditions: temperature 15℃~35℃, relative humidity 40%~60%.

[0147] Test equipment and test conditions:

[0148] 1. Thermogravimetric analysis (TGA)

[0149] Test equipment: Perkinelmer PE Pyrisl TGA;

[0150] Test conditions: sample mass 3-5 mg, gas flow rate 40 mL min -1 , heating rate is 10℃·min -1The test temperature range was 50-800°C and the flow rate was 20 mL min -1 ) atmosphere.

[0151] 2. Dynamic Mechanical Analysis (DMA)

[0152] Test equipment: DMA Q800;

[0153] Test conditions: film sample, tested in film stretching mode, test frequency of 1 Hz, tested in air atmosphere, heating rate of 10 °C min -1 .

[0154] 3. Thermomechanical Diffraction (TMA)

[0155] Test equipment: TMA Q400;

[0156] Test conditions: film sample, tested on film stretching fixture, test frequency 1 Hz, tested in air atmosphere, heating rate 10℃·min -1

[0157] 4. Ultraviolet-visible spectrometer (UV)

[0158] Test equipment: SHIMADZU U-3900 UV-Vis spectrometer

[0159] Test conditions: The test spectrum is of transmission type, and the scanning rate is 300nm·min -1 , scanning range 200~800nm.

[0160] 5. Gel Permeation Chromatography (GPC):

[0161] Test equipment: Breeze GP system from Waters;

[0162] Test conditions: The test solvent is DMF, and the sample concentration is 1-2 mg·mL -1 , polymethyl methacrylate was used as the standard sample.

[0163] The test results are as follows:

[0164] 1. Optical performance

[0165] Table 1

[0166]

[0167]

[0168] Where: T 400 is the transmittance of the film at 400nm; λ0 is the cut-off wavelength.

[0169] As shown in Table 1, the optical properties of polyimide are basically maintained by introducing aromatic polyamide into polyimide through in-situ polymerization.

[0170] 2 Thermal performance

[0171] Table 2

[0172]

[0173] Where: T1% and T5% represent the temperatures at which the thermal weight loss is 1% and 5% respectively in a nitrogen atmosphere; T g represents the glass transition temperature measured by DMA method; CTE represents the coefficient of thermal expansion measured by TMA method, ranging from 50 to 250°C; M n 、M w and PDI represent the number average molecular weight, weight average molecular weight and dispersity index respectively as measured by GPC method.

[0174] As shown in Table 2, the thermal properties of polyimide are well maintained by introducing polyamide into polyimide through in-situ polymerization. As the content of aromatic polyamide increases, the CTE decreases significantly. When the ratio of aromatic polyamide content to polyimide content reaches 0.67:1, the CTE value is 0.8ppm·K -1 , which was reduced by 98.7% compared with the control group.

[0175] The above data show that the polyamide-polyimide composite film prepared by the present invention can effectively improve the problem of poor dimensional stability and mechanical properties of the polyimide film while maintaining the unique optical transparency and thermal properties of the polyimide film. The polyamide-polyimide composite film prepared by the preparation method of the present invention has a lower thermal expansion coefficient and a higher glass transition temperature, and has excellent dimensional thermal stability.

[0176] The method designed by the present invention adopts in-situ polymerization to uniformly disperse the reinforcing phase aromatic polyamide molecular chains into the polyimide matrix, and can obtain a double-chain interpenetrating network structure formed by large molecular weight polyimide molecular chains and aromatic polyamide molecular chains; the interaction between the double chains minimizes the interface void ratio, can effectively avoid light scattering, and achieve high light transmittance of the film; the interpenetrating hydrogen bond network structure between the double chains increases the rigidity of the molecular chains, reduces the relative mobility, reduces the molecular distance, and closely stacks the chain segments, which can effectively improve the thermal dimensional stability of the film, and the low thermal expansion coefficient makes the film not easy to curl or peel off during the device processing; the high glass transition temperature ensures that the film does not change in size or even melt when processed in a high-temperature atmosphere.

[0177] The present invention is not limited to the above-mentioned embodiments. If various changes or modifications to the present invention do not depart from the spirit and scope of the present invention, and if these changes and modifications fall within the scope of the claims and equivalent technologies of the present invention, the present invention is also intended to include these changes and modifications.

Claims

1. A method for preparing a polyamide-polyimide composite, characterized in that: The diamine monomer is dissolved in a soluble polyimide solution, and at least one polymer monomer that introduces hydrogen bonding is slowly added to the solution to generate an aromatic polyamide molecular chain, and the aromatic polyamide molecular chain is chemically blended with the polyimide molecular chain through in-situ polymerization to obtain an aromatic polyamide-polyimide double-chain blended polymer, wherein the aromatic polyamide-polyimide double-chain blended polymer has a double-chain structure formed by an aromatic polyamide molecular chain and a polyimide molecular chain, and the double-chain has an interpenetrating hydrogen bond network structure, and its structural formula is: Wherein, m and n are positive integers representing the degree of polymerization, 5≤m≤100, 10≤n≤550, R1, R2, R3, R4 are the same or different, and each independently represents a substituted or unsubstituted cycloalkyl, aryl, saturated or unsaturated heterocyclic group, or a skeleton structure formed by a combination thereof.

2. The preparation method according to claim 1, characterized in that: The molar ratio of the aromatic polyamide molecular chain to the polyimide molecular chain is in the range of (0.1-0.7):

1.

3. A polyamide-polyimide composite, characterized in that: The composite has a double-chain structure formed by aromatic polyamide molecular chains and polyimide molecular chains, and the double-chains have an interpenetrating hydrogen bond network structure, and its structural formula is: Wherein, m and n are positive integers representing the degree of polymerization, 5≤m≤100, 10≤n≤550, R1, R2, R3, R4 are the same or different, and each independently represents a substituted or unsubstituted cycloalkyl, aryl, saturated or unsaturated heterocyclic group, or a skeleton structure formed by a combination thereof.

4. The polyamide-polyimide composite according to claim 3, characterized in that: The polyimide is a soluble polyimide.

5. The polyamide-polyimide composite according to claim 4, characterized in that: The cycloalkyl group is a C4-C30 cycloalkyl group, the aryl group is a C6-C30 aryl group, and the saturated or unsaturated heterocyclic group is a C3-C30 heterocyclic group containing one or more identical or different heteroatoms, wherein the heteroatoms are selected from oxygen, nitrogen, and sulfur.

6. The polyamide-polyimide composite according to claim 4, characterized in that: The substituted cycloalkyl, aryl, saturated or unsaturated heterocyclic group has one or more substituents, and the substituents are selected from C1-C6 alkyl, C1-C6 halogen-substituted alkyl, -O-, halogen, phenyl or a substituent composed of a plurality of these groups.

7. The polyamide-polyimide composite according to claim 4, characterized in that: R1 in the aromatic polyamide molecular chain is the same or different and is independently selected from: In the above structural formulas, R5, R6, R7, R8, R 10 The same or different, each independently is H or selected from: R9 in the above structural formulas are the same or different and are independently selected from: Among them, the wavy line represents a connecting bond, and P is a positive integer.

8. The polyamide-polyimide composite according to claim 4, characterized in that: R2 in the aromatic polyamide molecular chain and R4 in the polyimide molecular chain are the same or different and are independently selected from: In the above structural formulas, R 11 are the same or different, each independently selected from: methyl, trifluoromethyl, fluorine atom, hydrogen atom, The dotted line represents a ring connection.

9. The polyamide-polyimide composite according to claim 4, characterized in that: R3 in the polyimide molecular chain is the same or different and is independently selected from: The dotted line represents a ring connection.

10. The polyamide-polyimide composite according to any one of claims 3 to 9, which is made into a thin film material and used in flexible electronic devices.

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