Solvent-soluble polyimide and method for producing the same

Abstract

The present invention provides a polyimide comprising a dianhydride acid monomer and a diamine monomer containing 4,4'-methylenebis(2,6-diethylaniline) (MEDA) as polymerization units, wherein the polymerization units are arranged irregularly in a random copolymer.

Description

Technical Field

[0001] The present invention relates to a solvent-soluble polyimide and a method for producing the same. Specifically, the present invention relates to a polyimide having excellent thermal and mechanical properties and having a soluble property in an organic solvent, and a method for producing the same.

Background Art

[0002] Generally, polyimide (PI) is a polymer material based on an imide ring with a very excellent chemical stability together with a rigid aromatic main chain, and has the highest level of heat resistance, chemical resistance, electrical insulation, chemical resistance, and weather resistance among organic materials, and can be produced in various forms such as films, fiberization, and membranes. Due to such characteristics, polyimide is widely used in a wide range of fields as a leading material and an insulating coating agent in the fields of electric and electronic, semiconductor, display, automobile, aviation, and space materials.

[0003] Polyimide can be produced by dissolving a dianhydride having two acid anhydride groups in a molecule and a diamine having two amino groups in a molecule in a solvent to synthesize a polyimide precursor called polyamic acid (PAA), then coating and drying, and heat-treating at a temperature of about 350°C to imidize. Conventionally, there have been many demands for handling polyimide in a solution state, and many developments have been made on solvent-soluble polyimide.

[0004] However, conventionally, polyimide produced by imidization by a dehydration and ring closure reaction by a chemical method or a high-temperature method has a problem that it is difficult to process because it has an insoluble property in a solvent. In addition, in order to produce a solvent-soluble polyimide, generally, only monomers with high solubility can be used, but these monomers generally have low heat resistance, so the produced polyimide has problems of low heat resistance and chemical resistance. On the other hand, in order to use polyimide in the form of a solution while having heat resistance and chemical resistance, there is a method of forming a coating film with a polyamic acid solution which is a polyimide precursor and then imidizing to produce polyimide.

[0005] However, polyamic acid solutions have disadvantages: they are susceptible to humidity, making them difficult to handle and store, and they require a high-temperature heat treatment process to imide the polyamic acid.

[0006] Against this backdrop, there is a need to develop a polyimide that maintains the high heat resistance and insulating properties of polyimides, is easily soluble in organic solvents, and allows for the production of polyimide-based products solely through solvent drying without a high-temperature imidation process. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a polyimide (PI) that is soluble in organic solvents and also has excellent thermal and mechanical properties.

[0008] Furthermore, the present invention aims to provide a polyimide that is fully imidized and can be manufactured in various forms, such as films and fibers, simply by drying the solvent without a high-temperature imidization process.

[0009] Furthermore, the present invention aims to provide a polyimide solution containing the above-mentioned polyimide.

[0010] Furthermore, the present invention aims to provide a polyimide powder containing the above-mentioned polyimide.

[0011] Furthermore, the present invention aims to provide a polyimide film containing the above-mentioned polyimide.

[0012] Furthermore, the present invention aims to provide the above-mentioned polyimide in various forms, such as separation membranes, binders, insulating coatings, and coating materials.

[0013] Furthermore, the present invention aims to provide a method for producing the above-mentioned polyimide. [Means for solving the problem]

[0014] Because the present invention can be modified in various ways and has various embodiments, specific embodiments will be illustrated and described in detail. However, this should not be understood as limiting the present invention to specific embodiments, but rather as including all modifications, equivalents, or substitutions that fall within the spirit and technical scope of the present invention.

[0015] The terms used in this application are used solely to describe specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, terms such as “includes” or “having” specify the presence of features, figures, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood not to preclude the presence or possibility of adding one or more other features, figures, steps, actions, components, parts, or combinations thereof.

[0016] Wherever a quantity, concentration, or other value or parameter is given in this specification by enumeration of ranges, preferred ranges, preferred upper limits, and preferred lower limits, it should be understood that this specifically discloses all ranges formed by any pair of limits or preferred values ​​of any upper range and any limits or preferred values ​​of any lower range, regardless of whether the ranges are disclosed separately.

[0017] Where numerical ranges are referred to herein, unless otherwise specified, the range, its endpoints, and the scope of the invention within that range are not intended to be limited to the specific values ​​referred to when defining the range.

[0018] In this specification, “dianhydride” is intended to include its precursors or derivatives, but it may also be referred to as “dianhydric acid,” “dianhydride,” or “acidic dianhydride.” These may not be technically dianhydrides, but nevertheless react with diamines to form polyamic acids, which can also be converted to polyimides.

[0019] In this specification, “diamine” is intended to include its precursors or derivatives, which may not be technically diamines, but nevertheless react with dianhydride acids to form polyamic acids, which can also be converted to polyimides.

[0020] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as those generally understood by a person of ordinary skill in the art to which this invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having the meaning consistent with their meaning in the context of the relevant art, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application. The specific details for realizing the invention are described below.

[0021] This invention relates to polyimides (PI) that are soluble in organic solvents.

[0022] Polyimide The present invention provides a polyimide comprising a dianhydride acid monomer and a diamine monomer containing 4,4'-methylenebis(2,6-diethylaniline) (MEDA) as polymerization units, wherein the polymerization units are arranged irregularly in a random copolymer.

[0023] The random copolymer is a copolymer composed of three or more types of polymerization units (repeating units), and means that the order of the polymerization units is randomly linked. For example, the expression of a random copolymer of polymerization units A to D, “-(A)a-(B)b-(C)c-(D)d-”, means that the polymerization units are randomly linked in various forms such as -(A-B-A-D-A-B-A-B-C)-, -(A-A-C-C-C-B-B-D-B)-, -(A-A-D-A-B-A-D-A-B-A-C-C)-, etc., and a, b, c, and d represent the ratios of the polymerization units A, B, C, and D.

[0024] The dianhydride acid monomer can include one or more selected from the group consisting of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), biphenyltetracarboxylic dianhydride (BPDA), and 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA). More specifically, it may be any one or a combination of one or more of the dianhydride acid monomers mentioned above. More specifically, the dianhydride acid monomer preferably consists of one type. More specifically, it preferably includes 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA).

[0025] The diamine monomer may further include one or more selected from the group consisting of 2,4-diaminotoluene (2,4-TDA), 2,6-diaminotoluene (2,6-TDA), m-phenylenediamine (m-PD), and p-phenylenediamine (p-PD). More specifically, it may be a combination that further includes any one or one or more of the diamine monomers mentioned above. More specifically, the diamine monomer preferably further includes one type. More specifically, it preferably includes 2,4-diaminotoluene (2,4-TDA).

[0026] In one embodiment, the polyimide can include 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) as a dianhydride monomer; and 4,4′-methylenebis(2,6-diethylaniline) (MEDA) and 2,4-diaminotoluene (2,4-TDA) as diamine monomers, as polymerization units.

[0027] Among all the diamine monomers, the content of 4,4′-methylenebis(2,6-diethylaniline) (MEDA) may be more than 0 mol% and 15 mol% or less. For example, the upper limit may be 15 mol% or less, 14 mol% or less, 13 mol% or less, 12 mol% or less, 11 mol% or less, and the lower limit may be 0.1 mol% or more, 0.5 mol% or more, 1 mol% or more, 2 mol% or more, 3 mol% or more, 4 mol% or more. Specifically, the MEDA content may be 3 to 12 mol%.

[0028] Among all the diamine monomers, the content of 2,4-diaminotoluene (2,4-TDA) may be less than 100 mol% and 85 mol% or more. For example, the lower limit may be 85 mol% or more, 86 mol% or more, 87 mol% or more, 88 mol% or more, 89 mol% or more, and the upper limit may be 99.9 mol% or less, 99.5 mol% or less, 99 mol% or less, 98 mol% or less, 97 mol% or less, 96 mol% or less. Specifically, it may be 88 to 97 mol%.

[0029] The polyimide can contain 90 to 110 mol% of the diamine monomer, preferably 95 to 105 mol%, and more preferably 100 mol%.

[0030] The polyimide can contain 90 to 110 mol% of the dianhydride acid monomer, preferably 95 to 105 mol%, and more preferably 100 mol%.

[0031] The polyimide can contain the dianhydride acid monomer and the diamine monomer in a molar ratio of 1:2 to 2:1, preferably in a molar ratio of 1:1.

[0032] The polyimide exhibits excellent solubility in organic solvents at solid content concentrations of 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, 23 wt%, 24 wt%, or 25 wt% or more. In one embodiment, 20 wt% of the polyimide solid content was added at room temperature, stirred for 30 minutes, and the turbidity of the solution was visually confirmed.

[0033] The organic solvent may be an aprotic polar organic solvent, and specifically, it may contain one or more selected from the group consisting of N-methylpyrrolidone (NMP), N,N'-dimethylformamide (DMF), N,N'-diethylformamide (DEF), N,N'-dimethylacetamide (DMAc), dimethylpropanamide (DMPA), and N,N-diethylacetamide (DEAc).

[0034] In this invention, we identified the thermal decomposition temperature (Td), which is mainly used as a criterion for determining the thermal properties of the polyimide, and the glass transition temperature (Tg), which can predict thermal properties and also ensure mechanical properties.

[0035] The 5% wt% thermal decomposition temperature (Td) of the polyimide may be 485°C or higher. For example, the lower limit of the thermal decomposition temperature may be 487±1°C, 490±1°C, 493±1°C, 495±1°C, or 496±1°C or higher. The thermal decomposition temperature can be measured using a TA-Q50 thermogravimetric analysis model. In a specific example, the polyimide is heated to 100°C at a rate of 10°C / min under a nitrogen atmosphere, and then kept isothermal for 1 hour to remove moisture. Next, the temperature is raised to 600°C at a rate of 10°C / min, and the temperature at which a 5% weight loss occurs can be measured.

[0036] The glass transition temperature (Tg) of the polyimide may be 300°C or higher. For example, the lower limit of the glass transition temperature may be 305±1°C, 310±1°C, 312±1°C, 315±1°C, 317±1°C, or 318±1°C or higher. The glass transition temperature can be measured for the polyimide using DMA at a rate of 5°C / min.

[0037] The polyimide of the present invention is characterized by maintaining excellent thermal properties and having excellent solubility in organic solvents.

[0038] The polyimide of the present invention achieves heat resistance by reducing the MEDA content to 15 mol% or less through the irregular arrangement of polymerization units, while also realizing solubility in solvents. As a result, it is easily soluble in organic solvents, and films, fibers, and the like can be manufactured simply by drying the solvent, without the need for a high-temperature imidation process.

[0039] Furthermore, the polyimide film has a tensile strength of 90 MPa or higher, preferably 95 MPa or higher, and there is no particular upper limit, although it may be 400 MPa or lower. The tensile strength was measured using an Instron 5564 UTM instrument manufactured by INSTRON.

[0040] The polyimide film has a modulus of 2.5 GPa or higher, preferably 3 GPa or higher. The modulus was measured using an Instron 5564 UTM instrument manufactured by INSTRON.

[0041] The polyimide film has an elongation of 3.5% or more, preferably 4.0% or more. The elongation was measured using an Instron 5564 UTM instrument manufactured by INSTRON.

[0042] In another aspect, the present invention provides a polyimide solution comprising the polyimide and an organic solvent.

[0043] The polyimide of the present invention has excellent solubility in organic solvents, and therefore has the advantage of being easily usable in polyimide films, fibers, or coatings when used in the form of a solution dissolved in an organic solvent.

[0044] In the present invention, the polyimide solution may contain a polyimide solid content of 15 to 50% by weight per 100 parts by weight of the polyimide solution. The lower limit of the solid content by weight may be 16, 17, 18, 19, or 20% by weight or more, and the upper limit of the solid content by weight may be 45, 40, 35, 30, 27, or 25% by weight or less. By adjusting the solid content of the polyimide solution, the increase in viscosity can be controlled, and the process time during the curing process can be shortened.

[0045] In one embodiment, the viscosity of the polyimide solution of the present invention, measured at a temperature of 23°C and a shear rate of 1 s⁻¹, may be in the range of 200 to 30,000 cP. Specifically, the lower limit of the viscosity of the polyimide solution may be 300 cP or more, 400 cP or more, 500 cP or more, 600 cP or more, 700 cP or more, or 800 cP or more, and the upper limit may be 20,000 cP or less, 15,000 cP or less, 10,000 cP or less, 9,000 cP or less, 8,000 cP or less, 7,000 cP or less, 6,500 cP or less, 6,300 cP or less, or 6,100 cP or less. By adjusting the viscosity range of the polyimide solution, it is possible to produce a polyimide cured product with excellent processability and desired physical properties. The viscosity is the viscosity obtained by redissolving 20 wt% of polyimide solids in an organic solvent.

[0046] In another aspect, the present invention provides a polyimide powder containing the polyimide.

[0047] In another aspect, the present invention provides a polyimide film containing the polyimide.

[0048] The thickness of the polyimide film can be appropriately selected considering the application, usage environment, and physical properties of the polyimide film. For example, the thickness of the polyimide film may be 1 to 100 μm, 5 to 50 μm, 10 to 40 μm, or 15 to 25 μm, but is not limited to these.

[0049] In another aspect, the present invention provides a part that includes a molded body formed from the polyimide.

[0050] Specifically, the components may be, but are not limited to, electronic circuit board components, semiconductor devices, lithium-ion battery components, solar cell components, fuel cell components, motor windings, engine peripheral components, paints, optical components, heat dissipation materials, electromagnetic shielding materials, surge components, dental materials, slide coatings, and electrostatic chucks.

[0051] Furthermore, the present invention provides a separation membrane containing the polyimide described above.

[0052] Furthermore, the present invention provides a fiber containing the polyimide described above.

[0053] Furthermore, the present invention provides an insulating layer containing the polyimide described above. Furthermore, the present invention provides a coating layer containing the polyimide described above.

[0054] Method for producing polyimide The present invention provides a method for producing polyimide, comprising the steps of (a) adding a dianhydride acid monomer to a diamine monomer containing 4,4'-methylenebis(2,6-diethylaniline) (MEDA), and (b) randomly polymerizing the diamine monomer and the dianhydride acid monomer.

[0055] The dianhydride acid monomer may include one or more selected from the group consisting of 3,3',4,4'-benzophenone tetracarboxylic dianehydride (BTDA), oxydiphthalic dianehydride (ODPA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), biphenyltetracarboxylic acid dianhydride (BPDA), and 3,3',4,4'-diphenylsulfone tetracarboxylic dianehydride (DSDA).

[0056] The diamine monomer may further contain one or more selected from the group consisting of 2,4-diaminotoluene (2,4-TDA), 2,6-diaminotoluene (2,6-TDA), m-phenylenediamine (m-PD), and p-phenylenediamine (p-PD).

[0057] Step (a) may include (a-1) dissolving a diamine monomer containing 4,4'-methylenebis(2,6-diethylaniline) (MEDA) in an organic solvent, and (a-2) adding a dianhydride monomer to the dissolved diamine monomer.

[0058] Specifically, step (a) may be a step in which the entire diamine monomer is dissolved in an organic solvent, and then the entire dianhydride monomer is added and dissolved.

[0059] The random polymerization in step (b) may be carried out for 10 to 120 minutes, preferably for 30 to 100 minutes, and more preferably for 50 to 70 minutes.

[0060] In one embodiment, polyamic acid (PAA) can be produced by random polymerization of the diamine monomer and the dianhydride monomer, wherein the polyamic acid is produced at a temperature of 23°C and 1 s -1The viscosity measured under the shear rate conditions may be in the range of 200 to 30,000 cP. Specifically, the lower limit of the viscosity of the polyimide solution may be 300 cP or higher, 400 cP or higher, 500 cP or higher, 600 cP or higher, 700 cP or higher, or 800 cP or higher, and the upper limit may be 20,000 cP or lower, 15,000 cP or lower, 10,000 cP or lower, 9,000 cP or lower, 8,000 cP or lower, 7,000 cP or lower, 6,500 cP or lower, 6,300 cP or lower, or 6,100 cP or lower. By adjusting the viscosity range of the polyamic acid, it is possible to produce a polyimide solution and / or cured product with excellent processability and desired physical properties.

[0061] In step (b), the diamine monomer and the dianhydride monomer are polymerized to produce a polyamic acid, and after step (b), the step (c) may further include imidizing the polyamic acid to produce a polyimide.

[0062] In step (c), a dehydrating agent and a catalyst may be added to the polyamic acid in order to imide the polyamic acid. The dehydrating agent is not particularly limited as long as it can promote the ring-closing reaction by dehydrating the polyamic acid, and examples of such dehydrating agents include acetic anhydride. The catalyst is not particularly limited as long as it can promote the ring-closing reaction of the polyamic acid, and examples of such catalysts include tertiary amines, such as quinoline, isoquinoline (IQ), and β-picoline (BP).

[0063] The imidation reaction carried out in step (c) above results in an imidation rate of 97-100%, preferably 98-100%, more preferably 99-100%, and most preferably 100%.

[0064] The process may further include step (d) purifying and filtering the polyimide, followed by drying.

[0065] In step (d), the polyimide can be purified by precipitation in a non-solvent to remove impurities. Examples of the non-solvent include, but are not limited to, water, methanol, ethanol, n-propanol, isopropanol, butanol, butanediol, ethylene glycol, glycerol, γ-butyrolactone, or mixtures thereof.

[0066] Furthermore, the filtration may be carried out by one or more combinations selected from the group consisting of gravity filtration, reduced pressure filtration, vacuum filtration, pressure filtration, compression filtration, centrifugal filtration, microfiltration, ultrafiltration, and reverse osmosis.

[0067] Furthermore, the drying may be carried out by one or more combinations selected from the group consisting of natural drying, pressure drying, hot air drying, spray drying, coating drying, vacuum drying, freeze drying, spray freeze drying, electromagnetic wave drying, and flash drying methods. [Effects of the Invention]

[0068] The polyimide according to the present invention has excellent solubility in organic solvents and also exhibits excellent thermal and mechanical properties.

[0069] Furthermore, the polyimide according to the present invention is fully imidized and can be manufactured in various forms such as films and fibers simply by drying the solvent, without the need for a high-temperature imidization process, thus improving the ease of the manufacturing process.

[0070] Furthermore, the polyimide according to the present invention has the effect of being applicable to various fields such as separation membranes, binders, insulating coatings, coating materials, and fibers. [Brief explanation of the drawing]

[0071] [Figure 1] This shows the evaluation results of the solubility of polyimides produced in Examples 1 and 2 and Comparative Example 1 in organic solvents. [Modes for carrying out the invention]

[0072] To aid in understanding the present invention, examples are provided below. The following examples are provided to facilitate understanding of the present invention and do not limit the scope of the invention.

[0073] <Examples> Example 1: Production of polyimide Under a nitrogen / room temperature atmosphere, 5 mol% of 4,4'-methylenebis(2,6-diethylaniline) (MEDA) and 95 mol% of 2,4-diaminotoluene (2,4-TDA) were dissolved in dimethylformamide (DMF) organic solvent. Then, 100 mol% of 3,3',4,4'-benzophenone tetracarboxylic dianehydride (BTDA) was added, and the MEDA, 2,4-TDA, and BTDA were randomly polymerized for 1 hour to obtain a polyamic acid composition.

[0074] To the obtained polyamic acid composition, a tertiary catalyst (BP, β-picoline) and a dehydrating agent (acetic anhydride, AA) were added, and a chemical imidation process was carried out in a continuous batch polymerization process at 60°C. Next, after the reaction was complete, the polymer was precipitated in an ethanol-free solvent to remove impurities (unreacted material, tertiary catalyst, AA, etc.), and this was dried in a vacuum oven at a temperature of less than 150°C for 24 hours to produce polyimide powder (solids content 20 wt%).

[0075] Example 2: Production of polyimide Polyimide powder was prepared in the same manner as in Example 1, except that instead of using 5 mol% methylenebis(2,6-diethylaniline)(MEDA) and 95 mol% 2,4-diaminotoluene(2,4-TDA) as in Example 1, 10 mol% methylenebis(2,6-diethylaniline)(MEDA) and 90 mol% 2,4-diaminotoluene(2,4-TDA) were used.

[0076] Comparative Example 1: Production of Polyimide Under a nitrogen / room temperature atmosphere, 5 mol% of 4,4'-methylenebis(2,6-diethylaniline) (MEDA) was dissolved in dimethylformamide (DMF) organic solvent, and then 100 mol% of 3,3',4,4'-benzophenone tetracarboxylic dianehydride (BTDA) was added and block polymerization was carried out for 1 hour. Subsequently, 95 mol% of 2,4-diaminotoluene (2,4-TDA) was added and block polymerization was carried out for 1 hour to obtain a polyamic acid composition.

[0077] The obtained polyamic acid composition was mixed with a tertiary catalyst (BP, β-picoline) and a dehydrating agent (acetic anhydride, AA), and a chemical imidation process was carried out in a continuous batch polymerization process at 60°C. After the reaction was complete, the polymer was precipitated in an ethanol-free solvent to remove impurities (unreacted material, tertiary catalyst, AA, etc.), and this was dried in a vacuum oven at a temperature of less than 150°C for 24 hours to produce polyimide powder (solids content 20 wt%).

[0078] Table 1 below lists the monomer components, content, polymerization method, etc., of Examples 1 and 2 and Comparative Example 1. In Table 1 below, viscosity is given at a temperature of 23°C and 1s. -1 The measurements were taken under the specified shear rate conditions, and the molecular weight was measured using gel chromatography (GPC). In Table 1 below, PAA polymerization viscosity refers to the viscosity of the polyamic acid composition, PAA molecular weight refers to the molecular weight of the polyamic acid composition, 20 wt% redissolution viscosity refers to the viscosity obtained by redissolving polyimide powder (20 wt% solids) in an organic solvent, and redissolution PI molecular weight refers to the molecular weight obtained by redissolving polyimide powder (20 wt% solids) in an organic solvent.

[0079] [Table 1]

[0080] Example 3: Production of polyimide film The polyimide powder produced in Example 1 was dissolved in an organic solvent (DMF) to obtain a 20 wt% solids solution. This solution was then coated onto a glass substrate to a thickness of 20 μm using a spin coater (MS-B200, Mikasa) and dried at 250°C for 20 minutes. The coating method is not particularly limited. After cooling at 25°C, the solution was separated from the glass substrate to produce a polyimide film with a thickness of approximately 20 μm.

[0081] Example 4: Production of polyimide film A polyimide film was manufactured in the same manner as in Example 3, except that the polyimide powder manufactured in Example 2 was used instead of the polyimide powder manufactured in Example 1.

[0082] Comparative Example 3: Manufacturing of Polyimide Film A polyimide film was manufactured in the same manner as in Example 3, except that instead of using the polyimide powder manufactured in Example 1, the polyimide powder manufactured in Comparative Example 1 was used in Example 3.

[0083] <Example of experiment> Experimental Example 1. Evaluation of Solubility The solubility of polyimide in organic solvents was evaluated by adding 20 g of polyimide powder prepared in Examples 1 and 2 and Comparative Example 1 to 80 g of the organic solvent N,N'-dimethylformamide (DMF) and visually checking the solution. Specifically, at room temperature, 20 wt% of polyimide solids was added, the mixture was stirred for 30 minutes, and the turbidity of the solution was visually checked. The results are shown in Figure 1.

[0084] As shown in Figure 1, in Examples 1 and 2, the polyimide dissolved well in the organic solvent without any suspended matter, confirming its solubility. On the other hand, in Comparative Example 1, suspended matter appeared, confirming that it did not dissolve well in the organic solvent.

[0085] In other words, although the polyimides of Example 1 and Comparative Example 1 had the same composition, it was found that Example 1 achieved solubility by randomly arranging the polymerization units, unlike Comparative Example 1 in which the polymerization units were arranged regularly. Therefore, the present invention was able to achieve solubility while reducing the MEDA to at least 5 mol% by randomly arranging the polymerization units.

[0086] Experimental Example 2. Evaluation of Glass Transition Temperature (Tg) For the polyimide films produced in Examples 3 and 4 and Comparative Example 3, the point at which rapid expansion occurred was measured using DMA at a temperature of 5°C / min, and this point was defined as the on-set point. The results are shown in Table 2.

[0087] Experimental Example 3: Evaluation of the thermal decomposition temperature (Td) of 5% by weight. Using a TA-manufactured thermogravimetric analysis (Q50 model), the polyimide films produced in Examples 3 and 4 and Comparative Example 3 were heated to 100°C at a rate of 10°C / min under a nitrogen atmosphere, and then kept isothermal for 1 hour to remove moisture. Next, the temperature was increased to 600°C at a rate of 10°C / min, and the temperature at which a 5% weight loss occurred was measured. The results are shown in Table 2 below.

[0088] Table 2 below shows the solubility, glass transition temperature (Tg), and 5% wt thermal decomposition temperature (Td) of the polyimide films produced in Examples 3 and 4 and Comparative Example 3.

[0089] [Table 2]

[0090] Table 2 shows that the polyimide films (random polymerization) produced in Examples 3 and 4 not only exhibited excellent solubility in DMF, a non-protic polar organic solvent, but also maintained excellent thermal properties. On the other hand, in Comparative Example 3, the polyimide powder (block polymerization) from Comparative Example 1 did not dissolve in the organic solvent, and therefore a film could not be produced.

[0091] These results show that by randomly arranging polymerization units and reducing the MEDA content to approximately 10 mol% and 5 mol%, solubility in aprotic polar organic solvents (e.g., DMF) can be achieved, and an improvement in heat resistance (Tg and Td at 5 wt%) can also be confirmed.

[0092] In this specification, details of matters that can be easily understood and inferred by a person with ordinary skill in the art of the present invention have been omitted. Beyond the specific examples described herein, a wide variety of modifications are possible without altering the technical concept or essential configuration of the present invention. Therefore, the present invention can be implemented in ways different from those specifically described and illustrated herein, and this is something that a person with ordinary skill in the art of the present invention can understand.

Claims

1. Dianhydride acid monomers, A polyimide comprising a diamine monomer containing 4,4'-methylenebis(2,6-diethylaniline) (MEDA) as a polymerization unit, The polyimide is a random copolymer in which the polymerization units are irregularly arranged.

2. The polyimide according to claim 1, wherein the dianhydride monomer comprises one or more selected from the group consisting of 3,3',4,4'-benzophenone tetracarboxylic dianehydride (BTDA), oxydiphthalic dianehydride (ODPA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), biphenyltetracarboxylic dianhydride (BPDA), and 3,3',4,4'-diphenylsulfone tetracarboxylic dianehydride (DSDA).

3. The polyimide according to claim 1, wherein the diamine monomer further comprises one or more selected from the group consisting of 2,4-diaminotoluene (2,4-TDA), 2,6-diaminotoluene (2,6-TDA), m-phenylenediamine (m-PD), and p-phenylenediamine (p-PD).

4. The polyimide according to claim 1, wherein the content of 4,4'-methylenebis(2,6-diethylaniline) (MEDA) in the total diamine monomer is greater than 0 mol% and 15 mol% or less.

5. The polyimide according to claim 3, wherein the content of 2,4-diaminotoluene (2,4-TDA) in the total diamine monomer is 85 mol% or more and less than 100 mol%.

6. The polyimide according to claim 1, wherein the polyimide exhibits solubility in organic solvents when the solid content is 15 wt% or more.

7. The polyimide according to claim 6, wherein the organic solvent comprises one or more selected from the group consisting of N-methylpyrrolidone (NMP), N,N'-dimethylformamide (DMF), N,N'-diethylformamide (DEF), N,N'-dimethylacetamide (DMAc), dimethylpropanamide (DMPA), and N,N-diethylacetamide (DEAc).

8. The polyimide according to claim 1, wherein the polyimide has a 5% by weight thermal decomposition temperature (Td) of 485°C or higher.

9. The polyimide according to claim 1, wherein the polyimide has a glass transition temperature (Tg) of 300°C or higher.

10. A polyimide solution comprising the polyimide and organic solvent according to any one of claims 1 to 9.

11. A polyimide film comprising the polyimide described in any one of claims 1 to 9.

12. (a) A step of adding a dianhydride monomer to a diamine monomer containing 4,4'-methylenebis(2,6-diethylaniline) (MEDA), (b) A method for producing polyimide, comprising the step of randomly polymerizing the diamine monomer and the dianhydride monomer.

13. The method for producing polyimide according to claim 12, wherein the dianhydride acid monomer comprises one or more selected from the group consisting of 3,3',4,4'-benzophenone tetracarboxylic dianehydride (BTDA), oxydiphthalic dianehydride (ODPA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), biphenyltetracarboxylic acid dianhydride (BPDA), and 3,3',4,4'-diphenylsulfone tetracarboxylic dianehydride (DSDA).

14. The method for producing polyimide according to claim 12, wherein the diamine monomer further comprises one or more selected from the group consisting of 2,4-diaminotoluene (2,4-TDA), 2,6-diaminotoluene (2,6-TDA), m-phenylenediamine (m-PD), and p-phenylenediamine (p-PD).

15. Step (a) is, (a-1) A step of dissolving a diamine monomer containing 4,4'-methylenebis(2,6-diethylaniline) (MEDA) in an organic solvent, (a-2) A method for producing polyimide according to claim 12, comprising the step of adding a dianhydride acid monomer to the dissolved diamine monomer.

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