Solvent soluble polyimide with simplified preparation method and preparation method thereof

Abstract

The present invention provides a method for preparing a polyimide, comprising: (a) polymerizing a diamine monomer and a dianhydride monomer to prepare a polyamic acid; and (b) reacting the polyamic acid with the carbonyldiimidazole to produce a soluble polyimide, wherein the soluble polyimide is in the form of a paint.

Description

Technical Field

[0001] This invention relates to solvent-soluble polyimides and methods for their preparation. More specifically, this invention relates to polyimides possessing excellent thermal and mechanical properties while simplifying the process, and methods for their preparation. Background Technology

[0002] Polyimide (PI) is typically a polymer material based on an imide ring and a rigid aromatic backbone, exhibiting excellent chemical stability. It possesses the highest levels of heat resistance, chemical resistance, electrical insulation, and weather resistance among organic materials, allowing it to be fabricated in various forms such as films, fibers, and thin films. Due to these properties, polyimide is used as an advanced material and insulating coating in a wide range of fields, including electrical and electronic, semiconductor, display, automotive, aerospace, and other materials applications.

[0003] Polyimides can be prepared by dissolving an acid dianhydride having two anhydride groups in its molecule and a diamine having two amino groups in its molecule in a solvent to synthesize a polyimide precursor called polyamic acid (PAA), followed by applying the polyimide precursor and drying it, and then heat-treating it at about 350°C to perform imidization. Due to the high demand for processing polyimides in solution, extensive development has been undertaken on solvent-soluble polyimides.

[0004] However, conventional polyimides prepared by imidization through dehydration and ring-closing reactions using conventional chemical or thermal (high-temperature) methods are insoluble in solvents, leading to processing difficulties. Furthermore, to prepare solvent-soluble polyimides, there is usually no choice but to use highly soluble monomers, but these monomers typically have low heat resistance, resulting in polyimides with low heat and chemical resistance. Meanwhile, to use polyimides that are both heat-resistant and chemically resistant while remaining in solution form, there are methods for preparing polyimides by forming a coating film with a polyamic acid solution (which is a polyimide precursor) followed by imidization.

[0005] Meanwhile, polyamic acid solutions have the disadvantages of being susceptible to moisture and difficult to handle and store, and require complex and lengthy processing or high-temperature heat treatment to imidize polyamic acid.

[0006] In this context, there is a need to develop polyimides that can maintain their high heat resistance and insulation properties, while being readily soluble in organic solvents and capable of producing polyimide-based products through a simple process. Summary of the Invention

[0007] Technical issues

[0008] One object of the present invention is to provide a method for preparing polyimides with excellent thermal and mechanical properties, while simplifying the preparation process by omitting purification, filtration and drying steps for removing byproducts (impurities).

[0009] Furthermore, another object of the present invention is to provide a method for preparing a fully imidized polyimide that is soluble in an organic solvent.

[0010] Furthermore, another object of the present invention is to provide a polyimide prepared according to the method for preparing a polyimide.

[0011] Furthermore, another object of the present invention is to provide various forms of polyimide, such as separators (films), adhesives, insulating coatings, and coating materials containing polyimide.

[0012] Furthermore, another object of the present invention is to provide a composition for preparing polyimides that can be used in the method for preparing polyimides.

[0013] Technical solution

[0014] Various modifications and multiple embodiments are possible in this invention, and specific embodiments are shown and described in detail in the accompanying drawings. However, these embodiments are not intended to limit the invention to the specific embodiments, but should be understood to include all modifications, equivalents, and alternatives included within the spirit and scope of the invention.

[0015] The terminology used in this application is for describing particular embodiments only and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising / including” or “having” are intended to specify the presence of the features, quantities, steps, operations, components, parts, or combinations thereof described in the specification, and should not be construed as excluding the possibility of the presence or addition of one or more other features, quantities, steps, operations, components, parts, or combinations thereof.

[0016] When quantities, concentrations, or other values ​​or parameters in this document are given as ranges, preferred ranges, or lists of upper and lower expected values, it should be understood that all ranges formed by any pair of any upper or preferred values ​​and any lower or preferred values ​​are specifically disclosed, whether or not such ranges are disclosed individually.

[0017] Unless otherwise stated, when ranges of numerical values ​​are stated herein, the endpoints of the range and the scope of the invention within the range are not limited to the specific values ​​stated when defining the range.

[0018] As used herein, “dianhydride” is intended to include its precursors or derivatives, which are also known as “diacid anhydrides” or “acid dianhydrides”. These products may not be technically dianhydrides, but will still react with diamines to form polyamic acid, and polyamic acid can be converted back to polyimide.

[0019] As used herein, “diamine” is intended to include its precursors or derivatives, which may not be technically diamines but will still react with dianhydrides to form polyamic acid, and polyamic acid can be converted back to polyimide.

[0020] Furthermore, unless otherwise defined, all terms used herein (including technical or scientific terms) have the same meaning as commonly understood by one 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 a meaning consistent with their meaning in the context of the relevant art, and are not to be interpreted in an idealized or overly formal sense unless expressly defined in this application. Specific details for implementing the invention will be described below.

[0021] This invention relates to a method for preparing polyimides, which can produce polyimides with excellent thermal and mechanical properties, while simplifying the preparation process by omitting purification, filtration, and drying steps for removing byproducts (impurities).

[0022] Methods for preparing polyimide

[0023] In one general aspect, the present invention provides a method for preparing a polyimide, comprising: (a) polymerizing a diamine monomer with a dianhydride monomer to prepare a polyamic acid; and (b) reacting the polyamic acid with a carbonyl diimidazole to prepare a soluble polyimide, wherein the soluble polyimide is in the form of a varnish.

[0024] After step (b), the purification process, which includes purification, filtration and drying steps, may be omitted.

[0025] In conventional chemical imidization, polyimide undergoes purification processes such as purification, washing, filtration, and drying to remove byproducts, thereby obtaining it in powder form, which is then dissolved in a polar organic solvent. However, by using the additive carbonyl diimidazole (CDI), which has both catalytic and dehydrating functions, the present invention allows the direct use of polyimide in paint form, while omitting purification processes such as purification, filtration, and drying steps.

[0026] In step (a), 0.5 to 1.5 mol equivalents of carbonyl diimidazole can be reacted with 1 mol equivalent of polyamic acid. For example, the upper limit can be 1.5, 1.4, 1.3, 1.2, 1.1 mol equivalents or less, and the lower limit can be 0.5, 0.6, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or more mol equivalents. When carbonyl diimidazole reacts in amounts less than 0.5 mol equivalents, it is not preferred because the physical properties of the prepared polyimide deteriorate. When carbonyl diimidazole reacts in amounts exceeding 1.5 mol equivalents, it is not preferred because an additional purification process is required.

[0027] Purification can refer to a series of processes after imidization to remove byproducts (impurities, catalysts, unreacted components, etc.), such as purification, washing, filtration, and drying.

[0028] In addition, purification can include purification methods commonly used in polymer synthesis, including reprecipitation, such as alcohol precipitation.

[0029] Step (b) can be performed at temperatures ranging from 20°C to 60°C. For example, the upper limit can be 60°C, 58°C, 55°C, 52°C, 50°C, 48°C, 45°C, 44°C, 43°C, 42°C, 41°C or lower, and the lower limit can be 20°C, 22°C, 25°C, 28°C, 30°C, 32°C, 35°C, 36°C, 37°C, 38°C or higher.

[0030] Step (b) can last from 0.5 hours to 5 hours. For example, its upper limit can be 5 hours, 4.5 hours, 4 hours, 3.5 hours, 3 hours, 2.7 hours or less, and its lower limit can be 0.5 hours, 0.8 hours, 1 hour, 1.2 hours, 1.5 hours, 2.0 hours, 2.3 hours or longer.

[0031] The reaction in step (b) is an imidization reaction, and the imidization rate can be 97% to 100%, preferably 98% to 100%, more preferably 99% to 100%, and most preferably 100%.

[0032] In step (a), the polymerization can be random polymerization or block polymerization.

[0033] Specifically, when random polymerization is carried out, random copolymers can be prepared, and more specifically, copolymers composed of two or more types of polymeric units (repeating units). For example, the expression "-(A)a-(B)b-(C)c-(D)d-" (which is a random copolymer of polymeric units A to D) means that the polymeric units are randomly connected in various forms, such as -(ABADABABC)-, -(AACCCBBDB)-, -(AADABADABACC)-, etc., where a, b, c, and d are the proportions of polymeric units A, B, C, and D, respectively.

[0034] Furthermore, step (a) may include: (a-1) adding the total dianhydride monomer to the total diamine monomer; and (a-2) performing random polymerization on the total dianhydride monomer and the total diamine monomer. For example, when performing random polymerization, the total diamine monomer can be dissolved in an organic solvent, and then the total dianhydride monomer can be added and dissolved, followed by polymerization to prepare polyamic acid.

[0035] Specifically, when block polymerization is performed, block copolymers can be prepared, and more specifically, copolymers composed of two or more types of polymeric units (repeating units). For example, the expression "-(A)a-(B)b-(C)c-(D)d-" (which is a block copolymer of polymeric units A to D) means that the same polymeric units are sequentially connected in the form of -(AAABBBBBCCCCDDD)-, where a, b, c, and d are the proportions of polymeric units A, B, C, and D, respectively.

[0036] Furthermore, step (a) may include: (a-1) adding any dianhydride monomer to any diamine monomer; and (a-2) performing block polymerization on any diamine monomer and any dianhydride monomer, and steps (a-1) and (a-2) may be repeated multiple times. For example, block polymerization can be performed by repeating the following steps to prepare polyamic acid: dissolving a diamine monomer in an organic solvent, adding a dianhydride monomer, followed by polymerization, then adding another diamine monomer, followed by polymerization, adding another dianhydride monomer, followed by polymerization.

[0037] The dianhydride monomer may include at least one selected from the following: pyromellitic dianhydride (PMDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), oxyphthalic dianhydride (ODPA), 4,4'-(hexafluoroisopropylidene)phthalic anhydride (6FDA), biphenyl tetracarboxylic dianhydride (BPDA), 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride (DSDA), and 2,2-bis(4-(3,4-dicarboxyphenoxy)phenyl)propane dianhydride. More specifically, the dianhydride monomer may be any one or a combination of two or more of the above-mentioned dianhydride monomers. More specifically, the dianhydride monomer preferably includes one type, and more specifically, preferably includes 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA).

[0038] The diamine monomer may include at least one of the following: 4,4'-methylenebis(2,6-diethylaniline) (MEDA), 2,4-diaminotoluene (2,4-TDA), 2,6-diaminotoluene (2,6-TDA), m-phenylenediamine (m-PD), p-phenylenediamine (p-PD), 3,3''-diaminodiphenyl sulfone (3,3''-DDS), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 3,5-diethyltoluene-2,6-diamine, 3,5-diethyltoluene-2,4-diamine, and 4,4'-methylenebis(2-ethyl-6-methylaniline) (MEMA). More specifically, the diamine monomer may be any one or a combination of two or more of the above diamine monomers. More specifically, the diamine monomer preferably includes at least one type, and more specifically, preferably includes 4,4'-methylenebis(2,6-diethylaniline) (MEDA) and 2,4-diaminotoluene (2,4-TDA).

[0039] In one embodiment, the polyamic acid can be a polymerization of dianhydride monomer 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) and diamine monomers 4,4'-methylenebis(2,6-diethylaniline) (MEDA) and 2,4-diaminotoluene (2,4-TDA).

[0040] The amount of 4,4'-methylenebis(2,6-diethylaniline) (MEDA) in the total diamine monomers can be greater than 0 mol% and less than or equal to 50 mol%. For example, its upper limit can be 50 mol%, 40 mol%, 30 mol%, 20 mol%, 18 mol%, 17 mol%, 15 mol%, 13 mol%, 12 mol% or less, and its lower limit can be 0.1 mol%, 1 mol%, 2 mol%, 3 mol%, 4 mol% or greater.

[0041] The amount of 2,4-diaminotoluene (2,4-TDA) in the total diamine monomers can be less than 100 mol% but equal to or greater than 50 mol%. For example, its upper limit can be 99.9 mol%, 99 mol%, 98 mol%, 97 mol%, 96 mol% or less, and its lower limit can be 50 mol%, 60 mol%, 70 mol%, 72 mol%, 73 mol%, 75 mol%, 78 mol%, 80 mol% or greater.

[0042] The polyimide may contain a diamine monomer in an amount of 90 mol% to 110 mol%, preferably 95 mol% to 105 mol%, and more preferably 100 mol%.

[0043] The polyimide may contain dianhydride monomers in an amount of 90 mol% to 110 mol%, preferably 95 mol% to 105 mol%, and more preferably 100 mol%.

[0044] Polyimide may contain dianhydride monomers and diamine monomers in a molar ratio of 1:2 to 2:1, preferably in a molar ratio of 1:1.

[0045] Polyimide can be a highly soluble polyimide having a solids content 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 greater in an organic solvent. There is no particular upper limit, but it can be 50 wt% or lower.

[0046] The organic solvent may be an aprotic polar organic solvent, and specifically may include at least one of the following: N-methylpyrrolidone (NMP), N,N'-dimethylformamide (DMF), N,N'-diethylformamide (DEF), N,N'-dimethylacetamide (DMAc), dimethylpropionamide (DMPA), and N,N-diethylacetamide (DEAc).

[0047] In this invention, the thermal decomposition temperature (Td) and the glass transition temperature (Tg) are measured. The thermal decomposition temperature is mainly used as a standard for judging the thermal properties of polyimide, while the glass transition temperature can predict thermal properties and also ensure mechanical properties.

[0048] The thermal decomposition temperature (Td) of polyimide at 5% weight loss can be 485°C or higher. For example, the lower limit of the thermal decomposition temperature of polyimide can be 487±1°C, 490±1°C, 493±1°C, or 495±1°C or higher, and its upper limit can be 600°C or lower, but is not particularly limited thereto. The thermal decomposition temperature can be measured using a TA thermogravimetric analyzer Q50. In one specific example, polyimide can be heated to 100°C at a rate of 10°C / min under a nitrogen atmosphere, and then held isothermally for 1 hour to remove moisture. The temperature can then be increased to 600°C at a rate of 10°C / min, and the temperature at which 5% weight loss occurs can be measured.

[0049] The glass transition temperature (Tg) of polyimide can be 300°C or higher. For example, the lower limit of the glass transition temperature can be 305±1°C, 310±1°C, 312±1°C, 315±1°C, 317±1°C, or 318±1°C or higher, and the upper limit can be 500°C or lower, but is not particularly limited thereto. The glass transition temperature of polyimide can be measured using dynamic mechanical analysis (DMA) at a rate of 5°C / minute.

[0050] Furthermore, the modulus of the polyimide can be 3.0 GPa or greater, preferably 3.3 GPa or greater, and there is no specific upper limit, but it can be less than or equal to 30.0 GPa. The modulus can be measured using an Instron 5564 UTM from INSTRON.

[0051] The tensile strength of polyimide can be 110 MPa or greater, preferably 115 MPa or greater, and there is no particular upper limit, but it can be 400 MPa or less. Tensile strength can be measured using an Instron 5564UTM from INSTRON.

[0052] The elongation of the polyimide can be 5% or greater, preferably 5.2% or greater, and there is no specific upper limit, but it can be less than or equal to 30%. The elongation can be measured using an Instron 5564 UTM from INSTRON.

[0053] Typically, to imidize polyamic acid, a dehydrating agent and a catalyst are added to the polyamic acid, followed by purification and filtration, and drying to remove impurities. However, by using the additive CDI, the method for preparing polyimides according to the present invention can omit the purification process for removing byproducts (impurities), such as purification, filtration, and drying, thereby simplifying the preparation process while producing polyimides with excellent thermal and mechanical properties as well as excellent solubility in solvents.

[0054] In another aspect, the present invention provides a polyimide prepared according to the method for preparing a polyimide. Here, the polyimide may be a solvent-soluble polyimide.

[0055] Polyimide can be in the form of paint, and advantageously, polyimide can be used directly in paint form without any purification process (including purification, filtration and drying steps), thus making it easy to use in polyimide films, fibers or coatings.

[0056] In yet another aspect, the present invention provides a polyimide film comprising the polyimide of the present invention.

[0057] The thickness of the polyimide film can be appropriately selected based on its intended use, operating environment, and physical properties. For example, the thickness of the polyimide film can be 1 μm to 100 μm, 5 μm to 50 μm, 10 μm to 40 μm, or 15 μm to 25 μm, but it is not limited to these values.

[0058] Furthermore, in another aspect, the present invention provides a component comprising a molded body formed from said polyimide.

[0059] Specifically, the components may include, 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, coatings, optical components, thermal insulators, electromagnetic shielding materials, surge components, dental materials, slide coatings, and electrostatic chucks.

[0060] In another aspect, the present invention provides separators (films), fibers, insulating layers, or coatings comprising polyimide as described above.

[0061] In another aspect, the present invention provides a composition for preparing a soluble polyimide, the composition comprising a polyamic acid containing a dianhydride monomer and a diamine monomer as polymerization units; and a carbonyl diimidazole.

[0062] Beneficial effects

[0063] The method for preparing polyimide according to the present invention can omit the purification, filtration and drying steps for removing by-products (impurities), thereby simplifying the preparation process and preparing polyimide with excellent thermal and mechanical properties.

[0064] Furthermore, fully imidized polyimides that are soluble in organic solvents can be prepared.

[0065] Furthermore, the polyimide according to the present invention can be applied to various fields, such as separators (films), adhesives, insulating coatings, coating materials, fibers, etc. Attached Figure Description

[0066] Figure 1 Optical images of polyimide films according to Examples 5-1 and Comparative Examples 9 and 10 are shown. Detailed Implementation

[0067] The following embodiments are presented to aid in understanding the present invention. These embodiments are provided merely to facilitate a clearer understanding of the invention, but the scope of the invention is not limited to these embodiments.

[0068] <Example>

[0069] Example 1: Preparation of polyimide (random copolymer)

[0070] Example 1-1

[0071] In dimethylformamide (DMF) organic solvent, 5 mol% of 4,4'-methylenebis(2,6-diethylaniline) (MEDA) and 95 mol% of 2,4-diaminotoluene (2,4-TDA) were dissolved under a nitrogen / room temperature atmosphere. Then, 100 mol% of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) was added, followed by random polymerization of MEDA, 2,4-TDA, and BTDA for 1 hour to obtain a polyamic acid composition.

[0072] 1.0 mol equivalent of carbonyl diimidazole (CDI) was added to the obtained polyamic acid composition, and a chemical imidization process was carried out in a continuous polymerization batch at 40°C for 2.5 hours to prepare a soluble polyimide (20% by weight solids content) for use as a paint without purification, filtration, and drying. This means that the polyimide is soluble in organic solvents (DMF).

[0073] Examples 1-2

[0074] Soluble polyimide was prepared in the same manner as in Examples 1-1, except that 0.9 molar equivalents of carbonyl diimidazole (CDI) were added instead of 1.0 molar equivalents of carbonyl diimidazole (CDI).

[0075] Examples 1-3

[0076] Soluble polyimide was prepared in the same manner as in Examples 1-1, except that 10 mol% of methylene bis(2,6-diethylaniline) (MEDA) and 90 mol% of 2,4-diaminotoluene (2,4-TDA) was used instead of 5 mol% of methylene bis(2,6-diethylaniline) (MEDA) and 95 mol% of 2,4-diaminotoluene (2,4-TDA).

[0077] Example 2: Preparation of polyimide (block copolymer)

[0078] Example 2-1

[0079] 10 mol% of 4,4'-methylenebis(2,6-diethylaniline) (MEDA) was dissolved in dimethylformamide (DMF) organic solvent under a nitrogen / room temperature atmosphere. Then, 100 mol% of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) was added to the resulting mixture, followed by block polymerization for 1 hour. Next, 90 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.

[0080] 1.0 molar equivalent of carbonyl diimidazole (CDI) was added to the obtained polyamic acid composition, and a chemical imidization process was carried out in a continuous polymerization batch at 40°C for 2.5 hours to prepare a soluble polyimide (20% by weight solids content) for use in the form of a varnish without purification, filtration, and drying.

[0081] Example 2-2

[0082] Soluble polyimide was prepared in the same manner as in Example 2-1, except that 20 mol% of 4,4'-methylenebis(2,6-diethylaniline) (MEDA) and 80 mol% of 2,4-diaminotoluene (2,4-TDA) were added instead of 10 mol% of 4,4'-methylenebis(2,6-diethylaniline) (MEDA) and 90 mol% of 2,4-diaminotoluene (2,4-TDA).

[0083] Example 3: Preparation of polyimide (random copolymer)

[0084] Examples 3-1 to 3-3

[0085] Soluble polyimides were prepared in the same manner as in Examples 1-1, using different types and amounts of monomers and additives as shown in Table 1 below.

[0086] Example 4: Preparation of polyimide (block copolymer)

[0087] Examples 4-1 to 4-3

[0088] Soluble polyimides were prepared in the same manner as in Example 2-1, using different types and amounts of monomers and additives as shown in Table 1 below.

[0089] Comparative Example 1: Preparation of polyimide (using catalyst and dehydrating agent)

[0090] In dimethylformamide (DMF) organic solvent, 5 mol% of 4,4'-methylenebis(2,6-diethylaniline) (MEDA) and 95 mol% of 2,4-diaminotoluene (2,4-TDA) were dissolved under a nitrogen / room temperature atmosphere. Then, 100 mol% of 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) was added, followed by random polymerization of MEDA, 2,4-TDA, and BTDA for 1 hour to obtain a polyamic acid composition.

[0091] The obtained polyamic acid composition was added with 0.3 mol equivalents of pyridine (catalyst, Py) and 1.0 mol equivalents of acetic anhydride (dehydrating agent, AA), and the resulting mixture was subjected to a chemical imidization process in continuous batches at 60 °C. Next, after the reaction was complete, the polymer was subjected to a purification process, including precipitation in an ethanol-free solvent to remove impurities (unreacted components, catalyst, AA, etc.), and drying in a vacuum oven at a temperature below 150 °C for 24 hours to prepare a polyimide powder (20% by weight solids content).

[0092] Comparative Example 2: Preparation of polyimide (including purification process)

[0093] The soluble polyimide prepared according to Examples 1-1 was further subjected to a purification process, including precipitation in an ethanol non-solvent to remove impurities (unreacted components, catalysts, AA, etc.) and drying in a vacuum oven at a temperature below 150°C for 24 hours to prepare polyimide powder.

[0094] Comparative Examples 3 and 4: Preparation of Polyimide

[0095] Polyimide powder was prepared in the same manner as in Comparative Example 1, using different types and amounts of monomers and additives as shown in Table 1 below, and different polymerization methods.

[0096] Comparative Examples 5 to 8: Preparation of Polyimide

[0097] Polyimide powder was prepared in the same manner as in Comparative Example 2, using different types and amounts of monomers and additives as shown in Table 1 below, and different polymerization methods.

[0098] Table 1 below describes the monomer type and amount, polymerization method, type and amount of additives, whether a purification process was performed, and the presence of solubility for the examples and comparative examples. To assess solubility, the polyimide powder of the comparative examples was added to the organic solvent N,N'-dimethylformamide (DMF) and stirred for 30 minutes, and the turbidity of the solution was visually determined.

[0099] [Table 1]

[0100]

[0101] Example 5: Preparation of polyimide (random copolymer) film

[0102] Example 5-1

[0103] The polyimide varnish prepared according to Examples 1-1 was 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. The resulting product was then cooled at 25°C and separated from the glass substrate to prepare a polyimide film with a thickness of approximately 20 μm.

[0104] Examples 5-2 and 5-3

[0105] The polyimide film was prepared in the same manner as in Example 5-1, except that the polyimide varnishes according to Examples 1-2 and 1-3 were used instead of the polyimide varnish according to Example 1-1.

[0106] Example 6: Preparation of polyimide (block copolymer) film

[0107] Examples 6-1 and 6-2

[0108] The polyimide film was prepared in the same manner as in Example 5-1, except that the polyimide varnishes according to Examples 2-1 and 2-2 were used instead of the polyimide varnishes according to Example 1-1.

[0109] Example 7: Preparation of polyimide (random copolymer) film

[0110] Examples 7-1 to 7-3

[0111] The polyimide film was prepared in the same manner as in Example 5-1, except that the polyimide varnish according to Examples 3-1 to 3-3 was used instead of the polyimide varnish according to Example 1-1.

[0112] Example 8: Preparation of polyimide (block copolymer) film

[0113] Examples 8-1 to 8-3

[0114] The polyimide film was prepared in the same manner as in Example 5-1, except that the polyimide varnish according to Examples 4-1 to 4-3 was used instead of the polyimide varnish according to Example 1-1.

[0115] Comparative Example 9: Preparation of Polyimide Films

[0116] The polyimide powder prepared according to Comparative Example 1 was dissolved in an organic solvent (DMF) to obtain a solution containing 20% ​​by weight of solids. The resulting 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 was not particularly limited. The resulting product was then cooled at 25°C and separated from the glass substrate to prepare a polyimide film with a thickness of approximately 20 μm.

[0117] Comparative Examples 10 to 16: Preparation of Polyimide Films

[0118] The polyimide film was prepared in the same manner as in Comparative Example 9, except that the polyimide powder prepared according to Comparative Examples 2 to 8 was used instead of the polyimide powder prepared according to Comparative Example 1.

[0119] <Experimental Example>

[0120] Experimental Example 1: Comparison of polyimides considering appearance

[0121] Figure 1 Optical images of polyimide films according to Examples 5-1 and Comparative Examples 9 and 10 are shown.

[0122] Reference Figure 1 As can be seen, the polyimide film of Example 5-1 has a darker color compared to Comparative Examples 9 and 10. Conventional soluble polyimides achieve solubility by imparting flexibility to the molecular chains to reduce the charge transfer complex (CTC) of the imide groups, or by introducing bulky substituents into the side chains to increase steric hindrance, wherein the film is transparent and exhibits reduced mechanical properties. However, the polyimide film according to the invention has a darker color, indicating that the presence of imidazoles between the polyimide polymer chains enhances intermolecular attraction due to hydrogen bonding, and improves mechanical properties compared to conventional soluble polyimides due to CTC.

[0123] Therefore, it can be understood that by using CDI, the present invention can prepare polyimide membranes with excellent physical properties even without purification, filtration and drying processes.

[0124] Experimental Example 2: Evaluation of the physical properties of polyimide

[0125] (1) Glass transition temperature (Tg)

[0126] For each polyimide film prepared according to the examples and comparative examples, the starting point was measured using dynamic mechanical analysis (DMA) at the point where the polyimide rapidly expanded at 5°C / min. The results are shown in Table 2.

[0127] (2) Thermal decomposition temperature (Td) at 5% weight loss

[0128] Using a TA thermogravimetric analyzer Q50, the polyimide films prepared according to the examples and comparative examples were heated to 100°C at a rate of 10°C / min under a nitrogen atmosphere, and then held isothermally for 1 hour to remove moisture. The temperature at which a 5% weight loss occurred after heating at a rate of 10°C / min to 600°C was then measured. The results are shown in Table 2 below.

[0129] (3) Young's modulus

[0130] Regarding the polyimide films prepared according to the examples and comparative examples, the modulus of samples with a length of 400 mm and a width of 10 mm was measured at a certain rate (20 mm / min) using an Instron 5564UTM from INSTRON, and the average value of 10 samples was calculated. The results are shown in Table 3 below.

[0131] (4) Tensile strength

[0132] Regarding the polyimide films prepared according to the examples and comparative examples, the tensile strength of samples with a length of 400 mm and a width of 10 mm was measured at a certain rate (20 mm / min) using an Instron 5564UTM from INSTRON, and the average value of 10 samples was calculated. The results are shown in Table 3 below.

[0133] (5) Elongation

[0134] The elongation of the polyimide films of the examples and comparative examples was measured at room temperature using an Instron 5564 UTM from INSTRON according to the ASTM D882 method. The results are shown in Table 3 below.

[0135] [Table 2]

[0136]

[0137] [Table 3]

[0138]

[0139] Table 2 shows that, compared with Comparative Examples 9, 10 and 12 to 16, the polyimide films prepared according to Examples 5-1 to 7-2 and 8-2 have similar or improved glass transition temperatures (310°C or higher Tg) and thermal decomposition temperatures (495°C or higher Td 5% by weight).

[0140] Specifically, the polyimide film according to Example 5-1 exhibits the best heat resistance properties, indicating that adding additive CDI in substantially equimolar amounts with polyamic acid is desirable. Furthermore, it is understood that examples 5-1 to 5-3 with random polymerization and examples 6-1 to 6-2 with block polymerization both exhibit excellent heat resistance properties, but examples 5-1 to 5-3 with randomly arranged polymerization units exhibit even better heat resistance properties. In other words, it has been found that the present invention, by using CDI, exhibits excellent heat resistance properties (Tg and Td 5% by weight) even without purification, filtration, and drying processes.

[0141] Table 3 also shows that, compared with Comparative Examples 9, 10, 12 and 16, the polyimide films prepared according to Examples 5-1 to 7-2 and 8-2 have similar or improved modulus (3.03 GPa or greater), tensile strength (110 MPa) and elongation (4.2% or greater).

[0142] Specifically, it can be determined that the polyimide film of Example 5-1 exhibits improved mechanical properties, such as Young's modulus, strength, and elongation, compared to Comparative Examples 9 and 10. In other words, as described in Experimental Example 1 above, it can be understood that by using CDI, the present invention can prepare polyimide films with excellent mechanical properties even without purification, filtration, and drying processes.

[0143] Therefore, by using the additive CDI, the present invention can prepare polyimide membranes with excellent heat resistance (Tg and Td 5 wt%) and mechanical properties, while simplifying the process by omitting purification, filtration and drying processes.

[0144] In this specification, details that can be fully understood and inferred by those skilled in the art have been omitted, and various modifications can be made without altering the technical spirit or basic configuration of the invention, other than the specific examples described herein. Therefore, the invention can be practiced in ways other than those specifically described and illustrated herein that can be understood by those skilled in the art.

Claims

1. A method for preparing polyimide, comprising: (a) Polymerizing diamine monomers with dianhydride monomers to prepare polyamic acid; as well as (b) Reacting the polyamic acid with carbonyl diimidazole to prepare a soluble polyimide, The soluble polyimide therein is in the form of a varnish.

2. The method according to claim 1, wherein no purification, filtration and drying steps are performed after step (b).

3. The method according to claim 1, wherein 0.5 to 1.5 molar equivalents of the carbonyl diimidazole are reacted with 1 molar equivalent of the polyamic acid.

4. The method according to claim 1, wherein step (b) is performed at a temperature of 20°C to 60°C.

5. The method according to claim 1, wherein step (b) is performed for 0.5 hours to 5 hours.

6. The method according to claim 1, wherein the polymerization in step (a) is random polymerization or block polymerization.

7. The method according to claim 1, wherein the dianhydride monomer comprises at least one selected from the group consisting of: pyromellitic dianhydride (PMDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), oxydiphthalic dianhydride (ODPA), 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), biphenyl tetracarboxylic dianhydride (BPDA), 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride (DSDA), and 2,2-bis(4-(3,4-dicarboxyphenoxy)phenyl)propane dianhydride.

8. The method according to claim 1, wherein the diamine monomer comprises at least one selected from the group consisting of 4,4'-methylenebis(2,6-diethylaniline) (MEDA), 2,4-diaminotoluene (2,4-TDA), 2,6-diaminotoluene (2,6-TDA), m-phenylenediamine (m-PD), p-phenylenediamine (p-PD), 3,3''-diaminodiphenyl sulfone (3,3''-DDS), 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FAP), 3,5-diethyltoluene-2,6-diamine, 3,5-diethyltoluene-2,4-diamine, and 4,4'-methylenebis(2-ethyl-6-methylaniline) (MEMA).

9. The method according to claim 8, wherein the amount of 4,4'-methylenebis(2,6-diethylaniline) (MEDA) in the total diamine monomer is greater than 0 mol% and less than or equal to 50 mol%.

10. The method according to claim 8, wherein the amount of 2,4-diaminotoluene (2,4-TDA) in the total diamine monomer is 50 mol% or more and less than 100 mol%.

11. The method of claim 1, wherein the soluble polyimide exhibits solubility in an organic solvent with a solid content of 15% by weight or greater.

12. The method of claim 1, wherein the thermal decomposition temperature (Td) of the soluble polyimide at a 5% weight loss is 485°C or higher.

13. The method of claim 1, wherein the glass transition temperature (Tg) of the soluble polyimide is 300°C or higher.

14. The method of claim 1, wherein the soluble polyimide has a modulus of 3.0 GPa or greater, a tensile strength of 110 MPa or greater, and an elongation of 5% or greater.

15. A soluble polyimide prepared according to any one of claims 1 to 14 for preparing a polyimide.

16. A composition for preparing soluble polyimide, characterized in that, Include: Polyamic acids comprising dianhydride monomers and diamine monomers as polymerization units; and Carbonyl diimidazole.

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