Aromatic diamine, polyimide precursor, polyimide, and method for producing the same

Abstract

To provide a polyimide having solvent solubility, high transparency, and low dielectric constant characteristics.SOLUTION: A polyimide precursor is obtained by polymerizing an aromatic diamine represented by the following formula (1) and tetracarboxylic acid dianhydride. A polyimide is obtained by subjecting the polyimide precursor thus obtained to cyclization reaction.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aromatic diamine, a polyimide precursor, a polyimide, and methods for producing the same. [Background technology]

[0002] Polyimides have excellent heat resistance, chemical resistance, radiation resistance, electrical insulation, mechanical strength, etc. Therefore, polyimides are currently widely used in various electronic devices as materials for flexible printed wiring circuit substrates, base materials for tape automation bonding, protective films for semiconductor elements, interlayer insulating films for integrated circuits, etc.

[0003] However, conventionally used general-purpose polyimides have disadvantageous properties for use in the high-performance electronic devices that have been developed in recent years, such as being poorly soluble in organic solvents, having low transparency, and having a high dielectric constant.

[0004] Known examples of conventionally used general-purpose polyimides include polyimides obtained by polymerizing p-phenylenediamine (PDA) or 4,4'-diaminodiphenyl ether (ODA) with 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), as shown in Patent Document 1. These general-purpose polyimides are poorly soluble in organic solvents, and their molded articles are colored yellow, resulting in low transparency, and their relative dielectric constant is relatively high at around 3.5.

[0005] Therefore, in order to improve the above-mentioned properties, for example, introduction of a fluorine substituent into the aromatic skeleton of the polyimide (see Non-Patent Document 1 below) or replacement of the aromatic skeleton of the polyimide with an alicyclic skeleton (see Non-Patent Document 2 below) have been investigated. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 60-42817 [Non-patent literature]

[0007] [Non-Patent Document 1] Macromolecules,1991,Vol.24,No.18,p.5001-5005 [Non-patent document 2] Macromolecules,1999,Vol.32,No.15,p.4933-4939 Summary of the Invention [Problem to be solved by the invention]

[0008] However, it is not easy to obtain polyimides that have solvent solubility, high transparency, and low dielectric constant properties while maintaining the excellent heat resistance, mechanical strength, and other properties of polyimides, and almost no polyimides that have such properties and can be used in applications such as highly functional electronic devices that have been developed in recent years are known.

[0009] The present invention has been made in view of the above points, and an object of the present invention is to provide a polyimide having solvent solubility, high transparency and low dielectric constant properties. A further object of the present invention is to provide a polyimide precursor used in the production of the polyimide, and an aromatic diamine used in the production of the polyimide precursor. A further object of the present invention is to provide a method for producing the aromatic diamine, a method for producing the polyimide precursor, and a method for producing the polyimide. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to achieve the above object, and as a result have newly discovered that the above problems can be solved by a polyimide obtained in the following manner, and have thus completed the present invention. Specifically, an aromatic diamine (BPF-P-AN) represented by the following formula (1) is first obtained by reducing an aromatic dinitro compound (BPF-P-NB) represented by the following formula (2). Then, BPF-P-AN is polymerized with a carboxylic dianhydride to obtain a polyimide precursor having a repeating unit represented by the following formula (3). This is then cyclized to obtain a polyimide having a repeating unit represented by the following formula (4). The polyimide thus obtained is solvent-soluble, highly transparent, and has a low dielectric constant.

[0011] That is, the present invention provides the following [1] to [6].

[0012] [1] Formula (1): [ka] An aromatic diamine represented by the formula:

[0013] [2] Formula (2): [ka] The method for producing an aromatic diamine comprises reducing an aromatic dinitro compound represented by the following formula (1):

[0014] [3] Formula (3): [ka] [In formula (3), A represents a residue obtained by removing two acid anhydride groups from a tetracarboxylic dianhydride.] A polyimide precursor having a repeating unit represented by the formula: In this specification, the term "acid anhydride group" refers to a -CO-O-CO- group obtained by intramolecular dehydration condensation of two carboxylic acid molecules.

[0015] [4] A method for producing a polyimide precursor, comprising polymerizing the aromatic diamine described in [1] above with a tetracarboxylic dianhydride to obtain the polyimide precursor described in [3] above.

[0016] [5] Formula (4): [ka] [In formula (4), A represents a residue obtained by removing two acid anhydride groups from a tetracarboxylic dianhydride.] A polyimide having a repeating unit represented by the formula:

[0017] [6] A method for producing a polyimide, comprising subjecting the polyimide precursor described in [3] above to a cyclization reaction to obtain the polyimide described in [5] above. [Effects of the Invention]

[0018] According to the present invention, a polyimide having solvent solubility, high transparency, and low dielectric constant properties can be provided. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a proton NMR spectrum of BPF-P-AN described in Example 1. [Figure 2] FIG. 1 is a differential scanning calorimetry curve of BPF-P-AN described in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments described below are merely examples, and the present invention is not limited to the embodiments described below.

[0021] [Aromatic diamines] The aromatic diamine (BPF-P-AN) of the present invention is a compound represented by the following formula (1).

[0022] [ka]

[0023] <Method for producing aromatic diamine> The method for producing the aromatic diamine (BPF-P-AN) of the present invention is not particularly limited, but may be a method for producing the aromatic diamine (BPF-P-AN) of the present invention by reacting a compound represented by the following formula (2): [ka] Preferably, the method is a method of reducing an aromatic dinitro compound (BPF-P-NB) represented by the following formula to obtain BPF-P-AN. An example of a method for producing the aromatic diamine (BPF-P-AN) of the present invention is production method (A), which comprises a first step of condensing 9,9-bis(4-(4-hydroxyphenoxy)phenyl)fluorene and 4-chloronitrobenzene to obtain an aromatic dinitro compound (BPF-P-NB), and a second step of reducing the aromatic dinitro compound (BPF-P-NB) obtained in the first step using a reducing agent such as hydrogen or hydrazine.

[0024] Next, the method (A) for producing the aromatic diamine (BPF-P-AN) will be specifically described. The amounts and ratios of the compounds used described below are merely examples, and the amounts and ratios of the compounds used are not limited to those described below. In the first step, α (α is an arbitrary value) moles of 9,9-bis(4-(4-hydroxyphenoxy)phenyl)fluorene and 2×α moles of 4-chloronitrobenzene are added to a solvent (A) to obtain a solution. 2×α moles of an alkali compound are added to this solution, and the temperature is raised to the reaction temperature (A) while stirring. After the reaction temperature (A) is reached, the mixture is stirred under heating for a certain period of time to perform aging. The aging time is, for example, 5 to 10 hours. After aging is complete, the mixture is cooled, and the precipitate is filtered off to obtain a solution containing BPF-P-NB. Water is added to the solution containing BPF-P-NB, and the precipitate is filtered off to obtain a powder of BPF-P-NB. Next, in the second step, the BPF-P-NB powder and palladium-carbon as a hydrogenation catalyst are added to a solvent (B) to obtain a slurry, which is then heated to a reaction temperature (B). The reaction temperature (B) is, for example, 70°C. After heating, 4×α mol of hydrazine monohydrate is added dropwise to the slurry to carry out a reduction reaction. The reduction reaction is carried out while maintaining the reaction temperature (B). After the reaction is completed, the mixture is cooled, and a solvent (C) is added to dissolve the target BPF-P-AN. The palladium-carbon is then filtered off to obtain a reaction solution. A powder containing BPF-P-AN can be obtained by recrystallization from the reaction solution. Alternatively, a powder containing BPF-P-AN can be obtained by adding water to the reaction solution and filtering off the precipitate. The powder containing BPF-P-AN is then repulped and washed with water, alcohol, or the like, and then vacuum-dried. The temperature during vacuum drying is preferably between 50°C and 100°C. The vacuum drying time is preferably 10 hours or more and 30 hours or less, which allows the production of high-purity BPF-P-AN.

[0025] The solvent (A) used in the first step is not particularly limited, and examples thereof include toluene, xylene, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, hexamethylphosphoramide, dimethyl sulfoxide, γ-butyrolactone, 1,3-dimethyl-2-imidazolidinone, etc., and may be used alone or in combination of two or more. Among these, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, etc. are preferred.

[0026] The reaction temperature (A) in the first step is preferably 100°C or higher, more preferably 120°C or higher, and preferably 180°C or lower, more preferably 150°C or lower. When the reaction temperature (A) is equal to or higher than the lower limit, the reaction can proceed sufficiently. When the reaction temperature (A) is equal to or lower than the upper limit, side reactions can be suppressed.

[0027] The alkaline compound used in the first step is not particularly limited, and examples thereof include inorganic bases such as potassium carbonate, sodium hydroxide, potassium hydroxide, etc. Among these, potassium carbonate is preferred.

[0028] The solvent (B) used in the second step is not particularly limited, and examples thereof include alcohol solvents such as methanol, ethanol, and 2-propanol, as well as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylformamide, hexamethylphosphoramide, dimethyl sulfoxide, γ-butyrolactone, and 1,3-dimethyl-2-imidazolidinone, and may be used alone or in combination of two or more. Among these, alcohol solvents such as methanol, ethanol, and 2-propanol are preferred.

[0029] The solvent (C) used in the second step is not particularly limited, and examples thereof include the same solvents as those usable as the solvents (A) and (B). Of these, N,N-dimethylformamide is preferred.

[0030] [Polyimide precursor] The polyimide precursor of the present invention is a polyimide precursor having a repeating unit represented by the following formula (3).

[0031] [ka]

[0032] In the above formula (3), A represents a residue obtained by removing two acid anhydride groups from a tetracarboxylic dianhydride. The residue obtained by removing two acid anhydride groups from a tetracarboxylic dianhydride is not particularly limited, but is preferably, for example, a residue obtained by removing two acid anhydride groups from at least one tetracarboxylic dianhydride selected from the group consisting of an aromatic carboxylic dianhydride, an alicyclic carboxylic dianhydride, and a chain aliphatic carboxylic dianhydride. Examples of the aromatic carboxylic dianhydride, the alicyclic carboxylic dianhydride, and the chain aliphatic carboxylic dianhydride include those described below.

[0033] <Method for producing polyimide precursor> The method for producing the polyimide precursor of the present invention is not particularly limited and may be any known method for producing a polyimide precursor. However, for example, production method (B) is preferred, in which a diamine including the aromatic diamine (BPF-P-AN) of the present invention is polymerized with a tetracarboxylic dianhydride to obtain the polyimide precursor of the present invention.

[0034] The above production method (B) will be described below. First, β (β is an arbitrary value) moles of diamine including the aromatic diamine (BPF-P-AN) of the present invention are dissolved in a polymerization solvent, and β moles of tetracarboxylic dianhydride powder are gradually added thereto. The mixture is stirred using a mechanical stirrer or the like to polymerize. This produces a solution containing the polyimide precursor of the present invention. The stirring temperature is preferably 0°C or higher, more preferably 5°C or higher, and preferably 100°C or lower, more preferably 60°C or lower. The stirring time is preferably 0.5 hours or longer, more preferably 1 hour or longer, and preferably 100 hours or shorter, more preferably 50 hours or shorter. The total concentration of the monomers (aromatic diamine and tetracarboxylic dianhydride) in the polymerization solvent is preferably 5% by mass or more, and more preferably 10% by mass or more, because the degree of polymerization of the polyimide precursor is increased and the use of such a polyimide precursor allows the production of a polyimide that exhibits flexibility.

[0035] The carboxylic acid dianhydride is not particularly limited as long as it does not significantly impair the polymerization reactivity of the polyimide precursor or the required properties of the polyimide obtained from the polyimide precursor. The carboxylic acid dianhydride is preferably at least one carboxylic acid dianhydride selected from the group consisting of aromatic carboxylic acid dianhydrides, alicyclic carboxylic acid dianhydrides, and chain aliphatic carboxylic acid dianhydrides, and among these, aromatic carboxylic acid dianhydrides are more preferred.

[0036] Examples of aromatic carboxylic dianhydrides include pyromellitic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,3,5,6-pyridinetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, 4,4'-sulfonyldiphthalic dianhydride, 4,4'-oxydiphthalic dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, etc. Two or more of these may be used in combination. Among these, pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, and the like are preferred as aromatic carboxylic dianhydrides.

[0037] Examples of alicyclic tetracarboxylic dianhydrides include 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, etc. Two or more of these may be used in combination.

[0038] Examples of the chain aliphatic tetracarboxylic dianhydride include ethylene tetracarboxylic dianhydride, butane tetracarboxylic dianhydride, meso-butane-1,2,3,4-tetracarboxylic dianhydride, etc. Two or more of these may be used in combination.

[0039] The polymerization solvent is not particularly limited as long as it can dissolve the aromatic diamine and tetracarboxylic dianhydride monomers, but a protic solvent is preferred. Specific preferred examples include amide solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone; cyclic ester solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, γ-caprolactone, ε-caprolactone, and α-methyl-γ-butyrolactone; carbonate solvents such as ethylene carbonate and propylene carbonate; glycol solvents such as triethylene glycol; phenol solvents such as m-cresol, p-cresol, 3-chlorophenol, and 4-chlorophenol; acetophenone, 1,3-dimethyl-2-imidazolidinone, sulfolane, and dimethyl sulfoxide. Furthermore, other common organic solvents, specifically, for example, phenol, o-cresol, butyl acetate, ethyl acetate, isobutyl acetate, propylene glycol methyl acetate, ethyl cellosolve, butyl cellosolve, 2-methyl cellosolve acetate, ethyl cellosolve acetate, butyl cellosolve acetate, tetrahydrofuran, dimethoxyethane, diethoxyethane, dibutyl ether, diethylene glycol dimethyl ether, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, methyl ethyl ketone, acetone, butanol, ethanol, xylene, toluene, chlorobenzene, turpentine, mineral spirits, petroleum naphtha-based solvents, and the like can also be used.

[0040] In the production method (B), the diamine contains the aromatic diamine (BPF-P-AN) of the present invention, and may optionally contain other diamines. The other diamine is not particularly limited as long as it does not significantly impair the polymerization reactivity of the polyimide precursor or the required properties of the polyimide obtained from the polyimide precursor. Specific examples include 4,4'-diaminodiphenyl ether (ODA) and p-phenylenediamine (PDA).

[0041] The intrinsic viscosity of the polyimide precursor of the present invention is preferably 0.1 dL / g or more, more preferably 0.5 dL / g or more, because this allows the polyimide to exhibit flexibility. On the other hand, the intrinsic viscosity of the polyimide precursor of the present invention is preferably 8.0 dL / g or less, more preferably 5.0 dL / g or less, because the resulting polyimide has good solubility in organic solvents.

[0042] The solution containing the polyimide precursor of the present invention obtained in the production method (B) can be diluted, if necessary, by further adding a polymerization solvent or the like, and used in the polyimide production method described below. Alternatively, a powdered polyimide precursor can be obtained by adding dropwise a solution containing the polyimide precursor (hereinafter also referred to as a "polyimide precursor solution") to a large amount of a poor solvent such as water or methanol, followed by filtration and drying.

[0043] [Polyimide] The polyimide of the present invention is a polyimide having a repeating unit represented by the following formula (4).

[0044] [ka]

[0045] In the above formula (4), A represents a residue obtained by removing two acid anhydride groups from a tetracarboxylic dianhydride. The residue obtained by removing two acid anhydride groups from a tetracarboxylic dianhydride is not particularly limited, but is preferably, for example, a residue obtained by removing two acid anhydride groups from at least one tetracarboxylic dianhydride selected from the group consisting of an aromatic carboxylic dianhydride, an alicyclic carboxylic dianhydride, and a chain aliphatic carboxylic dianhydride. Examples of the aromatic carboxylic dianhydride, the alicyclic carboxylic dianhydride, and the chain aliphatic carboxylic dianhydride include those described above.

[0046] <Polyimide manufacturing method> The method for producing the polyimide of the present invention is not particularly limited, and is preferably a method for subjecting the polyimide precursor of the present invention to a cyclization reaction (imidization reaction). The method for subjecting the polyimide precursor to a cyclization reaction may be a known method. The cyclization reaction can be carried out regardless of whether the polyimide precursor of the present invention is in the form of a film, a coating film, a powder, a molded body, or a solution.

[0047] First, a method for producing a polyimide film (hereinafter also referred to as a "polyimide film") will be described. The polyimide precursor solution is applied to a substrate made of glass, steel, aluminum, silicon, or the like, and then heated and dried in an oven. The temperature during heating and drying is preferably 40°C or higher, more preferably 50°C or higher, and is preferably 210°C or lower, more preferably 205°C or lower. In this way, a film of the polyimide precursor (hereinafter also referred to as "polyimide precursor film") is obtained. The polyimide precursor film obtained above is heated and dried on the substrate, whereby a cyclization reaction of the polyimide precursor occurs, and a polyimide film is obtained on the substrate. In order to allow the cyclization reaction to proceed sufficiently, the temperature during the heat drying is preferably 200°C or higher, more preferably 250°C or higher. On the other hand, from the viewpoint of preventing the resulting polyimide film from being discolored and preventing a portion of the polyimide film from being thermally decomposed, the temperature during heat drying is preferably 430°C or lower, and more preferably 400°C or lower. The heat drying during the cyclization reaction is preferably carried out in vacuum or in an inert gas such as nitrogen, from the viewpoint of preventing the resulting polyimide film from being discolored or from being partially thermally decomposed. However, the heat drying may be carried out in air as long as the heat drying temperature is 350°C or lower.

[0048] The cyclization reaction of the polyimide precursor can be carried out by a method other than heating the polyimide precursor film, for example, by immersing the polyimide precursor film in a solution containing at least a tertiary amine such as pyridine or triethylamine and a dehydrating agent such as acetic anhydride.

[0049] Alternatively, a solution containing polyimide (hereinafter also referred to as "polyimide solution") can be obtained by heating the polyimide precursor solution directly or after diluting it appropriately with the above-mentioned polymerization solvent to 150 to 200°C. Toluene, xylene, or the like may be added to the polyimide precursor solution to azeotropically remove water and other by-products of the cyclization reaction. A base such as γ-picoline may also be added to the polyimide precursor solution as a catalyst.

[0050] A polyimide powder can also be obtained by adding the polyimide solution dropwise to a large amount of a poor solvent such as water or methanol, followed by filtration and drying. The powdered polyimide can also be redissolved in the above-mentioned polymerization solvent to obtain a polyimide solution. A polyimide film can also be formed by applying a polyimide solution to a substrate and drying it by heating. To prevent discoloration of the resulting polyimide film and thermal decomposition of a portion of the polyimide film, the temperature during heating is preferably 40°C or higher, more preferably 100°C or higher, and preferably 400°C or lower, more preferably 250°C or lower. To prevent discoloration of the resulting polyimide film and thermal decomposition of a portion of the polyimide film, heating the polyimide solution on the substrate is preferably carried out in a vacuum or in an inert gas such as nitrogen. However, heating may be carried out in air as long as the heating temperature is 350°C or lower. Furthermore, a polyimide molded article can be produced by heat-compressing a powdered polyimide. The temperature during heat-compression is preferably 200°C or higher, more preferably 250°C or higher, and is preferably 450°C or lower, more preferably 430°C or lower.

[0051] In the method for producing a polyimide of the present invention, the cyclization reaction of the polyimide precursor may be a method in which the polyimide precursor is polyisoimidized and then cyclized, as shown below. A dehydrating agent such as N,N-dicyclohexylcarbodiimide or trifluoroacetic anhydride is added to a polyimide precursor solution, and the mixture is stirred to allow the reaction to occur. The reaction temperature is preferably 0°C or higher, and preferably 100°C or lower, and more preferably 60°C or lower. This produces polyisoimide, an isomer of polyimide, and a polyisoimide solution (hereinafter also referred to as a "polyisoimide solution") is obtained. The reaction in which polyisoimide is obtained from a polyimide precursor is also referred to as polyisoimidization. A polyisoimide film (hereinafter also referred to as a "polyisoimide film") can be obtained by applying a polyisoimide solution onto a substrate and drying it by heating. The temperature during drying by heating is preferably 40°C or higher, more preferably 50°C or higher, and is preferably 180°C or lower, more preferably 150°C or lower. Alternatively, a polyisoimide film can be obtained by immersing a polyimide precursor film in a solution containing a dehydrating agent to cause polyisoimidization. The polyisoimide film can be converted into a polyimide film by heating and drying it. The temperature during heating and drying is preferably 250°C or higher, more preferably 270°C or higher, and is preferably 450°C or lower, more preferably 400°C or lower.

[0052] Additives such as an oxidation stabilizer, a filler, a silane coupling agent, a photosensitizer, a photopolymerization initiator, and a sensitizer may be added to the polyimide solution and polyimide precursor solution as required. [Example]

[0053] The present invention will be specifically described below with reference to examples, but the present invention is not limited to the examples described below. In the following description, "%" and "parts" that represent amounts are by mass unless otherwise specified.

[0054] <Physical property measurement> The physical properties of the aromatic diamine and polyimide films obtained in the following examples were measured by the following methods.

[0055] <Proton NMR spectrum> To confirm the molecular structure of the aromatic diamine, proton NMR spectra were measured in dimethyl sulfoxide-d6 using a benchtop NMR (Magritek, spinsolve 80 Carbon).

[0056] <Differential scanning calorimetry (melting point and melting curve)> The melting point and melting curve of the aromatic diamine were measured using a differential scanning calorimeter (Shimadzu Corporation, DSC-60) in a nitrogen atmosphere at a temperature rise rate of 5°C / min.

[0057] 《Total light transmittance》 The total light transmittance of the polyimide film was measured using a turbidity meter (HAZE METER NDH 5000, manufactured by Nippon Denshoku Industries Co., Ltd.).

[0058] <<Elastic modulus, breaking strength and breaking elongation>> A tensile test (stretching rate: 102 mm / min) was performed on polyimide film specimens (10 mm x 70 mm) using a tensile testing machine (Shimadzu Corporation, Autograph AGS-J). The elastic modulus (GPa) was calculated from the initial slope of the stress-strain curve, the breaking strength (MPa) from the load at which the film broke, and the breaking elongation (%) from the elongation at that time.

[0059] Glass transition temperature: Tg Dynamic viscoelasticity measurements were carried out using a dynamic viscoelasticity measuring device (DMAQ800, manufactured by TA Instruments), and the glass transition temperature of the polyimide film was determined from the loss peak at a frequency of 0.1 Hz and a heating rate of 5°C / min.

[0060] 《5% mass reduction temperature: Td 5 》 Using a thermogravimetric analyzer (Shimadzu Corporation, DTG-60), the temperature at which the initial mass of the polyimide film decreased by 5% (5% mass loss temperature: Td 5 The higher the 5% mass loss temperature, the higher the thermal stability of the polyimide film.

[0061] <Coefficient of Linear Thermal Expansion: CTE> Thermomechanical analysis was performed using a thermomechanical analyzer (TMA60, manufactured by Shimadzu Corporation), and the linear thermal expansion coefficient of the polyimide film was calculated as the average value in the range of 50 to 150°C from the elongation of the test piece at a load of 1.6 g / film thickness of 1 μm and a heating rate of 10°C / min.

[0062] <<Relative permittivity and dielectric loss tangent>> The dielectric constant and dielectric loss tangent of the polyimide film were measured at 25°C under dry conditions at 1 GHz and 10 GHz by a cavity resonator method using a microwave signal generator (Hittite Microwave Corporation, HMC-T2220).

[0063] <Solvent soluble> 90 parts by mass of N,N-dimethylacetamide was added to 10 parts by mass of polyimide film at 25°C. If the polyimide film was completely dissolved, the polyimide film was judged to be solvent-soluble (+), and if the polyimide film was not completely dissolved, the polyimide film was judged to be solvent-insoluble (-).

[0064] Example 1 <Production of aromatic diamine> A DMF solution was obtained by adding 50 mmol of 9,9-bis(4-(4-hydroxyphenoxy)phenyl)fluorene, 100 mmol of 4-chloronitrobenzene, and 150 mL of N,N-dimethylformamide (DMF) as a solvent to a recovery flask. 100 mmol of potassium carbonate was added to the resulting DMF solution, and the temperature was raised to 150 °C with stirring. After reaching 150 °C, the solution was aged with stirring for 6 hours. After aging, the solution was cooled and the precipitate was filtered off to obtain a DMF solution containing BPF-P-NB obtained by the reaction. 300 mL of water was added to the resulting DMF solution containing BPF-P-NB, and the precipitate was filtered off to obtain BPF-P-NB powder. Next, the resulting BPF-P-NB powder, 150 mL of 2-propanol, and 3 g of 5% palladium-carbon were added to a recovery flask to obtain a slurry, which was then heated to 70 °C. 200 mmol of hydrazine monohydrate was added dropwise to the slurry to carry out a reduction reaction. The reduction reaction was carried out while maintaining the temperature at 70 °C. After the reaction was completed, the mixture was cooled, and 150 mL of DMF was added to dissolve the target BPF-P-AN. The palladium-carbon was then filtered off to obtain a reaction solution. 300 mL of water was added to the reaction solution, and the precipitate was filtered off to obtain a powder containing BPF-P-AN. The resulting powder containing BPF-P-AN was thoroughly washed with water and vacuum-dried at 100 °C for 24 hours to obtain BPF-P-AN in an 82.9 mol% yield. Furthermore, the resulting BPF-P-AN could be further repulped and washed with methanol to obtain a higher-purity BPF-P-AN. The proton NMR spectrum and differential scanning calorimetry curve (melting curve) of the obtained BPF-P-AN are shown in Figure 1 and Figure 2, respectively.

[0065] <Production of Polyimide Precursor> In a well-dried, sealed reaction vessel equipped with a stirrer, 10 mmol of BPF-P-AN (as a monomer) was dissolved in N,N-dimethylacetamide (as a polymerization solvent) to obtain a solution. 10.0 mmol of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) (as a monomer) was gradually added to the resulting solution, and the polymerization reaction was carried out at 25°C for 22 hours with stirring using a mechanical stirrer. During the polymerization reaction, the total concentration of the monomers (BPF-P-AN and BPDA) in the polymerization solvent (N,N-dimethylacetamide) was 20-30% by mass. After the polymerization reaction, a transparent, viscous polyimide precursor solution was obtained. The resulting polyimide precursor solution was applied to a glass substrate and dried by heating at 100°C for 30 minutes, 150°C for 30 minutes, and 200°C for 30 minutes, to obtain a polyimide precursor film. The resulting polyimide precursor film exhibited flexibility, and no visible fractures were observed in a 180° bending test (a simple test in which the film is folded completely in half). This indicates that the degree of polymerization of the resulting polyimide precursor was sufficiently high.

[0066] <Production of polyimide film> The resulting polyimide precursor film was then dried by heating on a glass substrate at 200°C for 10 minutes, 250°C for 30 minutes, and 350°C for 30 minutes, to allow for a cyclization reaction. A flexible polyimide film with a thickness of approximately 50 μm was thus obtained. The resulting polyimide film exhibited flexibility, and no visible fractures were observed in a 180° bending test.

[0067] The physical properties of the obtained polyimide film were as follows: The elastic modulus was 1.9 GPa, the breaking strength was 89 MPa, and the breaking elongation was 20%. The glass transition temperature (Tg) was 280°C, demonstrating high heat resistance. 5% mass loss temperature (T d 5 ) was 565°C, indicating high thermal stability. The coefficient of linear thermal expansion (CTE) was 44 ppm / K. The dielectric constant and dissipation factor were 3.17 and 0.0034 at 1 GHz, respectively, and 3.09 and 0.0045 at 10 GHz. 10 parts by mass of polyimide film could be completely dissolved in 90 parts by mass of N,N-dimethylacetamide at 25°C, and the polyimide film was determined to be solvent-soluble (+). The evaluation results are also shown in Table 1.

[0068] Comparative Example 1 A polyimide film was prepared and evaluated in the same manner as in Example 1, except that 4,4'-diaminodiphenyl ether (ODA) was used instead of BPF-P-AN. The evaluation results are shown in Table 1. The obtained polyimide film exhibited flexibility, and no visible breakage was observed in a 180° bending test.

[0069] [Table 1]

[0070] <Summary of evaluation results> Although some of the mechanical properties and thermal properties of Example 1 were lower than those of Comparative Example 1, they were still at a level that could be used in various industrial fields. Furthermore, the polyimide film of Example 1 has solvent solubility, higher transparency than Comparative Example 1, and a lower dielectric constant. [Industrial Applicability]

[0071] The polyimide of the present invention is suitable as a material for use in, for example, substrates for organic electroluminescence (EL) displays and substrates for high-frequency circuits, and can be used in various industrial fields. The polyimide of the present invention can be suitably used, for example, in electrical insulating films in various electronic devices, flexible printed wiring boards, substrates for liquid crystal displays, substrates for electronic paper, substrates for solar cells, photosensitive materials, and the like.

Claims

1. The following formula (1): 【Chemical 1】 An aromatic diamine represented by the formula:

2. The following formula (2): 【Chemistry 2】 A method for producing an aromatic diamine, comprising reducing an aromatic dinitro compound represented by the formula:

3. The following formula (3): 【Chemistry 3】 [In formula (3), A represents a residue obtained by removing two acid anhydride groups from a tetracarboxylic dianhydride.] A polyimide precursor having a repeating unit represented by the formula:

4. A method for producing a polyimide precursor, comprising polymerizing a diamine containing the aromatic diamine according to claim 1 with a tetracarboxylic dianhydride to obtain the polyimide precursor according to claim 3.

5. The following formula (4): 【Chemistry 4】 [In formula (4), A represents a residue obtained by removing two acid anhydride groups from a tetracarboxylic dianhydride.] A polyimide having a repeating unit represented by the formula:

6. A method for producing a polyimide, comprising subjecting the polyimide precursor according to claim 3 to a cyclization reaction to obtain the polyimide according to claim 5.

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