Polyimide with an isocyanuric acid skeleton

Abstract

To provide a polyimide material that is soluble in organic solvents and has a low dielectric constant without the use of expensive fluorine atom-containing monomers.SOLUTION: A polyimide is formed by polymerization of: acid dianhydrides including at least 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride and 1,2,3,4-cyclobutane tetracarboxylic dianhydride; and diamines including at least the compound shown in the general formula (1).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a polyimide having an isocyanuric acid skeleton. [Background technology]

[0002] Polyimide is a resin material with excellent mechanical strength, heat resistance, chemical resistance, and electrical insulation properties, and has been used in the electronics field. For example, flexible printed circuit boards (FPCBs) are manufactured using polyimide film as a substrate material, with circuits formed on the substrate, and these boards are used in various electronic devices. Furthermore, photosensitive polyimide materials, which are made by imparting photosensitivity to polyimide, are used as surface protection films for semiconductor elements and interlayer insulating films for rewiring sections.

[0003] Fifth-generation mobile communication systems (5G), characterized by "high-speed, large-capacity," "low-latency communications," and "multiple connections," utilize high-frequency signal frequencies. As these signals become more frequent, there is a need to reduce transmission loss and the decrease in propagation speed of electrical signals. The dielectric loss contributed by the dielectric (resin material) is expressed by equation (A). Therefore, to reduce transmission loss, it is necessary to reduce the dielectric tangent and permittivity of polyimide materials. To achieve low-latency communications, it is necessary to lower the permittivity of polyimide materials. In other words, the propagation speed of electrical signals is expressed by equation (B), and the lower the permittivity of the resin material, the faster the propagation speed. (Note that k is a constant in equations (A) and (B).) Dielectric loss = k × frequency × speed of light -1 × dielectric loss tangent × dielectric constant 1 / 2 (A) Signal propagation speed = k × speed of light × dielectric constant -1 / 2 (B)

[0004] In view of the above circumstances, there is a demand for low-dielectric-constant polyimide materials. Generally, techniques for lowering the dielectric constant of polyimides include the use of fluorine-containing monomers and blending fluororesins into polyimide resins. For example, Patent Document 1 discloses a polyimide using the fluorine-containing monomer 2,2-bis(4-aminophenyl)-hexadecafluorooctane. Patent Document 2, which primarily aims to lower the dielectric constant of insulating resin layers for flexible metal-clad laminates, specifically discloses an insulating layer containing polytetrafluoroethylene (PTFE) powder in a polyimide derived from 90 mol% pyromellitic dianhydride, 10 mol% 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride, and 100 mol% 2,2'-bis(trifluoromethyl)benzidine.

[0005] Fluorine-containing monomers such as those disclosed in Patent Document 1 are sometimes expensive and difficult to produce or obtain industrially, leaving problems in terms of practicality. When blending a fluororesin into a polyimide resin as disclosed in Patent Document 2, it is sometimes difficult to uniformly disperse the fluororesin, which poses a problem of variations in properties depending on the location on the film. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-146077 [Patent Document 2] Special Publication No. 2014-526399 [Patent Document 3] Special Publication No. 2014-058452 Summary of the Invention [Problem to be solved by the invention]

[0007] The inventors focused on an isocyanuric acid skeleton, which has a symmetric polar structure that affects the dielectric constant and may contribute to reducing the dielectric constant, and studied polyimides having this skeleton. Patent Document 3 describes polyimides having a cyanuric acid skeleton, but does not describe their dielectric properties.

[0008] In the design of conventional low-dielectric-constant polyimides, when attempting to achieve a dielectric constant of 2.6 or less, a certain degree of effect has been achieved by using a monomer with a high fluorine content. However, monomers with a high fluorine atom content can be expensive or difficult to produce industrially, which has significantly limited the design of low-dielectric-constant polyimides. Therefore, the problem to be solved by the present invention is to provide low-dielectric-constant polyimides using only fluorine-free monomers. [Means for solving the problem]

[0009] The present invention can solve the above problems by providing the following novel polyimide containing a cyanuric acid skeleton.

[0010] (1) A polyimide obtained by polymerizing an acid dianhydride containing at least 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride and 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and a diamine containing at least a compound represented by general formula (1). [ka]

[0011] (2) The polyimide according to (1), characterized in that the content of 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride in the total acid dianhydrides is 65 mol % or more.

[0012] (3) The polyimide according to (1) or (2), characterized in that the dielectric constant at a temperature of 23°C, a humidity of 50%, and 10 GHz is 2.6 or less.

[0013] (4) The polyimide according to any one of (1) to (3), characterized in that it is soluble in a concentration of 1 wt % or more in at least one solvent selected from N,N'-dimethylformamide, N,N'-dimethylacetamide, 1-methylpyrrolidone, γ-butyrolactone, dichloromethane, tetrahydrofuran, 1,4-dioxane, acetone, 2-butanone, cyclopentanone, cyclohexanone, 2-heptanone, ethyl acetate, ethyl acetoacetate, butyl acetate, ethyl lactate, ethyl cellosolve acetate, ethyl pyruvate, propylene glycol monoethyl ether, 3-methoxybutyl acetate, methyl 3-methoxypropionate, propylene glycol monopropyl ether, and propylene glycol monomethyl ether acetate.

[0014] (5) The polyimide according to any one of (1) to (4), which does not contain fluorine atoms. [Effects of the Invention]

[0015] The polyimide having an isocyanuric acid skeleton of the present invention provides a polyimide that exhibits a low dielectric constant without using a fluorine-containing monomer. DETAILED DESCRIPTION OF THE INVENTION

[0016] Although the embodiments of the present invention are described below, the present invention is not limited thereto. All academic documents and patent documents described in this specification are incorporated herein by reference. Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)."

[0017] The polyimide having a cyanuric acid skeleton of the present invention is a polyimide obtained by polymerizing an acid dianhydride containing at least 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride and 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and a diamine containing at least a compound represented by general formula (1). [ka]

[0018] The present inventors have discovered that a low dielectric constant can be achieved with a polyimide that uses a diamine compound derived from isocyanuric acid and a specific acid dianhydride as a monomer. A feature of the present invention is that a low dielectric constant is achieved by copolymerizing the diamine compound with 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride (hereinafter referred to as BISDA) and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (hereinafter referred to as CBDA) as acid dianhydrides.

[0019] Furthermore, it is surprising that a low dielectric constant of 2.6 or less was achieved at 23°C, 50% humidity, and 10 GHz without the presence of fluorine atom-containing monomers, which are essential for low-dielectric-constant polyimides. A second feature of this polyimide is that it is soluble in organic solvents.

[0020] Generally, polyimides are often insoluble in organic solvents, but it is known that they can be made soluble in organic solvents by optimizing the copolymerized monomers. In the present invention, it has been found that organic solvent-soluble polyimides can be obtained by using specific monomers in specific ratios. This makes it possible to provide low-dielectric-constant polyimides that are organic solvent-soluble and highly processable without using expensive fluorine-containing monomers. The cyanuric acid-containing polyimide of the present invention and the monomers that constitute it will be described in more detail below.

[0021] (Polyimide) First, we will explain the polymerization of polyimide. Any known method can be used for polyimide polymerization. Typically, a solution of substantially equimolar amounts of an aromatic acid dianhydride and an aromatic diamine dissolved in an organic solvent is stirred under controlled temperature conditions until polymerization of the acid dianhydride and the diamine is complete, yielding a polyamic acid solution, which is a polyimide precursor. This polyamic acid is then imidized using known imidization techniques to obtain a polyimide. The polyamic acid solution is typically obtained at a concentration of 5 to 35% by weight, preferably 10 to 30% by weight. A concentration within this range ensures appropriate molecular weight and solution viscosity.

[0022] Any known polymerization method or a combination thereof can be used. Representative polymerization methods include: 1) dissolving an aromatic diamine in an organic polar solvent and reacting it with a substantially equimolar amount of an aromatic tetracarboxylic dianhydride to polymerize; 2) reacting an aromatic tetracarboxylic dianhydride with a molar excess of an aromatic diamine compound in an organic polar solvent to obtain a prepolymer having acid anhydride groups at both ends. Subsequently, polymerization is performed using an aromatic diamine compound so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound are substantially equimolar throughout all steps; and 3) reacting an aromatic tetracarboxylic dianhydride with a molar excess of an aromatic diamine compound in an organic polar solvent to obtain a prepolymer having amino groups at both ends. Subsequently, an aromatic diamine compound is further added thereto, and then polymerization is carried out using an aromatic tetracarboxylic dianhydride so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound are substantially equimolar throughout all steps; 4) a method in which an aromatic tetracarboxylic dianhydride is dissolved and / or dispersed in an organic polar solvent, and then polymerization is carried out using an aromatic diamine compound so that the aromatic tetracarboxylic dianhydride and the aromatic diamine compound are substantially equimolar; and 5) a method in which a mixture of substantially equimolar aromatic tetracarboxylic dianhydride and aromatic diamine is reacted in an organic polar solvent to polymerize. These methods may be used alone or in combination.

[0023] The order of addition of the diamine and acid dianhydride raw materials is not particularly limited, and the properties of the resulting polyimide can be controlled not only by controlling the chemical structure of the raw materials but also by controlling the order of addition.

[0024] Generally, polyimides are insoluble in organic solvents. Therefore, they are often formed in the form of a polyamic acid solution and then imidized (described later) to produce polyimides. However, by optimizing the monomer structure, it is possible to produce polyimides that are soluble in organic solvents. In this case, polyamic acid is imidized in solution in a reaction vessel, and the polyimide is isolated and obtained.

[0025] (diamine) In the present invention, a diamine represented by general formula (1) is always used to achieve a low dielectric constant, but a different diamine may be copolymerized in addition to the diamine. The different diamine is not particularly limited, and any diamine monomer generally used in polyimide synthesis can be used. There are no particular limitations on the method for synthesizing the diamine represented by general formula (1), and any known organic synthesis method can be used. For example, the diamine can be synthesized as shown in the synthesis example described below.

[0026] (acid dianhydride) In the present invention, to achieve a low dielectric constant, 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride (hereinafter sometimes referred to as BISDA) and 1,2,3,4-cyclobutanetetracarboxylic dianhydride (hereinafter sometimes referred to as CBDA) are used as acid dianhydride monomers. In particular, the BISDA content of the total acid dianhydrides is preferably 65 mol% or more, more preferably 65 mol% to 95 mol%. If the CBDA content is too high, the resulting polymer may be insoluble in organic solvents. In addition to the above two acid dianhydrides, other acid dianhydrides may also be copolymerized within a range that does not impair physical properties such as dielectric constant. In this case, the type of monomer that can be used is not particularly limited, and any acid dianhydride monomer commonly used in polyimide synthesis can be used.

[0027] (solvent) The solvent used in polyimide polymerization is not particularly limited, but is required to be one that does not react with diamines or acid dianhydrides and can dissolve polyamic acid. For example, amide-based solvents that have high solubility for polyamic acid, such as 1-methylpyrrolidone, N,N-diethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, 3-methoxy-N,N-dimethylpropanamide, and 3-methoxy-N,N-dibutylpropanamide, are preferred. One or more amide-based solvents selected from 1-methylpyrrolidone, N,N-diethylformamide, and N,N-dimethylacetamide are preferred. These solvents are typically used alone or in combination as needed. From the standpoint of solubility and polymerizability, one or more amide-based solvents selected from 1-methylpyrrolidone, N,N-diethylformamide, and N,N-dimethylacetamide are preferred. Two or more solvents can also be mixed and used as needed. The solvent mixing method is not particularly limited.

[0028] (Imidization) Polyimides are generally obtained by dehydration (dehydration ring-closure) of polyimide precursors, i.e., polyamic acids. The two most widely known methods for this conversion reaction are the thermal curing method, which uses only heat, and the chemical curing method, which uses imidization reagents and imidization catalysts. Either method can be used in the present invention. However, the chemical curing method, in which an imidization reagent and imidization catalyst are added to a polyamic acid solution, imidization proceeds in the solution, and the polyimide is isolated, is preferred because it does not require high-temperature heating. In solution imidization, the polyimide solution obtained by chemical curing is mixed with a poor solvent to precipitate and isolate the polyimide. The polyimide is then dissolved in a polyimide molding solvent to obtain a molding-ready polyimide solution. The advantages of the polyimide precipitation method include the ability to wash away imidization reagents and imidization catalysts during imidization using a poor solvent, and the ability to use solvents that are appropriate for the polyimide molding conditions and that do not impose a burden on the electronic device manufacturing process.

[0029] The imidization agent referred to here is a dehydration ring-closing agent for polyamic acid, and aliphatic acid anhydrides, aromatic acid anhydrides, N,N'-dialkylcarbodiimides, lower aliphatic halides, halogenated lower aliphatic acid anhydrides, arylsulfonic acid dihalides, thionyl halides, or mixtures of two or more thereof are preferably used. Among these, aliphatic acid anhydrides and aromatic acid anhydrides work better. Acetic anhydride is particularly preferred. The suitable amount of dehydration agent to be introduced is 1.0 to 4.0 mol, preferably 1.0 to 3.0 mol, and particularly preferably 1.0 to 2.0 mol per mol of amic acid units in the polyamic acid contained in the solution. Addition above this range results in excessive addition, increasing the cost of the imidization agent. Addition below this range may result in insufficient progress of the imidization reaction.

[0030] The imidization catalyst is a component that promotes dehydration and cyclization of polyamic acid. Examples of suitable catalysts include aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines. Among these, nitrogen-containing heterocyclic compounds such as pyridine, imidazole, benzimidazole, isoquinoline, quinoline, and pyridine compounds substituted with alkyl groups at the β- and / or γ-positions are preferred. Pyridine, isoquinoline, and pyridine compounds substituted with alkyl groups at the β- and / or γ-positions are particularly preferred. The preferred amount of imidization catalyst is 1.0 to 3.0 mol, preferably 1.0 to 2.0 mol, and particularly preferably 1.0 to 1.5 mol, per mol of amic acid units in the polyamic acid contained in the solution containing the imidization catalyst. If the amount exceeds this range, the catalyst may not be completely removed by washing with a poor solvent. If the amount is below this range, the imidization reaction may not be completed.

[0031] When polyimide is processed, it is desirable to dissolve the isolated polyimide in an organic solvent to prepare a polyimide solution, which is then processed. Here, the processing is not particularly limited, but includes, for example, coating a polyimide solution on a substrate, drying it, and then peeling it off to form a film, or coating a polyimide solution on a semiconductor element and drying it to form a protective film or an interlayer insulating film. The organic solvent in which the polyimide resin is dissolved is not particularly limited as long as it is capable of dissolving the polyimide resin. However, from the viewpoints of solubility and process compatibility in the electronic device field, it is preferable to dissolve the polyimide resin at a concentration of 1 wt % or more in at least one solvent selected from N,N'-dimethylformamide, N,N'-dimethylacetamide, 1-methylpyrrolidone, γ-butyrolactone, dichloromethane, tetrahydrofuran, 1,4-dioxane, methanol, ethanol, 2-propanol, acetone, 2-butanone, cyclopentanone, cyclohexanone, 2-heptanone, ethyl acetate, ethyl acetoacetate, butyl acetate, ethyl lactate, ethyl cellosolve acetate, ethyl pyruvate, propylene glycol monoethyl ether, 3-methoxybutyl acetate, methyl 3-methoxypropionate, propylene glycol monopropyl ether, and propylene glycol monomethyl ether acetate.

[0032] A filler can also be added to the polyimide solution to improve various film properties such as sliding properties, thermal conductivity, electrical conductivity, corona resistance, and loop stiffness. Any filler can be used, but preferred examples include silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, and mica. The polyimide solution may also contain additives, such as leveling agents, plasticizers, surfactants, adhesion promoters, crosslinking agents, photosensitizers, photopolymerization initiators, ultraviolet absorbers, and pigments.

[0033] (Dielectric constant, fluorine-containing polyimide) In the present invention, this refers to the dielectric constant measured in an environment of 23°C and 50% humidity. A low dielectric constant is preferable to achieve low transmission loss and low latency in large-capacity, high-speed communications. Generally, the dielectric constant of polyimide is about 2.5 to 3.3, but to achieve a dielectric constant of 2.6 or less, the use of a fluorine-containing monomer is required. Known fluorine-containing monomers used in polyimide include 4,4'-(hexafluoroisopropylidene)diphthalic anhydride and 2,2'-bis(trifluoromethyl)benzidine, but both are expensive and their use has been limited.

[0034] (Application) The isocyanuric acid skeleton-containing polyimide of the present invention can be used in a variety of applications, including adhesives, pressure-sensitive adhesives, electronic materials, insulating materials (including printed circuit boards, wire coatings, etc.), high-voltage insulating materials, interlayer insulating films, TFT passivation films, TFT gate insulating films, TFT interlayer insulating films, TFT transparent planarizing films, insulating packing, insulating coating materials, adhesives, highly heat-resistant adhesives, highly heat-dissipating adhesives, optical adhesives, adhesives for LED elements, adhesives for various substrates, adhesives for heat sinks, paints, UV powder paints, inks, colored inks, UV inkjet inks, coating materials (including hard coats, sheets, films, release paper coats, optical disk coats, and optical fiber coats), and molding materials (including sheets, films, FRP, etc.). ), sealing materials, potting materials, encapsulating materials, encapsulating materials for light-emitting diodes, liquid crystal sealants, sealants for display devices, encapsulating materials for electrical materials, encapsulating materials for various solar cells, high-heat-resistant sealants, resist materials, liquid resist materials, colored resists, dry film resist materials, solder resist materials, binder resins for color filters, transparent planarizing materials for color filters, binder resins for black matrices, photospacer materials for liquid crystal cells, transparent encapsulating materials for OLED elements, photolithography, materials for solar cells, materials for fuel cells, display materials, recording materials, vibration-proof materials, waterproof materials, moisture-proof materials, photosensitive drums for copiers, solid electrolytes for batteries, etc. The isocyanuric acid skeleton-containing polymer may also be used as an additive to other resins, etc. Needless to say, the uses are not limited to those listed below. [Example]

[0035] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0036] (Method for evaluating dielectric constant) Measurements were made using a Hewlett Packard 8719C network analyzer and a Kanto Electronics Application Development Co., Ltd. CP511 cavity resonator vibration method dielectric constant measurement device. Polyimide film samples were cut into 2mm x 100mm pieces and measured after 24 hours of humidity conditioning in a 23°C / 50% RH environment. Measurements were made at 10GHz.

[0037] (Synthesis example of diamine represented by general formula (1)) Under a nitrogen atmosphere, 33.8 g (0.20 mol) of 1-allyl isocyanurate, 75.4 g (0.44 mol) of 4-nitrobenzyl chloride, and 500 mL of tetrahydrofuran were placed in a 2 L flask equipped with a thermometer and a propeller, and the reaction solution was heated to 70°C. The reaction solution was thoroughly stirred, and 44.5 g of triethylamine was slowly added dropwise thereto while taking care to avoid a sudden rise in temperature. After completion of the addition, the solution was stirred at 70°C for 3 hours.

[0038] After cooling, the mixture was concentrated to dryness under reduced pressure, and 1 L of water was added to the resulting concentrated solid, which was then washed. This washing procedure was repeated two more times to obtain a solid. Recrystallization was carried out using a mixed solvent of ethyl acetate and hexane to obtain 1-allyl-3,5-bis[(4-nitrophenyl)methyl]isocyanurate.

[0039] A reaction mixture was prepared by adding 10 g (22.6 mmol) of 1-allyl-3,5-bis[(4-nitrophenyl)methyl]isocyanurate, 1.0 g of Pd / C, and 500 mL of N,N-dimethylacetamide to a 2 L autoclave equipped with a thermometer and stirrer. This reaction mixture was stirred at 80 °C under a hydrogen atmosphere for 24 hours and then cooled to room temperature. The Pd / C was filtered off from the reaction mixture, and the filtrate was concentrated to dryness under reduced pressure. The resulting concentrate was added to 100 mL of water, mixed with 300 mL of chloroform, shaken in a separatory funnel, and allowed to stand. The organic layer was then separated. This separation procedure was repeated two more times, and the chloroform was removed from the organic layer under reduced pressure. The product was recrystallized from a mixed solvent of chloroform and methanol to obtain 1,3-bis[(4-aminophenyl)methyl]-5-propyl isocyanurate.

[0040] Example 1 Under a nitrogen atmosphere at room temperature, 28 g of DMF was placed in a 500 ml glass flask equipped with a propeller, and 5.26 g of 1,3-bis[(4-aminophenyl)methyl]-5-propyl isocyanurate (hereinafter referred to as MAICDA) obtained in Synthesis Example 1 was dissolved therein. 6.47 g of BISDA and 0.271 g of CBDA were added sequentially and stirred for 30 minutes to dissolve and react. After complete dissolution of the monomers, the mixture was stirred for an additional 2 hours to complete the polymerization reaction. 37.2 g of DMF, 3.40 g of pyridine, and 4.39 g of acetic anhydride were added, and the mixture was heated and stirred at 90°C for 3 hours to complete the imidization reaction. Polymerization was evaluated by assigning a ◯ to cases where the imidization reaction proceeded without the resin precipitating and remained dissolved, and an × to cases where the resin precipitated. The results are shown in Table 1. After completion of the imidization reaction, the mixture was allowed to cool to room temperature, and the reaction solution was slowly poured into 1.00 L of isopropyl alcohol to precipitate the resin. The isolated resin was washed with 500 mL of isopropyl alcohol and filtered. The same washing and filtration process was repeated once more. The isolated resin was dried in a vacuum oven at 80°C for 6 hours. The obtained resin was subjected to solubility tests in various organic solvents. The results are shown in Table 1. In the solubility test, 1 g of resin was added to 10 g of organic solvent and left at room temperature for 24 hours. If the resin completely dissolved, it was evaluated as OK; otherwise, it was evaluated as ×. The results of the solubility test are shown in Table 2. To prepare a sample for dielectric constant evaluation, 5 g of resin was dissolved in 15 g of DMAc and applied to a 10 cm square glass plate using an applicator. The sample was then dried in a hot air oven at 50°C for 1 hour, 100°C for 1 hour, 150°C for 1 hour, and 200°C for 1 hour. The polyimide film was obtained by peeling the coating from the glass substrate. The film thickness was approximately 50 μm. The film was subjected to the dielectric constant measurement described above. The results of the dielectric constant measurement are shown in Table 1.

[0041] Example 2 The resin was polymerized in the same manner as in Example 1, except that 5.08 g of MAICDA was used as the diamine, 5.97 g of BISDA and 0.562 g of CBDA were used as the acid dianhydrides in the polyimide polymerization, and 3.40 g of pyridine and 4.39 g of acetic anhydride were used in the imidization reaction. A solubility test and evaluation of the dielectric constant of the film were then performed. The results are shown in Tables 1 and 2.

[0042] Example 3 The resin was polymerized in the same manner as in Example 1, except that 5.69 g of MAICDA was used as the diamine, 5.43 g of BISDA and 0.88 g of CBDA were used as the acid dianhydrides in the polyimide polymerization, and 3.54 g of pyridine and 4.57 g of acetic anhydride were used in the imidization reaction. A solubility test and evaluation of the dielectric constant of the film were then performed. The results are shown in Tables 1 and 2.

[0043] Example 4 The resin was polymerized in the same manner as in Example 1, except that 5.81 g of MAICDA was used as the diamine, 5.15 g of BISDA and 1.05 g of CBDA were used as the acid dianhydrides in the polyimide polymerization, and 3.61 g of pyridine and 4.66 g of acetic anhydride were used in the imidization reaction. A solubility test and evaluation of the dielectric constant of the film were then performed. The results are shown in Tables 1 and 2.

[0044] (Comparative Example 1) The resin was polymerized in the same manner as in Example 1, except that 5.47 g of MAICDA was used as the diamine and 6.93 g of BISDA was used as the acid dianhydride in the polyimide polymerization, and 3.16 g of pyridine and 4.08 g of acetic anhydride were used in the imidization reaction. A solubility test and evaluation of the dielectric constant of the film were then performed. The results are shown in Tables 1 and 2.

[0045] (Comparative Example 2) The resin was polymerized in the same manner as in Example 1, except that 7.93 g of MAICDA was used as the diamine and 4.08 g of CBDA was used as the acid dianhydride in the polyimide polymerization, and 4.93 g of pyridine and 6.36 g of acetic anhydride were used in the imidization reaction. However, the resin became insoluble and precipitated during the imidization reaction, so the operation was discontinued. The solubility in organic solvents was determined to be insoluble in all of the solvents listed in Table 2.

[0046] (Comparative Example 3) The resin was polymerized in the same manner as in Example 1, except that 5.47 g of 2,2'-bis(trifluoromethyl)benzidine (TFMB) was used as the diamine and 6.93 g of 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) was used as the acid dianhydride in the polyimide polymerization, and 3.73 g of pyridine and 4.81 g of acetic anhydride were used in the imidization reaction. A solubility test and evaluation of the dielectric constant of the film were then performed. The results are shown in Tables 1 and 2.

[0047] [Table 1]

[0048] [Table 2]

[0049] The solubilities of the polyimides in various organic solvents and the dielectric constants of the examples and comparative examples are shown in Tables 1 and 2. Compared to the comparative examples, the polyimides in Examples 1 to 4 exhibited good solubility and a decrease in the dielectric constant was confirmed.

Claims

1. A polyimide obtained by polymerizing an acid dianhydride containing at least 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride and 1,2,3,4-cyclobutanetetracarboxylic dianhydride, and a diamine containing at least a compound represented by general formula (1): 【Chemistry 1】

2. 2. The polyimide according to claim 1, wherein the content of 4,4'-(4,4'-isopropylidenediphenoxy)diphthalic anhydride in the total acid dianhydrides is 65 mol % or more.

3. 3. The polyimide according to claim 1, wherein the polyimide has a dielectric constant of 2.6 or less at a temperature of 23° C., a humidity of 50%, and a frequency of 10 GHz.

4. 3. The polyimide according to claim 1, wherein the polyimide is dissolved at a concentration of 1 wt % or more in at least one solvent selected from the group consisting of N,N'-dimethylformamide, N,N'-dimethylacetamide, 1-methylpyrrolidone, γ-butyrolactone, dichloromethane, tetrahydrofuran, 1,4-dioxane, acetone, 2-butanone, cyclopentanone, cyclohexanone, 2-heptanone, ethyl acetate, ethyl acetoacetate, butyl acetate, ethyl lactate, ethyl cellosolve acetate, ethyl pyruvate, propylene glycol monoethyl ether, 3-methoxybutyl acetate, methyl 3-methoxypropionate, propylene glycol monopropyl ether, and propylene glycol monomethyl ether acetate.

5. 3. The polyimide according to claim 1, wherein the polyimide does not contain fluorine atoms.

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