Copolymer, method for producing copolymer, and resin composition containing copolymer

Abstract

Provided are a copolymer capable of suppressing discoloration even after heating and a method for producing the same.　A copolymer containing a structural unit (A) derived from 1,1-dicyanoethylene and a structural unit (B) derived from a compound represented by general formula (I), CH2=CR1R2 (I), wherein the copolymer is characterized by containing the following four triplet structures (U-1) to (U-4) composed of the structural unit (A) and the structural unit (B), (A)-(A)-(A)…(U-1), (A)-(A)-(B)…(U-2), (B)-(A)-(A)…(U-3), (B)-(A)-(B)…(U-4), and by the total content of (U-2) and (U-3) in the total amount of the four triplet structures being 5.5 mol% or less.

Description

Copolymer, method for producing the copolymer, and resin composition containing the copolymer

[0001] The present invention relates to a copolymer containing structural units derived from 1,1-dicyanoethylene and structural units derived from a specific polymerizable monomer in a specific sequence, a method for producing the copolymer, and a resin composition containing the copolymer.

[0002] Films using copolymers obtained by radical polymerization of 1,1-dicyanoethylene and polymerizable monomers have excellent transparency and are therefore suitable for use as materials for optical components, lighting components, signboard components, decorative components, etc. (For example, Patent Document 1) Research on polymers using 1,1-dicyanoethylene has been actively conducted, and for example, Non-Patent Document 1 describes an analytical method for a copolymer of 1,1-dicyanoethylene and styrene.

[0003] Japanese Patent Application Publication No. 01-103614

[0004] Polymer,1988,29,144-151

[0005] As described above, films using copolymers obtained by radical polymerization of 1,1-dicyanoethylene and polymerizable monomers have excellent transparency, but there has been a problem in that the copolymers become discolored when heated, impairing their appearance.

[0006] The present invention has been made in view of the above-mentioned problems in the prior art, and an object of the present invention is to provide a copolymer that can suppress coloration even after heating, and a method for producing the same. Another object of the present invention is to provide a resin composition containing the copolymer, and a molded article and a film using the copolymer.

[0007] The present inventors conducted studies and found that radical polymerization of 1,1-dicyanoethylene and a specific polymerizable monomer at a relatively low temperature in a specific charge ratio results in the polymerization of structural units derived from 1,1-dicyanoethylene and structural units derived from the polymerizable monomer in a specific sequence. Based on this finding, the present inventors conducted further studies and found that by controlling the sequence of each monomer, a copolymer can be obtained that exhibits reduced coloration even after heating, thereby completing the present invention.

[0008] That is, the present invention provides the following items [1] to

[10] : [1] A copolymer containing a structural unit (A) derived from 1,1-dicyanoethylene and a structural unit (B) derived from a compound represented by the following general formula (I), wherein: CH2=CR 1 R 2 (I) The copolymer contains the following four types of triad structures (U-1) to (U-4) composed of the structural unit (A) and the structural unit (B), (A)-(A)-(A) ... (U-1) (A)-(A)-(B) ... (U-2) (B)-(A)-(A) ... (U-3) (B)-(A)-(B) ... (U-4) The copolymer is characterized in that the content of (U-2) and (U-3) is 5.5 mol % or less in the total amount of the four types of triad structures. (In general formula (I), R 1 is at least one selected from a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, and a halogen atom; 2is one or more selected from a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, a halogen atom, and a haloalkyl group.) [2] The copolymer according to [1] above, wherein the content of (U-1) is 1.8 mol % or less based on the total amount of the four types of triad structures. [3] The copolymer according to [1] or [2] above, wherein the content of the structural unit (A) is 30 to 55 mol % based on the total amount of the copolymer. [4] The copolymer according to any of [1] to [3] above, wherein the compound represented by general formula (I) is one or more selected from the group consisting of styrene, α-methylstyrene, p-methylstyrene, isobutylene, 1-hexene, propylene, and ethylene. [5] A method for producing the copolymer according to any one of [1] to [4] above, wherein the polymerization temperature is 45°C or less, the amount of the compound represented by general formula (I) charged is 0.80 to 3.5 equivalents relative to the amount of 1,1-dicyanoethylene charged, and the copolymer is produced in the presence of a radical polymerization initiator. [6] A resin composition containing the copolymer according to any one of [1] to [4] above. [7] A molded product using the copolymer according to any one of [1] to [4] above or the resin composition according to [6] above. [8] A film using the copolymer according to any one of [1] to [4] above or the resin composition according to [6] above, wherein the difference in yellowness between before heating and after heating at 140°C under normal pressure for 1 hour is 2.5% or less. [9] A conductive film obtained by laminating a conductive layer on the film according to [8] above.

[10] A film capacitor including the film according to [8] above or the conductive film according to claim 9.

[0009] According to the present invention, there are provided a copolymer that can suppress coloration even after heating, and a method for producing the copolymer. Furthermore, according to the present invention, there are provided a resin composition containing the copolymer, and a molded article and a film using the copolymer.

[0010] [Copolymer] The copolymer of the present invention is a copolymer containing a structural unit (A) derived from 1,1-dicyanoethylene and a structural unit (B) derived from a compound represented by the following general formula (I): CH2=CR 1 R 2(I) The copolymer contains the following four types of triad structures (U-1) to (U-4) composed of the structural unit (A) and the structural unit (B), (A)-(A)-(A) ... (U-1) (A)-(A)-(B) ... (U-2) (B)-(A)-(A) ... (U-3) (B)-(A)-(B) ... (U-4) The copolymer is characterized in that the total content of (U-2) and (U-3) is 5.5 mol % or less of the total amount of the four types of triad structures. (In general formula (I), R 1 is at least one selected from a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, and a halogen atom; 2 is at least one selected from a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, a halogen atom, and a haloalkyl group.

[0011] In the present invention, the term "triad structure" refers to a structure in which three structural units (A) derived from 1,1-dicyanoethylene and three structural units (B) derived from the compound represented by the general formula (I) are linked together. One of the four types of triad structures, "(A)-(A)-(A)," refers to a triad structure in which three structural units (A) derived from 1,1-dicyanoethylene are bonded in succession, and "(A)-(A)-(B)" refers to a triad structure in which two structural units (A) derived from 1,1-dicyanoethylene are bonded in succession, followed by the structural unit (B) derived from the compound represented by the general formula (I). The other triad structures have similar meanings.

[0012] In the present invention, the amounts of four types of triad structures (U-1) to (U-4) are specified, and the amount of triad structure (U-1) means "the content (mol %) of (A) bonded between two (As) in the (A)-(A)-(A) structure constituting (U-1)." Similarly, the content of triad structure (U-2) means "the content (mol %) of (A) bonded between (A) and (B) in the (A)-(A)-(B) structure constituting (U-2)." The contents of other triad structures have the same meaning. Note that the contents of each of the triad structures (U-1) to (U-4) in the present invention are 13It can be measured by C-NMR, specifically by the method described in the Examples.

[0013] The present invention is characterized in that the total content of (U-2) and (U-3) in the total amount of the four triad structures is 5.5 mol% or less. When the total content of (U-2) and (U-3) is 5.5 mol% or less, the amount of sequences that cause thermal discoloration, specifically sequences in which (A) are continuous, can be reduced, making it possible to suppress discoloration in molded articles using the copolymer of the present invention, even after heating. From the viewpoint of effectively suppressing discoloration, the total content of (U-2) and (U-3) in the total amount of the four triad structures is 5.5 mol% or less, preferably 5.2 mol% or less, preferably 5.0 mol% or less, preferably 4.8 mol% or less, and more preferably 4.6 mol% or less. The lower limit is usually 0.5 mol% or more, but may be lower, preferably 0.1 mol% or more. The total content of (U-2) and (U-3) can be adjusted by controlling the amount of monomer charged at a relatively low temperature of 50°C or less.

[0014] Furthermore, in the present invention, the content of (U-1) is preferably 1.8 mol% or less based on the total amount of the four types of triad structures. When the content of (U-1) is equal to or less than the upper limit, the number of consecutive sequences of (A) in the copolymer is reduced, and as a result, discoloration of molded articles using the copolymer of the present invention after heating is further suppressed. From this viewpoint, the content of (U-1) based on the total amount of the four types of triad structures is preferably 1.7 mol% or less, more preferably 1.5 mol% or less, and even more preferably 0.5 mol% or less.

[0015] <Structural Unit (A) Derived from 1,1-Dicyanoethylene> The copolymer of the present invention contains a structural unit (A) derived from 1,1-dicyanoethylene. 1,1-Dicyanoethylene gives a copolymer with high transparency upon radical polymerization, and therefore the copolymer of the present invention can be suitably used for molded articles and the like that require transparency. 1,1-Dicyanoethylene can be produced by the production methods described in J. Am. Chem. Soc., 1989, 111, 9078-9081 and U.S. Patent Application Publication No. 2,476,270.

[0016] <Structural Unit (B) Derived from Compound Represented by General Formula (I)> The copolymer of the present invention contains a structural unit (B) derived from a compound represented by the following general formula (I): CH═CR 1 R 2 (I)

[0017] In general formula (I), R 1 is at least one selected from a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, and a halogen atom; 2 is at least one selected from a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, a halogen atom, and a haloalkyl group.

[0018] In general formula (I), R 1 R is at least one selected from a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, and a halogen atom. 1 The alkyl group is preferably an alkyl group having 1 to 12 carbon atoms, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group, a heptyl group, an octyl group, a decyl group, and a dodecyl group.

[0019] R 1 The cycloalkyl group of R is preferably a cycloalkyl group having 3 to 12 carbon atoms, and examples thereof include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. 1The aryl group is preferably an aryl group having 6 to 20 carbon atoms, and examples thereof include a phenyl group, a tolyl group, a xylyl group, and a naphthyl group.

[0020] R 1 The alkoxy group is preferably an alkoxy group having 1 to 10 carbon atoms, and examples thereof include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group, and a tert-butoxy group.

[0021] R 1 Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0022] R 1 Among these, from the viewpoint of suppressing discoloration of a molded article using the copolymer of the present invention after heating, is preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and even more preferably a hydrogen atom or a methyl group.

[0023] In general formula (I), R 2 is at least one selected from a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, a halogen atom, and a haloalkyl group.

[0024] R 2 The alkyl group is preferably an alkyl group having 1 to 12 carbon atoms, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a neopentyl group, and an n-hexyl group.

[0025] R 2 The alkenyl group represented by is preferably an alkenyl group having 2 to 12 carbon atoms, and examples thereof include a vinyl group, an allyl group, a propenyl group, an isopropenyl group, a butenyl group, an isobutenyl group, a pentenyl group, a prenyl group, a hexenyl group (such as a cis-3-hexenyl group), and a cyclohexenyl group.

[0026] R 2The cycloalkyl group of R is preferably a cycloalkyl group having 3 to 12 carbon atoms, and examples thereof include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. 2 The aryl group is preferably an aryl group having 6 to 20 carbon atoms, and examples thereof include a phenyl group, a tolyl group, a xylyl group, and a naphthyl group.

[0027] R 2 Examples of the halogen atom in R include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. 2 The haloalkyl group is preferably a haloalkyl group having 1 to 12 carbon atoms, and more preferably a haloalkyl group having 1 to 6 carbon atoms. Examples of halogen atoms constituting the haloalkyl group include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0028] R 2 Among these, from the viewpoint of suppressing discoloration of a molded article using the copolymer of the present invention after heating, is preferably one selected from the group consisting of a hydrogen atom, an alkyl group, an alkenyl group, and an aryl group, more preferably an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 10 carbon atoms, and even more preferably an alkyl group having 1 to 4 carbon atoms or an aryl group having 6 to 10 carbon atoms.

[0029] More specifically, from the viewpoint of suppressing discoloration, the compound represented by the general formula (I) is preferably at least one selected from the group consisting of styrene, α-methylstyrene, p-methylstyrene, isobutylene, 1-hexene, propylene, and ethylene. Use of these compounds makes it possible to more effectively suppress discoloration. The compound represented by the general formula (I) is readily available as a commercially available product, and can also be produced by known methods.

[0030] <Content of each structural unit in the copolymer> The content of the structural unit (A) in the copolymer of the present invention is preferably 30 to 55 mol%, more preferably 40 to 53 mol%, and even more preferably 48 to 51 mol%. On the other hand, the content of the structural unit (B) is preferably 20 to 80 mol%, preferably 45 to 70 mol%, more preferably 47 to 60 mol%, even more preferably 49 to 52 mol%, and even more preferably 50 to 51 mol%. When the content of each structural unit is within the above range, molded articles using the copolymer of the present invention are less likely to discolor even after heating. The content of each structural unit is 1 It can be measured by H-NMR, specifically by the method described in the Examples.

[0031] <Other Structural Units> The copolymer of the present invention may contain structural units derived from other monomers other than the structural unit (A) derived from 1,1-dicyanoethylene and the structural unit (B) derived from the compound represented by general formula (I). There are no particular restrictions on the other structural units, and examples include vinyl acetate, vinyl propionate, methyl acrylate, ethyl acrylate, and butyl acrylate. When the copolymer of the present invention contains structural units derived from other monomers, the content thereof in the copolymer is preferably 20 mol % or less, more preferably 10 mol % or less, and even more preferably 5 mol % or less.

[0032] [Method for Producing the Copolymer] The method for producing the copolymer of the present invention is not particularly limited, but it is preferable to produce the copolymer by the method for producing the copolymer of the present invention in which the polymerization temperature is 45°C or less and the copolymer is produced in the presence of a radical initiator. By setting the polymerization temperature to 45°C or less, it becomes easy to adjust the content of (U-2) and (U-3) to 5.5 mol% or less in the total amount of the four types of triad structures. From the viewpoint of adjusting the content of (U-2) and (U-3), the polymerization temperature is preferably 44°C or less, more preferably 43°C or less, and even more preferably 40°C or less.

[0033] From the viewpoint of polymerization rate and productivity, the polymerization temperature is preferably 10° C. or higher, more preferably 20° C. or higher, and even more preferably 30° C. or higher.

[0034] <Radical Polymerization Initiator> The copolymer of the present invention is preferably produced in the presence of a radical polymerization initiator. Use of a radical polymerization initiator makes it easier to adjust the total content of (U-2) and (U-3) in the total amount of the triad structure. Examples of radical polymerization initiators that can be used in the present invention include azo compounds such as azobisisobutyronitrile, 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis[2-(2-imidazolin-2-yl)propane], and 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]hydrate; inorganic peroxides such as sodium persulfate, potassium persulfate, and hydrogen peroxide; organic peroxides such as t-butyl hydroperoxide, cumene hydroperoxide, and p-menthane hydroperoxide; and redox initiators that combine an oxidizing agent and a reducing agent, such as hydrogen peroxide and an iron(II) salt, or a persulfate and sodium hydrogen sulfite. These may be used alone or in combination of two or more. As described above, the copolymer of the present invention can be easily adjusted in the total content of (U-2) and (U-3) in the total amount of the triad structure by carrying out radical polymerization at low temperatures. Therefore, among these radical polymerization initiators, azo compounds such as azobisisobutyronitrile and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) and redox initiators, which are easy to use at low temperatures, are preferred.

[0035] The amount of the radical polymerization initiator used is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, and even more preferably 0.08 to 3 parts by mass, relative to 100 parts by mass of all the monomers that are raw materials for the copolymer.

[0036] <Ratio of Charge Amounts in Production of Copolymer> In the production of the copolymer of the present invention, the charge amount of the compound represented by general formula (I) relative to the charge amount of 1,1-dicyanoethylene is preferably 0.80 equivalents or more, more preferably 0.85 equivalents or more, and even more preferably 0.90 equivalents or more, and is usually preferably 3.5 equivalents or less from the viewpoint of reducing production costs. When the charge amount of the compound represented by general formula (I) relative to the charge amount of 1,1-dicyanoethylene is equal to or greater than the lower limit, it becomes easier to adjust the total content of (U-2) and (U-3) in the total amount of the triad structure, and as a result, discoloration of a molded article using the copolymer after heating can be suppressed.

[0037] In the production of the copolymer of the present invention, a low water content in the 1,1-dicyanoethylene is preferred from the viewpoint of suppressing ionic polymerization. The water content in the 1,1-dicyanoethylene is preferably 10,000 ppm or less, more preferably 1,000 ppm or less, even more preferably 500 ppm or less, even more preferably 200 ppm or less, and even more preferably 100 ppm or less. When the water content in the 1,1-dicyanoethylene is equal to or less than the upper limit, it becomes easier to adjust the total content of (U-2) and (U-3) in the total amount of the triad structure, and as a result, discoloration of molded articles using the copolymer after heating can be suppressed. The water content in the 1,1-dicyanoethylene can be measured, for example, by a method conforming to JIS K0068:2001.

[0038] [Resin Composition] The resin composition of the present invention contains the copolymer and can be suitably used as a raw material for molded products and the like. As described above, the copolymer of the present invention is particularly suitable as a material for films and the like because it can suppress coloration even after heating. The resin composition of the present invention is not particularly limited as long as it contains the copolymer, but may also contain a synthetic resin in addition to the copolymer. Examples of other synthetic resins include polyolefin resins such as polyethylene, polypropylene, copolymers of ethylene and one or more α-olefins having 3 to 20 carbon atoms (e.g., propylene, 1-butene, 1-pentene, 1-hexene, etc.), ethylene-propylene-diene copolymer (EPDM), ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer, polyurethane resin, polyamide resin, polyester resin, and polycarbonate resin.

[0039] In addition to the copolymer of the present invention and the synthetic resin, the resin composition of the present invention may contain other components as needed, such as solvents, fillers, thickeners, antioxidants, plasticizers, flame retardants, stabilizers, and antioxidants.

[0040] From the viewpoint of suppressing coloration, the content of the copolymer in the resin composition of the present invention is preferably 0.1% by mass or more, more preferably 20% by mass or more, and even more preferably 50% by mass or more. On the other hand, when the resin composition of the present invention contains optional components, i.e., the synthetic resin and other components, the total content thereof is preferably 10% by mass or less, preferably 3% by mass or less, and preferably 0.001% by mass or more, based on the total amount of the resin composition.

[0041] <Method for producing resin composition> There is no particular limitation on the method for producing the resin composition, and the resin composition can be produced by a production method including a mixing step of mixing the copolymer of the present invention and the synthetic resin and other components used as needed. The method for mixing the components is also no particular limitation, and they can be mixed by a known method.

[0042] [Molded Articles and Films] The molded articles and films of the present invention are made using the copolymer or resin composition of the present invention. The shape of the molded articles is not limited as long as they can be produced using the copolymer or resin composition of the present invention, and various shapes such as films, pellets, sheets, plates, pipes, tubes, rods, and granules can be mentioned. The method for producing the molded articles is not particularly limited, and they can be molded by various conventionally known molding methods, such as injection molding, blow molding, press molding, extrusion molding, and calendar molding.

[0043] The molded article of the present invention is preferably a film. As described above, the molded article using the copolymer of the present invention can suppress coloration even after heating, and therefore, by processing it into a film, a film with a better appearance can be obtained.

[0044] Since the film of the present invention can suppress coloration even after heating, the difference between the yellowness index before heating and the yellowness index after heating at 140°C under normal pressure for 1 hour is preferably 2.5% or less, more preferably 2.0% or less, even more preferably 1.0% or less, and even more preferably 0.9% or less. The yellowness index in the present invention is the yellowness index measured in accordance with JIS Z8722:2009, and specifically can be measured by the method described in the examples.

[0045] The film of the present invention preferably has a low yellowness index after heating, and the yellowness index after heating at 140°C under normal pressure for 1 hour is preferably 2.5% or less, more preferably 1.5% or less, even more preferably 1.0% or less, and even more preferably 0.8% or less.

[0046] The thickness of the film of the present invention is not particularly limited, but from the viewpoint of improving the transparency of the film, it is preferably 0.001 to 5.0 mm, more preferably 0.005 to 1.5 mm, even more preferably 0.01 to 1.0 mm, still more preferably 0.01 to 0.5 mm, and even more preferably 0.01 to 0.1 mm.

[0047] The method for producing the film of the present invention is not particularly limited, and the film can be formed by a conventionally known method, such as solution casting, melt extrusion, calendering, compression molding, and injection molding.

[0048] [Conductive Film, Film Capacitor] The conductive film of the present invention is obtained by laminating a conductive layer on the film, and the film capacitor of the present invention includes the film or the conductive film. The conductive film of the present invention uses the film of the present invention, which has an excellent dielectric constant, and therefore exhibits excellent performance as a film capacitor.

[0049] The conductive layer constituting the conductive film is not particularly limited, but is generally preferably a layer made of a conductive metal such as aluminum, zinc, gold, platinum, or copper, and is a metal foil or a metal coating (e.g., a vapor-deposited metal coating), or both may be used in combination. Among these, a vapor-deposited metal coating is preferred from the viewpoints of making the conductive layer thin and increasing the capacitance relative to the volume, improving adhesion with the dielectric, and further reducing thickness variation.

[0050] For the purpose of imparting moisture resistance to the vapor-deposited metal coating, a semiconductor aluminum oxide layer may be further formed on the aluminum layer to form a multilayer structure, as described in, for example, Japanese Patent Application Laid-Open No. 2-250306.

[0051] Although there are no particular limitations on the thickness of the vapor-deposited metal coating, it is preferably 10 to 200 nm, and more preferably 20 to 100 nm, because a thickness within this range allows the capacitor to have both sufficient capacitance and strength.

[0052] When a vapor-deposited metal coating is used as the conductive layer, the method for forming the coating is not particularly limited, and for example, vacuum deposition, sputtering, ion plating, etc. can be used, with vacuum deposition being generally preferred.

[0053] The conductive layer can be formed by a batch method applied to molded products, a semi-continuous method applied to long products, or a continuous (air to air) method, with the semi-continuous method being the most common. In the semi-continuous metal vapor deposition method, metal vapor deposition is carried out in a vacuum system, and after winding up, the vacuum system is returned to an atmospheric system and the vapor-deposited film is taken out.

[0054] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The water content of 1,1-dicyanoethylene in the examples, comparative examples, and reference examples was measured according to a method in accordance with JIS K0068:2001. Example 1 A 100 ml four-neck flask equipped with a stirrer, a Dimroth stirrer, and a thermometer was charged with 2.0 g (0.026 mol, water content 390 ppm) of 1,1-dicyanoethylene synthesized according to the method described in the aforementioned literature, 2.7 g (0.026 mol, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 17 ml of toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 18 mg of 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), and radical polymerization was carried out by heating and stirring at 40°C for 4 hours under a nitrogen gas stream.

[0055] After the polymerization was completed, the precipitated copolymer was filtered. It was then washed with toluene and n-hexane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in that order, and then dried overnight at 80°C under reduced pressure. The yield of the product (copolymer powder) was 4.4 g, and the yield was 95%. The NMR spectrum of the obtained copolymer was measured by the method described below. The results are shown in Table 1.

[0056] The obtained copolymer was dissolved in N,N-dimethylacetamide (Tokyo Chemical Industry Co., Ltd.), applied to a thickness of 50 μm by solution casting using a film applicator (Tester Sangyo Co., Ltd.), and vacuum dried at 40°C and 1 kPa for 7 days to produce a pre-heated film. The yellowness of the obtained film was measured by the method described below. The results are shown in Table 1.

[0057] The dielectric constant of the obtained film was measured by the method described below. The results are shown in Table 1. As shown in Table 1, the film of the present invention can suppress yellowness to a low level and has a high dielectric constant. Such a material with a high dielectric constant is suitable for use in film capacitors, as described in JP 2008-034189 A.

[0058] Example 2 and Comparative Examples 1 to 4 Films were produced in the same manner as in Example 1, except that the water concentration in 1,1-dicyanoethylene, the polymerization temperature, and the ratio of the charged amounts were changed as shown in Tables 1 and 2. The resulting copolymers were subjected to NMR spectrum measurement in the same manner as in Example 1, and the resulting films were also subjected to yellowness index measurement. The results are shown in Tables 1 and 2.

[0059] Example 3 A 300 ml autoclave equipped with a stirrer and a thermometer was charged with 2.0 g (0.026 mol, water content 390 ppm) of 1,1-dicyanoethylene synthesized by the method described in the aforementioned literature, 3.6 g (0.064 mol, manufactured by Tokyo Chemical Industry Co., Ltd.), 6.7 ml of ethyl acetate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 18 mg of 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile), and the mixture was heated and stirred at 40° C. for 6 hours under a nitrogen gas stream to carry out radical polymerization.

[0060] After the polymerization was completed, the precipitated copolymer was filtered. It was then washed with ethyl acetate and n-hexane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in that order, and then dried overnight at 80°C under reduced pressure to obtain a product (copolymer powder). The NMR spectrum of the obtained copolymer was measured by the method described below, and a film was produced using the obtained copolymer in the same manner as in Example 1, and the yellowness index was measured. The results are shown in Table 1.

[0061] Example 4 A 300 ml autoclave equipped with a stirrer and a thermometer was charged with 2.0 g (0.026 mol, water content 390 ppm) of 1,1-dicyanoethylene synthesized by the method described in the aforementioned document, 2.7 g (0.064 mol, manufactured by Takachiho Chemical Industry Co., Ltd.), 8.9 ml of ethyl acetate (manufactured by Fujifilm Wako Pure Chemical Industries Co., Ltd.), and 18 mg of 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile), and the mixture was heated and stirred at 40° C. for 6 hours under a nitrogen gas stream to carry out radical polymerization.

[0062] Examples 5 to 8, Comparative Examples 5 to 8 Films were produced in the same manner as in Example 3, except that the water concentration in 1,1-dicyanoethylene, the polymerization temperature, and the ratio of the charged amounts were changed as shown in Tables 1 and 2. The resulting copolymers were subjected to NMR spectrum measurement in the same manner as in Example 3, and the resulting films were also subjected to yellowness index measurement. The results are shown in Tables 1 and 2.

[0063] Example 9, Comparative Examples 9 to 10 Films were produced in the same manner as in Example 4, except that the water concentration in 1,1-dicyanoethylene, the polymerization temperature, and the ratio of the charged amounts were changed as shown in Tables 1 and 2. The resulting copolymer was subjected to NMR spectrum measurement in the same manner as in Example 4, and the resulting film was also measured for yellowness. The results are shown in Tables 1 and 2.

[0064] After the polymerization was completed, the precipitated copolymer was filtered. It was then washed with ethyl acetate and n-hexane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in that order, and then dried overnight at 80°C under reduced pressure to obtain a product (copolymer powder). The NMR spectrum of the obtained copolymer was measured by the method described below, and a film was produced using the obtained copolymer in the same manner as in Example 1, and the yellowness index was measured. The results are shown in Table 1.

[0065] Reference Examples 1 to 5 Copolymers were produced with the water concentration in 1,1-dicyanoethylene, polymerization temperature, and charge ratios shown in Table 3 with reference to U.S. Patent Application Publication No. 2,615,868, and films were produced in the same manner as in Example 1. The resulting copolymers were subjected to NMR spectrum measurement in the same manner as in Example 1, and the resulting films were also measured for yellowness index. The results are shown in Table 3.

[0066] <Measurement method> (1) NMR spectrum measurement of copolymer Using a nuclear magnetic resonance spectrometer (NMR), the product (copolymer powder) 1 H-NMR and 13 The C-NMR spectrum was measured under the following conditions. Using the measurement results, the ratio of each triad structure was calculated in accordance with the method described in Non-Patent Document 1. The results are shown in Tables 1 to 3.

[0067] [ 1 H-NMR measurement conditions: Apparatus: JNM-ECX400 manufactured by JEOL Ltd. Measurement solvent: Dimethyl sulfoxide-d6 Measurement temperature: 65°C Chemical shift value standard: Tetramethylsilane

[0068] [ 13 C-NMR measurement conditions] Apparatus: JNM-ECX400 manufactured by JEOL Ltd. Measurement solvent: Dimethyl sulfoxide-d6 Measurement temperature: 65°C Measurement method: Proton decoupling method Pulse width: 45°C Pulse repetition time: 10 seconds Chemical shift value reference: Tetramethylsilane

[0069] (2) Measurement of Yellowness of Film The films obtained in the Examples, Comparative Examples, and Reference Examples were heated in a clean oven DE-41 (manufactured by Yamato Scientific Co., Ltd.) at 140°C for 1 hour under normal pressure. The yellowness of the films before and after heating was measured using a haze meter SH7000 (manufactured by Nippon Denshoku Kogyo Co., Ltd.) in accordance with JIS Z8722:2009. The yellowness was measured at three locations on each film, and the average value was used as the yellowness. The results are shown in Tables 1 to 3.

[0070] (3) Measurement of the Dielectric Constant of the Films The films obtained in the Examples, Comparative Examples, and Reference Examples were conditioned at 26°C and 60% RH. A 30 mm diameter Au-Pd alloy was then vapor-deposited onto the film surface until surface conductivity was achieved. Vapor deposition was then repeated on the opposite side to form a conductive layer, resulting in film capacitor samples. The capacitance (C) of the samples was measured using an LCR meter (Keysight Corporation). The dielectric constant was calculated from the capacitance, electrode area (S), and film thickness (d) using the formula C = ε × ε × S / d (ε is the dielectric constant of a vacuum). The results are shown in Tables 1 to 3.

[0071]

[0072]

[0073]

[0074] As is clear from the results in Tables 1 to 3, the copolymers of the present invention can suppress discoloration even after heating, and are therefore suitable for use in molded products such as films. As mentioned above, Reference Examples 1 to 5 were conducted in accordance with the description of U.S. Patent Application Publication No. 2,615,868. However, the copolymers obtained by the method described in the literature did not have a content of (U-2) and (U-3) of 5.5 mol% or less of the total amount of the four triad structures. Therefore, the films of Reference Examples 1 to 5 produced using these copolymers were discolored after heating.

Claims

1. A copolymer comprising a structural unit (A) derived from 1,1-dicyanoethylene and a structural unit (B) derived from a compound represented by the following general formula (I), CH 2 =CR 1 R 2 (I) wherein the copolymer contains the following four types of triplet structures (U-1) to (U-4) composed of the structural unit (A) and the structural unit (B), (A)-(A)-(A) ・・・ (U-1) (A)-(A)-(B) ・・・ (U-2) (B)-(A)-(A) ・・・ (U-3) (B)-(A)-(B) ・・・ (U-4) A copolymer characterized in that the contents of (U-2) and (U-3) are 5.5 mol% or less in the total amount of the four types of triplet structures. (In general formula (I), R 1 is one or more selected from a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, and a halogen atom, R 2 is one or more selected from a hydrogen atom, an alkyl group, an alkenyl group, a cycloalkyl group, an aryl group, a halogen atom, and a haloalkyl group.)

2. The copolymer according to Claim 1, wherein the content of (U-1) is 1.8 mol% or less in the total amount of the four types of triplet structures.

3. The copolymer according to Claim 1 or 2, wherein the content of the structural unit (A) in the total amount of the copolymer is 30 to 55 mol%.

4. The copolymer according to Claim 1 or 2, wherein the compound represented by the general formula (I) is at least one selected from the group consisting of styrene, α-methylstyrene, p-methylstyrene, isobutylene, 1-hexene, propylene, and ethylene.

5. A method for producing the copolymer according to Claim 1 or 2, wherein the polymerization temperature is 45°C or lower, the charged amount of the compound represented by the general formula (I) is 0.80 to 3.5 equivalents relative to the charged amount of 1,1-dicyanoethylene, and the copolymer is produced in the presence of a radical polymerization initiator.

6. A resin composition containing the copolymer according to Claim 1 or 2.

7. A molded article using the copolymer according to Claim 1 or 2.

8. A film using the copolymer according to Claim 1 or 2, wherein the difference between the yellowness before heating and the yellowness after heating at 140°C for 1 hour under normal pressure is 2.5% or less.

9. A conductive film in which a conductive layer is laminated on the film according to Claim 8.

10. A film capacitor containing the film according to Claim 8.