Copolymer, curing agent for epoxy resin, and cured product for copper-clad laminate

Abstract

To provide a copolymer that enables enhancement of low dielectric performance and thermal resistance in a cured product thereof.SOLUTION: One aspect of the present invention is a copolymer comprising an acid anhydride monomer unit and a maleimide-based monomer unit, wherein the content of an amine compound remaining in the copolymer is 3000 ppm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a copolymer, a curing agent for epoxy resins, and a cured product for copper-clad laminates. [Background technology]

[0002] Copper clad laminates (CCLs) are known as printed circuit boards that electrically connect and insulate electronic components that make up circuits and mechanically arrange and fix components. CCLs are made by impregnating glass fibers with a thermosetting resin composition containing an epoxy resin or polyphenylene ether resin and a reactive curing agent to obtain a prepreg, which is a semi-cured resin sheet, and then sandwiching both sides of this prepreg between copper foils, stacking multiple sheets of the prepreg, and bonding them under heat and pressure.

[0003] Styrene-maleic anhydride copolymer (SMA) is often used as a reactive curing agent because of its low dielectric loss. It is also known that styrene (St)-maleic anhydride (MAH)-N-phenylmaleimide (NPMI) copolymer can be used as a reactive curing agent (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2020-169276 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-197242 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, with the trend toward higher signal frequencies, there has been a growing need for circuit board materials with lower dielectric loss tangents. In addition, because resin sheets are bonded to copper foil, dimensional differences can occur at high temperatures, which can lead to warping and other problems.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a copolymer that can improve the low dielectric properties and heat resistance of a cured product. [Means for solving the problem]

[0007] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by employing specific components as monomers of a copolymer and by controlling the amount of residual compounds in the copolymer to a specific amount, and have thus completed the present invention.

[0008] According to the present invention, the following is provided: [1] A copolymer containing an acid anhydride monomer unit and a maleimide-based monomer unit, wherein the content of a residual amine compound in the copolymer is 3000 ppm or less. [2] The amine compound contains a primary amine represented by the following formula (1): JPEG2025155395000001.jpg953The copolymer according to [1], wherein R is an alkyl group in formula (1). [3] The copolymer according to [1] or [2], wherein the amine compound contains cyclohexylamine. [4] The copolymer according to any one of [1] to [3], wherein the content of the amine compound is 10 to 3000 ppm. [5] The copolymer according to any one of [1] to [4], further comprising a hydrocarbon-based monomer unit (excluding a styrene monomer unit). [6] The maleimide-based monomer unit is represented by the following formula (2): JPEG2025155395000002.jpg58128The copolymer according to any one of [1] to [5], wherein in formula (2), R is an alkyl group. [7] The copolymer according to any one of [1] to [6], wherein the maleimide-based monomer unit is an N-cyclohexylmaleimide unit. [8] The copolymer according to any one of [1] to [7], wherein 100% by mass of the copolymer contains 2 to 25% by mass of the acid anhydride monomer units, 2 to 50% by mass of the maleimide monomer units, 5 to 50% by mass of hydrocarbon monomer units (excluding styrene monomer units), and 0 to 40% by mass of styrene monomer units. [9] The copolymer according to any one of [1] to [8], which has a weight-average molecular weight of 50,000 or less.

[10] The copolymer according to any one of [1] to [9], wherein Mw / Mn is 1.5 to 3.5, where Mw is the weight average molecular weight and Mn is the number average molecular weight.

[11] A curing agent for epoxy resins, comprising the copolymer according to any one of [1] to

[10] .

[12] A cured product for copper-clad laminates, comprising the epoxy resin curing agent according to

[11] and an epoxy resin. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a copolymer that can improve the low dielectric properties and heat resistance of a cured product. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below. The present invention is not limited to these descriptions. The features of the following embodiments can be combined with each other. Furthermore, each feature can be an invention independently. Furthermore, elements of the following embodiments that are not defined in the claims are optional elements and can be omitted.

[0011] <Terminology> In this specification, for example, the description "X to Y" means equal to or greater than X and equal to or less than Y. In this specification, any number of "0"s (for example, one or two) may be added to the end of a numerical value. For example, one or two "0"s may be added after "1.4" to make it "1.40" or "1.400."

[0012] 1.Copolymer The copolymer according to this embodiment is a copolymer containing an acid anhydride monomer unit and a maleimide-based monomer unit, and may further contain one or more of a hydrocarbon-based monomer unit (excluding a styrene monomer unit) and a styrene monomer unit.

[0013] 1.1 Components in the copolymer 1.1.1 Monomer units in copolymers 1.1.1.1 Acid anhydride monomer units Examples of acid anhydride monomer units that can be used in the copolymer of this embodiment include unsaturated acid anhydride monomers such as maleic anhydride, itaconic anhydride, citraconic anhydride, and aconitic anhydride. Among these, maleic anhydride is preferred as the acid anhydride monomer unit of this embodiment because it effectively imparts curability to the thermosetting resin composition. Since the copolymer of this embodiment contains acid anhydride monomer units, the resulting cured product has more crosslinking points, enabling network-like crosslinking and improving heat resistance. These acid anhydride monomer units may be used alone or in combination of two or more. These acid anhydride monomer units may be obtained from petroleum-derived raw materials or biomass-derived raw materials.

[0014] In 100% by mass of the copolymer according to this embodiment, the content of acid anhydride monomer units is preferably 2 to 25% by mass, and more preferably 5 to 20% by mass. In 100% by mass of the copolymer, the content of acid anhydride monomer units is, for example, 2, 5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, or 25% by mass, and may be within a range between any two of the values ​​exemplified here. The content of acid anhydride monomer units in the copolymer is 13The content of the acid anhydride monomer units can be measured using C-NMR. When the content of the acid anhydride monomer units is equal to or greater than the lower limit, the heat resistance of the resulting cured product is further improved. When the content of the acid anhydride monomer units is equal to or less than the upper limit, the copolymer has excellent solubility in solvents such as methyl ethyl ketone (MEK) and exhibits a desirable solution viscosity. Furthermore, the polarity of the copolymer is reduced, further improving the low dielectric properties of the resulting cured product. The content of the acid anhydride monomer units in the copolymer can be adjusted by adjusting the conditions of the post-imidization method described below.

[0015] 1.1.1.2 Maleimide-based monomer units Examples of maleimide-based monomer units that can be used in the copolymer according to this embodiment include an N-alkylmaleimide unit and an N-arylmaleimide unit (e.g., an N-phenylmaleimide unit, an N-chlorophenylmaleimide unit, an N-methylphenylmaleimide unit, an N-methoxyphenylmaleimide unit, and an N-tribromophenylmaleimide unit). The maleimide-based monomer unit according to this embodiment is preferably an N-alkylmaleimide. Specifically, the maleimide-based monomer unit is preferably represented by the following formula (2). In formula (2), R is an alkyl group. R may be a linear, branched, or cyclic alkyl group, and is preferably a cyclic alkyl group. The number of carbon atoms in R may be, for example, 1 to 12, preferably 5 to 6, and more preferably 6. Such types of maleimide-based monomer units have low polarity, resulting in a cured product with improved low dielectric properties. [ka]

[0016] Examples of the N-alkylmaleimide unit according to this embodiment include an N-methylmaleimide unit, an N-butylmaleimide unit, and an N-cycloalkylmaleimide unit. As the N-alkylmaleimide unit according to this embodiment, an N-cycloalkylmaleimide unit is more preferred, and an N-cyclohexylmaleimide unit is particularly preferred. These maleimide-based monomers may be used alone or in combination of two or more. These maleimide-based monomer units may be obtained from petroleum-derived raw materials or biomass-derived raw materials.

[0017] In 100% by mass of the copolymer according to this embodiment, the content of maleimide-based monomer units is preferably 2 to 50% by mass, and more preferably 15 to 40% by mass. In 100% by mass of the copolymer, the content of maleimide-based monomer units is, for example, 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50% by mass, and may be within a range between any two of the values ​​exemplified here. The content of maleimide-based monomer units in the copolymer is 13 The viscosity can be measured using C-NMR. When the content of the maleimide-based monomer unit is equal to or greater than the lower limit, the low dielectric properties of the resulting cured product are further improved. When the content of the maleimide-based monomer unit is equal to or less than the upper limit, the copolymer has excellent solubility in solvents such as methyl ethyl ketone (MEK), resulting in a desirable solution viscosity.

[0018] 1.1.1.3 Hydrocarbon monomer units The copolymer according to this embodiment may contain a hydrocarbon-based monomer unit. Examples of hydrocarbon-based monomer units that can be used in the copolymer according to this embodiment include methylstyrene, dimethylstyrene, ethylstyrene, butylstyrene, norbornene, indene, acenaphthylene, benzocyclobutene, dicyclopentadiene, and vinylnaphthalene, as well as compounds obtained by substituting these compounds with a substituent. The substituent may be a saturated hydrocarbon group having 1 to 6 carbon atoms, specifically, a methyl group, an ethyl group, a t-butyl group, and a cyclohexyl group. Among these, α-methylstyrene and norbornene are preferred as the hydrocarbon-based monomer units according to this embodiment because they improve the heat resistance and low dielectric constant of the resulting cured product. α-methylstyrene is particularly preferred because they further improve the heat resistance of the resulting cured product. The inclusion of a hydrocarbon-based monomer unit in the copolymer enhances structural stability, thereby further improving the low dielectric constant of the resulting cured product. These hydrocarbon-based monomer units may be used alone or in combination of two or more. These hydrocarbon monomer units may be obtained from petroleum-derived raw materials or biomass-derived raw materials.

[0019] In 100% by mass of the copolymer according to this embodiment, the content of hydrocarbon-based monomer units is preferably 5 to 50% by mass, and more preferably 10 to 45% by mass. In 100% by mass of the copolymer, the content of hydrocarbon-based monomer units is, for example, 5, 10, 15, 20, 25, 30, 31, 32, 33, 34, 35, 40, 45, or 50% by mass, and may be within a range between any two of the values ​​exemplified here. The content of hydrocarbon-based monomer units in the copolymer is 13 It can be measured using C-NMR. When the content of hydrocarbon-based monomer units is equal to or greater than the lower limit, the low dielectric properties and heat resistance of the resulting cured product are further improved. When the content of hydrocarbon-based monomer units is equal to or less than the upper limit, the contents of acid anhydride monomer units and maleimide monomer units become relatively appropriate, and the copolymer has excellent solubility in solvents such as methyl ethyl ketone (MEK).

[0020] 1.1.1.4 Styrene monomer unit The copolymer according to this embodiment may contain styrene monomer units. When the copolymer contains styrene monomer units, copolymerization during polymerization is improved, and further, the copolymer has excellent solubility in solvents such as MEK, resulting in a preferable solution viscosity. In 100% by mass of the copolymer according to this embodiment, the content of styrene monomer units is preferably 0 to 40% by mass, and more preferably 0 to 25% by mass. In 100% by mass of the copolymer, the content of styrene monomer units is, for example, 0, 5, 10, 15, 20, 25, 30, 35, or 40% by mass, and may be within a range between any two of the numerical values ​​exemplified here. The content of styrene monomer units in the copolymer is, 13 The styrene monomer unit content can be measured using a C-NMR method. When the content of the styrene monomer unit is equal to or less than the upper limit, the low dielectric property and heat resistance of the obtained cured product are further improved. The styrene monomer unit may be obtained from a petroleum-derived raw material or a biomass-derived raw material.

[0021] 1.1.1.5 Other monomeric units The copolymer according to this embodiment may be copolymerized with other copolymerizable monomers other than acid anhydride monomers, maleimide monomers, hydrocarbon monomers, and styrene monomers, as long as the effects of the present invention are not impaired. Examples of monomers copolymerizable into the copolymer include vinyl cyanide monomers, acrylic acid ester monomers, methacrylic acid ester monomers, vinyl carboxylic acid monomers, acrylic acid amides, and methacrylic acid amides. Among these, vinyl cyanide monomers and methacrylic acid ester monomers are preferred because of their favorable affinity with epoxy resins. The monomer units copolymerizable into these copolymers may be obtained from petroleum-derived raw materials or biomass-derived raw materials.

[0022] Examples of vinyl cyanide monomers according to this embodiment include acrylonitrile, methacrylonitrile, ethacrylonitrile, and fumaronitrile. Examples of acrylic acid ester monomers according to this embodiment include methyl acrylic acid ester, ethyl acrylic acid ester, and butyl acrylic acid ester. Examples of methacrylic acid ester monomers according to this embodiment include methyl methacrylic acid ester and ethyl methacrylic acid ester. Examples of vinyl carboxylic acid monomers according to this embodiment include acrylic acid and methacrylic acid. Other monomers copolymerizable with these copolymers may be used alone or in combination of two or more.

[0023] The above-mentioned other monomers can be copolymerized to the extent that the effects of the present invention are not impaired. However, since this provides a good balance between the affinity of the copolymer with the epoxy resin and its solubility in solvents such as MEK, the other monomer units may be contained in an amount of 0 to 20% by mass relative to 100% by mass of the copolymer. In other words, the total content of the acid anhydride monomer, maleimide monomer, hydrocarbon monomer, and styrene monomer in 100% by mass of the copolymer according to this embodiment is preferably 80 to 100% by mass. The content of the other monomer units in 100% by mass of the copolymer is, for example, 0, 0.1, 0.5, 1, 2, 5, 10, 15, or 20% by mass, and may be within a range between any two of the values ​​exemplified here. The content of the other monomers in the copolymer is, 13 It can be measured using C-NMR. When the copolymer contains other monomer units, its affinity with epoxy resins improves. When the content of other monomer units is below the upper limit, the copolymer has excellent solubility in solvents such as MEK.

[0024] 1.1.2 Residual compounds in copolymers 1.1.2.1 Amine compounds The content of the amine compound remaining in the copolymer according to this embodiment is 3000 ppm or less, and more preferably 2000 ppm or less. Because the copolymer according to this embodiment is produced by a post-imidization method, the amine compound may remain in the copolymer (e.g., 10 ppm or more). However, by keeping the content of the remaining amine compound below the upper limit, hydroxyl groups are less likely to be generated during reaction with the resin, and the resulting cured product has excellent low dielectric properties. The content of the amine compound remaining in the copolymer may be, for example, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 500, 1000, 2000, or 3000 ppm, or may be within a range between any two of the values ​​exemplified here. The content of the amine compound remaining in the copolymer can be determined by pre-treating the copolymer by weighing 0.3 to 0.4 g into a 50 mL Erlenmeyer flask, adding 10 mL of DMF containing an internal standard (cyclopentanol) to dissolve the copolymer, and then measuring the content under the following conditions. Device name: GC-12A (Shimadzu Corporation) Detector: FID Column: 3 m glass column (filler: liquid phase PEG20M + TCEP (15 + 5)) Temperature: INJ 150℃, DET 150℃, Column 115℃ Injection volume: 1μL The content of the amine compound remaining in the copolymer can be reduced, for example, by extending the reaction time in the post-imidization step or by increasing the devolatilization temperature.

[0025] The amine compound remaining in the copolymer according to this embodiment preferably contains an alkylamine and preferably contains a primary amine. Specifically, it preferably contains a primary amine represented by the following formula (1). In formula (1), R is an alkyl group. R may be a linear, branched, or cyclic alkyl group, and is preferably a cyclic alkyl group. The number of carbon atoms in R may be, for example, 1 to 12, preferably 5 to 6, and more preferably 6. When these amine compounds are used in the post-imidization method, the polarity of the resulting copolymer is reduced, and the resulting cured product has better low dielectric properties. [ka]

[0026] Examples of the amine compound according to this embodiment include methylamine, butylamine, cycloalkylamine, and aniline. The amine compound according to this embodiment particularly preferably contains cyclohexylamine. The amount of cyclohexylamine remaining in the copolymer according to this embodiment is preferably 0 to 3000 ppm, more preferably 10 to 1000 ppm, and even more preferably 50 to 300 ppm. The amount of aniline remaining in the copolymer according to this embodiment is preferably 500 ppm or less, more preferably 300 ppm or less, and even more preferably 100 ppm or less. It is particularly preferred that the copolymer according to this embodiment does not contain aniline (0 ppm or less than the detection limit (e.g., 10 ppm)).

[0027] 1.1.2.2 Hydrocarbon monomers and styrene monomers The total content of hydrocarbon monomers and styrene monomers remaining in the copolymer according to this embodiment is 3000 ppm or less, and more preferably 2000 ppm or less. By setting the total content of the remaining hydrocarbon monomers and styrene monomers to the upper limit or less, the plasticity of the resulting cured product is reduced and the heat resistance is improved. The lower limit of the content of aromatic vinyl monomers remaining in the copolymer is not particularly limited, but is preferably zero (0 ppm) or less than the detection limit (e.g., 10 ppm). The content of the aromatic vinyl monomer remaining in the copolymer is, for example, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 500, 1000, 2000, or 3000 ppm, and may be within a range between any two of the values ​​exemplified here. The content of the aromatic vinyl monomer remaining in the copolymer can be determined as a value measured under the following conditions after pretreatment, in which 0.3 to 0.4 g of the copolymer is weighed into a 50 mL Erlenmeyer flask, and 10 mL of DMF containing an internal standard (cyclopentanol) is added to dissolve the copolymer. Device name: GC-12A (Shimadzu Corporation) Detector: FID Column: 3 m glass column (filler: liquid phase PEG20M + TCEP (15 + 5)) Temperature: INJ 150℃, DET 150℃, Column 115℃ Injection volume: 1μL The content of the aromatic vinyl monomer remaining in the copolymer can be reduced, for example, by reducing the amount of chain transfer agent in the polymerization step.

[0028] 1.2 Copolymer production method The polymerization method for the copolymer according to this embodiment includes, for example, solution polymerization and bulk polymerization. Solution polymerization is preferred because polymerization while performing fractional addition, etc., can produce a copolymer with a more uniform copolymer composition. The solvent for solution polymerization is preferably non-polymerizable because it is less likely to produce by-products and has fewer adverse effects. Examples of solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and acetophenone; ethers such as tetrahydrofuran and 1,4-dioxane; aromatic hydrocarbons such as benzene, toluene, xylene, and chlorobenzene; N,N-dimethylformamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone. Methyl ethyl ketone and methyl isobutyl ketone are preferred because of the ease of solvent removal during devolatilization and recovery of the copolymer. The polymerization process can be a continuous polymerization method, a batch method (batch method), or a semi-batch method.

[0029] The copolymer can be produced by any method, but is preferably obtained by radical polymerization, and the polymerization temperature is preferably in the range of 80 to 150°C. The polymerization initiator can be any of known azo compounds such as azobisisobutyronitrile, azobiscyclohexanecarbonitrile, azobismethylpropionitrile, and azobismethylbutyronitrile, and known organic peroxides such as benzoyl peroxide, t-butylperoxybenzoate, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-butylperoxyisopropyl monocarbonate, t-butylperoxy-2-ethylhexanoate, di-t-butylperoxide, dicumyl peroxide, and ethyl-3,3-di-(t-butylperoxy)butyrate. These can be used alone or in combination. From the viewpoint of controlling the polymerization reaction rate and polymerization rate, it is preferable to use an azo compound or organic peroxide with a 10-hour half-life of 70 to 120°C. The amount of polymerization initiator used is not particularly limited, but is preferably 0.1 to 1.5% by mass, and more preferably 0.1 to 1.0% by mass, relative to 100% by mass of all monomer units. A polymerization initiator used in an amount of 0.1% by mass or more is preferred because a sufficient polymerization rate can be obtained. A polymerization initiator used in an amount of 1.5% by mass or less can suppress the polymerization rate, making it easier to control the reaction and achieve the target molecular weight.

[0030] A chain transfer agent can be used in the production of the copolymer. The chain transfer agent used is not particularly limited, but examples include n-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, α-methylstyrene dimer, ethyl thioglycolate, limonene, and terpinolene. The amount of chain transfer agent used is not particularly limited as long as the target molecular weight is obtained, but is preferably 0.01 to 2.0 mass% and more preferably 0.1 to 1.5 mass% relative to 100 mass% of all monomer units. The target molecular weight can be easily obtained when the amount of chain transfer agent used is 0.01 to 2.0 mass%. The chain transfer agent is preferably added in multiple portions (for example, preferably two or more portions, more preferably three or more portions). This addition method can reduce low-molecular-weight components, thereby reducing the Mw / Mn value of the copolymer.

[0031] One method for introducing maleimide-based monomer units into a copolymer is to first copolymerize an acid anhydride monomer, a hydrocarbon monomer, a styrene monomer, and other monomers, and then convert the unsaturated acid anhydride groups into maleimide-based monomer units by reacting them with ammonia or a primary amine (post-imidization method). This post-imidization method is preferred because it reduces the amount of maleimide-based monomer remaining in the copolymer. Furthermore, converting the unsaturated acid anhydride groups into maleimide-based monomer units using the post-imidization method reduces the polarity of the copolymer, further improving the low dielectric properties of the resulting cured product.

[0032] Examples of primary amines used in the post-imidization method include alkylamines such as methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, n-pentylamine, n-hexylamine, n-octylamine, cyclohexylamine, and decylamine, as well as chlorine- or bromine-substituted alkylamines, and aromatic amines such as aniline, toluidine, and naphthylamine. Among these, aniline and cyclohexylamine are preferred, with cyclohexylamine being particularly preferred. These primary amines may be used alone or in combination of two or more. The amount of primary amine added can be determined depending on the amount of unsaturated acid anhydride groups to be converted to maleimide groups. The amount is preferably 0.2 to 1.0 molar equivalents relative to the unsaturated acid anhydride groups contained in the copolymer (in the crude product raw material), and is preferably 1.0 to 1.1 molar equivalents, more preferably 1.0 to 1.05 molar equivalents, relative to the unsaturated acid anhydride groups to be converted to maleimide groups. A molar equivalent of 0.2 or more relative to the unsaturated acid anhydride monomer units in the crude product raw material is preferred because it provides a good balance between the thermal stability of the copolymer and the low dielectric constant of the resulting cured product. A molar equivalent of 1.0 or less is also preferred because it reduces the content of primary amines remaining in the copolymer. The reaction time for the post-imidization step is preferably, for example, 6 hours or more, and more preferably 10 hours or more. By setting the reaction time for the post-imidization step to the lower limit or higher, the content of amine compounds in the copolymer can be reduced.

[0033] A catalyst may be used when introducing maleimide-based monomer units by post-imidization. The catalyst can improve the dehydration ring-closure reaction in the reaction between ammonia or a primary amine and an unsaturated acid anhydride group, particularly in the reaction converting the unsaturated acid anhydride group to a maleimide group. The type of catalyst is not particularly limited, but a tertiary amine can be used, for example. Examples of tertiary amines include, but are not limited to, trimethylamine, triethylamine, tripropylamine, tributylamine, N,N-dimethylaniline, and N,N-diethylaniline. The amount of tertiary amine added is not particularly limited, but is preferably 0.01 molar equivalents or more relative to the unsaturated acid anhydride group. The temperature of the imidization reaction according to this embodiment is preferably 100 to 250°C, more preferably 120 to 200°C. An imidization reaction temperature of 100°C or higher is preferable from the viewpoint of productivity, since the reaction rate is sufficiently fast. An imidization reaction temperature of 250°C or lower is preferable, since it can suppress deterioration of the physical properties of the copolymer due to thermal degradation.

[0034] Known methods can be used to remove volatile components (devolatilization methods), such as the solvent used in solution polymerization and unreacted monomers, from the solution after solution polymerization of the copolymer or the solution after post-imidization. For example, a vacuum devolatilization tank equipped with a heater or a vented devolatilization extruder can be used. The devolatilization temperature is preferably 250°C or higher, and more preferably 280°C or higher. By raising the devolatilization temperature above the lower limit, the content of the amine compound in the copolymer can be reduced. The devolatilized molten copolymer is transferred to a granulation process, extruded into strands through a multi-hole die, and processed into pellets by cold cutting, in-air hot cutting, or underwater hot cutting. The resulting pellets can be processed into powder by a pulverization process. Converting the copolymer into powder has the advantage of increasing the dissolution rate when blended into a thermosetting resin composition. When the weight-average molecular weight of the copolymer is reduced, the extruded copolymer may be recovered and pulverized to form powder without the pelletization process. The pulverization method is not particularly limited, and known pulverization techniques can be used. Suitable pulverization devices include a rotary blade pulverizer, a turbo mill pulverizer, a turbo disk mill pulverizer, a turbo cutter pulverizer, a jet mill pulverizer, an impact pulverizer, a hammer pulverizer, and a vibration pulverizer.

[0035] 1.3 Physical properties of copolymers 1.3.1 Weight average molecular weight (Mw) of copolymer The weight-average molecular weight (Mw) of the copolymer according to this embodiment is preferably 50,000 or less, and more preferably 30,000 or less. The lower limit of the weight-average molecular weight of the copolymer according to this embodiment is not particularly limited, but is, for example, 3,000. The weight-average molecular weight of the copolymer is preferably, for example, 3,000, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000, 11,000, 12,000, 13,000, 14,000, 15,000, 20,000, 30,000, 40,000, or 50,000, and may be within a range between any two of the values ​​exemplified here. The weight-average molecular weight can be, for example, a polystyrene-equivalent value measured using gel permeation chromatography (GPC). Specifically, it can be a value measured under the following conditions. Equipment: SYSTEM-21 Shodex (manufactured by Resonac Co., Ltd.) Column: Three PL gel MIXED-B columns (Polymer Laboratories) in series Temperature: 40℃ Detection: Differential refractive index Solvent: tetrahydrofuran Concentration: 2% by mass Calibration curve: Created using standard polystyrene (PS) (manufactured by Polymer Laboratories) When the weight-average molecular weight of the copolymer is equal to or less than the upper limit, the copolymer has excellent solubility in solvents such as MEK, a preferable solution viscosity, and excellent reactivity with epoxy resins. The weight-average molecular weight of the copolymer can be adjusted by the polymerization temperature, polymerization time, solvent concentration, amount of polymerization initiator used, and amount of chain transfer agent used, and can be adjusted particularly by the amount of chain transfer agent used.

[0036] 1.3.2 Number average molecular weight of copolymer (Mn) The number average molecular weight (Mn) of the copolymer according to this embodiment is preferably 40,000 or less, and more preferably 10,000 or less. The lower limit of the number average molecular weight of the copolymer according to this embodiment is not particularly limited, but is, for example, 1,000. The number average molecular weight of the copolymer is, for example, 1,000, 2,000, 3,000, 4,000, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000, 15,000, 20,000, 30,000, or 40,000, and may be within a range between any two of the values ​​exemplified here. The number average molecular weight can be, for example, a polystyrene-equivalent value measured using gel permeation chromatography (GPC), similar to the weight average molecular weight described above. When the number average molecular weight of the copolymer is equal to or greater than the lower limit, the amount of chain transfer agent used in the copolymer polymerization step is reduced, thereby reducing the amount of VOCs contained in the resulting copolymer. When the number average molecular weight of the copolymer is equal to or less than the upper limit, the solubility of the copolymer in solvents such as MEK is improved, and the effect of imparting curability to the thermosetting resin composition is improved. The number average molecular weight of the copolymer can be adjusted by the polymerization temperature, polymerization time, solvent concentration, amount of polymerization initiator used, and amount of chain transfer agent used, and can be adjusted particularly by the amount of chain transfer agent used.

[0037] 1.3.3 Molecular weight distribution The copolymer according to this embodiment preferably has a Mw / Mn ratio of 1.5 to 3.5, more preferably 2.0 to 3.0, where Mw is the weight-average molecular weight and Mn is the number-average molecular weight. The Mw / Mn ratio of the copolymer is, for example, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, or 3.5, and may be within a range between any two of the values ​​exemplified here. When the Mw / Mn ratio of the copolymer is equal to or greater than the lower limit, the degassing load of the solution is reduced. When the Mw / Mn ratio of the copolymer is equal to or less than the upper limit, the number of crosslinking points increases, enabling network-like crosslinking, resulting in improved low dielectric properties and heat resistance of the resulting cured product. The Mw / Mn ratio of the copolymer can be adjusted by the number of times a chain transfer agent is added.

[0038] 2.Thermosetting resin composition The copolymer according to this embodiment can be used as a reactive curing agent, and is particularly suitable as a curing agent for epoxy resins. Accordingly, one embodiment of the present invention is an epoxy resin curing agent containing the copolymer. The thermosetting resin composition according to this embodiment can be obtained by blending the epoxy resin curing agent with a thermosetting resin, preferably an epoxy resin.

[0039] The thermosetting resin composition according to this embodiment may contain a resin other than the epoxy resin, as long as the effects of the present invention are not impaired. The thermosetting resin composition according to this embodiment may contain, for example, a resin such as a cyanate resin or a bismaleimide resin. The thermosetting resin composition according to this embodiment may also contain an elastomer such as butadiene rubber, isoprene rubber, acrylate rubber, a graft copolymer containing these, or a hydrogenated product of the graft copolymer. By including such a rubber or elastomer, peeling between the cured product obtained from the thermosetting resin composition and the metal foil can be suppressed.

[0040] The thermosetting resin composition according to this embodiment may further contain another copolymer other than the copolymer described above (the epoxy resin curing agent according to this embodiment). As the other copolymer, for example, a copolymer containing an acid anhydride monomer unit and an aromatic vinyl monomer unit but not containing a maleimide-based monomer unit can be used. In the thermosetting resin composition according to this embodiment, the content of the copolymer (the total of the copolymer according to this embodiment and the other copolymer described above) relative to the thermosetting resin ((thermosetting resin):(copolymer)) is preferably 1:0.1-10, more preferably 1:0.5-1.5.

[0041] The thermosetting resin composition according to this embodiment may contain additives as long as the effects of the present invention are not impaired. For the purpose of accelerating the curing of the reactive curing agent, it is preferable to use one or more curing accelerators selected from the group consisting of imidazole-based curing accelerators, amine-based curing accelerators, ammonium salt-based curing accelerators, phosphine-based curing accelerators, phosphonium salt-based curing accelerators, urea-based curing accelerators, and fatty acid metal salts. It is particularly preferable to use an imidazole-based curing accelerator as the curing accelerator.

[0042] The imidazole curing accelerator according to this embodiment is a compound having an imidazole skeleton. Examples of the imidazole curing accelerator include 2-ethyl-4-methylimidazole, 1-cyanoethyl-2-ethyl-4-methylimidazole, and bisphenol A bis{3-(2-phenyl)imidazolyl-2-hydroxypropyl} ether. These imidazole curing accelerators may be used alone or in combination of two or more. In the thermosetting resin composition according to this embodiment, the content of the imidazole curing accelerator is preferably 0.1 to 5.0 parts by mass, more preferably 0.1 to 3.0 parts by mass, based on 100 parts by mass of the total of the resin and copolymer.

[0043] The thermosetting resin composition according to this embodiment may contain additives other than the curing accelerator as long as the effects of the present invention are not impaired. For the purpose of imparting flame retardancy to the thermosetting resin composition and its cured product, other additives may be blended, such as phosphate flame retardants such as tricresyl phosphate and triphenyl phosphate, and inorganic flame retardants such as red phosphorus, antimony trioxide, aluminum hydroxide, and magnesium hydroxide. Furthermore, for the purpose of achieving a low coefficient of thermal expansion and a high modulus of elasticity, inorganic fillers such as silica, mica, talc, short glass fiber, fine glass powder, and hollow glass may be blended.

[0044] The thermosetting resin composition according to the present embodiment is obtained by dissolving the reactive curing agent according to the present embodiment, the epoxy resin, and optionally other resins and / or additives in an organic solvent and mixing them together. Examples of the organic solvent according to the present embodiment include ketones such as MEK, cyclohexanone, and methyl isobutyl ketone.

[0045] 3.Cured product A cured product can be obtained by heating and drying the thermosetting resin composition according to this embodiment. By using the copolymer according to this embodiment as a reactive curing agent, the low dielectric properties and heat resistance of the cured product are improved. Therefore, the thermosetting resin composition according to this embodiment can be suitably used as a prepreg material for copper-clad laminates. A cured product for copper-clad laminates can be obtained by impregnating a glass fiber substrate such as glass fiber cloth or glass fiber nonwoven fabric with the thermosetting resin composition according to this embodiment and curing the material. The cured product for copper-clad laminates according to this embodiment has excellent low dielectric properties, thereby reducing dielectric loss. Furthermore, the cured product for copper-clad laminates according to this embodiment has excellent heat resistance, so even when laminated with copper foils having different expansion coefficients, dimensional differences at high temperatures and warping are unlikely to occur.

[0046] 3.1 Low dielectric constant The cured product according to this embodiment has excellent low dielectric properties. Specifically, the dielectric loss tangent (Df) of the cured product according to this embodiment is preferably 0.028 or less, more preferably 0.026 or less, and even more preferably 0.023 or less. The lower limit of the dielectric loss tangent (Df) of the cured product according to this embodiment is not particularly limited, but is, for example, 0.010. The cured product can be obtained, for example, by (1) dissolving 50 parts by mass of the copolymer (25 parts by mass of the copolymer according to this embodiment and 25 parts by mass of a styrene-maleic anhydride copolymer), 50 parts by mass of an epoxy resin, and 0.5 parts by mass of a curing accelerator in MEK to form a thermosetting resin composition; (2) spreading the thermosetting resin composition on a Teflon (registered trademark) film, heating and drying it under vacuum at 90°C for 8 minutes, and then casting to remove the solid content; and (3) pressing the solid content at a pressure of 18 MPa at a temperature of 130°C for 2 hours and then at 180°C for 4 hours. The dielectric loss tangent (Df) can be determined, for example, by using a 0.2 mm×50 mm×50 mm sample cut out from the cured product and measuring it at 23° C. and 10 GHz using a cavity resonance method.

[0047] 3.2 Heat resistance The cured product according to this embodiment has excellent heat resistance. Specifically, the glass transition temperature (Tg) of the cured product according to this embodiment is preferably 170°C or higher, and more preferably 180°C or higher. The upper limit of the glass transition temperature (Tg) of the cured product according to this embodiment is not particularly limited, but is, for example, 250°C. The glass transition temperature (Tg) can be, for example, the value measured by the DMA method (tensile method) in accordance with JIS C 6481:1996 for the cured product obtained by the above-mentioned method. [Example]

[0048] The present invention will be described in more detail below based on examples. Note that the examples described below are representative examples of the present invention and should not be construed as narrowing the scope of the present invention. In the tables, MAH stands for maleic anhydride, CHMI stands for N-cyclohexylmaleimide, NPMI stands for N-phenylmaleimide, AMS stands for α-methylstyrene, NBN stands for norbornene, and St stands for styrene.

[0049] <Preparation of Copolymer (A-1)> A 120-liter autoclave equipped with a stirrer was charged with 14 parts by weight of styrene, 40 parts by weight of α-methylstyrene, 1 part by weight of maleic anhydride, 0.4 parts by weight of tert-dodecyl mercaptan, and 105 parts by weight of methyl isobutyl ketone. The gas phase was then purged with nitrogen gas and the temperature was raised to 92°C over 40 minutes with stirring. After the temperature was raised to 92°C, a solution of 6 parts by weight of styrene, 39 parts by weight of maleic anhydride, and 1 part by weight of t-butyl peroxy-2-ethylhexanoate in 115 parts by weight of methyl isobutyl ketone was continuously added over 5 hours while maintaining the temperature at 92°C. Two hours after the start of the continuous addition, 0.3 parts by weight of tert-dodecyl mercaptan was added, followed by 0.3 parts by weight of tert-dodecyl mercaptan four hours later. After the addition was completed, the temperature was raised to 120°C and the reaction was allowed to proceed for 1 hour to complete the polymerization. Then, 25 parts by mass of cyclohexylamine and 0.6 parts by mass of triethylamine were added to the polymerization solution, and the mixture was reacted at 140°C for 6 hours, then heated to 150°C and reacted for another 6 hours. After the reaction was completed, the imidization reaction solution was fed into a vent-type screw extruder with a barrel temperature of 290°C, and the volatile matter was removed to obtain a block copolymer. The obtained block copolymer was pulverized in a pulverizer to obtain a granular copolymer (A-1). 13 The composition of the copolymer (A-1) was analyzed by C-NMR, and found to be 13% by mass of maleic anhydride, 37% by mass of N-cyclohexylmaleimide, 33% by mass of α-methylstyrene, and 17% by mass of styrene. The analytical results of the obtained copolymer (A-1) are shown in Table 1.

[0050] <Preparation of Copolymer (A-2)> It was produced in the same manner as in the copolymer (A-1), except that 23 parts by mass of aniline was added to the polymerization solution instead of 25 parts by mass of cyclohexylamine. 13 The composition of the copolymer (A-2) was analyzed by C-NMR, and found to be 13% by mass of maleic anhydride, 37% by mass of N-phenylmaleimide, 33% by mass of α-methylstyrene, and 17% by mass of styrene. The analytical results of the obtained copolymer (A-2) are shown in Table 1.

[0051] <Preparation of Copolymer (A-3)> It was produced in the same manner as in the case of copolymer A-1, except that the amount of cyclohexylamine added to the polymerization solution was changed from 25 parts by mass to 18 parts by mass. 13 The composition of the copolymer (A-3) was analyzed by C-NMR, and found to be 19% by mass of maleic anhydride, 29% by mass of N-cyclohexylmaleimide, 35% by mass of α-methylstyrene, and 17% by mass of styrene. The analytical results of the obtained copolymer (A-3) are shown in Table 1.

[0052] <Preparation of Copolymer (A-4)> A 120-liter autoclave equipped with a stirrer was charged with 27 parts by weight of styrene, 30 parts by weight of α-methylstyrene, 1 part by weight of maleic anhydride, 0.4 parts by weight of tert-dodecyl mercaptan, and 100 parts by weight of methyl isobutyl ketone. The gas phase was then purged with nitrogen gas and the temperature was raised to 92°C over 40 minutes with stirring. After the temperature was raised to 92°C, a solution of 15 parts by weight of styrene, 27 parts by weight of maleic anhydride, and 1 part by weight of t-butyl peroxy-2-ethylhexanoate in 120 parts by weight of methyl isobutyl ketone was continuously added over 5 hours while maintaining the temperature at 92°C. Two hours after the start of the continuous addition, 0.3 parts by weight of tert-dodecyl mercaptan was added, followed by 0.3 parts by weight of tert-dodecyl mercaptan four hours later. After the addition was completed, the temperature was raised to 120°C and the reaction was allowed to proceed for 1 hour to complete the polymerization. Thereafter, 6 parts by mass of cyclohexylamine and 0.4 parts by mass of triethylamine were added to the polymerization solution, and the mixture was reacted at 140°C for 6 hours, then heated to 150°C and reacted for another 6 hours. After the reaction was completed, the imidization reaction solution was fed into a vent-type screw extruder with a barrel temperature of 290°C, and the volatile matter was removed to obtain a block copolymer. The obtained block copolymer was pulverized in a pulverizer to obtain a granular copolymer (A-4). 13 The composition of the copolymer (A-4) was analyzed by C-NMR, and found to be 21% by mass of maleic anhydride, 10% by mass of N-cyclohexylmaleimide, 29% by mass of α-methylstyrene, and 40% by mass of styrene. The analytical results of the obtained copolymer (A-4) are shown in Table 1.

[0053] <Preparation of Copolymer (A-5)> A 120-liter autoclave equipped with a stirrer was charged with 49 parts by weight of norbornene, 0.004 parts by weight of tert-dodecyl mercaptan, and 100 parts by weight of methyl isobutyl ketone. The gas phase was purged with nitrogen gas, and the mixture was heated to 92°C over 40 minutes with stirring. After heating to 92°C, a solution of 51 parts by weight of maleic anhydride and 1 part by weight of t-butyl peroxy-2-ethylhexanoate in 250 parts by weight of methyl isobutyl ketone was continuously added over 5 hours while maintaining the temperature at 92°C. Two hours after the start of the continuous addition, 0.003 parts by weight of tert-dodecyl mercaptan was added, followed by 0.003 parts by weight of tert-dodecyl mercaptan four hours later. After the addition was completed, the mixture was heated to 120°C and allowed to react for 1 hour to complete the polymerization. Thereafter, 35 parts by mass of cyclohexylamine and 0.8 parts by mass of triethylamine were added to the polymerization solution, and the mixture was reacted at 140°C for 6 hours, then heated to 150°C and reacted for another 6 hours. After the reaction was completed, the imidization reaction solution was fed into a vent-type screw extruder with a barrel temperature of 290°C, and the volatile matter was removed to obtain a block copolymer. The obtained block copolymer was pulverized in a pulverizer to obtain a granular copolymer (A-5). 13 The composition of the copolymer (A-5) was analyzed by C-NMR, and found to be 13% by mass of maleic anhydride, 49% by mass of N-cyclohexylmaleimide, and 38% by mass of norbornene. The analytical results of the obtained copolymer (A-5) are shown in Table 1.

[0054] <Preparation of Copolymer (A-6)> A 120-liter autoclave equipped with a stirrer was charged with 64 parts by weight of styrene, 1 part by weight of maleic anhydride, 0.004 parts by weight of tert-dodecyl mercaptan, and 100 parts by weight of methyl isobutyl ketone. The gas phase was purged with nitrogen gas, and the mixture was heated to 92°C over 40 minutes with stirring. After heating to 92°C, a solution of 35 parts by weight of maleic anhydride and 0.3 parts by weight of t-butyl peroxy-2-ethylhexanoate in 120 parts by weight of methyl isobutyl ketone was continuously added over 5 hours while maintaining the temperature at 92°C. Two hours after the start of the continuous addition, 0.003 parts by weight of tert-dodecyl mercaptan was added, followed by 0.003 parts by weight of tert-dodecyl mercaptan four hours later. After the addition was completed, the mixture was heated to 120°C and allowed to react for 1 hour to complete the polymerization. Thereafter, 33 parts by mass of aniline and 0.6 parts by mass of triethylamine were added to the polymerization solution, and the mixture was reacted at 140°C for 6 hours, then heated to 150°C and reacted for another 6 hours. After the reaction was completed, the imidization reaction solution was fed into a vent-type screw extruder with a barrel temperature of 290°C, and volatile matter was removed to obtain a block copolymer. The obtained block copolymer was pulverized in a pulverizer to obtain a granular copolymer (A-6). 13 The composition of the copolymer (A-6) was analyzed by C-NMR, and it was found to consist of 1% by mass of maleic anhydride, 48% by mass of N-phenylmaleimide, and 51% by mass of styrene. The analytical results of the obtained copolymer (A-6) are shown in Table 1.

[0055] <Preparation of Copolymer (A-7)> The granular copolymer (A-1) was fed into a vent-type screw extruder with a barrel temperature of 290°C, and volatile matter was removed to obtain a bulk copolymer. The obtained bulk copolymer was pulverized in a pulverizer to obtain a granular copolymer (A-7). 13 The composition of the copolymer (A-7) was analyzed by C-NMR, and found to be 13% by mass of maleic anhydride, 37% by mass of N-cyclohexylmaleimide, 33% by mass of α-methylstyrene, and 17% by mass of styrene. The analytical results of the obtained copolymer (A-7) are shown in Table 1.

[0056] <Preparation of Copolymer (B-1)> After completing the polymerization in the same manner as for copolymer (A-1), 25 parts by mass of cyclohexylamine and 0.6 parts by mass of triethylamine were added to the polymerization solution, and the mixture was allowed to react at 140°C for 6 hours. After the reaction was completed, the imidization reaction solution was fed into a vent-type screw extruder with a barrel temperature of 210°C, and volatile matter was removed to obtain a block copolymer. The obtained block copolymer was pulverized in a pulverizer to obtain granular copolymer (B-1). 13 The composition of the copolymer (B-1) was analyzed by C-NMR, and found to be 13% by mass of maleic anhydride, 37% by mass of N-cyclohexylmaleimide, 33% by mass of α-methylstyrene, and 17% by mass of styrene. The analytical results of the obtained copolymer (B-1) are shown in Table 1.

[0057] <Preparation of Copolymer (B-2)> After completing the polymerization in the same manner as for copolymer (A-1), the polymerization liquid was fed into a vent-type screw extruder with a barrel temperature of 230°C, and the volatile matter was removed to obtain a bulk copolymer. The obtained bulk copolymer was pulverized in a pulverizer to obtain granular copolymer (B-2). 13 The composition of the copolymer (B-2) was analyzed by C-NMR, and it was found to consist of 40% by mass of maleic anhydride, 40% by mass of α-methylstyrene, and 20% by mass of styrene. The analytical results of the obtained copolymer (B-2) are shown in Table 1.

[0058] <Preparation of Copolymer (B-3)> A 120-liter autoclave equipped with a stirrer was charged with 55 parts by weight of α-methylstyrene, 1 part by weight of maleic anhydride, 0.4 parts by weight of tert-dodecyl mercaptan, and 90 parts by weight of methyl isobutyl ketone. The gas phase was then purged with nitrogen gas and the mixture was heated to 92°C over 40 minutes with stirring. After the temperature was raised to 92°C, a solution of 44 parts by weight of maleic anhydride and 1 part by weight of t-butyl peroxy-2-ethylhexanoate in 130 parts by weight of methyl isobutyl ketone was continuously added over 5 hours while maintaining the temperature at 92°C. Two hours after the start of the continuous addition, 0.3 parts by weight of tert-dodecyl mercaptan was added, followed by 0.3 parts by weight of tert-dodecyl mercaptan four hours later. After the addition was completed, the mixture was heated to 120°C and allowed to react for 1 hour to complete the polymerization. Thereafter, 46 parts by mass of cyclohexylamine and 0.7 parts by mass of triethylamine were added to the polymerization solution, and the mixture was reacted at 140°C for 6 hours, then heated to 150°C and reacted for another 6 hours. After the reaction was completed, the imidization reaction solution was fed into a vent-type screw extruder with a barrel temperature of 290°C, and the volatile matter was removed to obtain a block copolymer. The obtained block copolymer was pulverized in a pulverizer to obtain a granular copolymer (B-3). 13 The composition of the copolymer (B-3) was analyzed by C-NMR, and it was found to consist of 40% by mass of α-methylstyrene and 60% by mass of N-cyclohexylmaleimide. The analytical results of the obtained copolymer (B-3) are shown in Table 1.

[0059] <Analysis of copolymers> (composition analysis) The composition analysis of the copolymer is 13 Measurement was performed using C-NMR under the following conditions. Device name: FT-NMR AVANCE300 (BRUKER) Solvent: deuterated chloroform Concentration: 14% by mass Temperature: 27℃ Accumulation count: 8000 times

[0060] (Weight average molecular weight, number average molecular weight, molecular weight distribution) The weight average molecular weight (Mw) and number average molecular weight (Mn) of the copolymer were measured by gel permeation chromatography (GPC) under the following conditions: Equipment: SYSTEM-21 Shodex (manufactured by Resonac Co., Ltd.) Column: Three PL gel MIXED-B columns (Polymer Laboratories) in series Temperature: 40℃ Detection: Differential refractive index Solvent: tetrahydrofuran Concentration: 2% by mass Calibration curve: Created using standard polystyrene (PS) (manufactured by Polymer Laboratories)

[0061] (Amine compound content remaining in copolymer) As a pretreatment, the content of the amine compound remaining in the copolymer was measured under the following conditions after weighing 0.3 to 0.4 g of the copolymer into a 50 mL Erlenmeyer flask and dissolving it in 10 mL of DMF containing an internal standard (cyclopentanol). Device name: GC-12A (Shimadzu Corporation) Detector: FID Column: 3 m glass column (filler: liquid phase PEG20M + TCEP (15 + 5)) Temperature: INJ 150℃, DET 150℃, Column 115℃ Injection volume: 1μL In all copolymers, the triethylamine content was below the detection limit (less than 10 ppm).

[0062] [Table 1]

[0063] <Preparation of cured product> 25 parts by mass of each copolymer, 25 parts by mass of a styrene-maleic anhydride copolymer ("EF40" manufactured by CRAY VALLEY), 50 parts by mass of an epoxy resin ("jER (registered trademark) 828US" manufactured by Mitsubishi Chemical Corporation), and 0.5 parts by mass of a curing accelerator (2-ethyl-4-methylimidazole; "2E4MZ" manufactured by Shikoku Chemicals Corporation) were dissolved in 50 parts by mass of MEK to obtain a thermosetting resin composition.

[0064] Each thermosetting resin composition was spread on Teflon® film, dried by heating under vacuum at 90°C for 8 minutes, and the solid was extracted by casting. This solid was then pressed at 18 MPa and 130°C for 2 hours and then at 180°C for 4 hours to obtain a resin plate (cured product). The analytical results of the obtained cured product are shown in Table 2.

[0065] <Analysis of the cured product> (Dielectric loss tangent (Df)) Using a 0.2 mm x 50 mm x 50 mm sample cut out from the cured product, values ​​were measured at 23°C and 10 GHz using the cavity resonance method (Anritsu MS46122B network analyzer, KEYCOM TE cavity resonator).

[0066] (glass transition temperature (Tg)) The glass transition temperature (Tg) of the cured product was measured by the DMA method (tensile method) in accordance with JIS C 6481:1996.

[0067] [Table 2]

[0068] The results in Table 2 show that the examples using the copolymer of the present invention had a dielectric dissipation factor (Df) of 0.028 or less and a glass transition temperature (Tg) of 170°C or more, and were able to improve the low dielectric property and heat resistance of the cured product. On the other hand, the results in Table 2 show that the comparative examples using polymers that do not satisfy the constitution of the present invention were inferior in at least one of the low dielectric property and heat resistance of the cured product.

Claims

1. A copolymer containing an acid anhydride monomer unit and a maleimide-based monomer unit, A copolymer, wherein the content of a residual amine compound in the copolymer is 3000 ppm or less.

2. The amine compound contains a primary amine represented by the following formula (1): The copolymer according to claim 1 , wherein in formula (1), R is an alkyl group.

3. The copolymer of claim 1 , wherein the amine compound comprises cyclohexylamine.

4. The copolymer according to claim 1, wherein the content of the amine compound is 10 to 3000 ppm.

5. The copolymer according to claim 1 , further comprising hydrocarbon-based monomer units (excluding styrene monomer units).

6. The maleimide-based monomer unit is represented by the following formula (2): The copolymer according to claim 1 , wherein in formula (2), R is an alkyl group.

7. 7. The copolymer according to claim 6, wherein the maleimide-based monomer unit is an N-cyclohexylmaleimide unit.

8. 2. The copolymer according to claim 1, wherein the copolymer contains, based on 100% by mass, 2 to 25% by mass of the acid anhydride monomer units, 2 to 50% by mass of the maleimide monomer units, 5 to 50% by mass of hydrocarbon monomer units (excluding styrene monomer units), and 0 to 40% by mass of styrene monomer units.

9. The copolymer according to claim 1, having a weight average molecular weight of 50,000 or less.

10. 2. The copolymer according to claim 1, wherein Mw / Mn is 1.5 to 3.5, where Mw is the weight average molecular weight and Mn is the number average molecular weight.

11. A curing agent for epoxy resins, comprising the copolymer according to any one of claims 1 to 10.

12. A cured product for copper-clad laminates, comprising the epoxy resin curing agent according to claim 11 and an epoxy resin.

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