Polyfunctional vinyl aromatic copolymer, method for producing same, curable resin composition and cured product of same

Abstract

Provided are a novel polyfunctional vinyl aromatic copolymer that exhibits improved reactivity and is capable of providing a cured product or molded body having improved uniformity and mechanical properties, and a method for producing the same.　Specifically provided is a polyfunctional vinyl aromatic copolymer having: a structural unit derived from a divinyl aromatic compound (a); an ester group-containing vinyl aromatic compound (b) represented by formula (1); and a structural unit derived from a monovinyl aromatic compound (c), said polyfunctional vinyl aromatic copolymer being characterized by having a number average molecular weight of 300-100,000, having a molecular weight distribution (Mw / Mn) expressing the ratio of the weight average molecular weight and the number average molecular weight of 100 or less, and being soluble in a solvent. In the formula, Ar1 and Ar2 are each independently an aromatic ring group that is either a benzene ring or a naphthalene ring, and the aromatic ring in each or either of Ar1 and Ar2 contains a C1-15 ester group as a substituent.

Description

Polyfunctional vinyl aromatic copolymer, its production method, curable resin composition and cured product thereof

[0001] The present invention relates to a novel polyfunctional vinyl aromatic copolymer, a method for producing the same, and a curable resin composition containing the copolymer.

[0002] With the recent increase in the volume of information and communication, information communication in the high frequency band has become more prevalent. This has created a demand for electrical insulating materials with better electrical properties, particularly low dielectric constants and low dielectric loss tangents, to reduce transmission loss in the high frequency band.

[0003] Conventionally, thermosetting resins such as phenolic resins, epoxy resins, and polyimide resins have been used for printed wiring boards. While these resins offer a well-balanced range of performance, they lack sufficient dielectric properties in the high-frequency range. Resin compositions containing a radically polymerizable compound and an epoxy resin have been disclosed as new materials that address this issue (see Patent Documents 1 and 2). However, the resin compositions containing an epoxy resin and a radically polymerizable compound disclosed in Patent Documents 1 and 2 undergo independent crosslinking reactions, resulting in the formation of two types of three-dimensional networks in the cured product. This leads to phase separation in the cured product, insufficient crosslink density, and difficulty in achieving high mechanical properties. Therefore, there has been a problem in that it is not possible to increase the amount of vinyl resin, which has excellent dielectric properties.

[0004] Patent Document 3 discloses a polyfunctional vinyl aromatic copolymer having structural units derived from a divinyl aromatic compound as a radically polymerizable compound. Because this polyfunctional vinyl aromatic copolymer itself contains polymerizable double bonds, curing it produces a cured product with a high glass transition temperature. Therefore, this cured product or polyfunctional vinyl aromatic copolymer can be said to be a polymer or its precursor with excellent heat resistance. Furthermore, this polyfunctional vinyl aromatic copolymer is copolymerized with other radically polymerizable monomers to produce a cured product, which also produces a polymer with excellent heat resistance. However, this copolymer is a compound that only possesses radical polymerizability and does not react with epoxy resins.

[0005] Japanese Patent Publication No. 7263069 Japanese Patent Application Laid-Open No. 2015-48458 International Publication No. 2018 / 181842

[0006] The present invention aims to provide a novel polyfunctional vinyl aromatic copolymer, which can improve the reactivity of a vinyl resin, particularly a composition of a vinyl resin with an epoxy resin or the like, and can provide a cured product or molded article with improved uniformity and mechanical properties, and a method for producing the same.

[0007] The present inventors have conducted extensive research to solve the above-mentioned problems and have found that a novel polyfunctional vinyl aromatic copolymer having a specific active ester group can improve the reactivity of a resin composition with an epoxy resin or the like, improve the uniformity of the cured product, and also achieve excellent mechanical properties, thereby completing the present invention.

[0008] That is, the present invention provides a polyfunctional vinyl aromatic copolymer obtained by using 2 mol % or more but less than 95 mol % of a divinylaromatic compound (a), 2 mol % or more but less than 93 mol % of an ester group-containing vinyl aromatic compound (b) represented by the following formula (1), and 5 mol % or more but less than 96 mol % of structural units derived from a monovinyl aromatic compound (c), wherein the copolymer contains structural units represented by the following formula (a1) derived from the divinylaromatic compound (a) and structural units represented by the following formula (b1) derived from the ester group-containing vinyl aromatic compound (b), and is characterized by having a number average molecular weight of 300 to 100,000, a molecular weight distribution (Mw / Mn) expressed as the ratio of the weight average molecular weight to the number average molecular weight of 100 or less, and being soluble in a solvent. In the formula, Ar1 and Ar2 each independently represent an aromatic ring group of either a benzene ring or a naphthalene ring, and these aromatic rings may contain an ester group having 1 to 15 carbon atoms as a substituent in either or both of Ar1 and Ar2, and may have an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an aryl group having 6 to 11 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, an aryloxy group having 6 to 11 carbon atoms, or an aralkyloxy group having 7 to 12 carbon atoms as a substituent. R1 is a direct bond or a divalent group selected from the group consisting of hydrocarbon groups having 1 to 20 carbon atoms, -CO-, -O-, -S-, -SO2-, and -C(CF3)2-. n is 0 to 1. In the formula, R2 represents an aromatic hydrocarbon group having 6 to 30 carbon atoms. In the formula, Ar1, Ar2, R1, and n have the same meanings as in formula (1).

[0009] The present invention provides a method for producing a polyfunctional vinyl aromatic copolymer by polymerizing a divinylaromatic compound (a), an ester group-containing vinyl aromatic compound (b) represented by formula (1), and a monovinyl aromatic compound (c) in the presence of a Lewis acid catalyst, wherein the divinylaromatic compound (a) accounts for 2 mol % to less than 95 mol %, the ester group-containing vinyl aromatic compound (b) represented by formula (1) below accounts for 2 mol % to less than 93 mol %, and the monovinyl aromatic compound (c) accounts for 5 mol % to less than 96 mol %, based on the total of (a), (b), and (c), and the polymerization is carried out at a temperature of -20 to 120°C. In this production method, it is desirable that the Lewis acid catalyst (f) is a metal fluoride or a complex thereof.

[0010] Furthermore, the present invention relates to a curable resin composition containing a polyfunctional vinyl aromatic copolymer and a radical polymerization initiator. It is also a curable resin composition containing a polyfunctional vinyl aromatic copolymer and an epoxy resin. The epoxy resin preferably has two or more epoxy groups in one molecule.

[0011] In the polyfunctional vinyl aromatic copolymer of the present invention, the active ester group contained in the structural unit represented by the above formula (b1) derived from the ester group-containing vinyl aromatic compound (b) represented by formula (1) can undergo crosslinking reaction with the epoxy group, and can also undergo crosslinking reaction with the vinyl group by radical polymerization reaction.Therefore, the polyfunctional vinyl aromatic copolymer of the present invention has improved uniformity in the cured product and improved mechanical properties.

[0012] 1 is an IR chart of the polyfunctional vinyl aromatic copolymer of Example 1. FIG. 2 is a GPC chart of the polyfunctional vinyl aromatic copolymer of Example 1.

[0013] The polyfunctional vinyl aromatic copolymer of the present invention contains a structural unit derived from a divinyl aromatic compound (a), a structure derived from an ester group-containing vinyl aromatic compound (b) represented by formula (1), and a structural unit derived from a monovinyl aromatic compound (c). It has a number-average molecular weight Mn of 300 to 100,000, a molecular weight distribution (Mw / Mn) expressed as the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn of 100 or less, and is soluble in a solvent. The structural unit referred to in this specification includes repeating units present in the main chain of the copolymer and units or terminal groups present at the terminals or side chains.

[0014] The vinyl group constituting the formula (a1) derived from the divinyl aromatic compound (a) acts as a cross-linking component and contributes to the development of heat resistance of the polyfunctional vinyl aromatic copolymer. On the other hand, the structural units derived from the ester group-containing vinyl aromatic compound (b) and the monovinyl aromatic compound (c) represented by formula (1) are generally considered to undergo polymerization via a 1,2-addition reaction of the vinyl group, and therefore do not act as a cross-linking component with the vinyl group, since no vinyl group remains.

[0015] The structural unit (b1) derived from the ester group-containing vinyl aromatic compound (b) represented by formula (1) has an active ester group that acts as a crosslinking component by reacting with an epoxy group, and therefore improves the reactivity in a resin composition with an epoxy resin, contributing to improving the uniformity and mechanical properties of the cured product.

[0016] The structural unit derived from the monovinyl aromatic compound (c) does not act as a crosslinking component with the vinyl group and the epoxy group, but is used to adjust the active ester equivalent and vinyl equivalent to any desired value, and contributes to the development of moldability.

[0017] The structural units derived from the divinylaromatic compound (a) account for 2 mol% or more and less than 95 mol% of the total structural units derived from (a), (b), and (c). The structural units derived from the divinylaromatic compound (a) can take multiple forms, such as structures in which two vinyl groups have reacted singly or doubly. Of these, the repeating units represented by formula (a1) in which only one vinyl group has reacted are preferably contained in an amount of 2 to 80 mol%. This is more preferably 5 to 70 mol%, even more preferably 10 to 60%, and particularly preferably 15 to 50%. By adjusting the content to 2 to 80 mol%, the resulting resin composition has a low dielectric tangent, high toughness, excellent heat resistance, and excellent compatibility with other resins. Furthermore, when formed into a resin composition, the resulting resin composition has excellent moist heat resistance, thermal oxidative degradation resistance, and moldability. If the content is less than 2 mol%, heat resistance tends to decrease, while if it exceeds 80 mol%, interlayer peel strength tends to decrease when formed into a laminate.

[0018] The structural units derived from the ester group-containing vinyl aromatic compound (b) represented by formula (1) are contained in an amount of 2 mol% or more and less than 93 mol% relative to the total of the structural units derived from (a), (b), and (c). It is more preferably 5 to 80 mol%, even more preferably 5 to 70 mol%, and particularly preferably 5 to 60 mol%. If it is less than 2 mol%, the resin composition with the epoxy resin tends to fail to achieve sufficient crosslinking density, resulting in poor improvement in mechanical properties. If it exceeds 93 mol%, the interlayer peel strength of the resulting laminate tends to decrease. Almost all of the structural units derived from the ester group-containing vinyl aromatic compound (b) represented by formula (1) are structural units represented by formula (b1).

[0019] The structural units derived from the monovinyl aromatic compound (c) account for 5 mol % or more but less than 96 mol % of the total structural units derived from (a), (b), and (c), preferably 10% to 80%, more preferably 15% to 70%. If the molar fraction of the structural units derived from (b) and (c) is less than 0.05, molding processability will be insufficient, and if (c) exceeds 98%, the heat resistance of the cured product will be insufficient.

[0020] The active ester equivalent (g / eq) of the polyfunctional vinyl aromatic copolymer is preferably 150 to 6000, more preferably 200 to 5000, even more preferably 250 to 4000, and particularly preferably 250 to 3000. The vinyl equivalent (g / eq) of the polyfunctional vinyl aromatic copolymer is preferably 200 to 5000, more preferably 250 to 4000, even more preferably 300 to 3000, and particularly preferably 350 to 1500.

[0021] The number average molecular weight (Mn: number average molecular weight in terms of standard polystyrene measured using gel permeation chromatography) of the polyfunctional vinyl aromatic copolymer is preferably 300 to 100,000, more preferably 400 to 50,000, and even more preferably 500 to 10,000. If Mn is less than 300, the amount of monofunctional copolymer component contained in the polyfunctional vinyl aromatic copolymer increases, tending to reduce the heat resistance of the cured product. On the other hand, if Mn exceeds 100,000, gel formation becomes more likely and the viscosity increases, tending to reduce moldability. The molecular weight distribution (Mw / Mn), expressed as the ratio of the weight average molecular weight (Mw: weight average molecular weight in terms of standard polystyrene measured using gel permeation chromatography) to Mn, is 100.0 or less, preferably 50.0 or less, more preferably 1.5 to 30.0, and most preferably 2.0 to 20.0. If Mw / Mn exceeds 100.0, the processing characteristics of the polyfunctional vinyl aromatic copolymer tend to deteriorate and gel tends to form.

[0022] The polyfunctional vinyl aromatic copolymer is soluble in a solvent. In particular, it is soluble in organic solvents such as toluene, xylene, tetrahydrofuran, dichloroethane, or chloroform, and preferably soluble in any of these solvents. In order to be a polyfunctional copolymer soluble in a solvent, it is necessary that a portion of the vinyl groups of divinylbenzene remain uncrosslinked and have an appropriate degree of crosslinking. Here, "solvent-soluble" means that the polyfunctional vinyl aromatic copolymer dissolves in 100 g of solvent in an amount of 5 g or more, more preferably 30 g or more, and particularly preferably 50 g or more.

[0023] Next, a method for producing a polyfunctional vinyl aromatic copolymer of the present invention will be described. The method for producing a polyfunctional vinyl aromatic copolymer of the present invention is a method for producing a polyfunctional vinyl aromatic copolymer by polymerizing a vinyl aromatic compound (a), a vinyl aromatic compound (b) represented by formula (1), and a monovinyl aromatic compound (c) in the presence of a Lewis acid catalyst, in which, based on the total of (a), (b), and (c), 2 mol% to less than 95 mol% of the divinyl aromatic compound (a), 2 mol% to less than 93 mol% of the vinyl aromatic compound (b) represented by formula (1), and 5 mol% to less than 96 mol% of the monovinyl aromatic compound (c) are used, and the polymerization is carried out at a temperature of -20 to 120°C.

[0024] The divinylaromatic compound (a) serves to form a branched structure to impart multifunctionality, and also serves as a cross-linking component to impart heat resistance when the resulting multifunctional vinyl aromatic copolymer is thermally cured. Examples of the divinylaromatic compound (a) are not limited as long as they are aromatic compounds having two vinyl groups, but preferred examples include divinylbenzene (including positional isomers or mixtures thereof), divinylnaphthalene (including positional isomers or mixtures thereof), and divinylbiphenyl (including positional isomers or mixtures thereof). These compounds may be used alone or in combination of two or more. From the viewpoint of moldability, divinylbenzene (m-isomer, p-isomer, or a mixture of positional isomers thereof) is more preferred.

[0025] The ester group-containing vinyl aromatic compound (b) represented by formula (1) plays a role in improving mechanical properties by reacting the active ester groups with the epoxy groups to increase the crosslink density when the resulting polyfunctional vinyl aromatic copolymer is thermally cured together with an epoxy resin. The ester group-containing vinyl aromatic compounds (b) represented by formula (1) each independently represent an aromatic ring group of either a benzene ring or a naphthalene ring, and these aromatic rings contain an ester group consisting of Ar-O-C(═O)-R6 or Ar-C(═O)-O-R7 as a substituent on both or either Ar1 and Ar2. R6 represents a hydrocarbon group having 1 to 15 carbon atoms. From the viewpoint of realizing a resin composition that exhibits excellent curing reaction with epoxy resins, the hydrocarbon group has 1 to 15 carbon atoms, preferably an alkyl group having 1 to 6 carbon atoms or an aryl group having 6 to 14 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms or an aryl group having 6 to 10 carbon atoms. R7 represents an aryl group having 6 to 14 carbon atoms, preferably an aryl group having 6 to 10 carbon atoms. Ar1 or Ar2 may have, as a substituent, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an aryl group having 6 to 11 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, an aryloxy group having 6 to 11 carbon atoms, or an aralkyloxy group having 7 to 12 carbon atoms. R1 is a direct bond or a divalent group selected from the group consisting of a hydrocarbon group having 1 to 20 carbon atoms, -CO-, -O-, -S-, -SO2-, and -C(CF3)2-. n is 0 or 1.

[0026] Examples of the vinyl aromatic compound (b) represented by formula (1) include 4-acetoxystyrene, 3-acetoxystyrene, 3,4-diacetoxystyrene, monoacetoxymonovinylnaphthalene, diacetoxymonovinylnaphthalene, 4-vinylphenylbenzoate, 4-acetoxy-4'-vinylbiphenyl, 4-vinylphenyl naphthalenecarboxylate, 3-vinylphenyl naphthalenecarboxylate, 4-vinylphenyl anthracenecarboxylate, 3-vinylphenyl anthracenecarboxylate, phenyl 4-vinylbenzoate, and phenyl 4-vinylnaphthalenecarboxylate.

[0027] In particular, ester group-containing styrene represented by the following formula (1a) is preferred. In formula (1a), R6 represents a hydrocarbon group having 1 to 15 carbon atoms, R4 represents an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an aryl group having 6 to 11 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, an aryloxy group having 6 to 11 carbon atoms, or an aralkyloxy group having 7 to 12 carbon atoms, m represents 1 to 3, and n represents 0 to 3.

[0028] The monovinyl aromatic compound is a monovinyl aromatic compound (c) other than the ester group-containing vinyl aromatic compound represented by formula (1). It serves to impart low dielectric properties and thermal oxidative degradation resistance to the polyfunctional vinyl aromatic copolymer, and also serves to introduce vinyl groups to the terminals of the polyfunctional vinyl aromatic copolymer.

[0029] Examples of the monovinyl aromatic compound (c) include, but are not limited to, aromatic vinyl compounds having one vinyl group, such as styrene, vinylnaphthalene, and vinylbiphenyl; and nuclear alkyl-substituted vinylaromatic compounds such as o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylvinylbenzene, m-ethylvinylbenzene, and p-ethylvinylbenzene. These compounds can be used alone or in combination of two or more. Styrene is preferred because it prevents gelation of the polyfunctional vinylaromatic copolymer, is highly effective in improving solvent solubility and processability, is low cost, and is easily available. Furthermore, from the viewpoint of improving solvent solubility, processability, and dielectric properties, ethylvinylbenzene (including each positional isomer or a mixture thereof), ethylvinylbiphenyl (including each positional isomer or a mixture thereof), and ethylvinylnaphthalene (including each positional isomer or a mixture thereof) are preferred. From the viewpoint of dielectric properties and cost, styrene and ethylvinylbenzene (m-isomer, p-isomer, or a mixture of these positional isomers) are more preferred.

[0030] In addition to the divinyl aromatic compound (a), the ester group-containing vinyl aromatic compound (b) represented by the above formula (1), and the monovinyl aromatic compound (c), other monomer components (d) such as trivinyl aromatic compounds, trivinyl aliphatic compounds, divinyl aliphatic compounds, and monovinyl aliphatic compounds can be used to introduce structural units derived from the other monomer components (d) into the polyfunctional vinyl aromatic copolymer, as long as the effects of the present invention are not impaired.

[0031] Examples of the other monomer component (d) include 1,3,5-trivinylbenzene, 1,3,5-trivinylnaphthalene, 1,2,4-trivinylcyclohexane, ethylene glycol diacrylate, butadiene, 1,4-butanediol divinyl ether, cyclohexanedimethanol divinyl ether, diethylene glycol divinyl ether, and triallyl isocyanurate. These can be used alone or in combination of two or more. The molar fraction of the other monomer component (d) relative to the sum of all monomer components (a), (b), (c), and (d) is preferably less than 30 mol%. In other words, the molar fraction of the repeating units derived from the other monomer component (d) relative to the sum of all structural units derived from all monomer components (a), (b), (c), and (d) constituting the copolymer is preferably less than 30 mol%.

[0032] If necessary, a hydroxyl group-containing vinyl compound (e) such as hydroxyethyl (meth)acrylate or hydroxypropyl (meth)acrylate can be used as another monomer, and the structural unit derived from (e) can be introduced into the polyfunctional vinyl aromatic copolymer.The hydroxyl group-containing vinyl compound (e) is preferably contained in a molar fraction of less than 10 mol%, more preferably less than 5 mol%, based on the total of all monomer components (a), (b), (c), (d) and (e).In other words, the structural unit (e) derived from the hydroxyl group-containing vinyl compound (e) is preferably contained in a molar fraction of less than 10 mol% based on the total of all structural units in the polyfunctional vinyl aromatic copolymer.

[0033] The proportions of the essential monomer components (a), (b), and (c) used are such that, based on the total of (a), (b), and (c), the divinyl aromatic compound (a) is used in an amount of 2 mol% or more and less than 95 mol%, the ester group-containing vinyl aromatic compound (b) represented by formula (1) is used in an amount of 2 mol% or more and less than 93 mol%, and the monovinyl aromatic compound (c) is used in an amount of 5 mol% or more and less than 96 mol%, in total, and these monomer components (a), (b), and (c) are polymerized at a temperature of -20 to 120°C.

[0034] The amount of the divinylaromatic compound (a) is preferably 5 to 80 mol%, more preferably 7 to 70 mol%, and even more preferably 10 to 60 mol%. The amount of the ester group-containing vinyl aromatic compound (b) represented by formula (1) is preferably 2 to 80 mol%, more preferably 5 to 70 mol%, and even more preferably 5 to 60 mol%. The total amount of the monovinyl aromatic compound (c) is preferably 5 to 90 mol%, more preferably 10 to 80 mol%, and particularly preferably 15 to 70 mol%.

[0035] The Lewis acid catalyst (f) is a compound consisting of a metal ion (acid) and a ligand (base) and can accept an electron pair, and can be used without any particular limitation. Among these, from the viewpoint of thermal decomposition resistance of the resulting polyfunctional vinyl aromatic copolymer, metal fluorides or complexes thereof are preferred, and divalent to hexavalent metal fluorides or complexes thereof, such as B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Ti, W, Zn, Fe, and V, are particularly preferred. These catalysts can be used alone or in combination of two or more. From the viewpoint of controlling the molecular weight and molecular weight distribution of the resulting polyfunctional vinyl aromatic copolymer and polymerization activity, boron trifluoride ether complexes are most preferably used. Examples of ethers in the ether complex include diethyl ether and dimethyl ether. The Lewis acid catalyst (f) is preferably used in an amount of 0.001 to 100 moles, more preferably 0.01 to 50 moles, per 100 moles of all monomer components. It is most preferably 0.1 to 20 moles. If the amount exceeds 100 moles, the polymerization rate becomes too high, making it difficult to control the molecular weight distribution, whereas if the amount is less than 0.001 moles, the polymerization rate becomes too low, resulting in increased costs and making the process unsuitable for industrial implementation.

[0036] In the method for producing a polyfunctional vinyl aromatic copolymer of the present invention, one or more Lewis base compounds may be used as the co-catalyst (g). Specific examples of Lewis base compounds include ester compounds such as propyl acetate, thioester compounds such as methyl mercaptopropionic acid, ketone compounds such as methyl ethyl ketone, amine compounds such as methylamine, ether compounds such as diethyl ether, thioether compounds such as diethyl sulfide, and phosphine compounds such as tripropylphosphine. Among these, one or more compounds selected from the group consisting of ester compounds, ketone compounds, and ether compounds are preferred because they act synergistically with the Lewis acid catalyst (f) to easily control the polymerization rate and the molecular weight distribution of the polymer. These Lewis base compounds can be used alone or in combination.

[0037] During the polymerization reaction, the Lewis base compound coordinates with the Lewis acid catalyst (f), which is a counter anion, thereby controlling the interaction between the carbocation, which is an active species, and the counter anion, thereby adjusting the relative reaction frequency between the monomers (a), (b), and (c), which also function as a chain transfer agent. Usually, the addition of a Lewis base compound strengthens the interaction between the carbocation, which is an active species, and the counter anion, thereby suppressing excessive insertion reactions of the monomers (a), (b), and (c) and facilitating the chain transfer reaction after the insertion reaction of the monomers (a), (b), and (c), thereby facilitating control of the molecular weight.

[0038] In addition to Lewis base compounds, compounds containing a hydroxyl group can also be used as co-catalysts. It is believed that the hydroxyl group-containing co-catalyst reacts with the Lewis acid catalyst (f) during the polymerization reaction to generate a carbocation, which is an active species, and reacts with the vinyl groups of the monomers (a), (b), and (c), thereby causing the polymerization reaction to proceed. The hydroxyl group-containing co-catalyst may be used alone or in combination with a Lewis base compound. Specific examples of the hydroxyl group-containing co-catalyst include alcohol compounds represented by the following formula (2), such as aromatic compounds such as 1-phenylethanol, 2-phenyl-2-propanol, and 2-propanol, and hydrocarbon compounds such as tert-butyl alcohol. In the formula, R3 and R4 each independently represent an alkyl group having 1 to 6 carbon atoms or an aromatic hydrocarbon group having 6 to 30 carbon atoms. R5 represents hydrogen, an alkyl group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 6 to 30 carbon atoms. Among these, one or more compounds selected from the group consisting of aromatic compounds are preferably used because they act synergistically with the Lewis acid catalyst (f) and can easily control the polymerization rate and the molecular weight distribution of the polymer. These hydroxyl group-containing co-catalysts can be used alone or in combination.

[0039] When a Lewis base compound is used, the co-catalyst (g) is preferably 0.1 to 1000 mol, more preferably 1.0 to 500 mol, and particularly preferably 10 to 200 mol, relative to 100 mol of all monomer components. When a hydroxyl group-containing co-catalyst is used, the co-catalyst is preferably 0.1 to 1000 mol, more preferably 0.5 to 500 mol, and particularly preferably 1 to 200 mol, relative to 100 mol of all monomer components. Within the above range, the polymerization rate is appropriately maintained and the selectivity of the reaction between monomers is improved, resulting in excellent productivity and suppression of excessive increase or decrease in molecular weight, resulting in a polyfunctional vinyl aromatic copolymer with excellent moldability.

[0040] In the polymerization reaction, for example, a polymerization raw material containing a mixture of monomers is subjected to cationic copolymerization at a temperature of −20 to 120° C. to obtain a copolymer.

[0041] A solvent can be added if desired. The solvent is a compound that does not essentially inhibit cationic polymerization and dissolves the Lewis acid catalyst (f), cocatalyst (g), monomer components, and the resulting polyfunctional vinyl aromatic copolymer to form a homogeneous solution. Organic solvents with a dielectric constant of 2 to 15 are preferred, and they can be used alone or in combination of two or more. A solvent with a dielectric constant of less than 2 is undesirable because it broadens the molecular weight distribution, while a solvent with a dielectric constant exceeding 15 reduces the polymerization rate. From the viewpoint of the balance between polymerization activity and solubility, toluene, xylene, n-hexane, cyclohexane, methylcyclohexane, or ethylcyclohexane are particularly preferred as organic solvents. The amount of solvent used is determined, taking into account the viscosity of the resulting polymerization solution and ease of heat removal, so that the concentration of the copolymer in the polymerization solution at the end of polymerization is 1 to 90 wt %, preferably 10 to 80 wt %, and particularly preferably 20 to 70 wt %. If this concentration is less than 1 wt %, the polymerization efficiency will be low, resulting in increased costs, while if it exceeds 90 wt %, the molecular weight and molecular weight distribution of the resulting polyfunctional vinyl aromatic copolymer will increase, resulting in reduced moldability.

[0042] When producing a polyfunctional vinyl aromatic copolymer, it is necessary to polymerize the monomers (a), (b), and (c) at a temperature of -20 to 120°C. The temperature is preferably 0 to 110°C. Particularly preferably, it is 30 to 90°C. If the polymerization temperature exceeds 120°C, the selectivity of the reaction decreases, resulting in problems such as an increase in molecular weight distribution and the generation of gel. If the polymerization is carried out at a temperature below -20°C, the catalytic activity decreases significantly, making it necessary to add a large amount of catalyst. There are no particular limitations on the method for recovering the polyfunctional vinyl aromatic copolymer after the polymerization reaction has stopped, and commonly used methods such as heat concentration, steam stripping, and precipitation in a poor solvent may be used.

[0043] Next, the curable resin composition of the present invention will be described. The curable resin composition of the present invention contains the polyfunctional vinyl aromatic copolymer of the present invention (including the polyfunctional vinyl aromatic copolymer obtained by the production method of the present invention) and a radical polymerization initiator (h) (also referred to as a radical polymerization catalyst). The radical polymerization initiator can promote the crosslinking reaction of unsaturated groups and can efficiently adjust the curing time and curing temperature.

[0044] Known substances can be used as the radical polymerization initiator (h). Representative examples include peroxides such as benzoyl peroxide, cumene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, di-t-butyl peroxide, t-butylcumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, dicumyl peroxide, di-t-butylperoxyisophthalate, t-butylperoxybenzoate, 2,2-bis(t-butylperoxy)butane, 2,2-bis(t-butylperoxy)octane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, di(trimethylsilyl)peroxide, and trimethylsilyltriphenylsilyl peroxide, but are not limited to these. Although not a peroxide, 2,3-dimethyl-2,3-diphenylbutane can also be used as the radical polymerization initiator (h). However, the radical polymerization initiator (h) is not limited to these examples. Among these, α,α'-bis(t-butylperoxy-m-isopropyl)benzene is preferably used. α,α'-bis(t-butylperoxy-m-isopropyl)benzene has a relatively high reaction initiation temperature. Therefore, it is possible to suppress the acceleration of the curing reaction when curing is not necessary, such as during prepreg drying, and to suppress deterioration of the shelf life of the curable resin composition of the present invention. Furthermore, α,α'-bis(t-butylperoxy-m-isopropyl)benzene has low volatility and does not volatilize during prepreg drying or storage, thereby providing good stability. The radical polymerization initiator (h) may be used alone or in combination of two or more types. The amount of radical polymerization initiator (h) is preferably in the range of 0.01 to 10 parts by weight, more preferably 0.1 to 8 parts by weight, per 100 parts by weight of the polyfunctional vinyl aromatic copolymer. Within this range, the curing reaction proceeds smoothly without being inhibited.

[0045] In addition, the curable resin composition of the present invention is also a resin composition containing the polyfunctional vinyl aromatic copolymer of the present invention and an epoxy resin.

[0046] The epoxy resin preferably has two or more epoxy groups in the molecule, and examples thereof include bisphenol A type epoxy resins, bisphenol F type epoxy resins, bisphenol S type epoxy resins, bisphenol AF type epoxy resins, bisphenol Z type epoxy resins, bisphenol fluorene type epoxy resins, diphenyl sulfide type epoxy resins, diphenyl ether type epoxy resins, naphthalene type epoxy resins, hydroquinone type epoxy resins, resorcinol type epoxy resins, phenol novolac type epoxy resins, cresol novolac type epoxy resins, and alkyl novolac. Examples of epoxy resins include various epoxy resins such as styrene-type epoxy resins, styrenated phenol novolac-type epoxy resins, bisphenol novolac-type epoxy resins, naphthol novolac-type epoxy resins, phenol aralkyl-type epoxy resins, β-naphthol aralkyl-type epoxy resins, naphthalenediol aralkyl-type epoxy resins, α-naphthol aralkyl-type epoxy resins, biphenyl aralkylphenol-type epoxy resins, biphenyl-type epoxy resins, triphenylmethane-type epoxy resins, dicyclopentadiene-type epoxy resins, alkylene glycol-type epoxy resins, and aliphatic cyclic epoxy resins.

[0047] The resin composition containing the polyfunctional vinyl aromatic copolymer of the present invention and an epoxy resin may further contain a radical polymerization initiator for the purpose of promoting the crosslinking reaction of the unsaturated groups. Examples of the radical polymerization initiator include the substances mentioned above.

[0048] The resin composition of the present invention containing the polyfunctional vinyl aromatic copolymer and an epoxy resin may further contain an organic base. By containing the organic base, the curing reaction with the epoxy group can be accelerated, and the curing time and curing temperature can be efficiently adjusted. As the organic base, it is preferable to use one or more selected from amine-based curing accelerators, organic phosphorus-based curing accelerators, and imidazole-based curing accelerators, which are conventionally known as curing accelerators for epoxy resins.

[0049] When the resin composition containing the polyfunctional vinyl aromatic copolymer of the present invention and an epoxy resin contains a radical polymerization initiator, the amount of the radical polymerization initiator is preferably in the range of 0.01 to 10 parts by weight, more preferably 0.05 to 8 parts by weight, per 100 parts by weight of the resin component in the resin composition. When the resin composition containing the polyfunctional vinyl aromatic copolymer of the present invention and an epoxy resin contains an organic base, the amount of the organic base is preferably in the range of 0.01 to 10 parts by weight, more preferably 0.1 to 8 parts by weight, per 100 parts by weight of the resin component in the resin composition.

[0050] In addition to the polyfunctional vinyl aromatic copolymer of the present invention, a resin composition containing an epoxy resin and the polyfunctional vinyl aromatic copolymer of the present invention can also contain a curing agent for the epoxy resin. The epoxy resin curing agent is not particularly limited, and any commonly known epoxy resin curing agent can be used. From the viewpoint of improving heat resistance, preferred curing agents include phenol-based curing agents, amide-based curing agents, imidazoles, and active ester-based curing agents. These curing agents may be used alone or in combination of two or more.

[0051] Active ester curing agents are preferred from the viewpoint of enhancing low dielectric constant and low dielectric dissipation factor. For example, compounds having two or more highly reactive ester groups per molecule, such as phenol esters, thiophenol esters, N-hydroxyamine esters, and esters of heterocyclic hydroxy compounds, are preferred. Among these, phenol esters obtained by reacting a carboxylic acid compound with an aromatic compound having a phenolic hydroxyl group are more preferred. Specific examples of carboxylic acid compounds include benzoic acid, acetic acid, succinic acid, maleic acid, itaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and pyromellitic acid. Examples of aromatic compounds having a phenolic hydroxyl group include catechol, 1,5-dihydroxynaphthalene, 1,6-dihydroxynaphthalene, 2,6-dihydroxynaphthalene, dihydroxybenzophenone, trihydroxybenzophenone, tetrahydroxybenzophenone, phloroglucin, benzenetriol, dicyclopentadienyl diphenol, and phenol novolak.

[0052] The curable resin composition may further contain a known curable reactive resin or thermoplastic resin. Examples of the curable reactive resin include thermosetting resins and resins or compounds that copolymerize with a polyfunctional vinyl aromatic copolymer to produce a cured resin. Examples include vinyl ester resins, polyvinylbenzyl resins, unsaturated polyester resins, curable vinyl resins, curable polyphenylene ether resins, maleimide resins, polycyanate resins, phenolic resins, and one or more vinyl compounds having one or more polymerizable unsaturated hydrocarbon groups in the molecule. Examples of thermoplastic resins include polystyrene, polyphenylene ether resin, polyetherimide resin, polyethersulfone resin, PPS resin, polycyclopentadiene resin, polycycloolefin resin, and phenoxy resin; known thermoplastic elastomers such as styrene-ethylene-propylene copolymer, styrene-ethylene-butylene copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, hydrogenated styrene-butadiene copolymer, and hydrogenated styrene-isoprene copolymer; and rubbers such as polybutadiene and polyisoprene.

[0053] From the viewpoints of the dielectric properties, heat resistance, adhesion, and compatibility with polyfunctional vinyl aromatic copolymers as a curable resin composition, preferred curable reactive resins include polyvinylbenzyl resins, curable vinyl resins, curable polyphenylene ether resins, and one or more vinyl compounds having one or more polymerizable unsaturated hydrocarbon groups in the molecule. Examples of thermoplastic resins include polystyrene, polyphenylene ether resins, styrene-ethylene-propylene copolymers, styrene-ethylene-butylene copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, hydrogenated styrene-butadiene copolymers, and hydrogenated styrene-isoprene copolymers. More preferred curable reactive resins include polyvinylbenzyl resins, curable polyphenylene ether resins, epoxy resins, and one or more vinyl compounds having one or more polymerizable unsaturated hydrocarbon groups in the molecule. Examples of thermoplastic resins (j) include polyphenylene ether resins and hydrogenated styrene-butadiene copolymers.

[0054] When the curable reactive resin is a curable polyphenylene ether resin, it is more preferably a modified polyphenylene ether compound having a curable terminal functional group. Even more preferably, it is a modified polyphenylene ether compound containing an unsaturated hydrocarbon group. It is a modified polyphenylene ether compound terminally modified with a substituent having a carbon-carbon unsaturated double bond. Most preferably, it is a modified polyphenylene ether compound having a curable terminal functional group, in which the substituent having a carbon-carbon unsaturated double bond is a substituent selected from the group consisting of a vinylbenzyl group, a vinyl group, an acrylate group, and a methacrylate group. The average number of unsaturated hydrocarbon groups (number of terminal functional groups) per molecule of the modified polyphenylene ether compound containing terminal unsaturated hydrocarbon groups is not particularly limited. From the viewpoint of the balance between the heat resistance of the cured product and the storage stability and fluidity of the curable resin composition, it is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1.5 to 3.

[0055] The Mn of the curable polyphenylene ether resin is not particularly limited, but is preferably 500 to 7,000, more preferably 800 to 5,000, and most preferably 1,000 to 3,000. Here, Mn may be measured by a common molecular weight measurement method, specifically, a value measured using gel permeation chromatography (GPC), etc. When the Mn of the curable polyphenylene ether resin is within this range, the toughness and moldability of the cured product of the obtained curable resin composition are improved. This is because when the number-average molecular weight of the curable polyphenylene ether resin is within this range, the relatively low molecular weight improves flowability while maintaining toughness. When a typical polyphenylene ether having such a low molecular weight is used, the heat resistance and toughness of the cured product tend to decrease. However, since the curable polyphenylene ether resin has a polymerizable unsaturated double bond at its terminal, by copolymerizing or curing it with a vinyl curable resin such as the copolymer of the present invention, crosslinking between the two proceeds favorably, and a cured product having sufficiently high heat resistance and toughness can be obtained. Therefore, the cured product of the obtained curable resin composition has excellent heat resistance and toughness.

[0056] When the curable reactive resin is one or more vinyl compounds (id) having one or more polymerizable unsaturated hydrocarbon groups in the molecule, there are no particular limitations. That is, (id) may be any compound that can form crosslinks and harden by reacting with the polyfunctional vinyl aromatic copolymer of the present invention. The polymerizable unsaturated hydrocarbon group is preferably a carbon-carbon unsaturated double bond, and more preferably a compound having two or more carbon-carbon unsaturated double bonds in the molecule.

[0057] The weight-average molecular weight (Mw) of the vinyl compounds used as the curable reactive resin is preferably 100 to 5,000, more preferably 100 to 4,000, and even more preferably 100 to 3,000. If the Mw is less than 100, (id) may be more likely to volatilize from the components of the curable resin composition. Furthermore, if the Mw exceeds 5,000, the viscosity of the varnish of the curable resin composition and the melt viscosity during heat molding may become too high. Therefore, when the Mw of (id) is within this range, a curable resin composition with excellent heat resistance can be obtained. This is thought to be due to the favorable formation of crosslinks by the reaction between the polyfunctional vinyl aromatic copolymer and (id). Here, Mw may be measured using a common molecular weight measurement method, specifically, a value measured using gel permeation chromatography (GPC) may be used.

[0058] The average number of carbon-carbon unsaturated double bonds (number of terminal double bonds) per molecule of vinyl compounds as curable reactive resins varies depending on the Mw, but is preferably 1 to 20, and more preferably 2 to 18. If the number of terminal double bonds is too small, it tends to be difficult to obtain a cured product with sufficient heat resistance. On the other hand, if the number of terminal double bonds is too large, the reactivity becomes too high, which may cause problems such as a decrease in the storage stability of the curable resin composition or a decrease in the flowability of the curable resin composition.

[0059] Examples of vinyl compounds (id) as curable reactive resins include trialkenyl isocyanurate compounds such as triallyl isocyanurate (TAIC), polyfunctional methacrylate compounds having two or more methacrylic groups in the molecule, polyfunctional acrylate compounds having two or more acrylic groups in the molecule, vinyl compounds having two or more vinyl groups in the molecule (polyfunctional vinyl compounds) such as polybutadiene, and vinylbenzyl compounds such as styrene and divinylbenzene having vinylbenzyl groups in the molecule. Among these, compounds having two or more carbon-carbon double bonds in the molecule are preferred. Specific examples include trialkenyl isocyanurate compounds, polyfunctional acrylate compounds, polyfunctional methacrylate compounds, polyfunctional vinyl compounds, and divinylbenzene compounds. The use of these compounds is believed to more favorably form crosslinks through the curing reaction, thereby further enhancing the heat resistance of the cured product of the curable resin composition. These compounds may be used alone or in combination of two or more. A compound having one carbon-carbon unsaturated double bond in the molecule may also be used in combination. Examples of compounds having one carbon-carbon unsaturated double bond in the molecule include compounds having one vinyl group in the molecule (monovinyl compounds).

[0060] The content of the polyfunctional vinyl aromatic copolymer is preferably 30 to 90 parts by mass, more preferably 50 to 90 parts by mass, per 100 parts by mass of the polyfunctional vinyl aromatic copolymer and the vinyl compounds (id) as the curable reactive resin. The content of the vinyl compounds (id) as the curable reactive resin is preferably 10 to 70 parts by mass, more preferably 10 to 50 parts by mass, per 100 parts by mass of the polyfunctional vinyl aromatic copolymer and (id). That is, the content ratio of the polyfunctional vinyl aromatic copolymer to the vinyl compounds (id) as the curable reactive resin is preferably 90:10 to 30:70, more preferably 90:10 to 50:50, by mass. If the content satisfies the above ratio, the cured product will have excellent heat resistance and flame retardancy. This is thought to be because the curing reaction between the polyfunctional vinyl aromatic copolymer and the vinyl compounds (id) as the curable reactive resin proceeds smoothly.

[0061] The curable resin composition of the present invention can be blended with a known flame retardant (k). The flame retardant (k) can further enhance the flame retardancy of the cured product of the curable resin composition. The flame retardant (k) is not particularly limited. Specifically, in fields where halogen-based flame retardants such as bromine-based flame retardants are used, for example, ethylene dipentabromobenzene, ethylene bistetrabromoimide, decabromodiphenyl oxide, and tetradecabromodiphenoxybenzene, which have melting points of 300°C or higher, are preferred. The use of a halogen-based flame retardant is thought to suppress halogen elimination at high temperatures and prevent a decrease in heat resistance. In fields where halogen-free materials are required, phosphate ester-based flame retardants, phosphazene-based flame retardants, and phosphinate-based flame retardants can be used. A specific example of a phosphate ester-based flame retardant is condensed phosphate ester of dixylenyl phosphate. A specific example of a phosphazene-based flame retardant is phenoxyphosphazene. Specific examples of phosphinate-based flame retardants include metal phosphinates of aluminum dialkylphosphinates. Each of the exemplified flame retardants may be used alone or in combination of two or more.

[0062] The curable resin composition of the present invention can be blended with a known filler (l). Examples of filler (l) include, but are not limited to, those added to enhance the heat resistance and flame retardancy of the cured product of the curable resin composition. By incorporating filler (l), the heat resistance, flame retardancy, and the like can be further enhanced. Specific examples include silica such as spherical silica, metal oxides such as alumina, titanium oxide, and mica, metal hydroxides such as aluminum hydroxide and magnesium hydroxide, talc, aluminum borate, barium sulfate, and calcium carbonate. Among these, silica, mica, and talc are preferred, and spherical silica is more preferred. These may be used alone or in combination of two or more. They may be used as is, or may be surface-treated with a silane coupling agent such as an epoxy silane or amino silane. As the silane coupling agent, vinylsilane, methacryloxysilane, acryloxysilane, and styrylsilane types are preferred from the viewpoint of reactivity with the radical polymerization initiator (h). This increases the adhesive strength with the metal foil and the interlayer adhesive strength between resins. Instead of pre-surface treating the filler (l), the silane coupling agent may be added by integral blending. The content of the filler (l) is preferably 10 to 200 parts by mass, and more preferably 30 to 150 parts by mass, per 100 parts by mass of the total of the organic components such as monomers and the flame retardant.

[0063] The curable resin composition of the present invention may further contain additives other than the flame retardant and the filler, such as antifoaming agents such as silicone antifoaming agents and acrylate antifoaming agents, heat stabilizers, antistatic agents, ultraviolet absorbers, dyes and pigments, lubricants, and dispersants such as wetting and dispersing agents.

[0064] The curable resin composition of the present invention can be prepared into a varnish to be used for impregnating a substrate (fibrous substrate) for forming a prepreg when producing a prepreg, or for use as a circuit board material for forming a circuit board. The resin varnish contains a polyfunctional vinyl aromatic copolymer, a radical polymerization initiator (h), and a solvent. If desired, it may contain a curable reactive resin, a thermoplastic resin, a flame retardant, a filler, and other additives. This resin varnish is suitable for circuit boards and can be used as a varnish for circuit board materials. Specific applications of the circuit board material include printed wiring boards, printed circuit boards, flexible printed wiring boards, and build-up wiring boards.

[0065] The resin varnish is prepared, for example, as follows. First, components soluble in organic solvents, such as the polyfunctional vinyl aromatic copolymer and the curable reactive resin (i), are added to the organic solvent and dissolved. Heating may be performed, if necessary. Then, if necessary, components insoluble in organic solvents, such as an inorganic filler, are added and dispersed using a ball mill, bead mill, planetary mixer, roll mill, or the like, to prepare a varnish-like curable resin composition. The organic solvent used here is not particularly limited as long as it dissolves the polyfunctional vinyl aromatic copolymer and (i) and does not inhibit the curing reaction. Examples of suitable organic solvents include ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as ethyl acetate, propyl acetate, and butyl acetate; polar solvents such as dimethylacetamide and dimethylformamide; and aromatic hydrocarbon solvents such as toluene and xylene. These solvents may be used alone or in combination. From the viewpoint of dielectric properties, aromatic hydrocarbons such as benzene, toluene, and xylene are preferred. The amount of organic solvent used when preparing a resin varnish is preferably 5 to 900% by weight, more preferably 10 to 700% by weight, and particularly preferably 20 to 500% by weight, relative to 100% by weight of the curable resin composition of the present invention. When the curable resin composition of the present invention is an organic solvent solution such as a resin varnish, the amount of the organic solvent is not included in the calculation of the composition.

[0066] The cured product obtained by curing the curable resin composition of the present invention can be used as a molded product, laminate, cast product, adhesive, coating, or film. For example, a cured product of a semiconductor encapsulating material is a cast product or molded product. A cured product for such applications can be obtained by casting the curable resin composition or molding it using a transfer molding machine, injection molding machine, or the like, and then heating it at 80 to 230°C for 0.5 to 10 hours. A cured product of a circuit board varnish is a laminate. This cured product can be obtained by impregnating a substrate such as glass fiber, carbon fiber, polyester fiber, polyamide fiber, alumina fiber, or paper with the varnish, heating and drying the substrate to obtain a prepreg, which can then be laminated alone or with a metal foil such as copper foil and hot-press molded.

[0067] By blending an inorganic high dielectric powder such as barium titanate or an inorganic magnetic material such as ferrite into a curable resin composition or resin varnish, the composition becomes an excellent material for electronic components, particularly for high-frequency electronic components.

[0068] The curable resin composition of the present invention can be used by laminating it with a metal foil (which includes a metal plate; the same applies hereinafter) in the same manner as the cured composite material described below.

[0069] Next, a curable composite material and its cured product made from the curable resin composition of the present invention will be described. A substrate is added to the curable composite material made from the curable resin composition of the present invention to enhance mechanical strength and dimensional stability. Known materials can be used as such substrates, including various glass fabrics such as roving cloth, cloth, chopped mat, and surfacing mat; asbestos cloth, metal fiber fabric, and other synthetic or natural inorganic fiber fabrics; woven or nonwoven fabrics obtained from liquid crystal fibers such as wholly aromatic polyamide fibers, wholly aromatic polyester fibers, and polybenzozal fibers; woven or nonwoven fabrics obtained from synthetic fibers such as polyvinyl alcohol fibers, polyester fibers, and acrylic fibers; natural fiber fabrics such as cotton cloth, linen cloth, and felt; carbon fiber cloth; and natural cellulose-based fabrics such as kraft paper, cotton paper, and paper-glass mixed fiber paper. These fabrics and papers can be used alone or in combination of two or more. The proportion of the substrate in the curable composite material is preferably 5 to 90 wt %, more preferably 10 to 80 wt %, and even more preferably 20 to 70 wt %. If the substrate content is less than 5 wt%, the dimensional stability and strength of the composite material after curing are insufficient, and if the substrate content is more than 90 wt%, the dielectric properties of the composite material are poor, which is not preferable. If necessary, a coupling agent can be used in the curable composite material of the present invention to improve adhesion at the interface between the resin and the substrate. Common coupling agents such as silane coupling agents, titanate coupling agents, aluminum-based coupling agents, and zircoaluminate coupling agents can be used.

[0070] A method for producing the curable composite material of the present invention includes, for example, uniformly dissolving or dispersing the curable resin composition of the present invention and, if necessary, other components in the aforementioned aromatic or ketone solvent or a mixed solvent thereof, impregnating the substrate with the solution, and then drying. Impregnation is performed by immersion (dipping), coating, or the like. Impregnation can be repeated multiple times as needed, and in this case, impregnation can be repeated using multiple solutions with different compositions and concentrations, allowing the final desired resin composition and resin amount to be adjusted.

[0071] A cured composite material can be obtained by curing the curable composite material of the present invention by a method such as heating. The production method is not particularly limited; for example, multiple sheets of the curable composite material can be stacked, and the layers can be bonded together under heat and pressure, while simultaneously thermally curing, to obtain a cured composite material of the desired thickness. It is also possible to combine a cured composite material that has already been bonded and cured with a curable composite material to obtain a cured composite material with a new layer structure. Lamination molding and curing are usually performed simultaneously using a heat press or the like, but the two may also be performed independently. That is, an uncured or semi-cured composite material previously obtained by lamination molding can be cured by heat treatment or another method. The curing, or molding and curing, of the curable resin composition or curable composite material of the present invention is preferably performed at a temperature of 80 to 300°C and a pressure of 0.1 to 1,000 kg / cm. ２ , the time is in the range of 1 minute to 10 hours, more preferably the temperature is 150 to 250°C and the pressure is 1 to 500 kg / cm ２ The time can be in the range of 1 minute to 5 hours.

[0072] The laminate of the present invention is composed of a layer of the cured composite material of the present invention and a layer of metal foil. Examples of metal foil include copper foil and aluminum foil. The thickness is not particularly limited, but is preferably in the range of 3 to 200 μm, more preferably 3 to 105 μm. A method for producing the laminate of the present invention includes, for example, laminating the curable composite material obtained from the curable resin composition of the present invention and a substrate with metal foil in a layer configuration appropriate for the purpose, and then bonding the layers together under heat and pressure while simultaneously thermally curing the layers. In a laminate of the curable resin composition of the present invention, the cured composite material and metal foil are laminated in any layer configuration. The metal foil can be used as either a surface layer or an intermediate layer. It is also possible to repeat the lamination and curing process multiple times to create a multilayer structure. An adhesive can also be used to bond the metal foil. Examples of adhesives include, but are not limited to, epoxy, acrylic, phenolic, and cyanoacrylate types. Lamination molding and curing can be carried out under the same conditions as those for producing the cured composite material of the present invention.

[0073] The curable resin composition of the present invention can be molded into a film, which is one form of the curable resin composition of the present invention. The thickness is not particularly limited, but is preferably in the range of 3 to 200 μm, more preferably 5 to 105 μm. The method for producing the film of the present invention is not particularly limited, and examples include a method in which the curable resin composition is uniformly dissolved or dispersed in an aromatic solvent, a ketone solvent, or a mixed solvent thereof, and then coated onto a resin film such as a PET film and then dried. The coating can be repeated multiple times as needed, and in this case, multiple solutions with different compositions and concentrations can be used to repeatedly coat the film, thereby adjusting the final resin composition and resin amount to the desired value.

[0074] The resin-coated metal foil of the present invention is composed of the curable resin composition of the present invention and a metal foil. Examples of metal foils include copper foil and aluminum foil. The thickness is not particularly limited, but is preferably in the range of 3 to 200 μm, more preferably 5 to 105 μm. The method for producing the resin-coated metal foil of the present invention is not particularly limited, and examples include a method in which the curable resin composition is uniformly dissolved or dispersed in an aromatic solvent, ketone solvent, or a mixed solvent thereof, and then coated onto the metal foil and dried. The coating can be repeated multiple times as needed, and in this case, it is possible to repeatedly coat multiple solutions with different compositions and concentrations to adjust the final resin composition and resin amount to the desired level.

[0075] The polyfunctional vinyl aromatic copolymer of the present invention can be processed into molding materials, sheets, or films, and can be used as low-dielectric materials, insulating materials, heat-resistant materials, structural materials, etc., which satisfy properties such as low dielectric constant, low water absorption, and high heat resistance in fields such as the electrical industry, the aerospace and aircraft industry, and the automotive industry. In particular, it can be used as single-sided, double-sided, and multilayer printed circuit boards, flexible printed circuit boards, build-up boards, etc. It can also be used in semiconductor-related materials or optical materials, as well as paints, photosensitive materials, adhesives, sewage treatment agents, heavy metal scavengers, ion exchange resins, antistatic agents, antioxidants, antifogging agents, rust inhibitors, stain-resistant agents, fungicides, insect repellents, medical materials, flocculants, surfactants, lubricants, binders for solid fuels, conductive treatment agents, resin modifiers, asphalt modifier plasticizers, sintering binders, etc.

[0076] The curable resin composition of the present invention provides a cured product that has high dielectric properties (low dielectric constant and low dielectric dissipation factor) even after severe thermal history, and has high adhesion reliability even under harsh environments. It also has excellent resin fluidity, low linear expansion, and excellent wiring embedding flatness. Therefore, in fields such as the electrical and electronics industries and the aerospace and aircraft industries, it can be used as a dielectric material, insulating material, heat-resistant material, structural material, etc., to provide cured molded products that are free from molding defects such as warping, in response to the strong demand for smaller and thinner products in recent years. Furthermore, due to its excellent wiring embedding flatness and excellent adhesion to different materials, it is possible to realize a curable resin composition, cured product, or material containing the same that has excellent reliability.

[0077] The present invention will now be described with reference to examples, but is not limited to these examples. All parts in the examples are by weight. Physical properties in the examples were measured by the following methods.

[0078] 1) Weight-average molecular weight: Determined by GPC measurement. Specifically, a HLC8320 GPC (manufactured by Tosoh Corporation) equipped with columns (TSKgel Super H-H, Super H2000, Super HM-H, Super HM-H, all manufactured by Tosoh Corporation) in series was used, and the column temperature was set to 40°C. Tetrahydrofuran (THF) was used as the eluent at a flow rate of 1 mL / min, and a differential refractive index detector was used as the detector. 20 μL of the measurement sample, prepared by dissolving 0.1 g of solid content in 10 mL of THF and filtering through a 0.45 μm microfilter, was used. Mw was calculated from a calibration curve obtained from standard polyethylene oxides (manufactured by Tosoh Corporation, SE-2, SE-5, SE-8, SE-15, SE-30, SE-70, SE-150). 2) Polymer Structure: The presence or absence of the structure of formula (b1) was determined by C-NMR and H-NMR analysis using a JEOL JNM-LA600 nuclear magnetic resonance spectrometer. Chloroform-d1 was used as the solvent, and the resonance line of tetramethylsilane was used as the internal standard. 3) Active Ester Equivalent: This was measured in accordance with JIS K0070. Specifically, the sample was dissolved in THF and reacted with a 0.5 mol / L ethanolic solution of potassium hydroxide. The ester value was then determined by neutralization titration with 0.5 mol / L hydrochloric acid using phenolphthalein as an indicator. 4) Vinyl Equivalent: This was measured in accordance with JIS K0070. Specifically, the sample was reacted with Wiess's solution (iodine monochloride solution) and left in the dark. The excess iodine chloride was then reduced to iodine, and the iodine content was titrated with sodium thiosulfate to calculate the iodine value. The iodine value was converted to vinyl equivalent. 5) Tan δ in dynamic viscoelasticity measurement A cured resin molded to a thickness of 2 mm was processed into a test piece (length 60 mm x width 10 mm), and the dynamic viscoelasticity was measured using a dynamic viscoelasticity measuring device (Hitachi High-Tech Corporation DMA7100) at a frequency of 10 Hz, a temperature rise rate of 5°C / min, and in the range of 20°C to 250°C, and the resulting peak temperature of Tan δ was read. When multiple peaks were observed, each temperature was read.6) Flexural Properties of Cured Product Cured resin molded to a thickness of 2 mm was processed into test pieces (length 100 mm x width 10 mm), and the flexural properties of the resin test pieces were measured using a universal testing machine (AGS-X manufactured by Shimadzu Corporation) equipped with a 1000 N load cell. The flexural modulus of the test pieces and the stress at the breaking point were measured using a three-point bending jig under an environment of 23°C temperature and 50% RH humidity. 7) Haze Measurement of Cured Product Cured resin molded to a thickness of 0.7 mm was processed into a 50 mm x 50 mm piece, and the haze value was measured using a spectrophotometer (CM-5 manufactured by Konica Minolta).

[0079] Example 1 Divinylbenzene 0.60 moles (78 g), 0.35 moles (46 g) of ethylvinylbenzene, 1.75 moles (182 g) of styrene, 4-acetoxystyrene 0.30 mol (49 g), 0.12 moles (15 g) of 1-phenylethanol as a cocatalyst, 250 g of toluene, and 7.9 g of boron trifluoride diethyl ether complex as a catalyst were added to a 1.0 L reactor and reacted at 40°C for 6 hours. The polymerization solution was terminated with methanol and aqueous sodium bicarbonate solution, and the oil layer was washed three times with pure water. The volatile matter was removed under reduced pressure at 40°C to obtain Copolymer 1. NMR measurement of Copolymer 1 obtained in Example 1 confirmed that it had a structural unit represented by formula (b1). Furthermore, the active ester equivalent and vinyl equivalent were measured, and the active ester equivalent of Copolymer 1 obtained in Example 1 was 1015 g / eq. and the vinyl equivalent was 623 g / eq. The IR chart of the copolymer is shown in Figure 1, and the GPC chart is shown in Figure 2.

[0080] Example 2 0.60 mol (78.1 g) of divinylbenzene, 0.35 mol (46.3 g) of ethylvinylbenzene, 1.75 mol (182.3 g) of styrene, 0.30 mol (48.7 g) of 4-acetoxystyrene, 307 g of propyl acetate, 0.17 g of water, and 8.5 g of a boron trifluoride diethyl ether complex were placed in a 1.0 L reactor and reacted for 8 hours at 70° C. The polymerization solution was terminated with methanol and an aqueous sodium bicarbonate solution, and the oil layer was washed three times with pure water and devolatilized under reduced pressure at 40° C. to obtain Copolymer 2.

[0081] Examples 3 to 5 According to the amounts (parts) of each raw material shown in Table 1, the same operations as in Example 1 were carried out to obtain Copolymer 3, Copolymer 4 and Copolymer 5.

[0082] Comparative Example 1 Copolymer 6 was obtained in the same manner as in Example 1, except that 4-acetoxystyrene was not used, according to the amounts (parts) of each raw material shown in Table 1. Various physical properties of the copolymers obtained in Examples 1 to 5 and Comparative Example 1 were measured, and the results are shown in Table 1.

[0083]

[0084] Next, examples of cured products with epoxy resins will be described, and the components used are as follows: [Epoxy Resin] Epoxy resin: A mixture of bisphenol A epoxy resin and bisphenol F epoxy resin (ZX-1059, manufactured by Nippon Steel Chemical & Material Co., Ltd., epoxy equivalent: 166 g / eq.)

[0085] Synthesis Example 1: Active Ester Curing Agent A reaction apparatus equipped with a stirrer, thermometer, nitrogen inlet, dropping funnel, and condenser was charged with 165 parts of phenolated dicyclopentadiene (J-DPP-85, manufactured by JFE Chemical Corporation, hydroxyl equivalent: 165), 144 parts of 1-naphthol, 203 parts of isophthalic acid chloride, 10 parts of tetra-n-butylammonium bromide, and 1,280 parts of toluene, and the mixture was heated to 50°C to dissolve. While controlling the temperature in the system to 60°C or less, 400 parts of a 20% aqueous sodium hydroxide solution was added dropwise over 3 hours, and then stirring was continued at the same temperature for another 4 hours. The reaction mixture was allowed to stand for liquid separation, and the water bath was removed. This operation was repeated until the pH of the water bath reached 7. Thereafter, water was removed by reflux dehydration, and an active ester resin was obtained in the form of a toluene solution with a non-volatile content of 65%. The active ester equivalent calculated from the amounts of the raw materials charged was 220 g / eq.

[0086] [Peroxide] α,α'-bis(2-t-butylperoxyisopropyl)benzene (Perbutyl P, manufactured by NOF Corporation) [Catalyst] N,N'-dimethylaminopyridine (DMAP, manufactured by Tokyo Chemical Industry Co., Ltd.)

[0087] Example 6: 23.3 parts of copolymer 1 obtained in Example 1, 10 parts of epoxy resin ZX-1059, 13.3 parts of the active ester curing agent obtained in Synthesis Example 1, 0.1 parts of perbutyl P peroxide, and 0.1 parts of DMAP catalyst were mixed and further diluted with toluene to a nonvolatile content of 50% to obtain a resin composition. These were then applied to a PET film to a thickness of 150 μm and dried at 130°C for 15 minutes using a dryer. The resulting dried powder was pressed for 90 minutes under conditions of a vacuum of 0.5 kPa, a heating temperature of 220°C, and a press pressure of 2 MPa to obtain a cured product with a thickness of 2 mm. A 2 mm spacer was used to adjust the thickness. The dynamic viscoelasticity (Tan δ), haze value, and mechanical strength (bending stress at break) of the resulting cured product were measured, and the results are shown in Table 2.

[0088] Examples 7 to 12 and Comparative Examples 2 to 4 Cured products were obtained using the formulations shown in Table 2 and the same procedure as in Example 6. The dynamic viscoelasticity (Tan δ), haze value, and mechanical strength (bending stress at break) of the obtained cured products were measured, and the results are shown in Table 2.

[0089]

[0090] According to the examples, the polyfunctional vinyl aromatic copolymer of the present invention exhibited a single Tan δ peak in the cured product of a resin composition with an epoxy resin, and the haze value was also reduced, which indicates that the crosslinking reaction with the epoxy resin improved the uniformity and reactivity in the cured product, and further improved the mechanical strength.

[0091] The polyfunctional vinyl aromatic copolymer of the present invention is useful as an electrical insulating material for high-speed communication devices, particularly for printed wiring boards.

Claims

1. A polyfunctional vinyl aromatic copolymer obtained by using 2 mol% or more but less than 95 mol% of a divinylaromatic compound (a), 2 mol% or more but less than 93 mol% of an ester group-containing vinyl aromatic compound (b) represented by the following formula (1), and 5 mol% or more but less than 96 mol% of a monovinyl aromatic compound (c), wherein the copolymer contains a structural unit represented by the following formula (a1) derived from the divinylaromatic compound (a) and a structural unit represented by the following formula (b1) derived from the ester group-containing vinyl aromatic compound (b), and is characterized by having a number average molecular weight of 300 to 100,000, a molecular weight distribution (Mw / Mn) represented by the ratio of the weight average molecular weight to the number average molecular weight of 100 or less, and being soluble in a solvent. In the formula, Ar1 and Ar2 each independently represent an aromatic ring group of either a benzene ring or a naphthalene ring, and these aromatic rings may contain an ester group having 1 to 15 carbon atoms as a substituent in either or both of Ar1 and Ar2, and may have an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an aryl group having 6 to 11 carbon atoms, an aralkyl group having 7 to 12 carbon atoms, an aryloxy group having 6 to 11 carbon atoms, or an aralkyloxy group having 7 to 12 carbon atoms as a substituent. R1 is a direct bond or a divalent group selected from the group consisting of hydrocarbon groups having 1 to 20 carbon atoms, -CO-, -O-, -S-, -SO2-, and -C(CF3)2-. n is 0 or 1. In the formula, R2 represents an aromatic hydrocarbon group having 6 to 30 carbon atoms. In the formula, Ar1, Ar2, R1, and n have the same meanings as in formula (1).

2. The polyfunctional vinyl aromatic copolymer according to claim 1, wherein the active ester equivalent is 150 to 6,000 g / eq. and the vinyl equivalent is 200 to 5,000 g / eq.

3. A curable resin composition comprising the polyfunctional vinyl aromatic copolymer according to claim 1 and a radical polymerization initiator.

4. A resin composition comprising the polyfunctional vinyl aromatic copolymer of claim 1 and an epoxy resin.

5. A curable resin composition comprising the polyfunctional vinyl aromatic copolymer according to claim 1 and a curable reactive resin or a thermoplastic resin, or a flame retardant or filler.

6. A cured product obtained by curing the curable resin composition according to any one of claims 3 to 5.

7. A method for producing a polyfunctional vinyl aromatic copolymer by polymerizing a divinylaromatic compound (a), an ester group-containing vinyl aromatic compound (b) represented by formula (1), and a monovinyl aromatic compound (c) in the presence of a Lewis acid catalyst (f) and a co-catalyst (g), characterized in that the divinylaromatic compound (a) accounts for 2 mol% or more but less than 95 mol%, the ester group-containing vinyl aromatic compound (b) represented by formula (1), and the monovinyl aromatic compound (c) accounts for 2 mol% or more but less than 93 mol%, and the monovinyl aromatic compound (c) accounts for 5 mol% or more but less than 96 mol%, based on the total of (a), (b), and (c), and the polymerization is carried out at a temperature of -20 to 120°C.

8. The method for producing a polyfunctional vinyl aromatic copolymer according to claim 7, wherein the Lewis acid catalyst (f) is a metal fluoride or a complex thereof.

9. The method for producing a polyfunctional vinyl aromatic copolymer according to claim 7, wherein the co-catalyst is one or more compounds selected from the group consisting of ester compounds, ketone compounds, ether compounds, and compounds represented by the following formula (2): In the formula, R3 and R4 each independently represent an alkyl group having 1 to 6 carbon atoms or an aromatic hydrocarbon group having 6 to 30 carbon atoms, and R5 represents hydrogen, an alkyl group having 1 to 6 carbon atoms, or an aromatic hydrocarbon group having 6 to 30 carbon atoms.

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