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

Abstract

The purpose of the present invention is to provide: a novel soluble polyfunctional vinyl aromatic copolymer which has improved thermal oxidation deterioration resistance of dielectric characteristics while having high dielectric characteristics; a method for producing the same; and a curable resin composition which contains the copolymer.　Provided is a soluble polyfunctional vinyl aromatic copolymer which contains structural units that are derived from a divinyl aromatic compound (a), styrene (b), and a monovinyl compound (c) other than styrene. This soluble polyfunctional vinyl aromatic copolymer is characterized by containing end groups represented by formulae (t2) and (t3) at the ends of the copolymer and being soluble in a solvent.

Description

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

[0001] The present invention relates to a novel soluble polyfunctional vinyl aromatic copolymer having improved resistance to thermal oxidative degradation, a method for producing the same, and a curable resin composition containing the same.

[0002] With the recent increase in the volume of information and communications, high-frequency communications have become increasingly common. This demand for electrical insulating materials with superior electrical properties, particularly those with low dielectric constants and low dielectric dissipation factors, and particularly those with minimal change in dielectric properties after water absorption, is essential to reduce transmission loss in high-frequency bands. Furthermore, printed circuit boards and electronic components using these insulating materials are exposed to high-temperature solder reflow during assembly, so materials with high heat resistance, i.e., high glass transition temperatures, are desirable. Recently, environmental concerns have led to the use of lead-free solders with high melting points, which has led to an increased demand for more heat-resistant insulating materials. To meet these demands, curable resins using vinyl compounds with various chemical structures have been proposed.

[0003] As such a cured resin, for example, Patent Document 1 discloses a soluble polyfunctional vinyl aromatic copolymer obtained by polymerizing a divinyl aromatic compound and a monovinyl aromatic compound in an organic solvent in the presence of a Lewis acid catalyst and an initiator of a specific structure such as 1-chloroethylbenzene at a temperature of 20 to 100° C. Furthermore, Patent Document 2 discloses a method for producing a soluble polyfunctional vinyl aromatic copolymer having a controlled molecular weight distribution by cationic polymerization of a monomer component containing 20 to 100 mol % of a divinyl aromatic compound at a temperature of 20 to 120° C. using a Lewis acid catalyst and an initiator of a specific structure in the presence of a quaternary ammonium salt.

[0004] The soluble polyfunctional vinyl aromatic copolymers obtained by these techniques contain polymerizable double bonds, and when cured, they give cured products with high glass transition temperatures. Therefore, these cured products or soluble polyfunctional vinyl aromatic copolymers can be said to be polymers or precursors thereof with excellent heat resistance. Furthermore, these soluble polyfunctional vinyl aromatic copolymers are copolymerized with other radically polymerizable monomers to give cured products, and these cured products also have excellent heat resistance.

[0005] However, the soluble polyfunctional vinyl aromatic copolymers disclosed in the above patent documents are not sufficient in terms of dielectric properties and resistance to thermal oxidative degradation during continuous use at high temperatures.

[0006] Patent Document 3 discloses a soluble polyfunctional vinyl aromatic copolymer obtained by copolymerizing a divinyl aromatic compound and a monovinyl aromatic compound, the copolymer having a chain hydrocarbon group or an aromatic hydrocarbon group at some of its terminal groups via an ether bond or a thioether bond. However, this soluble polyfunctional vinyl aromatic copolymer contains a chain hydrocarbon group or an aromatic hydrocarbon group at the terminal via either an ether bond or a thioether bond because polar compounds such as a chain hydrocarbon compound and an aromatic hydrocarbon compound having an alcoholic hydroxyl group and a chain hydrocarbon compound and an aromatic hydrocarbon compound having a thioalcoholic mercapto group are used as chain transfer agents to adjust the molecular weight. Therefore, it is difficult to say that this soluble polyfunctional vinyl aromatic copolymer is suitable for use as a substrate material in cutting-edge technology fields requiring high dielectric properties.

[0007] Patent Document 4 discloses a polyfunctional vinyl aromatic copolymer having a terminal group derived from an aromatic ether compound, and Patent Document 5 discloses a soluble polyfunctional vinyl aromatic copolymer having a terminal group derived from a thio(meth)acrylate compound. However, the soluble polyfunctional vinyl aromatic copolymers disclosed in these documents do not have low dielectric properties in the high frequency band that has accompanied the recent increase in information communication traffic, and it is difficult to say that they are suitable for cutting-edge technological fields such as advanced electrical and electronic fields that require high functionality and advanced electrical properties, thermal and mechanical properties.

[0008] Furthermore, Patent Document 6 discloses a curable resin composition comprising a polyfunctional vinyl aromatic copolymer having structural units derived from monomers consisting of a divinyl aromatic compound, styrene, and a monovinyl aromatic compound other than styrene. However, although this curable resin composition using the polyfunctional vinyl aromatic copolymer exhibits low dielectric properties, it cannot be said that the change in dielectric properties due to heat is sufficient, and further improvement is desired. Therefore, until now, there has not been an electrical insulating material that has the high dielectric properties desired in recent cutting-edge electrical and electronic fields while also fully satisfying resistance to thermal degradation of dielectric properties (thermal oxidative degradation resistance).

[0009] JP 2004-123873 A JP 2005-213443 A JP 2007-332273 A JP 2010-229263 A JP 2010-209279 A WO2018 / 181842

[0010] Therefore, the present invention aims to provide a novel soluble polyfunctional vinyl aromatic copolymer that has high dielectric properties and improved resistance to thermal oxidative degradation of the dielectric properties, a method for producing the same, and a curable resin composition containing the copolymer. Another object of the present invention is to provide a cured product obtained by curing a curable resin composition containing the copolymer.

[0011] As a result of extensive research into the above-mentioned problems, the present inventors have found that a polyfunctional soluble vinyl polymer containing a specific structure has excellent dielectric properties and also excellent resistance to oxidative degradation, thereby completing the present invention.

[0012] That is, the present invention provides a vinyl aromatic copolymer containing structural units derived from a divinylaromatic compound (a), styrene (b), and a monovinyl compound other than styrene (c), the copolymer containing a structural unit derived from the divinylaromatic compound (a) and represented by the following formula (t1): In the formula, R1 represents an aromatic hydrocarbon group having 6 to 30 carbon atoms. The copolymer contains terminal groups represented by the following formulas (t2) and (t3) at its terminals: In the formula, R2 and R3 each independently represent an aromatic hydrocarbon group having 6 to 30 carbon atoms. Z2 and Z3 each independently represent a vinyl group, a hydrogen atom, or a hydrocarbon group having 1 to 18 carbon atoms. * represents the bonding point to the main chain, and the same applies hereinafter. In the formula, R4 and R5 each independently represent an aromatic hydrocarbon group having 6 to 30 carbon atoms. Z4 and Z5 each independently represent a vinyl group, a hydrogen atom, or a hydrocarbon group having 1 to 18 carbon atoms. The total molar fraction of the terminal groups derived from formulas (t2) and (t3) satisfies the following mathematical formula (1): The soluble polyfunctional vinyl aromatic copolymer has a number average molecular weight of 500 to 10,000, a molecular weight distribution (Mw / Mn) expressed as the ratio of the weight average molecular weight to the number average molecular weight of 40 or less, and is soluble in toluene, xylene, tetrahydrofuran, dichloroethane, or chloroform.

[0013] The present invention relates to a method for producing a polyfunctional vinyl aromatic copolymer by polymerizing a divinyl aromatic compound (a), styrene (b), and a monovinyl compound other than styrene (c) in the presence of a Lewis acid catalyst (f), a hydroxyl group-containing cocatalyst (g), and an aromatic solvent (h), wherein the polymerization is carried out at a temperature of -20 to 120°C.

[0014] In the above production method, the Lewis acid catalyst (f) is preferably a metal fluoride or a complex thereof, the hydroxyl group-containing co-catalyst (g) is preferably a compound of formula (2), and the aromatic solvent (h) is preferably a compound of formula (3). R6 and R7 each independently represent an alkyl group having 1 to 30 carbon atoms or an aromatic hydrocarbon group having 6 to 30 carbon atoms. R8 represents hydrogen, an alkyl group having 1 to 30 carbon atoms, or an aromatic hydrocarbon group having 6 to 30 carbon atoms. R9 and R10 each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

[0015] Furthermore, the present invention provides a curable resin composition comprising the above-mentioned soluble polyfunctional vinyl aromatic copolymer and a radical polymerization initiator.

[0016] The soluble polyfunctional vinyl aromatic copolymer of the present invention or a cured product obtained from a material containing the copolymer has improved dielectric properties and thermal oxidative degradation resistance. According to the production method of the present invention, the soluble polyfunctional vinyl aromatic copolymer can be produced with high efficiency. Furthermore, the soluble polyfunctional vinyl aromatic copolymer of the present invention has a large intramolecular free volume, few polar groups, and specific terminal groups that exhibit excellent thermal oxidative degradation resistance. Therefore, when used as a curable compound, the copolymer simultaneously exhibits high levels of dielectric properties and thermal oxidative degradation resistance.

[0017] 1 is an NMR chart of Copolymer 1 obtained in Example 1. FIG. 2 is a GPC chart of Copolymer 1 obtained in Example 1.

[0018] The present invention will be described in detail below. In the description of the present invention, the soluble polyfunctional aromatic copolymer of the present invention may be simply referred to as "copolymer".

[0019] The soluble polyfunctional vinyl aromatic copolymer of the present invention contains structural units derived from a divinyl aromatic compound (a) and structural units derived from styrene (b) and a monovinyl compound other than styrene (c).

[0020] The structural units derived from the divinylaromatic compound (a) account for 2 mol% or more but 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 have multiple structures, such as structures in which two vinyl groups have reacted singly or doubly. Among these, it is preferable that the repeating unit represented by the following formula (t1) in which only one vinyl group has reacted is contained in 2 to 80 mol%. This is more preferably 5 to 70 mol%, even more preferably 10 to 60 mol%, and particularly preferably 15 to 50 mol%. By containing 2 to 80 mol%, the resulting composition has a low dielectric loss tangent, high toughness, excellent heat resistance, and excellent compatibility with other resins. Furthermore, when formed into a resin composition, it 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. In the formula, R1 represents an aromatic hydrocarbon group having 6 to 30 carbon atoms.

[0021] The aromatic hydrocarbon group having 6 to 30 carbon atoms is not particularly limited, but examples thereof include those in which two hydrogen atoms have been removed from a single-ring aromatic compound such as benzene, furan, pyrrole, thiophene, imidazole, pyrazole, oxazole, isoxazole, thiazole, isothiazole, pyridine, pyrimidine, pyridazine, pyrazine, and triazine; and those in which two hydrogen atoms have been removed from a fused-ring aromatic compound such as naphthalene, anthracene, phenalene, phenanthrene, quinoline, isoquinoline, quinazoline, phthalazine, pteridine, coumarin, indole, benzimidazole, benzofuran, and acridine. Combinations of these aromatic compounds may also be used, including those in which two hydrogen atoms have been removed from a ring-assembly aromatic compound such as biphenyl, binaphthalene, bipyridine, bithiophene, phenylpyridine, phenylthiophene, terphenyl, diphenylthiophene, and quaterphenyl. Benzene, naphthalene, biphenyl, and anthracene are preferred. Benzene is even more preferred.

[0022] The structural units derived from styrene (b) and a monovinyl compound other than styrene (c) account for 2 mol% or more and less than 80 mol% of the total structural units derived from (a), (b), and (c). Preferably, it is 5 mol% or more and less than 70 mol%, and more preferably, it is 10 mol% or more and less than 60 mol%. If the molar fraction of the structural units derived from (b) and (c) is less than 2 mol%, molding processability will be insufficient, and if it exceeds 80 mol%, the heat resistance of the cured product will be insufficient.

[0023] The molar fraction of the structural unit (b1) derived from styrene (b) and the structural unit (c1) derived from a monovinyl compound other than styrene (c) is preferably (b1):(c1) 99:1 to 20:80, since this provides both thermal oxidative degradation resistance and moldability. It is more preferably 98:2 to 30:70. When the structural unit (b1) derived from styrene (b) is more than 99:1, heat resistance tends to decrease, while when the structural unit (c1) derived from a monovinyl compound other than styrene (c) is more than 20:80, moldability tends to decrease.

[0024] The vinyl group constituting the above formula (t1) derived from the divinyl aromatic compound (a) acts as a cross-linking component and contributes to the development of heat resistance of the soluble polyfunctional vinyl aromatic copolymer. On the other hand, the structural units derived from styrene (b) and monovinyl compounds other than styrene (c) do not have vinyl groups, since polymerization is generally believed to proceed by a 1,2-addition reaction of vinyl groups. In other words, the structural units derived from styrene (b) and monovinyl compounds other than styrene (c) do not act as cross-linking components, but contribute to the development of moldability.

[0025] The divinyl aromatic compound (a), styrene (b), and the monovinyl compound other than styrene (c) not only form repeating units containing (t1) through polymerization, but also form terminal groups, specifically, terminal groups represented by the following formulae (t2) and (t3) at the terminals of the polyfunctional vinyl aromatic copolymer. The introduction of these terminal groups can control the properties of the soluble polyfunctional vinyl aromatic copolymer. Therefore, it is important to control the formation of the terminal groups represented by formulae (t2) and (t3) during the polymerization reaction, i.e., the termination reaction mechanism. In the formula, R2 and R3 each independently represent an aromatic hydrocarbon group having 6 to 30 carbon atoms. Z2 and Z3 each independently represent a vinyl group, a hydrogen atom, or a hydrocarbon group having 1 to 18 carbon atoms. * represents the bonding point to the main chain, and the same applies hereinafter. In the formula, R4 and R5 each independently represent an aromatic hydrocarbon group having 6 to 30 carbon atoms, and Z4 and Z5 each independently represent a vinyl group, a hydrogen atom, or a hydrocarbon group having 1 to 18 carbon atoms.

[0026] The terminal group of formula (t2) is formed during the production process of a polyfunctional vinyl aromatic copolymer by electrophilic substitution reaction of a carbocation at a growing end with the aromatic ring of the monomer immediately preceding the growing polymer chain. Here, the terminal group of formula (t2) is formed by an intramolecular electrophilic substitution reaction, and results in different terminal structures as follows depending on the structural units derived from monomers (a), (b), and (c). When both molecules contain structural units derived from a divinyl aromatic compound (a), the terminal structure is represented by formula (t2-1) below. When both molecules contain structural units derived from a divinyl aromatic compound (a) and structural units derived from styrene (b) or a monovinyl compound other than styrene (c), the terminal structure is represented by formula (t2-2) or (t2-3). When both molecules contain structural units derived from styrene (b) or a monovinyl compound other than styrene (c), the terminal structure is represented by formula (t2-4) below. In the formula, R2 and R3 have the same meanings as in formula (t2), and Y1 and Y2 independently represent a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms.

[0027] The terminal group of formula (t3) is formed by an electrophilic substitution reaction of a growing terminal carbocation with an aromatic compound during the production process of a polyfunctional vinyl aromatic copolymer. Not only the aromatic compound monomers (a), (b), and (c), but also the aromatic solvent (h) can participate in this reaction. Here, the terminal group of formula (t3) is formed by an electrophilic substitution reaction involving two molecules, and the terminal structure varies depending on the structural units derived from the monomers (a), (b), and (c) and the aromatic solvent (h), as follows: When the copolymer is composed of a structural unit derived from a divinylaromatic compound (a) and a structural unit derived from the divinylaromatic compound (a), styrene (b), or a monovinyl compound (c) having an aromatic ring other than styrene, the terminal structure is represented by formula (t3-1) below. When the copolymer is composed of a structural unit derived from a styrene (b) or a monovinyl compound (c) having an aromatic ring other than styrene, and a structural unit derived from the divinylaromatic compound (a), styrene (b), or a monovinyl compound (c) having an aromatic ring other than styrene, the terminal structure is represented by formula (t3-2). When the copolymer is composed of a structural unit derived from a divinyl aromatic compound (a) and a structural unit derived from an aromatic solvent (h), the terminal structure is represented by (t3-3). When the copolymer is composed of a structural unit derived from styrene (b) or a monovinyl compound (c) having an aromatic ring other than styrene and a structural unit derived from an aromatic solvent (h), the terminal structure is represented by the following formula (t3-4). That is, the terminal group in formula (t3) represents the sum of the terminal groups from (t3-1) to (t3-4). In the formula, R4 and R5 have the same meanings as in formula (t3), and Y3 and Y4 represent a hydrogen atom or a hydrocarbon group having 1 to 18 carbon atoms.

[0028] The aromatic hydrocarbon group having 6 to 30 carbon atoms is not particularly limited, but examples thereof include those in which two hydrogen atoms have been removed from a single-ring aromatic compound such as benzene, furan, pyrrole, thiophene, imidazole, pyrazole, oxazole, isoxazole, thiazole, isothiazole, pyridine, pyrimidine, pyridazine, pyrazine, and triazine; and those in which two hydrogen atoms have been removed from a fused-ring aromatic compound such as naphthalene, anthracene, phenalene, phenanthrene, quinoline, isoquinoline, quinazoline, phthalazine, pteridine, coumarin, indole, benzimidazole, benzofuran, and acridine. Combinations of these aromatic compounds may also be used, including those in which two hydrogen atoms have been removed from a ring-assembly aromatic compound such as biphenyl, binaphthalene, bipyridine, bithiophene, phenylpyridine, phenylthiophene, terphenyl, diphenylthiophene, and quaterphenyl. Benzene, naphthalene, biphenyl, and anthracene are preferred. Benzene is even more preferred.

[0029] Examples of hydrocarbon groups having 1 to 18 carbon atoms include, but are not limited to, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, tert-pentyl, neopentyl, 1,2-dimethylpropyl, n-hexyl, isohexyl, n-nonyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and cyclononyl groups, of which methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, and tert-butyl groups are preferred, and methyl and ethyl groups are more preferred.

[0030] The terminal groups of the soluble multifunctional vinyl copolymer satisfy the relationship shown in Formula 1 below. In other words, the structures t2 and t3 account for more than 5 mol% of the terminal structures. When the repeating structural unit t1 and the terminal structures t2 and t3 satisfy the relationship shown in Formula 1, low dielectric properties are achieved and resistance to thermal oxidative degradation is significantly improved. Although the reason for this is unknown, it is speculated that the introduction of a low-polarity, rigid aromatic ring into the terminal structure improves resistance to thermal degradation. It is preferably 0.10 or more, more preferably 0.15 or more. On the other hand, the upper limit is preferably less than 0.50, more preferably less than 0.45. The terminal structures (t2) and (t3) are preferably contained in an amount of 1 mol % or more and 20 mol % or less relative to the total of the structural units derived from (a), (b), and (c). More preferably, it is contained in an amount of 2 mol or more and 10 mol % or less.

[0031] The above formulas are calculated from the integrated values ​​of the 1H-NMR peaks derived from each structure. Specifically, the structural unit (t1) was calculated as the integrated value of the peaks of H1 and H2 (chemical shift: ranges of 5.1 to 5.3 ppm and 5.5 to 5.8 ppm) shown in the following formula (t1-H), the terminal group of t2 was calculated as the integrated value of the peak of H3 (chemical shift: range of 4.1 to 4.5 ppm) shown in the following formula (t2-H), and the terminal group of t3 was calculated as the integrated value of the peak of H4 (chemical shift: range of 3.2 to 3.8 ppm) shown in the following formula (t3-H).

[0032] In the copolymer, the mole percentages of (t1), (t2), and (t3) relative to the total of the divinyl aromatic compound (a), styrene (b), and monovinyl compound other than styrene (c) are in the range of 2 to 80 mole percent. This refers to the content of vinyl groups and terminal groups in the soluble polyfunctional vinyl aromatic copolymer. If this mole percentage is less than 2 mole percent, heat resistance decreases, and if it is greater than 80 mole percent, the interlayer peel strength decreases when the copolymer is formed into a laminate. It is preferably 5 to 80 mole percent, more preferably 10 to 70 mole percent, and particularly preferably 15 to 65 mole percent. The preferred mole percentages remain the same even when structural units derived from monomers other than (a), (b), and (c) are included.

[0033] In particular, the mol % of vinyl groups in the structural units of formula (t1) and the terminal groups of formulae (t2-1), (t2-2), (t2-3), (t3-1), (t3-2) and (t3-3), i.e., in the main chain and terminal groups, relative to the total of the divinyl aromatic compound (a), styrene (b) and monovinyl compound other than styrene (c) is preferably in the range of 5 to 80 mol %, more preferably 10 to 70 mol %, particularly preferably 15 to 65 mol %, since both heat resistance and interlayer peel strength are obtained.

[0034] In the copolymer, the amount of vinyl group-containing end groups (tv) introduced is 0.2 or more per molecule. Here, the vinyl group-containing end groups (tv) are (t2) in which Z2 and / or Z3 are vinyl groups, and (t3) in which Z4 and / or Z5 are vinyl groups. The amount of vinyl group-containing end groups (tv) introduced means the total of formulas (t2-1), (t2-2), (t2-3), (t3-1), (t3-2), and (t3-3). If the amount of vinyl group-containing end groups (tv) introduced is less than 0.2, the curability and heat resistance will decrease. Preferably, it is 0.5 or more, more preferably 0.6 or more per molecule.

[0035] The copolymer has a number-average molecular weight Mn of 500 to 10,000, 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 40 or less, and is soluble in solvents such as toluene, xylene, tetrahydrofuran, dichloroethane, or chloroform. The soluble polyfunctional vinyl aromatic copolymer of the present invention is characterized by its solvent solubility. As used herein, the term "structural unit" includes repeating units present in the main chain of the copolymer and units or terminal groups present at the terminals or side chains. The number-average molecular weight (Mn: number-average molecular weight in terms of standard polystyrene measured using gel permeation chromatography) of the soluble polyfunctional vinyl aromatic copolymer is preferably 500 to 10,000, more preferably 600 to 9,000, and even more preferably 700 to 8,000. If Mn is less than 500, the amount of monofunctional copolymer components contained in the soluble polyfunctional vinyl aromatic copolymer increases, tending to reduce the heat resistance of the cured product. On the other hand, if Mn exceeds 10,000, gel formation is more likely, and viscosity increases, tending to reduce moldability. The molecular weight distribution (Mw / Mn), expressed as the ratio of weight average molecular weight (Mw: weight average molecular weight in terms of standard polystyrene measured using gel permeation chromatography) to Mn, is 40.0 or less, preferably 35.0 or less, more preferably 1.5 to 30.0, and most preferably 2.0 to 25.0. If Mw / Mn exceeds 40.0, the processing characteristics of the soluble polyfunctional vinyl aromatic copolymer tend to deteriorate, and gel formation is more likely.

[0036] The copolymer is soluble in toluene, xylene, tetrahydrofuran, dichloroethane or chloroform as a solvent, and preferably in any of the above solvents.To be a solvent-soluble and multifunctional copolymer, it is necessary that a part of the vinyl groups of divinylbenzene remain uncrosslinked and have an appropriate degree of crosslinking.Here, "solvent-soluble" means that the soluble multifunctional vinyl aromatic copolymer dissolves in 100g of the above solvent in an amount of 5g or more, more preferably 30g or more, particularly preferably 50g or more.

[0037] Next, a method for producing the soluble polyfunctional vinyl aromatic copolymer of the present invention will be described, which can advantageously produce the polyfunctional vinyl aromatic copolymer.

[0038] The method for producing a soluble polyfunctional vinyl aromatic copolymer of the present invention comprises polymerizing a divinyl aromatic compound (a), styrene (b), and a monovinyl compound other than styrene (c) in the presence of a Lewis acid catalyst (f), a hydroxyl group-containing cocatalyst (g), and an aromatic solvent (h), and the polymerization is carried out at a temperature of −20 to 120° C. Here, the Lewis acid catalyst (f) acts as a catalyst, and the hydroxyl group-containing cocatalyst (g) acts as a cocatalyst.

[0039] The divinyl aromatic 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 soluble multifunctional vinyl aromatic copolymer is thermally cured. Examples of the divinyl aromatic 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.

[0040] The monovinyl compounds are styrene (b) and a monovinyl compound other than styrene (c). As the monovinyl compound, styrene (b) is essential, and it is also necessary to use a monovinyl compound other than styrene (c) in combination.

[0041] Styrene (b) acts as a monomer component to impart low dielectric properties and thermal oxidation resistance to the soluble polyfunctional vinyl aromatic copolymer, and also acts as a chain transfer agent to control the molecular weight of the soluble polyfunctional vinyl aromatic copolymer and introduce vinyl groups to the terminals of the soluble polyfunctional vinyl aromatic copolymer. The monovinyl compound (c) other than styrene improves the solvent solubility and processability of the soluble polyfunctional vinyl aromatic copolymer.

[0042] Examples of the monovinyl compound (c) other than styrene are not limited as long as they are monomers other than styrene having one vinyl group, but include vinyl aromatic compounds such as vinylnaphthalene and vinylbiphenyl; nuclear alkyl-substituted vinyl aromatic compounds such as o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylvinylbenzene, m-ethylvinylbenzene, and p-ethylvinylbenzene; and monovinyl aliphatic compounds such as propylene, 1-pentene, 2-pentene, 2-methyl-1-butene, 3-methyl-1-butene, and 2,4,4-trimethylpentene-1. Preferred are 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) because they prevent gelation of the soluble polyfunctional vinyl aromatic copolymer, are highly effective in improving solvent solubility and processability, are low cost, and are easily available. More preferred is ethylvinylbenzene (m-isomer, p-isomer or a mixture of positional isomers thereof) from the viewpoints of dielectric properties and cost.

[0043] In addition to the divinyl aromatic compound (a), styrene (b) and the monovinyl compound other than styrene (c), a trivinyl aromatic compound, a trivinyl aliphatic compound or a divinyl aliphatic compound may be used to introduce structural units derived from other monomer components (d) into the soluble polyfunctional vinyl aromatic copolymer, as long as the effects of the present invention are not impaired.

[0044] Examples of other monomer components (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, triallyl isocyanurate, etc. These can be used alone or in combination of two or more.

[0045] The molar fraction of the other monomer component (d) relative to the sum of all the 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 the structural units derived from all the monomer components (a), (b), (c), and (d) constituting the copolymer is preferably less than 30 mol %.

[0046] The proportions of the essential monomer components (a), (b), and (c) used are such that the divinyl aromatic compound (a) is used in an amount of 2 mol % or more and less than 95 mol % relative to the total of (a), (b), and (c), and the styrene (b) and the monovinyl compound other than styrene (c) are used in an amount of 5 mol % or more and less than 98 mol %, respectively, and these monomer components (a), (b), and (c) are polymerized at a temperature of −20 to 120° C.

[0047] The blending 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%, and the blending amount of the styrene (b) and the monovinyl compound other than styrene (c) is preferably 95 to 20 mol%, more preferably 93 to 30 mol%, and particularly preferably 90 to 40 mol%.

[0048] Styrene (b) generally has lower reactivity than other monomer components such as divinyl aromatic compounds (a) and monovinyl compounds other than styrene (c), particularly nuclear alkyl-substituted vinyl aromatic compounds. Therefore, it is preferable to use an excess amount of styrene (b) so that a portion of the styrene (b) remains unreacted. The remaining unreacted styrene (b) is removed during the purification process of the soluble polyfunctional vinyl aromatic copolymer. The proportion of styrene (b) used is preferably 95 to 20 mol%, more preferably 90 to 30 mol%, and more preferably 80 to 35 mol%, based on the total of the monomer components (a), (b), and (c).

[0049] In the method for producing the copolymer of the present invention, the individual monomer components are used so that the total molar fraction of the terminal groups derived from formulae (t2) and (t3) satisfies the following mathematical formula (1). In particular, it is preferable to use each monomer component so that 10 mol% or more of the total of all terminal groups of the soluble polyfunctional vinyl aromatic copolymer are terminal groups derived from styrene (b) and monovinyl compounds other than styrene (c), i.e., (t2-2), (t2-3), (t3-2), or (t3-3). More preferably, this is 20 mol% or more, even more preferably 30 mol% or more, and particularly preferably 40 mol% or more. Within these ranges, the amount of vinyl groups introduced into the terminals of the soluble polyfunctional vinyl aromatic copolymer is appropriate, and the copolymer has low dielectric properties, resistance to thermal oxidative degradation, solvent solubility, and processability.

[0050] The Lewis acid catalyst (f) is a compound consisting of a metal ion (acid) and a ligand (base), and can be used without any particular limitation as long as it is capable of accepting an electron pair. Among these, from the viewpoint of the thermal decomposition resistance of the resulting soluble 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 soluble polyfunctional vinyl aromatic copolymer and the polymerization activity, boron trifluoride ether complexes are most preferably used. Here, examples of ethers for the ether complex include diethyl ether and dimethyl ether.

[0051] The Lewis acid catalyst (f) is preferably used in an amount within a range of 0.001 to 100 moles, more preferably 0.01 to 50 moles, relative to a total of 100 moles of all monomer components. It is most preferably 0.1 to 20 moles. If it exceeds 100 moles, the polymerization rate becomes too high, making it difficult to control the molecular weight distribution. If it is less than 0.001 mole, the polymerization rate becomes low, the reaction time becomes long, or the polymerization reaction does not proceed, which is undesirable.

[0052] In the process for producing a soluble polyfunctional vinyl aromatic copolymer of the present invention, one or more hydroxyl group-containing cocatalysts (g) represented by the following formula 2 are used as the cocatalyst. In the formula, R6 and R7 each independently represent an alkyl group having 1 to 30 carbon atoms or an aromatic hydrocarbon group having 6 to 30 carbon atoms. R8 represents hydrogen, an alkyl group having 1 to 30 carbon atoms, or an aromatic hydrocarbon group having 6 to 30 carbon atoms. In the case of an alkyl group, it is preferably an alkyl group having 1 to 6 carbon atoms.

[0053] Specific examples of the co-catalyst (g) containing a hydroxyl group include aromatic compounds containing a hydroxyl group, such as 1-phenylethanol and 2-phenyl-2-propanol, and chain hydrocarbon compounds containing a hydroxyl group, such as 2-propanol and tert-butyl alcohol. Among these, one or more compounds selected from the group consisting of aromatic compounds are preferably used, as they act synergistically with the Lewis acid catalyst (f) to easily control the polymerization rate and the molecular weight distribution of the polymer. One or more of these co-catalysts (g) containing a hydroxyl group may be used.

[0054] During the polymerization reaction, the hydroxyl-containing cocatalyst (g) reacts with the Lewis acid catalyst (f) to generate an active species, a carbocation, which then reacts with the vinyl groups of the monomers (a), (b), and (c), thereby promoting the polymerization reaction. As described in Patent Document 3, when alcohols with a hydroxyl group bonded to a primary carbon, such as benzyl alcohol, are used to control the reaction, they generate terminal chain hydrocarbon groups or aromatic hydrocarbon groups via ether bonds, which deteriorates the dielectric properties. However, when alcohols with a hydroxyl group bonded to a secondary or tertiary carbon are used to control the reaction, as in the present invention, the alcohol acts as an initiator, reacting with the catalyst to generate cations, resulting in the synthesis of a compound without an ether bond.

[0055] The amount of the hydroxyl group-containing cocatalyst (g) is preferably 0.1 to 1,000 mol, more preferably 1.0 to 500 mol, and particularly preferably 10 to 200 mol, per 100 mol of the total of all monomer components. Within the above range, the polymerization rate is appropriately maintained and at the same time, the selectivity of the reaction between the monomers is improved, resulting in excellent productivity and suppression of excessive increase or decrease in molecular weight, thereby providing a soluble polyfunctional vinyl aromatic copolymer with excellent moldability.

[0056] In the polymerization reaction, a polymerization raw material containing the above-mentioned mixture of monomers, a Lewis acid catalyst (f) and a hydroxyl group-containing co-catalyst (g) is cationic copolymerized at a temperature of 20 to 120° C. to obtain a copolymer.

[0057] An aromatic solvent (h) is used as the solvent. Not only the aromatic monomers (a), (b), and (c) can participate in the polymerization reaction, but also the aromatic solvent (h). It is a compound that does not essentially inhibit cationic polymerization and dissolves the Lewis acid catalyst (f), the hydroxyl group-containing cocatalyst (g), the monomer components, and the resulting soluble polyfunctional vinyl aromatic copolymer to form a homogeneous solution. Organic solvents with a dielectric constant in the range 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.

[0058] As the aromatic solvent (h), toluene and xylene are particularly preferred from the viewpoint of the balance between polymerization activity and solubility. Furthermore, the amount of solvent used is determined, taking into consideration 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%, particularly preferably 20 to 70 wt%. If this concentration is less than 1 wt%, the polymerization efficiency will be low, resulting in increased costs. If it exceeds 90 wt%, the molecular weight and molecular weight distribution of the resulting soluble polyfunctional vinyl aromatic copolymer will increase, resulting in reduced moldability.

[0059] The copolymer of the present invention can be obtained by copolymerizing monomers consisting of a divinylaromatic compound (a), styrene (b), and a monovinyl compound other than styrene (c). Typically, copolymerization of a divinylaromatic compound (a), styrene (b), and a monovinyl compound other than styrene (c) in an aromatic solvent results in a high polymerization rate of the highly reactive divinylaromatic compound (a), making it difficult to control the molecular weight, resulting in problems such as an increase in molecular weight distribution and gel formation, and making it impossible to obtain a solvent-soluble polymer. However, when a hydroxyl-containing compound represented by the above formula (2) is used as a cocatalyst and the reaction is carried out in an aromatic solvent, the reaction terminates with the formation of an end group of formula (t3), which is thought to enable molecular weight control. Therefore, in order to obtain a solvent-soluble copolymer containing the end structure of (t3) from a divinylaromatic compound (a), styrene (b), and a monovinyl compound other than styrene (c), it is necessary to carry out the reaction in the presence of the Lewis acid catalyst (f) of the present invention, a hydroxyl-containing cocatalyst (g), and an aromatic solvent (h). Since the aromatic solvent (h) does not have a polar group, (t3) exhibits high dielectric properties and also serves as a terminal group with excellent resistance to heat deterioration due to the aromatic ring.

[0060] When producing a soluble polyfunctional vinyl aromatic copolymer, it is necessary to polymerize the monomers (a), (b), and (c) at a temperature of −20 to 120° C. Preferably, it is 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.

[0061] After the polymerization reaction has been stopped, the method for recovering the soluble polyfunctional vinyl aromatic copolymer is not particularly limited, and any commonly used method such as heat concentration, steam stripping, or precipitation in a poor solvent may be used.

[0062] The soluble polyfunctional vinyl aromatic copolymer obtained by the above production method contains 2 mol % or more but less than 95 mol % of structural units derived from a divinyl aromatic compound (a), and 5 mol % or more but less than 98 mol % of repeating units derived from styrene (b) and a monovinyl compound other than styrene (c), and contains repeating units consisting of an unsaturated hydrocarbon group represented by the above formula (t1), and contains terminal groups represented by the above formulas (t2) and (t3). The copolymer satisfies the above mathematical formula (1), has an Mn of 500 to 10,000, an Mw / Mn ratio of 40 or less, and is soluble in toluene, xylene, tetrahydrofuran, dichloroethane, or chloroform.

[0063] Next, the curable resin composition of the present invention will be described. The curable resin composition of the present invention contains the soluble polyfunctional vinyl aromatic copolymer of the present invention (including the soluble polyfunctional vinyl aromatic copolymer obtained by the production method of the present invention) and a radical polymerization initiator (i) (also referred to as a radical polymerization catalyst). For example, the curable resin composition of the present invention is cured by a crosslinking reaction caused by heating or other means, as described below, and a radical polymerization initiator is contained for the purpose of lowering the reaction temperature during this reaction or promoting the crosslinking reaction of unsaturated groups.

[0064] Known substances can be used as the radical polymerization initiator (i). 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 (i). However, the radical polymerization initiator (i) 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 storage stability of the curable resin composition of the present invention. Furthermore, α,α'-bis(t-butylperoxy-m-isopropyl)benzene has low volatility and therefore does not volatilize during prepreg drying or storage, thereby providing good stability. Furthermore, the radical polymerization initiator (i) may be used alone or in combination of two or more types.

[0065] The amount of the radical polymerization initiator (i) to be added 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 soluble polyfunctional vinyl aromatic copolymer. Within this range, the curing reaction proceeds smoothly without being inhibited.

[0066] The curable resin composition can contain a known curable reactive resin (j) or thermoplastic resin (k). Examples of the curable reactive resin (j) include thermosetting resins and resins or compounds that copolymerize with a soluble 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, epoxy resins, polycyanate resins, phenolic resins, and one or more vinyl compounds having one or more polymerizable unsaturated hydrocarbon groups in the molecule. Examples of the thermoplastic resin (k) include polystyrene, polyphenylene ether resin, polyetherimide resin, polyethersulfone resin, PPS resin, polycyclopentazine resin, polycycloolefin resin, etc.; known thermoplastic elastomers, such as styrene-ethylene-propylene copolymer, styrene-ethylene-butylene copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, hydrogenated styrene-butadiene copolymer, hydrogenated styrene-isoprene copolymer, etc.; and rubbers, such as polybutadiene and polyisoprene.

[0067] From the viewpoints of the dielectric properties, heat resistance, adhesion, and compatibility with polyfunctional vinyl aromatic copolymers as a curable resin composition, preferred examples of the curable reactive resin (j) include polyvinylbenzyl resin, curable vinyl resin, curable polyphenylene ether resin, epoxy resin, and one or more vinyl compounds having one or more polymerizable unsaturated hydrocarbon groups in the molecule. Examples of the thermoplastic resin include polystyrene, polyphenylene ether resin, styrene-ethylene-propylene copolymer, styrene-ethylene-butylene copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, hydrogenated styrene-butadiene copolymer, and hydrogenated styrene-isoprene copolymer. More preferred examples of the curable reactive resin include polyvinylbenzyl resin, curable polyphenylene ether resin, epoxy resin, and one or more vinyl compounds having one or more polymerizable unsaturated hydrocarbon groups in the molecule. Examples of the thermoplastic resin (k) include polyphenylene ether resin and hydrogenated styrene-butadiene copolymer. More preferably, the curable reactive resin (j) is a curable polyphenylene ether resin, an epoxy resin, or one or more vinyl compounds (jd) having one or more polymerizable unsaturated hydrocarbon groups in the molecule.

[0068] When the curable reactive resin (j) is a curable polyphenylene ether resin, it is more preferably a modified polyphenylene ether compound (ja) having a curable terminal functional group. Even more preferred is a modified polyphenylene ether compound containing an unsaturated hydrocarbon group. It is a modified polyphenylene ether compound (ja) terminally modified with a substituent having a carbon-carbon unsaturated double bond. Most preferred 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.

[0069] The Mn of the curable polyphenylene ether resin is not particularly limited, but is preferably 500 to 7000, more preferably 800 to 5000, and most preferably 1000 to 3000. Here, Mn may be measured by a general molecular weight measurement method, and specific examples include values ​​measured using gel permeation chromatography (GPC).

[0070] 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 resin has a relatively low molecular weight, thereby improving flowability while maintaining toughness. When a conventional 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 terminal polymerizable unsaturated double bond, copolymerization or curing with a vinyl curable resin such as the copolymer of the present invention allows crosslinking of both resins to proceed smoothly, resulting in a cured product with sufficiently high heat resistance and toughness. Therefore, the cured product of the obtained curable resin composition has excellent heat resistance and toughness.

[0071] When the curable reactive resin (j) is an epoxy resin, it is preferably one or more epoxy resins (jb) selected from the group consisting of epoxy resins having two or more epoxy groups per molecule. Examples of (jb) include cresol novolac epoxy resins, triphenylmethane epoxy resins, biphenyl epoxy resins, naphthalene epoxy resins, bisphenol A epoxy resins, and bisphenol F epoxy resins. These may be used alone or in combination of two or more. It is preferable that the curable resin composition of the present invention does not contain a halogenated epoxy resin, but it may be incorporated as needed as long as it does not impair the effects of the present invention.

[0072] It is believed that the use of such an epoxy resin will sufficiently improve the heat resistance and adhesion of the cured product without impairing the excellent dielectric properties and fluidity of the soluble polyfunctional vinyl aromatic copolymer.

[0073] When the curable reactive resin (j) is one or more vinyl compounds (jd) having one or more polymerizable unsaturated hydrocarbon groups in the molecule, there are no particular limitations. That is, (jd) 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.

[0074] The vinyl compounds (jd) used as curable reactive resins preferably have a weight-average molecular weight (Mw) of 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, (jd) may be more likely to volatilize from the components of the curable resin composition. Furthermore, if the Mw exceeds 5,000, the varnish viscosity of the curable resin composition and the melt viscosity during heat molding may become too high. Therefore, when the Mw of (jd) 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 soluble polyfunctional vinyl aromatic copolymer and (jd). The Mw may be measured using a common molecular weight measurement method, specifically, a value measured using gel permeation chromatography (GPC), etc.

[0075] The average number of carbon-carbon unsaturated double bonds (number of terminal double bonds) per molecule of the vinyl compounds (jd) as curable reactive resins varies depending on the Mw of (jd), 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. If the number of terminal double bonds is too large, the reactivity becomes too high, and problems such as reduced storage stability of the curable resin composition or reduced fluidity of the curable resin composition may occur.

[0076] Examples of vinyl compounds (jd) 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 (polyfunctional vinyl compounds) having two or more vinyl groups in the molecule 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).

[0077] The content of the soluble 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 total of the soluble polyfunctional vinyl aromatic copolymer and the vinyl compounds (jd) as the curable reactive resin. The content of the vinyl compounds (jd) 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 total of the soluble polyfunctional vinyl aromatic copolymer and (jd). That is, the content ratio of the soluble polyfunctional vinyl aromatic copolymer to the vinyl compounds (jd) 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 superior heat resistance and flame retardancy. This is believed to be because the curing reaction between the soluble polyfunctional vinyl aromatic copolymer and the vinyl compounds (jd) as the curable reactive resin proceeds favorably.

[0078] The curable resin composition of the present invention can be blended with a known flame retardant (1). The flame retardant (1) can further enhance the flame retardancy of the cured product of the curable resin composition. The flame retardant (1) 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.

[0079] The curable resin composition of the present invention can be blended with a known filler (m). Examples of the filler (m) include those added to enhance the heat resistance and flame retardancy of the cured product of the curable resin composition, and are not particularly limited. By incorporating the filler (m), 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. The filler 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 type, methacryloxysilane type, acryloxysilane type, and styrylsilane type silane coupling agents are preferred from the viewpoint of reactivity with the radical polymerization initiator (i). This increases the adhesive strength with the metal foil and the interlayer adhesive strength between resins. Instead of a method of pre-surface treating the filler (m), the silane coupling agent may be added by integral blending.

[0080] The content of the filler (m) 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 component such as the monomer and the flame retardant (l).

[0081] The curable resin composition of the present invention may further contain additives other than the flame retardant (l) and the filler (m). Examples of the additives include antifoaming agents such as silicone antifoaming agents and acrylate ester antifoaming agents, heat stabilizers, antistatic agents, ultraviolet absorbers, dyes and pigments, lubricants, dispersants such as wetting and dispersing agents, etc.

[0082] The curable resin composition of the present invention can be prepared into a varnish form 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 soluble polyfunctional vinyl aromatic copolymer, a radical polymerization initiator (i), and a solvent. If desired, it may contain a curable reactive resin (j), a thermoplastic resin (k), a flame retardant (l), a filler (m), 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 referred to here include printed wiring boards, printed circuit boards, flexible printed wiring boards, build-up wiring boards, etc.

[0083] The resin varnish is prepared, for example, as follows. First, components soluble in organic solvents, such as the soluble polyfunctional vinyl aromatic copolymer and the curable reactive resin (j), are added to the organic solvent and dissolved. Heating may be performed, if necessary. Then, if necessary, components insoluble in organic solvents, such as inorganic fillers, 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 soluble polyfunctional vinyl aromatic copolymer (j) and the like 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] The curable resin composition of the present invention is also useful as a curable composite material. A substrate is added to the curable composite material made from the curable resin composition of the present invention in order to increase the mechanical strength and dimensional stability.

[0088] As such a substrate, known materials are used, and examples thereof include 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 fiber, wholly aromatic polyester fiber, and polybenzozal fiber; woven or nonwoven fabrics obtained from synthetic fibers such as polyvinyl alcohol fiber, polyester fiber, and acrylic fiber; natural fiber fabrics such as cotton cloth, linen cloth, and felt; carbon fiber cloth; natural cellulose-based fabrics such as kraft paper, cotton paper, and paper-glass mixed fiber paper; and papers, which may be used alone or in combination of two or more kinds.

[0089] 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 proportion of the substrate is less than 5 wt %, the dimensional stability and strength of the composite material after curing will be insufficient, and if the proportion of the substrate is more than 90 wt %, the dielectric properties of the composite material will be poor, which is not preferred.

[0090] If necessary, a coupling agent can be used in the curable composite material 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.

[0091] A method for producing a curable composite material 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.

[0092] A cured composite material can be obtained by curing a curable composite material by heating or other methods. The production method is not particularly limited; for example, multiple sheets of 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 can also be performed separately. That is, an uncured or semi-cured composite material obtained in advance by laminate molding can be cured by heat treatment or another method.

[0093] The curing, or molding and curing, of the curable resin composition or curable composite material of the present invention can be carried out preferably at a temperature of 80 to 300°C, at a pressure of 0.1 to 1000 kg / cm2, and for a time period of 1 minute to 10 hours, more preferably at a temperature of 150 to 250°C, at a pressure of 1 to 500 kg / cm2, and for a time period of 1 minute to 5 hours.

[0094] The resin composition containing the soluble vinyl copolymer of the present invention can also be used in a laminate. Specifically, it is composed of a layer of the above-mentioned cured composite material and a layer of metal foil. Examples of the metal foil used here include copper foil and aluminum foil. The thickness is not particularly limited, but is in the range of 3 to 200 μm, more preferably 3 to 105 μm.

[0095] A method for producing a laminate can include, for example, laminating a 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 both a surface layer and an intermediate layer. It is also possible to create a multilayer structure by repeating lamination and curing multiple times.

[0096] Adhesives can be used to bond the metal foil. Examples of adhesives include, but are not limited to, epoxy, acrylic, phenolic, and cyanoacrylate adhesives. Lamination molding and curing can be carried out under the same conditions as those for producing the cured composite material of the present invention.

[0097] The curable resin composition of the present invention can be formed into a film by molding it into a film shape. The thickness of the film is not particularly limited, but is preferably in the range of 3 to 200 μm, more preferably 5 to 105 μm.

[0098] The method for producing the film is not particularly limited, and examples thereof 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 on a resin film such as a PET film, followed by drying. The coating can be repeated multiple times as necessary, and in this case, it is also possible to repeat the coating using multiple solutions with different compositions and concentrations, and adjust the final resin composition and resin amount to the desired one.

[0099] The resin-coated metal foil is composed of the curable resin composition of the present invention and a metal foil. Examples of the metal foil used here include copper foil and aluminum foil. The thickness of the metal foil is not particularly limited, but is preferably in the range of 3 to 200 μm, more preferably 5 to 105 μm.

[0100] The method for producing a resin-coated metal foil is not particularly limited, and examples thereof include a method in which a curable resin composition is uniformly dissolved or dispersed in an aromatic solvent, a ketone solvent, or a mixed solvent thereof, and then coated on a metal foil and dried.

[0101] The coating can be repeated multiple times as necessary. In this case, coating can be repeated using multiple solutions with different compositions and concentrations, and the final resin composition and resin amount can be adjusted to the desired one.

[0102] 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.

[0103] 1) Molecular Weight and Molecular Weight Distribution of Polymers The molecular weight and molecular weight distribution of polymers were measured using a Tosoh HLC-8320GPC, tetrahydrofuran as the solvent, a flow rate of 1.0 ml / min, a column temperature of 40°C, and a calibration curve based on monodisperse polystyrene. 2) Gas Chromatography The monomer consumption rate was quantified using a Shimadzu GC-2014 capillary column by the internal standard method. The monomer consumption rate was calculated from the difference between the initial and final reaction times, and the mole percent was calculated from the total amount of consumed monomer. 3) Evaluation of Dielectric Properties of Cured Products The dielectric properties of cured products obtained in the examples were evaluated. The measurement equipment used a Keysight Technologies network analyzer (E8363C) and split post dielectric resonators (SPDR) as the resonators. Measurements were performed in a 23°C / 50% humidity environment. 4) Polymer structure: Determined by C-NMR and H-NMR analysis using a JNM-ECZ400R / S1 manufactured by JEOL RESONANCE. Chloroform-d1 was used as the solvent, and the resonance line of tetramethylsilane was used as the internal standard. 5) Analysis of end groups: The end groups were calculated by calculating the amount of specific structural units introduced into the terminals from the C-NMR and H-NMR measurement results, as well as data on the total amount of each structural unit introduced into the copolymer obtained from GC analysis. The number of terminal groups of specific structural units contained in one molecule of the polyfunctional vinyl aromatic copolymer was calculated from the amount of specific structural units introduced into the terminals and the number average molecular weight obtained from the GPC measurement.

[0104] The monomers and solvents used were purchased as reagents. The radical polymerization initiator used in the blending was VR-110 (Fujifilm Wako Pure Chemical Industries, Ltd., azo-based polymerization initiator).

[0105] Example 1 Synthesis of Copolymer 1 In a 1000 mL reaction vessel, divinylbenzene (18 g; 0.14 mol), ethylvinylbenzene (15 g; 0.11 mol), Styrene (72 g; 0.69 mol), Toluene (358 g; 3.89 mol), Boron trifluoride diethyl ether complex (6 g), 1-phenylethanol (2 g; 0.02 mol), Water (0.7 g) was added and the reaction was carried out at 40°C for 4 hours. The polymerization solution was terminated with methanol and an 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. The amount of consumed monomer was quantified using gas chromatography to determine the molar ratio of units in the copolymer. The molar fraction of the terminal structure was determined using NMR as shown in Figure 1. Mn and Mw were calculated using GPC as shown in Figure 2. The results are shown in Table 1.

[0106] Example 2 Synthesis of Copolymer 2 Divinylbenzene (28 g), ethylvinylbenzene (17 g), styrene (115 g), toluene (119 g), boron trifluoride diethyl ether complex (5 g), 1-phenylethanol (10 g), and water (1.1 g) were placed in a 500 mL reaction vessel and reacted at 40°C for 4 hours. The polymerization solution was terminated with methanol and an aqueous sodium bicarbonate solution, and the oil layer was washed three times with pure water. The mixture was then devolatilized under reduced pressure at 40°C to recover the copolymer. The resulting copolymer was weighed to obtain Copolymer 2. The resulting Copolymer 2 was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0107] Example 3: Synthesis of Copolymer 3 Divinylbenzene (28 g), ethylvinylbenzene (17 g), styrene (115 g), toluene (119 g), boron trifluoride diethyl ether complex (3 g), 1-phenylethanol (2 g), and water (0.5 g) were added to a 500 mL reaction vessel and reacted at 40°C for 4 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 copolymer was recovered by devolatilization under reduced pressure at 40°C. The resulting copolymer was weighed to obtain Copolymer 3. The resulting Copolymer 3 was evaluated in the same manner as in Example 1. The results are shown in Table 1. The molar ratios of units in the copolymers were determined by quantifying the amount of consumed monomer using gas chromatography for the resulting Copolymers 1 to 3. The terminal groups represented by formulas (t2) and (t3) of the resulting Copolymers 1 to 3 have structures represented by the following formulas (t2-5) and (t3-5). In the formula, R11 and R12 are derived from the substituents of three compounds: styrene, ethylvinylbenzene, and divinylbenzene, and give a hydrogen atom, an ethyl group, and a vinyl group, respectively. Therefore, there are a total of nine possible structures for (t2-5). In the formula, R13 is a substituent derived from styrene, ethylvinylbenzene, or divinylbenzene, which gives a hydrogen atom, an ethyl group, or a vinyl group, respectively, so (t3-5) has three possible structures.

[0108] Comparative Example 1 Synthesis of Copolymer 4 Divinylbenzene (28 g), ethylvinylbenzene (17 g), styrene (115 g), n-propyl acetate (119 g), boron trifluoride diethyl ether complex (3 g), and water (0.05 g) were added to a 500 mL reaction vessel and reacted at 70°C for 4 hours. After the polymerization solution was terminated with an aqueous sodium bicarbonate solution, the oil layer was washed three times with pure water, and the copolymer was recovered by devolatilization under reduced pressure at 40°C. The resulting copolymer was weighed to obtain Copolymer 4. The resulting Copolymer 4 was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0109] Comparative Example 2 Synthesis of Copolymer 5 Divinylbenzene (28 g), ethylvinylbenzene (17 g), styrene (115 g), n-propyl acetate (119 g), boron trifluoride diethyl ether complex (5 g), 1-phenylethanol (10 g), and water (0.05 g) were added to a 500 mL reaction vessel and reacted at 70°C for 4 hours. The polymerization solution was terminated with an aqueous sodium bicarbonate solution, and the oil layer was washed three times with pure water. The mixture was then subjected to reduced pressure devolatilization at 40°C to recover the copolymer. The resulting copolymer was weighed to obtain Copolymer 5. The resulting Copolymer 5 was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0110] Comparative Example 3 Synthesis of Copolymer 6 Divinylbenzene (46 g), ethylvinylbenzene (2 g), styrene (13 g), toluene (150 g), n-propyl acetate (4 g), boron trifluoride diethyl ether complex (2 g), and benzyl alcohol (6 g) were added to a 500 mL reaction vessel and reacted at 50°C for 5 hours. After the polymerization solution was terminated with an aqueous sodium bicarbonate solution, the oil layer was washed three times with pure water, and the copolymer was recovered by devolatilization under reduced pressure at 40°C. The resulting copolymer was weighed to obtain Copolymer 6. The resulting Copolymer 6 was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0111] Comparative Example 4 Synthesis of Copolymer 7 Divinylbenzene (28 g), ethylvinylbenzene (17 g), styrene (115 g), toluene (119 g), boron trifluoride diethyl ether complex (5 g), and water (1.1 g) were added to a 500 mL reaction vessel and reacted at 40° C., but gelation occurred and Copolymer 7 could not be obtained.

[0112] Examples 4-6 and Comparative Examples 5-7: Copolymers 1-6 obtained in Examples 1-3 and Comparative Examples 1-3 were used, and VR-110 (polymerization initiator) was added to the mixture to a concentration of 0.5 wt% of the nonvolatile content. The mixture was then diluted with toluene to a nonvolatile content of 50% and shaken in a shaker for 10 minutes to obtain a uniform varnish. This varnish was cast onto a PET film and dried at 130°C for 10 minutes to obtain a film-like resin film. This resin film was then crushed and filled into a mold. A curing reaction was carried out using a vacuum press (Kitagawa Seiki KVHC-III) at 150°C for 30 minutes, then at 200°C for 45 minutes at a pressure of 4 MPa, yielding a plate-like cured product approximately 0.8 mm thick. The dielectric properties of the resulting cured product were evaluated. The results are shown in Tables 1 and 2.

[0113]

[0114]

[0115] In Examples 1 to 3, the use of 1-phenylethanol ensures that the molar fractions of the terminal groups (t2) and (t3) in formula (1) are 0.05 or more. However, in Comparative Examples 1 and 3, the hydroxyl group-containing cocatalyst (g) and aromatic solvent (h) in formula (2) are not used, so formula (1) is not satisfied. In Comparative Example 2, the aromatic solvent (h) is not used, so formula (1) is not satisfied. In Comparative Example 4, the hydroxyl group-containing cocatalyst (g) is not used, so the reaction cannot be controlled, gelation occurs, and no copolymer is obtained.

[0116] In Examples 4 to 6, the molar fraction of the terminal groups (t2) and (t3) in formula (1) was 0.05 or more, so the ratio (F2 - F1) / F1 of the dielectric loss tangent F1 after curing to the dielectric loss tangent F2 after heat treatment at 150°C for 24 hours was 3.0 or less, resulting in excellent dielectric properties, particularly improved resistance to oxidation degradation. On the other hand, in Comparative Examples 5 to 7, the molar fraction of the terminal groups (t2) and (t3) in formula (1) did not satisfy 0.05, so the ratio (F2 - F1) / F1 of the dielectric loss tangent F1 after curing to the dielectric loss tangent F2 after heat treatment at 150°C for 24 hours was 3.0 or more, resulting in degradation of the dielectric properties due to oxidation.

[0117] The polyfunctional vinyl aromatic copolymer of the present invention is useful for electrical insulating materials, particularly for printed circuit boards and electrical and electronic parts.

Claims

1. A vinyl copolymer containing structural units derived from a divinyl aromatic compound (a), styrene (b), and a monovinyl compound (c) other than styrene, which contains a structural unit represented by the following formula (t1) derived from the divinyl aromatic compound (a). In the formula, R1 represents an aromatic hydrocarbon group having 6 to 30 carbon atoms. The copolymer contains end groups represented by the following formulas (t2) and (t3) at its terminals. In the formulas, R2 and R3 each independently represent an aromatic hydrocarbon group having 6 to 30 carbon atoms. Z2 and Z3 each independently represent a vinyl group, a hydrogen atom, or a hydrocarbon group having 1 to 18 carbon atoms. In the formula, R4 and R5 represent an aromatic hydrocarbon group having 6 to 30 carbon atoms. Z4 and Z5 represent a vinyl group, a hydrogen atom, or a hydrocarbon group having 1 to 18 carbon atoms. The total molar fraction of the end groups derived from formulas (t2) and (t3) satisfies the following mathematical formula (1). A soluble polyfunctional vinyl aromatic copolymer, which is soluble in toluene, xylene, tetrahydrofuran, dichloroethane, or chloroform.

2. The soluble polyfunctional vinyl aromatic copolymer according to claim 1, having a number average molecular weight of 500 to 10,000 and a molecular weight distribution (Mw / Mn) represented by the ratio of the weight average molecular weight to the number average molecular weight of 40 or less.

3. A method for producing a polyfunctional vinyl aromatic copolymer by polymerizing a divinyl aromatic compound (a), styrene (b), and a monovinyl compound (c) other than styrene in the presence of a Lewis acid catalyst (f), a cocatalyst (g) containing a hydroxyl group, and an aromatic solvent (h), characterized in that the polymerization is carried out at a temperature of -20 to 120°C, which is the method for producing the soluble polyfunctional vinyl aromatic copolymer according to claim 1 or 2.

4. The method for producing a soluble polyfunctional vinyl aromatic copolymer according to claim 3, wherein the Lewis acid catalyst (f) is a metal fluoride or a complex thereof.

5. The method for producing a soluble polyfunctional vinyl aromatic copolymer according to claim 3, wherein the cocatalyst (g) containing a hydroxyl group is a compound of formula (2). R6 and R7 each independently represent an alkyl group having 1 to 30 carbon atoms or an aromatic hydrocarbon group having 6 to 30 carbon atoms. R8 represents hydrogen, an alkyl group having 1 to 30 carbon atoms, or an aromatic hydrocarbon group having 6 to 30 carbon atoms.

6. The method for producing a soluble polyfunctional vinyl aromatic copolymer according to claim 3, wherein the aromatic solvent (h) is a compound of formula (3). R9 and R10 each independently represent hydrogen or an alkyl group having 1 to 4 carbon atoms.

7. A curable resin composition characterized by containing the soluble polyfunctional vinyl aromatic copolymer according to claim 1 and a radical polymerization initiator.

8. A cured product obtained by curing the curable resin composition according to claim 7.

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