WO2025182560A1 - Polyfunctional vinyl aromatic copolymer, method for producing same, curable resin composition and cured product of same - Google Patents

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

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

With the recent increase in the volume of information and communication, high-frequency data communication has become increasingly common. This has created a demand for electrical insulating materials with superior electrical properties, particularly low dielectric constants and low dielectric dissipation factors, to reduce transmission loss in high-frequency bands.

Conventionally, thermosetting resins such as phenolic resins, epoxy resins, and polyimide resins have been used for printed wiring boards. Although these resins have a good balance of various performance characteristics, they have insufficient dielectric properties in the high frequency range. As a new material that solves this problem, a resin composition containing a radical polymerizable compound and an epoxy resin has been disclosed (Patent Documents 1 and 2).
However, the resin compositions disclosed in Patent Documents 1 and 2, which contain an epoxy resin and a radically polymerizable compound, undergo crosslinking reactions independently, resulting in the formation of two types of three-dimensional networks in the cured product. This causes phase separation in the cured product, leading to insufficient crosslink density and making it difficult to achieve high mechanical properties. This has led to the problem of being unable to increase the blending amount of vinyl resin, which has excellent dielectric properties.

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 gives 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. This polyfunctional vinyl aromatic copolymer is then copolymerized with other radically polymerizable monomers to give a cured product, and this cured product also becomes a polymer with excellent heat resistance. However, this copolymer is a compound that only has radical polymerizability and does not react with epoxy resins.

Patent No. 7263069 JP 2015-48458 A International Publication No. 2018/181842

The present invention aims to provide a novel polyfunctional vinyl aromatic copolymer, which can improve reactivity and produce cured products or molded articles with improved uniformity and mechanical properties, by studying compositions of vinyl resins, particularly those containing epoxy resins, and a method for producing the same.

In order to solve the above-mentioned problems, the inventors conducted extensive research and discovered that a novel polyfunctional vinyl aromatic copolymer containing specific active ester groups can improve reactivity in resin compositions with epoxy resins and the like, improve the uniformity of the cured product, and also achieve excellent mechanical properties, leading to the completion of the present invention.

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).

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, 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) below 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.
In the production method, the Lewis acid catalyst (f) is preferably a metal fluoride or a complex thereof.

Furthermore, the present invention provides a curable resin composition comprising a polyfunctional vinyl aromatic copolymer and a radical polymerization initiator.
The present invention also provides a curable resin composition comprising a polyfunctional vinyl aromatic copolymer and an epoxy resin, the epoxy resin preferably having two or more epoxy groups in one molecule.

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

1 is an IR chart of the polyfunctional vinyl aromatic copolymer of Example 1. 1 is a GPC chart of the polyfunctional vinyl aromatic copolymer of Example 1.

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).
The number average molecular weight Mn is 300 to 100,000, the molecular weight distribution (Mw/Mn) expressed as the ratio of the weight average molecular weight Mw to the number average molecular weight Mn is 100 or less, and the polymer is soluble in a solvent.
The structural units referred to in this specification include repeating units present in the main chain of the copolymer and units or terminal groups present at the terminals or side chains.

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

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.

The structural units derived from the monovinyl aromatic compound (c) do not act as cross-linking components with vinyl groups and epoxy groups, but are used to adjust the active ester equivalent and vinyl equivalent to any desired value, thereby contributing to the development of moldability.

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 a variety of forms, such as structures in which two vinyl groups have reacted singly or doubly.
Among these, it is preferable that the repeating unit represented by formula (a1) in which only one vinyl group has reacted is contained in 2 to 80 mol %. It is more preferably 5 to 70 mol %, even more preferably 10 to 60 mol %, and particularly preferably 15 to 50 mol %. By adjusting it to 2 to 80 mol %, the resin 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, resistance to thermal oxidative degradation, and moldability. If it is less than 2 mol %, heat resistance tends to decrease, and if it exceeds 80 mol %, the interlayer peel strength when formed into a laminate tends to decrease.

The structural units derived from the ester group-containing vinyl aromatic compound (b) represented by formula (1) account for 2 mol% or more and less than 93 mol% of the total 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 tends to decrease when formed into a laminate. 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).

The structural units derived from the monovinyl aromatic compound (c) account for 5 mol% or more and less than 96 mol% of the total structural units derived from (a), (b), and (c). It is preferably 10% to 80%, and more preferably 15% to 70%. If the molar fraction of 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.

The active ester equivalent (g/eq) of the polyfunctional vinyl aromatic copolymer is preferably 150 to 6,000, more preferably 200 to 5,000, even more preferably 250 to 4,000, and particularly preferably 250 to 3,000.
The vinyl equivalent (g/eq) of the polyfunctional vinyl aromatic copolymer is preferably 200 to 5,000, more preferably 250 to 4,000, even more preferably 300 to 3,000, and particularly preferably 350 to 1,500.

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, and the heat resistance of the cured product tends to decrease. If Mn is more than 100,000, gel tends to be easily formed and the viscosity increases, and therefore moldability tends to decrease.
The molecular weight distribution (Mw/Mn), which is the ratio of the weight average molecular weight (Mw: weight average molecular weight in terms of standard polystyrene measured by 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.

The polyfunctional vinyl aromatic copolymer is soluble in a solvent. It is particularly soluble in organic solvents such as toluene, xylene, tetrahydrofuran, dichloroethane, or chloroform, and is preferably soluble in all of these solvents. In order for the copolymer to be soluble in a solvent and polyfunctional, some of the vinyl groups in the divinylbenzene must remain uncrosslinked, resulting in an appropriate degree of crosslinking. Here, "soluble in a solvent" means that 5 g or more of the polyfunctional vinyl aromatic copolymer can be dissolved in 100 g of solvent, more preferably 30 g or more, and particularly preferably 50 g or more.

Next, the method for producing the 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,
The copolymer contains 2 mol % or more and less than 95 mol % of a divinyl aromatic compound (a) relative to the total of (a), (b), and (c), 2 mol % or more and less than 93 mol % of a vinyl aromatic compound (b) represented by formula (1), and 5 mol % or more and less than 96 mol % of a monovinyl aromatic compound (c), and the copolymerization is carried out at a temperature of -20 to 120°C.

The divinyl aromatic compound (a) plays a role in forming a branched structure to impart multifunctionality, and also plays a role as a crosslinking component to impart heat resistance when the resulting 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 each positional isomer or a mixture thereof), divinylnaphthalene (including each positional isomer or a mixture thereof), and divinylbiphenyl (including each positional isomer or a mixture 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 these positional isomers) is more preferred.

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.

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.

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.

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, as well as to introduce vinyl groups to the terminals of the polyfunctional vinyl aromatic copolymer.

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

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 other monomer components (d) into the polyfunctional vinyl aromatic copolymer, as long as the effects of the present invention are not impaired.

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.
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 %.

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

The proportions of the essential monomer components (a), (b), and (c) used are such that, relative to the total of (a), (b), and (c), the divinyl aromatic compound (a) is used in an amount of 2 mol% or more but 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 but less than 93 mol%, and the monovinyl aromatic compound (c) is used in a total amount of 5 mol% or more but less than 96 mol%, and these monomer components (a), (b), and (c) are polymerized at a temperature of -20 to 120°C.

The amount of the divinylaromatic compound (a) to be blended 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 %.

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 them, from the viewpoint of the 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. Here, examples of ethers for the ether complex include diethyl ether and dimethyl ether.
The Lewis acid catalyst (f) is preferably used in an amount within the range of 0.001 to 100 moles, more preferably 0.01 to 50 moles, per 100 moles of the total 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. 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.

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 the Lewis base compound 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, as 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.

During the polymerization reaction, the Lewis base compound coordinates with the counter anion, the Lewis acid catalyst (f), thereby controlling the interaction between the active species, the carbocation, and the counter anion, thereby adjusting the relative reaction frequency between the monomers (a), (b), and (c), which also function as chain transfer agents. Typically, the addition of a Lewis base compound strengthens the interaction between the active species, the carbocation, and the counter anion, thereby suppressing excessive insertion reactions of the monomers (a), (b), and (c) and facilitating chain transfer reactions after the insertion reaction of the monomers (a), (b), and (c), making it easier to control the molecular weight.

In addition to Lewis base compounds, compounds containing hydroxyl groups can also be used as co-catalysts. It is believed that the co-catalyst containing hydroxyl groups reacts with the Lewis acid catalyst (f) during the polymerization reaction to generate carbocations, which are active species, and react with the vinyl groups of the monomers (a), (b), and (c), thereby causing the polymerization reaction to proceed. The co-catalyst containing hydroxyl groups may be used alone or in combination with a Lewis base compound.
Specific examples of the co-catalyst containing a hydroxyl group include alcohol compounds represented by the following formula (2): 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, and 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 of two or more.

When a Lewis base compound is used, the amount of the co-catalyst (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 all monomer components. When a hydroxyl group-containing co-catalyst is used, the amount is preferably 0.1 to 1,000 mol, more preferably 0.5 to 500 mol, and particularly preferably 1 to 200 mol, per 100 mol 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 also suppressing excessive increase or decrease in molecular weight, thereby obtaining a polyfunctional vinyl aromatic copolymer with excellent moldability.

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.

If desired, a solvent can be added. The solvent is a compound that does not essentially inhibit cationic polymerization and dissolves the Lewis acid catalyst (f), co-catalyst (g), monomer components, and the resulting 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.
As the organic solvent, from the viewpoint of the balance between polymerization activity and solubility, toluene, xylene, n-hexane, cyclohexane, methylcyclohexane, or ethylcyclohexane is particularly preferred. 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%, 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.

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

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.

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 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 (h) may be used alone or in combination of two or more types.
The amount of the radical polymerization initiator (h) to be added is preferably in the range of 0.01 to 10 parts by weight, more preferably in the range of 0.1 to 8 parts by weight, based on 100 parts by weight of the polyfunctional vinyl aromatic copolymer. Within this range, the curing reaction proceeds smoothly without being inhibited.

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.

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

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 radical polymerization initiators include the substances mentioned above.

The resin composition of the present invention containing the polyfunctional vinyl aromatic copolymer and an epoxy resin may further contain an organic base. By including an organic base, the curing reaction with the epoxy groups 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 types selected from the group consisting of amine-based curing accelerators, organic phosphorus-based curing accelerators, and imidazole-based curing accelerators, which are conventionally known as curing accelerators for epoxy resins.

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 added is preferably in the range of 0.01 to 10 parts by weight, more preferably in the range of 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 in the range of 0.1 to 8 parts by weight, per 100 parts by weight of the resin component in the resin composition.

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. There are no particular restrictions on the epoxy resin curing agent, and any curing agent generally known as an epoxy resin curing agent can be used. From the perspective 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 types.

Active ester curing agents are preferred from the viewpoint of achieving a low dielectric constant and a low dielectric loss tangent, and examples thereof include 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, and 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 the carboxylic acid compound 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, dicyclopentadienyldiphenol, and phenol novolak.

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.

In terms 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 resin, curable vinyl resin, curable polyphenylene ether resin, 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, 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 curable reactive resins 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 thermoplastic resin (j) include polyphenylene ether resin and hydrogenated styrene-butadiene copolymer.

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. It is even more preferably a modified polyphenylene ether compound containing an unsaturated hydrocarbon group. It is also preferably a modified polyphenylene ether compound whose terminals are modified with a substituent having a carbon-carbon unsaturated double bond. It is most preferably 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, and is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1.5 to 3, from the viewpoint of the balance between the heat resistance of the cured product and the storage stability and flowability of the curable resin composition.

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).
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.

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 restrictions. In other words, (id) may be any compound that can form crosslinks and harden by reacting with the polyfunctional vinyl aromatic copolymer of the present invention. It is more preferable that the polymerizable unsaturated hydrocarbon group is a carbon-carbon unsaturated double bond, and more preferable is a compound having two or more carbon-carbon unsaturated double bonds in the molecule.

The vinyl compounds 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, (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, if 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, and specific examples include values measured using gel permeation chromatography (GPC).

The average number of carbon-carbon unsaturated double bonds (number of terminal double bonds) per molecule of vinyl compounds used 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 low, it tends to be difficult to obtain sufficient heat resistance for the cured product. On the other hand, if the number of terminal double bonds is too high, the reactivity may become too high, which may result in problems such as reduced shelf life or reduced fluidity of the curable resin composition.

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 (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 effectively form crosslinks during the curing reaction, 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. Compounds 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).

The content of the polyfunctional vinyl aromatic copolymer is preferably 30 to 90 parts by mass, and more preferably 50 to 90 parts by mass, per 100 parts by mass of the polyfunctional vinyl aromatic copolymer and the vinyl compounds (id) serving as the curable reactive resin. The content of the vinyl compounds (id) serving as the curable reactive resin is preferably 10 to 70 parts by mass, and 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) serving as the curable reactive resin is preferably 90:10 to 30:70, and more preferably 90:10 to 50:50, by mass. A content satisfying the above ratio results in a curable resin composition with superior heat resistance and flame retardancy of the cured product. This is thought to be due to the favorable curing reaction between the polyfunctional vinyl aromatic copolymer and the vinyl compounds (id) serving as the curable reactive resin.

A known flame retardant (k) can be blended into the curable resin composition of the present invention. 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. It is believed that the use of a halogen-based flame retardant can suppress elimination of halogen at high temperatures, thereby suppressing a decrease in heat resistance.
In fields where halogen-free flame retardants are required, phosphate ester flame retardants, phosphazene flame retardants, and phosphinate flame retardants are exemplified. A specific example of a phosphate ester flame retardant is a condensed phosphate ester of dixylenyl phosphate. A specific example of a phosphazene flame retardant is phenoxyphosphazene. A specific example of a phosphinate flame retardant is a metal phosphinate salt of an aluminum dialkylphosphinate. Each of the exemplified flame retardants may be used alone or in combination of two or more.

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 type, methacryloxysilane type, acryloxysilane type, and styrylsilane type silane coupling agents 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 a method 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.

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

When producing a prepreg, the curable resin composition of the present invention can be prepared into a varnish form to be used as a resin varnish for the purpose of impregnating a substrate (fibrous substrate) for forming a prepreg, or for the purpose of using the composition 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.

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 an 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 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.

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. For example, 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 circuit board varnish and drying it under heat to obtain a prepreg, which can then be laminated alone or with metal foil such as copper foil and hot-press molded.

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

The curable resin composition of the present invention can be used by laminating it with metal foil (which includes metal plate; the same applies hereinafter), similar to the cured composite material described below.

Next, the curable composite material of the curable resin composition of the present invention and its cured product will be described. A base material is added to the curable composite material of the curable resin composition of the present invention in order to increase the mechanical strength and dimensional stability.
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.
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.
In the curable composite material of the present invention, a coupling agent can be used, if necessary, 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.

One example of a method for producing the curable composite material of the present invention is to uniformly dissolve or disperse 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, impregnate the substrate, and then dry it. Impregnation is carried out by immersion (dipping), coating, etc. 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 resin composition and resin amount to be adjusted to the desired level.

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 another 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 separately. That is, an uncured or semi-cured composite material obtained by prior 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 can be carried out preferably at a temperature of 80 to 300°C, at a pressure of 0.1 to 1000 kg/ ^cm2 , for a time 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 , for a time of 1 minute to 5 hours.

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 of the metal foil is not particularly limited, but is in the range of 3 to 200 μm, more preferably 3 to 105 μm.
A method for producing the laminate of the present invention can include, for example, laminating a curable composite material obtained from the curable resin composition of the present invention and a substrate, and a metal foil in a layer configuration appropriate for the purpose, and then bonding the layers together under heat and pressure while simultaneously thermally curing. In a laminate of the curable resin composition of the present invention, the cured composite material and the 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.
Adhesives can be used to bond the metal foil, including, but not limited to, epoxy, acrylic, phenolic, and cyanoacrylate adhesives.
Lamination and curing can be carried out under conditions similar to those used to produce the cured composite material of the present invention.

The curable resin composition of the present invention can be formed into a film, which is one form of the curable resin composition of the present invention. 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.
The method for producing the film of the present invention 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 onto a resin film such as a PET film, followed by drying. The coating can be repeated multiple times as necessary, and in this case, coating can be repeated using multiple solutions with different compositions and concentrations, allowing adjustment to the final desired resin composition and resin amount.

The resin-coated metal foil of the present invention is composed of the curable resin composition of the present invention and a metal foil, such as copper foil or aluminum foil.
There are no particular limitations on the thickness, but it 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 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 the metal foil and dried. 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.

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. that 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 automobile industry, etc. In particular, it can be used as single-sided, double-sided, and multilayer printed circuit boards, flexible printed circuit boards, build-up boards, etc.
The compounds can be applied to 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, anti-fogging agents, rust inhibitors, anti-staining agents, disinfectants, insect repellents, medical materials, flocculants, surfactants, lubricants, binders for solid fuels, conductive treatment agents, resin modifiers, asphalt modifier plasticizers, sintering binders, etc.

The curable resin composition of the present invention retains high dielectric properties (low dielectric constant and low dielectric dissipation factor) even after severe thermal history, and provides a cured product with high adhesion reliability even in 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, meeting the strong demand for smaller and thinner products in recent years. Furthermore, due to its excellent wiring embedding flatness and excellent adhesion to dissimilar materials, it is possible to realize a curable resin composition, cured product, or material containing the same that has excellent reliability.

The present invention will now be described with reference to examples, but is not limited to these examples. In each example, all parts are by weight.
The physical properties in the examples were measured by the following methods.

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 K 0070. Specifically, a sample was dissolved in THF and reacted with a 0.5 mol/L ethanol solution of potassium hydroxide, and then neutralization titration was performed with 0.5 mol/L hydrochloric acid using phenolphthalein as an indicator to test the ester value.
4) Vinyl equivalent: Measurement was performed with reference to JIS K0070. Specifically, the sample was reacted with Wiess's solution (iodine monochloride solution) and left in a dark place. After that, excess iodine chloride was 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
The cured resin molded to a thickness of 2 mm was processed into a test piece (length 60 mm x width 10 mm). The dynamic viscoelasticity was measured using a dynamic viscoelasticity measuring device (Hitachi High-Technologies 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 A cured resin molded to a thickness of 2 mm was processed into a test piece (length 100 mm x width 10 mm), and the flexural properties of the resin test piece were measured using a universal testing machine (AGS-X manufactured by Shimadzu Corporation) equipped with a 1000 N load cell. The flexural modulus of elasticity and stress at the breaking point of the test piece were measured using a three-point bending jig under an environment of a temperature of 23°C and a humidity of 50% RH.
7) Measurement of Haze of Cured Product A cured resin molded to a thickness of 0.7 mm was cut into a 50 mm x 50 mm piece, and the haze value was measured using a spectrophotometer (CM-5 manufactured by Konica Minolta, Inc.).

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 mol (15 g) of 1-phenylethanol as a cocatalyst, 250 g of toluene, and 7.9 g of a boron trifluoride diethyl ether complex as a catalyst were added to a 1.0 L reactor, and the reaction was carried out for 6 hours at 40° C. After the polymerization solution was terminated with methanol and an aqueous sodium bicarbonate solution, the oil layer was washed three times with pure water and devolatilized under reduced pressure at 40° C. to obtain Copolymer 1.
Copolymer 1 obtained in Example 1 was confirmed by NMR measurement to have a structural unit represented by formula (b1). Furthermore, the active ester equivalent and vinyl equivalent were measured, and as a result, 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.

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 added to a 1.0 L reactor and reacted for 8 hours at 70° C. After the polymerization solution was terminated with methanol and an aqueous sodium bicarbonate solution, the oil layer was washed three times with pure water and devolatilized under reduced pressure at 40° C. to obtain Copolymer 2.

Examples 3 to 5
Using the amounts (parts) of each raw material shown in Table 1, the same procedure as in Example 1 was carried out to obtain Copolymer 3, Copolymer 4, and Copolymer 5.

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.
The copolymers obtained in Examples 1 to 5 and Comparative Example 1 were measured for various physical properties, and the results are shown in Table 1.

 

Next, examples of cured products with epoxy resins will be described. 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.)

[Synthesis Example 1: Active ester curing agent]
A reactor equipped with a stirrer, thermometer, nitrogen inlet, dropping funnel, and condenser was charged with 165 parts of phenolized 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 activated ester resin in the form of a toluene solution with a nonvolatile content of 65% was obtained. The active ester equivalent calculated from the amount of raw materials charged was 220 g/eq.

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

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.

Examples 7 to 12, Comparative Examples 2 to 4
A cured product was obtained using the formulation 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 product were measured, and the results are shown in Table 2.

 

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

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 (9)

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). The polyfunctional vinyl aromatic copolymer according to claim 1, having an active ester equivalent of 150 to 6,000 g/eq. and a vinyl equivalent of 200 to 5,000 g/eq. A curable resin composition comprising the polyfunctional vinyl aromatic copolymer of claim 1 and a radical polymerization initiator. A resin composition comprising the polyfunctional vinyl aromatic copolymer of claim 1 and an epoxy resin. A curable resin composition comprising the polyfunctional vinyl aromatic copolymer according to claim 1 and a curable reactive resin, a thermoplastic resin, or a flame retardant or filler. A cured product obtained by curing the curable resin composition described in any one of claims 3 to 5. The method for producing a polyfunctional vinyl aromatic copolymer according to claim 1, characterized in that the polymerization is carried out at a temperature of -20 to 120°C, using 2 mol% or more and less than 95 mol% of the divinyl aromatic compound (a), 2 mol% or more and less than 93 mol% of the ester group-containing vinyl aromatic compound (b) represented by formula (1), and 5 mol% or more and less than 96 mol% of the monovinyl aromatic compound (c), relative to the total of (a), (b), and (c). 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. 8. 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.