Polyfunctional vinyl aromatic copolymer, method for producing the same, and resin composition

Abstract

To provide a novel polyfunctional vinyl aromatic copolymer having excellent heat resistance and dielectric characteristics and a method for producing the same, and a curable resin composition comprising the copolymer.SOLUTION: A polyfunctional vinyl aromatic copolymer is provided by using a monovinyl aromatic compound (a) and a divinyl aromatic compound (b) as monomers, and an olefin compound (c) as a polymerization terminator, and has structures derived from these compounds (a), (b), and (c). The monovinyl aromatic compound includes a condensed polycyclic vinyl aromatic compound (a1) as an essential component. The copolymer has a structural unit derived from the divinyl aromatic compound (formula (1)). The terminal structure formed by the polymerization termination reaction has a specific structure.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a novel polyfunctional vinyl aromatic copolymer having improved heat resistance, compatibility, dielectric properties, damp heat reliability, and heat-resistant oxidation degradation properties, a method for producing the same, and a curable resin composition containing the copolymer.

Background Art

[0002] With the recent increase in information communication volume, information communication in high-frequency bands has become active. In order to reduce transmission loss in high-frequency bands, in particular, electrical insulating materials with low dielectric constant and low dielectric tangent are required. Furthermore, printed circuit boards or electronic components using these electrical insulating materials are exposed to high-temperature solder reflow during mounting, so materials with high heat resistance, that is, materials showing a high glass transition temperature, are desired. Especially recently, due to environmental problems, lead-free solder with a high melting point is used, so the demand for electrical insulating materials with higher heat resistance has been increasing. In response to these demands, conventionally, curable resins using vinyl compounds having various chemical structures have been proposed.

[0003] As such curable resins, for example, Patent Document 1 discloses a polyfunctional vinyl aromatic copolymer having an indane structure together with a structural unit derived from a monomer composed of a divinyl aromatic compound and a monovinyl aromatic compound. Patent Document 2 discloses a polyfunctional vinyl aromatic copolymer having a structural unit derived from a divinyl aromatic compound, styrene, and a monovinyl aromatic compound other than styrene, and a specific terminal group.

[0004] Since the polyfunctional vinyl aromatic copolymer obtained by these techniques itself has a polymerizable double bond, curing it gives a cured product having a high glass transition temperature. Therefore, it can be said that this cured product or polyfunctional vinyl aromatic copolymer is a polymer or its precursor having excellent heat resistance. And this polyfunctional vinyl aromatic copolymer copolymerizes with other radically polymerizable monomers to give a cured product, and this cured product also becomes a polymer having excellent heat resistance.

[0005] However, with the recent increase in communication speed, these polymers have insufficient dielectric properties, particularly dielectric loss tangent, and there is a market demand for materials with a lower dielectric loss tangent.

[0006] Patent Document 3 discloses a polyfunctional vinyl aromatic copolymer having structural units derived from a divinyl aromatic compound, a monovinyl aromatic compound, and an olefin-based compound containing an aromatic condensed ring structure as a polyfunctional resin. However, in the examples of this document, the olefin skeleton is randomly introduced into the molecule, and it is considered to have copolymerizability in the polymerization reaction and is not involved only in the terminal structure. Furthermore, since it has not been studied for electronic material applications, it is unclear whether it can be applied as a material for recent high-speed communication speeds.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a novel polyfunctional vinyl aromatic copolymer having excellent heat resistance and compatibility, and capable of providing a cured product or molded article with improved dielectric properties, particularly dielectric loss tangent, a method for producing the same, and a curable resin composition containing the copolymer.

Means for Solving the Problems

[0009] That is, the present invention is a polyfunctional vinyl aromatic copolymer using a monovinyl aromatic compound (a) and a divinyl aromatic compound (b) as monomers, and an olefin compound (c) as a polymerization terminator, and having a structure derived from these compounds (a), (b), and (c). The monovinyl aromatic compound contains a condensed polycyclic vinyl aromatic compound (a1) represented by the following formula as an essential component. The copolymer has a structural unit represented by the following formula (1) derived from the divinyl aromatic compound, and the terminal structure generated by the polymerization termination reaction has any one of the structures represented by formula (2), formula (3), and formula (4). [Chemical formula] (R2 is hydrogen or a hydrocarbon group having 1 to 5 carbon atoms, and n is an integer of 1 or 2) [Chemical formula] [Chemical formula] (R3 is hydrogen or CH3, and R4 is a hydrocarbon group having 1 to 18 carbon atoms) [Chemical formula] (R1 represents an aromatic hydrocarbon group having 6 to 30 carbon atoms) [Chemical formula] (n is an integer from 0 to 2, R2 is hydrogen or a hydrocarbon group having 1 to 5 carbon atoms, R3 is hydrogen or a methyl group, and R4 is a hydrocarbon group having 1 to 18 carbon atoms) [Chemical formula] (n is an integer from 0 to 2, R2 is hydrogen or a hydrocarbon group having 1 to 5 carbon atoms, R3 is hydrogen or a methyl group, and R4 is a hydrocarbon group having 1 to 18 carbon atoms) [Chemical formula] (n is an integer from 0 to 2, R2 is hydrogen or a hydrocarbon group having 1 to 5 carbon atoms, R3 is hydrogen or a methyl group, and R4 is a hydrocarbon group having 1 to 18 carbon atoms)

[0010] The present invention also relates to a method for producing a polyfunctional vinyl aromatic copolymer, which comprises dissolving a raw material containing a monovinyl compound (a), a divinyl compound (b), and an olefin compound (c) in a homogeneous solvent obtained by dissolving the raw material in an organic solvent having a dielectric constant of 2.0 to 15.0, and polymerizing the solution in the presence of a Lewis acid catalyst at a temperature of 0 to 120°C. In the above production method, the Lewis acid catalyst is preferably selected from any of BF3·diethyl ether complex, titanium chloride, and tin chloride.

Advantages of the Invention

[0011] The polyfunctional vinyl aromatic copolymer of the present invention or a cured product obtained from a material containing the same has improved heat resistance, compatibility, and dielectric properties. Further, according to the production method of the present invention, the above polyfunctional vinyl aromatic copolymer can be produced with high efficiency. Further, by using the polyfunctional vinyl aromatic copolymer of the present invention as a curable compound, since the cured product has a large free volume with a large molecular size and few polar groups in the molecule, a cured product with low dielectric properties can be obtained.

Embodiments for Carrying Out the Invention

[0012] The polyfunctional vinyl aromatic copolymer of the present invention contains structural units derived from a monovinyl aromatic compound (a) and a divinyl aromatic compound (b), and contains structural units derived from an olefin compound (c) which is a polymerization terminator at the end of the polymerization. The monovinyl aromatic compound (a) contains a condensed polycyclic vinyl aromatic compound (a1) as an essential component. This polyfunctional vinyl aromatic copolymer has a number average molecular weight Mn of 300 to 100,000, a molecular weight distribution (Mw / Mn) represented by the ratio of the weight average molecular weight Mw to the number average molecular weight Mn of 100 or less, and is soluble in solvents such as toluene, xylene, tetrahydrofuran, dichloroethane, or chloroform. The structural unit as used herein includes a repeating unit present in the main chain of the copolymer, a unit or end group present at the end or side chain.

[0013] The monovinyl aromatic compound (a) is not particularly limited as long as it is a compound having a vinyl group directly bonded to an aromatic ring, but a compound represented by the formula (a) is preferred.

Chemical formula

[0014] The aromatic hydrocarbon group having 6 to 30 carbon atoms is not particularly limited, but those obtained by removing one hydrogen atom from monocyclic aromatic compounds such as benzene, furan, pyrrole, thiophene, imidazole, pyrazole, oxazole, isoxazole, thiazole, isothiazole, pyridine, pyrimidine, pyridazine, pyrazine, triazine, etc., those obtained by removing one hydrogen atom from condensed-ring aromatic compounds such as naphthalene, anthracene, phenalene, phenanthrene, quinoline, isoquinoline, quinazoline, phthalazine, pteridine, coumarin, indole, benzimidazole, benzofuran, acridine, etc. are mentioned. Further, those obtained by combining a plurality of these aromatic compounds may also be used. For example, those obtained by removing two hydrogen atoms from ring-aggregated aromatic compounds such as biphenyl, binaphthalene, bipyridine, bithiophene, phenylpyridine, phenylthiophene, terphenyl, diphenylthiophene, quaterphenyl, etc. are mentioned. Preferably, they are benzene, naphthalene, biphenyl and anthracene.

[0015] The structural unit derived from the monovinyl aromatic compound (a) is 5 mol% or more and 90 mol% or less, preferably 10 mol% to 60 mol%, based on 100 mol% of the total of the structural units derived from (a), (b), and (c). When it is lower than 5 mol%, heat resistance is not exhibited. When it exceeds 90 mol%, the number of monomer units derived from other components, particularly the divinyl aromatic compound (b), is small, so that the crosslinking reaction hardly occurs and curability is not exhibited.

[0016] The monovinyl aromatic compound (a) contains a condensed polycyclic vinyl aromatic compound (a1) as an essential component. The condensed polycyclic vinyl aromatic compound (a1) is represented by the following formula (a1), is a compound having a condensed aromatic ring, and may have a substituent.

Chemical formula

[0017] The structural unit derived from the condensed polycyclic vinyl aromatic compound (a1) is 5 mol% or more, preferably 5 mol% or more and less than 98 mol%, more preferably 5 mol% or more and less than 70 mol% among the structural units derived from the monovinyl aromatic compound (a).

[0018] The divinyl aromatic compound (b) forms a branched structure and serves as a multifunctional component, and also serves as a crosslinking component for developing heat resistance when the obtained multifunctional vinyl aromatic copolymer is thermoset.

Chemical formula

[0019] The structural unit derived from the divinyl aromatic compound (b) is preferably contained in an amount of 2 mol% or more and less than 95 mol% based on 100 mol% of the total of the structural units derived from (a), (b) and (c). The structural unit derived from the divinyl aromatic compound (b) can have a plurality of structures such as those in which only one of the two vinyl groups has reacted and those in which two vinyl groups have reacted. Preferably, it contains 2 to 80 mol% of the repeating unit in which only one vinyl group has reacted. More preferably, it is 5 to 70 mol%, still more preferably 10 to 60 mol%, and particularly preferably 15 to 50 mol%. By setting it to 2 to 80 mol%, it has a low dielectric tangent, high toughness, excellent heat resistance, and excellent compatibility with other resins. Further, when it is made into a resin composition, it is excellent in hygrothermal resistance, heat-oxidation degradation resistance, and moldability. When it is less than 2 mol%, the heat resistance tends to decrease, and when it exceeds 80 mol%, the interlayer peel strength when formed into a laminate tends to decrease.

[0020] The polyfunctional vinyl aromatic copolymer is formed by a polymerization reaction of a monovinyl aromatic compound (a) and a divinyl aromatic compound (b), and particularly has a structural unit represented by the following formula (1) derived from the divinyl aromatic compound.

Chemical formula

[0021] In this polymerization reaction, an olefin compound (c) is used as a polymerization terminator.

Chemical formula

Chemical formula

Chem.

Chem.

[0022] This is due to the reactivity of the growth end derived from the olefin compound (c). Since the structure of the growth end formed by the olefin compound (c) added to the growth end is unstable, the termination reaction preferentially occurs rather than the polymerization reaction with other vinyl compounds. For this reason, the structure derived from the olefin compound (c) exists only at the polymerization end and is not included in the main chain skeleton, so it is considered to function as a polymerization terminator. The structural unit derived from this olefin compound (c) is contained in an amount of 5 mol% or more and less than 80 mol% based on the total 100 mol% of the structural units derived from (a), (b), and (c). When it contains 80 mol% or more, the molecular weight does not sufficiently increase, and many branched structures are formed, and other monomer components, particularly divinyl aromatic compounds, are not introduced, so the moldability is not exhibited. On the other hand, when it is less than 5 mol%, the molecular weight becomes too large, and as a result, the viscosity increases and the relatively non-polar olefin compound (c) decreases, so the dielectric properties deteriorate. The number of olefin compounds (c) present in the copolymer molecule is preferably 1.0 or more on average. If it is less than 1.0, there is a high possibility that no olefin compound is introduced as the terminal structure of the molecular chain. More preferably, it is 2.0 to 5.0, and still more preferably 2.5 to 4.0.

[0023] The polyfunctional vinyl aromatic copolymer preferably has a number average molecular weight (Mn: number average molecular weight in terms of standard polystyrene measured using gel permeation chromatography) of 300 to 100,000, more preferably 400 to 50,000, and still more preferably 500 to 10,000. When Mn is less than 300, the amount of the monofunctional copolymer component contained in the polyfunctional vinyl aromatic copolymer increases, so the heat resistance of the cured product tends to decrease. On the other hand, when Mn exceeds 100,000, gels are likely to be formed and the viscosity becomes high, so the molding processability tends to decrease. Also, the value of the molecular weight distribution (Mw / Mn) represented by the ratio of the weight average molecular weight (Mw: weight average molecular weight in terms of standard polystyrene measured using gel permeation chromatography) to Mn is 100.0 or less, preferably 50.0 or less, more preferably 1.5 to 30.0, and most preferably 2.0 to 20.0. When Mw / Mn exceeds 100.0, the processing characteristics of the polyfunctional vinyl aromatic copolymer tend to deteriorate and gels tend to occur.

[0024] The polyfunctional vinyl aromatic copolymer is soluble in toluene, xylene, tetrahydrofuran, dichloroethane, or chloroform as a solvent, and is preferably soluble in any of the above solvents. In order to be a polyfunctional copolymer soluble in a solvent, it is necessary that a part of the vinyl groups of divinylbenzene remains without crosslinking and has an appropriate degree of crosslinking. Here, being soluble in a solvent means that 5 g or more of the polyfunctional vinyl aromatic copolymer dissolves in 100 g of the above solvent, more preferably 30 g or more dissolves, and particularly preferably 50 g or more dissolves.

[0025] Next, a method for producing the polyfunctional vinyl aromatic copolymer of the present invention will be described. The above polyfunctional vinyl aromatic copolymer can be advantageously produced by the following production method. The manufacturing method is a method of polymerizing a monovinyl aromatic compound (a), a divinyl aromatic compound (b), and an olefin compound (c) in the presence of a Lewis acid catalyst at a temperature of -20 to 120°C, wherein the divinyl aromatic compound (b) is used in an amount of 2 mol% or more and less than 95 mol%, and the vinyl compound (a) is used in an amount of 5 mol% or more and less than 98 mol%, based on the total amount of (a), (b), and (c).

[0026] Among these, the monovinyl aromatic compound (a) contains a predetermined amount of a condensed polycyclic vinyl aromatic compound (a1) as an essential component. Among the monovinyl aromatic compound (a), the condensed polycyclic vinyl aromatic compound (a1) is preferably used in an amount of 5 mol% or more, more preferably 5 mol% or more and less than 98 mol%, and still more preferably 7 mol% or more and less than 70 mol%. By containing a predetermined amount of the condensed polycyclic vinyl aromatic compound (a1), heat resistance is imparted, and the reactivity is controlled by resonance stabilization of the growth terminal, and the polymerization reaction proceeds. Examples of the condensed polycyclic vinyl aromatic compound (a1) include 1-vinylnaphthalene, 2-vinylnaphthalene, ethylvinylnaphthalene (including each positional isomer or a mixture thereof), 2-vinylanthracene, 9-vinylanthracene, etc., and they can be used alone or in combination of two or more. Preferably, 2-vinylnaphthalene is used from the viewpoints of heat resistance and reactivity.

[0027] The monovinyl aromatic compound (a) other than the condensed polycyclic vinyl aromatic compound (a1) is not limited as long as it is an aromatic compound having one vinyl group. Examples thereof include vinyl aromatic compounds such as styrene, vinylbiphenyl, and vinyltriphenyl, and alkyl-substituted vinyl aromatic compounds such as o-methylstyrene, m-methylstyrene, p-methylstyrene, o,p-dimethylstyrene, o-ethylvinylbenzene, m-ethylvinylbenzene, p-ethylvinylbenzene, and p-tert-butylstyrene. Preferably, in order to prevent the gelation of the polyfunctional vinyl aromatic copolymer, have a high effect of improving solvent solubility and processability, low cost, and easy availability, ethyl vinylbenzene (including each positional isomer or a mixture thereof), ethyl vinylbiphenyl (including each positional isomer or a mixture thereof) are used. More preferably, from the viewpoints of dielectric properties and cost, ethyl vinylbenzene (m-isomer, p-isomer or a mixture of these positional isomers) is used.

[0028] The divinyl aromatic compound (b) plays a role in forming a branched structure and making it polyfunctional, and also plays a role as a crosslinking component for expressing heat resistance when the obtained polyfunctional vinyl aromatic copolymer is thermally cured. Examples of this divinyl aromatic compound are not limited as long as it is a compound having two vinyl groups, but divinylbenzene (including each positional isomer or a mixture thereof), divinylnaphthalene (including each positional isomer or a mixture thereof), divinylbiphenyl (including each positional isomer or a mixture thereof) are preferably used. Also, these can be used alone or in combination of two or more. As this divinyl aromatic compound (b), divinylbenzene (including each positional isomer or a mixture thereof) is preferably used from the viewpoints of solubility, heat resistance, and reactivity during curing.

[0029] The Lewis acid catalyst is a compound composed of a metal ion (acid) and a ligand (base), and can be used without particular limitation as long as it can receive an electron pair. Among them, from the viewpoint of the thermal decomposability of the obtained polyfunctional vinyl aromatic copolymer, metal fluorides or their complexes are preferred, and in particular, divalent to hexavalent metal fluorides, chlorides, or their complexes such as B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Ti, W, Zn, Fe, and V are preferred. These catalysts can be used alone or in combination of two or more. From the viewpoints of controlling the molecular weight and molecular weight distribution of the obtained polyfunctional vinyl aromatic copolymer and polymerization activity, boron trifluoride ether complex, titanium chloride, tin chloride are suitable, and further, boron trifluoride ether complex is most preferably used. Here, as the ether of the ether complex, there are diethyl ether, dimethyl ether, etc.

[0030] In the method for producing the polyfunctional vinyl aromatic copolymer of the present invention, one or more Lewis base compounds can be used as a cocatalyst. Specific examples of the Lewis base compound (g) include the following compounds. 1) Ester compounds such as ethyl acetate, propyl acetate, butyl acetate, phenyl acetate, and methyl propionate, 2) Thioester compounds such as methyl mercaptopropionic acid and ethyl mercaptopropionic acid, 3) Ketone compounds such as methyl ethyl ketone, methyl isobutyl ketone, and benzophenone , 4) Amine compounds such as methylamine, ethylamine, propylamine, butylamine, cyclohexylamine, methyl ethylamine, dimethylamine, diethylamine, dipropylamine, and dibutylamine, 5) Ether compounds such as diethyl ether and tetrahydrofuran, 6) Thioether compounds such as diethyl sulfide and diphenyl sulfide, and 7) Phosphine compounds such as tripropylphosphine, tributylphosphine, trihexylphosphine, tricyclohexylphosphine, trioctylphosphine, vinylphosphine, propenylphosphine, cyclohexenylphosphine, dialkenylphosphine, and trialkenylphosphine. Among these, from the viewpoint of synergistically acting with the Lewis acid catalyst and easily controlling the polymerization rate and the molecular weight distribution of the polymer, it is preferably one or more compounds selected from the group consisting of ester compounds, ketone compounds, ketone compounds, and ether compounds, and ester compounds and ketone compounds are more preferably used. These Lewis base compounds can be used alone or in combination of two or more.

[0031] The Lewis base compound (g) is preferably 0.1 to 1000 mol, more preferably 1.0 to 500 mol, and particularly preferably 10 to 200 mol, based on 100 mol of the total monomer components. Within the above range, the polymerization rate is appropriately maintained, while the selectivity of the reaction between monomers is improved, resulting in excellent productivity. At the same time, excessive increase or decrease in molecular weight is suppressed, and a polyfunctional vinyl aromatic copolymer with excellent moldability can be obtained.

[0032] In this polymerization reaction, a solvent can be added as needed. The solvent is a compound that does not substantially inhibit cationic polymerization and can dissolve the Lewis acid catalyst, Lewis base compound, monomer components, and the resulting polyfunctional vinyl aromatic copolymer to form a homogeneous solution. An aromatic organic solvent with a dielectric constant in the range of 2 to 15 is preferred and can be used alone or in combination of two or more. If the dielectric constant of the solvent is less than 2, the molecular weight distribution becomes broad, which is not preferred. If it exceeds 15, the polymerization rate decreases.

[0033] From the perspective of the balance between polymerization activity and solubility, the organic solvent is preferably an aromatic compound, and toluene and xylene are particularly preferred. This is because after the olefin compound is added to the polymerization terminal in the polymerization reaction, an addition reaction to the aromatic compound occurs, causing a termination reaction. Since this reaction is necessary for controlling the molecular weight, the amount of the solvent used is determined such 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%, considering the viscosity of the resulting polymerization solution and the ease of heat removal. If this concentration is less than 1 wt%, an increase in cost is caused due to low polymerization efficiency. If it exceeds 90 wt%, the molecular weight and molecular weight distribution of the resulting polyfunctional vinyl aromatic copolymer increase, leading to a decrease in moldability.

[0034] When producing a polyfunctional vinyl aromatic copolymer, it is necessary to polymerize 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. When the polymerization temperature exceeds 120°C, the selectivity of the reaction decreases, resulting in problems such as an increase in the molecular weight distribution and the generation of gels. When polymerization is carried out below -20°C, the catalytic activity significantly decreases, so it is necessary to add a large amount of catalyst.

[0035] After the polymerization reaction is stopped, the method for recovering the polyfunctional vinyl aromatic copolymer is not particularly limited. For example, commonly used methods such as heat concentration method, steam stripping method, precipitation in a poor solvent, etc. can be used.

[0036] The polyfunctional vinyl aromatic copolymer obtained by the above production method contains a repeating unit derived from the monovinyl aromatic compound (a) in an amount of 5 mol% or more and less than 98 mol%, a structural unit derived from the divinyl aromatic compound (b) in an amount of 2 mol% or more and less than 95 mol%, a structural unit derived from the olefin compound (c) in an amount of 2 mol% or more and less than 95 mol%, has a structural unit represented by the above formula (1) derived from the divinyl aromatic compound, and the terminal structure generated by the polymerization termination reaction has any of the structures represented by the above formulas (2), (3), and (4). And Mn is 300 to 100,000, Mw / Mn is 100 or less, and it is soluble in toluene, xylene, tetrahydrofuran, dichloroethane, or chloroform.

[0037] 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 (also referred to as a radical polymerization catalyst). As the radical polymerization initiator, for example, the curable resin composition of the present invention undergoes a crosslinking reaction and cures by means such as heating as described later. In this case, a radical polymerization initiator is contained for the purpose of lowering the reaction temperature or promoting the crosslinking reaction of unsaturated groups.

[0038] As the radical polymerization initiator, known substances are used. Typical 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-butyl cumyl peroxide, α,α'-bis(t-butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, dicumyl peroxide, di-t-butyl peroxydiisophthalate, t-butyl peroxybenzoate, 2,2-bis(t-butylperoxy)butane, 2,2-bis(t-butylperoxy)octane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, di(trimethylsilyl) peroxide, trimethylsilyl triphenylsilyl peroxide, etc., and azo compounds such as 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]·tetrahydrate, 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2'-azobis[2-(2-imidazolin-2-yl)propane], dimethyl 2,2'-azobis(2-methylpropionate), 2,2'-azobis(2,4,4-trimethylpentane), 2,2'-azobis(N-butyl-2-methylpropionamide), 1,1'-azobis(cyclohexane-1-carbonitrile), dimethyl 1,1'-azobis(1-cyclohexanecarboxylate), 2,2'-azobis(isobutyronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), etc., but are not limited thereto. Also, although it is not a peroxide or an azo compound, 2,3-dimethyl-2,3-diphenylbutane can also be used as the radical polymerization initiator (h). Among these, α,α'-bis(t-butylperoxy-m-isopropyl)benzene and 2,2'-azobis(2,4,4-trimethylpentane) are preferably used. α,α'-bis(t-butylperoxy-m-isopropyl)benzene has a relatively high reaction start temperature.Therefore, it is possible to suppress the acceleration of the curing reaction at the time when curing is not necessary, such as during prepreg drying, and it is possible to suppress the deterioration of the storage stability of the curable resin composition of the present invention. Further, α,α'-bis(t-butylperoxy-m-isopropyl)benzene has low volatility, so it does not volatilize during prepreg drying or storage, and has good stability. 2,2'-azobis(2,4,4-trimethylpentane) is composed of only hydrocarbon radicals generated, so a cured product excellent in the dielectric properties of the cured product, particularly the dielectric loss tangent, can be obtained. These radical polymerization initiators may be used alone or in combination of two or more.

[0039] The blending amount of the radical polymerization initiator (h) 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 above-mentioned polyfunctional vinyl aromatic copolymer. If it is within this range, the reaction proceeds well without inhibiting the curing reaction.

[0040] A known curable reaction type resin or thermoplastic resin can be blended in the above-mentioned curable resin composition. Examples of the curable reaction type resin include, in addition to the thermosetting resin, a resin or compound that copolymerizes with the polyfunctional vinyl aromatic copolymer to give a cured resin. For example, vinyl ester resin, polyvinyl benzyl resin, unsaturated polyester resin, curable vinyl resin, curable polyphenylene ether-based resin, maleimide resin, epoxy resin, polyisocyanate resin, phenol resin, and one or more vinyl compounds having one or more polymerizable unsaturated hydrocarbon groups in the molecule can be mentioned. Examples of the thermoplastic resin include polystyrene, polyphenylene ether resin, polyetherimide resin, polyethersulfone resin, PPS resin, polycyclopentadiene resin, polycycloolefin resin, and 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, or rubbers such as polybutadiene and polyisoprene. As the curable reactive resin, from the viewpoints of dielectric properties, heat resistance, adhesion, and compatibility with the polyfunctional vinyl aromatic copolymer as a curable resin composition, preferably, polyvinylbenzyl resin, curable vinyl resin, curable polyphenylene ether-based resin, epoxy resin, and one or more vinyl compounds having one or more polymerizable unsaturated hydrocarbon groups in the molecule can be mentioned. As the thermoplastic resin, 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 can be mentioned. More preferably, as the curable reactive resin, polyvinylbenzyl resin, curable polyphenylene ether-based resin, epoxy resin, and one or more vinyl compounds having one or more polymerizable unsaturated hydrocarbon groups in the molecule can be mentioned. As the thermoplastic resin, polyphenylene ether resin and hydrogenated styrene-butadiene copolymer can be mentioned.

[0041] Known flame retardants can be incorporated into the curable resin composition of the present invention. The flame retardant can further enhance the flame retardancy of the cured product of the curable resin composition. The flame retardant is not particularly limited. Specifically, in fields where halogen-based flame retardants such as bromine-based flame retardants are used, for example, ethylenedipentabromobenzene, ethylenebistetrabromoimide, decabromodiphenyl oxide, and tetradecabromodiphenoxybenzene having a melting point of 300 °C or higher are preferred. By using a halogen-based flame retardant, it is considered that the desorption of halogen at high temperatures can be suppressed and a decrease in heat resistance can be suppressed. In addition, in fields where halogen-free is required, phosphate ester-based flame retardants, phosphazene-based flame retardants, and phosphinate-based flame retardants can be mentioned. Specific examples of phosphate ester-based flame retardants include condensed phosphate esters of dixylenyl phosphate. Specific examples of phosphazene-based flame retardants include phenoxyphosphazene. Specific examples of phosphinate-based flame retardants include, for example, metal phosphinates such as aluminum dialkylphosphinate salts. Each of the exemplified flame retardants may be used alone or in combination of two or more.

[0042] Known fillers can be incorporated into the curable resin composition of the present invention. Examples of the filler 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. Further, by containing the filler, the heat resistance, flame retardancy, etc. can be further enhanced. Specifically, 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 can be mentioned. Among these, silica, mica, and talc are preferred, and spherical silica is more preferred. Also, one of these may be used alone, or two or more of them may be used in combination. Further, they may be used as they are, or those surface-treated with a silane coupling agent such as an epoxy silane type or an amino silane type may be used. From the viewpoint of reactivity with a radical polymerization initiator, vinyl silane type, methacryloxy silane type, acryloxy silane type, and styryl silane type silane coupling agents are preferred as this silane coupling agent. Thereby, the adhesive strength with the metal foil and the interlayer adhesive strength between the resins are increased. Further, instead of the method of surface-treating the filler in advance, the above silane coupling agent may be added and used by the integral blend method.

[0043] The content of the filler is preferably 10 to 200 parts by mass, and more preferably 30 to 150 parts by mass, based on 100 parts by mass in total of the organic components such as monomers and the flame retardant.

[0044] The curable resin composition of the present invention may further contain additives other than the flame retardant and the filler. Examples of the additives include defoaming agents such as silicone-based defoaming agents and acrylate-based defoaming agents, heat stabilizers, antistatic agents, ultraviolet absorbers, dyes and pigments, lubricants, and dispersants such as wetting dispersants.

Examples

[0045] Next, the present invention will be described by way of examples, but the present invention is not limited thereto. All parts in each example are by weight. The physical property measurements in the examples were carried out by the methods shown below.

[0046] 1) Molecular weight and molecular weight distribution of the polymer The measurement of the molecular weight and molecular weight distribution of the polymer was carried out using HLC-8320GPC manufactured by Tosoh Corporation, with tetrahydrofuran as the solvent, a flow rate of 1.0 ml / min, a column temperature of 40 °C, and a calibration curve using monodisperse polystyrene. 2) Glass transition temperature (Tg) of the cured product The glass transition temperature was measured in the compression mode of TMA for sample pieces cut into about 2 mm□ using the cured product obtained from the example. The measurement conditions were carried out for 2 cycles under a nitrogen stream at 20 °C - 200 °C and a heating rate of 10 °C / min, and the glass transition temperature was determined from the change in the linear expansion coefficient (change points of α1 and α2) in the second cycle. 3) Gas chromatography The consumption rate of the monomer was quantified by the internal standard method using GC-2014 manufactured by Shimadzu Corporation and a capillary column. The monomer consumption rate was calculated from the difference between the initial and end of the reaction, and the mol% was calculated from the total amount of the consumed monomer. 4) Evaluation of dielectric properties of the cured product The evaluation of the dielectric properties was carried out using the cured product obtained from the example. The measuring device used was a network analyzer, Keysight Technologies network analyzer (E8363C), and a split post dielectric resonator (SPDR) was used as the resonator, and the measurement was carried out in an environment of 23 °C and 50%.

[0047] Example 1 As the monomer 2-vinylnaphthalene 23.1 g (0.15 mol),

Chemical formula

[0048] Example 2 As monomers, 30.8 g (0.20 mol) of 2-vinylnaphthalene, 65.1 g (0.50 mol) of divinylbenzene, 38.2 g (0.29 mol) of ethylvinylbenzene, 17.2 g (0.17 mol) of styrene, 94.4 g (0.84 mol) of diisobutylene as a polymerization terminator, 20.4 g (0.20 mol) of n-propyl acetate as a solvent, and 138.2 g (1.5 mol) of toluene were put into a 1 L separable flask equipped with a stirring blade, a reflux tube, a nitrogen introduction tube, and a thermocouple. After heating to 70°C, 1.51 mL (12 mmol) of boron trifluoride-diethyl ether complex was added and reacted for 5 hours. After stopping the polymerization solution with an aqueous sodium hydrogen carbonate solution, the oil layer was washed 3 times with pure water, and 441 g of a copolymer varnish was obtained by devolatilization under reduced pressure with an evaporator at 40°C. The obtained copolymer varnish was evaluated in the same manner as in Example 1.

[0049] Comparative Example 1 As monomers, 52.1 g (0.40 mol) of divinylbenzene, 30.6 g (0.23 mol) of ethylvinylbenzene, 38.9 g (0.37 mol) of styrene, 94.4 g (0.84 mol) of diisobutylene as a polymerization terminator, 20.4 g (0.20 mol) of n-propyl acetate as a solvent, and 138.2 g (1.5 mol) of toluene were charged into a 1 L separable flask equipped with a stirring blade, a reflux tube, a nitrogen inlet tube, and a thermocouple. After heating to 70 °C, 1.51 mL (12 mmol) of boron trifluoride-diethyl ether complex was added and reacted for 6 hours. After terminating the polymerization solution with an aqueous sodium hydrogen carbonate solution, the oil layer was washed 3 times with pure water and devolatilized under reduced pressure using an evaporator at 40 °C to obtain 414 g of a copolymer varnish. The obtained copolymer varnish was evaluated in the same manner as in Example 1.

[0050] Regarding Examples 1 and 2, since the number of olefin compounds in the molecule is from 2.6 to 3.2, the branching is considered to be about 1 to 3, and the olefin compound is considered to be introduced at the end of the molecular chain. On the other hand, in Comparative Example 1, since it is less than 0.9 and 1, it is considered that there is a structure in which no olefin compound is introduced at the end of the molecular chain. Also, regarding Examples 1 and 2, the glass transition temperature exceeds 90 °C, and among the dielectric properties, the dielectric loss tangent is 0.001 or less, achieving both excellent heat resistance and dielectric properties. On the other hand, regarding Comparative Example 1, the dielectric loss tangent among the dielectric properties exceeds 0.001, and furthermore, the glass transition temperature is below 80 °C, so the dielectric properties are insufficient and the heat resistance is also poor.

[0051]

Table 1

Claims

1. A polyfunctional vinyl aromatic copolymer having structures derived from a monovinyl aromatic compound (a), a divinyl aromatic compound (b) as monomers, and an olefin compound (c) as a polymerization terminator, wherein the monovinyl aromatic compound contains a condensed polycyclic vinyl aromatic compound (a1) represented by the following formula as an essential component, the copolymer has a structural unit represented by the following formula (1) derived from the divinyl aromatic compound, and the terminal structure formed by the polymerization termination reaction has any one of the structures represented by formula (2), formula (3), and formula (4). 【Chemical 1】 (R2 is hydrogen or a hydrocarbon group having 1 to 5 carbon atoms, and n is an integer from 1 to 2) 【Chemical 2】 【Chemical Formula 3】 (R3 is hydrogen or CH3, and R4 is a hydrocarbon group having 1 to 18 carbon atoms) [Chemical Formula 4] (R1 represents an aromatic hydrocarbon group having 6 to 30 carbon atoms) 【Chemical Formula 5】 (n is an integer from 0 to 2, R2 is hydrogen or a hydrocarbon group having 1 to 5 carbon atoms, R3 is hydrogen or a methyl group, and R4 is a hydrocarbon group having 1 to 18 carbon atoms) 【Chemical Formula 6】 (n is an integer from 0 to 2, R2 is hydrogen or a hydrocarbon group having 1 to 5 carbon atoms, R3 is hydrogen or a methyl group, and R4 is a hydrocarbon group having 1 to 18 carbon atoms) 【Chemical Formula 7】 (n is an integer from 0 to 2, R2 is hydrogen or a hydrocarbon group having 1 to 5 carbon atoms, R3 is hydrogen or a methyl group, and R4 is a hydrocarbon group having 1 to 18 carbon atoms)

2. The polyfunctional vinyl aromatic copolymer according to claim 1, wherein the structural unit derived from the condensed polycyclic vinyl aromatic compound (a1) is 5 mol% or more of the structural units derived from the monovinyl aromatic compound (a).

3. The polyfunctional vinyl aromatic copolymer according to claim 1, wherein the number average molecular weight Mn is 300 to 100,000, and the molecular weight distribution (Mw / Mn) represented by the ratio of the weight average molecular weight Mw to the number average molecular weight Mn is 100 or less.

4. The polyfunctional vinyl aromatic copolymer according to claim 1, wherein the olefin compound (c) as a polymerization terminator has 5 or more carbon atoms.

5. A method for producing the polyfunctional vinyl aromatic copolymer according to any one of claims 1 to 4, characterized in that a raw material containing a monovinyl aromatic compound (a), a divinyl aromatic compound (b), and an olefin compound (c) is polymerized at a temperature of 0 to 120°C in the presence of a Lewis acid catalyst in a homogeneous solvent obtained by dissolving the raw material in an organic solvent having a dielectric constant of 2.0 to 15.

0.

6. The method for producing a polyfunctional vinyl aromatic copolymer according to claim 5, wherein the Lewis acid catalyst is selected from any one of BF3·diethyl ether complex, titanium chloride, and tin chloride.

7. The method for producing a polyfunctional vinyl aromatic copolymer according to claim 5, wherein the organic solvent for polymerization is an aromatic compound.

8. A resin composition containing a curable resin and a radical polymerization initiator, wherein the curable resin contains the polyfunctional vinyl aromatic copolymer according to claim 1.

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