JP7631797B2 - Curable resin, curable resin composition, and cured product - Google Patents

Description

The present invention relates to a curable resin having a specific structure, a curable resin composition containing the curable resin, and a cured product obtained from the curable resin composition.

As the volume of information and communication traffic has increased in recent years, information and communication in the high frequency band has become more prevalent, and there is a demand for electrical insulating materials with better electrical properties, particularly low dielectric constants and low dielectric tangents, to reduce transmission loss in the high frequency band.

Furthermore, printed circuit boards and electronic components that use these electrical insulating materials are exposed to high-temperature solder reflow during installation, so materials with excellent heat resistance and a high glass transition temperature are required. In particular, lead-free solder with a high melting point has recently been used from the perspective of environmental issues, so there is an increasing demand for electrical insulating materials with higher heat resistance.

In response to these demands, vinyl group-containing curable resins with various chemical structures have been proposed. Examples of such curable resins include divinylbenzyl ether of bisphenol and polyvinylbenzyl ether of novolac (see, for example, Patent Documents 1 and 2). However, these vinylbenzyl ethers cannot give a cured product with sufficiently small dielectric properties, and the obtained cured product has problems in being used stably in high frequency bands, and furthermore, divinylbenzyl ether of bisphenol does not have sufficiently high heat resistance.

In order to improve the dielectric properties of vinylbenzyl ethers with the above-mentioned improved properties, several polyvinylbenzyl ethers with specific structures have been proposed (see, for example, Patent Documents 3 to 9). However, although attempts have been made to suppress the dielectric tangent and improve the heat resistance, the improvements in these properties are still not sufficient, and further improvements in properties are desired.

As described above, conventional vinyl group-containing curable resins, including polyvinyl benzyl ether, do not provide cured products that have both the low dielectric tangent required for electrical insulating material applications, particularly for high-frequency electrical insulating material applications, and the heat resistance required for lead-free solder processing.

Japanese Unexamined Patent Publication No. 63-68537 Japanese Unexamined Patent Publication No. 64-65110 Special Publication No. 1-503238 Japanese Patent Application Publication No. 5-43623 Japanese Patent Application Publication No. 6-172242 Japanese Patent Application Publication No. 9-31006 JP 2005-281618 A JP 2005-314556 A JP 2015-030776 A JP 2015-189925 A

The problem that this invention aims to solve is therefore to provide a cured product with excellent heat resistance (high glass transition temperature) and low dielectric properties by using a curable resin with a specific structure.

The inventors conducted extensive research to solve the above problems and discovered that a curable resin that can contribute to heat resistance and low dielectric properties, and a cured product obtained from a curable resin composition containing the curable resin, have excellent heat resistance and low dielectric properties, and thus completed the present invention.

That is, the present invention relates to a curable resin represented by the following general formula (1).
(In the formula, Ra and Rb each independently represent an alkyl group, an aryl group, an aralkyl group, or a cycloalkyl group having 1 to 12 carbon atoms. Rc and Rd each independently represent a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, or a cycloalkyl group having 1 to 12 carbon atoms. X represents a vinylbenzyl ether group, a (meth)acryloyloxy group, or an allyl ether group. m represents an integer of 0 to 3.)

In the curable resin of the present invention, the above general formula (1) is preferably represented by the following general formula (2).

The present invention relates to a curable resin composition containing the curable resin.

The present invention relates to a cured product obtained by subjecting the curable resin composition to a curing reaction.

The curable resin of the present invention can contribute to heat resistance and low dielectric properties, so that the cured product obtained from the curable resin composition containing the curable resin has excellent heat resistance and low dielectric properties (particularly low dielectric tangent), and is useful.

The present invention is described in detail below.

<Curable Resin>
The present invention relates to a curable resin represented by the following general formula (1):
(In the formula, Ra and Rb each independently represent an alkyl group, an aryl group, an aralkyl group, or a cycloalkyl group having 1 to 12 carbon atoms. Rc and Rd each independently represent a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, or a cycloalkyl group having 1 to 12 carbon atoms. X represents a vinylbenzyl ether group, a (meth)acryloyloxy group, or an allyl ether group. m represents an integer of 0 to 3.)

In the above general formula (1), Ra and Rb each independently represent an alkyl group, an aryl group, an aralkyl group, or a cycloalkyl group having 1 to 12 carbon atoms, and are preferably an alkyl group, an aryl group, or a cycloalkyl group having 1 to 12 carbon atoms. When Ra and Rb are an alkyl group having 1 to 12 carbon atoms, the molecular mobility of the polar group derived from the crosslinking group (X) is restricted, and the dielectric tangent is lowered, which is preferable.

In the above general formula (1), m represents an integer of 0 to 3, and is preferably an integer of 1 to 2. When m is within the above range, the planarity in the vicinity of the benzene ring in the above general formula (1) is reduced, and the reduced crystallinity improves the solvent solubility and lowers the melting point, making this a preferred embodiment.

In the above general formula (1), Rc and Rd each independently represent hydrogen, an alkyl group having 1 to 12 carbon atoms, an aryl group, an aralkyl group, or a cycloalkyl group, and are preferably hydrogen, an alkyl group having 1 to 12 carbon atoms, an aryl group, or a cycloalkyl group. When Rc and Rd are hydrogen or the like, the compound has a structure consisting of only hydrogen atoms or hydrogen atoms and carbon atoms (hydrocarbon group), which is non-polar, and the dielectric constant and dielectric tangent of the obtained cured product are low, which is a preferred embodiment.

In the above general formula (1), X is a vinylbenzyl ether group, a (meth)acryloyloxy group, or an allyl ether group, preferably a vinylbenzyl ether group or a (meth)acryloyloxy group, more preferably a methacryloyloxy group or a vinylbenzyl ether group, and particularly preferably a vinylbenzyl ether group. By having the crosslinking group (X) in the curable resin, a cured product having a low dielectric tangent is obtained, which is a preferred embodiment. Although the detailed reason is not clear, in the present invention, the vinylbenzyl ether group is preferred because it can obtain a cured product having a lower dielectric tangent compared to other crosslinking groups (e.g., a (meth)acryloyloxy group or an allyl ether group).
In addition, the crosslinking group X is also a polar group, but the adjacent substituents Ra and Rb (particularly the Ra) cause steric hindrance, suppressing the molecular mobility of X, and lowering the dielectric tangent of the resulting cured product, which is a preferred embodiment. In addition, the crosslinking group (X) located at the center of the curable resin also suppresses the molecular mobility of X due to the adjacent substituent Rd and a structure containing it, which lowers the dielectric tangent of the resulting cured product, which is a preferred embodiment.

When the number of crosslinking groups (X) in the curable resin is 3, multiple crosslinking groups are present, increasing the crosslinking density. In particular, the crosslinking groups (X) are evenly arranged, resulting in uniform crosslinking points and high crosslinking density, and therefore the resulting cured product has excellent heat resistance and is preferable. Note that when the number of crosslinking groups (X) is less than 3, the heat resistance decreases, which is problematic in practical use, and when the number of crosslinking groups (X) is more than 3, the crosslinking density increases, making the molded product (cured product) brittle, which is not preferable.

In the curable resin of the present invention, the general formula (1) is preferably represented by the following general formula (2): In the curable resin represented by the general formula (1), Rc is a methyl group and Rd is hydrogen, whereby the polarity of the entire molecular structure is suppressed, and the dielectric constant and dielectric loss tangent of the obtained cured product are reduced, which is a preferred embodiment.

In addition, in the above general formula (2), the same symbols, the same substituents, and the same functional groups (X, Ra, Rb, and m) as those in the above general formula (1) are considered to be common.

<Method for producing intermediate phenol compound>
As a method for producing the curable resin, first, a method for producing an intermediate phenol compound, which is a raw material (precursor) of the curable resin, will be described below.

As a method for producing the intermediate phenol compound, a diol phenol compound represented by the following general formula (3-1), a divinyl phenol compound represented by the following general formula (3-2) (hereinafter, sometimes referred to as "compound (a)"), and a phenol derivative represented by the following general formula (4) (hereinafter, sometimes referred to as "compound (b)") are mixed and reacted in the presence of an acid catalyst to obtain an intermediate phenol compound represented by the following general formula (5).

In the above general formula (3-1), Re each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an aryl group, an aralkyl group, or a cycloalkyl group, and is preferably a hydrogen atom, a methyl group, or an ethyl group. When Re is a hydrogen atom, a methyl group, an ethyl group, or the like, the purity of the intermediate phenol compound obtained is high, which is a preferred embodiment.

In the above general formulas (3-1), (3-2), (4), and (5), the same symbols, the same substituents, and the same functional groups (Ra, Rb, Rc, Rd, and m) as those in the above general formula (1) are considered to be common.

Specific examples of the compound (a) include 2,6-di(hydroxymethyl)phenol, 2,6-di(methoxymethyl)phenol, 2,6-divinyl-4-methyl)phenol, and phenol compounds in which the hydrogen at the 4th position of the phenol compound such as the 2,6-di(hydroxymethyl)phenol is replaced with a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a cyclopentyl group, a cyclohexyl group, a phenyl group, chlorine, or bromine. These compounds (a) may be used alone or in combination of two or more. Among them, from the viewpoint of industrial availability, examples of the compound (a) include 2,6-di(hydroxymethyl)phenol and 2,6-di(hydroxymethyl)-p-cresol, and it is more preferable to use 2,6-di(hydroxymethyl)-p-cresol.

The compound (b) is not particularly limited, but specific examples thereof include cresols such as o-cresol, m-cresol, and p-cresol; xylenols such as 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol (2,6-dimethylphenol), 3,4-xylenol, 3,5-xylenol, and 3,6-xylenol; 2,3,5-trimethylphenol and 2,3,6-trimethylphenol; ethylphenols such as o-ethylphenol (2-ethylphenol), m-ethylphenol, and p-ethylphenol; butylphenols such as isopropylphenol, butylphenol, and p-t-butylphenol; alkylphenols such as p-pentylphenol, p-octylphenol, p-nonylphenol, and p-cumylphenol; and mono-substituted phenols such as o-phenylphenol, p-phenylphenol, 2-cyclohexylphenol, and 2-benzylphenol. These compounds (b) may be used alone or in combination of two or more. Among these, from the viewpoint of ease of industrial availability, it is more preferable to use, for example, xylenol or 2,6-xylenol as compound (b).

In the method for producing the intermediate phenol compound, the compound (a) and the compound (b) are charged in a molar ratio of the compound (b) to the compound (a) (compound (b)/compound (a)) of preferably 2.5/1 to 1.05/1, more preferably 2/1 to 1.1/1, and reacted in the presence of an acid catalyst to obtain the intermediate phenol compound, which is the reaction product (c) between the compound (a) and the compound (b).

Examples of acid catalysts used in the reaction include inorganic acids such as phosphoric acid, hydrochloric acid, and sulfuric acid; organic acids such as oxalic acid, benzenesulfonic acid, toluenesulfonic acid, methanesulfonic acid, and fluoromethanesulfonic acid; solid acids such as activated clay, acid clay, silica alumina, zeolite, and strongly acidic ion exchange resins; and heteropolyacid salts. However, it is preferable to use homogeneous catalysts such as oxalic acid, benzenesulfonic acid, toluenesulfonic acid, methanesulfonic acid, and fluoromethanesulfonic acid, which can be easily removed by neutralization with a base and washing with water after the reaction.

The amount of the acid catalyst is in the range of 0.001 to 40 parts by mass per 100 parts by mass of the total amount of the raw materials (a) and (b) initially charged, but from the standpoint of ease of handling and economy, 0.001 to 25 parts by mass is preferred.

The reaction temperature is usually in the range of 40 to 80°C, but in order to suppress the formation of isomeric structures, avoid side reactions such as thermal decomposition, and obtain a high-purity intermediate phenol compound, a temperature of 40 to 45°C is preferred.

The reaction time is usually in the range of 0.5 to 24 hours in total under the above reaction temperature conditions, but is preferably in the range of 0.5 to 15 hours in total, since the reaction does not proceed completely if it is short and side reactions such as thermal decomposition of the product occur if it is long.

In the method for producing the intermediate phenol compound, the raw material may also serve as the solvent, so it is not necessary to use another solvent, but it is possible to use a solvent. In addition, a method may be adopted in which the solvent (e.g., methanol, etc.) generated during the reaction is distilled off before the reaction is carried out within the above reaction temperature range.

Organic solvents used to synthesize the intermediate phenolic compound include ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, cyclohexanone, acetophenone, etc.; alcohols such as 2-ethoxyethanol, methanol, etc.; aprotic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, acetonitrile, sulfolane, etc.; cyclic ethers such as dioxane, tetrahydrofuran, etc.; esters such as ethyl acetate, butyl acetate, etc.; aromatic solvents such as benzene, toluene, xylene, etc.; and these may be used alone or in combination.

<Method for producing curable resin>
The method for producing the curable resin (introduction of a vinylbenzyl ether group, a (meth)acryloyloxy group, or an allyl ether group into an intermediate phenol compound) will be described below.

The curable resin can be obtained by a known method such as reacting the intermediate phenol compound (reaction product (c)) with (meth)acrylic anhydride, (meth)acrylic acid chloride, chloromethylstyrene, chlorostyrene, allyl chloride, allyl bromide, or the like (hereinafter sometimes referred to as "compound (d)") in the presence of a basic or acidic catalyst. By reacting these, a crosslinking group (X) can be introduced into the intermediate phenol compound, and the compound becomes thermosetting with a low dielectric constant and low dielectric tangent, which is a preferred embodiment.

As the compound (d) (functions as a crosslinking group introduction agent), the (meth)acrylic anhydride is acrylic anhydride, methacrylic anhydride, the (meth)acrylic chloride is acrylic chloride, methacrylic chloride, the chloromethylstyrene is, for example, p-chloromethylstyrene (4-chloromethylstyrene) and m-chloromethylstyrene, the chlorostyrene is, for example, p-chlorostyrene and m-chlorostyrene, the allyl chloride is, for example, 3-chloro-1-propene, and the allyl bromide is, for example, 3-bromo-1-propene. These may be used alone or in combination. Among them, it is preferable to use methacrylic anhydride, methacrylic chloride, p-chlorostyrene, m-chlorostyrene, etc., since a cured product with a lower dielectric tangent can be obtained, and it is particularly preferable to use p-chloromethylstyrene.

Specific examples of the basic catalyst include dimethylaminopyridine, alkaline earth metal hydroxides, alkali metal carbonates, and alkali metal hydroxides.Specific examples of the acidic catalyst include sulfuric acid and methanesulfonic acid.Dimethylaminopyridine is particularly excellent in terms of catalytic activity.

The reaction between the intermediate phenol compound and the compound (d) can be carried out by adding 1 to 10 moles of the compound (d) per mole of hydroxyl groups contained in the intermediate phenol compound, and reacting for 1 to 40 hours at a temperature of 30 to 150°C while adding 0.01 to 0.2 moles of a basic catalyst all at once or gradually.

In addition, the reaction rate in the synthesis of the curable resin can be increased by using an organic solvent in the reaction with the compound (d) (introduction of a crosslinking group). Such organic solvents are not particularly limited, but examples thereof include ketones such as acetone and methyl ethyl ketone, alcohols such as methanol, ethanol, 1-propyl alcohol, isopropyl alcohol, 1-butanol, secondary butanol, and tertiary butanol, cellosolves such as methyl cellosolve and ethyl cellosolve, ethers such as tetrahydrofuran, 1,4-dioxane, 1,3-dioxane, and diethoxyethane, aprotic polar solvents such as acetonitrile, dimethyl sulfoxide, and dimethylformamide, and toluene. These organic solvents may be used alone, or two or more of them may be used in combination as appropriate to adjust the polarity.

After the reaction with compound (d) (introduction of a crosslinking group) is completed, the reaction product is reprecipitated in a poor solvent, and the precipitate is stirred in the poor solvent at a temperature of 20 to 100°C for 0.1 to 5 hours, filtered under reduced pressure, and then dried at a temperature of 40 to 80°C for 1 to 10 hours to obtain the desired curable resin. Examples of poor solvents include hexane.

The curable resin of the present invention is characterized by containing a curable resin having the structure of the above general formula (1) (or (2)). Even if the above manufacturing method contains a structure other than the above general formula (1) (or (2)) as a side reaction, there is no particular problem as long as it does not affect the properties of the curable resin in the present invention.

<Curable resin composition>
The present invention relates to a curable resin composition containing the curable resin. The curable resin can contribute to heat resistance and low dielectric properties, so that a cured product obtained by using the curable resin composition containing the curable resin has excellent heat resistance and low dielectric properties, which is a preferred embodiment.

[Other resins, etc.]
In the curable resin composition of the present invention, in addition to the curable resin, other resins, curing agents, curing accelerators, etc. can be used without particular limitation within the scope of not impairing the object of the present invention. As described later, the curable resin can obtain a cured product by heating or the like without blending a curing agent, but for example, when blending other resins, etc., they can be used by blending a curing agent, a curing accelerator, etc.
The curable resin composition of the present invention contains the curable resin. However, among the curable resins, when X is an allyl ether group, unlike when X is a vinylbenzyl ether group or a (meth)acryloyloxy group, the curable resin cannot homopolymerize (crosslink) (cannot obtain a cured product by itself), and therefore, when X is an allyl ether group, it is necessary to use a curing agent, a curing accelerator, or the like.

[Other resins]
Examples of the other resins that can be added include alkenyl group-containing compounds such as bismaleimides, allyl ether compounds, allyl amine compounds, triallyl cyanurate, alkenyl phenol compounds, vinyl group-containing polyolefin compounds, etc. In addition, other thermosetting resins such as thermosetting polyimide resins, epoxy resins, phenolic resins, active ester resins, benzoxazine resins, cyanate resins, etc. can also be appropriately blended depending on the purpose.

[Hardening agent]
Examples of the curing agent include amine compounds, amide compounds, acid anhydride compounds, phenol compounds, cyanate ester compounds, etc. These curing agents may be used alone or in combination of two or more kinds.

[Curing Accelerator]
As the curing accelerator, various types can be used, for example, phosphorus compounds, tertiary amines, imidazoles, organic acid metal salts, Lewis acids, amine complex salts, etc. In particular, when used as a semiconductor encapsulation material, phosphorus compounds such as triphenylphosphine or imidazoles are preferred because of their excellent curability, heat resistance, electrical properties, moisture resistance reliability, etc. These curing accelerators can be used alone or in combination of two or more.

[Flame retardant]
The curable resin composition of the present invention may contain a flame retardant as necessary to exhibit flame retardancy, and among these, it is preferable to contain a non-halogen flame retardant that does not substantially contain halogen atoms. Examples of the non-halogen flame retardant include phosphorus-based flame retardants, nitrogen-based flame retardants, silicone-based flame retardants, inorganic flame retardants, and organic metal salt-based flame retardants, and these flame retardants may be used alone or in combination of two or more kinds.

[Filler]
The curable resin composition of the present invention may contain an inorganic filler as required. Examples of the inorganic filler include fused silica, crystalline silica, alumina, silicon nitride, and aluminum hydroxide. When the amount of the inorganic filler is particularly large, it is preferable to use fused silica. The fused silica may be either crushed or spherical, but in order to increase the amount of fused silica and suppress the increase in the melt viscosity of the molding material, it is preferable to mainly use spherical silica. In order to further increase the amount of spherical silica, it is preferable to appropriately adjust the particle size distribution of the spherical silica. In addition, when the curable resin composition is used for applications such as a conductive paste described in detail below, a conductive filler such as silver powder or copper powder can be used.

[Other compounding agents]
To the curable resin composition of the present invention, various compounding agents such as a silane coupling agent, a release agent, a pigment, an emulsifier, etc. may be added, if necessary.

<Cured Product>
The present invention relates to a cured product obtained by subjecting the curable resin composition to a curing reaction. The curable resin composition can be obtained by uniformly mixing the curable resin alone or the curable resin and each component such as the curing agent described above, and can be easily cured by a method similar to a conventionally known method. Examples of the cured product include molded cured products such as laminates, cast products, adhesive layers, coatings, and films.

The curing reaction includes heat curing and ultraviolet curing reactions. Heat curing reactions are easily carried out without a catalyst, but if you want to make the reaction faster, it is effective to add a polymerization initiator such as an organic peroxide or an azo compound, or a basic catalyst such as a phosphine compound or a tertiary amine. Examples include benzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile, triphenylphosphine, triethylamine, imidazoles, etc.

<Applications>
The cured product obtained by the curable resin composition of the present invention has excellent heat resistance and low dielectric properties, and therefore can be suitably used for heat-resistant members and electronic members. In particular, it can be suitably used for prepregs, circuit boards, semiconductor encapsulants, semiconductor devices, build-up films, build-up boards, adhesives, resist materials, etc. It can also be suitably used for matrix resins of fiber-reinforced resins, and is particularly suitable as highly heat-resistant prepregs. In addition, the curable resin contained in the curable resin composition exhibits excellent solubility in various solvents, and can be made into paint. The heat-resistant members and electronic members thus obtained can be suitably used for various applications, such as industrial machine parts, general machine parts, automobile, railway, vehicle parts, space and aviation related parts, electronic and electrical parts, building materials, containers and packaging parts, daily necessities, sports and leisure goods, and housing parts for wind power generation, but are not limited thereto.

The present invention will be described in detail below with reference to examples and comparative examples. "Parts" and "%" are by weight unless otherwise specified. A curable resin and a cured product obtained by using the curable resin were synthesized under the conditions shown below, and the obtained cured product was measured and evaluated under the conditions shown below.

< ^1H -NMR measurement>
¹ H-NMR: “JNM-ECA400” manufactured by JEOL RESONANCE
Magnetic field strength: 400MHz
Number of times accumulated: 16 Solvent: chloroform-d1
Sample concentration: 1% by mass
From the results of the ¹ H-NMR chart, a peak derived from the target product was confirmed, and it was confirmed that the target product was obtained in each reaction (see FIG. 1 of Example 1 and FIG. 2 of Example 2). Note that, for Examples 3 to 10 and Comparative Examples 1 to 3, ¹ H-NMR measurements were similarly performed to confirm the synthesis of the target product (not shown).

Example 1
34.5g (0.28mol) of 2,6-dimethylphenol, 15g of methanol, 6.5g of water and 1.83g of 96% sulfuric acid were charged into a 200mL flask equipped with a thermometer, a condenser and a stirrer, and heated to 45°C while stirring. 9.6g (0.57mol) of 2,6-bis(hydroxymethyl)-p-cresol was then added for 1 hour, and the mixture was reacted at 45°C for 5 hours. After the reaction was completed, the reaction mixture was cooled to room temperature, 90g of water was added to the reaction liquid, and the mixture was neutralized with an aqueous sodium hydroxide solution. The mixture was then stirred at 40°C for 4 hours, and the precipitated solid was filtered off, washed with hot water, and then dried in vacuum. 15.4g (0.041mol) of an intermediate phenol compound was obtained.
In a 1 L flask equipped with a thermometer, a condenser, and a stirrer, 15.4 g (0.041 mol) of the intermediate phenol compound obtained, 40 g of N,N-dimethylformamide, 34.3 g (0.228 mol) of 4-chloromethylstyrene, and 22.4 g of 48% aqueous potassium hydroxide solution were charged, and the mixture was heated to 60°C with stirring and reacted for 20 hours. The reaction liquid was poured into 300 g of methanol, and the precipitated solid was filtered off and dried in vacuum. A curable resin with the following structural formula was obtained. ¹ H-NMR measurement was performed to determine the structure of the product (see Figure 1).

Example 2
34.5g (0.28mol) of 2,6-dimethylphenol, 15g of methanol, 6.5g of water and 1.83g of 96% sulfuric acid were charged into a 200mL flask equipped with a thermometer, a condenser and a stirrer, and heated to 45°C while stirring. 9.6g (0.57mol) of 2,6-bis(hydroxymethyl)-p-cresol was then added for 1 hour, and the mixture was reacted at 45°C for 5 hours. After the reaction was completed, the reaction mixture was cooled to room temperature, 90g of water was added to the reaction liquid, and the mixture was neutralized with an aqueous sodium hydroxide solution. The mixture was then stirred at 40°C for 4 hours, and the precipitated solid was filtered off, washed with hot water, and then dried in vacuum. 15.4g (0.041mol) of an intermediate phenol compound was obtained.
In a 200 mL flask equipped with a thermometer, a condenser, and a stirrer, 20 g of toluene and 15.4 g (0.041 mol) of the intermediate were mixed and heated to about 85° C. 0.92 g (0.0075 mol) of dimethylaminopyridine was added. When it appeared that all the solids had dissolved, 38.5 g (0.25 mol) of methacrylic anhydride was gradually added. The resulting solution was maintained at 85° C. for 3 hours with continuous mixing. The solution was then cooled to room temperature and dropped over 30 minutes into 360 g of hexane in a 1 L beaker that was vigorously stirred with a magnetic stirrer. The resulting precipitate was filtered under reduced pressure and dried to obtain 11.6 g of a curable resin of the following structural formula. ¹ H-NMR measurements were performed to determine the structure of the product (see FIG. 2).

Example 3
A curable resin having the following structural formula was obtained by carrying out synthesis in the same manner as in Example 1, except that the methacrylic anhydride in Example 2 was changed to 31.5 g (0.25 mol) of acrylic anhydride.

Example 4
A curable resin having the following structural formula was obtained by carrying out synthesis in the same manner as in Example 1, except that 2,6-dimethylphenol in Example 1 was changed to 47.7 g (0.28 mol) of o-phenylphenol.

Example 5
A curable resin having the following structural formula was obtained by carrying out synthesis in the same manner as in Example 1, except that the 2,6-dimethylphenol in Example 1 was changed to 49.3 g (0.28 mol) of 2-cyclohexylphenol.

Example 6
The synthesis was carried out in the same manner as in Example 2, except that the 2,6-dimethylphenol in Example 2 was changed to 49.3 g (0.28 mol) of 2-cyclohexylphenol, to obtain a curable resin having the following structural formula.

(Example 7)
A curable resin having the following structural formula was obtained by carrying out synthesis in the same manner as in Example 1, except that 2,6-dimethylphenol in Example 1 was changed to 51.6 g (0.28 mol) of 2-benzylphenol.

(Example 8)
The synthesis was carried out in the same manner as in Example 1, except that 2,6-bis(hydroxymethyl)-p-cresol in Example 1 was changed to 134.7 g (0.57 mol) of 5-cyclohexyl-2-hydroxy-1,3-phenylenedimethanol, to obtain a curable resin having the following structural formula.

(Example 9)
The synthesis was carried out in the same manner as in Example 1, except that 2,6-bis(hydroxymethyl)-p-cresol in Example 1 was changed to 91.3 g (0.57 mol) of (2,6-divinyl-4-methyl)phenol, to obtain a curable resin having the following structural formula.

(Example 10)
A curable resin having the following structural formula was obtained by carrying out synthesis in the same manner as in Example 1, except that 4-chloromethylstyrene in Example 1 was changed to 17.4 g (0.228 mol) of allyl chloride.

(Comparative Example 1)
A curable resin having the following structural formula was obtained by carrying out synthesis in the same manner as in Example 1, except that the 2,6-dimethylphenol in Example 1 was changed to 26.4 g (0.28 mol) of phenol.

(Comparative Example 2)
The synthesis was carried out in the same manner as in Example 1, except that the 2,6-dimethylphenol in Example 2 was changed to 26.4 g (0.28 mol) of phenol, to obtain a curable resin having the following structural formula.

(Comparative Example 3)
The synthesis was carried out in the same manner as in Example 1, except that the intermediate phenol compound 15.4 g (0.041 mol) in Example 1 was changed to 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane 11.7 g (0.041 mol), to obtain a curable resin having the following structural formula.

<Preparation of Resin Film (Cured Product)>
The curable resin (solid powder) obtained in the examples and comparative examples was placed in a 5 cm square mold, sandwiched between stainless steel plates, and set in a vacuum press. The pressure was increased to 1.5 MPa at normal pressure and room temperature. Next, the pressure was reduced to 10 torr, and the temperature was increased to a temperature 50° C. higher than the heat curing temperature over 30 minutes. After being left to stand for another 2 hours, the temperature was gradually cooled to room temperature. As a result, a uniform resin film (cured product) with an average thickness of 100 μm was produced. In addition, in the curable resin obtained in Example 10 (X is an allyl ether group), homopolymerization (crosslinking) of the curable resin alone does not proceed, so only the production of the curable resin was confirmed, and the following evaluation based on the resin film (cured product) was not performed.

<Evaluation of dielectric properties>
Regarding the dielectric properties in the in-plane direction of the obtained resin film (cured product), the dielectric constant and dielectric loss tangent were measured at a frequency of 10 GHz by a split post dielectric resonator method using a network analyzer N5247A from Keysight Technologies. The dielectric loss tangent is practically acceptable if it is 10.0×10 ⁻³ or less, preferably 5.0×10 ⁻³ or less, more preferably 3.0×10 ⁻³ or less, and even more preferably 2.5×10 ⁻³ or less. The dielectric constant is practically acceptable if it is 3 or less, preferably 2.7 or less, and more preferably 2.5 or less.

<Evaluation of heat resistance (glass transition temperature)>
The obtained resin film (cured product) was measured using a PerkinElmer DSC device (Pyris Diamond) at a temperature rise of 20°C/min from room temperature to observe the exothermic peak temperature (thermosetting temperature), and then held at a temperature 50°C higher than that for 30 minutes. The sample was then cooled to room temperature at a temperature drop of 20°C/min, and then heated again at a temperature rise of 20°C/min to measure the glass transition temperature (Tg) (°C) of the resin film (cured product). Note that as long as the glass transition temperature (Tg) is 100°C or higher, there is no practical problem, and it is preferably 150°C or higher.

From the evaluation results in Table 1 above, it was confirmed that in Examples 1 to 9, the cured products obtained by using the desired curable resins were able to achieve both heat resistance and low dielectric properties, and were at a level that was not problematic for practical use.

On the other hand, from the evaluation results in Table 1 above, in Comparative Example 1, a curable resin that does not have hydrocarbon groups corresponding to Ra and Rb contained in the structure of the desired curable resin was used, so the molecular mobility of the crosslinking group (X) was not restricted, and the dielectric tangent and dielectric constant of the obtained cured product were higher than those of the Examples, and it was confirmed that the dielectric properties (low dielectric properties) were inferior. In Comparative Example 2, a curable resin that does not have hydrocarbon groups corresponding to Ra and Rb contained in the structure of the desired curable resin was used, so the molecular mobility of the crosslinking group (X) was not restricted, and the dielectric tangent and dielectric constant of the obtained cured product were higher than those of the Examples, and it was confirmed that the dielectric properties (low dielectric properties) were inferior. In Comparative Example 3, an intermediate phenolic compound as used in the Examples was not used, and a curable resin with a small number of crosslinking groups (X) was used for synthesis, so the glass transition temperature of the obtained cured product was very low, and it was confirmed that the heat resistance was inferior.

The cured product obtained using the cured resin of the present invention has excellent heat resistance and dielectric properties (low dielectric properties), and is therefore suitable for use in heat-resistant components and electronic components, particularly in prepregs, semiconductor encapsulants, circuit boards, build-up films, build-up boards, and the like, as well as adhesives and resist materials. It can also be used as a matrix resin for fiber-reinforced resins, and is suitable as a highly heat-resistant prepreg.

1 is a ¹ H-NMR spectrum of the curable resin obtained in Example 1. 1 is a ¹ H-NMR spectrum of the curable resin obtained in Example 2.

Claims (4)

A curable resin represented by the following general formula (1):
(In the formula, Ra and Rb each independently represent an alkyl group, an aryl group, an aralkyl group, or a cycloalkyl group having 1 to 12 carbon atoms. Rc and Rd each independently represent a hydrogen atom, an alkyl group, an aryl group, an aralkyl group, or a cycloalkyl group having 1 to 12 carbon atoms. X represents a vinylbenzyl ether group, a (meth)acryloyloxy group, or an allyl ether group. m represents an integer of 0 to 3.) The curable resin according to claim 1, characterized in that the general formula (1) is represented by the following general formula (2):
A curable resin composition comprising the curable resin according to claim 1 or 2. A cured product obtained by subjecting the curable resin composition according to claim 3 to a curing reaction.