Thermosetting compositions, resin films, prepregs, metal-clad laminates, and printed circuit boards

Abstract

To provide a thermosetting composition that yields a thermosetting resin having excellent dielectric properties and heat resistance. [Solution] A thermosetting composition containing a polymerization initiator and a radical polymerizable compound, wherein the polymerization initiator is a compound represented by the following general formula (1). JPEG2026055830000010.jpg43133

Description

[Technical Field]

[0001] The present invention relates to thermosetting compositions, resin films, prepregs, metal-clad laminates, and printed circuit boards. [Background technology]

[0002] With the remarkable advancements in information network technology and the expansion of services utilizing information networks, there is a growing demand for electronic devices capable of handling large amounts of information and processing at high speeds. This trend is accelerating further with the spread of fifth-generation mobile communication systems. For this reason, electronic circuit board materials such as printed wiring boards used in electronic devices require excellent dielectric properties such as low dielectric constant and low dielectric loss tangent to reduce electrical signal loss, and high heat resistance is also required to prevent deformation and damage to the board due to heat during board processing and equipment operation.

[0003] Furthermore, recent advances in resin development have shown that using polyphenylene ethers and maleimides, which have radically polymerizable double bonds at their molecular ends, in thermosetting resins can yield excellent properties and are therefore being favorably used. In many cases, organic peroxides are used as polymerization initiators in the curing process (Patent Document 1).

[0004] However, using organic peroxides as polymerization initiators can improve the heat resistance of resins, but it may also worsen their dielectric properties (Patent Document 2). This is thought to be because oxy radicals generated by heat not only attach to double bonds in the resin, but also cause secondary decomposition and hydrogen abstraction within the resin, resulting in the presence of polar impurities such as alcohols.

[0005] Furthermore, development is underway on resin systems that do not use polymerization initiators (Patent Document 3) and polymerization initiators other than organic peroxides (Patent Document 4), but these have challenges such as requiring high processing temperatures exceeding 200°C and not being able to ensure the heat resistance of the resin. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2020 / 158849 [Patent Document 2] Japanese Patent Publication No. 2014-1276 [Patent Document 3] Japanese Patent Publication No. 2016-191073 [Patent Document 4] Japanese Patent Publication No. 2009-161638 [Overview of the project] [Problems that the invention aims to solve]

[0007] When substances used as polymerization initiators, such as organic peroxides, have polarizable structures such as oxygen atoms within their molecules, radicals that could not be attached to the monomer become polar low-molecular-weight molecules with hydroxyl or carbonyl groups. Furthermore, the presence of these polar low-molecular-weight molecules scattered within the resin may worsen dielectric properties such as dielectric constant and dielectric loss tangent.

[0008] This invention has been made in view of the above circumstances, and aims to provide a thermosetting composition that can produce a thermosetting resin having excellent dielectric properties and heat resistance. [Means for solving the problem]

[0009] In other words, the present invention relates to a thermosetting composition containing a polymerization initiator and a radical polymerizable compound, wherein the polymerization initiator is General formula (1): [ka] This relates to a thermosetting composition which is a compound represented by [formula].

[0010] Furthermore, the present invention relates to the thermosetting composition in which the radical polymerizable compound is preferably a polyphenylene ether.

[0011] The present invention also relates to a resin film formed from the thermosetting composition.

[0012] The present invention also relates to a prepreg in which the thermosetting composition is impregnated or coated on a fibrous substrate.

[0013] The present invention also relates to a metal-clad laminate in which the resin film and a metal foil are laminated.

[0014] The present invention also relates to a metal-clad laminate in which the prepreg and a metal foil are laminated.

[0015] The present invention also relates to a printed wiring board in which a part of the metal foil is removed from the metal-clad laminate.

Advantages of the Invention

[0016] The thermosetting composition of the present invention contains a polymerization initiator represented by the above general formula (1) and a radically polymerizable compound. In the thermosetting composition of the present invention, the above polymerization initiator improves the heat resistance of the cured resin, and shows good dielectric properties because it is composed of non-polar substances, and can smoothly flow the current in the vicinity of the resin. In addition, since the above polymerization initiator does not contain polar impurities, it is difficult to combine with moisture in the air during curing and processing, and it is also possible to suppress deterioration of dielectric properties due to molding defects and moisture absorption. Therefore, the thermosetting resin obtained from the thermosetting composition of the present invention can achieve both excellent dielectric properties and heat resistance.

Embodiments for Carrying Out the Invention

[0017] <Thermosetting Composition> The thermosetting composition of the present invention contains the following polymerization initiator and radically polymerizable compound.

[0018] <Polymerization Initiator> The polymerization initiator of the present invention has the general formula (1):

Chemical formula

[0019] The method for producing the polymerization initiator represented by the general formula (1) is not limited in any way, but for example, general formula (2): [ka] (1-ethylpropyl)benzene, represented by general formula (3): [ka] One step involves reacting with di-t-butyl peroxide represented by [formula].

[0020] In the above step, commercially available products can be used for (1-ethylpropyl)benzene represented by general formula (2) and the peroxide represented by general formula (3).

[0021] In the above step, the (1-ethylpropyl)benzene represented by general formula (2) is preferably used in an amount of 0.5 to 5.0 moles, and more preferably 0.8 to 3.0 moles, per 1.0 mole of the peroxide represented by general formula (3), from the viewpoint of increasing the yield of the target product.

[0022] The reaction temperature in the above step is preferably 110°C or higher, more preferably 120°C or higher, from the viewpoint of increasing the yield of the target product, and preferably 200°C or lower, and more preferably 180°C or lower, from the viewpoint of safety.

[0023] The reaction time for the above process cannot be determined definitively as it varies depending on the raw materials and reaction temperature, but generally, from the viewpoint of increasing the yield of the target product, it is preferable to have a reaction time of 0.5 hours or more, more preferably 1.5 hours or more, and preferably 5 hours or less.

[0024] The above process can be carried out under normal atmospheric pressure, but it can also be carried out under a nitrogen atmosphere or a nitrogen stream.

[0025] After the above process, 3,4-diethyl-3,4-diphenylhexane can be purified by recrystallization using a good solvent such as toluene or acetone and a poor solvent such as methanol or deionized water in order to remove excess raw materials and by-products.

[0026] The obtained 3,4-diethyl-3,4-diphenylhexane can be identified using methods such as gas chromatography (GC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), infrared spectroscopy (IR), and mass spectrometry (MS).

[0027] In the above analysis, the purity of the polymerization initiator is preferably 90.0% or higher, and more preferably 95.0% or higher, from the viewpoint of ensuring reproducibility in the curing reaction and efficiently promoting the reaction.

[0028] <Radical polymerizable compounds> The radical polymerizable compound is not particularly limited as long as it can be polymerized by a thermal radical polymerization reaction. Examples include compounds having ethylenically unsaturated groups such as vinyl groups, allyl groups, methacrylic groups, styryl groups, meth(acrylic) groups, and maleimide groups. From the viewpoint of improving the dielectric properties and heat resistance of the thermosetting resin using the above polymerization initiator, polyphenylene ethers are preferred, for example.

[0029] The polyphenylene ether is not particularly limited as long as it has a radically polymerizable double bond at its molecular terminus. The polyphenylene ether having a radically polymerizable double bond can be used alone or in combination of two or more types.

[0030] Specific examples of the structural units of the polyphenylene ether include, for example, poly(2,6-dimethyl-1,4-phenylene ether), poly(2-methyl-6-ethyl-1,4-phenylene ether), poly(2-methyl-6-phenyl-1,4-phenylene ether), and poly(2,6-dichloro-1,4-phenylene ether). From the viewpoint of excellent dielectric properties and heat resistance, poly(2,6-dimethyl-1,4-phenylene ether) is preferred. Furthermore, specific examples of the structural units of the polyphenylene ether include, for example, copolymers of 2,6-dimethylphenol and other phenols (e.g., 2,3,6-trimethylphenol, 2-methyl-6-butylphenol, 2-allylphenol, etc.); polyphenylene ether copolymers obtained by coupling 2,6-dimethylphenol with biphenols or bisphenols; and polyphenylene ethers having a linear or branched structure obtained by heating poly(2,6-dimethyl-1,4-phenylene ether), etc., with phenol compounds such as bisphenols or trisphenols in a toluene solvent in the presence of an organic peroxide and undergoing a redistribution reaction. The phenylene group in the phenylene ether unit may have substituents, and the polyphenylene ether may contain other structural units other than the phenylene ether unit, as long as they do not hinder the effects of the present invention.

[0031] Examples of the radical polymerizable double bonds at the molecular ends include (meth)acryloyl groups, styryl groups, vinylbenzyl groups, vinyl groups, allyl groups, and 1,3-butadienyl groups. Among these, (meth)acryloyl groups and vinylbenzyl groups are preferred from the viewpoint of high reactivity during thermosetting and excellent dielectric constant and dielectric loss tangent of the thermosetting resin.

[0032] The number of radically polymerizable double bonds in one molecule of the polyphenylene ether having a radically polymerizable double bond at the molecular terminus is preferably 1.5 to 6 on average, more preferably 1.6 to 4 on average, and even more preferably 1.7 to 3 on average.

[0033] The number of ethylenically unsaturated double bonds in a single molecule of polyphenylene ether having a radically polymerizable double bond at its molecular end can be measured, for example, by measuring the number of hydroxyl groups remaining in the polyphenylene ether and calculating the decrease from the number of hydroxyl groups in the polyphenylene ether before modification with a compound having an ethylenically unsaturated double bond. The method for measuring the number of hydroxyl groups remaining in the polyphenylene ether follows the method described in Polymer Science, Vol. 51, No. 7, p. 480 (1994), where tetraethylammonium hydroxide is added to a methylene chloride solution of polyphenylene ether, and the absorbance of the mixed solution at a wavelength of 318 nm is measured.

[0034] Furthermore, the polyphenylene ether having a radically polymerizable double bond at its molecular terminus preferably has the structure of the following general formula (4). [ka] (In formula (4), X is any a-valent linking group, Y is a radical polymerizable double bond at the molecular terminus, and a is between 1 and 6.)

[0035] In formula (4) above, specific examples of X include divalent phenols such as bisphenol A, bisphenol F, bisphenol S, fluorenebisphenol, 4,4'-dihydroxybiphenyl, 2,2'-dihydroxybiphenyl, 4,4'-dihydroxy-3,3'5,5'-tetramethylbiphenyl, 4,4'-dihydroxy-2,2',3,3'5,5'-hexamethylbiphenyl, hydroquinone, and resorcinol, as well as trivalent or higher phenols such as tris-(4-hydroxyphenyl)methane, 1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, phenol novolac, o-cresol novolac, and naphthol novolac.

[0036] The polyphenylene ether having radically polymerizable double bonds at its molecular ends is preferably 800 to 5000 in number average molecular weight, more preferably 900 to 4500, and even more preferably 1000 to 3000, from the viewpoint of dielectric properties and impregnation into fibrous substrates.

[0037] The number-average molecular weight can be any value measured using a general molecular weight measurement method, such as the polystyrene-equivalent value measured using gel permeation chromatography (GPC). Specifically, after preparing a sample with a concentration of 0.2 w / vol% (solvent: chloroform), the measurement can be performed using an HLC-8220GPC (manufactured by Tosoh Corporation) as the measuring instrument, with the following conditions: column: ShodexGPC KF-405L HQ×3 (manufactured by Showa Denko K.K.), eluent: chloroform, injection volume: 20 μL, flow rate: 0.3 mL / min, column temperature: 40°C, and detector: RI.

[0038] The method for synthesizing the polyphenylene ether having a radically polymerizable double bond at its molecular terminus is not particularly limited, as long as it can synthesize a modified polyphenylene ether modified with a radically polymerizable double bond. Specifically, one example is a method in which the polyphenylene ether before modification is reacted with a compound having an ethylenically unsaturated double bond and a chlorine atom. Examples of compounds having an ethylenically unsaturated double bond and a chlorine atom include (meth)acryloyl chloride and vinyl benzyl chloride. Furthermore, commercially available polyphenylene ethers having a radically polymerizable double bond at their molecular terminus may also be used, such as the product names "OPE-2St" (manufactured by Mitsubishi Gas Chemical Co., Ltd.) and "Noryl SA9000" (manufactured by SABIC Innovative Plastics Co., Ltd.).

[0039] The polymerization initiator may be used in any amount relative to the radical polymerizable compound, and is usually preferably 0.05 to 15 parts by mass, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the radical polymerizable compound.

[0040] <Other ingredients> The thermosetting composition of the present invention may further contain other components in appropriate combinations. Examples of other components include polyfunctional monomers, solvents, organic peroxides, azo compounds, bismaleimide, polyisoprene, polybutadiene, styrene-butadiene rubber, butyl rubber, ethylene propylene rubber, ethylene propylene die rubber, styrene-butadiene styrene block copolymer, styrene-ethylene-butylene styrene block copolymer, ethylene styrene-divinylbenzene copolymer, ethylene hexene-styrene-divinylbenzene copolymer, fluororubber, silicone rubber and other elastomers, inorganic fillers such as natural silica, fused silica, synthetic silica, amorphous silica, hollow silica, alumina, boron nitride, aluminum nitride, clay, talc and glass short fibers, silane coupling agents such as γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-(meth)acryloxypropyltrimethoxysilane, flame retardants, polymerization inhibitors, ultraviolet absorbers, light stabilizers, metal deactivators, surfactants, lubricants, thickeners, defoamers, antistatic agents, pigments, dyes, and the like.

[0041] The polyfunctional monomer can be incorporated from the viewpoint of adjusting the viscosity of the thermosetting composition or improving the heat resistance of the thermosetting resin. Examples of the polyfunctional monomer include polyfunctional (meth)acrylates such as ethylene glycol di(meth)acrylate, hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, and dipentaerythritol hexa(meth)acrylate; vinylbenzene derivatives such as 1,4-divinylbenzene and 4-vinylbenzoate-2-acryloylethyl ester; alkenyl isocyanurate derivatives such as triallyl isocyanurate (TAIC); and alkenyl cyanurate derivatives such as triallyl cyanurate (TAC). Among these, triallyl isocyanurate and triallyl cyanurate are preferred because they have excellent heat resistance. The polyfunctional monomer can be used alone or in combination of two or more.

[0042] The polyfunctional monomer is preferably 5 to 50 parts by mass, more preferably 7 to 40 parts by mass, and even more preferably 10 to 30 parts by mass, based on 100 parts by mass of the radical polymerizable compound.

[0043] The aforementioned solvent can be added from the viewpoint of improving the viscosity of the thermosetting composition, its impregnation into the glass cloth, and the smoothness of the cured film. The aforementioned solvent is not particularly limited as long as it can dissolve or disperse the above components and is a solvent that volatilizes when dried. From the viewpoint of solubility, the solvent is preferably an aromatic solvent such as toluene or xylene; a ketone solvent such as acetone, methyl ethyl ketone, cyclopentanone, or cyclohexanone; or an amide solvent such as dimethylformamide, dimethylacetamide, or N-methylpyrrolidone. These solvents can be used individually or in combination of two or more. The amount of solvent used is preferably 10 to 1000 parts by mass, and more preferably 20 to 500 parts by mass, per 100 parts by mass of solids of the thermosetting composition, from the viewpoint of solubility of the thermosetting composition in the solvent and ease of the volatilization process.

[0044] <Method for preparing a thermosetting composition> When preparing the thermosetting composition, the polymerization initiator, the radical polymerizable compound, and other components as needed are placed in a storage container and dissolved or dispersed according to conventional methods using a ball mill, bead mill, planetary mixer, roll mill, etc. Heating may be used as needed during this process. When dissolving the radical polymerizable compound in a solvent by heating, unwanted gelation can be suppressed by cooling to 50°C or below after dissolution before adding the polymerization initiator. Filtration may also be performed using a mesh or membrane filter as needed.

[0045] <Resin film> The resin film of the present invention is formed from the thermosetting composition. The resin film contains the thermosetting composition before curing, but a portion of the thermosetting composition may be cured. The resin film can be obtained, for example, by drying a resin varnish which is a mixture of the thermosetting composition and the solvent alone, or by applying the resin varnish to a support such as a support film and then drying it. The solvent is dried and removed using a hot air dryer or the like, for example, at a temperature of 20°C to 180°C. The drying temperature is preferably 20°C to 150°C, and more preferably 50°C to 130°C.

[0046] Examples of the support material for the resin film include polyester such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polyethylene, polypropylene, and polyvinyl chloride, polycarbonate, polyimide, ethylene tetrafluoroethylene copolymer, metal foils such as copper foil and aluminum foil, and release paper. After applying the thermosetting composition to a metal foil, the material obtained by drying and removing the solvent using a hot air dryer or the like is also called resin-coated metal foil. The support material may be subjected to chemical or physical treatments such as mud treatment, corona treatment, or release treatment.

[0047] The aforementioned resin film is suitable as an interlayer insulating sheet, adhesive film, etc., for laminates such as multilayer printed circuit boards.

[0048] <Prepreg> The prepreg of the present invention is a composite of a fibrous substrate and the thermosetting composition. The prepreg contains the thermosetting composition before curing, but a portion of the thermosetting composition may be cured. Preferably, the prepreg is a composite of a fibrous substrate and the thermosetting composition impregnated or coated onto the fibrous substrate. Even if the thermosetting composition is coated on the surface of the fibrous substrate to form a layer, a structure in which the thermosetting resin of the thermosetting composition is impregnated into the substrate can be obtained by press molding to cure the prepreg. The prepreg can be obtained, for example, by impregnating or coating a substrate such as glass cloth with a resin varnish which is a mixture of the thermosetting composition of the present invention and a solvent, and then drying and removing the solvent. It is also possible to repeat the impregnation or coating multiple times. Furthermore, by repeating the impregnation or coating using multiple thermosetting compositions with different concentrations and compositions, it is possible to adjust the amount of impregnation to the desired amount. Drying and removing the solvent is performed using a hot air dryer or the like, for example, at a temperature of 20°C to 180°C. The drying temperature is preferably between 20°C and 150°C, and more preferably between 50°C and 130°C.

[0049] Examples of the fibrous substrate include glass cloth, aramid cloth, polyester cloth, glass nonwoven fabric, aramid nonwoven fabric, pulp paper, and linter paper. Among these, glass cloth is preferred because it provides excellent mechanical strength for printed circuit boards, and flattened glass cloth is even more preferred. These fibrous substrates can be used individually or in combination of two or more. The thickness of the fibrous substrate can be, for example, 1 to 300 μm.

[0050] The proportion of the thermosetting composition in the solid content of the prepreg is preferably 30 to 80% by mass, and more preferably 40 to 70% by mass. If the above proportion is less than 30% by mass, the insulation reliability tends to be poor when the prepreg is used for electronic circuit boards, etc. Also, if the above proportion is more than 80% by mass, the mechanical properties such as the flexural modulus tend to be poor when used for electronic circuit boards, etc.

[0051] <Metal-clad laminate> The metal-clad laminate of the present invention is a laminate formed by laminating the resin film or prepreg with a metal foil. The laminate can be manufactured by stacking one or more of the resin films and / or prepregs with a substrate such as a metal foil, and then curing the thermosetting composition by press molding to form an insulating layer. It is also possible to use the resin-coated metal foil instead of the metal foil. Heat molding is performed, for example, at a temperature of 180°C to 240°C, a heating time of 30 to 300 minutes, and a surface pressure of 20 kgf / cm². 2 From 40 kgf / cm² 2 It can be done in this way.

[0052] The aforementioned metal foil is not particularly limited, but examples include aluminum and copper foil, with copper foil being preferred due to its low electrical resistance. The thickness of the metal foil can be, for example, 1 to 50 μm.

[0053] The resin film and prepreg combined with the metal foil may be one or multiple sheets, and depending on the application, the metal foil may be layered on one or both sides to form a laminate. The metal-clad laminate is particularly suitable as a printed circuit board.

[0054] <Printed wiring board> The printed circuit board of the present invention is obtained by partially removing the metal foil on the surface of the metal-clad laminate by etching or the like, and forming wiring, thereby forming a circuit on the surface of a resin film or prepreg. The printed circuit board, by containing the thermosetting composition, has excellent dielectric properties such as dielectric constant and dielectric loss tangent, as well as moldability and heat resistance.

[0055] In addition to the above, the thermosetting composition is used in applications such as molding, lamination, adhesives, and composite materials such as copper-clad laminates. In particular, when the isocyanate or epoxy is used alone or in combination, typical examples include prepregs made by partially curing resin and laminates made by curing these prepregs. When the epoxy is used, typical examples include its use as a semiconductor encapsulant. [Examples]

[0056] The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples.

[0057] <Manufacturing Example 1> (1-ethylpropyl)benzene (99% purity, 7.41 g, 0.050 mol) and di-t-butyl peroxide (98.4% purity, 5.94 g, 0.041 mol) were added to a 50 mL three-necked flask and stirred. A Dean-Stark tube and a condenser were attached to the three-necked flask, and the solution was heated to 140°C. The mixture was stirred for 2 hours while removing low-boiling by-products using the Dean-Stark tube. After cooling to 50°C, methanol (20 g) was added, and the mixture was cooled to -30°C. After standing at -30°C for 24 hours, the precipitate was collected by suction filtration and dried at 30°C for 48 hours to obtain 3,4-diethyl-3,4-diphenylhexane (3.27 g, 99.1% purity, 27.2% yield by mass).

[0058] The structure of 3,4-diethyl-3,4-diphenylhexane described above was obtained using an AVANCEN NMR spectrometer (BRUCKER). 1 H-NMR measurement, 13 The compound was identified by 13C-NMR and TOFMS (manufactured by JEOL Ltd.). Purity was calculated using the simple area method in HPLC. The EI-MS and [results of the results of the analysis of compound 1 are also shown.] 1 Table 1 shows the results of the analysis using 1H-NMR.

[0059] [HPLC conditions] HPLC chromatography was performed using a UV-2075 Plus (JASCO) UV detector and an ERC ODS-1262 (SHIMADZU) column. The developing solvent was an aqueous methanol solution (methanol / water = 85 / 15), the column temperature was 45°C, the flow rate was 1.0 ml / min, the sample injection concentration was 20% by mass, the injection volume was 5 microliters, and the detection wavelength was 250 nm.

[0060] <Comparative Manufacturing Example 1> The compound was prepared in the same manner as in Production Example 1, except that (1-ethylpropyl)benzene was replaced with cumene, to obtain 2,3-dimethyl-2,3-diphenylbutane (5.42 g, purity 99.8%, yield 55.3% by mass). The EI-MS and 1 Table 1 shows the results of the analysis using 1H-NMR.

[0061] <Comparative Manufacturing Example 2> The compound was prepared in the same manner as in Preparation Example 1, except that (1-ethylpropyl)benzene was replaced with (1-propylbutyl)benzene, to obtain 4,5-dipropyl-4,5-diphenyloctane (2.10 g, purity 99.1%, yield 14.9% by mass). The EI-MS and 1 Table 1 shows the results of the analysis using 1H-NMR.

[0062] <Comparative Manufacturing Example 3> In a 500 mL round-bottom flask, t-butylhydroperoxidetoluene solution (40.0% purity, 228.6 g, 1.02 mol), 1,3-bis(α,α'-dihydroxyisopropyl)benzene (99% purity, 73.8 g, 0.38 mol), and acetic acid (99% purity, 63.9 g, 1.064 mol) were added and stirred. While maintaining the above solution at 31-34°C, a mixture of perchloric acid (70% purity, 1.77 g, 0.0325 mol) and acetic acid (99% purity, 12.8 g, 0.56 mol) was added dropwise. After the dropwise addition was complete, the mixture was stirred for 2 hours. The resulting solution was washed with aqueous sodium hydroxide solution and water, and then dehydrated with sodium sulfate and magnesium sulfate to obtain a toluene solution of di(t-butylperoxy)1,3-bis(α,α'-dihydroxyisopropyl)benzene (226.7 g, concentration 45.9% by mass, yield 79.5% by mass). Subsequently, vacuum distillation was performed using an evaporator and vacuum controller at a rate of 30-40 mmHg / min to 80 mmHg to obtain a concentrated solution (134.1 g, concentration 76.3% by mass). The obtained solution was added dropwise to methanol (310.6 g) at 0°C and reprecipitation occurred. The solid precipitated in the solution was recovered by filtration and air-dried at 40°C for 48 hours to obtain α,α'-di(t-butylperoxy)-diisopropylbenzene (79.2 g, purity 98.4%, yield 60.6% by mass). The EI-MS and 1 Table 1 shows the results of the analysis using 1H-NMR.

[0063] [Table 1]

[0064] <Evaluation of decomposition start temperature> A Hitachi High-Tech Science Corporation "DSC-7000X" differential scanning calorimetry (DSC) was used. For the measurements, approximately 8 mg of the synthesized sample was placed in a SUS cell and heated from 50°C to 300°C under a nitrogen atmosphere at a heating rate of 10°C per minute. The decomposition onset temperature was defined as the intersection of the tangent line between the original baseline and the inflection point of the DSC. Table 2 shows the measurement results of the decomposition onset temperatures (°C) of the compounds prepared in Production Example 1 and Comparative Production Examples 1-3.

[0065] [Table 2]

[0066] <Manufacturing of thermosetting resins and evaluation of their appearance and dielectric properties> Each component (parts by mass) shown in Table 3 was diluted with toluene to a concentration of 50% by mass. 6 g of the solvent solution of the composition was placed in an aluminum dish and dried in a vacuum dryer (EYELA VACUUM OVEN VOS-3LSD) at 400 Pa and 60°C for 2 hours, followed by solvent drying at 80°C for another 2 hours. The resulting powder was molded using a hand press (Toyo Seiki Co., Ltd.) at 130°C, cured at 200°C for 2 hours, and dried in a dryer at 130°C for 24 hours to obtain a thermosetting resin (film, 10 cm square, 100 μm thick). After visually evaluating the appearance of the obtained thermosetting resin, the dielectric constant and dielectric loss tangent at 10 GHz were measured according to the method compliant with IPC-TM-650-2.5.5.9, and the obtained values ​​were evaluated according to the following criteria. The results are shown in Table 3. An evaluation of ○ or higher is considered a pass. [Criteria for evaluating appearance] ◎: 0-5 voids or cracks are visible. ○: There are 6 to 15 voids or cracks. △: More than 16 voids or cracks are observed, or the sample is damaged before measurement. [Evaluation Criteria for Dielectric Properties] ◎: Dielectric loss tangent is less than 0.0025 ○: Dielectric loss tangent is 0.0025 or greater and less than 0.0030 △: Dielectric loss tangent is 0.0035 or higher

[0067] <Heat resistance evaluation> The glass transition temperature of the above thermosetting resin was measured using "DMA 7100" manufactured by Hitachi High-Tech Science Corporation as DMA (dynamic viscoelasticity measurement). For the measurement, a film with a width of 10 mm and a length of 40 mm was cut out from the above thermosetting resin, and the temperature was raised from 50 °C to 300 °C at a rate of 2 °C per minute in a nitrogen atmosphere. The glass transition temperature was defined as the temperature at the peak top of the loss tangent (loss elastic modulus / storage elastic modulus) curve, and the storage elastic modulus was taken as the value at 180 °C. The obtained values were evaluated according to the following criteria. The results are shown in Table 3. An evaluation of ○ or higher is considered a pass. [Evaluation Criteria for Glass Transition Temperature] ◎: 220 °C or higher 〇: 210 °C or higher and less than 220 °C △: Less than 210 °C [Evaluation Criteria for Storage Elastic Modulus] ◎: 1.5×10 9 Pa or higher 〇: 1.0×10 9 Pa or higher and less than 1.5×10 9 Pa △: Less than 1.0×10 9 Pa ×: Unmeasurable

[0068]

Table 3

[0069] In Table 3, SA9000 is polyphenylene ether having an average of 2 ethylenically unsaturated double bonds at the molecular ends (number average molecular weight is 2756), manufactured by SABIC Innovative Plastics; OPE-2St 2200 is polyphenylene ether having an average of 2 ethylenically unsaturated double bonds at the molecular ends (number average molecular weight is 2200), manufactured by Mitsubishi Gas Chemical Company, Inc.; OPE-2St 1200 is polyphenylene ether having an average of 2 ethylenically unsaturated double bonds at the molecular ends (number average molecular weight is 1200), manufactured by Mitsubishi Gas Chemical Company, Inc.; TAIC indicates triallyl isocyanurate, manufactured by Tokyo Chemical Industry Co., Ltd.

[0070] Examples 1-5 exhibit superior characteristics compared to Comparative Examples 1-5.

Claims

1. A thermosetting composition containing a polymerization initiator and a radical polymerizable compound, The polymerization initiator is General formula (1): 【Chemistry 1】 A thermosetting composition characterized by being a compound represented by [the formula shown].

2. The thermosetting composition according to claim 1, characterized in that the radical polymerizable compound is a polyphenylene ether.

3. A resin film characterized by being formed from the thermosetting composition described in claim 2.

4. A prepreg characterized by being impregnated or coated with the thermosetting composition described in claim 2 onto a fibrous substrate.

5. A metal-clad laminate characterized by being laminated with a resin film according to claim 3 or a prepreg according to claim 4 and a metal foil.

6. A printed circuit board characterized in that a portion of the metal foil is removed from the metal-clad laminate according to claim 5.

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