Crosslinking agent, curable composition, prepreg, laminate, metal-clad laminate, wiring board, and novel organophosphorus compound

Abstract

Provided are a wiring board, metal-clad laminate, laminate, prepreg, curable composition, novel crosslinking agent, and novel organophosphorus compound enabling excellent electrical characteristics, flame retardancy, and heat resistance to be imparted.　The crosslinking agent is represented by formula (1). In formula (1): R1 represents a hydrocarbon group that may contain a hetero atom; each L independently represents a single bond, an oxygen atom, or a divalent hydrocarbon group optionally including a hetero atom; n is 2 or 3; each benzene ring optionally has a substituent; and the combination of components satisfies a specific relation.

Description

Crosslinking agents, curable compositions, prepregs, laminates, metal-clad laminates, wiring boards, and novel organophosphorus compounds

[0001] This disclosure relates to crosslinking agents, curable compositions, prepregs, laminates, metal-clad laminates, wiring boards, and novel organophosphorus compounds.

[0002] Resins used in electrical equipment and electronic components require high flame retardancy from the standpoint of fire prevention. Therefore, conventionally, halogen-containing compounds, primarily bromine compounds, have been used in these resins. However, halogen-containing compounds may generate harmful compounds such as corrosive hydrogen halides during combustion. For this reason, in recent years, phosphorus-containing compounds have been considered as alternative flame-retardant resins to halogen-containing compounds, due to their environmental impact.

[0003] Patent Document 1 discloses a curable resin composition containing a specific vinylphosphonic acid diester with improved flame retardancy.

[0004] Japanese Patent Publication No. 2020-15800

[0005] When a curable resin composition containing a specific vinylphosphonic acid diester described in Patent Document 1 was used in electronic components, etc., it sometimes exhibited inferior electrical properties and heat resistance.

[0006] This disclosure has been made in view of the above-mentioned problems and aims to provide novel organophosphorus compounds, crosslinking agents, curable compositions, prepregs, laminates, metal-clad laminates, and wiring boards that can impart excellent electrical properties, flame retardancy, and heat resistance.

[0007] This disclosure includes the following aspects: [1] A crosslinking agent represented by the following formula (1).

[0008] In the above formula (1), R １ represents a hydrocarbon group which may contain a heteroatom, L independently represents a divalent hydrocarbon group which may contain a single bond, an oxygen atom, or a heteroatom, n is 2 or 3, each benzene ring may independently have substituents, and each combination of components satisfies at least one of the following (A) to (E). (A) n is 2, R１ is a carbocyclic group which may contain a hetero atom, L is an oxygen atom, and the vinyl group bonded to the benzene ring is bonded to the ortho position as viewed from L. (B) n is 2, and R １ is a hydrocarbon group which may contain a hetero atom other than a carbocyclic group. (C) The vinyl group bonded to the benzene ring is bonded to the meta position as viewed from L. (D) n is 2, and L is a single bond or a divalent hydrocarbon group which may contain a hetero atom. (E) n is 3, and L is a single bond, a divalent carbocyclic group which may contain a hetero atom, or a divalent linear or branched hydrocarbon group. [2] R １ is a crosslinking agent according to [1] which does not have an epoxy group. [3] R １ is a hydrocarbon group in which the atom bonded to P may be an oxygen atom, the crosslinking agent according to [1] or [2]. [4] R １ is a linear alkyl group, a branched alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, an aryl group, or an aryloxy group, the crosslinking agent according to any one of [1] to [3]. [5] Satisfying the above (B), and R １ represents an alkyl group having 1 to 20 carbon atoms which may contain a hetero atom, the crosslinking agent according to any one of [1] to [4]. [6] Satisfying the above (B), and R １ is a group represented by the following formula (11), the crosslinking agent according to any one of [1] to [5]. R １１ -{ (O) ｎ１２ R １２} ｎ１３ -(O) ｎ１１ -* …(11) However, R １１ is a monovalent hydrocarbon group having no hetero atom, or a monovalent heterocyclic group, R １２ are each independently a divalent hydrocarbon group having no hetero atom, or a divalent heterocyclic group, n11 and n12 are each independently 0 or 1, n13 is an integer of 0 to 6, * indicates the bonding position to P. [7] Satisfying the above (C) or (D), and R １However, the crosslinking agent according to any one of [1] to [6] represents an alkyl group having 1 to 20 carbon atoms which may contain a heteroatom, or a carbon ring group having 1 to 20 carbon atoms which may contain a heteroatom. [8] Satisfying the above (C), R １The crosslinking agent according to any one of [1] to [7], wherein L is independently a single bond, an oxygen atom, a divalent carbocyclic group having 1 to 20 carbon atoms that may contain a heteroatom, or a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms that may contain a heteroatom. The crosslinking agent according to any one of [1] to [8], wherein L is independently a single bond, an oxygen atom, or a linear or branched alkylene group having 1 to 5 carbon atoms that may contain an oxygen atom. The crosslinking agent according to any one of [1] to [9], wherein L is independently a single bond, an oxygen atom, or a linear or branched alkylene group having 1 to 5 carbon atoms that may contain an oxygen atom.

[11] A crosslinking agent according to any one of [1] to

[10] that satisfies (D) or (E), wherein L independently represents a single bond, a divalent carbon ring group having 1 to 20 carbon atoms which may contain a heteroatom, or a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms which may contain a heteroatom.

[12] A crosslinking agent according to any one of [1] to

[11] that satisfies (D) or (E), wherein L independently represents a single bond, or a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms which may contain a heteroatom.

[13] A crosslinking agent according to any one of [1] to

[12] that satisfies (D) or (E), wherein L independently represents a single bond, or a linear or branched alkylene group having 1 to 5 carbon atoms which may contain an oxygen atom.

[14] A crosslinking agent according to any one of [1] to

[13] that satisfies (C) or (E) and at least one of the benzene rings has a linear or branched hydrocarbon group having 1 to 5 carbon atoms as a substituent.

[15] A crosslinking agent according to

[14] in which the substituent is bonded to the ortho position of the benzene ring.

[16] A crosslinking agent according to any one of [1] to

[15] that satisfies (E) and in which the vinyl groups are each independently bonded to the meta or para position of the benzene ring.

[17] A crosslinking agent according to any one of [1] to

[16] for use in a curable composition used in the manufacture of a prepreg, a metal-clad laminate, or a wiring board.

[18] A curable composition comprising a crosslinking agent according to any one of [1] to

[16] and a curable compound having a crosslinkable functional group that can crosslink with the crosslinking agent.

[19] A prepreg comprising a fibrous substrate and a semi-cured or cured product of the curable composition described in

[18] .

[20] A laminate comprising a substrate and a curable composition layer composed of the curable composition described in

[18] .

[21] A laminate comprising a substrate and a cured product-containing layer comprising a semi-cured or cured product of the curable composition described in

[18] .

[22] The laminate according to

[21] , wherein the substrate is a resin film or metal foil.

[23] The laminate according to

[21] , wherein the substrate is a resin film or metal foil.

[24] A metal-clad laminate comprising an insulating layer containing a cured product of the curable composition described in

[18] and metal foil.

[25] A wiring board comprising an insulating layer containing a cured product of the curable composition described in

[18] and wiring.

[26] An organophosphorus compound represented by the following formula (1).

[0009] In the above formula (1), R １ represents a hydrocarbon group which may contain a heteroatom, L independently represents a divalent hydrocarbon group which may contain a single bond, an oxygen atom, or a heteroatom, n is 2 or 3, each benzene ring may independently have substituents, and each combination of components satisfies at least one of the following (A) to (C). (A) n is 2, R １ (B) n is 2, R １ This is a hydrocarbon group which may contain heteroatoms other than a carbocyclic group. (C)n is 2 or 3, and the vinyl group bonded to the benzene ring is bonded at the meta position relative to L.

[0010] This disclosure provides novel organophosphorus compounds, novel crosslinking agents, curable compositions, prepregs, laminates, metal-clad laminates, and wiring substrates that can impart excellent electrical properties, flame retardancy, and heat resistance.

[0011] In this specification, numerical ranges indicated using "~" include the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise in this specification, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another stepwise numerical range. Also, in numerical ranges described in this specification, the upper or lower limit of that range may be replaced by the values ​​shown in the examples. When identical symbols exist in a chemical formula, these identical symbols may represent identical structures or different structures within a defined range.

[0012] The following describes in detail embodiments of the crosslinking agent, curable composition, prepreg, laminate, metal-clad laminate, wiring board, and novel organophosphorus compounds relating to this disclosure. However, this disclosure is not limited to these embodiments. Furthermore, it can be modified and implemented at will without departing from the gist of this disclosure.

[0013] <Crosslinking agent> The crosslinking agent relating to this disclosure (hereinafter also referred to as "this crosslinking agent") is represented by the following formula (1).

[0014] In the above formula (1), R １ represents a hydrocarbon group which may contain a heteroatom, L independently represents a divalent hydrocarbon group which may contain a single bond, an oxygen atom, or a heteroatom, n is 2 or 3, each benzene ring may independently have substituents, and each combination of components satisfies at least one of the following (A) to (E). (A) n is 2, R １ (B) n is 2, R １(C) n is a group other than a carbocyclic group which may contain a heteroatom. (D) n is 2 and L is a divalent hydrocarbon group which may contain a single bond or a heteroatom. (E) n is 3 and L is a divalent carbocyclic group which may contain a single bond or a heteroatom, or a divalent linear or branched hydrocarbon group which may contain a single bond or a heteroatom. Note that the above "benzene ring" is R １ This does not indicate a benzene ring that may be present, but rather a benzene ring bonded to L in formula (1).

[0015] As described above, this crosslinking agent can impart excellent electrical properties, flame retardancy, and heat resistance. Here, the electrical properties are presumed to be due to the introduction of styryl groups, which are composed of hydrocarbon skeletons, as crosslinkable functional groups, and to the fact that it is a polyfunctional styrene compound whose mobility can be controlled by the crosslinked structure. Furthermore, the flame retardancy is presumed to be due to the air barrier effect caused by the formation of a char layer resulting from the oxidation of phosphorus atoms in the structure, and the combustion delay effect due to radical scavenging during combustion. The char layer (carbonized layer) is a cohesive zone (solid phase) that is difficult to burn and has low reactivity, and it acts as an insulating layer, preventing the spread of fire. Furthermore, the heat resistance is presumed to be due to the fact that a three-dimensional network structure can be formed by the crosslinking reaction.

[0016] R １Examples of hydrocarbon groups represented by include saturated hydrocarbon groups, unsaturated hydrocarbon groups, and aromatic hydrocarbon groups. Saturated hydrocarbon groups may be linear, branched, or cyclic, but linear saturated hydrocarbon groups or branched hydrocarbon groups are preferred. From the viewpoint of electrical properties and ease of synthesis, the number of carbon atoms in the saturated hydrocarbon group is preferably 1 to 20, more preferably 1 to 18, even more preferably 1 to 14, and particularly preferably 1 to 6. Examples of saturated hydrocarbon groups include linear or branched alkyl groups and cycloalkyl groups. More specifically, examples of saturated hydrocarbon groups include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group, cyclopropyl group, cyclopentyl group, cyclohexyl group, and adamantyl group. Unsaturated hydrocarbon groups may be linear, branched, or cyclic, and examples include alkenyl groups and cycloalkenyl groups. The number of carbon atoms in the unsaturated hydrocarbon group is preferably 1 to 20, and more preferably 1 to 12. Aromatic hydrocarbon groups are preferably those with 5 to 20 carbon atoms, such as phenyl groups, monovalent biphenyl groups, tolyl groups, naphthyl groups, and other aryl groups. These hydrocarbon groups may contain heteroatoms in their structure. Examples of heteroatoms include, but are not limited to, oxygen atoms, nitrogen atoms, and sulfur atoms. For example, an oxygen atom may be contained within the main chain skeleton of the hydrocarbon group in an ether bond (-C-O-C-), or it may be bonded to a carbon-hydrogen group as a substituent, such as a hydroxyl group, carboxyl group, or alkoxy group. In other words, the hydrocarbon group may or may not have substituents, and the number of substituents is not particularly limited. Among these, it is preferable that the heteroatom be located within the carbon skeleton of the hydrocarbon group, i.e., between carbon atoms, or at the terminal bonded to P in formula (1). Also, R １ However, when representing a carbon ring group, R １R may be a heterocyclic group. Examples of heterocyclic groups include furan rings, thiophene rings, pyrrole rings, imidazole rings, pyridine rings, pyrimidine rings, pyrazine rings, morpholine rings, pyrrolidine rings, piperidine rings, and imidazole rings. However, R １ It is preferable that it does not have an epoxy group (a three-membered ring consisting of two carbon atoms and one oxygen atom).

[0017] R １ Among these, the group represented by the following formula (11) is preferred. R １１ - {(O) ｎ１２ R １２} ｎ１３ - (O) ｎ１１ - * ... (11) However, R １１ R is a monovalent hydrocarbon group or a monovalent heterocyclic group that does not have a heteroatom. １２ Each of the following is independently a divalent hydrocarbon group or a divalent heterocyclic group that does not have a heteroatom, n11 and n12 are independently 0 or 1, n13 is an integer from 0 to 6, and * indicates the bond position with P.

[0018] R １１ Examples of monovalent hydrocarbon groups in R include alkyl groups, alkenyl groups, and aryl groups. １１ The alkyl group in R may be a linear alkyl group, a branched alkyl group, or a cyclic alkyl group. The number of carbon atoms in the alkyl group is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 4. Specific examples of alkyl groups include methyl group, ethyl group, n-propyl group, n-butyl group, tert-butyl group, and cyclohexyl group. １１ The alkenyl group in this context refers to a group in which any carbon-carbon bond of the alkyl group is a double bond. Specific examples of alkenyl groups include vinyl groups, allyl groups, and cycloalkenyl groups such as cyclohexenyl groups. １１ Examples of aryl groups in this include phenyl groups and naphthyl groups. １１Examples of heterocyclic groups in this context include substituents obtained by removing a hydrogen atom from a carbon atom of a furan ring, thiophene ring, pyrrole ring, imidazole ring, pyridine ring, pyrimidine ring, pyrazine ring, morpholine ring, pyrrolidine ring, piperidine ring, or imidazole ring.

[0019] R １２ Examples of divalent hydrocarbon groups in this context include alkylene groups and arylene groups. １２ The alkylene group in R may be a linear alkylene group, a branched alkylene group, or a cyclic alkylene group. The number of carbon atoms in the alkylene group is preferably 1 to 10, more preferably 1 to 6, and even more preferably 1 to 4. Specific examples of alkylene groups include methylene, ethylene, propylene, butylene, and cyclohexylene groups. １２ Examples of arylene groups in this include phenylene groups and naphthylene groups. １２ Examples of heterocyclic groups in this context include divalent substituents in which one hydrogen atom is removed from each of two carbon atoms, such as furan rings, thiophene rings, pyrrole rings, imidazole rings, pyridine rings, pyrimidine rings, pyrazine rings, morpholine rings, pyrrolidine rings, piperidine rings, and imidazole rings.

[0020] n11 is either 0 or 1. If n11 is 0, the end of R1 is a carbon atom. If n11 is 1, the end of R1 is an oxygen atom. n12 is either 0 or 1. If n12 is 0, two adjacent hydrocarbon groups are linked. Specific examples of such structures include biphenylene groups and terphenylene groups.

[0021] n13 is {(O) ｎ１２ R １２ This represents the number of repetitions of} and is an integer from 0 to 6. When n13 is 0, equation (11) is expressed as equation (12) below. R １１ - (O) ｎ１１ - * ... (12) However, each symbol is as described above.

[0022] R １Among these, the group represented by formula (12) is preferred. Specific examples of the group represented by formula (12) include linear alkyl groups, branched alkyl groups, cycloalkyl groups, alkenyl groups, cycloalkenyl groups, aryl groups, and aryloxy groups.

[0023] Also, R １ From the viewpoint of reducing dielectric loss, improving solubility in solvents, and improving heat resistance, it is preferable that the group is a linear or branched saturated hydrocarbon group (e.g., an alkyl group having 1 to 20 carbon atoms) which may contain heteroatoms, or a carbon ring group (e.g., an aromatic hydrocarbon group such as a phenyl group) which may contain heteroatoms (e.g., an aromatic hydrocarbon group having 1 to 20 carbon atoms).

[0024] When L represents a single bond, the phosphorus atom is directly bonded to the vinylphenyl group. Examples of divalent hydrocarbon groups represented by L include divalent saturated hydrocarbon groups, divalent unsaturated hydrocarbon groups, and divalent aromatic hydrocarbon groups. Divalent saturated hydrocarbon groups may be linear, branched, or cyclic. From the viewpoint of ease of synthesis, the number of carbon atoms in the saturated hydrocarbon group is preferably 1 to 20, more preferably 1 to 12, even more preferably 1 to 10, even more preferably 1 to 7, and particularly preferably 1 to 4. Examples of divalent saturated hydrocarbon groups include linear or branched alkylene groups and cycloalkylene groups. More specifically, examples of divalent saturated hydrocarbon groups include methylene groups, ethylene groups, propylene groups, isopropylene groups, butylene groups, isobutylene groups, pentylene groups, hexylene groups, and cyclopropylene groups. As for divalent unsaturated hydrocarbon groups, those having 2 to 20 carbon atoms are preferred, for example, alkenylene groups and alkylylene groups. As for divalent aromatic hydrocarbon groups, those having 5 to 20 carbon atoms are preferred, for example, phenylene groups and divalent biphenyl groups (-C ６ H ５ -C ６ H ５Examples include the terphenylene group. These divalent hydrocarbon groups may contain heteroatoms in their structure. Examples of heteroatoms include, but are not limited to, oxygen, nitrogen, and sulfur atoms. The heteroatom may be included in the main chain skeleton of the divalent hydrocarbon group, for example, as an ether bond, or it may be bonded to the divalent carbon-hydrogen group as a substituent, such as a hydroxyl group, carboxyl group, or alkoxy group. In other words, the divalent hydrocarbon group may or may not have substituents, and the number of substituents is not particularly limited.

[0025] Furthermore, L is preferably a divalent carbon ring group having 1 to 20 carbon atoms, which may contain a single bond, an oxygen atom, or a heteroatom, or a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms, which may contain a heteroatom, from the viewpoint of reducing dielectric loss, improving the availability of synthesis raw materials, and improving heat resistance. More specifically, examples of such L include a linear or branched alkylene group having 1 to 5 carbon atoms, which may contain a single bond, an oxygen atom, or an oxygen atom. An example of a linear or branched alkylene group which may contain an oxygen atom is *-O-R Ａ -** (R Ａ (where * represents a linear or branched alkylene group (e.g., having 1 to 5 carbon atoms), * represents the bond position with the phosphorus atom, and ** represents the bond position with the vinylphenyl group.)

[0026] When L is a divalent hydrocarbon group which may contain a heteroatom, the group represented by the following formula (21) is preferred: *-(O) ｎ２１ R ２１ - {(O) ｎ２２ R ２２} ｎ２４ - (O) ｎ２３ -** ... (21) However, R ２１ and R ２２ Each of the following is independently a divalent hydrocarbon group or a divalent heterocyclic group that does not have a heteroatom, n21, n22, and n23 are independently 0 or 1, n24 is an integer from 0 to 6, * indicates the bond position with P, and ** indicates the bond position with the benzene ring.

[0027] R ２１ and R ２２ is the aforementioned R １２ Similar examples include the following: n21 is 0 or 1. If n21 is 0, the P-side end of L is a carbon atom. If n21 is 1, the P-side end of L is an oxygen atom. n23 is 0 or 1. If n23 is 0, the benzene ring-side end of L is a carbon atom. If n23 is 1, the benzene ring side of L is an oxygen atom. n22 is 0 or 1. If n12 is 0, two adjacent hydrocarbon groups are linked. Specific examples of such structures include the biphenylene group and the terphenylene group.

[0028] n24 is {(O) ｎ２２ R ２２ This represents the number of repetitions of} and is an integer from 0 to 6. When n24 is 0, equation (21) is expressed as equation (22) below. *-(O) ｎ２１ R ２１ - (O) ｎ２３ -** …(22) However, each symbol is as described above.

[0029] L is preferably a single bond, an oxygen atom, or a group represented by formula (22).

[0030] n is a real number between 2 and 3. The crosslinking agent may be, for example, a single compound of the crosslinking agent with n = 2, a single compound of the crosslinking agent with n = 3, or a mixture thereof.

[0031] In the crosslinking agent represented by formula (1), the substitution position of the vinyl group on the benzene ring can be the ortho, meta, or para position. Unless otherwise specified, the ortho, meta, and para positions are determined based on the position of substituent L.

[0032] The benzene ring in the vinylphenyl group may or may not have other substituents, and the number of such substituents is not particularly limited. Examples of substituents that the benzene ring may have include alkyl groups (e.g., having 1 to 20 carbon atoms) such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, hexyl, and octyl groups; alkenyl groups such as vinyl and allyl groups; alkoxy groups such as methoxy, ethoxy, and propoxy groups; and aryl groups such as phenyl and tolyl groups, but are not limited to these. However, from the viewpoint of electrical properties, the substituents on the benzene ring are preferably nonpolar groups. For example, the benzene ring may have two or more vinyl groups.

[0033] From the viewpoint of excellent electrical properties, flame retardancy, and heat resistance, this crosslinking agent satisfies at least one of the following combinations of components in formula (1): (A) n is 2, and R １ (B) n is 2, R １ (C) is a hydrocarbon group which may contain heteroatoms other than a carbocyclic group. (D) is a divalent hydrocarbon group which may contain a single bond or a heteroatom, and n is 2 or 3, and the vinyl group bonded to the benzene ring is bonded at the meta position relative to L. (E) is a divalent carbocyclic group which may contain a single bond or a heteroatom, and n is 3, and L is a divalent linear or branched hydrocarbon group which may contain a single bond or a heteroatom.

[0034] Hereinafter, a compound that satisfies condition (A) above may be referred to as compound (A). The same applies to conditions (B) to (E) above. Note that this crosslinking agent may be a compound that satisfies two or more of conditions (A) to (E) above.

[0035] (Compound (A)) Compound (A) is represented by the following formula (A).

[0036] However, R １ This is a carbon ring group that may contain heteroatoms.

[0037] Examples of carbocyclic groups include cyclic saturated hydrocarbon groups, cyclic unsaturated hydrocarbon groups, and aromatic hydrocarbon groups. From the viewpoint of ease of synthesis, the number of carbon atoms in cyclic saturated hydrocarbon groups is preferably 3 to 20, more preferably 3 to 10, even more preferably 3 to 8, and particularly preferably 3 to 6. Examples of cyclic saturated hydrocarbon groups include cycloalkyl groups. Examples of cyclic saturated hydrocarbon groups include cyclopropyl groups, cyclobutyl groups, cyclopentyl groups, cyclohexyl groups, cyclooctyl groups, and adamantyl groups. The number of carbon atoms in cyclic unsaturated hydrocarbon groups is preferably 3 to 20, more preferably 3 to 10, even more preferably 3 to 8, and particularly preferably 3 to 6. Examples of cyclic unsaturated hydrocarbon groups include cycloalkenyl groups and cycloalkynyl groups. Aromatic hydrocarbon groups are preferably those with 5 to 20 carbon atoms, such as phenyl groups, naphthyl groups, and biphenyl groups (-C). ６ H ５ -C ６ Examples include H6) and terphenylene groups. These divalent carbocyclic groups may contain heteroatoms in their structure. Examples of heteroatoms include, but are not limited to, oxygen, nitrogen, and sulfur atoms. The heteroatom, for example, an oxygen atom, may be included in the main chain skeleton of the carbocyclic group as an ether bond, or it may be bonded to the carbocyclic group as a substituent, such as a hydroxyl group, carboxyl group, or alkoxy group. In other words, the divalent carbocyclic group may or may not have substituents, and the number of substituents is not particularly limited. １ In this, the carbocyclic group having a heteroatom may be a heterocyclic group. Examples of heterocyclic groups include furan rings, thiophene rings, pyrrole rings, imidazole rings, pyridine rings, pyrimidine rings, pyrazine rings, morpholine rings, pyrrolidine rings, piperidine rings, and imidazole rings.

[0038] The benzene ring in the vinylphenyl group may or may not have substituents, and the number of substituents is not particularly limited. Examples of substituents that the benzene ring may have include alkyl groups (e.g., having 1 to 20 carbon atoms) such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, hexyl, and octyl groups; alkenyl groups such as vinyl and allyl groups; alkoxy groups such as methoxy, ethoxy, and propoxy groups; and aryl groups such as phenyl and tolyl groups, but are not limited to these. However, from the viewpoint of electrical properties, the substituents on the benzene ring are preferably nonpolar groups. For example, the benzene ring may have two or more vinyl groups, and the bonding positions of these vinyl groups are arbitrary except in the case described above.

[0039] (Compound (B)) Compound (B) is represented by the following formula (B).

[0040] However, R １ is a hydrocarbon group which may contain heteroatoms other than a carbocyclic group, and L is the same as in formula (1).

[0041] R １ Groups other than the carbocyclic group which may contain heteroatoms include linear or branched saturated hydrocarbon groups and linear or branched unsaturated hydrocarbon groups. Specific examples of these are the same as those mentioned above. R in compound (B) １ Among these, alkyl groups having 1 to 20 carbon atoms, which may contain heteroatoms, are preferred.

[0042] L is the same as described in formula (1). From the viewpoint of further improving electrical properties, flame retardancy and heat resistance, L in compound (B) is preferably a divalent carbon ring group having 1 to 20 carbon atoms that may contain a single bond, an oxygen atom, or a heteroatom, or a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms that may contain a heteroatom, and more preferably a linear or branched alkylene group having 1 to 5 carbon atoms that may contain a single bond, an oxygen atom, or an oxygen atom.

[0043] The substitution position of the vinyl group on the benzene ring is arbitrary, i.e., it may be at the ortho, meta, or para position. In compound (B), the substitution position of the vinyl group is preferably the para position, from the viewpoint of minimizing steric hindrance during the crosslinking reaction and facilitating the acquisition of raw materials and synthesis.

[0044] (Compound (C)) Compound (C) is represented by the following formula (C).

[0045] However, R １ , L and n are the same as in equation (1).

[0046] R １ This is the same as described in formula (1). From the viewpoint of further improving electrical properties, flame retardancy and heat resistance, R in compound (C) １ C1 to C20 alkyl groups which may contain heteroatoms, or C1 to C20 carbon-based carbocyclic groups which may contain heteroatoms, and C1 to C20 aromatic carbocyclic groups which may contain heteroatoms are more preferred. Furthermore, L is the same as described in formula (1). From the viewpoint of further improving electrical properties, flame retardancy and heat resistance, L in compound (C) is preferably a single bond, an oxygen atom, a C1 to C20 divalent carbocyclic group which may contain heteroatoms, or a C1 to C10 divalent linear or branched hydrocarbon group which may contain heteroatoms, and is more preferably a single bond, an oxygen atom, or a C1 to C5 linear or branched alkylene group which may contain oxygen atoms.

[0047] In compound (C), the benzene ring in the vinylphenyl group may have other substituents. In compound (C), it is preferable that the other substituents be linear or branched hydrocarbon groups having 1 to 5 carbon atoms, and it is more preferable that the substituents are located in the ortho position.

[0048] (Compound (D)) Compound (D) is represented by the following formula (D).

[0049] However, R １ This is the same as formula (1), where L is a divalent hydrocarbon group which may contain a single bond or a heteroatom.

[0050] R １ This is the same as described in formula (1). In terms of further improving electrical properties, flame retardancy, and heat resistance, R in compound (D) １ Preferably, L in compound (D) is a C1-C20 alkyl group that may contain heteroatoms, or a C1-C20 carbon ring group that may contain heteroatoms. Furthermore, from the viewpoint of further improving electrical properties, flame retardancy, and heat resistance, L is preferably a single bond, a C1-C20 divalent carbon ring group that may contain heteroatoms, or a C1-C10 divalent linear or branched hydrocarbon group that may contain heteroatoms, more preferably a single bond, or a C1-C5 divalent linear or branched hydrocarbon group that may contain heteroatoms, and even more preferably a single bond, or a C1-C5 linear or branched alkylene group that may contain oxygen atoms.

[0051] (Compound (E)) Compound (E) is represented by the following formula (E).

[0052] However, L independently represents a single bond, a divalent carbocyclic group which may contain a heteroatom, or a divalent linear or branched hydrocarbon group which contains a heteroatom. When L represents a single bond, the phosphorus atom is directly bonded to the vinylphenyl group.

[0053] Examples of the divalent carbocyclic group represented by L include a divalent cyclic saturated hydrocarbon group, a divalent cyclic unsaturated hydrocarbon group, and a divalent aromatic hydrocarbon group. From the viewpoint of ease of synthesis, the number of carbon atoms in the divalent cyclic saturated hydrocarbon group is preferably 3 to 20, more preferably 3 to 10, still more preferably 3 to 8, and particularly preferably 3 to 6. Examples of the divalent cyclic saturated hydrocarbon group include a cycloalkylene group. More specifically, examples of the divalent cyclic saturated hydrocarbon group include a cyclopropylene group, a cyclobutylene group, a cyclopentylene group, a cyclohexylene group, a cycloheptylene group, a cyclooctylene group, and the like. The number of carbon atoms in the divalent cyclic unsaturated hydrocarbon group is preferably 3 to 20, more preferably 3 to 10, still more preferably 3 to 8, and particularly preferably 3 to 6. Examples of the divalent cyclic unsaturated hydrocarbon group include a cycloalkenylene group and a cycloalkynylene group. The divalent aromatic hydrocarbon group preferably has 5 to 20 carbon atoms, and examples thereof include a phenylene group, a divalent biphenyl group (-C ６ H ５ -C ６ H ５ -), and a terphenylene group. These divalent carbocyclic groups may contain heteroatoms in their structures. Examples of the heteroatom include, but are not limited to, an oxygen atom, a nitrogen atom, and a sulfur atom. Taking an oxygen atom as an example, the heteroatom may be contained in the main chain skeleton of the divalent carbocyclic group like an ether bond, or may be bonded to the divalent carbocyclic group as a substituent like a hydroxyl group, a carboxyl group, or an alkoxy group. That is, the divalent carbocyclic group may or may not have a substituent, and the number of such substituents is not particularly limited.

[0054] Examples of divalent linear or branched hydrocarbon groups represented by L include linear or branched divalent saturated hydrocarbon groups and divalent unsaturated hydrocarbon groups. From the viewpoint of ease of synthesis, the number of carbon atoms in the linear or branched divalent saturated hydrocarbon group is preferably 1 to 20, more preferably 1 to 12, even more preferably 1 to 10, even more preferably 1 to 7, and particularly preferably 1 to 4. Examples of such divalent saturated hydrocarbon groups include linear or branched alkylene groups. More specifically, examples of such divalent saturated hydrocarbon groups include methylene groups, ethylene groups, propylene groups, isopropylene groups, butylene groups, isobutylene groups, pentylene groups, and hexylene groups. Examples of linear or branched divalent unsaturated hydrocarbon groups include those with 2 to 20 carbon atoms, such as alkenylene groups and alkylylene groups. The above-mentioned divalent linear or branched hydrocarbon groups contain heteroatoms in their structure. Examples of heteroatoms include, but are not limited to, oxygen, nitrogen, and sulfur atoms. Furthermore, heteroatoms, for example, oxygen atoms, may be included in the main chain skeleton of a divalent hydrocarbon group, such as in an ether bond, or they may be bonded to a divalent carbon-hydrogen group as substituents, such as hydroxyl, carboxyl, or alkoxy groups. In other words, the divalent hydrocarbon group may or may not have substituents, and the number of substituents is not particularly limited.

[0055] Furthermore, L is preferably a divalent carbon ring group having 1 to 20 carbon atoms, which may contain a single bond or a heteroatom, or a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms, which may contain a heteroatom, from the viewpoint of reducing dielectric loss, improving the availability of synthesis raw materials, and improving heat resistance. More preferably, it is a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms, which may contain a single bond or a heteroatom, and even more preferably, it is a linear or branched alkylene group having 1 to 5 carbon atoms, which may contain a single bond or an oxygen atom. An example of a linear or branched alkylene group containing an oxygen atom is *-O-R Ａ -** (R Ａ(where * represents a linear or branched alkylene group (e.g., having 1 to 5 carbon atoms), * represents the bond position with the phosphorus atom, and ** represents the bond position with the vinylphenyl group.)

[0056] The benzene ring in the vinylphenyl group may or may not have substituents, and the number of substituents is not particularly limited. Furthermore, as mentioned above, the substitution position of the vinyl group on the benzene ring is arbitrary, i.e., it may be at the ortho, meta, or para position. However, from the viewpoint of minimizing steric hindrance during the crosslinking reaction and facilitating raw material acquisition and synthesis, the substitution position of the vinyl group is preferably at the meta or para position, and more preferably at the para position. Examples of substituents that the benzene ring may have include hydrocarbon groups that may contain heteroatoms. The number of carbon atoms in the hydrocarbon group as a substituent can be, for example, 1 to 20, and preferably 1 to 5. Furthermore, the hydrocarbon group as a substituent may be linear, branched, or cyclic, but is preferably linear or branched. Thus, at least one of the benzene rings may have, for example, a linear or branched hydrocarbon group having 1 to 5 carbon atoms as a substituent. Specific examples of the substituents include, but are not limited to, alkyl groups (e.g., C1-C20) such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, hexyl, and octyl groups; alkenyl groups such as vinyl and allyl groups; alkoxy groups such as methoxy, ethoxy, and propoxy groups; and aryl groups such as phenyl and tolyl groups. However, from the viewpoint of electrical properties, the substituents on the benzene ring are preferably nonpolar groups. As described above, the substitution position of the substituents on the benzene ring is not particularly limited, but for example, they can be bonded to the ortho position of the benzene ring. Also, for example, there may be two or more vinyl groups on the benzene ring, and the bond positions of these vinyl groups are also arbitrary as described above.

[0057] This crosslinking agent can be synthesized by known synthesis methods. For specific synthesis examples, please refer to the examples described later. As mentioned above, this crosslinking agent has a structure in which multiple styryl groups (vinylphenyl groups), which have excellent dielectric properties and reactivity, are substituted on the phosphorus atom, and therefore it can have excellent flame retardancy, crosslinkability, dielectric properties (excellent even under high-frequency conditions, for example), and heat resistance. Furthermore, when this crosslinking agent is used, good mechanical properties can be imparted, and because it can form a chemical bond with the curable compound through the crosslinking reaction, it can also suppress a decrease in processability such as bleed-out. For this reason, this crosslinking agent can be used in any application such as a crosslinking agent or flame retardant, and is suitable for curable compositions, prepregs, laminates, metal-clad laminates, and wiring boards.

[0058] <Organophosphorus Compounds> Compounds (A) to (C) above are novel organophosphorus compounds. These organophosphorus compounds have a structure in which multiple styryl groups (vinylphenyl groups), which have excellent dielectric properties and reactivity, are substituted, and can therefore have excellent flame retardancy, crosslinkability, dielectric properties (even under high-frequency conditions, for example), and heat resistance. Furthermore, when these phosphorus compounds are used, good mechanical properties can be imparted, and since they can form chemical bonds with curable compounds through crosslinking reactions, it is also possible to suppress a decrease in processability such as bleed-out.

[0059] <Curable Composition> The curable composition according to this disclosure (hereinafter also referred to as "this composition") comprises the crosslinking agent and a curable compound having (for example, two or more) crosslinkable functional groups that can crosslink with the crosslinking agent. The crosslinking agent contained in this composition may be a single type or two or more types may be used in combination. The curable compound contained in this composition may be a single type or two or more types may be used in combination. This composition may be thermosetting or active energy ray curable. An active energy ray curable composition is a composition that hardens upon irradiation with active energy rays such as ultraviolet rays and electron beams. Thermosetting is preferred for applications such as metal-clad laminates and wiring boards. Furthermore, "this composition" may refer to the mixture in its pre-curing state or to the (semi-)cured state.

[0060] Examples of curable compounds (resin components) include monomers, oligomers, and prepolymers, and include those in the pre-curing and (semi-)cured states. As described above, one type of curable compound (resin component) may be used alone, or two or more types may be used in combination, for example. The molecular weight of the oligomers and prepolymers is not particularly limited. The number-average molecular weight (Mn) of the oligomer can be, for example, 1000 to 5000. The curable compounds are not particularly limited, but examples include polyethylene resin, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene-styrene (ABS) resin, methyl methacrylate-butadiene-styrene resin (MBS resin), methyl methacrylate-acrylonitrile-butadiene-styrene resin (MABS resin), acrylonitrile-acrylic rubber-styrene resin (AAS resin), polymethyl (meth)acrylate resin, polyphenylene ether (PPE) resin, bismaleimide resin, epoxy resin, fluororesin, polyimide resin, olefin resin, polyester resin, polystyrene resin, hydrocarbon elastomer, benzoxazine resin, activated ester resin, cyanate ester resin, butadiene resin, hydrogenated or unhydrogenated styrene-butadiene resin, vinyl resin, cycloolefin polymer, aromatic polymer, and divinyl aromatic polymer. Examples include polyethylene terephthalate resin, polybutylene terephthalate resin, polyethylene naphthalate, unsaturated polyester resin, polyesterimide resin, polyketone resin, polycarbonate resin, polyamide resin, polyamideimide resin, polycarbodiimide resin, polyetherimide resin, polyetherketone resin, polyetheretherketone resin (PEEK resin), polyethersulfone resin, polythioethersulfone resin, polysulfone resin, polyphenylene sulfide resin, polyethernitrile resin, polyarylate resin, polybenzimidazole resin, benzoxazine resin, liquid crystal polymer resin, silicone resin, epoxy resin, polyurethane resin, phenol resin, melamine resin, urea resin, diallyl phthalate resin, resins having vinylsilyl groups in the side chains, resins having olefin structures at the terminals, and combinations thereof.

[0061] Examples of resins having vinylsilyl groups in the side chains include, but are not particularly limited to, resins containing a structure represented by the following formula.

[0062]

[0063] Furthermore, the resin having olefin structures (for example, two or more) at its terminal end (hereinafter also referred to as a terminal olefin resin) may have, for example, isoalkenyl groups, more specifically, C2-C10 alkenyl groups at its terminal end. That is, the olefin structure may be a carbon-carbon double bond of the C2-C10 alkenyl group. The alkenyl group may be linear or branched, and may be, for example, a normal alkenyl group or an isoalkenyl group. More specifically, examples of such alkenyl groups include a normal propenyl group, an isopropenyl group, a 2-butenyl group, a 3-butenyl group, and the like.

[0064] For applications such as metal-clad laminates and wiring boards, the curable compound preferably includes, for example, PPE resin and the above-mentioned terminal olein resin. In this specification, unless otherwise specified, PPE resin includes unmodified polyphenylene ether resin and modified polyphenylene ether resin. As the PPE resin, any PPE resin conventionally known in the field of wiring boards can be used as appropriate.

[0065] Furthermore, if the above-mentioned terminal olefin resin has an isopropenyl group as an olefin structure at the terminal part of its molecular structure, it can be represented, for example, by the following formula (2).

[0066] In formula (2), E represents a polymer chain.

[0067] Further, the terminal olefin resin may have a benzene ring structure in its molecular structure. The benzene ring structure may or may not have a substituent on the benzene ring. Examples of the substituent include a hydroxyl group, a halogen group, an alkyl group having 1 to 20 carbon atoms, a halogenated alkyl group having 1 to 20 carbon atoms, a cycloalkyl group having 5 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms. Examples of the halogen group include -F, -Cl, -Br, and -I. Examples of the alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an isopropenyl group, a t-butyl group, and an n-butyl group. The halogenated alkyl group is one in which a hydrogen atom of the alkyl group is substituted with a halogen atom, and examples of the halogen atom include F, Cl, Br, and I. Examples of the cycloalkyl group having 5 to 20 carbon atoms include a cyclopentyl group and a cyclohexyl group. Examples of the aralkyl group having 7 to 20 carbon atoms include a phenylmethyl group (benzyl group), a phenylethyl group (phenethyl group), a phenylpropyl group, and a diphenylmethyl group.

[0068] The terminal olefin resin may have, for example, a structure represented by the following formula (2-1).

[0069] In formula (2-1), E １ represents a polymer chain, and R ２４ each independently represents a hydrocarbon group having 1 to 10 carbon atoms or a halogenated alkyl group, and m13 represents a real number of 0 to 4. Here, R ２４ is preferably a hydrocarbon group having 1 to 5 carbon atoms, more preferably a hydrocarbon group having 1 to 3 carbon atoms, from the viewpoint of electrical properties. Examples of the hydrocarbon group having 1 to 10 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an isopropenyl group, a t-butyl group, and an n-butyl group. The halogenated alkyl group is one in which a hydrogen atom of the alkyl group is substituted with a halogen atom, and examples of the halogen atom include F, Cl, Br, and I. The number of carbon atoms of the alkyl group is, for example, 1 to 10. R ２４If there are multiple R ２４ These may be the same group or different groups. Also, in formula (2-1), m13 is a real number from 0 to 4, preferably from 0 to 3, and more preferably 0. Note that in the structure shown in formula (2-1) above, the isopropenyl group and m bonded to the benzene ring are １３ Individual R ２４ The bonding position is not particularly limited.

[0070] The above-mentioned terminal olefin resin may be, for example, a compound derived from a raw material compound having a benzene ring and a plurality of alkenyl groups (e.g., isoalkenyl groups) or a compound derived from a precursor of the said raw material compound. The said raw material compound may be 1,3-diisoalkenylbenzene (e.g., 1,3-diisopropenylbenzene) or 1,4-diisoalkenylbenzene (e.g., 1,4-diisopropenylbenzene).

[0071] The above-mentioned terminal olefin resin can be a compound (polymer) obtained, for example, by polymerizing a compound having multiple alkenyl groups (e.g., a diisoalkenyl compound) under an acid catalyst at a specific reaction temperature. Compounds having multiple alkenyl groups can be those produced by known methods. The above-mentioned diisoalkenyl compound can be produced, for example, by adding an alkene to an aromatic compound and performing a dehydrogenation reaction. Alternatively, for example, a diisopropenyl compound can be synthesized by oxidizing a cumyl group and performing intramolecular dehydration from a diol compound obtained by hydrogen reduction. The raw material compound (raw material monomer) for producing the above-mentioned terminal olefin resin may be a precursor of a compound having multiple alkenyl groups (e.g., a diisopropenyl compound precursor). Two or more types of the above-mentioned terminal olefin resin may be used, and the blending ratio of each resin can be appropriately set within the range in which the effects of the present invention can be obtained. Furthermore, the composition may contain, for example, a terminal olefin resin and other resins (e.g., resins having an olefin structure other than the terminal portion), or, as described above, may contain two or more types of the terminal olefin resin.

[0072] When, for example, 1,3- or 1,4-diisopropenylbenzene is used as the raw material compound, the terminal olefin resin can be a resin having at least one of the following six structures.

[0073] Here, R １７ ~R ２３ Each of the following independently represents a hydrocarbon group having 1 to 10 carbon atoms or an alkyl halogenated group; m6, m8, m9, and m12 independently represent a real number from 0 to 4; m7 represents a real number from 0 to 3; m10 and m11 independently represent a real number from 0 to 2; and * and ** represent bond positions, respectively. R １７ ~R ２３ These may be the same group or different groups. １７ ~R ２３ From the viewpoint of electrical properties, is preferably a hydrocarbon group having 1 to 5 carbon atoms, and more preferably a hydrocarbon group having 1 to 3 carbon atoms. Examples of the hydrocarbon group having 1 to 10 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, isopropenyl group, t-butyl group, and n-butyl group. The halogenated alkyl group is one in which the hydrogen atoms of the alkyl group are substituted with halogen atoms, and examples of halogen atoms include F, Cl, Br, and I. The number of carbon atoms in the alkyl group is, for example, 1 to 10. m6, m8, m9, and m12 are real numbers from 0 to 4, preferably 0 to 3, and more preferably 0. m7 is a real number from 0 to 3, preferably 0 to 2, and more preferably 0. m10 and m11 are real numbers from 0 to 2, preferably 0 to 1, and more preferably 0. In the above six structures, R is bonded to the benzene ring structure. １７ ~R ２３ The bonding positions of the isopropenyl group and other bonding groups are not particularly limited.

[0074] In formula (2), the polymer chain represented by E may include at least one of the six structures described above. Also, in formula (2-1) above, E １ The polymer chain represented by can also include at least one of the six structures described above.

[0075] The weight-average molecular weight Mw of the terminal olefin resin is preferably 2,500 or more, more preferably 5,000 or more, and even more preferably 10,000 or more, from the viewpoint of curability and heat resistance. Furthermore, the weight-average molecular weight Mw of the terminal olefin resin is preferably 500,000 or less, more preferably 200,000 or less, even more preferably 150,000 or less, and particularly preferably 100,000 or less, from the viewpoint of solvent solubility. The method for measuring the weight-average molecular weight will be described later.

[0076] The (semi-)cured product of this composition includes the reaction product of the curable compound and the crosslinking agent. Herein, in this specification, (semi-)cured is a general term for semi-cured and cured products, and may be either semi-cured or cured. Semi-cured can include all states between the pre-cured state and the (completely) cured state.

[0077] The composition preferably contains one or more polymerization initiators. Suitable polymerization initiators include organic peroxides, azo compounds, other known polymerization initiators, and combinations thereof. The polymerization initiator can be appropriately selected depending on the polymerization method of the composition. Examples of polymerization initiators include thermal polymerization initiators, photopolymerization initiators, and radical polymerization initiators.

[0078] Examples of thermal polymerization initiators include azo compounds such as 2,2-azobisisobutyronitrile (AIBN), 2,2-azobis(2-methylbutyronitrile), azobis-2,4-dimethylvaleronitrile, azobiscyclohexylnitrile, and azobiscyanovaleric acid; peroxides such as benzoyl peroxide, dicumyl peroxide, and diisopropyl peroxydicarbonate; and acid generators such as aromatic sulfonates. These may be used individually or in combination of two or more.

[0079] Examples of photopolymerization initiators include acetophenone-based photopolymerization initiators, benzophenone-based photopolymerization initiators, benzoin-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, sulfonium-based photopolymerization initiators, and iodonium-based photopolymerization initiators. These may be used individually or in combination of two or more. When using a photopolymerization initiator, a sensitizer such as a tertiary amine may be used in combination as needed.

[0080] Examples of radical polymerization initiators include 2,3-dimethyl-2,3-diphenylbutane, di-t-butyl peroxide, 2,5-dimethyl-2,5-di(t-butyl peroxide)hexane, 2,5-dimethyl-2,5-di(t-butyl peroxide)hexyne-3, α,α'-di(t-butyl peroxy)diisopropylbenzene, t-butyl peroxybenzoate, cumene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, 2,5-dimethyl-2,5-di(tert-butyl peroxy)hexyne-3, and tert-butylcumyl peroxide. Examples of peroxides include di(iodide), α,α'-di(tert-butylperoxy)diisopropylbenzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, di-tert-butylperoxyisophthalate, tert-butylperoxybenzoate, 2,2-bis(tert-butylperoxy)butane, 2,2-bis(tert-butylperoxy)octane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, di(trimethylsilyl)peroxide, trimethylsilyltriphenylsilylperoxide, and azobisisobutyronitrile. These may be used individually or in combination of two or more.

[0081] The amount of polymerization initiator in this composition is not particularly limited, but is preferably 0.001 to 20 parts by mass, more preferably 0.01 to 15 parts by mass, and even more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the curable compound.

[0082] This composition may optionally contain one or more additives. Examples of additives include inorganic fillers, compatibilizers, and flame retardants (excluding the crosslinking agent). The amounts of each additive are not particularly limited and can be set as appropriate within the range in which the effects of this disclosure are obtained.

[0083] Examples of inorganic fillers include silica such as spherical silica, metal oxides such as alumina, titanium oxide, and mica; metal hydroxides such as aluminum hydroxide and magnesium hydroxide; talc; aluminum borate; barium sulfate; and calcium carbonate. One or more of these can be used. Among these, silica, mica, and talc are preferred from the viewpoint of low thermal expansion, and spherical silica is more preferred. The inorganic filler may be surface-treated with an epoxysilane type, vinylsilane type, methacrylicsilane type, or aminosilane type silane coupling agent. The timing of the surface treatment with the silane coupling agent is not particularly limited. The inorganic filler may be prepared in advance with a silane coupling agent, or the silane coupling agent may be added by integral blending during the preparation of this composition.

[0084] Examples of flame retardants include halogenated flame retardants and phosphorus-based flame retardants (excluding this crosslinking agent). One or more of these can be used. Examples of halogenated flame retardants include bromine-based flame retardants such as pentabromodiphenyl ether, octabromodiphenyl ether, decabromodiphenyl ether, tetrabromobisphenol A, and hexabromocyclododecane; and chlorine-based flame retardants such as chlorinated paraffins. Examples of phosphorus-based flame retardants include phosphate esters such as condensed phosphate esters and cyclic phosphate esters; phosphazene compounds such as cyclic phosphazene compounds; phosphinate-based flame retardants such as aluminum dialkylphosphinate salts; melamine-based flame retardants such as melamine phosphate and polymelamine phosphate; phosphine oxide compounds having a diphenylphosphine oxide group; and phosphonic acid esters such as cyclic phosphonic acid esters. However, from the viewpoint of environmental protection, it is preferable to use other phosphorus-based flame retardants in addition to this crosslinking agent.

[0085] This composition may optionally contain one or more organic solvents. The organic solvents are not particularly limited and include ketones such as methyl ethyl ketone; ethers such as dibutyl ether; esters such as ethyl acetate; amides such as dimethylformamide; aromatic hydrocarbons such as benzene, toluene, and xylene; and chlorinated hydrocarbons such as trichloroethylene.

[0086] The amount of the crosslinking agent in this composition is not particularly limited, but is preferably 1 to 150 parts by mass, more preferably 1 to 50 parts by mass, and even more preferably 2 to 30 parts by mass, relative to 100 parts by mass of the curable compound described above.

[0087] The amount of curable compound in this composition (solid content excluding inorganic fillers) is not particularly limited, but for example, 20% by mass or more is preferred, 25% by mass or more is more preferred, and 30% by mass or more is even more preferred. Furthermore, the amount of curable compound in this composition (solid content excluding inorganic fillers) is, for example, 90% by mass or less is preferred, 85% by mass or less is more preferred, and 80% by mass or less is even more preferred.

[0088] In this composition, the solid content concentration and blending composition can be designed according to the application. For example, in applications such as prepregs, the solid content concentration is preferably 50 to 90% by mass.

[0089] <Prepreg> The prepreg relating to this disclosure (hereinafter also referred to as "this prepreg") comprises a fibrous substrate and a (semi)cured product of the composition. The (semi)cured product may optionally contain additives such as inorganic fillers. The prepreg can be manufactured by impregnating the fibrous substrate with the composition and (semi)curing it by heat curing or the like.

[0090] The material for the fiber substrate is not particularly limited and includes, for example, inorganic fibers such as glass fibers, silica fibers, and carbon fibers; organic fibers such as aramid fibers and polyester fibers; and combinations thereof. For applications such as metal-clad laminates and wiring boards, glass fibers are preferred as the material for the fiber substrate. Examples of glass fiber substrate forms include glass cloth, glass paper, and glass mat.

[0091] The curing conditions for this composition can be set according to the composition of the curable composition, and semi-curing conditions (conditions that do not fully cure) are preferred. For example, when using a curable composition containing PPE resin or terminal olefin resin, curing can be achieved by thermal curing, for example, heating at 80 to 200°C for 1 to 10 minutes. For applications such as metal-clad laminates and wiring boards, it is preferable to adjust the composition of the curable composition and the curing conditions so that the resin content in the resulting prepreg is in the range of 40 to 80% by mass.

[0092] <Laminates> The first laminate according to this disclosure includes a substrate and a curable composition layer composed of the composition. The second laminate according to this disclosure includes a substrate and a cured product-containing layer containing a (semi-)cured product of the composition.

[0093] In the first and second laminates relating to this disclosure, the substrate is not particularly limited and includes resin films, metal foils, and combinations thereof. The cured product-containing layer may be a layer containing a fibrous substrate and a (semi-)cured product of the composition. The resin film is not particularly limited and known resins can be used. Examples of constituent resins of the resin film include polyimide, polyethylene terephthalate (PET), polyethylene naphthalate, cycloolefin polymers, and polyether sulfide. Due to their low electrical resistance, copper foil, silver foil, gold foil, aluminum foil, and combinations thereof are preferred as metal foils, with copper foil being more preferred.

[0094] <Metal-clad laminate> The metal-clad laminate according to this disclosure (hereinafter also referred to as "this metal-clad laminate") comprises an insulating layer containing a cured product of the composition and a metal foil. This metal-clad laminate is suitable for wiring boards used in various electrical equipment and various electronic devices. The insulating layer may be a layer comprising a fibrous substrate and a cured product of the composition. Due to its low electrical resistance, the metal foil is preferably copper foil, silver foil, gold foil, aluminum foil, or a combination thereof, with copper foil being more preferred. The metal foil may have a metal plating layer on its surface. The metal foil may be a carrier-equipped metal foil comprising an ultrathin metal foil and a carrier metal foil supporting it. The metal foil may have surface treatments such as rust prevention treatment, silane treatment, roughening treatment, and barrier formation treatment applied to at least one surface. The thickness of the metal foil is not particularly limited, but is preferably 0.1 to 100 μm, more preferably 0.2 to 50 μm, and particularly preferably 1.0 to 40 μm, as it is suitable for forming conductor patterns (circuit patterns) such as wiring.

[0095] The metal-clad laminate may be a single-sided metal-clad laminate having metal foil on one side, or a double-sided metal-clad laminate having metal foil on both sides, with the double-sided metal-clad laminate being preferable. A single-sided metal-clad laminate can be manufactured by stacking one or more of the above-mentioned prepregs and metal foil, and then heating and pressurizing the resulting first temporary laminate. A double-sided metal-clad laminate can be manufactured by sandwiching one or more of the above-mentioned prepregs with a pair of metal foils, and then heating and pressurizing the resulting first temporary laminate. A metal-clad laminate using copper foil as the metal foil is called a copper-clad laminate (CCL).

[0096] The insulating layer is preferably made of a heated and pressed prepreg. The heated and pressed prepreg contains a fibrous base material and a resin, and may optionally contain one or more additives such as inorganic fillers and flame retardants. The heated and pressed prepreg is also called a composite base material. The heating and pressing conditions for the first temporary laminate are not particularly limited, but for example, a temperature of 170 to 250°C, a pressure of 0.3 to 30 MPa, and a time of 3 to 240 minutes are preferred.

[0097] Based on the above, the metal-clad laminate can be made from a heated and pressurized prepreg, and can be a single-sided or double-sided metal-clad laminate (laminated body) in which a metal foil (metal layer) is laminated on one or both sides of a composite substrate (cured material-containing layer) containing the cured product of the composition.

[0098] Furthermore, this metal-clad laminate may have other layers besides those mentioned above. For example, this metal-clad laminate may have an adhesive layer between the composite substrate (cured material-containing layer) and the metal foil (metal layer) to enhance their adhesion. Known materials can be used for the adhesive layer, including epoxy resins, cyanate ester resins, acrylic resins, polyimide resins, maleimide resins, adhesive fluororesins, and combinations thereof. Examples of commercially available adhesive fluororesins include those manufactured by AGC Corporation, such as "Fluon LM-ETFE LH-8000," "AH-5000," "AH-2000," and "EA-2000."

[0099] The thickness of the composite substrate can be appropriately designed depending on the application. From the viewpoint of preventing disconnection of the wiring board, it is preferably 50 μm or more, more preferably 70 μm or more, and particularly preferably 100 μm or more. From the viewpoint of flexibility, miniaturization, and weight reduction of the wiring board, it is preferably 300 μm or less, more preferably 250 μm or less, and particularly preferably 200 μm or less.

[0100] In recent years, applications such as portable electronic devices have seen advancements in communication speed and capacity, leading to higher signal frequencies. Wiring boards used in these applications require reduced transmission loss in the high-frequency range. Therefore, the resin contained in the composite substrate of wiring boards used in these applications requires reduced dielectric loss in the high-frequency range. Generally, the dielectric loss tangent (D) is... ｆ ) depends on frequency, and for the same material, the higher the frequency, the greater the dielectric loss tangent (D ｆ ) tends to be large. The resin contained in the composite substrate has a dielectric loss tangent (D) under high frequency conditions. ｆ It is preferable that the dielectric loss tangent (D) of the (semi-)cured product of this composition and the composite substrate containing it under high-frequency conditions is low. ｆ) is preferably within the following range, for example: Dielectric loss tangent (D) at a frequency of 10 GHz ｆ The relative permittivity (D) at a frequency of 10 GHz is preferably small, preferably 0.01 or less, more preferably 0.005 or less, even more preferably 0.003 or less, and particularly preferably less than 0.001. The lower limit is not particularly limited, for example, 0.0001. The method for measuring the dielectric loss tangent will be described later. Also, the relative permittivity (D) at a frequency of 10 GHz is ｋ The relative permittivity is also preferably small, preferably 1.5 to 3.0, and more preferably 2.0 to 2.8. The method for measuring the relative permittivity will be described later.

[0101] For example, wiring boards may be used in relatively high-temperature environments. Even in this case, in order to ensure the reliability of the wiring board, it is preferable that the resin contained in the prepreg and composite substrate has a sufficiently high glass transition temperature (Tg). Therefore, the glass transition temperature (Tg) of the (semi-)cured product of this composition is preferably 125°C or higher, more preferably 130°C or higher, and particularly preferably 135°C or higher. The upper limit is not particularly limited, for example, 300°C.

[0102] <Wiring Board> The wiring board according to this disclosure (hereinafter also referred to as "this wiring board") comprises an insulating layer containing a cured product of the composition and wiring. This wiring board is suitable for portable electronic devices such as mobile phones, smartphones, personal digital assistants and laptop computers; antennas for mobile phone base stations and automobiles; electronic devices such as servers, routers and backplanes; wireless infrastructure; radar for collision avoidance, etc.; and various sensors (for example, automotive sensors such as engine management sensors). This wiring board is particularly suitable for applications that use high-frequency signals for communication and is suitable for various applications where reduction of transmission loss is required in the high-frequency range (for example, the range of frequencies of 1 GHz or higher).

[0103] This wiring board can be manufactured by forming a conductor pattern (circuit pattern), such as wiring, using the metal foil on the outermost surface (at least one of the surfaces) of the metal-clad laminate. Methods for forming a conductor pattern, such as wiring, include the subtractive method, which forms wiring by etching the metal foil, and the MSAP (Modified Semi-Additive Process) method, which forms wiring by plating on the metal foil.

[0104] This wiring board can be made of a heated and pressurized prepreg, and a conductive pattern (circuit pattern), such as wiring, can be formed on at least one side of a composite substrate (cured material-containing layer, insulating layer) containing a cured product of the present composition. Furthermore, a multilayer wiring board (multilayer printed circuit board) may be manufactured by stacking one or more prepregs on the obtained wiring board, sandwiching it with a pair of metal foils, heating and pressurizing the resulting second temporary laminate, and forming a conductive pattern, such as wiring, using the outermost metal foil. The outermost metal foil may be placed only on one side of the temporary laminate. This wiring board is suitable for use in the high-frequency range (for example, the range of frequencies of 1 GHz or higher (for example, 10 GHz or higher)).

[0105] The present disclosure will be further explained below using several examples, but the present disclosure is not limited to these examples. Unless otherwise specified, room temperature is 25°C. The reference numerals and other symbols in each group of examples are independent of each other, except for the common items described below.

[0106] [Common points for each group of examples] In the following experimental examples, unless otherwise specified, commercially available catalysts and reagents were used in the reactions as they were. Dehydrated and deoxygenated commercially available solvents were used.

[0107] <Method for analyzing the structure of compounds> The structure of the compounds described below will be analyzed as follows: １ H-NMR and １３ Identified using C-NMR. １ (H-NMR) The substance to be measured (compound 1) is treated with chloroform-d １ Dissolve in it, １The measurement was performed using 1H-NMR (Bruker, product name: Avance NEO400). Tetramethylsilane was used as the internal standard. １３ (C-NMR) The substance to be measured (compound 1) is treated with chloroform-d １ Dissolve it in a solution to a concentration of 20% by mass. １３ Measurements were performed using 1C-NMR (JEOL, product name: ECZ600). Hexamethyldisiloxane was used as an internal standard. Spectral analysis was performed using Delta v6.0 (analysis software manufactured by JEOL Ltd.).

[0108] <Structural Analysis Method for Organophosphorus Compounds (Crosslinking Agents)> The structures of the organophosphorus compounds used in each example were analyzed using a nuclear magnetic resonance spectrometer (Brker "AVANCE NEO400") to determine the structure of the target substance (e.g., a synthesized organophosphorus compound). １ H-NMR, ３１ The structure was identified by measurement using P-NMR.

[0109] <Molecular Weight Measurement Method> The weight-average molecular weight Mw and number-average molecular weight Mn were measured using gel permeation chromatography (GPC) (Tosoh Corporation, product name: HLC-8420 GPC). The column used was a combination of Tosoh Corporation's Guard Column "HXL-L" (product name), Tosoh Corporation's "SuperH-RC" (product name), Tosoh Corporation's "TSKgel SuperHZ2000" (product name), Tosoh Corporation's "TSKgel SuperHZ2500" (product name), Tosoh Corporation's "TSKgel SuperHZ3000" (product name), and Tosoh Corporation's "TSKgel SuperHZ4000" (product name). For the measurement, the developing solvent was tetrahydrofuran, the flow rate was 1.0 ml / min, the column temperature was 40°C, and the detector was an RI (differential refractometer), and a calibration curve using monodisperse polystyrene was used. For data processing, we used the "EcoSEC-WorkStation" GPC workstation manufactured by Tosoh Corporation.

[0110] <Method for preparing evaluation samples (film-like cured material)> Compound 1, the organophosphorus compound or hydrocarbon compound synthesized or prepared in each example, 2,3-dimethyl-2,3-diphenylbutane (CCDF) as an additive, and toluene were mixed in the mass ratios shown in the tables below, in a mass ratio of 49:10:1:40, and stirred at room temperature to prepare a toluene solution (curable composition). Next, using an applicator (manufactured by Yoshimitsu Seiki Co., Ltd.), the above-mentioned toluene solution was applied onto a 125 μm thick polyimide film to form a coating film with a thickness of 250 μm. The coating film was heated and dried in an oven under an air atmosphere at 80°C for 30 minutes, and then heated under a nitrogen atmosphere at 200°C for 2 hours to thermally cure (thermal crosslinking reaction) the coating film to obtain an evaluation sample (film-like cured material) with a thickness of 100 μm. The following evaluations were performed on each of the obtained evaluation samples.

[0111] <Evaluation items and evaluation methods for film-like cured products> (Relative permittivity (D) ｋ ) and dielectric loss tangent (D ｆ )) Relative permittivity (D) of the evaluation sample (film-like cured material) at 10 GHz ｋ ) and dielectric loss tangent (D ｆ The relative permittivity (D) was measured at room temperature using a vector network analyzer (Agilent Technologies "E8361C") by the SPDR method. The evaluation was also performed according to the following evaluation criteria: - Relative permittivity (D) ｋ Evaluation criteria for (D): A: 3.0 or less B: Greater than 3.0, Dielectric loss tangent (D ｆ Evaluation criteria for ) A: Less than 0.001 B: 0.001 or higher

[0112] (Glass transition temperature Tg) The above-mentioned film-like cured material was prepared, and its glass transition temperature was determined by differential scanning calorimetry (DSC) using a NETZSCH 204 F1 Phoenix. 5 mg of the sample (film-like cured material) was heated from room temperature to 300°C at a rate of 10°C / min under a nitrogen stream of 50 mL / min, then cooled to 30°C at a rate of 10°C / min, and then heated again to 300°C at a rate of 10°C / min. The DSC curve was measured, and the temperature at which the slope of the curve representing the stepped portion of the glass transition was maximized was defined as the glass transition temperature. Evaluation was also performed according to the following evaluation criteria: ・Tg evaluation criteria A: 135°C or higher B: 130°C or higher C: 125°C or higher D: Less than 125°C

[0113] (Evaluation of Flame Retardancy) The above-mentioned film-like cured material was used as a sample, and the heat release rate [W / g] was compared in the temperature range of 75°C to 850°C using the MCC (Microscale Combustion Calorimeter) test. A lower peak value of the heat release rate indicates superior flame retardancy. The evaluation criteria are shown for each example group.

[0114] <Production of Compound 1 (Curable Resin)> N ２Under flow conditions, 480 g of paraxylene, 2.0 g (14.1 mmol) of boron trifluoride / diethyl ether complex (manufactured by Tokyo Chemical Industry Co., Ltd.) as an acid catalyst, and 2.87 g (28.1 mmol) of propyl acetate as a co-catalyst were added to a 1 L glass reaction vessel equipped with a stirring blade and a fluororesin-coated thermocouple. The mixture was then maintained at 25°C for 2 hours. Subsequently, while maintaining the reaction temperature at 50°C, 120.0 g of 1,3-diisopropenylbenzene (manufactured by Tokyo Chemical Industry Co., Ltd.) was added dropwise to the reaction vessel over 2 hours using a syringe pump. After the dropwise addition, as a maturation step, the mixture was reacted for 60 minutes (maturation time) while maintaining the temperature at 50°C (maturation temperature). Then, 100 g of a 5% by mass aqueous solution of sodium bicarbonate was added to the reaction vessel to terminate the reaction. Subsequently, the aqueous phase in the reaction vessel was discarded, and the mixture was separated and washed three times with 300 ml of deionized water to obtain compound 1 solution. Next, 2200 g of methanol was added to another 6 L flask, and the compound 1 solution was gradually added to reprecipitate the compound. A cake was then obtained by filtration. The cake was redispersed in 2200 g of methanol, washed, and filtered twice. The resulting compound was then vacuum-dried at 60°C to obtain compound 1:107.9 g. Structural analysis and molecular weight measurement of the obtained compound 1 (curable resin) were performed according to the method described above. As a result, the molecular weight of the obtained compound 1 was Mn: 2,460, Mw: 23,800. The molecular structure of the obtained compound 1 contained an olefin structure at its terminal end. １３ C-NMR and １ This was confirmed by H-NMR.

[0115] [Examples Group α] Examples 1α to 6α are examples relating to compounds (A) and (B) of the present disclosure, and Examples 7α and 8α are comparative examples.

[0116] <Preparation of Organophosphorus Compounds> [Example 1α] Synthesis of Ethyl-di(4-vinylphenyl)phosphine oxide, compound (1a) Under a nitrogen atmosphere, at room temperature, magnesium (Mg) (cut flakes, 1.32 g, 54.3 mmol), tetrahydrofuran (THF) (101 mL), and iodine (6.74 mg, 0.0266 mmol) were charged into a 300 mL four-necked flask and stirred. 4-chlorostyrene (7.55 g, 54.5 mmol) was added to the suspension, and the mixture was reacted at 70°C for 2 hours. After cooling to room temperature, a solution of ethylphosphonic acid dichloride (4.00 g, 27.2 mmol) in tetrahydrofuran (12 mL) was added dropwise to the reaction mixture over 30 minutes, and the mixture was stirred for a further 18 hours. The flask was cooled in an ice bath, and an aqueous solution of ammonium chloride (96 mL) was added dropwise to the reaction mixture. The reaction solution was then filtered to remove insoluble matter. The obtained filtrate was separated to isolate the organic phase. Furthermore, ethyl acetate (96 mL) was added to the aqueous phase for extraction, and the organic phase was isolated. The organic phases obtained from these extractions were combined, dried using magnesium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (ethyl acetate:chloroform = 1:3), and 4-tert-butylpyrocatechol (4.8 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 1.29 g of the compound represented by the following formula (1a) (organophosphorus compound 1a) as a colorless solid (yield: 17%). The reaction scheme and NMR analysis results are as follows.

[0117]

[0118] １ H-NMR (CDCl ３ ): d (ppm) 7.69 (dd, 4H, J = 8.11, 11.0Hz, Ar-H), 7.49 (dd, 4H, J = 2.62, 8.11Hz, Ar-H), 6.73 (dd, 2H, J = 11.0, 17.6Hz ), 5.84 (d, 2H, J = 17.6Hz), 5.37 (d, 2H, J = 11.0Hz), 2.27 (qd, 2H, J = 7.63, 11.4Hz), 1.20 (qt, 2H, J = 7.63, 17.4Hz). ３１ P-NMR (CDCl ３ ): d (ppm) 33.6 (s).​

[0119] [Example 2α] Synthesis of tert-butylbis(4-vinylphenyl)phosphonate, compound (1b) Under a nitrogen atmosphere, 4-vinylphenol (1.88 g, 14.8 mmol) and tetrahydrofuran (18 mL) were charged into a 50 mL four-necked flask. The flask was cooled in an ice bath, and sodium hydride (NaH) (55-65%, dispersed in paraffin sulfate, 0.686 g, 15.7 mmol) was added to the solution and stirred at the same temperature for 1 hour. Next, a solution of tert-butylphosphonic acid dichloride (1.25 g, 7.14 mmol) in tetrahydrofuran (THF) (3.1 mL) was added dropwise to the reaction mixture over 10 minutes, and the flask was warmed to room temperature and stirred for 90 hours. The flask was cooled in an ice bath, and deionized water (3.9 mL) and hydrochloric acid (1 mol / L, 14.3 mL) were added to the reaction mixture in that order and stirred to separate the organic phase. Furthermore, ethyl acetate (25 mL) was added to the aqueous phase for extraction, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (ethyl acetate:n-hexane = 1:20), and 4-tert-butylpyrocatechol (1.8 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 1.25 g of the compound represented by the following formula (1b) (organophosphorus compound 1b) as a colorless liquid (yield: 51%). The reaction scheme and NMR analysis results are as follows.

[0120]

[0121] １ H-NMR (CDCl ３ ): d (ppm) 7.32 (dm, 4H, J=8.82Hz, Ar-H), 7.10 (ddm, 4H, J=1.19, 8.58Hz, Ar-H), 6.65 (dd, 2H, J=11. 0,17.6Hz), 5.65 (dd, 2H, J=0.72, 17.6Hz), 5.20 (dd, 2H, J=0.72, 11.0Hz), 1.40 (d, 9H, J=17.9Hz). ３１ P-NMR (CDCl ３ ): d (ppm) 30.5 (s).

[0122] ​[Example 3α] Synthesis of tert-butylbis(3-vinylphenyl)phosphonate, compound (1c) Under a nitrogen atmosphere, 3-vinylphenol (2.30 g, 18.8 mmol) and tetrahydrofuran (21.5 mL) were charged into a 50 mL four-necked flask and stirred. The flask was cooled in an ice bath, and sodium hydride (NaH) (0.823 g, 18.9 mmol, 55%, dispersed in liquid paraffin) was added and stirred at the same temperature for 1 hour. Next, a solution of tert-butylphosphonate dichloride (1.50 g, 8.57 mmol) in tetrahydrofuran (THF) (3.8 mL) was added dropwise to the reaction mixture over 10 minutes, and the flask was returned to room temperature and stirred for 42 hours. The flask was transferred to an ice bath and cooled, and deionized water (4.6 mL) and hydrochloric acid (1 mol / L, 17.1 mL) were added to the reaction mixture in that order and stirred to separate the organic phase. Furthermore, ethyl acetate (30 mL) was added to the aqueous phase for extraction, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (ethyl acetate:n-hexane = 1:20), and 4-tert-butylpyrocatechol (1.5 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 2.11 g of the compound represented by the following formula (1c) (organophosphorus compound 1c) as a colorless liquid (yield: 72%). The reaction scheme and NMR analysis results are as follows.

[0123]

[0124] １ H-NMR (CDCl ３ ): d (ppm) 7.23 (dm, 2H, J = 8.34Hz, Ar-H), 7.19-7.10 (m, 4H, Ar-H), 7.05 (dm, 2H, J = 8.34Hz, Ar-H), 6.62 (dd, 2H, J=11.0, 17.6Hz), 5.67 (dd, 2H, J=0.72, 17.6Hz), 5.24 (dd, 2H, J=0.72, 11.0Hz), 1.42 (d, 9H, J=17.9Hz). ３１ P-NMR (CDCl ３ ): d (ppm) 30.4 (s).

[0125] ​[Example 4α] Synthesis of tert-butylbis(4-vinylbenzyl)phosphonate, compound (1d) (Synthesis of 4-vinylbenzyl alcohol, compound HMS) Under a nitrogen atmosphere, at room temperature, 4-vinylbenzyl acetate (5.00 g, 28.4 mmol), ethanol (EtOH) (9.83 mL), and 20% by mass aqueous sodium hydroxide solution (NaOH aq.) (9.81 mL, 59.8 mmol) were charged into a 50 mL four-necked flask, and the mixture was heated and refluxed for 4 hours. After cooling the reaction mixture to room temperature, it was extracted three times with ethyl acetate (20 mL). The obtained organic phases were combined, washed with saturated brine (20 mL), and dried using anhydrous sodium sulfate. Insoluble matter was filtered off, and the resulting filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (chloroform), and 4-tert-butylpyrocatechol (6.00 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 2.79 g of the compound HMS, represented by the following formula (HMS), as a brown liquid (yield: 73%). The reaction scheme and NMR analysis results are as follows.

[0126]

[0127] １ H-NMR (CDCl ３ ): d (ppm) 7.40 (d, 2H, J = 8.11 Hz, Ar-H), 7.32 (d, 2H, J = 8.11, Ar-H), 6.71 (dd, 2H, J = 10.7, 17.6 Hz), 5.75 ( dd, 2H, J = 0.95, 17.6Hz), 5.25 (dd, 2H, J = 0.95, 10.7Hz), 4.67 (d, 2H, J = 5.72Hz), 1.76 (t, 1H, J = 5.96Hz).

[0128] ​(Synthesis of tert-butylbis(4-vinylbenzyl)phosphonate, compound (1d)) Under a nitrogen atmosphere, compound HMS (1.26 g, 9.39 mmol) and tetrahydrofuran (THF) (10.7 mL) were charged into a 50 mL four-necked flask and stirred. The flask was cooled in an ice bath, and sodium hydride (0.411 g, 9.42 mmol, 55%, dispersed in liquid paraffin) was added in portions and stirred at the same temperature for 1 hour. Next, a solution of tert-butylphosphonate dichloride (0.750 g, 4.29 mmol) in tetrahydrofuran (3.75 mL) was added dropwise to the reaction mixture over 20 minutes, and the flask was returned to room temperature and stirred for 93 hours. The flask was transferred to an ice bath and cooled, and deionized water (2.32 mL) and hydrochloric acid (1 mol / L, 8.57 mL) were added to the reaction mixture in that order and stirred to separate the organic phase. Furthermore, ethyl acetate (15 mL) was added to the aqueous phase for extraction, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (ethyl acetate:n-hexane = 1:4), and 4-tert-butylpyrocatechol (1.5 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 1.00 g of the compound represented by the following formula (1d) (organophosphorus compound 1d) as a colorless solid (yield 63%). The reaction scheme and NMR analysis results are as follows.

[0129]

[0130] １ H-NMR (CDCl ３ ): d (ppm) 7.38 (dm, 2H, J = 8.11Hz, Ar-H), 7.28 (d, 2H, J = 8.11Hz, Ar-H), 6.71 (dd, 2H, J = 10.7, 17.6 Hz), 5.75 (dd, 2H, J = 0.72, 17.6Hz), 5.26 (dd, 2H, J = 0.72, 17.6Hz), 5.03 (dd, 2H, J=8.82Hz, J=11.9Hz), 4.96 (dd, 2H, J=7.15Hz, 12.2Hz), 1.19 (d, 9H, J=16.9Hz). ３１ P-NMR (CDCl ３ ):d(ppm))-18.0(s).​

[0131] [Example 5α] Synthesis of ethylbis(4-vinylphenyl)phosphonate, compound (1e) Under a nitrogen atmosphere, 4-vinylphenol (2.60 g, 20.4 mmol), dichloromethane (38 mL), and triethylamine (5.69 mL, 40.8 mmol) were charged into a 100 mL four-necked flask. Next, a solution of ethylphosphonic acid dichloride (1.50 g, 10.2 mmol) in dichloromethane (9.3 mL) was added dropwise to the reaction mixture over 20 minutes, and the flask was warmed to room temperature and stirred for 18 hours. The flask was cooled in an ice bath, and ion-exchanged water (37 mL) was added to the reaction mixture and stirred to separate the organic phase. Furthermore, dichloromethane (20 mL) was added to the aqueous phase and extracted, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried over sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (ethyl acetate:n-hexane = 1:4), and 4-tert-butylpyrocatechol (1.8 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 2.87 g of the compound represented by the following formula (1e) (organophosphorus compound 1e) as a colorless liquid (yield: 90%). The reaction scheme and NMR analysis results are as follows.

[0132]

[0133] 1H-NMR (CDCl3): d (ppm) 7.32 (dm, 4H, J = 8.82Hz, Ar-H), 7.10 (ddm, 4H, J = 1.19, 8.58Hz, Ar-H), 6.65 (dd, 2H, J = 11.0, 17.6 Hz), 5.65 (dd, 2H, J = 0.72, 17.6Hz), 5.20 (dd, 2H, J = 0.72, 11.0Hz), 1.40 (d, 9H, J = 17.9Hz). 31P-NMR (CDCl3): d (ppm)) 27.0 (s).

[0134] [Example 6α] Synthesis of phenylbis(4-vinylphenyl) phosphate, compound (1f) Under a nitrogen atmosphere, 4-vinylphenol (1.79 g, 14.2 mmol), dichloromethane (20 mL), and triethylamine (2.97 mL, 21.3 mmol) were charged into a 50 mL four-necked flask. The flask was then cooled in an ice bath, and a solution of phenyl dichlorophosphate (1.50 g, 7.11 mmol) in dichloromethane (6.6 mL) was added dropwise to the reaction mixture over 30 minutes. The flask was then warmed to room temperature and stirred for 24 hours. The flask was cooled in an ice bath, hydrochloric acid (2 mol / L, 15 mL) was added to the reaction mixture and stirred to separate the organic phase. The obtained organic phase was further washed with hydrochloric acid (2 mol / L, 15 mL) and deionized water (15 mL). The organic phase was dried over sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (ethyl acetate:n-hexane = 1:4), and 4-tert-butylpyrocatechol (1.8 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 2.56 g of the compound represented by the following formula (1f) (organophosphorus compound 1f) as a colorless liquid (yield: 95%). The reaction scheme and NMR analysis results are as follows.

[0135] １ H-NMR (CDCl ３ ): d (ppm) 7.38 (d, 4H, J = 8.58Hz), 7.36-7.14 (m, 9H), 6.68 (dd, 2H, J=10.8, 17.5Hz), 5.69 (d, 2H, J=17.6Hz), 5.25 (d, 2H, J=11.0Hz). ３１ P-NMR (CDCl ３ ):d(ppm))-18.0(s).

[0136] [Example 7α] For comparison, diethyl vinyl phosphonate (DVP, manufactured by Tokyo Chemical Industry Co., Ltd.), a known organophosphorus flame retardant, was prepared as shown below.

[0137]

[0138] ​<Preparation of hydrocarbon compounds> [Example 8α] As a hydrocarbon compound for flame retardancy comparison, 1,2-bis(4-vinylphenyl)ethane (BVPE), as shown below, was prepared.

[0139]

[0140] <Evaluation and Results> In Examples 1α to 8α, evaluation samples were prepared using the organophosphorus compounds and hydrocarbon compounds described above, according to the [Method for Preparing Evaluation Samples (Film-like Cured Products)] described above, and evaluated. The evaluation results are shown in Table 1 below.

[0141] The flame retardancy method was as described above, and the evaluation was carried out according to the evaluation criteria. • Evaluation Criteria for Flame Retardancy A: The peak value of the heat dissipation rate is lower than the measurement results of Example 8α described later. B: The peak value of the heat dissipation rate is the same as or higher than that of Example 8α.

[0142] Based on the above, using this crosslinking agent results in excellent flame retardancy and a dielectric loss tangent (D) under high-frequency conditions. ｆ It can be seen that the ) can be effectively reduced and a film-like cured product with a sufficiently high glass transition temperature (Tg) can be obtained. In other words, it can be seen that by using this crosslinking agent, a wiring board and the like can be obtained that has excellent electrical properties, flame retardancy and heat resistance, and satisfies practical properties in a well-balanced manner.

[0143] [Examples β] Examples 1β to 3β are examples relating to compound (C) of the present disclosure, and Examples 4β and 5β are comparative examples.

[0144] <Preparation of Organophosphorus Compounds> [Example 1β] Synthesis of tert-butylbis(3-vinylphenyl)phosphonate, compound (1a) Under a nitrogen atmosphere, 3-vinylphenol (2.30 g, 18.8 mmol) and tetrahydrofuran (21.5 mL) were charged into a 50 mL four-necked flask and stirred. The flask was cooled in an ice bath, and sodium hydride (NaH) (0.823 g, 18.9 mmol, 55%, dispersed in liquid paraffin) was added and stirred at the same temperature for 1 hour. Next, a solution of tert-butylphosphonic acid dichloride (1.50 g, 8.57 mmol) in tetrahydrofuran (THF) (3.8 mL) was added dropwise to the reaction mixture over 10 minutes, and the flask was returned to room temperature and stirred for 42 hours. The flask was transferred to an ice bath and cooled, and deionized water (4.6 mL) and hydrochloric acid (1 mol / L, 17.1 mL) were added to the reaction mixture in that order and stirred to separate the organic phase. Furthermore, ethyl acetate (30 mL) was added to the aqueous phase for extraction, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (ethyl acetate:n-hexane = 1:20), and 4-tert-butylpyrocatechol (1.5 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 2.11 g of the compound represented by the following formula (1a) (organophosphorus compound 1a) as a colorless liquid (yield: 72%). The reaction scheme and NMR analysis results are as follows.

[0145]

[0146] １ H-NMR (CDCl ３ ): d (ppm) 7.23 (dm, 2H, J = 8.34Hz, Ar-H), 7.19-7.10 (m, 4H, Ar-H), 7.05 (dm, 2H, J = 8.34Hz, Ar-H), 6.62 (dd, 2H, J=11.0, 17.6Hz), 5.67 (dd, 2H, J=0.72, 17.6Hz), 5.24 (dd, 2H, J=0.72, 11.0Hz), 1.42 (d, 9H, J=17.9Hz). ３１ P-NMR (CDCl ３ ): d (ppm) 30.4 (s). ​

[0147] [Example 2β] Synthesis of phenylbis(3-vinylphenyl)phosphine oxide, compound (1b)

[0148] (Synthesis of phenylbis(3-vinylphenyl)phosphine, compound DSPP) Under a nitrogen atmosphere, at room temperature, magnesium (Mg) (cuttings, 0.57 g, 23.5 mmol), tetrahydrofuran (THF) (12.3 mL) and iodine (I) were added to a 100 mL four-necked flask. ２ (4.91 mg, 0.0193 mmol) was added and stirred. A solution of 3-bromostyrene (4.43 g, 23.5 mmol) in tetrahydrofuran (18.2 mL) was added dropwise to the reaction mixture over 1 hour, and the flask was allowed to return to room temperature and stirred for 1 hour. After cooling the flask in an ice bath, dichlorophenylphosphine (PhPCL) was added to the reaction mixture. ２ A solution of tetrahydrofuran (2.00 g, 11.2 mmol) in tetrahydrofuran (6.1 mL) was added dropwise over 30 minutes, and the flask was allowed to return to room temperature and stirred for 18 hours. The flask was cooled in an ice bath, and 15% by mass aqueous solution of ammonium chloride (44 mL) was added dropwise to the reaction mixture, followed by the addition of ethyl acetate (20 mL) to separate the organic phase. Further extraction was performed by adding ethyl acetate (44 mL) to the aqueous phase, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried over magnesium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (n-hexane), and 4-tert-butylpyrocatechol (2.4 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 2.40 g of the compound DSPP, represented by the following formula DSPP, as a colorless liquid (yield: 68%). The reaction scheme and NMR analysis results are as follows.

[0149]

[0150] １ H-NMR (CDCl ３ ​): d (ppm) 7.45-7.26 (m, 11H), 7.16 (dddm, 2H, J = 1.43, 7.15, 7.39Hz), 6.65 (dd, 2H , J=11.0, 17.6Hz), 5.67 (dd, 2H, J=0.95, 17.6Hz), 5.22 (dd, 2H, J=0.72, 11.0Hz). ３１ P-NMR (CDCl ３ ): d (ppm) - 5.54 (s).

[0151] (Synthesis of phenylbis(3-vinylphenyl)phosphine oxide, compound (1b)) At room temperature, compound DSPP (2.40 g, 7.63 mmol) and dichloromethane (CH) were added to a 50 mL round-bottom flask. ２ Cl ２ A solution consisting of (22 mL) is mixed with hydrogen peroxide (H ２ O ２ ) (30% by mass concentration, 4.40 mL, 43.1 mmol) was added dropwise over 30 minutes, and the mixture was stirred for a further 1 hour. The reaction solution was separated, and the organic phase obtained was washed with deionized water (17 mL) and saturated saline solution (17 mL), dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (ethyl acetate:chloroform = 1:20) to obtain 2.32 g of the compound represented by the following formula (1b) (organophosphorus compound 1b) as a pale yellow liquid (yield: 92%). The reaction scheme and NMR analysis results are as follows.

[0152]

[0153] １ H-NMR (CDCl ３ ): d (ppm) 7.79 (dt, 2H, J = 1.67, 12.6Hz), 7.68 (ddm, 2H, J = 1.43, 8.34Hz), 7.59 (ddm, 2H, J = 1.43, 7.63Hz), 7.55 (ddm, 1H, J = 1.67, 7.39Hz), 7.51-7.35 (6H, m), 6.70 (dd, 2H, J = 11.0, 17.6Hz), 5.76 (dd, 2H, J = 0.72, 17.4Hz), 5.30 (dm, 2H, J = 11.2Hz). ３１ P-NMR (CDCl ３ ​): d (ppm) 28.9 (s).

[0154] [Example 3β] Synthesis of tri(3-vinylphenyl)phosphine oxide, compound (1c) (Synthesis of tri(3-vinylphenyl)phosphine, compound TMVP) Under a nitrogen atmosphere, at room temperature, magnesium (Mg) (cut flakes, 0.61 g, 25.2 mmol), tetrahydrofuran (THF) (13.0 mL) and iodine (I) were added to a 100 mL four-necked flask. ２ (5.29 mg, 0.0208 mmol) was added and stirred. A solution of 3-bromostyrene (4.76 g, 25.2 mmol) in tetrahydrofuran (19.6 mL) was added dropwise to the reaction mixture over 1 hour, and then the flask was allowed to return to room temperature and stirred for 1 hour. After cooling the flask in an ice bath, phosphorus trichloride (PCL) was added to the reaction mixture. ３ A solution of tetrahydrofuran (2.00 g, 11.2 mmol) in tetrahydrofuran (6.5 mL) was added dropwise over 30 minutes, and the flask was allowed to return to room temperature and stirred for 18 hours. The flask was cooled in an ice bath, and 15% by mass aqueous solution of ammonium chloride (44 mL) was added dropwise to the reaction mixture, followed by the addition of ethyl acetate (20 mL) to separate the organic phase. Further extraction was performed by adding ethyl acetate (44 mL) to the aqueous phase, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried over magnesium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (n-hexane), and 4-tert-butylpyrocatechol (1.3 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 1.46 g of the compound TMVP, represented by the following formula TMVP, as a colorless liquid (yield: 54%). The reaction scheme and NMR analysis results are as follows.

[0155]

[0156] １ H-NMR (CDCl ３ ​): d (ppm) 7.45-7.35 (m, 6H, Ar-H), 7.30 (ddd, 3H, J = 1.67, 7.63, 8.11Hz), 7.17 (dddm, 3H, J = 1.67, 7.15, 7.39Hz), 6.65 (dd, 3H, J = 11.0, 17.6Hz), 5.68 (dd, 3H, J = 0.95, 17.6Hz), 5.28 (dd, 3H, J = 0.72, 11.0Hz). ３１ P-NMR (CDCl ３ ): d(ppm)-5.39(s).

[0157] (Synthesis of tri(3-vinylphenyl)phosphine oxide, compound (1c)) At room temperature, compound TMVP (1.45 g, 4.26 mmol) and dichloromethane (CH) were added to a 20 mL round-bottom flask. ２ Cl ２ A solution consisting of (12 mL) is mixed with hydrogen peroxide (H ２ O ２ (30% by mass concentration, 2.45 mL, 24.0 mmol) was added dropwise over 30 minutes, and the mixture was stirred for a further 2 hours. The reaction solution was separated, and the resulting organic phase was washed with deionized water (10 mL) and saturated brine (10 mL). The mixture was dried over sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (ethyl acetate:chloroform = 1:20) to obtain 1.24 g of the compound represented by the following formula (1c) (organophosphorus compound 1c) as a colorless solid (yield: 82%). The reaction scheme and NMR analysis results are as follows.

[0158]

[0159] １ H-NMR (CDCl ３ ): d (ppm) 7.79 (dt, 3H, J = 1.67, 12.6 Hz, Ar-H), 7.60 (ddm, 3H, J = 1.43, 7.39 Hz, Ar-H), 7.51-7.33 (6 H, m, Ar-H), 6.70 (dd, 3H, J=10.7, 17.4Hz), 5.77 (dd, 3H, J=0.72, 17.6Hz), 5.30 (dm, 3H, J=11.0Hz). ３１ P-NMR (CDCl ３ ): d (ppm) 29.2 (s).​

[0160] [Example 4β] For comparison, we prepared diethyl vinyl phosphonate (DVP, manufactured by Tokyo Chemical Industry Co., Ltd.), a known organophosphorus flame retardant, as shown below.

[0161]

[0162] <Preparation of hydrocarbon compounds> [Example 5β] As a hydrocarbon compound for flame retardancy comparison, 1,2-bis(4-vinylphenyl)ethane (BVPE), as shown below, was prepared.

[0163]

[0164] <Evaluation and Results> In Examples 1β to 5β, evaluation samples were prepared using the crosslinking agent and hydrocarbon compounds described above, according to the [Method for Preparing Evaluation Samples (Film-like Cured Products)] described above, and evaluated. The evaluation results are shown in Table 2 below.

[0165] The flame retardancy method was as described above, and the evaluation was carried out according to the evaluation criteria. • Evaluation Criteria for Flame Retardancy A: The peak value of the heat dissipation rate is lower than the measurement results of Example 5β described later. B: The peak value of the heat dissipation rate is equivalent to or higher than that of Example 5β.

[0166] Based on the above, using this phosphorus compound results in excellent flame retardancy and a dielectric loss tangent (D) under high-frequency conditions. ｆ It can be seen that the ) can be effectively reduced and a film-like cured product with a sufficiently high glass transition temperature (Tg) can be obtained. In other words, it can be seen that by using this phosphorus compound, a wiring board and the like can be obtained that has excellent electrical properties, flame retardancy and heat resistance, and satisfies practical properties in a well-balanced manner.

[0167] [Examples γ] Examples 1γ to 6γ are examples relating to compound (D) of the present disclosure, and Examples 7γ and 8γ are comparative examples.

[0168] <Preparation of Crosslinking Agent> [Example 1γ] Synthesis of Ethyl-di(4-vinylphenyl)phosphine oxide and crosslinking agent (1a) Under a nitrogen atmosphere, at room temperature, magnesium (Mg) (cut flakes, 1.32 g, 54.3 mmol), tetrahydrofuran (THF) (101 mL), and iodine (6.74 mg, 0.0266 mmol) were charged into a 300 mL four-necked flask and stirred. 4-chlorostyrene (7.55 g, 54.5 mmol) was added to the suspension, and the mixture was reacted at 70°C for 2 hours. After cooling to room temperature, a solution of ethylphosphonic acid dichloride (4.00 g, 27.2 mmol) in tetrahydrofuran (12 mL) was added dropwise to the reaction mixture over 30 minutes, and the mixture was stirred for a further 18 hours. The flask was cooled in an ice bath, and ammonium chloride aqueous solution (96 mL) was added dropwise to the reaction mixture. The reaction solution was then filtered to remove insoluble matter. The obtained filtrate was separated to isolate the organic phase. Furthermore, ethyl acetate (96 mL) was added to the aqueous phase for extraction, and the organic phase was isolated. The organic phases obtained from these extractions were combined, dried using magnesium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (ethyl acetate:chloroform = 1:3), and 4-tert-butylpyrocatechol (4.8 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 1.29 g of the compound represented by the following formula (1a) (crosslinking agent 1a) as a colorless solid (yield: 17%). The reaction scheme and NMR analysis results are as follows.

[0169]

[0170] １ H-NMR (CDCl ３ ): d (ppm) 7.69 (dd, 4H, J = 8.11, 11.0Hz, Ar-H), 7.49 (dd, 4H, J = 2.62, 8.11Hz, Ar-H), 6.73 (dd, 2H, J = 11.0, 17.6Hz ), 5.84 (d, 2H, J = 17.6Hz), 5.37 (d, 2H, J = 11.0Hz), 2.27 (qd, 2H, J = 7.63, 11.4Hz), 1.20 (qt, 2H, J = 7.63, 17.4Hz). ３１ P-NMR (CDCl ３ ): d (ppm) 33.6 (s). ​

[0171] [Example 2γ] Synthesis of phenylbis(3-vinylphenyl)phosphine oxide and crosslinking agent (1b)

[0172] (Synthesis of phenylbis(3-vinylphenyl)phosphine, compound DSPP) Under a nitrogen atmosphere, at room temperature, magnesium (Mg) (cuttings, 0.57 g, 23.5 mmol), tetrahydrofuran (THF) (12.3 mL) and iodine (I) were added to a 100 mL four-necked flask. ２ (4.91 mg, 0.0193 mmol) was added and stirred. A solution of 3-bromostyrene (4.43 g, 23.5 mmol) in tetrahydrofuran (18.2 mL) was added dropwise to the reaction mixture over 1 hour, and the flask was allowed to return to room temperature and stirred for 1 hour. After cooling the flask in an ice bath, dichlorophenylphosphine (PhPCL) was added to the reaction mixture. ２ A solution of tetrahydrofuran (2.00 g, 11.2 mmol) in tetrahydrofuran (6.1 mL) was added dropwise over 30 minutes, and the flask was allowed to return to room temperature and stirred for 18 hours. The flask was cooled in an ice bath, and 15% by mass aqueous solution of ammonium chloride (44 mL) was added dropwise to the reaction mixture, followed by the addition of ethyl acetate (20 mL) to separate the organic phase. Further extraction was performed by adding ethyl acetate (44 mL) to the aqueous phase, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried over magnesium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (n-hexane), and 4-tert-butylpyrocatechol (2.4 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 2.40 g of the compound DSPP, represented by the following formula DSPP, as a colorless liquid (yield: 68%). The reaction scheme and NMR analysis results are as follows.

[0173]

[0174] １ H-NMR (CDCl ３ ​): d (ppm) 7.45-7.26 (m, 11H), 7.16 (dddm, 2H, J = 1.43, 7.15, 7.39Hz), 6.65 (dd, 2H , J=11.0, 17.6Hz), 5.67 (dd, 2H, J=0.95, 17.6Hz), 5.22 (dd, 2H, J=0.72, 11.0Hz). ３１ P-NMR (CDCl ３ ): d (ppm) - 5.54 (s).

[0175] (Synthesis of phenylbis(3-vinylphenyl)phosphine oxide and crosslinking agent (1b)) At room temperature, in a 50 mL round-bottom flask, combine compound DSPP (2.40 g, 7.63 mmol) and dichloromethane (CH₃). ２ Cl ２ A solution consisting of (22 mL) is mixed with hydrogen peroxide (H ２ O ２ ) (30% by mass concentration, 4.40 mL, 43.1 mmol) was added dropwise over 30 minutes, and the mixture was stirred for a further 1 hour. The reaction solution was separated, and the obtained organic phase was washed with deionized water (17 mL) and saturated brine (17 mL), dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (ethyl acetate:chloroform = 1:20) to obtain 2.32 g of the compound represented by the following formula (1b) (crosslinking agent 1b) as a pale yellow liquid (yield: 92%). The reaction scheme and NMR analysis results are as follows.

[0176]

[0177] １ H-NMR (CDCl ３ ): d (ppm) 7.79 (dt, 2H, J = 1.67, 12.6Hz), 7.68 (ddm, 2H, J = 1.43, 8.34Hz), 7.59 (ddm, 2H, J = 1.43, 7.63Hz), 7.55 (ddm, 1H, J = 1.67, 7.39Hz), 7.51-7.35 (6H, m), 6.70 (dd, 2H, J = 11.0, 17.6Hz), 5.76 (dd, 2H, J = 0.72, 17.4Hz), 5.30 (dm, 2H, J = 11.2Hz). ３１ P-NMR (CDCl ３ ​): d (ppm) 28.9 (s).

[0178] [Example 3γ] Synthesis of tert-butylbis(4-vinylbenzyl)phosphonate and crosslinking agent (1c)

[0179] (Synthesis of 4-vinylbenzyl alcohol, compound HMS) Under a nitrogen atmosphere, at room temperature, 4-vinylbenzyl acetate (5.00 g, 28.4 mmol), ethanol (EtOH) (9.83 mL), and 20% by mass aqueous sodium hydroxide solution (NaOH aq.) (9.81 mL, 59.8 mmol) were charged into a 50 mL four-necked flask. The mixture was heated and refluxed for 4 hours. After cooling the reaction mixture to room temperature, it was extracted three times with ethyl acetate (20 mL). The resulting organic phases were combined, washed with saturated brine (20 mL), and dried over anhydrous sodium sulfate. Insoluble matter was filtered off, and the resulting filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (chloroform), and 4-tert-butylpyrocatechol (6.00 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 2.79 g of compound HMS, represented by the following formula (HMS), as a brown liquid (yield: 73%). The reaction scheme and NMR analysis results are as follows.

[0180]

[0181] １ H-NMR (CDCl ３ ): d (ppm) 7.40 (d, 2H, J = 8.11 Hz, Ar-H), 7.32 (d, 2H, J = 8.11, Ar-H), 6.71 (dd, 2H, J = 10.7, 17.6 Hz), 5.75 ( dd, 2H, J = 0.95, 17.6Hz), 5.25 (dd, 2H, J = 0.95, 10.7Hz), 4.67 (d, 2H, J = 5.72Hz), 1.76 (t, 1H, J = 5.96Hz).

[0182] ​(Synthesis of tert-butylbis(4-vinylbenzyl)phosphonate and crosslinking agent (1c)) Under a nitrogen atmosphere, compound HMS (1.26 g, 9.39 mmol) and tetrahydrofuran (THF) (10.7 mL) were charged into a 50 mL four-necked flask and stirred. The flask was cooled in an ice bath, and sodium hydride (0.411 g, 9.42 mmol, 55%, dispersed in liquid paraffin) was added in portions and stirred at the same temperature for 1 hour. Next, a solution of tert-butylphosphonate dichloride (0.750 g, 4.29 mmol) in tetrahydrofuran (3.75 mL) was added dropwise to the reaction mixture over 20 minutes, and the flask was returned to room temperature and stirred for 93 hours. The flask was transferred to an ice bath and cooled, and deionized water (2.32 mL) and hydrochloric acid (1 mol / L, 8.57 mL) were added to the reaction mixture in that order and stirred to separate the organic phase. Furthermore, ethyl acetate (15 mL) was added to the aqueous phase for extraction, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (ethyl acetate:n-hexane = 1:4), and 4-tert-butylpyrocatechol (1.5 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 1.00 g of the compound represented by the following formula (1c) (crosslinking agent 1c) as a colorless solid (yield 63%). The reaction scheme and NMR analysis results are as follows.

[0183]

[0184] １ H-NMR (CDCl ３ ): d (ppm) 7.38 (dm, 2H, J = 8.11Hz, Ar-H), 7.28 (d, 2H, J = 8.11Hz, Ar-H), 6.71 (dd, 2H, J = 10.7, 17.6 Hz), 5.75 (dd, 2H, J = 0.72, 17.6Hz), 5.26 (dd, 2H, J = 0.72, 17.6Hz), 5.03 (dd, 2H, J=8.82Hz, J=11.9Hz), 4.96 (dd, 2H, J=7.15Hz, 12.2Hz), 1.19 (d, 9H, J=16.9Hz). ３１ P-NMR (CDCl ３ ):d(ppm))-18.0(s).​

[0185] [Example 4γ] Synthesis of phenylbis(4-vinylphenyl)phosphine oxide and crosslinking agent (1d)

[0186] (Synthesis of phenylbis(4-vinylphenyl)phosphine, compound DSPP2) Under a nitrogen atmosphere, at room temperature, a 2 L four-necked flask was filled with magnesium (Mg) (cut flakes, 10.7 g, 440 mmol), tetrahydrofuran (THF) (318 mL), and iodine (I) ２ (85.9 mg, 0.338 mmol) was added and stirred. After cooling the flask in a water bath, a solution of 4-bromostyrene (83.0 g, 440 mmol) in tetrahydrofuran (215 mL) was added dropwise to the reaction mixture over 1 hour. After the addition, the flask was allowed to return to room temperature and stirred for 1 hour. After cooling the flask in an ice bath, dichlorophenylphosphine (PhPCL) was added to the reaction mixture. ２ A solution of tetrahydrofuran (35.0 g, 196 mmol) in tetrahydrofuran (106 mL) was added dropwise over 30 minutes, and the flask was allowed to return to room temperature and stirred for 16 hours. The flask was cooled in an ice bath, and a 15% by mass aqueous solution of ammonium chloride (420 mL) was added dropwise to the reaction mixture, followed by the addition of ethyl acetate (200 mL) to separate the organic phase. Further extraction was performed by adding ethyl acetate (350 mL) to the aqueous phase, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried over sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (chloroform:n-hexane = 1:4), and 4-tert-butylpyrocatechol (42.0 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 37.3 g of the compound represented by the following formula DSPP2 as a colorless liquid (yield: 61%). The reaction scheme and NMR analysis results are as follows.

[0187]

[0188] １ H-NMR (CDCl ３ ​): d (ppm) 7.42-7.20 (m, 13H), 6.70 (dd, 2H, J = 10.7, 17.6Hz), 5.77 (dd, 2H, J = 0.72, 17.6Hz), 5.27 (dd, 2H, J = 0.72, 11.0Hz). ３１ P-NMR (CDCl ３ ): d(ppm)-18.0(s).

[0189] (Synthesis of phenylbis(4-vinylphenyl)phosphine oxide and crosslinking agent (1d)) At room temperature, compound DSPP2 (37.3 g, 119 mmol) and dichloromethane (CH) were added to a 500 mL round-bottom flask. ２ Cl ２ A solution consisting of (274 mL) is mixed with hydrogen peroxide (H ２ O ２ ) (30% by mass concentration, 68.3 mL, 669 mmol) was added dropwise over 30 minutes, and the mixture was stirred for a further 1 hour. The reaction solution was separated, and the obtained organic phase was washed with deionized water (261 mL) and saturated brine (261 mL), dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (ethyl acetate:n-hexane = 2:1) to obtain 36.4 g of the compound represented by the following formula (1d) (crosslinking agent 1d) as a colorless solid (yield: 93%). The reaction scheme and NMR analysis results are as follows.

[0190]

[0191] １ H-NMR (CDCl ３ ): d (ppm) 7.73-7.41 (m, 13H), 6.74 (dd, 2H, J = 10.7, 17.6Hz), 5.85 (d, 2H, J = 17.4Hz), 5.38 (d, 2H, J = 11.0Hz). ３１ P-NMR (CDCl ３ ): d (ppm) 28.4 (s).

[0192] [Example 5γ] Synthesis of phenylbis(2-vinylphenyl)phosphine oxide and crosslinking agent (1e)

[0193] ​Under a nitrogen atmosphere, at room temperature, magnesium (Mg) (cuttings, 4.00 g, 165 mmol) and tetrahydrofuran (THF) (101 mL) were charged into a 500 mL four-necked flask and stirred. 2-bromostyrene (30.1 g, 164 mmol) was added dropwise to the reaction mixture over 15 minutes. After addition, the flask was transferred to an oil bath and heated under reflux for 5.5 hours. After cooling the flask in an ice bath, phenylphosphonic acid dichloride (PhPOCl) was added to the reaction mixture. ２ ) (15.5 g, 79.5 mmol) was added dropwise over 50 minutes, and the flask was allowed to return to room temperature and stirred for 19 hours. The flask was cooled in an ice bath, sulfuric acid (0.1 mol / L, 301 mL) was added dropwise to the reaction mixture, and then chloroform (300 mL) was added to separate the organic phase. The obtained organic phase was washed with saturated sodium bicarbonate aqueous solution (200 mL), dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. Diethyl ether (70 mL) was added to the crude product and stirred, and the insoluble solid was removed by filtration and the filtrate was concentrated. The concentrate was purified using silica gel column chromatography (chloroform), and 4-tert-butylpyrocatechol (1.86 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 2.13 g of the compound represented by the following formula (1e) (organophosphorus compound 1e) as a colorless solid (yield: 8.1%). The reaction scheme and NMR analysis results are as follows.

[0194]

[0195] １ H-NMR (CDCl ３ ): d (ppm) 7.72 (dd, 2H, J = 4.05, 7.87Hz), 7.7-7.4 (m, 9H), 7.20 (td, 2H, J = 1.19, 7.63Hz), 7.07 ( ddd, 2H, J = 0.95, 7.63, 14.3Hz), 5.63 (dd, 2H, J = 1.19, 17.2Hz), 5.17 (dd, 2H, J = 1.19, 11.0Hz). ３１ P-NMR (CDCl ３ ): d (ppm) 34.8 (s).

[0196] ​[Example 6γ] Synthesis of phenylbis(2-methyl-4-vinylphenyl)phosphine oxide and crosslinking agent (1f)

[0197] (Synthesis of 1-bromo-2-methyl-4-vinylbenzene, compound BMVB) Under a nitrogen atmosphere, methyltriphenylphosphonium bromide (49.6 g, 139 mmol) and tetrahydrofuran (THF) (101 mL) were charged into a 500 mL four-necked flask at room temperature, and the flask was cooled in an ice bath. Potassium tert-butoxide (15.6 g, 139 mmol) was added to the reaction mixture and stirred for 30 minutes. Next, 4-bromo-3-methylbenzaldehyde (9.50 g, 46.3 mmol) was added dropwise to the reaction mixture over 8 minutes, and the flask was warmed to room temperature and stirred for 1.5 hours. After cooling the flask in an ice bath, deionized water (143 mL) was added dropwise to the reaction mixture over 12 minutes, and then ethyl acetate (100 mL) was added to separate the organic phase. Furthermore, ethyl acetate (238 mL) was added to the aqueous phase for extraction, and the organic phase was separated. The organic phases obtained from these extractions were combined and washed with deionized water (143 mL), then dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. n-hexane (400 mL) and diethyl ether (100 mL) were added to the crude product and stirred. The insoluble solid was filtered off, and the filtrate was concentrated. The concentrate was purified using silica gel column chromatography (n-hexane), and 4-tert-butylpyrocatechol (1.14 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 6.85 g of the compound represented by the following formula (BMVB) as a yellow liquid (yield: 73%). The reaction scheme and NMR analysis results are as follows.

[0198]

[0199] １ H-NMR (CDCl ３ ​): d (ppm) 7.46 (d, 1H, J = 8.11Hz), 7.25 (s, 1H), 7.09 (dd, 1H, J = 2.15, 8.34Hz), 6.62 (dd, 1H, J = 1 0.7Hz, 17.4Hz), 5.73 (dd, 1H, J = 0.72, 17.4Hz), 5.25 (dd, 1H, J = 0.72Hz, 10.7Hz), 2.39 (s, 3H).

[0200] (Synthesis of phenylbis(2-methyl-4-vinylphenyl)phosphine oxide and crosslinking agent (1f))

[0201] Under a nitrogen atmosphere, at room temperature, magnesium (Mg) (cuttings, 0.568 g, 23.4 mmol) and tetrahydrofuran (THF) (13.8 mL) were charged into a 200 mL four-necked flask and stirred. 1,2-dibromoethane (29.2 μL, 0.338 mmol) was added to the reaction mixture, and then a solution of BMVB (4.60 g, 23.3 mmol) in THF (2.30 mL) was added dropwise over 48 minutes, followed by stirring for another hour. After the dropwise addition, THF (41.3 mL) was added to the reaction mixture. The flask was transferred to an ice bath for cooling, and then phenylphosphonic acid dichloride (PhPOCl) was added to the reaction mixture. ２ A solution of (2.20 g, 11.3 mmol) of THF (4.59 mL) was added dropwise over 19 minutes, and the flask was allowed to return to room temperature and stirred for 19 hours. The flask was cooled in an ice bath, and sulfuric acid (0.1 mol / L, 42.8 mL) was added dropwise to the reaction mixture, followed by the addition of chloroform (300 mL) to separate the organic phase. Further extraction was performed by adding chloroform (90.5 mL) to the aqueous phase, and the organic phase was separated. The organic phases obtained from these extractions were washed with saturated brine (90 mL), dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (chloroform), and the recovered fraction was concentrated under reduced pressure to obtain 0.477 g of the compound represented by the following formula (1f) (organophosphorus compound 1f) as a colorless solid (yield: 12%). The reaction scheme and NMR analysis results are as follows.

[0202]

[0203] １ ​H-NMR (CDCl ３ ): d (ppm) 7.7-7.4 (m, 5H), 7.33 (d, 2H, J = 2.62), 7.17 (dm, 2H, J = 7.87Hz), 7.00 (dd, 2H, J = 8.11, 13.8 3Hz), 6.70 (dd, 2H, J = 10.97, 17.6Hz), 5.83 (d, 2H, J = 17.4Hz), 5.35 (d, 2H, J = 11.4Hz), 2.51 (s, 3H). ３１ P-NMR (CDCl ３ ): d (ppm) 33.9 (s).

[0204] <Preparation of other organophosphorus compounds> [Example 7γ] As an organophosphorus compound for comparison, diethyl vinyl phosphonate (DVP, manufactured by Tokyo Chemical Industry Co., Ltd.), a known organophosphorus flame retardant, was prepared as shown below.

[0205]

[0206] <Preparation of hydrocarbon compounds> [Example 8γ] As a hydrocarbon compound for flame retardancy comparison, 1,2-bis(4-vinylphenyl)ethane (BVPE), as shown below, was prepared.

[0207]

[0208] <Evaluation and Results> In Examples 1γ to 8γ, evaluation samples were prepared using the crosslinking agent, comparative organophosphorus compounds, and hydrocarbon compounds described above, according to the [Method for Preparing Evaluation Samples (Film-like Cured Products)] described above, and evaluated. The evaluation results are shown in Table 3 below.

[0209] The flame retardancy method was as described above, and the evaluation was carried out according to the evaluation criteria. • Evaluation Criteria for Flame Retardancy A: The peak value of the heat dissipation rate is lower than the measurement results of Example 8γ described later. B: The peak value of the heat dissipation rate is equivalent to or higher than that of Example 8γ.

[0210] Based on the above, using this crosslinking agent results in excellent flame retardancy and a dielectric loss tangent (D) under high-frequency conditions. ｆIt can be seen that the ) can be effectively reduced and a film-like cured product with a sufficiently high glass transition temperature (Tg) can be obtained. In other words, it can be seen that by using this crosslinking agent, a wiring board and the like can be obtained that has excellent electrical properties, flame retardancy and heat resistance, and satisfies practical properties in a well-balanced manner.

[0211] [Examples δ] Examples 1δ to 3δ are examples relating to compound (E) of the present disclosure, and Examples 4δ and 5δ are comparative examples.

[0212] <Manufacturing of Crosslinking Agents> [Example 1δ] Synthesis of tri(3-vinylphenyl)phosphine oxide and crosslinking agent (1a)

[0213] (Synthesis of tri(3-vinylphenyl)phosphine, compound TMVP) Under a nitrogen atmosphere, at room temperature, magnesium (Mg) (cuttings, 0.61 g, 25.2 mmol), tetrahydrofuran (THF) (13.0 mL) and iodine (I) were added to a 100 mL four-necked flask. ２ (5.29 mg, 0.0208 mmol) was added and stirred. A solution of 3-bromostyrene (4.76 g, 25.2 mmol) in tetrahydrofuran (19.6 mL) was added dropwise to the reaction mixture over 1 hour, and then the flask was allowed to return to room temperature and stirred for 1 hour. After cooling the flask in an ice bath, phosphorus trichloride (PCL) was added to the reaction mixture. ３ A solution of tetrahydrofuran (2.00 g, 11.2 mmol) in tetrahydrofuran (6.5 mL) was added dropwise over 30 minutes, and the flask was allowed to return to room temperature and stirred for 18 hours. The flask was cooled in an ice bath, and 15% by mass aqueous solution of ammonium chloride (44 mL) was added dropwise to the reaction mixture, followed by the addition of ethyl acetate (20 mL) to separate the organic phase. Further extraction was performed by adding ethyl acetate (44 mL) to the aqueous phase, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried over magnesium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (n-hexane), and 4-tert-butylpyrocatechol (1.3 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 1.46 g of the compound TMVP, represented by the following formula TMVP, as a colorless liquid (yield: 54%). The reaction scheme and NMR analysis results are as follows.

[0214]

[0215] １ H-NMR (CDCl ３ ): d (ppm) 7.45-7.35 (m, 6H, Ar-H), 7.30 (ddd, 3H, J = 1.67, 7.63, 8.11Hz), 7.17 (dddm, 3H, J = 1.67, 7.15, 7.39Hz), 6.65 (dd, 3H, J = 11.0, 17.6Hz), 5.68 (dd, 3H, J = 0.95, 17.6Hz), 5.28 (dd, 3H, J = 0.72, 11.0Hz). ３１ P-NMR (CDCl ３ ): d (ppm) - 5.39 (s).

[0216] (Synthesis of tri(3-vinylphenyl)phosphine oxide and crosslinking agent (1a)) At room temperature, compound TMVP (1.45 g, 4.26 mmol) and dichloromethane (CH) were added to a 20 mL round-bottom flask. ２ Cl ２ A solution consisting of (12 mL) is mixed with hydrogen peroxide (H ２ O ２ (30% by mass concentration, 2.45 mL, 24.0 mmol) was added dropwise over 30 minutes, and the mixture was stirred for a further 2 hours. The reaction solution was separated, and the resulting organic phase was washed with deionized water (10 mL) and saturated brine (10 mL). The mixture was dried over sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (ethyl acetate:chloroform = 1:20) to obtain 1.24 g of the compound represented by the following formula (1a) (crosslinking agent 1a) as a colorless solid (yield: 82%). The reaction scheme and NMR analysis results are as follows.

[0217]

[0218] １ H-NMR (CDCl ３ ​​): d (ppm) 7.79 (dt, 3H, J = 1.67, 12.6 Hz, Ar-H), 7.60 (ddm, 3H, J = 1.43, 7.39 Hz, Ar-H), 7.51-7.33 (6 H, m, Ar-H), 6.70 (dd, 3H, J=10.7, 17.4Hz), 5.77 (dd, 3H, J=0.72, 17.6Hz), 5.30 (dm, 3H, J=11.0Hz). ３１ P-NMR (CDCl ３ ): d (ppm) 29.2 (s).

[0219] [Example 2δ] Synthesis of tri(4-vinylphenyl)phosphine oxide and crosslinking agent (1b)

[0220] (Synthesis of tri(4-vinylphenyl)phosphine, compound TPVP) Under a nitrogen atmosphere, at room temperature, a 200 mL four-necked flask was filled with magnesium (Mg) (cut flakes, 2.03 g, 83.5 mmol), tetrahydrofuran (THF) (101 mL), and iodine (I ２ (6.75 mg, 0.0266 mmol) was added and stirred. 4-chlorostyrene (10.1 g, 72.9 mmol) was added to the resulting suspension and the mixture was reacted at 70°C for 2 hours. After cooling the flask in an ice bath, phosphorus trichloride (PCL) was added to the reaction mixture. ３ A solution of tetrahydrofuran (2.50 g, 18.2 mmol) in tetrahydrofuran (10 mL) was added dropwise over 30 minutes, and the mixture was stirred for a further 18 hours. The flask was cooled in an ice bath, and ammonium chloride aqueous solution (100 mL) was added dropwise to the reaction mixture. The reaction mixture was then filtered to remove insoluble matter. The resulting filtrate was separated to isolate the organic phase. Ethyl acetate (100 mL) was added to the aqueous phase for extraction, and the organic phase was isolated. The organic phases obtained from these extractions were combined, dried over magnesium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (n-hexane), and 4-tert-butylpyrocatechol (1.2 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 1.35 g of the compound TPVP, represented by the following formula TPVP, as a colorless solid (yield: 22%). The reaction scheme and NMR analysis results are as follows.

[0221]

[0222] １ H-NMR (CDCl ３ ): d (ppm) 7.37 (dd, 6H, J = 1.4, 8.1Hz, Ar-H), 7.27 (m, 6H, Ar-H), 6.70 (dd, 3H, J=10.8, 17.5Hz), 5.77 (dd, 3H, J=1.0, 17.6Hz), 5.28 (dd, 3H, J=1.0, 10.8Hz). ３１ P-NMR (CDCl ３ ): d(ppm)-7.08(s).

[0223] (Synthesis of tri(4-vinylphenyl)phosphine oxide and crosslinking agent (1b)) At room temperature, in a 30 mL four-necked flask, add tri(4-vinylphenyl)phosphine (compound TPVP) (1.35 g, 3.97 mmol) and dichloromethane (CH4). ２ Cl ２ ) (12 mL) and hydrogen peroxide solution (H ２ O ２ A solution of 2.28 mL (30% by mass concentration, 22.3 mmol) was added and stirred for 3 hours. The reaction mixture was separated, and the resulting organic phase was washed with deionized water (21 mL) and saturated brine (21 mL). The mixture was dried over sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified using silica gel column chromatography (ethyl acetate:chloroform = 1:5) to obtain 1.46 g of the compound represented by the following formula (1b) (crosslinking agent 1b) as a colorless solid (yield: 100%). The reaction scheme and NMR analysis results are as follows.

[0224]

[0225] １ H-NMR (CDCl ３ ): d (ppm) 7.63 (dd, 6H, J = 8.3, 11.7Hz, Ar-H), 7.48 (dd, 6H, J = 2.6, 8.1Hz, Ar-H) , 6.74 (dd, 3H, J = 11.0, 17.6Hz), 5.85 (d, 3H, J = 17.6Hz), 5.38 (d, 3H, J = 11.0Hz). ３１ P-NMR (CDCl ３ ): d (ppm) 28.2 (s). ​​

[0226] [Example 3δ] Synthesis of tri(4-vinylbenzyl)phosphate and crosslinking agent (1c)

[0227] (4-Vinylbenzyl alcohol, synthesis of compound HMS) The synthetic intermediate HMS was synthesized according to the procedure described in [Example 3γ].

[0228]

[0229] (Synthesis of tri(4-vinylbenzyl)phosphate and crosslinking agent (1c)) Under a nitrogen atmosphere, compound HMS (5.60 g, 41.7 mmol) and tetrahydrofuran (THF) (49.0 mL) were charged into a 200 mL four-necked flask and stirred. The flask was cooled in an ice bath, and sodium hydride (1.82 g, 41.7 mmol, 55%, dispersed in liquid paraffin) was added in portions and stirred at the same temperature for 1 hour. Next, a solution of phosphoryl chloride (2.00 g, 13.0 mmol) in tetrahydrofuran (5.00 mL) was added dropwise to the reaction mixture over 40 minutes, and the flask was returned to room temperature and stirred for 21 hours. The flask was transferred to an ice bath and cooled, and deionized water (10.6 mL) and hydrochloric acid (1 mol / L, 39.1 mL) were added to the reaction mixture in that order and stirred to separate the organic phase. Furthermore, ethyl acetate (60 mL) was added to the aqueous phase for extraction, and the organic phase was separated. The organic phases obtained from these extractions were combined, dried with sodium sulfate, filtered, and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography (ethyl acetate:n-hexane = 1:4), and 4-tert-butylpyrocatechol (2.40 mg) was added to the recovered fraction and concentrated under reduced pressure to obtain 2.54 g of the compound represented by the following formula (1c) (crosslinking agent 1c) as a pale yellow solid (yield 44%). The reaction scheme and NMR analysis results are as follows.

[0230]

[0231] １ H-NMR (CDCl ３ ​): d (ppm) 7.36 (dm, 6H, J = 8.11Hz, Ar-H), 7.24 (d, 6H, J = 8.11Hz, Ar-H), 6.70 (dd, 3H, J = 11.0, 1 7.6Hz), 5.75 (dd, 3H, J = 0.95, 17.6Hz), 5.27 (dd, 3H, J = 0.72, 17.6Hz), 4.99 (d, 6H, J = 8.34Hz).

[0232] <Preparation of other organophosphorus compounds> [Example 4δ] As an organophosphorus compound for comparison, diethyl vinyl phosphonate (DVP, manufactured by Tokyo Chemical Industry Co., Ltd.), a known organophosphorus flame retardant, was prepared as shown below.

[0233]

[0234] <Preparation of hydrocarbon compounds> [Example 5δ] As a hydrocarbon compound for flame retardancy comparison, 1,2-bis(4-vinylphenyl)ethane (BVPE), as shown below, was prepared.

[0235]

[0236] <Evaluation and Results> In Examples 1δ to 5δ, evaluation samples were prepared using the crosslinking agent, comparative organophosphorus compounds, and hydrocarbon compounds described above, according to the [Method for Preparing Evaluation Samples (Film-like Cured Products)] described above, and evaluated. The evaluation results are shown in Table 4 below.

[0237] The flame retardancy method was as described above, and the evaluation was carried out according to the evaluation criteria. • Evaluation Criteria for Flame Retardancy A: The peak value of the heat dissipation rate is lower than the measurement results of Example 5δ described later. B: The peak value of the heat dissipation rate is equivalent to or higher than that of Example 5δ.

[0238] Based on the above, using this crosslinking agent results in excellent flame retardancy and a dielectric loss tangent (D) under high-frequency conditions. ｆ It can be seen that the ) can be effectively reduced and a film-like cured product with a sufficiently high glass transition temperature (Tg) can be obtained. In other words, it can be seen that by using this crosslinking agent, a wiring board and the like can be obtained that has excellent electrical properties, flame retardancy and heat resistance, and satisfies practical properties in a well-balanced manner.

[0239] Based on the above, the novel organophosphorus compounds and novel crosslinking agents relating to this disclosure are suitable for use in curable compositions used in applications such as prepregs, metal-clad laminates, and wiring boards, but can be used in any application.

[0240] This disclosure is not limited to the embodiments described above, and may be modified as appropriate without departing from its spirit. Furthermore, this disclosure may be implemented by combining the embodiments described above or examples thereof as appropriate.

[0241] This application claims priority based on Japanese Patent Applications 2024-189639, 2024-189640, 2024-189681 and 2024-189682, filed on 29 October 2024, and incorporates all of their disclosures herein.

Claims

1. A crosslinking agent represented by the following formula (1). In the above formula (1), R １ represents a hydrocarbon group which may contain a heteroatom, L independently represents a divalent hydrocarbon group which may contain a single bond, an oxygen atom, or a heteroatom, n is 2 or 3, each benzene ring may independently have substituents, and each combination of components satisfies at least one of the following (A) to (E). (A) n is 2, R １ (B) n is 2, R １ (C) is a hydrocarbon group which may contain heteroatoms other than a carbocyclic group. (D) is a divalent hydrocarbon group which has n = 2 and may contain a single bond or a heteroatom. (E) is a divalent carbocyclic group which has n = 3 and may contain a single bond or a heteroatom, or a divalent linear or branched hydrocarbon group.

2. R １ The crosslinking agent according to claim 1, wherein it does not have an epoxy group.

3. R １ The crosslinking agent according to claim 1, wherein the atom bonded to P may be an oxygen atom in the hydrocarbon group.

4. R １ The crosslinking agent according to claim 1, wherein is a linear alkyl group, a branched alkyl group, a cycloalkyl group, an alkenyl group, a cycloalkenyl group, an aryl group, or an aryloxy group.

5. Satisfying (B) above, R １ The crosslinking agent according to claim 1, wherein the crosslinking agent represents an alkyl group having 1 to 20 carbon atoms, which may contain heteroatoms.

6. Satisfying the above (B), R １ is a group represented by the following formula (11). The crosslinking agent according to claim 1. R １１ -{ (O) ｎ１２ R １２} ｎ１３ -(O) ｎ１１ -*...(11) However, １１ R is a monovalent hydrocarbon group having no hetero atom or a monovalent heterocyclic group, １２ R are each independently a divalent hydrocarbon group having no hetero atom or a divalent heterocyclic group, n11 and n12 are each independently 0 or 1, n13 is an integer from 0 to 6, * indicates the bonding position with P.

7. Satisfying (C) or (D) above, R １ The crosslinking agent according to claim 1, wherein the crosslinking agent represents an alkyl group having 1 to 20 carbon atoms, which may contain a heteroatom, or a carbon ring group having 1 to 20 carbon atoms, which may contain a heteroatom.

8. Satisfying (C) above, R １ The crosslinking agent according to claim 7, wherein the crosslinking agent represents an aromatic carbon ring group having 1 to 20 carbon atoms, which may contain heteroatoms.

9. The crosslinking agent according to claim 1, which satisfies (B) or (C) above, wherein L independently represents a single bond, an oxygen atom, a divalent carbon ring group having 1 to 20 carbon atoms which may contain a heteroatom, or a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms which may contain a heteroatom.

10. The crosslinking agent according to claim 9, wherein L satisfies (B) or (C) above, and L independently represents a single bond, an oxygen atom, or a linear or branched alkylene group having 1 to 5 carbon atoms that may contain an oxygen atom.

11. The crosslinking agent according to claim 1, which satisfies (D) or (E) above, wherein L independently represents a single bond, a divalent carbon ring group having 1 to 20 carbon atoms which may contain heteroatoms, or a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms which may contain heteroatoms.

12. The crosslinking agent according to claim 11, wherein L satisfies (D) or (E) above, and L independently represents a divalent linear or branched hydrocarbon group having 1 to 10 carbon atoms, which may contain a single bond or a heteroatom.

13. The crosslinking agent according to claim 12, wherein L satisfies (D) or (E) above, and L independently represents a single bond or a linear or branched alkylene group having 1 to 5 carbon atoms, which may contain an oxygen atom.

14. The crosslinking agent according to claim 1, which satisfies (C) or (E) above, wherein at least one of the benzene rings has a linear or branched hydrocarbon group having 1 to 5 carbon atoms as a substituent.

15. The crosslinking agent according to claim 14, wherein the substituent is bonded to the ortho position of the benzene ring.

16. The crosslinking agent according to claim 1, wherein the (E) is satisfied, and the vinyl groups are each independently bonded to the meta or para position of the benzene ring.

17. A crosslinking agent according to any one of claims 1 to 16, for use in a curable composition used in the manufacture of prepregs, metal-clad laminates, or wiring boards.

18. A curable composition comprising a crosslinking agent according to any one of claims 1 to 16 and a curable compound having a crosslinkable functional group that can crosslink with the crosslinking agent.

19. A prepreg comprising a fibrous substrate and a semi-cured or cured product of the curable composition described in claim 18.

20. A laminate comprising a substrate and a curable composition layer composed of the curable composition described in claim 18.

21. A laminate comprising a base material and a cured product-containing layer comprising a semi-cured or cured product of the curable composition described in claim 18.

22. The laminate according to claim 21, wherein the substrate is a resin film or a metal foil.

23. The laminate according to claim 21, wherein the substrate is a resin film or a metal foil.

24. A metal-clad laminate comprising an insulating layer containing a cured product of the curable composition according to claim 18, and a metal foil.

25. A wiring substrate comprising an insulating layer containing a cured product of the curable composition according to claim 18, and wiring.

26. An organophosphorus compound represented by the following formula (1). In the above formula (1), R １ represents a hydrocarbon group which may contain a heteroatom, L independently represents a divalent hydrocarbon group which may contain a single bond, an oxygen atom, or a heteroatom, n is 2 or 3, each benzene ring may independently have substituents, and each combination of components satisfies at least one of the following (A) to (C). (A) n is 2, R １ (B) n is 2, R １ This is a hydrocarbon group which may contain heteroatoms other than a carbocyclic group. (C)n is 2 or 3, and the vinyl group bonded to the benzene ring is bonded at the meta position relative to L.

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