Benzooxazine compounds and their uses

Abstract

To provide benzoxazine compounds that can be easily decomposed and offer superior heat resistance and mechanical strength, and their utilization techniques.SOLUTION: A benzoxazine compound according to one embodiment includes a diacyl hydrazine structure represented by a specific chemical formula, and a benzoxazine structure.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to benzoxazine compounds and their uses.

Background Art

[0002] In recent years, in order to suppress environmental destruction and effectively utilize resources, it has been required to recycle used polymers. However, many used polymers are subjected to thermal recycling in which they are burned to recover thermal energy, and it is hard to say that chemical recycling in which raw materials are recovered and reused has become widespread. Generally, thermosetting resins are considered to be difficult to decompose and depolymerize because they have a strong cross-linked structure, but some technologies have been developed to make thermosetting resins decomposable as needed. For example, Patent Document 1 describes a technique in which a diacylhydrazine structure is incorporated into the main chain of an epoxy resin to enable oxidative decomposition with a specific oxidizing agent.

[0003] By the way, a thermosetting resin having a benzoxazine ring in its molecular structure described in, for example, Patent Document 2 has excellent properties such as heat resistance, flame retardancy, dimensional stability, electrical insulation, and low water absorption, which are not found in other thermosetting resins. Therefore, it has attracted attention as an electronics material such as a laminate or a semiconductor encapsulant, and a binder such as a friction material or a grinding wheel.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, recyclable technologies for thermosetting resins containing benzoxazine rings are still not sufficiently developed, and the development of new technologies is needed.

[0006] Furthermore, conventional thermosetting resins containing benzoxazine rings often have a rigid structure and are brittle, leaving room for improvement in terms of mechanical strength. In addition, conventional methods for improving mechanical strength also had room for improvement in terms of heat resistance.

[0007] Therefore, one aspect of the present invention aims to provide a benzoxazine compound that is easily decomposable and has excellent heat resistance and mechanical strength, as well as a technology for utilizing the same. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the present inventors have discovered for the first time that by combining a benzoxazine compound with a diacylhydrazine structure, a strong polymer skeleton is formed by crosslinking of the benzoxazine ring, while the benzoxazine compound becomes easily degradable due to the diacylhydrazine bond, thus completing the present invention.

[0009] Therefore, the benzoxazine compound according to one embodiment of the present invention (hereinafter also referred to as the benzoxazine compound) has a diacylhydrazine structure represented by the following formula (1) and a benzoxazine structure represented by the following formula (2).

[0010] [ka]

[0011] (In formula (1), R1 is hydrogen, an alkyl group having 1 to 3 carbon atoms, or a phenyl group.)

[0012] [ka]

[0013] (In formula (2), the benzene ring is unsubstituted or has a monovalent organic group as a substituent. When the benzene ring has a plurality of monovalent organic groups, they may be bonded to each other to form a cyclic structure.) [Advantages of the Invention]

[0014] According to one aspect of the present invention, it is possible to provide a benzoxazine compound that can be easily decomposed and has excellent heat resistance and mechanical strength, and a utilization technology thereof. [Modes for Carrying Out the Invention]

[0015] Embodiments of the present invention will be described in detail below. Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)".

[0016] [1. Benzoxazine Compound] This benzoxazine compound has a diacylhydrazine structure represented by the following formula (1) and a benzoxazine structure represented by the following formula (2).

[0017] [Chemical Formula]

[0018] (In formula (1), R1 is hydrogen, an alkyl group having 1 to 3 carbon atoms, or a phenyl group.)

[0019] [Chemical Formula]

[0020] (In formula (2), the benzene ring is unsubstituted or has a monovalent organic group as a substituent. When the benzene ring has a plurality of monovalent organic groups, they may be bonded to each other to form a cyclic structure.) Because this benzoxazine compound contains the structures represented by formulas (1) and (2) above, the resulting benzoxazine resin is easily decomposable and exhibits excellent heat resistance and mechanical strength. More specifically, the benzoxazine resin is decomposed by oxidation and cleavage of the diacylhydrazine structure shown in formula (1) above, for example, by an oxidizing agent such as hypochlorite. Furthermore, the carboxylic acid generated from the decomposed benzoxazine resin can be reused via carboxylic acid esters or acyl halides. Therefore, the benzoxazine resin cured from this benzoxazine compound is recyclable.

[0021] In this specification, "easily decomposable" means readily soluble in a solution containing a specific oxidizing agent capable of decomposing the diacylhydrazine structure, such as hypochlorite.

[0022] Patent Document 1 describes using a compound having a diacylhydrazine structure as an epoxy curing agent, and curing it by crosslinking the hydroxyl or amino group with the epoxy compound. The epoxy resin thus obtained can be easily recycled by oxidative decomposition of the contained diacylhydrazine structure. However, epoxy resins having a diacylhydrazine structure have the problem of poor mechanical strength and heat resistance because the main chain structure is linear and unbranched. The present inventors have succeeded in making a benzoxazine-based resin with excellent mechanical strength and heat resistance decomposable and recyclable by selecting benzoxazine as the basic skeleton of a thermosetting polymer and incorporating a diacylhydrazine structure.

[0023] Having the diacylhydrazine structure shown in formula (1) above allows for improved heat resistance and mechanical strength when benzoxazine compounds are cured to form benzoxazine resins. As mentioned above, most commercially available benzoxazine resins are rigid and brittle. Methods to improve the mechanical strength of such benzoxazine resins have been known, such as introducing flexible units like methylene chains or creating hybrids with polysiloxane and epoxy resins, but all of these methods have the problem of reduced heat resistance.

[0024] On the other hand, because the diacylhydrazine structure is flexible and can form an intermolecular network through hydrogen bonding, the benzoxazine resin obtained by curing this benzoxazine compound has excellent mechanical strength without a decrease in heat resistance.

[0025] With the configuration described above, the resulting benzoxazine resin is highly durable and reusable, thus contributing to the achievement and realization of Sustainable Development Goal (SDG) 12, "Ensure sustainable consumption and production patterns."

[0026] The benzoxazine compound has a diacylhydrazine structure represented by formula (1) above. The number of diacylhydrazine structures contained in one molecule of the benzoxazine compound is not particularly limited, but is, for example, 1 to 10,000, preferably 1 to 5,000, and more preferably 1 to 3,000.

[0027] In formula (1) above, R1 is hydrogen, an alkyl group having 1 to 3 carbon atoms, or a phenyl group, preferably hydrogen or an alkyl group having 1 to 3 carbon atoms, more preferably hydrogen. The R1s in formula (1) above may be the same or different from each other.

[0028] The benzoxazine compound has a benzoxazine structure represented by formula (2) above. The number of benzoxazine structures contained in one molecule of the benzoxazine compound is not particularly limited, but is, for example, 20,000 to 20,000, preferably 20,000 to 10,000, and more preferably 2,000 to 6,000.

[0029] In formula (2) above, the benzene ring is unsubstituted or has a monovalent organic group as a substituent. The monovalent organic group is not particularly limited, but examples include halogen atoms, alkyl groups, cycloalkyl groups, alkyl halides, hydroxyl groups, carboxyl groups, amino groups, alkoxy groups, cyano groups, aryl groups (e.g., phenyl groups), aryloxy groups, and aralkyloxy groups. If the benzene ring has multiple monovalent organic groups, they may bond to each other to form a cyclic structure. An example of such a structure is a fused benzene ring with another benzoxazine ring. Among these, from the viewpoint of excellent mechanical strength after curing, it is preferable that the benzene ring is unsubstituted or has a structure in which an alkyl group having 1 to 4 carbon atoms, or a phenyl group and / or another benzoxazine ring are fused as a substituent.

[0030] The benzoxazine compound is preferably structured by any of the following formulas (3) to (9) from the viewpoint of ease of synthesis and the physical properties of the resulting cured product. In formulas (3) to (9), R1 is hydrogen, an alkyl group having 1 to 3 carbon atoms, or a phenyl group; R2, R4, R5, and R7 are directly bonded or divalent organic groups; R3 and R6 are hydrogen or monovalent organic groups; and multiple R1 to R7 in a single molecule may be the same or different. n is an integer of 2 or more. In this specification, "directly bonded" means a single bond.

[0031] [ka]

[0032] In terms of ease of synthesis and the physical properties of the resulting cured product, the preferred combinations in formulas (3) to (9) above are: R1 is hydrogen, R2 is a divalent organic group having 1 to 10 carbon atoms, R3 is hydrogen, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, R4 is directly linked or a divalent organic group having 1 to 20 carbon atoms, R5 is directly linked or a divalent organic group having 1 to 6 carbon atoms, R6 is a monovalent organic group having 3 to 10 carbon atoms, and R7 is a divalent organic group having 6 to 20 carbon atoms.

[0033] Furthermore, in terms of ease of synthesis and the physical properties of the resulting cured product, the most preferred combinations in formulas (3) to (9) above are: R1 is hydrogen, R2 is an aromatic group, R3 is hydrogen, R4 is a divalent organic group having 1 to 10 carbon atoms, R5 is a direct link, and R6 is an aryl group.

[0034] The monovalent organic groups mentioned above are as described above. Examples of divalent organic groups include aromatic groups, alkylene groups, and alkenylene groups.

[0035] Examples of the alkylene groups mentioned above include methylene, ethylene, propylene, butylene, pentylene, and hexylene groups. Examples of the alkenylene groups mentioned above include vinylene, 1-methylvinylene, propenylene, butenylene, and pentenylene groups. Examples of the aromatic groups mentioned above include phenylene, biphenylene, naphthylene, anthranylene, phenanthylene, pyrenylene, colonylene, terphenylene, furanylene, thienylene, or fluorenylene groups.

[0036] In this specification, aromatic groups include structures in which two or more identical groups, or two or more different groups, are linked by one or more divalent linking groups. Furthermore, non-benzene aromatic groups and heteroaromatic groups are also included. Examples of divalent linking groups include alkylene groups, ether groups, carbonyl groups, amide groups, imino groups, azo groups, sulfide groups, sulfonyl groups, sulfide groups, isopropylidene groups, and hexafluorinated isopropylidene groups. Examples of non-benzene aromatic groups include annulene, azulene, tropone, metallocene, and other aromatic compounds having three-membered, five-membered, or seven-membered ring structures.

[0037] If the aromatic group has substituents, examples of substituents include halogen atoms, alkyl groups, cycloalkyl groups, alkyl halides, hydroxyl groups, carboxyl groups, amino groups, alkoxy groups, cyano groups, aryloxy groups, aralkyloxy groups, and the like.

[0038] In the above formulas (4), (6) to (9), n is an integer of 2 or more, preferably an integer between 20,000 and 10,000, more preferably an integer between 2,000 and 5,000, and even more preferably an integer between 2,000 and 3,000.

[0039] [2. Method for producing benzoxazine compounds] The method for producing this benzoxazine compound includes the steps of forming a diacylhydrazine structure of formula (1) below and forming a benzoxazine structure of formula (2) below. For formulas (1) and (2) below, R1 and the benzene ring are as described in [1. Benzoxazine Compounds].

[0040] [ka]

[0041] [ka]

[0042] The step of forming the diacylhydrazine structure of formula (1) above can be carried out according to known methods. The step of forming the diacylhydrazine structure may include, for example, a step of oxidative coupling of acylhydrazides, a step of reacting an acylhydrazide with an acyl halide, or a step of reacting an acyl halide or carboxylic acid ester with a hydrazine compound.

[0043] Furthermore, the acylhydrazide can also be obtained by reacting the acyl halide or carboxylic acid ester with a hydrazine compound. That is, for example, a diacylhydrazine structure may be directly formed by reacting the acyl halide or carboxylic acid ester with a hydrazine compound, or an acylhydrazide may be formed by the above method, and then the obtained acylhydrazide may be oxidatively coupled to form a diacylhydrazine structure.

[0044] The method for oxidative coupling of the above acyl hydrazides is not particularly limited, and various methods involving reaction with oxidizing agents can be employed. Examples of such oxidizing agents include potassium peroxymonosulfate, double salt of potassium peroxymonosulfate / potassium bisulfate / potassium sulfate (Oxon®, manufactured by DuPont), potassium peroxodisulfate, potassium nitrate, sodium perchlorate, potassium permanganate, cerium ammonium nitrate, chromium oxide, potassium dichromate, hydrogen peroxide, and ozone. Among the oxidizing agents, potassium peroxymonosulfate, Oxon®, potassium peroxodisulfate, potassium nitrate, sodium perchlorate, and potassium permanganate are preferred due to their excellent reactivity, and potassium peroxymonosulfate, Oxon®, potassium peroxodisulfate, and potassium nitrate are more preferred.

[0045] Furthermore, from the viewpoint of ease of handling, it is preferable that the above oxidation coupling be carried out in a solvent. Examples of solvents that can be used for the above oxidation coupling include chloroform, tetrahydrofuran, N-methyl-2-pyrrolidone, acetonitrile, and water.

[0046] The benzoxazine structure of formula (2) above can be formed according to known methods. Examples of such methods include reacting an aromatic hydroxyl group-containing compound with an amine and a formaldehyde derivative, or reacting an aromatic hydroxyl group-containing compound with a triazine derivative and a formaldehyde derivative. Examples of solvents that can be used here include toluene, 1,4-dioxane, ethanol, chloroform, a mixed solvent of toluene and methanol, a mixed solvent of toluene and ethanol, a mixed solvent of toluene and isobutanol, and tetrahydrofuran.

[0047] The order in which the structures of formula (1) and formula (2) are formed is not particularly limited. That is, the structure of formula (1) may be formed first and then the structure of formula (2), or the structure of formula (2) may be formed first and then the structure of formula (1), or the structures of formula (1) and (2) may be formed simultaneously.

[0048] Furthermore, when producing this benzoxazine compound via an acylhydrazide, it is preferable to first convert the acylhydrazide to a diacylhydrazine to form the structure of formula (1) above, and then form the structure of formula (2) above. Following this order can suppress side reactions such as the reaction of the amino group at the acylhydrazide terminus with a phenolic hydroxyl group.

[0049] Examples of the hydrazine compounds mentioned above include hydrazine (anhydrous), hydrazine monohydrate, hydrazine monohydrochloride, and hydrazine dihydrochloride. Examples of the acylhydrazides mentioned above include 4-aminobenzohydrazide, salicylic acid hydrazide, 4-hydroxybenzohydrazide, 2-aminobenzohydrazide, and amino group-containing acylhydrazides derived from various amino acids. Examples of the acylhalides mentioned above include 4-aminobenzoic acid chloride, 4-hydroxybenzoic acid chloride, salicylic acid chloride, 5-chlorosalicylic acid chloride, and amino group-containing acylhalides derived from various amino acids.

[0050] Aromatic hydroxyl group-containing compounds include phenol, o-cresol, m-cresol, p-cresol, p-tert-butylphenol, p-octylphenol, p-cumylphenol, dodecylphenol, o-phenylphenol, p-phenylphenol, 1-naphthol, 2-naphthol, m-methoxyphenol, p-methoxyphenol, m-ethoxyphenol, p-ethoxyphenol, 3,4-dimethylphenol, 3,5-dimethylphenol, dihydroxydiphenylmethane compounds, dihydroxydiphenylethane compounds, dihydroxydiphenylpropane compounds, dihydroxydiphenylbutane compounds, dihydroxydiphenylcyclohexane compounds, and other dihydroxyphenyl compounds.

[0051] The above amines include aniline, 4,4'-(1,3-phenylenedioxy)dianiline, 4,4'-oxydianiline, 1,4-diaminobenzene, 1,3-diaminobenzene, 2,4-diaminotoluene, 2,6-diaminotoluene, 3-(aminomethyl)benzylamine, 4-(aminomethyl)benzylamine, 3,3'-sulfonyldianiline, 4,4'-sulfonyldianiline, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, and 1,3-bis(4-amine). Examples include nophenoxy)benzene, 1,3-bis(3-aminophenoxy)benzene, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(4-aminophenoxy)phenyl]sulfone, 4,4'-bis(3-aminophenoxy)biphenyl, 4,4'-bis(4-aminophenoxy)biphenyl, 9,9-bis(4-aminophenyl)fluorene, 2,2'-bis(trifluoromethyl)benzidine, and 4,4'-diaminodiphenylsulfone.

[0052] Examples of the above-mentioned triazine derivatives include hexahydro-1,3,5-triphenyl-1,3,5-triazine compounds derived from the above-mentioned amines, such as hexahydro-1,3,5-triazine.

[0053] Examples of the formaldehyde derivatives mentioned above include paraformaldehyde, which is a polymer of formaldehyde, or formalin, which is in the form of an aqueous solution.

[0054] Furthermore, when forming the structure of formula (1) before forming the structure of formula (2), a diacylhydrazine having an amino group may be used as the amine, and a diacylhydrazine having both an aromatic group and a hydroxyl group may be used as the aromatic hydroxyl group-containing compound.

[0055] [3. Benzooxazine resin composition] The benzoxazine compound of the present invention may be used alone as a cured product, but it is preferable to composite it with various fillers, fibers, polymers, etc., to form a benzoxazine resin composition, as this improves heat resistance and strength.

[0056] A benzoxazine resin composition according to one embodiment of the present invention (hereinafter also referred to as "this benzoxazine resin composition") comprises this benzoxazine compound and one or more fillers selected from the group consisting of carbon fibers, glass fibers, carbon nanotubes, cellulose nanofibers, clay, graphite, and silica. The above fillers may consist of only one type or multiple types. From the viewpoint of improving the physical properties of the resulting benzoxazine resin, the above fillers are preferably carbon fibers, glass fibers, carbon nanotubes, and cellulose nanofibers, and more preferably carbon fibers. Although carbon fibers are expensive, when composited with this benzoxazine compound, they can be recovered and reused.

[0057] The method for mixing the benzoxazine compound and the filler is not particularly limited. For example, the benzoxazine compound may be heated and melted before mixing, or the benzoxazine compound may be dissolved in a solvent before mixing, and then the solvent may be evaporated and removed.

[0058] Furthermore, when using carbon fiber as a filler, carbon fiber is generally sizing-treated, but it can be used as is, or if necessary, fibers with less sizing agent can be used, or the sizing agent can be removed by existing methods such as organic solvent treatment or heat treatment. In addition, the fiber bundles of carbon fiber may be opened in advance using air or rollers, and treated to facilitate resin impregnation between the individual carbon fibers.

[0059] This benzoxazine compound may be mixed with other polymers having a benzoxazine structure (benzoxazine polymers) before curing. The content of other benzoxazine polymers is preferably 1 to 1000 parts by weight, more preferably 10 to 500 parts by weight, and even more preferably 20 to 200 parts by weight, per 100 parts by weight of this benzoxazine compound. Mixing this benzoxazine compound with other benzoxazine polymers can improve the physical properties of the cured product.

[0060] This benzoxazine resin composition may optionally contain fillers, release agents, flame retardants, colorants, coupling agents, etc. These may be mixed during the manufacturing of this benzoxazine resin composition or during the curing of this benzoxazine resin composition.

[0061] [4. Benzooxazine resin] A benzoxazine resin according to one embodiment of the present invention (hereinafter also referred to as "this benzoxazine resin") is obtained by curing this benzoxazine compound or this benzoxazine resin composition.

[0062] The method for curing the benzoxazine compound or the benzoxazine resin composition is not particularly limited, but it can be cured by heating, for example. The heating conditions are not particularly limited, but heating at a temperature range of 100°C to 300°C for 10 minutes to 5 hours is preferred, and heating at a temperature range of 150°C to 250°C for 30 minutes to 3 hours is more preferred, as it allows the crosslinking reaction by ring opening of benzoxazine to proceed sufficiently. Heating may be performed in one step or in multiple steps. Even when heating is performed multiple times, the heating temperature and time do not need to be constant.

[0063] The tensile breaking strength of this benzoxazine resin is preferably 20 MPa or higher, more preferably 25 MPa or higher, and even more preferably 30 MPa or higher. The above tensile breaking strength can be measured by the method described in the examples below.

[0064] This benzoxazine resin can be suitably used in electronic materials such as electronic components, laminates and printed circuit boards, semiconductor encapsulation materials, and semiconductor mounting modules, as well as in automobiles or vehicles, aircraft parts, building materials, machine tools, and the like.

[0065] [5. Recycling Methods] One aspect of the present invention is a method for recycling benzoxazine resin, comprising the step of decomposing the benzoxazine resin by reacting it with an oxidizing agent. The benzoxazine resin can be easily decomposed by cleaving the diacylhydrazine portion by reacting it with an oxidizing agent. The decomposed benzoxazine resin can be recycled by various methods, such as dissolving it in a solvent or melting it by heating. Therefore, "the benzoxazine resin is decomposable" can be rephrased as "the benzoxazine resin is recyclable."

[0066] Examples of the oxidizing agents mentioned above include hydrogen peroxide, nitrogen oxides (e.g., dinitrogen monoxide, nitric oxide, nitrogen dioxide), chlorine, chlorine oxides (e.g., dichlorine monoxide, monochlorine dioxide, dichlorine heptaoxide), and hypochlorites. Among these, hypochlorites are preferred in terms of decomposition efficiency.

[0067] One specific recycling method involves decomposing this benzoxazine resin, which has been used as a carbon fiber reinforced plastic by incorporating carbon fibers, with hypochlorite. This allows for the recovery of the carbon fibers contained in the benzoxazine resin. Furthermore, the decomposed benzoxazine resin has carboxyl groups because the diacylhydrazine portion has been cleaved. Therefore, after recovering the carbon fibers from the solution in which the benzoxazine resin is dissolved, it can be reused as a polymer by converting it through carboxylic acids to carboxylic acid esters or acyl halides, etc.

[0068] When recycling this benzoxazine resin, it may be converted back into a benzoxazine resin having diacylhydrazine bonds, or the ester bonds may be regenerated to produce a polymer other than benzoxazine resin. For example, after generating the carboxylic acid ester or acyl halide mentioned above, the diacylhydrazine bonds can be regenerated by reacting them with a hydrazine compound, allowing the resin to be used again as benzoxazine resin. Other polymers that can be obtained from the decomposition products of this benzoxazine resin include, for example, polyesters and polyamides.

[0069] The above-mentioned hypochlorite salt is not particularly limited and includes, for example, sodium hypochlorite, calcium hypochlorite, and aqueous solutions thereof. From the viewpoint of availability, aqueous sodium hypochlorite solution is preferred.

[0070] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0071] [6. Other] This invention includes the following configuration. <1> A benzoxazine compound having a diacylhydrazine structure represented by formula (1) below and a benzoxazine structure represented by formula (2) below.

[0072] [ka]

[0073] (In formula (1), R1 is hydrogen, an alkyl group having 1 to 3 carbon atoms, or a phenyl group.)

[0074] [ka]

[0075] (In formula (2), the benzene ring is either unsubstituted or has a monovalent organic group as a substituent. If the benzene ring has multiple monovalent organic groups, they may bond to each other to form a cyclic structure.) <2> A benzoxazine compound according to claim 1, represented by any of the following formulas (3) to (9) (wherein formulas (3) to (9) below, R1 is hydrogen, an alkyl group having 1 to 3 carbon atoms, or a phenyl group; R2, R4, R5, and R7 are directly linked or divalent organic groups; R3 and R6 are hydrogen or monovalent organic groups; R1 to R7 in a single molecule are either identical or different; and n is an integer of 2 or more).

[0076] [ka]

[0077] <3> In formulas (3) to (9) above, R1 is hydrogen, R2 is a divalent organic group having 1 to 10 carbon atoms, R3 is hydrogen, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, R4 is directly linked or a divalent organic group having 1 to 20 carbon atoms, R5 is directly linked or a divalent organic group having 1 to 6 carbon atoms, R6 is a monovalent organic group having 3 to 10 carbon atoms, and R7 is a divalent organic group having 6 to 20 carbon atoms. <2> The benzoxazine compounds described above. <4> In the above formulas (3) to (9), R1 is hydrogen, R2 is an aromatic group, R3 is hydrogen, R4 is a divalent organic group having 1 to 10 carbon atoms, R5 is a direct bond, R6 is an aryl group, and R7 is a divalent organic group having 6 to 20 carbon atoms. <2> or <3> The benzoxazine compounds described above. <5> <1> ~ <4> A benzoxazine resin composition comprising a benzoxazine compound as described in any of the above, and one or more fillers selected from the group consisting of carbon fibers, glass fibers, carbon nanotubes, cellulose nanofibers, clay, graphite, and silica. <6> <1> ~ <4> A benzoxazine compound as described in any of the following, or <5> A benzoxazine resin obtained by curing the benzoxazine resin composition described above. <7> <6> A method for recycling benzoxazine resin, comprising the step of reacting the benzoxazine resin described above with an oxidizing agent to decompose the benzoxazine resin. <8> The oxidizing agent mentioned above is hypochlorite. <7> The recycling method for benzoxazine resin described in [the document]. <9> The process includes the steps of forming a diacylhydrazine structure of formula (1) below and forming a benzoxazine structure of formula (2) below.

[0078] [ka]

[0079] (In formula (1), R1 is hydrogen, an alkyl group having 1 to 3 carbon atoms, or a phenyl group.)

[0080] [ka]

[0081] (In formula (2), the benzene ring is either unsubstituted or has a monovalent organic group as a substituent. If the benzene ring has multiple monovalent organic groups, they may bond to each other to form a cyclic structure.) <10> The step of forming the diacylhydrazine structure of formula (1) above includes a step of oxidative coupling of acylhydrazides. <9> A method for producing the benzoxazine compound described above. <11> The step of forming the diacylhydrazine structure of formula (1) above includes a step of reacting a carboxylic acid ester or acyl halide with a hydrazine compound. <9> A method for producing the benzoxazine compound described above. [Examples]

[0082] Examples and comparative examples illustrating one embodiment of the present invention are shown below, but these are not intended to limit the present invention. In the examples, a benzoxazine compound or a benzoxazine resin obtained by curing a benzoxazine resin composition is referred to as "cured film." In addition, a benzoxazine compound may be simply referred to as "compound."

[0083] [Test Method] (Tensile test) The mechanical properties of the cured film were evaluated using a tensile testing apparatus (Shimadzu Corporation, EZ-SX). The test temperature was room temperature, the tensile speed was 5 mm / min, and the test specimen was 40 mm in length, 3 mm in width, and 0.1 mm in thickness. Ten samples were measured, and the average value was taken to determine the tensile modulus, tensile strength, and tensile elongation.

[0084] (thermal analysis) Thermal analysis of the cured film was performed using a differential scanning calorimetry (DSC, Hitachi High-Tech Science Corporation, DSC7000X). The film was heated to 400°C under a nitrogen flow rate of 40 mL / min and a heating rate of 5°C / min. The glass transition temperature (Tg) of the cured film was calculated from the baseline shift in the DSC curve. A higher Tg indicates higher heat resistance of the cured film.

[0085] [Example 1] Salicylhydrazide (0.500 g), hexahydro-1,3,5-triphenyl-1,3,5-triazine (0.330 g), paraformaldehyde (0.096 g), and toluene (7.14 g) were placed in a 50 mL round-bottom flask, and a reflux condenser was attached to the flask. The mixture in the round-bottom flask was heated at 115°C for 20 hours while stirring with a magnetic stirrer. This yielded an acylhydrazide containing a benzoxazine ring. After removing the solvent under reduced pressure, NMP (N-methyl-2-pyrrolidone) (2.8 g), acetonitrile (2.8 g), water (2.8 g), and Oxon® persulfate chloride (1.725 g) (manufactured by DuPont) were added, and the mixture was stirred at room temperature for 8 hours. The resulting precipitate was filtered, washed with water, and dried under reduced pressure to obtain compound 1 (0.503 g), a brown powder having a diacylhydrazine structure and two benzoxazine rings, which is the oxidative coupling product of the above acylhydrazide. The specific reaction equation for obtaining compound 1 is shown in formula (10) below.

[0086] [ka]

[0087] The obtained compound 1 powder was hot-pressed at 190°C / 2MPa / 1 hour, followed by 220°C / 2MPa / 30 minutes to produce a cured film. The Tg of the obtained cured film was 210°C. When this cured film was placed in 1,4-dioxane and sodium hypochlorite aqueous solution was added, the cured film dissolved while producing bubbles.

[0088] [Example 2] Salicylhydrazide (0.500 g) was dissolved in a mixed solvent of NMP (2.0 g), acetonitrile (2.0 g), and pure water (2.0 g), and Oxon® monosulfate compound (2.21 g) was added and the mixture was stirred at room temperature for 24 hours. The resulting mixture was filtered, and the solid on the filter paper was washed with water and methanol, and then dried under reduced pressure. This yielded the salicylhydrazide oxidative coupling compound in powder form. The obtained powder (0.200 g) was placed in a 50 mL three-necked flask, and toluene (2.0 g), hexahydro-1,3,5-triphenyl-1,3,5-triazine (0.155 g), and paraformaldehyde (0.045 g) were added. The mixture was heated and stirred at 110 °C for 3 hours to obtain a jelly-like compound 2, which was the reaction mixture. The specific reaction equation for obtaining compound 2 is shown in formula (11) below.

[0089] [ka]

[0090] The obtained compound 2 was placed on a Teflon® sheet, heated on a hot plate at 60°C for 7 hours, and then dried under reduced pressure to volatilize toluene. The dried compound 2 was hot-pressed at 190°C / 2MPa / 1 hour, followed by 220°C / 2MPa / 30 minutes to produce a cured film. The Tg of the obtained cured film was 212°C. When this cured film was placed in 1,4-dioxane and sodium hypochlorite aqueous solution was added, it dissolved while producing bubbles.

[0091] [Example 3] 4-hydroxybenzohydrazide (0.500 g) was placed in a mixed solvent of NMP (2.0 g), acetonitrile (2.0 g), and pure water (2.0 g). Oxon® monosulfate compound (2.02 g) was added while stirring, and the mixture was stirred at room temperature for 24 hours to obtain the reaction mixture. The reaction mixture was filtered, and the solid on the filter paper was washed with water and methanol, and dried under reduced pressure. This yielded the oxidative coupling compound of 4-hydroxybenzohydrazide as a solid. The obtained solid (0.137 g) was placed in a 50 mL round-bottom flask, and NMP (2.0 g), 1,4-dioxane (6.7 g), 4,4'-(1,3-phenylenedioxy)dianiline (0.146 g), and paraformaldehyde (0.061 g) were added, and the mixture was heated and stirred at 60°C for 12 hours. The reaction mixture was added to 50 mL of pure water, and the resulting white precipitate was filtered, washed with water, and dried under reduced pressure to obtain compound 3. The specific reaction equation for compound 3 is shown below in (12).

[0092] [ka]

[0093] The solid of compound 3 obtained was hot-pressed at 190°C / 2MPa / 1 hour, followed by 220°C / 2MPa / 30 minutes to produce a cured film. The resulting cured film was placed in 1,4-dioxane, and when an aqueous sodium hypochlorite solution was added, it dissolved while producing bubbles. The mechanical properties of this cured film were evaluated by tensile testing. The tensile modulus was 1.27 GPa, the tensile breaking strength was 39.5 MPa, and the tensile elongation at breaking was 2.3%. The Tg of the cured film was 238°C.

[0094] [Example 4] 4-aminobenzohydrazide (0.500 g) was placed in a round-bottom flask and dissolved with NMP (6.08 g). A solution of Oxon® persulfate compound (1.97 g) dissolved in pure water (7.11 g) was added, and the mixture was stirred at room temperature for 3 hours to obtain the reaction mixture. Pure water (50 mL) was added to the reaction mixture and filtered. The precipitate was further washed with pure water, and then dried under reduced pressure to obtain the oxidative coupling compound of 4-aminobenzohydrazide as a yellowish-brown powder (0.412 g, yield 92.2%). The obtained powder (0.410 g) was placed in a round-bottom flask and dissolved with DMSO (18.0 g). Paraformaldehyde (0.186 g) and phenol (0.290 g) were added, and the mixture was heated and stirred at 70°C for 15 hours. The reaction mixture was transferred to a Teflon® sheet and heated at 150°C for 3 hours to obtain compound 4 as a dark brown solid. The specific reaction equation for obtaining compound 4 is shown in equation (13) below.

[0095] [ka]

[0096] The obtained compound 4 solid was further hot-pressed at 190°C / 2MPa / 1 hour, followed by 220°C / 2MPa / 30 minutes to produce a cured film. The obtained cured film was placed in 1,4-dioxane and dissolved with the addition of an aqueous sodium hypochlorite solution, effervescently. The mechanical properties of this cured film were evaluated by tensile testing. The tensile modulus was 1.18 GPa, the tensile breaking strength was 46.2 MPa, and the tensile elongation at breaking was 2.5%. The Tg of the cured film was 229°C.

[0097] [Example 5] 4-aminobenzohydrazide (0.503 g) was placed in a screw-top tube, and NMP (2.02 g) and acetonitrile (2.01 g) were added and dissolved. A suspension of Oxon® monosulfate compound (1.98 g) in pure water (3.99 g) was added, and the mixture was stirred at room temperature for 24 hours to obtain the reaction mixture. Pure water (36 mL) was added to the reaction mixture and filtered. The precipitate was further washed with pure water, and then dried under reduced pressure to obtain the oxidative coupling compound of 4-aminobenzohydrazide as a yellowish-brown powder (0.411 g, yield 94.2%). The obtained coupling compound powder (0.403 g) was placed in a round-bottom flask and dissolved with chloroform (16.6 g). Paraformaldehyde (0.178 g) and phenol (0.283 g) were added, and the mixture was heated and stirred at room temperature for 1 hour and then at 55°C for 16 hours. The reaction mixture was transferred to a Teflon® sheet and heated at 60°C for 5 hours to obtain a dark brown solid of compound 5. The specific reaction equation for obtaining compound 5 is the same as that of equation (13) above.

[0098] A hardened film was prepared by hot-pressing the solid compound 5 at 190°C / 2 MPa / 1 hour, followed by 220°C / 2 MPa / 30 minutes. The hardened film was placed in 1,4-dioxane and dissolved with the addition of an aqueous sodium hypochlorite solution, effervescently. The mechanical properties of this hardened film were evaluated by tensile testing. The tensile modulus was 1.75 GPa, the tensile breaking strength was 45.5 MPa, and the tensile elongation at breaking was 2.1%. The Tg of the hardened film was 226°C.

[0099] (Manufacturing Example 1) Bisphenol A (BPA) (10.0 g), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) (18.0 g), and paraformaldehyde (5.8 g) were placed in a 100 mL round-bottom flask, chloroform (60 mL) was added, and the mixture was stirred at 50°C for 8 hours. Chloroform was removed under reduced pressure, and a benzoxazine polymer in which BPA and BAPP were linked by an oxazine ring was obtained as a white solid (29.0 g, yield 86.5%). The specific reaction equation for obtaining the above benzoxazine polymer is shown in formula (14) below.

[0100] [ka]

[0101] [Example 6] 4-hydroxybenzohydrazide (2.00 g) was placed in a 100 mL round-bottom flask, and N-methyl-2-pyrrolidone (8.0 g) and acetonitrile (8.0 g) were added and stirred at room temperature. Pure water (8.0 g) was added, and Oxon® monosulfate compound (8.08 g) was slowly added in solid form. After stirring at room temperature for 8 hours, the solvent was removed under reduced pressure to obtain the oxidative coupling product of 4-hydroxybenzohydrazide as a yellowish-white solid. 1,4-dioxane (60.1 g) was added to the obtained yellowish-white solid, and paraformaldehyde (1.58 g) and aniline (2.48 g) were added while stirring, and the mixture was stirred at 80°C for 7 hours. After cooling to room temperature, the contents were washed twice with pure water (300 mL), and the resulting orange solid was dried under reduced pressure to obtain compound 6. The specific reaction equation for obtaining compound 6 is shown in equation (15) below.

[0102] [ka]

[0103] The obtained compound 6 (0.16 g) and the benzoxazine polymer from Production Example 1 (0.60 g) were mixed in a mortar while still in solid form. A cured film was then prepared by hot pressing at 190°C / 2 MPa / 1 hour, followed by 220°C / 2 MPa / 30 minutes. The obtained cured film was placed in 1,4-dioxane and dissolved with the addition of an aqueous sodium hypochlorite solution, effervescently. The mechanical properties of this cured film were evaluated by tensile testing. The tensile modulus was 1.86 GPa, the tensile breaking strength was 31.2 MPa, and the tensile elongation at breaking was 1.8%. The Tg of the cured film was 232°C.

[0104] [Example 7] Compound 6 (0.30 g) synthesized in Example 6 and the benzoxazine polymer (0.50 g) from Production Example 1 were mixed in a mortar while still in solid form. A cured film was then prepared by hot pressing at 190°C / 2 MPa / 1 hour, followed by 220°C / 2 MPa / 30 minutes. The resulting cured film was placed in 1,4-dioxane and dissolved with the addition of an aqueous sodium hypochlorite solution, effervescently. The mechanical properties of this cured film were evaluated by tensile testing. The tensile modulus was 1.98 GPa, the tensile breaking strength was 37.8 MPa, and the tensile elongation at breaking was 2.1%. The Tg of the cured film was 230°C.

[0105] [Example 8] Compound 6 (0.50 g) synthesized in Example 6 and the benzoxazine polymer (0.50 g) from Production Example 1 were mixed in a mortar while still in solid form. A cured film was then prepared by hot pressing at 190°C / 2 MPa / 1 hour, followed by 220°C / 2 MPa / 30 minutes. The resulting cured film was placed in 1,4-dioxane and dissolved with the addition of an aqueous sodium hypochlorite solution, effervescently. The mechanical properties of this cured film were evaluated by tensile testing. The tensile modulus was 1.27 GPa, the tensile breaking strength was 39.5 MPa, and the tensile elongation at breaking was 2.3%. The Tg of the cured film was 225°C.

[0106] [Comparative Example 1] A commercially available benzoxazine monomer Pd (manufactured by Shikoku Chemicals, Inc.) (0.90 g) was heated at 100°C for 10 minutes, then immediately hot-pressed at 190°C / 2 MPa / 1 hour, followed by 220°C / 2 MPa / 30 minutes to produce a cured film. The obtained cured film was placed in 1,4-dioxane and sodium hypochlorite aqueous solution was added, but no change was observed. The mechanical properties of this cured film were evaluated by tensile testing. The tensile modulus was 2.17 GPa, the tensile breaking strength was 11.7 MPa, and the tensile elongation at breaking was 0.6%. The Tg of the cured film was 181°C. The chemical formula of the compound of Comparative Example 1 is shown in formula (16) below.

[0107] [ka]

[0108] [Comparative Example 2] 4-hydroxybenzaldehyde (0.367 g), paraformaldehyde (0.090 g), and 4,4'-(1,3-phenylenedioxy)dianiline (0.439 g) were added to 1,4-dioxane (4 mL) and stirred at room temperature for 5 hours, then heated at 80°C for 5 hours to obtain a suspension. The obtained suspension was dried on a Teflon® sheet and then hot-pressed at 190°C / 2 MPa / 1 hour, followed by 220°C / 2 MPa / 30 minutes to produce a cured film. The obtained cured film was placed in 1,4-dioxane and sodium hypochlorite aqueous solution was added, but no change was observed. The mechanical properties of this cured film were evaluated by tensile testing. The tensile modulus was 0.51 GPa, the tensile breaking strength was 5.6 MPa, and the tensile elongation at breaking was 0.6%. The Tg of the cured film was 201°C. The chemical formula of the compound of Comparative Example 2 is shown in formula (17) below.

[0109] [ka]

[0110] The test results for Examples 1-8 and Comparative Examples 1 and 2 are shown in Table 1. In Table 1, "-" indicates that the test was not performed.

[0111] [Table 1]

[0112] Table 1 shows that the cured films of Comparative Examples 1 and 2 did not dissolve when immersed in an aqueous sodium hypochlorite solution. On the other hand, the cured films of Examples 1 to 8 all dissolved in an aqueous sodium hypochlorite solution. Furthermore, the cured films of Examples 1 to 8 were superior to Comparative Examples 1 and 2, which do not have a diacylhydrazine structure, in tensile breaking strength and tensile breaking elongation, and also showed high values ​​for tensile modulus. In addition, the cured films of Examples 1 to 8 showed higher Tg values ​​than Comparative Examples 1 and 2. Therefore, it was found that this benzoxazine resin is easily decomposable and has excellent heat resistance and mechanical strength. [Industrial applicability]

[0113] The present invention can be suitably used in electronic materials such as electronic components, laminates for printed circuit boards and printed circuit boards, semiconductor encapsulation materials, and semiconductor mounting modules, as well as in automobiles or vehicles, aircraft parts, building materials, machine tools, and the like.

Claims

1. A benzoxazine compound represented by any one of the following formulas (3) to (6) (in the following formulas (3) to (6), R １ is hydrogen, an alkyl group having 1 to 3 carbon atoms, or a phenyl group, and R ２ is a direct bond or a divalent aromatic group, alkylene group, or alkenylene group having 1 to 10 carbon atoms, and R ３ is hydrogen, an alkyl group having 1 to 4 carbon atoms, or a phenyl group, and R ４ is a direct bond or a divalent aromatic group, alkylene group, or alkenylene group having 1 to 20 carbon atoms, and R ５ is a direct bond or a divalent aromatic group, alkylene group, or alkenylene group having 1 to 6 carbon atoms, and R ６ is an alkyl group, cycloalkyl group, halogenated alkyl group, alkoxy group, aryl group, aryloxy group, or aralkyloxy group having 3 to 10 carbon atoms, and R ７ is a direct bond or a divalent aromatic group, alkylene group, or alkenylene group having 6 to 20 carbon atoms, and R １ to R ７ in one molecule are the same or different from each other, and n is an integer of 2 or more.). 【Chemistry 1】

2. In the above equations (3) to (6), R １ Hydrogen, R ２ R is a divalent aromatic group having 6 to 10 carbon atoms. ３ Hydrogen, R ４ R is a divalent aromatic group having 1 to 10 carbon atoms, an alkylene group, or an alkenylene group. ５ Direct connection, R ６ is a phenyl group, R ７ The benzoxazine compound according to claim 1, wherein is a divalent aromatic group having 6 to 20 carbon atoms, an alkylene group, or an alkenylene group.

3. A benzoxazine resin composition comprising a benzoxazine compound according to claim 1 or 2, and one or more fillers selected from the group consisting of carbon fibers, glass fibers, carbon nanotubes, cellulose nanofibers, clay, graphite, and silica.

4. A benzoxazine resin obtained by curing the benzoxazine compound according to claim 1 or 2.

5. A method for recycling a benzoxazine resin, comprising the step of reacting the benzoxazine resin described in claim 4 with an oxidizing agent to decompose the benzoxazine resin.

6. The method for recycling benzoxazine resin according to claim 5, wherein the oxidizing agent is a hypochlorite salt.

7. The process of forming the diacylhydrazine structure of formula (1) below, The process includes forming a benzoxazine structure of the following formula (2), A method for producing a benzoxazine compound represented by any of the following formulas (3) to (6). 【Chemistry 2】 (In formula (1), R １ (These are hydrogen, an alkyl group having 1 to 3 carbon atoms, or a phenyl group.) 【Transformation 3】 (In formula (2), the benzene ring is unsubstituted, or has a C1-C4 alkyl group or a phenyl group as a substituent.) 【Chemistry 4】 (In the above formulas (3) to (6), R １ R is hydrogen, an alkyl group having 1 to 3 carbon atoms, or a phenyl group. ２ R is a directly bonded or divalent aromatic group, alkylene group, or alkenylene group having 1 to 10 carbon atoms, ３ R is hydrogen, an alkyl group having 1 to 4 carbon atoms, or a phenyl group. ４ R is a directly bonded or divalent aromatic group, alkylene group, or alkenylene group having 1 to 20 carbon atoms, ５ R is a directly bonded or divalent aromatic group, alkylene group, or alkenylene group having 1 to 6 carbon atoms, ６ R is an alkyl group having 3 to 10 carbon atoms, a cycloalkyl group, a halogenated alkyl group, an alkoxy group, an aryl group, an aryloxy group, or an aralkyloxy group. ７ R is a directly linked or divalent aromatic group, alkylene group, or alkenylene group having 6 to 20 carbon atoms, and R is present in one molecule. １ ~R ７ (Each element is either identical or different, and n is an integer greater than or equal to 2.)

8. The method for producing a benzoxazine compound according to claim 7, wherein the step of forming the diacylhydrazine structure of formula (1) above includes a step of oxidative coupling of acylhydrazides.

9. The method for producing a benzoxazine compound according to claim 7, wherein the step of forming the diacylhydrazine structure of formula (1) above includes a step of reacting a carboxylic acid ester or acyl halide with a hydrazine compound.

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