Compound, curing agent for epoxy resin comprising the same, curable composition, cured product, and method for curing epoxy resin

Abstract

To provide a curing agent for an epoxy resin, capable of giving a cured product which has prescribed durability when used and is easily decomposable when not used.SOLUTION: The epoxy resin is cured by using a compound having two or more partial structures represented by general formula (P) as a curing agent. The cured product of the epoxy resin crosslinked and cured by this compound can be decomposed by oxidation and treatment with a base when the cured product becomes unnecessary because the crosslinked portion is easily cut by the action of oxidation and a base. In General Formula (P), X is a divalent linking group or a bond, R is a hydroxyl, thiol, or NHR2 group, each R1 is independently hydrogen or the like, R2 is hydrogen or the like, and when R is a hydroxyl group, X to which it is bonded is an arylene group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a compound, a curing agent for epoxy resins comprising the compound, a curable composition, a cured product, and a method for curing epoxy resins. [Background technology]

[0002] In recent years, from the viewpoint of environmental protection, etc., there has been active development of degradable polymer materials, such as biodegradable polymers and photodegradable polymers, which are naturally decomposed when discarded. However, biodegradable polymers and photodegradable polymers have the problem of deteriorating over time in normal usage environments.

[0003] For this reason, there is a demand for polymers that do not deteriorate over time during use and can be quickly decomposed when disposed of. Several examples of polymer compounds that can be easily decomposed with an oxidizing agent when disposed of have been proposed, including poly(diacylhydrazines) obtained by polycondensing dicarboxylic acids or their reactive derivatives (acid chlorides or active ester derivatives) with hydrazine or dihydrazides of dicarboxylic acids (see, for example, Patent Documents 1 and 2).

[0004] Patent Document 3 discloses a polymer compound having a partial structure represented by the following general formula (Z) in its main chain. This polymer compound has a sulfide (sulfur atom) as shown in general formula (Z). A carbonyloxy group, which can form a stable anion and become a leaving group, is bonded to the carbon atom at the β-position of the sulfide. When this sulfide is oxidized with an oxidizing agent and then treated with a base, the carbonyloxy group becomes an anion under the action of the base and is eliminated from the β-carbon, as shown in the following chemical reaction formulas (A) to (D), resulting in cleavage of the polymer chain. [ka] [ka]

[0005] Specifically, the partial structure represented by the general formula (Z) is first oxidized by an oxidizing agent, converting the sulfide moiety to sulfone as shown in (B). This oxidation converts sulfide to sulfone, decreasing the electron density at the α-carbon of the sulfone, and increasing the acidity of the hydrogen atom attached to this carbon. If a base is present nearby, the hydrogen atom at the α-carbon is protonated, resulting in intermediate (C), a carbanion. If a carbonyloxy group, which can exist stably as an anion, is attached to the β-carbon in intermediate (C), this carbonyloxy group becomes a carboxylate anion, resulting in intramolecular cleavage as shown in (D). In other words, a polymer compound having the partial structure represented by the general formula (Z) in its main chain undergoes a series of reactions shown in (A) to (D), resulting in a lower molecular weight compound suitable for reuse or disposal.

[0006] As is well known, a curable composition is widely used that combines a viscous epoxy resin made of a compound such as a monomer or oligomer having an epoxy group in its molecule with a curing agent made of an amine compound, a bisphenol compound, or the like. Such curable compositions are used not only as so-called epoxy adhesives for everyday items and industrial products, but also, in recent years, for obtaining carbon fiber composite materials (CFRP) that are cured into a desired shape by combining them with carbon fibers. Because such CFRPs are lightweight and have strength comparable to that of steel, they are widely used in a variety of applications, from sports applications such as golf clubs to aircraft, automobiles, and the like. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-022315 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-052075 [Patent Document 3] International Publication WO2024 / 004741 A1 Summary of the Invention [Problem to be solved by the invention]

[0008] Because cured epoxy resins have excellent adhesive properties, heat resistance, and chemical resistance, it takes a great deal of effort to reconnect components bonded with epoxy adhesives or to dispose of cured epoxy resins, including CFRP. In particular, because the carbon fibers contained in CFRP are expensive, removing the cured epoxy resin from discarded CFRP and reusing it would be extremely cost-effective. However, because cured epoxy resins have the excellent resistance described above, it is technically difficult to remove only the cured epoxy resin from CFRP.

[0009] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a curing agent for epoxy resins that can give a cured product that has a predetermined durability during use and that can be easily decomposed when no longer needed. [Means for solving the problem]

[0010] The present inventors have conducted extensive research to solve the above problems and have found that by using a compound having a partial structure represented by the above chemical formula (Z) in its molecule as a curing agent for epoxy resins, the partial structure represented by the above chemical formula (Z) is introduced into the molecule of the resulting cured product, and this cured product is easily decomposed by the action of oxidation and a base as described above. The present invention was made based on this finding and provides the following.

[0011] (1) The present invention is a compound having two or more partial structures represented by the following general formula (P): [ka] (In the general formula (P), X is a divalent linking group or a single bond, and R is a hydroxyl group, a thiol group, or NHR 2 and each R 1are each independently a hydrogen atom, a group of a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R 2 represents a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and when R is a hydroxyl group, X to which it is bonded is an arylene group.

[0012] (2) The present invention also provides a compound according to item (1), which is represented by any one of the following general formulas (1) to (3). [ka] (In general formula (1), each X is independently a divalent linking group or a single bond, and each R is independently a hydroxyl group, a thiol group, or NHR 2 and each R 1 are each independently a hydrogen atom, a group of a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R 2 is a hydrogen atom, a group in which a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and when R is a hydroxyl group, X to which it is bonded is an arylene group. In general formula (2), each X is independently a divalent linking group or a single bond, and each R is independently a hydroxyl group, a thiol group, or NHR 2 and X 1 is a divalent linking group, and each R 1 are each independently a hydrogen atom, a group of a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R 2is a hydrogen atom, a group in which a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and when R is a hydroxyl group, X to which it is bonded is an arylene group. In general formula (3), each X is independently a divalent linking group or a single bond, and each R is independently a hydroxyl group, a thiol group, or NHR 2 and each R 1 are each independently a hydrogen atom, a group of a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R 2 represents a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent; Y represents an n-valent linking group, n being a number of 2 or more; and when R is a hydroxyl group, X to which it is bonded is an arylene group.

[0013] (3) Furthermore, the present invention provides a method for forming a compound in which each X is independently an arylene group, an alkylene group, an alkylidene group, a divalent atom, or —N(R 3 )- or a single bond, and R 3 is a hydrogen atom, a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent.

[0014] (4) The present invention also provides a compound according to any one of items (1) to (3), which is represented by the following general formula (1a): [ka] (In general formula (1a), each R is independently a hydroxyl group, a thiol group, or NHR 2 and each R 1are each independently a hydrogen atom, a group of a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R 2 is a hydrogen atom, a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent.

[0015] (5) The present invention also relates to a compound according to any one of items (1) to (4), which is represented by the following general formula (1b): [ka] (In general formula (1a), each R is independently a hydroxyl group, a thiol group, or NHR 2 and each R 1 are each independently a hydrogen atom, a group of a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R 2 is a hydrogen atom, a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent.

[0016] (6) The present invention also provides a compound according to any one of items (1) to (5), which is represented by the following chemical formula (1c): [ka]

[0017] (7) The present invention also provides a compound represented by the above general formula (2), wherein X 1 is a carbon chain having 1 to 6 carbon atoms which may have a heteroatom in the middle.

[0018] (8) The present invention also provides a compound according to any one of items (1), (2), and (7), which is represented by the following general formula (2a): [ka] In general formula (2a), each X is independently a divalent linking group or a single bond, and each R is independently a hydroxyl group, a thiol group, or NHR 2 and each R 1 are each independently a hydrogen atom, a group of a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R 2 represents a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and when R is a hydroxyl group, X to which it is bonded is an arylene group.

[0019] (9) The present invention also relates to a curing agent for epoxy resins, which comprises the compound according to any one of (1) to (8).

[0020] (10) The present invention also relates to a curable composition comprising an epoxy resin and the curing agent described in (9).

[0021] (11) The present invention also relates to a cured product having a structure in which an epoxy resin is crosslinked by the curing agent according to (9).

[0022] (12) The present invention also provides a method for curing an epoxy resin, characterized by allowing the curing agent described in (9) to act on the epoxy resin. [Effects of the Invention]

[0023] According to the present invention, there is provided a curing agent for epoxy resins that can give a cured product that has a predetermined durability during use and that can be easily decomposed when no longer needed. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, one embodiment of the compound of the present invention, one embodiment of the curing agent for epoxy resins of the present invention, one embodiment of the curable composition of the present invention, one embodiment of the cured product of the present invention, and one embodiment of the method for curing epoxy resins of the present invention will be described. Note that the present invention is not limited to the following embodiments and examples, and can be practiced with appropriate modifications within the scope of the present invention.

[0025] <Compound> The compound of the present invention is a compound having two or more partial structures represented by the following general formula (P), and is used as a curing agent for epoxy resins. As is well known, epoxy resins are compounds with molecular weights comparable to those of monomers or oligomers, and have multiple epoxy groups per molecule. These epoxy groups have the property of reacting with reactive substituents such as phenolic hydroxyl groups, amino groups with active hydrogen, and thiol groups to form bonds. Therefore, when a compound having two or more such reactive substituents in its molecule is used with an epoxy resin, the monomers and oligomers contained in the epoxy resin are crosslinked and cured by the compound. Therefore, compounds having the above reactive substituents serve as curing agents for epoxy resins. The compound of the present invention has two or more groups that serve as reactive substituents represented by R, and crosslinks the epoxy groups contained in the epoxy resin to each other, thereby curing the resin.

[0026] A compound having two or more partial structures represented by the following general formula (P) contains two or more Rs serving as reactive substituents, and a crosslinking moiety consisting of multiple atoms exists between each of these two or more Rs. That is, an epoxy resin cured by crosslinking with this compound will have the above-mentioned crosslinking moiety within its crosslinked structure. Since this crosslinking moiety contains the structure represented by the above general formula (Z), as described above, this crosslinking moiety is cleaved by the action of oxidation and a base along the pathways (A) to (D) in the above chemical reaction formula. The epoxy resin cured by crosslinking can then no longer maintain its cured state due to the release of the crosslinks, making it easily removable. Thus, when the compound of the present invention is used as a curing agent for an epoxy resin, a cured product can be obtained that can be easily removed by the action of oxidation and a base. As mentioned above, the structure represented by general formula (Z) contained in the crosslinking moiety contains a sulfide, and the oxidation of this sulfide initiates the cleavage reaction of the crosslinking moiety. However, while sulfides are generally not easily oxidized by oxygen molecules, which are radical oxidizing agents, they are easily oxidized by two-electron oxidation with oxidizing agents such as peroxides. Therefore, the oxidation reaction (A) → (B) described above, which is the first step in the cleavage reaction of the crosslinking moiety, does not occur when the cured epoxy resin is used in air, but only occurs after treatment with an oxidizing agent. Therefore, the cured epoxy resin obtained using the compound of the present invention has sufficient durability when used, but can be easily decrosslinked and removed when disposed of by the action of the above-mentioned oxidation and base.

[0027] [ka]

[0028] In general formula (P), X is a divalent linking group or a single bond. The compound of the present invention has two or more partial structures represented by general formula (P), and therefore has two or more Xs contained in this formula. These two or more Xs are each independently determined. In the present invention, "independently" means that the content of multiple objects present is independently determined, and these may be the same as each other or different from each other. In other words, when two or more Xs contained in the compound of the present invention are "independently determined," this means that the two or more Xs present may be the same as each other, some may be the same and the others may be different from each other, or all may be different from each other.

[0029] The divalent linking group is a group for connecting the reactive substituent R to the crosslinking moiety. Since it is used to connect functional moieties (i.e., a crosslinking moiety containing a reactive substituent and a unit corresponding to general formula (Z)) to each other, any divalent group may be used. Preferred examples of such divalent groups include arylene groups, alkylene groups, alkylidene groups, and divalent groups that are carbon chains of 1 to 10 carbon atoms, which may contain heteroatoms or unsaturated bonds along the chain and may be substituted. An arylene group is a divalent aromatic ring. A divalent aromatic ring is a divalent group formed by removing substituents such as hydrogen atoms from two of the carbon atoms constituting the aromatic ring. This aromatic ring may be a fused ring or may have any substituent. A preferred example of such an aromatic ring is a benzene ring. Preferred examples of the alkyl group include alkyl groups of 1 to 6 carbon atoms, which may be branched.

[0030] R is a hydroxyl group, a thiol group, or NHR 2 As with the above X, the compound of the present invention has two or more Rs, and these two or more Rs are determined independently. R is a group that allows the compound of the present invention to form a bond with the epoxy group of the epoxy resin, i.e., a reactive substituent. The hydroxyl group, thiol group, and NHR 2All of these can react with an epoxy group to form a bond, but when a hydroxyl group is selected as R, this hydroxyl group must be a phenolic hydroxyl group, so X, to which the hydroxyl group R is bonded, must be an arylene group. Note that when R is a hydroxyl group, i.e., a phenolic hydroxyl group, it is necessary to use a catalyst such as imidazole, triphenylphosphine, cyanamide, or an organic base in combination in order for the compound of the present invention to function as a curing agent for epoxy resins. R 2 is a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent. A preferred example of this "group which is a carbon chain which may have a substituent and / or an unsaturated bond and may have a heteroatom along the chain" is an alkyl group having 1 to 6 carbon atoms which may have a branch, but is not limited to this. In addition, R 2 The terminal atom bonded to the nitrogen in the group is preferably carbon. Examples of heteroatoms contained in this group include an oxygen atom, a sulfur atom, and an -N(R')- group (R' is an alkyl group having 1 to 6 carbon atoms).

[0031] Each R 1 are each independently a hydrogen atom, a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent. 1 A hydrogen atom is preferred as each R 1 It is more preferable that all of R are hydrogen atoms. A preferable example of the "carbon chain group which may have a substituent and / or an unsaturated bond and may have a heteroatom in the middle" is an alkyl group having 1 to 6 carbon atoms which may have a branch, but is not limited thereto. 1 The terminal atom on the side bonding to another atom is preferably carbon. Examples of heteroatoms contained in this group include an oxygen atom, a sulfur atom, and an -N(R')- group (wherein R' is an alkyl group having 1 to 6 carbon atoms).

[0032] Preferred examples of the compound of the present invention include compounds represented by the following general formulas (1) to (3). [ka]

[0033] In general formula (1), each X is independently a divalent linking group or a single bond. This linking group is the same as the linking group for X in general formula (P) above.

[0034] In general formula (1), each R is independently a hydroxyl group, a thiol group, or NHR 2 and each R 1 are each independently a hydrogen atom, a group in which a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent. When R is a hydroxyl group, X to which it is bonded is an arylene group. 2 is a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent. 1 and R 2 is the same as:

[0035] A preferred example of the compound represented by the above general formula (1) is a compound represented by the following general formula (1a). [ka]

[0036] The general formula (1a) is the same as the general formula (1) except that X is a phenylene group. 1 is the same as in the above general formula (1).

[0037] A preferred example of the compound represented by the above general formula (1a) is the compound represented by the following general formula (1b). [ka]

[0038] The general formula (1b) specifies that the phenylene group in the general formula (1a) is a p-phenylene group. 1 is the same as in the above general formula (1).

[0039] A preferred example of the compound represented by the general formula (1b) is a compound represented by the following chemical formula (1c): Note that the present invention is not limited to the compound represented by the following chemical formula (1c). [ka]

[0040] The compound represented by the above chemical formula (1c) can be easily obtained by various reactions, one example being transesterification with 4-hydroxybenzoic acid ester using 2,2'-thiodiethanol in the presence of a suitable catalyst. Examples of the catalyst include acid catalysts such as sulfuric acid and p-toluenesulfonic acid, as well as tin compounds such as monoalkyl(hydroxy)stannanones, dialkylstannanones, and dialkyldialkoxystannanes.

[0041] In general formula (2), each X is independently a divalent linking group or a single bond. The linking group is the same as the linking group for X in general formula (P) above.

[0042] In general formula (2), each R is independently a hydroxyl group, a thiol group, or NHR 2 and each R 1are each independently a hydrogen atom, a group in which a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent. When R is a hydroxyl group, X to which it is bonded is an arylene group. 2 is a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent. 1 and R 2 is the same as:

[0043] In general formula (2), X 1 is a divalent linking group. 1 is a group that simply connects the partial structures represented by the general formula (P) together, and as described above, the compound of the present invention exhibits its effect when it has two or more partial structures represented by the general formula (P). Therefore, X in the general formula (2) 1 may be any group. Examples of such groups include a divalent group having a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the way, such as an arylene group, an alkylenearylene group, an alkylenearylenealkylene group, and an arylenealkylene group. Preferred examples of the divalent group having a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the way include an alkylene group and an alkylidene group. Examples of heteroatoms contained in this group include an oxygen atom, a sulfur atom, and -N(R')- (wherein R' is an alkyl group having 1 to 6 carbon atoms).

[0044] A preferred example of the compound represented by general formula (2) is a compound represented by the following general formula (2a). [ka]

[0045] The general formula (2a) is X in the general formula (2). 1In the general formula (2a), X, R and R are specified as an ethylene group. 1 is the same as in the above general formula (2).

[0046] In general formula (3), each X is independently a divalent linking group or a single bond. The linking group is the same as the linking group for X in general formula (P) above.

[0047] In general formula (3), each R is independently a hydroxyl group, a thiol group, or NHR 2 and each R 1 are each independently a hydrogen atom, a group in which a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent. When R is a hydroxyl group, X to which it is bonded is an arylene group. 2 is a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent. 1 and R 2 is the same as:

[0048] In general formula (3), Y is an n-valent linking group. Y simply connects the partial structures represented by general formula (P) together. As described above, the compound of the present invention exhibits its effect as long as it has two or more partial structures represented by general formula (P). Therefore, Y in general formula (3) may be any group. Examples of such Y include carbon chains, aromatic rings, alicyclic rings, etc., which may have substituents and / or unsaturated bonds and may have heteroatoms, aromatic rings, alicyclic rings, etc., along the chain. Furthermore, Y may also include any oligomer or polymer skeleton. Note that the monovalent group enclosed in parentheses in general formula (3) can be bonded to any atom (limited to those chemically permissible) contained in Y. A preferred example of such an atom is a carbon atom. Furthermore, as described above, when Y is formed from an oligomer or polymer skeleton, the monovalent group enclosed in parentheses in general formula (3) can be bonded to any position of the main chain or side chain contained in the skeleton.

[0049] In general formula (3), n is a number equal to or greater than 2 and is the same as the valence of the linking group Y. The compound of the present invention may be prepared as a mixture of compounds consisting of a plurality of molecules each having a linking group Y with a different valence, in which case n is the average value of the valence of Y in each molecule. It may be difficult to determine the upper limit of the valence of Y, i.e., the upper limit of n, particularly when Y has a polymer skeleton, but a tentative upper limit of n may be about 100 to 1000. However, if Y is a low-molecular-weight compound without a polymer skeleton, the upper limit of n is preferably about 10, and more preferably about 6.

[0050] <Curing agent for epoxy resin> The curing agent for epoxy resins, which is made of the above compound, also constitutes one aspect of the present invention. As this has already been explained, further explanation will be omitted here.

[0051] <Curable composition> The present invention also includes a curable composition comprising an epoxy resin and the curing agent, which is the compound of the present invention. As described above, the compound of the present invention has two or more reactive substituents (i.e., R in the general formula (P) or the like) that react with the epoxy groups contained in the epoxy resin to form bonds, and therefore crosslinks and cures the epoxy resin.

[0052] Various epoxy resins are commercially available for use in the curable composition, and such commercially available products can be obtained and used.

[0053] The curable composition comprising an epoxy resin and the compound of the present invention may be a two-component type that is mixed at the time of use, or a one-component type in which the two components are mixed in advance. The mixing ratio of the epoxy resin and the compound of the present invention may be such that the number of equivalents of the epoxy group in the epoxy resin matches the number of equivalents of the reactive substituent (i.e., R) contained in the compound of the present invention. The number of equivalents per reactive substituent is determined by the following formula: 2 (R 2 is a hydrogen atom.) the value is 1, and when R is NH2 the value is 2. That is, when m Rs contained in the compound of the present invention are all hydroxyl groups, thiol groups, or NHR 2 (R 2 is a hydrogen atom. In this case, the number of equivalents of reactive substituents per mole of the compound of the present invention is m, and when all m Rs are NH2, the number of equivalents of reactive substituents per mole of the compound of the present invention is 2m.

[0054] Furthermore, when the compound of the present invention is one in which R in general formula (P) or the like is a phenolic hydroxyl group, it is difficult to cure the epoxy resin and the compound of the present invention alone, so a catalyst must be used. As the catalyst, well-known curing catalysts for epoxy resins can be used. Examples of such curing catalysts include imidazole, triphenylphosphine, cyanamide, and organic bases. The amount of catalyst used in the curable composition can be about 1 to 10% equivalent relative to the equivalent weight of epoxy groups contained in the epoxy resin.

[0055] The curable composition of the present invention cures at room temperature or by heating. When the curable composition of the present invention is used as an adhesive, the curable composition may be applied to the joining surfaces of the objects to be adhered and then heated. When the curable composition of the present invention is used to form a structural material, the curable composition may be impregnated into fibers such as carbon fibers to form a prepreg, which may then be processed into a desired shape and then heated.

[0056] <Cured product> The present invention also includes a cured product having a structure in which an epoxy resin is crosslinked by the curing agent of the present invention, i.e., the compound of the present invention. Such a cured product can be obtained by adding the compound of the present invention to an epoxy resin, optionally adding a catalyst, and then heating the resulting mixture, as described above.

[0057] As already mentioned, the cured product of the present invention can be easily decomposed and removed or recycled by the action of oxidation and a base, which releases crosslinks. The following two modes of treatment with oxidation and a base can be mentioned.

[0058] In the first embodiment, the cured product of the present invention is decomposed by the action of an oxidizing agent under basic conditions. As already mentioned, the cured product of the present invention is crosslinked by the structure represented by the above general formula (Z), and this structure is cleaved by the action of an oxidizing agent and a base, thereby releasing the crosslinks. This makes it easy to recycle or dispose of the cured product after use.

[0059] In this embodiment, the cured product of the present invention is decomposed by contacting it with a basic solution containing an oxidizing agent. As already mentioned, decomposition of the cured product of the present invention occurs through a two-step process: (1) oxidation of sulfide to sulfone by an oxidizing agent, and (2) abstraction of the hydrogen atom bonded to the α-carbon of the sulfone by a base, followed by intramolecular cleavage. In this embodiment, these reactions are carried out in a single step. In this case, it is preferable to use a catalyst in addition to the oxidizing agent and basic compound.

[0060] Examples of basic compounds include sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, sodium hydroxide, potassium hydroxide, triethylamine, sodium phosphate, disodium monohydrogen phosphate, 1,8-diazabicyclo[5.4.0]undec-7-ene, and tetramethylguanidine. Among these, sodium carbonate is preferred. The amount of basic compound in the solution can be about 1 to 10 equivalents relative to the number of partial structures represented by general formula (Z) contained in the cured product, but more amounts may also be used.

[0061] Examples of the oxidizing agent include, but are not limited to, common oxidizing agents, such as hydrogen peroxide, metachloroperbenzoic acid and its salts, perbenzoic acid and its salts, peracetic acid and its salts, persulfuric acid and its salts, perboric acid and its salts, chlorine, bromine, iodine, hypochlorous acid and its salts, hypobromous acid and its salts, hypoiodous acid and its salts, chlorous acid and its salts, bromous acid and its salts, iodous acid and its salts, chloric acid and its salts, bromic acid and its salts, iodic acid and its salts, perchloric acid and its salts, perbromic acid and its salts, periodic acid and its salts, hypervalent iodine compounds, ozone, nitrogen dioxide, and nitric oxide. It is known that the oxidizing activity of hydrogen peroxide and organic peroxides decreases under basic conditions, but hydrogen peroxide and organic peroxides can also be preferably used as oxidizing agents by using a catalyst described below in combination. The amount of oxidizing agent in the solution may be about 1 to 10 equivalents relative to the number of partial structures represented by the general formula (Z) contained in the cured product, but a greater amount may also be used.

[0062] The catalyst used is at least one selected from the group consisting of oxoacids of vanadium, niobium, tantalum, chromium, molybdenum, or tungsten or salts thereof, and heteropolyacids or salts thereof obtained by condensing such oxoacids with oxoacids of heteroatoms.

[0063] Oxoacids of vanadium, niobium, tantalum, chromium, molybdenum, or tungsten are acids containing an anion formed by combining vanadium(V), niobium(V), tantalum(V), chromium(VI), molybdenum(VI), or tungsten(VI) with oxygen, such as vanadic acid, niobic acid, tantalic acid, chromic acid, molybdic acid, and tungstic acid. Examples of these salts include lithium salts, sodium salts, potassium salts, cesium salts, and ammonium salts.

[0064] Heteropolyacids obtained by condensing an oxoacid of vanadium, niobium, tantalum, chromium, molybdenum, or tungsten with an oxoacid of a heteroatom can also be used as the catalyst of the present invention. Examples of heteroatoms in this case include Si, P, As, S, I, Fe, Co, Ni, Cu, Al, and Ga. Preferred examples of such heteropolyacids include phosphotungstic acid, silicotungstic acid, phosphomolybdic acid, silicomolybdic acid, phosphovanadic acid, silicovanadic acid, tungstomolybdophosphoric acid, tungstomolybdosilicic acid, and phosphovanadomolybdic acid. Examples of their salts include lithium salts, sodium salts, potassium salts, cesium salts, and ammonium salts.

[0065] The amount of catalyst in the solution may be about 0.001 to 0.5 equivalents relative to the number of partial structures represented by the general formula (Z) contained in the cured product, but a greater amount may also be used.

[0066] The solvent constituting the solution is not particularly limited as long as it dissolves the above-mentioned basic compound, oxidizing agent, and catalyst. Such a solvent is preferably an aqueous solvent. In the present invention, "aqueous solvent" refers to water, a water-miscible organic solvent, or a mixed solvent of water and a water-miscible organic solvent. Hydrogen peroxide is commercially available as an aqueous solution of hydrogen peroxide. When hydrogen peroxide is used as the oxidizing agent, the water contained therein is supplied to the reaction system. Thus, the water contained in hydrogen peroxide is naturally included in the "aqueous solvent" of the present invention. Preferred examples of water-miscible organic solvents used as aqueous solvents in the present invention include alcohol, tetrahydrofuran, dimethylacetamide, 1,4-dioxane, methyl cellosolve, butyl cellosolve, N-methylpiperidinone, 1,2-dimethoxyethane, diglyme, acetonitrile, etc. Preferred examples of alcohol include methanol, ethanol, propanol, and isopropanol.

[0067] In the second embodiment, the cured product of the present invention is treated with an oxidizing agent, and then further treated with a base to decompose the product. The oxidizing agent, basic compound, and solvent used in this embodiment are the same as those described in the first embodiment, and therefore will not be described here.

[0068] <Epoxy resin curing method> The present invention also includes a method for curing an epoxy resin, which comprises reacting the epoxy resin with a curing agent that is the compound of the present invention. These matters have already been explained, so further explanation will be omitted here. [Example]

[0069] The present invention will be explained in more detail below by showing examples, but the present invention is not limited to the following examples in any way.

[0070] Synthesis of 2,2'-thiodi(ethane-2,1-diyl)di(4-hydroxybenzoate) [ka]

[0071] A mixture of 1.22 g of 2,2'-thiodiethanol, 3.97 g of methyl 4-hydroxybenzoate, and 0.55 g of butyl(hydroxy)stannanone was stirred under reduced pressure at 90°C for 20 days. The reaction mixture was recrystallized from chloroform or isopropanol-water to give white crystals of 2,2'-thiodi(ethane-2,1-diyl)di(4-hydroxybenzoate).

[0072] [Epoxy resin hardening] 1.15 g of 2,2'-thiodi(ethane-2,1-diyl)di(4-hydroxybenzoate) obtained by the above procedure, 1.08 g of bisphenol A diglycidyl ether, and 0.01 g of imidazole were placed on a glass plate, heated to 150°C, mixed, and then heated for 2 hours to form a cured epoxy resin on the glass plate.

[0073] [Decomposition of the cured product] When the cured product formed on a glass plate using the above procedure was immersed for 4 hours in a mixture of 10 mL of tetrahydrofuran, 10 mL of 30% hydrogen peroxide, 1 g of sodium carbonate, and 0.1 g of sodium phosphomolybdate hydrate, the cured product decomposed and dissolved away. When the glass plate was removed and washed with water, no residue was found on the glass plate. This indicated that the cured product had decomposed due to the action of oxidation and a base.

Claims

1. A compound having two or more partial structures represented by the following general formula (P): 【Chemistry 1】 (In general formula (P), X is a divalent linking group or a single bond, and R is a hydroxyl group, a thiol group, or an NHR ２ and each R １ are each independently a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R ２ represents a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and when R is a hydroxyl group, X to which it is bonded is an arylene group.

2. The compound according to claim 1, which is represented by any one of the following general formulas (1) to (3): 【Chemistry 2】 (In general formula (1), each X is independently a divalent linking group or a single bond, and each R is independently a hydroxyl group, a thiol group, or an NHR ２ and each R １ are each independently a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R ２ is a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and when R is a hydroxyl group, X to which it is bonded is an arylene group. In general formula (2), each X is independently a divalent linking group or a single bond, and each R is independently a hydroxyl group, a thiol group, or NHR ２ and X １ is a divalent linking group, and each R １ are each independently a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R ２ is a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and when R is a hydroxyl group, X to which it is bonded is an arylene group. In general formula (3), each X is independently a divalent linking group or a single bond, and each R is independently a hydroxyl group, a thiol group, or NHR ２ and each R １ are each independently a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R ２ represents a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent; Y represents an n-valent linking group, n being a number of 2 or more; and when R is a hydroxyl group, X to which it is bonded is an arylene group.

3. Each X is independently an arylene group, an alkylene group, an alkylidene group, a divalent atom, or —N(R ３ )- or a single bond, and R ３ is a hydrogen atom, a group of a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent.

4. The compound according to claim 2, which is represented by the following general formula (1a): 【Transformation 3】 (In general formula (1a), each R is independently a hydroxyl group, a thiol group, or an NHR ２ and each R １ are each independently a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R ２ is a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent.

5. The compound according to claim 2, which is represented by the following general formula (1b): 【Chemistry 4】 (In general formula (1a), each R is independently a hydroxyl group, a thiol group, or an NHR ２ and each R １ are each independently a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R ２ is a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent.

6. The compound according to claim 2, represented by the following chemical formula (1c): 【Transformation 5】

7. Represented by the general formula (2), X １ The compound according to claim 2, wherein is a carbon chain having 1 to 6 carbon atoms which may have a heteroatom in the middle.

8. The compound according to claim 2, which is represented by the following general formula (2a): 【Transformation 6】 (In general formula (2a), each X is independently a divalent linking group or a single bond, and each R is independently a hydroxyl group, a thiol group, or an NHR ２ and each R １ are each independently a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and R ２ represents a hydrogen atom, a group which is a carbon chain which may have a substituent and / or an unsaturated bond and which may have a heteroatom along the chain, an aryl group which may have a substituent, or an aralkyl group which may have a substituent, and when R is a hydroxyl group, X to which it is bonded is an arylene group.

9. A curing agent for epoxy resins comprising the compound according to any one of claims 1 to 8.

10. A curable composition comprising an epoxy resin and the curing agent of claim 9.

11. A cured product having a structure in which an epoxy resin is crosslinked by the curing agent according to claim 9.

12. A method for curing an epoxy resin, comprising reacting the curing agent according to claim 9 with the epoxy resin.

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