JP7761248B2 - Epoxy resin composition, epoxy resin cured product, decomposable epoxy resin composition, recycled cured product, method for decomposing and recycling epoxy resin cured product, monomer compound, dimer compound, trimer compound and cured product thereof - Google Patents

Description

The present invention relates to an epoxy resin composition, a cured epoxy resin, a decomposable epoxy resin composition, a recycled cured product, a method for decomposing and recycling a cured epoxy resin, a monomer compound, a dimer compound, a trimer compound, and cured products thereof.

Epoxy resins are one of the most common polymeric materials and are used in a wide range of applications, including coatings, paints, primers, adhesives, and composite materials. While epoxy resins generally exhibit excellent heat resistance, mechanical properties, and chemical resistance due to their cross-linked polymer network structure, they are often thermosetting, making them difficult to recycle or rework. As a result, epoxy resins and their composites are typically disposed of by landfilling or incineration, causing significant adverse effects on the ecosystem as a whole. In particular, epoxy resins used in everyday life are considered one of the sources of microplastics. Therefore, there is a strong demand for the development of degradable and reusable thermosetting epoxy resins.

For example, Patent Document 1 describes a technique for decomposing cured epoxy resin materials, in which a substrate coated with a cured epoxy resin material is immersed in a cleaving agent solution containing a biomolecule such as glutathione.

JP 2013-535552 A

However, the method described in Patent Document 1 is aimed simply at decomposing the cured epoxy resin material, and the composition of the epoxy resin composition makes it difficult to recycle the decomposed material. In other words, in response to the need to establish an environmentally friendly recycling system as described above, there is a demand for epoxy resin compositions that not only enable the decomposition of the cured material, but also enable the creation of recycled cured materials in which a network structure is reconstructed from the decomposed material.

The present invention was made in consideration of the above circumstances, and aims to provide an epoxy resin composition that allows for decomposition and recycling (re-curing) of cured epoxy resin products. It also aims to provide cured products of this epoxy resin composition, decomposable epoxy resin compositions, recycled cured products, methods for decomposing and recycling cured epoxy resin products, and monomeric, dimeric, and trimeric compounds and their cured products.

To solve the above problems, the epoxy resin composition of the present invention has the following characteristics:

[1] an epoxy resin monomer (A1) having epoxy groups at both ends and a disulfide bond (—S—S—);
a curing agent (B) capable of bonding with an epoxy group;
Includes:

[2] The epoxy resin monomer (A1) includes a compound represented by the following formula:

(X is a disulfide bond (S—S), and R ¹ and R ² are the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain.)

[3] The curing agent has a disulfide bond (-S-S-).

[4] The curing agent includes a curing agent (B1) represented by the following formula:

( ^R3 and ^R4 may be the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain; ^R5 and ^R6 may be the same or different and represent a primary, secondary, or tertiary amine, imidazole, acid anhydride, or organic acid hydrazide.)

[5] the molar ratio (A1/A2) of the epoxy resin monomer (A1) to the epoxy resin monomer (A2) not having a disulfide bond (—S—S—) is 100/0 to 25/75;
The curing agent is a curing agent (B1) represented by the following formula:

( ^R3 and ^R4 may be the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain; ^R5 and ^R6 may be the same or different and represent a primary, secondary, or tertiary amine, imidazole, acid anhydride, or organic acid hydrazide.)
and,
the curing agent (B2) having no disulfide bond (—S—S—),
The molar ratio (B1/B2) of the curing agent (B1) to the curing agent (B2) is 100/0 to 0/100.

[6] The content of the curing agent (B1) in the curing agent (B) exceeds 75/25 in the molar ratio (B1/B2), the molar ratio (A1/A2) is 100/0 to 25/75, and the molar ratio (A1:B1) of the epoxy resin monomer (A1) to the curing agent (B1) is 2:1 to 0.5:1.

[7] The content of the curing agent (B1) in the curing agent (B) is 75/25 to 50/50 in the molar ratio (B1/B2), the molar ratio (A1/A2) is 100/0 to 50/50, and the molar ratio (A1:B1) of the epoxy resin monomer (A1) to the curing agent (B1) is 2:0.5 to 1:0.5.

[8] The content of the curing agent (B1) in the curing agent (B) is less than 50/50 to 25/75 in the molar ratio (B1/B2), the molar ratio (A1/A2) is 100/0 to 75/25, and the molar ratio (A1:B1) of the epoxy resin monomer (A1) to the curing agent (B1) is 2:0.25 to 1.5:0.25.

[9] The content of the curing agent (B1) in the curing agent (B) is less than 25/75 in the molar ratio (B1/B2), the molar ratio (A1/A2) is 100/0 to 75/25, and the molar ratio (A1:B1) of the epoxy resin monomer (A1) to the curing agent (B1) is 2:0.01 to 1.5:0.25 or 1:0.

The cured epoxy resin of the present invention is characterized as follows:

[10] A cured product of the epoxy resin composition of any one of [1] to [9].

[11] The proportion of disulfide bonds (-S-S-) is 1 equivalent or more relative to the repeating units of the epoxy resin.

[12] Contains a repeating unit formed by bonding 2 equivalents of the epoxy resin monomer to 1 equivalent of the curing agent.

The epoxy resin decomposable composition of the present invention is characterized by the following:

[13] The epoxy resin cured product according to any one of [10] to [12],
and a water-soluble biomolecular compound having a thiol group (—SH).

The epoxy resin decomposition composition of the present invention is characterized by the following:

[14] Contains a hydroxy thiol compound having a hydroxy group (-OH) and a thiol group (-SH), which is a decomposition reaction product of the epoxy resin decomposable composition of [13].

The recycled cured product of the present invention is characterized by the following:

[15] A recycled cured product of the epoxy resin decomposition composition according to [14],
The composition contains the hydroxy thiol compound and has an epoxy resin network structure.

[16] FT-NIR detects unreacted, non-disulfonated thiol groups (-SH).

[17] A cured product of the epoxy resin composition of [1],
Unreacted, non-disulfonated thiol groups (-SH) are detected by FT-NIR.

The method for decomposing cured epoxy resin materials of the present invention is characterized by the following:

[18] In a two-phase solvent system consisting of an aqueous phase and an organic phase, the cured epoxy resin material according to any one of [10] to [12] is contacted with a water-soluble biomolecular compound having a thiol group (-SH), to produce a hydroxythiol compound having a hydroxy group (-OH) and a thiol group (-SH) as a decomposition product in the organic phase;
Includes:

The recycling method for cured epoxy resin materials of the present invention is characterized by the following:

[19] The following steps:
The method includes: contacting the cured epoxy resin material of any one of claims 10 to 12 with a water-soluble biomolecular compound having a thiol group (-SH) in a two-phase solvent system consisting of an aqueous phase and an organic phase, to produce a hydroxy thiol compound having a hydroxy group (-OH) and a thiol group (-SH) in the organic phase as a decomposition product; and heating the liquid containing the hydroxy thiol compound to cure it, thereby obtaining a cured material having an epoxy resin network structure containing disulfide bonds (-S-S-).

The monomer compound of the present invention is characterized as follows:

[20] Has a unit structure represented by the following formula:

(R ⁷ and R ⁸ are the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^R9 represents an aromatic carbocycle, an aromatic carbocyclic alkyl chain, an aliphatic carbocycle, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^Z1 represents a nitrogen atom, benzene, or phenol;
^Y1 represents a thiol group (-SH).

The dimeric compound of the present invention is characterized by the following:

[21] A unit structure represented by the following formula:

(R ⁷ and R ⁸ are the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^R9 represents an aromatic carbocycle, an aromatic carbocyclic alkyl chain, an aliphatic carbocycle, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^Z1 represents a nitrogen atom, benzene, or phenol;
Of the three ^Y2s located at the terminals, two are thiol groups (-SH) and the other is a sulfide (-S-).
Contains two
The two unit structures are bonded to each other via a disulfide bond (-S-S-) linked by the sulfides (-S-).

The trimer compound of the present invention is characterized by the following:

[22] A unit structure represented by the following formula:

(R ⁷ and R ⁸ are the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^R9 represents an aromatic carbocycle, an aromatic carbocyclic alkyl chain, an aliphatic carbocycle, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^Z1 represents a nitrogen atom, benzene, or phenol.
Includes three
One of the three unit structures has three terminal ^Y3s , one of which is a thiol group (-SH) and the other two are sulfides (-S-),
The other two of the three unit structures have three terminal ^Y3s , two of which are thiol groups (-SH) and the other is a sulfide (-S-),
The sulfides (--S--) of the three unit structures are bonded to each other via disulfide bonds (--S--S--).

The cured product of the present invention is characterized by the following:

[23] A cured product of a composition containing any one of the compounds [20] to [22].

The epoxy resin composition of the present invention allows for the decomposition and recycling of its cured product, an epoxy resin cured product. The recycled cured product has the same mechanical strength as the cured product before recycling.

The cured epoxy resin composition and decomposable epoxy resin composition of the present invention allow for decomposition and recycling of the cured epoxy resin composition, and the recycled cured product has the same mechanical strength as the cured product before recycling.

The recycled cured product of the present invention can be disassembled and recycled, and has the same mechanical strength as the cured product before recycling.

The method for decomposing and recycling cured epoxy resin materials of the present invention makes it possible to decompose and recycle cured epoxy resin materials.

FIG. 1 is a diagram illustrating a scheme for obtaining a cured epoxy resin material by mixing two equivalents of epoxy resin monomers (A1, A2) and one equivalent of curing agent (B1, B2). FIG. 2 illustrates a scheme for obtaining an epoxy resin decomposition composition by allowing glutathione (a water-soluble biomolecular compound) to act on the cured epoxy resin shown in FIG. 1 to cleave disulfide bonds (-S-S-), and a scheme for recycling the epoxy resin decomposition composition. FIG. 1 shows the results of Fourier transform near infrared spectroscopy (FT-NIR) performed on uncured and cured ERDs having the combination (C1) shown in Table 1. FIG. 1 shows the results of quantitative evaluation of the reaction mixture by 1H-NMR spectroscopy in the degradation of ERD using glutathione (GSH). FIG. 1 shows the results of quantitative evaluation of the reaction mixture by 1H-NMR spectroscopy in the degradation of ERD using glutathione (GSH). FIG. 1 shows the chemical reaction balance between the CDCl ₃ phase and the D ₂ O phase. FIG. 1 is a diagram summarizing the decomposition results of ERD in terms of the composition ratio of epoxy resin monomer (A1 or A2) and diamine curing agent (B1 or B2). FIG. 1 illustrates the structure of a cured epoxy resin material containing an epoxy resin monomer (BGPDS or DGEBA) and an amine curing agent (DTDA or DDM), and the structure of the cured epoxy resin material after decomposition. FIG. 1 shows the 1H-NMR spectrum of the CDCl ₃ phase after removal of tributylphosphine (TBP). FIG. 1 shows the FT-IR spectrum of the decomposed soluble portion of ERD-C1 in a CHCl ₃ phase. FIG. 1 shows the UV-vis spectrum of the CHCl ₃ phase measured at 254 nm over time. FIG. 10 is a diagram showing the results of a swelling test of an ERD before recycling and an ERD after recycling. FIG. 2 is a graph showing normalized stress relaxation of a cured epoxy resin material before and after recycling. FIG. 1 is a diagram showing the disassembly and recycling of a CFRP structure using the ERD matrix of Example 1.

The following describes one embodiment of the epoxy resin composition, cured epoxy resin product, decomposable epoxy resin composition, recycled cured product, and method for decomposing and recycling the cured epoxy resin product of the present invention.

In this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower and upper limits.

Furthermore, in the description of groups (atomic groups) in this specification, when a notation does not specify whether they are substituted or unsubstituted, it encompasses both unsubstituted and substituted groups, as long as the effects of the present invention are not impaired.

(Epoxy resin composition)
The epoxy resin composition of the present invention contains an epoxy resin monomer (A1) having epoxy groups at both ends and a disulfide bond (-S-S-), and a curing agent (B) capable of bonding to the epoxy groups.

The epoxy resin composition of the present invention can contain, as epoxy resin monomers, an epoxy resin monomer (A2) not having a disulfide bond (-S-S-) together with an epoxy resin monomer (A1) having a disulfide bond (-S-S-) (hereinafter, these may be simply referred to as "epoxy resin monomer (A1)" and "epoxy resin monomer (A2)").
The specific structures of the epoxy resin monomer (A1) and the epoxy resin monomer (A2) are not particularly limited, and examples thereof include glycidyl ether types (bisphenol A type, bisphenol F type, novolak type, alcohol type, etc.), glycidyl ester types (hydrophthalic acid type, dimer acid type, etc.), glycidyl amine types (aromatic amine type, aminophenol type, etc.), and oxide types (alicyclic type, etc.).

Of these, the epoxy resin monomer (A1) is preferably a compound represented by the following chemical formula (1):

In the epoxy resin monomer (A1), X in chemical formula (1) represents a disulfide bond (S—S), and R ¹ and R ² are the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain.

Specifically, examples of the epoxy resin monomer (A1) include bis(4-glycidyloxyphenyl)disulfide (BGPDS), 1,2-bis((oxiran-2-ylmethoxy)methyl)disulfane,
1,2-bis(4-(oxiran-2-ylmethoxy)cyclohexyl)disulfane is more preferred.

Furthermore, the epoxy resin monomer (A2) does not have the symbol X representing a disulfide bond (S—S) in the above chemical formula (1), and may be an aromatic carbon ring, an aromatic carbocyclic alkyl chain, an aliphatic carbon ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain at the sites of ^R1 and ^R2 , similar to the epoxy resin monomer (A1).

More specifically, the epoxy resin monomer (A2) is preferably diglycidyl ether of bisphenol A (DGEBA), ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, or hydrogenated bisphenol A diglycidyl ether.

The molar ratio (A1/A2) of the epoxy resin monomer (A1) to the epoxy resin monomer (A2) is preferably 100/0 to 25/75, more preferably 100/0 to 50/50, and even more preferably 100/0 to 75/25. When the molar ratio (A1/A2) is within this range, the resulting epoxy resin composition can be decomposed and reused as a cured epoxy resin.

Furthermore, the epoxy resin composition can use, as the curing agent (B), one or more of a curing agent (B1) having a disulfide bond (-S-S-) and a curing agent (B2) not having a disulfide bond (-S-S-) (hereinafter, these may be simply referred to as "curing agent (B1)" and "curing agent (B2)").
The curing agent (B1) and the curing agent (B2) are not particularly limited as long as they can bond to an epoxy group, and examples thereof include polyamines (including diamines), modified polyamines, acid anhydrides, hydrazine derivatives, and polyphenols.

For example, examples of polyamine-based curing agents include aliphatic polyamines, alicyclic polyamines, and aromatic polyamines. Examples of aliphatic polyamines include diethylenetriamine, triethylenetetramine, tetraethylenepentamine, m-xylenediamine, trimethylhexamethylenediamine, 2-methylpentamethylenediamine, and diethylaminopropylamine. Examples of alicyclic polyamines include isophoronediamine, 1,3-bisaminomethylcyclohexane, bis(4-aminocyclohexyl)methane, norbornenediamine, 1,2-diaminocyclohexane, and laromine. Examples of aromatic polyamines include diaminodiphenylmethane, metaphenylenediamine, and diaminodiphenylsulfone. Examples of acid anhydrides include hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, methylnadic anhydride, hydrogenated methylnadic anhydride, trialkyltetrahydrophthalic anhydride, methylcyclohexenetetracarboxylic dianhydride, trimellitic anhydride, pyromellitic anhydride-free, benzophenonetetracarboxylic dianhydride, and aliphatic dibasic acid polyanhydrides. Examples of polyphenol-based curing agents include phenol novolac, xylene novolac, bis A novolac, triphenylmethane novolac, biphenyl novolac, dicyclopentadiene phenol novolac, and terpene phenol novolac.

Of these, it is preferable that the curing agent (B1) is a compound represented by the following chemical formula:

In the curing agent (B1), ^R3 and ^R4 may be the same or different and represent an aromatic carbon ring, an aromatic carbon ring alkyl chain, an aliphatic carbon ring, an aliphatic carbon ring alkyl chain, or an aliphatic carbon chain, and ^R5 and ^R6 may be the same or different and represent a primary, secondary, or tertiary amine, imidazole, acid anhydride, or organic acid hydrazide.

Of these, diamine curing agents are more preferred, with 4,4'-dithiodianiline (DTDA), cystamine, cystine dimethyl ester, and cystine diethyl ester being particularly preferred.

The curing agent (B2) is also preferably a diamine curing agent, which may be one in which the disulfide bond (-S-S-) in the above chemical formula (2) is substituted with an aromatic group, a (poly)ether group, an alkyl group, or the like. Specifically, the curing agent (B2) is more preferably diaminodiphenylmethane (DDM), ethylenedimine, diethylenetriamine, triethylenetetramine, or norbornanediamine.

The molar ratio (B1/B2) between curing agent (B1) and curing agent (B2) is 100/0 to 0/100. In other words, the composition may contain at least one of curing agent (B1) and curing agent (B2), and the ratio between curing agent (B1) and curing agent (B2) can be appropriately set depending on the ratio between epoxy resin monomer (A1) and epoxy resin monomer (A2), etc. In particular, the molar ratio (B1/B2) is preferably 100/0 to 25/75, more preferably 100/0 to 50/50, and even more preferably 100/0 to 75/25.

In one preferred embodiment of the epoxy resin composition of the present invention, the molar ratio (A1/A2) of the epoxy resin monomer (A1) to the epoxy resin monomer (A2) is 100/0 to 25/75, and the molar ratio (B1/B2) of the curing agent (B1) to the curing agent (B2) is 100/0 to 0/100.

More specifically, when the content of curing agent (B1) in curing agent (B) exceeds 75/25 in terms of the molar ratio (B1/B2), it is preferable that the molar ratio (A1/A2) is 100/0 to 25/75, and the molar ratio (A1:B1) of epoxy resin monomer (A1) to curing agent (B1) is 2:1 to 0.5:1.

When the content of curing agent (B1) in curing agent (B) is in the molar ratio (B1/B2) of 75/25 to 50/50, it is preferable that the molar ratio (A1/A2) is 100/0 to 50/50 and the molar ratio (A1:B1) is 2:0.5 to 1:0.5.

When the content of curing agent (B1) in curing agent (B) is less than 50/50 and between 25/75 in terms of the molar ratio (B1/B2), it is preferable that the molar ratio (A1/A2) is between 100/0 and 75/25, and the molar ratio (A1:B1) is between 2:0.25 and 1.5:0.25.

When the content of curing agent (B1) in curing agent (B) is less than 25/75 in terms of the molar ratio (B1/B2), it is preferable that the molar ratio (A1/A2) is 100/0 to 75/25 and the molar ratio (A1:B1) is 2:0.01 to 1.5:0.25 or 1:0.

The epoxy resin composition of the present invention can be cured into epoxy resin cured products that can be decomposed and reused, making it possible to build an environmentally friendly recycling system.

(Epoxy resin cured product)
The cured epoxy resin material of the present invention is a cured product of the above-mentioned epoxy resin composition of the present invention. Hereinafter, the cured epoxy resin material having a disulfide bond may be referred to as "ERD."

The curing method and conditions for obtaining a cured epoxy resin product are not particularly limited, and known methods and conditions can be used as appropriate. Specifically, for example, an example method involves mixing an epoxy resin monomer and a curing agent in a predetermined ratio, and then heating the mixture at 90 to 200°C while stirring as necessary to cause curing.

The structure of the cured epoxy resin of the present invention is not specifically limited, but the proportion of disulfide bonds (-S-S-) relative to the repeating units of the epoxy resin is preferably 1 equivalent or more, and more preferably 2 equivalents or more.

It is also preferable that the composition contains a repeating unit in which two equivalents of epoxy resin monomer are bonded to one equivalent of curing agent.

Figure 1 illustrates a scheme for obtaining a cured epoxy resin by mixing two equivalents of epoxy resin monomers (A1, A2) with one equivalent of curing agent (B1, B2).

For example, as shown in Figure 1, when diglycidyl ether of bisphenol A (DGEBA) is used as A1 and 4,4'-dithiodianiline (DTDA) is used as B1, a cured epoxy resin (ERD) containing repeating units formed by bonding two equivalents of epoxy resin monomer (A1) to one equivalent of curing agent (B1) can be obtained. Furthermore, this cured epoxy resin (ERD) has a disulfide bond (-S-S-) ratio of three equivalents relative to the repeating epoxy resin units (X = S-S, Y = S-S).

The cured epoxy resin of the present invention contains a specific proportion of disulfide bonds (-S-S-) in the repeating units of the epoxy resin, making it possible to decompose and reuse it, thereby enabling the creation of an environmentally friendly recycling system.

(Epoxy resin decomposition composition, method for decomposing epoxy resin cured material, and epoxy resin decomposition composition)
The epoxy resin decomposable composition of the present invention contains the above-mentioned cured epoxy resin of the present invention and a water-soluble biomolecular compound having a thiol group (—SH).

Examples of water-soluble biomolecular compounds having a thiol group (-SH) include one or more of glutathione, thioredoxin, peroxiredoxin, and dithiothreitol (DTT). Of these, glutathione is preferred from the standpoint of the decomposability and water solubility of the epoxy resin.

The epoxy resin decomposable composition of the present invention can contain a cured epoxy resin (ERD) and a water-soluble biomolecular compound having a thiol group (-SH) in a two-phase solvent system consisting of an aqueous phase and an organic phase.

The organic solvent that makes up the organic phase may be a known material, such as aromatic hydrocarbons or their substituted derivatives, such as benzene, tert-butylbenzene, or chlorobenzene; aliphatic hydrocarbons, such as cyclohexane, n-hexane, n-pentane, or n-octane; or chlorinated aliphatic hydrocarbons, such as carbon tetrachloride, chloroform, dichloromethyl, or dichloroethane.

The epoxy resin-decomposing composition of the present invention can reliably decompose cured epoxy resin materials because the disulfide bonds (-S-S-) in the cured epoxy resin materials (ERD) are cleaved by the action of the thiol groups (-SH) of the water-soluble biomolecular compound.

The method for decomposing a cured epoxy resin material of the present invention includes the steps of contacting the cured epoxy resin material (ERD) of the present invention with a water-soluble biomolecular compound having a thiol group (-SH) in a two-phase solvent system consisting of an aqueous phase and an organic phase, and producing a hydroxythiol compound having a hydroxy group (-OH) and a thiol group (-SH) as a decomposition product in the organic phase.

As mentioned above, the organic solvent that constitutes the organic phase may be a known material.

By contacting a cured epoxy resin (ERD) with a water-soluble biomolecular compound containing a thiol group (-SH) in a two-phase solvent consisting of an aqueous phase and an organic phase, the dynamic disulfide bonds in the epoxy resin are cleaved by a thiol-disulfide exchange reaction and exchanged with the S-H bond of a water-soluble biomolecule such as glutathione. This allows the residue of the decomposed epoxy resin (epoxy resin decomposition composition) to dissolve in the organic phase. Meanwhile, the exchange product with, for example, glutathione, can be dissolved in the aqueous phase due to the presence of hydrophilic groups.

Accordingly, the epoxy resin decomposition composition of the present invention contains a hydroxy thiol compound having a hydroxy group (-OH) and a thiol group (-SH), which is a decomposition reaction product of the epoxy resin decomposition composition.

Specifically, for example, when the epoxy resin monomer of the above-mentioned chemical formula (1) and the curing agent of the chemical formula (2) are used, a compound (e.g., a monomer compound, a dimer compound, or a trimer compound) containing a unit structure represented by the following chemical formula (3) can be obtained as the epoxy resin decomposition composition.

In chemical formula (3), ^R7 and ^R8 are the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain. ^R9 represents an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain. ^Z1 represents a nitrogen atom, benzene, phenol, or the like. Y represents a thiol group (-SH) or a sulfide (-S-).

If the epoxy resin decomposition composition is a monomer compound,

In chemical formula (4), all of the three Y ^1s located at the terminals are thiol groups (—SH).

If the epoxy resin decomposition composition is a dimer compound,

In chemical formula (5), two of the three ^Y2s located at the terminals are thiol groups (-SH) and the other is a sulfide (-S-), and the sulfides (-S-) of the two unit structures represented by chemical formula (5) are bonded to each other via a disulfide bond (-S-S-).

When the epoxy resin decomposition composition is a trimer compound, one of the three unit structures that make up the trimer compound is

In chemical formula (6), one of the three ^Y3s located at the terminals is a thiol group (-SH), and the other two are sulfide groups (-S-). The other two unit structures constituting the trimer compound are each composed of three ^Y3s located at the terminals in chemical formula (6), two of which are thiol groups (-SH), and the other is a sulfide group (-S-). The trimer compound is bonded to each other via a disulfide bond (-S-S-) linking the sulfides (-S-) of these three unit structures.

Figure 2 illustrates a scheme for obtaining an epoxy resin decomposition composition by treating the cured epoxy resin shown in Figure 1 with glutathione (a water-soluble biomolecular compound) to cleave disulfide bonds (-S-S-), and a scheme for recycling the epoxy resin decomposition composition. In this embodiment, an epoxy resin decomposition composition represented by the following chemical formula (7) is obtained.

In chemical formula (7), similarly to chemical formula (3), terminal Y represents a thiol group (-SH) or a sulfide (-S-).

For example, such monomeric compounds, dimeric compounds, and trimeric compounds have excellent solubility in organic phases. Compositions containing such monomeric compounds, dimeric compounds, and trimeric compounds can be cured by heat treatment to obtain a cured product.

The epoxy resin decomposition composition of the present invention can be reused as a cured product by curing it, enabling the creation of an environmentally friendly recycling system. Furthermore, the cured product (recycled cured product) has mechanical strength roughly equivalent to that of the initial epoxy resin cured product.

(Recycling method and recycled hardened product)
The recycling method of the present invention includes the following steps.

In a two-phase solvent system consisting of an aqueous phase and an organic phase, the cured epoxy resin of the present invention is contacted with a water-soluble biomolecular compound having a thiol group (-SH), producing a hydroxythiol compound having a hydroxyl group (-OH) and a thiol group (-SH) as a decomposition product in the organic phase (Step 1).

The liquid containing the hydroxy thiol compound is heated and cured to obtain a cured product with an epoxy resin network structure containing disulfide bonds (-S-S-) (second step).

The first step is the same as the method for decomposing a cured epoxy resin material of the present invention described above, so a detailed explanation will be omitted.

The heating method and conditions in the second step are not particularly limited, and known methods and conditions can be used as appropriate. Specifically, for example, a method can be used in which the decomposed epoxy resin residue (a liquid containing a hydroxythiol compound) is poured into a desired mold and heated at approximately 90°C to 250°C for approximately 30 minutes to 10 hours.

The recycling method of the present invention produces a recycled cured product of the epoxy resin decomposition composition that contains a hydroxy thiol compound and has an epoxy resin network structure.

The recycled cured product of the present invention has an epoxy resin network structure that is common to the cured epoxy resin product before recycling, but contains unreacted thiol groups (-SH) that were not disulfonated during recycling. Specifically, for example, an absorption band derived from thiol groups (-SH) is detected around 2500 cm ^-1 by Fourier transform infrared spectroscopy (FT-NIR).

The recycled cured product of the present invention has mechanical strength roughly equivalent to that of the cured epoxy resin before recycling, making it suitable for a variety of uses.

The epoxy resin composition, cured epoxy resin composition, decomposable epoxy resin composition, recycled cured product, and method for decomposing and recycling a cured epoxy resin product of the present invention are not limited to the above embodiments.

For example, the epoxy resin composition may contain known curing accelerators as compounds other than the above-mentioned compounds. Furthermore, for example, the cured product of the epoxy resin composition or the recycled cured product may be in the form of a carbon fiber reinforced plastic (CFRP) containing carbon fiber.

The epoxy resin composition, cured epoxy resin product, decomposable epoxy resin composition, recycled cured product, and method for decomposing and recycling the cured epoxy resin product of the present invention will be described below with examples, but the present invention is not limited to the following examples.

Example 1 Synthesis of Cured Epoxy Resin (ERD) A cured epoxy resin (ERD) was prepared using bis(4-glycidyloxyphenyl) disulfide (BGPDS, A1) as an epoxy resin monomer and 4,4′-dithiodianiline (DTDA, B1) as a curing agent (diamine curing agent) ( FIG. 1 ).

Specifically, to clarify the thiol-disulfide exchange reaction, diglycidyl ether of bisphenol A (DGEBA, A2) and diaminodiphenylmethane (DDM, B2), which do not contain disulfide bonds (-S-S-), were employed as analogues of BGPDS and DTDA, respectively. The chemical reactivity of the aromatic disulfides in the epoxy resin monomer and diamine curing agent was assumed to be nearly identical. ERDs were prepared by combining epoxy resin monomer (either A1 or A2) with diamine curing agents (either B1 or B2).

Detailed combinations of epoxy resin monomer (A1 or A2) and diamine curing agent (B1 or B2) are shown in Table 1.

As a pretreatment, a mixture of epoxy resin monomer and diamine curing agent was stirred at a stoichiometric molar ratio (2:1) at 90°C for 30 minutes. The pre-cured mixture was transferred to a polytetrafluoroethylene mold and cured sequentially at 120°C, 140°C, and 160°C for 2 hours each. After cooling, ERD was obtained as a brown solid. Note that C25 in Table 1 was used as a control containing no disulfide bonds.

To monitor the curing process, Fourier transform near-infrared spectroscopy (FT-NIR) was performed. Figure 3 shows examples of uncured and cured ERDs with the combination (C1) shown in Table 1. In the nIR region from 7200-4000 cm ^-1 , bands related to epoxy resin monomers and primary amines were observed, including a combination band of the C-H stretching vibration and the second overtone of the epoxy ring stretching vibration (approximately 4530 cm ^-1 ) and a combination band of the NH stretching vibration and bending vibration (approximately 5000-5100 cm ^-1 ).

Thus, the epoxy resin monomer was reduced during the curing process, resulting in a decrease in the C-H stretching vibration band from about 4530 cm ^-1 and a decrease in the weak terminal _CH2 overtone from about 6060 cm ^-1 . The primary amine bond band at 5000 cm ^-1 also decreased, while the O-H overtone band at 7000 cm ^-1 increased. The O-H overtone band at 7000 cm ^-1 increased as a result of the oxirane ring-opening reaction.

Example 2: Degradation of ERD using glutathione (GSH) Prior to demonstrating the degradation of ERD using glutathione (GSH), degradation experiments were performed using disulfide-containing small molecules in an aqueous-organic binary system. Here, DTDA was selected as a model disulfide-containing molecule. DTDA and GSH were dissolved in deuterated chloroform (CDCl ₃ ) (250 mM) and deuterated water (D ₂ O) (250 mM), respectively. The solutions were mixed 1:1 (v/v) and stored in the dark, covered with aluminum foil, to avoid unexpected light-induced reactions.

The reaction mixture was quantitatively evaluated by 1H-NMR spectroscopy (Figures 4 and 5). 1H-NMR spectroscopy was performed at 25°C and 400 MHz using a JEOL ECS-400 spectrometer.

Figures 4(a) and (b) show the time-dependent changes in the 1H-NMR spectra of the CDCl ₃ phase and the D ₂ O phase, respectively. In the CDCl ₃ phase, 1H-NMR signals of the aromatic rings of DTDA (a) and (b) appeared at 6.55 ppm and 7.22 ppm, respectively. The 1H-NMR signal at 7.12 ppm was identified as the aromatic ring (b') of 4-aminobenzenethiol (4-ABT), which is presumed to be the reducing agent for DTDA (Figure 4(a)). Furthermore, no peaks were observed in the range of 2 to 3 ppm, suggesting that neither GSH nor its reaction products were present in the CDCl ₃ phase.

On the other hand, in the D ₂ O phase, a new 1 H-NMR signal (e') appeared at 3.12 ppm, suggesting the formation of an S—S bond between GSH and 4-ABT (FIG. 4(b)).

Furthermore, 1H-NMR peaks (c) and (d) appeared at 7.15 ppm and 7.5 ppm, respectively, and increased in intensity at the same time as peak (e'), suggesting that the water-soluble reaction product GSH-ABT was produced by an exchange reaction between DTDA and GSH. Furthermore, there was no significant change in peak intensity between 7.25 ppm and 7.5 ppm, suggesting that a small amount of DTDA was dissolved in the aqueous phase. Compared to diphenyl disulfide shown in Figure 5, the solubility of DTDA in water was improved, confirming that the exchange reaction between the thiol bond of GSH and the disulfide bond of DTDA was promoted.

Next, we further evaluated the time evolution of the composition in CDCl ₃ /D ₂ O. Figure 4(c) shows the rate of change of DTDA and 4-aminobenzenethiol calculated from the peak areas of 1H-NMR signals (b) and (b') in CDCl ₃ , respectively.

As a result, DTDA decreased immediately over time, reaching equilibrium at 60 minutes. Correspondingly, 4-ABT began to be produced immediately after stirring, reaching equilibrium at 60 minutes, in contrast to DTDA.

Similarly, Fig. 4(d) shows the time evolution of the decrease in GSH and the increase in the water-soluble reactants of GSH and 4-ABT in the D ₂ O phase. Similar to the CDCl ₃ phase, the increase in GSH and the decrease in the water-soluble reactants of GSH/4-ABT tended to change symmetrically and reached equilibrium at approximately 60 min.

Furthermore, the molar ratios of increasing and decreasing compositions were kept at 30 mol % for both the CDCl ₃ phase and the D ₂ O phase.

From these results, the chemical reaction balance between the CDCl ₃ phase and the D ₂ O phase is shown in Figure 6. A thiol-disulfide exchange reaction between DTDA and GSH occurred at the interface between CDCl ₃ and D ₂ O, producing a water-soluble reaction product of GSH and 4-ABT (GSH-ABT), while unreacted 4-ABT remained dissolved in CDCl ₃ .

Since it was confirmed that the thiol-disulfide exchange reaction proceeds in a binary system of CHCl ₃ /water via GSH, a degradation test of ERD was carried out under the same binary system conditions.

First, ERD was pulverized by ball milling at a frequency of 25 Hz for 1 hour. The resulting ERD powder was suspended in CHCl ₃ , and a 20 mM aqueous GSH solution was added. Here, tributylphosphine (TBP) (10 mol%) was used to promote the thiol-disulfide exchange reaction. The 1H-NMR spectrum of the small molecule model with TBP added, shown in Figure 5, indicated that the product generated by the thiol-disulfide exchange reaction was the same as that without TBP added.

The binary solution was then vigorously stirred at room temperature. After a certain period of time, the solution was separated into two parts: one in which ERD had completely dissolved in the CHCl ₃ phase, forming a yellow solution, and the other in which a precipitate had formed.

Figure 7 summarizes the decomposition results of ERD by composition ratio of epoxy resin monomer (A1 or A2) and diamine curing agent (B1 or B2). Figure 7 also summarizes the molar equivalents of disulfide bonds in each repeating unit of ERD for various combinations of BGPDS/DGEBA (A1/A2) and DTDA/DDM (B1/B2).

As shown in Figure 7, it was confirmed that the ERD was completely dissolved in C1-C13 and C16. Furthermore, the amine curing agent (DTDA or DDM) can react with two equivalents of the epoxy resin monomer (BGPDS or DGEBA), suggesting that disulfide bonds can be introduced up to three equivalents of the ERD repeat unit, as shown in the structural formula in Figure 8. After removing the CHCl ₃ solvent under vacuum from the completely dissolved portion, a viscous yellow liquid was obtained.

To identify the chemical structure of these residues, 1H-NMR and FT-nIR spectroscopy of ERD-C1 were performed, respectively.

FIG. 9 shows the 1H-NMR spectrum of the CDCl ₃ phase after removal of tributylphosphine (TBP), indicating pure resolved ERD-C1.

In this spectrum, a signal from the aromatic ring of decomposed ERD was detected in the range of 6.5 to 7.5 ppm. Furthermore, a peak from 3.0 to 4.0 ppm was associated with alkyl protons generated by the ring-opening reaction of the epoxy group. Furthermore, no peak was detected in the range of 2.0 to 3.0 ppm, proving the absence of GSH and exchange products in the CDCl ₃ phase. Furthermore, no signal was observed in the range of 1.0 to 1.5 ppm, indicating that tributylphosphine had been completely removed. This demonstrates that although ERD was decomposed into soluble oligomers, the epoxy structure was maintained, as shown in Figure 2.

Furthermore, Figure 10 shows the FT-IR spectrum of the soluble portion of ERD-C1 decomposed in the CHCl ₃ phase. As shown in Figure 10(a), the spectrum of this residue was almost identical to that of ERD in the NIR region from 4000 cm-1 to 7500 cm ^-1 . This indicates that this liquid residue retains the epoxy structure of ERD. Meanwhile, a new absorption band derived from thiol appeared at 2550 cm ^-1 (Figure 10(b)). This indicates that this fragment contains a thiol group due to the reduction of the disulfide group of ERD by GSH.

The solubility of ERD can be discussed in terms of the stoichiometric ratio of disulfide groups to ERD repeat units (Figure 7). When the disulfide groups were 1.5 equivalents or more relative to the ERD repeat units, ERD was completely dissolved in CHCl ₃ , and ERD was decomposed into dimers or monomers. On the other hand, when the stoichiometric ratio of disulfide groups was less than 1.5 equivalents, most of the repeat units were trimers or higher, resulting in the formation of precipitates.

Furthermore, to investigate the decomposition tendency of ERD, the UV-vis spectrum of the CHCl ₃ phase was measured at 254 nm over time (Figure 11).

When a suspension of ERD-C1 in CHCl ₃ was mixed with a GSH/water solution, the UV absorption at 245 nm immediately increased and followed a saturation curve. After 4 h, it reached a plateau region with a constant value, suggesting that ERD-C1 was completely dissolved in the CHCl ₃ phase. The resolution of ERD was clearly correlated with the number of disulfide bonds in the epoxy resin.

<Example 3> Rework test Generally, amine-cured epoxy resins are considered to have a network structure with amine bonds as crosslinking points, but ERD can also be considered to be a dynamic covalent network polymer with disulfide bonds as repeating units. Therefore, even if ERD is decomposed and regenerated by forming disulfide bonds, it was thought that the structure and physical properties of the original amine-cured epoxy resin ERD would not change.

The decomposed epoxy resin residue (epoxy resin decomposition composition) was poured into a polytetrafluoroethylene mold and heated at 180°C for 6 hours. As a result, the liquid residue became a dark brown solid. FT-NIR measurement revealed that the recycled ERD had hardened through the formation of disulfide bonds. This indicates that the decomposed yellow liquid contained thiol groups. After hardening (after recycling), the peak at 2550 cm ^-1 corresponding to thiol groups almost disappeared (Figure 10b). However, FT-NIR measurement of the recycled ERD confirmed the presence of traces of thiol groups.

Furthermore, dynamic mechanical analysis (DMA) was performed to evaluate the thermal and mechanical properties of the disulfide-containing epoxy resin before and after recycling. The results are shown in Table 2.

In terms of mechanical properties, the storage modulus of the original ERD before recycling was 1.8 GPa, which was confirmed to be equivalent to that of conventional epoxy resins (1.88 GPa) without disulfide bonds. It was confirmed that the storage modulus of the recycled ERD maintained approximately 90% of its initial value at room temperature.

The glass transition temperature (Tg) decreased from 131°C to 82°C due to partial incomplete reconnection of the network.

In addition, to evaluate the crosslink density before and after recycling, a swelling test was conducted on the ERD before and after recycling. The results are shown in Figure 12.

As shown in Figure 12, the swelling ratio after immersion in toluene at room temperature for 72 hours was approximately 3% for the initial cured material, while it was 13-16% for the recycled cured material. This result indicates that the crosslink density of the recycled ERD does not completely return to its original structure, causing a decrease in the glass transition temperature and mechanical strength at room temperature (from 1.8 GPa to 1.6 GPa), while also causing an increase in the rubber-like storage modulus (from 14.3 MPa to 49.9 MPa).

Figure 13 shows the normalized stress relaxation curves for cured epoxy resin before and after recycling at 130°C. Based on the Maxwell model, stress relaxation time was defined as the time required to release 63% of the initial stress. The stress relaxation time for the cured recycled epoxy resin at 130°C was 152 seconds, confirming that the time required for the cured recycled epoxy resin to release 63% of the initial stress was shorter. This confirmed that the regenerated network of the cured recycled epoxy resin exhibited stress relaxation above the Tg, a typical dynamic network resulting from the reformation of dynamic disulfide bonds. Furthermore, because the cured recycled epoxy resin had a relatively low Tg, segmental chain motion occurred at low temperatures, accelerating the exchange reaction and resulting in stress relaxation.

<Example 4> Recycling of CFRP Carbon fiber reinforced plastic (CFRP) is a structural material that has attracted attention in fields such as aircraft and automobiles, where lightweight construction and creep resistance are required. Generally, thermosetting resins such as epoxy are used as the matrix resin in CFRP structures, making reworking and recycling difficult, and waste disposal issues have become apparent.

Therefore, we investigated a recycling system for CFRP structures using the ERD matrix of Example 1.

The carbon fiber reinforced plastic (CFRP) structure was fabricated using the following procedure.

First, carbon fiber cloth was placed on an aluminum plate covered with polytetrafluoroethylene tape. An epoxy resin monomer (BGPDS) and a diamine curing agent (DTDA) were mixed in a glass vial at a molecular ratio of 2:1 and mixed at 90°C for 30 minutes. After mixing, the mixture was poured onto the aluminum plate covered with the fiber cloth and surrounded by another aluminum plate covered with polytetrafluoroethylene tape. The resulting sample and mold were cured in an oven at 120°C for 2 hours, 140°C for 2 hours, and 160°C for 2 hours, and finally cooled to room temperature in the oven.

The cured CFRP structure was then fixed with clips in two liquid phases: an aqueous phase and an organic phase ( _CHCl3 phase) (Figs. 14(a) and 14(b)). After 24 hours of vigorous stirring under atmospheric pressure, the ERD, which constituted the CFRP structure's matrix, was decomposed into the _CHCl3 phase (Fig. 14(c)). After dissolving the matrix, the carbon fibers were completely recovered by washing with water and acetone and drying at 100°C (Fig. 14(d)). Meanwhile, the decomposed epoxy residue (epoxy resin decomposition composition) dissolved in the chloroform solution was obtained by evaporating the solvent (Fig. 14(e)). This epoxy residue easily transitioned into the epoxy resin network by forming disulfide bonds (Fig. 14(f)).

As described above, we have proposed a reworking and recycling system for epoxy resins containing disulfide bonds. First, by introducing dynamic disulfide bonds, we obtained recyclable and reworkable cured epoxy resins containing disulfide bonds. Next, by using a thiol-disulfide exchange reaction to cleave the dynamic disulfide bonds in the epoxy resin and exchange them with S-H bonds of water-soluble biomolecules such as glutathione, the decomposed epoxy resin (decomposition composition) residue can be dissolved in chloroform. The exchange product was confirmed to distribute in the aqueous phase due to the presence of hydrophilic peptide groups in glutathione. Finally, the epoxy residues containing S-H bonds were heated to obtain recycled cured epoxy resins with a disulfide-containing epoxy resin network structure. The recycled cured epoxy resins obtained in this way retain approximately 90% of the mechanical strength of the original epoxy resin, making them potentially applicable to a variety of applications. Furthermore, this method has the potential to be applied to carbon fiber-reinforced composites, potentially expanding the scope of reuse for both embedded materials and matrix resins.

Claims (8)

a cured epoxy resin material which is a cured product of an epoxy resin composition containing an epoxy resin monomer (A1) having epoxy groups at both ends and a disulfide bond (-S-S-) and a diamine curing agent (B);
a water-soluble biomolecular compound having a thiol group (-SH); and a recycled cured product of an epoxy resin decomposition composition containing a hydroxy thiol compound having a hydroxy group (-OH) and a thiol group (-SH), the hydroxy thiol compound being a decomposition reaction product of an epoxy resin decomposition composition containing a water-soluble biomolecular compound having a thiol group (-SH),
the water-soluble biomolecular compound is at least one selected from the group consisting of glutathione, thioredoxin, peroxiredoxin, and dithiothreitol (DTT);
A recycled cured product comprising the hydroxy thiol compound and having an epoxy resin network structure. The recycled cured material of claim 1, characterized in that unreacted thiol groups (-SH) that have not been disulfonated are detected by FT-NIR. 2. The recycled cured product according to claim 1, wherein the diamine curing agent (B) is at least one selected from the group consisting of 4,4'-dithiodianiline (DTDA), cystamine, cystine dimethyl ester, and cystine diethyl ester. In a two-phase solvent system consisting of an aqueous phase and an organic phase, a cured epoxy resin material, which is a cured product of an epoxy resin composition comprising an epoxy resin monomer (A1) having epoxy groups at both ends and a disulfide bond (-S-S-) and a diamine curing agent (B), is brought into contact with a water-soluble biomolecular compound having a thiol group (-SH), to produce a hydroxythiol compound having a hydroxy group (-OH) and a thiol group (-SH) as a decomposition product in the organic phase;
Including,
A method for decomposing a cured epoxy resin material, wherein the water-soluble biomolecular compound is at least one selected from the group consisting of glutathione, thioredoxin, peroxiredoxin, and dithiothreitol (DTT) . 5. The method for decomposing a cured epoxy resin material according to claim 4, wherein the diamine curing agent (B) is at least one selected from the group consisting of 4,4'-dithiodianiline (DTDA), cystamine, cystine dimethyl ester, and cystine diethyl ester. The following steps:
The method comprises: bringing a cured epoxy resin material, which is a cured product of an epoxy resin composition comprising an epoxy resin monomer (A1) having epoxy groups at both ends and a disulfide bond (-S-S-) and a diamine curing agent (B), into contact with a water-soluble biomolecular compound having a thiol group (-SH) in a two-phase solvent system consisting of an aqueous phase and an organic phase, to produce a hydroxy thiol compound having a hydroxy group (-OH) and a thiol group (-SH) as a decomposition product in the organic phase; and heating the liquid containing the hydroxy thiol compound to cure it, thereby obtaining a cured product having an epoxy resin network structure containing a disulfide bond (-S-S-) ,
A method for recycling a cured epoxy resin material, wherein the water-soluble biomolecular compound is at least one selected from the group consisting of glutathione, thioredoxin, peroxiredoxin, and dithiothreitol (DTT) . 7. The method for recycling a cured epoxy resin material according to claim 6, wherein the diamine curing agent (B) is at least one selected from the group consisting of 4,4'-dithiodianiline (DTDA), cystamine, cystine dimethyl ester, and cystine diethyl ester. A monomer compound having a unit structure represented by the following formula:
(R ⁷ and R ⁸ are the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^R9 represents an aromatic carbocycle, an aromatic carbocyclic alkyl chain, an aliphatic carbocycle, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^Z1 represents a nitrogen atom;
^Y1 represents a thiol group (-SH).
and,
The unit structure represented by the following formula:
(R ⁷ and R ⁸ are the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^R9 represents an aromatic carbocycle, an aromatic carbocyclic alkyl chain, an aliphatic carbocycle, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^Z1 represents a nitrogen atom;
Of the three ^Y2s located at the terminals, two are thiol groups (-SH) and the other is a sulfide (-S-).
Contains two
a dimeric compound in which two of the unit structures are bonded to each other via a disulfide bond (—S—S—) in which the sulfides (—S—) are linked;
A unit structure represented by the following formula:
(R ⁷ and R ⁸ are the same or different and represent an aromatic carbocyclic ring, an aromatic carbocyclic alkyl chain, an aliphatic carbocyclic ring, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^R9 represents an aromatic carbocycle, an aromatic carbocyclic alkyl chain, an aliphatic carbocycle, an aliphatic carbocyclic alkyl chain, or an aliphatic carbon chain;
^Z1 represents a nitrogen atom.
Includes three
One of the three unit structures has three terminal ^Y3s , one of which is a thiol group (-SH) and the other two are sulfides (-S-),
The other two of the three unit structures have three terminal ^Y3s , two of which are thiol groups (-SH) and the other is a sulfide (-S-),
a trimeric compound in which the sulfides (—S—) of three of the unit structures are bonded to each other via a disulfide bond (—S—S—);
A water-soluble biomolecular compound having a thiol group (-SH), which is at least one selected from the group consisting of glutathione, thioredoxin, peroxiredoxin, and dithiothreitol (DTT).
and,
A cured product characterized by being a cured product of a composition comprising: