JP7537028B2 - Epoxy resin, its hardened product, and method for producing epoxy resin - Google Patents

Description

The present invention relates to an epoxy resin having a truxillic acid ester structure and its cured product.

Because petroleum is a limited resource and causes global environmental problems such as carbon dioxide emissions, there has been a demand in recent years for the use of alternative resources. The use of biomass has attracted attention as an alternative resource to petroleum. Resins made from biomass, such as polylactic acid and polyhydroxybutyric acid, have been commercialized, and production is increasing due to expanding demand, particularly in the EU.

Edible biomass is mainly used as biomass from the viewpoint of ease of handling, but since edible biomass competes with the use of food, there is a growing demand to use non-edible biomass, and various researches are being conducted. For example, Non-Patent Document 1 discloses that a bifunctional epoxy resin obtained using ferulic acid, which can be obtained by depolymerization of lignin, shows a higher glass transition temperature and superior tensile strength than conventional bisphenol A type epoxy resins, and further shows that the performance is improved by compounding with glycidyl ether of furfuryl alcohol.

In recent years, the production of valuable materials using microorganisms has also been studied. For example, it is known that compounds having a hydroxycinnamic acid structure, such as p-coumaric acid, can be synthesized from biomass-derived compounds, such as L-tyrosine, using microorganisms. Generally, microbial reactions are highly efficient and can be carried out in a mild environment.

Compounds that can be synthesized by microorganisms are also being considered for use in resin production. For example, Patent Document 1 discloses that an epoxy resin is synthesized by reacting p-hydroxycinnamic acid with epichlorohydrin, and the resulting epoxy resin is cured together with glycidyl furfuryl ether using a curing agent, resulting in a high glass transition temperature and excellent mechanical strength.

China Publication No. 112409298

Jiale Ye et al. “High-performance bio-based epoxies from ferulic acid and furfuryl alcohol: synthesis and properties”, Green Chem., 2021,23, 1772-1781

However, because non-edible biomass-derived components such as lignin are poorly degradable, it is difficult to efficiently obtain the raw material compounds, and the process for synthesizing epoxy resins tends to be complicated. In addition, compounds obtained from biomass generally have inferior performance compared to polymers derived from petrochemicals.

Therefore, the objective of the present invention is to provide an epoxy resin that is a compound that can be obtained from biomass, yet is easy to produce and has good thermal performance.

なお、式（１）において、Ｒ^４及びＲ^５はそれぞれ独立に、水素原子、アルコキシ基、及び－ＯＧのいずれかである。＊は他の構造との結合部位となってもよい。Ｇはグリシジル基を表す。
［２］以下の式（１－１）で表される構造を有する上記［１］に記載のエポキシ樹脂。

なお、式（１－１）において、Ｒ^１及びＲ^３は、それぞれ独立にヘテロ原子を有してもよい炭素数１～２０の１価の炭化水素基、若しくはグリシジル基であり、Ｒ^２はヘテロ原子を有してもよい炭素数２～２０の２価の炭化水素基である。各ベンゼン環においてそれぞれ独立に、Ｒ^４及びＲ^５のうち一方が水素原子であり、他方が水素原子、－ＯＣＨ_３、及び－ＯＧのいずれかである。ｎは０～１００の整数である。
［３］以下の式（１－２）で表される構造を有する上記［１］に記載のエポキシ樹脂。

なお、式（１－２）において、Ｒ^１及びＲ^３は、それぞれ独立にヘテロ原子を有してもよい炭素数１～２０の１価の炭化水素基、若しくはグリシジル基であり、Ｒ^２はヘテロ原子を有してもよい炭素数２～２０の２価の炭化水素基である。ｎは０～１００の整数である。
［４］Ｒ^１及びＲ^３がグリシジル基であり、ｎが０である上記［２］又は［３］に記載のエポキシ樹脂。
［５］Ｒ^１及びＲ^３が炭素数１～６のアルキル基であり、ｎが０である上記［２］又は［３］に記載のエポキシ樹脂。
［６］Ｒ^１及びＲ^３がメチル基である上記［２］又は［３］に記載のエポキシ樹脂。
［７］以下の式（１－３）で表される構造を有する上記［１］に記載のエポキシ樹脂。

式（１－３）の各ベンゼン環において、それぞれ独立にＲ^４及びＲ^５のうち一方が水素原子であり、他方が水素原子、－ＯＣＨ_３、及び－ＯＧのいずれかである。また、Ｒ^６が水素原子、－ＣＯＯＧ、及び－ＣＯＯＲ^１のいずれかであり、Ｒ^７が水素原子、－ＣＯＯＧ、及び－ＣＯＯＲ^３のいずれかである。Ｒ^１及びＲ^３はアルキル基である。
［８］式（１）で表される骨格が、バイオマス由来である、上記［１］～［７］のいずれか１項に記載のエポキシ樹脂。
［９］上記［１］～［８］のいずれか１項に記載のエポキシ樹脂を硬化させて得られた硬化体。
［１０］以下の式（２）に示す骨格を有する化合物と、エピハロヒドリンを反応させてエポキシ樹脂を得る、エポキシ樹脂の製造方法。

なお、式（２）において、Ｒ^１４及びＲ^１５はそれぞれ独立に、水素原子、アルコキシ基、及び－ＯＨのいずれかである。＊は他の構造との結合部位となってもよい。
［１１］以下の式（２－１）に示す化合物と、エピハロヒドリンを反応させてエポキシ樹脂を得る、上記［１０］に記載のエポキシ樹脂の製造方法。

上記式（２－１）において、Ｒ^１１、Ｒ^１３は、それぞれ独立に水素原子、又はヘテロ原子を有してもよい炭素数１～２０の１価の炭化水素基である。Ｒ^１２は、ヘテロ原子を有してもよい炭素数２～２０の２価の炭化水素基である。各ベンゼン環において、それぞれ独立にＲ^１４及びＲ^１５のうち一方が水素原子であり、他方が水素原子、－ＯＣＨ_３、及び－ＯＨのいずれかである。ｍは０～１００の整数である。
［１２］以下の式（２－２）に示す化合物と、エピハロヒドリンを反応させてエポキシ樹脂を得る、上記［１０］に記載のエポキシ樹脂の製造方法。

上記式（２－２）において、Ｒ^１１、Ｒ^１３は、それぞれ独立に水素原子、又はヘテロ原子を有してもよい炭素数１～２０の１価の炭化水素基である。Ｒ^１２は、ヘテロ原子を有してもよい炭素数２～２０の２価の炭化水素基である。ｍは０～１００の整数である。
［１３］以下の式（２－３）に示す化合物と、エピハロヒドリンを反応させてエポキシ樹脂を得る、上記［１０］に記載のエポキシ樹脂の製造方法。

式（２－３）の各ベンゼン環において、それぞれ独立にＲ^１４及びＲ^１５のうち一方が水素原子であり、他方が水素原子、－ＯＣＨ_３、及び－ＯＨのいずれかである。Ｒ^１６が水素原子又は－ＣＯＯＲ^１１であり、かつＲ^１７が水素原子又は－ＣＯＯＲ^１３である。Ｒ^１１、Ｒ^１３は、それぞれ独立に水素原子、又はアルキル基である。 The present inventors have found that the above problems can be solved by an epoxy resin obtained from dihydroxytruxillic acid, which is a dimer of paracoumaric acid that can be easily produced by a microorganism, and have completed the present invention. The present invention provides the following [1] to [13].
[1] An epoxy resin having a skeleton represented by the following formula (1):

In the formula (1), ^R4 and ^R5 are each independently any one of a hydrogen atom, an alkoxy group, and -OG. * may be a bonding site with other structures. G represents a glycidyl group.
[2] The epoxy resin according to the above [1], having a structure represented by the following formula (1-1):

In formula (1-1), ^R1 and ^R3 are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom, or a glycidyl group, and ^R2 is a divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom. In each benzene ring, one of ^R4 and ^R5 is independently a hydrogen atom, and the other is either a hydrogen atom, _-OCH3 , or -OG. n is an integer from 0 to 100.
[3] The epoxy resin according to the above [1], having a structure represented by the following formula (1-2):

In formula (1-2), ^R1 and ^R3 are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom or a glycidyl group, ^R2 is a divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom, and n is an integer from 0 to 100.
[4] The epoxy resin according to the above [2] or [3], wherein R ¹ and R ³ are glycidyl groups and n is 0.
[5] The epoxy resin according to the above [2] or [3], wherein R ¹ and R ³ are alkyl groups having 1 to 6 carbon atoms, and n is 0.
[6] The epoxy resin according to the above [2] or [3], wherein R ¹ and R ³ are methyl groups.
[7] The epoxy resin according to the above [1], having a structure represented by the following formula (1-3):

In each benzene ring of formula (1-3), one of ^R4 and ^R5 is independently a hydrogen atom, and the other is any one of a hydrogen atom, _-OCH3 , and -OG. ^R6 is any one of a hydrogen atom, -COOG, and ^-COOR1 , and ^R7 is any one of a hydrogen atom, -COOG, and ^-COOR3 . ^R1 and ^R3 are alkyl groups.
[8] The epoxy resin according to any one of the above [1] to [7], wherein the skeleton represented by formula (1) is derived from biomass.
[9] A cured product obtained by curing the epoxy resin according to any one of [1] to [8] above.
[10] A method for producing an epoxy resin, comprising reacting a compound having a skeleton represented by the following formula (2) with epihalohydrin to obtain an epoxy resin:

In formula (2), R ¹⁴ and R ¹⁵ are each independently any one of a hydrogen atom, an alkoxy group, and -OH. * may be a bonding site with other structures.
[11] The method for producing an epoxy resin according to the above [10], comprising reacting a compound represented by the following formula (2-1) with epihalohydrin to obtain an epoxy resin.

In the above formula (2-1), R ¹¹ and R ¹³ are each independently a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom. R ¹² is a divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom. In each benzene ring, one of R ¹⁴ and R ¹⁵ is independently a hydrogen atom, and the other is either a hydrogen atom, -OCH ₃ , or -OH. m is an integer of 0 to 100.
[12] The method for producing an epoxy resin according to the above [10], comprising reacting a compound represented by the following formula (2-2) with epihalohydrin to obtain an epoxy resin.

In the above formula (2-2), R ¹¹ and R ¹³ are each independently a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom. R ¹² is a divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom. m is an integer of 0 to 100.
[13] The method for producing an epoxy resin according to the above [10], comprising reacting a compound represented by the following formula (2-3) with epihalohydrin to obtain an epoxy resin.

In each benzene ring of formula (2-3), one of R ¹⁴ and R ¹⁵ is independently a hydrogen atom, and the other is either a hydrogen atom, -OCH ₃ , or -OH. R ¹⁶ is a hydrogen atom or -COOR ¹¹ , and R ¹⁷ is a hydrogen atom or -COOR ^13. R ¹¹ and R ¹³ are independently a hydrogen atom or an alkyl group.

The present invention provides an epoxy resin that is a compound that can be obtained from biomass, yet is easy to produce and has good thermal performance.

1 shows the ¹ H-NMR spectrum of dimethyl 4,4′-dihydroxytruxillate synthesized in Example 1. 1 shows the ¹ H-NMR spectrum of the epoxy resin synthesized in Example 1.

<Epoxy resin>
The present invention will be described in further detail below with reference to embodiments.
The epoxy resin of the present invention has a skeleton represented by the following formula (1). Although the epoxy resin having the skeleton of the following formula (1) is a compound that can be obtained from biomass, it can be easily produced and has good thermal performance.

式（１）において、Ｒ^４及びＲ^５はそれぞれ独立に、水素原子、アルコキシ基、及び－ＯＧのいずれかである。＊は他の構造との結合部位となってもよい。Ｇはグリシジル基を表す。

In formula (1), ^R4 and ^R5 each independently represent a hydrogen atom, an alkoxy group, or -OG. * may be a bonding site with other structures. G represents a glycidyl group.

In the above formula (1), the alkoxy group of ^R4 and ^R5 may be, for example, an alkoxy group having 1 to 4 carbon atoms, such as a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, a sec-butoxy group, or a tert-butoxy group, and among these, a methoxy group ( _-OCH3 ) is preferred.
In formula (1), R ⁴ and R ⁵ in each benzene ring may be the same or different, but it is preferable that, independently in each benzene ring, one of R ⁴ and R ⁵ is a hydrogen atom and the other is a hydrogen atom, an alkoxy group, or -OG. It is preferable that the other of R ⁴ and R ⁵ in one molecule is the same group.
When either one of ^R4 and ^R5 is a hydrogen atom, the compound can be easily produced from coumaric acid or a compound obtained by a reaction of coumaric acid using an enzyme, as described below.

When * serves as a bonding site, it may be bonded to another skeleton represented by formula (1) via a linking group (for example, -COO-R ² -COO- described below) or to another functional group (for example, functional groups represented by -COOR ¹ and -COOR ³ described below). When * does not serve as a bonding site, it may serve as a site bonded to two hydrogen atoms.

式（１－１）において、Ｒ^１及びＲ^３は、それぞれ独立にヘテロ原子を有してもよい炭素数１～２０の１価の炭化水素基、若しくはグリシジル基であり、Ｒ^２はヘテロ原子を有してもよい炭素数２～２０の２価の炭化水素基である。ｎは０～１００の整数である。Ｇはグリシジル基を表す。
また、Ｒ^４及びＲ^５は、上記と同一である。したがって、各ベンゼン環においてそれぞれ独立に、Ｒ^４及びＲ^５のうち一方が水素原子であり、他方が水素原子、－ＯＣＨ_３、及び－ＯＧのいずれかであることが好ましい。なお、一分子中においてＲ^４及びＲ^５のうちの他方は、全て同じ基であることが好ましい。 The epoxy resin of the present invention is preferably a compound having a structure represented by the following formula (1-1).

In formula (1-1), ^R1 and ^R3 each independently represent a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom, or a glycidyl group, and ^R2 represents a divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom. n represents an integer of 0 to 100. G represents a glycidyl group.
Furthermore, R ⁴ and R ⁵ are the same as above. Therefore, it is preferable that, independently in each benzene ring, one of R ⁴ and R ⁵ is a hydrogen atom and the other is any of a hydrogen atom, -OCH ₃ , and -OG. It is preferable that the other of R ⁴ and R ⁵ in one molecule are all the same group.

In addition, in the formulas (1) and (1-1), from the viewpoint of ease of synthesis from biomass, it is preferable that both R ⁴ and R ⁵ are hydrogen atoms. Therefore, the epoxy resin of the present invention preferably has a structure represented by the following formula (1-2).

なお、式（１－２）において、Ｒ^１及びＲ^３は、それぞれ独立にヘテロ原子を有してもよい炭素数１～２０の１価の炭化水素基、若しくはグリシジル基であり、Ｒ^２はヘテロ原子を有してもよい炭素数２～２０の２価の炭化水素基である。ｎは０～１００の整数である。Ｇはグリシジル基を表す。

In formula (1-2), ^R1 and ^R3 are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom, or a glycidyl group, and ^R2 is a divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom. n is an integer of 0 to 100. G represents a glycidyl group.

In the above formulas (1-1) and (1-2), the monovalent hydrocarbon group having 1 to 20 carbon atoms in R ¹ and R ³ may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group having an aromatic ring. These may or may not have a heteroatom. Examples of the heteroatom include a nitrogen atom, a sulfur atom, an oxygen atom, a halogen atom, and a phosphorus atom. Examples of the heteroatom are not particularly limited, but include an oxygen atom constituting an ether bond, an ester bond, a keto group, an alkoxy group, etc., a sulfur atom constituting a sulfonyl group, a thiol bond, etc., and a halogen atom substituted for a hydrogen atom of a hydrocarbon group.
The monovalent hydrocarbon group preferably has 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 3 carbon atoms.

The aliphatic hydrocarbon group in R ¹ and R ³ may be either a saturated or unsaturated hydrocarbon group, and examples thereof include an alkyl group and an alkenyl group. The monovalent hydrocarbon group in R ¹ and R ³ is preferably an alkyl group, since it is easy to manufacture and the thermal stability is easily improved. The alkyl group may be linear, have a branched structure, or have a cyclic structure. Specific examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, various pentyl groups, various hexyl groups, various heptyl groups, and various octyl groups. In addition, "various" means various isomers including sec-, tert-, iso-, and the like in addition to linear (n-), and the same applies below. The alkyl group may also have a cyclic structure, such as a cyclohexyl group.
The alkyl groups in ^R1 and ^R3 each independently preferably have 1 to 10 carbon atoms, more preferably have 1 to 6 carbon atoms, and even more preferably have 1 to 3 carbon atoms, and most preferably both are a methyl group.

In each of formulas (1-1) and (1-2), n is 0 to 100 as described above, but is preferably 0 to 50, more preferably 0 to 10, even more preferably 0 to 5, and particularly preferably 0. By making the number of n small, it is possible to prevent the epoxy resin from becoming too high in molecular weight, suppressing variation in quality and improving handleability.

The divalent hydrocarbon group having 2 to 20 carbon atoms in ^R2 may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group having an aromatic ring. These may or may not have a heteroatom. Details of the heteroatom are as described for ^R1 and ^R3 .
The aliphatic hydrocarbon group in ^R2 may be either a saturated or unsaturated hydrocarbon group, but is preferably a saturated hydrocarbon group. The saturated hydrocarbon group in ^R2 may be linear, may have a branched structure, or may have a cyclic structure. As described above, the saturated hydrocarbon group may or may not have a heteroatom, but it is preferable that it does not have one. The number of carbon atoms in the divalent hydrocarbon group in ^R2 is preferably 2 to 10, more preferably 2 to 6, and even more preferably 2 to 4.

In addition, the aliphatic hydrocarbon group in ^R2 which may have a heteroatom is preferably a hydroxypropylene group in addition to the above. A hydroxypropylene group is a functional group obtained by removing two hydrogen atoms bonded to a carbon atom from hydroxypropane, and is also called a hydroxypropanediyl group. A hydroxypropylene group is a structural unit derived from epihalohydrin, which will be described later.
The hydroxypropylene group is typically a 2-hydroxypropane-1,3-diyl group (-CH ₂ CHOHCH ₂ -), although the positions of the hydrogen atoms to be removed and the hydroxyl groups are arbitrary. Since R ² is a 2-hydroxypropane-1,3-diyl group, the compounds represented by formulas (1-1) and (1-2) can be easily synthesized from an epihalohydrin described below and a compound represented by formula (2) (particularly the compounds represented by formulas (2-4) to (2-6)).
When there are multiple ^R2 in one molecule, the multiple ^R2 in one molecule may be the same or different. Among the above, ^R2 is preferably a hydroxypropylene group.

In the present invention, in the structures shown by formulae (1-1) and (1-2), it is preferable that both R ¹ and R ³ are glycidyl groups. An epoxy resin in which both R ¹ and R ³ are glycidyl groups is more likely to produce an epoxy cured product with high crosslink density. Even when both R ¹ and R ³ are glycidyl groups, R ² and n are as described above in the epoxy resins having the structures shown by formulae (1-1) and (1-2), respectively. Therefore, it is particularly preferable that n is 0 in the epoxy resin in which both R ¹ and R ³ are glycidyl groups.

In the present invention, the compounds represented by formulae (1-1) and (1-2) each preferably have an embodiment in which R ¹ and R ³ are both monovalent hydrocarbon groups which may have a heteroatom. In the epoxy resins having the structures represented by formulae (1-1) and (1-2) according to this embodiment, R ² and n are as described above, and the preferred embodiments of the monovalent hydrocarbon groups which may have a heteroatom in R ¹ and R ³ are also as described above. Therefore, in this embodiment, it is preferable that both R ¹ and R ³ are alkyl groups, and the number of carbon atoms in the alkyl group is preferably 1 to 10, more preferably 1 to 6, even more preferably 1 to 3, and most preferably both R ¹ and R ³ are methyl groups. And, in this embodiment, n is particularly preferably 0 as described above. The epoxy resin in this embodiment makes it easier to obtain an epoxy cured product with relatively excellent flexibility.

式（１－３）において、Ｒ^６は水素原子又は－ＣＯＯＲ^１であり、かつＲ^７は水素原子又は－ＣＯＯＲ^３である。Ｒ^１、Ｒ^３、Ｒ^４及びＲ^５は上記の通りである。 As described above, the epoxy resin of the present invention is preferably one in which n is 0, and therefore is also preferably a compound having a structure represented by the following formula (1-3).

In formula (1-3), R ⁶ is a hydrogen atom or —COOR ¹ , and R ⁷ is a hydrogen atom or —COOR ^{3. R 1} , R ³ , R ⁴ and R ⁵ are as defined above.

The details of the preferred aspects of R ⁴ and R ⁵ are as described above. Therefore, in formula (1-3), it is preferred that, independently in each benzene ring, one of R ⁴ and R ⁵ is a hydrogen atom and the other is any one of a hydrogen atom, -OCH ₃ , and -OG, and in this case, it is more preferred that the other of R ⁴ and R ⁵ in one molecule is the same functional group. And it is even more preferred that both R ⁴ and R ⁵ are hydrogen atoms.
The preferred embodiments of R ¹ and R ³ are also as described above. Therefore, in formula (1-3), it is preferred that R ⁶ is any one of a hydrogen atom, -COOG, and -COOR ¹ , R ⁷ is any one of a hydrogen atom, -COOG, and -COOR ³ , and R ¹ and R ³ are alkyl groups. Of these, it is more preferred that R ⁶ and R ⁷ are both a hydrogen atom, -COOG, or -COOR.

As the epoxy resin having the structure of the above formula (1-3), compounds having structures represented by the following formulas (1-4) to (1-10) are preferred, and among these, compounds having a structure represented by formula (1-4) are more preferred. Compounds having structures represented by the following formulas (1-4) to (1-10) can be easily synthesized from coumaric acid, ferulic acid or caffeic acid obtained by enzymatic conversion reaction of coumaric acid, or 4-vinylphenol obtained by enzymatic conversion of coumaric acid and decarbonation reaction, and therefore can be easily produced from biomass raw materials.

（なお、式（１－８）、（１－９）、及び（１－１０）において、Ｒはアルキル基である。アルキル基の詳細は上記の通りである。）

(In addition, in formulas (1-8), (1-9), and (1-10), R is an alkyl group. Details of the alkyl group are as described above.)

なお、式（２）において、Ｒ^１４及びＲ^１５はそれぞれ独立に、水素原子、アルコキシ基、及び－ＯＨのいずれかである。＊は他の構造との結合部位となってもよい。
上記式（２）において、Ｒ^１４及びＲ^１５のアルコキシ基は、上記したＲ^４及びＲ^５におけるアルコキシ基と同じであり、好ましくはメトキシ基である。
式（２）において、各ベンゼン環においてＲ^１４及びＲ^１５は、互いに同一であってもよいし、異なってもよいが、各ベンゼン環においてそれぞれ独立に、Ｒ^１４及びＲ^１５のうちいずれか一方が水素原子で、他方が水素原子、メトキシ基などのアルコキシ基、－ＯＨのいずれかであることが好ましい。なお、一分子中においてＲ^１４及びＲ^１５のうちの他方は、同じ基であることが好ましい。 <Method of manufacturing epoxy resin>
The epoxy resin of the present invention can be synthesized by reacting a compound having a skeleton represented by the following formula (2) (hereinafter also referred to as a raw material compound) with epihalohydrin.

In formula (2), R ¹⁴ and R ¹⁵ are each independently any one of a hydrogen atom, an alkoxy group, and -OH. * may be a bonding site with other structures.
In the above formula (2), the alkoxy group of R ¹⁴ and R ¹⁵ is the same as the alkoxy group in R ⁴ and R ⁵ described above, and is preferably a methoxy group.
In formula (2), R ¹⁴ and R ¹⁵ in each benzene ring may be the same or different, but it is preferable that, independently in each benzene ring, one of R ¹⁴ and R ¹⁵ is a hydrogen atom and the other is a hydrogen atom, an alkoxy group such as a methoxy group, or -OH. It is preferable that the other of R ¹⁴ and R ¹⁵ in one molecule is the same group.

In the above formula (2-1), R ¹¹ and R ¹³ are each independently a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom. R ¹² is a divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom. Details of the monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom and the divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom are as described above. However, the divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom is usually a structural unit derived from a dihydroxy compound described later, and therefore is usually other than a hydroxypropylene group, and for example, a saturated hydrocarbon group having no heteroatom or a saturated hydrocarbon group having an ether bond as a heteroatom is preferred.
R ¹⁴ and R ¹⁵ are as defined above.
In formula (2-1), m is an integer of 0 to 100, preferably 0 to 50, more preferably 0 to 10, still more preferably 0 to 5, and particularly preferably 0.

In addition, in formulas (2) and (2-1), it is preferable that both R ¹⁴ and R ¹⁵ are hydrogen atoms. Therefore, it is preferable that the raw material compound has a structure represented by the following formula (2-2).

式（２－２）に示す化合物において、Ｒ^１１、Ｒ^１２、Ｒ^１３及びｍは、上記で述べたとおりである。

In the compound represented by formula (2-2), R ¹¹ , R ¹² , R ¹³ and m are as defined above.

式（２－３）において、Ｒ^１６は水素原子又は－ＣＯＯＲ^１１であり、かつＲ^１７は水素原子又は－ＣＯＯＲ^１３である。Ｒ^１１、Ｒ^１３、Ｒ^１４及びＲ^１５は上記の通りである。 As described above, the starting compound of the present invention is preferably one in which m is 0, and therefore is preferably a compound having a structure represented by the following formula (2-3).

In formula (2-3), R ¹⁶ is a hydrogen atom or —COOR ¹¹ , and R ¹⁷ is a hydrogen atom or —COOR ^{13. R 11} , R ¹³ , R ¹⁴ and R ¹⁵ are as defined above.

Preferred aspects of R ¹⁴ and R ¹⁵ are as described above. Therefore, in formula (2-3), it is preferred that, independently in each benzene ring, one of R ¹⁴ and R ¹⁵ is a hydrogen atom and the other is any one of a hydrogen atom, -OCH ₃ , and -OH, and in this case, it is more preferred that the other of R ¹⁴ and R ¹⁵ is the same functional group. And it is even more preferred that both R ¹⁴ and R ¹⁵ are hydrogen atoms.
The preferred embodiments of R ¹¹ and R ¹³ are also as described above. In formula (2-3), R ¹⁶ is a hydrogen atom or -COOR ¹¹ , and R ¹⁷ is a hydrogen atom or -COOR ^13. R ¹¹ and R ¹³ are each independently a hydrogen atom or an alkyl group. It is more preferable that R ¹⁶ and R ¹⁷ are both a hydrogen atom, -COOH, or -COOR (R is an alkyl group).

More specifically, the raw material compound is preferably dihydroxytruxillic acid represented by the following formula (2-4) or an ester compound thereof.

Dihydroxytruxillic acid shown in the above formula (2-4) is a para-coumaric acid dimer, and can be obtained by dimerizing para-coumaric acid. The method for dimerizing para-coumaric acid is not particularly limited, but examples include a method of dimerization by light irradiation such as ultraviolet light irradiation. Para-coumaric acid is dimerized by cleaving the double bond at the beta position of para-coumaric acid upon UV irradiation, and the resulting molecules recombine with each other to obtain a para-coumaric acid dimer having the structure shown in the above formula (2-4).

The raw material compound may be any of the compounds shown in the following formulas (2-5) to (2-7), or an ester compound of the compound shown in (2-5) or (2-6). Each of the compounds shown in the following formulas (2-5) to (2-7) can be obtained by dimerizing ferulic acid, caffeic acid, and 4-vinylphenol. The dimerization method is not particularly limited, but includes a method of dimerization by light irradiation such as ultraviolet irradiation, as in the case of paracoumaric acid. Ferulic acid, caffeic acid, and 4-vinylphenol can be obtained by enzymatic conversion reaction of coumaric acid, or by enzymatic conversion of coumaric acid and decarbonation reaction, and therefore can be easily produced from biomass raw materials, as in the case of dihydroxytruxillic acid shown in formula (2-4).

As the ester compound of dihydroxytruxillic acid represented by the above formula (2-4), a compound having a structure represented by the following formula (2-8) in which the above dihydroxytruxillic acid is esterified with a monohydroxy compound is preferably mentioned.

In the above formula (2-8), R ¹⁸ and R ¹⁹ are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom. Details of the monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom are as described above. Therefore, it is preferable that R ¹⁸ and R ¹⁹ are each independently an alkyl group, more preferably an alkyl group having 1 to 10 carbon atoms, even more preferably an alkyl group having 1 to 6 carbon atoms, and even more preferably an alkyl group having 1 to 3 carbon atoms, and most preferably both R ¹⁸ and R ¹⁹ are methyl groups.

上記式（２－９）、（２－１０）において、Ｒ^１８、Ｒ^１９は、上記式（２－８）で述べたとおりである。 Preferable examples of the ester compound of the compound represented by the above formula (2-5) or (2-6) include a compound having a structure represented by formula (2-9) and a compound having a structure represented by formula (2-10).

In the above formulas (2-9) and (2-10), R ¹⁸ and R ¹⁹ are as defined in the above formula (2-8).

The ester compound of paracoumaric acid represented by formula (2-4) may be a compound obtained by esterifying the dihydroxytruxillic acid with a dihydroxy compound, or with a dihydroxy compound and a monohydroxy compound. The compound esterified with at least a dihydroxy compound is a compound represented by formula (2-1) or formula (2-2) in which m is 1 or more.
When esterification is performed with a dihydroxy compound and a monohydroxy compound, dihydroxytruxillic acid may be esterified with a dihydroxy compound and then further esterified with a monohydroxy compound, or it may be esterified with a monohydroxy compound and then esterified with a dihydroxy compound, or esterification with a dihydroxy compound and esterification with a monohydroxy compound may be performed in parallel.
When esterification is performed with a dihydroxy compound and a monohydroxy compound, m in formula (2-1) or (2-2) is 1 or more, and at least one of R ¹¹ and R ¹³ is a monovalent hydrocarbon group which may have a heteroatom, but it is preferable that both R ¹¹ and R ¹³ are monovalent hydrocarbon groups which may have a heteroatom.

The method for esterifying dihydroxytruxillic acid with a hydroxy compound (monohydroxy compound, dihydroxy compound, or both) is not particularly limited, but includes, but is not limited to, a method in which a carboxylic acid and a hydroxy compound are condensed with an acid catalyst, and a method in which dihydroxytruxillic acid is converted into an acid halide such as an acid chloride and then reacted with a hydroxy compound.

The monohydroxy compound used in the esterification may be an aromatic monohydroxy compound or an aliphatic monohydroxy compound, but is preferably an aliphatic monohydroxy compound, and more preferably an alkyl monoalcohol. The alkyl monoalcohol may be a straight-chain alcohol, but may have a branched structure or a cyclic structure.
Specific examples of alkyl monoalcohols include methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, sec-butanol, tert-butanol, various pentanols, various hexanols, various heptanols, various octanols, various nonanols, various decanols, cyclopentanol, cyclohexanol, methylcyclohexanol, and cyclohexanemethanol. Of these, methal is particularly preferred.

The dihydroxy compound used in the esterification may be an aromatic dihydroxy compound or an aliphatic dihydroxy compound, but is preferably an aliphatic dihydroxy compound, and more preferably an alkyl diol. The aliphatic dihydroxy compound may be a straight-chain alcohol, but may have a branched structure or a cyclic structure.
Specific examples of the aliphatic dihydroxy compound include ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, etc. Of these, ethylene glycol is preferred.

The ester compound of the compound represented by formula (2-5) or (2-6) may be a compound obtained by esterifying the compound represented by formula (2-5) or (2-6) with a dihydroxy compound, or with a dihydroxy compound and a monohydroxy compound. The compound esterified with at least a dihydroxy compound is a compound represented by formula (2-1) or (2-2) in which m is 1 or more.
The details of the compound obtained by esterifying the compound represented by formula (2-5) or formula (2-6) with a dihydroxy compound, or a dihydroxy compound and a monohydroxy compound are similar to those of the compound represented by formula (2-4), and therefore the description thereof will be omitted.

Epihalohydrins that can be used in the synthesis of epoxy resins include epifluorohydrin, epichlorohydrin, epibromohydrin, and epiiodohydrin, of which epichlorohydrin is preferred in terms of reactivity and economy.

As described above, the epoxy resin of the present invention can be obtained by reacting a compound having the skeleton represented by formula (2) with epihalohydrin. The epoxy resin can be obtained by, for example, mixing and reacting the compound having the skeleton represented by formula (2) with epihalohydrin in a reactor.
In this production method, the amount of epihalohydrin added to the compound having the skeleton shown in formula (2) in the reaction system is preferably 1 equivalent or more. By adding the amount of epihalohydrin to be 1 equivalent or more, the compound shown in formula (1) can be synthesized. Note that the equivalent is the molar equivalent to the functional groups (hydroxyl group and carboxy group) of the compound having the skeleton shown in formula (2), and the same applies below.
In addition, from the viewpoint of reducing the number of n and synthesizing the compound represented by formula (1) in which n is small, preferably n is 0, in high yield, it is preferable that the amount of epihalohydrin added is in large excess. Specifically, it is preferably 2 equivalents or more, more preferably 5 equivalents or more, and even more preferably 8 equivalents or more.
Furthermore, from the viewpoints of facilitating removal of unreacted epihalohydrin after the reaction and increasing production efficiency, the amount of the epihalohydrin added is preferably 50 equivalents or less, more preferably 30 equivalents or less, even more preferably 20 equivalents or less, and still more preferably 15 equivalents or less, relative to the functional groups of the compound represented by formula (2).

When a compound represented by formula (2-1), formula (2-2) or formula (2-3) (wherein in formula (2-3), R ¹⁶ and R ¹⁷ are --COOR ¹¹ and --COOR ¹³ , respectively) is used as a raw material compound, R ¹¹ and R ¹³ are hydrogen atoms (particularly when a compound represented by any of formulas (2-4) to (2-6) is used as a raw material), and the number of n is large, the amount of epihalohydrin added may be reduced, for example, to 2 equivalents or less. When R ¹¹ and R ¹³ are hydrogen atoms and the amount of epihalohydrin added is reduced, oligomerization of the compound having the skeleton represented by formula (2) and epihalohydrin proceeds more easily, and a compound represented by formula (1-1) or formula (1-2) in which the number of n is large is more easily obtained.

The reaction of the compound having the skeleton shown in formula (2) with epihalohydrin is preferably carried out in the presence of a catalyst. Examples of the catalyst include quaternary ammonium salts such as benzyltriethylammonium chloride, benzyltriethylammonium bromide, tetrabutylammonium fluoride, and tetrabutylammonium bromide. The catalyst may be used alone or in combination of two or more. The amount of catalyst added is preferably 0.01 to 2 moles, more preferably 0.05 to 1 mole, and even more preferably 0.1 to 0.5 moles, per mole of the compound having the skeleton shown in formula (2).

The above reaction may be carried out in the presence of a solvent, or may be carried out without a solvent. The compound having the skeleton shown in formula (2) is appropriately diluted with epihalohydrin by using a large excess of epihalohydrin as described above, and the above reaction can be carried out appropriately without a solvent or with a small amount of solvent. As the reaction solvent, an aliphatic hydrocarbon solvent, an aromatic hydrocarbon solvent, a halogen-based solvent, an ester-based solvent, an ether-based solvent, etc. can be used.
The reaction in the presence of the catalyst is carried out, for example, at 40 to 150° C., preferably 60 to 120° C., for example, for 30 minutes to 24 hours, preferably 2 to 12 hours.

In addition, in this production method, it is preferable to add a basic compound to the reaction system in addition to the above catalyst. By adding a basic compound, dehydrohalogenation proceeds more easily, making it possible to improve the yield of the desired epoxy resin. It is preferable that the basic compound is added to the reaction system after reacting for a certain period of time in the presence of the above catalyst, and then allowed to react for a further certain period of time. The reaction after the addition of the basic compound is carried out, for example, at -10 to 30°C, preferably 0 to 15°C, for example, for 10 minutes to 24 hours, preferably 30 minutes to 12 hours.

The basic compound to be used is not particularly limited as long as it acts as a base.Specific examples include metal bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, cesium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, lithium hydride, sodium hydride, potassium hydride, lithium carbonate, sodium carbonate, potassium carbonate, cesium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, lithium alkoxide, sodium alkoxide, and potassium alkoxide.Of these, it is preferable to use at least one of sodium hydroxide and potassium hydroxide from the viewpoint of economy and availability.
The basic compound is not particularly limited, and may be added to the reaction system, for example, as an aqueous solution.
The amount of the basic compound added may be, for example, more than 1 equivalent, preferably 1.5 to 20 equivalents, and more preferably 2 to 15 equivalents, relative to the functional group of the compound having the skeleton represented by formula (2).

In this production method, the target epoxy resin can be purified by distilling off epihalohydrin, distilling off the reaction solvent used as necessary, separating the target epoxy resin from the water-soluble compound by an extraction operation using water and a hydrophobic solvent, distilling off the extraction solvent, or by other general unit operations such as distillation, or by an appropriate combination of these.

At least a part of the raw materials of the epoxy resin of the present invention can be produced from biomass, and an epoxy resin with a high bio content can be obtained. Specifically, dihydroxytruxillic acid shown in formula (2-4) can be obtained by obtaining paracoumaric acid by microbial synthesis from L-tyrosine, a compound derived from biomass, and then photodimerizing the paracoumaric acid as described above. Similarly, the compounds shown in formulas (2-5) to (2-7) can also be produced from biomass as described above. Therefore, the skeleton shown in formula (1) of the present invention can be derived from biomass, particularly from a compound synthesized by a microorganism. Among them, it is preferable that the structural unit derived from dihydroxytruxillic acid in formula (1-2) is derived from biomass, particularly from a compound synthesized by a microorganism.
In addition, the method of obtaining para-coumaric acid by microbial synthesis has stereoselectivity and can obtain para-coumaric acid in high yield, and the subsequent dimerization and epoxidation are also relatively simple. Therefore, the epoxy resin having the skeleton represented by formula (1) of the present invention can be easily produced, even though it is a compound obtainable from biomass.

Furthermore, in the compounds shown in formulas (1-1) to (1-3), R ¹ and R ³ are derived from a monohydroxy compound, and R ² may be derived from a dihydroxy compound. However, it is preferable that the monohydroxy compound and dihydroxy compound used as raw materials are derived from biomass. By deriving these from biomass, an epoxy resin with an even higher bio content can be obtained. Specifically, known examples of monohydroxy compounds include methanol, ethanol, and butanol derived from biomass, and known examples of dihydroxy compounds include ethylene glycol, 1,3-propanediol, and 1,4-butanediol derived from biomass. By using these, the bio content of the epoxy resin can be further improved.

<Hardened body>
The cured product of the present invention (hereinafter also referred to as "epoxy cured product") is obtained by curing the above-mentioned epoxy resin. The epoxy cured product is generally cured with a curing agent, and therefore is preferably a cured product of a curable composition containing an epoxy resin and a curing agent.
There are no particular limitations on the curing agent that can be used in the epoxy cured product as long as it is capable of curing the epoxy resin, but a compound that reacts with the epoxy resin to form a three-dimensional network structure (network polymer) is preferred.
Specific examples of the curing agent include amine-based curing agents, acid anhydride-based curing agents, polyamide resins which are condensates of dimer or trimer acid and polyamine, Lewis acids such as boron trifluoride-amine complex, phenol or its derivatives, etc. Furthermore, mercapto-based curing agents can also be used as the curing agent.

Examples of the amine-based curing agent include polyamines such as aliphatic polyamines and aromatic polyamines. Examples of the aliphatic polyamines include ethylenediamine, diethylenetriamine, triethylenetetramine, dipropylenetriamine, tetraethylenepentamine, dimethylaminopropylamine, bishexamethylenetriamine, cyclohexylaminopropylamine, aminoethylethanolamine, monohydroxyethyldiethylenetriamine, bishydroxyethyldiethylenetriamine, N-(2-hydroxypropyl)ethylenediamine, hexamethylenediamine, diethyleneglycolbis(3-aminopropyl)ether, diethylaminopropylamine, 3,9-bis(3-aminopropyl)-2,4,8,10-tetrasoxaspiro[5,5]undecane, menthanediamine, isophoronediamine, 4,4'-methylenebis(cyclohexylamine), bis(4-amino-3-methylcyclohexyl)methane, and N-aminoethylpiperazine.
The aromatic polyamine is an amine having an aromatic ring, and specific examples thereof include phenylenediamine, diaminodiphenylmethane, diaminoanisole, toluenediamine, various xylylenediamines such as metaxylylenediamine, and diaminodiphenylsulfone.

The amine-based curing agent may be an imidazole-based curing agent, an amidoamine-based curing agent, etc. Examples of the imidazole-based curing agent include 2-methylimidazole, 2-ethylimidazole, 2-undecylimidazole, 2,4-dimethylimidazole, 2-heptadecylimidazole, 1,2-dimethylimidazole, 1,2-diethylimidazole, 2-phenyl-4-methylimidazole, 2,4,5-triphenylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 1-benzyl-2-phenylimidazole, 1-cyanoethyl-2-methylimidazole, 1-cyanoethyl-2-undecylimid ... Examples of the aryl-2-methylimidazole include 2-phenyl-4,5-dihydroxymethylimidazole, 2-aryl-4,5-diphenylimidazole, 2,4-diamino-6-[2'-methylimidazolyl-(1)']-ethyl-S-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1)']-ethyl-S-triazine, 2,4-diamino-6-[2'-methylimidazolyl-(1)']-ethyl-S-triazine isocyanuric acid adduct, and 2-phenyl-4-methyl-5-hydroxymethylimidazole. Examples of the amidoamine curing agent include dicyandiamide.

Examples of the acid anhydride curing agent include phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, benzophenone tetracarboxylic anhydride, chlorendic anhydride, dodecynyl succinic anhydride, methyltetrahydrophthalic anhydride, methylendomethylenetetrahydrophthalic anhydride, and methylhexahydrophthalic anhydride represented by 4-methylhexahydrophthalic anhydride.
Examples of the phenol derivatives include bisphenols such as bisphenol F and bisphenol A and derivatives thereof, trifunctional phenols such as tri(hydroxyphenyl)methane and tri(hydroxyphenyl)ethane and derivatives thereof, and compounds obtained by reacting phenols such as phenol novolak with formaldehyde.
As the mercapto-based curing agent, a compound having two mercapto groups in the molecule, such as 1,4-bis(3-mercaptobutyryloxy)butane, or a compound having three or more mercapto groups, such as pentaerythritol tetrakis(3-mercaptobutyrate), can also be used.
The curing agent may be used alone or in combination of two or more kinds.

As the curing agent, among the above, amine-based curing agents are preferred, and polyamines are particularly preferred. Polyamines preferably have a total of two or more primary amino groups and secondary amino groups in one molecule, and preferably have at least one primary amino group, and more preferably have two or more primary amino groups. The total number of primary amino groups and secondary amino groups in one molecule of polyamines is not particularly limited, but is, for example, 8 or less, preferably 5 or less, and more preferably 3 or less.

The amount of the curing agent is, for example, 1 to 100 parts by mass, preferably 2 to 50 parts by mass, relative to 100 parts by mass of the epoxy resin. If the amount is equal to or more than these lower limits, the curing agent can be appropriately cured, and for example, when a three-dimensional network structure is formed, the structure becomes strong, and the mechanical properties and thermal properties tend to be good. Furthermore, if the amount is equal to or less than these upper limits, the amount of the curing agent is prevented from becoming greater than necessary, and the mechanical properties and thermal properties tend to be good.
The amount of the curing agent may be appropriately adjusted according to the epoxy equivalent of the epoxy resin, and further, in the case of using an amine-based curing agent, according to the amount of active hydrogen of the amine-based curing agent (i.e., hydrogen atoms bonded to nitrogen atoms in amino groups). For example, it may be adjusted so that the ratio of the number of active hydrogens to the number of epoxy groups is 1 or close to 1, specifically 0.5 to 2, preferably 0.75 to 1.5, and more preferably 0.9 to 1.1.

The glass transition temperature (Tg) of the epoxy cured product measured by a differential scanning calorimeter is preferably 150° C. or higher. By setting the temperature to 150° C. or higher, the thermal performance can be improved, and the heat resistance of the epoxy cured product becomes good. The glass transition temperature (Tg) of the epoxy cured product is more preferably 160° C. or higher, and further preferably 170° C. or higher. The glass transition temperature (Tg) of the epoxy cured product is not particularly limited, but is, for example, 300° C. or lower.
From the same viewpoint, the glass transition temperature (Tg) of the epoxy cured product measured with a dynamic viscoelasticity apparatus is preferably 150° C. or higher, more preferably 160° C. or higher, and even more preferably 170° C. or higher, and is, for example, 300° C. or lower.

The epoxy cured product can be produced by, but is not limited to, mixing an epoxy resin with a curing agent to obtain a curable composition, and heating it as necessary. The heating temperature is, but is not limited to, for example, room temperature (23°C) to 300°C, preferably 40°C to 250°C, and heating may be performed within the above temperature range for, for example, 10 minutes to 13 hours, preferably 1 to 6 hours. The heating temperature may be increased stepwise as the curing progresses. In addition, the curable composition containing an epoxy resin and a curing agent may be diluted by adding a solvent or the like, or may contain other components as appropriate. When diluted with a solvent, the solvent may be removed by drying appropriately by heating as described above.

The curable composition may contain a curing accelerator in addition to the epoxy resin and curing agent of the present invention.
The curing accelerator is a component that accelerates the curing by the curing agent. For example, since dicyandiamide and the like among the curing agents have a high curing temperature when used alone, a curing accelerator can be used to enhance the curing activity of dicyandiamide and the like. Examples of the curing accelerator for dicyandiamide include urea-based, imidazole-based, tertiary amine-based, and caprolactam. Among these, urea-based and imidazole-based are preferred, and 2,4-diamino-6-(2-methylimidazolyl-(1))-ethyl-s-triazine, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and 3-(3,4-dichlorophenyl)-1,1-dimethylurea) are more preferred. The content of the curing accelerator is, for example, about 0.1 to 10 parts by mass relative to 100 parts by mass of the epoxy resin.

The epoxy resin and epoxy cured product of the present invention can be used in various fields, including, but not limited to, any field such as the electrical field, the transportation field, the civil engineering field, the architectural field, the mechanical field, the medical field, etc. The epoxy resin and epoxy cured product of the present invention can be used in various forms, such as various molded products, adhesives, paints, fillers, films, powders, composite materials, and foams.
More specifically, the composition can be used for various applications such as adhesives for dissimilar materials, rubber-resin adhesives, well bonds, bonding between substrates and semiconductor elements such as die attach, bonding films for bonding flexible substrates, various adhesives for construction and civil engineering applications, various paint applications such as anti-fogging paints, paints for electrodeposition coating, anti-corrosion paints, floor coating agents, and other paints for construction and civil engineering applications, sealing materials for sealing coated electric wires, fiber bundling agents, fiber reinforcement such as for prepregs, electrical insulating materials and protective materials for electronic components, photosensitive resins, lens applications, and dental materials, but is not limited to these applications.

The epoxy resin-containing composition containing the epoxy resin of the present invention can contain various components depending on the application. In addition to the above-mentioned curing agent and curing accelerator, such components include resins other than the epoxy resin of the present invention, latex, filler, pigment, silane coupling agent, surfactant, UV absorber, antioxidant, stabilizer, plasticizer, leveling agent, defoamer, antistatic agent, flame retardant, lubricant, dispersant, etc.
The compositions containing the epoxy resin of the present invention (hereinafter also referred to as "epoxy resin-containing compositions") used for various applications and compositions having components derived from the epoxy resin of the present invention will be described in more detail below. However, each of the compositions below may appropriately contain components other than the components specifically described below, as necessary.

(Adhesive applications)
For example, when used as an adhesive, the epoxy resin-containing composition may contain an epoxy resin and a curing agent, but in addition to these, from the viewpoint of improving the adhesive strength of the adhesive and imparting impact properties, for example, polymer fine particles may be contained as a filler component. When the polymer fine particles are contained, the adhesive is preferably used for dissimilar material adhesive applications in fields such as automobiles and for weld bond applications. Examples of dissimilar materials in dissimilar adhesive applications include combinations of two types selected from various materials such as various steel materials, aluminum, aluminum alloys, fiber-reinforced plastic (FRP) plates such as carbon fiber and glass fiber, and carbon fiber reinforced plastic (CFRP). In addition, the epoxy resin-containing composition used for the above adhesive application may contain an epoxy resin other than the epoxy resin of the present invention in addition to the epoxy resin of the present invention.

The polymer particles are preferably polymer particles having a core-shell structure. The polymer particles having a core-shell structure refer to polymer particles having different molecular structures at the center (core) and the outer periphery (shell).
Examples of components constituting the core of the polymer microparticles having a core-shell structure include butadiene rubber (BR), acrylic rubber (ACM), silicone rubber (Si), butyl rubber (IIR), nitrile rubber (NBR), styrene butadiene rubber (SBR), isoprene rubber (IR), and ethylene propylene rubber (EPR). Among these, butadiene rubber is preferred. The components constituting the shell of the polymer microparticles having a core-shell structure are preferably graft-polymerized to the core and covalently bonded to the polymer constituting the core component. Examples of components constituting the shell include acrylic acid ester monomers, methacrylic acid ester monomers, and aromatic vinyl monomers.
The content of the polymer fine particles is, for example, 1 to 100 parts by mass, preferably 2 to 80 parts by mass, and more preferably 4 to 60 parts by mass, based on 100 parts by mass of the epoxy resin contained in the curable composition. The polymer fine particles having a core-shell structure may be used alone or in combination of two or more kinds.

In the adhesive for the above-mentioned dissimilar material adhesive or weld bond application, the epoxy resin-containing composition may appropriately use the above-mentioned curing agents, among which it is preferable to contain dicyandiamide. The content of the curing agent is preferably 0.01 to 30 parts by mass, more preferably 0.1 to 25 parts by mass, and even more preferably 1 to 20 parts by mass, relative to 100 parts by mass of the epoxy resin.
In addition, when the adhesive is used for weld bonding, the epoxy resin-containing composition preferably contains a blocked urethane. The blocked urethane is intended to be an elastomer type compound that contains a urethane group and/or a urea group and has an isocyanate group at its end, and in which all or a part of the terminal isocyanate group of the compound is capped with various blocking agents having an active hydrogen group. In particular, a compound in which all of the terminal isocyanate groups are capped with a blocking agent is preferred. Specific examples of blocked urethane include the compounds described in International Publication WO 2016/163491.
The content of the blocked urethane in the epoxy resin-containing composition is preferably 1 to 50 parts by mass, more preferably 2 to 40 parts by mass, and even more preferably 5 to 30 parts by mass, based on 100 parts by mass of the epoxy resin.

The epoxy resin-containing composition may also be used as a rubber-resin adhesive in tires, etc. An example of a rubber-resin adhesive is a curable composition containing a synthetic rubber latex in addition to the epoxy resin of the present invention.
The synthetic rubber latex is not particularly limited, but examples thereof include those having an unsaturated diene, such as styrene-butadiene copolymer rubber latex, vinylpyridine-styrene-butadiene copolymer rubber latex, carboxyl group-modified styrene-butadiene copolymer rubber latex, nitrile rubber latex, chloroprene rubber latex, etc. These may be used alone or in combination of two or more.
In the epoxy resin-containing composition used in the rubber-resin adhesive, the content of the synthetic rubber latex is not particularly limited, but is, for example, 25 to 80 mass %, preferably 35 to 75 mass %, and more preferably 55 to 75 mass %, based on the solid content.

In addition, it is preferable that the curable composition containing synthetic rubber latex further contains a water-soluble carbodiimide. Water-soluble carbodiimide means a carbodiimide that is soluble in water, and includes carbodiimides that are aqueous and partially water-soluble. The water-soluble carbodiimide is a compound having a carbodiimide (chemical formula: -N=C=N-) and a hydrophilic segment in the molecule. The water-soluble carbodiimide can be used as a dehydration condensation agent that can form an ester bond or an amide bond between a COOH group and an OH group or an amino group of a compound contained in an aqueous solution. For example, 1-ethyl-3-(3-(dimethylaminopropyl)carbodiimide (WSC) is known to activate a carboxyl group, and the active intermediate reacts with an amino group and a hydroxyl group to form an amide and an ester.

It is presumed that the water-soluble carbodiimide coats the surface of the synthetic rubber latex having an unsaturated diene while crosslinking, and combines with the epoxy resin of the present invention to bond the resin of the adherend to the rubber.
The water-soluble carbodiimide is preferably a water-soluble salt such as a hydrochloride or a sulfate. More specifically, examples of the water-soluble carbodiimide include 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC); water-soluble salts of 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide such as 1-cyclohexyl-3-(2-morpholinoethyl)carbodiimide-meth-p-toluene sulfate; triazine-based condensing agents such as 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM); and the like. Of these, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) is preferably used.
In the thermosetting composition used as a rubber-resin adhesive, the content of the water-soluble carbodiimide is not particularly limited, but is preferably 0.1 to 15 mass %, more preferably 0.3 to 10 mass %, even more preferably 0.5 to 7 mass %, and even more preferably 0.5 to 5 mass %, based on the solid content.

The epoxy resin of the present invention used in the rubber-resin adhesive may have two or more epoxy groups in one molecule, but preferably contains four or more epoxy groups in one molecule.
In the epoxy resin-containing composition of the rubber-resin adhesive, the content of the epoxy resin is not particularly limited, but is preferably 0.1 to 40 mass %, more preferably 0.4 to 40 mass %, and particularly preferably 1.0 to 30 mass %, based on the solid content.
The epoxy resin-containing composition for use as a rubber-resin adhesive is not particularly limited, but it is preferable that each component is dispersed or dissolved in water and used as a dispersion.

In adhesive applications, the adhesive may be used in electronic devices, for example, for bonding a substrate and a semiconductor element. More specifically, the adhesive may be used in die-attach applications, or may be used as a silver paste material by mixing silver particles therein.
When used as a silver paste material, the epoxy resin-containing composition may contain silver particles, the epoxy resin of the present invention, and a curing agent, and the composition may be diluted with a solvent before use. The epoxy resin-containing composition may contain an epoxy resin other than the epoxy resin of the present invention. In addition, the curing agent is preferably a phenol derivative or dicyandiamide, and these may be used in combination.
In the epoxy resin-containing composition, the content of the silver particles is, for example, 70 to 98 mass %, preferably 75 to 95 mass %, based on the solid content. The content of the epoxy resin is, for example, 1 to 20 mass %, preferably 2 to 15 mass %, based on the solid content. The content of the curing agent is, for example, 0.1 to 1.5 mass %, preferably 0.2 to 1.0 mass %.

When used as an adhesive, it may be used for flexible substrates. As an adhesive for flexible substrates, it may be used to bond, for example, copper foil and a polyimide film constituting the substrate, and may be used, for example, as a bonding film.
The epoxy resin-containing composition for flexible substrates may be a curable resin composition containing the epoxy resin of the present invention and a curing agent, and may also contain an epoxy resin other than the epoxy resin of the present invention or a resin other than the epoxy resin. Examples of such resins include polyester-based polymers such as polyester polyurethane resins. The polyester polyurethane resin may be a resin obtained by reacting at least polyester polyol, polyisocyanate, and a chain extender such as a diol compound other than polyester polyol as raw materials. In addition to the polyester polyurethane resin, a resin having a carboxy group or a carboxylic anhydride structure may also be contained.
As the curing agent, the above-mentioned compounds may be used appropriately, but imidazole derivatives such as imidazole silane compounds may also be used.
Furthermore, the epoxy resin-containing composition for the flexible substrate may contain an organic filler, a metal filler, an inorganic filler other than a metal filler, or the like.
In the above-mentioned epoxy resin-containing composition used for a flexible substrate, the content of the epoxy resin is preferably 1 to 60 mass %, more preferably 2 to 40 mass %, and even more preferably 3 to 20 mass %, based on the total amount of components other than the above-mentioned filler.

(Paint applications)
The epoxy resin of the present invention may be used for coating applications, or may be used as a binder resin for coatings. Specifically, for example, when used as an anti-fog coating, it may be used in a coating composition containing the epoxy resin of the present invention and silica particles. The coating composition may contain a silane coupling agent or the like as appropriate. When used as an anti-fog coating, the coating composition is preferably used as a dispersion in which each component is dispersed or dissolved in a liquid medium such as water. In addition, the binder resin may contain an epoxy resin other than the epoxy resin of the present invention, or a resin other than an epoxy resin.
As the silica particles, water-dispersed silica is preferred, and it is also preferred to use colloidal silica. As the liquid medium, water and organic solvents can be mentioned, and water or a mixed solvent of water and an organic solvent is preferred. In the case of a mixed solvent, the organic solvent may be any solvent capable of dispersing silica, for example, ethylene glycol monobutyl ether, etc. may be used. In the coating composition, the content of the epoxy resin may be 0.1 to 1000 parts by mass, 0.5 to 500 parts by mass, or 1 to 100 parts by mass, relative to 100 parts by mass of the silica particles.

(For electrocoating)
For example, when used for electrodeposition coating, the epoxy resin may be reacted with an amine to be used as an aminated epoxy resin. Specific examples of the amine include primary amines such as butylamine, octylamine, and monoethanolamine; secondary amines such as diethylamine, dibutylamine, methylbutylamine, diethanolamine, and N-methylethanolamine; and complex amines such as diethylenetriamine. The primary amines can form ketimine groups using ketone compounds to control the reaction by so-called blocking. In addition, tertiary amines may be used as the amine, and specific examples thereof include triethylamine, N,N-dimethylbenzylamine, and N,N-dimethylethanolamine.
The coating composition for electrodeposition coating may contain, for example, an aminated epoxy resin and a curing agent such as a blocked polyisocyanate curing agent, and may further contain a pigment dispersion paste as necessary. The pigment dispersion paste contains a pigment dispersion resin and a pigment. The coating composition for electrodeposition coating may be used as an emulsion or the like.

(Anti-corrosion paint)
In the coating application, the coating composition may be a cured composition containing the epoxy resin of the present invention and a curing agent. Such a coating composition may contain an epoxy resin other than the epoxy resin of the present invention, a pigment or a pigment dispersant, or a silane coupling agent for improving adhesion. In addition, it may be generally used after being diluted with an organic solvent. The coating composition containing the epoxy resin and the curing agent is preferably used, for example, in a corrosion prevention coating composition, and is preferably used for corrosion prevention of ships. In the coating composition, the content of the epoxy resin is preferably 1 to 60 mass%, more preferably 5 to 50 mass%, based on the solid content.

(Floor coating agent)
The epoxy resin of the present invention may be used for construction and civil engineering applications, and may be used, for example, as a floor coating agent. The epoxy resin-containing composition used as a floor coating agent may contain the epoxy resin of the present invention and a curing agent, but preferably further contains an inorganic filler. As the inorganic filler, a known inorganic filler used as a floor coating agent such as carbon nanotubes, silica, silica sand, barite, calcium carbonate, talc, etc. may be used. In addition to these inorganic fillers, pigments used as colorants may also be appropriately blended. The epoxy resin may also contain an epoxy resin other than that of the present invention.
In the epoxy resin-containing composition for floor coating agents, the content of the inorganic filler is, for example, about 1 to 1,000 parts by mass, preferably 10 to 200 parts by mass, and more preferably 20 to 100 parts by mass, per 100 parts by mass of the epoxy resin.
Of course, the epoxy resin-containing composition may be used in construction and civil engineering applications other than floor coating agents, and may be used as a paint for tanks, paint for pipe interiors, paint for exteriors, etc. Also, it may be used as an adhesive in construction and civil engineering applications, for example, to bond various structures.

(For sealing purposes)
When the epoxy resin of the present invention is used for sealing material applications, preferably for sealing coated electric wires, it may be used, for example, as a curable composition containing an epoxy resin and a curing agent. The curing agent used in sealing material applications may be any of the above-mentioned curing agents, but amine-based curing agents and mercapto-based curing agents are preferably used. In addition, the curable composition used for sealing material applications preferably contains a silane coupling agent.

(Fiber sizing agent)
When the epoxy resin of the present invention is used as a fiber bundling agent, it is preferable to use it in combination with a polyester resin having a sulfonate group. As the polyester resin having a sulfonate group, an aromatic polyester resin or an aliphatic polyester resin can be used, but it is preferable to use an aromatic polyester resin. As the aromatic polyester resin, it is preferable to have a structural unit derived from an aromatic dicarboxylic acid such as isophthalic acid or terephthalic acid.
In addition, the epoxy resin-containing composition for fiber sizing agents preferably contains a surfactant in addition to the above-mentioned epoxy resin and polyester resin having a sulfonate group, and the surfactant is preferably an aromatic nonionic surfactant. Examples of the aromatic nonionic surfactant include polyoxyalkylene alkyl phenyl ether, polyoxyalkylene styrenated phenyl ether, polyoxyalkylene benzyl phenyl ether, polyoxyalkylene cumyl phenyl ether, polyoxyalkylene naphthyl phenyl ether, and polyoxyalkylene styrenated (alkyl phenyl ether), and among these, polyoxyalkylene styrenated phenyl ether such as polyoxyethylene styrenated phenyl ether is preferred.
The epoxy resin-containing composition for a fiber sizing agent may contain an epoxy resin other than the epoxy resin of the present invention.
The epoxy resin-containing composition for a fiber sizing agent is preferably used as an aqueous composition, for example, as an aqueous dispersant.
In the epoxy resin-containing composition for a fiber sizing agent, the content of the epoxy resin is, for example, 75 to 95 mass % on a solid content basis, and preferably 80 to 95 mass %.

(Prepreg applications)
The epoxy resin of the present invention may be used in prepreg applications, and may be used as a matrix resin to be impregnated into fibrous materials such as reinforcing fibers used in prepreg applications.
When used as a matrix resin, the epoxy resin-containing composition may be any curable composition that contains the epoxy resin of the present invention and a curing agent.
In addition, in the epoxy resin-containing composition, the epoxy resin of the present invention may be used alone as a resin component, or may be used in combination with other resin components, and may contain an epoxy resin other than the epoxy resin of the present invention, a polyfunctional (meth)acrylate compound, a cyanate ester resin containing two or more cyanate groups, etc. In addition, it is also preferable that the epoxy resin-containing composition contains a thermoplastic resin. In addition, the epoxy resin-containing composition used for prepreg applications may contain a flame retardant. Examples of the flame retardant include phosphorus-containing compounds such as phosphoric acid esters, nitrogen-containing compounds such as red phosphorus, melamine, melamine cyanurate, and melamine isocyanurate, metal hydroxides, metal oxides, etc.
In the epoxy resin-containing composition used for prepreg applications, the content of the epoxy resin is preferably about 20 to 99% by mass, more preferably about 50 to 80% by mass, and the content of the curing agent is preferably about 1 to 25% by mass, more preferably about 2 to 20% by mass.

(Electrical insulating and protective materials)
The epoxy resin of the present invention may be used in electronic substrates and the like, specifically, it may be used as a protective material or an electrical insulating material for forming an electrical insulating layer and the like.
When used as an electrical insulating material or a protective material, the curable resin composition preferably contains a filler in addition to the epoxy resin of the present invention and a curing agent. The filler preferably has insulating properties. Examples of such fillers include silica, alumina, aluminum nitride, boron nitride, silicon carbide, and silicon nitride. In addition, fillers other than the inorganic fillers described above may be used, and organic fillers may also be used. In the curable resin composition, the content of the filler is, for example, 50 to 90 mass%, preferably 65 to 85 mass%, based on the solid content.

The curable resin composition used for electrical insulating materials and protective materials may contain a resin other than the epoxy resin of the present invention, for example, a rubbery polymer compound such as a conjugated diene rubber. The content of the rubbery polymer compound is, for example, 30 to 70 mass%, preferably 40 to 60 mass%, based on the solid content of the total amount of components other than the filler. In addition, the composition may contain an epoxy resin other than the epoxy resin of the present invention, and may contain a thermosetting resin other than the epoxy resin, such as a phenoxy resin. In addition, the composition may contain a silane coupling agent, etc.
In the curable resin composition used for the electrical insulating material or protective material, the content of the epoxy resin is, for example, 20 to 70 mass %, preferably 25 to 40 mass %, based on the solid content of the total amount of components other than the filler.

(Photosensitive resin)
When used as an electrical insulating material or protective material for electronic substrates, the epoxy resin-containing composition may be used as a photosensitive resin composition. In such a case, the composition may contain, in addition to the epoxy resin, a photosensitive resin such as a carboxyl group-containing photosensitive resin, a photopolymerization initiator, a reactive diluent, a photosensitive monomer, a filler, and the like.
In addition, when used as a photosensitive resin composition, it may be used for applications other than the above-mentioned electronic substrate protective material and electrical insulating material. When used in a photosensitive resin composition, the epoxy resin of the present invention may be used in combination with a photoacid generator such as an iodonium salt, a sulfonium salt, or a pyridinium salt. The photoacid generator is an agent that generates an acid by irradiation with light, and the epoxy resin may be polymerized by the acid generated by decomposition of the photoacid generator.
In addition, when used as a photosensitive resin composition as described above, the applications include, but are not limited to, dental applications, more specifically, filling and restorative materials used to repair damaged teeth, denture base lining materials, hybrid ceramics for crown restoration, etc. In addition, it may be used for lenses, etc., as described below.

(For lenses)
In lens applications, the epoxy resin of the present invention may be used in combination with resin components such as epoxy resins other than the epoxy resin of the present invention and oxacene compounds, and therefore, the epoxy resin-containing composition for lens applications may contain other epoxy resins and oxacene compounds in addition to the epoxy resin of the present invention. Examples of other epoxy resins include diglycidyl ether compounds having a bisphenol skeleton, bifunctional alicyclic epoxy compounds not having a bisphenol skeleton, and polyfunctional epoxy compounds having an isocyanurate ring structure and having three or more functional groups. In addition, when used in lens applications, the epoxy resin-containing composition is preferably a photosensitive resin composition, and may contain, for example, the above-mentioned photoacid generator.
The uses and the specific formulations for each use described above are merely examples, and the composition may be used for uses other than those described above, and the formulation of each composition in each use may be other than the above formulation.

The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The measurement conditions in the following examples are as follows.
<Measurement conditions>
[ ^1H -NMR Spectral Measurement]
The measurements were carried out at 23° C. using an NMR spectrometer "ECX-400" manufactured by JEOL Ltd. and deuterated dimethyl sulfoxide (deuterated DMSO) or THF as a solvent.

[Glass transition temperature (Tg)]
Using a differential scanning calorimeter (trade name "DSC-60") manufactured by Shimadzu Corporation, measurements were performed under an argon atmosphere at a temperature rise rate of 10°C/min, and the midpoint of the baseline shift was taken as the glass transition temperature. At this time, the glass transition temperature was measured when the temperature was raised to 250°C at a rate of 10°C/min, then lowered to 30°C, and then raised again.
Using a dynamic viscoelasticity device manufactured by UBM Corporation (product name "Rheogel-E4000"), measurements were performed in a nitrogen atmosphere at a temperature increase rate of 3°C/min, and the peak top temperature of tan δ was taken as the glass transition temperature.

Synthesis Example 1
[Synthesis of para-coumaric acid dimer]
Para-coumaric acid (Tokyo Chemical Industry Co., Ltd.) was suspended in hexane, and the suspension was irradiated with UV light from an incandescent mercury lamp. The double bond at the beta position of para-coumaric acid was cleaved by UV irradiation, and the molecules were recombined to dimerize. After removing hexane from the reaction solution, the solution was resuspended in ethanol and filtered. The powder remaining on the filtration membrane was obtained as para-coumaric acid dimer. When the powder remaining on the filtration membrane was subjected to ¹ H-NMR measurement, it was confirmed that it was para-coumaric acid dimer (4,4'-dihydroxytruxillic acid) represented by formula (2-1).

[Synthesis of epoxy resin]
Example 1
5 g of the paracoumaric acid dimer obtained in Synthesis Example 1 was suspended in 50 ml of methanol and 0.3 ml of concentrated sulfuric acid, and reacted at 80° C. for 6 hours. After the reaction was completed, methanol was removed and the mixture was dried. The dried methyl ester was dissolved in 50 ml of ethyl acetate, and then washed twice with a 5% by mass NaHCO ₃ solution. It was further washed twice with saturated saline, and the ethyl acetate layer was recovered. Anhydrous magnesium sulfate was added to the obtained organic phase for dehydration, and then ethyl acetate and remaining volatiles were removed to obtain 3.31 g of a methyl ester (dimethyl 4,4'-dihydroxytruxillate) (yield 61.0%). The structure was identified by ¹ H-NMR measurement in THF. ^{The 1} H-NMR spectrum is shown in FIG. 1.

1 g of the methyl ester obtained by the above method, 5.2 g of epichlorohydrin (10 equivalents relative to the methyl ester), and 0.18 g of tetrabutylammonium bromide were reacted at 100° C. for 5 hours. After the reaction was completed, 2.5 ml of 40% by mass aqueous sodium hydroxide solution was dropped while cooling the solution with ice, and then the reaction was carried out in ice-cold water for 1 hour. 20 ml of ion-exchanged water was added to the solution after the reaction to dissolve the precipitated salt, and then 30 ml of ethyl acetate was added and mixed well to separate the aqueous phase. Anhydrous magnesium sulfate was added to the obtained organic phase for dehydration, and then ethyl acetate and remaining volatiles were removed to obtain 0.57 g of the desired epoxy resin (yield 44.0%). The structure was identified by ¹ H-NMR measurement in THF. ^{The 1} H-NMR spectrum is shown in FIG. 2. The reaction formula in Example 1 is also shown below.

[Preparation of epoxy cured body]
Example 2
4.64 g of the epoxy resin obtained in Example 1 was mixed with 0.85 g of isophoronediamine. The mixture was then heated at 100° C. for 1 hour, at 160° C. for 1 hour, and then at 200° C. for 1 hour to produce a cured product. The cured product obtained was crushed into small pieces, and the Tg was measured by a differential scanning calorimeter (DSC), which was 165° C., indicating good heat resistance.

Example 3
[Synthesis of epoxy resin]
5 g of the paracoumaric acid dimer obtained in Synthesis Example 1, 56.4 g of epichlorohydrin (10 equivalents relative to the paracoumaric acid dimer), and 1 g of tetrabutylammonium bromide were reacted at 100° C. for 5 hours. After the reaction was completed, 2.5 ml of a 40% by mass aqueous sodium hydroxide solution was dropped while cooling the solution on ice, and then the reaction was carried out in ice-cold water for 1 hour. 20 ml of ion-exchanged water was added to the solution after the reaction to dissolve the precipitated salt, and then 30 ml of ethyl acetate was added and mixed well to separate the aqueous phase. Anhydrous magnesium sulfate was added to the obtained organic phase for dehydration, and then ethyl acetate and remaining volatiles were removed to obtain 5.42 g of the desired epoxy resin (yield 63.3%). The structure was identified by ¹ H-NMR measurement in deuterated DMSO, and it was confirmed that the desired epoxy resin was synthesized. The reaction formula in Example 3 is shown below.

[Preparation of epoxy cured body]
Example 4
5.52 g of the epoxy resin obtained in Example 3 was mixed with 1.70 g of isophorone diamine. The mixture was then heated at 100°C for 1 hour, at 160°C for 1 hour, and then at 200°C for 1 hour to produce a cured product. The cured product was crushed into small pieces, and the Tg was measured by a differential scanning calorimeter (DSC), but no clear Tg was observed. Therefore, the product was measured by a dynamic viscoelasticity method (DMA), and the Tg was found to be 251°C from the peak top temperature of tan δ. Good heat resistance was observed.

Comparative Example 1
A petroleum-derived bisphenol A epoxy resin (product name "jER828", manufactured by Mitsubishi Chemical Corporation) was mixed with isophoronediamine as a curing agent in an epoxy group:NH group ratio of 1:1, and curing was carried out under the same conditions as in Examples 2 and 4 to produce a cured product. The resulting cured product was cut into small pieces, and the Tg was measured by a differential scanning calorimeter (DSC), resulting in a Tg of 152°C.

Claims (7)

An epoxy resin having a structure represented by the following formula (1-2).
In formula (1-2), ^R1 and ^R3 are each independently a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom, or a glycidyl group, and ^R2 is a divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom. n is an integer of 0 to 100. G represents a glycidyl group. 2. The epoxy resin according to claim 1, wherein ^R1 and ^R3 are glycidyl groups and n is 0. 2. The epoxy resin according to claim 1, wherein R ¹ and R ³ are alkyl groups having 1 to 6 carbon atoms, and n is 0. The epoxy resin according to claim 3, wherein ^R1 and ^R3 are methyl groups. The epoxy resin according to any one of claims 1 to 4, wherein the epoxy resin is made from dihydroxytruxillic acid as a raw material compound, and the dihydroxytruxillic acid is derived from biomass. A cured product obtained by curing the epoxy resin according to any one of claims 1 to 4. A method for producing an epoxy resin, comprising reacting a compound represented by the following formula (2-2) with epihalohydrin to obtain an epoxy resin:
In the above formula (2-2), R ¹¹ and R ¹³ are each independently a hydrogen atom or a monovalent hydrocarbon group having 1 to 20 carbon atoms which may have a heteroatom. R ¹² is a divalent hydrocarbon group having 2 to 20 carbon atoms which may have a heteroatom. m is an integer of 0 to 100.

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