Resin containing an aromatic lactone, method for producing the same, and curable resin composition

Abstract

The present application provides an aromatic lactone-containing resin represented by the following general formula (1). In the formula, R1, R2, and R3 each independently represent an alkyl group having 1 to 8 carbon atoms, X represents -CH2-, or a hydrocarbon group having 8 to 24 carbon atoms containing an aromatic ring and an alkylene group, a hydrogen atom of the hydrocarbon group can be substituted with a hydroxyl group, a represents an integer of 0 to 3, b represents an integer of 0 to 2, c represents an integer of 0 to 3, and n represents an integer of 0 to 10.

Description

Technical Field

[0001] This invention relates to resins containing aromatic lactones, curable resin compositions containing the same, and methods for manufacturing resins containing aromatic lactones. Background Technology

[0002] Previously, for semiconductor device sealing materials, from a reliability perspective, excellent heat resistance under operating temperature conditions was required. As raw materials for semiconductor devices, Si-based raw materials were the mainstream, using cured resin compositions containing corresponding epoxy resins as the main component. In recent years, SiC and GaN have gained attention, leading to increased usage. Along with this, the required operating temperature for semiconductor sealing materials has increased significantly from approximately below 200°C to above 250°C. However, sealing materials for semiconductor devices manufactured using Si-based raw materials do not meet the heat resistance requirements for sealing materials used in semiconductor devices manufactured using SiC and GaN. Therefore, resin compositions that can produce sealing materials with high heat resistance are being researched and developed. For example, Patent Document 1 discloses a sealing resin composition for use in high-temperature environments, employing SiC and GaN, which contains maleimide resin, benzoxazine resin, and inorganic filler having specific chemical structures. It is believed that the benzoxazine resin functions as a curing agent in this sealing resin composition. This document describes how, by using benzoxazine resin, a sealing material with improved mechanical properties and excellent temperature cycling reliability can be provided without reducing the heat resistance of the sealing material.

[0003] In addition, for sealing materials of semiconductor devices, in the past, from the perspective of reliability, sealing materials with excellent insulation and water resistance were required. For example, Patent Document 2 describes that the curable resin composition containing phenolic resin and melamine cyanurate has excellent resistance to tracking.

[0004] Furthermore, Patent Document 3 discloses an epoxy resin composition containing an epoxy resin, a 6-membered lactone fused to an aromatic or heteroaromatic backbone, and a curing accelerator. This document states that the epoxy resin composition described herein can provide cured epoxy resin products with low curing shrinkage and high elastic modulus.

[0005] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2018-115233 Patent Document 2: Japanese Patent Application Publication No. 2021-105168 Patent Document 3: Japanese Patent Application Publication No. 2013-032510 Summary of the Invention

[0006] As described in Patent Document 1, the resin composition containing benzoxazine resin has a high crosslinking density matrix in the cured product due to its curing mechanism, resulting in a hard and brittle cured product. As a result, sealing materials manufactured using the sealing resin composition described in Patent Document 1, even if they have a certain degree of high heat resistance, are not sufficiently tough. In addition, as described in Patent Document 2, if it is desired to improve the resistance to tracking in phenolic resins, it is sometimes necessary to adopt special methods such as adding melamine cyanurate.

[0007] On the other hand, Patent Document 3 makes no research whatsoever on cured materials that combine high heat resistance and toughness, or cured materials that are resistant to tracking and have excellent water resistance.

[0008] Therefore, the object of the present invention is to provide compounds that yield cured products with the following characteristics: a cured product exhibiting reactivity with epoxy resin, high heat resistance, and excellent toughness; or a cured product exhibiting high resistance to tracking and high water resistance. Furthermore, the object of the present invention is to provide curable resin compositions that yield cured products with high heat resistance and excellent toughness; or curable resin compositions that yield cured products with high resistance to tracking and high water resistance. Moreover, an object of the present invention is to provide a method for manufacturing resins containing aromatic lactones, which enables the industrially advantageous manufacture of the aforementioned aromatic lactone-containing resins.

[0009] The inventors conducted in-depth research and found that the above-mentioned problems could be solved by using a resin containing aromatic lactones with a specific chemical structure, thus completing the present invention.

[0010] That is, the present invention provides the following [1] to [9]. [1] A resin containing aromatic lactones, represented by the following general formula (1).

[0011]

[0012] In the formula, R1, R2 and R3 each independently represent an alkyl group with 1 to 8 carbon atoms, X represents -CH2-, or a hydrocarbon group with 8 to 24 carbon atoms containing an aromatic ring and an alkylene group, the hydrogen atom of which may be replaced by a hydroxyl group, a represents an integer from 0 to 3, b represents an integer from 0 to 2, c represents an integer from 0 to 3, and n represents an integer from 0 to 10. [2] The resin containing aromatic lactones according to [1] is represented by the following formula (2).

[0013]

[0014] In the formula, n represents an integer from 0 to 10.

[0015] [3] A curable resin composition comprising the aromatic lactone-containing resin described in [1] or [2], an epoxy resin, and a curing accelerator.

[0016] [4] The curable resin composition according to [3] further contains a maleimide compound comprising at least two maleimide groups in one molecule.

[0017] [5] The curable resin composition according to [3] or [4] further contains inorganic filler material.

[0018] [6] A semiconductor sealing material formed from any one of the curable resin compositions described in [3] to [5].

[0019] [7] A cured product, which is obtained by heating and curing any one of the curable resin compositions described in [3] to [5].

[0020] [8] A semiconductor device having the cured material described in [7].

[0021] The method for manufacturing the resin containing aromatic lactones as described in [9], [1] or [2] includes a step of reacting an aromatic lactone monomer represented by the following general formula (3) with a crosslinking agent in the presence of an acid catalyst.

[0022]

[0023] In the formula, R represents an alkyl group with 1 to 8 carbon atoms, and d represents an integer from 0 to 3. Detailed Implementation

[0024] The embodiments of the present invention will now be described in detail. As described above, the aromatic lactone-containing resin of the present invention can provide a curable resin composition that yields a cured product with excellent heat resistance, toughness, temperature cycling reliability and durability, or a cured product with excellent resistance to tracking and water resistance.

[0025] When the aromatic lactone-containing resin of the present invention reacts with epoxy resin, the lactone ring opens and reacts, resulting in alkylene chains such as ethylene chains or ether groups, which easily lead to the curing of the product with flexibility. Furthermore, the aromatic lactone-containing resin of the present invention undergoes anionic copolymerization through reaction with epoxy resin, easily generating a cured product with high crosslinking density, thus easily improving heat resistance, especially through reaction with epoxy resin and maleimide compounds. For these reasons, using the aromatic lactone-containing resin of the present invention readily yields both toughness and heat resistance. It should be noted that, in this specification, "excellent toughness" includes high flexibility of the cured product or excellent flexural strength. Additionally, examples of high heat resistance in this specification include a high glass transition temperature and a low coefficient of linear expansion at high temperatures (e.g., 260–280°C). Furthermore, the aromatic lactone-containing resins disclosed in this specification provide cured products with excellent heat resistance, toughness, and low elasticity at high temperatures. These cured products also exhibit superior temperature cycling reliability.

[0026] Furthermore, the chain structure with ether groups and alkylene chains generated by the ring-opening of the aromatic lactone-containing resin of the present invention when reacting with epoxy resin can easily sever the carbonization conduction pathway, thereby improving the resistance to tracking. Furthermore, compared to phenolic resins, the aromatic lactone-containing resins of the present invention readily produce cured products with excellent water resistance. This is because, when phenolic resins react with epoxy groups, the cured product has secondary hydroxyl groups, but theoretically, the reaction product of the aromatic lactone-containing resins of the present invention with epoxy groups will not produce hydroxyl groups. For these reasons, if the aromatic lactone-containing resins of the present invention are used, the cured product obtained from the reaction with epoxy resins readily possesses both resistance to tracking and water resistance.

[0027] Furthermore, the aromatic lactone-containing resins of the present invention readily possess both tracking resistance and flame retardancy. Specifically, as described above, the aromatic lactone-containing resins of the present invention readily improve tracking resistance; on the other hand, the open-ring structure of the aromatic lactone-containing resins has an aromatic ring, thus easily ensuring the char residue required for flame retardancy. Particularly in the present invention, when X has an aromatic group, particularly a biphenyl structure, flame retardancy is particularly easily improved.

[0028] The above describes the mechanisms hypothesized in this invention, but this invention is not limited to these mechanisms.

[0029] (Resins containing aromatic lactones) First, the aromatic lactone-containing resin of the present invention will be described. The aromatic lactone-containing resin of the present invention has a structure represented by the following general formula (1).

[0030]

[0031] In the formula, R1, R2 and R3 each independently represent an alkyl group with 1 to 8 carbon atoms, X represents -CH2-, or a hydrocarbon group with 8 to 24 carbon atoms containing an aromatic ring and an alkylene group, the hydrogen atom of which may be replaced by a hydroxyl group, a represents an integer from 0 to 3, b represents an integer from 0 to 2, c represents an integer from 0 to 3, and n represents an integer from 0 to 10.

[0032] In general formula (1), the alkyl groups represented by R1, R2, and R3, having 1 to 8 carbon atoms, can be either straight-chain or branched. Examples of straight-chain alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, and octyl. Examples of branched alkyl groups include isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, tert-pentyl, isooctyl, 2-ethylhexyl, and tert-octyl.

[0033] In this invention, the hydrocarbon group represented by X, comprising an aromatic ring and an alkylene ring with 8 to 24 carbon atoms, can be exemplified by the hydrocarbon group represented by the following formula (a). It should be noted that the number of carbon atoms 8 to 24 refers to the number of carbon atoms comprising both the alkylene ring and the aromatic ring.

[0034] -BAB- (a) In the formula, A represents arylene or phenylalkylene. B represents a directly bonded or alkylene group with 1 to 4 carbon atoms. The two Bs can be the same or different. When A is an arylene, B represents an alkylene group with 1 to 4 carbon atoms.

[0035] In general formula (a), the alkylene group represented by B, which has 1 to 4 carbon atoms, can be either linear or branched. Examples of linear alkylene groups include methylene, ethylene, propylene, and butylene. Examples of branched alkylene groups include isopropylene, isobutylene, secondary butylene, and tert-butylene.

[0036] In general formula (a), the arylene group represented by A can contain either a monocyclic aromatic ring or a fused-ring aromatic ring. Examples of arylene groups containing a monocyclic aromatic ring include: phenylene; biphenylene; methylene diphenylene, ethyl diphenylene, propylene diphenylene, monomethyl methylene diphenylene, and dimethyl methylene diphenylene, etc. Examples of arylene groups containing a fused-ring aromatic ring include: naphthylene, binatylene, anthraceneylene, and phenanthrene.

[0037] Examples of phenyl alkylene groups include phenylmethylene (1-phenylmethane-1,1-diyl, etc.), phenylethylene (1-phenylethane-1,1-diyl, etc.), phenylpropylene (1-phenylpropane-1,1-diyl, etc.), and phenylbutylene (1-phenylbutane-1,1-diyl, etc.).

[0038] X substitutes for the hydrogen atoms on the benzene ring in each dihydrocoumarin structure of formula (1) and bonds to the benzene ring. In addition, when a is 2 or more, multiple R1s can be the same or different. When b is 2 or more, multiple R2 values ​​can be the same or different. When c is 2 or higher, multiple R3s can be the same or different.

[0039] In this invention, from the viewpoint of the polymerizability of resins containing aromatic lactones, a and c in general formula (1) are each preferably integers from 0 to 2, more preferably integers from 0 to 1, and most preferably 0.

[0040] In this invention, from the viewpoint of the polymerizability of resins containing aromatic lactones, b in general formula (1) is preferably an integer from 0 to 1, and more preferably 0.

[0041] From the viewpoint of the polymerization of resins containing aromatic lactones, the steric hindrance of epoxy resins using resins containing aromatic lactones, or the polymerization of epoxy resins with maleimide compounds, the groups represented by R1, R2, and R3 in general formula (1) are each preferably alkyl groups having 1 to 8 carbon atoms, more preferably alkyl groups having 1 to 4 carbon atoms, and particularly preferably alkyl groups having 1 to 2 carbon atoms. It should be noted that the description in this specification such as "polymerization of epoxy resins or epoxy resins with maleimide compounds" naturally allows for the addition of other curing components to "epoxy resins or epoxy resins with maleimide compounds".

[0042] When the group represented by X in general formula (1) is a hydrocarbon group with 8 to 24 carbon atoms containing an aromatic ring and an alkylene group, from the viewpoints of material availability, curability, heat resistance of the cured product, low elasticity under heat, and low water absorption, B in general formula (a) is preferably a directly bonded or straight-chain alkylene group with 1 to 4 carbon atoms, more preferably a directly bonded or methylene group. From the same viewpoint, the aryl group represented by A in general formula (a) preferably contains an aromatic ring with a monocyclic structure, more preferably a phenylene, biphenylene, or phenylalkylene group.

[0043] As a specific example of a hydrocarbon group containing an aromatic ring and an alkylene group with 8 to 24 carbon atoms, represented by X in general formula (1), for example, the group represented by any of the following formulas (α) to (γ) can be cited.

[0044] In the formula, R 11 R 12 R 13 and R 15 Each can independently represent a hydroxyl group or an alkyl group having 1 to 5 carbon atoms. R14 This indicates an alkyl group with 1 to 5 carbon atoms or hydrogen atoms. n11, n12, and n13 each independently represent an integer from 0 to 4. n15 represents an integer from 0 to 5. L each independently represents an alkylene group with 1 to 4 carbon atoms.

[0045] From the perspectives of material availability and polymerizability of resins containing aromatic lactones, n11, n12, n13 and n15 are each preferably integers from 0 to 2, and particularly preferably 0. As R 11 R 12 R 13 R 14 and R 15 The alkyl group represented can be those that are the same as those represented by R1 in general formula (1). Considering the polymerization of resins containing aromatic lactones, the steric hindrance during the polymerization of epoxy resins using resins containing aromatic lactones, or the polymerization of epoxy resins with maleimide compounds, R 11 R 12 R 13 R 15 Each is preferably an alkyl group having 1 to 2 carbon atoms, and particularly preferably a methyl group. 14 Preferably, it is a hydrogen atom or a methyl group, particularly preferably a hydrogen atom. In (α), the methylene groups are preferably bonded to each other at the para position, and in (β), they are preferably bonded at the 4,4' position of the biphenyl. Examples of L and its preferred examples are the same as those of B described above.

[0046] From the viewpoint of ease of material availability and polymerizability of resins containing aromatic lactones, preferred examples of the groups represented by X above include the groups represented by (i) to (v) below.

[0047]

[0048] When X is -CH2- (formula (i)), the crosslinking density of the cured product obtained by curing epoxy resin or a combination of epoxy resin and maleimide compound will be higher, which is preferred from the perspective of heat resistance and other aspects.

[0049] Furthermore, considering factors such as heat resistance, low water absorption, and low elastic modulus at heat, X is preferably a hydrocarbon group containing an aromatic ring and an alkylene group with 8 to 24 carbon atoms. When X is a hydrocarbon group containing an aromatic ring and an alkylene group, X is preferably a group represented by any one of (α) to (γ), wherein, considering the combination of heat resistance, low water absorption, and low elastic modulus at heat, or considering the combination of flame retardancy, resistance to tracking, and water resistance, the group represented by (β) is preferred, and particularly, the group represented by (ii) or (iii) is most preferred.

[0050] In particular, as a particularly preferred embodiment of the aromatic lactone-containing resin of the present invention, an example of an aromatic lactone-containing resin represented by the following general formula (2) can be cited.

[0051]

[0052] In the formula, n represents an integer from 0 to 10.

[0053] From the viewpoint of operability in processing when preparing curable resin compositions such as resins containing aromatic lactones, epoxy resin compositions, and maleimide compositions, the softening point of the resin containing aromatic lactones of the present invention is preferably 50°C or higher, more preferably 55°C or higher, and even more preferably 60°C or higher. Furthermore, from the viewpoint of operability in the mixing process with inorganic fillers when preparing curable resin compositions such as epoxy resin compositions and maleimide compositions, the softening point of resins containing aromatic lactones is preferably 130°C or less, more preferably 120°C or less, and even more preferably 110°C or less. The softening point of resins containing aromatic lactones can be determined by the method described in the examples below.

[0054] From the viewpoint of the flowability of curable resin compositions such as epoxy resin compositions and maleimide compositions, the melt viscosity of the aromatic lactone-containing resin of the present invention at 150°C is preferably 2.0 Pa·s or less, more preferably 1.7 Pa·s or less, and particularly preferably 1.5 Pa·s or less. Furthermore, considering aspects such as overflow from the mold during molding, the melt viscosity of the aromatic lactone-containing resin at 150°C is preferably 0.01 Pa·s or more, more preferably 0.02 Pa·s or more. The melt viscosity of the aromatic lactone-containing resin can be determined by the method described in the examples below.

[0055] In this invention, considering factors such as suppressing the increase in softening point caused by the crystallinity of the resin containing aromatic lactones, it is preferable to contain a component in formula (1) where n is 1 or more (hereinafter also referred to as "a component with n=1 or more"). In the resin containing aromatic lactones represented by formula (1), the content of the component with n=1 or more is preferably 5% or more, more preferably 10% or more, particularly preferably 20% or more, especially preferably 30% or more, and even more preferably 40% or more. The content of the component with n=1 or less in the resin containing aromatic lactones represented by formula (1) is not limited, and is sometimes 99% or less, and sometimes 95% or less. For example, from an operational point of view, in a resin containing aromatic lactones, the content of the component with n=0 in formula (1) (hereinafter also referred to as "n=0 component") can be 0-90%, particularly 20-80%, of the resin containing aromatic lactones represented by formula (1), and the content of the component with n=1 in formula (1) (hereinafter also referred to as "n=1 component") can be 0-50%, particularly 10-40%, of the resin containing aromatic lactones represented by formula (1). These numerical ranges may satisfy only one, or any combination thereof, or only any upper or lower limit may be selected. In the resin A containing aromatic lactones obtained in Example 1 described later, the proportion of the n=0 component in the resin containing aromatic lactones represented by formula (1) is in the range of 20-80%, and the proportion of the n=1 component is in the range of 10-40%.

[0056] (Preferred manufacturing method for resins containing aromatic lactones) The aromatic lactone-containing resin of the present invention can preferably be synthesized, for example, by reacting an aromatic lactone monomer represented by the following general formula (3) with a crosslinking agent in the presence of an acid catalyst.

[0057]

[0058] In the formula, R represents an alkyl group with 1 to 8 carbon atoms, and d represents an integer from 0 to 3.

[0059] As for the alkyl group represented by R in general formula (3), there are those that are the same as the alkyl groups represented by R1 in general formula (1).

[0060] Considering the ease of obtaining materials and reactivity, d in general formula (3) is preferably an integer from 0 to 2, more preferably an integer from 0 to 1, and most preferably 0.

[0061] The crosslinking agent used in the synthesis of the aromatic lactone-containing resin of the present invention is not particularly limited, and can be arbitrarily selected from known crosslinking agents according to the desired structure of the aromatic lactone-containing resin. For example, X in formula (1) is -CH2- or represented by formula (γ) and R 14 Crosslinking agents that are hydrogen atoms include aldehydes such as formaldehyde, benzaldehyde, or hydroxybenzaldehyde. Additionally, as a crosslinking agent when X is represented by formula (α) or formula (β), examples include compounds in which alkoxy or halogen atoms (e.g., Y1 described later) are bonded to the two bonding sites (the two L bonding sites opposite to the benzene ring) in formula (α) or formula (β).

[0062] In this invention, as a crosslinking agent, compounds represented by general formula (4-1) or general formula (4-2) are preferably used, especially compounds represented by general formula (4-2), and even more preferably compounds represented by general formula (4A).

[0063]

[0064] In the formula R 11 n11 is the same as equation (α), R 12 R 13 n12 and n13 are the same as in formula (β). Y1 represents a halogen atom or an alkoxy group with 1 to 4 carbon atoms.

[0065]

[0066] In the formula, Y1 is the same as in formulas (4-1) and (4-2).

[0067] Examples of halogen atoms represented by Y1 in general formulas (4-1) and (4-2) include fluorine, chlorine, bromine, and iodine atoms. Examples of alkoxy groups with 1 to 4 carbon atoms represented by Y1 in general formulas (4-1) and (4-2) include methoxy, ethoxy, propoxy, and butoxy. In this invention, considering reactivity and ease of acquisition, the group represented by Y1 in general formulas (4-1) and (4-2) is preferably a chlorine atom or an alkoxy group with 1 to 3 carbon atoms, more preferably a methoxy group or a chlorine atom, and even more preferably a methoxy group.

[0068] When reacting the aromatic lactone monomer represented by general formula (3) with the crosslinking agent, the crosslinking agent is preferably set to 0.05 to 0.80 moles relative to 1 mole of aromatic lactone monomer, more preferably 0.10 to 0.70 moles, and even more preferably 0.20 to 0.60 moles. By setting the molar ratio of aromatic lactone monomer to crosslinking agent to the above range, the softening point and melt viscosity of the aromatic lactone-containing resin of the present invention can be set to a specified range.

[0069] As the acid catalyst used in the synthesis of the aromatic lactone-containing resin of the present invention, the polycondensation reaction can be carried out under an acidic catalyst. There are no particular limitations on the acid catalyst used in the polycondensation reaction; known acid catalysts such as hydrochloric acid, oxalic acid, sulfuric acid, phosphoric acid, and p-toluenesulfonic acid can be used alone or in combination of two or more. Preferably, at least one selected from p-toluenesulfonic acid, hydrochloric acid, sulfuric acid, and oxalic acid is used.

[0070] In the manufacturing process of resins containing aromatic lactones, solvents may or may not be used. Examples of solvents used include water and lower alcohols (aliphatic alcohols with 1 to 6 carbon atoms). Specific examples include methanol, ethanol, propanol, butanol, pentanol, hexanol, and cyclohexanol. When using a solvent, there is no particular limitation on the amount used; however, considering the cost of solvent removal and recovery, it is preferably 100% by mass or less relative to the aromatic lactone monomer, more preferably 50% by mass or less, and even more preferably less than 30% by mass.

[0071] The reaction temperature for the polycondensation reaction is not particularly limited, but is typically 50–200°C, preferably 70–180°C, and more preferably 80–170°C. If the temperature is above 50°C, the reaction can proceed easily; conversely, if the temperature is below 200°C, the reaction can be easily controlled, and the target aromatic lactone-containing resin of the present invention can be stably obtained.

[0072] The reaction time of polycondensation depends on the reaction temperature and is typically around 0.1 to 20 hours. Regarding the reaction pressure, polycondensation is usually carried out at atmospheric pressure, but it can also be carried out under pressure or depressurization.

[0073] The synthesis of resins containing aromatic lactones can be carried out in an inert gas atmosphere such as nitrogen and argon, or in an atmospheric atmosphere. In this invention, considering factors such as suppressing the oxidation of the products, it is preferable to carry out the synthesis in an inert gas atmosphere.

[0074] The aromatic lactone-containing resin of the present invention is suitable for use as a curing agent for epoxy resins. As shown in the examples described later, the curable resin composition of the present invention, containing an aromatic lactone-containing resin and an epoxy resin, can provide cured products with high heat resistance, excellent mechanical properties such as flexural strength, low elastic modulus at heat, and / or excellent resistance to tracking and water resistance.

[0075] Next, the curable resin composition of the present invention will be described. In addition to the resin containing aromatic lactones represented by the above general formula (1), the curable resin composition of the present invention also contains an epoxy resin and a curing accelerator.

[0076] The epoxy resin contained in the curable resin composition of the present invention has two or more epoxy groups in its molecule. In this invention, epoxy resins used in the technical field to which this invention pertains can be used without particular limitation. Specific examples of epoxy resins include: phenolic varnish-type epoxy resins, cresol phenolic varnish-type epoxy resins, biphenyl-type epoxy resins, triphenylmethane-type epoxy resins, phenol arylalkyl phenolic varnish-type epoxy resins, biphenyl arylalkyl-type epoxy resins, phenol-biphenyl arylalkyl-type epoxy resins, bisphenol A type epoxy resins, and bisphenol F type epoxy resins, as well as glycidyl ether type epoxy resins; glycidyl ester type epoxy resins; glycidyl amine type epoxy resins; and halogenated epoxy resins, etc. One of these epoxy resins can be used alone, or two or more can be used in combination. In this invention, from the viewpoint of the heat resistance and mechanical properties of the cured product, glycidyl ether type epoxy resin is preferred as the epoxy resin, epoxy resin having a structure obtained by reacting an aromatic compound with phenolic hydroxyl groups with epichlorohydrin is preferred, and biphenyl type epoxy resin or phenol-biphenyl aralkyl type epoxy resin is more preferred.

[0077] In the curable resin composition of the present invention, the resin containing aromatic lactones represented by general formula (1) functions as a curing agent as described above. In addition to the resin containing aromatic lactones represented by general formula (1), the curable resin composition of the present invention may also contain other curing agents. The types of other curing agents are not particularly limited, and various curing agents may be used depending on the intended use of the curable resin composition. Examples of other curing agents include phenolic resins, amine curing agents, amide curing agents, and anhydride curing agents.

[0078] From the viewpoint of fully improving the heat resistance and mechanical properties of the cured product, in the curable resin composition of the present invention, the proportion of the resin containing aromatic lactone represented by general formula (1) in the curing agent (e.g., epoxy resin curing agent) is preferably 30% by mass or more, more preferably 50% by mass or more, further preferably 70% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass.

[0079] In the curable resin composition of the present invention, which uses an aromatic lactone-containing resin as a curing agent and includes an epoxy resin, the ratio of the equivalent number of -OCO- groups of the lactone to the equivalent number of epoxy groups of the epoxy resin (equivalent number of -OCO- groups / equivalent number of epoxy groups) is preferably 0.3 or more and 3.0 or less, more preferably 0.4 or more and 1.5 or less.

[0080] As a curing accelerator contained in the curable resin composition of the present invention, known compounds used as curing accelerators in the technical field to which the present invention pertains can be used without particular limitation. Specific examples of curing accelerators include, for instance, known curing accelerators used for curing epoxy resins with phenolic resins. Examples include organophosphorus compounds and their borates, tertiary amines, quaternary ammonium salts, imidazoles, tetraphenylboranes, cycloamidiniums, and quaternary phosphonium salts. These curing accelerators can be used alone or in combination of two or more. The proportion of the curing accelerator added to the epoxy resin can be the same as that in known epoxy resin compositions, preferably 0.1 parts by mass or more and 25 parts by mass or less, more preferably 1 part by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the epoxy resin.

[0081] From the viewpoint of the heat resistance and mechanical properties of the cured product, the curable resin composition of the present invention may further contain maleimide compounds. In this invention, maleimide compounds used in the technical field to which this invention pertains may be used without particular limitation.

[0082] In this invention, as a maleimide compound, a compound containing at least two maleimide groups per molecule can be used. Examples of maleimide compounds containing at least two maleimide groups per molecule include the maleimide compound represented by general formula (5) and the maleimide compound represented by general formula (6).

[0083]

[0084] In the formula, Y is a divalent group with a carbon-carbon double bond as the main chain, and Z is a divalent group with 2 to 40 carbon atoms.

[0085]

[0086] In the formula, Y is a divalent group with a carbon-carbon double bond as the main chain, and s is 0 or a value above 0.

[0087] In general formulas (5) and (6), Y is preferably -CR 1 =CR 2 -(R 1 and R 2 Each can independently represent a hydrogen atom or a hydrocarbon group having 1 to 5 carbon atoms. In addition, in general formula (5), Z can be a cyclic aliphatic hydrocarbon group, a straight-chain aliphatic hydrocarbon group, a branched aliphatic hydrocarbon group, an aromatic hydrocarbon group or a heterocyclic group, or a group composed of two or more of them. In general formula (5), s is preferably 0 or more and 4 or less, and more preferably 0 or more and 2 or less.

[0088] As a maleimide compound containing at least two maleimide groups in one molecule, for example, an aromatic maleimide compound having two or more maleimide groups in one molecule, and an aliphatic maleimide compound having two or more maleimide groups in one molecule can be used.

[0089] The aforementioned aromatic maleimide compounds are maleimide compounds having one or more aromatic rings in their skeleton. Specific examples of aromatic maleimide compounds include N,N'-p-phenylene bismaleimide, N,N'-m-phenylene bismaleimide, N,N'-2,4-toluene bismaleimide, N,N'-2,6-toluene bismaleimide, N,N'-4,4-diphenylmethane bismaleimide, N,N'-3,3-diphenylmethane bismaleimide, N,N'-4,4-diphenyl ether bismaleimide, N,N'-3,3-diphenyl ether bismaleimide, and N,N'-4,4-diphenyl sulfide bismaleimide. Imide, N,N'-3,3-diphenyl sulfide bismaleimide, N,N'-4,4-diphenyl sulfone bismaleimide, N,N'-3,3-diphenyl sulfone bismaleimide, N,N'-4,4-diphenyl ketone bismaleimide, N,N'-3,3-diphenyl ketone bismaleimide, N,N'-4,4-biphenyl bismaleimide, N,N'-3,3-biphenyl bismaleimide, N,N'-4,4-diphenyl-1,1-propane bismaleimide, N,N'-3,3-diphenyl-1,1-propane bismaleimide, 3 3'-Dimethyl-N,N'-4,4-diphenylmethane bismaleimide, 3,3'-Dimethyl-N,N'-4,4'-biphenyl bismaleimide, 1,3-bis(3-maleimidephenoxy)benzene, bis[4-(3-maleimidephenoxy)phenyl]methane, 1,1-bis[4-(3-maleimidephenoxy)phenyl]ethane, 1,2-bis[4-(3-maleimidephenoxy)phenyl]ethane, 2,2-bis[4-(3-maleimidephenoxy)phenyl]propane, 2,2-bis[4-(4-maleimidephenoxy)phenyl]propane, [4,2-(3-maleimidephenoxy)phenyl]propane, 2,2-bis[4-(3-maleimidephenoxy)phenyl]butane, 2,2-bis[4-(3-maleimidephenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 4,4'-bis(3-maleimidephenoxy)biphenyl, bis[4-(3-maleimidephenoxy)phenyl]ketone, bis[4-(3-maleimidephenoxy)phenyl]sulfoxide, bis[4-(3-maleimidephenoxy)phenyl]sulfone, bis[4-(3-maleimidephenoxy)phenyl]ether, and polyphenylmethane maleimide.

[0090] The aforementioned aliphatic maleimide compounds refer to maleimide compounds that have an aliphatic structure in their backbone. Aliphatic maleimide compounds may or may not have an aliphatic cyclic structure in their backbone. Examples of aliphatic maleimide compounds that do not have an aliphatic chain structure on their skeleton include 1,6-bismaleimide-(2,2,4-trimethyl)hexane, 1,6-bismaleimide-(2,4,4-trimethyl)hexane, N,N'-decamethylenebismaleimide, N,N'-octamethylenebismaleimide, N,N'-hexamethylenebismaleimide, N,N'-trimethylenebismaleimide, N,N'-ethylidenebismaleimide, hexamethylenediaminebismaleimide, N,N'-1,2-ethylidenebismaleimide, N,N'-1,3-propylidenebismaleimide, and N,N'-1,4-tetramethylenebismaleimide. Examples of aliphatic maleimide compounds with an aliphatic cyclic structure on their skeleton include bis[(2,5-dioxo-2,5-dihydropyrrole-1-yl)methyl]bicyclo[2,2,1]heptane.

[0091] In this invention, one of the above-mentioned maleimide compounds can be used alone, or two or more can be used in combination.

[0092] In this invention, aromatic maleimide compounds are preferably used as maleimide compounds containing at least two maleimide groups per molecule.

[0093] The amount of maleimide compound in the curable resin composition of the present invention may be less than 100 parts by weight or less than 50 parts by weight relative to 100 parts by weight of epoxy resin. From the viewpoint of obtaining a cured product with higher heat resistance and better mechanical properties such as flexural strength, the content of maleimide compound is preferably 100 to 600 parts by weight relative to 100 parts by weight of epoxy resin, and more preferably 200 to 500 parts by weight.

[0094] From the viewpoint of the heat resistance and mechanical properties of the cured product, the curable resin composition of the present invention preferably contains an inorganic filler. In the present invention, inorganic fillers used in the technical field to which this invention pertains can be used without particular limitation. Specific examples of inorganic fillers include silica such as amorphous silica and crystalline silica, alumina, calcium silicate, calcium carbonate, talc, mica, barium sulfate, and magnesium oxide.

[0095] From the viewpoint of the heat resistance and mechanical properties of the cured product, the content of inorganic filler in the curable resin composition of the present invention is preferably 60-95% by mass, more preferably 65-95% by mass. The content of inorganic filler is calculated by the following formula.

[0096] The content of inorganic filler material = [mass of inorganic filler material in the curing resin composition / mass of the curing resin composition × 100]

[0097] The curable resin composition of the present invention may contain solvents and other additives used in the technical field to which this invention pertains. Examples of other additives include mold release agents, colorants, coupling agents, and flame retardants.

[0098] The shape of the curable resin composition of the present invention is not particularly limited, and can be set to a specified shape such as powder, granules, or ingots. In the present invention, granules refer to an aggregate formed by fixing powdered curable resin composition powder together. Ingots refer to a molded body with a specified shape by pressing the curable resin composition under high pressure.

[0099] The curable resin composition of the present invention can be obtained by melting and mixing an aromatic lactone-containing resin, epoxy resin, and curing accelerator represented by the above general formula (1), as needed, using a mixing device such as a biaxial kneader or a twin-roller. The obtained curable resin composition is then suitably pulverized using a pulverizer.

[0100] The uses of the curable resin composition of the present invention are not particularly limited; for example, it can be suitable for use as a semiconductor sealing material. The cured product of the curable resin composition of the present invention has high heat resistance and mechanical properties. Therefore, in addition to its good mechanical properties, it is particularly suitable as a semiconductor sealing material for semiconductor devices manufactured using SiC or GaN that require high heat resistance.

[0101] A cured product can be obtained by heating the curable resin composition of the present invention to cure it (heat curing). There are no particular limitations on the curing method and conditions of the curable resin composition; curing methods and conditions employed in the technical field to which this invention pertains can be used. For example, the curable resin composition of the present invention can be cured by heat treatment at 100°C to 350°C for 0.01 to 20 hours. By setting the heating temperature to 100°C or higher, the curable resin composition can be cured easily, and by setting it to 350°C or lower, performance degradation due to thermal decomposition can be prevented. In addition, by setting the heating time to 0.01 hours or higher, the reaction can be easily completed, and by setting it to 20 hours or lower, productivity can be improved.

[0102] The cured product of the curable resin composition of the present invention is suitable for use as a sealing material for semiconductor devices. Specifically, in a semiconductor device having a substrate, a semiconductor element mounted on the substrate, and a sealing material for sealing the semiconductor element, the sealing material is composed of the cured product of the curable resin composition of the present invention. As semiconductor elements, in addition to SiC elements such as power chips like IGBTs (Insulated Gate Bipolar Transistors) or diode chips, examples include Si elements, GaN elements, Ga2O3 elements, diamond elements, ZnO elements, etc. Regarding the sealing material of the present invention, even when using SiC elements, GaN elements, Ga2O3 elements, diamond elements, etc., in high-temperature environments above 200°C or 250°C, it exhibits excellent temperature cycling reliability and durability for long-term use due to its heat resistance, toughness, and low elastic modulus at high temperatures.

[0103] The present invention will be further described in detail below through embodiments. However, the present invention is not limited to these embodiments in any way.

[0104] [Example 1] Synthesis of Resins Containing Aromatic Lactones In a 1000 mL glass flask equipped with a thermometer, feed / distillation outlet, cooler, and stirrer, 296 g (2.0 mol) of 3,4-dihydrocoumarin and 121 g (0.5 mol) of 4,4'-dimethoxymethylbiphenyl were added as raw materials. The mixture was heated to 50 °C under a nitrogen atmosphere to dissolve the raw materials. 5.9 g of p-toluenesulfonic acid was added as an acid catalyst, and the reaction was carried out at 130 °C for 7 hours, followed by a further reaction at 165 °C for 7 hours to obtain the reaction product. The reaction product was washed with water, heated to 165 °C, and subjected to reduced pressure treatment to obtain resin A containing aromatic lactones. Resin A containing aromatic lactones has a softening point of 102 °C, a melt viscosity of 1.5 Pa·s at 150 °C, and a content of components with n=1 or higher of 50%.

[0105] [Determination of softening point] Use the following equipment to determine the softening point. Equipment used: FP83HT dropping point and softening point measuring system, manufactured by Mettler-Toledo Corporation. Measurement conditions: Heating rate 2℃ / min Measurement method: Molten sample is injected into a sample cup and allowed to harden. A cartridge is placed over the upper and lower parts of the sample cup containing the sample and inserted into a furnace. After the resin softens, it flows down from the orifice. The temperature of the lower end as it passes through the optical path is detected by a photoelectric unit and used as the softening point (°C).

[0106] [Determination of melt viscosity] The melt viscosity (Pa·s) at 150°C was determined using the following equipment. Equipment used: BROOKFIELD Type B viscometer "DV2T" by Yinghong Precision Machinery Co., Ltd. Measurement temperature: 150℃ Test method: Set the furnace temperature of the B-type viscometer to 150℃ and weigh the specified amount of sample in the cup. Place the weighed sample cup into the furnace to melt the resin, then insert the rotor from the top. Rotate the rotor until the displayed viscosity value stabilizes, then read that value as the melt viscosity.

[0107] [Content percentage of components with n=1 or higher] The molecular weight distribution of resins containing aromatic lactones was determined using a gel permeation chromatography (GPC) analyzer. The percentage of components with more than one trimer (n=1) was calculated as the ratio of the area of ​​each component to the total area of ​​the resin containing aromatic lactones. The area of ​​each component is calculated as follows: using the straight line portion before and after the peak of the resin containing aromatic lactones as the baseline, the peaks are separated by vertical cutting at the lowest point between each component peak. The instruments and conditions used in the measurement are shown below. Equipment used: Waters Alliance 2695 Column: SHODEX KF-804 × 1 piece KF-803 × 1 piece KF-802 × 1 piece KF-802.5×1 piece KF-801 x 1 piece Protective pillar: SHODEX KF-G Solution: Tetrahydrofuran (THF) Detector: UV-Visible Detector 2489 Detection wavelength: 254nm Flow rate: 1 mL / min. Column oven temperature: 40℃ Injection volume: 100 μL Sample concentration: 0.1 mg / mL Analysis software: Empower3 (manufactured by Waters)

[0108] [Examples 2-4 and Comparative Example 1] <Preparation of Curable Resin Compositions 1> The components shown in Table 1 were combined in the proportions shown in Table 1 to obtain a mixture. The resulting mixture was then subjected to two-roll milling at 80°C to 100°C, followed by pulverization to obtain the curable resin compositions of Examples 2-4 and Comparative Example 1. The components in Table 1 are as follows. The values ​​in Table 1 represent parts by mass.

[0109] • Resin A containing aromatic lactones: Resin A containing aromatic lactones synthesized in Example 1 ·Benzoxazine Resin A': Pd-type benzoxazine (manufactured by Shikoku Chemical Industry Co., Ltd.) • Epoxy Resin B-1: Polyphenol-modified biphenyl aralkyl type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., "NC-3500", epoxy equivalent: 205g / eq) • Epoxy Resin B-2: Biphenyl-type epoxy resin (Mitsubishi Chemical Corporation "YX-4000", epoxy equivalent: 185g / eq) • Maleimide compound C-1: The compound represented by the following formula (C-1) (manufactured by Yamato Chemical Co., Ltd., "BMI-4000") • Maleimide compound C-2: The compound represented by the following formula (C-2) (manufactured by Yamato Chemical Co., Ltd., "BMI-2300") • Curing accelerator D (curing catalyst): 2-methylimidazole (manufactured by Shikoku Chemical Industry Co., Ltd., "2MZ-H") • Inorganic filler material E: Silica (manufactured by DENKA Corporation, "FB-950")

[0110]

[0111]

[0112] Table 1

[0113] <Evaluation> Ingots were prepared using the curable resin compositions obtained in the examples and comparative examples. Test pieces were prepared by injecting the ingots, which were made under conditions of a mold temperature of 175°C, an injection pressure of 6.8 MPa, and a holding time of 600 seconds, using a low-pressure transfer molding machine. The test pieces were then post-cured at 180°C for 8 hours to produce EMC (Epoxy Molding Compound) test pieces. The thermal and mechanical properties of the prepared EMC test pieces were evaluated through the following tests.

[0114] <Mechanical Property Evaluation> The EMC test specimens were machined into a shape of 2 mm thickness × 25 mm width × 40 mm length to serve as samples. The stress, strain, and modulus of elasticity of the samples were determined using a universal testing machine with a thermostatic bath (manufactured by A&D) under the following conditions. The results are shown in Table 2. (Measurement conditions) Test speed: 2 mm / min; Distance between pivots: 60mm Temperature: 23℃

[0115] <Thermal Properties Evaluation> The storage modulus, glass transition temperature, and coefficients of linear expansion (α1, α2) of the EMC test specimens were determined using the following methods. The results are shown in Table 2.

[0116] (1) Glass transition temperature (Tg(DMA)) and storage modulus The EMC test piece was cut into 40mm × 2mm × 4mm pieces as the test specimen. The dynamic viscoelasticity (DMA) measurement was performed using a TA Instruments "RSA-G2" apparatus. Under air atmosphere, the storage modulus was measured while heating from 30℃ at a rate of 3℃ / min, and the storage modulus at 30℃ and 330℃ was determined. Furthermore, the peak temperature of Tanδ was set as Tg(DMA).

[0117] (2) Glass transition temperature (Tg(TMA)) and coefficients of linear expansion (α1, α2) The EMC test piece was cut into 10mm × 6mm × 4mm pieces as the test specimen. Using a thermomechanical analysis apparatus (Shimadzu Corporation "TMA-60"), under a nitrogen atmosphere, the glass transition temperature Tg (TMA) and the coefficients of linear expansion (α1, α2) of the specimen were measured while heating from 30℃ at a rate of 3℃ / min. The coefficient of linear expansion from 60℃ to 100℃ was defined as α1, and the coefficient of linear expansion from 260℃ to 280℃ was defined as α2.

[0118] Table 2

[0119] As shown in Table 2, the cured resin compositions of Examples 2-4, which use the aromatic lactone-containing resin of the present invention, exhibit a lower coefficient of linear expansion at 260-280°C than the resin containing benzoxazine, while having the same glass transition temperature, demonstrating high heat resistance. Furthermore, the cured compositions of Examples 2-4 show superior flexural strength compared to Comparative Example 1. Additionally, the strain of the cured compositions of Examples 2-4 is as small as that of Comparative Example 1. Moreover, the cured compositions of Examples 2-4 also exhibit excellent low modulus of elasticity at 330°C. As described above, the aromatic lactone-containing resin of the present invention can provide a semiconductor sealing material with excellent heat resistance, toughness, low elasticity at high temperatures, and high reliability even when used at high temperatures.

[0120] [Examples 5-6 and Comparative Examples 2-3] <Preparation of Curable Resin Compositions 2> The components shown in Table 3 were combined in the proportions shown in Table 3 to obtain a mixture. The obtained mixture was then subjected to two-roll milling at 30°C to 80°C, followed by pulverization to obtain the curable resin compositions of Examples 5-6 and Comparative Examples 2-3. The components in Table 3 are as follows. The values ​​in Table 3 represent parts by mass.

[0121] • Resin A containing aromatic lactones: Resin A containing aromatic lactones synthesized in Example 1 • Phenolic resin A”: The biphenyl aralkyl type phenolic resin represented by the following formula (A”) (hydroxyl equivalent: 134 g / eq, weight average molecular weight (Mw): 1350) (In the formula, n is any number that achieves the above Mw, and p', q', and r' are each an independent integer of 0 or 1.) • Phenolic resin A”’: The triphenylmethane-type phenolic resin represented by the following formula (A”’) (hydroxyl equivalent: 98 g / eq, weight-average molecular weight (Mw): 680) (In the formula, n is any number that achieves the above Mw.) • Epoxy Resin B-1: Polyphenol-modified biphenyl aralkyl type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., "NC-3500", epoxy equivalent: 205g / eq) • Epoxy Resin B-3: Triphenolmethane type epoxy resin (manufactured by Nippon Kayaku Co., Ltd., "EPPN-501H", epoxy equivalent: 166g / eq) • Curing accelerator D-2: Manufactured by Hokuko Chemical Industry Co., Ltd. ("TPP")

[0122] Table 3

[0123] <Evaluation> Ingots were prepared using the curable resin compositions obtained in the examples and comparative examples. Test pieces were prepared by injecting the ingots, which were made at a mold temperature of 175°C, an injection pressure of 6.8 MPa, and a holding time of 120 seconds, using a low-pressure transfer molding machine. The test pieces were then post-cured at 180°C for 8 hours to prepare EMC (Epoxy Molding Compound) test pieces. The prepared EMC test pieces were evaluated using the methods described above through the following tests.

[0124] <Flame Retardant Evaluation> (i) flammability The following EMC test pieces of the specified dimensions are used as the basis for judgment according to UL-94. Test piece size: 127mm × 13mm × 1mm

[0125] <Electrical Characteristics Evaluation> (ii) Tracking resistance index (compared to tracking index (CTI)) The EMC test pieces of the following dimensions were used as the test subjects, and the measurements were performed in accordance with JIS C 2134. Test piece size: 19mm×19mm×4mm Test electrode: Platinum (30° tip) Electrode configuration: 4.0mm ± 0.1mm (opposite angle 60°) Electrolyte: Solution A (NH4Cl) 0.1%±0.002%, resistivity: 3.95Ω·m±0.05Ω·m Experimental conditions: 50 drops confirm n=5, 100 drops confirm n=5 Test environment: 23℃±2℃, 50%RH±5%RH Testing apparatus: HAT-112-3 Tracking Resistance Tester (manufactured by YAMAYO Testing Machine)

[0126] <Evaluation of Physical Properties> (iii) Water resistance Using test pieces of the following dimensions as the subjects, the water absorption rate (%) was determined by the following method. Test piece dimensions: 50mm diameter × 3mm thickness Test conditions: The test piece was immersed in pure water and heated at 95°C for 24 hours. The water absorption rate is calculated using the following formula based on the change in mass of the test piece before and after water absorption. Water absorption rate (%) = (W1 - W0) / W0 × 100 W0: Mass of the test piece before water absorption (g) W1: Mass of the test piece after water absorption (g)

[0127] Table 4

[0128] As shown in Table 4, the cured resin compositions of Examples 5-6, which used the aromatic lactone-containing resin of the present invention, exhibited excellent resistance to tracking, water resistance, and flame retardancy. On the other hand, the cured compositions of Comparative Examples 2 and 3, which used phenolic resin, showed poor resistance to tracking and water resistance, and the cured composition of Comparative Example 3 also exhibited poor flame retardancy. In particular, it has been difficult for cured products using phenolic resins to combine tracking resistance and flame retardancy. However, the cured products of the curable resin compositions of Examples 5-6 using the aromatic lactone-containing resin of the present invention exhibit excellent tracking resistance and combine tracking resistance and flame retardancy even without special methods such as adding melamine cyanurate. Industrial availability

[0129] The aromatic lactone-containing resins of the present invention provide curable resin compositions that yield cured products with excellent mechanical properties such as high heat resistance and toughness, or excellent resistance to tracking and water resistance. Sealing materials using the curable resin compositions of the present invention exhibit excellent temperature cycling reliability and long-term durability under high-temperature environments, or excellent insulation properties and water resistance.

Claims

1. A resin containing an aromatic lactone, represented by the following general formula (1), In the formula, R1, R2, and R3 each independently represent an alkyl group having 1 to 8 carbon atoms. X represents -CH2-, or a hydrocarbon group with 8 to 24 carbon atoms containing an aromatic ring and an alkylene group, wherein the hydrogen atoms of the hydrocarbon group can be replaced by hydroxyl groups. a represents an integer from 0 to 3. b represents an integer from 0 to 2. c represents an integer from 0 to 3. n represents an integer from 0 to 10.

2. The resin containing aromatic lactones according to claim 1, which is represented by the following formula (2), In the formula, n represents an integer from 0 to 10.

3. A curable resin composition comprising the resin containing aromatic lactones as described in claim 1, an epoxy resin, and a curing accelerator.

4. The curable resin composition according to claim 3, further comprising a maleimide compound containing at least two maleimide groups in one molecule.

5. The curable resin composition according to claim 3 or 4, further comprising an inorganic filler.

6. A semiconductor sealing material formed from the curable resin composition of claim 3 or 4.

7. A cured product obtained by heating and curing the curable resin composition of claim 3 or 4.

8. A semiconductor device having the cured material of claim 7.

9. A method for manufacturing the resin containing aromatic lactones according to claim 1, comprising the step of reacting an aromatic lactone monomer represented by the following general formula (3) with a crosslinking agent in the presence of an acid catalyst. In the formula, R represents an alkyl group with 1 to 8 carbon atoms, and d represents an integer from 0 to 3.

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