JP7748607B2 - Thermally cationically polymerizable composition, its uses, cationic polymerization method using the same, and stabilizer for thermally cationically polymerizable composition - Google Patents

Description

The present invention relates to a thermally cationically polymerizable composition in which cationic polymerization proceeds upon heating, and uses thereof. It also relates to a cationic polymerization method using the thermally cationically polymerizable composition. Furthermore, it relates to a stabilizer for the thermally cationically polymerizable composition.

A widely used method is to heat a cationically polymerizable composition containing a cationically polymerizable compound and a cationic polymerization initiator to cause cationic polymerization. For example, a cured epoxy resin can be obtained by mixing a liquid epoxy compound with a cationic polymerization initiator and then heating the mixture. Such epoxy resins are widely used in a variety of applications, including bonding and sealing electronic components.

Onium salts, such as sulfonium salts, are widely used as cationic polymerization initiators. The anion species contained in these onium salts is often derived from a superacid, such as tetrakis(pentafluorophenyl)borate or hexafluoroantimonate, which allows for a lower initiation temperature for cationic polymerization. Lowering the initiation temperature is desirable for reasons of suppressing shrinkage after curing, protecting electronic components, and reducing energy consumption. However, cationic polymerization in cationic polymerizable compositions with low initiation temperatures can progress during storage, resulting in a short pot life. Therefore, stabilizers are sometimes used to inhibit the progression of cationic polymerization during storage.

For example, Patent Document 1 describes a method for stabilizing alicyclic epoxy resins, in which a sulfonium salt containing hexafluoroantimonate, hexafluorophosphate, tetrakis(pentafluorophenyl)borate, or the like as an anion species is used as a polymerization initiator for the alicyclic epoxy resin, and a sulfonium salt containing methyl sulfate or ethyl sulfate as an anion species, combined with an aromatic sulfide, is blended as a stabilizer. However, the stabilizing effect is still insufficient, making it difficult to achieve a long pot life in some cases.

Meanwhile, Patent Document 2 describes the use of a sulfonium salt containing trifluoromethanesulfonate as the anion species as a polymerization initiator. However, this polymerization initiator has the problem of requiring a high polymerization initiation temperature.

Japanese Patent Application Laid-Open No. 2019-189698 Japanese Patent Application Laid-Open No. 2004-217551

The present invention was made to solve the above-mentioned problems, and aims to provide a thermally cationically polymerizable composition that has a long pot life even when using a cationic polymerization initiator with a low polymerization initiation temperature, and uses thereof. It also aims to provide a cationic polymerization method using the thermally cationically polymerizable composition. It is also an object of the present invention to provide a stabilizer for a thermally cationically polymerizable composition that has a long pot life.

The above problem is solved by a thermally cationically polymerizable composition comprising a cationically polymerizable compound (A), a cationic polymerization initiator (B) represented by the following formula (1), and a stabilizer (C) represented by the following formula (2):
The problem is solved by providing a thermally cationically polymerizable composition comprising 0.01 to 20 parts by mass of a cationic polymerization initiator (B) relative to 100 parts by mass of a cationic polymerizable compound (A), and 0.1 to 50 parts by mass of a stabilizer (C) relative to 100 parts by mass of the cationic polymerization initiator (B).

In formula (1), R ¹ , R ² and R ³ each independently represent an alkyl group having 1 to 10 carbon atoms which may have a substituent, an aryl group having 6 to 15 carbon atoms which may have a substituent, or an aralkyl group having 7 to 15 carbon atoms which may have a substituent. X is B(R _f ¹ ) ₄ , Sb(R _f ² ) ₆ , P(R _f ³ ) ₆ , N(R _f ⁴ ) ₂ , C(R _f ⁵ ) ₃ , Al(R _f ⁶ ) ₄ or Ga(R _f ⁷ ) ₄ , and R _f ^{1 to R f 7} are each independently a fluorine-containing group selected from the group consisting of a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroaryl group having 6 to 10 carbon atoms, a perfluoroalkyl-substituted aryl group having 7 to 14 carbon atoms, a perfluoroalkylsulfonyl group having 1 to 6 carbon atoms, and a perfluoroalkoxy group having 1 to 6 carbon atoms. Multiple perfluoroalkyl groups, perfluoroalkylsulfonyl groups, or perfluoroalkoxy groups may be bonded to form a ring.]

[In formula (2), R ⁴ , R ⁵ and R ⁶ each independently represent an alkyl group having 1 to 10 carbon atoms which may have a substituent, an aryl group having 6 to 15 carbon atoms which may have a substituent, or an aralkyl group having 7 to 15 carbon atoms which may have a substituent.]

In this case, in the formula (1),
R _f ¹ is a fluorine atom, a perfluoroaryl group having 6 to 10 carbon atoms, a perfluoroalkyl-substituted aryl group having 7 to 14 carbon atoms, or a perfluoroalkoxy group having 1 to 6 carbon atoms;
R _f ² is a fluorine atom;
R _f ³ is a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms;
R _f ⁴ is a perfluoroalkylsulfonyl group having 1 to 6 carbon atoms;
R _f ⁵ is a perfluoroalkylsulfonyl group having 1 to 6 carbon atoms;
It is preferable that R _f ⁶ is a perfluoroalkoxy group having 1 to 6 carbon atoms, and R _f ⁷ is a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroaryl group having 6 to 10 carbon atoms, or a perfluoroalkyl-substituted aryl group having 7 to 14 carbon atoms.

In this case, any of the above thermally cationically polymerizable compositions may contain 0.001 to 1,000 parts by mass of organic solvent (D) per 100 parts by mass of cationically polymerizable compound (A). Furthermore, the organic solvent (D) may be an organic solvent (d1) capable of dissolving the same mass of cationic polymerization initiator (B) at 25°C, and the composition may contain 10 to 1,000 parts by mass of organic solvent (d1) per 100 parts by mass of cationic polymerization initiator (B).

In this case, the content of the organic solvent (D) in any of the above-mentioned thermally cationically polymerizable compositions may be less than 10 parts by mass per 100 parts by mass of the cationic polymerization initiator (B). Furthermore, the thermally cationically polymerizable composition may be substantially free of the organic solvent (D).

The above-mentioned problem can also be solved by providing a cationic polymerization method in which any of the above-mentioned thermally cationically polymerizable compositions is optionally dried and then heated to allow cationic polymerization to proceed. The above-mentioned problem can also be solved by providing a cationic polymerization method in which any of the above-mentioned thermally cationically polymerizable compositions is transported outdoors, then optionally dried and then heated to allow cationic polymerization to proceed. Furthermore, a preferred embodiment is an adhesive or coating agent made from the above-mentioned thermally cationically polymerizable composition.

Furthermore, the above problem can also be solved by providing a stabilizer (C) for a thermally cationically polymerizable composition represented by the following formula (2):

[In formula (2), R ⁴ , R ⁵ and R ⁶ each independently represent an alkyl group having 1 to 10 carbon atoms which may have a substituent, an aryl group having 6 to 15 carbon atoms which may have a substituent, or an aralkyl group having 7 to 15 carbon atoms which may have a substituent.]

The thermally cationic polymerizable composition of the present invention has a long pot life despite using a cationic polymerization initiator with a low polymerization initiation temperature. This allows for greater flexibility in the preparation, storage, and transportation methods of the thermally cationic polymerizable composition, and minimizes fluctuations in the physical properties of the composition during the coating and curing processes. Furthermore, the manufacturing method of the present invention makes it possible to produce such a thermally cationic polymerizable composition. Furthermore, by using the stabilizer of the present invention, a thermally cationic polymerizable composition with a long pot life can be obtained.

1 shows DSC curves of the thermally cationically polymerizable compositions of Example 1, Example 5, Comparative Example 1, and Comparative Example 6.

The present invention relates to a thermally cationically polymerizable composition comprising a cationic polymerizable compound (A), a cationic polymerization initiator (B), and a stabilizer (C). Specifically, a composition comprising the cationic polymerizable compound (A), the cationic polymerization initiator (B), and the stabilizer (C) is used for thermal cationic polymerization. When the thermally cationically polymerizable composition of the present invention is heated, the cationic polymerization initiator (B) thermally decomposes, and the resulting cationic species react with the cationic polymerizable compound (A), initiating a polymerization reaction of the cationic polymerizable compound (A) to produce a polymer. The stabilizer (C) functions to prevent the polymerization reaction from proceeding during storage. Each component is described in detail below.

The cationically polymerizable compound (A) may be any compound capable of undergoing cation polymerization, and is not particularly limited. Examples include compounds having a cyclic ether group such as an epoxy group or an oxetane group; compounds having a cyclic thioether group; vinyl ether group; and compounds having a styryl group. Among these, compounds having a cyclic ether group such as an epoxy group or an oxetane group are preferred from the standpoints of adhesiveness and chemical resistance. Epoxy compounds having an epoxy group in the molecule are particularly preferred. Furthermore, from the standpoint of handleability, the cationically polymerizable compound (A) is preferably a liquid at room temperature (25°C). It is also preferable that the molecular weight of the cationically polymerizable compound (A) be 100 to 700.

Epoxy compounds may be monoepoxy compounds containing one epoxy group per molecule, or polyepoxy compounds containing two or more epoxy groups per molecule, or a mixture of these may be used. Polyepoxy compounds are preferred to increase the hardness and modulus of elasticity of the cured epoxy resin. Polyepoxy compounds typically contain 2 to 7 epoxy groups per molecule. From the perspective of fluidity and suppressing unreacted epoxy groups, it is preferable for one molecule to contain two epoxy groups. Furthermore, from the perspective of cationic polymerization, alicyclic epoxy compounds are preferred, and compounds containing epoxycyclohexane groups are particularly preferred. Therefore, compounds containing two epoxycyclohexane groups per molecule are particularly preferred, a typical example of which is 3',4'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate.

The cationic polymerization initiator (B) is a compound represented by the following formula (1): The cationic polymerization initiator (B) is decomposed by heating, and one of ^R1 , ^R2 , or ^R3 becomes a cation, and the remaining portion forms a sulfide. The cation of ^R1 , ^R2 , or ^R3 thus generated reacts with the cationically polymerizable compound (A) such as an epoxy group, and cationic polymerization proceeds from there.

In the above formula (1), R ¹ , R ² , and R ³ are each independently an alkyl group having 1 to 10 carbon atoms, which may have a substituent, an aryl group having 6 to 15 carbon atoms, which may have a substituent, or an aralkyl group having 7 to 15 carbon atoms, which may have a substituent. ^{R 1} , R ² , and R ³ may be the same group or different groups. The alkyl group preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a normal propyl group, and an isopropyl group. The aryl group preferably has 6 to 10 carbon atoms, more preferably 6 to 8 carbon atoms. Specific examples of the aryl group include a 4-hydroxyphenyl group and a 4-acetoxyphenyl group. The aralkyl group preferably has 7 to 11 carbon atoms, more preferably 7 to 9 carbon atoms. Specific examples of the aralkyl group include a benzyl group, a 2-methylbenzyl group, a 4-methylbenzyl group, and a 1-naphthylmethyl group.

In formula (1), it is preferred that R ¹ is an aryl group or an alkyl group, R ² is an alkyl group or an aralkyl group, and R ³ is an alkyl group.

In formula (1), X is B(R _f ¹ ) ₄ , Sb(R _f ² ) ₆ , P(R _f ³ ) ₆ , N(R _f ⁴ ) ₂ , C(R _f ⁵ ) ₃ , Al(R _f ⁶ ) ₄ , or Ga(R _f ⁷ ) ₄ , and R _f ^{1 to R f 7} are each independently a fluorine-containing group selected from the group consisting of a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroaryl group having 6 to 10 carbon atoms, a perfluoroalkyl-substituted aryl group having 7 to 14 carbon atoms, a perfluoroalkylsulfonyl group having 1 to 6 carbon atoms, and a perfluoroalkoxy group having 1 to 6 carbon atoms. B, Sb, P, N, C, Al, or Ga is selected as the central metal, and the R _f group, which is a strong electron-withdrawing group containing fluorine, is bonded to it to form an anion species (X ⁻ ) that can form a monovalent anion as a whole. Multiple _Rf groups bonded to the same central element may be the same or different, but all of the bonded groups must be _Rf groups. Multiple perfluoroalkyl groups, perfluoroalkylsulfonyl groups, and perfluoroalkoxy groups bonded to one central element may be bonded to each other to form a perfluoroalkylene group, thereby forming a ring. The conjugate acids (HX) of these anionic species are all stronger acids than trifluoromethanesulfonic acid. Therefore, the pKa values at 25°C of the conjugate acids (HX) of these anionic species are all smaller than that of trifluoromethanesulfonic acid.

In the formula (1),
R _f ¹ is a fluorine atom, a perfluoroaryl group having 6 to 10 carbon atoms, a perfluoroalkyl-substituted aryl group having 7 to 14 carbon atoms, or a perfluoroalkoxy group having 1 to 6 carbon atoms;
R _f ² is a fluorine atom;
R _f ³ is a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms;
R _f ⁴ is a perfluoroalkylsulfonyl group having 1 to 6 carbon atoms;
R _f ⁵ is a perfluoroalkylsulfonyl group having 1 to 6 carbon atoms;
It is preferable that R _f ⁶ is a perfluoroalkoxy group having 1 to 6 carbon atoms, and R _f ⁷ is a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroaryl group having 6 to 10 carbon atoms, or a perfluoroalkyl-substituted aryl group having 7 to 14 carbon atoms. Again, a plurality of perfluoroalkyl groups, perfluoroalkylsulfonyl groups, and perfluoroalkoxy groups bonded to one central element may be bonded to each other to form a perfluoroalkylene group, thereby forming a ring.

In addition, in the formula (1), the number of carbon atoms in the perfluoroalkyl group is preferably 1 to 4, more preferably 1 to 3. Specific examples of perfluoroalkyl groups include trifluoromethyl, pentafluoroethyl, heptafluoro-normal-propyl, heptafluoroisopropyl, and nonafluoro-t-butyl. The number of carbon atoms in the perfluoroaryl group is preferably 6 to 8, more preferably 6 to 7. Specific examples of perfluoroaryl groups include pentafluorophenyl. A perfluoroalkyl-substituted aryl group is a group in which at least a portion of the hydrogen atoms bonded to the aromatic ring of an aryl group are replaced with perfluoroalkyl groups, and hydrogen atoms bonded to the aromatic ring may remain. The number of carbon atoms in the perfluoroalkyl-substituted aryl group is preferably 7 to 12, more preferably 7 to 10. Specific examples of perfluoroalkyl-substituted aryl groups include 3,5-bistrifluoromethylphenyl. The number of carbon atoms in the perfluoroalkylsulfonyl group is preferably 1 to 4, more preferably 1 to 3. Specific examples of perfluoroalkylsulfonyl groups include trifluoromethanesulfonyl groups. Also suitable are groups in which two perfluoroalkylsulfonyl groups are bonded together and the two sulfonyl groups are connected via a hexafluoropropylene group. The number of carbon atoms in the perfluoroalkoxy group is preferably 1 to 4. Specific examples of perfluoroalkoxy groups include nonafluoro-t-butyloxy groups.

In the formula (1), specific examples of suitable anions represented by "X ^- " include anions represented by the following formulas (1x) to (11x). Among these, the significance of employing the thermally cationic polymerizable composition of the present invention is great when the cationic polymerization initiator (B) is likely to generate cations and the polymerization initiation temperature is low. From this viewpoint, anions represented by the formulas (1x) to (10x) are preferred, anions represented by the formulas (1x) to (7x) are more preferred, and anions represented by the formulas (1x) to (2x) are even more preferred.

As the cationic polymerization initiator (B), which is the compound represented by formula (1), various sulfonium salts commercially available as cationic polymerization initiators can be used. Alternatively, a commercially available sulfonium salt can be used as a starting material to exchange the anion to produce a cationic polymerization initiator.

The stabilizer (C) is a compound represented by the following formula (2):

The anion species in formula (2) is trifluoromethanesulfonate. By using trifluoromethanesulfonate as the anion species of stabilizer (C), the increase in viscosity of the thermally cationically polymerizable composition at low temperatures can be effectively suppressed, maintaining the composition in a low-viscosity liquid state and extending its pot life. As described in Patent Document 2, the compound represented by formula (2) itself can function as a cationic polymerization initiator, but when combined with a more active cationic polymerization initiator (B), it is possible to suppress the increase in viscosity of the thermally cationically polymerizable composition over a long period of time during storage at low temperatures.

In formula (2), R ⁴ , R ⁵ , and R ⁶ are each independently an alkyl group having 1 to 10 carbon atoms, which may have a substituent, an aryl group having 6 to 15 carbon atoms, which may have a substituent, or an aralkyl group having 7 to 15 carbon atoms, which may have a substituent. R ⁴ , R ⁵ , and R ⁶ may be the same group or different groups. The alkyl group preferably has 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms. Specific examples of the alkyl group include a methyl group, an ethyl group, a normal propyl group, and an isopropyl group. The aryl group preferably has 6 to 10 carbon atoms, more preferably 6 to 8 carbon atoms. Specific examples of the aryl group include a 4-hydroxyphenyl group and a 4-acetoxyphenyl group. The aralkyl group preferably has 7 to 11 carbon atoms, more preferably 7 to 9 carbon atoms. Specific examples of the aralkyl group include a benzyl group, a 2-methylbenzyl group, a 4-methylbenzyl group, and a 1-naphthylmethyl group.

In formula (2), it is preferred that R ⁴ is an aryl group or an alkyl group, R ⁵ is an alkyl group or an aralkyl group, and R ⁶ is an alkyl group.

There are no particular limitations on the method for producing the compound represented by formula (2) used as stabilizer (C). As described in Patent Document 2, it can be produced by reacting sulfonium chloride with sodium trifluoromethanesulfonate. It can also be produced by reacting sulfonium methyl sulfate with sodium trifluoromethanesulfonate. It can also be produced by reacting a sulfide with an alkyl trifluoromethanesulfonate.

The thermally cationically polymerizable composition of the present invention contains 0.01 to 20 parts by mass of a cationic polymerization initiator (B) per 100 parts by mass of a cationic polymerizable compound (A), and also contains 0.1 to 50 parts by mass of a stabilizer (C) per 100 parts by mass of the cationic polymerization initiator (B).

If the content of cationic polymerization initiator (B) per 100 parts by mass of cationic polymerizable compound (A) is less than 0.01 parts by mass, the polymerization reaction may not proceed sufficiently, resulting in a low hardness of the cured product and an increased amount of unreacted monomer. The content of cationic polymerization initiator (B) is preferably 0.02 parts by mass or more, more preferably 0.04 parts by mass or more. On the other hand, if the content of cationic polymerization initiator (B) per 100 parts by mass of cationic polymerizable compound (A) exceeds 20 parts by mass, the amount of volatile decomposition products increases and production costs also rise. The content of cationic polymerization initiator (B) is preferably 5 parts by mass or less, more preferably 2 parts by mass or less.

Furthermore, if the content of stabilizer (C) per 100 parts by mass of cationic polymerization initiator (B) is less than 0.1 parts by mass, the storage stability of the thermally cationic polymerizable composition will decrease, resulting in a shortened pot life. The content of stabilizer (C) is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more. On the other hand, if the content of stabilizer (C) per 100 parts by mass of cationic polymerization initiator (B) exceeds 50 parts by mass, the polymerization reaction will not proceed sufficiently at relatively low temperatures, resulting in a decrease in hardness of the cured product and an increase in the amount of unreacted monomer. The content of stabilizer (C) is preferably 20 parts by mass or less, more preferably 10 parts by mass or less.

The thermally cationic polymerizable composition of the present invention may contain an organic solvent (D) in addition to the cationic polymerizable compound (A), cationic polymerization initiator (B), and stabilizer (C). The composition may contain 0.001 to 1,000 parts by mass of the organic solvent (D) per 100 parts by mass of the cationic polymerizable compound (A). The inclusion of an organic solvent may reduce viscosity and improve coatability. It also facilitates dissolution of the cationic polymerization initiator (B) and stabilizer (C) in the thermally cationic polymerizable composition. If used to adjust viscosity, the content of the organic solvent (D) may be 5 to 500 parts by mass, or 10 to 200 parts by mass, per 100 parts by mass of the cationic polymerizable compound (A).

The organic solvent (D) is an organic solvent (d1) capable of dissolving the same mass of cationic polymerization initiator (B) at 25°C. A preferred embodiment is one in which the organic solvent (d1) is contained in an amount of 10 to 1,000 parts by mass per 100 parts by mass of cationic polymerization initiator (B). This means that the composition contains only a small amount of good solvent necessary to dissolve the cationic polymerization initiator (B). Because the content of organic solvent (d1) in the thermally cationic polymerizable composition is low, energy consumption during the drying process is low and the surrounding environment is less likely to be polluted. If the content is low, the drying process may be omitted to allow cationic polymerization to proceed. The content of organic solvent (d1) per 100 parts by mass of cationic polymerization initiator (B) may be 20 to 500 parts by mass or 50 to 200 parts by mass.

When preparing a thermally cationically polymerizable composition containing an organic solvent (d1), it is preferable to dissolve the cationic polymerization initiator (B) and stabilizer (C) in the organic solvent (d1) beforehand and then mix them with the cationic polymerizable compound (A). This allows the cationic polymerization initiator (B) and stabilizer (C) to be uniformly mixed in the thermally cationically polymerizable composition. Alternatively, the cationic polymerization initiator (B) can be dissolved in the organic solvent (d1) beforehand and then mixed with the cationic polymerizable compound (A) in which the stabilizer (C) has been dissolved. The stabilizer (C) of the present invention has superior solubility in the cationic polymerizable compound (A) compared to the compound described in Patent Document 1 (sulfonium methyl sulfate: Comparative Example 1).

On the other hand, the content of organic solvent (D) in the thermally cationic polymerizable composition may be less than 10 parts by mass per 100 parts by mass of cationic polymerization initiator (B). This can suppress the generation of organic volatile components, and in some cases, the drying step can be omitted. Furthermore, it is preferable that the thermally cationic polymerizable composition is substantially free of organic solvent (D), which can suppress the generation of organic volatile components and also eliminate the need for a drying step. This is particularly important in the manufacturing processes of electronic components and semiconductors, where contamination of the working environment is undesirable.

In this way, when the thermally cationic polymerizable composition does not substantially contain an organic solvent (D), it is preferable to first dissolve the stabilizer (C) in the cationic polymerizable compound (A) and then mix the resulting mixture with the cationic polymerization initiator (B) to produce the thermally cationic polymerizable composition. Alternatively, the thermally cationic polymerizable composition can also be produced by adding both the cationic polymerization initiator (B) and the stabilizer (C) to the cationic polymerizable compound (A) and mixing them together. In these cases, it is preferable to use a cationic polymerization initiator (B) that has excellent solubility in organic compounds, and a cationic polymerization initiator (B) represented by formula (1) in which X is B(R _f ¹ ) ₄ is preferred.

The thermally cationically polymerizable composition of the present invention may contain components other than the cationically polymerizable compound (A), cationic polymerization initiator (B), stabilizer (C), and organic solvent (D), as long as the effects of the present invention are not impaired. Various other components may be added depending on the intended use, such as fillers, reinforcing fibers, conductive particles, colorants, photopolymerization initiators, UV absorbers, photosensitizers, antioxidants, flame retardants, leveling agents, silane coupling agents, radically polymerizable compounds, (meth)acrylic resins, polyurethane resins, polyamide resins, and polyester resins. The amount of components that are added as solids and do not dissolve or melt and do not directly participate in the cationic polymerization reaction, such as fillers, fibers, and particles, is not particularly limited and can be adjusted appropriately depending on the intended use. The amount of such components may be, for example, 0.1 to 1,000 parts by weight per 100 parts by weight of the cationically polymerizable compound (A). On the other hand, the content of other components that are uniformly mixed with (A), (B), (C), and (D) is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

The preferred cationic polymerization method of the present invention involves optionally drying the thermally cationic polymerizable composition and then heating it to cause cationic polymerization. In many cases, the thermally cationic polymerizable composition, which is liquid at room temperature, is heated to cause cationic polymerization (curing reaction) and obtain a product (cured composition). In this case, it is preferable to dry the thermally cationic polymerizable composition at a temperature of 50°C or less and then heat it at 60 to 260°C for 1 to 300 minutes to cause cationic polymerization. A heating temperature of 60°C or higher allows the cationic polymerization initiator (B) to release reactive cations, facilitating the progress of cationic polymerization. A heating temperature of 80°C or higher is more preferred, and 100°C or higher is even more preferred. The higher the reaction temperature, the faster the reaction rate, allowing cationic polymerization to proceed in a shorter time. However, curing at high temperatures can result in shrinkage upon cooling after curing, which can cause adhesion problems. Furthermore, high temperatures can also affect electrical performance in applications such as bonding or sealing electronic components or semiconductors. Therefore, the heating temperature is preferably 260°C or less, more preferably 230°C or less, and even more preferably 200°C or less.

The thermally cationically polymerizable composition of the present invention, which contains stabilizer (C), has a long pot life because it remains liquid for long periods without increasing in viscosity. This allows for a longer shelf life. This point is also demonstrated in the examples of the present application, where it was found that the number of days (pot life) until the viscosity doubled compared to before storage, when refrigerated at 5°C, was extended by approximately three days, from 4-5 days to 7-8 days, compared to previous stabilizers. The approximately three-day extension of the refrigerated shelf life is extremely significant from a process management perspective. Until now, due to the short pot life, thermally cationically polymerizable compositions were mostly prepared at user factories by blending cationic polymerizable compound (A), cationic polymerization initiator (B), and stabilizer (C), where the composition was cured by heating. However, with the present invention, pharmaceutical manufacturers can now blend cationic polymerizable compound (A), cationic polymerization initiator (B), and stabilizer (C) to produce a thermally cationically polymerizable composition, transport it outdoors, optionally dry it, and then heat it to allow the cationic polymerization to proceed. This allows pharmaceutical manufacturers to manufacture products in bulk, eliminating the burden of operating and managing mixing equipment for users. While there are no particular limitations on the means of outdoor transportation, refrigerated transportation under temperature control is preferred. The refrigeration temperature is preferably 15°C or lower, and more preferably 10°C or lower. On the other hand, to avoid freezing, it is preferably 0°C or higher.

Furthermore, it has been found that the thermally cationic polymerizable composition of the present invention has a longer pot life, while at the same time exhibiting a lower polymerization initiation temperature than conventional stabilizers, as shown in the DSC curves of the examples (Figure 1). This makes it possible to suppress unnecessary polymerization reactions at storage temperatures while also suppressing increases in the polymerization initiation temperature, thereby achieving both long-term storage and low-temperature curing. The thermally cationic polymerizable composition of the present invention preferably has an exothermic onset temperature of 80°C or lower when measured by DSC at a temperature rise rate (10°C/min). The exothermic onset temperature is more preferably 78°C or lower, and even more preferably 76°C or lower. Meanwhile, the exothermic onset temperature is typically 60°C or higher.

As shown in the DSC curves of the examples (Figure 1), when no organic solvent (d1) is used (Example 5), the exothermic onset temperature is higher than when organic solvent (d1) is used (Example 1). However, the calorific value of the first exothermic peak (first peak) is significantly larger, which is thought to be useful for rapid curing. Furthermore, because no organic solvent is used, a drying process is not required, and the evaporation of organic solvent (d1) into the work environment is suppressed, making this useful.

Generally, the addition of a stabilizer reduces the electrical resistivity of a cured product of a thermally cationic polymerizable composition. However, the electrical resistivity of the cured product of the thermally cationic polymerizable composition of the present invention is less likely to decrease than when a conventional stabilizer is used. Therefore, the composition is suitable for applications requiring high insulating properties. The electrical resistivity of the cured product of the thermally cationic polymerizable composition of the present invention is preferably 3×10 ⁷ Ω·m or more, and more preferably 4×10 ⁷ Ω·m or more. However, when the organic solvent (d1) was not used (Example 5), the electrical resistivity was lower than when an organic solvent and a conventional stabilizer were used. Although this level does not pose a problem for general insulating properties, it is preferable to use different stabilizers depending on the application.

While there are no particular limitations on the applications of such thermally cationically polymerizable compositions, they are ideally used as thermosetting liquid resin compositions. The thermally cationically polymerizable compositions of the present invention can be cured at relatively low temperatures and exhibit good adhesion to resins, metals, and other materials, making them ideal for use as adhesives and coatings. Adhesives can be used to bond multiple components, and include a variety of adhesives. For example, compositions containing conductive particles can be used as conductive pastes or anisotropically conductive films (ACFs). Coating agents can be used to cover the surfaces of components, and include a variety of coating agents. For example, they can be used as sealants, insulating materials, resist materials, and more. In addition, the thermally cationically polymerizable compositions of the present invention are also useful as fiber-reinforced plastics (FRPs) and nanoimprinting materials. Because the thermally cationically polymerizable compositions of the present invention can be cured at relatively low temperatures, they can suppress thermal damage to electronic components, semiconductors, and other devices. Furthermore, they can reduce the amount of volatile organic solvents used, making them suitable for applications such as electronic components and semiconductors.

As explained above, it has been revealed that the thermally cationic polymerizable composition of the present invention, by including the new stabilizer (C), has a longer pot life and can suppress an increase in the heat generation initiation temperature compared to conventional stabilizers. In fact, the use of a compound represented by formula (2) as a stabilizer for a thermally cationic polymerizable composition is itself novel. Therefore, the object of the present invention is also achieved by providing a stabilizer (C) for a thermally cationic polymerizable composition represented by formula (2). In other words, the present invention provides a novel and useful stabilizer.

Example 1
[Synthesis of stabilizer]
A 200 mL four-neck flask was charged with 6.66 g (25 mmol) of 4-hydroxyphenyldimethylsulfonium methyl sulfate (Sanshin Chemical Industry Co., Ltd., "San-Aid SI-S": formula (2e) in Comparative Example 1), 4.3 g (25 mmol) of sodium trifluoromethanesulfonate, and 85 mL of ethanol, and the mixture was stirred at 25°C for 24 hours. The reaction mixture was filtered, and the resulting filtrate was concentrated. 100 mL of hexane was added to the concentrate, and the mixture was stirred. The resulting precipitate was filtered, yielding white crystalline 4-hydroxyphenyldimethylsulfonium trifluoromethanesulfonate (formula (2a) below) in a 95% yield. [ ¹ H-NMR (400 MHz, CD ₃ CN): δ 8.50 (s, 1H), 7.82 (d, 2H), 7.11 (d, 2H), 3.17 (s, 6H)]. The stabilizer (2a) is summarized in Table 1.

[Solubility of stabilizer]
At 25 ° C., 1 g of stabilizer (2a) was placed in a 30 mL screw tube, and 1 g of solvent was added at a time and mixed using a THINKY CORPORATION centrifugal mixer "ARE-310." The mass Ws (g) of solvent required for complete dissolution of stabilizer (2a) was measured. The solubility (S), which is the mass of solute that can be dissolved in 100 g of solvent, was calculated according to the following formula. The solubility when dissolved in 1 g of solvent is indicated as "≧100," and the solubility when not completely dissolved even after adding 100 g of solvent is indicated as "<1." Water, propylene carbonate (PC), methyl isobutyl ketone (MIBK), and propylene glycol monomethyl ether acetate (PGMAc) were used as solvents. The cationically polymerizable compound, 3',4'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate "Celloxide 2021P," was also subjected to the same test to evaluate the solubility of the stabilizer. As a result, the solubility of stabilizer (2a) was 100 [g/100 g-solv.] or more in water, PC, MIBK, and PGMAc, and 25 [g/100 g-solv.] in "Celloxide 2021P."
S[g/100g-solv. ]=1/(Ws/100)

[Preparation of Thermally Cationic Polymerizable Composition]
A thermally cationically polymerizable composition was prepared using the stabilizer (2a) thus obtained. First, 20.0 mg of 4-acetoxyphenylbenzylmethylsulfonium tetrakis(pentafluorophenyl)borate ("San-Aid SI-B3A" manufactured by Sanshin Chemical Industry Co., Ltd.: Formula (1a) below) as a polymerization initiator and 0.2 mg of stabilizer (2a) were placed in a 10 mL screw tube, and 20.0 mg of propylene carbonate was added as a solvent and completely dissolved to prepare an initiator solution. 20.1 mg of the prepared initiator solution was placed in a 30 mL screw tube, and 10 g of 3',4'-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate ("Celloxide 2021P" manufactured by Daicel Corporation: Formula (3a) below) as a cationically polymerizable compound was added. The mixture was immediately mixed using an ARE-310 planetary centrifugal mixer to prepare a thermally cationically polymerizable composition. The resulting thermally cationically polymerizable composition is summarized in Table 2.

[Storage stability]
The prepared thermally cationically polymerizable composition was placed in a 30 mL screw tube and allowed to stand in a thermostatic bath at 5°C, and the viscosity of the sample at 25°C was measured every few days. An E-type viscometer "TV-100EH" manufactured by Toki Sangyo Co., Ltd. was used for the viscosity measurements. The pot life was defined as 7 days, which is the number of days until the viscosity doubled compared to before the start of storage.

[Thermosetting]
5.0 mg of the prepared thermally cationically polymerizable composition (thermosetting composition) was weighed out and heated from 30°C to 310°C at a rate of 10°C/min in a nitrogen gas flow of 40 mL/min using a Hitachi High-Technologies Corporation differential scanning calorimeter "X-DSC7000." A DSC curve was obtained. The resulting DSC curve is shown in Figure 1. In the DSC curve, exotherm was observed in the range of approximately 70 to approximately 250°C, and three exothermic peaks were observed. The first (lowest temperature) exothermic peak was designated as the first exothermic peak. The first exothermic peak temperature was 81°C, and the heat generation amount (peak height) of the first exothermic peak was 8 mW. The exothermic onset temperature was 72°C, which is the temperature at the intersection of the tangent to the low-temperature inflection point of the first exothermic peak and the baseline.

[Electrical resistivity]
A sample was prepared by applying a thermally cationically polymerizable composition to the electrode surface of a polyimide resin film on which a tin-plated copper comb electrode was formed, and the sample was set in an "LT-451" dielectric analyzer manufactured by Syscom Co., Ltd. An AC voltage of 1 kHz and 1 V was applied, while the temperature of the sample was maintained at 70°C, and the electrical resistivity was monitored. After 2 hours, the thermally cationically polymerizable composition had cured, and the electrical resistivity of the cured product was 5.1 x 10 ⁷ Ω·m. After curing, the thermally cationically polymerizable composition was firmly adhered to both the metal surface of the comb electrode and the resin surface of its substrate.

Example 2
A 200 mL four-neck flask was charged with 3.51 g (25 mmol) of 4-(methylthio)phenol, 3.85 g (25 mmol) of diethyl sulfate, and 25 mL of acetonitrile, and the mixture was stirred at 40°C for 24 hours. The resulting reaction solution was concentrated to obtain the intermediate, 4-hydroxyphenylmethylethylsulfonium ethyl sulfate. 4.3 g (25 mmol) of sodium trifluoromethanesulfonate and 85 mL of ethanol were added to this intermediate, and the mixture was stirred at 25°C for 24 hours. The reaction solution was filtered, and the resulting filtrate was concentrated. 100 mL of hexane was then added to the concentrate, and the mixture was stirred. The resulting precipitate was filtered, yielding a transparent liquid, 4-hydroxyphenylmethylethylsulfonium trifluoromethanesulfonate (formula (2b) below), in an 84% yield. Using the resulting stabilizer (2b), a thermally polymerizable composition was prepared in the same manner as in Example 1. [ ¹ H-NMR (400 MHz, CD ₃ CN): δ 9.62 (s, 1H), 7.73 (d, 2H), 7.10 (d, 2H), 3.96 (q, 2H), 3.13 (s, 3H), 1.16 (t, 3H)]. The stabilizer (2b) and the thermally cationically polymerizable composition obtained were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Example 3
A 200 mL four-neck flask was charged with 3.51 g (25 mmol) of 4-(methylthio)phenol, 3.16 g (25 mmol) of benzyl chloride, and 25 mL of acetonitrile, and the mixture was stirred at 40°C for 24 hours. The resulting reaction solution was concentrated to obtain the intermediate, 4-hydroxyphenylmethylbenzylsulfonium chloride. Using this intermediate, the same procedure as in Example 2 was repeated to obtain white crystalline 4-hydroxyphenylmethylbenzylsulfonium trifluoromethanesulfonate (formula (2c) below) in a 96% yield. [ ¹ H-NMR (400 MHz, CD ₃ CN): δ 6.72-7.40 (m, 10H), 4.43 (q, 2H), 2.79 (s, 3H)]. The resulting stabilizer (2c) was used to prepare a thermally cationically polymerizable composition in the same manner as in Example 1. The resulting stabilizer (2c) and the thermally cationically polymerizable composition were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Example 4
A 200 mL four-neck flask was charged with 3.46 g (25 mmol) of benzyl methyl sulfide, 3.15 g (25 mmol) of dimethyl sulfate, and 25 mL of acetonitrile, and the mixture was stirred at 40°C for 24 hours. The resulting reaction solution was concentrated to obtain the intermediate, benzyl dimethyl sulfonium methyl sulfate. A transparent liquid, benzyl dimethyl sulfonium trifluoromethanesulfonate (formula (2d) below), was obtained in a 93% yield in the same manner as in Example 2, except for using this intermediate. [ ¹ H-NMR (400 MHz, CD ₃ CN): δ 7.15-7.50 (m, 5H), 4.00 (s, 2H), 2.80 (s, 6H)]. A thermally cationically polymerizable composition was prepared using the resulting stabilizer (2d) in the same manner as in Example 1. The resulting stabilizer (2d) and the thermally cationically polymerizable composition were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Example 5
0.2 mg of the stabilizer (2a) obtained in Example 1 was placed in a 30 mL screw tube, and 20 g of the cationically polymerizable compound "Celloxide 2021P" was added thereto and mixed using a planetary centrifugal mixer "ARE-310" to achieve complete dissolution. Subsequently, 20.0 mg of "Sanaid SI-B3A" (1a) was added as a polymerization initiator, and further mixed using the planetary centrifugal mixer to prepare a thermally cationically polymerizable composition that did not contain the solvent propylene carbonate. The obtained thermally cationically polymerizable composition was evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2 and FIG. 1.

Comparative Example 1
A thermally cationically polymerizable composition was prepared in the same manner as in Example 1, except that 0.2 mg of 4-hydroxyphenyldimethylsulfonium methyl sulfate ("San-Aid SI-S" manufactured by Sanshin Chemical Industry Co., Ltd.: formula (2e) below) was used as a stabilizer. The stabilizer (2e) and the thermally cationically polymerizable composition were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2 and FIG. 1. Note that when a thermally cationically polymerizable composition was prepared without using the solvent (PC) in the same manner as in Example 5, the compound (2e) did not completely dissolve.

Comparative Example 2
A 200 mL four-neck flask was charged with 6.66 g (25 mmol) of 4-hydroxyphenyldimethylsulfonium methyl sulfate (Sanshin Chemical Industry Co., Ltd.'s "Sanaid SI-S": formula (2e) of Comparative Example 1), 2.95 g (25 mmol) of sodium methyl sulfite, and 85 mL of ethanol, and the mixture was stirred at 25°C for 24 hours. The reaction mixture was filtered, and the resulting filtrate was concentrated. 100 mL of hexane was added to the concentrate, and the mixture was stirred. The resulting precipitate was filtered, yielding 4-hydroxyphenyldimethylsulfonium methyl sulfite (formula (2f) below) in a 91% yield. [ ¹ H-NMR (400 MHz, CD ₃ OD): δ 7.87 (d, 2H), 7.12 (d, 2H), 5.18 (s, 1H), 3.26 (s, 6H), 2.71 (s, 3H)]. Using the resulting stabilizer (2f), a thermally polymerizable composition was prepared in the same manner as in Example 1. The obtained stabilizer (2f) and the thermally cationically polymerizable composition were evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.

Comparative Example 3
4-Hydroxyphenyldimethylsulfonium dimethylphosphate (2g) was obtained in a yield of 85% in the same manner as in Comparative Example 2, except that 2.95g of sodium methyl sulfite was replaced with 3.7g of sodium dimethyl phosphate. [ ¹ H-NMR (400 MHz, CD ₃ OD): δ 7.89 (d, 2H), 7.15 (d, 2H), 5.90 (s, 1H), 3.59 (d, 6H), 3.29 (s, 6H)]. A thermally cationically polymerizable composition was prepared using the resulting stabilizer (2g) in the same manner as in Example 1. The resulting stabilizer (2g) and the thermally cationically polymerizable composition were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Comparative Example 4
4-Hydroxyphenyldimethylsulfonium p-toluenesulfonate (formula (2h) below) was obtained in a yield of 89% in the same manner as in Comparative Example 2, except that 2.95 g of sodium methyl sulfite was replaced with 4.86 g of sodium p-toluenesulfonate. [ ¹ H-NMR (400 MHz, _CD CN): δ 9.02 (s, 1H), 7.69 (d, 4H), 7.15 (d, 2H), 7.05 (d, 2H), 3.09 (s, 6H), 2.26 (s, 3H)]. A thermally cationically polymerizable composition was prepared using the obtained stabilizer (2h) in the same manner as in Example 1. The obtained stabilizer (2h) and the thermally cationically polymerizable composition were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Comparative Example 5
4-Hydroxyphenyldimethylsulfonium methanesulfonate (formula (2i) below) was obtained in a yield of 94% in the same manner as in Comparative Example 2, except that 2.95 g of sodium methyl sulfite was replaced with 2.95 g of sodium methanesulfonate. [ ¹ H-NMR (400 MHz, CD ₃ CN): δ 7.75 (d, 2H), 7.15 (d, 2H), 3.28 (s, 1H), 3.09 (s, 6H), 2.76 (s, 3H)]. A thermally cationically polymerizable composition was prepared using the obtained stabilizer (2i) in the same manner as in Example 1. The obtained stabilizer (2i) and the thermally cationically polymerizable composition were evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2.

Comparative Example 6
A thermally cationically polymerizable composition was prepared without using a stabilizer. First, 20.0 mg of "Sanaid SI-B3A" (formula (1a) in Example 1) as a polymerization initiator and 20.0 mg of propylene carbonate as a solvent were added to a 10 mL screw tube and completely dissolved to prepare an initiator solution. A thermally cationically polymerizable composition was prepared in the same manner as in Example 1, except that the initiator solution thus obtained was used. The obtained thermally cationically polymerizable composition was evaluated in the same manner as in Example 1, and the results are shown in Tables 1 and 2 and FIG. 1.

Claims (9)

A thermally cationically polymerizable composition comprising a cationically polymerizable compound (A), a cationic polymerization initiator (B) represented by the following formula (1), and a stabilizer (C) represented by the following formula (2),
A thermally cationically polymerizable composition comprising: a cationic polymerization initiator (B) in an amount of 0.01 to 20 parts by mass relative to 100 parts by mass of a cationic polymerizable compound (A); and a stabilizer (C) in an amount of 0.1 to 50 parts by mass relative to 100 parts by mass of the cationic polymerization initiator (B).
In formula (1), R ¹ , R ² and R ³ each independently represent an alkyl group having 1 to 10 carbon atoms which may have a substituent, an aryl group having 6 to 15 carbon atoms which may have a substituent, or an aralkyl group having 7 to 15 carbon atoms which may have a substituent. X is B(R _f ¹ ) ₄ , Sb(R _f ² ) ₆ , P(R _f ³ ) ₆ , N(R _f ⁴ ) ₂ , C(R _f ⁵ ) ₃ , Al(R _f ⁶ ) ₄ or Ga(R _f ⁷ ) ₄ , and R _f ^{1 to R f 7} are each independently a fluorine-containing group selected from the group consisting of a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroaryl group having 6 to 10 carbon atoms, a perfluoroalkyl-substituted aryl group having 7 to 14 carbon atoms, a perfluoroalkylsulfonyl group having 1 to 6 carbon atoms, and a perfluoroalkoxy group having 1 to 6 carbon atoms. Multiple perfluoroalkyl groups, perfluoroalkylsulfonyl groups, or perfluoroalkoxy groups may be bonded to form a ring.]
[In formula (2), R ⁴ , R ⁵ and R ⁶ are each independently an alkyl group having 1 to 10 carbon atoms which may have a substituent, an aryl group having 6 to 15 carbon atoms which may have a substituent, or an aralkyl group having 7 to 15 carbon atoms which may have a substituent (excluding the case where all of R ⁴ , R ⁵ and R ⁶ are aryl groups)] In the formula (1),
R _f ¹ is a fluorine atom, a perfluoroaryl group having 6 to 10 carbon atoms, a perfluoroalkyl-substituted aryl group having 7 to 14 carbon atoms, or a perfluoroalkoxy group having 1 to 6 carbon atoms;
R _f ² is a fluorine atom;
R _f ³ is a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms;
R _f ⁴ is a perfluoroalkylsulfonyl group having 1 to 6 carbon atoms;
R _f ⁵ is a perfluoroalkylsulfonyl group having 1 to 6 carbon atoms;
2. The thermally cationically polymerizable composition according to claim 1, wherein R _f ⁶ is a perfluoroalkoxy group having 1 to 6 carbon atoms, and R _f ⁷ is a fluorine atom, a perfluoroalkyl group having 1 to 6 carbon atoms, a perfluoroaryl group having 6 to 10 carbon atoms, or a perfluoroalkyl-substituted aryl group having 7 to 14 carbon atoms. The thermally cationically polymerizable composition according to claim 1, comprising 0.001 to 1,000 parts by mass of organic solvent (D) per 100 parts by mass of cationically polymerizable compound (A). The thermally cationically polymerizable composition according to claim 3, wherein the organic solvent (D) is an organic solvent (d1) capable of dissolving the same mass of cationic polymerization initiator (B) at 25°C, and the organic solvent (d1) is contained in an amount of 10 to 1,000 parts by mass per 100 parts by mass of the cationic polymerization initiator (B). The thermally cationically polymerizable composition according to claim 1, wherein the content of the organic solvent (D) is less than 10 parts by mass per 100 parts by mass of the cationic polymerization initiator (B). The thermally cationically polymerizable composition according to claim 5, which is substantially free of organic solvent (D). A cationic polymerization method in which the thermally cationically polymerizable composition according to any one of claims 1 to 6 is optionally dried and then heated to allow cationic polymerization to proceed. A cationic polymerization method in which the thermally cationically polymerizable composition according to any one of claims 1 to 6 is transported outdoors, optionally dried, and then heated to allow cationic polymerization to proceed. An adhesive or coating agent comprising the thermally cationic polymerizable composition according to any one of claims 1 to 6.