JPS6043868B2 - Polysiloxane compositions that can be cured at room temperature - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is stable even when stored for a long period of time in a moisture-blocked state, exists stably without curing into a rubber-like elastic body, and cures at room temperature by the action of moisture. Regarding one-component room-temperature-curing polysiloxane compositions that become rubber-like elastic bodies, in particular, one-component room-temperature-curing polysiloxanes that cure by releasing oxime-based compounds during curing and that can adhere well to various materials. There is something about the composition.

Conventionally, a polyfunctional silane compound or siloxane compound that is easily hydrolyzed by moisture is uniformly mixed with a silanol-terminated polyorganosiloxane in the presence of a catalyst such as an organotin compound, and the mixture is kept for a long period of time in a moisture-blocked state. So-called one-component room temperature-curing polysiloxane compositions are known, which are stored, taken out into the air, and cured by the action of moisture in the air to obtain a rubber-like elastic body.

These are widely used as architectural and industrial sealants because there is no need to prepare a composition before use. Depending on the substance released during curing, such compositions include a deacetic acid type that releases monoacetic acid, a deoxime type that releases 2 oxime compounds, a dealcohol type that releases 3 alcohols, and a dealcohol type that releases 4 amide compounds. A deamidated type that releases amines, and a deamined type that releases 5-amines are known, but each of these has advantages and disadvantages depending on the curing reaction. In other words, the acetic acid-removed type (1) has the advantage of having the fastest curing speed among the one-component room temperature curing polysiloxanes, but has disadvantages such as emitting an acetic acid odor when handled and corroding metals. The deamidated type (3) and the deamidated type (4) do not corrode the metal, but require a long time to harden, and the deamidated type (5). The min type has problems such as amine odor during handling, yellowing during storage, and yellowing after curing, each of which limits its use. The oxime-free type (No. 2) has a moderate curing speed and is based on a cross-linked system with relatively few problems of corrosion to metals and odor during handling, but it has poor adhesion to various adherends. As such, it has been proposed to improve adhesion by the addition of adhesion promoters.

The most effective method for improving adhesion is the
These are amino group-containing alkoxysilanes proposed in Publication No. 272. However, among these amino group-containing alkoxysilanes, those containing primary amino groups such as γ-aminopropyltriethoxysilane and γ-(N-β-aminoethyl)aminopropyltrimethoxysilane are When left in the room for a long time and/or heated to high temperature in the air, the primary amino groups are oxidized and colored yellow, thus causing a yellowing phenomenon in the cured conomoidal elastomer. may further cause deterioration of the rubber-like elastic body.

The inventor discovered that such yellowing and deterioration can be avoided by using alkoxysilanes containing a secondary amino group instead of a primary amino group. Containing alkoxysilanes are extremely difficult to synthesize. In other words, among the conventional methods for producing amino group-containing alkoxysilanes, hydrogenation of nitrile-substituted alkoxysilanes essentially yields only primary amino group-containing alkoxysilanes. In addition, in the reaction between alkoxysilanes containing a halogenated alkyl group and amines, when a chlorine atom is used as the halogen, the reaction with ethylenediamine proceeds relatively easily, resulting in silanes having a β-aminoethylamino group. , but the second
Special conditions such as high pressure are required to obtain silanes with secondary amino groups, and although it is possible to obtain silanes containing secondary amino groups from those with bromine atoms as halogens, it is difficult to obtain silanes containing secondary amino groups. There are some difficulties, such as the difficulty of introducing certain bromoalkyl groups into silanes. In other words, there is no industrially advantageous method for synthesizing silanes that contain only secondary amino groups without containing primary amino groups.Therefore, there are no effective measures against the yellowing and deterioration of rubber-like elastic bodies mentioned above. I couldn't stand. In addition, this oxime-free one-component room temperature curing polysiloxane composition has the following properties when stored for a long period in an uncured state:
Yellowing was also caused by oxime compounds, and countermeasures were needed. As a result of various studies on adhesion improvers to solve the yellowing and thermal deterioration of such oxime-free room temperature curing polysiloxanes, the present invention has developed an epoxy group-containing silane or its partially hydrolyzed silane. By using a reaction product with a primary or secondary amine as an adhesion improver, there is no yellowing of the comb-shaped elastic body during uncured storage, after curing, or when heated, and the self-adhesive property and The present inventors have discovered that it is possible to obtain a room-temperature-curable polysiloxane composition of the oxime-free type with improved durability, and have accomplished the present invention.

That is, the present invention provides (A) a silanol-terminated polydiorganosiloxane 1 having a viscosity of 500 to 200,000:1st at 25°C;
00 parts by weight, (B) General formula RlaSi(0R2)b(0N=X)4-8-, (wherein R1 is a monovalent substituted or unsubstituted hydrocarbon group,
R2 is a monovalent group selected from an alkyl group and an alkoxyalkyl group, X is a divalent group represented by -C. or an unsubstituted hydrocarbon group, R5 is an alkylene group having 4 to 6 carbon atoms, a is a number of 0 or 1, and b is 0
0.5 to 25 parts by weight of an oxime group-containing organosilicon compound selected from oxime group-containing silanes represented by (or 1) and partial hydrolysates thereof;
) General formula (S-based, where Y is a monovalent substituted hydrocarbon group containing an oxysilane oxygen atom and containing or not containing an ether oxygen atom at the bonding site with R6, R6 is a divalent carbide group) (2) an epoxy group-containing organosilicon compound selected from an epoxy group-containing silane represented by a hydrogen group, R7 represents a monovalent substituted or unsubstituted hydrocarbon group, and a partial hydrolyzate thereof; The present invention relates to a polysiloxane composition curable at room temperature, characterized in that it comprises from 0.01 to 1 part by weight of a reaction product with no primary or secondary amine.

The capacitor component used in the present invention is a silanol-terminated polydiorganosilosiloxane that is normally used in this type of condensed polysiloxane composition that can be cured at room temperature. Along with giving
In order to impart excellent mechanical properties to the rubber-like elastic body after curing, it is necessary that the viscosity at 25° C. be in the range of 500 to 2,000,001) St.

When the viscosity is less than 500 cSt, the elongation of the comb-like elastic body after curing is insufficient, and when the viscosity exceeds 200,000 cSt, a uniform composition cannot be obtained and extrusion workability deteriorates. A particularly preferred range is from 3,000 to 150,000 Cst in order to better balance the properties of the composition before and after curing. Examples of organic groups directly bonded to silicon atoms include alkyl groups such as methyl, ethyl, propyl, butyl, and hexyl; alkenyl groups such as vinyl and allyl; aryl groups such as phenyl; Aralkyl groups such as β-phenylethyl, and 3,3,
Examples include monovalent substituted hydrocarbon groups such as 3-trifluoropropyl group, chloromethyl group, and β-dianoethyl group. Hydrocarbon radicals are generally advantageous; other organic radicals are recommended only to impart special properties to the cured elastomer, such as oil resistance or paintability. Among them, the methyl group not only provides the easiest raw material intermediate, but also provides the lowest viscosity in relation to the degree of polymerization of siloxane, improving the physical properties of the rubber-like elastomer after curing and the extrusion process of the composition before curing. Sex Ba. It is preferred that 85% or more of the total organic groups are methyl groups, and it is more preferred that substantially all the organic groups are methyl groups in order to favor lance. However, when cold resistance or heat resistance is required for the rubber-like elastic body after curing, it is recommended to use phenonyl groups as part of the organic groups. (B) used in the present invention cures the composition into a rubber-like elastic body by reacting with the silanol groups of the silanol-terminated polysiloxane (4) to form a network structure. General formula RlaSi7(0R2), (0N=
X) 4-a? It is an oxime group-containing silane and/or an oxime group-containing siloxane which is a partially hydrolyzed product thereof, represented by b (S 几, in which R1, R2, XNa and b are as described above).

Such an oxime group-containing organosilicon compound can be obtained by reacting the corresponding organochlorosilane with a ketoxime or an aldoxime in the presence of a hydrogen chloride acceptor, and further causing a substitution reaction with an alcohol if necessary. It is publicly known that R1 is a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group,
Alkyl groups such as hexyl groups and octyl groups, alkenyl groups such as vinyl groups and allyl groups, aryl groups such as phenyl groups, aralkyl groups such as styrenyl groups, and 3・3●3-trifluoropropyl groups, Examples include monovalent substituted hydrocarbon groups such as a chloromethyl group and a β-cyanoethyl group, but a methyl group is preferred for ease of synthesis and ease of handling. R2 is an alkyl group or an alkoxyalkyl group, and is preferably a methyl group, ethyl group, propyl group, methoxyethyl group, or ethoxyethyl group because of ease of handling and appropriate reactivity. X is a divalent \^j group represented by =C or -9 5.

R3 and R4 are a hydrogen atom and a monovalent substituted or unsubstituted hydrocarbon group, respectively; Although such alkenyl groups are exemplified, methyl groups or ethyl groups, which may be the same or different from each other, are preferred from the viewpoint of easy availability of raw materials and ease of handling. R5 is an alkylene group having 4 to 6 carbon atoms, and examples include a butylene group, a bentylene group, a 1-methylbutylene group, a 2-methylpentylene group, and a 1-ethylbutylene group; ,
A pentylene group is preferred. Examples of oxime group-containing organosilicon compounds having such groups include tetrakis. (acetone oxime) silane, methyl tris (
acetone oxime) silane, methyl tris (butanone oxime type) silane, methyl tris (diethyl ketoxime) silane, methyl tris (cyclohexanone oxime) silane, vinyl tris (pta.nonoxime) silane, methyl methoxybis (acetone oxime) silane, methyl (methoxyethyl) Bis(butanone oxime) silane, 1●3-dimethyl-1●1,3,3-tetrakis(
Examples include butanone oxime) disiloxane. Oxime group-containing organosilicon compounds such as these tend to be easily hydrolyzed by the action of a small amount of moisture and also tend to be colored yellow. The amount of these oxime group-containing organosilicon compounds added is 0.5 to 2 parts by weight per 100 parts by weight of the silanol-terminated polydiorganosilosiloxane (4).
5 parts by weight, preferably 2 to 1 parts by weight.

If the amount added is less than 0.5 parts by weight, the curing speed of the composition will be extremely high, and stability will be poor when this composition is stored together with component (4) and the catalyst in the same container. Furthermore, if added in a larger amount than necessary, not only will it not work effectively as a hardening agent, but it will also separate and precipitate out of the system during storage, or deteriorate the physical properties of the comb-like elastic body after hardening. . Component (C) used in the present invention is an additive for improving self-adhesiveness of the siloxane composition, and has the general formula (1) (
Y-R6)S1(0R7)3(YlR6 in the Stl formula,
R7 is as described above) by reacting the epoxy group-containing silane and/or its hydrolyzate with (2) a primary or secondary amine that does not contain a silicon atom. be synthesized.

In the epoxy group-containing silane and/or its hydrolyzate of (1), Y is a glycidoxy group and 3
-4-oxycyclohexyl group is exemplified, and R6 is exemplified by methylene group, ethylene group, propylene group, butylene group, hexylene group, and p-phenylene group, but from the viewpoint of compound stability, Y In -R6, the oxirane oxygen atom or ether oxygen atom is preferably bonded to the silicon atom through at least three carbon atoms. Examples of such Y-R6 include γ-glycidoxypropyl group and β-(3,4-oxycyclohexyl)ethyl group. R7 is a monovalent unsubstituted hydrocarbon group, and because it is easy to synthesize and provides good adhesive properties, R7 is an alkyl group having 1 to 3 carbon atoms and an alkoxy group having 1 to 2 carbon atoms. An ethyl group substituted with is preferable, and a methyl group is most preferable because an intermediate can be easily obtained. (
The amine in 2) is selected from ordinary aliphatic, alicyclic, or aromatic primary or secondary amines that do not contain silicon atoms and have one or two active hydrogen atoms, such as methylamine, Examples include ethylamine, propylamine, butylamine, benzylamine, cyclohexylamine, aniline, dimethylamine, diethylamine, dipropylamine, dicyclohexylamine, piperidine, N-methylaniline, and methylethylamine. The epoxy group-containing organosilicon compound (1) and the amine (2) are synthesized by stoichiometric reaction in the absence of a solvent or in a dehydrated inert solvent. Examples of the solvent include benzene, toluene, xylene, heptane, dibutyl ether, and the like. The reaction product is usually separated from unreacted substances and purified by vacuum distillation. The component (C) thus obtained improves the self-adhesiveness of the composition, prevents the yellowing of the component (B) during storage, and prevents the yellowing of the comb-shaped elastic body after curing. It has the effect of The amount of component (C) added is 0.01 to 1 part by weight, preferably 0.1 to 3 parts by weight, per 100 parts by weight of the silanol-terminated polydiorganosiloxane (4). This is 0.
If the amount is less than 1 part by weight, the effect of preventing yellowing of the oxime group-containing organosilicon compound and the rubber-like elastic body after curing, and the effect of improving the self-adhesiveness of the composition will be small; if it is added in excess of 1 part by weight, This is because it adversely affects the storage stability and extrusion workability of the composition and deteriorates the physical properties of the comb-like elastic body after curing. The composition of the present invention consisting of the above (4) to (C) imparts appropriate fluidity or extrudability to the composition before curing, and provides mechanical strength and hardness to the rubber-like elastic body after curing. In order to do this, an inorganic filler is usually used in combination.

Inorganic fillers may be those known to those skilled in the art, such as fumed silica, precipitated silica, silica aerogel, ground quartz, diatomaceous earth, iron oxide, titanium oxide, calcium carbonate, and the like. These inorganic fillers may be used alone or in combination of two or more, and even if used as is, the surface may be treated with polydimethylsiloxane, octamethylcyclotetrasiloxane, or hexamethyldisilazane. It may be treated with an organic silicon compound. Further, it is desirable to add a catalyst to the composition of the present invention to promote the curing reaction.

Catalysts include amines such as dimethylhexylamine, tributylamine, tetramethylenepentamine, diethylhydroxylamine, quaternary ammonium salts such as tetramethylammonium acetate, trimethylhexylammonium chloride, tin octoate, dibutyltin diacetate. , dibutyltin dioctoate, dibutyltin dilaurate, diphenyltin diacetate,
Organic acid salts of tin such as dibutyltin dimaleate and dioctyltin dimaleate, and organic tin compounds such as dibutyltin oxide are used. The amount of these additions is not particularly limited, but for example, in the case of dibutyltin dilaurate, it is 0.05 to 1 part by volume per 10 parts by weight of the silanol-terminated polydiorganosilosiloxane (4).
Parts by weight are appropriate. The composition of the present invention contains a pigment, a thixotropic agent, and various additives such as a viscosity modifier, an ultraviolet inhibitor, a fungicide, a heat resistance improver, and a flame retardant to improve extrusion workability. can be added. The composition of the present invention is prepared by mixing all the ingredients and, if necessary, inorganic fillers, catalysts, and/or various additives in a moisture-free condition, storing the mixture in a closed container, and exposing it to air when used. It can be used as a so-called one-component room temperature curing polysiloxane composition which is cured by exposure to moisture. In addition, a so-called two-component room temperature curing polysiloxane composition in which component (4), component (B), component (C) and, if necessary, a catalyst are stored in separate containers and mixed together at the time of use. It can also be used as an object. The present invention has made it possible to produce an oxime-free curable polysiloxane composition with improved self-adhesiveness and durability, and which does not yellow during storage or after curing. That is, this composition has better self-adhesive properties and stronger anti-yellowing properties than a composition mainly composed of components (4) and (B) without using component (C). Furthermore, yellowing of the rubber-like elastic body after curing was observed even when using a conventionally known self-adhesion improver such as γ-aminopropyltriethoxysilane in place of component (C). It has a remarkable effect on preventing. The composition of the present invention is widely used as a sealing material for buildings, a sealing material in the electronic industry, etc. because of its excellent self-adhesiveness and color stability.

Hereinafter, the present invention will be explained with reference to Examples. In the Examples, all parts represent parts by weight. Example 1 N-propylamine 59y (1
mol) and γ-glycidoxypropyltrimethoxysilane 236y (1 mol) were reacted by heating at a temperature of 80°C for 5 hours with stirring in a dry nitrogen atmosphere to form the reaction product (1) 295y. Obtained.

A curing agent mixture was obtained by mixing 0.25 parts of (1) with 5 parts of methyltris(acetone oxime silane) and 0.1 part of dibutyltin dilaurate.

The above curing agent mixture was added to a base compound obtained by uniformly kneading 1 (1) part of silanol-terminated polydimethylsiloxane (viscosity 10,000 Cst at 25 Cst) and w part of fumed silica having a surface area of 200 d1y in dry air. Prepare a polysiloxane composition by uniformly kneading with
It was filled into an aluminum tube and stored tightly. 1st
This composition was applied to the adherend shown in the table, and the temperature was 25°C.
The peel adhesion strength and cohesive failure rate were measured for the product which was left to cure for 7 days at a relative humidity of 60%. Also,
Uncured samples were stored in aluminum tubes for 6 months, and cured samples were stored at a temperature of 150'C for 1 month.
We investigated the color change when left for a week. A similar experiment,
One in which 0.05 part of n-propylamine was added instead of (1) (Comparative Example 1a), and one in which 0.2 part of γ-glycidoxypropylmethoxysilane was added (Comparative Example F1).
I followed b). The results of these experiments are shown in Table 1. Example 2 Piperidine 85y (1 mol) and γ-glycidoxypropyltrimethoxysilane 236y were placed in a 1f Mitsuro flask.
(1 mol) was taken and stirred in a dry nitrogen atmosphere.
The mixture was heated at a temperature of 10° C. for 8 hours to react, and a reaction product (■) 321y was obtained.

0.5 parts (■) of vinyl tris (butanone oxime)
A curing agent mixture was obtained by mixing 7 parts of silane and 0.1 part of dioctyltin dimaleate.

In advance, 100 parts of silanol-terminated polydimethylsiloxane (viscosity 300 St at 25°C) and a surface area of 20
0 pore Iy, fumed silica whose surface is treated with polydimethylsiloxane 1? A thixotropic polysiloxane composition was prepared by uniformly kneading the above curing agent mixture into a paste compound obtained by uniformly kneading the above composition in dry air, and the thixotropic polysiloxane composition was filled into an aluminum tube and stored tightly closed. After storing for 6 months, the same experiment as in Example 1 was conducted.

For comparison, instead of (■), piperidine 0.1
Similar experiments were also carried out for a sample containing 3 parts of γ-glycidoxypropyltrimethoxysilane (Comparative Example 2a) and a sample containing 0.37 part of γ-glycidoxypropyltrimethoxysilane (Comparative Example 2b). The results of these experiments are shown in Table 2. Example 3 Cyclohexylamine 98y (
1 mole) and β-(3,4-oxycyclohexyl)ethyltrimethoxysilane 288y (1 mole) were heated in a dry nitrogen atmosphere at a temperature of 120°C for 8 hours with stirring to cause a reaction. Product (■) 386f1 was obtained.

A curing agent mixture was obtained by mixing 0.5 parts of (■) with 7 parts of tetrakisacetone oxime silane and 0.15 parts of diphenyltin diacetate.

1 (a) part of silanol-terminated polydimethylsiloxane (viscosity 20,000 Cst at 25 °C), 2 parts of trimethylsilyl-terminated polydimethylsiloxane (viscosity 10 cCst at 25 °C) , and calcium carbonate 1
A fluid polysiloxane composition was prepared by uniformly kneading the previous curable mixture into the base compound obtained by uniformly kneading the nodule in dry air, which was then filled into an aluminum tube and stored tightly closed. . After storage for 6 months, the same experiment as in Example 1 was conducted.

A similar experiment was carried out with the addition of 0.14 parts of cyclohexylamine instead of (■) (Comparative Example 3a) and β-(
The test was carried out on a product to which 0.36 part of 3,4-oxycyclohexyl)ethyltrimethoxysilane was added (Comparative Example 3b). The results of these experiments are shown in Table 3. Example 41
n-butylamine 73y (1 mol) and γ-glycidoxypropyltrimethoxysilane 23 in a three-necked flask.
6V (1 mol) was taken and reacted by heating at a temperature of 80° C. for 4 hours with stirring in a dry nitrogen atmosphere to obtain a reaction product (■) 309y.

0.25 parts of (■), 7 parts of methyltris(cyclohexanone oxime)silane, and 0.25 parts of dibutyltin dimaleate.
05 parts to obtain a curing agent mixture.

Silanol-terminated polydimethylsiloxane containing 5 mol% diphenylsiloxy units (viscosity 10,000 at 25°C)
Cst) 10(2), 8 parts of fumed silica with a surface area of 200rrIIy, the surface of which was treated with polydimethylsiloxane, and 1 part of diatomaceous soil were uniformly kneaded to form a base compound, and the hardening agent mixture was added to it in dry air. A polysiloxane composition was prepared by uniformly kneading the mixture. This composition was applied to the adherends shown in Table 4, and the same experiment as in Example 1 was conducted. A similar experiment was performed with n− instead of (■).
Added 0.06 part of butylamine (Comparative Example 4a)
and γ-glycidoxypropyltrimethoxysilane 0
．． The test was carried out on the product to which part P was added (Comparative Example 4b).
The results of these experiments are shown in Table 4. Example 5 1 (1) part of silanol-terminated polydimethylsiloxane (viscosity 10,000 cSt at 25°C) was treated with octamethylcyclotetrasiloxane to give a surface area of 3,200.
n1Iy fumed silica 1? A curing agent composition obtained by mixing 7 parts of methyltris(acetone oxime) silane, 0.1 part of dibutyltin dilaurate, and 0.3 part of the adhesion improver listed in Table 5 into a base compound uniformly kneaded. Material sample? -51 were uniformly kneaded in dry air to prepare a polysiloxane composition.

Coated on an aluminum plate, temperature 25℃, relative humidity 60
% for 7 days to cure, and its adhesion was examined. This was further heated at a temperature of 150° C. for one week and the color change was observed. However, the sample number? ~? is a comparative example. Example 6 Sample used in Example 5? -51 was sealed in an aluminum tube and stored at room temperature for 6 months, and all had good extrudability.

The color change during storage is shown in Table 6. Example 7 Samples 7a to 7f were prepared in the same manner as in Example 5, except that the curing agent mixture shown in Table 7 was used.

Table 7 shows the results of experiments similar to those in Example 5 performed on these samples. Example 8 As a silanol-terminated polydiorganosiloxane,
Samples were prepared in the same manner as in Example 5 except that those shown in Table 8 were used. I got ~ pieces.

Claims (1)

[Claims] 1 (A) 100 parts by weight of a silanol-terminated polydiorganosiloxane having a viscosity of 500 to 200,000 cSt at 25°C, (B) general formula R^1_aSi(OR^2)_b(ON=X)_4_ −
_a_-_b (wherein R^1 is a monovalent substituted or unsubstituted hydrocarbon group, R^2 is a monovalent group selected from an alkyl group and an alkoxyalkyl group, X is a ▲ mathematical formula, a chemical formula, A divalent group represented by ▼ or ▲ Numerical formulas, chemical formulas, tables, etc. ▼, where R^3 and R^4 are a hydrogen atom and a monovalent substituted or unsubstituted hydrocarbon group, respectively. ^5 is an alkylene group having 4 to 6 carbon atoms, a is 0
or the number 1, b represents the number 0 or 1), and an oxime group-containing organosilicon compound selected from silanes containing oxime groups, and partial hydrolysis thereof.
Part by weight (C) (1) General formula (Y-R^6)Si(OR^7)_3 (However, in the formula, Y contains an oxirane oxygen atom and an ether oxygen atom at the bond with R^6. containing or not containing a monovalent substituted hydrocarbon group, R^6 is a divalent hydrocarbon group, and R^7 is a monovalent substituted or unsubstituted hydrocarbon group). an epoxy group-containing organosilicon compound selected from silane and its partial hydrolyzate; and (2) a primary or secondary compound that does not contain silicon atoms.
or (D) a catalyst amount selected from amines, quaternary ammonium salts, organic acid salts of tin, and organic tin compounds. A polysiloxane composition that is curable at room temperature. 2. The composition according to claim 1, wherein the organic group of the silanol-terminated polydiorganosiloxane (A) is a monovalent hydrocarbon group selected from a methyl group, a vinyl group, and a phenyl group. 3. The composition according to claim 2, wherein the acid group of the silanol-terminated polydiorganosiloxane (A) is a methyl group. 4. The composition according to claim 1, wherein R^1 is a methyl group. 5. The composition according to claim 1, wherein R^3 and R^4 are each the same or different alkyl groups having 1 to 2 carbon atoms. 6. The composition according to claim 1, wherein (Y-R^6) is a γ-glycidoxypropyl group. 7. The composition according to claim 1, wherein (Y-R^6) is a β-(3,4-oxycyclohexyl)ethyl group. 8. The composition according to claim 1, wherein R^7 is a monovalent group selected from an alkyl group having 1 to 3 carbon atoms and an ethyl group substituted with an alkoxy group having 1 to 2 carbon atoms. thing.