JP2024069801A - Organopolysiloxane and rubber composition - Google Patents

Abstract

The present invention provides an organopolysiloxane that, when added to a rubber composition, is excellent in vulcanization characteristics, tensile characteristics after vulcanization, wet grip properties, and low rolling resistance, thereby enabling the realization of a desired fuel-efficient tire. The organopolysiloxane is represented by the following average composition formula (1): (R1)a(R2)b(OR3)c(R4)dSiO(4-2a-b-c-d)/2(1) (Each R1 is independently an arylene group having 6 to 10 carbon atoms or an alkylene group having 1 to 10 carbon atoms; each R2 is independently a mercapto group-containing organic group; each R3 is independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms; each R4 is independently an alkyl group having 1 to 12 carbon atoms; and each a, b, c, and d are numbers that satisfy 0<a<1, 0<b<1, 0<c<3, 0≦d<1, and 0<2a+b+c+d<4.) [Selected Figure] None

Description

The present invention relates to an organopolysiloxane and a rubber composition, and more specifically to an organopolysiloxane containing a mercapto group, a divalent hydrocarbon group, and an organooxy group and/or a hydroxyl group, and a rubber composition containing the same.

Tires made of silica-filled rubber compositions have excellent performance in automotive applications, particularly in terms of abrasion resistance, rolling resistance, and wet grip. Improvements in these performances are closely related to improvements in the fuel economy of tires, and therefore have been the subject of active research in recent years.

In order to improve fuel economy, it is essential to increase the silica filling rate of the rubber composition, and although a silica-filled rubber composition reduces the rolling resistance of a tire and improves wet grip, it has a high unvulcanized viscosity, requires multi-stage kneading, etc., and has problems with workability. Therefore, in a rubber composition in which an inorganic filler such as silica is simply blended, the dispersion of the filler is insufficient, and problems arise in that the breaking strength and abrasion resistance are significantly reduced.
Therefore, a sulfur-containing organosilicon compound was essential in order to improve the dispersibility of the inorganic filler in the rubber and to chemically bond the inorganic filler to the rubber matrix.

As sulfur-containing organosilicon compounds, compounds containing an alkoxysilyl group and a polysulfide silyl group in the molecule, such as bis-triethoxysilylpropyl tetrasulfide and bis-triethoxysilylpropyl disulfide, are known to be effective (see Patent Documents 1 to 4).
In addition to the above-mentioned organosilicon compounds having polysulfide groups, the use of thioester-type organosilicon compounds containing blocked mercapto groups, which are advantageous for the dispersibility of silica, and sulfur-containing organosilicon compounds of the type in which an aminoalcohol compound is transesterified with a hydrolyzable silyl group moiety, which is advantageous for affinity with silica through hydrogen bonding, is also known (see Patent Documents 5 to 9).

However, even if the sulfur-containing organosilicon compounds disclosed in the above-mentioned patent documents are used, it has not yet been possible to obtain a rubber composition for tires that achieves the desired fuel efficiency. Furthermore, these sulfur-containing organosilicon compounds are more expensive than sulfide-type compounds, and the manufacturing method is complicated, which means that there are problems with productivity, and various other issues remain.

Patent Document 10 discloses a rubber composition for tires that uses a polysiloxane having a mercapto group and a long-chain alkyl group. However, although tires made from this composition have improved rolling resistance and wet grip properties, they suffer from a problem of significantly deteriorating vulcanization characteristics.

JP 2004-525230 A JP 2004-18511 A JP 2002-145890 A U.S. Pat. No. 6,229,036 JP 2005-8639 A JP 2008-150546 A JP 2010-132604 A Patent No. 4571125 U.S. Pat. No. 6,414,061 Japanese Patent No. 5339008

The present invention has been made in consideration of the above circumstances, and aims to provide an organopolysiloxane that, when added to a rubber composition, is excellent in vulcanization characteristics, tensile properties after vulcanization, wet grip properties, and low rolling resistance, and can realize a desired fuel-efficient tire, and a rubber composition containing this organopolysiloxane.

As a result of intensive research conducted by the present inventors to achieve the above object, they discovered that when an organopolysiloxane containing an arylene group and/or an alkylene group, a mercapto group-containing organic group, and an organooxy group and/or a hydroxyl group is added to a rubber composition, it is possible to improve the vulcanization characteristics, tensile properties after vulcanization, wet grip properties, and rolling resistance, and that a tire made from this rubber composition can achieve low fuel consumption tire properties, thus completing the present invention.

（式中、ｍは、１～１０の整数を表し、ｎは、１～１０の整数を表し、破線は、結合手を表す。）
３． 前記ｄが、０＜ｄ＜１を満たす数である１のオルガノポリシロキサン、
４． １～３のいずれかのオルガノポリシロキサンを含むゴム組成物
を提供する。 That is, the present invention provides
1. An organopolysiloxane represented by the following average composition formula (1):
( ^R1 ) _a ( ^R2 ) _b ( ^OR3 ) _c ( ^R4 ) _d SiO _(4-2a-bcd)/2 (1)
(In the formula, R ¹ 's each independently represent an arylene group having 6 to 10 carbon atoms or an alkylene group having 1 to 10 carbon atoms; R ² 's each independently represent a mercapto group-containing organic group; R ^{3's each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms; R 4 's} each independently represent an alkyl group having 1 to 12 carbon atoms; and a, b, c, and d each represent a number satisfying 0<a<1, 0<b<1, 0<c<3, 0≦d<1, and 0<2a+b+c+d<4.)
2. The organopolysiloxane according to 1, wherein R ¹ is a group represented by the following general formula (2) and R ² is a group represented by the following general formula (3):

(In the formula, m represents an integer of 1 to 10, n represents an integer of 1 to 10, and the dashed line represents a bond.)
3. An organopolysiloxane in which d is a number satisfying 0<d<1;
4. A rubber composition containing the organopolysiloxane of any one of 1 to 3 is provided.

The rubber composition containing the organopolysiloxane of the present invention has excellent vulcanization characteristics, as well as tensile properties after vulcanization, wet grip properties, and low rolling resistance, and tires formed using this rubber composition can achieve low fuel consumption tire characteristics.

The present invention will be specifically described below.
[1] Organopolysiloxane The organopolysiloxane according to the present invention is represented by the following average composition formula (1).
( ^R1 ) _a ( ^R2 ) _b ( ^OR3 ) _c ( ^R4 ) _d SiO _(4-2a-bcd)/2 (1)

In the above formula (1), R ¹ 's each independently represent an arylene group having 6 to 10 carbon atoms or an alkylene group having 1 to 10 carbon atoms.
Examples of the arylene group having 6 to 10 carbon atoms include phenylene, biphenylene, and naphthylene groups.
The alkylene group having 1 to 10 carbon atoms may be linear, branched or cyclic, and examples thereof include methylene, ethylene, propylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, nonamethylene and decamethylene groups.
Among these, R ¹ is preferably a linear alkylene group represented by the following formula (2).

（式中、ｍは、１～１０の整数を表す。破線は結合手を表す（以下同じ）。）

(In the formula, m represents an integer of 1 to 10. The dashed lines represent bonds (the same applies below).)

Specific examples of the alkylene group represented by the above formula (2) include, but are not limited to, the groups represented by the following formulas:

Each ^R2 independently represents a mercapto group-containing organic group.
Examples of this organic group include alkyl groups having 1 to 10 carbon atoms, such as methyl, ethyl, n-propyl, n-butyl, n-hexyl, n-octyl, and n-decyl groups; aryl groups having 6 to 10 carbon atoms, such as phenyl and naphthyl groups; and aralkyl groups having 7 to 10 carbon atoms, such as benzyl and phenylethyl groups.
Among these, ^R2 is preferably a mercapto group-containing alkyl group represented by the following formula (3).

（式中、ｎは、１～１０の整数を表す。）

(In the formula, n represents an integer of 1 to 10.)

Specific examples of the mercapto-containing alkyl group represented by the above formula (3) include, but are not limited to, those represented by the following formulas:

^* _-CH2SH
^* _{-C2H4SH ​}
^* _{-C3H6SH ​}
^* _{-C4H8SH ​}
^* _{-C5H10SH ​}
^* _{-C6H12SH ​}
^* _{-C7H14SH ​}
^* _{-C8H16SH ​}
^* _{-C9H18SH ​}
^* _{-C10H20SH ​}
(In the formula, ^* - indicates a bond. The same applies below.)

^Each R3 independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 3 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms.
Specific examples of alkyl groups having 1 to 20 carbon atoms include methyl, ethyl, n-propyl, n-butyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, undecyl, dodecyl, and octadecyl groups.
Specific examples of the alkenyl group having 2 to 10 carbon atoms include vinyl, propenyl, and pentenyl groups.
Examples of the aryl group having 6 to 10 carbon atoms and the aralkyl group having 7 to 10 carbon atoms include the same groups as those exemplified for R ² above.
Among these, ^R3 is preferably a hydrogen atom, a methyl group, or an ethyl group, and more preferably an ethyl group.

R ⁴ each independently represents an alkyl group having 1 to 12 carbon atoms, and specific examples thereof include those having 1 to 12 carbon atoms among the alkyl groups having 1 to 20 carbon atoms exemplified for R ³ above.
Among these, from the viewpoint of improving processability by reducing the viscosity of the rubber composition and further improving fuel economy, R ⁴ is preferably an alkyl group having 6 to 12 carbon atoms, and more preferably an alkyl group having 6 to 10 carbon atoms.

a, b, c, and d represent the average number of moles of each organic group when the total number of moles of silicon atoms is taken as 1, and represent numbers that satisfy 0<2a<1, 0<b<1, 0<c<3, 0≦d<1, and 0<2a+b+c+d<4. From the viewpoint of silica dispersibility and rubber properties, the numbers preferably satisfy 0<2a<1, 0<b<1, 0<c<3, and 0<d<1, more preferably 0.2≦2a≦0.95, 0.05≦b≦0.8, 1≦c≦2.5, and 0<d≦0.6, and even more preferably 0.3≦2a≦0.8, 0.05≦b≦0.7, 1≦c≦2.5, and 0.1≦d≦0.5.

There are no particular limitations on the kinetic viscosity of the organopolysiloxane of the present invention at 25° C. as measured with a capillary kinetic viscometer, but from the standpoint of processability it is preferably 2 to 10,000 mm ² /s, and more preferably 10 to 5,000 mm ² /s.

The organopolysiloxane of the present invention can be produced, for example, by co-hydrolysis and condensation of an organosilicon compound represented by the following general formula (4), an organosilicon compound represented by the following general formula (5), and, if necessary, an organosilicon compound represented by the following general formula (6).

（式中、Ｒ³およびｍは、上記と同じ意味を表し、Ｒ⁵は、それぞれ独立して、炭素数１～１２のアルキル基、炭素数６～１０のアリール基、または炭素数７～１０のアラルキル基を表し、ｙは、１～３の整数、好ましくは、２または３を表す。）

(In the formula, ^R3 and m are as defined above, ^R5 each independently represents an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 10 carbon atoms, or an aralkyl group having 7 to 10 carbon atoms, and y represents an integer of 1 to 3, preferably 2 or 3.)

（式中、Ｒ³、Ｒ⁵、ｎおよびｙは、上記と同じ意味を表す。）

(In the formula, R ³ , R ⁵ , n and y have the same meanings as above.)

（式中、Ｒ³、Ｒ⁴およびｙは、上記と同じ意味を表す。）

(In the formula, R ³ , R ⁴ and y are as defined above.)

Examples of the alkyl group having 1 to 12 carbon atoms, the aryl group having 6 to 10 carbon atoms, and the aralkyl group having 7 to 10 carbon atoms for ^R5 include the same groups as exemplified for ^R2 and ^R4 above. Among these, ^R5 is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group.

Specific examples of the organosilicon compound represented by the above formula (4) include bistrimethoxysilylethyl, bistriethoxysilylethyl, bistrimethoxysilylpropyl, bistriethoxysilylpropyl, bistrimethoxysilylhexyl, and bistriethoxysilylhexyl.
Specific examples of the organosilicon compound represented by the above formula (5) include α-mercaptomethyltrimethoxysilane, α-mercaptomethylmethyldimethoxysilane, α-mercaptomethyltriethoxysilane, α-mercaptomethylmethyldiethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropylmethyldimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-mercaptopropylmethyldiethoxysilane, and the like.

Specific examples of the organosilicon compound represented by the above formula (6) include methyltrimethoxysilane, dimethyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, ethyltrimethoxysilane, ethylmethyldimethoxysilane, ethyltriethoxysilane, ethylmethyldiethoxysilane, butyltrimethoxysilane, butylmethyldimethoxysilane, butyltriethoxysilane, butylmethyldiethoxysilane, hexyltrimethoxysilane, hexylmethyldimethoxysilane, hexyltriethoxysilane, hexylmethyldiethoxysilane, octyltrimethoxysilane, Examples of organic silicon compounds containing alkyl groups include octylmethyldimethoxysilane, octyltriethoxysilane, octylmethyldiethoxysilane, decyltrimethoxysilane, decylmethyldimethoxysilane, decyltriethoxysilane, and decylmethyldiethoxysilane; and organic silicon compounds containing aryl groups include phenyltrimethoxysilane, diphenyldimethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, p-styryltrimethoxysilane, p-styrylmethyldimethoxysilane, p-styryltriethoxysilane, and p-styrylmethyldiethoxysilane.

The amounts of the organosilicon compounds represented by the above formulas (4), (5) and (6) used are selected so that a to d in the above formula (1) are the numbers described above. With respect to the total amount of the organosilicon compounds represented by the formulas (4), (5) and (6), the organosilicon compound represented by formula (4) is preferably 20 to 95 mol %, more preferably 30 to 80 mol %, the organosilicon compound represented by formula (5) is preferably 5 to 80 mol %, more preferably 5 to 70 mol %, and the organosilicon compound represented by formula (6) is preferably 0 to 60 mol %, more preferably 5 to 50 mol %.

The co-hydrolysis condensation can be carried out by a known method. The amount of water used can also be a known amount, usually 0.3 to 0.99 moles per mole of the total of hydrolyzable silyl groups in the organosilicon compound, with 0.4 to 0.9 moles being preferred.

In producing the organopolysiloxane of the present invention, an organic solvent may be used as necessary.
Specific examples of the organic solvent include aliphatic hydrocarbon solvents such as pentane, hexane, heptane, and decane; ether solvents such as diethyl ether, tetrahydrofuran, and 1,4-dioxane; amide solvents such as formamide, dimethylformamide, and N-methylpyrrolidone; aromatic hydrocarbon solvents such as benzene, toluene, and xylene; and alcohol solvents such as methanol, ethanol, n-propanol, and i-propanol.
Among these, ethanol and i-propanol are preferred from the viewpoint of excellent hydrolysis reactivity.
When a solvent is used, its amount is not particularly limited, but is preferably about twice the mass of the organosilicon compound or less, and more preferably about the same amount as the mass of the organosilicon compound or less.

In addition, a catalyst may be used, if necessary, in the production of the organopolysiloxane of the present invention.
Specific examples of the catalyst include acidic catalysts such as hydrochloric acid and acetic acid; Lewis acid catalysts such as tetrabutyl orthotitanate and ammonium fluoride; alkali metal salts such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium acetate, potassium acetate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, calcium carbonate, sodium methoxide, and sodium ethoxide; and amine compounds such as triethylamine, tributylamine, pyridine, and 4-dimethylaminopyridine.
Hydrochloric acid, for example, can be used as a catalyst for the hydrolysis reaction (and/or partial condensation) of silanes, and potassium hydroxide, for example, can be used as a catalyst for the condensation (oligomerization) of silanols.
From the viewpoint of excellent reactivity, the amount of catalyst (when a catalyst for the silane hydrolysis reaction and a catalyst for the silanol condensation reaction are used in combination, the amount of each catalyst) is preferably 0.0001 to 0.05 (unit: molar equivalent) per mole of the total of hydrolyzable silyl groups in the organosilicon compound.

The reaction conditions for the cohydrolysis condensation are usually 20 to 100°C, preferably 60 to 85°C, and usually 30 minutes to 20 hours, preferably 1 minute to 10 hours.

[2] Rubber Composition The rubber composition of the present invention contains the organopolysiloxane (A) represented by the above-mentioned formula (1), and may further contain a diene rubber (B) and a filler (C).
Taking into consideration the physical properties of the resulting rubber and the balance between the degree of effect exerted and economic efficiency, the blending amount of organopolysiloxane (A) represented by the above formula (1) is preferably 3 to 20 parts by mass, and more preferably 5 to 12 parts by mass, per 100 parts by mass of filler (C) described below.

As the diene rubber (B), any rubber that has been generally used in various rubber compositions can be used. Specific examples include natural rubber (NR); diene rubbers such as various isoprene rubbers (IR), various styrene-butadiene copolymer rubbers (SBR), various polybutadiene rubbers (BR), and acrylonitrile-butadiene copolymer rubbers (NBR), and these may be used alone or in combination of two or more. In addition to diene rubbers, non-diene rubbers such as butyl rubber (IIR) and ethylene-propylene copolymer rubbers (EPR, EPDM) can also be used in combination.

Examples of the filler (C) include silica, talc, clay, aluminum hydroxide, magnesium hydroxide, calcium carbonate, titanium oxide, etc. Among these, silica is preferred, and the rubber composition of the present invention is more preferably used as a silica-containing rubber composition.
In this case, taking into consideration the physical properties of the resulting rubber and the balance between the degree of effect exerted and economic efficiency, the amount of filler (C) compounded is preferably 5 to 200 parts by mass, and more preferably 30 to 120 parts by mass, per 100 parts by mass of diene rubber.

In addition to the above components (A) to (C), the rubber composition of the present invention may contain various additives that are generally used in tires and other general rubbers, such as carbon black, vulcanizing agents, crosslinking agents, vulcanization accelerators, crosslinking accelerators, various oils, antioxidants, and plasticizers. The amounts of these additives may be conventional amounts, provided they do not conflict with the objectives of the present invention.

The rubber composition of the present invention can be obtained by adding and kneading the above components (A) to (C) and, if necessary, other components, according to a conventional method.

[3] Rubber products (tires)
The rubber composition of the present invention can be used for the production of rubber products, such as tires, by vulcanizing or crosslinking the rubber composition. In particular, when tires are produced, it is preferable that the rubber composition of the present invention is used in the tread.

A tire obtained by using the rubber composition of the present invention has significantly improved rolling resistance performance and wet grip performance, and therefore can achieve the desired low fuel consumption.
The structure of the tire may be a conventionally known structure, and the manufacturing method may be a conventionally known manufacturing method. In the case of a gas-filled tire, the gas to be filled in the tire may be normal air, air with an adjusted oxygen partial pressure, or an inert gas such as nitrogen, argon, or helium.

The present invention will be described in more detail below with reference to synthesis examples, examples, and comparative examples, but the present invention is not limited to these examples. In the following examples, "parts" means parts by mass, and the kinetic viscosity is a value measured at 25°C using a capillary kinetic viscometer.

[1] Synthesis of organopolysiloxane [Example 1-1]
In a 1 L separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer, 231 g (0.6 mol) of bistriethoxysilylethane (KBE-3026, Shin-Etsu Chemical Co., Ltd.), 95.2 g (0.4 mol) of 3-mercaptopropyltriethoxysilane (KBE-803, Shin-Etsu Chemical Co., Ltd.), 55.4 g (0.2 mol) of octyltriethoxysilane (KBE-3083, Shin-Etsu Chemical Co., Ltd.), and 200 g of ethanol were placed, and then 16.2 g of 0.5 N hydrochloric acid (0.9 mol of water) was dropped at 25° C. Then, the mixture was stirred at 80° C. for 10 hours. Then, 3.0 g of propylene oxide was dropped and the mixture was stirred at 80° C. for 2 hours. Further, the mixture was concentrated under reduced pressure and filtered to obtain a colorless transparent liquid having a kinetic viscosity of 10 mm ² /s. The resulting organopolysiloxane had a mercapto equivalent of 800 and was represented by the following average composition formula:
( _{-C2H6- ) 0.33 ( -C3H6SH} ) _{0.22 ( -OC2H5} ) _{2.00 ( -C8H17} ) _0.11 SiO _0.50

[Example 1-2]
Into a 1 L separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer, 231 g (0.6 mol) of bistriethoxysilylethane (Shin-Etsu Chemical Co., Ltd., KBE-3026), 95.2 g (0.4 mol) of 3-mercaptopropyltriethoxysilane (Shin-Etsu Chemical Co., Ltd., KBE-803), 55.4 g (0.2 mol) of octyltriethoxysilane (Shin-Etsu Chemical Co., Ltd., KBE-3083), and 200 g of ethanol were placed, and then 19.4 g of 0.5 N hydrochloric acid (1.08 mol of water) was dropped at 25° C. Then, the mixture was stirred at 80° C. for 10 hours. Then, 3.0 g of propylene oxide was dropped, and the mixture was stirred at 80° C. for 2 hours. Further, the mixture was concentrated under reduced pressure and filtered to obtain a colorless and transparent liquid having a kinetic viscosity of 30 mm ² /s. The resulting organopolysiloxane had a mercapto equivalent of 750 and was represented by the following average composition formula:
( _{-C2H6- ) 0.33 ( -C3H6SH} ) _{0.22 ( -OC2H5} ) _{1.67 ( -C8H17} ) _0.11 SiO _0.67

[Examples 1-3]
Into a 1 L separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer, 231 g (0.6 mol) of bistriethoxysilylethane (Shin-Etsu Chemical Co., Ltd., KBE-3026), 47.6 g (0.2 mol) of 3-mercaptopropyltriethoxysilane (Shin-Etsu Chemical Co., Ltd., KBE-803), 111 g (0.4 mol) of octyltriethoxysilane (Shin-Etsu Chemical Co., Ltd., KBE-3083), and 200 g of ethanol were placed, and then 16.2 g of 0.5 N hydrochloric acid (0.9 mol of water) was dropped at 25° C. Then, the mixture was stirred at 80° C. for 10 hours. Then, 3.0 g of propylene oxide was dropped, and the mixture was stirred at 80° C. for 2 hours. Further, the mixture was concentrated under reduced pressure and filtered to obtain a colorless transparent liquid having a kinetic viscosity of 10 mm ² /s. The resulting organopolysiloxane had a mercapto equivalent of 1,600 and was represented by the following average composition formula:
( _{-C2H6- ) 0.33 ( -C3H6SH} ) _{0.11 ( -OC2H5} ) _2.00 ( _{-C8H17 ) 0.22} SiO _0.50

[Examples 1 to 4]
Into a 1 L separable flask equipped with a stirrer, a reflux condenser, a dropping funnel and a thermometer, 246 g (0.6 mol) of bistriethoxysilylhexane (KBE-3066, manufactured by Shin-Etsu Chemical Co., Ltd.), 95.2 g (0.4 mol) of 3-mercaptopropyltriethoxysilane (KBE-803, manufactured by Shin-Etsu Chemical Co., Ltd.), 55.4 g (0.2 mol) of octyltriethoxysilane (KBE-3083, manufactured by Shin-Etsu Chemical Co., Ltd.), and 200 g of ethanol were placed, and then 19.4 g of 0.5 N hydrochloric acid (1.08 mol of water) was dropped at 25° C. Then, the mixture was stirred at 80° C. for 10 hours. Then, 3.0 g of propylene oxide was dropped, and the mixture was stirred at 80° C. for 2 hours. Further, the mixture was concentrated under reduced pressure and filtered to obtain a colorless and transparent liquid having a kinetic viscosity of 25 mm ² /s. The resulting organopolysiloxane had a mercapto equivalent of 800 and was represented by the following average composition formula:
( _{-C6H12- ) 0.33} ( _-C3H6SH ) _{0.22 ( -OC2H5} ) _{1.67 ( -C8H17 ) 0.11} SiO _0.67

[Synthesis Example 1]
238 g (1.0 mol) of 3-mercaptopropyltriethoxysilane (KBE-803, manufactured by Shin-Etsu Chemical Co., Ltd.), 831 g (3.0 mol) of octyltriethoxysilane (KBE-3083, manufactured by Shin-Etsu Chemical Co., Ltd.), and 100 g of ethanol were placed in a 2 L separable flask equipped with a stirrer, reflux condenser, dropping funnel, and thermometer, and then 54 g of 0.5 N hydrochloric acid solution (3.0 mol of water) was dropped into the mixture at 25° C. The mixture was then stirred at 80° C. for 10 hours and then cooled to 25° C. 3.0 g of propylene oxide was dropped into the mixture, stirred at 25° C. for 1 hour, concentrated under reduced pressure, and filtered to obtain a colorless, transparent liquid with a kinetic viscosity of 10 mm ² /s. The mercapto equivalent of the obtained organopolysiloxane was 850 and was represented by the following average composition formula:
( _{-C3H6 -SH} ) _0.25 ( _-OC2H5 ) _{1.50 ( -C8H17 ) 0.75} SiO _0.75

[2] Preparation of rubber composition [Examples 2-1 to 2-5, Comparative Examples 2-1 and 2-2]
The SBR and BR shown in Table 1 were mixed for 30 seconds using a 4 L internal mixer (MIXTRON, manufactured by Kobe Steel, Ltd.).
Next, the oil components, carbon black, silica, sulfide silane, organopolysiloxanes obtained in the Examples and Synthesis Examples, stearic acid, antioxidants, and waxes shown in Table 1 were added, the internal temperature was raised to 150°C, and the mixture was held at 150°C for 2 minutes and then discharged. It was then stretched using rolls. The obtained rubber was again kneaded using an internal mixer (MIXTRON, manufactured by Kobe Steel, Ltd.) until the internal temperature reached 140°C, discharged, and then stretched using rolls.
To this was added zinc oxide, a vulcanization accelerator and sulfur as shown in Table 1, and the mixture was kneaded to obtain a rubber composition.

SBR: SLR-4602 (manufactured by Trinseo)
BR: BR-01 (manufactured by JSR Corporation)
Oil: AC-12 (Idemitsu Kosan Co., Ltd.)
Carbon black: Seast 3 (manufactured by Tokai Carbon Co., Ltd.)
Silica: Nipsil AQ (manufactured by Tosoh Silica Corporation)
Sulfide silane: KBE-846 (manufactured by Shin-Etsu Chemical Co., Ltd.)
Stearic acid: industrial stearic acid (Kao Corporation)
Anti-aging agent: Nocrac 6C (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
Wax: Ozoace 0355 (manufactured by Nippon Seiro Co., Ltd.)
Zinc oxide: Zinc oxide No. 3 (manufactured by Mitsui Mining & Smelting Co., Ltd.)
Vulcanization accelerator (a): Noccelaer D (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
Vulcanization accelerator (b): Noccela DM-P (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
Vulcanization accelerator (c): Noccela CZ-G (manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)
Sulfur: 5% oil-treated sulfur (manufactured by Hosoi Chemical Industry Co., Ltd.)

The unvulcanized and vulcanized properties of the rubber compositions obtained in Examples 2-1 to 2-5 and Comparative Examples 2-1 and 2-2 were measured by the following methods. The results are shown in Tables 1 and 2. The vulcanized properties were measured using vulcanized rubber sheets (thickness 2 mm) obtained by press molding (160°C, 10 to 40 minutes) the obtained rubber compositions.

[Unvulcanized physical properties]
(1) Mooney Viscosity Measured according to JIS K 6300-1:2013 with 1 minute residual heat, 4 minutes measurement, and at a temperature of 130°C, and expressed as an index with Comparative Example 2-1 being 100. The smaller the index value, the lower the Mooney viscosity and the better the processability.
(2) Vulcanization characteristics (T90)
The vulcanization rate at 160°C was measured using a rotorless rheometer, and the minimum torque ML and maximum torque MH were obtained from the vulcanization curve, and T90 (the time (min) required to reach 90% of the maximum torque) was calculated. Comparative Example 2-1 was set to 100 and expressed as an index. The smaller the index value, the faster the vulcanization rate and the more excellent the productivity.
[Vulcanization properties]
(3) Hardness The durometer (type A) hardness was measured in accordance with JIS K 6253-3:2012, and expressed as an index with Comparative Example 2-1 being 100. The larger the index value, the higher and more excellent the hardness.
(4) Tensile properties JIS No. 3 dumbbell-shaped test pieces were punched out, and a tensile test was carried out in accordance with JIS K6251 at a tensile speed of 500 mm/min to measure the 300% modulus (M ₃₀₀ ) [MPa] at 25° C. The results were expressed as an index, with Comparative Example 2-1 being set at 100. A larger index value indicates a higher modulus and more excellent tensile properties.
(5) Dynamic viscoelasticity (strain dispersion)
A viscoelasticity measuring device (manufactured by Metravib) was used to measure the storage modulus E' (0.5%) at a strain of 0.5% and the storage modulus E' (3.0%) at a strain of 3.0% at a temperature of 25°C and a frequency of 55 Hz, and the value of [E' (0.5%) - E' (3.0%)] was calculated. Note that a sheet having a thickness of 0.2 cm and a width of 0.5 cm was used as the test piece, the clamp distance was 2 cm, and the initial load was 1 N.
The value of [E'(0.5%)-E'(3.0%)] is expressed as an index with Comparative Example 2-1 being set at 100, and the smaller the index value, the better the dispersibility of silica.
(6) Dynamic viscoelasticity (temperature dispersion)
A viscoelasticity measuring device (manufactured by Metravib) was used to measure under conditions of a tensile dynamic strain of 1% and a frequency of 55 Hz. The test specimen was a sheet having a thickness of 0.2 cm and a width of 0.5 cm, with a clamp distance of 2 cm and an initial load of 1 N.
The values of tan δ (0°C) and tan δ (60°C) are expressed as indexes with Comparative Example 2-1 being 100. The larger the index value of tan δ (0°C), the better the wet grip performance. The smaller the index value of tan δ (60°C), the better the rolling resistance.

As shown in Table 1, the rubber compositions of Examples 2-1 to 2-5 have excellent vulcanization characteristics, and are good in tensile properties, silica dispersibility, wet grip properties, and rolling resistance after vulcanization, compared to the rubber composition of Comparative Example 2-1 which does not contain the organopolysiloxane of the present invention.
On the other hand, the rubber composition of Comparative Example 2-2, which uses a mercapto group-containing organopolysiloxane that does not have alkylene groups or arylene groups that directly bond silicon atoms to each other, shows significantly reduced vulcanization characteristics, and is inferior in tensile properties and rolling resistance after vulcanization.

Claims (4)

An organopolysiloxane represented by the following average composition formula (1):
( ^R1 ) _a ( ^R2 ) _b ( ^OR3 ) _c ( ^R4 ) _d SiO _(4-2a-bcd)/2 (1)
(In the formula, R ¹ 's each independently represent an arylene group having 6 to 10 carbon atoms or an alkylene group having 1 to 10 carbon atoms; R ² 's each independently represent a mercapto group-containing organic group; R ^{3's each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 10 carbon atoms, an aralkyl group having 7 to 10 carbon atoms, or an alkenyl group having 2 to 10 carbon atoms; R 4 's} each independently represent an alkyl group having 1 to 12 carbon atoms; and a, b, c, and d each represent numbers satisfying 0<a<1, 0<b<1, 0<c<3, 0≦d<1, and 0<2a+b+c+d<4.) 2. The organopolysiloxane according to claim 1, wherein R ¹ is a group represented by the following general formula (2), and R ² is a group represented by the following general formula (3).

(In the formula, m represents an integer of 1 to 10, n represents an integer of 1 to 10, and the dashed line represents a bond.) The organopolysiloxane according to claim 1, wherein d is a number satisfying 0<d<1. A rubber composition containing the organopolysiloxane according to any one of claims 1 to 3.