Rubber composition

Abstract

To provide a rubber composition which prevents production of quinone and is excellent in anti-aging property.SOLUTION: A rubber composition contains 100 pts.mass of diene-based rubber, and 0.1 to 10 pts.mass of at least one compound selected from a compound group containing a compound represented by the following formula. In the formula, Ra and Rb each independently represent an aromatic ring or an alkyl group having 3 to 10 carbon atoms. R1 to R3 each dependently represent a hydrogen atom or a substituent.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a rubber composition. [Background technology]

[0002] 2. Description of the Related Art Conventionally, rubber compositions containing a phenylenediamine-based antioxidant (for example, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD)) as an antioxidant have been known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-046554 [Non-patent literature]

[0004] [Non-Patent Document 1] Science,2021,371,6525,185-189 Summary of the Invention [Problem to be solved by the invention]

[0005] On the other hand, there are concerns about environmental pollution due to 6PPD quinone (see below) generated by quinonization of 6PPD (Non-Patent Document 1).

[0006] [ka]

[0007] Furthermore, in recent years, with the increasing demand for higher safety levels, there has been a demand for further improvement in the anti-aging properties of rubber products such as tires.

[0008] In view of the above circumstances, an object of the present invention is to provide a rubber composition which is less likely to produce quinone and has excellent anti-aging properties. [Means for solving the problem]

[0009] As a result of extensive investigations into the above problems, the present inventors have found that the above problems can be solved by blending a specific compound in a predetermined amount, thereby completing the present invention. That is, the present inventors have found that the above problems can be solved by the following configuration.

[0010] (1) 100 parts by mass of a diene rubber; A rubber composition comprising 0.1 to 10 parts by mass of at least one compound selected from the group consisting of a compound represented by formula (I) described below and a compound represented by formula (II) described below. (2) The rubber composition according to the above (1), wherein at least one of R1 and R3 in the above formula (I) and the above formula (II) is an electron-donating group. (3) The rubber composition according to (1) or (2) above, wherein in the formula (I) and the formula (II), R2 is an electron-withdrawing group or an aromatic ring. Effect of the Invention

[0011] As will be described below, according to the present invention, it is possible to provide a rubber composition which is less likely to produce quinone and has excellent anti-aging properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The rubber composition of the present invention will be described below. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In addition, each component may be used alone or in combination of two or more. When two or more components are used in combination, the content of the components refers to the total content unless otherwise specified. In addition, when quinone is hardly generated, anti-aging properties are excellent, and breaking elongation is large, it is also said that "the effects of the present invention are excellent."

[0013] The rubber composition of the present invention (hereinafter also referred to as "the composition of the present invention") is 100 parts by mass of a diene rubber; The rubber composition contains 0.1 to 10 parts by mass of at least one compound (hereinafter also referred to as "specific compound") selected from the group consisting of a compound represented by formula (I) described later and a compound represented by formula (II) described later.

[0014] It is believed that the composition of the present invention has such a structure and therefore solves the above-mentioned problems. The reason for this is not clear, but is thought to be roughly as follows.

[0015] Diene rubbers are known to be degraded by radicals. When radicals are generated in the composition of the present invention, it is believed that the amine moiety or sulfide moiety of the specific compound contained in the composition deactivates the radicals, thereby suppressing deterioration of the diene rubber. Here, the specific compound is difficult to be quinonized because it lacks the quinonization sites (in the case of 6PPD, the sites a and b below).

[0016] [ka]

[0017] As a result, it is believed that the composition of the present invention is less likely to produce quinones and has excellent anti-aging properties.

[0018] Each component contained in the composition of the present invention will be described below.

[0019] [Diene rubber] The diene rubber contained in the composition of the present invention is not particularly limited. The compositions of the present invention may contain one or more diene rubbers.

[0020] [Specific examples] Specific examples of the diene rubber include natural rubber (NR), butadiene rubber (BR), aromatic vinyl-conjugated diene copolymer rubber, isoprene rubber (IR), acrylonitrile-butadiene copolymer rubber (NBR), butyl rubber (IIR), halogenated butyl rubber (Br-IIR, Cl-IIR), chloroprene rubber (CR), etc. Examples of the aromatic vinyl-conjugated diene copolymer rubber include styrene-butadiene rubber (SBR), styrene-isoprene copolymer rubber, butyl rubber, etc.

[0021] [Molecular weight] The weight average molecular weight (Mw) of the diene rubber is not particularly limited, but in order to obtain better effects of the present invention, it is preferably 100,000 to 5,000,000, more preferably 200,000 to 3,000,000, and even more preferably 300,000 to 2,000,000.

[0022] In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are values ​​calculated as standard polystyrene by gel permeation chromatography (GPC).

[0023] [Specific compound] The composition of the present invention contains at least one compound (specific compound) selected from the group consisting of a compound represented by the following formula (I) and a compound represented by the following formula (II).

[0024] Formula (I) [ka]

[0025] Formula (II) [ka]

[0026] In formula (I) and formula (II), R a and R beach independently represents an aromatic ring or an alkyl group having 3 to 10 carbon atoms. R1 to R3 each independently represent a hydrogen atom or a substituent.

[0027] [R a and R b 〕 As described above, in formula (I) and formula (II), R a and R b each independently represents an aromatic ring or an alkyl group having 3 to 10 carbon atoms.

[0028] Examples of the aromatic ring include an aromatic hydrocarbon ring and an aromatic heterocycle. Examples of the aromatic hydrocarbon ring include aromatic hydrocarbon rings having 6 to 18 carbon atoms, such as a benzene ring, a toluene ring, a xylene ring, and a naphthalene ring. Examples of the aromatic heterocycle include those containing a heteroatom such as a nitrogen atom, a sulfur atom, and an oxygen atom, and specific examples thereof include a pyridine ring and a thiophene ring. The aromatic ring is preferably an aromatic hydrocarbon ring, more preferably a benzene ring, because the effects of the present invention are more excellent. The aromatic ring may further have a substituent (for example, specific examples of which will be described later).

[0029] The alkyl group may be linear, branched, or cyclic (alicyclic). The alkyl group may further have a substituent (for example, specific examples of which will be described later).

[0030] [R1~R3] As described above, in formula (I) and formula (II), R1 to R3 each independently represent a hydrogen atom or a substituent (for example, specific examples described later).

[0031] At least one of R1 and R3 is preferably an electron-donating group because the effects of the present invention are more excellent. In addition, the above R2 is preferably an electron-withdrawing group or an aromatic ring because the effects of the present invention are more excellent. The definition, specific examples and preferred embodiments of the aromatic ring are as described above in R a and R b is the same as:

[0032] <Electron-donating group and electron-withdrawing group> In this specification, the electron donating group is a group having a Hammett's substituent constant σ p The value of the Hammett substituent constant σ is 0 or less. p Refers to a group with a value greater than zero. Here, Hammett's substituent constant σ p The Hammett rule is an empirical rule proposed by L.P. Hammett in 1935 to quantitatively discuss the effect of substituents on the reaction or equilibrium of benzene derivatives, and is widely accepted as valid today. The substituent constants obtained by the Hammett rule include σ p Value and σ m These values ​​can be found in many general textbooks, for example, "Lange's and book of Chemistry" edited by JADean, 12th edition, 1979 (McGraw-Hill) and "Chemical Domain" special edition, No. 122, pp. 96-103, 1979 (Nankodo). When the structure (group) is a polyvalent group, it is judged whether it is an electron donating group or an electron withdrawing group as a monovalent group (one in which a hydrogen atom is bonded to the other bonding position).

[0033] Specific examples of the electron donating group include an alkyl group, a halogenated alkyl group, and an alkoxy group. Among them, an alkoxy group is preferable because the effects of the present invention are more excellent. The number of carbon atoms in the electron donating group is not particularly limited, but is preferably 1 to 10 because the effects of the present invention are more excellent.

[0034] Specific examples of the electron-withdrawing group include an acid group (particularly a carboxy group), a carboxylate group (RO-CO-: R is a hydrocarbon group), a cyano group, an amide group (-CO-NR2: R is a hydrogen atom or a hydrocarbon group), a hydroxyl group, an alkoxysilyl group, an amino group, and a carbonyl group (-CO-). Among these, a carboxylate group is preferred because it provides better effects of the present invention. The number of carbon atoms in the electron-withdrawing group is not particularly limited, but is preferably 1 to 10 because it provides better effects of the present invention.

[0035] [Specific examples of substituents] Specific examples of the substituent in this specification include a halogeno group (halogen atom), an alkyl group (e.g., a tert-butyl group) (including a cycloalkyl group, a bicycloalkyl group, and a tricycloalkyl group), an alkenyl group (including a cycloalkenyl group and a bicycloalkenyl group), an alkynyl group, an aryl group, a heterocyclic group (which may also be called a heterocyclic group), a cyano group, a hydroxy group, a nitro group, a carboxy group, an alkoxy group, an aryloxy group, a silyloxy group, a heterocyclic oxy group, an acyloxy group, a carbamoyl group, a carbamoyloxy group, an alkoxycarbonyloxy group, an aryloxycarbonyloxy group, an amino group (including an anilino group), an ammonio group, a dialkylamino group, an acylamino group, an aminocarbonylamino group, an a Examples of the substituent include an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfamoylamino group, an alkyl or arylsulfonylamino group, a mercapto group, an alkylthio group, an arylthio group, a heterocyclic thio group, a sulfamoyl group, a sulfo group, an alkyl or arylsulfinyl group, an alkyl or arylsulfonyl group, an acyl group, an aryloxycarbonyl group, an alkoxycarbonyl group, an aryl or heterocyclic azo group, an imido group, a phosphino group, a phosphinyl group, a phosphinyloxy group, a phosphinylamino group, a phosphono group, a silyl group, a hydrazino group, a ureido group, a boronic acid group (-B(OH)2), a phosphato group (-OPO(OH)2), a sulfato group (-OSO3H), and other known substituents.

[0036] [Molecular weight] The molecular weight of the specific compound is not particularly limited, but is preferably 100 to 1000, more preferably 200 to 800, and even more preferably 300 to 500, for reasons such as better effects of the present invention.

[0037] [Method for producing specific compound] The method for producing the specific compound is not particularly limited, but a production method including the following steps (1) to (3) in this order is preferred because it provides better effects of the present invention. Process (1): Oxidation process A process for oxidizing phenylenediamine-based antioxidants Process (2): Mixing process A step of mixing the oxidized phenylenediamine-based antioxidant with an allyl mercapto compound. Process (3): Heating process A step of heating the mixture obtained by the mixing step.

[0038] Each step will be described below.

[0039] <Oxidation process> The oxidation process is a process for oxidizing the phenylenediamine-based antioxidant, which becomes a diimine through the oxidation process.

[0040] (Phenylenediamine-based antioxidant) Phenylenediamine-based antioxidants are antioxidants whose molecular structure contains an aromatic ring with two secondary amines as substituents. Specific examples of phenylenediamine-based antioxidants include N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), N-phenyl-N'-(1-methylheptyl)-p-phenylenediamine, N-phenyl-N'-isopropyl-p-phenylenediamine, N,N'-di-2-naphthyl-p-phenylenediamine, N,N'-diphenyl-p-phenylenediamine, etc. Among these, N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD) is preferred because it provides superior effects of the present invention.

[0041] (Oxidation) The method for oxidation is not particularly limited, but examples thereof include a method in which the material is mixed with an oxidizing agent.

[0042] <Mixing process> The mixing step is a step of mixing the oxidized phenylenediamine-based antioxidant obtained in the oxidation step with an allyl mercapto compound, so that the mercapto group of the allyl mercapto compound reacts with the phenylenediamine-based antioxidant that has become a diimine in the mixing step.

[0043] (Allyl mercapto compounds) The allyl mercapto compound is preferably a compound represented by the following formula (1) because the effects of the present invention are more excellent.

[0044] [ka] (1)

[0045] In formula (1), R1 to R3 each independently represent a hydrogen atom or a substituent. The definitions, specific examples and preferred embodiments of the above-mentioned substituents are the same as those of R1 to R3 in the above-mentioned formula (I) and formula (II).

[0046] The boiling point of the allyl mercapto compound is preferably 100° C. or higher, more preferably 150° C. or higher, for reasons of superior effects of the present invention and from the viewpoint of odor. The upper limit of the boiling point is not particularly limited, but is usually 300° C. or lower. In this specification, the boiling point is the value at 1 atmospheric pressure.

[0047] <Heating process> The heating step is a step of heating the reaction product obtained in the mixing step, whereby a ring structure is formed to obtain a specific compound.

[0048] For example, when the allyl mercapto compound is a compound represented by formula (1) (R1 to R3 are hydrogen atoms), the reaction proceeds as shown in the following reaction formula. Note that in the following reaction formula, only an aromatic ring having two secondary amines as substituents is shown for the phenylenediamine-based antiaging agent. In addition, although a five-membered ring is ultimately formed in the following reaction formula, a six-membered ring may be formed in some cases.

[0049] [ka]

[0050] (heating) The heating temperature is not particularly limited, but is preferably 100 to 200°C, and more preferably 130 to 170°C, for reasons such as better effects of the present invention.

[0051] [Content] In the composition of the present invention, the content of the specific compound is 0.1 to 10 parts by mass relative to 100 parts by mass of the diene rubber. Among them, the content is preferably 0.5 to 5 parts by mass, and more preferably 0.5 to 3 parts by mass, for reasons such as better effects of the present invention.

[0052] [Optional ingredients] The composition of the present invention may further contain other components (optional components) as necessary, provided that the effects and objects of the composition are not impaired. Examples of the optional components include various additives that are generally used in rubber compositions, such as fillers (e.g., silica, carbon black), silane coupling agents, terpene resins (e.g., aromatic modified terpene resins), thermally expandable microcapsules, zinc oxide (zinc white), stearic acid, antioxidants, waxes, processing aids, oils, liquid polymers, thermosetting resins, vulcanizing agents (e.g., sulfur), and vulcanization accelerators.

[0053] [Carbon Black] The composition of the present invention preferably contains carbon black because the effects of the present invention are more excellent. The carbon black is not particularly limited, and various grades such as SAF-HS, SAF, ISAF-HS, ISAF, ISAF-LS, IISAF-HS, HAF-HS, HAF, HAF-LS, and FEF can be used. The nitrogen adsorption specific surface area (N2SA) of the carbon black is not particularly limited, but is preferably 50 to 200 m for the reason that the effects of the present invention are more excellent. 2 / g, and 70 to 150m 2 It is more preferable that the molecular weight is / g. Here, the nitrogen adsorption specific surface area (N2SA) is the amount of nitrogen adsorbed on the surface of carbon black measured according to JIS K6217-2:2001 "Part 2: Determination of specific surface area - Nitrogen adsorption method - Single point method."

[0054] <Content> In the composition of the present invention, the content of carbon black is not particularly limited, but in order to obtain better effects of the present invention, the content is preferably 1 to 100 parts by mass, and more preferably 2 to 50 parts by mass, per 100 parts by mass of the diene rubber described above.

[0055] 〔silica〕 The composition of the present invention preferably contains silica because the effects of the present invention are more excellent. The silica is not particularly limited, and any conventionally known silica can be used. Examples of the silica include wet silica, dry silica, fumed silica, diatomaceous earth, etc. The silica may be used alone or in combination of two or more kinds.

[0056] The cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​the silica (hereinafter, the "CTAB adsorption specific surface area" may be simply referred to as "CTAB") is not particularly limited. However, in order to improve the effects of the present invention, it is preferred to use a silica having a cetyltrimethylammonium bromide (CTAB) adsorption specific surface area of ​​100 to 300 m. 2 / g, and 150 to 200m 2 It is more preferable that the molecular weight is / g. Here, the CTAB adsorption specific surface area is a value obtained by measuring the amount of CTAB adsorbed on the silica surface in accordance with JIS K6217-3:2001 "Part 3: Determination of specific surface area - CTAB adsorption method."

[0057] <Content> In the composition of the present invention, the content of silica is not particularly limited, but in order to obtain better effects of the present invention, the content is preferably 10 to 150 parts by mass, and more preferably 50 to 100 parts by mass, per 100 parts by mass of the diene rubber.

[0058] [Manufacturing method] The method for producing the composition of the present invention is not particularly limited, and specific examples thereof include a method of kneading the above-mentioned components using a known method and device (e.g., a Banbury mixer, a kneader, a roll, etc.). When the composition of the present invention contains a vulcanizing agent (e.g., sulfur) and a vulcanization accelerator, it is preferable to first mix the components other than the vulcanizing agent and vulcanization accelerator at a high temperature (preferably 100 to 155°C), cool the mixture, and then mix the vulcanizing agent and vulcanization accelerator, because the effects of the present invention are more excellent for the resulting composition. The composition of the present invention can be vulcanized or crosslinked under conventionally known vulcanization or crosslinking conditions.

[0059] [Application] The composition of the present invention is preferably used as a rubber material. For example, it is preferably used for tires (particularly pneumatic tires), conveyor belts, hoses, vibration-proof materials, rubber rolls, outer covers of railway vehicles, etc. Among them, it is preferably used for tires (particularly treads). EXAMPLES

[0060] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0061] [Synthesis of specific compounds] Compounds 1 to 3 were synthesized as follows. All of compounds 1 to 3 are specific compounds.

[0062] [Compound 1] First, a phenylenediamine antioxidant (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine) (6PPD) was oxidized with an oxidizing agent. Then, an allyl mercapto compound 1 (a compound represented by formula (1), where R1 to R3 are hydrogen atoms) was mixed and heated (150°C).

[0063] The resulting compound is a compound represented by formula (I) (R a is a 1,3-dimethylbutyl group, R b is a benzene ring, and R1 to R3 are hydrogen atoms) and a compound represented by formula (II) (R a is a 1,3-dimethylbutyl group, R b is a benzene ring, and R1 to R3 are hydrogen atoms). The resulting compound (mixture) is also referred to as "Compound 1."

[0064] [Compound 2] The compound was synthesized according to the same procedure as for compound 1, except that allyl mercapto compound 2 (a compound represented by formula (1), in which R1 is a methoxy group, and R2 and R3 are hydrogen atoms) was used instead of allyl mercapto compound 1.

[0065] The resulting compound is a compound represented by formula (I) (R a is a 1,3-dimethylbutyl group, R b is a benzene ring, R1 is a methoxy group, R2 and R3 are hydrogen atoms) and a compound represented by formula (II) (R a is a 1,3-dimethylbutyl group, R b is a benzene ring, R1 is a methoxy group, and R2 and R3 are hydrogen atoms). The resulting compound (mixture) is also referred to as "Compound 2."

[0066] [Compound 3] The compound was synthesized according to the same procedure as for compound 1, except that allyl mercapto compound 3 (a compound represented by formula (1), in which R1 and R3 are hydrogen atoms and R2 is a methyl ester group (CH3-O-CO-)) was used instead of allyl mercapto compound 1.

[0067] The resulting compound is a compound represented by formula (I) (R a is a 1,3-dimethylbutyl group, R b is a benzene ring, R1 and R3 are hydrogen atoms, and R2 is a methyl ester group (CH3-O-CO-)) and a compound represented by formula (II) (R a is a 1,3-dimethylbutyl group, R b was a mixture of R1 and R2, where R1 was a benzene ring, R1 and R3 were hydrogen atoms, and R2 was a methyl ester group (CH3-O-CO-). The resulting compound (mixture) is also referred to as "Compound 3."

[0068] [Ozone exposure test] The phenylenediamine-based antioxidant (N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine) (6PPD) and the obtained compounds 1 to 3 were analyzed using a volume of 1000 cm 3 After sealing the sample at the bottom of the glass container, ozone was flowed from the ozone generator under the specified conditions to perform an ozone exposure test on the compound (room temperature (25°C), concentration: 500 pphm (500 x 10 -8 ) and 1 week) and the proportion of quinones converted (quinone conversion rate) was examined. As a result, the quinone ratio of 6PPD was 3.8 mol %. On the other hand, no quinone was detected in compounds 1 to 3 (nd).

[0069] [Production of rubber composition] The components in Table 1 below were mixed in the composition (parts by mass) shown in the same table. Specifically, first, the components other than sulfur and the vulcanization accelerator in Table 1 were mixed in a 1.8 L internal mixer at 130°C for 5 minutes, and a master batch was discharged. Then, sulfur and the vulcanization accelerator were added to the master batch, and the mixture was mixed at 80°C using an open roll to produce each rubber composition.

[0070] [EB after aging] Each of the obtained rubber compositions (unvulcanized) was press-vulcanized in a mold (15 cm x 15 cm x 0.2 cm) at 150°C for 30 minutes to produce a vulcanized rubber sheet. The obtained vulcanized rubber sheet was then subjected to an aging test (left in an 80°C environment for 168 hours (2 weeks)). Next, in accordance with JIS K6251:2010, JIS No. 3 dumbbell-shaped test pieces (thickness 2 mm) were punched out and evaluated for breaking elongation at a temperature of 20°C and a tensile speed of 500 mm / min. The results are shown in Table 1 (EB after aging). The results are expressed as an index with Comparative Example 1 being 100. From the viewpoint of anti-aging properties, an index of 101 or more is preferable.

[0071] [Table 1]

[0072] Details of each component in Table 1 are as follows. Natural rubber: Natural rubber Carbon black: Show Black N234 (manufactured by Showa Cabot Corporation) Zinc oxide: 3 types of zinc oxide (manufactured by Seido Chemical Industry Co., Ltd.) Stearic acid: Beads Stearic Acid YR (manufactured by NOF Corporation) Phenylenediamine-based antioxidant: N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD) Compounds 1 to 3: Compounds 1 to 3 synthesized as described above Sulfur: Oil-treated sulfur (Karuizawa Refinery Co., Ltd.) Vulcanization accelerator TBBS: Sancerer NS-G (manufactured by Sanshin Chemical Industry Co., Ltd.)

[0073] In Table 1, the column "boiling point" indicates the boiling point of the allyl mercapto compound (allyl mercapto compounds 1 to 3) used in the synthesis of each example compound (compounds 1 to 3).

[0074] In addition, in Table 1, the column "Model 3-step rate-determining activation energy" shows the largest activation energy [kcal] obtained by quantum chemical calculation (conditions: B3LYP / 6-31G) when the phenylenediamine antioxidant (6PPD) and the allyl mercapto compounds (allyl mercapto compounds 1-3) used in the synthesis of the compounds (compounds 1-3) used in each example react as described above ((thio)Claisen rearrangement, thiol-ene reaction) to form a five-membered ring. The above activation energy of compound 1 is expressed as an index of 100. It is considered that the smaller this value, the more easily the above reaction proceeds.

[0075] In addition, in Table 1, the column "quinone conversion rate" indicates the quinone conversion rate of the compound (6PPD, compounds 1 to 3) used in each example.

[0076] From the results of the ozone exposure test described above, it can be said that quinone is less likely to be generated in Examples 1 to 3, which used Compounds 1 to 3 (Specific Compounds), compared to Comparative Example 1, which used a phenylenediamine-based antioxidant.

[0077] Furthermore, as can be seen from Table 1, Examples 1 to 3, which used Compounds 1 to 3 (specific compounds), exhibited excellent antiaging properties, compared with Comparative Example 1, which used a phenylenediamine-based antiaging agent.

Claims

1. 100 parts by mass of a diene rubber; A rubber composition comprising 0.1 to 10 parts by mass of at least one compound selected from the group consisting of a compound represented by the following formula (I) and a compound represented by the following formula (II): 【Chemistry 1】 (I) 【Chemistry 2】 (II) In formula (I) and formula (II), R ａ and R ｂ R each independently represents an aromatic ring or an alkyl group having 3 to 10 carbon atoms. １ ~R ３ each independently represents a hydrogen atom or a substituent.

2. In the formula (I) and the formula (II), R １ and R ３ The rubber composition according to claim 1 , wherein at least one of the following groups is an electron donating group.

3. In the formula (I) and the formula (II), R ２ The rubber composition according to claim 1 or 2, wherein is an electron-withdrawing group or an aromatic ring.

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