Modified conjugated diene polymer, rubber composition, and tire

Abstract

To provide a polymer excellent in crack growth resistance.SOLUTION: Provided is a modified conjugated diene-based polymer, the polymer having at least a conjugated diene unit, and having three or more modified groups represented by -SO3M1 / n (M is a metal atom, and n is an integer selected from 1 to 4 in terms of the valence that the M can take as a cation) in one molecule of the polymer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a modified conjugated diene polymer, a rubber composition, and a tire. [Background technology]

[0002] In recent years, demands for improved fuel economy for automobiles have become more stringent. To meet these demands, there is also a need for reduced rolling resistance in tires. The most common method for reducing tire rolling resistance is to use a rubber composition with a lower heat buildup (low loss).

[0003] As such a method, for example, a method in which carbon black is used as a filler and the polymerization active terminal is modified with a tin compound (see, for example, Patent Document 1), and a method in which carbon black is similarly used and an amino group is introduced into the polymerization active terminal (see, for example, Patent Document 2) have been disclosed. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 60-255838 [Patent Document 2] Japanese Patent Application Publication No. 62-207342 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in general, the lower the hysteresis loss of a polymeric material, the more energy is diverted to material fracture, resulting in a decrease in durability, particularly crack growth resistance. Therefore, conventional polymeric materials have room for improvement in terms of improving crack growth resistance while maintaining low loss.

[0006] Therefore, an object of the present invention is to provide a polymer having excellent crack growth resistance, a rubber composition having excellent crack growth resistance, and a tire having excellent crack growth resistance. [Means for solving the problem]

[0007] As a result of intensive research to achieve the above object, the present inventors have found that a polymer obtained by introducing a predetermined modifying group into a conjugated diene polymer (modified conjugated diene polymer) can exhibit extremely high crack growth resistance, leading to the present invention.

[0008] That is, the modified conjugated diene polymer of the present invention is a polymer having at least a conjugated diene unit, and the polymer has a molecular weight of -SO3M 1 / n (M is a metal atom, and n is a valence that M can take as a cation and is selected from integers of 1 to 4). The modified conjugated diene polymer of the present invention has excellent crack growth resistance.

[0009] In the modified conjugated diene polymer of the present invention, the metal atom M is preferably one or more metal atoms selected from Groups 1 and 2 of the periodic table, which can more effectively improve the crack growth resistance.

[0010] In the modified conjugated diene polymer of the present invention, the polymer is preferably polybutadiene, a styrene-butadiene copolymer, or polyisoprene, which is relatively easy to produce and can more fully achieve the desired effects.

[0011] In the modified conjugated diene polymer of the present invention, the total proportion of 1,2-bonded and 3,4-bonded conjugated diene units in the entire conjugated diene units is preferably 10 mol % or more and 70 mol % or less, which allows for the introduction of a more sufficient amount of modifying groups and ensures sufficient crosslinking sites during crosslinking.

[0012] In the modified conjugated diene polymer of the present invention, it is preferred that the conjugated diene unit contains a 1,2- or 3,4-bonded conjugated diene unit, and the group containing the modifying group is bonded to a carbon atom in a side chain of the 1,2- or 3,4-bonded conjugated diene unit. In this case, the double bonds in the main chain of the polymer are not consumed, and therefore adverse effects on other physical properties can be reduced, such as ensuring sufficient reinforcing properties when a filler is compounded and sufficient crosslinked portions during crosslinking.

[0013] The modified conjugated diene polymer of the present invention preferably has a proportion of the modifying group of 0.1% by mass or more and 3.0% by mass or less, which can more reliably improve crack growth resistance and also improve ease of production.

[0014] The rubber composition of the present invention is characterized by containing the modified conjugated diene polymer.The rubber composition of the present invention has excellent crack growth resistance.

[0015] The tire of the present invention is characterized by using the above rubber composition. The tire of the present invention has excellent crack growth resistance. [Effects of the Invention]

[0016] According to the present invention, a polymer having excellent crack growth resistance can be provided. Also, according to the present invention, a rubber composition having excellent crack growth resistance can be provided. Also, according to the present invention, a tire having excellent crack growth resistance can be provided. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, embodiments of the present invention will be described. These descriptions are for the purpose of illustrating the present invention and are not intended to limit the present invention in any way.

[0018] (Modified conjugated diene polymer) The modified conjugated diene polymer according to one embodiment of the present invention (hereinafter, may be referred to as "the modified conjugated diene polymer of the present embodiment") contains at least a conjugated diene unit, and in one molecule of the polymer, -SO3M 1 / n (M is a metal atom, and n is a valence that M can take as a cation and is selected from integers of 1 to 4.) Such a modified conjugated diene polymer has excellent crack growth resistance.

[0019] The modifying group is a group having a sulfonyl group, and is also -SO3 - (M n+ ) 1 / n , or -S(=O)2-OM 1 / n It can also be expressed as:

[0020] In the modified conjugated diene polymer of this embodiment, the specific modifying groups have a unique non-covalent bond, which can form a weak bond between polymer molecules. More specifically, an O atom in a modifying group in one modified conjugated diene polymer molecule can coordinate to a metal atom M in a modifying group in another modified conjugated diene polymer molecule, forming a coordinate bond, an ionic bond, or other non-covalent bond. In a low-strain region, the non-covalent bond is maintained, suppressing polymer movement, thereby maintaining low loss properties comparable to conventional polymers. On the other hand, as the strain increases, the non-covalent bond breaks, resulting in energy loss. This energy loss is presumed to improve crack growth resistance. In particular, it has been found that the improvement in crack growth resistance resulting from the specific modifying group described above tends to be greater than that of other known modified polymers. Furthermore, the non-covalent bond is reversible and can repeatedly dissociate and recombine, which can be expected to result in long-term high crack growth resistance.

[0021] The metal atom M in the modifying group is not particularly limited and may be a heavy metal (e.g., Cu) or a light metal. The metal atom M may be one type alone or a combination of two or more types. Among these, the metal atom M in the modifying group is preferably one or more metal atoms selected from Groups 1 and 2 of the periodic table, more preferably one or more metal atoms selected from Li, Na, and K, from the viewpoint of more effectively improving crack growth resistance due to a higher affinity with O atoms.

[0022] Here, for example, when the metal atom M is an atom that can become a monovalent cation (such as an atom in Group 1 of the periodic table), n=1, i.e., the modifying group is represented by -SO3M. Also, for example, when the metal atom M is an atom that can become a divalent cation (such as an atom in Group 2 of the periodic table), n=2, i.e., the modifying group is represented by -SO3M. 1 / 2 It is expressed as:

[0023] The number of modifying groups per molecule of the modified conjugated diene polymer of this embodiment is 3 or more. From the viewpoint of further improving crack growth resistance, the number of modifying groups is preferably 3 or more, and from the viewpoint of handleability, the number is preferably 30 or less.

[0024] The number of modifying groups per polymer molecule was calculated from the number average molecular weight (Mn) of the polymer before modification to obtain the number of molecules per 100 g. 1 The amount of modifying group per 100 g (mol of modifying group / 100 g) is determined from the H-NMR spectrum, and the amount can be determined by dividing the result.

[0025] Furthermore, means for increasing the number of the modifying groups include, but are not limited to, increasing the proportion of conjugated diene units in the polymer, increasing the proportion of 1,2-bonded and 3,4-bonded conjugated diene units, and increasing the amount of raw material (modifying agent) used when introducing the modifying group, from which the modifying group is derived.

[0026] The proportion of the modifying group (modification rate) in the modified conjugated diene polymer of this embodiment is preferably 0.1% by mass or more. If the proportion is 0.1% by mass or more, the crack growth resistance can be improved more reliably. From the same viewpoint, the proportion is preferably 0.4% by mass or more, and more preferably 0.6% by mass or more. Furthermore, from the viewpoint of ease of production, the proportion is preferably 3.0% by mass or less.

[0027] The proportion of the modifying group in the polymer is 1 It can be determined from the H-NMR spectrum. Furthermore, means for increasing the proportion of the modifying group include, but are not limited to, increasing the proportion of conjugated diene units in the polymer, increasing the proportion of 1,2-bonded and 3,4-bonded conjugated diene units, and increasing the amount of raw material (modifying agent) used to introduce the modifying group, from which the modifying group is derived.

[0028] The modified conjugated diene polymer of this embodiment is, as the name suggests, a polymer having at least a conjugated diene unit. The conjugated diene unit is a monomer unit derived from a conjugated diene compound, which enables crosslinking (vulcanization) of the polymer and can improve the elongation and strength of the rubber. For example, "butadiene unit" refers to a unit derived from butadiene, and the same applies to other units.

[0029] A conjugated diene compound usually has the basic structure (i.e., butadiene skeleton) shown in the following (1). [ka]

[0030] Specific examples of such conjugated diene compounds include 1,3-butadiene (sometimes simply referred to as "butadiene" in this specification), isoprene, 1,3-pentadiene, and 2,3-dimethyl-1,3-butadiene. One type of conjugated diene compound may be used alone, or two or more types may be used in combination. In one embodiment, the conjugated diene compound is one or more types selected from 1,3-butadiene and isoprene. In another embodiment, the conjugated diene compound is 1,3-butadiene alone or isoprene alone.

[0031] The polymer may also contain units other than conjugated diene units, such as monomer units derived from aromatic vinyl compounds such as styrene and methylstyrene (o-methylstyrene, p-methylstyrene, m-methylstyrene), and monomer units derived from non-conjugated olefin compounds such as ethylene and propylene.

[0032] The polymer is preferably polybutadiene (i.e., the monomer units are substantially composed of only butadiene units), a styrene-butadiene copolymer (i.e., the monomer units are substantially composed of only butadiene units and styrene-based units), or polyisoprene (i.e., the monomer units are substantially composed of only isoprene units). In other words, the modified conjugated diene polymer of this embodiment is preferably modified polybutadiene, a modified styrene-butadiene copolymer, or a modified polyisoprene. In this case, the polymer is relatively easy to produce and can more fully achieve the desired effects. The styrene-based units refer to monomer units derived from styrene-based compounds such as styrene and methylstyrene (o-methylstyrene, p-methylstyrene, m-methylstyrene).

[0033] When the polymer is a styrene-butadiene copolymer, the proportion of butadiene units in the polymer is, for example, 20 mol% or more, 40 mol% or more, 60 mol% or more, 80 mol% or more, 90 mol% or more, or 95 mol% or more, and 95 mol% or less, 90 mol% or less, 80 mol% or less, 60 mol% or less, 40 mol% or less, or 20 mol% or less. The above ratio is as follows: 1 It can be determined from the integral ratio of the H-NMR spectrum.

[0034] In the modified conjugated diene polymer of this embodiment, the total proportion of 1,2-bonds and 3,4-bonds (so-called vinyl bond content) of all conjugated diene units is preferably 10 mol% or more and 70 mol% or less. If the proportion is 10 mol% or more, a more sufficient amount of modifying groups can be introduced. Furthermore, if the proportion is 70 mol% or less, a sufficient amount of crosslinked moieties can be secured during crosslinking. From the same viewpoint, the proportion of 1,2-bonds or 3,4-bonds of all conjugated diene units is more preferably 20 mol% or more, even more preferably 30 mol% or more, and more preferably 65 mol% or less, even more preferably 62 mol% or less.

[0035] Bonding modes other than 1,2-bonds and 3,4-bonds include cis-1,4 bonds and trans-1,4 bonds, both of which have a double bond in the main chain.

[0036] Here, the 1,2-bonded conjugated diene unit in the polymer has the structure shown in the following (2) in accordance with the basic structure of (1) above.

[0037] [ka]

[0038] Furthermore, the 3,4-bonded conjugated diene unit in the polymer has the structure shown in the following (3) based on the basic structure of (1) above.

[0039] [ka]

[0040] As described above, the 1,2-bonded conjugated diene unit and the 3,4-bonded conjugated diene unit usually have a vinyl bond remaining in the side chain. For example, in the case of 1,3-butadiene, since it has a symmetrical structure, the 1,2-bond and the 3,4-bond are synonymous and are collectively referred to as the 1,2-bond.

[0041] In the modified conjugated diene polymer of this embodiment, the group containing the modifying group is preferably bonded to a carbon atom in a side chain of a 1,2- or 3,4-bonded conjugated diene unit (i.e., the carbon atom that constituted the vinyl bond before the introduction of the modifying group). In this case, the double bond in the main chain of the polymer is not consumed, which reduces adverse effects on other physical properties, such as reinforcing properties when a filler is blended and sufficient crosslinked portions during crosslinking. Furthermore, the polymer of this embodiment can be suitably produced by employing the production method described below. Whether or not the above group is bonded to a carbon atom of the side chain can be determined by 1 This can be confirmed from H-NMR spectra. For example, hydrogen atoms attached to carbon atoms in 1,2- or 3,4-bonded conjugated diene units exhibit a broad peak at around 3.5 ppm in NMR. The amount of modified group introduced can be calculated from the area of ​​this peak and the area of ​​the conjugated diene / aromatic vinyl.

[0042] The number-average molecular weight (Mn) of the modified conjugated diene polymer is not particularly limited, but is preferably 100,000 or more, and more preferably 150,000 or more. In this case, low loss and crack growth resistance can be highly compatible. The number-average molecular weight (Mn) of the modified conjugated diene polymer is not particularly limited, but can be 1,000,000 or less, or 500,000 or less. The number average molecular weight (Mn) is a polystyrene-equivalent number average molecular weight and can be determined by the method described in the Examples. In this specification, the number average molecular weight (Mn) refers to the Mn of the polymer before modification.

[0043] (Method of producing modified conjugated diene polymer) The method for producing the modified conjugated diene polymer of the present embodiment is not particularly limited, but may be, for example, (i) a step of polymerizing a conjugated diene compound alone or copolymerizing a conjugated diene compound with another monomer such as an aromatic vinyl compound to synthesize an (unmodified) conjugated diene polymer; (ii) A modified conjugated diene polymer can be suitably produced by a method including a step of dissolving the conjugated diene polymer synthesized in step (i) in a solvent and reacting it with a modifying agent (modification reaction) to introduce a modifying group into the conjugated diene polymer.

[0044] The above step (i) can be carried out in the same manner as the conventionally known anionic polymerization described in, for example, JP-A Nos. 2013-249379, 2016-003246, and 2014-227458.

[0045] When a conjugated diene compound and an aromatic vinyl compound are copolymerized in step (i), a non-conjugated olefin compound may be further copolymerized in addition to the conjugated diene compound and the aromatic vinyl compound. Examples of the non-conjugated olefin compound include ethylene, propylene, 1-butene, isobutene, 1-pentene, 1-hexene, 1-heptene, and 1-octene.

[0046] In step (i), the total ratio of 1,2-bonds and 3,4-bonds (so-called vinyl bond content) among all conjugated diene units can be adjusted by a known method.

[0047] It is preferable to use a polar solvent such as pyridine as the solvent for dissolving the polymer in step (ii). In this regard, for example, if the polymer is kneaded with the modifier without dissolving it in a solvent, the reaction with the modifier does not proceed due to the large difference in polarity between the polymer and the modifier. Furthermore, if other known low-polarity solvents such as cyclohexane or toluene are used as the solvent, it becomes difficult to dissolve both the polymer and the modifier. That is, in either of the above cases, it is highly likely that a polymer having excellent crack growth resistance, and thus the modified conjugated diene-based polymer of this embodiment, cannot be obtained.

[0048] The modification reaction in step (ii) is not particularly limited as long as it can introduce a predetermined modifying group into the polymer, but examples include the radical addition reaction of a metal mercaptoalkylsulfonate; the addition reaction of a metal azide alkylsulfonate; the addition reaction of a carbanion or an alkoxy anion with sulfur oxide; and the oxidation of a thioester or thiocarbamate. The modifying agent used in the modification reaction includes a thiol compound having a metal sulfonate, specifically, sodium 2-mercaptoethanesulfonate, sodium 3-mercaptopropylsulfonate, metal 2-azidoethanesulfonate, metal 8-azidooctylethanesulfonate, and 2-acetylthio-1-ethanethiol. The amount of the modifying agent is not particularly limited and may be adjusted as needed.

[0049] In step (ii), it is preferable to use a reaction initiator together with the modifying agent. Examples of such reaction initiators include radical initiators such as azo compounds and peroxy compounds. Specific examples include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine]n hydrate, cumene hydroperoxide, benzoyl peroxide, and peracetic acid. The amount of the reaction initiator is not particularly limited and may be adjusted appropriately.

[0050] In step (ii), a group derived from a modifier and containing a predetermined modifying group can be bonded to a carbon atom in the conjugated diene polymer, particularly to a carbon atom that previously constituted a vinyl bond in the side chain of a 1,2- or 3,4-bonded conjugated diene unit. For example, in step (i), 1,3-butadiene is used as the conjugated diene compound to synthesize a conjugated diene polymer, and in step (ii), 2-mercaptoethanesulfonic acid metal salt [(HS-(CH)-SO)M] is used as the modifier. 1 / n When the compound (I) is used, a modifying group can be introduced into the side chain of at least a 1,2-bonded conjugated diene unit in the following embodiment (4). This reaction is based on a mechanism in which a thiol-ene reaction occurs between a 2-mercaptoethanesulfonic acid metal salt and a double bond of a conjugated diene compound to form a thioether bond and introduce a sulfonic acid metal salt. Note that the following embodiment (4) is an embodiment in which a group containing a modifying group (-S-(CH2)2- modifying group) is bonded to a carbon atom in the side chain of a 1,2-bonded conjugated diene unit.

[0051] [ka]

[0052] After the step (ii), a step of washing the obtained modified conjugated diene polymer may be carried out. The solvent used for washing is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include methanol, ethanol, isopropanol, water, and buffer water.

[0053] (Rubber composition) A rubber composition according to one embodiment of the present invention (hereinafter sometimes referred to as "rubber composition of the present embodiment") is characterized by containing the above-mentioned modified conjugated diene polymer. Such a rubber composition has excellent crack growth resistance. The modified conjugated diene polymer may be used alone or in combination of two or more.

[0054] In particular, in the cross-linked product of the rubber composition of this embodiment, the non-covalent bonds of the modified conjugated diene polymer are sacrificially broken when strain is applied, and therefore, the rubber composition of this embodiment can exhibit the effect of improving crack growth resistance due to the breaking of the non-covalent bonds as described above.

[0055] The rubber composition of this embodiment may or may not further contain other rubber components in addition to the modified conjugated diene polymer. The other rubber components can be appropriately selected from known rubber components, such as natural rubber, synthetic isoprene rubber, butadiene rubber, styrene-butadiene rubber, butyl rubber, bromide of a copolymer of isobutylene and p-methylstyrene, halogenated butyl rubber, acrylonitrile butadiene rubber, chloroprene rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber, styrene-isoprene rubber, styrene-isoprene-butadiene rubber, isoprene-butadiene rubber, chlorosulfonated polyethylene, acrylic rubber, epichlorohydrin rubber, polysulfide rubber, silicone rubber, fluororubber, and urethane rubber. These other rubber components may be used alone or in combination of two or more.

[0056] In addition to the modified conjugated diene polymer and other optional rubber components, the rubber composition of this embodiment may contain known additives that are compounded into rubber compositions. Examples of such additives include fillers, vulcanizing agents (crosslinking agents), vulcanization accelerators, antioxidants, reinforcing agents, softeners, vulcanization aids, colorants, flame retardants, lubricants, foaming agents, plasticizers, processing aids, antioxidants, scorch inhibitors, ultraviolet inhibitors, antistatic agents, color inhibitors, and oils. These may be used alone or in combination of two or more.

[0057] Examples of fillers include inorganic fillers and carbon black, which may be used singly or in combination of two or more.

[0058] Examples of inorganic fillers include silica, aluminum hydroxide, clay, alumina, talc, mica, kaolin, glass balloons, glass beads, calcium carbonate, magnesium carbonate, magnesium hydroxide, calcium carbonate, magnesium oxide, titanium oxide, potassium titanate, and barium sulfate.

[0059] When an inorganic filler is used, the surface of the inorganic filler may be appropriately treated using a silane coupling agent or the like.

[0060] Examples of carbon black include general purpose furnace (GPF), fast extruding furnace (FEF), semi-reinforcing furnace (SRF), high abrasion furnace (HAF), super abrasion furnace (SAF), and intermediate SAF (ISAF) grades.

[0061] When the rubber composition of the present embodiment contains a filler, the content thereof may be adjusted appropriately, for example, from 5 to 200 parts by mass, from 10 to 200 parts by mass, or from 10 to 130 parts by mass per 100 parts by mass of the rubber component.

[0062] The vulcanizing agent (crosslinking agent) is not particularly limited, and examples thereof include sulfur-based crosslinking agents, organic peroxide-based crosslinking agents, inorganic crosslinking agents, polyamine crosslinking agents, resin crosslinking agents, sulfur compound-based crosslinking agents, and oxime-nitrosamine-based crosslinking agents. When the rubber composition of this embodiment contains a crosslinking agent, the content thereof may be appropriately adjusted. For example, the content is 0.1 to 20 parts by mass or 0.1 to 10 parts by mass per 100 parts by mass of the rubber component.

[0063] The vulcanization accelerator is not particularly limited, and examples thereof include guanidine-based compounds, aldehyde-amine-based compounds, aldehyde-ammonia-based compounds, thiazole-based compounds, sulfenamide-based compounds, thiourea-based compounds, thiuram-based compounds, dithiocarbamate-based compounds, and xanthate-based compounds. When the rubber composition of this embodiment contains a vulcanization accelerator, the content thereof may be appropriately adjusted. For example, the content is 0.1 to 20 parts by mass or 0.1 to 10 parts by mass per 100 parts by mass of the rubber component.

[0064] The method for preparing the rubber composition of this embodiment is not particularly limited, and known methods can be used. For example, the rubber composition can be obtained by kneading each component including the modified conjugated diene polymer using a kneading machine such as a Banbury mixer, a roll, or an internal mixer. Alternatively, the rubber composition can be prepared by mixing components other than the vulcanization accelerator and the crosslinking agent in a non-production (non-pro) stage, and then compounding and mixing the vulcanization accelerator and the crosslinking agent into the mixture in a production (pro) stage.

[0065] Rubber products obtainable using the rubber composition of the present embodiment are not particularly limited, but examples thereof include tires, conveyor belts, vibration-proof rubber, seismic isolation rubber, rubber crawlers, hoses, and foams.

[0066] The method for obtaining a rubber product using the rubber composition according to the present invention is not particularly limited, and any known method can be used. The conditions for crosslinking or vulcanizing the rubber composition can be appropriately adjusted, for example, at a temperature of 120 to 200°C and for a heating time of 1 to 900 minutes.

[0067] (tire) A tire according to one embodiment of the present invention is characterized by using the rubber composition of the present embodiment. The tire has excellent crack growth resistance because it uses the modified conjugated diene copolymer of the present embodiment.

[0068] The application portion of the rubber composition in the tire is not particularly limited, but examples thereof include tread rubber, base tread rubber, sidewall rubber, side reinforcing rubber, and bead filler.

[0069] The method for manufacturing the tire is not particularly limited, and any known method can be used. [Example]

[0070] The present invention will be described in more detail below by way of examples, but these examples are intended to illustrate the present invention and are not intended to limit the present invention in any way.

[0071] In the following, the proportion of butadiene units in the polymer and the proportion of 1,2-bonded butadiene units in the total butadiene units are as follows: 1 It was calculated from the integral ratio of the H-NMR spectrum. The number average molecular weight (Mn) of the polymer was determined in terms of polystyrene by gel permeation chromatography [GPC: Tosoh HLC-8020, column: Tosoh GMH-XL (two columns in series), detector: differential refractometer (RI)] using a calibration curve prepared from monodisperse polystyrene. The proportion of modifying groups in the modified polymer and the number of modifying groups in one polymer molecule were determined by the methods described above.

[0072] (Preparation of Polymer A (unmodified)) Cyclohexane (140 g), butadiene / cyclohexane solution (25% by weight, 229 g), and styrene / cyclohexane solution (26% by weight, 53.8 g) were mixed in an inert atmosphere glass bottle, followed by the addition of 2,2-di-(2-tetrahydrofuryl)propane / cyclohexane solution (1 M, 0.47 mL) and n-butyllithium (1.6 M, 0.56 mL). The mixture was gently shaken at 50 °C for 2 hours, followed by the addition of an appropriate amount of degassed isopropanol to terminate the polymerization. The resulting polymer cement was reprecipitated with isopropanol, and 0.5 mL of an isopropanol solution of 2,6-di-tert-butyl-p-cresol (BHT) (BHT concentration: 5% by weight) was added. The mixture was then dried under reduced pressure to obtain Polymer A (unmodified styrene-butadiene copolymer). This Polymer A was also used to prepare Polymer C, which will be described later.

[0073] In Polymer A, the proportion of butadiene units was 21% by mass, the proportion of 1,2-bonds in all butadiene units was 59%, and the number average molecular weight (Mn) was 196,000.

[0074] (Preparation of Polymer C (COOLi Modified)) In an inert atmosphere glass bottle, cyclohexane (240 g), butadiene / cyclohexane solution (25% by mass, 194 g), styrene / cyclohexane solution (27% by mass, 46 g), and 4-methylstyrene (425 mg) were mixed and then 2,2-di-(2-tetrahydrofuryl)propane / cyclohexane solution (1 M, 0.35 mL) and n-butyllithium (1.6 M, 0.32 mL) were added. The mixture was gently shaken at 50 °C for 1 hour to complete the polymerization, and the formation of a styrene-butadiene copolymer was confirmed. Next, N,N,N',N'-tetramethylethylenediamine (418 mg) and sec-butyllithium (1.0 M, 3.2 mL) were added to the solution containing the conjugated diene polymer and shaken at 70 °C for 2 hours. Carbon dioxide gas was then bubbled into the solution until the color disappeared, completing the modification reaction. Then, 0.5 mL of an isopropanol solution of 2,6-di-t-butyl-p-cresol (BHT) (BHT concentration: 5% by mass) was added to the obtained polymer cement, and the mixture was reprecipitated with isopropanol and dried under reduced pressure to obtain polymer C (COOLi-modified styrene-butadiene copolymer).

[0075] In addition, the proportion of butadiene units in polymer C was 81 mol%, the proportion of 1,2-bonds in all butadiene units was 64%, and the number average molecular weight (Mn) was 189,000.In addition, in polymer B, the number of modifying groups (-COOLi) in one molecule was 13.

[0076] (Preparation of Polymer D (SO3Na modified)) Polymer A (unmodified styrene-butadiene copolymer) (40 g) was added to a glass bottle under an inert atmosphere and dissolved in pyridine (200 mL) to obtain a polymer cement. Sodium 2-mercaptoethanesulfonate (7.2 g, 43.9 mmol) and 2,2'-azobisisobutyronitrile (180 mg, 1.09 mmol) were added to the resulting polymer cement, and nitrogen was bubbled through for 30 minutes. The mixture was then gently shaken at 80°C for 3 hours, and the reaction was terminated by opening the glass bottle in air. The mixture was then reprecipitated with isopropanol, and 0.4 mL of an isopropanol solution of 2,6-di-t-butyl-p-cresol (BHT) (BHT concentration: 5% by mass) was added, followed by drying under reduced pressure. A sufficient amount of tetrahydrofuran (THF) was then added to completely dissolve the polymer, followed by reprecipitation with isopropanol. This procedure was repeated until the polymer (precipitate) became transparent, and the raw material sodium 2-mercaptoethanesulfonate was removed. Polymer D (SO3Na-modified styrene-butadiene copolymer) was then obtained by drying under reduced pressure.

[0077] For polymer D, the proportion of modifying groups was 0.72% by mass, and the number of modifying groups (-SO3Na) per molecule calculated using the number average molecular weight of polymer A was 8.6.

[0078] In this polymer D, an O atom in the modifying group in one molecule can coordinate to a Na atom in the modifying group in another molecule to form a coordinate bond, which is a type of non-covalent bond, or an ionic bond. Since the Na atom has a coordination number of 6, O atoms in the modifying groups in five more molecules can coordinate to the above Na atom.

[0079] (Preparation of Rubber Composition) For each example, the above polymer was used as the rubber component to prepare a rubber composition according to the formulation shown in Table 1. The rubber composition was then vulcanized at 160°C for 20 minutes. The resulting rubber vulcanizate was then evaluated for 100% stress, low loss, and crack growth resistance according to the following procedures. The results are shown in Table 1.

[0080] <100% stress> For each rubber composition, a JIS dumbbell No. 3 test piece was prepared in accordance with JIS K 6251, and the tensile stress (MPa) at 100% elongation was measured at a test temperature of 24±4° C. A larger measured value indicates better durability.

[0081] <Low loss evaluation> The loss tangent (tanδ) was measured at a temperature of 50°C, a frequency of 15 Hz, and a strain of 10% using a viscoelasticity measuring device manufactured by TA Instruments. The reciprocal of the tanδ value was taken and expressed as an index, with the value of Comparative Example 1 set to 100. A larger index value indicates better low loss properties.

[0082] <Crack growth resistance> A 0.5 mm crack was made in the center of a JIS No. 3 test piece, and fatigue was repeatedly applied at room temperature with a constant strain of 40 to 150%, and the number of times it was applied until the sample broke was measured. The results were expressed as an index, with Comparative Example 1 set to 100. A larger index value indicates better crack growth resistance.

[0083] [Table 1]

[0084] *1 Polymer B (Sn-modified): JSR Corporation "SL563", solution polymerization SBR *2 Carbon black: Asahi #80 manufactured by Asahi Carbon Co., Ltd. *3 Oil: Sankyo Yuka Kogyo Co., Ltd. "A / O MIX" *4 Wax: "Suntite (registered trademark) A" manufactured by Seiko Chemical Co., Ltd. *5 Antioxidant: "Nocrac 6C" manufactured by Ouchi Shinko Chemical Industry Co., Ltd., N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine *6 Vulcanization accelerator: Ouchi Shinko Chemical Industry Co., Ltd.'s "Noccela CZ", N-(cyclohexyl)-2-benzothiazole sulfenamide

[0085] From Table 1, it can be seen that in the examples using polymer D (SO3Na-modified styrene-butadiene copolymer), very high durability and crack growth resistance were exhibited while maintaining low loss properties equivalent to those of conventional polymers. [Industrial Applicability]

[0086] According to the present invention, a polymer having excellent crack growth resistance can be provided. Also, according to the present invention, a rubber composition having excellent crack growth resistance can be provided. Also, according to the present invention, a tire having excellent crack growth resistance can be provided.

Claims

1. A polymer having at least a conjugated diene unit, and per molecule of the polymer, -SO ３ M １／ｎ (M is a metal atom, and n is a valence that M can take as a cation and is selected from integers of 1 to 4), A tire characterized by using a rubber composition containing a modified conjugated diene polymer having a number average molecular weight (Mn) of 100,000 or more and 1,000,000 or less.

2. The tire described in claim 1, wherein the metal atom M of the modified conjugated diene polymer is one or more types of metal atoms selected from Group 1 and Group 2 of the periodic table.

3. 3. The tire according to claim 1, wherein the polymer is polybutadiene, a styrene-butadiene copolymer, or polyisoprene.

4. A tire described in any one of claims 1 to 3, wherein the modified conjugated diene polymer has a total proportion of 1,2-bonded and 3,4-bonded conjugated diene units of 10 mol% or more and 70 mol% or less of the total conjugated diene units.

5. The tire according to any one of claims 1 to 4, wherein the modified conjugated diene polymer has a conjugated diene unit containing a 1,2-bond or a 3,4-bond conjugated diene unit, and the group containing the modifying group is bonded to a carbon atom in a side chain of the 1,2-bond or 3,4-bond conjugated diene unit.

6. A tire described in any one of claims 1 to 5, wherein the modified conjugated diene polymer has a proportion of the modified group of 0.1 mass% or more and 3.0 mass% or less.

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