Patent Publication Number: US-10774174-B2

Title: Use of crosslinked rubber

Description:
TECHNICAL FIELD 
     The present invention relates to a crosslinked rubber obtained by using a monocyclic olefin ring-opening polymer and more specifically, relates to a crosslinked rubber having excellent cold resistance that is obtained by using a monocyclic olefin ring-opening polymer and use of such a crosslinked rubber as a member for use in an environment at −10° C. or less. 
     BACKGROUND ART 
     Conventionally, butadiene rubber has been widely used for forming various rubber parts. Butadiene, the raw material of butadiene rubber, is produced as a by-product in producing ethylene by means of naphtha cracking. In recent years, as methods for producing ethylene, those in which natural gas such as ethane is used as the raw material are spreading, a reduction in the production of butadiene is predicted. Thus, use of synthetic rubbers not including butadiene as the raw material as an alternative material for butadiene rubber has been investigated in various ways. 
     One example of synthetic rubbers that have been investigated as alternative materials for butadiene rubber is a monocyclic olefin ring-opening polymer (e.g., a cyclopentene ring-opening polymer or cyclooctadiene ring-opening polymer), which can be obtained by ring-opening polymerizing a monocyclic olefin. For example, Patent Document 1 discloses a rubber composition for tires that contains a cyclopentene ring-opening polymer, a solution-polymerized styrene-butadiene rubber, and silica. In accordance with the technique of this Patent Document 1, the composition is suitable for a tire application in which low heat generation properties and cold resistance are required, but is not necessarily suitable for applications in which lower temperature use is required. 
     RELATED ART 
     Patent Documents 
     Patent Document 1: International Publication No. WO 2016/060267 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a crosslinked rubber having excellent cold resistance and obtained by using a monocyclic olefin ring-opening polymer and use of such a crosslinked rubber as a member for use in an environment at −10° C. or less. 
     Means for Solving the Problem 
     As a result of intensive studies to achieve the object described above, the present inventors have found that the object described above can be achieved by a crosslinked rubber that is produced by crosslinking a polymer composition including a rubber component that contains a monocyclic olefin ring-opening polymer having the proportion of cis bond of a structural unit derived from a monocyclic olefin within a specific range and a predetermined amount of carbon black, and thus have completed the present invention. 
     Specifically, according to the present invention, provided is use of a crosslinked rubber as a member for use in an environment at −10° C. or less, the crosslinked rubber being produced by crosslinking a polymer composition containing 100 parts by weight of a rubber component containing a monocyclic olefin ring-opening polymer having a proportion of cis bond of a structural unit derived from a monocyclic olefin of 45 to 95% and 20 to 200 parts by weight of carbon black. 
     Preferably, the monocyclic olefin ring-opening polymer is a polymer consisting only of a structural unit derived from a monocyclic monoolefin or a copolymer comprising a structural unit derived from a monocyclic monoolefin and a structural unit derived from a monomer copolymerizable with the monocyclic monoolefin. 
     Preferably, the monocyclic olefin ring-opening polymer is a polymer consisting only of a structural unit derived from cyclopentene or a copolymer comprising a structural unit derived from cyclopentene and a structural unit derived from a monomer copolymerizable with cyclopentene. 
     Preferably, the content of the monocyclic olefin ring-opening polymer in the rubber component is 50% by weight or more with respect to 100% by weight of the total rubber component. 
     Preferably, the monocyclic olefin ring-opening polymer has a modifying group containing an atom selected from the group consisting of atoms in Group XV of the Periodic Table, atoms in Group XVI of the Periodic Table, and a silicon atom. 
     Preferably, the modifying group is an oxysilyl group. 
     Preferably, the monocyclic olefin ring-opening polymer has the modifying group at an end of its polymer chain. 
     Preferably, the carbon black is furnace black. 
     Effects of Invention 
     According to the present invention, it is possible to provide a crosslinked rubber that has excellent cold resistance and thus is suitable as a member for use in an environment at −10° C. or less, and use of such a crosslinked rubber as a member for use in an environment at −10° C. or less. 
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the present invention, a crosslinked rubber is used as a member for use in an environment at −10° C. or less, the crosslinked rubber being produced by crosslinking a polymer composition containing 100 parts by weight of a rubber component containing a monocyclic olefin ring-opening polymer having a proportion of cis bond of a structural unit derived from a monocyclic olefin of 45 to 95% and 20 to 200 parts by weight of carbon black. 
     The rubber component to be used in the present invention contains a monocyclic olefin ring-opening polymer. The monocyclic olefin ring-opening polymer to be used in the present invention is a polymer containing a repeat unit formed by ring-opening polymerizing a monocyclic olefin, as the repeat unit that constitutes the main chain of the polymer, the polymer having a proportion of cis bond of a structural unit derived from the monocyclic olefin of 45 to 95%. 
     The monocyclic olefin ring-opening polymer has the proportion of the repeat units formed by ring-opening polymerizing a monocyclic olefin of preferably 80 mol % or more, more preferably 90 mol % or more, still more preferably 95 mol % or more, with respect to the total repeat units. It is particularly preferred that the monocyclic olefin ring-opening polymer substantially consist only of the repeat unit formed by ring-opening polymerizing a monocyclic olefin. However, as long as the properties of the monocyclic olefin ring-opening polymer are maintained, the polymer may contain a repeat unit derived from other monomers copolymerizable with the monocyclic olefin. The proportion of the repeat units derived from other monomers is preferably 20 mol % or less, more preferably 10 mol % or less, still more preferably 5 mol % or less, with respect to the total repeat units. A monocyclic olefin is a hydrocarbon compound comprising one ring and having a carbon-carbon double bond(s) in the ring. The number of the carbon-carbon double bonds may be one or plural (provided that no aromatic ring is contained). Specific examples of such monocyclic olefins include monocyclic monoolefins having one carbon-carbon double bond in the ring such as cyclopentene that may have a substituent and cyclooctene that may have a substituent; monocyclic dienes having two carbon-carbon double bonds in the ring such as 1,5-cyclooctadiene that may have a substituent; monocyclic trienes having three carbon-carbon double bonds such as 1,5,9-cyclododecatriene that may have a substituent; and the like. Examples of the other monomers copolymerizable with the monocyclic olefin include polycyclic cycloolefins, polycyclic cyclodienes, polycyclic cyclotrienes, and the like. Examples of the polycyclic cycloolefins, polycyclic cyclodienes, and polycyclic cyclotrienes include norbornene compounds that may have a substituent, such as 2-norbornene, dicyclopentadiene, 1,4-methano-1,4,4a,9a-tetrahydro-9H-fluorene, and tetracyclo[6.2.1.1 3,6 .0 2,7 ]dodeca-4-ene. 
     When the monocyclic olefin ring-opening polymer is a copolymer, the copolymer may be any of a copolymer of one monocyclic olefin and one or more monomers other than the monocyclic olefin, a copolymer of two or more monocyclic olefins, and a copolymer of two or more monocyclic olefins and one or more monomers other than the monocyclic olefins. When the monocyclic olefin ring-opening polymer has the structural units derived from two or more monocyclic olefins, the proportion of structural units derived from all the monocyclic olefins contained in the monocyclic olefin ring-opening polymer may be set within the range described above. 
     As for the repeat unit that constitutes the main chain, the monocyclic olefin ring-opening polymer to be used in the present invention is preferably a polymer consisting only of a structural unit derived from a monocyclic monoolefin or a copolymer comprising a structural unit derived from a monocyclic monoolefin and a structural unit derived from a monomer copolymerizable with the monocyclic monoolefin (including a structural unit derived from a monocyclic olefin other than the monocyclic monoolefin), in view of having excellent heat resistance and ozone resistance in addition to the operation and effects of the present invention, and is more preferably a polymer consisting only of a structural unit derived from cyclopentene or a copolymer comprising cyclopentene and a structural unit derived from a monomer copolymerizable with cyclopentene (including a structural unit derived from a monocyclic olefin other than cyclopentene). 
     The monocyclic olefin ring-opening polymer to be used in the present invention has a proportion of cis bond of a structural unit derived from the monocyclic olefin of 45 to 95%, preferably of 47 to 93%, more preferably of 50 to 90%. Setting the proportion of cis bond of the structural unit derived from the monocyclic olefin within the range described above and compounding a specific amount of carbon black thereto enables the crosslinked rubber to be obtained to have sufficient mechanical physical properties as well as to have excellent cold resistance. In contrast, with the excessively small or large proportion of cis bond, the crosslinked rubber to be obtained may have inferior cold resistance. The “proportion of cis bond of the structural unit derived from the monocyclic olefin” is the proportion of the structural unit derived from the monocyclic olefin having a cis type carbon-carbon double bond to all the structural units derived from the monocyclic olefin that constitutes the monocyclic olefin ring-opening polymer, expressed in percentage. The proportion of cis bond can be determined by  13 C-NMR spectrum measurement on the monocyclic olefin ring-opening polymer. Note that, in the case where the monocyclic olefin ring-opening polymer has monomer units derived from two or more monocyclic olefins, the proportion of cis bond to all the structural units derived from the monocyclic olefin contained in the monocyclic olefin ring-opening polymer may be set within the range described above. 
     Examples of a method for setting the proportion of cis bond of the monocyclic olefin ring-opening polymer within the range described above include, but not particularly limited to, a method involving controlling polymerization conditions when the monocyclic olefin is polymerized to obtain a monocyclic olefin ring-opening polymer and the like. By way of an example, the lower the polymerization temperature in polymerizing the monocyclic olefin is, the higher the proportion of cis bond can be. Also, the higher the monomer concentration in the polymerization solution is, the higher the proportion of cis bond can be. 
     The molecular weight of the monocyclic olefin ring-opening polymer is preferably, but not particularly limited to, 100,000 to 1,000,000, preferably 150,000 to 900,000, more preferably 200,000 to 800,000, as the value of the weight average molecular weight in terms of polystyrene (Mw), measured by gel permeation chromatography. When the monocyclic olefin ring-opening polymer has such a molecular weight, it is possible to make the mechanical physical properties of the crosslinked rubber more excellent. 
     The ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the monocyclic olefin ring-opening polymer (Mw/Mn), in terms of polystyrene, measured by gel permeation chromatography is usually, but not particularly limited to, 4.0 or less, preferably 3.5 or less, more preferably 3.0 or less. When the monocyclic olefin ring-opening polymer has such Mw/Mn, it is possible to make the mechanical physical properties of the crosslinked rubber more excellent. 
     The glass transition temperature of the monocyclic olefin ring-opening polymer is preferably, but not particularly limited to, −90° C. or less, more preferably −95° C. or less, still more preferably −98° C. or less, in view of making the polymer exhibit excellent properties at low temperatures. The glass transition temperature of the monocyclic olefin ring-opening polymer can be adjusted by adjusting, for example, the proportion of cis bond of the structural unit derived from the monocyclic olefin within the range described above. 
     The monocyclic olefin ring-opening polymer may have a molecular structure consisting only of carbon atoms and hydrogen atoms. Alternatively, the monocyclic olefin ring-opening polymer may contain atoms other than carbon atoms and hydrogen atoms in its molecular structure. More specifically, the polymer may contain a modifying group containing an atom selected from the group consisting of atoms in Group XV of the Periodic Table, atoms in Group XVI of the Periodic Table, and a silicon atom. 
     As such a modifying group, a modifying group containing an atom selected from the group consisting of a nitrogen atom, oxygen atom, phosphorous atom, sulfur atom, and silicon atom is suitable. Of these, a modifying group containing an atom selected from the group consisting of a nitrogen atom, oxygen atom, and silicon atom is more suitable, and a modifying group containing a silicon atom is still more suitable. 
     Examples of the modifying group containing a nitrogen atom include an amino group, pyridyl group, imino group, amide group, nitro group, urethane bond group, and hydrocarbon groups containing any of these groups. Examples of the modifying group containing an oxygen atom include a hydroxyl group, carboxylic group, ether group, ester group, carbonyl group, aldehyde group, epoxy group, and hydrocarbon groups containing any of these groups. Examples of the modifying group containing a silicon atom include an alkylsilyl group, oxysilyl group, or hydrocarbon groups containing these groups. Examples of the modifying group containing a phosphorous atom include a phosphate group, phosphino group, and hydrocarbon groups containing any of these groups. Examples of the modifying group containing a sulfur group include a sulfonyl group, thiol group, thioether group, and hydrocarbon groups containing any of these groups. The modifying group may be a modifying group containing a plurality of the groups described above. Of these, specific examples of a particularly preferable modifying group include an amino group, pyridyl group, imino group, amide group, hydroxyl group, carboxylic group, aldehyde group, epoxy group, oxysilyl group, and hydrocarbon groups containing any of these groups, and an oxysilyl group is particularly preferable. Herein, the oxysilyl group refers to a group having a silicon-oxygen bond. 
     Specific examples of the oxysilyl group include an alkoxysilyl group, aryloxysilyl group, acyloxy group, alkylsiloxysilyl group, arylsiloxysilyl group, hydroxysilyl group, and the like. Of these, in view of its high introduction effect, an alkoxysilyl group is preferable. 
     An alkoxysilyl group is a group formed by binding one or more alkoxy groups to a silicon atom, and specific examples thereof include a trimethoxysilyl group, a (dimethoxy)(methyl)silyl group, (methoxy)(dimethyl)silyl group, triethoxysilyl group, (diethoxy)(methyl)silyl group, (ethoxy)(dimethyl)silyl group, (dimethoxy)(ethoxy)silyl group, (methoxy)(diethoxy)silyl group, tripropoxysilyl group, tributoxysilyl group, and the like. 
     An aryloxysilyl group is a group formed by binding one or more aryloxy group to a silicon atom, and specific examples thereof include a triphenoxysilyl group, (diphenoxy)(methyl)silyl group, (phenoxy)(dimethyl)silyl group, (diphenoxy)(ethoxy)silyl group, (phenoxy)(diethoxy)silyl group, and the like. Of these, the (diphenoxy)(ethoxy)silyl group and (phenoxy)(diethoxy)silyl group may be classified also into alkoxysilyl groups because of having an alkoxy group in addition to an aryloxy group. 
     An aryloxysilyl group is a group formed by binding one or more acyloxy groups to a silicon atom, and examples thereof include a triacyloxysilyl group, (diacyloxy)(methyl)silyl group, (acyloxy)(dimethyl)silyl group, and the like. 
     An alkylsiloxysilyl group is a group formed by binding one or more alkylsiloxy groups to a silicon atom, and specific examples thereof include a tris(trimethylsiloxy)silyl group, trimethylsiloxy(dimethyl)silyl group, triethylsiloxy(diethyl)silyl group, tris(dimethylsiloxy)silyl group, and the like. 
     An arylsiloxysilyl group is a group formed by binding one or more arylsiloxy groups to a silicon atom, and specific examples thereof include a tris(phenylsiloxy)silyl group, triphenylsiloxy(dimethyl)silyl group, tris(diphenylsiloxy)silyl group, and the like. 
     A hydroxysilyl group is a group formed by binding one or more hydroxy groups to a silicon atom, and specific examples thereof include a trihydroxysilyl group, (dihydroxy)(methyl)silyl group, (hydroxy)(dimethyl)silyl group, (dihydroxy)(ethoxy)silyl group, (hydroxy)(diethoxy)silyl group, and the like. Of these, the (dihydroxy)(ethoxy)silyl group and (hydroxy)(diethoxy)silyl group may be classified also into alkoxysilyl groups because of having an alkoxy group in addition to a hydroxy group. 
     When the monocyclic olefin ring-opening polymer have such a modifying group, the position at which the modifying group is introduced is not particularly limited, but, in view of enhancing the introduction effect, the polymer preferably has a modifying group at an end(s) of polymer chains. 
     When the monocyclic olefin ring-opening polymer has a modifying group at an end(s) of the polymer chains, the polymer chains may have the modifying group introduced at one end of the polymer chains (single end) or at each of both ends of the polymer chains (both ends), or these polymer chains may be mixed. Any of these polymers and an unmodified monocyclic olefin ring-opening polymer into which a specific modifying group is not introduced at an end(s) of the polymer chains may be mixed. 
     When the monocyclic olefin ring-opening polymer has a modifying group at an end(s) of the polymer chains, the proportion of the modifying group introduced at the polymer chain end(s) of the monocyclic olefin ring-opening polymer is preferably, but not particularly limited to, 60% or more, more preferably 80% or more, still more preferably 100% or more, in terms of a percentage value of the number of monocyclic olefin ring-opening polymer chain ends at which the modifying group is introduced/the number of monocyclic olefin ring-opening polymer chains. Methods for measuring the proportion of the modifying group introduced at polymer chain ends are not particularly limited. For example, the proportion can be determined from the peak area ratio corresponding to the modifying groups obtained by  1 H-NMR spectrum measurement and the number average molecular weight obtained by gel permeation chromatography. 
     Methods for synthesizing the monocyclic olefin ring-opening polymer are not particularly limited as long as the intended polymer can be obtained. The polymer may be synthesized by a conventional method, and for example, can be synthesized in accordance with a method described below. 
     Specifically, the monocyclic olefin ring-opening polymer can be obtained by ring-opening polymerizing a monocyclic olefin in the presence of a polymerization catalyst containing a transition metal compound (A) of Group VI of the Periodic Table and an organoaluminum compound (B) represented by the following general formula (1):
 
(R 1 ) 3-x Al(OR 2 ) x    (1)
 
wherein each of R 1  and R 2  represents a hydrocarbon group having 1 to 20 carbon atoms, and x is 0&lt;x&lt;3.
 
     The transition metal compound (A) of Group VI of the Periodic Table is a compound having a transition metal atom of Group VI of the Periodic Table (Long-Period Periodic Table, the same applies to the following), specifically, a compound having a chromium atom, molybdenum atom, or tungsten atom, preferably a compound having a molybdenum atom, or a compound having a tungsten atom, in particular, more preferably a compound having a tungsten atom in view of having a high solubility in monocyclic olefin. The transition metal compound (A) of Group VI of the Periodic Table may be a compound having any transition metal atom of Group VI of the Periodic Table, and examples thereof include, but not particularly limited to, halides, alcoholates, arylates, oxylates, and the like of any transition metal atom of Group VI of the Periodic Table. Of these, halides are preferable in view of a high polymerization activity. 
     Specific examples of such a transition metal compound (A) of Group VI of the Periodic Table include molybdenum compounds such as molybdenum pentachloride, molybdenum oxotetrachloride, and molybdenum(phenylimide)tetrachloride; tungsten compounds such as tungsten hexachloride, tungsten oxotetrachloride, tungsten (phenylimide)tetrachloride, monocatecholate tungsten tetrachloride, bis(3,5-di-tert-butyl)catecholate tungsten dichloride, bis(2-chloroetherate)tetrachloride, and tungsten oxotetraphenolate; and the like. 
     The amount of transition metal compound (A) of Group VI of the Periodic Table to be used is usually in the range of 1:100 to 1:200,000, preferably in the range of 1:200 to 1:150,000, more preferably in the range of 1:500 to 1:100,000, in terms of the molar ratio of “transition metal atom of Group VI in the polymerization catalyst:monocyclic olefin”. If the amount of the transition metal compound (A) of Group VI of the Periodic Table to be used is excessively small, the polymerization reaction may not sufficiently proceed. In contrast, if the amount is excessively large, it may be difficult to remove the catalyst residue from the monocyclic olefin ring-opening polymer and thus various properties of the crosslinked rubber to be obtained may be degraded. 
     The organoaluminum compound (B) is the compound represented by the above general formula (1). Specific examples the hydrocarbon groups having 1 to 20 carbon atoms represented by R 1  and R 2  in the general formula (1) include alkyl groups such as a methyl group, ethyl group, isopropyl group, n-propyl group, isobutyl group, n-butyl group, t-butyl group, n-hexyl group, and cyclohexyl group; aryl groups such as a phenyl group, 4-methylphenyl group, 2,6-dimethylphenyl group, 2,6-diisopropylphenyl group, and naphthyl group; and the like. The groups represented by R 1  and R 2  in the compound represented by the general formula (1) may be the same or may be different, but in view of controlling the proportion of cis bond in the monocyclic olefin ring-opening polymer to be obtained within the suitable range described above, at least R 2  of R 1  and R 2  is preferably an alkyl group having 4 or more carbon atoms consecutively bonded together, particularly more preferably a n-butyl group, 2-methyl-pentyl group, n-hexyl group, cyclohexyl group, n-octyl group, or n-decyl group. 
     In the above general formula (1), x is 0&lt;x&lt;3. That is, in the general formula (1), the compositional ratio of R 1  and OR 2  can be any value in each range of 0&lt;3-x&lt;3 and 0&lt;x&lt;3, respectively. x is preferably 0.5&lt;x&lt;1.5 in view of the high polymerization activity and also in view of controlling the proportion of cis bond in the monocyclic olefin ring-opening polymer within the suitable range described above. 
     The organoaluminum compound (B) represented by the above general formula (1) can be synthesized by, for example, a reaction of trialkyl aluminum and alcohol as shown in the following general formula (2):
 
(R 1 ) 3 Al+ x R 2 OH→(R 1 ) 3-x Al(OR 2 ) x +(R 1 ) x H   (2)
 
     x in the above general formula (1) can be arbitrarily controlled by defining the reaction ratio of the corresponding trialkyl aluminum and alcohol as shown in the above general formula (2). 
     The amount of the organoaluminum compound (B) to be used is preferably 0.1 to 100 times by mole, more preferably 0.2 to 50 times by mole, still more preferably 0.5 to 20 times by mole, with respect to the transition metal atom of Group VI of the Periodic Table forming the transition metal compound (A) of Group VI of the Periodic Table, depending on the type of the organoaluminum compound (B) used. If the amount of the organoaluminum compound (B) to be used is excessively small, the polymerization activity may be insufficient, and if the amount is excessively large, a side reaction tends to occur during ring-opening polymerization. 
     The ring-opening polymerization reaction may be performed without a solvent or in a solution. Solvents to be used when the ring-opening polymerization reaction is performed in a solution are not particularly limited as long as the solvents are inert in the polymerization reaction and can dissolve monocyclic olefin and the polymerization catalyst described above that are used in the ring-opening polymerization. Examples of the solvents include hydrocarbon-based solvents or halogen-based solvents, and the like. Specific examples of the hydrocarbon-based solvents include aromatic hydrocarbon such as benzene, toluene, xylene, and ethylbenzene; aliphatic hydrocarbon such as n-hexane, n-heptane, and n-octane; alicyclic hydrocarbon such as cyclohexane, cyclopentane, and methylcyclohexane; and the like. Specific examples of the halogen-based solvents include alkyl halogens such as dichloromethane and chloroform; aromatic halogens such as chlorobenzene and dichlorobenzene; and the like. 
     When a modifying group-containing olefinically unsaturated hydrocarbon (C), which is a compound having the modifying group mentioned above and having one olefinic carbon-carbon double bond having metathesis reactivity, is placed in the polymerization reaction system of the ring-opening polymerization reaction, it is possible to introduce the modifying group to a polymer chain end of the monocyclic olefin ring-opening polymer. For example, when an oxysilyl group is introduced to a polymer chain end of the monocyclic olefin ring-opening polymer, an oxysilyl group-containing olefinically unsaturated hydrocarbon may be placed in the polymerization reaction system. 
     Examples of such an oxysilyl group-containing olefinically unsaturated hydrocarbon include, as a hydrocarbon used for introducing the modifying group to only one end of the polymer chain (single end) of the monocyclic olefin ring-opening polymer, alkoxysilane compounds such as vinyl(trimethoxy)silane, vinyl(triethoxy)silane, allyl(trimethoxy)silane, allyl (methoxy)(dimethyl)silane, allyl(triethoxy)silane, allyl(ethoxy)(dimethyl)silane, styryl(trimethoxy)silane, styryl(triethoxy)silane, 2-styrylethyl(triethoxy)silane, allyl(triethoxysilylmethyl)ether, and allyl(triethoxysilylmethyl)(ethyl)amine; aryloxysilane compounds such as vinyl(triphenoxy)silane, allyl(triphenoxy)silane, and allyl(phenoxy)(dimethyl)silane; acyloxysilane compounds such as vinyl(triacetoxy)silane, allyl(triacetoxy)silane, allyl(diacetoxy)methylsilane, and allyl(acetoxy)(dimethyl)silane; alkylsiloxysilane compounds such as allyltris(trimethylsiloxy)silane; arylsiloxysilane compounds such as allyltris(triphenylsiloxy)silane; polysiloxane compounds such as 1-allylheptamethyltrisiloxane, 1-allylnonamethyltetrasiloxane, 1-allylnonamethylcyclopentasiloxane, and 1-allylundecamethylcyclohexasiloxane; and the like. Examples thereof also include, as a hydrocarbon used for introducing the modifying groups to both polymer chain ends (both ends) of the monocyclic olefin ring-opening polymer, alkoxysilane compounds such as 1,4-bis(trimethoxysilyl)-2-butene, 1,4-bis(triethoxysilyl)-2-butene, and 1,4-bis(trimethoxysilylmethoxy)-2-butene; aryloxysilane compounds such as 1,4-bis(triphenoxysilyl)-2-butene; acyloxysilane compounds such as 1,4-bis(triacetoxysilyl)-2-butene; alkylsiloxysilane compounds such as 1,4-bis[tris(trimethylsiloxy)silyl]-2-butene; arylsiloxysilane compounds such as 1,4-bis[tris(triphenylsiloxy)silyl]-2-butene; polysiloxane compound such as 1,4-bis(heptamethyltrisiloxy)-2-butene, and 1,4-bis(undecamethylcyclohexasiloxy)-2-butene; and the like. 
     The amount of the modifying group-containing olefinically unsaturated hydrocarbon (C) such as the oxysilyl group-containing olefinically unsaturated hydrocarbon to be used may be appropriately selected depending on the molecular weight of the monocyclic olefin ring-opening polymer to be produced, but the molar ratio thereof to monocyclic olefin in use for polymerization is usually in the range of 1/100 to 1/100,000, preferably in the range of 1/200 to 1/50,000, more preferably in the range of 1/500 to 1/10,000. The modifying group-containing olefinically unsaturated hydrocarbon (C) not only serves to introduce the modifying group to a polymer chain end of the monocyclic olefin ring-opening polymer, but also acts as a molecular weight adjuster. 
     Alternatively, when the modifying group mentioned above is not introduced to the monocyclic olefin ring-opening polymer, in order to adjust the molecular weight of the monocyclic olefin ring-opening polymer to be obtained, an olefin compound such as 1-butene, 1-pentene, 1-hexene, and 1-octene or a diolefin compound such as 1,4-pentadiene, 1,4-hexadiene, 1,5-hexadiene, 1,6-heptadiene, 2-methyl-1,4-pentadiene, and 2,5-dimethyl-1,5-hexadiene, as a molecular weight adjuster, may be used to be added to the polymerization reaction system. The amount of the molecular weight adjuster to be used may be appropriately selected in the same range as that of the modifying group-containing olefinically unsaturated hydrocarbon (C) mentioned above. 
     The polymerization reaction temperature is, but not particularly limited to, preferably −100° C. or more, more preferably −50° C. or more, still more preferably −20° C. or more, particularly preferably 0° C. or more. The upper limit of the polymerization reaction temperature is, but not particularly limited to, preferably less than 100° C., more preferably less than 90° C., still more preferably less than 80° C., particularly preferably less than 70° C. The polymerization reaction time is also not particularly limited, but is preferably 1 minute to 72 hours, more preferably 10 minutes to 20 hours. 
     Alternatively, as a method for obtaining a monocyclic olefin ring-opening polymer having a desired proportion of cis bond by polymerizing a monocyclic diene or monocyclic triene of monocyclic olefins, it is also possible to produce a monocyclic olefin ring-opening polymer by ring-opening polymerizing a monocyclic olefin in the presence of the ruthenium-carbene complex used as the polymerization catalyst, instead of the method involving use of the polymerization catalyst including the transition metal compound (A) of Group VI of the Periodic Table and the organoaluminum compound (B) represented by the general formula (1) mentioned above. Copolymerization of a monocyclic diene or monocyclic triene with a monocyclic monoolefin can also be performed by this method. 
     The ruthenium-carbene complex is not particularly limited as long as the complex serves as a ring-opening polymerization catalyst for the monocyclic olefin. Specific examples of the ruthenium-carbene complex preferably used may include bis(tricyclohexylphosphine)benzylidene ruthenium dichloride, bis(triphenylphosphine)-3,3-diphenylpropenylidene ruthenium dichloride, (3-phenyl-1H-inden-1-ylidene)bis(tricyclohexylphosphine) ruthenium dichloride, bis(tricyclohexylphosphine)t-butylvinylidene ruthenium dichloride, bis(1,3-diisopropylimidazolin-2-ylidene)benzylidene ruthenium dichloride, bis(1,3-dicyclohexylimidazolin-2-ylidene)benzylidene ruthenium dichloride, (1,3-dimesitylimidazolin-2-ylidene)(tricyclohexylphosphine)benzylidene ruthenium dichloride, (1,3-dimesitylimidazolidin-2-ylidene)(tricyclohexylphosphine)benzylidene ruthenium dichloride, bis(tricyclohexylphosphine)ethoxymethylidene ruthenium dichloride, (1,3-dimesitylimidazolidin-2-ylidene)(tricyclohexylphosphine)ethoxymethylidene ruthenium dichloride, and the like. 
     As for the amount of the ruthenium-carbene complex to be used, the molar ratio of (metal ruthenium in the catalyst: monocyclic olefin) is usually in the range of 1:2,000 to 1:2,000,000, preferably in the range of 1:5,000 to 1:1,500,000, more preferably in the range of 1:10,000 to 1:1,000,000. When the amount of the ruthenium-carbene complex to be used is excessively small, the polymerization reaction may not sufficiently proceed. In contrast, if the amount is excessively large, it may be difficult to remove the catalyst residue from the monocyclic olefin ring-opening polymer to be obtained, and thus various properties of the crosslinked rubber to be obtained may be degraded when the crosslinked rubber is produced. 
     The ring-opening polymerization reaction in the case where the ruthenium-carbene complex is used as the polymerization catalyst may be performed without a solvent or in a solution. As the solvent to be used when the ring-opening polymerization reaction is performed in a solution, it is possible to use a solvent similar to the one in the case where the polymerization catalyst containing the transition metal compound (A) of Group VI of the Periodic Table and the organoaluminum compound (B) represented by the general formula (1) mentioned above is used. 
     The polymerization reaction temperature and the polymerization reaction time are also similar to the those in the case where the polymerization catalyst containing the transition metal compound (A) of Group VI of the Periodic Table and the organoaluminum compound (B) represented by the general formula (1) mentioned above is used. 
     To the monocyclic olefin ring-opening polymer obtained by the method in which the polymerization catalyst containing the transition metal compound (A) of Group VI of the Periodic Table and the organoaluminum compound (B) represented by the general formula (1) described above or by the method in which the ruthenium-carbene complex is used as the polymerization catalyst, an antiaging agent such as a phenol-based stabilizer, phosphorus-based stabilizer, and sulfur-based stabilizer may be added as desired. The amount of the antiaging agent may be appropriately determined depending on the type thereof and the like. Furthermore, an extender oil may also be compounded therein, as desired. When the monocyclic olefin ring-opening polymer is obtained as a polymerization solution, a known collection method may be employed in order to collect the polymer from the polymerization solution. For example, a method including separating the solvent by steam stripping or the like, filtering the solid off, and then drying the solid to obtain a solid rubber, and the like may be employed. 
     The rubber component to be used in the present invention may contain other rubbers in addition to the monocyclic olefin ring-opening polymer. Examples of the rubbers other than the monocyclic olefin ring-opening polymer include natural rubber (NR), polyisoprene rubber (IR), solution-polymerized SBR (solution-polymerized styrene-butadiene rubber), emulsion-polymerized SBR (emulsion-polymerized styrene-butadiene rubber), low-cis BR (polybutadiene rubber), high-cis BR, high-trans BR (the trans-bond content in the butadiene moiety: 70 to 95%), styrene-isoprene copolymer rubber, butadiene-isoprene copolymer rubber, ethylene-propylene-diene rubber (EPDM), emulsion-polymerized styrene-acrylonitrile-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, polyisoprene-SBR block copolymer rubber, polystyrene-polybutadiene-polystyrene block copolymer, acrylic rubber, epichlorohydrin rubber, fluororubber, silicone rubber, ethylene-propylene rubber, urethane rubber, and the like. Of these, NR, BR, IR, solution-polymerized SBR, emulsion-polymerized SBR, and EPDM are preferably used. Each of these rubbers may be used singly or two or more of these may be used in combination. 
     The content of the monocyclic olefin ring-opening polymer in the rubber component to be used in the present invention is preferably 10% by weight or more, more preferably 50% by weight or more, still more preferably 70% by weight or more, with respect to the total rubber component, in view of making the effect of the present invention more profound. In contrast, the content of the rubber other than the monocyclic olefin ring-opening polymer is preferably 90% by weight or less, more preferably 50% by weight or less, still more preferably 30% by weight or less, with respect to the total rubber component. In the present invention, as the rubber component used in the present invention, a component consisting only of the monocyclic olefin ring-opening polymer (i.e., a component of the monocyclic olefin ring-opening polymer of 100% by weight) may be used, in view of making the effect of the present invention more profound. 
     The polymer composition to be used in the present invention is prepared by compounding carbon black to the rubber component containing the monocyclic olefin ring-opening polymer mentioned above. 
     Examples of the carbon black include furnace black, acetylene black, thermal black, channel black, graphite, and the like. Of these, furnace black is preferably used, and specific examples thereof include SAF, ISAF, ISAF-HS, ISAF-LS, IISAF-HS, HAF, HAF-HS, HAF-LS, MAF, FEF, and the like. Each of these may be used singly or two or more of these may be used in combination. 
     The carbon black has a nitrogen adsorption specific surface area (N 2 SA) of preferably 5 to 200 m 2 /g, more preferably 20 to 150 m 2 /g, and has a dibutylphthalate (DBP) adsorption of preferably 5 to 200 ml/100 g, more preferably 50 to 160 ml/100 g. The nitrogen adsorption specific surface area can be measured by the BE1 method in accordance with ASTM D-4820. 
     The content of the carbon black in the polymer composition to be used in the present invention is 20 to 200 parts by weight, preferably 25 to 150 parts by weight, more preferably 30 to 100 parts by weight, with respect to 100 parts by weight of the rubber component containing the monocyclic olefin ring-opening polymer. Setting the content of the carbon black in the range described above can improve the cold resistance when a crosslinked rubber is produced to thereby make the crosslinked rubber adaptable as a member for use in an environment at −10° C. or less. If the content of the carbon black is excessively low, the crosslinked rubber to be obtained will have inferior mechanical physical properties. In contrast, if the content of the carbon black is excessively high, the processability of the polymer composition will be degraded. Also according to the present invention, advantageously, it is also possible to improve the compression set resistance of the crosslinked rubber by setting the content of the carbon black in the range described above. 
     To the polymer composition to be used in the present invention, compounding agents such as a crosslinking agent, crosslinking accelerator, crosslinking activator, antiaging agent, activator, process oil, plasticizer, wax, and filler other than carbon black may be compounded, in addition to the components mentioned above, each in a necessary amount in the conventional manner. 
     Examples of the crosslinking agent include sulfur, sulfur halide, organic peroxide, quinone dioximes, organic polyvalent amine compounds, zinc acrylates, alkylphenol resins having a methylol group, and the like. Of these, sulfur is preferably used. The amount of the crosslinking agent to be compounded is preferably 0.5 to 5 parts by weight, more preferably 0.7 to 4 parts by weight, still more preferably 1 to 3 parts by weight, with respect to 100 parts by weight of the rubber component in the polymer composition. 
     Examples of the crosslinking accelerator include sulfenamide-based crosslinking accelerators such as N-cyclohexyl-2-benzothiazolylsulfenamide, N-t-butyl-2-benzothiazolylsulfenamide, N-oxyethylene-2-benzothiazolylsulfenamide, N-oxyethylene-2-benzothiazolylsulfenamide, and N,N′-diisopropyl-2-benzothiazolylsulfenamide; guanidine-based crosslinking accelerator such as 1,3-diphenylguanidine, 1,3-diorthotolylguanidine, and 1-orthotolylbiguanidine; thiourea-based cross-linking accelerators; thiazole-based cross-linking accelerators; thiuram-based cross-linking accelerators; dithiocarbamic acid-based cross-linking accelerators; xanthogenic acid-based cross-linking accelerators; and the like. Of these, those containing a sulfenamide-based cross-linking accelerator are particularly preferable. Each of these crosslinking accelerators may be used singly or two or more of these may be used in combination. The amount of the crosslinking accelerator to be compounded is preferably 0.1 to 15 parts by weight, more preferably 0.5 to 5 parts by weight, with respect to 100 parts by weight of the rubber component in the polymer composition. 
     Examples of the crosslinking activator include higher fatty acids such as stearic acid, zinc oxide, and the like. The amount of the crosslinking activator to be compounded is not particularly limited. When a higher fatty acid is used as the crosslinking activator, the amount to be compounded is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 5 parts by weight, with respect to 100 parts by weight of the rubber component in the polymer composition. When zinc oxide is used as the crosslinking activator, the amount to be compounded is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 5 parts by weight, with respect to 100 parts by weight of the rubber component in the polymer composition. 
     As the process oil, a mineral oil or synthetic oil may be used. As the mineral oil, aroma oil, naphthene oil, paraffin oil, and the like are usually used. 
     Examples of fillers other than carbon black include metal powders such as aluminum powder; inorganic powders such as hard clay, talc, calcium carbonate, titanium oxide, calcium sulfate, calcium carbonate, and aluminum hydroxide; powders such as organic powders, for example, starch and polystyrene powder; short fibers such as glass fibers (milled fibers), carbon fibers, aramid fibers, and potassium titanate whiskers; silica and mica; and the like. Each of these fillers may be used singly or two or more of these may be used in combination. 
     The method for obtaining the polymer composition to be used in the present invention is not particularly limited, and each of components may be kneaded in accordance with a conventional method. By way of example, the intended composition can be obtained by kneading compounding agents such as carbon black except for the crosslinking agent and crosslinking accelerator with the rubber component such as a monocyclic olefin ring-opening polymer, and then, mixing the crosslinking agent and crosslinking accelerator into the kneaded material. The temperature for kneading the compounding agents except for the crosslinking agent and crosslinking accelerator with the rubber component is preferably 70 to 200° C., more preferably 100 to 180° C. The kneading time is preferably 30 seconds to 30 minutes. The kneaded material is mixed with the crosslinking agent and crosslinking accelerator after cooling down to usually 100° C. or less, preferably 80° C. or less. 
     The crosslinked rubber according to the present invention can be obtained by crosslinking the polymer composition mentioned above. The crosslinking method is not particularly limited and may be selected depending on the shape, the size, and the like of the crosslinked rubber. Crosslinking may be performed simultaneously with molding by filling a mold with the polymer composition and then heating the mold, or the polymer composition molded in advance may be crosslinked by heating. The crosslinking temperature is preferably 120 to 200° C., more preferably 140 to 180° C. and the crosslinking time is usually 1 to about 120 minutes. 
     Also, the crosslinked rubber may not be crosslinked enough to the inside thereof although the surface thereof has been crosslinked, depending on the shape, size, and the like thereof. In such a case, the crosslinked rubber may be further heated for secondary crosslinking. 
     As the heating method, a common method used for crosslinking rubber may be appropriately selected, such as press heating, steam heating, oven heating, and hot air heating. 
     Then, the crosslinked rubber according to the present invention thus obtained has excellent cold resistance. Specifically, in a TR test (low-temperature retraction test) under a condition of an elongation of 50% in accordance with JIS K6261:2006, the crosslinked rubber according to the present invention shows TR10 (temperature when the length of the specimen shrinks (recovers) by 10% by a temperature rise after the crosslinked rubber is frozen) of preferably −60° C. or less, more preferably −65° C. or less. The crosslinked rubber also shows TR30 (temperature when the length of the specimen shrinks (recovers) by 30% by a temperature rise after the crosslinked rubber is frozen) of preferably −55° C. or less, more preferably −60° C. or less, and shows TR50 (temperature when the length of the specimen shrinks (recovers) by 50% by a temperature rise after the crosslinked rubber is frozen) of preferably −52° C. or less, more preferably −57° C. or less. Furthermore, the crosslinked rubber shows TR70 (temperature when the length of the specimen shrinks (recovers) by 70% by a temperature rise after the crosslinked rubber is frozen) of preferably −45° C. or less, more preferably −50° C. or less. 
     The crosslinked rubber according to the present invention has a tensile strength of preferably 10 MPa or more, more preferably 12 MPa or more, still more preferably 14 MPa or more in a tensile test in which a specimen in the shape of the dumbbell No. 6 is used in accordance with JIS K6251:2010. Also in view of the stability when the crosslinked rubber is used as a member, the crosslinked rubber has a tensile strength of particularly preferably 15 MPa or more. The upper limit of the tensile strength is not particularly limited, but is preferably 30 MPa or less. When the crosslinked rubber according to the present invention has a tensile strength within the range described above, the crosslinked rubber has excellent physical properties as a crosslinked rubber. 
     Then, in the present invention, such a crosslinked rubber is used as a member for use in an environment at −10° C. or less. The member for use in an environment at −10° C. or less may be suitably used in various applications including, but not particularly limited to, electrically-insulating covering materials for wires and connectors; support rubber materials for use in bridges and buildings; various rubber members for use in vehicles for railway, automobile, or the like, such as vibration-proof rubber, rubber members for window frames, wiper blades, constant velocity joint boots, and dust covers; vibration-proof rubber for use in various industrial machines; electrically-insulating covering materials for electrical wiring and cables included in various industrial machines; seal materials, such as sealing materials, packings, rubber plugs, and O-rings, for use in various fields such as the aerospace field; containers, connectors, packing and hoses for use in the liquefied gas technology; strength-imparting agents for tackifiers and adhesives; and the like. In the present invention, the crosslinked rubber mentioned above is used as a member for use in an environment at −10° C. or less. In view of making the effects of the present invention more profound, the crosslinked rubber is used preferably as a member for use in an environment at −20° C. or less, more preferably as a member for use in an environment at −25° C. or less. 
     EXAMPLES 
     Hereinafter, the present invention will be explained based on more detailed examples, but the present invention is not limited to these examples. In the examples, “parts” are based on weight unless otherwise indicated. The tests and evaluations were performed in accordance with the following methods. 
     [Molecular Weight of Monocyclic Olefin Ring-Opening Polymer] 
     Using a gel permeation chromatography (GPC) system HLC-8220 (manufactured by TOSOH CORPORATION) with two H-type columns HZ-M (made by TOSOH CORPORATION) connected in serial, measurement was performed at a column temperature of 40° C. with tetrahydrofuran as a solvent. As a detector, a differential refractometer RI-8320 (manufactured by TOSOH CORPORATION) was used. The weight average molecular weight (Mw) and number average molecular weight (Mn) of a monocyclic olefin ring-opening polymer were measured as values in terms of polystyrene. 
     [Glass Transition Temperature (Tg) of Monocyclic Olefin Ring-Opening Polymer] 
     Measurement was performed using a differential scanning calorimeter (DSC, X-DSC7000 manufactured by Hitachi High-Tech Science Corporation) from −150° C. to +40° C. at a temperature rising rate of 10° C./minute. 
     [Cis/Trans Ratio of Monocyclic Olefin Ring-Opening Polymer] 
     The ratios were determined by  13 C-NMR spectrum measurement. 
     [Ratio of Introduction of Oxysilyl Group in End-modified Monocyclic Olefin Ring-Opening Polymer] 
     The ratio of the peak integral value derived from the oxysilyl group and the peak integral value derived from the carbon-carbon double bond in the end-modified monocyclic olefin ring-opening polymer main chain was determined by use of  1 H-NMR spectroscopy. Based on the ratio of the peak integral values and the measurement value of the number average molecular weight (Mn) measured by GPC, the ratio of introduction of the oxysilyl group [percentage of (number of monocyclic olefin ring-opening polymer chain ends in which the oxysilyl group was introduced/total number of end-modified monocyclic olefin ring-opening polymer chains)] was calculated. 
     [Tensile Test] 
     A polymer composition as a sample was press-crosslinked at 150° C. for 25 minutes to produce a crosslinked rubber sheet. A dumbbell shaped specimen was obtained by punching the crosslinked rubber sheet to the shape of dumbbell No. 6 in parallel to the grain direction. Then, the dumbbell-shaped specimen was subjected to a tensile test using a tensile testing machine (product name “TENSOMETER10K” manufactured by ALPHA TECHNOLOGIES) as the tester in accordance with JIS K6251:2010 under conditions of 23° C. and 500 mm/minute to thereby measure the tensile strength, elongation, 100% tensile stress, and 300% tensile stress. 
     [Cold Resistance] 
     A polymer composition as a sample a specimen was press-crosslinked at 150° C. for 25 minutes to produce a crosslinked rubber sheet. A specimen was obtained by punching it to a piece of 50 mm in length×2 mm in width×2 mm in thickness. Then, the specimen obtained was subjected to a TR test (low-temperature retraction test) using a low temperature retraction tester (TR tester, No. 145L, manufactured by YASUDA SEIKI SEISAKUSHO, LTD.) under a condition of an elongation of 50%, in accordance with JIS K6261:2006, to thereby measure the cold resistance of the crosslinked rubber. Specifically, the elongated specimen was frozen, and the temperature thereof was continuously raised using ethanol as a heat medium to measure the recoverability of the elongated specimen. The temperature when the length of the specimen shrunk (recovered) by 10% by a temperature rise, TR10; the temperature when the length of the specimen shrunk (recovered) by 30% by a temperature rise, TR30; the temperature when the length of the specimen shrunk (recovered) by 50% by a temperature rise, TR50; and the temperature when the length of the specimen shrunk (recovered) by 70% by a temperature rise, TR70 were measured. When the TR10, TR30, TR50, and TR70 are lower, it can be determined that the cold resistance is higher, and it can therefore be said that the crosslinked rubber can be suitably used at lower temperatures. In the present example, when TR10, TR30, TR50, or TR70 was −70° C., the actual value thereof can be considered to be −70° C. or less because the temperature rise in the TR test was begun at 70° C. 
     [Compression Set] 
     The polymer composition was press-molded with using a mold while pressure was applied at 150° C. for 30 minutes to obtain a crosslinked rubber cylinder having a diameter of 29 mm and a thickness of 12.5 mm. Then, the crosslinked rubber cylinder obtained was used to measure the compression set in accordance with JIS K6262:2013. Specifically, the distance between two flat faces sandwiching the crosslinked rubber cylinder was compressed by 25% in the disk thickness direction in a Geer&#39;s aging oven (product name “AG-1110”,manufactured by Ueshima Seisakusho Co., Ltd.) at 100° C. and the crosslinked rubber cylinder was maintained in such a state for 72 hours, followed by carrying out the measurement. 
     REFERENCE EXAMPLE 1 
     Preparation of Diisobutyl Aluminum Mono(n-hexoxide)/Toluene Solution (2.5% by Weight) 
     Under a nitrogen atmosphere, 88 parts of toluene and 7.8 parts of 25.4% by weight triisobutyl aluminum/n-hexane solution (manufactured by TOSOH FINECHEM CORPORATION) were added to a glass vessel containing a stir bar. Then, the vessel was cooled to −45° C., and 1.02 parts of n-hexanol (the same molar amount as triisobutyl aluminum) were slowly added dropwise thereto under vigorous stirring. Subsequently, the mixture was left under stirring until it reached room temperature to prepare a diisobutyl aluminum mono(n-hexoxide)/toluene solution (2.5% by weight). 
     SYNTHESIS EXAMPLE 1 
     Under a nitrogen atmosphere, 87 parts of a 1.0% by weight WCl 6 /toluene solution and 43 parts of a 2.5% by weight diisobutyl aluminum mono(n-hexoxide)/toluene solution prepared in Reference example 1 were added to a glass vessel containing a stir bar and stirred for 15 minutes to obtain a catalyst solution. Then, under a nitrogen atmosphere, 300 parts of cyclopentene and 1.24 parts of 1,4-bis(triethoxysilyl)-2-butene were added to a pressure resistant glass reaction vessel equipped with a stirrer. Then, 130 parts of the catalyst solution prepared above was added thereto, and polymerization reaction was performed at 25° C. for 4 hours. After 4 hours of the polymerization reaction, an excess amount of ethyl alcohol was added to the pressure resistant glass reaction vessel to terminate the polymerization reaction, and then, as an antiaging agent, 0.2 parts of Irganox 1520L (manufactured by Ciba Specialty Chemicals Inc.) was added with respect to 100 parts of the polymer obtained by the polymerization. Then, the polymer was solidified with a large amount of ethanol and collected, and dried under vacuum at 40° C. for 3 days to thereby obtain 78 parts of the both end-modified cyclopentene ring-opening polymer in which triethoxysilyl was introduced to both the ends (a1), as a monocyclic olefin ring-opening polymer. The both end-modified cyclopentene ring-opening polymer (a1) obtained had a weight average molecular weight (Mw) of 366,000, a glass transition temperature (Tg) of −106° C., a cis/trans ratio of cis/trans=55/45, and a ratio of introduction of the oxysilyl group of 143%. 
     SYNTHESIS EXAMPLE 2 
     Under a nitrogen atmosphere, 87 parts of a 1.0% by weight WCl 6 /toluene solution and 43 parts of a 2.5% by weight diisobutyl aluminum mono(n-hexoxide)/toluene solution prepared in Reference example 1 were added to a glass vessel containing a stir bar and stirred for 15 minutes to obtain a catalyst solution. Then, under a nitrogen atmosphere, 300 parts of cyclopentene and 0.26 parts of 1-hexene were added to a pressure resistant glass reaction vessel equipped with a stirrer. Then, 130 parts of the catalyst solution prepared above was added thereto, and polymerization reaction was performed at 0° C. for 4 hours. After 4 hours of the polymerization reaction, an excess amount of ethyl alcohol was added to the pressure resistant glass reaction vessel to terminate the polymerization reaction, and then, as an antiaging agent, 0.2 parts of Irganox 1520L (manufactured by Ciba Specialty Chemicals Inc.) was added with respect to 100 parts of the polymer obtained by the polymerization. Then, the polymer was solidified with a large amount of ethanol and collected. The polymer collected was dried under vacuum at 40° C. for 3 days to thereby obtain 74 parts of an unmodified cyclopentene ring-opening polymer (a2), as a monocyclic olefin ring-opening polymer. The unmodified cyclopentene ring-opening polymer (a2) obtained had a weight average molecular weight (Mw) of 389,000, a glass transition temperature (Tg) of −110° C., and a cis/trans ratio of cis/trans=81/19. 
     SYNTHESIS EXAMPLE 3 
     Under a nitrogen atmosphere, 1600 parts of 1,5-cyclooctadiene, 0.15 parts of 1-hexene, and 990 parts of toluene were added to a pressure resistant glass reaction vessel containing a magnetic stir bar. Subsequently, 0.068 parts of (3-phenyl-1H-inden-1-ylidene)bis(tricyclohexylphosphine)ruthenium dichloride dissolved in 10 parts of toluene were added thereto, and the mixture was polymerized at room temperature for 3 hours. After 3 hours of the polymerization reaction, an excess amount of ethyl vinyl ether was added to the pressure resistant glass reaction vessel to terminate the polymerization reaction, and then, as an antiaging agent, 0.2 parts of Irganox 1520L (manufactured by Ciba Specialty Chemicals Inc.) was added with respect to 100 parts of the polymer obtained by the polymerization. Then, the polymer was solidified with a large amount of ethanol and collected. The polymer collected was dried under vacuum at 50° C. for 24 hours to thereby obtain 1010 parts of an unmodified 1,5-cyclooctadiene ring-opening polymer (a3), as a monocyclic olefin ring-opening polymer. The unmodified 1,5-cyclooctadiene ring-opening polymer (a3) obtained has a weight average molecular weight (Mw) of 415,000, a glass transition temperature (Tg) of −104° C., and a cis/trans ratio of cis/trans=73/27. 
     EXAMPLE 1 
     In a Banbury type mixer, 100 parts of the both end-modified cyclopentene ring-opening polymer (a1) obtained in Synthesis Example 1 was masticated for 30 seconds, and then, 2 parts of stearic acid, 3 parts of zinc oxide, 60 parts of carbon black (product name “IRB #8”, manufactured by Continental Carbon Company, nitrogen adsorption specific surface area (BET method): 76.3 m 2 /g, furnace black), and 15 parts of a process oil (manufactured by JX Nippon Oil &amp; Energy Corporation, product name “Aromax T-DAE”) were added thereto. After the mixture was kneaded at 110° C. for 180 seconds, the compounding agents remaining on the top of the ram were cleaned, the mixture was kneaded for further 150 seconds, and then, the kneaded material was discharged from the mixer. Then, after the kneaded material was cooled to room temperature, the kneaded material obtained, 1.5 parts of sulfur, and 0.9 parts of N-(tert-butyl)-2-benzothiazolylsulfenamide (manufactured by OUCHI SHINKO CHEMICAL INDUSTRIAL CO., LTD., product name “Nocceler NS-P”) as a crosslinking accelerator were kneaded in an open roll at 23° C. to obtain a polymer composition in the form of a sheet. 
     Then, the polymer composition obtained was used to obtain a crosslinked rubber in accordance with the method described above, and a tensile test, cold resistance, and measurement of compression set were performed. The results are shown in Table 1. 
     EXAMPLE 2 
     A polymer composition was obtained in the same manner as in Example 1 except that 100 parts of the both end-modified cyclopentene ring-opening polymer (a1) obtained in Synthesis Example 1 was replaced by the 100 parts of the unmodified cyclopentene ring-opening polymer (a2) obtained in Synthesis Example 2, and the evaluation was performed in the same manner. The results are shown in Table 1. 
     EXAMPLE 3 
     A polymer composition was obtained in the same manner as in Example 1 except that 100 parts of the both end-modified cyclopentene ring-opening polymer (a1) obtained in Synthesis Example 1 was replaced by 100 parts of the unmodified 1, 5-cyclooctadiene ring-opening polymer (a3) obtained in Synthesis Example 3, and the evaluation was performed in the same manner. The results are shown in Table 1. 
     COMPARATIVE EXAMPLE 1 
     A polymer composition was obtained in the same manner as in Example 1 except that 100 parts of the both end-modified cyclopentene ring-opening polymer (a1) obtained in Synthesis Example 1 was replaced by 100 parts of an unmodified butadiene rubber (product name “Nipol BR1220” manufactured by Nippon Zeon Co., Ltd., cis content: 97% or more) and the evaluation was performed in the same manner. The results are shown in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                   
                 Comparative 
               
               
                   
                 Example 
                 Example 
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 
                 2 
                 3 
                 1 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Formulation 
                   
                   
                   
                   
                   
               
               
                 Both end-modified cyclopentene 
                 (parts) 
                 100 
                 — 
                 — 
                 — 
               
               
                 ring-opening polymer (a1) 
               
               
                 (Cis/trans = 55/45) 
               
               
                 Unmodified cyclopentene 
                 (parts) 
                 — 
                 100 
                 — 
                 — 
               
               
                 ring-opening polymer (a2) 
               
               
                 (Cis/trans = 81/19) 
               
               
                 Unmodified 1,5-cyclooctadiene 
                 (parts) 
                 — 
                 — 
                 100 
                 — 
               
               
                 ring-opening polymer (a3) 
               
               
                 (Cis/trans = 73/27) 
               
               
                 Unmodified butadiene rubber 
                 (parts) 
                 — 
                 — 
                 — 
                 100 
               
               
                 Stearic acid 
                 (parts) 
                 2 
                 2 
                 2 
                 2 
               
               
                 Zinc oxide 
                 (parts) 
                 3 
                 3 
                 3 
                 3 
               
               
                 Carbon black 
                 (parts) 
                 60 
                 60 
                 60 
                 60 
               
               
                 Sulfur 
                 (parts) 
                 1.5 
                 1.5 
                 1.5 
                 1.5 
               
               
                 Crosslinking accelerator 
                 (parts) 
                 0.9 
                 0.9 
                 0.9 
                 0.9 
               
               
                 Process oil 
                 (parts) 
                 15 
                 15 
                 15 
                 15 
               
               
                 Evaluation results 
               
               
                 Tensile Test 
               
               
                 Tensile strength 
                 (MPa) 
                 16.1 
                 14.4 
                 14.8 
                 19.9 
               
               
                 Elongation 
                 (%) 
                 380 
                 420 
                 410 
                 520 
               
               
                 100% Tensile stress 
                 (MPa) 
                 3.11 
                 2.65 
                 2.68 
                 1.98 
               
               
                 300% Tensile stress 
                 (MPa) 
                 11.9 
                 9.51 
                 9.89 
                 10.0 
               
               
                 Cold resistance test 
               
               
                 TR10 
                 (° C.) 
                 −70 
                 −70 
                 −70 
                 −24 
               
               
                 TR30 
                 (° C.) 
                 −70 
                 −70 
                 −70 
                 −23 
               
               
                 TR50 
                 (° C.) 
                 −70 
                 −70 
                 −70 
                 −23 
               
               
                 TR70 
                 (° C.) 
                 −67 
                 −69 
                 −68 
                 −23 
               
               
                 Compression set 
               
               
                 Compression set 
                 (%) 
                 49 
                 45 
                 50 
                 53 
               
               
                   
               
            
           
         
       
     
     As clear from the results of Examples 1 to 3 shown in Table 1, it can be said that the crosslinked rubber produced by crosslinking a polymer composition that contains a monocyclic olefin ring-opening polymer having the proportion of cis bond of the structural unit derived from the monocyclic olefin of 45 to 95% and a predetermined amount of carbon black had a lower value for each of TR10, TR30, TR50, and TR70, i.e., had excellent cold resistance, in comparison with that in the case where the monocyclic olefin ring-opening polymer was replaced by butadiene rubber (Comparative Example 1), and thus can be suitably used as a member for use in an environment at −10° C. or less. Also as clear from the results of Examples 1 to 3, the crosslinked rubber produced by crosslinking a polymer composition that contains a monocyclic olefin ring-opening polymer having a proportion of cis bond of the structural unit derived from the monocyclic olefin of 45 to 95% and a predetermined amount of carbon black had a low compression set and was thus excellent in compression set resistance.