RUBBER COMPOSITION, AND TIRE

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PROBLEM TO BE SOLVED : To provide a rubber composition containing a modified conjugated dienic polymer made by modifying a terminal-active polymer obtained by using a catalyst containing a lanthanum-based rare earth element-containing compound, having a high content of cis-1, 4 bond and having a terminal modified ratio of a specific value or higher, and being excellent in low heat generation, fracture property and wear resistance; and to provide a tire made by using the rubber composition and having the above properties. SOLUTION : A polymer is made by modifying with a modifying agent, a polymer having an active organometal site obtained by using a catalyst containing a lanthanum-based rare earth element-containing compound and by polymerizing a conjugated dienic compound in an organic solvent, wherein the modifying agent is at least one selected from specific compounds; the modification rate is ≥15%; the cis-1, 4-bond content of the conjugated diene moiety measured by a Fourier transform infrared spectrometry satisfies the following expression (I) : (cis-1, 4-bond content)≥98.00 (%)...(I); and the conjugated dienic polymer having a number-average molecular weight (Mn) of 100, 000 to 500, 000 is contained in a proportion of ≥10 mass% in the whole rubber component. COPYRIGHT : (C)2014, JPO&INPIT