Conjugated diene polymer, process for its production and rubber compositions containing the same

A process for producing a conjugated diene-based polymer which comprises, in the first modification, modifying a conjugated diene-based polymer having active chain ends, which is obtained by polymerizing a diene-based monomer singly or with other monomers and has a content of a cis-1,4 unit of 75% by mole or greater in the conjugated diene portion of the main chain, by reacting the active chain ends with a hydrocarbyloxysilane compound and reacting the modified polymer with a specific compound such as a hydrocarbyloxysilane compound, and a rubber composition containing the polymer modified in accordance with the above process and, preferably, 10 to 100 parts by weight of silica and/or carbon black per 100 parts by weight of the rubber component containing the modified polymer, are provided. The rubber composition containing silica and/or carbon black exhibits improved fracture properties, abrasion resistance, low heat buildup property and excellent workability. A process for producing a conjugated diene-based polymer exhibiting improved cold flow, a polymer produced in accordance with the process, and a rubber composition and a tire using the polymer are also provided.