Abstract: A catalyst composition for polymerizing a conjugated diene which comprises the following (a), (b) and (c) components:(a) an organolithium-aluminum compound represented by the formula:LiAlR.sup.1 R.sup.2 R.sup.3 R.sup.4(b) an organobarium-aluminum compound represented by the formula:Ba(AlR.sup.1 R.sup.2 R.sup.3 R.sup.4).sub.2 or Ba[AlR.sup.1 R.sup.2 R.sup.3 (OR.sup.4)].sub.2(c) a lithium alkoxide represented by the formula:LiOR.sup.5The conjugated diene polymer or copolymer obtained by polymerizing a conjugated diene alone or in combination with other monomer with the above catalyst composition in an inert organic solvent has a high trans-1,4 bond content, a low vinyl bond content and a low cis-1,4 bond content.

Abstract: A rubber composition comprising not less than 20% by weight of an amino group-containing diene based polymer in a rubber component, and 10 to 100 parts by weight of silica as a filler with respect to 100 parts by weight of the rubber component. The amino group-containing diene based polymer is obtained by polymerizing a monomer or copolymerizing the monomer in an organic solvent in the presence of at least one of an organic alkali metal and an organic alkaline earth metal.

Abstract: A butadiene-based rubber composition is disclosed, which contains not less than 20% by weight of a butadiene-based homopolymer or copolymer having a glass transition temperature (Tg) of not less than -105.degree. C., but less than -70.degree. C. and a Mooney viscosity (ML.sub.1+4, 100.degree. C.) of 10 to 150. The butadiene-based homopolymer or copolymer is obtained by polymerizing butadiene or random-copolymerizing butadiene with at least one kind of a monomer selected from the group consisting of another conjugated diene and an aromatic vinyl compound, and then reacting polymerization-active terminals thereof with an isocyanate compound and/or an isothiocyanate compound. The butadiene-based rubber composition has excellent resilience, fracture strength, and wear resistance as a vulcanizate as well as excellent processability as an unvulcanized rubber, and can be used as tire applications such as tire treads, undertreads, sidewalls, bead portions, etc.

Abstract: A rubber composition containing not less than 20% of a conjugated diene based polymer or copolymer. The polymer or copolymer is obtained by polymerizing a conjugated diene or copolymerizing the conjugated diene with at least one kind of other conjugated diene and an aromatic vinyl compound with use of a lithium initiator, and then reacting an isocyanate compound with active terminals of the thus obtained polymer or copolymer. The conjugated diene is butadiene or isoprene, while other conjugated diene is selected from pentadiene, 2,3-dimethylbutadiene as well as isoprene and butadiene, and an aromatic vinyl compound may be styrene, vinyltoluene, .alpha.-methylstyrene, etc. The rubber composition is applicable as tread portion, carcass, side wall portion of tires, vibration resistant rubber, window frame, hose, and various industrial articles.