Abstract: Conjugated diene polymers having good wear resistance, mechanical properties, storage stability, processability and a reduced cold flow are produced by polymerizing a conjugated diene compound with a catalyst of rare earth element compound, a compound containing at least one halogen atom, an aluminoxane, and an organoaluminum compound in an organic solvent and reacting the resulting polymer just after the polymerization with at least one compound selected from the group consisting of a halogenated organometallic compound, a halogenated metal compound, an organometallic compound, a heterocumulene compound, a hetero three-membered-ring containing compound, a halogenated isocyano compound, a carboxylic acid, an acid halide, an ester compound, a carbonic ester compound, an acid anhydride and a metal salt of a carboxylic acid as a modifying agent.

Abstract: Novel conjugated diene polymers having good wear resistance, mechanical properties, storage stability, processability and a reduced cold flow are produced by polymerizing a conjugated diene compound with a catalyst of rare earth element compound and reacting the resulting polymer just after the polymerization with at least one compound selected from the group consisting of a halogenated organometallic compound, a halogenated metal compound, an organometallic compound, a heterocumulene compound, a hetero three-membered-ring containing compound, a halogenated isocyano compound, a carboxylic acid, an acid halide, an ester compound, a carbonic ester compound, an acid anhydride and a metal salt of a carboxylic acid as a modifying agent.

Abstract: A conjugated diene polymer is obtained by using a specified catalyst system consisting of components (a)-(d) and indicating a high polymerization activity to a conjugated diene compound. Further, a modified conjugated diene polymer is obtained by reacting with at least one specified compound selected from the group consisting of components (e)-(j).

Abstract: A method for preparing a conjugated diene polymer characterized by polymerizing a conjugated diene in vapor phase in the presence of an inorganic filler used as a rubber reinforcement agent and a catalyst which comprises (a) a compound containing a rare earth element of an atomic number of from 57 to 71 in the Periodic Table or a compound obtained by the reaction of this rare earth element-containing compound and a Lewis base, (b) an organic aluminum compound of the formula AlR.sup.1 R.sup.2 R.sup.3 or an almoxane, and (c) a halogen-containing compound. The vapor phase polymerization ensures easy control of the molecular weight of the polymer better dispersion of a rubber enforcement agent, and provides a rubber composition with improved rupture characteristics and abrasion resistance.

Abstract: A process for producing a polybutadiene rubber having a cis-1,4 content of 94% or more, a ratio of weight average molecular weight to number average molecular weight of 2.5 to 3.5 as measured by a gel permeation chromatography and a Mooney viscosity (ML.sub.1+4, 100.degree. C.) of 20 to 100, which process comprises polymerizing 1,3-butadiene in an inert organic solvent with a catalyst comprising as the main components (a) a nickel compound; (b) a specific fluorine compound; (c) a trialkylaluminum; and (d) a halogenated aldehyde and/or a quinone compound. The use of the specific catalyst enables the production in a high yield of a polybutadiene rubber which maintains the abrasion resistance, high impact resilience and low heat buildup which are the characteristics of polybutadiene rubber and has a small die swell when extruded in the form of a blend with a natural rubber and is excellent in physical properties of vulcanizate.

Abstract: A process for producing a high trans low vinyl conjugated diene (co)polymer, comprising polymerizing at least one conjugated diene alone or in combination with at least one alkenyl compound using a catalyst composition comprising (a) a barium compound, (b) an organoaluminum compound, (c) an organolithium compound and (d) a hydroxyl group-containing organic compound. This process enables the easy production of a high trans low vinyl conjugated diene (co)polymer having a high trans 1,4 bond content, a low vinyl bond content and a high molecular weight, at a high polymerization activity.

Abstract: A rubber composition suitable for use in tire tread is disclosed, which contains at least 20 parts by weight of a block copolymer per 100 parts by weight of total rubber content. This block copolymer comprises (A) a polymer segment obtained by starting from conjugated diolefin and monovinyl aromatic hydrocarbon and having a content of monovinyl aromatic hydrocarbon bond of not more than 10% by weight and (B) a copolymer segment obtained by copolymerization of conjugated diolefin and monovinyl aromatic hydrocarbon and having a content of monovinyl aromatic hydrocarbon bond of 15-50% by weight.

Abstract: A styrene-butadiene block copolymer having a Mooney viscosity (ML.sub.1+4, 100.degree. C.) of 10 to 150 comprising two specific random styrene-butadiene copolymer blocks different in bound styrene content and in vinyl content in the butadiene portion, and optionally polybutadiene blocks, wherein the total vinyl content in the whole bound butadiene is 30 to 70% and the total bound styrene content is 10 to 40% by weight. Said block copolymer is excellent in wet skid resistance and rolling resistance, well-balanced in fracture and wear characteristics and also satisfactory in processability and cold flow property.