Abstract: A diene rubber (iii) can be obtained by mixing in a solution state:a modified styrene-butadiene rubber (i) having a weight-average molecular weight of 150,000-500,000, obtained by reacting a diene polymer having a bound active metal in the molecule, with a modifier such as N-methyl-.epsilon.-caprolactam or the like, anda branched styrene-butadiene rubber (ii) having a weight-average molecular weight of 800,000 or more.This diene rubber (iii) and a rubber composition comprising the diene rubber (iii) and other diene rubber (iv) have superior processability when unvulcanized and give a vulcanized rubber having improved abrasion resistance, resiliency and low-temperature properties.

Abstract: The present invention provides a rubber composition which is balanced in wet skid resistance, low-temperature properties and low fuel consumption and which is suitable as a material for all-weather tire. This rubber composition comprises a random copolymer A having a glass transition temperature of -20.degree. C. or higher, a random copolymer B having a glass transition temperature of -50.degree. C. or lower, and a block copolymer C composed of said two copolymers as block units. The copolymers A, B and C can be produced by copolymerizing an aromatic vinyl compound and a conjugated diene using an alkali metal-based catalyst.

Abstract: An abrasion-resistant rubber composition comprises as rubber components (A) 30-95 wt. % of an end-modified butadiene polymer and (B) 70-5 wt. % of a diene rubber other than the end-modified butadiene polymer (A). The end-modified butadiene polymer (A) is obtained by reacting at least one compound to active terminals of a starting butadiene polymer having a trans 1,4 bond content of 70-95 wt. %. The at least one compound is selected from N-substituted aminoketones, N-substituted thioaminoketones, N-substituted amino-aldehydes, N-substituted thioaminoaldehydes and compounds containing in the molecules thereof an atomic group represented by the following formula: ##STR1## in which M stands for an oxygen or sulfur atom.

Abstract: There are provided a process for producing a diene polymer having markedly improved tensil strength and wear resistance and further having improved heat build-up, refound resilience, processability and wet skid resistance, as well as a rubber composition containing said diene polymer and having improved tensil strength, wear resistance, etc. Said diene polymer is produced by polymerizing a conjugated diene monomer or a mixture of the conjugated diene monomer and an aromatic vinyl monomer in a hydrocarbon solvent using a composite initiator containing an alkaline earth metal, and reacting active ends of the obtained active diene polymer with (a) a compound represented by the formula M.dbd.C.dbd.M (wherein M denotes an oxygen atom or a sulfur atom) or (b) N-substituted aminoketone, N-substituted thioaminoketone, N-substituted aminoaldehyde, N-substituted thioaminoaldehyde or a compound having an atomic group in a molecule represented by the formula --C(.dbd.M)--N< in a molecule.

Abstract: A rubber composition comprises as rubber components (A) 30-95 wt. % of an end-modified styrene-butadiene copolymer and (B) 70-5 wt. % of a diene rubber other than the end-modified styrene-butadiene copolymer (A). The end-modified styrene-butadiene copolymer (A) is obtained by reacting at least one compound to active terminals of a starting styrene-butadiene copolymer containing butadiene moieties, the trans-1,4 bond content of which is 70-95 wt. %, and having a styrene content of 5-60 wt. %. The at least one compound is selected from N-substituted aminoketones, N-substituted thioaminoketones, N-substituted aminoaldehydes, N-substituted thioaminoaldehydes and compounds containing in the molecules thereof an atomic group represented by the following formula: ##STR1## in which M stands for an oxygen or sulfur atom. The diene rubber (B) has a glass transition temperature higher than -60.degree. C.

Abstract: A rubber composition comprising, as rubber components, 10-40 % by weight of (1) a styrene-butadiene copolymer rubber obtained by solution polymerization, having a styrene content of less than 20% by weight and a trans-1,4 bond content in butadiene portion, of more than 90% by weight and 60-90% by weight of (2) a diene rubber other than the styrene-butadiene copolymer rubber (1), having a glass transition temperature of -60.degree. C. or below.

Abstract: A rubber composition for tire treads which comprises 100 parts by weight of a rubber component comprising 10 to 100 parts by weight of a styrene-butadiene copolymer rubber produced by a solution polymerization and 90 to 0 parts by weight of at least one of other diene rubbers having a glass transition temperature (Tg) of -60.degree. C. at lowest, and at least 70 parts by weight of a carbon black mixed in the rubber component, the styrene-butadiene copolymer rubber having a styrene content of 45 to 65% by weight, a content of butadiene derived vinyl groups of 20 to 70 parts by weight and a content of a styrene sequence consisting of not less than 8 bonded styrene monomer units of at largest 10% by weight of the above styrene content.

Abstract: A rubber composition which gives a rubber vibration insulator having excellent low-temperature properties comprises as a main rubber component a blend composed of (a) 10 to 90 parts by weight of a tapered styrene/butadiene copolymer rubber which has an average bound styrene content of 10 to 40% by weight and a 1,2-bond content in the butadiene portion of at least 50% by weight and in which the bound styrene content increases or decreases in one direction along the copolymer molecular chain and (b) 90 to 10 parts by weight of natural rubber and/or synthetic polyisoprene rubber.

Abstract: A rubber composition for tire tread, comprising a rubber mixture composed of two kinds of styrene-butadiene copolymer rubber different from each other in the styrene content and the vinyl bond content in butadiene, polybutadiene rubber, natural rubber and/or synthetic polyisoprene rubber.