Rubber compositions

Claim 2

A rubber composition comprising: (a) a starting rubber comprising from 20 to 80 parts by weight of at least one rubber selected from the group consisting of natural rubber and synthetic polyisoprene rubber, and from 80 to 20 parts by weight of styrene-butadiene rubber having a styrene content of 10 to 30 percent by weight and a 1,2-vinyl bond content of from 10 to 80 percent by weight, said styrene-butadiene rubber containing either in the molecular chain or at the terminal end thereof at least one atomic group of the formula ##STR5## wherein X is OH or SH, the total amount of said starting rubber being 100 parts by weight; and (b) from 30 to 80 parts by weight of carbon black per 100 parts of starting rubber, said carbon black having an iodine adsorption of from 60 to 70 mg/g, a specific surface area ratio of nitrogen adsorption to iodine adsorption of from 1.18 to 1.40 and a median width of Stokes' particle size distribution of from 70 to 130 millimicrons.

Claim 3

The rubber composition of claim 1 wherein said styrene-butadiene rubber is a modified rubber derived from reaction of an unmodified styrene-butadiene copolymer with a compound containing a bond of the formula ##STR6## where M is an oxygen or sulfur atom.

Claim 4

The rubber composition of claim 2 wherein said compound is N,N-dimethylformaldehyde, N,N-diethylformaldehyde, N,N-diethylacetamide, aminoacetamide, N,N-dimethyl-N',N'-dimethylaminoacetamide, N-phenyldiacetamide, N,N-dimethyl-acrylamide, N,N-dimethylmethacrylamide, pripionamide, N,N-dimethylpropionamide, 4-pyridylamide, N,N-dimethyl-4-pyridylamide, N,N-dimethylbenzamide, p-aminobenzamide, N',N'-(p-dimethylamino)benzamide, N,N-dimethyl-N'-(p-ethylamino)benzamide, N-acetyl-N-2-naphthylbenzamide, nicotinamide, N,N-diethylnicotinamide, amide succinate, amide maleate, N,N,N',N'-tetramethylamide maleate, imide succinate, maleimide, N-methylmaleimide, N-methylphthalimide, 1,2-cyclohexanecarboxyimide, N-methyl-1,2-cyclohexanedicarboxyimide, oxamide, 2-furlamide, N,N,N',N'-tetramethyloxamide, N,N-dimethyl-2-furlamide, N,N-dimethyl-8-quinolinecarboxyamide, N,N-dimethyl-p-amino-benzylacetamide, N,N-dimethyl-N',N'-(p'-dimethylamino)cinnamylideneacetamide, N,N-dimethyl-N',N'-(2-dimethylamino)vinylamide, N'-(2-methylamino)vinylamide, urea, N,N'-dimethylurea, N,N,N',N'-tetramethylurea, methyl carbamate, N,N-diethylmethyl carbamate, ε-caprolactum, N-methyl-ε-caprolactum, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-acetyl-2-pyrrolidone, 2-piperidone, N-methyl-2-piperidone, 2-quinolone, N-methyl-2-quinolone, 2-indolinone, N-methyl-2-indolinone, isocyanuric acid or N,N',N"-trimethylisocyanurate, or a sulfur-containing compound thereof.

Claim 5

The rubber composition of claim 1 wherein said styrene-butadiene rubber further includes a tin-butadienyl branched polymer.