The present invention provides a compounding agent which, when used in a rubber composition containing a reinforcing filler, exhibits excellent dispersibility, workability, toughness, low heat build-up, and wear resistance; and a rubber composition containing the compounding agent. A modified butadiene polymer of the present invention has a functional group containing a nitrogen atom and silicon atom at a terminal, a weight average molecular weight of the modified butadiene polymer being from 1000 to 15000, and a molecular weight distribution of the modified butadiene polymer being 2.0 or less.

The present invention provides a compounding agent which, when used in a rubber composition containing a reinforcing filler, exhibits excellent dispersibility, workability, toughness, low heat build-up, and wear resistance; and a rubber composition containing the compounding agent. A modified butadiene polymer of the present invention has a functional group containing a nitrogen atom and silicon atom at a terminal, a weight average molecular weight of the modified butadiene polymer being from 1000 to 15000, and a molecular weight distribution of the modified butadiene polymer being 2.0 or less.

A rubber composition having an adhesion to a composition based on natural rubber, the composition being at least based on 5 to 95 phr of polyisoprene comprising a content by weight of 1,4-cis bonds of at least 90% of the weight of the polyisoprene; 5 to 95 phr of copolymer of ethylene and of a 1,3-diene of formula CH.sub.2═CR—CH═CH.sub.2, the ethylene units in the copolymer representing more than 50 mol % of the monomer units of the copolymer, the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms; and a crosslinking system. Also disclosed is a tire, in particular a tire provided with a sidewall, comprising this composition.

A rubber composition having an adhesion to a composition based on natural rubber, the composition being at least based on 5 to 95 phr of polyisoprene comprising a content by weight of 1,4-cis bonds of at least 90% of the weight of the polyisoprene; 5 to 95 phr of copolymer of ethylene and of a 1,3-diene of formula CH.sub.2═CR—CH═CH.sub.2, the ethylene units in the copolymer representing more than 50 mol % of the monomer units of the copolymer, the symbol R representing a hydrocarbon chain having 3 to 20 carbon atoms; and a crosslinking system. Also disclosed is a tire, in particular a tire provided with a sidewall, comprising this composition.

Disclosed is a rubber composition which suppresses poor mixing or poor dispersion from occurring between an organic polymer material derived from natural rubber and an inorganic material such as silica and exhibits excellent viscoelastic properties, and a silane coupling agent composition used in the same. Also disclosed is a silane coupling agent composition comprising a silane compound represented by Formula (1):

##STR00001##

wherein each variable is as defined herein.

Disclosed is a rubber composition which suppresses poor mixing or poor dispersion from occurring between an organic polymer material derived from natural rubber and an inorganic material such as silica and exhibits excellent viscoelastic properties, and a silane coupling agent composition used in the same. Also disclosed is a silane coupling agent composition comprising a silane compound represented by Formula (1):

##STR00001##

wherein each variable is as defined herein.

A rubber composition is based on at least: from 60 to 100 phr of one or more diene elastomers, referred to as very low glass transition temperature (Tg) diene elastomers, exhibiting a Tg within a range extending from −110° C. to −70° C., chosen from butadiene homopolymers, copolymers of butadiene and of vinylaromatic monomer, exhibiting a content of vinylaromatic unit of between 0% and 5% by weight, and the mixtures of these; a reinforcing filler; crosslinking system; and from 50 to 150 phr of at least one hydrocarbon resin predominantly composed of units resulting from α-pinene monomers, the resin exhibiting an aliphatic proton content of greater than 95%.

A rubber composition is based on at least: from 60 to 100 phr of one or more diene elastomers, referred to as very low glass transition temperature (Tg) diene elastomers, exhibiting a Tg within a range extending from −110° C. to −70° C., chosen from butadiene homopolymers, copolymers of butadiene and of vinylaromatic monomer, exhibiting a content of vinylaromatic unit of between 0% and 5% by weight, and the mixtures of these; a reinforcing filler; crosslinking system; and from 50 to 150 phr of at least one hydrocarbon resin predominantly composed of units resulting from α-pinene monomers, the resin exhibiting an aliphatic proton content of greater than 95%.

A rubber composition is based on at least: from 60 to 100 phr of one or more diene elastomers, referred to as very low glass transition temperature (Tg) diene elastomers, exhibiting a Tg within a range extending from −110° C. to −70° C., chosen from butadiene homopolymers, copolymers of butadiene and of vinylaromatic monomer, exhibiting a content of vinylaromatic unit of between 0% and 5% by weight, and the mixtures of these; a reinforcing filler; crosslinking system; and from 50 to 150 phr of at least one hydrocarbon resin predominantly composed of units resulting from α-pinene monomers, the resin exhibiting an aliphatic proton content of greater than 95%.

A rubber composition for a tennis ball includes a base rubber and a filler having a degree of flatness DL of not less than 50, the degree of flatness DL being obtained by dividing an average particle diameter D.sub.50 (μm) of the filler by an average thickness T (μm) of the filler. An amount of the filler per 100 parts by weight of the base rubber is not less than 1 part by weight and not greater than 150 parts by weight. A gas permeability coefficient GPS and a loss tangent tan δS of the rubber composition and a gas permeability coefficient GPL and a loss tangent tan δL of a rubber composition obtained by replacing the filler with kaolin clay having a degree of flatness DL of 20 satisfy (1): GPL/GPS≥1.02 and (2): |tan δL−tan δS|≤0.03. A tennis ball 2 includes a core 4 formed using the rubber composition.