A tire tread comprising a rubber composition based on at least one highly saturated elastomer, a reinforcing filler and a vulcanization system is provided. The highly saturated diene elastomer contains 1,3-diene units and more than 50 mol % of ethylene units, the vulcanization system comprises a dithiosulfate salt of formula MO.sub.3S-S-A-S-SO.sub.3M in which the symbol A represents an alkanediyl group or a group comprising two or more alkanediyl units, which units are connected in pairs by means of an oxygen or sulfur atom, of a group of formula —SO.sub.2—, —NH—, —NH.sub.2.sup.+—, —N(C.sub.1—C.sub.16 alkyl)- or —COO—, or of an arylene or cycloalkylene group and the symbol M represents a metal atom. An improved compromise between the bubbling of the tread at the exit of curing presses and its hysteresis can be achieved.

A rubber composition comprising 0.1 to 2.5 parts by weight of a lubricant having a flow temperature of 50 to 100° C. based on 100 parts by weight of an ethylene/butene/5-ethylidene-2-norbornene terpolymer. This rubber composition is compounded with a specific lubricant, has the following effects. That is, the rubber composition prevents difficulties caused by sticking between unvulcanized rubber compound, improves productivity in the rubber compound preparation process and the vulcanization molding process of crosslinked molded products, such as seal members, and does not impair the low temperature properties of the crosslinked molded products. This rubber composition is effectively used as a crosslinking molding material for seal parts, for which a high pressure gas sealing function is particularly required in a low temperature environment, e.g., −39° C. or lower.

A rubber composition comprising 0.1 to 2.5 parts by weight of a lubricant having a flow temperature of 50 to 100° C. based on 100 parts by weight of an ethylene/butene/5-ethylidene-2-norbornene terpolymer. This rubber composition is compounded with a specific lubricant, has the following effects. That is, the rubber composition prevents difficulties caused by sticking between unvulcanized rubber compound, improves productivity in the rubber compound preparation process and the vulcanization molding process of crosslinked molded products, such as seal members, and does not impair the low temperature properties of the crosslinked molded products. This rubber composition is effectively used as a crosslinking molding material for seal parts, for which a high pressure gas sealing function is particularly required in a low temperature environment, e.g., −39° C. or lower.

A rubber composition which comprises at least one reinforcing inorganic filler and a highly saturated elastomer comprising 1,3-diene units and ethylene units and bearing, at the chain end, a functional group F.sup.1 which is a silanol or alkoxysilane function is provided. The ethylene units represent more than 50 mol % of all the monomer units of the elastomer. The rubber composition has an improved hysteresis/stiffness compromise.

A rubber composition which comprises at least one reinforcing inorganic filler and a highly saturated elastomer comprising 1,3-diene units and ethylene units and bearing, at the chain end, a functional group F.sup.1 which is a silanol or alkoxysilane function is provided. The ethylene units represent more than 50 mol % of all the monomer units of the elastomer. The rubber composition has an improved hysteresis/stiffness compromise.

A copolymer of ethylene and of a 1,3-diene of formula CH.sub.2CRCHCH.sub.2 is provided. The ethylene units represent between 50 mol % and 95 mol % of the ethylene units and of the units of the 1,3-diene, and the units of the 1,3-diene of 1,2 and 3,4 configuration represent more than 50 mol % of the units of the 1,3-diene. The symbol R represents a hydrocarbon chain having from 3 to 20 carbon atoms. Such a copolymer exhibits an improved compromise between the degree of crystallinity and the stiffness and makes it possible to widen the field of application of ethylene-rich diene copolymers in rubber compositions.

A polypropylene composition for a dyeable polypropylene filament yarn includes a polypropylene having a melt flow rate ranging from 30 g/10 min to 40 g/10 min, a polyester serving to modify the polypropylene and having a melt flow rate ranging from 40 g/10 min to 50 g/10 min, and a compatibilizer serving to improve compatibility between the polypropylene and the polyester. The polypropylene composition has a melt flow rate ranging from 30 g/10 min to 40 g/10 min.

A copolymer of ethylene and of myrcene, in which the ethylene units represent between 50 mol % and 95 mol % of the ethylene units and of the myrcene units, and the myrcene units of 1,2 and 3,4 configuration represent more than 50 mol % of the myrcene units, is provided. Such a copolymer exhibits an improved compromise between the degree of crystallinity and the stiffness. It therefore makes it possible to widen the field of application of ethylene-rich diene copolymers in rubber compositions, and also to increase the production capacity of a unit for the synthesis of ethylene-rich diene polymers.

An object of the present invention is to provide a novel ethylene/-olefin/non-conjugated polyene copolymer containing a certain non-conjugated polyene such as VNB as a copolymerization component, having a low long-chain branching content, excellent in cure characteristics in the case of crosslinking by using peroxide, and having good processability. The ethylene/-olefin/non-conjugated polyene copolymer according to the present invention has constitutional units derived from ethylene (A), an -olefin (B) having 3 to 20 carbon atoms, and a non-conjugated polyene (C) having a total of two or more partial structures selected from the group consisting of the following general formulas (I) and (II) in a molecule, and satisfies certain requirements.

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A rubber composition having a reduced adhesion to the surface of a kneading machine, particularly an open roll kneading machine, in consideration of keading processability, the rubber composition comprising 20 to 60 parts by weight of carbon black having a DBP oil absorption of 100 ml/100 g or more and an iodine value of 75 to 90 g/kg based on 100 parts by weight of an ethylene/butene/5-ethylidene-2-norbornene terpolymer. Stable and safe productivity of the rubber composition can be obtained, and the rubber composition is effectively used for seal parts, for which a high pressure gas sealing function is particularly required in a low temperature environment, e.g., 30 to 60 C.