METHOD OF PREPARING BLOCK COPOLYMERS FOR TYRE TREAD COMPOSITIONS AND THE COPOLYMERS THUS PREPARED

摘要

The invention relates to: a method of preparing a two-block copolymer which can be used in a sulphur-crosslinkable rubber composition having reduced hysterises in the crosslinked state; one such block copolymer in which one of the blocks comprises a polyisoprene and the other block comprises a diene elastomer other than polyisoprene; and said rubber composition which is intended for tyre treads. The inventive method of preparing said copolymer consists in copolymerising one or more monomers comprising a conjugated diene other than isoprene using a catalytic system containing: at least one hydrocarbon solvent; a compound A of a metal from group IIIA; a compound B of an alkaline-earth metal; and a polymer initiator C comprising a bond C-Li which is formed by a monolithiated polyisoprene that is intended to form said polyisoprene block, the number-average molecular weight M>n1< of said polyisoprene block having a value of between 2 500 and 20 000 g/mol. In this way, said method can be used to obtain the aforementioned copolymer in which the other block comprising the diene elastomer has a number-average molecular weight M>n2< of between 65 000 and 350 000 g/mol and a 1,4-trans chaining content that is equal to or greater than 70 %.