| 摘要 |
A preparation process for a copolymer having two blocks usable in a sulphur-cross-linkable rubber composition of reduced hysteresis in the cross-linked state, such a block copolymer in which one of the blocks is a polyisoprene and the other a diene elastomer other than a polyisoprene, and this rubber composition for tire treads. A process for the preparation of this copolymer involves copolymerizing one or more monomers including a conjugated diene other than isoprene using a catalytic system including at least one hydrocarbon solvent, a compound A of a metal of group IIIA, a compound B of an alkaline-earth metal and a polymeric initiator C having a C-Li bond which is constituted of a monolithiated polyisoprene intended to form the polyisoprene block, the number-average molecular weight M<SUB>n1 </SUB>of the polyisoprene block being between 2,500 and 20,000 g/mol. A copolymer is obtained in which the block composed of the diene elastomer has a number-average molecular weight M<SUB>n2 </SUB>of between 65,000 and 350,000 g/mol and a content of trans-1,4 linkages equal to or greater than 70%.
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