Patent ID: 7205360

Claim:
A preparation process for a copolymer, whether functional or not, having two blocks, which is usable in a sulphur-cross-linkable rubber composition of reduced hysteresis in the cross-linked state, one of said blocks being constituted of a polyisoprene and the other of a diene elastomer other than a polyisoprene, the molar ratio of units originating from conjugated dienes of which is greater than 15%, said process comprising copolymerizing one or more monomers comprising a conjugated diene other than isoprene using a catalytic system comprising 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 comprising a C—Li bond which is constituted of a monolithiated polyisoprene intended to form said polyisoprene block, the number-average molecular weight M n1 of said polyisoprene block being between 2,500 and 20,000 g/mol, in order to obtain said copolymer in which the block comprising said diene elastomer has a number-average molecular weight M n2 of between 65,000 and 350,000 g/mol and a content of trans-1,4 linkages equal to or greater than 70%.