Abstract: The present invention relates to a process for preparing a diene elastomer. The invention especially applies to the production of a polybutadiene with a high level of cis-1,4 linkages that has at the same time a Mooney viscosity ML (1+4) greater than or equal to 40, a polydispersity index less than 2.1 and a reduced cold flow and of a polyisoprene. The process according to the invention comprises a reaction of a catalyst system with at least one conjugated diene monomer, this catalyst system being based on at least: one conjugated diene; one organic phosphoric acid salt of one or more rare-earth metals, said salt being in suspension and in at least one saturated and aliphatic or alicyclic, and inert hydrocarbon-based solvent; one alkylating agent composed of an alkyl aluminum for formula AlR3 or HAlR2 and a halogen donor belonging to the family of alkylaluminium halides, with the exclusion of alkylaluminium sesquihalides.

Abstract: The present invention relates to a process for preparing a diene elastomer. The invention especially applies to the production of a polybutadiene with a high level of cis-1,4 linkages that has at the same time a Mooney viscosity ML (1+4) greater than or equal to 40, a polydispersity index less than 2.1 and a reduced cold flow and of a polyisoprene. The process according to the invention comprises a reaction of a catalyst system with at least one conjugated diene monomer, this catalyst system being based on at least: one conjugated diene; one organic phosphoric acid salt of one or more rare-earth metals, said salt being in suspension and in at least one saturated and aliphatic or alicyclic, and inert hydrocarbon-based solvent; one alkylating agent composed of an alkyl aluminium for formula AlR3 or HAlR2 and a halogen donor belonging to the family of alkylaluminium halides, with the exclusion of alkylaluminium sesquihalides.