Process for the preparation of a dilithiated initiator and anionic polymerization process

A process for the preparation by anionic polymerization of a living diene elastomer which is provided with a carbon-lithium group at each of the chain ends thereof, said process comprising:

• reacting, in an aliphatic or alicyclic hydrocarbon solvent, at least one conjugated diene monomer with a dilithiated initiator,
• wherein said dilithiated initiator is obtained by reacting a dialkenyl benzene bearing two double bonds and secondary butyllithium, in the presence of a diamine, in an aliphatic or alicyclic hydrocarbon solvent,
• such that the ratio of the number of moles of dialkenyl benzene to the number of moles of secondary butyllithium is substantially equal to 0.5, to form the dilithiated initiator,
• said initiator being a bi-adduct having a molecule of the secondary butyllithium added to each of the two double bonds of the dialkenyl benzene,
• wherein the lithium groups of said initiator are equi-reactive during polymerization.

A process for the preparation of a copolymer having three blocks, the central block of which comprises a diene elastomer and the end blocks of which are identical, comprising:

• a) preparing by anionic polymerization a living diene elastomer which is provided with a carbon-lithium group at each of the chain ends thereof comprising reacting, in an aliphatic or alicyclic hydrocarbon solvent, at least one conjugated diene monomer with a dilithiated initiator,
• wherein said dilithiated initiator is obtained by reacting a dialkenyl benzene bearing two double bonds and secondary butyllithium, in the presence of a diamine, in an aliphatic or alicyclic hydrocarbon solvent,
• such that the ratio of the number of moles of dialkenyl benzene to the number of moles of secondary butyllithium is substantially equal to 0.5, to form a dilithiated initiator,
• said initiator being a bi-adduct having a molecule of the secondary butyllithium added to each of the two double bonds of the dialkenyl benzene,
• wherein the lithium groups of said initiator are equi-reactive during polymerization, and
• b) grafting a polymer that comprises each of said end blocks on to said living diene elastomer.