The invention relates to the use of an alkali metal salt derivative of a specific vinyl aromatic monomer, as an initiator for the copolymerisation of i) one or more conjugated diene monomers and ii) one or more vinyl aromatic monomers. Furthermore, the invention relates to a process for the preparation of a copolymer component comprising coupled copolymer and terminally modified copolymer, and to the copolymer component. Also, the invention relates to a method for preparing a rubber, and to the rubber. Moreover, the invention relates to a rubber composition comprising the rubber. Finally, the invention relates to a tire component comprising the rubber, and to a tire comprising the tire component.