Process for manufacturing multiarmed asymmetrical radial block copolymers

A process for the manufacture of six-armed radial asymmetric block copolymers, comprising the steps of:

• polymerization of a conjugated diene and/or a monoalkenyl aromatic hydrocarbon by means of an anionic monofunctional organo alkali metal initiator to form first polymer arms having a single reactive metal end group on each polymer arm;
• contacting the first polymer arms with a non-polymerizable coupling agent containing 6 functional groups which react with the reactive end groups, the amount of the first polymer arms being substantially stoichiometrically corresponding with 4 of the 6 functional groups on the coupling agent, in a way that the reaction between the first polymer arms and the coupling agent proceeds substantially to completion;
• preparing second polymer arms, different from said first polymer arms living polymer either in the same reactor or a different reactor by polymerization of a conjugated diene which is 1,3-butadiene and/or a monoalkenyl aromatic hydrocarbon initiated by an anionic monofunctional organoalkali metal initiator;
• adding a polar compound capable of increasing the reactivity of the residual functional groups of the coupling agent and reacting these residual functional groups with the second polymer arms until all residual functional groups of the coupling agents have completely reacted;
• and
• recovering the six-armed asymmetric radial polymer.