Radial multi-block copolymers

A process for making a radial multi-block copolymer, comprising the steps of:

• (a) anionically polymerizing styrene monomer A1, p-methylstyrene and/or p-tertbutylstyrene monomer A2 and 1,3-butadiene and/or isoprene monomer B1 using a lithium-based initiator to form block copolymer chains, wherein the monomers A1, A2, and B1 are polymerized simultaneously or in any sequential order;
• (b) adding an alkyl aluminum compound after initiating anionic polymerization in step (a) and before reaching peak reaction temperature in step (a), wherein the molar ratio of the alkyl aluminum compound to lithium ranges from 2:1 to 5:1, wherein a polymerization system is used in steps (a) and (b), and wherein the polymerization system may or may not include a tertiary amine and/or an ether compound but otherwise consists of the lithium-based initiator and the alkyl aluminum compound for promoting a coupling reaction;
• and
• (c) adding a coupling agent to form the radial multi-block copolymer, wherein the coupling agent is a polyester, polyacrylate, polymethacrylate or a polyketone compound, and wherein the radial multi-block copolymer comprises a residue Z derived from the coupling agent and block copolymer chains from step (b) coupled to the residue Z.