An alternative approach to the synthesis of well-defined star polymers with hetero-arms was described. An azide-functionalized dithioester chain transfer agent (CTA-N-3) was designed and synthesized. Using CTA-N3 as the reversible addition-fragmentation chain transfer (RAFT) agent, styrene was polymerized in a controlled manner. The so-obtained polystyrene showed a high proportion of azide-functionalized chains (PS-N-3, about 92%). The azide end-capped PS-N-3 could be assembled. via click reaction with a bromide-containing trialkyne coupling agent, to form a 3-arm star polystyrene (PS3-Br) with a narrow molecular weight distribution. PS3-Br could further serve as a macro-initiator for the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). Accordingly, well-defined star polymers containing three polystyrene and one poly(methyl methacrylate) (PMMA) arms, and with a narrow molecular weight distribution, were successful] prepared. (C) 2007 Published by Elsevier Ltd.