Design and synthesis of star polymers with hetero-arms by the combination of controlled radical polymerizations and click chemistry

An alternative approach to the synthesis of well-defined star polymers with hetero-arms was described. An azide-functionalized dithioester chain transfer agent (CTA-N3) 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-N3, about 92%). The azide end-capped PS-N3 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 successfully prepared.