Facile synthesis of AB₂‐type miktoarm star polymers through the combination of atom transfer radical polymerization and ring‐opening polymerization

A novel miktofunctional initiator ( 1 ), 2‐hydroxyethyl 3‐[(2‐bromopropanoyl)oxy]‐2‐{[(2‐bromopropanoyl)oxy]methyl}‐2‐methyl‐propanoate, possessing one initiating site for ring‐opening polymerization (ROP) and two initiating sites for atom transfer radical polymerization (ATRP), was synthesized in a three‐step reaction sequence. This initiator was first used in the ROP of ϵ‐caprolactone, and this led to a corresponding polymer with secondary bromide end groups. The obtained poly(ϵ‐caprolactone) (PCL) was then used as a macroinitiator for the ATRP of tert ‐butyl acrylate or methyl methacrylate, and this resulted in AB 2 ‐type PCL–[poly( tert ‐butyl acrylate)] 2 or PCL–[poly(methyl methacrylate)] 2 miktoarm star polymers with controlled molecular weights and low polydispersities (weight‐average molecular weight/number‐average molecular weight < 1.23) via the ROP–ATRP sequence.