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 tent-butyl acrylate or methyl methacrylate, and this resulted in AB₂-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.