Synthesis and Properties of Asymmetric Heteroarm PEO<i>_n</i>-<i>b</i>-PS<i>_m</i> Star Polymers with End Functionalities

We report on the “core-first” synthesis of asymmetric three- and four-arm poly(ethylene oxide) (PEO)−polystyrene (PS) star polymers with functional terminal groups of a general formula PEOn-b-PSm with n = 0, 1, and 2 and n + m ≤ 4. The synthesis was conducted by anionic polymerization of ethylene oxide and followed by atom transfer radical polymerization (ATRP) of styrene. The properties of asymmetric star-shaped macromolecules with different numbers of arms (n = 1; m = 2 and 3) and similar lengths of the PEO arm were compared with homoarm star polymers (PEO4 and PS4) and corresponding linear polymers. All star polymers obtained here possessed well-defined architecture with a relatively narrow molecular weight distribution as confirmed by NMR, FTIR, and arm-disassembling techniques. Star polymers showed suppression of melting temperature and lower crystallinity PEO phase due to the presence of a junction point. Preliminary studies demonstrated surface activities of these block copolymers with a rich polymorphism of micellar surface structures expected for amphiphilic block copolymers despite the presence of the bulky terminal functionalized groups.