Newly designed star-shaped and dendrimer-like copolymers made of poly(ethylene oxide) (PEO) and polystyrene (PS) were synthesized by sequential anionic polymerization of ethylene oxide and atom transfer radical polymerization (ATRP) of styrene, the switch from the first to the second mechanism being obtained by selective transformation of “living” oxanionic sites. First, tri- and tetrafunctional initiators were used to anionically polymerize ethylene oxide and produce tri- and tetraarmed PEO stars. Next, the OH end groups of PEO star branches were derivatized into 2-bromopropionate groups giving rise to the corresponding tri- and tetrabromoester ended-PEO stars; the latter served as macroinitiators for the ATRP of styrene at 100 °C in the presence of CuBr/2,2‘-bipyridine catalyst system affording amphiphilic star block copolymers PEOn-b-PSn (n = 3 or 4). PEOn-b-PS2n (n = 3 or 4) dendrimer-like copolymers constituted of an inner PEO part and an outer PS layer were prepared by introducing a branching agent ...