Well-defined amphiphilic four-arm star P(AA-b-STY) block copolymers have been dispersed in water to form core-shell micelles in which the shell consists of tethered PAA loops. The entropic penalty for having such loops resulted in a less densely packed PSTY core when compared to linear diblock copolymers of the same arm length. The surface of the shell is irregular because of the tethering points, but when cleaved the PAA chains extend to form a regular and relatively uniform corona.