The self-assembly of two star copolymers, each consisting of four diblock arms of either poly(epsilon-caprolactone)-block-poly(ethylene oxide), PCL-PEO, or polylactide-block-poly(ethylene oxide), PLA-PEO, with PEO blocks in the centers of the stars, have been studied by a combination of light scattering, atomic force microscopy, fluorometry and H-1 NMR spectroscopy. Results of the study show that despite the very similar architecture of both star copolymers, the structures of their self-assembled nanoparticles differ. Unlike the (PLA-PEO)(4) star copolymer which forms core/shell flower-like micelles, the association of the (PCL-PEO)(4) copolymer leads to large micellar aggregates in which individual micelles are interconnected by shared unimers, having joint coronas formed by hydrophilic centers of the stars. (C) 2009 Elsevier Ltd. All rights reserved.