Well-defined star polymers were synthesized with a combination of the core-first method and atom transfer radical polymerization. The control of the architecture of the macroinitiator based on beta-cyclodextrin bearing functional bromide groups was determined by C-13 NMR, fast atom bombardment mass spectrometry, and elemental analysis. In a second step, the polymerization of the tert-butyl acrylate monomer was optimized to avoid a star-star coupling reaction and allowed the synthesis of a well-defined organosoluble polymer star. The determination of the macromolecular dimensions of these new star polymers by size exclusion chromatography/ light scattering was in agreement with the structure of armed star polymers in a large range of predicted molecular weights. This article describes a new approach to polyelectrolyte star polymers by postmodification of poly(tert-butyl acrylate) by acrylic arm hydrolysis in a water-soluble system. (c) 2005 Wiley Periodicals, Inc.