Well-defined star polymers; containing a functionalized Core Supply a Molecular nanocavity and may be used to control formation of inorganic nanoparticles. Herein, platinum (Pt) nanoparticlcs of 2-4 nm were prepared by using (poly(acrylic acid)-b-polystyrene)(6) (PAA-b-PS)(6) amphiphilic star block copolymer as a novel single molecular stabilizer. This PAA core functionalized star polymer was obtained by hydrolysis of (poly(tert-butyl acrylate)-b-polystyre)(6) (PtBA-b-PS)(6), which was synthesized by sequential atom transfer radical polymerization (ATRP) of tert-butyl acrylate and styrene with an initiator bearing six 2-bromoisobutyloxyl groups. Pt(IV) ions were loaded by ion exchange to the core of the star polymer and Pt nanoparticle stabilized by single star polymer was produced by a reduction with NaBH4. (c) 2005 Elsevier Inc. All rights reserved.