A new synthetic approach to thiol functional, well-defined amphiphilic block copolymers, which can be used to prepare multifunctional polymers and polymeric nanoparticles, is presented. Starting with a hydrophilic macroRAFT transfer agent and hydrophobic (meth)acrylate monomers that possess protected thiol groups, amphiphilic block copolymers are prepared in high yield. It is proven that the protected thiol groups in the monomer do not interfere with the RAFT polymerization process. Polymers with defined molecular weight, narrow polydispersities (PDI < 1.30) and varying length of the hydrophobic block are presented. Polymers with thiol groups in side chains and chain ends are obtained by aminolysis. With pyrene fluorescence spectroscopy and NMR measurements, it is shown that all synthesized polymers self-assemble into micelles. Furthermore, the possible application of these new polymers is exemplified by the preparation of polymer nanoparticles. (C) 2012 Elsevier Ltd. All rights reserved.