A simple methodology is described for the preparation of temperature sensitive star polymers with random number of arms and crosslinked core. In the first step, well defined, monodisperse poly(N-isopropylacrylamide) PNIPAAm polymers were prepared by reversible addition-fragmentation chain transfer polymerization (RAF-polymerization) by using 4-cyanopentanoic acid dithiobenzoate as chain transfer agent (CTA). In the second step, the PNIPAAm polymers were used as macro-CTA's for copolymerization with ethylene glycol dimethacrylate (EGDMA) by the RAFT-technique. Adjusting the macro-CTA to EGDMA ratio, nanometric star polymers with small or big core could be prepared as revealed by gel permeation chromatography (GPC), dynamic light scattering (DLS) and viscometry. The same methodology was applied for the preparation of star polymers with poly(NIPAAm)-b-poly(hexyl acrylate) arms. The so prepared temperature sensitive multiarm materials are a stable alternative to polymeric micelles as nano-carriers for drug-delivery applications. (C) 2011 Elsevier Ltd. All rights reserved.