In this work, the preparation of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEM) star polymers using reversible addition-fragmentation chain transfer (RAFT) polymerization, is reported. A trifunctional trithiocarbonate was used and the core was part of th e R group (leaving group) of the RAFT chain transfer agent. The R-core RAFT star polymerizations of PDMAEM showed excellent molecular weight control up to very high monomer conversions. PDMAEM-star polymer-protected gold nanoparticles (AuNPs) were prepared in the absence of any other reducing agent at 40 and 65 A degrees C in aqueous solution. The AuNPs were sphere-like with a diameter of 5-8 nm, which was independent of the star polymer concentration and star polymer molecular weight. Furthermore, the behavior of the pH- and temperature-sensitive AuNPs-star-PDMAEM was studied in aqueous solution by measuring the lower critical solution temperature (LCST) by dynamic light scattering. The measurements were performed at pH values of 8.4, and 10.5. By varying the pH, the LCST can be easily tuned between 35 and 43 A degrees C. The AuNPs show remarkable stability in water; this was demonstrated by monitoring absorbance of AuNPs over regular time periods within 4 months.