Thermally stable core-shell gold nanoparticles (Au NPs) with highly grafted polymer shells were synthesized by combining reversible addition-fragmentation transfer (RAFT) polymerization and click chemistry of copper-catalyzed azide-alkyne cycloaddition (CuAAC). First, alkyne-terminated poly(4-benzylchloride-b-styrene) (alkyne-PSCl-b-PS) was prepared from the alkyne-terminated RAFT agent. Then, an alkyne-PSCl-b-PS chain was coupled to azide-functionalized Au NPs via the CuAAC reaction. Careful characterization using FTIR, UV-Vis, and TGA showed that PSCl-b-PS chains were successfully grafted onto the Au NP surface with high grafting density. Finally, azide groups were introduced to PSCl-b-PS chains on the Au NP surface to produce thermally stable Au NPs with crosslinkable polymer shell (Au-PSN3-b-PS 1). As the control sample, PS-b-PSN3-coated Au NPs (Au-PSN3-b-PS 2) were made by the conventional "grafting to" approach. The grafting density of polymer chains on Au-PSN3-b-PS 1 was found to be much higher than that on Au-PSN3-b-PS 2. To demonstrate the importance of having the highly packed polymer shell on the nanoparticles, Au-PSN3-b-PS 1 particles were added into the PS and PS-b-poly(2-vinylpyridine) matrix, respectively. Consequently, it was found that Au-PSN3-b-PS 1 nanoparticles were well dispersed in the PS matrix and PS-b-P2VP matrix without any aggregation even after annealing at 220 degrees C for 2 days. Our simple and powerful approach could be easily extended to design other core-shell inorganic nanoparticles. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3464-3474, 2011