Self-stabilized nanoparticles with a temperature-responsive poly[(N,N-diethylacrylamide)-co-(N,N'-methylenebisacrylamide)] microgel core and a covalently attached hairy shell were synthesized via a simple nitroxide-mediated controlled free-radical aqueous dispersion polymerization, using a poly(sodium acrylate) alkoxyamine macroinitiator. With this method, high solid content, surfactant-free particle suspensions were prepared, with diameter ranging from 49 to 118 nm at high temperature, and able to reversibly swell with water at low temperature. The proposed method requires a limited number of reagents in a simple polymerization procedure and thus avoids many drawbacks generally encountered in the synthesis of thermally responsive microgel particles.