Hydrosols containing silver nanoparticles were prepared from copolymers of ethylene glycol (EG) and vinyl pyrrolidone (VPy). The copolymers were synthesized using a macro-azo-radical initiator appended with EG units. The hydrosols were prepared by simply stirring the copolymers with AgNO3 in water at room temperature. The nanoparticles conferred thermal stability to the hydrosols, up to 80 A degrees C. Spectroscopic, thermal, and gas chromatography analyses revealed that the silver nanoparticles were protected by EG and carbonyl groups with strong interaction between silver and the oxygen species of EG and VPy.