| Summary: | Three series of thermo- and/or pH-responsive polymer-grafted SiO<sub>2</sub> nanoparticles, SiO<sub>2</sub>-<i>graft</i>-poly(oligo(ethylene glycol) methacrylate) (SiO<sub>2</sub>-<i>g</i>-POEGMA), SiO<sub>2</sub>-<i>graft</i>-poly(acrylic acid) (SiO<sub>2</sub>-<i>g</i>-PAA) and SiO<sub>2</sub>-<i>graft</i>-poly(oligo(ethylene glycol) methacrylate-<i>stat</i><i>e</i>-acrylic acid (SiO<sub>2</sub>-<i>g</i>-P(OEGMA-<i>stat</i>-AA)), were prepared by grafting POEGMA and/or PAA onto the surface of silica nanoparticles through the surface-initiated atom transfer radical polymerization (SI-ATRP). The lower critical solution temperature (LCST) of SiO<sub>2</sub>-<i>g</i>-POEGMA (M<sub>OEGMA</sub> = 300 g/mol) was found to be 64 °C. For SiO<sub>2</sub>-<i>g</i>-PAA nanoparticles, at the pH range from 8 to 12, the hydrodynamic diameter of the nanoparticles increases with increasing pH, and the zeta potential of SiO<sub>2</sub>-<i>g</i>-PAA nanoparticles is negatively charged and decreases with increasing pH. Owing to the thermo- and pH-responsive, the hydrodynamic diameters of SiO<sub>2</sub>-<i>g</i>-P(OEGMA-<i>stat</i>-AA) nanoparticles increase with the increasing pH, and the LCSTs of those nanoparticles increase with the increase of POEGMA content.
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