Mesoporous silica particles were grafted with thermoresponsive poly(ethyleneoxide-b-N-vinylcaprolactam), PEO-b-PVCL. N-vinylcaprolactam was first polymerized on particle surfaces using surface initiated atom transfer radical polymerization (SI-ATRP) and then, the poly(ethyleneoxide) blocks were attached to the PVCL chain ends with click chemistry. The sizes, thermoresponsiviness, and colloidal stability of SiO2-PVCL and SiO2-PVCL-b-PEO particles and their aqueous dispersions were studied by scanning electron microscopy, turbidimetry, dynamic light scattering, zeta sizer, and microcalorimetry. The phase separation temperature of the PEO-b-PVCL grafted particles did not considerably differ from that of the SiO2-PVCL particles. The zeta potential of the grafted particles was close to zero at room temperature but decreased strongly upon heating. The decrease is related to the collapse of the PVCL blocks and correspondingly, the exposure of the silica surface toward the aqueous phase. The colloidal stability of the particles could be enhanced by adding PEO blocks to the chain ends of the PVCL grafts. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5012-5020