Hybrid nanomaterials were synthesized via grafting poly(N-isopropylacrylamide) (PNIPAM) over silica nanoparticles in a one-pot reaction using the internal and external surface of the nanoparticles as a microreactor system. Silica nanoparticle properties were tuned through templating and pore-swelling agents which allows obtaining spherical and elongated morphologies. Polymerization reactions were carried out at 80 °C for 4 h, using two initiator systems and N,N′-methylenebisacrylamide as a cross-linker. The structures obtained were studied by SEM and TEM micrographs, and the presence of polymer was confirmed through ¹HNMR and FTIR analysis. The thermoresponsive behavior was analyzed by DLS and DSC. It was found that the silica core structure and the initiator solubility affect considerably the aggregation and the size distribution of the grafted nanoparticles. Therefore, it is observed that different parameters can be used to drive grafting reactions without any previous functionalization step on the core surface, showing a straightforward method for their production.