The chemio-rheological behavior during the radical polymerization of the HEMA/grafted silica nanoparticles was found to be very dependent on the weight fraction of the silica particles. In the case of the neat HEMA. reactive system, the macrogelation occurs at the same time as the Trommosdorf effect. The reactive groups on the silica nanoparticles, which have a lower reactivity compared to that of the HEMA monomer, slow down the mean radical polymerization rate of the filled reactive system. The reactions between the grafted groups of the neighboring silica particles lead to the percolation, i.e., macrogelation, of the reactive system at low conversion degree, even if the reactive system is kinetically at the stationary state. The reactive medium of the HEMA/grafted silica nanoparticles systems could be divided to two parts: the percolating nanoparticles part for which the polymerization rate is very slow, and the bulk HEMA medium in which the radical polymerization rate is the same order of magnitude than for the neat HEMA.