CuBr/Bipyridine (Bpy) atom transfer radical polymerization (ATRP) catalysts are physisorbed and covalently tethered to nonporous fumed silica and are characterized by elemental analysis, thermogravimetric analysis, and UV/vis spectroscopy. The supported catalysts are used for the polymerization of methyl methacrylate (NIMA), promoting the polymerization to moderate conversions with good control, with molecular weights similar to theoretical values and low polydispersity indices (PDIs). The used, Cu(II)-containing catalysts are subjected to a regeneration process with AIBN as a reductant, producing increased concentrations of Cy(I) species on the Surface for the tethered system. Leaching experiments indicate that the tethered systems result in no detectable Soluble copper species and that the majority of the catalytic transformations occur with sites tethered to the surface. In contrast, use of the physisorbed catalyst results in a substantial amount of leached copper species, and the soluble species are capable of controlling the polymerization in the absence of the solid, although with extremely low polymerization rates. (c) 2005 Elsevier Inc. All rights reserved.