Poly(methyl methacrylate) (PMMA) brushes are grown by surface-initiated atom transfer radical polymerization on silicon surfaces at various polymerization temperatures. Kinetic studies show that the layer thickness scales linearly with the degree of polymerization of the polymers under some conditions, indicating a constant graft density of the surface-attached chains. At high temperatures, the layer growth is a controlled process only for short reaction times, and after a rapid increase, the film growth levels off, and a constant thickness is obtained. At lower reaction temperatures, polymers with a lower polydispersity are obtained, but at the expense of a much slower growth rate. Accordingly, intermediate temperatures yield the highest film thickness on experimentally feasible timescales. The reinitiation of these surface-grafted PMMA chains at room temperature to either extend the chains or grow a chemically different polyglycidylmethacrylate block demonstrates the presence of active ends and the living nature of the surface-grafted PMMA chains. © 2006 Wiley Periodicals, Inc.