The synthesis of poly(octadecyl methacrylate) brushes on planar Si substrates using surface-initiated atom transfer radical polymerization (SI-ATRP) is reported. SI-ATRP of octadecyl methacrylate from a silane initiator-modified Si substrate yielded well-defined homopolymer brushes of varying molar mass (5000–38 000 g mol−1) and film thickness from around 2 to 20 nm. Correlation of both free polymer molar mass and brush thicknesses confirmed controlled surface-initiated ATRP from these modified surfaces. By optimization of brush molar mass, film thickness and thin-film processing, we observed side chain crystallization of tethered poly(octadecyl methacrylate) chains, resulting in the formation of lamellar morphologies with high-aspect-ratio nanofibers. Copyright © 2013 John Wiley & Sons, Ltd.