Low polydispersity polydimethylsiloxane (PDMS) was end functionalized with a reversible addition fragmentation chain transfer (RAFT) agent by the esterification of hydroxyl terminated PDMS with a carboxylic acid functional RAFT agent. These PDMS‐RAFT agents were able to control the free radical polymerization of styrene and substituted styrene monomers to produce PDMS‐containing block copolymers with low polydispersities and targeted molecular weights. A thin film of polydimethylsiloxane‐block‐polystyrene was prepared by spin coating and exhibited a microphase separated morphology from scanning force microscopy measurements. Controlled swelling of these films in solvent vapor produced morphologies with significant long‐range order. This synthetic route will allow the straightforward production of PDMS‐containing block copolymer libraries that will be useful for investigating their thin film morphological behavior, which has applications in the templating of nanostructured materials.© 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010