Dihydroxy terminated poly(dimethyl siloxane) (PDMS) was modified to form a di(trithiocarbonate) functional molecule capable of forming tri-block copolymers via the reversible-addition-fragmentation chain transfer (RAFT) process. Two statistical copolymer blocks were grown from the central PDMS block, comprising units of N,N-dimethyl acrylamide (DMA) and 2-(N-butyl perfluorooctanefluoro-sulfonamido) ethyl acrylate (BFA), to form A-B-A triblock macromolecules. The molecular weight of these block copolymers were found to increase with conversion while the polydispersity of the molecular weight distribution remains under 1.25. An unusual and interesting kinetic phenomenon was observed in that the copolymerization behaviour of DMA and BFA was influenced by the initial PDMS block. We surmise that this might be a direct observation of a 'bootstrap' effect. (C) 2004 Elsevier Ltd. All rights reserved.