The reversible addition-fragmentation chain transfer (RAFT) polymerization process was used to synthesize well-defined N-acryloxysuccinimide (NAS) based copolymers, very useful reactive building blocks for various applications. Kinetic studies of RAFT copolymerization of NAS with a bi-substituted acrylamide derivative, N-acryloylmorpholine (NAM), were performed in the presence of tertbutyl dithiobenzoate (tBDB). An excellent control was reached with very high conversions (>95%), molecular weights (MW) up to 80 000 g mol(-1) and very narrow molecular weight distributions (MWD) (polydispersity indices, PDI < 1.1), as determined by aqueous size exclusion chromatography with on-line light scattering detector (SEC/LS). In addition, the comparison of RAFT and conventional NAM/NAS free radical copolymerization indicated that the apparent reactivity ratios in RAFT are similar to the reactivity ratios determined from conventional copolymerization. An identical azeotropic composition (60/40 NAM/NAS molar ratio) was obtained providing perfectly random poly(NAM-co-NAS) copolymers with full control of composition and MW. These copolymer chains with regularly-distributed reactive functions can be integrated into more complex architectures. As an example, poly [(NAM-co-NAS)-b-NAM] block copolymers with length-varying poly(NAM) block were synthesized with a very efficient control over MW, MWD and composition. (C) 2004 Published by Elsevier Ltd.