The amphiphilic block copolymer poly(styrene-b-N,N-diethylacrylamide) (PSt-b-PDEA) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of styrene and N,N-diethylacrylamide. The results of 1H-NMR and GPC analysis showed that the synthesized PSt-b-PDEA copolymer had controlled molecular weight and narrow polydispersity. Polymeric micelles having a unimodal size distribution with an average diameter of 40 +/- 0.5 nm were obtained from purified PSt-b-PDEA using a dialysis method. And the results showed that the clearance of homopolymer in copolymer is the key to prepare the unimodal distribution core-shell nanomicelles. The micelles were thermodynamically stable in aqueous media with a low critical micelle concentration value (0.1 mg L-1). The aqueous micelles solution underwent a reversible dispersion/aggregation transition at around 29 degrees C, which corresponds to the lower critical solution temperature (LCST) of the outer shell PDEA block chains. It is hoped that with their unique characteristics, those thermoresponsive polymric micelles would found application in drug delivery. (c) 2008 Wiley Periodicals, Inc.