The Unusual aggregation behavior of poly(N-isopropylacrylamide)-based amphiphilic block copolymers was investigated by a combination of dynamic and static laser light scattering, AFM, and H-1 NMR. The results revealed that PS-b-PNIPAM always forms large micelle aggregates in the transition process from an organic solvent to water due to the cononsolvency effect of PNIPAM. The cononsolvency effect of PNIPAM can be avoided to obtain classical micelles with PS29-b-PNIPAM(27) in acetone-water at low temperatures (below 20 degrees C). (C) 2007 Elsevier Inc. All rights reserved.