A series of thermosensitive ABA type triblock poly(epsilon-caprolactone)-b-poly(N-isopropylacrylamide)-b-poly(epsilon-caprolactone) (PCL-PNlPAAm-]PCL) copolymers with different molecular weights were synthesized by the combination of ring opening polymerization and reversible addition-fragmentation chain transfer (RAFT) polymerization. The critical micelle concentrations (CMCs) of the resulted four triblock copolymers in aqueous solution were determined to be 33.8, 39.8, 35.5, and 41.7 mg/L, respectively, by fluorescence spectroscopy using pyrene as a fluorescence probe. Optical absorption measurements showed that the lower critical solution temperatures (LCSTs) of the copolymers were 35.8, 36.2, 35.2, and 36.2 degrees C, respectively, in distilled water, and 33.9, 34.2, 33.3, 34.6 degrees C, respectively, in PBS (pH = 6.8, I = 0.1). Transmission electron microscopy (TEM) showed that the self-assembled micelles exhibited a well-defined spherical shape with diameter of around 100 nm. The drug-loaded PCL-PNIPAAm-PCL micelles displayed thermosensitive controlled release behaviors. (C) 2008 Wiley Periodicals, Inc.