A hetero-arm star polymer, polystyrene-poly(N-isopropylacrylamide)-poly(2-(dimethylamino)ethylmetha erylate) (PSt-PNIPAM-PDMAEMA), was synthesized by "clicking" the alkyne group at the junction of PSt-b-PNIPAM diblock copolymer onto the azide end-group of PDMAEMA homopolymer via 1,3-dipolar cycloaddition. The resultant polymer was characterized by gel permeation chromatography, proton nuclear magnetic resonance spectroscopy and Fourier transform infrared spectroscopy.PSt-PNIPAM-PDMAEMA micelles with PSt block as core and PNIPAM and PDMAEMA blocks as shell were formed when adding the copolymer solution in THF into 10 folds of water. Lower critical solution temperature (LCST) of PNIPAM and PDMAEMA homopolymer is 32 degrees C for PNIPAM and 40 to 50 degrees C for PDMAEMA, respectively. Upon continuous heating through their LCSTs, PSt-PNIPAM-PDMAEMA core-shell micelles exhibited two-stage thermally induced collapse. The first-stage collapse, from 20 to 34 degrees C, is ascribed to the shrinkage of PNIPAM chains; and the second-stage collapse, from 38 to 50 degrees C, is due to the shrinkage of PDMAEAM chains. Dynamic light scattering was used to confirm the double phase transitions. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 786-796, 2009