A series of novel star-like copolymers H20-poly(N-isopropylacrylamide)-random-poly(poly(ethylene glycol) methyl ether methacrylate) (H20-PNIPAm-r-PEGMA), which could respond to both temperature and ionic strength stimuli in aqueous solution were synthesized by atom transfer radical polymerization. Stimuli-response of these copolymers in aqueous solution was characterized by dynamic laser scattering (DLS), H-1-NMR and turbidity. In aqueous solution, these star-like copolymers exhibited response to temperature and ionic strength with tunable low-critical solution temperature (LCST) from 32 to 100 degrees C. The LCST values of copolymers increased with increasing PEGMA contents, while decreased with increasing ionic strength. An interesting phenomenon, which should be a unique character of star-like copolymer, was observed by the turbidity test of copolymer 1160. The addition of sodium chloride and increase of concentration can let copolymer 1160 behave normally, which was further confirmed by atomic force microscopy and DLS. (C) 2009 Wiley Periodicals, Inc. J Appi Polym Sci 115: 1831-1840, 2010