A series of water-soluble thermoresponsive hyperbranched copoly(oligoethylene glycol)s were synthesized by copolymerization of di(ethylene glycol) methacrylate (DEGMA) and oligo(ethylene glycol) methacrylate (OEG-MA, M-w = 475 g/mol), with ethylene glycol dimethacrylate (EGD-MA) used as the crosslinker, via reversible addition fragmentation chain transfer polymerization. Polymers were characterized by size exclusion chromatography and nuclear magnetic resonance analyses. According to the monomer composition, that is, the ratio of OEG-MA: DEG-MA: EGD-MA, the lower critical solution temperature (LCST) could be tuned from 25 degrees C to 90 degrees C. The thermoresponsive properties of these hyperbranched copolymers were studied carefully and compared with their linear analogs. It was found that molecular architecture influences thermoresponsive behavior, with a decrease of around 5-10 degrees C in the LCST of the hyperbranched polymers compared with the LCST of linear chains. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2783-2792, 2010