Novel AB(2)-type amphiphilic block copolymers of poly(ethylene glycol) and poly(N-isopropylacrylamide), PEG-b-(PNIPAM)(2), were successfully synthesized through single-electron transfer living radical polymerization (SET-LRP). A difunctional macroinitiator was prepared by esterification of 2,2-dichloroacetyl chloride with poly(ethylene glycol) monomethyl ether (PEG). The copolymers were obtained via the SET-LRP of N-isopropylacrylamide (NIPAM) with CuCl/tris(2-(dimethylamino)ethyl)amine (Me6TREN) as catalytic system and DMF/H2O (v/v = 3:1) mixture as solvent. The resulting copolymers were characterized by gel permeation chromatography and H-1 NMR. These block copolymers show controllable molecular weights and narrow molecular weight distributions (PDI < 1.15). Their phase transition temperatures and the corresponding enthalpy changes in aqueous solution were measured by differential scanning calorimetry. As a result, the phase transition temperature of PEG(44)-b-(PNIPAM(55))(2) is similar to that in the case of PEG(44)-b-PNIPAM(110); however, the corresponding enthalpy change is much lower, indicating the significant influence of the macromolecular architecture on the phase transition. This is the first study into the effect of macromolecular architecture on the phase transition using AB(2)-type amphiphilic block copolymer composed of PEG and PNIPAM. (C) 2009 Wiley Periodicals, Inc. J Polyrn Sci Part A: Polym Chem 47: 4420-4427, 2009