Diblock copolymers consisting of a multibranched polymethacrylate segment with densely grafted poly[2-(2-methoxyethoxy) ethyl vinyl ether] pendants and a poly(N-isopropylacrylamide) segment were synthesized by a combination of living cationic polymerization and RAFT polymerization. A macromonomer having both a poly[2-(2-methoxyethoxy) ethyl vinyl ether] backbone and a terminal methacryloyl group was synthesized by living cationic polymerization. The sequential RAFT copolymerizations of the macromonomer and N-isopropylacrylamide in this order were performed in aqueous media employing 4-cyanopentanoic acid dithiobenzoate as a chain transfer agent and 4,4'-azobis(4-cyanopentanoic acid) as an initiator. The obtained diblock copolymers possessed relatively narrow molecular weight distributions and controlled molecular weights. The thermoresponsive properties of these polymers were investigated. Upon heating, the aqueous solutions of the diblock copolymers exhibited two-stage thermoresponsive properties denoted by the appearance of two cloud points, indicating that the densely grafted poly[2-(2-methoxyethoxy) ethyl vinyl ether] pendants and the poly(N-isopropylacrylamide) segments independently responded to temperature. (C) 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 786-792