This paper describes the reversible phase transition behavior of a thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) shell at the surface of a hydrophilic core. Reversible addition-fragmentation transfer (RAFT) polymerization of N-isopropylacrylamide was conducted using a hydrophilic hyperbranched poly(glycidol) (HPG)-based macroRAFT agent. At lower temperatures (o30 1C), the resultant multiarm star block copolymer (HPG-PNIPAM) exists as unimolecular micelles, with hydrophilic HPG as the core and a densely grafted PNIPAM brush as the shell. In laser light scattering (LLS) studies, the concentration used for HPG-PNIPAM is 5Â10 À6 g ml À1 , to avoid any possible aggregation between dendritic unimolecular micelles above the lower critical solution temperature (B32 1C) of PNIPAM. What we observe for the phase transition of HPG-PNIPAM involves only unimolecular process. A combination of dynamic and static LLS studies of HPG-PNIPAM in aqueous solution reveals a reversible phase transition on heating and cooling.