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.

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Stimuli-responsive unimolecular polymeric micelles have attracted much interest because of their unique structures and properties. In this paper, the double phase transition behavior of unimolecular dendritic three-layer nanostructures with dual thermoresponsive shells is studied. By using a hydrophobic hyperbranched polyester (Bolton H40)-based macro reversible addition-fragmentation transfer (macro-RAFT) agent, the polymerizations of N-isopropylacrylamide (NIPAM) and N-isopropylmethacrylamide (NIPMAM) were conducted via the successive RAFT process. The dendritic core-shell architecture prepared, i.e. H40-PNIPAM(Py)-b-PNIMAM with inner shell labeling and H40-PNIPAM-b-PNIMAM(Py) with outer corona labeling. Laser light scattering, UV-visible transmittance, micro-differential scanning calorimetry and excimer fluorescence measurements were used in combination to probe the conformational changes of chains located at the inner layer and outer corona during the two-stage collapse upon heating. Results from all four techniques support the double phase transition behavior of this kind of three-layer dendritic polymer. H40-poly(N-isopropylacrylamide)-block-poly(N-isopropylmethacrylamide) (H40-PNIPAM-b-PNIPMAM), exists as unimolcular polymeric micelles with hydrophobic dendritic H40 as the core, PNIPAM as the inner shell and PNIPMAM as the corona. Upon continuous heating through the lower critical solution temperatures of PNIPAM and PNIPMAM, dendritic H40-PNIPAM-b-PNIMAM exhibits two-stage thermoresponsive collapse. Different parts of the shells of H40-PNIPAM-b-PNIMAM were selectively labeled with pyrene (Py) to result in