Temperature- and pH-responsive unimolecular micelles with a hydrophobic hyperbranched core

The dendritic unimolecular polymeric micelles with a hydrophobic dendritic polyester (Boltorn H40) as the core and the grafted biocompatible poly(N, N-diethylacrylamide)-b-poly(2-(dimethylamino) ethyl methacrylate) (PDEAAM-b-PDMAEMA) as the shell were synthesized by successive reversible addition-fragmentation transfer (RAFT) polymerization of N, N-diethylacrylamide (DEAAM) and 2-(dimethylamino) ethyl methacrylate (DMAEMA) monomers. Laser light scattering studies indicated that the resulting unimolecular polymeric micelles H40-PDEAAM-PDMAEMAwith double stimuli-responsive shells exhibited a reversible two-stage phase transition behavior. The effect of varying the block length of PDMAEMA on the thermosensitivity of unimolecular polymeric micelles was studied. With an increase in the outer corona length of PDMAEMA, the temperature range of phase transition for the inner shell PDEAAM would become broad. As pH decreased to 2, the high hydrophilic PDMAEMA blocks with high protonation were independent of temperature, and the size of unimolecular polymeric micelles increased due to the extended-chain conformation of outer layer. The internal core cavities of the unimolecular polymeric micelles exhibited a great potential of loading guest molecules according to the analysis of pyrene probe fluorescence spectra.