Two stage collapse of unimolecular micelles with double thermoresponsive coronas.
Phase transition behavior of unimolecular dendritic three layer nanostructures with dual thermoresponsive coronas is studied. Successive reversible addition fragmentation transfer (RAFT) polymerizations of N isopropylacrylamide (NIPAM) and 2 (dimethylamino)ethyl methacrylate (DMA) were conducted using fractionated fourth generation hyperbranched polyester (Bolton H40) based macroRAFT agent. At lower temperatures <20 degrees C) dendritic macromolecules H40 poly(N isopropylacrylamide) poly(2 (dimethylamino)ethyl methacrylate) (H40 PNIPAM PDMA) exist as unimolcular core shell corona nanostructures with hydrophobic H40 as the core, swollen PNIPAM as the inner shell, and swollen PDMA as the corona. PNIPAM and PDMA homopolymers undergo phase transitions at their lower critical solution temperatures (LCST) which are found to be 32 degrees C for PNIPAM and 40 50 degrees C for PDMA, respectively. Upon continuously heating through the LCSTs of PNIPAM and PDMA, such dendritic unimolecular micelles exhibit two stage thermally induced collapse. This process is reversible with a two stage reswelling upon cooling. Laser light scattering, micro differential scanning calorimetry, and excimer fluorescence measurements are used to investigate the double phase transitions.
Langmuir the ACS journal of surfaces and colloids