Preparation Of Stimuli-Responsive Unimolecular Micelles And Their Phase Transition Behavior

The dissertation with a title of "Preparation of Stimuli-Responsive Unimolecular Micelles and their Phase Transition Behavior" focuses on the synthesis of thermoresponsive unimolecular micelles by using reversible addition-fragmentation transfer (RAFT) process; and the thermoresponsive phase transition behavior of these novel unimolecular micelles is characterized in detail by a combination of dynamic and static laser light scattering (LLS), micro-differential scanning calorimetry (micro-DSC), and excimer fluorescence techniques.Firstly, we prepared an amphiphilic dendritic core-shell nanostructure with a temperature-sensitive shell. RAFT polymerization of N-isopropylacrylamide (NIPAM) was conducted using hyperbranched polyester (Boltorn H40) based macroRAFT agent. The resultant multiarm star block copolymer (H40-PNIPAM) exists as unimolecular micelles with hydrophobic H40 as the core, densely grafted PNIPAM brush as the shell. Therefore, the novel unimolecular micelles will have many properties, such as (1) having a structure like core-cross linked micelles, (2) with a dendritic morphology, (3) the grafting polymer chains take a polymer brush conformation, and (4) with stimuli-responsive behavior, and so on. It is well known that in aqueous solution amphiphilic block copolymers can self-assemble into micelles. The microstructure of block copolymer micelles is not static and there exists dynamic exchange between micelles and unimers, i.e., they tend to be disintegrated upon alteration of external conditions such as concentration, temperature, pH, and ionic strengths, etc. Chemical cross-linking of the micellar core or shell can lead to micelles with permanent stability. So here PNIPAM chains are tethered to the dendritic macromolecules, they can be considered as unimolecular micelles due to their structural resemblance to amphiphilic block copolymer micelles. Moreover, polymeric unimolecular micelles generally possess well-defmed chemical structures with pre-determined core size, controllable length and density of grafted chains, thus they could also serve as model systems for block copolymer micelles. At the same...