AbstractsChemistry

This dissertation focuses on the development of a "grafting through" methodology to synthesize molecular brushes with well-defined structures, as an attempt to construct nanostructures by covalent bonds totally. Detailed synthetic procedures for and characterization of molecular brushes, as well as complicated hierarchical nanostructures resulted from their self-assembly are reported. The synthesis of molecular brushes is achieved by combining orthogonal living polymerization techniques rationally, such as living/controlled radical polymerization, ring opening polymerization and ring opening metathesis polymerization. Generally, the strategy can be divided into two steps: the first step involves the preparation of linear macromonomers whose chain ends are functionalized with polymerizable groups and the second step is the polymerization of chain end functional groups. In this dissertation, living/controlled radical polymerization, ring opening polymerization and chain end modification have been applied in the first step to afford chain end functional macromonomers and ring opening metathesis polymerization is used in the second step to achieve the molecular brush architectures. Due to the high tolerance of Grubbs' catalysts towards functional groups, various functionalities can be incorporated into the molecular brush frameworks by changing the side chain structures, including poly(4-acetoxystyrene), poly(pentafluorostyrene), poly(methyl acrylate), poly(t-butyl acrylate), poly(methyl methacrylate), poly(t-butyl methacrylate), polylactide, poly(ethylene glycol) and polyhedral oligomeric silsesquioxane: POSS). The high versatility of our strategy is also used to increase the complexity of the resulting molecular brushes, by introducing block structures to either backbone or side chains, using the "livingness" characters of the employed polymerization techniques. Those block molecular brushes can be used as building blocks to construct more complicated hierarchical nanostructures, which are self assembled from simpler precursory nanostructures. The confinement of triblock copolymers within molecular brush architecture changes their self assembly behaviors. Dynamic cylindrical nanostructures are constructed from the PS-PMA-PAA triblock amphiphilic molecular brushes, while the same triblock copolymers, when not pre-connected into the molecular brush architectures, organize only into globular assemblies. The vast scope of macromonomers that are compatible with this strategy can also be applied to prepare molecular brushes with fine tunable properties, by introducing several functionalities to the molecular brush frameworks and adjusting their ratios accordingly.