| Contents Notes |
Fullerenes are fascinating carbon nanostructures with outstanding structural and functional properties, which critically rely on their spatial arrangements. However, their strong aggregation makes them difficult to pack into ordered structures in different dimensions and across multiple length scales. The purpose of this research is to develop "soft fullerene materials," in particular, using self-assemblies of polymers as templates to manipulate their order and symmetry. Synthesis of fullerene polymers with high purity and well-defined structure has been difficult due to the reactive nature of fullerene towards various reaction intermediates and the often unavoidable multiple additions. To address this, a "click chemistry" approach has been developed, as demonstrated by the model reaction between azide-functionalized polystyrene (PS-N3) and highly reactive alkyne-functionalized fullerene (Fulleryne01). Fullerynes with different structures and reactivities have been designed and synthesized. Combined with living/controlled polymerization techniques, the method has been successfully extended to fullerene polymers based on poly(ethylene oxide) (PEO) and poly(ethylene oxide)-block-polystyrene (PEO-b-PS) with controlled molecular weight and narrow polydispersity. The C60 was placed at the chain-end [PEO-C60 and PEO-b-PS-C60], or at the junction point between two blocks [PEO-(C60)-PS], or randomly tethered along one block [PEO-b-PS/C60]. The self-assembly of these polymers, such as crystallization from dilute solution, micellization in selective solvents, and phase separation in the bulk or thin films, have been studied. Preliminary results have shown that they could template the spatial arrangements of C60. For example, the single crystals of PEO-C60 have been grown to generate PEO single crystal lamellae with C60 tethered to the surface, forming a 2D C60 molecular sheet. The alternating, epitaxial growth of PEO and PEO-C60 single crystals might lead to near-1D ring patterns of C60. The diblock copolymers, PEO-(C60)-PS and PEO-b-PS-C60, were found to form micelles in DMS/water mixed solvent, in which C60 was either confined to the interface between the core and corona, or inside the core. The bulk self-assembly of PEO-(C60)-PS has shown an unusual decrease in d-spacing, as compared to its parent polymer PEO-(N3)-PS; whereas both PEO-b-PS-C60 and PEO-b-PS/C60 showed increase in d-spacing. This drastic difference was due to the location of C60 in the final structure. This study has demonstrated the concept and the promising future of "soft fullerene materials." In addition, during the development of these materials, a "retro-functional analysis" approach has been proposed as the molecular design principle for advanced materials. It enables efficient and modular development of functional molecular materials with engineered hierarchical structure across different length scales to exhibit a specific macroscopic property. Being function-oriented rather than synthesis-oriented, it fuels innovation in molecular design and provides future targets for material research. |
