The Chemical Synthesis, Self-Assembly, and Facial Crosslinking of Dendrimers for the Study of Ultra-Tough Mimics of Spider Dragline Silk

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An MPS Distinguished International Postdoctoral Research Fellowship (MPS-DRF) will be used to perform research at the Max Planck Institute for Polymer Science (MPIP) in Mainz, Germany with the guidance of Prof. Dr. Klaus Mullen and additional collaborators for specialized techniques that are not available the MPIP, including Prof. Dr. Martin Moller at the University of Ulm. The iterative design, synthesis, and characterization of a morphological, composite mimic of spider dragline silk, an ultra-tough tensile fiber, is the subject of this work. The branching units of prototypical dendrimers will be modified with multiple, chemically-immiscible oligomeric side chains. One side chain phase of the dendrimer will be crosslinked, and length of the chain ends at the periphery of the dendrimer will be optimized in order to suppress bulk crosslinking in a columnar mesophase. Upon dissolution, conformationally-restricted, dendrimeric dimers should be afforded. The accessibility that the non-centrosymmetric, dendrimer conformation needs to reach before dimerization will be probed using atomic force microscopy with chemically-modified surfaces, in solution through the interaction with phospholipid vesicles using fluorescence correlation spectroscopy, and in the bulk using differential scanning calorimetry. A second dendrimer scaffold will be synthesized bearing similar, chemically-immiscible side chains and chain ends, but with an additional, latent functionality in the branching unit side chain which will not initially undergo crosslinking. After dimerization, the latent functionality will be unmasked and used to incorporate linear chains for bulk crosslinking or physical entanglement in a final composite. The mechanical properties of the resulting composite are expected to mimic those of spider dragline silk.While this work is not expected to produce materials amenable to commercial application, it is expected to assess the theoretical mechanism of spider dragline silk responsible for its remarkable mechanical toughness. It is the hope that such conclusions will be drawn about the future of advanced composite materials and that they will be invaluable to the development of more practical materials.