Mechanically Entwined Double Helical Covalent Polymers

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With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professor Wei Zhang of the University of Colorado-Boulder will develop novel synthetic strategies for polymers that form long double helices, similar to naturally occurring DNA (2'-deoxyribonucleic acid) and collagen. This research aims to understand the critical parameters determining the folding, winding, and self-assembly of the polymers into double helical structures, which may exbibit unique materials properties. The proposed work will serve as a platform for providing new opportunities for education, outreach, and minority involvement on multiple levels. Graduate and undergraduate students will be trained in multidisciplinary research involving organic, supramolecular, polymer chemistry, and nanoscience.Chemists have been trying to build molecules that can rival the sophistication of Nature’s biomacromolecules for some time. However, synthesis of high molecular weight covalently bonded polymers that form extended double helices, similar to naturally occurring DNA and collagen, still represents a grand challenge. The goals of this research are to develop novel synthetic strategies for helical polymers connected with robust yet dynamic covalent linkages, to understand the double helical covalent polymer (HCP) formation process, and to establish a general design principle for HCPs. A series of rigid aromatic ring-based building blocks with varied physical dimensions, varied distribution of electron density, and varying number of reactive sites will be prepared to study the effect of monomer structure on HCP formation. Moreover, the only strategy of forming double helices over the past three decades has been maneuvering secondary attractive interactions between the two single-stranded subunits (intra-duplex bonding). By contrast, the novel chemical-mechanical hybrid bonding approach proposed herein (focused on inter-duplex bonding) may open up many new possibilities for the design and synthesis of higher order functional polymeric architectures, including double helical polymers and their assemblies. This new system would offer an alternative simple model to study the relationship between the structures of linear polymers and their potential to assemble into a double helix. It also suggests novel platforms for (i) linear polymer folding, (ii) supramolecular intertwining, and (ii) chirality propagation. More specifically, in the latter case, the possibility of forming chiral helical polymers by introducing chiral inducers will be explored. The anisotropy of electronic and mechanical properties of the highly-charged, long helical polymer crystals being targeted may be exploitable for the future development of novel nanoscale materials with properties that are distinct from those of native biopolymers and biosystems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.