The Development of Main-Chain Interlocked Macromolecules

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Catenanes and rotaxanes consist of two or more separate components that are interlocked together and held in place by the mechanical or topological bond. Macromolecular versions of these species are especially intriguing as they offer new polymeric architectures to explore. Interlocked macromolecular structures such as poly[n]catenanes and poly[3]rotaxanes have the mechanical bond as an integral part of the polymer backbone which should impart unusual properties on these materials. For example, they have the ability to expand/contract without significantly altering bond or torsion angles and as such, the ability to control such motions could result in new macromolecular actuators. Furthermore, unusual viscoelastic properties, e.g. very large modulus loss, low activation energy for viscous flow and rapid stress relaxation, are all predicted for such structures. The Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division of the National Science Foundation supports the research group of Prof. Rowan of Case Western Reserve University to develop novel synthetic protocols to allow access to these interesting macromolecules. The synthetic approach utilizes metal-ligand coordination as the thermodynamic driving force for the polymerization step and different covalent 'fixing' steps to access either the poly[n]catenanes or poly[3]rotaxanes. The proposed research is truly a mix of different disciplines within the chemistry arena and the integrated research approach will provide students, at high-school, undergraduate and graduate levels, a broad research education base. The outreach activities are designed to increase the fraction of underrepresented minorities in science and engineering, integrate research and education, provide an exciting learning environment, and create teaching opportunities for the student researchers. Part of this is the expansion and growth of successful outreach programs initiated by the Rowan group, for example the "Natures Materials" program which is part of the Cleveland Museum of Natural History's MLK day Discovery Day.