Covalent Polymer Mechanochemistry

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With this award the Macromolecular, Supramolecular and Nanochemistry Program is funding Professor Stephen Craig of Duke Unviersity to study covalent polymer mechanochemistry. This project involves the study of chemical reactions that are accelerated by an applied mechanical force. These reactions impact multiple aspects of materials design, including the macroscopic failure and mechanical limitations of current polymeric materials. In addition, mechanically responsive functional groups might serve as the critical elements in new stress-responsive and self-healing polymeric materials. These studies will provide insight into how the macroscopic mechanical forces experienced by polymers during use can be effectively channeled into desired chemical responses, providing a foundation for new classes of polymers. Broader impacts come from: (1) integration of research and education through new active learning modules and associated laboratory experiences in introductory chemistry and through coupled research experiences; (2) broadening the participation of underrepresented groups by engaging and recruiting young scientists before the onset of disproportionate attrition from the sciences; (3) disseminating the results of the research broadly; and, (4) probing molecular behavior in materials in a manner that will have an impact on polymer chemistry, physical organic chemistry, and self-healing and stress-responsive materials.The overarching technical objective is to lay a quantitative foundation for mechanochemical kinetics by employing state-of-the-art physical measurements and developing new methods for quantitation. The research plan includes the direct, experimental characterization and quantification of the effect of mechanical forces on covalent reactions triggered along overstretched polymer backbones. Because mechanical force, unlike conventional forms of energy input such as heat or light, is directional, the coupling between mechanical force and reactivity provides insights into the structure of transition states. Despite its importance, however, quantitative measures of the effect of force on chemical reactions are rare. The proposed work makes use of two novel approaches to quantifying mechanochemical reactivity: the single molecule force spectroscopy of multi-mechanophore, non-scissile polymers, and the pulsed sonication and molecular weight degradation of multi-mechanophore, scissile polymers. Models for the observed mechanochemical activity are expected to enable quantitative assessment of reactivity in both classes of mechanophores.