Lewis Pair Polymerization: Controlling Polymer Tacticity and Topology

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In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry, Professor Eugene Y. Chen of the Department of Chemistry at Colorado State University is developing new synthetic routes for the construction of industrially-important stereoregular polymeric materials. Stereochemistry is an essential aspect of chemistry that generally focuses on compounds in which carbon atoms are attached to four different groups. The specific arrangement of the groups on a carbon gives rise to mirror images that cannot be superimposed; These mirror images are called chiral molecules and they occur in pairs. [Notably, human hands are also chiral because the left hand is a mirror image of the right hand, but one cannot turn or move one of the hands to look exactly the same as the other.] Chirality is property that dictates biological, thermal and mechanical properties of compounds or materials. In the case of polymers, which are large molecules made by linking a large number of carbons together, the number of chiral possibilities can be very large. For example, in a relatively small polymer consisting of only 30 carbon atoms, the maximum number of unique chiral configurations is estimated at a billion. This research develops sophisticated methodologies that control and fine tune the number of chiral outcomes during the preparation of polymers, yielding a completely new and previously unexplored class of plastic materials. The activities associated with this award increase broadening participation and enable training of undergraduate and graduate students in the industrially-important field of polymer chemistry.In this work, a next generation Lewis pair polymerization (LLP) system is developed that can control the stereochemical outcomes and topologies of the resulting polymers, thereby enabling facile access to advanced polymeric materials with different tacticities or stereomicrostructures and cyclic topological structures. LLP methodology relies on an interacting or frustrated Lewis pair (LP) and exploits the synergy and cooperativity between the Lewis acidic and basic sites of LPs to effect cooperative monomer activation as well as chain initiation, propagation, termination and transfer events. The research includes synthetic, catalytic and mechanistic approaches, coupled with synergistic theoretical and computational methods. Investigated monomers include industrially-important polar vinyl monomers and crotonic esters. The latter monomers provide access to unique ditactic polymers which are currently unobtainable by other synthetic methods. Additionally, topological and stereochemical control in the LPP of acrylic monomers enables selective synthesis of cyclic acrylic polymers in chiral helical or achiral forms. The research in this work is highly innovative and transformative with the potential to significantly impact not only the field of polymer chemistry, but also synthetic organic chemistry and catalysis in general. Through carefully designed and planned activities, the research team provides tangible solutions to the control of tacticity, which has been traditionally one of the main weaknesses in modern synthetic polymer chemistry.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.