Development of Stereospecific Controlled/Living Radical Polymerization Using Rationally Engineered Chain-End Capping Agents

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With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Mingjiang Zhong of Yale University will develop new methods for the efficient preparation of polymers with control of stereochemistry. Stereochemistry of polymers originates from the orientation of pendant groups attached to the main backbone and has a significant influence on important materials properties, including mechanical stiffness, toughness, thermal behavior, crystallinity, and solubility. Tuning the stereochemistry of polymers can dramatically change the properties and therefore can lead to new applications of many polymers. However, currently existing methods to achieve control over stereochemistry are somewhat limited in scope; there is room for new methods development. This project aims to establish methods that are compatible with a broader scope of building blocks compared to traditional approaches, that can be carried out in environmentally friendly solvents, and that provide pathways for stereocontrolled access to new functional materials. The research activities affiliated with this project are expected to have broader scientific impact in the synthesis of mechanically robust materials, as well as materials with important biomedical uses. The associated teaching, mentoring, and outreach activities will create educational opportunities for a diverse group of trainees.This project proposes new approaches to synthesizing isotactic polymers via radical polymerization. Lewis acid-tethered stable radical species will be synthesized to control polymer tacticity via confined chain end conformation in controlled/living radical polymerizations. An array of stable radical species will be explored, across a range of reaction solvents and tethered ligands with the goal of expanding the space of polymerizable monomers. The Zhong research team will also investigate polymerization mechanisms with the aim of developing a deeper understanding of this catalytic system. Among the mechanistic features to be examined are included Lewis acid coordination to monomer units, chain end conformation during radical addition, and the kinetics and thermodynamics of the radical deactivation process. The successful development and deployment of these catalysts would be significant, particularly because they have the potential to provide a new approach to the important problem of stereocontrol in radical addition. This research also has potential industrial chemical implications due to the advantages of radical polymerization over polymerization conditions that require acidic or basic conditions, with radical polymerization approaches generally exhibiting greater functional group tolerance and milder reaction conditions.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.