Title: Adventures in Transition Metal-Mediated Controlled Radical Polymerizations
Abstract: Controlled radical polymerizations using transition metals rely on a dynamic exchange of propagating radicals between active and dormant states to precisely control the molecular weight, functionality, and architectural properties of polymers. The prevalent mechanisms include organometallic or catalyzed atom transfer radical processes involving one-electron redox reactivity of transition metal complexes. In this seminar, I will present my research on exploring new facets of transition metal-mediated controlled radical polymerizations. I will discuss external control of copper complexes in atom transfer radical polymerization (ATRP) describing their underlying mechanisms and principles of establishing structure-reactivity relationship for catalysts controlled by external stimuli. The second part of my presentation will focus on the discovery of new strategies to explore the selectivity and versatility of cobalt chemistry in radical polymerizations. A discrete initiation approach using cobalt hydride enabled rapid initiation and fast polymerization via organometallic mediation where the polymerization efficiency of the cobalt salen complexes could be precisely tuned by altering their ligand electronics. We discovered that cobalt is unique in its ability to offer both the organometallic and atom transfer mechanisms in a selective and efficient manner based on the structural properties of the ligand platform. We devised a bio-inspired catalytic approach where a vitamin B12-derived cobalt complex performed efficient ATRP catalysis, highlighting the importance of controlling the structural properties of transition metal complexes in diversifying their reactivity in controlled radical polymerizations.
