Photochemical Control of Homogeneous Olefin Polymerization Catalysts

Olefin polymerization catalysis is an ever-growing and ever-evolving field of strategic importance as scientists continually search for advanced polymeric materials. These catalysts regulate the incorporation of one or more monomers into a polymer chain, which can, in-turn, dictate the overall properties of the resultant material. If chemists can control when, how, and to what extent these monomers are enchained, researchers may selectively tailor materials for targeted applications. Traditionally, ligand scaffold design and metal-center identity have been utilized to control catalyst performance. However, this strategy is often limited by intricate and costly catalyst frameworks, as well as the inability to escape an inefficient “one catalyst, one polymer” mindset. To surpass these limitations, polymer chemists have begun to look for more versatile methods to enhance catalytic control.Common methods to promote olefin polymerization control include incorporating small molecules (comonomers or chemical reagents) or manipulating reaction conditions (temperature and monomer pressure). Recent progress in the more general field of polymer synthesis has highlighted that photo-sensitive/responsive polymerizations are a burgeoning tactic, which is used to achieve both spatial and temporal control. In order to take the next step towards advanced catalytic control in the field of olefin polymerizations, the following fundamental questions must be addressed: (1) Can an external stimulus, such as light, be used to influence an olefin polymerization catalyst? (2) Can we expand the utility of this new tool to provide precise control over initiation, propagation, or termination events?This dissertation addresses each of these questions in a series of investigations into how photochemistry may be used to influence olefin polymerizations. First, I address how the use of a photoreductant and light can be used to dictate the insertion mechanism of a redox-active catalyst. Following this work, I discuss how olefin polymerization precatalysts, differentiating in ligand structure and metal center, may be activated using UV light and photoacid generators. Lastly, I discuss how a photosensitizer in tandem with a photoacid generator permits visible light to activate olefin polymerization precatalysts. This work provides proof of concept that photochemical control of olefin polymerizations may be realized.