Atom transfer radical polymerization (ATRP), one of the most commonly used controlled radical polymerization techniques, enables facile synthesis of precision polymers using commercially available starting materials. More recently, the application of external stimuli to control ATRP has been investigated. For example, photoredox catalyzed variants of ATRP have been explored using Ru- and Ir- containing photocatalysts (PCs), enabling the synthesis of well-defined polymers under mild conditions using visible light to drive the reaction. While the development of photoredox catalyzed ATRP was a major advance, researchers sought to replace the transition metal-containing PCs used for these reactions with organic PCs to avoid issues with metal contamination of the polymer product and to provide more sustainable catalyst alternatives. This motivation led to the development of organocatalyzed ATRP (O-ATRP). Similar to traditional ATRP, the O-ATRP catalyst is responsible for controlling the polymerization through mediation of a reversible-deactivation equilibrium. Thus, design of improved O-ATRP catalysts is key for pushing the current bounds of this polymerization method. However, few organic PCs which can access excited states with sufficient reduction potentials to reduce typical ATRP initiators or the alkyl halide chain end of dormant polymer chains are well-studied. As such, a major challenge for the improvement of O-ATRP methods has been the identification and understanding of new organic PC families that can access strongly reducing excited states. To this end, the work disclosed herein is on the development of N-aryl phenoxazines as strongly reducing PCs for O-ATRP. Through the synthesis and characterization of phenoxazine derivatives bearing different N-aryl and/or core substituents, structure property relationships for altering the photophysical and redox properties of this class of molecules has been established. Moreover, the application of these PCs for the O-ATRP of methyl methacrylate was used to determine the effects of PC properties on catalytic performance.

Development of strongly reducing phenoxazine organic photoredox catalysts and their application in organocatalyzed atom transfer radical polymerization

2019 Spring National Meeting

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