Organocatalyzed Atom Transfer Radical Polymerization: Development, Catalyst Design, and Mechanistic Investigation

Theriot, Jordan Corinne

Graduate Thesis Or Dissertation

Organocatalyzed Atom Transfer Radical Polymerization: Development, Catalyst Design, and Mechanistic Investigation Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/9019s264k

Abstract

Atom transfer radical polymerization (ATRP) is one of the most powerful and most-used methodologies for the synthesis of precision polymeric materials with high levels of control over polymer molecular weight and chain-end functionality. ATRP is typically mediated by a metal catalyst, which has long been considered a limitation of the methodology due to the potential for metal contamination in the final product. This work describes the discovery and development of N,N-diaryl dihydrophenazines as a class of organic molecules capable of serving as photoredox catalysts for what has been named organocatalyzed ATRP, or O-ATRP. An investigation into the physical properties responsible for these catalysts’ ability to achieve polymerization results on par with traditional metal catalysts uncovers the importance of intramolecular charge transfer in the photoexcited state. These charge transfer states are further shown to allow a catalyst to perform O-ATRP in solvents with a wide range of polarities. Synthesis of bench-stable radical cation salts of phenazine catalysts enables a reverse-initiation study of O-ATRP and substantiates the radical cation bromide of the catalyst as the species responsible for deactivation. Radical addition to catalyst is identified as a potential termination pathway in O-ATRP. It is found that the use of substituted catalysts effectively blocks this termination pathway, resulting in increased initiator efficiency. Finally, phenazine photocatalysis is extended beyond O-ATRP to another type of controlled radical polymerization, photoinduced electron transfer reversible addition-fragmentation chain transfer polymerization (PET-RAFT), which allows for polymer synthesis through sequential PET-RAFT / O-ATRP and demonstrates the ability of these catalysts to produce transformative results throughout polymer chemistry.

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