Organocatalyzed atom transfer radical polymerization (O-ATRP) is a method for producing polymers with precise structures under mild conditions through the use of organic photoredox catalysts (PCs). To begin the polymerization, O-ATRP uses an alkyl halide initiator that is activated by a photoexcited PC to begin polymer growth. Successful PCs should be able to produce polymers with predictable molecular weights based on the amount of initiator and monomer in the reaction. When this is true, the polymerization should exhibit 100% initiator efficiency, indicating precise control over the polymer structure. In addition, ideal O-ATRP PCs should produce polymers with low dispersity, indicating a narrow molecular weight distribution (dispersity &lt; 1.5). Previously, one successful PC, PhenN-PhCF3, demonstrated good polymerization control, but initiator efficiency with this PC was consistently low (~80%). We hypothesized this low initiator efficiency was due to a side reaction which consumed the initiator through substitution of the PC. To test this hypothesis, we synthesized five substituted catalysts through reaction with different alkyl halide initiators and screened them in O-ATRP under typical reaction conditions to evaluate their catalytic properties. Excitingly, some substituted catalysts were found to exhibit improved reaction control with initiator efficiency close to 100%. The best substituted PC, PhenN-PhCF3-(EBP)4, was then further investigated to find the most effective conditions which resulted in low dispersity and high initiator efficiency, as well as low catalyst loadings.

Understanding the catalytic properties of alkyl core-substituted dihydrophenazines in organocatalyzed atom transfer radical polymerization

ACS Spring 2022

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