Organocatalyzed atom transfer radical polymerization (O-ATRP) is a controlled radical polymerization method mediated by organic photoredox catalysts (PCs). In O-ATRP, polymers are produced with well-defined compositions and architectures under metal-free conditions, making them suitable for metal-sensitive applications. One class of PCs, N,N-diaryl dihydrophenazines, is notable for high excited state reduction potentials and its success in providing polymerization control in this method. The ability to synthetically tune photophysical and redox properties has proven to be essential in the development of these PCs. Recent investigation into a side reaction observed in O-ATRP, in which the alkyl halide initiator adds to the core of the catalyst, reveals a synthetically facile method for modifying PC properties. In this work, alkyl core substitution is found to impact catalytically relevant properties and can improve polymerization outcomes in O-ATRP, as indicated by improved polymerization control and lower catalyst loadings. Additionally, the kinetics of this side reaction are explored to gain insight into the rate at which catalyst properties are modified during O-ATRP. Comparing the rate of alkyl core substitution for catalysts with different N-aryl group connectivity (i.e. 1-naphthyl versus 2-naphthyl) may provide insight into how this connectivity impacts PC performance in O-ATRP. In summary, this work has resulted in the development of a synthetic strategy for modifying catalyst properties and improving their ability to produce well-defined polymers in O-ATRP.

Tuning catalytic properties of N,N-diaryl dihydrophenazine photocatalysts through core substitution to improve performance in organocatalyzed atom transfer radical polymerization

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ACS Fall 2022

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