Controlled radical polymerizations allow for the synthesis of polymers with precise compositions and architectures, targeted molecular weights, and narrow molecular weight distributions. Organocatalyzed atom transfer radical polymerization (O-ATRP) uses an organic photoredox catalyst (PC) and visible light to access targeted polymer structures under mild, energy efficient conditions. N,N-diaryl dihydrophenazine photocatalysts in particular are notable for their high excited state reduction potentials and success in maintaining polymerization control in O-ATRP. However, low initiator efficiencies (I* &lt; 100%) are not uncommon with these PCs and prevent targeted molecular weights from being achieved. In this work, this side reactivity is identified as radical addition of the alkyl halide initiator to the catalyst core and is leveraged to create catalysts with improved polymerization control. Core substitution is found to alter catalytically relevant properties and can improve polymerization control in terms of initiator efficiency and dispersity, as well as enable lower catalyst loadings. Additionally, investigation into the rate of alkyl core substitution provides insight into the modification of catalytically relevant properties during O-ATRP. Examination of the rate of alkyl core substitution for catalysts with different N-aryl group connectivity (i.e. 1-naphthyl versus 2-naphthyl) may give insight into why catalysts with similar photophysical and redox properties may perform differently in O-ATRP. Overall, a new method for tuning PC properties has been developed that simultaneously facilitates improved O-ATRP outcomes.

Core substitution of N,N-diaryl dihydrophenazine photocatalysts for improved polymerization control and mechanistic insight in organocatalyzed atom transfer radical polymerization

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