Solvent Effects and Side Reactions in Organocatalyzed Atom Transfer Radical Polymerization for Enabling the Controlled Polymerization of Acrylates Catalyzed by Diaryl Dihydrophenazines

Investigation of the effects of a solvent on the photophysical and redox properties of the photoredox catalyst (PC), ,-di(2-naphthyl)-5,10-dihydrophenazine (PC ), revealed the opportunity to use tetrahydrofuran (THF) to modulate the reactivity of PC toward achieving a controlled organocatalyzed atom transfer radial polymerization (O-ATRP) of acrylates. Compared with dimethylacetamide (DMAc), in tetrahydrofuran (THF), PC exhibits a higher quantum yield of intersystem crossing (Φ = 0.02 in DMAc, 0.30 in THF), a longer singlet excited-state lifetime ( = 3.81 ns in DMAc, 21.5 ns in THF), and a longer triplet excited-state lifetime ( = 4.3 s in DMAc, 15.2 s in THF). Destabilization of , the proposed polymerization deactivator, in THF leads to an increase in the oxidation potential of this species by 120 mV ( = 0.22 V vs SCE in DMAc, 0.34 V vs SCE in THF). The O-ATRP of -butyl acrylate (-BA) catalyzed by PC proceeds in a more controlled fashion in THF than in DMAc, producing P(-BA) with low dispersity, ( < 1.2). Model reactions and spectroscopic experiments revealed that two initiator-derived alkyl radicals add to the core of PC to form an alkyl-substituted photocatalyst () during the polymerization. PC accesses a polar CT excited state that is ~40 meV higher in energy than PC and forms a slightly more oxidizing radical cation ( = 0.22 V for and 0.25 V for in DMAc). A new O-ATRP procedure was developed wherein PC is converted to . The application of this method enabled the O-ATRP of a number of acrylates to proceed with moderate to good control ( = 1.15-1.45 and * = 83-127%).