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), N,N-di(2-naphthyl)-5,10-dihydrophenazine (PC 1), revealed the opportunity to use tetrahydrofuran (THF) to modulate the reactivity of PC 1 toward achieving a controlled organocatalyzed atom transfer radial polymerization (O-ATRP) of acrylates. Compared with dimethylacetamide (DMAc), in tetrahydrofuran (THF), PC 1 exhibits a higher quantum yield of intersystem crossing (Phi(ISC) = 0.02 in DMAc, 0.30 in THF), a longer singlet excited-state lifetime (tau(singlet )= 3.81 ns in DMAc, 21.5 ns in THF), and a longer triplet excited-state lifetime (tau(Triplet) = 4.3 mu s in DMAc, 15.2 mu s in THF). Destabilization of 1(center dot+) the proposed polymerization deactivator, in THF leads to an increase in the oxidation potential of this species by 120 mV (E(1/2)0 = 0.22 V vs SCE in DMAc, 0.34 V vs SCE in THF). The O-ATRP of n-butyl acrylate (n-BA) catalyzed by PC 1 proceeds in a more controlled fashion in THF than in DMAc, producing P(n-BA) with low dispersity, D (D < 1.2). Model reactions and spectroscopic experiments revealed that two initiator-derived alkyl radicals add to the core of PC 1 to form an alkyl-substituted photocatalyst (2) during the polymerization. PC 2 accesses a polar CT excited state that is similar to 40 meV higher in energy than PC 1 and forms a slightly more oxidizing radical cation (E(1/2)0 = 0.22 V for 1(center dot+) and 0.25 V for 2(center dot+) in DMAc). A new O-ATRP procedure was developed wherein PC 1 is converted to 2 in situ. The application of this method enabled the O-ATRP of a number of acrylates to proceed with moderate to good control (D = 1.15-1.45 and I* = 83-127%).