Halogen Effect in Dual-Catalysis PhotoATRP

The effect of halogen type in dual-catalyzed photoinduced atom transfer radical polymerization (photoATRP) of methyl acrylate (MA) and methyl methacrylate (MMA) was systematically investigated under green LED irradiation (λ ∼ 527 nm) using rhodamine 6G (RD-6G) as a photocatalyst. Poly-(methyl acrylate) and poly-(methyl methacrylate) with ω-bromo and ω-chloro chain ends were synthesized via CuX₂/ligand (X = Br, Cl) complexes with excess ligand as an electron donor. Kinetic analyses revealed that Br-based systems exhibited significantly faster activation and allowed controlled polymerizations at markedly lower copper and photocatalyst loadings than their Cl-based counterparts. MA polymerizations were faster than MMA despite the latter's larger ATRP equilibrium constants, attributed to the higher propagation rate constant of acrylates and similar rates of reduction of CuX₂/ligand deactivators. Optimal ligand selection (Me₆TREN for MA, TPMA for MMA) was important for control of the polymerization rate and low dispersity. Chain-extension experiments confirmed high chain-end fidelity, and temporal control studies demonstrated efficient light-mediated regulation. These findings provide detailed design guidelines for halogen- and monomer-dependent optimization in dual-catalyzed photoATRP.