Visible Light‐ATRP Driven by Tris(2‐Pyridylmethyl)Amine (TPMA) Impurities in the Open Air

Atom transfer radical polymerization (ATRP) of oligo(ethylene oxide) monomethyl ether methacrylate (OEOMA 500 ) in water is enabled using CuBr 2 with tris(2‐pyridylmethyl)amine (TPMA) as a ligand under blue or green‐light irradiation without requiring any additional reagent, such as a photo‐reductant, or the need for prior deoxygenation. Polymers with low dispersity ( Đ = 1.18–1.25) are synthesized at high conversion (>95%) using TPMA from three different suppliers, while no polymerization occurred with TPMA is synthesized and purified in the laboratory. Based on spectroscopic studies, it is proposed that TPMA impurities (i.e., imine and nitrone dipyridine), which absorb blue and green light, can act as photosensitive co‐catalyst(s) in a light region where neither pure TPMA nor [(TPMA)CuBr] + absorbs light.