Evaluation of the Role of [{Cu(PMDETA)}₂(O₂^2–)]²⁺ in Open-Air Photo ATRP of Methyl Methacrylate

Herein, we report an open-air, photo accelerated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) without employing any deoxygenating agent. Under open-air photo ATRP conditions, oxygen reversibly binds with [{Cu (PMDETA)}₂(O₂ ^2-)]²⁺ <b>(1)</b> to form the required activator, which was demonstrated by simple benchtop oxygen/nitrogen purging experiments. The binding mode of oxygen in <b>(1)</b> (μ(η²-η²) peroxo dicopper(II)) was investigated using UV Visible-NIR, FT-Raman and X-ray photoelectron (XPS) spectroscopic techniques. DFT studies and electrochemical measurements further support the catalytic role of <b>(1)</b> in open-air photo ATRP. With the synergistic involvement of Cu (II)Br₂, PMDETA ligand and the intensity of light (365 nm, 4.2 mW cm^-2), a well-controlled rapid polymerization of MMA under open-air condition was achieved (1.25< <i>Đ</i> < 1.47, 94% conversion in 200 min). The bromo chain end fidelity was exemplified by chain extension experiment, block copolymerization and MALDI-ToF analysis. Other monomers such as methyl acrylate, glycidyl methacrylate, and benzyl methacrylate were also polymerized under open-air condition with reasonable control over molecular weight and <i>Đ</i>. An open-air photo polymerization methodology would be fruitful for applications like photocurable printing, dental, optoelectronics, stereolithography, and protective coatings where simple but rapid photopolymerizations are desirable.