Oxygen-Facilitated Photoinduced Atom Transfer Radical Polymerization Using Ionic Liquids as Cosolvents

Atom transfer radical polymerization (ATRP) has emerged as a leading technique in modern polymer chemistry, enabling the synthesis of polymers with low polydispersity and facilitating the production of well-defined polymers. Various approaches, such as photoinduced ATRP using Eosin Y (EY), have been investigated to achieve oxygen tolerance. However, these approaches require careful removal or consumption of oxygen by the system before polymerization is initiated, resulting in an induction period. In this study, a method for oxygen-facilitated photoinduced polymerization of hydrophilic methacrylate and acrylate monomers using the ionic liquid [EMIM][EtSO 4 ] as a cosolvent was developed. When [EMIM][EtSO 4 ] is used as a cosolvent, polymerization is initiated instantaneously upon irradiation with green light, without the need for degassing. The polymers synthesized using the developed method demonstrate reasonable temporal control under light irradiation, high chain-end fidelity, and the ability to produce polymers with degrees of polymerization ranging from 50 to 800 DP. Oxygen level measurement experiments show that in the presence of 25%v/v IL as cosolvent, oxygen was converted into superoxide radicals (O 2 •– ) in a few minutes. O 2 •– further react with IL to H 2 O 2 that was detected using the I 3– detection assay. H 2 O 2 can react with the excited state of EY(EY*) to form hydroxyl radicals (•OH), which can react with monomer to form carbon radicals, which can reduce Cu II to Cu I to initiate polymerization. After O 2 is consumed, the ATRP will further progress in the normal PET-ATRP mechanism with EY* to reduce Cu II to Cu I to initiate polymerization. The presence of H 2 O 2 indicates that our nondegassed method is oxygen-facilitated photo-ATRP at least for the early stage of polymerization.