Oxygen Tolerance in Living Radical Polymerization: Investigation of Mechanism and Implementation in Continuous Flow Polymerization

The production of a range of acrylate and acrylamide polymers in completely open reaction vessels has been achieved utilizing the PET-RAFT polymerization technique with zinc tetraphenylporphyrin (ZnTPP) as photoredox catalyst. Polymerization was conducted under extremely mild reaction conditions; low-intensity yellow light, ambient temperatures, and dimethyl sulfoxide (DMSO) as solvent were used. The resulting polymers display characteristics typical of RAFT polymerization, with narrow molecular weight distributions (typically, D < 1.10) and controlled molecular weights. One of the advantages of performing PET-RAFT using ZnTPP is the possibility to polymerize monomer in open vessels (i.e., in the presence of oxygen). Oxygen tolerance in DMSO was investigated and attributed to energy transfer from ZnTPP to oxygen to generate singlet oxygen. The effect of changing catalyst concentration and light intensity in these systems has been investigated. Extension of this polymerization technique to a flow system has demonstrated the robustness and effortless scalability of these systems.