Visible light controlled aqueous RAFT continuous flow polymerization with oxygen tolerance†
In this work, hydrophilic poly(ethylene glycol) methyl ether methacrylate (PPEGMA) was successfully synthesized via a fast visible light controlled reversible addition–fragmentation chain transfer (RAFT) polymerization in a continuous tubular reactor, using 4-cyano-4-(ethylthiocarbonothioylthio) pentanoic acid (CETP) as the chain transfer agent in the presence of water-soluble 2,2′-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (VA-044). Polymerizations were conducted under extremely mild reaction conditions: visible light (typically, purple LED light), room temperature, no deoxygenation and water as a green solvent. Flow photoreactors allow the speed up of the polymerization under visible light irradiation without the loss of controllability. In the case of purple LED light, high conversions are achieved in a relatively short time (less than 1 h), and the resulting polymers have comparatively narrow molecular weight distributions (Mw/Mn = 1.10–1.30). The removal of the deoxygenation process greatly simplified the operational procedures and reduced the requirements of experimental devices. Furthermore, a successful chain extension experiment was conducted in a two-stage continuous tubular reactor confirming the “living” feature of this polymerization system.