Catalyst-free iodine-mediated living radical polymerization under irradiation over a wide visible-light spectral scope

Abstract

Catalyst-free iodine-mediated living radical polymerization (LRP) employing the formation equilibrium between an alkyl iodide dormant species (Polymer-I) and a propagating radical (Polymer˙) over a wide visible light irradiation scope was studied with respect to its kinetics, mechanism and suitability. The polymerization of methyl methacrylate (MMA) or some functional methacrylates offered good control over the polymer molecular weights and distributions (M_w/M_n = 1.05–1.30) up to fairly high conversions (more than 95%). This polymerization system displayed instantaneous activation and deactivation in response to “on–off” switch of the irradiation source. The polymerization kinetic rate was sensitively modulated by tuning the irradiation wavelength. Attractive features of the developed polymerization system include the feasibility of use of irradiation in the visible light spectral scope, good polydispersity control, good tolerance to functional groups, satisfactory regulation over a wide range of wavelengths, environmental safety and external photo-irradiation response sensitivity. Sunlight was also proved to be an alternative illumination source for this iodine-mediated LRP.