Radical polymerization of methyl methacrylate in the presence of methylene blue and organobromides under visible light irradiation

The visible light-induced polymerization of methyl methacrylate in the presence of methylene blue as a photocatalyst and various bromine-containing organic compounds was first investigated. It was shown that polymerization may be successfully initiated even at low concentrations of methylene blue using conventional LED strips. The polymerization rate and the dependency of molecular weight parameters of the samples on monomer conversion are governed by the nature of light source as well as the structure of the initiator and introducing additional reagents. The use of warm white light seems to be more favorable for conducting the process to high conversions. Electron-donating additives such as aliphatic amines or formic acid accelerate the polymerization and determine the linear increase of molecular weight of the samples with the conversion growth typical for reversible deactivated radical polymerization. The performed quantum-chemical calculations and experimental studies show that the simultaneous realization of the metal-free atom transfer radical polymerization and light-induced stable free radical polymerization mechanisms is possible under the light irradiation. The simultaneous realization of two different processes determines the linear growth of the polymer chain upon conversion but results in average control over molecular weight distribution of the obtained samples.