Vinyl polymerization photosensitized by uranyl ions

Abstract

A systematic investigation of the kinetics of polymerization of the vinyl monomers methyl methacrylate, methyl acrylate, and acrylonitrile in aqueous solution, photosensitized by uranyl ions, was undertaken. Light of wavelengths 300-450 mμ was used for irradiation. Complex formation and ion-pair formation was kept to the minimum. The course of the reactions was followed in terms of rates of monomer disappearance, rates of uranous ion formation, and the chain length of the polymer formed. Under controlled conditions of acidity and ionic strength, quantitative correlations between the various rates and chain length, and the variables (1) fractional light absorption, (2) uranyl ion concentration, (3) wavelength of incident radiation, (4) monomer concentration, (5) light intensity, and (6) temperature of the reaction were obtained. The influence on the reaction of uranous ion present initially in the system was studied. The quenching of the fluorescence of uranyl ions by vinyl monomers and by other standard quenchers was compared. The tentative mechanism proposed for the overall reaction is discussed in the light of these experimental results. Ratios of specific rate constants and activation energies for the various steps have been evaluated.