Dye-sensitized polymerization of vinyl monomers in aqueous solution

The kinetics of the polymerization of the vinyl monomers methyl methacrylate, methyl acrylate, and acrylonitrile sensitized by dye-reducing agent systems have been studied systematically. The systems were irradiated with light of 350-450 mμ wavelength. The induction period before the onset of polymerization was kept to a minimum by suitable experimental conditions. All the experiments were conducted in the presence of oxygen. The redox system sodium fluorescein (Uranine)-ascorbic acid was used for polymerization. The systems were buffered with phosphate buffer. The effects of temperature, viscosity, etc., on the reaction system were studied. The course of the reactions was followed by the measurements of rate of monomer disappearance (gravimetrically), rate of dye disappearance (spectrophotometrically) and the chain length of the polymer formed (viscometrically). Light intensity, wavelength, monomer concentration, dye concentration, reducing agent concentration, temperature, etc., were variable. The tentative kinetic scheme proposed is examined in the light of the experimental results. The values for the specific rate constants for the various steps have been evaluated