Polymerization of acrylamide photoinitiated by cobalt ammine complexes

Abstract

The kinetics of polymerization photoinitiated by pentaammineoxalatocobalt(II1) and tetraamminebis(oxalato)cobalt(III) complexes were investigated in aqueous and mixed solvents by irradiation of these complexes in the charge-transfer bands at 35°C. Radiation of wavelength 420nm was employed and the kinetics were followed by measurement of the rate of monomer disappearance (gravimetrically) and chain lengths of polymer formed (viscometrically). The dependence of the rate of polymerization and of the chain lengths on factors like absorbed light intensity, light absorption fraction, monomer concentration, initiator concentration, hydrogen ion concentration, viscosity of the medium, and the nature of the outer anion were studied in detail. A kinetic scheme is proposed and discussed in the light of experimental results, involving (i) a primary photo-chemical act of excitation of the complex, followed by dark reaction of electron transfer within the complex, producing free radicals and bivalent Co2+ ions, (ii) initiation of polymerization by the free radicals generated, and (iii) termination of the active chain by a mixed process, namely mutual termination of macroradicals as well as termination by the complex depending on experimental condition.