Photopolymerization of vinyl monomers initiated by pentaaminecobalt (III) complexes

Abstract

The polymerization of acrylamide in aqueous solution can be initiated by free radicals formed during the irradiation of pentaaminecobalt(III) complexes with light of wavelengths corresponding to the charge transfer band of the initiators. The kinetics were studied for two different cobalt(III) complexes: the chloropurpureosalt [CoCl(NH3)5]‐Cl2 and the roseosalt [Co(H2O)(NH3)5](NO3)3. In both cases the dependence of the rate of polymerization on the initiator concentration indicates a termination reaction due to an oxidation of the growing chains by the metal complexes. The effect of the chloro complex on the photopolymerization rate of acrylamide initiated by riboflavine showed the same termination activity. A termination constant, kt = 1.5 × 103 liter/mole‐sec., could be calculated. The first‐order dependence of the rate of polymerization on the monomer concentration for the initiation by the chloro complex agrees with an internal charge transfer during the photochemical activation of the initiator. The second‐order dependence of the rate of polymerization on the monomer concentration for the initiation by the aquo complex can be attributed to a substitution of the coordinative bonded water by a monomer molecule. An electron transfer within the intermediate complex agrees with the observed initiation.