SPECTRAL INVESTIGATIONS OF COBALT PORPHYRINATES INTERACTION WITH RADICAL POLYMERIZATION INITIATORS

Abstract

The article presents the results of the kinetics study of the cobalt porphyrins interaction with radical polymerization initiators – benzoyl peroxide and lauryl peroxide – in solution by the spectrophotometric method. From disparate literature data, it is known that some metalloporphyrins can interact with benzoyl peroxide to form the tautomers of porphyrins – isoporphyrins. These compounds have a number of specific properties, for example, it can be catalysts of various processes. Perhaps the isoporphyrins formation is the reason for high activity of the initiating systems “cobalt porphyrin – benzoyl peroxide” in the polymerization of vinyl monomers. Cobalt(II)complexes of tetraphenylporphyrin, tetra-para-methoxyphenylporphyrin, 5,15-bis(4´-tert-butylphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetra-p-butylporphyrin were selected as the objects of this study. The influence of the porphyrin ligand structure on the formation of cobalt isoporphyrins was estimated. The interaction of cobalt (II) tetraphenylporphyrin and cobalt (II) tetra-para-methoxyphenylporphyrin with peroxides showed changes in the electronic absorption spectra of metalloporphyrins: deformation of the Soret band, reduction of the absorption band in the visible region, and the appearance of absorption bands in the near IR region. These changes are characteristic for metalloisoporphyrins. Data on the interaction of cobalt porphyrins with lauryl peroxide were obtained for the first time. The formation of isoporphyrins is possible with the different ratio of concentrations of reagents: with a lack of peroxide, with equimolar ratio, and also with a significant (100-fold) excess of peroxide. When 5,15-bis (4´-tert-butylphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetra-p-butylporphyrinate cobalt (II) reacted with peroxides, no isoporphyrinates were observed. The article presents the effective reaction rate constants of the cobalt isoporphyrinates formation at 25 °C. It is shown that the structure of both cobalt porphyrinates and organic peroxides affects the possibility and rate of isoporphyrins formation.