Phenylonium salts as third component of the photoinitiator system safranine O/triethanolamine: A comparative study in aqueous media

The efficiency of the photoinitiator system composed of safranine and triethanolamine for the polymerization of acrylamide in water was improved by the incorporation of onium salts. The phenylonium salts employed were diphenyliodonium chloride, triphenylsulfonium triflate, tetraphenyphosphonium chloride and tetraphenylarsonium chloride hydrate. Among them, diphenyliodonium presents the highest efficiency, followed by triphenylsulfonium. In an appropriate concentration of triethanolamine, the behavior of the sulfonium salt resembles that of iodonium. Tetraphenyphosphonium and tetraphenylarsonuim have little effect over the polymerization rate; however, interesting effects over the photophysical properties of the system were found. Two important conclusions emanate from the work: the phenylonium salts studied aggregate in water in a behavior similar to hydrotropes and several factors contribute to the accelerating effect of the onium salt on the polymerization rate. The main differences in the observed efficiency of the salts might reside in the redox potentials of the salts and in their ability to prevent the photobleaching of safranine in the presence of triethanolamine.