Synthesis, characterization and applications of azo-containing photodestructible surfactants

Abstract

Photodestructible surfactants, sodium 4-(2-cyano-2-undecylazo)benzoate and a series of sodium 4alkylphenylazosulfonates, have been synthesized and were shown to be surface active in solution, each exhibiting a distinct critical micelle concentration (CMC). UV irradiation of aqueous solutions of the alkylazobenzoate led to a distinct increase in surface tension, but even after complete photolysis significant surface activity remained, indicating a substantial amount of cage recombination after nitrogen evolution. UV irradiation of sodium 4-dodecylazosulfonate caused a photoscission reaction, completely destroying its surface active properties. In the case of azosulfonates with shorter alkyl chains, however, some residual surface activity remained after complete removal of the azo linkage, indicating that secondary surfactants were formed by the photolysis. The 4-alkylphenylazosulfonates were able to solubilize an oil-soluble dye in water to produce isotropic coloured solutions. Photoirradiation of these solutions led to complete loss of colour, presumably as a result of microprecipitation of the dye. The azosulfonate surfactants also readily emulsified vinyl monomers, such as styrene, in water. Attempts to achieve emulsion polymerization led to only low conversion of monomer, most likely owing to side reactions between initiating radicals and the azo linkage of the surfactant, leading in turn to disruption of the micelle.