Light decomposable emulsifiers: Application of alkyl-substituted aromatic azosulfonates in emulsion polymerization

Many waterborne (latex) paints films suffer from a certain level of water sensitivity due to the presence of different types of electrolytes, e.g. initiator fragments, buffer salts, soaps, pigment dispersants and thickeners. Since these substances are not assumed to exert any positive influence on film properties, it might be considered useful to design them in a way that at least part of them lose their hydrophilicity after him forming. We studied the synthesis, properties and use of light decomposable soaps, which consist of a hydrophobic moiety linked to an ionic one via the light-splittable diazophenyl bond. Three types of azosulfonate emulsifiers were made and characterized photochemically. Alkylbenzeneazosulfonates were used as soaps in the emulsion polymerization of methylmethacrylate. It could be shown that these latices indeed lose their stability in water, when irradiated. The coagulation occurs through conversion of the azosulfonate to the corresponding diazonium salt and mutual charge neutralization of the cationic and anionic species.