A Reactive, pH-Responsive, Cleavable Surfactant for Thiol-ene Emulsion Polymerization to Make Latex Degradable and Redispersible

A synthesis of a multifunction surfactant monomer (surfmer) is reported for the emulsion polyaddition of dithiol and diene monomers. Such compound features two reactive thiols, a cleavable thioester moiety and a pendant carboxylic acid. It was obtained by the reaction of 1,6-hexanedithiol with maleic anhydride. After partial deprotonation of the acid group, this surfactant monomer (surfmer) acts as an effective stabilizer for emulsion polymerization of 1,6-hexanedithiol with diallyl phthalate or 1,7-octadiene. The surfactant is soluble in the monomer phase and causes a significant decrease of the water/monomer interfacial tension. The resulting linear poly(thioether) latexes were studied as regards molar mass, particle size and composition. Their properties were compared to those of a conventional latex stabilized by a static surfactant, sodium dodecyl sulfate. After flocculation at low pH, the surfmer-stabilized latexes can be redispersed in a basic aqueous solution. In the presence of butylamine, the dried latexes are fully or partially degraded owing to thioester units along the polymer backbone.