Aryl Amidine and Tertiary Amine Switchable Surfactants and Their Application in the Emulsion Polymerization of Methyl Methacrylate

The switchability and bicarbonate formation of CO₂ triggered aryl amidine and tertiary amine switchable surfactants have been investigated. Despite the lower basicity of these compounds compared to alkylacetamidine switchable surfactants, it was found that amidinium and ammonium bicarbonates could be formed in sufficiently high enough concentrations to perform emulsion polymerization of methyl methacrylate and stabilize the resulting colloidal latexes. Particle sizes ranging from 80 to 470 nm were obtained, and the effects of surfactant concentration, surfactant basicity, initiator type, initiator concentration, and CO₂ pressure on particle size and ζ-potential have been examined. Destabilization of latexes is traditionally achieved by addition of salts, strong acids for anionically stabilized latexes, or alkalis for cationically stabilized latexes. However, with CO₂-triggered switchable surfactants, only air and heat are required to destabilize the latex by removing CO₂ from the system and switching the active amidinium or ammonium bicarbonate surfactant to a surface inactive neutral compound. This process occurs much more rapidly in the case of these less basic aryl amidine and tertiary amine based surfactants compared to previously reported alkyl amidine surfactants.