Reversibly Coagulatable and Redispersible Polystyrene Latex Prepared by Emulsion Polymerization of Styrene Containing Switchable Amidine

An easily coagulatable/redispersible polystyrene latex system was developed in this work. The coagulatability and redispersibility of the latexes were achieved by incorporating 1.6–5.3 wt % of newly synthesized amidine-containing styrene derivative in a soap free emulsion polymerization of styrene. The resulted latex particles were coagulated by adding a small amount of caustic soda and redispersed by CO2 bubbling, which switched amidine moieties between neutral and ionic states. The coagulation/redispersion processes were repeatable, even with washed and dried latexes. The styrene–butyl acrylate, styrene–methyl methacrylate, and styrene–acrylonitrile copolymer latexes produced with the same approach were also reversibly coagulatable and redispersible.