(577e) Reversibly Coagulatable and Re-Dispersable Polystyrene Latex Prepared by Emulsion Polymerization of Styrene Containing Switchable Amidine

Millions of tons of polymer latexes are produced annually by emulsion polymerization, offering a variety of applications in industry.  Both destabilizing latex particles (coagulation) and re-dispersing the coagulated particles are challenging. The advent of long-chain alkyl amidine compounds as switchable surfactant offers an alternative control on emulsion stability.  Surface activities of the surfactants were turned on and off by bubbling CO₂ and N₂ (or Ar) gases.  CO₂ in water reacts with amidine to form bicarbonate salt that stabilizes emulsion; bicarbonate salt decomposes to amidine to break the emulsion in the presence of N₂ or Ar.  We hypothesize that a reversibly coagulatable and re-dispersible latex product is achievable if amidine moieties can be covalently bounded to the particle surfaces.

In this work, we have successfully developed a coagulatable and re-dispersible polystyrene latex system through a soap-free emulsion copolymerization of styrene with a styrene derivative bearing amidine group.  The amidine-containing comonomer was reversibly switchable between ionic and neutral states by alternatively bubbling CO₂ and N₂.  Such a comonomer incorporated into the polystyrene chains acted as an effective stabilizer during the emulsion polymerization.  The latex particles thus formed could be easily coagulated by adding small amount of caustic soda.  The coagulated particles could be re-dispersed into water to prepare a stable latex without adding extra stabilizer.  The coagulation and re-dispersion processes were repeatable.  It was particularly plausible that the aggregated particles after washing and drying were still re-dispersible.  Such coagulatable/re-dispersible latex prepared directly from an emulsion polymerization is believed to have high potential in cost savings in the areas of separation, storage, and transportation and thus to benefit our economy and environment.