Surfactant-Free Polymerization
Forming Switchable
Latexes That Can Be Aggregated and Redispersed by CO<sub>2</sub> Removal
and Then Readdition
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Abstract
Polystyrene latexes prepared using the bicarbonate salt
of initiator
2,2′-azobis[2-(2-imidazolin-2-yl)propane] via surfactant-free
emulsion polymerization can be aggregated using only argon and gentle
heat and redispersed using carbon dioxide and sonication. The bicarbonate
and hydrochloride salts of the initiator have similar thermal decomposition
behavior, but only the bicarbonate salt of 2,2′-azobis[2-(2-imidazolin-2-yl)propane]
can be switchable between ionic and nonionic forms by addition and
removal of CO<sub>2</sub>. Measurements of particle size and zeta
potential were used to study the aggregation and redispersion of the
latexes. The latex is aggregated by heating and bubbling with argon
to remove CO<sub>2</sub> and convert the active cyclic amidinium groups
to their neutral form. When treated with sonication and bubbling with
CO<sub>2</sub>, the aggregated polystyrene latex can be redispersed
successfully, as evidenced by restoration of the original latex particle
size and zeta potential from the large aggregated polymer particles.
This is the simplest method to date to prepare a redispersible latex
stabilized by CO<sub>2</sub>