Preparation of Thermosensitive Submicrometer Gel Particles with Anionic and Cationic Charges

Aqueous redox polymerization using a surfactant was studied to prepare submicrometer-sized polyelectrolyte gel particles from a monomer solution containing N-isopropylacrylamide (NIPA), N,N'-methylenebisacrylamide (Bis), and acrylic acid (AAc) or 1-vinylimidazole (VI). Sodium dodecylbenzenesulfonate and ammonium persulfate were used as the surfactant and the initiator, respectively. The gel particles purified via dialysis were characterized by photon correlation spectroscopy. Since the AAc and VI contents of the monomer solutions were controllable within 0-30 mol %, the diameter ofthe gel particles with 30 mol % of AAc or VI increased from 125 to 600 nm at 25 °C when converting the carboxyl or imidazolyl groups into the corresponding salt form. However, a complete elimination of charges from the anionic or cationic gel particles gave rise to a neutral gel, the size of which varied from 125 nm at 25 °C (swollen state) to 50 nm at temperatures >35 °C (fully collapsed state). These swelling behaviors were the same as those of NIPA-based ionic bulk gels. Detailed examinations of the gel particles with 30 mol % AAc by potentiometric titration and electrophoretic light scattering showed that almost all of the COOH groups in the pregel solution were incorporated into the particle interiors without concentration on the particle surface.