Preparation of amphoteric microgels of poly(acrylamide/methacrylic acid/dimethylamino ethylene methacrylate) with a novel pH-volume transition

Amphoteric microgels consisting of poly(AAm/MAc/DMAEMA/MB) were prepared by semicontinuous polymerization in ethanol. Scanning electron microscopy (SEM) and dynamic light scattering (DLS) were employed for evaluating the microspheres and their pH-volume transitions in the aqueous solution, respectively. Monodispersed amphoteric microgels with a U-type of pH-volume transition, i.e., volume contracted in the pH range 6.5-7.5 and expanded beyond this, were prepared by adding MAc dropwise at a certain rate (20 g/80 min, standard recipes). It was observed that increasing [NaCl] or [CaCl2] served to decrease the hydrodynamic diameter of amphoteric microgels, irrespective of pH. Moreover, in the region of pH 2-3, the pH of amphoteric microgels increased with the increase of ion strength, whereas inversely, for pH 9-10, the pH decreased with an increase of ion strength, regardless of the types of salts. The U-type curve of diameter vs pH could be replaced along with the pH axis by adjusting the charged amount of DMAEMA. Control-releasing behavior of amphoteric microgels was also investigated. It was observed that the dye was released to the same extent when the pH was changed from 6.8 to either acidic or basic conditions.