Characteristics of pH-sensitive hydrogel microsphere of poly(acrylamide-co-meth acrylic acid) with sharp pH-volume transition

The forming process and characteristics of monodispersed hydrogel microspheres of poly(acrylamide-methacrylic acid) with sharp pH-volume transition were studied. pH-/ion-sensitive and thermosensitive behaviors of microspheres sampled at various stage of polymerization were evaluated by using the dynamic light scattering. It was observed that the sharpness of pH-volume transition increased with the increase in monomer conversion. Both thermo- and ion-sensitive behaviors were affected by pH. At pH 4.3, the hydrodynamic diameter of microspheres monotonically and slightly decreased with the increase in temperature, whereas at pH 3.5 and 3.8, the curves of thereto-volume transition were similar to those of pH-volume transition with a maximum temperature at 25 and 20 degrees C, respectively. Increasing the [CaCl2] was to decrease the hydrodynamic diameters of microspheres, irrespective of pH. However, a region at lower [NaCl] was found, where the diameter increased with the increase in [NaCI]. Moreover, the range of diameter increasing extended to higher [NaCI] as pH increased.