Inverse microemulsion polymerization of sterically stabilized polyampholyte microgels.

Polyampholyte microgels consisting of various compositions of poly(methacrylic acid) and poly(2-(dimethylamino)ethyl methacrylate) (PMAA-PDMA) cross-linked with allyl methacrylate (AM) were synthesized via the inverse microemulsion polymerization (IMEP) technique. To improve colloidal stability at the isoelectric point (IEP), steric stabilization via the grafting of poly(ethylene glycol) methyl ether methacrylate (PEGMA) on the surface of the microgel was performed. Potentiometric and conductometric titration showed good agreement between the targeted and experimental compositions of the microgel systems. The microgel swelled at low and high pH and possessed a compact structure near the IEP, and the diameter were in good agreement with data from the transmission electron microscopic (TEM) analyses. With increasing pH, the mobility decreased from +2 m(2)s(-1)V (1) at pH 2 to -2 m(2)s(-1)V (1) at pH 10. An empirical relationship describing the PMAA composition and IEP was proposed, where the IEP decreased with increasing PMAA content. The microgel exhibited thermal-responsive properties at high pH, which is dictated by the lower critical solution temperature of PDMA.