Synthesis and characterization of amphoteric latex particles

Stable monodisperse amphoteric latex particles were prepared by the semibatch surfactant-free emulsion copolymerization of methyl methacrylate and methacrylic acid (MAA) initiated by 2,2'-azobis(2-amidinopropane) dihydrochloride (V-50). These submicron particles have a net positive charge, which is attributed to the ionized amino group at low pH. In contrast, they become negatively charged owing to the ionized carboxyl group at high pH. There exists a pH at which these particles exhibit a net charge of zero (pI). At a constant level of V-50, the pI value of these latices decreases with increasing amount of MAA used in the polymerization recipe. The effect of pH on the colloidal stability of these amphoteric latices toward the addition of the negatively charged latex was investigated. The resultant coagulation kinetics was used to study the electrostatic interaction between the amphoteric particles and negatively charged particles.