PERMEABILITY CONTROL OF POLY(METHACRYLIC ACID) - POLY(ETHYLENIMINE) COMPLEX CAPSULE MEMBRANE RESPONDING TO EXTERNAL PH

Previously, permeability of partly crosslinked poly(acrylic acid)-poly (ethylenimine) complex capsule membranes has been shown to be controll ed responding to external pH [K. Kono, F. Tabata, and T. Takagishi, J. Membr. Sci., 76, 233 (1993)]. In order to improve pH-dependent permea tion behavior of the polyelectrolyte complex capsule membranes, poly(m ethacrylic acid), which has hydrophobic side groups, was used as a pol yanion component instead of poly(acrylic acid). The polyelectrolyte co mplex capsules composed of poly(methacrylic acid)-poly(ethylenimine) w ith a diameter of 5.2 mm were prepared. Permeation of phenylethylene g lycol, which was used as a permeant, through the capsule membrane was quite limited at pH between 4 and 8. The permeation of the permeant ac ross the capsule membrane in these pH regions was much less than that of poly(acrylic acid)-poly(ethylenimine) complex capsule membrane. How ever, the permeability constant was drastically increased in the order of 1 or 2 above pH 8 and below pH 4, depending on temperature. The Ar rhenius plot for the permeation of phenylethylene glycol through the c apsule membrane showed that the activation energy for the permeation i s almost constant in the pH region between 4.5 and 8, but greatly decr eases below pH 4 and above pH 8.8, suggesting occurrence of a signific ant change of the capsule membrane structure near these pH regions due to dissociation of polyelectrolyte complex. When environmental pH of the capsule was changed, release rate of phenylethylene glycol from th e capsule was altered quickly and reversibly under acidic condition.