Enhanced permeability of Rhodamine B into bilayers comprised of amphiphilic random block copolymers by incorporation of ionic segments in the hydrophobic chains

The permeability of Rhodamine B (Rh) into bilayers comprised of amphiphilic block copolymers was explored using ionic segments incorporated in the hydrophobic chains. The amphiphilic block copolymer consisting of a hydrophilic poly(methacrylic acid) block and a hydrophobic poly(methyl methacrylate-random-methacrylic acid) block containing 0.2 mol% units of the 3-sulfopropyl methacrylate potassium salt (SpMA) produced giant vesicles by photopolymerization-induced self-assembly in an aqueous methanol solution. The spherical vesicles were transformed into films as the SpMA ratio increased. The SpMA units incorporated in the hydrophobic chains enhanced the Rh permeability into the bilayer, whereas the vesicles without SpMA units captured no Rh molecules. However, the Rh was released from the hydrophobic phases in the isolation process of the bilayers by repeated sedimentation-redispersion. The permeability enhancement was attributed to the pore formation in the bilayers by the capture and release of the Rh by the SpMA units in the hydrophobic phases.