Vesicles prepared from amphiphilic copolymers

Two amphiphilic monomers from aspartic acid, N-methacryloyl dihexadecyl L-aspartate (A16-MA) and N-itaconyl dioctadecyl L-aspartate (A16-I) were synthesized. Three kinds of amphiphilic copolymers were obtained by copolymerization of A16-MA with hydroxyethyl methacrylate (HEMA) and 3-sulfopropyl methacrylate potassium salt (SPMAP) respectively and of A16-I with HEMA. The aggregation behavior of the two monomers and three copolymers were examined in an aqueous system. A16-MA and its copolymers with HEMA are very difficult to disperse in water to form regular aggregates; however, copolymers from A16-MA and SPMAP can be dispersed in aqueous media as stable vesicles. Both A16-I and its copolymers with HEMA can be easily dispersed in aqueous medium and form vesicular assemblies. These bilayer membranes undergo a typical gel-to-liquid crystal phase transition as confirmed by differential scanning calorimetry. The phase transition temperatures of the copolymer vesicles shift to slightly higher temperatures with a broader phase transition temperature range. The permeability of A16-I vesicles was studied by monitoring the release of encapsulated fluorescent probes; however, the encapsulated probes cannot be retained for very long in the vesicles prepared from amphiphilic copolymers. (C) 1999 Elsevier Science B.V. All rights reserved.