The molecular exchange of water molecules through membranes of dispersed vesicles prepared from different block copolymers was studied using nuclear magnetic resonance spectroscopy combined with pulsed field gradients. Vesicles from four different block copolymers with different hydrophobic sections (poly-2-vinylpyridine, polyisoprene, polybutadiene and polylactid) were used for the determination of average residence times for water molecules in the encapsulated state. The activation energies for the water transfer through the different membranes were obtained in a systematical variation of the dispersion temperature. (C) 2007 Elsevier B.V. All rights reserved.