SELF-DIFFUSION AND MOLECULAR MOBILITY IN PVA-BASED DISSOLUTION-CONTROLLED SYSTEMS FOR DRUG-DELIVERY

Nuclear magnetic resonance (NMR) microscopy has been used to monitor t he hydration of poly(vinyl alcohol) (PVA) samples of varying molecular weight. One-dimensional profiles weighted to predominantly show the v ariation of water concentration were acquired every 3 min during the f irst 30 min of hydration and subsequently at 1 and 2 h. Diffusion-weig hted profiles obtained after 30 min and 1 and 2 h were used to calcula te the spatial variation of the water self-diffusion coefficient. The resulting data provide supporting evidence for the hypothesis that phe nomena such as reptation are important near the glassy/rubbery interfa ce of polymers during dissolution, while the diffusion gradually chang es to Zimm type near the rubbery/solvent interface. (C) 1998 Elsevier Science Inc.