HYDROPHILIC SOLUTE RELEASE FROM A HYDROPHOBIC ELASTIC MATRIX

The release behavior of a highly water soluble solute from elastic nonswellable polymer matrices was studied to investigate the effect of osmotic pressure on the release profile, which has been considered as a minor factor in the explanation of solute release mechanisms from cross-linked polymer matrices. In this experimental design, the osmotic pressure developed inside the polymer matrix and elastic force of the end-linked poly(tetramethylene oxide) have been found to be critical factors in determining the release profile. A typical release profile observed in this study was a bimodal pattern. This profile consists of two phases, initial slow release phase until solvent fronts meet and second phase with a marked increase in release rate thereafter. The accelerated release was caused by the contracting elastic force of an expanded network due to osmotic pressure. This was confirmed with the water content of the solute containing polymer matrices during solute release. The release rate and water content of the second phase were simulated using phenomenological equations of irreversible thermodynamics for solute and water fluxes. The theory, with assumptions made for simplicity, qualitatively described the experimental results.