Swelling behavior of hydrophobic polymers in water/ethanol mixtures

Swelling behavior of poly(ethylene-co-vinyl alcohol) (EVAL), polyurethane ( PU) and poly(ethylene-co-vinyl acetate) (EVAc) in ethanol/water mixtures wa s investigated. In the case of EVAL, the total swelling curve rises to a ma ximum that is above the swelling of either pure constituent. On the other h and, in the PU and EVAc systems, the total swelling is intermediate between the swelling of the two pure components. In the case of PU, the total swel ling is close to the ideal system as the water-rich region is approached. H owever, in the case of EVAc, the deviation from ideal is significantly nega tive. Theoretical swelling values have been derived from Flory-Huggins ther mo-dynamics by using the equilibrium sorption data of the pure component. T he theoretical results show good agreement with the swelling behavior of PU and EVAc in ethanol/water mixtures. However, the agreement between theoret ical and experimental swelling values for EVAL is reasonably established wh en the Flory-Huggins equation was modified by incorporating a ternary inter action parameter chi(T) This is probably due to the fact that. the water/et hanol mixture produces the water-ethanol complex that has a greater affinit y for EVAL. In addition, the experimental results indicate that the shape o f hydrophobic polymer swelling curve in the water/ethanol mixture is mainly controlled by the interactions between water and the polymer. Therefore, t he correlation among the swelling equilibrium data, the polymer hydrophobic ity and the structuring of water around the hydrophobic polymers is discuss ed. It is concluded that the hydrophobic interactions between the polymer a nd water are a major factor to influence the polymer swelling due to change s in the structuring of water around the hydrophobic polymers. These result s might have important implications for the drug delivery and pervaporation . since these processes are influenced by the polymer swelling to a great d egree. (C) 2000 Elsevier Science Ltd. All rights reserved.