SORPTION ISOTHERM ANALYSIS OF WATER BY HYDROPHILIC POLYMER COMPOSED OF DIFFERENT ADSORPTION SITES USING MODIFIED BET EQUATION

In this study, two typical modeling samples composed of vinyl acetate (VAc) and vinyl alcohol(VA) copolymer were prepared in order to invest igate the relationship between polymer structure and water uptake. One consisted of homogeneously acetylated samples in which the hydroxyl g roup and acetoxyl group were distributed randomly, and the other consi sted of the heterogeneously acetylated samples which were composed of block copolymer of poly(VA) and poly(VAc-VA). The sorption isotherms o f water vapor by those samples with various contents of hydroxyl and a cetoxyl groups were measured. The BET adsorption theory was modified f or the system which has two different kinds of energy levels in water adsorption sites, that is, a hydroxyl group and an acetoxyl group, and applied in order to analyze the obtained sorption isotherms, The homo geneously acetylated VAc/ VA copolymer was amorphous polymer, and the heterogeneously acetylated VAc/VA copolymer was a partially crystalliz ed polymer. The number of adsorption sites in the homogeneously acetyl ated samples was larger than that in the heterogeneously acetylated sa mple. On the other hand, the interaction energy between the hydroxyl g roup and water in the heterogeneously acetylated sample was much large r than that in the homogeneously acetylated sample based on examinatio n with the modified BET equation. These results imply that the poly(vi nyl alcohol) crystal has a high adsorption energy, (C) 1998 Academic P ress.