In this study, the sorption isotherms of water vapor by chitosans with vari
ous molecular weights were measured. The BET adsorption theory was modified
for the system that has several different kinds of energy levels in the wa
ter adsorption sites, i.e. a hydroxyl group, an amino group, the polymer ch
ain end, etc, and applied it to the experimental results in order to examin
e the effect of the polymer chain end on the sorption isotherm of water-chi
tosan using the parameters which represented the total number of adsorption
sites, V-m, the interaction energy between water and the adsorption sites,
K, and the number of adsorbed layers, n. V-m and K increased as the molecu
lar weight decreased, and n remained constant. It has been proved that the
increase in V-m and K were caused by the hydrophilic groups in the polymer
chain end. (C) 2000 Elsevier Science Ltd. All rights reserved.