WATER-POLYMER INTERACTIONS AND CRITICAL PHENOMENA OF SWELLING IN INHOMOGENEOUS POLY(ACRYLONITRILE-ACRYLAMIDE-ACRYLIC ACID) GELS

The water uptake and swelling behaviour of physically crosslinked, inhomogeneous poly(acrylonitrile-acrylamide-acrylic acid) hydrogels from 10 to 60 degrees C were determined by gravimetry/differential scanning calorimetry and volume measurement, respectively. The contents of water and its non-bound portion were found to reach a minimum value at acrylamide content around 33.5 mol%, at which the water uptake of this gel does not vary with the temperature. The non-bound water was found to decrease gradually and then increase with increasing amide concentration. The duration of the post-gelation treatment between -10 and 10 degrees C was also shown to be one of the factors affecting the extent of the water uptake in gels. The critical endpoint temperatures (T(c)s) of hydrogels, obtained from volume phase transition data upon changing the acetone concentration in aqueous solutions at various temperatures, were shown to decrease with the increasing acid or amide contents. The water uptake for gels with lower amide contents decreases with increasing temperature. However, there is an opposite trend for water uptake in gels with higher amide content, and the critical points on the plots of the amount of water uptake versus temperature appear at a temperature equal to T-c.