FT-IR spectroscopy was used to study the specific interactions in an aliphatic polyacetamidine and its mixtures with a dicarboxylic acid. In the pure polyacetamidine, hydrogen bonds between the amidine groups were observed. After heating, considerable changes in the position of the interacting group vibration bands were found. These changes were reversible on cooling. In mixtures with glutaric acid strong acid base interactions resulting in the formation of ionic polymer networks were observed. These networks have proven stable up to at least 150 degreesC. (C) 2003 Elsevier Science Ltd. All rights reserved.