The purpose of this paper is to evaluate the respective hydrolysis stability of phthalic and naphthalenic imide structures through the study of model compounds. The NMR and IR spectroscopic analyses of model compounds, before and after aging in water, at temperature representative of fuel cell working temperature, indicated structural modifications according to imide ring structure. The phthalic model stability was inferior to 1 h at 80 degreesC whereas the confirmed naphthalenic model one was superior to 100 h in the same conditions. Moreover, a limited hydrolysis of naphthalenic imide cycle was also shown. (C) 2001 Elsevier Science Ltd. All rights reserved.