The microstructure of polyaniline-CSA films undergoes various modifications
during ageing, as revealed by the changes of the gas sorption characterist
ics. When the adsorbed gas is (paramagnetic) oxygen it results in a broaden
ing of the polaron ESR line, which is proportional to the local conductivit
y. Data of weight uptake and ESR line broadening upon oxygen exposure for s
amples after ageing at 135 degrees C for various times are used to get insi
ght into the ageing process.