Enthalpic ageing data for poly(methyl methacrylate) are reanalysed in
terms of a modified version of the Cowie-Ferguson model which takes ac
count of a time-dependent characteristic time, t(c). In terms of descr
ibing the time evolution of enthalpy changes occurring upon ageing, no
significant improvement in the fits to the data were found when compa
red with the original linear model.