PHYSICAL AGING IN POLYMERS - COMPARISON OF 2 WAYS OF DETERMINING NARAYANASWAMY PARAMETER

In this work. we have investigated by differential scanning calorimetr y the enthalpy relaxation of two poly[methyl(alpha-n-alkyl)acrylates] in which it is possible to change the length of the two alkyl chains. In particular, we have evaluated the Narayanaswamy parameter, which co ntrols relative contribution of temperature and of structure to the re laxation times, by two methods: Grenet's method (GM) and the peak-shif t method (PSM). The data obtained show that both methods lead to equiv alent results. Nevertheless, PSM requires fewer experiments than GM, a nd PSM appears to be more practical. The results obtained on the two a crylates show that the parameter x increases with the lateral chain le ngth, that Is to say, that the temperature effects increase as the len gth of the alkyl chain is increased.