TSC study of length ester side group effect on sub-vitreous relaxations in poly(n-alkyl methacrylates)

A comparative study by thermo-stimulated currents (TSC) of three poly(n-alkyl methacrylates) is performed. TSC complex spectra exhibit two dipolar relaxations considered in the following: the glass relaxation and a secondary relaxation related to motion of ester side groups. For each sample, the fractional polarisations protocol is applied to describe the fine structure of these complex spectra. It allows us to define the evolution of activation parameters with temperature. The influence of side chain architecture is then considered. It emphasises that the β mode is independent of the ester group length. On the contrary, the α mode is highly sensitive to structural change. These results are finally explained in terms of molecular mobility.