Oligomer-to-polymer transition of poly(propylene glycol) revealed by dielectric normal modes

The direct access to the overall chain dynamics provided by polymers with a dipole moment along their contour, was investigated. Poly(propylene glycol) (PPG) was selected for which the molecular weight dependence of the segmental dynamics has been well characterized. PPG served as a testing ground to clarify the mutual relation of α and β processes as a function of chain length. The polydispersity index M_w/M_n was 1.03 and for the longest chain was around 1.02. An electrical cleaning procedure was employed to enhance the visibility of the low frequency flank of the normal mode. In order to quantify the spectral changes the data were fitted using a sum of two Havriliak-Negami functions. The data were alternatively analyzed using the Williams-Watts product approach to check for systematic errors in the fitting procedure. It is concluded that the change from the Gaussian to non-Gaussian polymer behavior is displayed through the N independence of the static susceptibility of the dielectric normal mode.