Molecular dynamics of perfluorinated oligo and polyethers

Molecular dynamics in selected perfluoropolyethers (PFPEs) has been investigated by dielectric relaxation spectroscopy (DRS) technique. In the DRS spectra of investigated materials two relaxation processes can be revealed. At the lowest temperature range in some of the samples the subglass relaxation attributed to the local motions has been observed. The α-relaxation seen at higher temperature is related to segmental movements and exhibits non-Arrhenius type behavior. At higher temperatures and low frequency range the conductivity was observed. The PFPE materials have generally very low dielectric constant, which depends on the chemical structure of these materials. The incorporation of one methylol group CH2OH instead of fluorine atom in the terminal group results in the increase of the dielectric constant from 2.6 to 3.6 at 206 K for the samples with comparable molecular mass. The position of the primary molecular relaxation seems to depend on the molar mass rather than on the chemical structure. The glass transition temperatures for the investigated group of Krytox® oligomers differ by tens of degrees.