Linear Viscoelastic and Dielectric Properties of Phosphonium Siloxane Ionomers

The linear viscoelastic (LVE) and dielectric relaxation spectroscopic (DRS) properties of polysiloxanes with phosphonium (fraction f) and oligo(ethylene oxide) (fraction 1 - f) side groups with a fraction of ionic monomers f = 0-0.26 have been studied. LVE master curves of those ionomers have been constructed. The ionic dissociation has been witnessed as a delayed polymer relaxation in LVE with increasing ion content, as well as an α₂ ionic segmental relaxation process in DRS. LVE exhibits glassy and delayed rubbery relaxation at low ionic fraction f ≤ 11%, where the ionic dissociation time detected in DRS enables description of LVE with a sticky Rouse model. In contrast, the glassy and rubbery stress relaxation moduli merge into one broad process at high f ≥ 22%, where the whole LVE response from glassy to terminal relaxation can be described phenomenologically by a single Kohlrausch-Williams-Watts (KWW) equation with the lowest stretching exponent β = 0.10 ever seen for polymeric liquids, describing LVE over 15 decades of frequency.