Solvent Polarity Effects on Segmental Dynamics in Ionic Polymer Networks: Quasi Elastic Neutron Scattering Study*

Incorporating ionic groups into polymers drives formation of physical networks that affect the dynamics of the macromolecules. Here, using quasi elastic neutron scattering (QENS), segmental dynamics of slightly sulfonated (3mol%) polystyrene (PSS) networks formed in cyclohexane, a non-polar environment and a theta solvent for PS was studied, followed by tracking the polymer motion as the association of the sulfonated groups is disrupted by ethanol. Specifically, a 10%(w/w) PSS in cyclohexane/ethanol solutions was studies in the q range of 0.3 Å^-1 to 1.3 Å^-1 corresponding to 5 Å -21 Å. The relaxation times and segmental motion were extracted from a Kohlrausch-Williams-Watts (KWW) analysis. As expected for PSS in cyclohexane, the dynamics is constrained at larger dimensions but the polymer remains mobile on smaller length scales. Addition of less than 5%(v/v) of ethanol is enough to release the constrains. Surprisingly however, further increase in ethanol results in decrease in segmental motion. This reduction could be attributed to overall plasticization of the polymer in presence of ethanol.