Dynamic Viscoelasticity and Birefringence of Poly(ionic liquids) in the Vicinity of Glass Transition Zone

Abstract

Dynamic viscoelasticity and birefringence of two poly­(ionic liquid)­s, PC₄VITfO and PC₄VITFSI, are investigated to clarify the molecular origin of viscoelastic response of PILs. According to a previous study, PC₄VITFSI having larger counterions shows a broader viscoelastic relaxation spectra around the glass-to-rubber transition zone than PC₄VITfO. The rheo-optical data were analyzed with the modified stress-optical rule: The complex modulus for PC₄VITfO was separated into two components, the rubbery and the glassy component, similarly to the ordinary amorphous polymers while for PC₄VITFSI system an additional component was necessary in addition to the two ordinary components for a reasonable separation. From the frequency dependence, the additional component was attributed to the sub-Rouse mode of chain which is enhanced by the counterions decreasing the interchain interactions