Designing melt flow of poly(isobutylene)-based ionic liquids

Abstract

A series of novel poly(isobutylene)-based stable ionic liquids (PIB-ILs) with strongly temperature dependent nano- and mesostructures is reported. The molecular design relies on the use of a liquid polymer with an ionic liquid-head-group, introducing liquid properties by both the polymeric chain as well as the ionic liquid (IL) head-group thus enabling terminal flow in a range which cannot be addressed with classical ILs with respect to the design of potential self-healing materials. Modifying both the anchored cation and anion as well as the molecular weight of the attached polymer chain, the nanostructure and the viscoelastic behavior of PIB-ILs can be engineered. Detailed small-angle X-ray scattering (SAXS) investigations as well as rheology studies have been conducted to reveal structure, viscoelastic properties and relaxation behavior of the prepared PIB-ILs. All investigated PIB-ILs exhibited a defined nano- and mesoscale ordering at room temperature, whereas the nature of the anchored cation showed a strong impact on the temperature-dependence of the mesoscale-structure as well as on the flow behavior of PIB-ILs. Exchange of the bromide anion to bis(trifluoromethylsulfonyl)imide led to the loosening of the observed clusters and to lattice disorder–order transitions (LDOT) at lower temperatures, leading also to terminal flow at lower temperatures. Investigated PIB-ILs exhibited short relaxation times and the reestablishment of the nano/mesoscale morphology immediately after cooling at room temperature, which makes them suitable for the engineering of novel self-healing materials.