From Polymerizable Ionic Liquids to Poly(ionic liquid)s: Structure-Dependent Thermal, Crystalline, Conductivity, and Solution Thermoresponsive Behaviors

Abstract

This contribution describes the synthesis of 3-alkyl-1-vinylimidazolium bromide ionic liquid monomers (ILMs), ion exchange with bis(trifluoromethane)sulfonimide anion (NTf2–), and their radical polymerization to a homologous series of poly(ionic liquid)s (PILs) containing an imidazolium ion substituted with alkyl chains of different lengths (C2(n=7–11)). Owing to the presence of a long alkyl chain, all the ILMs show crystalline phases whose melting point and melting enthalpy increase sharply with increasing alkyl chain length, and those parameters decrease upon replacing Br– with a NTf2– anion. In addition to the solid crystalline phase, the ILMs with a Br– ion only show liquid crystalline mesophases above the melting of solid crystals. The corresponding PILs are semicrystalline in nature due to crystallizable alkyl side chain showing similar chain length and counteranion-dependent melting behaviors with poor crystallinity compared to those of ILMs. The formation of strong birefringent crystals of various...