A versatile design platform for multi-heterocyclic ionic liquid synthesis
Ionic liquids (ILs, briefly defined as salts exhibiting melting points below 100 degrees centrigrade) have been extensively researched in the past few decades, where properties controllable through selective variation in ion structure have supported a variety of discoveries in materials design. The modular combination of available `IL-forming' cations and anions provides retention of properties inherent to ILs such as low melting points, good thermal stability and negligible vapor pressure. Additionally, the dual-functional nature of ILs, whereby the design of functionalized ions is compartmentalized, can target specific physicochemical properties. Such transformable chemistry provides access to new design options from which contemporary problems in materials synthesis and applications may be strategically addressed. Due to the potential to reduce environmental health and safety hazards as well as access the systematic design of energetic materials, energetic ionic liquids (EILs) are identified as a class of materials which may afford new and improved alternatives to conventional propellants, explosives, and fuels. Rather than aiming to synthesize new energetic materials, the effort of this research was to develop a working knowledge of how to affect changes in EIL properties through modification of ion structure and composition, as well as to develop new design concepts that could provide effective strategies for future EIL synthesis. The approach to the investigations described here was two-fold, where the synthesis of EILs was achieved by either a conventional dual-functional strategy or multi-heterocyclic ionic liquid (MHIL) design. The main focus for this work includes (i) the synthesis ofN-cyanoalkyl-functionalized imidazolium salts with different energetic anions for examination of effects on IL thermal properties and reactivity, (ii) the conceptual development and experimental demonstration of a new design platform for MHIL synthesis with variable structure, charge, and symmetry, and (iii) the expansion of MHIL design to include new IL structures and to explore novel synthetic methodologies.