Influence of anions of imidazolium based ionic liquids on the molecular properties of poly(benzimidazolium – co – benzimidazolide) ionene’s

Understanding molecular interactions between ionic liquids (ILs) and charged polymer are essential for optimizing their performance in advanced applications like fuel cells, and separation processes. This paper performs molecular dynamics simulation to understand the structure, dynamics and thermodynamics of homo polymers of cationic poly (benzimidazolium) (CT) and anionic poly (benzimidazolide) (AN) and copolymers of benzimidazolium and benzimidazolide immersed ILs. We consider a common cation 1-ethyl-3-methylimidazolium [EMIM] and four anions: nitrate [NO₃], tetrafluoroborate [BF₄], hexafluorophosphate [PF₆], and bis(trifluoromethane)sulfonimide [BIS]. An increase in charge density of the polymer led to larger values of the radius of gyration ( R g ). Self-Diffusivity calculations showed that reduced ion mobility, while reduced density gradient (RDG) analysis show a shift from h-bonding interactions at lower charge density to van der Waals interactions at higher charge density. The results highlight how polymer charge density, anion size influences molecular interactions as well as structural transitions, for the design of Ionenes. • Copolymers of benzimidazolium (AN) and benzimidazolide (CT) were studied. • AN and CT repeat units behave differently in ionic liquids (ILs). • Rg decreases for AN and increases for CT with increasing anion size. • Van der Waals interactions dominant for CT homopolymer.