Modulating Ionic Conductivity in Star and Linear Poly(ionic liquids) by Dipolar Interactions

The ability to modulate the ionic conductivity of poly(ionic liquids) (PILs) through the molecular design of copolymer architectures or topologies provides an opportunity to advance the limited understanding of polar-dipolar interactions and their role. In these studies, using the reversible addition-fragmentation chain transfer (RAFT) method, we copolymerized a series of imidazolium-based ionic monomers to form random or block copolymers with star and linear topologies and variable aliphatic side-chain lengths. Using an array of spectroscopic, thermal, and conductivity measurements, these studies show that block star PILs exhibit 2-3 orders of magnitude higher ionic conductivity compared to their random star counterparts. Given similar cation-anion content, the conductivity enhancement is attributed to multiple inter- and intrachain dipolar interactions, which facilitate greater mobility in the proximity of ionic domains. Variable-length alkyl side groups also empower the tunability of the frequency-dependent ionic conductivities in block and random or star and linear PILs. Tweaking ionic conductivity through dipolar moieties of copolymer topologies may enable numerous applications where soft synthetic and biologically conductive interfaces are advantageous.