Effect of Poly(ethylene glycol) Crystallization onIonic Conduction and Dielectric Response of Imidazolium-Based CopolyesterIonomers

A molecular-level understanding of ion and polymer dynamics in imidazolium–poly(ethylene glycol) (PEG) copolyester ionomers having different counteranions [PF6– vs (CF3SO2)2N–], alkylene spacer lengths [(CH2)6 vs (CH2)11], and PEG segment lengths [(CH2CH2O)22 vs (CH2CH2O)44] is investigated for the development of fast single-ion conducting materials, using dielectric relaxation spectroscopy and X-ray scattering. The variations of the counteranion size and PEG segment length lead to substantial changes in simultaneously conducting counteranion content (p), their mobility (μ), ion (α2), and segmental (α) relaxations, with consequences for ion transport. However, there is no significant influence of the alkylene spacer length on the counteranion conductivity (σDC). Imidazolium–PEG copolyester ionomers with larger (CF3SO2)2N– (= Tf2N) counterions show higher p with lower activation energy and higher μ with lower Vogel temperature as well as fast α2 and α motions with lower glass transition temperature, result...