Ion transport in helical-helical polypeptide polymerized ionic liquid block copolymers

Helical-helical polypeptide polymerized ionic liquid block copolymers (PPIL BCPs) were designed to investigate the role of helical secondary structure on self-assembly and ionic conductivity. PPIL BCPs, consisting of a cationic polypeptide (PTPLG) with varying lengths and a neutral poly-(γ-benzyl-_L-glutamate) (PBLG) block with fixed length, exhibited stable helical conformations over a broad temperature range, and less than 5 K variation in glass transition (T_g) with composition. X-ray scattering confirmed microphase separation, and morphological evolution of PBLG-b-PTPLG films revealed a transition from poorly ordered to highly ordered lamellar (LAM) structures as PIL composition increased. The highest PIL content BCP formed a highly ordered bilayer LAM structure with close-packed helices and a 1.5 order of magnitude higher ionic conductivity after normalization by T_g and volume fraction. The morphology factor (f), which is 2/3 for ideal lamellae, was f > 0.8 compared to less ordered PPIL BCPs with f < 0.05. These results highlight the critical role of ordered nanoscale ionic domain, connectivity, confinement and helical structure in enhancing ion transport. This innovative approach of incorporating helical peptide structures into BCP electrolytes provides new insights into the relationship between helical conformation, self-assembly and ionic conductivity, offering a promising avenue for developing high-performance solid electrolytes.