Mixed-Polarity Copolymers Based on Ethylene Oxide and Cyclic Carbonate: Insights into Li-Ion Solvation and Conductivity

This study investigates the relationship between polarityand ionicconductivity in random and block copolymer electrolytes comprisinghighly flexible oligo-(ethylene oxide) methyl ether methacrylate (OEM)and highly polar but glassy glycerol carbonate methacrylate (GCMA)monomers, blended with either lithium bis-(trifluoromethanesulfonyl)-imide(LiTFSI) or lithium triflate. Interestingly, the high polarity ofGCMA did not significantly enhance ionic dissociation, and the randomcopolymers (POEM-r-PGCMA) showed similar or lowerionic conductivities than the POEM homopolymer. Further analysis revealedthat Li+ only interacts with OEM and its counterion, notwith GCMA. The less-intermixed and weakly phase-separated block copolymer(POEM-b-PGCMA) exhibited even lower conductivitiesthan the random copolymer. Our results suggest that Li+ solvation occurs only in the POEM-rich phase and that the largerPGCMA regions, depleted of Li+, disrupt long-range iontransport. These findings provide valuable insights into the designof polymer electrolytes and how segmental mobility and functionalgroups with contrasting polarities affect ion transport.