Fluorinated Poly(ionic liquid) Diblock Copolymers Obtained by Cobalt-Mediated Radical Polymerization-Induced Self-Assembly

Abstract

Poly(ionic liquid)s (PILs) have attracted considerable attention as innovative single-ion solid polyelectrolytes (SPEs) in substitution to the more conventional electrolytes for a variety of electrochemical devices. Herein, we report the precise synthesis, characterization, and use as single-ion SPEs of a novel double PIL-based amphiphilic diblock copolymer (BCP), i.e., where all monomer units are of <i>N</i>-vinyl-imidazolium type, with triethylene glycol pendant groups in the first block and a statistical distribution of <i>N</i>-vinyl-3-ethyl- and <i>N</i>-vinyl-3-perfluorooctyl-imidazolium bromides in the second block. BCP synthesis is achieved directly in water by a one-pot process, by cobalt-mediated radical polymerization-induced self-assembly (CMR-PISA). A subsequent anion exchange reaction substituting bis(trifluoromethylsulfonyl)imide (Tf₂N^-) for bromide (Br^-) counter-anions leads to PIL BCPs with two different lengths of the first block. They demonstrate ionic conductivity σ_DC = 1-3 × 10^-7 S cm^-1, as determined by broadband dielectric spectroscopy at 30 °C (under anhydrous conditions), and exhibit wide electrochemical stability (up to 4.8 V versus Li⁺/Li) and form free-standing films with mechanical properties suited for SPE applications (Young's modulus = 3.8 MPa, elongation at break of 250%) as determined by stress/strain experiments.