Synthesis of Vinylidene Fluoride-Based Copolymers Bearing Perfluorinated Ether Pendant Groups and Their Application in Gel Polymer Electrolytes

Vinylidene fluoride (VDF)-based copolymers bearing pendant perfluoroalkyl ether groups for potential application in gel polymer electrolytes were synthesized via conventional radical copolymerization of VDF with a 2-trifluoromethacrylate monomer bearing pendant perfluoroalkyl ether groups [2,3,3,3-tetrafluoro-2-[1,1,2,3,3,3-hexafluoro-2-(perfluoropropoxy)propoxy]propyl 2-(trifluoromethyl)acrylate (MAF-PFE)]. Two kinds of initiators (hydrogenated and a perfluorinated highly branched persistent radical that released CF3• radical from 80 °C) were used. Molar masses ranged between 35 000 and ca. 50 000 g·mol–1. The synthesized poly(VDF-co-MAF-PFE) copolymers were evaluated in gel polymer electrolytes based on ionic liquids. With this aim, the poly(VDF-co-MAF-PFE) copolymers were mixed with lithium bis(trifluoromethanesulfonyl)imide and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Homogeneous gels with conductivity values at room temperature reaching up to 3 × 10–3 S·cm–1 were obtained, while the transference number of lithium ions was 0.12 at 40 °C. Finally, such electrolytes displayed an electrochemical stability window between 1.5 and 4.4 V as determined by cyclic voltamperometry measurements.