Polymer electrolytes based on a ternary miscible blend of poly(ethylene oxide), poly(bisphenol A-co-epichlorohydrin) and poly(vinyl ethyl ether)

Abstract

Ternary blends of poly(ethylene oxide) (PEO), poly(bisphenol A-co-epichlorohydrin) (PBE) and poly(vinyl ethyl ether) (PVEE) were obtained as films and characterized by differential scanning calorimetry (DSC) and vibrational spectroscopy (FTIR). From the DSC results, phase diagrams for the ternary blends were determined, where the variation of the viscoelastic phase extent as a function of the polymers composition was determined. The DSC results also indicated miscibility of the system, exhibiting only one glass transition temperature (Tg) and decrease in the crystallinity of the system, as well as decrease in the crystallinity of PEO present in the blends. Vibrational spectroscopy (FTIR) provided information on the intermolecular interactions between the pairs PBE/PEO and PBE/PVEE, via hydrogen bond interaction. From the FTIR analyses, molecular model systems of equilibrium among the interacting structures were proposed as a molecular basis for the miscibility of the system.Polymer electrolytes based on the ternary blend containing 60/25/15 (PEO/PBE/PVEE) mass percent and lithium perchlorate (LiClO4) were obtained and characterized by DSC, FTIR, optical microscopy and electrochemical impedance spectroscopy (EIS). Solid electrolytes containing up to 10 wt% LiClO4 exhibited a single-phase behavior, evidenced by the DSC results. For these electrolytes, FTIR spectra indicated the formation of polymer–ion complexes, in which the cation (Li+) acts favoring the polymer–polymer miscibility. Electrolytes containing LiClO4 higher than 10 wt% exhibit a multiple phase behavior, in which a PEO-rich, salt-containing phase is present in equilibrium with PBE or PVEE-rich phases. Maximum ionic conductivity at room temperature, for the electrolyte containing 20 wt% LiClO4, reached 4.23 × 10−3 Ω−1 cm−1, while all samples exhibited conductivity of approximately 10−1 Ω−1 cm−1 at 80 °C.