Abstract
In this work, blends of Poly(ethylene oxide), PEO, and poly(1,6-hexanediol), PHD, were prepared in a wide composition range. They were examined by Differential Scanning Calorimetry (DSC), Polarized Light Optical Microscopy (PLOM) and Wide Angle X-ray Scattering (WAXS). Based on the results obtained, the blends were partially miscible in the melt and their crystallization was a function of miscibility and composition. Crystallization triggered phase separation. In blends with higher PEO contents both phases were able to crystallize due to the limited miscibility in this composition range. On the other hand, the blends with higher PHD contents display higher miscibility and therefore, only the PHD phase could crystallize in them. A nucleation effect of the PHD phase on the PEO phase was detected, probably caused by a transference of impurities mechanism. Since PEO is widely used as electrolyte in lithium batteries, the PEO/PHD blends were studied with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI), and the effect of Li-salt concentration was studied. We found that the lithium salt preferentially dissolves in the PEO phase without significantly affecting the PHD component. While the Li-salt reduced the spherulite growth rate of the PEO phase within the blends, the overall crystallization rate was enhanced because of the strong nucleating effect of the PHD component. The ionic conductivity was also determined for the blends with Li-salt. At high temperatures (>70 °C), the conductivity is in the order of ~10−3 S cm−1, and as the temperature decreases, the crystallization of PHD was detected. This improved the self-standing character of the blend films at high temperatures as compared to the one of neat PEO.
Highlights
Aliphatic polyethers are a broad class of polymers, nowadays used in a wide range of fields [1]
polyethylene oxide (PEO)/PHD blends were studied in the whole composition range to explore their miscibility and crystallization behavior
Blends of PEO and PHD were prepared by a solvent evaporation method
Summary
Aliphatic polyethers are a broad class of polymers, nowadays used in a wide range of fields [1]. Their industrial applications are limited to short-chain aliphatic polyethers. A sustainable route for the synthesis of medium- to long-chain aliphatic polyethers has been reported [5]. This synthetic method open the possibility of tuning the length of the aliphatic chain of polyethers, preparing different copolymers and fine tuning of their Tm and crystallinity [5,6,7]. Polyethylene oxide (PEO) stands out as the main host polymer for polymer electrolytes, due to its excellent capability to dissolve lithium salts, and because it exhibits high ionic conductivity values at relative high temperatures (>70 ◦ C) [9,10,11]
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