Complicated phase behavior and ionic conductivities of PVP-co-PMMA-based polymer electrolytes

Abstract

We have used DSC, FTIR spectroscopy, and ac impedance techniques to investigate the interactions that occur within complexes of poly(vinylpyrrolidone-co-methyl methacrylate) (PVP-co-PMMA) and lithium perchlorate (LiClO(4)) as well as these systems' phase behavior and ionic conductivities. The presence of MMA moieties in the PVP-co-PMMA random copolymer has an inert diluent effect that reduces the degree of self-association of the PVP molecules and causes a negative deviation in the glass transition temperature (T,). In the binary LiClO(4)/PVP blends, the presence of a small amount of LiClO(4) reduces the strong dipole-dipole interactions within PVP and leads to a lower T(g). Further addition of LiClO(4) increases T(g) as a result of ion-dipole interactions between LiClO(4) and PVP. In LiClO(4)/PVP-co-PMMA blend systems, for which the three individual systems-the PVP-co-PMMA copolymer and the LiClO(4)/PVP and LiClO(4)/PMMA blends-are miscible at all compositional ratios, a phase-separated loop exists at certain compositions due to a complicated series of interactions among the LiClO(4), PVP and PMMA units. The PMMA-rich component in the PVP-co-PMMA copolymer tends to be excluded, and this phenomenon results in phase separation. At a LiClO(4) content of 20 wt% salt, the maximum ionic conductivity occurred for a LiClO(4)/VP57 blend (i.e., 57 mol% VP units in the PVP-co-PMMA copolymer). (c) 2007 Elsevier Ltd. All rights reserved.