Ion conductivity studies of blends of poly(methyl methacrylate)-g-poly(ethylene glycol) and poly(ethylene glycol) complexed with $LiCF_3SO_3$

Abstract

New polymer electrolytes have been prepared by blending PMMA-g-PEG with PEG/$LiCF_3SO_3$ complexes. The ion conductivities of these polymer electrolyte systems were found to be greatly dependent on the graft degree of the PMMA-g-PEG. The increase in ion conductivities with increasing the graft degree is related to the improvement of compatibility between PMMA segments in PMMA-g-PEG and the added PEG due to the presence of side chain PEG. Tortuous pathway due to hard PMMA domain may be the principal cause of the decrease in ion conductivity for the samples with the lower graft degree. Therefore, as the graft degree increases, the blended system becomes compatible and ion-conducting pathway is less tortuous and consequently ion conductivities increase. The increase in ion conductivities with graft degree was offset by the intermolecular physical crosslinking of the hydroxyl end group of the PEG grafts through ion-dipole interaction with the cations. The molecular weight of the added PEG was also found to have a effect on the ion conductivities of PMMA-g-PEG/PEG/$LiCF_3SO_3$ blend systems : the ionic conductivities decreased with the increase in molecular weight of the added PEG at constant PEG composition. The molecular weight dependence is related to the degree of crystallinity of blended systems, which increases as the molecular weight of the added PEG increases. Another reason for the molecular weight dependence of ion conductivities is that the glass transition decrease with decrease in the molecular weight of the added PEG.