Thin films of poly (ethylene oxide) (PEO), poly (methyl methacrylate) (PMMA) and selected blends of PEO/PMMA with and without the addition of LiClO4 were prepared using solution casting technique. The presence of a single Tg which corresponds closely to that of the Gordon Taylor equation confirms the miscibility of both the salt-free and salt-doped blends. The Tgs and the ion conductivity (σ) at room temperature of PEO, PMMA and the PEO/PMMA blends generally increase with ascending salt concentration (Y). Variations in the σ value as a function of Y for all the three systems correlate closely with their respective Tg results. PMMA-salt complex records the lowest σ value at all salt concentrations. PEO/PMMA/LiClO4 blend with 75 wt% PEO exhibits the highest σ value of 5 x 10-7 S cm-1 at Y = 0.10. The σ value of the blend-salt system is observed to be slightly lower than that of the PEO-salt system. This is due to reduced segmental motion cause by increased Tg of the blend and a decrease in free ions in the amorphous phase of PEO as a small amount of the salt is solvated by PMMA in the blend. Therefore, the percolation path lies in the amorphous PEO rich phase of the blend.

Summary: In this study, thermal properties and ion-polymer interactions of lithium perchlorate (LiClO 4 ) in poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blend prepared by solution casting technique were elucidated. The spectroscopic studies of the salt-free and salt-doped PEO/PMMA blends were investigated using x-ray diffraction (XRD) and Fourier transform infra-red (FTIR), respectively. XRD study reveals that the crystalline structure of PEO is slight change when PMMA is blended to PEO. The thermal behaviour of PEO, PMMA and their blends with and without LiClO 4 was investigated by differential scanning calorimetry (DSC). The presence of a single and composition dependent glass transition temperature (T g ) reflects the miscibility of the salt-free PEO/PMMA blends in the molten state. The T g s of PEO, PMMA and the blends generally increase with ascending mass fraction of salt (W S ). However, PEO/PMMA 50/50 blend with W S ! 0.091 shows phase separation between the two polymers. The melting temperature (T m ) and crystallinity (X Ã ) of PEO are suppressed when blended with PMMA, thus, confirm the miscibility of the salt-free PEO/PMMA blends in the molten state. Presence of LiClO 4 to PEO, PMMA and their blends does not influences the X Ã of PEO. Investigation by FTIR does not show any specific interaction between PEO and PMMA for the salt-free blends whereas for the salt-doped blends, Li þ ions are observed to coordinate with the oxygen atom of both the PEO ether and the PMMA carboxyl groups. Impedance spectroscopy study demonstrates that the LiClO 4 -doped PEO/PMMA 75/25 blend has lower ion conductivity than that of the PEO þ LiClO 4 system but recorded enhanced conductivity as compared to PMMA þ LiClO 4 systems at W S ¼ 0.091.