Thermal Properties and Morphology of Poly(ethylene oxide)/Poly(n-butyl methacrylate) Blends

From the thermodynamic point of view, most of the high molar-mass binary polymer blends are immiscible due to the entropic contribution to the free energy of mixing is relatively small. The miscibility of the systems on the molecular scale can be assessed by the thermal properties such as quantities of glass transition temperature (T-g) and change in heat capacity (Delta C-p) of the polymers. For a semi-crystalline polymer such as poly(ethylene oxide) (PEO), the crystallinity (X*) and the melting temperature (T-m) can also give some hints on the miscibility. Apart from the thermal properties, additional scientific findings such as morphology of the blends are needed as supplementary evidences to support the results. We focus on the PEO as the polymer host, blends with poly(n-butyl methacrylate) (PnBMA) which were prepared using solution casting technique. Thermal properties of PEO/PnBMA polymer blends were investigated by modulated differential scanning calorimeter (MDSC) on the isothermal crystallized samples at 25 degrees C. T-g of PEO in the blends do not show significant variation with addition of PnBMA for entire composition range while for T-g of PnBMA in the blends, it is challenging to be estimated under the experimental condition due to the overlapping of the T-g of PnBMA and melting endotherm of PEO. Constancy of quantity T-g of PEO and Delta C-p of PEO corresponding to the content of PEO in the blends suggest that PEO and PnBMA are immiscible for entire blend composition. X* and T-m of PEO in the blends show insignificant variation in PEO/PnBMA blends, when PEO as major component. This implies that these blends are immiscible under the experimental conditions as agreed with results of T-g and Delta C-p. Spherulitic morphologies of PEO in the blends were studied by polarized optical microscopy (POM). PnBMA phase disperses randomly in PEO matrix when PEO in excess. The absence of significant change for the fibrillar spherulitic structures of PEO spherulites with addition of PnBMA (when PEO is the major component) suggests that immiscibility of PEO and PnBMA. Besides, the crystalline structure of PEO in PEO/PnBMA blends using X-ray diffraction (XRD) reveals that the crystalline structure of PEO is not disturbed with the addition of PnBMA when PEO is in excess as the two distinct peaks of PEO do not shift as compared to neat PEO. Impedance spectroscopy (IS) studies show that the ionic conductivities (sigma(DC)) of the polymer blends at room temperature slightly increase with increasing of PEO with the order of magnitude of 10(-11)-10(-10) S cm(-1). This system serves as a potential polymer host as solid polymer electrolytes when added with inorganic salt.