Blends of poly(p-oxybenzoate-co-p-phenylene isophthalate) and polycarbonate: Miscibility and free volume behaviors

Blends of a thermotropic liquid crystalline polymer [poly(p-oxybenzoate-co- p-phenylene isophthalate)] (HIQ45) and a polycarbonate (PC) are studied wit h regard to their miscibility and free volume behavior. The glass transitio n temperatures (T(g)s) of the blends are found to be uncharacteristically h igher than those of the pure components, even increasing with the addition of the low-T-g component, HIQ45. Based on the non-appearance of the T-g of HIQ45 in the tan delta spectra of the blends and the observed homogeneous m orphology of the blend, mixtures of HIQ45 and PC are concluded to be a misc ible blend system. The free volume properties determined by positron annihi lation lifetime spectroscopy show that close packing does not occur in thes e miscible blends as indicated by positive deviations in site and number co ncentration of free volume cavities from average values as a function of bl end composition. The increase in free volume is attributed to the loss of l iquid crystalline alignment of HIQ45 and disturbed packing of PC molecules due to intimate miscibility between different molecules. The free volume fr action index of the blend correlates well with measured blend density.