Miscibility and liquid crystal behaviour of p-azoxy anisole in polymer blends

The phase behaviour of two polymer/liquid crystal blends has been investigated by DSC and optical microscopy. In one case, blends of poly(octadecylethylene) (POE) and p-azoxyanisole (PAA) are found almost immiscible below the isotropization temperature of the liquid crystal. The crystallization process of PAA in the blends takes place with a sporadic growth of dendritic structures determined by the dispersion of the nematic phase in the molten polymer. In the other case, blends of poly(biphenylyloxyexylacrylate) (PBHA) and PAA display a different phase behaviour indicating partial miscibility of the two components at temperatures above the melting point of the polymer. At high concentrations of PAA a nematic phase dispersed in a isotropic liquid mixture of polymer and liquid crystal is observed. These results are accounted for by the different side-chain structure of the polymer components.