Thesis (M.Eng.)--Chulalongkorn University, 1997

The phase diagrams of the blend systems of polystyrene (PS) and poly (bisphenol-A-carbonate) (PC) with two low molar mass liquid crystals in phenyl-cychohexylbenzoates group (HP35 and HP5N) at low concentration range of low molar liquid crystal are studied in this work. Four different systems are: 1) blend of PS with HP35, 2) blend of PS with HP5N, 3) blend of PC with HP35, and 4) blend of PC with HP5N. The blends were prepared by solvent casting and their transition temperatures were measured at various annealed temperatures by differential scanning calorimeter (DSC). The standard procedure to study the phase diagrams of the blends of which only the glass transition temperature (Tg) of PS or PC rich phase in the blends can detected, was developed in this work. Scanning electron microscope (SEM) pictures were used to confirm the phase behaviour in the constructed phase diagrams. The phase behaviour determined from the DSC results was consistent with the micrographs from SEM. It was found that the phase diagram of PS blended with HP35 is likely to show the upper critical solutions temperature (UCST) behaviour. The phase diagram of PS blended with HP5N is partially miscible under 5.0 percent by weight of HP5N with PS. The phase diagram of PC blended with HP35 seems to be an hourglass-shaped phase boundary. The phase diagram of PC blended with HP5N seems to be an immiscible loop type. It was also found that by the decreasing in the Tg of PS and PC.