Search

A model is developed that describes the complicated rheology and morphology of thermoplastic polymers blended with relatively small amounts of liquid-crystalline polymers (LCPs). Such blends typically display properties superior to, but more complicated than, those of ordinary thermoplastic polymers. Viscosity predictions are obtained with this model that exhibit the wide range of behavior that is observed experimentally in these blended materials for both shear and elongational flows. For example, the viscosity-composition curve can display a minimum at low compositions of LCP, and the addition of an LCP to a thermoplastic polymer can result in a reduction in the shear viscosity but an increase in the elongational viscosity. Corresponding morphological descriptions are also obtained for the internal microstructure of the blends that provide information about the underlying causes of the complicated rheological behavior.

Several benzodiazepines were enantioresolved on a new carbohydrate chiral stationary phase based on maltooligosaccharides. The role of organic modifier, ionic strength, pH and temperature are examined and the results are discussed. In general, selectivity and retention were found to decrease with increasing organic modifier concentration. The appearance of two peaks for diazepam suggests that the reported separations are based on separation of conformers and was supported using circular dichroism detection. Counterintuitively, resolution and enantioselectivity were found to improve with increasing temperatures.

The retention behavior of polycyclic aromatic hydrocarbons (PAHs) in packed-column supercritical fluid chromatography (SFC) is studied for monomeric and polymeric C18 columns. Molecular shape discrimination (shape selectivity) is assessed through the use of Standard Reference Materials (SRMs), adn changes in selectivity are studied as a function of temperature, pressure, and mobile phase composition. Examples of separations of complex PAH isomer mixtures are presented, and guidelines are provided for modification and optimization of shape selectivity in SFC.