A DEUTERIUM NMR INVESTIGATION OF POLYMORPHISM IN BENZENE PIZZANES

The polymorphism of three members of the homologous series hexa(p-alko xyphenoxymethyl) benzene (benzene pizzanes) with 5, 6 and 7 carbons in the alkoxy chains and several of their deuteriated isotopomers have b een investigated by differential scanning calorimetry, polarizing opti cal microscopy, X-ray diffraction and deuterium NMR spectroscopy. Thes e homologues exhibit several solid phases and a high temperature M pha se, which is isomorphic in the three homologues and whose nature is di scussed. In the solid phases, the benzene cores of the molecules remai n rigid, but the side chains are mobile, as reflected by rapid pi-flip s of the benzene rings in the side chains. It is found that there are two types of such benzene rings, differing in the rates of flips. In t he M phase the molecules undergo fast overall reorientation and the si de chains are even more disordered than in the solid phases. However t he X-ray measurements do not provide a clear cut determination as to w hether this phase is crystalline or mesomorphic. Mixing of the benzene pizzanes with p-xylene yields lyomesophases, which appear to belong t o the D-ho class.