An X-ray Investigation of Terminally Cyano-substituted Side Chain Liquid Crystalline Polysiloxanes

Abstract

X-ray diffraction results are reported for a number of cyano substituted side chain liquid crystal polymers with polysiloxane backbones. The d-spacing of the smectic layer increases linearly with increasing length of the aliphatic spacer and, for each compound, shows a steady decrease with increasing temperature. The variation of intensity of the smectic layer reflection with temperature indicates that the length of the flexible aliphatic spacers linking the mesogenic units to the polymer determines the ease with which liquid crystalline order is obtained. The smectic order increases steadily with temperature for short spacers whereas the orientational freedom conferred by the longer spacers reduces the temperature dependence. The structural parameters, obtained from the X-ray studies, arc compared with repeat distances obtained from molecular models involving either interdigitation or tilting of the mesogenic units.