X-ray Photograhic Study of Some Cyano Biphenyl Sidechain Liquid Crystalline Polysiloxanes

Abstract

Abstract X-ray diffraction results are reported for a number of cyano substituted sidechain liquid crystal polymers with polysiloxane backbones. The structural parameters obtained from the X-ray studies are compared with repeat distances of models involving interdigitation of side chains. Where partial overlap occurred the d-spacing of the smectic layer decreased linearly with temperature; but for a mixed compound with complete overlap there was a small increase in d-spacing with temperature. Where a short flexible aliphatic spacer was used to link the mesogenic units to the polymer backbone, although there was also interdigitation, a different packing arrangement occurred from that normally observed when longer spacer units are present. Two diffuse equatorial maxima were observed in the diffraction patterns of all the samples, suggesting that these were columns consisting of groups of mesogenic units plus back-bone. One of the compounds had an additional diffuse axial reflection suggesting a six mesogenic unit periodicity along the backbone.