THERMOTROPIC HYDROCARBON SIDE-CHAIN LIQUID-CRYSTALLINE POLYMERS .3. CHARACTERIZATION OF LIQUID-CRYSTALLINE PHASES

A series of seven new hydrocarbon polymers with biphenyl mesogens have been characterized via differential scanning calorimetry (DSC), X-ray diffraction of fibers and powders, and polarizedlight optical microscopy (POM). The polymers consist of a biphenyl mesogen attached to a polyethylene backbone via four- or six-carbon alkylene spacer groups with H, ethyl, or n-butyl terminal groups or tails. The polymers without tails were not liquid crystalline, and the polymers with tails were liquid crystalline. The liquid-crystalline polymers displayed smectic E and smectic B phases. The new liquid-crystalline polymers are more closely related to long side-chain poly(l-alkene)s than to more traditional poly(siloxane) and poly(acrylate) side-chain liquid-crystalline polymers. Four-carbon tails were more effective than two-carbon tails for stabilizing the mesophase. The ability of the tail to stabilize the mesophase closely parallels the effect of the tails for monomers and model compounds. The tail apparently increases the effective axial ratio of the mesogen, resulting in liquid-crystalline behavior. © 1990, American Chemical Society. All rights reserved.