HELICAL SENSE IN THERMOTROPIC LIQUID-CRYSTAL COPOLYMERS IN RELATION TO THE STRUCTURE OF A PENDANT CHIRAL MOIETY

Chiral nematic copolymers based on optically active cholesterol, dihydrocholesterol, and (R)- (+)- and (S)-(-)-l-phenylethylamine were synthesized and characterized for the investigations of thermotropic and optical properties. With cholesterol and dihydrocholesterol possessing largely the same absolute configurations and molecular sizes but opposite signs in specific optical rotation, they both give lefthanded helical structures. However, cholesterol shows a helical twisting power 80% higher than dihydrocholesterol in otherwise identical macromolecular structural settings. Although helical sense does not appear to correlate with the sign of [α]D of the precursor chiral compound as suggested by the observations of cholesteryl and dihydrocholesteryl copolymers, the inversion of chirality in the pendant group, (R)-(+)- vs (S)-(-)-l-phenylethylamine, does lead to the opposite handedness in the resultant helical structure. To better understand the structure-property relationships involving helical sense and twisting power, systematic studies of the roles played by both nematogenic and chiral structures as well as other structural features of the comonomers should be conducted. © 1990, American Chemical Society. All rights reserved.