Conformational Analysis of Thermotropic Liquid Crystalline Polyesters

PCILO conformational calculations have been carried out on several model compounds of thermotropic liquid crystalline polyesters —OC—φ—φ—φ—CO—Os—R—O—] where R = (—CH₂—)₂; (—CHCH₃—)₂; (—CHCH₃—CH₂—). Several conformations corresponding to the trans and gauche states of the C-C single bonds are preferred, the TGT form being of lower energy than the TTT form. The replacement of—CH₂—group by—CH(CH₃) group results in a decrease of the number of the energy minima, an increase in the energy of the molecule in all the preferred conformations, compared to that of the TGT form, a sharpening of the potential energy wells and an increase in the energy barriers. The presence of a methyl group also shifts the aliphatic chain away from the ideal trans and gauche positions.