CHIRAL LIQUID-CRYSTAL POLYMERS .10. THERMOTROPIC MESOMORPHISM IN CHIRAL ISOMERIC POLYESTERS

A series of four samples of chiral thermotropic polyesters 1-4 based on smectogenic 4,4’-(terephthaloyldioxy)dibenzoic (HTH) acid and the three optically active isomers of dipropylene glycol (DPG) and a commercially available mixture of the three racemic isomers was prepared. The thermotropic mesomorphism of the polymer samples was investigated with reference to the isomeric structure of the chiral spacer segment incorporated into the polyester backbone. The four polyesters display strikingly different thermal responses. The relative topology of the two methyl substituents, and hence of the two chiral centers, within the flexible segments, is effective in defining the onset, stability, and nature of the mesophases. The evolutions of the structures of the mesophases were followed as a function of temperature, and the occurrence of polymorphic sequences is proposed, which involve ordered smectic, disordered smectic, and nematic (or cholesteric) mesophases. © 1990, American Chemical Society. All rights reserved.