Chiral Liquid Crystal Polymers. 5. Synthesis and Characterization of Thermotropic Polyesters of 3-O-alkylated Glycerols

Chiral liquid crystal polymers. 6. Preparation and properties in solution and in bulk of optically active thermotropic copolyesters

“…The unwinding of the helical array is in contrast to the trend commonly recorded with low molar mass cholesterics38 and with analogous homobipolyesters of HTH residue and optically active alkyl glycerol spacers. 4 An extension of the helical pitch with increasing temperature has been observed in thermotropic (hydroxypropyl)cellulose acetate39 and copolypeptides40 and lyo- tropic poly(7-benzyl L-glutamate).41,42 Such an anomalous behavior may be explained by assuming the occurrence of conformers originated by free rotation along the polymer backbone axis, as sufficiently enhanced by the introduction of small amounts of nonlinear units, which in turn would be able to reduce the anisotropy in the intermolecular potential.43…”

“…Furthermore, it has been established that the use of chiral flexible segments in the side chains of bipolyesters with different lengths and different enantiomeric compositions can be of value in modulating the incidence, nature, and interval of existence of thermotropic mesophases. 4 Indeed, in mesomorphic bipolyesters of (S)-l,2-propanediol [(S)-PG] the simple replacement of a hydrogen atom in the pendant methyl group by flexible alkoxy chains leads to a marked drop (>100 °C) of both melting and clearing temperatures, accompanied by improved solubility properties in conventional organic solvents.…”