Synthesis and characterization of liquid-crystalline polyesters with chiral and achiral twin spacers

A series of novel thermotropic main-chain chiral liquid-crystalline random copolyesters consisting of spacers of two different types-chiral and achiral-was synthesized. Polyesters (BmTa) with tartaric acid as the chiral spacer (Ta), aliphatic diols (with 'm' = 2-10 methylene groups) as the achiral spacers, and 4,4 ' -dihydroxy biphenyl (B) as the mesogen were synthesized via condensation polymerization in solution after duly protecting the 2,3-dihydroxy groups of tartaric acid by acetylation. The copolymers were characterized by Fourier transform infrared spectroscopy, H-1 and C-13 NMR spectral gel permeation chromatography, and thermogravimetric analysis. Transition temperatures for phase changes recorded by DSC were corroborated with the textures observed by a hot-stage optical polarizing microscope. The wide-angle X-ray diffraction (WAXD) profiles indicated a SmE phase at room temperature. The lower angle region at 2 theta = 0.5-2.45 covered by WAXD indicated a layer of thickness of 161 Angstrom, less than the molecular length for BOTa. The [alpha (D)] values were recorded on a digital polarimeter. The birefringence was lost at higher mesophase temperatures in lower members with m < 5, a behavior found in certain chiral systems, and the higher members with m > 5 showed a lesser number of phase transitions. On cooling, the polyesters produced a texture with the formation of transition bars. (C) 2001 John Wiley & Sons, Inc.