Mesomorphic phases of main‐chain liquid‐crystalline polymers with pendent sulfonic acid groups

Abstract

AbstractSome main‐chain liquid‐crystalline polymers were synthesized with pendent sulfonic acid groups (0–6 wt %) on the polymer backbone. The solution viscosity behavior, the chemical structures, and the liquid‐crystalline (LC) properties were characterized with Fourier transform infrared spectroscopy, elemental analysis, 1H‐NMR, differential scanning calorimetry, polarizing optical microscopy, and X‐ray measurements. All the polymers displayed a smectic mesophase with a mesogenic range of 142–155°C and good thermal stability. With an increasing concentration of sulfonic acid groups in the polymer systems, some of the polymers exhibited two kinds of mesophases, including smectic and nematic phases. The glass‐transition temperatures and isotropic‐transition temperature were elevated slightly, whereas the temperature of the smectic–nematic phase transition changed a little. For polymers with a few sulfonated benzene groups, the regular mesogen/soft matrix structures led to a smectic structure because of microdomains between the mesogenic moieties and the soft main‐chain matrix, whereas for polymers with an increased number of sulfonic groups, the ionic groups were distributed in both the soft matrix and the LC microphase. Although the increased ionic interactions between mesogens led to more crystalline phases, the strong electrostatic interactions in the ionic group/mesogen/soft matrix systems may have been tangled in domains. Therefore, they disturbed the regular mesogen/soft matrix smectic phase structure, leading to the appearance of a smectic–nematic transition. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008