Synthesis and characterization of a thermotropic liquid‐crystalline poly[2,5‐bis(4′‐alkoxycarbonylphenyl) styrene].

We report the synthesis and characterization of a series of novel mesogen‐jacketed liquid‐crystalline polymers, poly[2,5‐bis(4′‐alkoxycarbonylphenyl)styrene]s (1‐m, where m is the number of carbon atoms in the alkyl tails), along with the corresponding monomers, 2,5‐bis(4′‐alkoxycarbonylphenyl)styrenes (2‐m), and their precursors, 2,5‐bis(4′‐alkoxycarbonylphenyl)toluenes (3‐m). The influence of the tail length on the thermotropic properties of the two types of low‐molecular‐mass compounds and macromolecules was investigated with a combination of differential scanning calorimetry, polarized optical microscopy, and wide‐angle X‐ray diffraction techniques. Except for compound 3‐3, which exhibited a monotropic nematic phase, all members of the low‐molar‐mass molecules developed no mesophase during both heating and cooling processes. The glass‐transition temperatures of the polymers decreased as the tail lengths increased. The 5% weight loss temperatures of all the polymers under a nitrogen atmosphere were above 360 °C, indicating quite high thermal stability. Although polymers 1‐1 and 1‐2 were non‐liquid‐crystalline, columnar nematic phases were observed for the remaining homopolymers with longer alkyl tails. The mesophases of 1‐3 to 1‐9 that developed at high temperatures remained upon cooling to room temperature, whereas those of 1‐10 to 1‐12 disappeared during the cooling process. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 830–847, 2007. [ABSTRACT FROM AUTHOR]