Thermotropic liquid crystalline comb-like polymers with polyacrylamide main chain. (2) Influence of the nature of the substituents of the biphenyl mesogenic core

Comb-like polymers with polyacrylamide main chains and three types of lipophilic biphenyl side chains have been synthesized and their thermotropic behaviour has been determined. All the polymers exhibit two smectic mesophases as a function of temperature, but the nature of the smectic mesophases is governed by the nature of the substituent R of the biphenyl core. For R = H, the polymers exhibit a double layer, ordered, tilted smectic Si2 and a double layer, disordered, tilted smectic Sc2. For R = CN, the polymers exhibit a double layer, disordered, tilted smectic Sc2 and a double layer, disordered, perpendicular smectic SA2. For R = O-CH2-CH(CH3)-C2H5, the polymers exhibit a double layer, ordered, tilted smectic Sf2 and a double layer, disordered, tilted smectic Sc2, these two structures being chiral when the substituent R is chiral. Comparison of the thermotropic behaviour of the polyacrylamide polymers with that of polymers with the same mesogenic cores but different main chains shows the high smectogenic power of the polyacrylamide skeleton.