Optical isotropic mesophase in side chain copolymers containing isophthalic acid groups

Random side chain copolymers, containing cyanobiphenyl mesogenic units and 37–58 mol % of isophthalic acid monomer units, possess an unusual ability to produce optically isotropic mesophases. This is demonstrated by the absence of birefringence and by high optical transparency of their films. At the same time, corresponding DSC curves show a well pronounced first order transition with a heat of fusion of 1.5–2.34 kJ mol−1. A key reason behind the formation of an optically isotropic mesophase is likely to be related to the microphase separation between side groups of the copolymers.