Kerr effect in solutions of a thermotropically mesogenic alkylene-aromatic polyester

Abstract Electric birefringence (EB, Kerr effect) has been investigated for solutions of fractions of thermotropically liquid-crystalline alkylene-aromatic polyester (PE-10) and of its monomer. A very specific dependence of EB on the molecular weight ( M ) of the polymer was found: for low molecular weight substances the Kerr constant is negative, changes its sign with increasing M and, in the range of positive values, increases with M . These data are in quantitative agreement with the dependence of K on M predicted by the EB theory for kinetically rigid worm-like chains in which the longitudinal components of dipole moments of monomer units are “accumulated” with increasing chain length. The detected relationships show that in PE-10 solutions the Kerr effect is due to the large-scale chain motion in which the behaviour of a dipole molecule is similar to the motion of a kinetically rigid particle rotating as a whole by the action of the field.