ELECTROOPTICAL PROPERTIES OF LIQUID-CRYSTALLINE RIGID ROD-LIKE POLYMERS WITH NLO-ACTIVE SIDEGROUPS

The second order nonlinear susceptibility chi(2) of a novel class of p oled polymer films was investigated by means of the attenuated total r eflection (ATR) method. The polymers are composed of an aromatic polye ster backbone to which NLO active stilbene chromophores and flexible a lkyl side chains are alternately attached. The optical properties and the dynamics of relaxation of the poled state were strongly depending on the length of the aliphatic side chains. The relaxation determined at different temperatures above and below T(g) showed a temperature de pendence that differs from an Arrhenius type behaviour. An empirical e quation which relates the temperature dependence of the relaxation tim es to the glass transition temperature is presented. The polyester mai n chains could be macroscopically aligned in strong magnetic fields. E lectric poling of the samples with aligned main chains results in rati os of chi333(2)/X113(2) which deviate significantly from the ratio of 3 one obtains for samples with isotropically distributed main chains. This behaviour is explained by the solid state structure of this kind of polymer, which is best described by a sequence of alternating layer s of polyester backbones and flexible side chains.