Chiro-optical properties of lyotropic ethyl cellulose derivatives

Novel derivatives of partially substituted ethyl cellulose (EC) were prepared and their chiro-optical properties studied as a function of degree of substitution. As had been previously reported for acetyl ethyl cellulose (AEC), the propanoate (PEC) and hexanoate (HEC) esters of EC undergo a degree of substitution dependant reversal of their chiral nematic (N*) helical twisting sense. The critical degree of substitution (DS*), above which this reversal of handedness takes place, was found to be considerably lower (DS* congruent to 0.1) for these derivatives than that for the reversal of handedness of AEC (DS* congruent to 0.18-0.21) lyotropic solutions in chloroform. This reversal of supramolecular twisting sense was not observed for the benzoate ester of EC (BEC), rather these derivatives enter the compensated nematic state at low degrees of substitution (DS > 1.0) but no reversal of handedness is observed at higher DS. (C) 2000 Elsevier Science Ltd. All rights reserved.