INFRARED DICHROISM AND VIBRATIONAL SPECTROSCOPY OF A SIDE-CHAIN POLYACRYLATE LIQUID-CRYSTALLINE POLYMER

The infrared spectra of a polyacrylate side chain liquid crystalline polymer has been recorded and investigated as a function of temperature and the angle of polarisation of the IR incident beam. Variations in the absorbance and frequency are found to be governed by the phase transitions. The order parameter for various vibrational bands has been calculated from the infrared dichroism measurements. It is found that the liquid crystalline polymer alignment achieved by a surface treatment with polyvinyl-alcohol followed by rubbing of the windows does yield reasonable values of the order parameter. The order parameter for the alkyl chain is found to be only 15% of the maximum value; this shows a conformational disorder for the macromolecule in terms of the configuration of chains. Study of the vibrational frequency of bands with temperature shows a definite existence of the pretransition effects especially for SmA phase. Frequencies for most of the vibrational modes are seen to change abruptly at SmA-N and N-I transitions reflecting an alteration in the intermolecular interactions at the phase transitions.