CONSTITUTIONAL ISOMERIC EFFECT ON THE DIELECTRIC-RELAXATION OF A NEMATIC LIQUID-CRYSTALLINE POLYMETHACRYLATE CONTAINING A METHOXYMETHYLSTILBENE SIDE-GROUP

Broad band frequency (0.1 Hz-10 MHz) dielectric relaxation spectroscop y has been utilized to investigate nematic liquid crystalline polymeth acrylates containing a constitutional isomeric methoxy-methylstilbene mesogen in the side chain (4-6-PMA and 4'-6-PMA). While 4-6-PMA shows two typical relaxation processes in a side-chain liquid crystalline po lymer system, 4'-6-PMA essentially has one relaxation process. The tem perature-dependent relaxation times, obtained through Havriliak-Negami data fitting, show ''kinks'' near calorimetric nematic-isotropic tran sition and a non-Arrhenius characteristic toward the glass transition. The glass behavior has been fitted with a Vogel-Fulcher-Tammann-Hesse (VFTH) equation and a general formula for activation energy has been derived in terms of VFTH parameters.