CONSTITUTIONAL ISOMERIC EFFECT ON THE DIELECTRIC-RELAXATION OF A NEMATIC LIQUID-CRYSTALLINE POLYMETHACRYLATE CONTAINING A METHOXYMETHYLSTILBENE SIDE-GROUP
Zz. Zhong et al., CONSTITUTIONAL ISOMERIC EFFECT ON THE DIELECTRIC-RELAXATION OF A NEMATIC LIQUID-CRYSTALLINE POLYMETHACRYLATE CONTAINING A METHOXYMETHYLSTILBENE SIDE-GROUP, Macromolecules, 26(24), 1993, pp. 6403-6409
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.