Dielectric relaxation and molecular motion in the chiral main-chain liquidcrystalline copolyester, BB-4*(2-Me)/BB-6

Broad-band dielectric relaxation spectroscopy has been used to examine mole cular motions in a main-chain liquid crystalline copolyester BB-4*(2-Me)/BB -6 consisting of a biphenyldicarboxylic acid and equimolar mixture of chira l 2-methylbutanediol and hexanediol. From 60 to 140 degrees C where molecul es assume a chiral smectic C phase, BB-4* (2-Me)/BB-6 exhibits a Goldstone mode process whose relaxation strength rapidly decreases with increasing de bias field. Combining dielectric relaxation time and strength allows estim ate of interlayer rotational viscosity which is 10-100 times larger than th at of low molecular weight liquid crystals reflecting methylene chains conn ecting smectic layers. Decreasing temperature leads to two additional proce sses, Vogel-Fulcher type and Arrhenius types. These processes are analogous to segmental and local mode motion characteristic of non-crystalline polym ers. The former defines a T-g of 15 degrees C. The coexistence of the Golds tone mode and segmental mode indicates that BB-4*(2-Me)/BB-6 possesses both orientational order forming liquid crystalline phases and disorder require d to undergo glass transition.