Abstract
Broad-band dielectric relaxation spectroscopy has been used to examine molecular motions in a mainchain liquid crystalline copolyester BB-4*(2-Me)/BB-6 consisting of a biphenyldicarboxylic acid and equimolar mixture of chiral 2-methylbutanediol and hexanediol. From 60 to 140°C where molecules assume a chiral smectic C phase, BB-4* (2-Me)/BB-6 exhibits a Goldstone mode process whose relaxation strength rapidly decreases with increasing dc bias field. Combining dielectric relaxation time and strength allows estimate of interlayer rotational viscosity which is 10—100 times larger than that of low molecular weight liquid crystals reflecting methylene chains connecting smectic layers. Decreasing temperature leads to two additional processes, Vogel—Fulcher type and Arrhenius types. These processes are analogous to segmental and local mode motion characteristic of non-crystalline polymers. The former defines a Tg of 15°C. The coexistence of the Goldstone mode and segmental mode indicates that BB-4*(2-Me)/BB-6 possesses both orientational order forming liquid crystalline phases and disorder required to undergo glass transition.
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Furukawa, T., Uchinokura, O., Takahashi, Y. et al. Dielectric Relaxation and Molecular Motion in the Chiral Main-Chain Liquid Crystalline Copolyester, BB-4*(2-Me)/BB-6. Polym J 32, 122–126 (2000). https://doi.org/10.1295/polymj.32.122
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DOI: https://doi.org/10.1295/polymj.32.122