Ferroelectric nematic phases formed from polar rod-like polymers

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The aromatic polyesters composed of hydroxy benzoic acid and hydroxy naphthoic acid were prepared with different fractions of two components and different degrees of polymerization, and their thermotropic liquid crystalline behavior and structures were examined. The most interesting fact obtained is that the polymers with the degree of polymerization more than 30-40 can form a novel nematic liquid crystals with polar ordering along the nematic director. The second harmoinc generation (SHG) profiles as a function of incident of SH polarizations are well simulated under the model of Cs symmetry with a mirror plane rotationally disordered about the molecular axis. This means that the polar nematic liquid crystal is biaxial in which the polarity exists along the c-director as well as n-director. Cs symmetry can be altered to C v by the introduction of meta-hydroxy benzoic acid. This can be well explained by the occurence of the kink structure which can extinct the polarity perpendicular to the chain axis.