Liquid Crystal Transitions ofp-Sexiphenyl

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Abstract
Vorlander,1 studying the melting behavior of various polyphenyl compounds, reported that both p-quinquephenyl and p-sexiphenyl exhibited liquid crystalline behavior. Based on these early qualitative observations and subsequent melting point determinations,2 specific mesophase transitions were designated for each compound in the extensive compilations by Demus.3 Transformation temperatures for solid-to-nematic and nematic-to-isotropic states were assigned for p-quinquephenyl. On the other hand, two liquid crystal transitions, solid-to-smectic and smectic-to-nematic, were assigned to p-sexiphenyl. Since there is no direct evidence to confirm the nature of these phases and since the occurrence of a smectic transition for p-sexiphenyl is inconsistent with recent liquid crystal theory,4 we have reexamined the melting behavior of p-sexiphenyl with the aid of hot-stage polarized light microscopy and differential scanning calorimetry (DSC). The results provide definitive proof for the nature of the liquid crystalline states of p-sexiphenyl.

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