Abstract
The liquid crystalline properties and optical anisotropy of poly(diphenylacetylene) bearing an n-octadecylsilane moiety in the side chain, poly(1-phenyl-2-p-{dimethyl-n-octadecylsilylphenyl}acetylene) (C18-PDPA), were investigated in detail. C18-PDPA exhibited unexpected smectic phase liquid crystallinity in highly concentrated aromatic organic solvents such as toluene, despite its extremely high molecular weight of 4.18 × 106 g/mol and a fairly wide polydispersity index of 2.5. This lyotropic liquid crystallinity was derived from: a high molecular stiffness (expected from the high viscosity index of α ≈ 1.03), a high degree of intermolecular packing (the fractional free volume ≈ 0.16), and ultrahigh molecular weight. The two major absorption bands, located at 430 and 370 nm, are attributed to the π−π* transition parallel to the main chain and the localized π−π* transition with a charge-transfer characteristic among mesogenic repeating units perpendicular to the main chain axis, respectively. C18-PDPA ex...
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