Structures and properties of liquid-crystalline polymers based on laterally attached oligo p-phenylenes
The structures and proper-ties of liquid-crystalline polymers containing laterally attached p-terphenyl and p-pentaphenyl have been studied. In contrast to their mesogenic groups, that is, p-terphenyl and p-pentaphenyl, the polymers have much lower crystallinity and also lower nematic-to-isotropic transition temperatures. The significant depression in crystallinity can be attributed to flexible chain segments laterally attached to the oligo p-phenylene rods, which prevent close packing of the rods and thus disrupt the crystallization. The destabilization of the liquid-crystalline phase is due to the diluting effect of the flexible polymer backbones; that is, the concentration of the mesogenic groups is reduced. The polymer containing p-pentaphenyl can still exhibit good solubility in common solvents and emit light at about 402 nm in the solvent tetrahydrofuran. In the solid state, the emission redshifts to 418 nm, which is fairly close to the blue-light emission. An interdigitated packing structure of mesogenic groups has been proposed to represent the structure of the polymer in the oriented state. (c) 2005 Wiley Periodicals, Inc.