Copolymers derived from polyepichlorohydrin (PECH), bearing pendant mesogenic units are obtained by chemical modification of atactic samples of PECH with sodium 4-cyano-4'-biphenoxide. Rate and yield of substitution are strongly dependent on the molecular weight of the used PECH. A substantial rise (AT -110 "C) of glass transition temperature with the percentage of incorporated cyanobiphenyl groups is observed. Copolymers with an amount of substitution higher than 60% present thermotropic liquid-crystalline behaviour and form nematic phases. Chemical modification of PECH offers a simple method for the synthesis of new liquid-crystalline polyethers whose transition temperatures can be adjusted by varying the amount of substitution. 0 1992, Hiithig & Wepf Verlag, Basel CCC 0025-1 16X/92/$05.00
Racemic and chiral [(4-cyano-4'-biphenyl)oxyl and [(4methoxy-4'-biphenyl~oxylmethyloxiranes were prepared from racemic epichlorohydrin or racemic and chiral glycidols and polymerized in dimethylsulfoxide (DMSO) with Bu'OK as the initiator system. Initial phase identifications were made by differential scanning calorimetry (DSC) and optical microscopy techniques and confirmed by X-ray diffraction measurements. Upon heating, all the monomers show only a crystal-isotropic phase transition. The racemic and chiral [(4-cyano-4'-bipheny1)oxylmethyloxiranes exhibit a nematic and a cholesteric monotropic phase, respectively. Methoxybiphenyl substituted polyethers are crystalline and insoluble in virtually all common solvents. Cyanobiphenyl substituted polyethers are soluble under the same experimental conditions and show enantiotropic liquid crystalline properties. The racemic polymer exhibits a nematic phase, while the optically active polymer forms a cholesteric phase.
The liquid crystalline behavior of a poly(organophosphazene) with two 2-(((4-n-butylphenyl)azo)phenoxy)ethoxy side chains per phosphorus atom has been investigated by differential scanning calorimetry, polarized optical microscopy, and X-ray diffraction. On cooling from the isotropic liquid (above 185 °C) a viscous mesophase is first observed which shows the characteristic focal conic texture typical of low molar massemectic A phases. As the temperature falls below 160-155 °C, a smectic C-like mesophase appears.In these structures, pairs of side chains decorate the backbone at ca. 2.45-A intervals, and this congestion can be relieved in the cis-trans (2i helix) conformation when the stacking periodicity becomes 4.9 A. In the smectic phases it is likely that the backbone disorders sufficiently to allow the mesogenic side groups to stack and, aided by the flexible spacer, allow the creation of layers perpendicular to the stacking direction. In the smectic A phase, the layer thickness is ca. 25.5 A, which implies a "bilayer" structure in which the side chains would overlap in an antiparallel interdigitated structure. The smectic A-smectic C transition involves expansion in the plane orthogonal to the polymer chains. The interpenetration of the side groups disappears but the side chains tilt down with respect to the normal to the layer planes to stack closer. Below 150-145 °C the sample crystallizes and in the oriented form can be indexed on an orthorhombic unit cell with a = 35.7 A, b = 17.85 A, and c (fiber axis) = 9.85 A. This doubling of the 4.9-A chain repeat has been reported for other polyphosphazene structures and can arise from alternating perturbations of the side chains or a change in the backbone conformation.
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