Anselm C. Griffin

Polymeric Liquid Crystals Structurally Related to 4-Alkoxyphenyl 4′-Alkoxybenzoates

Abstract A new series of thermotropic liquid crystalline polymers has been synthesized. These materials have incorporated a mesomorphic moiety, 4-alkoxyphenyl 4′-alkoxybenzoate, into the polymer ba...

Effect of Molecular Structure on Mesomorphism. 18.1 Twin Dimers Having Methylene, Ethylene Oxide and Siloxane Spacers

Abstract Six Twin dimeric compounds having two rigid cores connected by a central spacer group are described. Two types of rigid units, 4-pentyloxyphenyl cinnamates and 4-cyano-4-oxybiphenyl, were employed. The spacer groups were pentamethylene (PM), diethylene oxide (EO) and disiloxane (DS). For each rigid core the nematic-isotropic temperature followed the order PM > EO > DS. Investigation of the ΔH and ΔS parameters for the nematic-isotropic (clearing) transition revealed that for these compounds the clearing transition was driven by ΔS. The EO mesogens have larger ΔS values than for the PM mesogens, which result in lowered clearing temperatures due to relatively constant ΔH values. The conformational preference for gauche isomers in the spacer of the EO compounds is seen as conducive to proper orientational alignment of the rigid cores in the nematic phase, better so than for the PM and DS spacers.

Behavior of the Anchoring Strength Coefficient Near a Structural Transition at a Nematic Substrate Interface

Abstract A nearly symmetric alkoxyphenylbenzoate monomer is found to exhibit a transition from perpendicular to tilted alignment at a lecithin-treated glass substrate several degrees below the nematic-isotropic phase transition. By means of the Freedericksz transition the coefficient B of the anchoring energy has been obtained. It is found that B rapidly decreases, and the tilt susceptibility increases on approaching this transition.

Photochemical Crosslinking of Novel Polycinnamate Main Chain Mesogens

Abstract A prototype cinnamate based main chain liquid crystalline polymer was synthesized and characterized. Its photochemistry was studied in the form of a thin film. The polymer undergoes photochemical crosslinking. Major photoreactions are postulated as 2+2 cycloaddition and photo-Fries rearrangement.

Effect of Molecular Structure on Mesomorphism 8. l A New Series of Trifluoromethyl Liquid Crystals

Abstract A new series of trifluoromethyl liquid crystals, the 4-n-alkoxybenzylidene-4′-trifluoromethylanilines, has been synthesized. All members of the series with three carbons or more in the alkoxy chain are enantiotropic smectics. There is an odd:even effect in the smectic-isotropic transition temperatures. The smectic phase is of the B type. Members of this series strongly promote enhanced smectic A phases in many binary mesophase systems.

Mesogenic Polymers. 5. 1Thermotropic Polyamide Liquid Crystals and Analogous Small Molecule Diamides

Abstract The use of substituents (X # H) ortho to the amide nitrogen in both aromatic polyamides and analogous diamides renders these compounds to be enantiotropic mesogens by lowering the solid → mesophase temperature. At the molecular level this is understood as a reduction in interchain hydrogen bonding through either a steric blocking effect and/or through formation of intramolecular hydrogen bonds (when X = C1, OCH3). DSC, optical microscopy and infrared data are presented for the eight compounds reported.

Structure of a self-assembled hydrogen-bonded 'living' main chain liquid crystalline polymer

A main chain hydrogen-bonded liquid crystalline polymer was formed by melt mixing two complementary components, A and B, which in their individual states do not exhibit liquid crystallinity. The structure of the polymer and the thermal stability of its mesophase were studied using synchrotron radiation SAXS/WAXS/DSC at Daresbury (UK) and by variable temperature Fourier transform infrared. The chain extension, or polymerization process, was accelerated at the point when the polymer formed a liquid crystalline phase upon cooling from the isotropic melt. The polymer has an aabb chain structure and forms a smectic layer with a length of the A-B repeating unit. The hydrogen-bonded main chain polymer studied here is a monotropic liquid crystal. Above 150°C, it exhibits kinetic stabilization of its monotropic smectic phase.

Effect of molecular structure on mesomorphism XX. Unsymmetrical dimeric mesogens

Abstract A series of unsymmetrical dimeric mesogens was prepared, members of which were composed of a 4′-pentyloxybiphenyl-4-carboxyl core and a 4′-substituted-benzylidene-4-oxyaniline core joined via an alklyene spacer. The structural variants were cyano, nitro and trifluoromethyl. Comparison of mesophase behaviour of the unsymmetrical dimers with that of corresponding monomeric ‘halves’ and also with that of corresponding symmetrical dimers indicated a tendency for the unsymmetrical dimers to form smectic phases although not as highly ordered as those of some of the monomers corresponding to a relevant core group.

Effect of Molecular Structure on Mesomorphism. Two Series of Novel Methylene-Bridged Liquid Crystals

Abstract Two series of novel methylene-bridged liquid crystals have been prepared. These molecules are quite wide and as a result only higher homologues exhibit mesomorphism. The enantiotropic mesophases are of the smectic C type. Trends in thermal behavior of these two series indicate that even higher homologues should possess extended smectic ranges.

Effect of Molecular Structure on Mesomorphism 22.1 Liquid Crystalline1-Alkanol Derivatives

Abstract Several 1-alkanols having a mesogenic unit attached to the omega-carbon have been prepared. Manyof these are liquid crystalline. The nematic mesophase is predominant for these materials. This ispresumably due to intermolecular hydrogen-bonding between polar terminal groups such as cyano ornitro and the primary hydroxyl functionality of a proximal molecule. The resulting end-to-end associationfavors a nematic mesophase.