Syntheses of dialkenes and diepoxides, and the influence of their structural parameters on liquid crystalline properties

Liquid crystalline dialkenes and diepoxides having different structural parameters were prepared and characterized. The compounds contained two or three aromatic rings in the mesogenic core. The base structure for the compounds containing two aromatic rings is the 4-(omega-oxiranylalkoxy) benzoic acid 4-(omega-oxiranylalkoxy) phenyl ester and for the compounds containing three aromatic rings the 4-{[4-(omega-oxiranylalkoxy) benzoyl]oxy}phenyl 4-(omega-oxiranylalkoxy)benzoate. The hydroquinone moiety is either unsubstituted or contains polar nitrile or fluorine groups as substituents. The flexible spacers consist of different numbers of methylene groups terminated with double bonds or epoxide groups. Some of the diepoxides undergo thermal polymerization of the epoxide group during the determination of the transition temperatures, and therefore the dialkenes were also investigated because of their almost analogous phase behaviour, but with higher thermal stability. Most of the compounds studied show liquid crystalline behaviour. A systematic study is presented of the influence of structural parameters such as the number of aromatic rings in the mesogenic core, substituents and length of the flexible side chain, on the transition temperatures. The diepoxides substituted with polar nitrile or fluorine groups are suitable precursors for ordered network polymers.