Synthesis and characterization of liquid crystalline monofunctionalized ‘two chain’ diols and corresponding low molecular weight siloxane derivatives

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Abstract
The selective synthesis and the thermal behaviour of some cis, cis-(3,5-dihydroxycyclohexyl) 3,4-(alkenyloxy, alkyloxy)benzoates (monofunctionalized ‘two chain’ diols) are described. Thus, several 3-(alkyloxy)-4-(undecenyloxy)benzoic acids and 4-(decyloxy)-3-(undecenyloxy)benzoic acid have been obtained. The monofunctionalized ‘two chain’ diols form a hexagonal columnar mesophase through hydrogen bonding. Subsequently, low molecular weight liquid crystalline siloxanes, model compounds for polymers, i.e. two twins and one cyclic product, were synthesized via a hydrosilylation reaction. With respect to the ‘two chain’ diols, the observed hexagonal columnar mesophase was stabilized and the intercolumnar distance was extended by the siloxane moieties. Remarkably, the thermal behaviour of the cyclosiloxane differs from that of the twins. A cubic mesophase, which can be observed very rarely in thermotropic mesogens, was formed at temperatures below the hexagonal columnar phase.

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