New fluorinated monomers containing an ester function in the spacer, precursors of side chain liquid crystalline polysiloxanes

Two series of monomers, 2-(perfluoro-n-alkyl)ethyl-4- [4-(allyloxy)phenyl]b enzoates and 2-(perfluoro-n-alkyl)ethyl-4- [4-(allyloxy)benzoyloxy]benzoate s have been synthesized. They contain a fluorinated chain obtained from 2-( perfluoro-n-alkyl)ethanol, an aliphatic chain containing a double bound on omega and a central mesogenic moiety. Their hydrosilylation by polymethylhy drogenosiloxane give the corresponding polysiloxanes. All of the compounds, characterized by a combination of techniques consisting of differential sc anning calorimetry (DSC) and thermal optical polarized microscopy, exhibite d high smectogen properties. Monomers, which differ only by the nature of t he rigid mesogenic core, showed enantiotropic smectogen mesophases over a w ide temperature range. It was shown that the peculiar effect of the bipheny l group leads to a thermotropic polymorphism, while phenyl benzoate group i nduces a monomorphic character. Transition temperatures are also dependent of the length of the fluorinated moiety. (C) 2000 Elsevier Science Ltd. All rights reserved.