Highly fluorinated monomers precursors of side-chain liquid crystalline polysiloxanes

Two series of monomers, 4-[4-(allyloxy)benzoyloxy]phenyl-3-(perfluoro-n-alk yl)ethyl propanoates and 2-(perfluoro-n-alkyl)ethyl-4-[4-(undec-10-en-1-oyl oxy)-benzoyloxy] benzoates have been synthesised. These compounds contain a fluorinated chain obtained from 2-(perfluoro-n-alkyl)ethanol or from 2-(pe rfluoro-n-alkyl)ethyliodide, and an aliphatic chain containing a double bon d attached to a mesogenic moiety. Their hydrosilylation with polymethylhydr ogenosiloxane gives the corresponding polysiloxanes with a spacer with thre e or ten methylene units. These new fluorinated compounds are characterized by a combination of techniques consisting of differential scanning calorim etry (DSC) and thermal optical polarized microscopy. All the monomers exhib ited smectogenic properties of type A but for the monomers with a long spac er between the unsaturated function and the mesogenic core (compounds B), t he mesophase range decreases dramatically. All of the corresponding polysil oxanes exhibited a liquid crystalline behaviour over a wide temperature ran ge. The influence of the fluorinated chain lengthening leads for the monome rs and the polymers to an increasing of the transition temperatures. (C) 19 99 John Wiley & Sons, Inc.