A new series of low molar mass ferroelectric organosiloxanes with unusual electro-optic properties

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Abstract
A new series of low molar mass chiral organosiloxanes A*B, C*B and a racemic analogue A(±)B have been synthesised and their mesomorphic and ferroelectric properties investigated. A* and C* denote the mesogenic moiety and B denotes the pentamethyldisiloxane tail. The following organosiloxane materials have been prepared: C8A*B, C10A*B, racemic C10A(±)B and C10C*B, where the C8 or C10 prefix indicates the number of methylene spacers between A* and C* and A* contains a 4-[(S)-2methylbutanoyloxy] and C* contains a chloro chiral end group. C8A*B exhibits only an unstable monotropic mesophase, C10A*B and C10C*B both exhibit one tilted enantiotropic ferroelectric smectic-C mesophase over a broad temperature range, with high tilt angles and high spontaneous polarisation (e.g. C10C*B 28 ° and 150nCcm−2 at 20°C). The achiral siloxane derivative C10A(±)B, exhibits one broad enantiotropic smectic-C phase. Electrooptic measurements on C10A*B and C10C*B indicate that the spontaneous polarisation is only weakly dependent on temperature between 10 °C and the SC* to isotropic transition at 51°C and 55°C, respectively whilst the tilt angles are temperature independent. These results are discussed in comparison with side-chain polymer liquid crystal structures.

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