Mesomorphic Properties of Main Chain Thermotropic PLCs and Model Compounds Containing a Tetramethyldisiloxane Moiety in the Spacer

Abstract

Main-chain thermotropic diesters (Model Compounds)

and polyesters

containing a tetramethyl disiloxane moiety in the flexible spacer were synthesized and studied in order to investigate the influence of a short sequence of siloxane bonds on the mesomorphic properties of main-chain liquid crystalline compounds. It was found that the introduction of the moiety into the flexible spacer substantially lowers the transition temperatures of both polymers and twin model compounds. In addition, a strong decrease of the order parameter of the siloxane containing twin-model compound was found. Interestingly, while most of the model compounds display monotropic nematic mesophases the corresponding polymers are either non-mesomorphic or smectic.