Synthesis and characterization of novel chiral liquid crystalline polysiloxanes

Several novel side chain liquid crystalline polysiloxanes have been prepare d containing a chiral cyanohydrin moiety prepared using enantioselective sy nthesis. Homopolymers incorporating a side chain with the chiral group exhi bited no liquid crystalline behavior. Copolymers of the side chain with the cyanohydrin group with an alkenyloxybenzoate yielded polymers exhibiting a N* phase. Increased amounts of the side chain with the cyanohydrin moiety led to a decrease in the transition temperatures of the resulting copolymer s. Dielectric relaxation studies showed that all polymers exhibited delta m otion due to relaxation of the longitudinal dipole of the mesogen around it s short axis. One copolymer with a large amount of the chiral unit and a lo ng flexible spacer exhibited distinct alpha and delta relaxations where the alpha relaxation is assigned to the motions of the dipoles perpendicular t o the side chain. The fact that both are clearly seen as independent peaks rather than in a broad peak which must be deconvoluted is indicative of the fact that long, flexible spacer chains decouple the two motions from each other. The delta process for the polymers with a small amount of the cyanoh ydrin side chain tended to be dominated by the nonchiral pendant group. The motion of the polymer with an increased amount of the pendant group contai ning the chiral moiety was dominated by the cyanohydrin side chain and the delta relaxation was much slower (longer relaxation time) due to the bulky nature of the chiral moiety.