Synthesis and thermotropic properties of novel side-chain dimer liquid crystalline polymers

A new class of side-chain liquid crystalline polymers with polymethacrylate or polyether backbones and two different mesogenic moieties in one side-chain, i.e. a biphenyl group and a cholesterol group, have been synthesized. The thermotropic behavior of both, the monomeric precursors and the polymers, has been investigated. The monomers exhibit smectic A and chiral nematic phases and the polymers exhibit smectic A mesophases. For both, monomers and polymers, the isotropization temperatures and the corresponding dimensionless entropy changes Delta S/R depend on the parity of the spacer between the two mesogens. Replacement of the biphenyl group in the polymethacrylates by a phenyl group lowers the isotropization temperatures, but the smectic A phase is retained.