Thermotropic liquid crystalline poly(β-thioester)s containing azoxybenzene mesogenic units

A new homologous series of thermotropic liquid crystalline poly(β-thioester)s was prepared by a Michael-type polyaddition of various α,ω- polymethylenedithiols to a diacrylate containing the mesogenic azoxybenzene unit. The mesomorphic properties were studied as a function of the dithiol spacer length. Analyses by DSC and optical microscopy demonstrated the occurrence of enantiotropic behaviour in the polymer containing the ethanedithiol residue, and of monotropic behaviour in the polymers containing the dithiol spacers with 3/6 methylene segments. The systems based on longer dithiol segments did not show mesomorphism. The poly(β-thioester)s were characterized by greater thermal stability than the corresponding poly(β-aminoester)s previously investigated. In the case of the poly(β-thioester) incorporating the pentanedithiol spacer, nematic schlieren textures with quite unusual high strength singularities S = 3 2 and S = 2 were detected.