SYNTHESIS, PHASE-BEHAVIOR AND POLYMERIZATION OF MESOGENIC MATERIALS BASED ON 3-SUBSTITUTED PYRROLES

Synthetic routes which lead to the formation of 3-substituted pyrroles with mesogenic units are described. Two particular compounds have bee n prepared: 3-{6-[4-(4-methoxyphenylazo)phenoxy]hexyl}pyrrole and 3-[6 -(4'-cyanobiphenyl-4-yloxy)hexyl]pyrrole. Both exhibit monotropic liqu id crystalline phases, and for the latter compound the stability of th e mesophase observed could be increased by incorporation of a small am ount of a commercially available Liquid crystal. Electrochemical inves tigations show that the azobenzene based material is a poor candidate for the formation of polypyrrole derivatives, because of the ease with which competing oxidative processes occur. The cyanobiphenyl derivati ve, in contrast, has been polymerised electrochemically to form electr ically conducting polymer films; these films reveal an electrochromic effect by virtue of reversible doping. It has also proved possible to polymerise this material chemically to give a polymeric material which is soluble in a variety of solvents. A further procedure involved oxi dation with bromine vapour to polymerise the material in an aligned st ate; the yields of such polymers, however, are poor, and considerably lower than those obtained for materials prepared in the isotropic melt .