Mesomorphic polyelectrolytes based on side-chain liquid-crystalline polymers containing side-on fixed mesogens and oligooxyethylenic spacers

Abstract

The synthesis and characterization of side-chain liquid-crystalline polysiloxanes based on 4′-cyanobiphenyl-4-yl 2-(2-allyloxyethoxy)-4-(4-methoxybenzyloxy)benzoate (11-1), 4′-cyanobiphenyl-4-yl 2-[2-(2-allyloxyethoxy) ethoxy]-4-(4-methoxybenzyloxy) benzoate (11-2) and 4′-cyanobiphenyl-4-yl 2-{2-[2-(2-allyloxyethoxy)ethoxy] ethoxy}-4-(4-methoxybenzyloxy)benzoate (11-3) side-on fixed mesogenic groups are presented. These polysiloxanes are the first examples of side-chain liquid-crystalline polymers containing oligooxyethylenic spacers and side-on fixed mesogenic groups. All the polysiloxanes synthesized display enantiotropic N mesophases. The complexation of the polysiloxane based on the monomer 11-3(i.e.12-3) with LiCF₃SO₃ resulted in an initial decrease and then a subsequent increase of the glass transition of the complexes, and in a decrease of the N–I transition temperature. These complexes are nematic liquid-crystalline polyelectrolytes up to a value of 0.4 mol LiCF₃SO₃ per mole repeat unit of polymer. Above this value, the N mesophase cannot form owing to its close proximity to the glass-transition temperature.