Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals, Vol.269, 1-1, 1995
Novel Ion Containing Liquid-Crystals and Liquid-Crystalline Main-Chain Polymers Based on Trans-1,2-bis(4-Pyridyl Ethylene) Mesogen
Ion bearing liquid crystalline compounds based on trans-1,2-bis (4-pyridinium) ethylene were synthesized and studied. These compounds included low molecular mass analogues, twin model compounds and main chain ionomers. Most of these exhibited liquid crystallinity of the smectic type. As a general rule the introduction of charges into the mesogenic moiety increased the stability (transition temperature) of the mesophase. Large supercooling effects, broad mesophase intervals and tendency to polymorphism are common features of these ionic mesogenic compounds. In the case of twin model compounds a variety of smectic phases were observed. The nature of these was dependent on the nature of the counterion and the thermal history of the compound. Tosylate or p.toluene sulfonate counterions promoted a higher degree of order in smectic mesophases as well as higher transition temperatures compared to methylsulfonate counterions. A pronounced odd-even effect of the isotropisation temperature of the twin compounds was observed. Compounds with even numbered methylene spacers display higher transition temperatures than those with an odd spacer. Only polymers with methylsulfonate and toluenesulfonate counterions were found to exhibit both, thermotropic and lyotropic mesophases. Thermotropic mesophases were characterized as smectic mesophases of lower order (S-A). The nature of lyotropic mesophases were not determined. High transition temperatures and concommitant oxydative crosslinking made the study of polymers with halogen counterions difficult. Polymers with halogen and perchlorate counterions were found to be poorly soluble in water precluding the formation of lyotropic mesophases. The introduction of a few siloxane bonds into the flexible spacer joining the charged mesogen moieties has a dramatic effect on lowering the transition temperatures and making possible the study of mesophases up to their isotropisation temperature. Preliminary characterization of polymers with siloxane containing spacer and methylsulfonate/tosylalte counterions suggest a smectic mesophase of lower order.