MOLECULAR DESIGN OF AMPHOTROPIC MATERIALS - INFLUENCE OF OLIGOOXYETHYLENE GROUPS ON THE MESOGENIC PROPERTIES OF CALAMITIC LIQUID-CRYSTALS

The syntheses and liquid-crystalline properties of novel oligoethylene glycol derivatives are described. These are amphiphiles and podand-li ke trimesogens. The hydrophobic sections of the amphiphiles consist of calamitic 4-(5-pentadecyl-1,3,4-thiadiazol-2-yl)-phenyl, 4'-dodecylox ybiphenyl-4-yl or 4-decylphenyl units, which are connected by a hydrop hilic 12,13-dihydroxy-1,4,7,10-tetraoxatridecyloxy, 9,10-dihydroxy-1,4 ,7-trioxadecyloxy, 6,7-dihydroxy-1,4-dioxaheptyloxy or 2,3-dihydroxypr opoxy groups. All these amphiphiles contain a 1,2-diol unit. In additi on the 12-hydroxy-1,4,7,10-tetraoxadodecyl-, 9-hydroxy-1,4,7-trioxanon yl, 6-hydroxy-1,4-dioxahexyl and 2-hydroxyethoxy derivatives of 4'-dod ecyloxybiphenyl are described. These compounds have only a single hydr oxy group at their hydrophilic termini. The podand-like trimers consis t of three 4'-dodecyloxybiphenyl units which are connected via oligoox yethylene chains with an alpha, alpha('),alpha ''-mesitylenetriyl unit . The thermotropic liquid-crystalline properties of these compounds we re investigated by polarising microscopy, differential scanning calori metry and, in some cases by X-ray scattering. Most diol derivatives ex hibited an S-A-S-C dimorphism. However, one of the biphenyl derivative s cyloxy-4'-(6,7-dihydroxy-1,4-dioxaheptyl)biphenyl] displays another phase instead of the S-C phase, probably a phase with a ribbon structu re. The liquid-crystalline phases of these diol derivatives were influ enced by the addition of protic solvents. Only lamellar phases were fo und for the biphenyl derivatives. Some thiadiazole derivatives additio nally formed lyomesophases consisting of curved aggregates. No thermot ropic liquid crystalline properties could be detected for the oligoeth ylene glycol monoethers without the 1,2-diol group. However, lyotropic liquid-crystalline phases could be induced by the addition of ethylen e glycol or formamide. Only those podands with a medium spacer length were thermotropic liquid crystals and no lyotropic mesophases were det ected for the podands.