Molecular design of amphotropic materials: influence of oligooxyethylene groups on the mesogenic properties of calamitic liquid crystals
作者:Bernhard Neumann、Christiane Sauer、Siegmar Diele、Carsten Tschierske
DOI:10.1039/jm9960601087
日期:——
The syntheses and liquid-crystalline properties of novel oligoethylene glycol derivatives are described. These are amphiphiles and podand-like trimesogens. The hydrophobic sections of the amphiphiles consist of calamitic 4-(5-pentadecyl-l,3,4-thiadiazol-2-yl)-phenyl, 4′-dodecyloxybiphenyl-4-yl or 4-decylphenyl units, which are connected by a hydrophilic 12,13-dihydroxy-l,4,7,10-tetraoxatridecyloxy, 9,10-dihydroxy-l,4,7-trioxadecyloxy, 6,7-dihydroxy-l,4-dioxaheptyloxy or 2,3-dihydroxypropoxy groups. All these amphiphiles contain a 1,2-diol unit. In addition the 12-hydroxy-l,4,7,10-tetraoxadodecyl-, 9-hydroxy-l,4,7-trioxanonyl, 6-hydroxy-l,4-dioxahexyl and 2-hydroxyethoxy derivatives of 4′-dodecyloxybiphenyl are described. These compounds have only a single hydroxy group at their hydrophilic termini. The podand-like trimers consist of three 4′-dodecyloxybiphenyl units which are connected via oligooxyethylene chains with an α, α′,α″-mesitylenetriyl unit. The thermotropic liquid-crystalline properties of these compounds were investigated by polarising microscopy, differential scanning calorimetry and, in some cases by X-ray scattering. Most diol derivatives exhibited an SA–SC dimorphism. However, one of the biphenyl derivatives [4-dodecyloxy-4′-(6,7-dihydroxy-l,4-dioxaheptyl)biphenyl] displays another phase instead of the SC phase, probably a phase with a ribbon structure. The liquid-crystalline phases of these diol derivatives were influenced by the addition of protic solvents. Only lamellar phases were found for the biphenyl derivatives. Some thiadiazole derivatives additionally formed lyomesophases consisting of curved aggregates. No thermotropic liquid crystalline properties could be detected for the oligoethylene glycol monoethers without the 1,2-diol group. However, lyotropic liquid-crystalline phases could be induced by the addition of ethylene glycol or formamide. Only those podands with a medium spacer length were thermotropic liquid crystals and no lyotropic mesophases were detected for the podands.
描述了新型聚乙烯醇醚衍生物的合成及其液晶特性。这些物质是两性分子和类聚合物的三聚体。两性分子的疏水部分由有序的4-(5-十五烷基-1,3,4-噻二唑-2-基)-苯基、4′-十二烷氧基联苯-4-基或4-癸基苯基单元组成,这些单元通过亲水性的12,13-二羟基-1,4,7,10-四氧三烷氧基、9,10-二羟基-1,4,7-三氧十烷氧基、6,7-二羟基-1,4-二氧庚烷氧基或2,3-二羟基丙氧基连接。所有这些两性分子都包含一个1,2-二醇单元。此外,还描述了4′-十二烷氧基联苯的12-羟基-1,4,7,10-四氧十二烷、9-羟基-1,4,7-三氧九烷、6-羟基-1,4-二氧六烷和2-羟基乙氧基衍生物。这些化合物在其亲水末端只有一个羟基。类聚合物的三聚体由三个4′-十二烷氧基联苯单元组成,这些单元通过希尔长链与α, α′,α″-美克三醇单元连接。这些化合物的热致液晶特性通过偏光显微镜、差示扫描量热法以及在某些情况下通过X射线散射进行了研究。大多数二醇衍生物表现出SA-SC二相现象。然而,其中一种联苯衍生物[4-十二烷氧基-4′-(6,7-二羟基-1,4-二氧庚基)联苯]显示出另一种相,而不是SC相,可能是具有带状结构的相。这些二醇衍生物的液晶相受到质子溶剂添加的影响。联苯衍生物只发现了层状相。一些噻二唑衍生物还形成了由弯曲聚集体组成的胶团相。对于没有1,2-二醇组的聚乙烯醇单醚,未能检测到热致液晶特性。然而,通过添加乙二醇或甲酰胺可以诱导形成液晶相。只有中等间隔长度的类聚合物是热致液晶,且未检测到类聚合物的溶液相。