Photopolymerization of carbohydrate-based discotic mesogens. Syntheses and phase

2020-03-30 07:56:08

liquid phase gp crystalline columnar

责任者: Mukkamala, R;Burns, CL;Catchings, RM;Weiss, RG 单位: GEORGETOWN UNIV,DEPT CHEM,WASHINGTON,DC 20057.;HOWARD UNIV,DEPT PHYS & ASTRON,WASHINGTON,DC 20059. 来源出处: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, v 118, OCT 9 1996, p 9498- 9508 摘要: The neat phase properties of the alpha and beta anomers of 1,2,3,4,6-penta-O-(trans-3,4-dialkoxycinnamoyl) (D)-glucopyranose (n alpha GP and n beta GP; n, the number of carbon atoms in the alkyl chains, is 6-8, 10, and 14) have been investigated by optical microscopy, differential scanning calorimetry, and X-ray powder diffraction. Each of the GP forms an enantiotropic and thermotropic discotic columnar liquid-crystalline phase. Irradiation of the 14GP in dilute solutions leads to two intramolecular [2 + 2] cycloaddition reactions between cinnamoyl double bonds. In the solid I (obtained by recrystallization from solvent and in which 14GP molecules are paired in each columnar stack) and isotropic melt phases, only short (<10 monomer unit), probably branched oligomers form upon irradiation due to the continued preference for intramolecular cycloadditions and the ability of each monomer to interact with more than two neighbors. Irradiation of the solid II phase (obtained by cooling the liquid-crystalline phase) provides unbranched oligomers with <20 monomer units. However; more than 30 14 alpha GP monomer units have been linked in unbranched chains upon irradiation of its liquid-crystalline phase. This is the greatest degree of columnar polymerization reported to date from a discotic mesophase. Qualitatively similar results are obtained upon irradiation of other GP in their various phases. Oligomerization of GP liquid-crystalline and solid I phases is intracolumnar, and the columnar packing arrangement of-the monomers is retained to ca. 100 degrees C above their clearing temperatures; each GP produces nanoscale cylinders of one diameter but varying lengths. The oligomers unwind and do not retake their original form when they are dissolved and reprecipitated or heated to above their clearing temperatures and cooled. The nature of the oligomerization processes is discussed, especially with regard to inter-/intramolecular and inter-/intracolumnar competitions for [2 + 2] cycloaddition reactions and the possibility of an anomeric effect on oligomer length. 关键词: carbon clusters; field evaporation; graphite; scanning tunneling microscopy microscopy; LIQUID-CRYSTALLINE SOLVENTS; CHOLESTERIC MESOPHASES; MECHANISTIC PROBES; BUILDING-BLOCKS; DERIVATIVES; MOLECULES; POLYMERS; BEHAVIOR; PROBES; BUILDING-BLOCKS; DERIVATIVES; MOLECULES; POLYMERS; BEHAVIOR; PHTHALOCYANINES; ISOMERIZATION PHTHALOCYANINES; ISOMERIZATION