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Linear Oligomers (linear + oligomer)

Distribution by Scientific Domains

Polymers and Materials Science	50%
Chemistry	50%

Selected Abstracts

Columnar Mesophase Formation of Cyclohexa- m -phenylene-Based Macrocycles

CHEMISTRY - AN ASIAN JOURNAL, Issue 1 2007
Wojciech Pisula Dr.
Abstract Two novel discotic macrocycles, substituted cyclohexa- m -phenylene (CHP) and cyclo-3,6-trisphenanthrylene (CTP), and the linear oligomer 3,3,:6,,3,,-terphenanthrene (TP) as a model substance have been synthesized by repetitive cross-coupling reactions. To correlate the molecular design with the supramolecular architecture and the established macroscopic order, 2D wide-angle X-ray scattering experiments were performed on mechanically extruded filaments. At room temperature in their crystalline phases, all three compounds revealed columnar assemblies in which the macrocycles self-organized by ,-stacking interactions. The degree of macroscopic order was found to depend upon the planarity and stiffness of the aromatic core. The flexible CHP ring showed a poor macroscopic order of the columnar structures and a low isotropization temperature, whereas the more-planar, less-flexible CTP self-assembled into well-defined superstructures. The larger ,-stacking area and the more-pronounced intermolecular interactions for CTP led to the formation of a mesophase over a very large temperature range. The surprising columnar organization of the "open" TP system was explained by back-folding of the molecule into a ringlike structure. [source]

V-Shaped Thiophene-Based Oligomers with Improved Electroluminescence Properties,

ADVANCED FUNCTIONAL MATERIALS, Issue 4 2005
G. Barbarella
Abstract The synthesis via the Stille coupling of a new family of oligomers derived from benzo[b]thiophene is reported. Owing to their branched molecular structure lacking any symmetry element, these compounds display a low tendency to crystallization and better film-forming properties than their linear counterparts. Spin-coated films show photoluminescence efficiencies up to 50,%. Light-emitting diodes with spin-coated films as the active layers display markedly improved performance with respect to similar devices based on linear oligothiophenes, with luminance values up to more than 10,000,cd,m,2. Semiempirical PM3 and ZINDO/S calculations provide insight into the molecular geometries and electron distribution of the frontier orbitals of the new compounds. Cyclic voltammetry data indicates that the transformation of the thienyl sulfur of benzo[b]thiophene to the corresponding thienyl- S,S -dioxide leads an increase in electron affinity by 0.5,0.7,V, analogous to that of the corresponding linear oligomers. [source]

H3PO4 in a direct synthesis of oligo,poly(ethylene phosphate)from ethylene glycol

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 7 2006
Julia Pretula
The direct reaction of H3PO4 with polyols has not yet been explored. In this preliminary note, we report on the reaction of H3PO4 with ethylene glycol. This reaction gives (according to the NMR spectra and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry) a series of well-defined linear oligomers with end groups either from the glycol or from the monoester of H3PO4. In some macromolecules, there are also oligo(ethylene glycol) units present. The best results were observed with Sc(CF3SO3)3 used as a catalyst. [source]

The Mechanism of Formation of Amide-Based Interlocked Compounds: Prediction of a New Rotaxane-Forming Motif

CHEMISTRY - A EUROPEAN JOURNAL, Issue 20 2004
David A. Leigh Prof.
Abstract Molecular modeling of four different reagent systems shows that the (free) energies of supramolecular interactions in the gas phase and in solution can explain the different reaction products (i.e., various sized macrocycles, catenanes, and linear oligomers) that are formed in classic amide-catenane-forming reactions. Self-assembly of the catenanes requires the formation of ordered intertwined chains and is driven by bifurcated hydrogen bonds, with , stacking only playing a lesser role. The understanding gained from the computational study was used to predict the possibility of a new rotaxane-forming system that does not permit catenane formation. The predictions were confirmed by the successful synthesis and characterization (including X-ray crystallography) of two novel rotaxanes. [source]