Conformational analysis of highly extended poly(ethylene terephthalate) chains by Monte Carlo calculations

The conformational disorder compatible with the highly extended chains found in mesomorphic poly(ethylene terephthalate) has been studied by Monte Carlo calculations on model oligomers confined inside cylindrical tubes. The distribution of torsional angles for such extended chains is characterized by O C C O bonds being always in the trans domain, while the C O C C bonds show an approximately similar probability of being found in trans and gauche states, the probability maxima being centered at 90° and −90° in the latter cases. At variance with the torsional angles of the O C C O and the ester bonds, always very close to 180°, the distributions for all other torsional angles show flat and broad probability maxima, indicating the possibility of substantial deviations from the average value inside each domain. This is also true for the fictitious O C˙˙˙C O bonds across the phenylene rings, for which a nearly trans geometry is preferred in extended conformations.     

Polypeptoids by Living Ring‐Opening Polymerization of N‐Substituted N‐Carboxyanhydrides from Solid Supports

The nucleophilic living ring‐opening polymerization of N‐substituted glycine N‐carboxyanhydrides using solid‐phase synthesis resins is reported. By variation of experimental parameters, products with near Poisson distributions are obtained. As opposed to reversible deactivation radical polymerization, the living polymerization is demonstrated to be viable to high monomer conversion and through multiple monomer addition steps. Successful preparation of a multiblock copolypeptoid is proof for a highly living and robust character of the solid‐phase peptoid polymerization.

     

Si-Tethered Bis- and Tris-Malonates for the Regioselective Preparation of Fullerene Multi-Adducts

Bis- and tris-malonates constructed around a silicon atom have been prepared by reaction of malonate derivatives bearing an alcohol function with di-tert-butylsilyl bis(trifluoromethanesulfonate) and tert-butyl(trichloro)silane, respectively. These compounds have been used for the regioselective bis- and tris-functionalization of C₆₀ under Bingel conditions. By changing the nature of the linker between the central Si atom and the reactive malonate groups, the malonate precursors have been optimized to produce specific bis- and tris-adducts with excellent regioselectivity. A complete understanding of the electronic and stereochemical factors governing the regioselectivity has been obtained by combining computational studies with a complete analysis of the by-products formed during the reactions of the Si-tethered tris-malonates with C₆₀. Finally, desilylation reactions of the resulting fullerene bis- and tris-adducts have been carried out to generate the corresponding acyclic fullerene bis- and tris-adducts bearing alcohol functions.     

Adaptive finite elements methods for virtual engineering design

The focus of this paper is the utilization of improved stresses on the surface of a construction for error estimation. The improved stresses are derived by using stress boundary conditions. They are applied for the calculation of recovered stresses required by the Zienkiewicz–Zhu error indicator. This approach leads to an enhancement of the error estimation on the boundary. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)