Crack propagation behavior in rubber materials

Within the linear viscoelastic theory, crack tip fields are calculated at various crack tip velocities. A transition from rubbery to glassy material behavior in the vicinity of the crack tip can be observed. Shear and bulk behavior is analyzed separately. Whereas the increase of tearing energy at higher crack tip velocities can be ascribed to the shear behavior, bulk behavior influences the fracture mechanism. The results support experimental investigations that the instability separating stable from unstable crack propagation is related to a change in the fracture mechanism. At low crack tip velocities, material separation is the result of formation, growth, and coalescence of cavities. At high crack tip velocities, cavitation is suppressed and fracture is driven by a rather brittle mechanism resulting in a decreased amount of energy to propagate the fracture process zone. Published in Russian in Vysokomolekulyarnye Soedineniya, Ser. A, 2008, Vol. 50, No. 5, pp. 882–891. This article was submitted by the authors in English.     

Theoretical foundation of molecular structures useful in structure/property relationships

Molecular-orbital methods are used to provide the geometric structures and electron distributions, to improve understanding of the chemical behaviour of molecular systems. Semi-empirical algorithms, based on modified (or complete) neglect of differential overlap (MNDO and CNDO/Fischer-Kollmar) methods were applied for investigating structures and infrared spectroscopic properties of formamide, oxirene, and olefin π-complexes of nickel. By considering alternative structures (isomers), it is possible to recognize the relationships between spatial structures and their dynamics (e.g., molecular vibrations), but structure and dynamics cannot be fully separated.     

Ringschlüsse an Chinonylmethanfarbstoffen und analogen Merocyaninen. 5. Mitteilung. Ein Ringschluss am substituierten Indandion

Cyclization of a substituted Indandion (Cyclization of Quinonylmethane Dyes, 5th Communication). An unexpected product was obtained from the reaction of 2-[1-ethoxyethylidene]indan-1,3-dione and 1-ethyl-3-methyl-2-methylidene-1,2-dihydroquinoxaline. The visible, ¹H-NMR., and mass spectra of the product are given.     

Synthese von 3,3,3-trifluoralanin aus hexafluoraceton

A new synthesis of 3,3,3-trifluoroalanine — starting from hexafluoroacetone — is described.