Isothermal anionic polymerization of ε‐caprolactam to polyamide‐6: kinetic modeling and application for production process

The in-situ anionic polymerization of ε-caprolactam (ε-CL) to polyamide-6 enables the production of large, near net shape fiber reinforced composites by thermoplastic resin transfer molding. For the propagation of the flow front as well as for the progress of the solidification, the simultaneous processes of polymerization and crystallization and the corresponding reaction kinetics play a central role. To investigate these processes, preparation of reactive mixtures consisting of ε-CL, activator, and initiator was carried out under inert atmosphere. A solvent-based activator and initiator were used, which hardly have been studied in the literature so far. In analogy to the resin transfer molding process, quasi-isothermal differential scanning calorimetry measurements were performed at various temperatures and the released enthalpy and the degree of crystallization were determined. From these isothermal measurements, a two-stage semi-empirical kinetic model was established for a solvent-based system for the first time, which reproduces the experimental data with high precision. To apply the obtained kinetic model to a thermoplastic resin transfer molding process it was finally correlated to dielectric sensor data, allowing real-time prediction of the total conversion

Fermi surface of MoO2 studied by angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations

A comprehensive study of the electronic properties of monoclinic MoO2 from both an experimental and a theoretical point of view is presented. We focus on the investigation of the Fermi body and the band structure using angle resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations. For the latter, the new full-potential augmented spherical wave (ASW) method has been applied. Very good agreement between the experimental and theoretical results is found. In particular, all Fermi surface sheets are correctly identified by all three approaches. Previous controversies concerning additional hole-like surfaces centered around the Z- and B-point could be resolved; these surfaces were an artefact of the atomic-sphere approximation used in the old calculations. Our results underline the importance of electronic structure calculations for the understanding of MoO2 and the neighbouring rutile-type early transition-metal dioxides. This includes the low-temperature insulating phases of VO2 and NbO2, which have crystal structures very similar to that of molybdenum dioxide and display the well-known prominent metal-insulator transitions.Comment: 17 pages, 21 figures, more information at http://www.physik.uni-augsburg.de/~eyert