Linear polybenzyls. III. Sterically assisted linear polymerization of 2,5-dimethylbenzyl chloride and α-methylbenzyl chloride

The low-temperature Friedel-Crafts step-growth polymerization reactions of 2,5-dimethylbenzyl chloride with TiCl₄—(C₂H₅)₂AlCl catalyst, and of α-methylbenzyl chloride with AlCl₃ catalyst were investigated for the effect of reaction conditions on polymer molecular weight, linearity, glass transition temperature, and crystalline properties. Premature precipitation of highly crystalline poly(2,5-dimethylbenzyl) prevented the preparation of high molecular weight products from this monomer, while most likely an indanyl-type termination reaction limited the molecular weight of poly(α-methylbenzyl). Model reactions indicated that, under proper conditions, the latter could be prepared with 99% para substitution, and these polymers were crystalline.     

Side-chain liquid crystalline polymers with silphenylene-siloxane main chains. II. Preparation and characterization of polymers containing biphenyl mesogens

Side-chain liquid crystalline polymers with poly(silphenylene-siloxane) backbones and 4,4′-biphenyl-containing pendant mesogenic groups have been prepared and characterized. Polymers with spacers having only three methylene groups were not liquid crystalline, LC, but those with spacers having eight methylene groups or more and a long terminal substituent were LC as indicated by an isotropization peak on the shoulder of the melting peak in the DSC thermogram and the appearance of a Schlieren texture on examination by polarized light microscopy. However, the LC behavior could not be confirmed by wide-angle X-ray diffraction, WAXD, because the crystalline pattern apparently remained up to the isotropization temperature, presumably because the melting transition and isotropization are too close. In contrast, polymethylsiloxanes with the same mesogenic side-chains revealed the presence of well-defined smectic phases by WAXD as well as by polarized light microscopy.     

Inverse resonance raman scattering and resonance raman amplification

The characteristics of Inverse Resonance Raman Scattering (IRRS) and Resonance Raman Amplification (RRA) are discussed. Both effects have been experimentally examined using an intracavity arrangement. With this technique which has a time resolution of 30 ns it was possible to obtain Raman lines from highly fluorescent dyes which were present in concentrations down to 10^-6 mole/

.     

Ultrasonic attenuation in the Gd-doped superconductor LaAl2

The ultrasonic attenuation (10–250MHz) in (LaGd)Al₂ with 0.23at% Gd has been measured between 293 K and 0.5 K. Below 10K the absorption is caused by superposition of phonon/electron absorption of Pippard type and a mechanical relaxation process which is attributed to a lattice defect of either vacancy, dislocation or impurity type. The relaxation takes place by interaction of the defect with both conduction electrons and lattice phonons with a mixed relaxation time. Superconductivity offers the unique chance to separate both relaxation mechanisms since during superconducting transition relaxation into the electronic system vanishes and leaves the phonon process alone to determine the defect dynamics. The temperature dependence of the individual relaxation times has been derived.     

Quadratische Formen und Kollineationsgruppen

Ohne ZusammenfassungHerrnReinhold Baer zum 60. Geburtstag     

Modeling and simulation of magnetic-shape-memory polymer composites

Composites of small magnetic-shape-memory (MSM) particles embedded in a polymer matrix have been proposed as an energy damping mechanism and as actuators. Compared to a single crystal bulk material, the production is simpler and more flexible, as both type of the polymer and geometry of the microstructure can be tuned. Compared to polycrystals, in composites the soft polymer matrix permits the active grains to deform to some extent independently; in particular the rigidity of grain boundaries arising from incompatible orientations is reduced. We study the magnetic-field-induced deformation of composites, on the basis of a continuous model incorporating elasticity and micromagnetism, in a reduced two-dimensional, plane-strain setting. The aim is to give conceptual guidance for the design of composite materials independent of the concrete macroscopic device. Thus, on the background of homogenization theory, we determine the macroscopic behavior by studying an affine-periodic cell problem. An energy descent algorithm is developed, whose main ingredients are a boundary element method for the computation of the elastic and magnetic field energies; and a combinatorial component reflecting the phase transition in the individual particles, which are assumed to be of single-domain type. Our numerical results demonstrate the behavior of the macroscopic material properties for different possible microstructures, and give suggestions for the optimization of the composite.     

Ueber die Untersuchung von Soldatenbrod

Ohne Zusammenfassung