Bestimmung der Energielücke von (Pb1–x*Snx)1–yTe y-Einkristallen. Vergleich indirekter mit direkten Methoden

For applications of Pb_1–xSn_xTe in infrared light emitting and light detecting devices it is necessary to control the energy gap. For determining the gap in as-grown Bridgman crystals indirect methods have to be used (measurement of lattice constant and density). The results of these indirect methods are compared with results obtained by more direct measurements (spectral photoresponse, intrinsic absorption edge).     

Combinatorial Materials Research in the Polymer Industry: Speed versus Flexibility

With combinatorial materials research (CMR), a new research approach toward the development and optimization of materials has been established at BASF. While adopting the basic ideas of combinatorial chemistry, CMR faces a whole bunch of challenges throughout the entire combinatorial process loop. New concepts for sample preparation on a smaller scale, i.e. synthesis and formulation, for parallel or fast sequential screening and characterization, and for appropriate management of yet unknown amounts of data have been developed. The integration of as many as possible workflow steps and the interplay of experts from various relevant fields, such as chemistry, engineering, robotics, informatics, and physics, are necessary. First results in the fields of polymer synthesis and coatings formulation give an impression of the innovative power and efficiency of this new kind of research.

     

Fractionated crystallization in blends of functionalized poly(tetrafluoroethylene) and polyamide

Blends of poly(tetrafluoroethylene)/polyamide (PTFE/PA) were prepared to combine the good processing properties of PA with the excellent sliding properties of PTFE. For the compatibilizing of the immiscible components the chemical reaction of functional groups of modified PTFE (micro powder produced by electron irradiation in air) and polar PA during a reactive extrusion process was used. The parameter influencing the efficiency of the in‐situ reaction between both components were varied. The crystallization and melting behaviour of the different blends was investigated by DSC. In dependence on the degree of compatibilization the phenomenon of fractionated crystallization of the dispersed PTFE component was observed. In this way a qualitative characterization of the dispersity of PTFE in dependence on the functionality of the components and the processing conditions is possible, and therefore an estimation of the efficiency of the in‐situ reaction.     

Structure and electronic properties of ladder polymers. A new class of conducting polymers

Theoretical calculations have been applied to design novel synthetic polymers which show metallic conductivity without doping. Some selected highly conjugated structures were calculated using a HUCKELMO method extended by introducing elastic sigma bonds. A group of highly conjugated aromatic ladder polymers is promising in this context. Another interesting group consists of laddered heteroaromatic structures in which carbon atoms are replaced by nitrogen. Ionization potentials, electron affinities, band widths, band gaps as well as oxidation and reduction potentials were calculated. Small, band gaps were obtained for polyacene, polyperinaphthalene and polypyridinopyridine. The values are in good aggreement with that obtained on the basis of the VEH method. This paper reports also some efforts to prepare polyacene, polyperinaphthalene and polypyridinopyridine, and to investigate their electronic properties. Concerning their electrochemical properties high specific capacities and good electrochemical stability has been found in aprotic lithium cells.     

Sulfonated multiblock copoly(ether sulfone)s as membrane materials for fuel cell applications

Arylene ether multiblock copolymers of the (AB)_n-type with various degrees of sulfonation have been prepared by a two-step polycondensation procedure. Multiblock copolymers in high yields and of high molecular weights were obtained. For comparison random copolymers with the same overall composition were synthesized. The theoretical ion-exchange capacities (IEC) of the materials were ranging from 0.50 mmol/g to 1.25 mmol/g. The water-uptake of the multiblock copolymers showed a linear dependency from the IEC and was increasing with increasing IEC. No differences were observed between random and block copolymers. Furthermore, the hydrolytic stability of aromatic sulfonic acid groups was investigated in this study. Aromatic sulfonic acids, having additional electron donating groups, especially in ortho- or para-position to the sulfonic acid group are sensitive to hydrolytic desulfonation. On the other hand electron-withdrawing groups in meta-position showed a stabilizing effect.