Bimodal polyethylene – Interplay of catalyst and process

HDPE specialities having tailored bimodal molecular mass distributions suitable for applications as e.g. pipe or film material are formed in the Hostalen^®‐BM low pressure slurry process. A cascade of two STHD (stirred tank heavy diluent) reactors is used to produce at extremely different reaction conditions in each step of the polymerization an in situ polyethylene blend consisting of a low molecular mass homopolymer and a high molecular mass copolymer. This way, a resin having a very broad molecular mass distribution and an inverse comonomer distribution is obtained. High impact strength, stress crack resistance, stiffness, tensile strength, and good processability are combined and materials showing outstanding properties are achieved.     

Versatile Design Principles for Facile Access to Unstrained Conjugated Organoborane Macrocycles

A facile and versatile approach was developed to access ambipolar boron‐containing macrocycles. Two examples of new conjugated cyclic motifs are presented with carbazole moieties as donors and borane moieties as acceptors embedded into the ring system. They were first predicted using computational methods. Possible targets with appropriately shaped π‐conjugated bridges that minimize the overall ring strain were identified and their geometry was optimized by DFT methods. The synthetic demonstration was then accomplished using organometallic condensation reactions under high dilution conditions. The resulting monodisperse macrocycles provide important insights into the design principles necessary for the preparation of new unstrained macrocycles with interesting optical and electronic characteristics. The current research also offers a more general approach to conjugated ambipolar B/N macrocycles as a promising new family of (opto)electronic materials.     

Influence of solvents on the properties of chemical compounds

Based on Sinanolu's solvent theory in connection with a method for the calculation of the molecular volume given by Beveridge a modified continuum model is suggested. The model is tested by the determination of the conformational structure of the title compounds. The predictions obtained by this model are in good agreement with the experimentally determined data.     

Enzyme electrode for urea with amperometric indication: Electrode with diffusional limitation

Urea can be determined amperometrically with an enzyme electrode consisting of urease trapped in a poly(vinyl alcohol) gel and confined by a dialysis membrane. A pH-dependent hydrazine oxidation at a platinum anode is used as the detector reaction. The current is a linear function of the urea sample concentration over the range 1–80 mM with 50-μl samples injected into 2 ml of hydrazine buffer in the cell. With enzyme loadings above 20 U cm^-2, the current became limited by the rate of mass transfer in the membrane arrangement. Forty samples per hour could be analyzed with negligible carry-over when the time derivative was used for quantitation.