Zum Mechanismus der thermischen Abspaltung von Chlorwasserstoff aus Polyvinylchlorid. 10. Mitt.:. Bestimmung des doppelbindungsgehaltes in polyvinylchlorid durch oxydative kettenspaltung

For determination of random unsaturation within the macromolecules of poly-vinyl chloride the oxidation of double bonds by potassium permanganate is used. After the cleavage of the polymer with potassium permanganate a remarkable decrease in molecular weight is observed. The oxidation reaction was investigated using N.N-dimethylacetamide as a solvent. From the temperature dependence of the reaction rate an activation energy of 23,9 keal/mole is calculated. A comparison of the molecular weights before and after oxidation gives the average content of double bonds within different samples, which was found for the products under investigation from 0.2 to 1.2 double bonds per 1000 carbon atoms by this method.     

Die einzelnen Lebensmittel (Chemie, Technologie, Analytik)

Ohne Zusammenfassung     

Über die hitzestabilisierung von PVC durch blei-, barium- und cadmiumoctoat

The following reactions between carbonic acid salts of bivalent metals as heat-stabilizers and PVC take place during heat-treatment:

• Chemical HCI-bonding by stabilizers (HCI-acceptance);
• esterification of isolated allylic chlorine atoms in the polymer chains, starting from a complex formed by stabilizer molecules and labile chlorine atoms:
• the stabilizer inhibits formation of longer polyene sequences by exchange reactions of the allylic chlorine atoms with the ester groups of the stabilizer.

Reaction (a) prevents an autocatalytic acceleration of the HCI splitting off by HCI. Reaction (b) eliminates ?labile”? chlorine atoms of the polymer which are responsible for the thermal instability of PVC. Reaction (c) prevents the formation of longer polyene sequences, which absorb in the visible range of the spectrum.     

Über die synergistische Wirkung von Cadmium-Barium-Seifen bei der Stabilisierung von PVC

It is reported on investigations concerning the thermal degradation of heat-stabilized PVC. As stabilizers several mixtures of Cadmium- and Bariumoctoate were applied, as well as the single components of each mixture. There is a pronounced shift towards a better stabilizing effect in the mixture compared with the single compounds. This so-called ‘synergism’ can also be seen in the retarded discolouration of the polymer in presence of the mixture. As a measure for the discolouration of the heat treated polymer conversion-distribution-curves of the polyene-sequences can be used. The curves demonstrate the enhancement of the stabilizing effect of the mixture in contrast to the single metal soaps. It is suggested that first the cadmium soap reacts with the PVC and that the formed metal chloride then reacts with the barium soap regenerating the cadmium soap.     

A 2-level environmental-stress-screening (ESS) model: amixed-distribution approach

Environmental stress screening (ESS) is used to reduce, if not eliminate, the occurrence of some types of failures from the field by fixing them before the product is deployed. This paper models a 2-level ESS program where screening is performed at the part and unit levels. The parts are screened for a specified duration before being assembled into a unit. Defects induced during the assembly process are screened at the unit level. These parts and connections are assumed to come from either a good or a substandard population, and their times-to-failure distributions are modeled by mixed distributions. The optimal screening durations are obtained by minimizing the life-cycle cost. The model is simple to use and its viability is illustrated using mixed exponential distributions. The implementation of screens at various levels depends on costs and failure distribution characteristics     

The Trypanosoma cruzi ribosomal RNA-encoding gene: analysis of promoter and upstream intergenic spacer sequences

The present study was designed to investigate the influence of endothelium-derived nitric oxide on the contractile responses of isolated human omental arteries to electrical field stimulation and noradrenaline. We measured isometric tension in artery rings obtained from portions of human omentum during the course of abdominal operations (32 patients). Electrical field stimulation induced frequency-dependent contractions which were abolished by tetrodotoxin (10(-6) M) and prazosin (10(-6) M), thus indicating that this effect was due to noradrenaline released from adrenergic nerves acting on alpha 1-adrenoceptors. The increases in tension induced by electrical field stimulation were of greater magnitude in arteries denuded of endothelium. NG-Nitro-L-arginine (L-NAME, 10(-4) M) potentiated the contractile response to electrical field stimulation in artery rings with endothelium but did not influence the contractile responses of endothelium-denuded arteries. The potentiation induced by L-NAME was completely reversed by L-arginine (10(-4) M), but not by D-arginine (10(-4) M). Contractile responses to noradrenaline were similar in arteries with and without endothelium. L-NAME (10(-4) M) had no significant effect on the contractile responses to noradrenaline. Our results suggest that electrical field stimulation releases endothelium-derived nitric oxide which inhibits the contractile responses of human omental arteries. The constrictor responses to noradrenaline are not modulated by the endothelium.     

Functional Perovskites – From Epitaxial Films to Nanostructured Arrays

Functional perovskite materials gain increasing significance due to their wide spectrum of attractive properties, including ferroelectric, ferromagnetic, conducting and multiferroic properties. Due to the developments of recent years, materials of this type can conveniently be grown, mainly by pulsed laser deposition, in the form of epitaxial films, multilayers, superlattices, and well‐ordered arrays of nanoislands. These structures allow for investigations of preparation–microstructure–property relations. A wide variation of the properties is possible, determined by strain, composition, defect contents, dimensional effects, and crystallographic orientation. An overview of our corresponding work of recent years is given, particularly focusing on epitaxial films, superlattices and nanoisland arrays of (anti)ferroelectric and multiferroic functional perovskites.