Effects of trivalent phosphorus compounds on vinyl polymerization. III. Anionic polymerization of acrylonitrile with triethyl phosphite

The polymerization of acrylonitrile catalyzed by triethyl phosphite was studied. It was found that the order with respect to the monomer concentration varies from two to three, depending on the polymerization temperature. From the results obtained for the molecular weight of the polymer and the phosphorus content in the polymer, it was thought that the zwitterion formed by the addition of triethyl phosphite to acrylonitrile is responsible for the initiation of polymerization. The following equation was suggested for the rate of the polymerization:      

Separation of traces of palladium using mercury as collector

Summary Microgram quantities of palladium are quantitatively deposited into mercury globules from various acid solutions. Mercury is removed by evaporation from the resulting amalgam before the subsequent determination.

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Zusammenfassung Mikrogrammengen Palladium werden von Quecksilbertröpfchen aus sauren Lösungen quantitativ extrahiert. Das Quecksilber wird aus dem entstandenen Amalgam vor der Bestimmung des Palladiums abgedampft.

     

Thin-layer chromatographic separation of rhodium(III) and iridium(III, IV) by anion exchange

Summary The TLC behaviour of Rh(III), Ir(III) and Ir(IV) has been investigated in the two systems consisting of DEAE-cellulose or ECTEOLA-cellulose and 5 M HCl media containing H₂O₂. These systems, especially in combination with a simple chemical pretreatment of samples (with LiCl, HCl and H₂O₂), can effectively be applied to the complete separation of mixtures of Rh(III) and Ir(III) or Ir(IV) in a wide range of ratios and amounts (Rh: Ir=1100 to 1001).

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Dünnschicht-chromatographische Trennung von Rhodium(III) und Iridium(III, IV) durch Anionenaustausch

Zusammenfassung Das dünnschicht-chromatographische Verhalten von Rh(III), Ir(III) und Ir(IV) wurde in H₂O₂-haltiger 5 M salzsaurer Lösung auf DEAE-sowie ECTEOLA-Cellulose untersucht. In Kombination mit einer einfachen chemischen Vorbehandlung der Probe (mit LiCl, HCl, H₂O₂) kann eine wirkungsvolle Trennung von Rh(III) und Ir(III) oder Ir(IV) über einen weiten Konzentrationsbereich erzielt werden (Rh: Ir=1100 bis 1001).

     

Efficient power coupling using taper-ended multimode optical fibres

Highly efficient power coupling of up to 97% between a d.h. laser and a multimode step-index fibre is demonstrated by employing a tapered fibre launcher. Also, it is shown theoretically that a tapered end increases the effective numerical aperture of a fibre. For a Lambertian emitter, the use of a taper launcher permits the maximum coupling efficiency allowed by the Liouville theorem.     

Titanocene(II)-promoted carbonyl allenation utilizing 1,1-dichloroalk-1-enes

Treatment of 1,1-dichloroalk-1-enes with Cp2Ti[P(OEt)3]2 produced organotitanium species, which afford allenes on treatment with aldehydes and ketones.     

Temperature dependence of formation of nanorods and dots of iodine compounds on an H-terminated Si(111) surface in a concentrated HI solution

Immersion of atomically flat, H-terminated Si(111) surfaces in 7.6 M HI for 0.5 - 4 h caused spontaneous formation of nanosized clusters at the Si surface. X-ray photoelectron spectroscopy analysis suggested that the clusters were composed of silicon iodides (such as SiHxI4-x), produced most probably by Si etching with HI. Atomic force microscopy inspection revealed that the immersion at a low temperature below about 30 degrees C led to the formation of long rod-shaped clusters, oriented in the (112) direction or equivalents, whereas the immersion at a high temperature above 30 degrees C led to the formation of circular dot clusters, their size and shape changing abruptly at about 70 degrees C. It is shown experimentally that the formation of dot clusters at a high immersion temperature is explained on the basis of thermodynamics, whereas that of oriented rod clusters at a low temperature is explained by a kinetics-controlled mechanism.     

Semi-Balanced Colorings of Graphs: Generalized 2-Colorings Based on a Relaxed Discrepancy Condition

We generalize the concept of a 2-coloring of a graph to what we call a semi-balanced coloring by relaxing a certain discrepancy condition on the shortest-paths hypergraph of the graph. Let G be an undirected, unweighted, connected graph with n vertices and m edges. We prove that the number of different semi-balanced colorings of G is: (1) at most n+1 if G is bipartite; (2) at most m if G is non-bipartite and triangle-free; and (3) at most m+1 if G is non-bipartite. Based on the above combinatorial investigation, we design an algorithm to enumerate all semi-balanced colorings of G in O(nm²) time.Acknowledgments The authors thank Tetsuo Asano, Naoki Katoh, Kunihiko Sadakane, and Hisao Tamaki for helpful discussions and comments.Supported in part by Sweden-Japan FoundationFinal version received: November 17, 2003