Polymerization of olefins in the presence of metal powders with homogeneous catalysts

Homogeneous catalysts based on metallocenes/methylaluminoxane are totally absorbed on surfaces of different metals. Because the methylaluminoxane is relatively stable against small molecules such as water covering metal surfaces, the aluminoxane can be fixed on powders without losing its activity. After treatment with the metallocene, active sites are only formed on the surface of the fillers. Upon injection of the olefins they are polymerized in the presence of the metals. Olefins such as ethene and propene, and cycloolefins or dienes, are used.     

Darstellung und spektroskopische charakterisierung verzweigter funktioneller hexasilangerüste

When 2-chloro-1,1,1,3,3,3-hexaphenyltrisilane is treated with an excess of HCl in a stainless steel autoclave, two phenyl groups per silicon atom are substituted by Cl yielding 1,1,2,3,3-pentachloro-1,3-diphenyltrisilane. All phenyl groups are replaced upon treatment with HCl/AlCl₃ in benzene solution. Coupling of the resulting trisilanes with (^tBu)₂Hg leads to branched hexasilanes (XCl₂Si)₂SiClSiCl(SiCl₂X)₂ (X = Ph, H), which are converted to the corresponding silicon hydrides by LiAlH₄. From the reaction of 1,4-diphenyl-2,3-bis(phenylsilyl)tetrasilane with HCl or HBr the tetrahalohexasilanes (ClH₂Si)₂SiHSiH(SiH₂Cl)₂ and (BrH₂Si)₂SiHSiH(SiH₂Br)₂ can be obtained.     

Proton instability of73Rb

The study of the stability of an astrophysically interesting nucleus⁷³Rb was performed by searching itsβ ⁺ and proton decay at the ISOLDE facility at CERN. Light rubidium isotopes were produced in a spallation reaction of a niobium target induced by a pulsed 1 GeV proton beam. The previously reported proton-unbound character of⁷³Rb was confirmed and the upper limit for its production cross-section was reduced by more than one order of magnitude.     

Exploring the Limits of Emulsion Polymerization of Styrene for the Synthesis of Polymer Nanoparticles

Summary. Suspensions of polymer nanoparticles in water (latices) with average particle diameters between 20 and 80 nm were synthesized by batch emulsion polymerization of styrene using sodium dodecyl sulphate (SDS) as surfactant and potassium persulphate (KPS) as initiator. The influence of surfactant concentration, initiator concentration, monomer concentration, and reaction temperature on the final average particle diameters and size distributions of the latices were studied. The number of particles generated was proportional to the 0.56 power of the emulsifier concentration and to the 0.37 power of the initiator concentration in the whole concentration range which was observed. Furthermore, the final number of particles was dependant on the reaction temperature to the 2.06 power. With these correlations the average particle number as well as the average particle size could be estimated, and the results were in good agreement (±6%) with the experimental values. A reduction of the monomer/water ratio from 1:5 to 1:20 yielded smaller particle diameters, while leaving the particle number unaffected. The lower particle size limits for monomer ratios of 1:10 and 1:15 were estimated with diameters of about 18 and 16 nm.     

Rigidity and polarity

Any projective polarity in 3-space transforms a statically (or equivalently, infinitesimally) rigid bar-and-joint framework into a statically rigid hinged sheetwork — a set of plane-statically rigid sheets, joined in pairs along hinge lines. In the more general class of jointed sheetworks, which is closed under polarity, static rigidity is also preserved by the polarities. In particular, the class of infinitesimally (or statically) rigid polyhedra, built with joints at the vertices and bars triangulating the faces, is closed under polarity.Work supported, in part, by grants from N.S.E.R.C. (Canada) and F.C.A.C. (Quebec), and a visiting appointment at McGill University.     

The phase transition to the quark-gluon plasma and its effect on hydrodynamic flow

It is shown that in ideal relativistic hydrodynamics a phase transition from hadron to quark and gluon degrees of freedom in the nuclear matter equation of state leads to a minimum in the excitation function of the transverse collective flow.