We theoretically explored new two-dimensional materials near the ionic instability (three-dimensional structures are favored), with covalent bonded systems (graphene) sitting at the opposite end of the spectrum. Accordingly, monolayer alkaline earth and transition metal halides, many of their bulk forms being layered structures, were investigated by density functional calculations. We thus pred...

In the previous studies, the several halocarbons (HC) were tested as promoters for a Ti-based Ziegler-Natta (ZN) catalyst at different polymerization conditions. The Results showed that chloro cyclohexane has the best operation in catalyst activity, polymer particle size growth, hydrogen responsibility and wax reduction too. For the first time in this study, the effect of Al/Ti ratio on the opt...

In a gas phase %uidized bed ole)n polymerization reactor, it is generally assumed that polymer particles are well mixed and near isothermal reaction conditions prevail. When a highly active Ziegler–Natta catalyst or other type of high activity supported catalyst is used in a gas phase %uidized bed reactor, a certain heterogeneity in the polymer properties is often observed in di4erent size part...

This paper presents new near-infrared observations of the planetary nebula NGC 2346. The data include a broad K– band image, an image in the H2 vibrationally excited 1–0S(1) line and K band slit spectra at three positions in the nebula. In the H2 1–0S(1) line, the nebula is characterized by a central, bright torus, surrounded by weaker emission with a typical butterfly shape, as seen in Hα and ...

Migratory insertion of carbon-based species into transition-metal-carbon bonds is a mechanistic manifold of vast significance: it underlies the Fischer-Tropsch process, Mizoroki-Heck reaction, Ziegler-Natta and analogous late-transition-metal-catalyzed olefin polymerizations, and a number of carbonylative methods for the synthesis of ketones and esters, among others. Although this type of react...

It is estimated that 60 to 70% of LLDPE enters the market as blends (Utracki 1989a), primarily with other members of the polyolefin family, e.g., LDPE or polypropylene (PP). Despite the long history of polyethylene (PE) blending and its widespread use, many questions about the homogeneity of such blends, with obvious implications for thermodynamics and for the rheology, are still not answered t...

Aluminum, the third most abundant element on the earth’s crust, occurs predominantly in oxidic and silicatic minerals. It was first obtained in a pure elemental form by F. Wöhler in 1827 by the reduction of AlCl3 with elemental potassium. In 1859 W. Hallwachs and S. Schafarik synthesized the first organoaluminum compound Et3Al2I3 from elemental Al and EtI, but it took almost 100 years before K....

This theoretical study was inspired by the perpetual debate over the so-called "dormancy" of the active sites in propylene polymerization, i.e., a drop in their activity after a regioerror (2,1-insertion), which was reported to occur in many (although not all) catalytic systems. To explore the range of possible situations, we have selected two homogeneous systems of fundamentally different stru...

In this paper, the implications of melt compatibility on thermal and solid-state properties of linear low density polyethylene/high density polyethylene (LLDPE/HDPE) blends were assessed with respect to the effect of composition distribution (CD) and branch content (BC). The effect of CD was studied by melt blending a metallocene (m-LLDPE) and a Ziegler-Natta (ZN) LLDPE with the same HDPE at 19...