INDEX alternative catalyst

Ans. CD3 and H cis to each other in the polymer chain that is, they have erythro configuration with respect to each other. With Natta catalyst a high isotacticity index is expected. An alternative configuration would be threo (CD3 and H turns to each other). The observed erythro configuration means alkene insertion is cis. 

Metallocene catalysis is an alternative to the traditional Ziegler-Natta vanadium-based catalysis for commercial polyolefin production, e.g. the use of metallocene-catalyzed ethylene alpha-olefin copolymers as viscosity index modifiers for lubricating oil compositions [23]. The catalyst is an activated metallocene transition metal, usually Ti, Zr or Hf, attached to one or two cyclopentadienyl rings and typically activated by methylaluminoxane. Metallocene catalysis achieves more stereo-regularity and also enables incorporation of higher alpha-olefins and/or other monomers into the polymer backbone. In addition, the low catalyst concentration does not require a cleanup step to remove ash. 

In the enzymic catalysis not only the index atoms must come into contact with the catalyst, but their extra-index substituents as well. The structural correspondence must be still more precise, which explains the high selectivity of enzymes (see Section 1,1). With some alternations the same refers to the antimetabolites (Section 1,1) and seemingly to antibodies (17). There exists a theory of scents which uses the principle of structural correspondence. Recently, the principle of structural correspondence was also used to explain the dependence of the physiological action of anesthetics upon the structure of the molecules (18). 

Description Olgone is an alternative solution to clay treating that is used to reduce olefins content and thus, lower the Bromine Index (Bl) of heavy reformate and aromatic extract streams. In this process, a stream of either mixed xylenes, benzene/toluene or a combination of each is preheated in a feed heater (1). The stream is then sent to a liquid-phase reactor (2) containing the ExxonMobil proprietary EM-1800 catalyst. Similar to a clay treater system, a typical Olgone treater system consists of two vessels with one in service and one in standby mode (3). 

An alternative route to the compatibilization of a filler such as clay with LDPE and HDPE, through the radical catalyzed polymerization of maleic anhydride (MAH) in the presence of the polymer and clay, has been shown to yield PE-g-MAH-clay composites having better mechanical properties than unfilled PE or PE-clay mixtures prepared in the absence of MAH and a radical catalyst, In the present paper, further improvements in the preparation and properties of HDPE-clay composites are described. These result from the use of high melt index HDPE as "coating PE" in the preparation of the PE/clay masterbatch and low melt index HDPE as "matrix PE" in the final HDPE-clay composite. The crosslinking which accompanies the graft polymerization of MAH onto PE also plays a significant role in the enhancement of the mechanical properties of the composite, ... 

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