CGC systems

As discussed above with Chevron-Phillips metallocene-based catalyst which is activated with solid acid catalyst supports, the introduction of low levels of long-chain branching is an important structural feature of polyethylene manufactured for commercial applications with single-site catalysts. Dow s CGC system is able to incorporate low levels of long-chain branching into the polyethylene due to the high level of vinyl-terminated polymer molecules, the relatively high polymerization temperature that is... 

Former BP gas-phase process Dow has formed a joint venture for using CGC system in gas-phase process. 

MMe], for which M=11, Zr, or Hf, showed that actiration barriers for insertion of ethylene into n(III)-Me and Ti(IV)-Me are 3.3 and 3.8 kcal mol", respertively. Meanwhile, the barriers for ethylene insertion into Zr(IV)-Me and Hf(IV)-Me bonds are both 5.1 kcal mol". Thus, for the CGC systems, titaniinn catalysts are generally more artive than zirconium, a trend that is opposite that found for metallocene systems. ... 

The traditional sample volumes in CGC (0.1-3 xL) limit sample preparation possibilities. Specialised large-volume injection (LVI) techniques are designed to load more sample in the GC system (typically 150 xL) by placing a length of uncoated fused-silica tubing in front of the analytical column. This procedure also provides... 

Cortes et al. [975] have used on-line p,SEC-CGC for rapid determination of a great variety of additives in an emulsion ABS-PVC blend, HIPS and a styrene-acrylate-ethylene rubber polymer. These systems are difficult to analyse, because of the high levels of insolubles such as fillers, pigments, or rubber modifiers. The additives were separated from the polymer fraction in a polymer/additive dissolution using p,SEC, and were... 

Helium MIP-MS is also a very sensitive detection system for organotin compounds, such as tetraethyltin (TET), tetrabutyltin (TBT), triethyltin bromide (TET-Br), tripropyltin chloride (TPT-C1), tributyltin chloride (TBT-C1), and others, separated by CGC [213]. Detection limits at sub-pg levels were achieved, and linear dynamic ranges of at least three orders of magnitude were obtained. 

In this regard, it should be noted at this point that one of the products identified by CGC/MS from these pyrolysis reactions was SbBr3- Furthermore, the data presented concerning the importance of the polymer substrate in the degradation of the DBDPO and the proposed chain radical transfer mechanism [7] would suggest that the condensed phase chemistry could be much more important in antimony oxide/organohalogen flame retardant systems than had been previously thought. 

This chapter covers the elementary steps which are relevant to the polymerization of olefins with group 4 catalysts, and special emphasis is dedicated to systems with a substituted biscyclopentadienyl-based ligand, or with a monocyclopentadienylamido-based ligand (the so-called constrained geometry catalysts, CGC) of Figure 1, since these are the most investigated (the mono-Cp systems to a less extent) and the ones of possible industrial relevance. 

Analysis of the Mixture of Organic Compounds from the Soil. The crude fractions were analyzed using a LKB-2091 capillary gas chromatograph/mass spectrometer/data analysis system (CGC/MS/DA). The capillary column used was a J W DB-1, 60 m x 0.32 mm, connected directly to Ae ion source of the mass spectrometer. Up to 1.0 tfL of a solution of the sample in an appropriate solvent was injected directly onto the column at 40 °C, whereupon the column temperature was immediately raised to 100 for 4 min, and programmed to 310 °C at a rate of 10°/min. and held there for 30 min. 

Table V. Compound Groups Obtained From Soil By Steam Distillation As Identified By CGC/MS/DA System...

A review appeared on the practice and theory of enantioselective CGC with optically active selectors, e.g. 3-(perfluorobutyryl)-(17 )-camphorate residues forming complexes on a functionalized polysiloxane stationary phase (e.g. Chirasil, 65) SEC operates at temperatures lower than those of CGC, thus allowing better resolution, especially of thermally unstable enantiomers (e.g. those based on restricted free rotation, as is the case of dimethyl l,l -binaphthyl-2,2 -dicarboxylate, 66 ). Various analytical problems were addressed, such as determination of enantiomeric excess, assignment of absolute configuration, the elusive separation of protio- and deuterio-substituted enantiomers and the semipreparative separation of enantiomers. The following chromatographic parameters are related to the chemical and thermodynamic properties enclosed in parentheses of the enantiomeric system (i) peak retention (chemoselectivity, —AG), (ii) peak separation... 

Hartung T, Coecke S, Bal-Price AK (2009) Gene expression as a sensitive endpoint to evaluate cell differentiation and maturation of the developing central nervous system in primary cultures of rat cerebellar granule cells (CGCs) exposed to pesticides. Toxicol Appl Pharmacol 235 268-286... 

Initial studies focused on lanthanocene-based catalyst systems that proofed to be efficient in the exo-specific cyclization of terminal aminoalkenes to form five-, six-, and seven-membered azacycles (Scheme 2). The reactions are predictably faster for the formation of smaller five-membered rings and in the presence of em-dialkyl substituents [117]. An increasing metal ionic radius and a more open coordination sphere, for example, in onra-lanthanocenes, are also beneficial for higher cyclization rates [103]. A further increase in catalytic activity is observed when sterically more open and more electrophilic CGC 17 (Fig. 15) are applied [118]. 

Other catalytic systems that generate long chain-branched polyolefins have been reported such as Dow s half-sandwich constrained geometry titanium catalysts (CGC) [14e], and Bayer s novel donor/acceptor metallocenes [14f]. This polymer structural feature improves material and processing properties. 

Determination thermal desorption-CGC-ICP-MS, LODs 0.1 pg/1 (procedure) and 10 fg/1 (instrumental) and a repeatability of 12% RSD Determination offline GC-AED recoveries of > 75% on the SFE/solvent system for all tri- and tetra substituted organotin compounds and for almost half of the disubstituted organotin compounds some of the recoveries were lower on the SFE/sorbent system... 

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