Mixed-catalyst System

One may realize that this can be performed for various total chain lengths n. This implies that in principle this N-PDF 5R(Ni) function of n. Now, the 

Molecular architectures can be structurally classified as being more comb-like or Cayley tree-like. Structure has impact on the radius of gyration, which is larger for linear molecules than for branched molecules of the same weight (number of monomer units), since the latter are more compact. The ratio between branched and linear radius is usually described by a contraction factor . Furthermore, Cayley tree-like structures are more compact than comb-like structures [33, 56]. We will show here how to obtain the contraction factor from the architectural information. The squared radius of gyration s is expressed in monomer sizes. According to a statistical-mechanical model [55] it follows from the architecture as represented in graph theoretical terms, the KirchhofF matrix, K, which is derived from the incidence matrix, C [33]  

n is the number of monomer units and Tr(A ii) denotes the trace of A ij, being the matrix with n — 1 reciprocals of the eigenvalues of the Kirchhoff matrix K. The full n X n sized matrix K is calculated from  

Note that the comb-Cayley tree ranking of molecules within a certain population in Eq. (186) is different in principle from that in Eq. (185), since the former excludes segment length effects. 

Introduction The rheological meaning of the concepts of seniority and priority has been explained previously elsewhere [46, 52]. Here, we will introduce them as merely topological qualifiers. The seniority Sj of a segment j is defined as the molecular distance to the nearest free arm. The seniority of a free arm is 1 the value for a segment ending on a terminal branch point is 2. Priority is defined as follows. 

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Rytter et al. reported polymerizations with the dual precatalyst system 14/15 in presence of MAO [30]. Under ethylene-hexene copolymerization conditions, 14/MAO produced a polymer with 0.7 mol% hexene, while the 15/MAO gave a copolymer with ca. 5 mol% hexene. In the mixed catalyst system, the activity and comonomer incorporation were approximate averages of what would be expected for the two catalysts. Using crystallization analysis fractionation (CRYSTAF) and differential scanning calorimetry (DSC) analysis, it was concluded in a later paper by Rytter that the material was a blend containing no block copolymer [31],... 

The GPC trace is dramatically different when a CSA is added in the mixed catalyst system in that a simple composite GPC is not obtained (Fig. 13). Inclusion of either TEA or DEZ in the polymerization produces a single peak in the GPC,... 

These requirements have met using a mixed catalystic system consisting of an iron catalyst complex that can oligomerize ethylene and a zirconium transition metal complex that can copolymerize ethylene and the nonconjugated monomer 5-ethylidene-2-norbomene. Using this catalytic pair nonbrancy poly(ethylene-co5-ethylidene-2-norbomene) and poly (ethylene-col,4-hexadiene) were prepared. 

Title Direct Epoxidation Process Using a Mixed Catalyst System... 

Bimodal molecular weight distribution may be achieved by several techniques. The simplest method is post-reactor blending of polyethylene with different melt indices. Two other methods involve in-reactor production of polyethylene. One approach involves use of mixed catalyst systems that polymerize ethylene in different ways to produce polyethylene with different molecular weights. The latter requires that the catalysts are compatible. Another technique employs use of reactors in series operated under different conditions (see section 7.6 in Chapter 7). Figure 1.9 illustrates polyethylene with a bimodal molecular weight distribution produced with a single site catalyst system in a Unipol gas-phase process. 

C. A. Jones, Direct epoxidation process using a mixed catalyst system, U.S. Patent No. 6,307,073, 2001, Assigned to ARCO Chemical Technology. 

NaBH4 and zinc chloride (Eq. 7) [16]. These additives are necessary for reduction of the catalyst precursor and for prevention of deactivation of the catalyst by excess cyanide anion in the aqueous phase, respectively. As the use of zinc chloride in a Zn/CN molar ratio of more than 0.25 1 is required, the active cyanide source may be tetracyanozincate or zinc cyanide [26], The efficiency of the counter-PTC in the heptane-water system exceeds that of the mixed catalyst system of lipophilic catalyst and normal PTC, though the cyanide anion is easily extractable by the normal PTCs (Table 6). 

The aim of the most studies on the water-soluble phosphines is to find separable, active, and selective catalysts. The water-soluble catalysts are additionally useful for the reactions of hydrophobic substrates with inorganic salts. So far, amphiphilic solvents or mixed catalyst systems of normal PTCs and normal transition metal complexes have been used for some reactions. Though the mixed system enables the easy separation of inorganic salts from the reaction mixture, the separa-... 

Kinnan, M.A. Ehrman, F.D. Shirodkar, P.P. Davis, M.B. Grief-Rust, M.L. Methods of polymerizing olefin monomers with mixed catalyst systems, U.S. Patent 6,833,416, December 21, 2004. 

In the 1960s, a new catalyst revolutionized the production of methanol, which had been made by the BASF high pressure or zinc oxide-chromia catalyst process since 1923. The new catalyst—copper, zinc oxide, and chromia or other oxide— had been known as a methanol catalyst for a considerable length of time. At ICI, researchers carried out a careful and systematic program of preparing and testing mixed catalyst systems. The new process operated under much milder conditions than the old one. Pressure was reduced from 200 to 50-100 atm and temperature dropped from 350 to 250°C. Virtually all methanol plants built after 1967 employed this technology (69). 

The demonstration of the viability of chain shuttling between different active species in mixed catalyst systems may offer alternative and possibly easier routes into well-controlled stereobloek polypropylenes and block (co)polymers in general. The fundamentals of this process still need to be better understood, but the fact that existing catalysts with a known behavior ean be employed makes the search for effective chain shuttling agents and conditions potentially of very broad scope and perspective. 

Alkyl halides do not fonnylate due to the propensity of the palladium species to undergo /3-hydride ehmination. The conversion of organic halides containing a /3-hydride to the methyl ketone was reported using tetramethyltin, but no mention of formylation has followed to the best of our knowledge. " Methyl alcohol was converted to acetaldehyde using a mixed catalyst system of CO and hi an earher report the acylpalladium... 

Broad studies [27,35] have been carried out revealing that especially potassium carbonate, sodium carbonate, calcium salts, and iron are the prime candidates for commercial use. As all substances are linked to some disadvantages, attempts have been made to combine catalytic effects in mixed catalyst systems (e.g., hematite and potassium carbonate) [30]. Also, with a focus on availability and the inexpensiveness of raw materials for catalyst mixtures, calcium and iron, derived from wastewater streams of the steel industry, have been found to offer reasonable performance [27,28,31]. 

The GPC trace is dramatically different when a CSA is added in the mixed catalyst system in that a simple composite GPC is not obtained (Figure 12). Inclusion of either triethylaluminum (TEA) or DEZ in the mn produces a single peak in the GPC, reflecting low Mn and narrow M /Mn (see Table 2). The octene incorporation data for mns with 8pmol of CSA indicate an intermediate incorporation level between those foimd for polymers made by 2 and 4 individually. These data indicate that both catalysts are aaive and undergoing rapid chain shuttling to produce statistical multiblock OBCs. 

Tnyl chloride [89] with or without a comonomer has been suspension polymerized using a mixed-catalyst system (i.e., lauroyl peroxide and 2-ethylhexyl peroxydicarbonate) with a reducing agent NaNOj in two reactors maintained at different temperatures. The polymerization was carried out according to the typical recipe presented in Table 8. After 50 hr, the conversion values in the first and second reactors were 15% and 90%, respec-... 

Employment of chiral bis(oxazolinylphenyl)amines such as SJS)-BopsL-dpm (Scheme 4-328) as ligands for iron catalysts leads to almost quantitative yields and high enantioselectivities for the asymmetric hydrosilylation of ketones and asymmetric conjugate hydrosilylation of enones with (diethoxy)methylsilane as reductant (Scheme 4-329). Both enantiomers of the hydrosilylation product can be obtained from the same chiral ligand by a slight variation of the reaction conditions. The mixed catalyst system of (S -Bopa-dpm and iron(II) acetate provides the (/ )-enantiomer of the alcohol... 

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