Catalyst activity Ziegler-Natta

TABLE 2. Properties of Polyethylene Containing 1-Hexene Prepared Using High-Activity Ziegler-Natta Catalysts... 

B. The (Butadiene)zirconocene Route to Active Ziegler-Natta Catalyst Systems... 

Butadiene)zirconocenes, 109-162 active Ziegler-Natta catalyst systems, 142-149... 

It is interesting that some heterogeneous superhigh-activity Ziegler-Natta catalysts such as MgC /TiCU/LB—AlEt3 also yield random ethylene/propylene copolymers. These copolymers, however, exhibit a blocky nature and highly isotactic propylene sequences (with no 2,1-inserted propylene units) that contribute to undesired crystallinity [68,456]. 

Table 5.1 Polymerisation of 1,3-butadiene with aluminium alkyl or hydride-activated Ziegler-Natta catalysts...

High molecular weight cis-1,4 polybutadiene is commercially produced using a solution butadiene polymerisation with aluminium alkyl-activated Ziegler Natta catalysts based on Ti, Co and Ni precursors, and, more recently, cata-... 

Industrial polymerisation processes with the use of titanium-, cobalt- and nickel-based aluminium alkyl-activated Ziegler-Natta catalysts, which are employed for the manufacture of cis- 1,4-poly butadiene, involve a solution polymerisation in low-boiling aromatic hydrocarbons such as toluene or in a mixture of aromatic and aliphatic hydrocarbons such as n-heptane or cyclohexane. The polymerisation is carried out in an anhydrous hydrocarbon solvent system. The proper ratio of butadiene monomer and solvent is blended and then completely dried in the tower, followed by molecular sieves. The alkyla-luminium activator is added, the mixture is agitated and then the transition metal precatalyst is introduced. This blend then passes through a series of reactors in a cascade system in which highly exothermic polymerisation occurs. Therefore, the reaction vessels are cooled to slightly below room temperature. 

The intensive search for the active cocatalyst responsible for this activation led in 1977 to the isolation of MAO, a component in which aluminum and oxygen atoms are positioned alternately and free valences are saturated by methyl groups (65, 66). When metallocenes, especially zirconocenes, are combined with MAO, the resulting catalyst can polymerize olefins 10-100 times faster than those used in the most active Ziegler-Natta systems (67). 

The above Cp2MQ2 species are immediate precursors for highly active Ziegler-Natta catalysts for die preparation of isotactic polypropylene with methylalumoxane as a cocatalyst die racemic mixtures can be directly employed in stereospecific propylene polymerizations (see Section IV,D,2) (225,227,228) the enantiomers are employed in asymmetric hydrooligomerizations ofa-olefins... 

TABLE 2. Selected high-activity Ziegler-Natta titanium catalysts used in the homopolymerization of ethylene. 

Seppala, J.V. Harkonen, M. Luciani, L. Effect of the structure of external alkoxysilane donors on the polymerization of propene with high activity Ziegler-Natta catalysts. Makromol. Chem. 1989, 190, 2535-2550. 

The copolymerization of C2H4 together with a diolefin, e.g., 1,7-octadiene, as comonomer produces a cross-linked polyethylene with rubber elasticity, insoluble in all organic solvents. With the aid of homogeneous, highly active Ziegler-Natta catalysts it is possible to polymerize olefins in the presence of starch, cellulose, or lignin. 

For the higher activity Ziegler-Natta catalysts (Table II) based on reaction products of specific magnesium, titanium, and aluminum compounds, the similarity in size, coordination preference, electronic structure, and electronegativity of Ti(IV), Mg(II), and Al(III) ions is reflected in structural parameters and chemical properties (38) (Table III). The similarity in size between Mg(II) and Ti(IV) probably permits an easy substitution between ions in a catalyst framework. 

The role of magnesium ions in high activity Ziegler-Natta catalysts has received some recent attention with particular emphasis on four points (39) ... 

After 30 years, olefin polymerization by a coordinated anionic mechanism continues to receive worldwide attention as evidenced by a voluminous patent and journal literature. Much attention has been directed to catalyst and process optimization and understanding of key reaction variables. The development of high-activity Ziegler-Natta catalysts has spurred a renewed interest in simplified processes requiring no post-treatment of the polymers. Recent announcements by Union Carbide of a low-pressure, fluid bed... 

Uses Catalyst in Ziegler-Natta type systems for olefin and diene polymerizations as reducing agent with selective activity in certain org. reduction reactions chem. intermediate mfg. of primary alcohols and olefins, pyrophoric fuel thixotrope in water-based paints Manuf./Distrib. Akzo Nobel http //WWW. akzonobel. com, Al bemarle http //www.albemarle.com, Aldrich http //WWW.sigma-aldrich. com, FI uka http //www.sigma-aldrich. com Triisobutylamine... 

Present generation high activity Ziegler-Natta catalyst is comprised of titanium tetrachloride supported on magnesium dichloride [1-4]. Performance of the catalyst... 

Ciardelli, F., Menconi, F., Altomare, A., and Carlini, C. (1988) Polymerization of olefins by highly active Ziegler-Natta catalysts in presence of vinyl esters as "external" Lewis bases, XVI Congress of Italian Chenoical Soc., Bononiachem 88, Bologna, October 9-14, Abstracts, p.278... 

Kaminsky W, Sinn H (1982) Homogeneous and high active Ziegler-Natta catalysts with altmioxane as component. In Proceedings of the lUPAC 28th macromolecular symposium, Amherst, 1982, p 247... 

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