Constrained-geometry catalysts

As mentioned in Section 10.3.2, there has been recent interest in the use of the Dow constrained geometry catalyst system to produce linear low-density polyethylenes with enhanced properties based, particularly, on ethylene and oct-l-ene. 

Structure 6. General structure of Constrained Geometry Catalysts. 

The sterically unencumbered catalyst active site allows the copolymerization of a wide variety of olefins with ethylene. Conventional heterogeneous Ziegler/Natta catalysts as well as most metallocene catalysts are much more reactive to ethylene than higher olefins. With constrained geometry catalysts, a-olefins such as propylene, butene, hexene, and octene are readily incorporated in large amounts. The kinetic reactivity ratio, rl, is approximately... 

Figure 5. Formation of cationic constrained geometry catalysts.

Scheme 1. Mechanism for formation of long-chain branching. Ti = active constrained geometry catalyst.

OS 62] ]R 1] ]P 45] The impact of the choice of catalyst on catalyst plug-induced ethylene polymerization was analyzed [1]. A constrained-geometry catalyst (CGC) with a cyclopentadienyl moiety was about 3.6 times more active than a CGC-indenyl catalyst. 

Species concentration Capillary number Concentration of species a Computer aided design Concentration of species b Charge-coupled device Eluid specific heat Computational fluid dynamics Constrained-geometry catalyst Concentration at node i Concentration of species i Elux limiter Specific heat... 

Boratabenzene analogues of commercially significant constrained geometry catalysts have also been investigated.49 For the MAO-activated copolymerization of ethylene/l-octene, the illustrated Ti(IV)-boratabenzene complex is about four times more active than the Zr(IV) complex. The level of 1-octene incorporation is significantly lower than for the corresponding Cp-derived catalysts, due perhaps to the greater steric demand of the amidoboratabenzene framework. 

Constrained geometry catalysts with alkoxide and phosphide donor arms have also been reported. The most active examples include complex (33), which polymerizes ethylene with an activity of 2,100 gmmol 1h 1 bar-1131 and (34), which exhibits an activity of 2,240 g mmol-1 h-1 bar-1 for the copolymerization of ethylene with 1-octene.132... 

Constituent properties of bainite, 23 280 of martensite, 23 280-281 of pearlite, 23 280 of tempered martensite, 23 281-282 Constrained geometry catalysts, 16 81 20 193... 

Constrained-geometry catalysts for C2H4 polymerization 88 that are counterparts of well-known ansa-metallocene systems have been prepared and shown to be active, in combination with MAO, toward polymerization of ethylene the product is almost entirely polyethylene, with ca. 1% of 1-octene obtained. The titanium complex was found to be four times as active as the zirconium species.1... 

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. 

Figure 1. General structure of group 4 polymerization catalysts. Generic bent bis-Cp metallocene, part a), generic mono-Cp or constrained geometry catalyst (CGC), part b).

Figure 10.22. Dow s constrained geometry catalyst Insite and DSM s Lovacat ...

CONSTRAINED GEOMETRY CATALYST, 154 CONTACT ANGLE, 262 CONTACT MOULDING, 246 CONTINUOUS EXTRUSION, 314 CONTINUOUS MOULDING, 312 CONTINUOUS... 

The ansa-sandwich complexes, sometimes called constrained-geometry catalysts, exhibit a good ability to incorporate co-monomers. The catalysts (a) to (g) are soluble in solvents such as toluene. In the catalyst (h) the metallocene is supported on silica. Such solid-supported catalysts can be suspended in hydrocarbons for metering into the polymerization reactor [4],... 

Three types ot metallocene catalysts are presently used in industry Kaminsky, ionic, and Dow constrained-geometry catalysts. 

In the early 1990s supported metallocenes were introduced to enable gas phase polymerisation. Also ethene/a-olefin copolymers with high comonomer content, cycloolefin copolymers and ethene-styrene interpolymers became available. In 1990 Stevens at Dow [22] discovered that titanium cy-clopentadienyl amido compounds (constrained geometry catalysts) are very beneficial for the copolymerisation of ethene and long-chain a-olefins. 

The constrained geometry catalyst (CGC), developed at Dow, was the first single-site catalyst [77, 78] discovered to be capable of producing long-chain branched polyethene. Since the announcement of the ability of CGC catalyst to produce small amounts of LCB, several conventional bis (cyclopentadi-enyl)-based metallocene complexes have been reported to produce low levels of LCB [59, 79, 80, 81, 82, 83]. 

These monocyclopentadienyl amidotitanium complexes, which are classified as constrained-geometry catalysts, are capable of producing low-density polyethylene (ethylene copolymers with C4, C(, or Cg 1-alkenes) that also contain long-chain branches, in contrast to strictly linear low-density polyethylene (ethylene copolymers with C4, C(, or Cg 1-alkenes) produced by bent metallocene-based catalysts [30,105,148,149]. 

In addition to the metallocenes described previously, so-called halfsandwich compounds or constrained-geometry catalysts (Fig. 3) such as dimethylsilyl-t-butylamido cyclopentadienyl titanium dichloride are used. These catalysts are excellent for producing polyethylenes with long-chain branching and can incorporate high amounts of comonomers such as 1-octene... 

Chum, P.S., Kao, C.I., and Knight, G.W., Structure/property relationships in polyolefins made by constrained geometry catalyst technology, Plast. Eng., June 1995, 21-23. 

Monocyclopentadienyl complexes have also been used as active polymerization catalysts. Indeed, titanium monocyclopentadienyl metallocenes—the so-called constrained geometry catalysts —have been focal points of Dow s activity in this area. A typical example of such a catalyst is shown by the structure 6.24. 

Z-selective cross-coupling of terminal alkynes with isocyanides to exclusively yield (Z)-l-aza-l,3-enyne products has been achieved for the first time using a constrained geometry catalysts [Y(C5Me4Si(Me2)NR)(Alk) (THF)X] (Aik = R, dimethylaminobenzyl R = lBu, Ph, 2,4,6-Me3C6H2. The intermediate was shown to be the acetylide-bridged dimer [Y(C5Me4Si (Me2)NR)(p-C=CPh)]2.41 [24]... 

The patterned amino-silica is used as a support for immobilizing a titanium constrained geometry catalyst, shown in Scheme 2. The amine sites are first reacted with chlorodimethyl-(2,3,4,5-tetramethyl-2,4-cyclopentadien-l -yl)... 

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