Non-Metallocene Single-Site Catalysts

More recent catalyst developments have identified additional catalyst compositions that are not based on a metallocene complex or the Dow constrained geometry system. Nova Chemicals Inc. has most likely 

Exxon/1991 Exact Exxpol high pressure process 0.87-0.92 g/cc Ethylene/1-butene Ethylene/1 -hexene 

Mitsui/1995 Evolue Gas Phase Process Ethylene/1 -hexene 0.90-0.94 g/cc Ml 1.0-3.8 

Chevron-Phillips/1996 Marflex/mPact Slurry Loop Process 0.91-0.94 g/cQ MI 0.5-20 Excellent film clarity Roto- and Inject-molding grades 

Two recent developments in non-metallocene single site catalysts for polyethylene are noteworthy  

These developments and non-metallocene single site catalysts in general represent the next wave of innovation in polyolefin catalysis which should permit production of polyethylenes with unique properties at lower cost. They will complement, and perhaps even supplant, many of the metallocene single site catalysts commercialized in the 1990s. 

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The product design capability will expand to include polar comonomer incorporation. Copolymerisation of polar comonomers with a-olefins will alter the properties significantly and lead to materials with improved dye-ability and adhesion properties, as well as better compatibility with non-ole-finic polymers. In particular, the novel non-metallocene single-site catalysts, developed by Brookhart, Grubbs and others, are extremely tolerant to polar groups. 

In the 1990s, polyethylenes produced with metallocene single site catalysts were commercialized and non-metallocene single-site catalysts were discovered by Brookhart and coworkers. 

Figure 6.4 Non-metallocene single site catalysts based on chelated late transition metals are illustrated here with an iron catalyst (See B. Small, M. Brookhart and A. Bennett, /. Am. Chem. Soc., 1998,120,4049 see also S. Ittel, L. Johnson and M. Brookhart, Chem. Rev. 2000,100,1169).

In 1999 Equistar Chem. Introduced high performance, non-metallocene single-site catalyst for PE s. 

Waymouth has polymerized silyl protected alcohols and amines, and non conjugated diene monomers, with cationic Group IV metallocene single site-catalysts. He has found that chiral [(EBTHI)ZrMc] X catalysts, where EBTHI = ethylene-1,2 bis(Ti -4,5,6,7-tetrahydro-l-indenyl), are more easily poisoned by silyl ethers than are [CP2 ZrMe] ] catalysts. Also [(EBTHI)ZrMe] X catalysts are inactive for the polymerization of 4-TMSO-l,6 heptadiene but readily polymerize with the more sterically hindered TBDMS protect monomer. 

In the late 1980s and in the 1990s, homogeneous metallocene-based Ziegler Natta and related aluminium-free catalysts as well as other non-metallocene-based homogeneous single-site catalysts, which are active in the syndiospecific polymerisation of styrene, were found also to promote the polymerisation of conjugated dienes [16,38 13],... 

There are two types of single site catalysts. The most well-known are based on metallocenes. Non-metallocene types are a relatively recent development and most are based upon chelated compounds of late transition metals, primarily Pd, Ni and Fe. Each single site catalyst type is addressed below. 

The alumoxane cocatalysts have at least two functions alkylation of the metallocene component, which takes place within seconds even at -60 °C (eq. (2)) and formation of the active species by abstraction of Me" (eq. (3)). The resulting active species is discussed as being a 14e (= 14 valence electron) cationic alkylmetallocenium ion formed by dissociation of the metallocene alumoxane complex [26,27]. The [alumoxane-Me]" anion is regarded as weakly or non-co-ordinating. Nearly every zirconocene atom is active, forming a single-site catalyst [28, 29]. 

Copolymerization of cyclic olefins such as cyclopentene and norbomene with ethene or propene yield cycloolefin copolymers in which the presence of non-cyclic units introduce flexibility in the polymer chain. Thus, the copolymers are amorphous, processable, and soluble in common organic solvents. Early attempts at such copolymerizations were made by using heterogeneous TiCV AlEt2Cl or vanadium catalysts, but real advancements were made utilizing metallocenes and other single-site catalysts, which are about ten times more active than vanadium systems and other Ziegler-Natta catalysts. 

In the case of lumped processes, hybrid model design focuses on reducing a complex set of static relationships with mat r fit parameters by overall fiizzy sub-models. These sub-models can be derived from measurements. A polymer reactor has been used as an example. In the liquid phase reactor, which is ideally stirred, monomer reacts to polymer by means of a single site metallocene catalyst. The inputs of the reactor are listed in Table 30.2 the load Fin, the hydrogen fraction of the feed xh2, the activated catalyst fraction Xc,a, the non-activated catalyst fraction Xc,na, the monomer fraction and the jacket temperature 7 adfe,. The most important outputs are the molecular weight distribution MWD (or q, the chain termination probability which is inversely proportional to MWD) and the conversion or (feed mass fraction conversion). The model is described in detail by Roffel and Betlem (2003). The requirements for the model of this reactor are ... 

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