Metallocenes single site catalyst

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. 

Polymerisation with Homogeneous Metallocene Single-site Catalysts... 

High-Density Polyethylene (HDPE). Polymerization of ethylene to polyethylenes is most often carried out at low temperature and pressure, using either the Ziegler aluminum triethyl plus titanium tetrachloride catalyst system, the Phillips chromic oxide plus silica plus alumina system, or more recently the newer metallocene single-site catalyst systems. 

Kaminsky, Sinn and coworkers discovered in the late 1970s that an enormous increase in activity with metallocene single-site catalysts is realized when methylaluminoxane (discussed in Chapter 6) is used as cocatalyst. 

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 6.3 Structures of metallocene single site catalysts used to produce stereoregular polypropylene (M. P. Stevens, Polymer Chemistry, S Edition, Oxford University Press, p 246,1999).

Though metallocenes have been known since 1951 (5), it was not until the work of Kaminsky, Sinn and coworkers (6, 7) in the mid- and late-1970s that the enormous potential of metallocene single site catalysts was realized. The key discovery was the dramatic increase in activity resulting from use of methylaluminoxanes in place of diethylaluminum chloride and other conventional cocatalysts. Commercial use of metallocene single site catalysts began in the early 1990s. 

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).

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. 

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 1968, Union Carbide introduced the gas-phase FBR low-pressure UNIPOL process. The first large-volume production unit started in 1970 in Sweden and later in the USA and 13 other countries. Initially the UNIPOL process used Z-N catalyst and after 1980 the metallocene single-site catalyst. In the early 1990s LLDPE constituted 25 % of the world production of PEs (Fraser et al. 1997 Univation Technol. 2007). A summary of conditions used in the solution- and gas-phase processes is presented in Table 18.2. 

Metallocene plastomers are plastomers made using metallocene single-site catalysts. Other polyolefins exist in this composition range made with conventional catalysts Dow ATTANE (10), Union Carbide FLEXOMER (11), and Mitsui TAFMER products (12). These are generally called very-low-density poly-ethylenes (VLDPEs) and ultra-low-density polyethylenes (ULDPEs), and are not discussed in this chapter. 

At the time of this writing a number of metallocene/single-site catalyst technologies are available with which to produce polypropylene (see Table 11). Metallocene-based polypropylenes are commercially available and even catalyst licenses are available (264). 

Additional Methods for Activating Metallocene Single-Site Catalysts... 

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