Metallocene catalysis polypropylenes

The application of metallocene catalysis to the preparation of polypropylenes reached a commercial stage with the production by Exxon of their Achieve range in 1996 and in 1997 by Targor, the BASF-Hoechst joint venture with the introduction of Metocene. Such metallocene polypropylenes are, however, only a small proportion of the total polypropylene market, predicted at only about 3% of the total in 2005. 

Polypropylenes produced by metallocene catalysis became available in the late 1990s. One such process adopts a standard gas phase process using a metallocene catalyst such as rac.-dimethylsilyleneto (2-methyl-l-benz(e)indenyl)zirconium dichloride in conjunction with methylaluminoxane (MAO) as cocatalyst. The exact choice of catalyst determines the direction by which the monomer approaches and attaches itself to the growing chain. Thus whereas the isotactic material is normally preferred, it is also possible to select catalysts which yield syndiotactic material. Yet another form is the so-called hemi-isotactic polypropylene in which an isotactic unit alternates with a random configuration. 

Isotactic polypropylenes produced by metallocene catalysis are now being produced by a number of different manufacturers and because different systems are used there is some variation in properties. Typically however such materials have similar density, hardness and tensile strength to conventional homopolymers but differ in having... 

One such reported example is the synthesis of polypropylene-6-polymethyl-methacrylate (PP-6-PMMA) copolymers utilizing metallocene catalysis and the borane chemistry. In the initial step, PP with chain-end olefinic unsaturations was prepared using metallocene catalysts such as Et(Ind)2ZrCl2/MAO. The unsaturation sites were then hydroborated by 9-borabicyclo[3.3.1]nonane (9-BBN) to produce borane-terminated PP (43) (Fig. 30), which was selectively oxidized and interconverted to a... 

A foamable isotactic polypropylene homopolymer is obtained by metallocene catalysis and has a molecular weight distribution and density, which fall within broad ranges. It may be prepared in a multiple stage polymerisation process nsing the same metallocene component in at least two stages. 

Antberg, M. Dolle, V. Klein, R. Rohrmann, J. Spaleck, W. Winter, A. Propylene Polymerization by Stereorigid Metallocene Catalysts Some New Aspects of the Metallocene Stmcture/polypropylene Microstructure Correlation. In Catalytic Olefin Polymerization, Studies in Surface Science and Catalysis-, Keii, T., Soga, K., Eds. Kodansha-Elsevier Tokyo, 1990 p 501. 

Polypropylene (PP) and polyethylene (PE) fibres float in water, they are not soluble in cold concentrated sulphuric acid but soluble in boiling perchloroethylene. They are also easily recognizable and distinguishable by their melting points PE 124-138 °C (occasionally up to 155 °C) (low density PE 105-129 °C), PP = 160-175 °C (if based on metallocene catalysis 15-20° C lower). 

Yang, K., Huang, Y, and Dong, J.-Y. 2007. Efficient preparation of isotactic polypropylene/ montmorillonite nanocomposites by in situ polymerization technique via a combined use of functional surfactant and metallocene catalysis. Polymer 48 6254-6261. 

SYNTHESIS OF THERMOPLASTIC-ELASTIC POLYPROPYLENES 9.3.1 Polypropylenes THROUGH Metallocene Catalysis... 

Figure 14.2 Upper. Illustration of metallocene catalyst structure, which must be specific for each stereo-specific polymer structure. Lower. Microstructures of polypropylene most can be made via metallocene catalysis polymerization.

Transition metal catalysis plays a key role in the polyolefin industry. The discovery by Ziegler and Natta of the coordination polymerization of ethylene, propylene, and other non-polar a-olefins using titanium-based catalysts, revolutionized the industry. These catalysts, along with titanium- and zirconium-based metallocene systems and aluminum cocatalysts, are still the workhorse in the manufacture of commodity polyolefin materials such as polyethylene and polypropylene [3-6],... 

Atactic polypropylenes are produced in catalysis by C2v-symmetric metallocenes that are achiral, such as Cp2MCl2 or (Me2Si(FLu)2)ZrCl2. The only stereocontrol observed is both of the chain-end type and low because the chiral center of the terminal monomer unit of the growing chain is in the P position as a consequence of the 1,2 insertion of the monomers. A significant influence on the tacticity is observed only at low temperatures, being much more pronounced for titanocenes and hafnocenes than zirconocenes as a consequence of their shorter M-Ca bonds, bringing the chiral p-carbon closer to the active center (147,148). 

Work in the application of metallocene-based catalysis to olefin polymers has become a research topic of growing interest in recent years. A great number of symmetrie and chiral zirconocenes have been synthesized to give totally different structures of isotactic, syndiotactic, atactic or block polymers. The isotactic sequence length of polypropylene is influenced by the nature of the ligands of the metallocene. New ring or bridge substituted metallocene/methylalumoxane catalysts for the olefin polymerization are described. 

LyondellBasell Polypropylene, Metallocene upgrade Propylene Metocene polypropylene (PP) technology upgrades existing and newly built PP plants by extending plant capability to cover specialty PP products with specific and unique features that can be produced with single-site catalysis, in addition to the existing conventional product portfolio 6 NA... 

The period following the Second World War saw the emergenee, with an accelerated speed, of new polymerization methods in 1953-1954, polymerization catalysis by coordination was developed by K. Ziegler and G. Natta (Nobel Prize, 1963), which led to for high-density polyethylene (PEHD) and polypropylene (PP). Anionic polymerization and the concept of living polymerization proposed by M. Szwarc in 1956 led to the design of blocks copolymers and the first macromolecular architectures. We then saw the emergence of catalysis by metallocene in 1980 by W. Kaminski. Radical polymerization controlled by M. Sawamoto and K. Matyjaszewski in 1994 combined the benefits of radical and ionic polymerization without the drawbacks of the former. 

As will be discussed later, the polymerization of propylene is catalyzed by either Ziegler-Natta catalyst or metallocene catalyst. In the Ziegler-Natta catalyzed polymerization, the propylene monomer accesses the reaction site between the metal and carbon atoms in two ways the head-to-tail and tail-to-head insertion. The head-to-tail insertion occurs primarily in isotactic polymerization [8-10], while the tail-to-head insertion occurs in the low-temperature catalysis with VCl4-Et2AlCl catalyst [11]. There are mostly head-to-tail insertions and very few head-to-head or tail-to-tail inversions in the main chain of polypropylene [12,13]. 

Industrial applications of metallocene catalysts are a recent development AU of them possess in their reaction center two aromatic rings, between which a complex bond holds a metal atom, in most cases zirconium. This type of catalysis produces polymers with exceptionally uniform structures. The chain lengths of the individual molecules closely approximate one another. The spatial structure is therefore well-defined. Polypropylene, for instance, is completely isotactic. It is even possible to produce polypropylene in which the pendant group orientation alternates between right and left. The resulting substance is known as a syndiotactic polypropylene (see above) [3]. 

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