Homopolymers metallocenes

Catalyst Development. Traditional slurry polypropylene homopolymer processes suffered from formation of excessive amounts of low grade amorphous polymer and catalyst residues. Introduction of catalysts with up to 30-fold higher activity together with better temperature control have almost eliminated these problems (7). Although low reactor volume and available heat-transfer surfaces ultimately limit further productivity increases, these limitations are less restrictive with the introduction of more finely suspended metallocene catalysts and the emergence of industrial gas-phase fluid-bed polymerization processes. 

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... 

Figure 11 Homopolymer polypropylene product range with metallocenes. (From Ref. 29, with permission from Sterling Publications Limited.)...

Table 14 Comparison of Conventional Random Copolymner with Metallocene Copolymer and Homopolymer...

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. 

For example, it is possible to synthesize isotactic as well as syndiotactic polypropylene in high configurational purity and high yields. The same holds for syndiotactic polystyrene. Furthermore, metallocene catalysts open the possibility to absolutely new homopolymers and copolymers like, e.g., cycloolefin copolymers (COG) and even (co)polymers of polar monomers.The simplest metallocene catalyst consists of two components. The first one is a n-complex (the actual metallocene) that can be bridged via a group X and therefore can become chiral ... 

Cyclopentene polymerization has been catalyzed by several metallocenes (Table XVII). In each case, the homopolymers were found to contain no 1,2 enchainments. Whereas a mechanism similar to that proposed for the formation of 1,3 enchainments in polypropylene is reasonable, there is no plausible explanation for the formation of trans structures. 

The large availability of nucleating agents based on sorbitol enables the fabrication of clear PP products, with transparencies between 89 (homopolymer) and 96% (metallocen random copolymers). 

Conv. copolymer Metallocene copolymer Metallocene homopolymer... 

Single-site metallocene catalysts are also highly reactive vis-a-vis cycloolefins such as cyclobutene, cyclopentene or norbornene. While homopolymers of these cycloolefins have melting temperatures (>380°C), much too high for technical processability, ethylene-cycloolefin copolymers (COC s) - e.g. ethylene-norbornene copolymers - are amorphous materials with glass transition temperatures, above which they become soft and processable [W. Kaminsky, J. Polym. Sci. A, Polym. Chem., 2004, 42, 3911]. 

With metallocene catalysts, not only homopolymers such as polyethylene or polypropylene can be synthesized but also many kinds of copolymers and elastomers, copolymers of cyclic olefins, polyolefin covered metal powders and inorganic fillers, oligomeric optically active hydrocarbons [20-25]. In addition, metallocene complexes represent a new class of catalysts for the cyclopolymerization of 1,5- and 1,6-dienes [26]. The enantio-selective cyclopolymerization of 1,5-hexadiene yields an optically active polymer whose chirality derives from its main chain stereochemistry. 

Application To produce polypropylene (PP) homopolymer, random copolymers and impact copolymers, including Metallocene PP in the No-volen process. 

Products The process can produce a wide variety of homopolymers, random copolymers including terpolymers and pentene copolymers, and impact copolymers with up to 50% rubber content. Product range also includes metallocene PP based on a simple drop-in technology. 

Lummus Novolen Technology Polypropylene homopolymer, random copolymers, impact copolymers, including Metallocene PP Propylene (and ethylene for production of copolymers) Polymerization of propylene in one or two gas-phase reactors stirred by helical agitators to produce a wide range of products 27 2010... 

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