Metallocene-based polyethylene products

Metallocene-based polyethylene does not offer the lower production costs associated with LLDPE. Hence there will be a price premium for the new materials but this is felt to be justified in view of their improved property profile. 

Metallocene based polyolefins and polyolefin elastomeric compositions (POE) are often noted in supplier product literature to exhibit useful (and commercially viable) properties in blends with other polyolefins. Metallocene based polyethylene has also been noted to have the potential to replace the LLDPE/LDPE blends that are employed in a myriad of film applications [32 ]. PP/metaUocene ethylene-a-olefin copolymer blends for car interior applications have been noted [33 ]. MetaUocene-LLDPE blends with HDPE have been proposed for heavy-duty industrial grade bags as well as food packaging films [34]. Exxon-Mobil product literature notes the utility and ease of blending the metallocene LLDPE Exceed with other polyolefins. PP/POE blends showed similar mechanical properties and lower viscosity than the more conventional PP/EPDM blends [35]. Polyolefin plastomers (POP) imder the tradename Affinity GA were introduced by Dow as a polymer blend additive to improve the flow without loss of... 

A narrow molecular weight distribution" (MWD) is a unique feature of polymer products of homogeneous metallocene-based catalysts. Typical values of Myj/Mn are 1.6-2.4 for polyethylenes and 1.9-2.6 for polypropy-... 

A unique feature of polymer products obtained with homogeneous metallocene-based catalysts is their narrow molecular weight distribution (MWD). Thus the values of for polyethylenes and polypropylenes are typically near 2 which... 

A unique feature of polymer products obtained with homogeneous metallocene-based catalysts is their narrow molecular weight distribution (MWD). Thus the values of My,jMn for polyethylenes and polypropylenes are typically near 2 which would indicate the presence of uniform active species in catalysts. Some researchers have thus suggested that the catalysts could be single site, while others have explained that two or more kinds of species can have very similar values for the kpjktr ratio, giving rise to narrow MWD products. 

Although ethylene/1-olefin copolymers were well documented in the late 1950s with the discovery of the chromium-based Phillips catalyst and the titanimn-based Ziegler catalyst, it was the discovery of metallocene-based single-site catalysts and the constrained geometry catalyst system that significantly increased the various types of new ethylene-based copolymers that are available for commercial applications. These new catalysts created new products, applications and markets for the polyethylene industry. 

Borealis has started up its metallocene-based slurry loop polyethylene (PE) plant at Ruenningen, Norway. Borealis will produce 30,000 t/yr of metallocene-based products at the plant in 1997. Borealis has agreed a licensing deal with Exxon Chemical which should avoid future patent conflicts over the companies respective metallocene technologies. In 1996... 

There are two methods used to blend polypropylene and EPDM rubber to make a TPO. The original method, still used extensively, is to simply mechanically blend the two polymers together with high shear mixing at an elevated temperature. However, a newer procedure employs new catalyst technology to blend EPDM and PP in the polymer reactor itself. This newer technique lowers the TPO production costs however, this type of TPO can only be obtained from the polymer manufacturers themselves. Reactor-produced TPOs can also be made softer than the mechanically blended TPO types. Some TPOs are also based on polyethylene as well (such as metallocene-catalyzed polyethylene), see Figure 6.7. 

Ziegler-Natta catalysts are widely used in the production of high-density and linear low-density polyethylene (HDPE and LLDPE). More than half the world production of HDPE and over 90%o of LLDPE is based on Ziegler-Natta catalysts, although increased use of metallocene and other single-site catalysts is expected throughout the next decade. 

It is claimed that the branching of polyethylene can be controlled to the extent that the product can even be more branched than conventional low-density polyethylene (1,2—300 branches/1,000 atoms) [18, 19]. The cationic Ni-diimine catalyst shown above (R = H, CH3), with the methylaluminoxane analog, has been found to polymerize ethylene in toluene at room temperature at the rate of 110,000 kg/Ni/h. This is comparable to the metallocene rates. The Pd-based catalysts are less active than their Ni analogs [19]. 

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