Metallocenes come of age

The number of materials based on metallocene-based catalysts is growing. One of the most recent is a hydrocarbon rubber, Nordel IP, which will give a consistent performance not previously available with EPDM. The result of a joint venture between Dow and DuPont, the application of metallocene technology to EPDM follows close on the heels of polyolefin elastomers and polyolefin plastomers using technology patented by Dow in this area.

The difference between metallocene-based technology systems and the conventional Ziegler-Natta catalysts in designing polymers lies in what is called a constrained geometry system. Ziegler-Natta catalysts feature multiple active sites, whereas a metallocene-based catalyst has only one. A single site system polymerises in a more uniform fashion so that every molecule is similar and polymer chains are more consistent in length. This results in a narrow molecular weight and co-monomer sequence distribution.

Uniformity leads to highly predictable physical and mechanical properties and allows scientists to relatively quickly develop polymers that precisely meet specific combinations of performance requirements.

The precise control of molecular weight and molecular weight distribution plus Mooney Viscosity, ethylene and ENB content in Nordel IP polymers yields highly predictable cure rates and physical properties, substantially reducing the variability common with current EPDMs.

Typical catalyst systems for the polymerisation of EPDM are based on vanadium or other transition metals. Compared to these systems, the Dow/DuPont catalyst produces EPDM with a catalyst efficiency 2 to 3 orders of magnitude greater, making Nordel IP the cleanest and most residue-free of the ethylene polymers available on the market today.

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