What Is a Ziegler-Natta Catalyst?
A Ziegler-Natta catalyst is one of three major catalyst types that are effective at polymerizing olefins, or hydrocarbon compounds with double carbon bonds. The three catalyst types in the Ziegler-Natta catalyst category are: solid and supported catalysts from titanium and a co-catalyst usually of aluminum; metallocene or transition metals with two cyclopentadienyl anions, or ions with a negative charge; and non-metallocene with oxygen or nitrogen ligands. All three of these catalysts are useful in vinyl polymerization and help to control tacticity, or the pendant groups sprouting from the vinyl’s carbon chain. The first catalyst, the titanium-based catalyst, was identified by Karl Ziegler in 1953. Giulio Natta then used the catalyst to make polymers.
When creating plastic or working with vinyl, it is imperative that chemical bonds are polymerized, or made into long chains of repeating elements. The most popular, and well used, catalyst for creating this effect is one of the Ziegler-Natta catalysts. A Ziegler-Natta catalyst is one of three catalyst types that are able to polymerize hydrocarbons with double bonds.
The first Ziegler-Natta catalyst created was the titanium variant. This catalyst starts with a titanium base. There is a co-catalyst added to the titanium, usually aluminum. Organic modifiers also are added to balance out the catalyst combination.
Metallocene catalysts are the combination of a transition metal and cyclopentadienyl. Cyclopentadienyl is a hydrocarbon combination with five carbon atoms and six hydrogen atoms, and there are two anions of this compound mixed with the transition metal. These metals are any which have an incomplete sub-shell, and are mostly found in the d-block of the elemental table.
Non-metallocene catalysts are the third Ziegler-Natta catalyst. These catalysts are first prepared with a scandium or actinoid metal, or soft to dense transition metals. After this, a ligand — an atom that binds to the central atom of the metal — is added to the metal of either oxygen or nitrogen.
All three of these catalysts are useful in vinyl polymerization, and all Ziegler-Natta catalyst types represent the major catalysts used in making plastic. This is because these catalysts help scientists and manufacturers control the vinyl’s tacticity, or how pendant groups are arranged in the vinyl polymer. The slightest change of the polymer skeleton changes the vinyl’s structure and use, so the skeleton has to be precise.
Two scientists are responsible for this group of catalysts. Ziegler made titanium-based catalysts. Natta took the concept and used in it polymerization. Natta also discovered the other two catalysts in the Ziegler-Natta catalyst category.
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