Mechanism of Ziegler-Natta Catalyst

The polymerization of olefin monomers into superior polymers best demonstrates the mechanism by which the Ziegler-Natta catalyst functions. This mechanism was initially proposed by Karl Ziegler and Giulio Natta based on their groundbreaking research in the 1950s.

• Coordination: The active sites on the catalyst surface are coordinated with olefin monomers, including ethylene and propylene. The interaction between the electron-rich olefin double bond and the electron-deficient catalyst metal core results in this coordination. The coordination complex is formed between the pi electrons of the monomer and transition metal.
• Catalyst Activation: The Ziegler-Natta catalyst is activated to start the process. These catalysts usually consist of compounds made of transition metals, such vanadium or titanium, supported on a carrier element, most frequently magnesium chloride. Triethylaluminum (AlEt₃), or any other organoaluminum molecule, is used to activate the catalyst by causing active species to develop on its surface. Polymerisation begins by inserting monomers at the joining of transition metal ion at the end of the chain.
• Chain Growth: The monomer that is injected joins the expanding polymer chain that is linked to the catalyst. As more monomers joins and coordinate at vacant orbital sites, new long polymer chains are formed. At this tage, the C=C is also inserted into Ti-C bond at the active center.

After the polymerization has been completed, there is need to end the step to obtain the polymer of specified degree. Let’s see how termination happens.

Termination Step: Chain Transfer

In the termination step of Ziegler-Natta polymerization, chain transfer can occur. In this step a growing polymer chain transfers to a chain transfer agent, disrupting the polymerization process. The growing polymer chain gains a hydrogen atom from the chain transfer agent during this transfer, which stops the growth of the original polymer chain and forms a new one on the chain transfer agent. Chain transfer agents are essential for regulating the molecular weight and characteristics of the resultant polymer.

So, the Ziegler-Natta polymerization mechanism is an important method of polymer production methods because it provides a flexible and effective way to produce high-quality polyolefins with desired features.

Ziegler Natta Catalyst is a class of catalysts that are made with the reaction of transition metal halide and organometallic compounds. In Chemistry, Ziegler-Natta catalysts are a class of catalysts widely used in the industrial production of polyolefins, like polyethylene and polypropylene, etc. These catalysts, which Karl Ziegler and Giulio Natta separately developed in the 1950s. They revolutionized polymerization methods and brought Ziegler and Natta the 1963 Nobel Prizes in Chemistry. Ziegler-Natta catalysts are significant in creating polymers with desired qualities such as high strength, flexibility, and thermal stability.

This article deals with Ziegler Natta Catalyst in detail by learning its formula, types, mechanism, applications, and limitations.