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Ziegler catalysts

A Ziegler catalyst has two components.

For example:

1. a titanium compound, TiCl4 or TiCl3 - the catalyst
2. an organoaluminium compound - the co-catalyst

The polymer forming in the pores of the catalyst particle causes it to split into smaller fragments, exposing more sites, so more polymer starts growing. The particles of catalyst split again and again as the polymer forms, until in the end there are extremely tiny particles of catalyst, completely invisible in the poly(ethene).

Typically 1 g of a commercial catalyst is capable of producing 10 kg of polymer - that's 10,000 times it's own weight! This figure may be higher or lower depending on the exact formulation of catalyst, and on the polymerisation conditions used

The titanium compounds are deposited on pores in the support and these very porous particles expose many active sites to the monomer.

The catalyst is not recovered, but Ziegler catalysts are so highly active, that the very low concentrations of minute catalyst particles can safely be left in the final polymer.

They are not cheap and are hard to handle being very sensitive to oxygen. Most are used on supports like silica, alumina, or MgCl2.

Ziegler catalysts need to be handled inside a glove box in an inert dry atmosphere