Catalysts are of enormous industrial use,as in the polymerisation of
ethene to give poly(ethene),usually called polythene.When this
was first manufactured by ICI in the early 1950s,a process was
used requiring a pressure of 2000 atmospheres and a temperature of
573k.The discovery of a catalyst for this process by Karl Ziegler in
the late 1950s enables the process to be run now at less than 50
atmospheres and at a temperature of between 310 and 360k.The catalyst
is a mixture of titanium(1v) chloride and treethylaluminium,the precise
details of which are secret.
The Italiano,Giulio Natta developed a
similar catalyst for the manufacture of poly(propene).As well as
accelerating the polymerisation,this catalyst made it possible to
produce stereoregular polypropene,which has a regular rather than
random arrangement of the methyl side chains.By controlling the precise
proportions of the different types of polymers,it is possible to tailor
the properties of the final plastic(such as density,tensile strength
and elasticity) to a particular specification.Ziegler and Natta
received the 1963 Nobel prize for their work on polymerization
catalysts.
Ziegler-Natta catalysts have two important
attributes.Firstly,they allow polymerization to take place under
relatively mild conditions of temperature and pressure.secondly,they
produce polymers of very regular geometry which has an important effect
on their properties.