Addition Polymerisation

Thousands of unsaturated molecules (alkenes) are added together to form one large molecule called a polymer. There are no by-products.

This addition polymerisation reaction will add many ethenes to make a polyethene.

Example used here:
• monomer is ethene:
• to make the polymer called polyethene
• by a polymerisation reaction

Polymerisation (reaction) of ethene (monomer) to produce polyethene (polymer)

Polythene is a substance that is:
How is polyethene made?
It is made from ethene, an unsaturated molecule. We call the ethene a monomer, because many of them are going to join to each other, to become the polymer called polyethene.
In addition polymerisation reactions, no by-products are formed.

Step 1
Three ethene monomers are shown, that will eventually combine to form the polymer.

Step 2
High temperatures and very high pressures are used.

The double bonds of ethene are broken, and free radicals are formed at each molecule, waiting to connect to each other.

These are not alkanes!

Step 3
The above are all joined to each other, and a very large molecule called polyethene is formed.

There are no by-products.
Of course, many thousands of such ethene molecules (the monomers) join together to form the very large molecule called polyethene.

This is how polyethene is represented. The n indicates many such repeating molecules as in the bracketts.


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