Page 32 - Curriculum Visions Dynamic Book

Making polymers
Polymers are made in two ways: by adding building blocks together in long chains to produce materials known as addition polymers, and by removing water molecules to produce materials known as condensation polymers. These two types of polymer are important, and they produce such a wide range of everyday materials. On the next few pages is information on addition polymers; condensation polymers are described on page 36.
The remainder of the book will look at some important polymers.
Addition polymerisation
Some hydrocarbon molecules are very reactive and can be joined together, or polymerised. The reactive units are those in which carbon atoms are joined by a double bond. Ethene, shown below, is an example.
To polymerise these units, or monomers, the double bond is broken and one bond used to join the unit to its neighbours. This builds long chains and is known as “addition polymerisation”.
Carbon
Hydrogen
 In the manufacture of polythene, ethene gas, obtained from refining petroleum, is bubbled through a solvent to dissolve the gas. In the presence of a catalyst, the monomer polymerises to form long chains made up of 30,000 to 40,000 molecules. These chains intertwine, so that the resultant molecules cannot easily move about, and thus the material is a solid.
Polythene is cheap to manufacture and is used to make polythene bags and buckets. The properties of this polymer can be altered by substituting some or all of the hydrogens in
the hydrocarbon chain with other elements or compounds. Some of these other polymers are shown on the opposite page.
 This represents a molecule of ethene. Units like this that can be polymerised are known as monomers.
 This represents a unit of addition polymerisation derived from ethene. The ethene molecules join together to form the polymer polyethene, more commonly known as polythene.
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