Polymers or plastics are materials that are found almost everywhere in modern life. Simply
look around the room where
you are sitting and there are probably many different polymers or plastic objects. However
most people would struggle to
name two or three different polymers or plastics despite the fact that there are
around 65 000 different polymers or
plastics in use around the world to make everything from toy ducks, mobile phone cases, paints, packaging and window
frames. Polymers are also found in the natural world e.g. cotton, silk, rubber, starch, DNA and many others could be
added to this list.
Polymers are giant covalent molecules made when lots of small molecules called monomers join together. Poly is a word normally meaning many and mono normally refers to one or a single object. Polymers are made when lots, normally thousands or even hundreds of thousands of small molecules called monomers join together to give one large molecule - a polymer. There are two basic ways to make polymers, addition polymerisation and condensation polymerisation, we will look at addition polymerisation on this page.
As a simple example of how an addition polymer is made consider the example below. A single
person could represent the monomer,
the small molecule which join together to form the polymer. The chain of people could
represent the polymer.
For addition polymerisation to work the molecules which are used as monomers must have
one noticeable feature, they
must be unsaturated, that is they must contain a carbon carbon double bond, C=C. They are alkenes,
The smallest and simplest unsaturated molecule is called ethene. Its molecular formula is C2H4. It contains 2
carbon atoms and 4 hydrogen atoms. It is an unsaturated molecule since it contains a double bond between the atoms
of carbon. A 3d model of it is shown opposite.
To turn the small unsaturated ethene molecule into the polymer poly(ethene) the C=C double bond needs to be split and the reactive intermediate molecules then link or join together, this is shown below:
The ends of the polymer chain extend to join with other ethene monomers to complete the polymer chain. We can think of the polymer a simply a series of repeating units that link over and over again, since all the monomers add together to form the polymer, this reaction is called addition polymerisation. This is shown below:
we could simply shorten this to:
where n is the number of monomers in the
polymer chain. Naming polymers is very simple. The name of the
monomer is enclosed in
brackets ( ) and the word poly is placed in front of the brackets. So in the example given the monomer
is ethene so
the polymer formed by the polymerisation of ethene would be called poly(ethene). This is
often shorten to polythene.
An equation for the reaction would be:
Hint: the polymer formula is usually enclosed in  as shown in the equation above.