Polymerisation

Hiya!

Today I've got another fab chemistry topic on polymerisation of alkenes and monomers! Hope you're all-keen to read this. Happy reading!

First let's start small. Monomers are small, reactive molecules that react together in a repeating pattern to from long structures like polymers. Polymers are very large molecules made up of repeating forms of monomers. These are complimentary definitions as you can tell!

In addition polymerisation, we use alkenes like ethene and propene to create polymers. Addition polymerisation is simply adding together many monomers to form a long chain called a polymer. We do this by using the C=C bond and breaking this so that the ethene can bond to other ethene monomers.

(Mike Alonso)

Condensation polymerisation is where monomers react together to form a large polymers and a smaller by-product. The difference between condensation polymerisation and addition polymerisation are relatively low but it's important to know that in condensation polymerisation, by-products are also produced (often water). A well-known example of condensation polymerisation is amino acids. All existing amino acids have the functional group COOH and NH2. The monomers (singular amino acids) bond together to produce a longer polymer and a molecule of water. For every monomer added, there is an extra molecule of water (H2O) produced. Let's highlight the differences between addition polymerisation and condensation polymerisation:

• AP requires monomers with a double carbon bond (C=C) whereas CP doesn't. 
• CP needs monomers with two functional groups each
• AP produces one long polymer, CP produces a polymer and a smaller by-product (often water)

(Joseph Grave)

There are many naturally occurring biological polymers so here are some good examples to note:

• DNA- DNA is the arranged double helix structure which consists of two intertwining polymers. These polymers consist of four different types of nucleotides which are all defined by their distinctive base changes.
• Enzymes (proteins) which are biological catalysts. The proteins, like DNA, are made up of amino acids which form the proteins for the enzyme
• Starch and cellulose. Both starch and cellulose are biological polymers as they are complex stores of glucose. Starch stores carbohydrates in plants whilst cellulose makes up cell walls which provides a strong outer layer.

Another example that we often look at is the usage of polyesters. Whilst we can find polyester chains naturally, we can also artificially create polyester using condensation polymerisation. A simple polyester can be made from a monomer with two hydroxyl (OH) functional groups and a monomer with two carboxylic acid funtional groups (COOH).