Polymers
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Explainer Video
Summary
Polymers
In a nutshell
Polymers are large molecules made up of many smaller molecules known as monomers. The monomers are joined together during a reaction known as polymerisation, in the presence of a catalyst.
Addition polymerisation
Addition polymers are made up of unsaturated monomers such as alkenes. One of the bonds in the bond is broken so the carbon is able to form a bond with the adjacent monomer. Addition polymers are inert hence useful in making durable everyday products.
Examples
Plastics, polystyrene cups, resin and nylon are useful products made from addition polymerisation.
Naming polymers
The name of a polymer is formed by putting the name of the monomer in brackets and adding the prefix 'poly.' Some textbooks and online material may not use the brackets.
Example
Let the monomer be propene. The polymer will be named poly(propene).
Repeat unit
Since polymers are (very) large molecules they are represented using repeat units in the displayed formula.
To draw a repeat unit:
PROCEDURE
| 1. | Change the double bond in the monomer to a single bond. |
| 2. | Draw brackets around the repeat unit. |
| 3. | Add a bond to the carbon atoms at the end of the repeat unit. Ensure that the bonds extend outside the brackets. This shows that the chain is longer. |
| 4. | Add a subscript 'n' on the bottom right hand corner. This indicates a large number of repeat units. |
| 5. | Add the rest of the groups in the same position found in the monomer |
Problems with the disposal of addition polymers
Addition polymers are inert, therefore are unable to biodegrade. Instead, they are required to be burned leading to the formation of toxic gases. Carbon dioxide is also released contributing to global warming.
Crude oil is also required to make most addition polymers. Crude oil is a finite and non-renewable resource so it will eventually run out.
Common addition polymers
The table below describes some common addition polymers and their properties.
Polymer | Properties | Examples |
| Poly(ethene) | This polymer is flexible and cheap. It is also a good electrical insulator. | Plastic bags |
| Poly(propene) | This polymer is flexible and shatterproof. | Food packaging, buckets |
| Poly(chloroethene) | This polymer is tougher and lasts a long time. | Pipes, wire insulation |
| Poly(tetrafluoroethene) | This polymer is even tougher and it is resistant to corrosion. | Non-stick coating on pans |
Biological polymers
Biological polymers are examples of condensation polymers. Some of these are described below.
biological polymer | essential information |
| DNA | DNA stores genetic material and is made up of monomers called nucleotides. These are adenine (A), thymine (T), guanine (G) and cytosine (C). The nucleotides form polymers which then join together through hydrogen bonding to form a double helix structure. |
| Starch | Starch is how plants store their energy. It is a polymer of glucose. |
| Cellulose | Cellulose is the main component of plant cell walls and it is formed by a condensation reaction with glucose molecules. |
| Protein | Proteins are polypeptides. They are formed from monomers called amino acids that have joined together through condensation reactions. Different proteins will be formed from different amino acid sequences and they will all have different functions as a result. |
FAQs - Frequently Asked Questions
What are condensation polymers?
Condensation polymers form when two monomers join together and produce a water molecule.
What are polymers?
Polymers are large molecules made up of many smaller molecules known as monomers.
How are polymers named?
The name of a polymer is formed by putting the name of the monomer in brackets and adding the prefix 'poly.'