1. Polymers
Noadswood Science, 2016

2. Polymers To be able to explain what a polymer is +
Saturday, June 09, 2018
Polymers
To be able to explain what a polymer is +

3. Precise Learning
Polymers have very large molecules. The atoms in the polymer molecules are linked to other atoms by strong covalent bonds. The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature.
Students should be able to recognise polymers from diagrams showing their bonding and structure.

4. Polymers What are polymers
Polymers are huge molecules which are made up of lots of smaller molecules (monomers) which have been joined together

5. Properties
Different polymers can be made by using different monomers – these polymers can have very different properties…
Polymers have properties that depend on the chemicals they are made from, and the conditions in which they are made
Modern polymers have many uses, including: -
Waterproof coatings
Fillings for teeth
Dressings for cuts
Hydrogels for making soft contact lenses and disposable nappy liners
Shape memory polymers for shrink-wrap packaging

6. Nylon
Nylon was the first commercially successful synthetic polymer – a thermoplastic (softens when heated) silky material originally used in toothbrushes and later as tights…
It is formed when a combination of smaller molecules join together: two solutions with different densities are layered
A film of nylon appears instantly where the two layers meet

7. Monomer  Polymer
Polymers are very large molecules made when many smaller molecules join together, end-to-end
The smaller molecules are called monomers +

8. Monomer  Polymer Polymer: Poly(ethene) - polythene
Many ethene monomers can join end-to-end to make poly(ethene) or polythene
Initially the C=C double bond of the ethene must be broken, and then the molecules can be added together…

9. Monomer  Polymer Initially the alkene double bond (C=C) is broken
Monomers are joined together
Polymer formed

10. Monomer  Polymer Polymer: Poly(chloroethene) – PVC
Many chloroethene monomers can join end-to-end to make poly(chloroethene) or PVC…

11. Polymer Problems
One of the useful properties of polymers is that they are unreactive, so they are suitable for storing food and chemicals safely, but this property makes it difficult to dispose of polymers
Most polymers, including poly(ethene) and poly(propene) are not biodegradable meaning that micro-organisms cannot break them down, so they may last for many years in rubbish dumps
However, it is possible to include chemicals that cause the polymer to break down more quickly – carrier bags and refuse bags made from such degradable polymers are already available

12. Polymer Problems
Polymers can be burnt or incinerated – they release a lot of heat energy when they burn and this can be used to heat homes or to generate electricity
There are problems with incineration as carbon dioxide is produced, which adds to global warming
Toxic gases are produced unless the polymers are incinerated at high temperatures

13. Polymer Problems
Many polymers can be recycled reducing the disposal problems and the amount of crude oil used
It is crucial different polymers are separated from each other first, and this can be difficult and expensive to do

14. Modern Plastic Bags
Many polymers can be recycled reducing the disposal problems and the amount of crude oil used
Some modern plastic bags are now being made from biodegradable polymers such as cornstarch which will increasingly provide useful replacements for the main polymers currently used…

15. Thermosoftening & Thermosetting
Polymers can fall into two categories: -
Thermosoftening – can be heated and shaped many times
Thermosetting – can only be heated and shaped once
Thermosetting polymers have their chains cross linked by covalent bonds – the polymer is originally placed into a mould and heated causing cross links to form (further heat will not cause the polymer to soften or change shape)

16. Thermosoftening & Thermosetting
Thermosoftening (top) and thermosetting (bottom) showing the cross link bonds which causes it to hold it’s shape

17. Plasticisers & Slime
Poly(ethenol) is a polymer that dissolves in water to make slime: the viscosity of the slime can be changed to make it thick or runny by varying the amount of water

18. Practice Questions
A polymer is made up of polymer chains with cross-links between the chains. Is it a thermosetting or a thermosoftening polymer?
Polystyrene softens when it is heated above 100oC. It can then be moulded to make lots of different products. Suggest whether polystyrene is a thermosetting or thermosoftening polymer with reasoning

19. Answers Thermosetting
Thermosoftening – they soften when heated and can be remoulded