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Understand Polymerisation

Worksheet Overview

Think of the most important things in your life – your phone, your tablet, your vacuum cleaner (if you like having a clean bedroom). They will all be made with plastics in them. The making of plastics was a revolution in chemistry – suddenly it was cheap and easy to make basically everything, and humans embraced plastics like the new future. It is easy to be critical of the overuse of plastics now, after all we know how much harm they can do to the environment, but back in the day, they were super.

 

The manufacture of plastics comes from oil. Polymers are very big molecules with long chains and they are made from many small molecules called monomersPoly- means many, mono- means one. When you stick together loads of monomers, you get a polymer – most of the time this is a plastic.

Ever heard of the plastic polypropane? Well, you get the name of the polymer if you add the prefix poly- before the name of the monomer. For example, poly(propane) which is used to make ropes, is made of lots of propane molecules joined in a long chain.


So, there are a few words you need to know when talking about polymers. Alkene is the big one here. In the diagram below, on the left-hand side you can see an alkene. If you look between the two carbons, you can see that there is a double bond (two lines). This is what makes an alkene. If it has a carbon-carbon double bond, then it is ripe for being made into a plastic.

 

An image showing how an alkene is made into a long chain polymer.

 

So, how do we make a monomer into a polymer?

 

We need a chemical reaction that breaks apart one of the double bonds in the alkene. When this is broken, it is freed up to bond with another alkene. This process means that one alkene can bond to make a chain of two, and then three and then four, you get the idea, until the chains are hundreds of bonds long.

 

“But I know that there are loads of different types of plastics – what makes them different?”

 

Good question – it’s all about the length of the chains. Longer chains mean that there are more intermolecular forces, and more intermolecular forces mean a harder plastic. Let’s look at a table to illustrate this.

 

Property of plastic Long chains Short chains
Strength Tend to be strong as there are a lot of intermolecular forces.  Tend to be weak as there are not a lot of intermolecular forces. 
Flexibility Tend to be more flexible as there are fewer branches on the polymer chains stopping them from flowing over each other.  Tend to be less flexible as there tend to be more branches on the chains that get caught up in each other and stop the flow. 
Hardness Tend to be less hard and the chains can slide over each other.  Tend to be harder as the chains cannot slide as easily. 
Melting point High melting point as there are more intermolecular forces between long chains Low melting point as there are fewer intermolecular forces between long chains

 

Let's move on to try some questions on this subject now.

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