Think of the most important things in your life – your phone, your Switch, your vacuum cleaner (if you like having a clean bedroom). They will all be made with plastics in them. Plastics where 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 monomers. Poly- 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 can get the name of the polymer if you add the prefix poly- before the name of the monomer. For example, poly(propane) is used to make ropes; lots of propane molecules form 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 in 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.
So – how do we make a monomer into a polymer?
All we do is 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 and 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 (just when we were talking about crude oil). 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 less intermolecular forces between long chains|