The Chemistry of Plastics

Ever wondered how plastics such as packaging supplies are made? Or even what they’re made from? This brief introduction into the chemistry of plastics will get you thinking and hopefully eager to learn more!

Plastics are what are known as polymers - notice the prefix “poly”, and how many plastics can you think of with “poly” in their name? “Poly” generally means “many, or one than one”. This very accurately describes the make up of plastics.

Polymers like plastics are made up of lots of smaller pieces, known as monomers (mono meaning “one”) - and this is why they are called what they are - many smaller pieces making one very long finished product. We’re talking on a molecular scale here, so that even a very small piece of plastics is made up of huge amounts of individual polymers.

The magnificent properties of plastics come from this molecular structure.

The process of joining lots of monomers together is called polymerisation. The video below shows the polymerisation of monomers known as ‘alkenes’ - alkenes are responsible for the production of polythene!

Polythene is only made up of two elements: carbon and hydrogen. That’s all! Other plastics do incorporate other elements sometimes, such as PVC which introduces chlorine into the structure.

The reason that alkenes join together to form a larger polymer is because of reactive bonds between the carbon atoms. The bonds break and reform, causing the monomers to join together.

In the case of the reaction in the video above, there is a “double bond” between the carbon atoms in the ethene monomers. In a reaction known as “addition polymerisation” the double bonds break, and two single bonds form, attached the monomers together. This happens over and over again, producing a huge chain of monomers.

Here are a few different types of plastic, the chemical name of the polymers and the monomers they’re made from:

Polythene - Polythene is made up of poly(ethene) polymers and ethene monomers. It is one of the most common examples of a plastic.

Polypropylene - Polypropylene is made up of poly(propene) polymers and propene monomers. Perhaps less heard of, polypropylene is stronger than polythene and is used for making materials like ropes and heavy-duty packaging

PVC - PVC is made up of poly(chloroethene) polymers and chloroethene (which used to be known as vinyl chloride) monomers. Because of it’s great heat stability, it is often used for applications such as the covering of wires or plugs.

Polystyrene - Polystyrene is made up of poly(phenylethene) polymers and phenyethene monomers. It is commonly used in a form where it is expanded with air and used for packaging.