Polyethylene terephthalate

Find a plastic bottle. There’s probably one not far from you. Now look at the bottom of it: do you see a little triangle with a number one inside? Well, that means the bottle is made from the compound polyethylene terephthalate. Yes, it’s a bit of a mouthful. That’s why lazy chemists usually call it PET.

PET is a polymer – a macromolecule made out of thousands of repeating monomer units. To produce PET, chemists use two different kinds of monomers: terephthalic acid and ethylene glycol. Both units undergo a reaction called esterification, where an organic acid and an alcohol combine to form an ester and water. But PET is not a normal ester – it’s a polymer, a poly-ester – and its properties are very different from other esters…