Repeating units
polymerA large molecule formed from many identical smaller molecules known as monomers. molecules are very large compared with most other moleculeA collection of two or more atoms held together by chemical bonds., so the idea of a repeat unitA part of a polymer that would make a complete polymer molecule if many of them were joined end to end. is used when drawing a displayed formula. When drawing one, you need to:
- change the double bond in the monomerSmall molecule, usually containing a C=C bond, that can join end to end with other monomers to form a polymer molecule. to a single bond in the repeat unit
- add a bond to each end of the repeat unit
- draw brackets around the repeating unit so that the brackets go through the middle of the bonds at the end
- put the letter n in subscriptA letter or number written below the line. after the brackets (n represents a very large number of the repeating unit)
Note that when drawing a polymerisation equation the letter n should go in front of the monomer to show there is a very large number of monomers.
It can be tricky to draw the repeat unit of poly(propene). Propene is usually drawn like this:
It is easier to construct the repeat unit for poly(propene) if you redraw the monomer like this:
You can then see how to convert this into the repeat unit.
The final polymer you need to be aware of is poly(tetrafluoroethene), also known as PTFE or Teflon.