Addition Polymerisation involves the joining together of many monomer molecules to produce one polymer chain and no other products. Addition polymers always have a continuous chain of carbon atoms.
Polyalkenes like polyethene and polychloroethene are the obvious examples – see section A5.
Condensation Polymerisation involves joining together monomer molecules where there are two different functional groups which react together, join the monomer molecules and eject a small molecule in the process. This small molecule could be
$\textsf H_\textsf2\textsf {O, HCl}$
or
$\textsf{NH}_3$
.
The reactive functional groups are on opposite ends of the monomer molecules – so the two molecule chains are joined together leaving a tell-tale link which could be:
An ester link – joining the two carbon chains R and R’ R and R’ could be the same or different chains
An amide link – joining the two carbon chains R and R
• Polyesters : the two monomers need 1. an
$\textsf{OH}$
group and 2. a
$\textsf{COOH}$
group.
Figure 9.3 Polyester
• Here we have a diol (ethan-1,2-diol) and benzene-1,2-dicarboxylic acid The molecule ejected during polymerisation is
$\textsf{H}_\textsf2\textsf O$
.
• The OH group of the dicarboxylic acid could be replaced by a chlorine atom, in which case we would get the same polymer, but an
$\textsf{HCl}$
molecule would be ejected.

## Author's tip 📌

Note the ester link. You can spot the C=OCO in esters (when written out in full)!
• Polyamides: the two monomers need 1. an
$\textsf{OH}$
group and 2. a
$\textsf{NH}_\textsf2$
group Here we have a dicarboxylic acid and a diamine. The molecule ejected dicarboxylic acid during the polymerisation is
$\textsf{H}_\textsf2\textsf{O}$
$\textsf{HCl}$