Polymerisation is defined as the process of bringing individual molecules, called monomers, together to form chains of these molecules called polymers. When this process is done with molecules containing double bonds, this is called addition polymerisation. When this process is done with 2 different functional groups to produce a polymer chain and a small molecule, this is called condensation polymerisation. The 2 different functional groups are able to react with each other which is what produces the small molecule. The most basic condensation polymerisation involves 2 monomers each containing 2 of the same functional groups which can then react with each other.