Polymerisation

Polymerisation is the chemical process in which many small monomer molecules join together to form a large polymer molecule. It is the reaction that turns a container of small units into a single macromolecule thousands of atoms long. Malay: pempolimeran · Chinese: 聚合反应.

The exam expects you to know that polymerisation comes in two types, decided by the monomer. In addition polymerisation, unsaturated monomers each open their carbon–carbon double bond and add directly to one another, so no other molecule is released. In condensation polymerisation, monomers with two functional groups join and eliminate a small molecule, most often water, every time a new bond forms. Recognising which type is happening, by looking for a double bond or for two functional groups, is one of the most common tasks the marking scheme sets, so the definition and the two types must be secure.

Example. Many ethene molecules, CH₂=CH₂, undergo addition polymerisation to make polythene, with nothing given off. In contrast, many amino acid molecules undergo condensation polymerisation to make a protein, releasing a water molecule at each link.

Confusion to avoid. Do not describe polymerisation as simply mixing molecules. It is a chemical reaction that forms new covalent bonds between the monomers, not a physical blend. Take care too not to swap the two types: addition releases nothing, while condensation always eliminates a small by-product such as water. A further slip is to say the monomer is “added” without noting that the C=C double bond must open first, it is the opening of that bond that lets one unit join the next.

Polymerisation is the central process of the whole chapter, linking monomers to polymers and setting up natural rubber, plastics and fibres, so a precise definition earns marks throughout SPM Chemistry.