Addition and Condensation

Polymers are giant molecules formed when smaller molecules, known as monomers, link together during the chemical reaction known as polymerisation.

There are two types of polymerisation reactions, addition and condensation. These are discussed briefly below in a simple manner for junior science students.
For a more detailed description of polymerisation visit the Organic Chemistry section.

Addition polymersiation involves the linking of monomers with double bonds. The double bond of one monomer breaks and links onto the neighbouring monomer. This process continues, as pictured on the right, to form polymers, some of which can be many thousands of monomers long.

The animation on the right is of ethene molecules linking together to form polyethene.

Condensation polymerisation involves monomers reacting together and releasing a small molecule in the process. The small molecule is commonly water or hydrochloric acid (HCl).
Countless of these polymers bunch together to form the solid plastic. Weak forces hold the polymers together and can be easily disrupted with the application of heat. The plastic can be easily melted. A plastic that melts is known as a thermoplastic.
Try some exercises