The process of polymerization is accomplished in one of two ways. The first way is by adding small molecules onto the active site of a chain of similar molecules to form giant molecules. The second method involves small molecules combining in a way that causes the loss of other molecules.
In addition polymerization, the first method, a very strong bond is formed when a molecule that has an unmatched electron attracts another molecule with an unmatched electron. The active site in a polymer chain is the location of an unmatched electron. The small molecules are called monomers. Once combined into the giant molecule, they are called polymers.
The second method is called condensation polymerization because water is usually the molecule that is lost during the process. Some polymers are made with natural monomers while others are formed from man-made substances. Natural polymers include starches and cellulose. Synthetic polymers include nylons and other polyesters.
In addition polymerization, the properties of the monomers are not changed or heightened. However, when condensation polymerization takes place, the resulting polymer is altered. The properties, such as hardness, strength and flexibility, increase with each additional monomer at first but then level off. Plastics that are formed by addition polymerization soften when heat in any form is applied.