In condensation polymerisation, two different monomers combine to form one large molecule. A small molecule is also removed in the process, which is often water. Unlike addition polymerisation, a C=C bond is not required to form the polymer.
This process produces both the condensation polymer and a small molecule, while addition polymerisation only produces the polymer molecule.
During condensation polymerisation, the monomers contain two functional groups. The functional group on the end of one monomer reacts with the functional group on the end of another monomer. This results in the formation of a long chain of molecules known as the condensation polymer.
Polyesters are a type of condensation polymer. To make a polyester, an alcohol and a carboxylic acid react to form an ester. During this reaction, a hydrogen ion (H⁺) and a hydroxide ion (OH⁻) combine to form a water molecule, which is removed from the reactants.
For example, if we combine ethane-1,2-diol (which has two alcohol groups) with hexanedioic acid (which has two carboxylic acid groups), we can form an ester and water.
We can continue adding more of these monomers to either end to create a long chain of esters. This is what makes up a polyester.
To simplify the chemical equations and make them easier to understand, we can use boxes to represent the carbon chains, instead of drawing out all the atoms.