When diacids and diols, both of which have two functional groups, are reacted together, the resulting esters are polymers. The best known of these is made by reacting together benzene-1,4-dicarboxylic acid and ethane-1,2-diol, and is well known commercially by the names Dacron and Terylene. Polyesters are often used in making synthetic fibres for use in clothing, such as the shirts shown in the photograph.
