Alcohols and carboxylic acids react to form esters and water.
If a molecule has 2 alcohol groups, it will react with an acid that has 2 acid groups to form a polyester.
Diol + dicarboxylic acid -> polyester
Differences/similarities between addition and condensation polymerisation:
Similarities - makes a polymer from monomers
Differences - addition polymerisation has alkene monomers but condensation has diol and dicarboxylic acid monomers, condensation forms water as well as a polymer, and addition forms polyalkenes but condensation forms polyesters