A polyester is a (a chain of units) where the individual units are held together by linkages.

Polyesters are polymers formed from a and a .

In condensation , when the monomers join together a small gets lost. That's different from polymerisation which produces polymers like poly(ethene) - in that case, nothing is lost when the monomers join together.

A polyester is made by a reaction involving an with two -COOH groups, and an with two -OH groups.

Polyesters are polymers in which the individual monomers are joined together by ester bonds.
They are made by reacting a carboxylic acid with two COOH groups, and an alcohol with two – groups, or molecules with both a hydroxyl and group, e.g. 4-hydroxy-benzoic acid. The reaction process is called .

Nylon 66 is a type of or nylon. Nylons come in many types, and the two most common for textile and plastics industries are nylon 6 and nylon 66. It has the chemical formula (C12H22N2O2)n

Hydrolysis of polyesters:
Simple are easily hydrolysed by reaction with acids or alkalis.

Polyesters are attacked readily by , but much more slowly by dilute acids. by water alone is so slow as to be completely unimportant. (You wouldn't expect your polyester fleece to fall to pieces if you went out in the rain!)

If you spill alkali on a fabric made from polyester, the linkages are broken. -1,2- is formed together with the salt of the .

Because you produce small molecules rather than the original polymer, the are destroyed, and you end up with a hole!