Intramolecular ester of 6-hexanolactone; a cyclic compound in which the ring opens during polymerization to produce polycaprolactone, a biodegradable polyester.

Caprolactone is a cyclic ester, known as a lactone, with a ring size of seven. It is a clear colorless liquid that is miscible with most organic solvents except aliphatic hydrocarbons. It reacts slowly with water to form 6-hydroxyhexanoic acid.