ring-opening polymerization

A polymerization in which a cyclic monomer yields a monomeric unit which is acyclic or contains fewer cycles than the monomer.
If the monomer is polycyclic, the opening of a single ring is sufficient to classify the reaction as ring-opening polymerization.
PAC, 1996, 68, 2287 (Glossary of basic terms in polymer science (IUPAC Recommendations 1996)) on page 2308