 Chain transfer can be either introduced deliberately into a polymerization (by use of a "chain transfer agent") or it may be an unavoidable side-reaction with various components of the polymerization.Chain transfer reactions occur in most forms of addition polymerization including radical polymerization, ring-opening polymerization, coordination polymerization, and cationic polymerization, as well as anionic polymerization.Chain transfer reactions are usually categorized by the nature of the molecule that reacts with the growing chain.