ABSTRACT
Ring-opening polymerization of lactams is an important method for the synthesis of a broad class of polyamides and copolymers with amide groups in the polymer chain. The nature of activation depends on the type of initiator and comprises protonated, coordinated, or otherwise electronegatively substituted lactam. The nucleophile is represented by the amine group, the anion of the initiating acid, lactam or anionically activated lactam. In polymerization processes, the ring-chain equilibrium is due to the ability of chains to attain conformations allowing the chain segments and active species to achieve conformations favorable for ring closure. The principle of equal reactivity of chain amide groups was proved by determination of 6-aminohexanoic acid in equilibrium polymerization products. The relative importance of any particular mechanism will strongly depend on the ring size and, consequently, on the permittivity of lactam, nature of the cation, and temperature in bulk polymerizations and, moreover, on the solvent properties in solution polymerization.
