Synthesis of High Molecular Weight Nylon 6 by Anionic Polymerization of ε-Caprolactam

Abstract

To obtain high molecular weight nylon 6, the anionic polymerization of ε-caprolactam was investigated in terms of water content in monomer and concentration of catalyst (Grignard reagent; ethyl magnesium bromide) and chain initiator (monofunctional; N-acetyl-ε-caprolactam or bifunctional; N,N′-adipoyl-bis-ε-caprolactam). The weight average molecular weight, Mw=7.0×105 (the intrinsic viscosity; [η]=11.2) was obtained using the monofunctional chain initiator, and Mw=9.5×105 ([η]=14.1) was found using the bifunctional chain initiator under the following conditions: water content, 0.013 mol%; concentration of catalyst, 0.1 mol%; concentration of chain initiator, 0.03 mol% (monofunctional), 0.015 mol% (bifunctional); polymerization temperature, 150°C. In the present study, the molecular weight of the polymer is governed by quantities of active molecular chains. Since water mainly terminates the propagation of molecular chains, minimizing water content in ε-caprolactam is indispensable to maximizing the molecular weight of the polymer.