Anionic Ring-Opening\nPolymerization of ε‑Caprolactam\nabove the Crystallization Temperature of Polyamide 6: A Study on the\nEffects of the Activator and Catalyst

The\nanionic ring-opening polymerization of ε-caprolactam\n(CL) offers significant potential for producing polyamide 6 (PA6).\nTo establish optimal conditions for designing an efficient and continuous\nPA6 production process, this study examines the anionic polymerization\nof CL at temperatures above the crystallization point of PA6. The\nfocus is on the effects of the temperature, activator type and concentration,\nand catalyst concentration on the polymerization process and product\n characteristics. At 220 °C, the use of bifunctional methylene\ndiphenyl diisocyanate (MDI) as an activator initiates cross-linking\nreactions, producing insoluble, nonmelting PA6. In contrast, anionic\npolymerization without an activator prevents gel formation but results\nin uncontrollably high molecular weights. The introduction of monofunctional <i>N</i>-acetyl caprolactam (AcCL) as an activator eliminates cross-linking\nreactions at temperatures above 220 °C while allowing precise\ncontrol of the product’s molecular weight through adjustments\nin AcCL concentration.