The anionic polymerization of lauryllactam was initiated at 270degreesC using sodium hydride as an initiator and NN'-ethylene-bisstearamide (EBS) as an activator (NaH:EBS molar ratio of 2). Polymerization occurred in less than 2 min and was successfully performed in an internal mixer and a twin-screw extruder with corotating intermeshing screws (Werner & Pfleiderer ZSK 25). The content of residual monomer, as determined by thermogravimetric analysis, was lower than 0.5 wt %. Molecular weight, as measured by size exclusion chromatography, was governed by the lauryllactam:NaH molar ratio calculated on a M-n of 25 kg/mol at a constant NaH:EBS molar ratio of 2. Blends were prepared in situ by polymerization of lauryllactam solutions of various polymers. When poly(ethylene-co-butylacrylate) (Lotryl(R); Atofina) was dissolved in lauryllactam, rubber-toughened polyamide 12 blends were obtained. Mechanical properties of the injection-molded polymers were examined by stress-strain as well as notched Charpy impact tests at different temperatures. Blend morphologies were imaged by scanning electron microscopy (SEM). (C) 2003 Wiley Periodicals, Inc.