This article examines the anionic polymerization of lauryl lactam into polyamide 12 and the copolymerization of lauryl lactam with a diisocyanate-end-capped polycaprolactone used to produce a poly(ester amide) block copolymer. The molecular weights of the polyester polyols used in the preparation of the diisocyanate-end-capped polycaprolactone were varied. The products were characterized with Fourier transform infrared spectroscopy and differential scanning calorimetry, and the mechanical properties were measured in a mechanical tester. The influence of the polyol molecular weight was considered. (C) 2003 Wiley Periodicals, Inc.