Anionic poly(epsilon-caprolactam), isothermally synthesized at temperatures between 155 and 195 degrees C by very fast carbamoyl-type activators, has been characterized by UV, DSC, and wide-angle X-ray scattering (WAXS) techniques in terms of high polymer yield, irregular structures along the chain, extent of cross-linking, T-g and T-m values, degree of crystallinity, and polymorphism. The specific role of four different activators on the above properties has been compared. From the whole set of characterization data it is evident that cyclohexylcarbamoylcaprolactam behaves as the most suitable activator and provides poly(epsilon-caprolactam) with properties that favorably match those of the corresponding hydrolytic polyamide.