Poly(N-vinylpyrrolidone) s (PNVPs) with well-defined macromolecular structure were prepared by organostibine-mediated living radical polymerization. PNVPs with expected number-average molecular weight (M-n) 3000-84 000) and low polydispersity indexes (PDIs) 1.1-1.3) were formed by heating a solution of organostibine mediator and NVP in the presence of AIBN at 60 degrees C. The polymer structure was analyzed by matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass and H-2 NMR spectroscopies after reduction of the organostibanyl polymer end by tributyltin deuteride. The analyses reveal that, while the addition of AIBN considerably enhances the rate of the polymerization, the effect of azobis(isobutyronitrile) (AIBN)derived radical to the omega-end structure is negligible. The analyses also reveal the existence of "dead" dormant species due to head-to-head addition followed by the organostibanyl group transfer. However, since the probability of the head-to-head addition is small (0.02-0.10%) compared to the normal head-to-tail addition, its effect on the controllability was negligible under the current conditions. Diblock copolymers poly( styrene [St]-block- NVP), poly(methyl methacrylate [MMA]-block-NVP), and poly(NVP-block-MMA) were successfully prepared by successive addition of corresponding monomers to the organostibine macromediators.