The driving force of the complete cyclization in the anionic cyclopolymerization of bis(dimethylvinylsilyl)methane with n-BuLi/TMEDA in hexane is clarified with resonance Raman and H-1 NMR measurements. Vinyl groups coordinating to the lithium cation are detected in both measurements of the polymerization mixture at -70 degrees C, and they, at least some part of them, are shown to be the vinyl groups in uncyclized end units. Disappearance of these species from the resonance Raman spectrum at -20 degrees C indicates that the cyclization proceeds fast and is accelerated by the coordination of the second vinyl group in the uncyclized end unit. This is the first case that the interaction between the vinyl group in an uncyclized end unit-and the counterion was found in ionic cyclopolymerization.