Anionic and radical polymerizations of N-methyl-N-allyl-2-(ethoxycarbonyl)allylamine (1) were undertaken to search the possibility for controlling the structure of the polymers therefrom. Completely cyclized polymers with a five-membered ring as a repeat cyclic unit were obtained by radical polymerizations. Anionic polymerizations by lithium compounds such as tert-butyl lithium and lithium 4-benzylpiperidide yielded highly isotactic uncyclized poly(1)s, while tert-butylmagnesium chloride afforded polymers with higher degree of cyclization (97%), the repeat cyclic units of which consist of a five-membered ring. The anionically obtained cyclopolymers were found to have fundamentally the same structure as those formed through a radical mechanism. These results along with those obtained from N-methyl-N-propyl-2-(ethoxycarbonyl)allylamine, one of the monofunctional counterparts of 1, led to the conclusion that anionic cyclopolymerizations proceed in the case where interaction of a counter cation with the propagating chain end and/or the monomer is weak and the mechanism of the five-membered ring formation is essentially the same as that in the radical polymerization. On the contrary, the strong intra- and intermolecular coordination power of the amino nitrogen of a growing polymer chain end and/or the monomer to the counter cation (Li+) have been attributed to the main factor controlling the stereochemistry leading to the highly isotactic uncyclized polymers. Polymers with six-membered rings as repeat units could not be obtained under the conditions employed. It is needed to seek an initiator that has specific interaction at a propagating chain end for the formation of six-membered rings. (C) 2003 Elsevier Ltd. All rights reserved.