A coordination polymerization of alkoxyallenes (2a-2f) by the [q3-(allyl)NiOCOCF3] (1) /PPh, system was carried out to obtain a polymer (3) bearing exomethylenes on the main chain. The structure of the obtained polymer was confirmed by 'H-, "C-NMR and IR spectra, and was revealed to consist of two units, one bearing an exomethylene side chain and the other an end ether side chain as a result of 1,2-and 2,3-~olymerization. In the case of methoxyallene, the ratio was estimated as 32:68. The number average molecular weight (M&f t& resulting polymer varied linearly with increasing ratio of monomer to initiator. The molecular weight distributions (MJM,,) of the polymers obtained here were always approximately 1.1.These results may strongly support that the present polymerization proceeds bya living mechanism. Under an inert atmosphere, the propagating end of the polymer was quite stable and could be kept without any decrease in activity for more than a week. The proportion of 1,2-and 2,3-polymerization was a little affected by the substituents on the alkoxyallenes, as the steric bulkiness of the substituents increased the content of 2,3-polymerization units.