The reaction between carbon monoxide and the Ti-polyethylene bond was investigated using a stopped-flow (short-time) polymerization method which provides quasi-living polymers with very low molecular weights. Ethylene polymerization was conducted with a typical homogeneous Cp(2)TiCl(2)-methylaluminoxane catalyst. The Ti-terminated polymers were introduced into toluene saturated with carbon monoxide or containing C-13-enriched carbon monoxide at -78 degrees C. The mixture was gradually heated up to room temperature, and a small portion of the reaction mixture was taken out at -78 degrees C, 0 degrees C and room temperature to analyse the structure of each polymer by FTi.r., gel permeation chromatography, H-1 n.m.r. and C-13 n.m.r. It was found from these analyses that carbon monoxide is incorporated into the polymer mainly as a ketone carbonyl.