CP2ZrCl2 confined inside the supercage of NaY zeolites [NaY/methylaluminoxane (MAO)/Cp2ZrCl2] exhibited the shape and diffusion of a monomer-controlled copolymerization mechanism that strongly depended on the molecular structure of the monomer and its size. For the ethylene-propylene copolymerization, NaY/MAO/Cp2ZrCl2 showed the effect of the comonomer on the increase in the polymerization rate in the presence of propylene, whereas the ethylene/1-hexene copolymerization showed little comonomer effect, and the ethylene/1-octene copolymerization instead showed a comonomer depression effect on the polymerization rate. Isobutylene, having a larger kinetic diameter, had little influence on the copolymerization behaviors with NaY/MAO/Cp2ZrCl2 for the ethylene-isobutylene copolymerization, which showed evidence of the shape and diffusion of a monomer-controlled mechanism. The content of the comonomer in the copolymer chain prepared with NaY/MAO/Cp2ZrCl2 decreased by about one-half in comparison with that of Cp2ZrCl2. A differential scanning calorimetry study on the melting endotherms after the successive annealing of the copolymers showed that the copolymers of NaY/MAO/Cp2ZrCl2 had narrow cornonomer distributions, whereas those of homogeneous Cp2ZrCl2 were broad. (C) 2003 Wiley Periodicals, Inc.