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Summary: Modified methylaluminoxane (MMAO), from which free AlMe3 and Al(iBu)3 were reduced to ca. 0.1 mol‐%, was supported on metal oxides, such as anhydrous silica gel, alumina, or magnesia; the metal oxide‐supported MMAO prepared were used as cocatalysts for propylene polymerization combined with a chelating (diamide)dimethyltitanium complex. The systems conducted living polymerization of propylene at 0 °C regardless of the support for MMAO. The propagation rate constants (kp) of these systems and the molecular weight distribution ($\overline M _{\rm w} {\rm /}\overline M _{\rm n}$) of the produced polymer depended on the metal oxide employed. The XPS analysis of the supported MMAOs suggested that the kp value increased with the Lewis acidity of MMAO on the support and the broadening $\overline M _{\rm w} {\rm /}\overline M _{\rm n}$ was ascribed to the distribution of kp caused by the heterogeneity of the supported cocatalyst.

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