AbstractThe microstructure distributions of ethylene‐propene(EP) copolymers and propene homopolymers prepared with supported titanium catalyst were analyzed by13C NMR spectroscopy. A two‐site model with an isospecific site and a non‐stereospecific site was used to describe the stereospecific polymerization of propene. A second two‐site model with individualr1r2= 1 was applied to the analysis of the ethylene‐propene copolymerization. The addition of an external base, ethyl benzoate (EB), alters the relative concentrations of catalytic sites. Based on the comparison of the results from the homopolymers and copolymers prepared under different EB concentrations, the correlations between the stereospecificity and the activity toward the monomers were established: the isospecific site produces the copolymer with lower ethylene content; the non‐stereospecific site gives the copolymer with higher ethyl