A series of MgCl2/NaCl/ID/TiCl4 type supported catalysts were prepared by comilling NaCl with MgCl2.nEtOH adduct and reacting the mixture with TiCl4 and internal electron donor (ID = di-n-butyl phthalate). Crystallites of NaCl were found in the doped catalysts as revealed by WAXD analysis. The NaCl doped catalysts showed lower catalytic activity and higher isospecificity in catalyzing propylene polymerization. There was a marked change of the molecular weight distribution (MWD) of polymer with NaCl content. Catalyst containing 16 mol% NaCl produced PP with much broadened MWD (PDI = 13) than the undoped catalyst when TEA was used as the activator, while the TIBA activated catalyst produced PP with much narrower MWD. The changes in catalyst's active center distribution were studied based on non-linear fitting of the polymer MWD curve by multiple Flory functions. Stereochemical structure of the polymer was studied by thermal analysis. Selective and reversible deactivation of active centers by Cl- from NaCl is proposed to be the main reason for the observed changes in polymerization behaviors and polymer structure caused by doping NaCl in the catalyst. (c) 2005 Elsevier B.V. All rights reserved.