The influence of MgCl2 crystal modification (α- MgCl2

β- MgCl2 ) on theproperties of supported catalyst for propylene polymerization has been studied bymeans of XRPD

IR and DTA-TG. The structural difference and similarity between α- MgCl2 and β- MgCl2 was still reclined in its milling produCt withdiisobutyl phthalate and in the catalysts prepared from α- MgCl

and β-MgCl2caaccers respectively. β-MgCl2 supported catslyst gives higher activity and lowerstcreospedficity than α- MgCl2. The catalyst prepared by using Mg(OEt)2 as carrier shows higher activity and stereospecificity than both a-MgCl2 and β-MgCl2 sup-ported catalysts.