Ebrahim Ahmadi - Department of chemistry, University of Zanjan, P.O. Box ۴۵۱۹۵-۳۱۳, Zanjan, Iran
Zahra Mohamadnian - Department of chemistry, Institute for Advanced Studies in Basic Sciences (IASBS), Gava zang,P. O. Box ۴۵۱۹۵-۱۱۵۹, Zanjan, Iran
Sajjad Rahimi - Department of Chemistry, College of Sciences, Shiraz University, Shiraz ۷۱۴۵۴, Iran
Mohammad Hasan Armanmehr - Department of Chemical Technologies, Iranian Research Organization for Science and Technology, P.O. Box۱۵۸۱۵-۳۵۳۸, Tehran, Iran

Ethylene polymerization was carried out using Phillips chromium catalyst based on silica supports such as silica aerogel, SiO2 (Grace 643), and titanium modifed SiO2 (G 643), and the results were compared with othercatalysts based on SiO2 (Aldrich), SBA-15(Hex), SBA-15(Sp) and MCM-41. A combination of TGA, DSC, XRD,nitrogen adsorption, SEM, ICP, FTIR and other analyses were used to characterize the materials. The results showedthat the chromium was successfully introduced into silica supports. Shish-kebab polyethylene was prepared via in situethylene polymerization with the Cr/SiO2 (G 643) and Cr/Ti/SiO2 (G 643) catalytic systems. A comparison betweendifferent types of catalysts revealed that the polymerization activity of Cr/SiO2 (G 643) was signifcantly increased to191 kg PE (g Cr)-1 h-1 due to the higher pore volume and pore diameter of Grace silica compared to the other supports.Also, the polymerization activity of the Cr/SiO2 (G 643) catalyst was signifcantly improved by Ti-modifcation.Polyolefns J 3:23-36

Silica aerogel; Grace silica; chromium catalyst; ethylene polymerization; shish-kebab