Impact of zirconia modification on supported metallocene catalyst via ethylene/1-Octene coplymerization

Abstract

For years, metallocene catalysts have brought much attention to research in olefin polymerization. As a matter of fact, it has led to an extensive effort for utilizing metallocene catalysts more efficiently. It is known that the copolymerization of ethylene with higher 1-olefins is a commercial importance for production of elastomer and linear low-density polyethylene (LLDPE). Metallocene catalysts with methylaluminoxane (MAO) have been studied for such a copolymerization. In particular, zirconozene catalysts along with MAO have been reported for a potential use to polymerize ethylene with 1-olefins. Nevertheless, it was found that a homogeneous metallocene catalytic system has two major disadvantages: the lack of morphology control of polymers produced and reactor fouling. Therefore, binding these metallocene catalysts onto inorganic supports can provide a promising way to overcome these drawbacks. Unfortunately, due to the supporting effect it is found that the catalytic activity of catalysts in the heterogeneous system is usually lower than the homogeneous one. It has been reported that many inorganic supports have been studied for years. In fact, silica has been one of the most supports used so far. However, the properties of silica itself may not be suitable. Hence, the modification of silica would be necessary. It was reported that zirconia modification on supports exhibited a promising enhancement for activity of many catalysts. In this thesis, impact of zirconia modification on the silica-supported metallocene catalyst was investigated. Experimentally, the zirconia-modified silica was prepared by impregnation of a zirconium (IV) n-propoxide solution onto the silica, then reacted with MAO. In order to study the catalytic behaviors during polymerization, the ethylene/1-olefin copolymerization reaction was carried out in a 100 mL semibatch stainless steel autoclave reactor. At first, 0.2 g of the supported MAO and the zirconozene catalyst (rac-Et[Ind]2ZrCl2) ([Al]MAO/[Zr]= 2270) and 0.018 mole of 1-olefin along with toluene were put into the reactor. The reactor was heated up to the polymerization temperature at 70C. By feeding ethylene (0.018 mole) into the reactor, the polymerization was started. The polymer samples were the chacracterized by means of 13C NMR and DSC. It was found that polymerization activities increased with Zr modification about 4 to 7 times. By means of 13C NMR, the Zr modification also resulted in higher degree insertion of 1-olefins resulting in low Tm of polymer obtained