Borane-functionalized silica supports: In situ activated heterogeneous zirconocene catalysts for MAO-free ethylene polymerization

Abstract

We treated silica with tris(pentafluorophenyl)borane, B(C 6F 5) 3, to create borane-functionalized support, SiO 2–B(C 6F 5) 3 which was then used as a support and co-catalyst for the in situ activated dichloro-zirconocene (Cp 2ZrCl 2/TIBA) and dimethyl-zirconocene catalyst systems (Cp 2Zr(CH 3) 2) for ethylene polymerization. The surface modifications of SiO 2–B(C 6F 5) 3 was investigated by SEM–EDX, FTIR and XPS to determine the distribution of fluorine and boron atoms on the silica surface as a measure of the presence of B(C 6F 5) 3 and interaction with the siloxane groups of the silica support. Catalytic performances are presented in the form of ethylene consumption rate profiles. The results show that the independent of the time dedicated to the in situ activation of the metallocene, all pre-activated systems showed activity decay. In contrast, the in situ activated systems either showed little or no activity decay. The presence of TIBA was adequate to make an active MAO-free catalyst system. The pre-activated and in situ activated metallocene systems produced polyethylene with slightly different molecular weights (MWs) and molecular weight distribution (MWD). MWDs were quite narrow ∼3. The bulk density of polyethylene product is highest for the in situ activated metallocenes, but there is no difference between the products of dichloro- and dimethyl-zirconocenes. Pre-activated and in situ activated catalysts show no reactor fouling.