Full Paper Macromolecular Reaction Engineering wileyonlinelibrary.com (1 of 21) 1600044 © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/mren.201600044 The polymerization of ethylene is investigated in a semibatch solution reactor using bis(n-propylcyclopentadienyl)hafnium dichloride catalyst and tetrakis(pentafluorophenyl) borate dimethylanilinium salt ([B(C 6 F 5 ) 4 ] - [Me 2 NHPh] + ) as the catalytic system. Trioctylalu- minum (TOA) is used as impurity scavenger and alkylating agent. Ethylene pressure, poly- merization temperature, TOA, borate, and catalyst concentrations are changed to investigate ethylene polymerization kinetics with this catalyst system. A 2 3 central composite design, augmented with extra runs to further explore the effect of some factors, is used as the sta- tistical basis for the polymerization study. Ethylene propagation follows first-order kinetics. Chain transfer to monomer, β-hydride elimination, and transfer to TOA are the main chain transfer reactions. In addi- tion to alkylating the catalyst precursor, TOA also deactivates the catalyst. The mode of reactor addition for catalyst, borate, and TOA has also been studied. When TOA and borate are added sequentially to the reactor, followed by the catalyst, the polymerization activity is lower than when the catalyst and borate are added simultaneously, suggesting that compl- exation with borate avoids deactivation reactions with TOA. Ethylene Polymerization with a Hafnocene Dichloride Catalyst Using Trioctyl Aluminum and Borate: Polymerization Kinetics and Polymer Characterization Saeid Mehdiabadi, João B. P. Soares,* Jeffrey Brinen Dr. S. Mehdiabadi, Prof. J. B. P. Soares Department of Chemical and Materials Engineering University of Alberta Edmonton, Alberta, Canada E-mail: jsoares@ualberta.ca Dr. J. Brinen Baytown Technology and Engineering Complex ExxonMobil Chemical Company Baytown, TX 77522, USA 1. Introduction Metallocene catalysts are as old as Ziegler–Natta cata- lysts. They were used in 1957 by Breslow and Newburg to polymerize ethylene with bis(cyclopentdienyl)tita- nium dichloride and diethylaluminum chloride. [1] The catalytic system had low activity, similarly to Natta and co-workers observations on a complex prepared with triethylaluminum. This catalytic system did not attract commercial interest because of its low poly- merization activity. Efforts to polymerize olefins using bis(cyclopentadienyl)zirconium complexes were also unsuccessful, and the catalytic system was described to be totally inactive. The field remained dormant until 1976 when Kaminsky and Sinn showed that adding a small amount of water to trimethylaluminum (TMA) before polymerizations with metallocenes could drasti- cally enhance activity by a factor of 10 000 or more. [2,3] This led to the discovery of the highly efficient activator methylaluminoxane (MAO), and revolutionized the field of olefin polymerization with molecular catalysts. Since then, polymerizations using metallocene complexes became one of the hottest areas of research in the poly- olefin field. [4,5] Macromol. React. Eng. 2017, , 1600044