Activation of Ziegler‐Natta catalysts by organohalide promoters: A combined experimental and density functional theory study

Several organohalide (HC) compounds were tested as promoters for a Ti‐based Ziegler‐Natta (Z‐N) catalyst at different polymerization conditions. Results show that the intensity of the promoting effect depends on the nature and amount of the promoters. A proper amount, especially optimum amount, of aliphatic type organohalides leads to a strong productivity, and aromatic ones leads to a weak productivity improvement; however, 3‐chloro‐1‐propene poison the catalyst even at lower HC/Ti molar ratios. Among studied compounds, chlorocyclohexane has the best activity promotion effect at HC/Ti molar ratio of 128, and with this as a promoter, the activity increases over 85%. To understand more details about this phenomenon, the rate of polymerization during time and the effect of polymerization conditions (the temperature and hydrogen partial pressure) on the performance of chlorocyclohexane as the most effective promoter were studied. Finally, to explore the mechanism of reactivation of catalyst species by organohalides, molecular modeling was employed and a new oxidation‐addition mechanism was proposed, which basically consisting of homolytic breaking of C? Cl bond in organohalides. It was found that reoxidation of the catalyst, restoring active center, by Cl rich organohalides is energetically more favored. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012