Supported Ziegler-Natta catalyst for ethylene polymerization: Novel data on the effect of polymerization temperature on the number of active centers and propagation rate constant

The number of active centers at ethylene polymerization over highly active supported catalyst TiCl4/MgCl2 + AlEt3 was determined at various polymerization temperatures. It was found that the increase in polymerization temperature in the range of 40-80 degrees C increases the number of active centers. The data on reversible changes in the polymerization rate with temperature in a single experiment give grounds for supposing that alteration of the number of active centers with temperature is a reversible process. The propagation rate constants and the activation energy of the propagation reaction (4.0 kcal mol(-1)) were calculated; the latter value being considerably lower than the effective activation energy of polymerization (16.5 kcal mol(-1)) due to the increase in C-p with rising temperature. (C) 2013 Elsevier B.V. All rights reserved.