Deviation of hydrogen response during propylene polymerization with various Ziegler-Natta catalysts

The influence of the catalyst type on the hydrogen response during propylene polymerization with Ziegler-Natta catalysts was investigated in terms of the variations in kinetic behavior, catalyst activity, molecular weight and its distribution, and microstructure of the resulting polymers. Three different types of supported Ziegler catalysts and a TiCl3 catalyst were used in this study. In all cases, the catalyst activity was found to significantly increase with the addition of hydrogen along with a sharp decrease in the molecular weights. The activity enhancement by hydrogen was remarkable during polymerizations with supported catalysts compared to the case of a TiCl3 catalyst system. Hydrogen was found to activate all of the supported catalysts to same degree, regardless of the type of internal donor and the preparation method. This phenomenon is considered to be mainly ascribed to no significant difference in the number of dormant sites formed on che supported catalysts. The influence of the catalyst type on the hydrogen response was remarkable for the molecular weight and its distributions, which may be due to the difference in the states of the active species on each catalyst. (C) 1999 Elsevier Science B.V. All rights reserved.