Active-center equilibrium in Ziegler-Natta butadiene polymerization

The Ziegler-Natta-catalyzed polymerization of 1,3-butadiene was investigate d at a low aluminum alkyl/cobalt (Al/Co) ratio using two different soluble catalyst systems: cobalt(II) octanoate/diethylaluminum chloride/water and c obalt(II) octanoate/ methylaluminoxane/tert-butyl chloride. When the active -center concentration was determined by the number-average molecular weight technique, it was found that the percentage of active cobalt depended on t he Al/Co ratio. Subsequently, an equilibrium reaction was proposed to be Co + 2Al = CoAl2, where Co is cobalt(II) octanoate, Al is either of the alumi num alkyl-activator species, and CoAl2 is the active catalyst. (C) 2001 Joh n Wiley & Sons, Inc.