Complementary experiments confirm the recent findings that the rate of propene polymerization is temporary enhanced if a small amount of ethylene is introduced during the polymerization, normalizing after consumption of ethylene by copolymerization. In addition, the study of the sequence distribution of propene monomeric units in the copolymerization carried out under various conditions revealed that the activation by ethylene does not involve the propagation steps, but the re-initiation after deactivation. A similar temporary activation effect was observed after the addition of small amounts of hydrogen. In this case, however, hydrogen is not consumed. Thus, the deactivation observed after the initial rate enhancement is due to another reason. The deactivation could be shown to be reversible after removal of the adsorbed hydrogen when either ethylene or hydrogen was added again to allow re-initiation of the polymerization. One of the important reasons of the continuous decrease of the propene homopolymerization rate may be due to the fact, that, after a transfer step, the re-initiation of polymerization does not take place spontaneously. Small amounts of ethylene or hydrogen allow the reinitiation to take place, at least for some kind of active sites.
R. Spitz, P. Masson, C. Bobichon
Macromolecular Chemistry and Physics