Polymerization mechanism for in situ supported metallocene catalysts

Abstract

The polymerization of ethylene was carried out with a novel in situ supported metallocene catalyst that eliminated the need for a supporting step before polymerization. In the absence of trimethyl aluminum (TMA), in situ supported Et[Ind]2ZrCl2 was not active, but the addition of TMA during polymerization activated the catalyst. Et[Ind]2Zr(CH3)2 was active even in the absence of TMA, whereas the addition of TMA during polymerization enhanced the catalytic activity. The polymerization-rate profiles of the in situ supported metallocene catalysts did not show rate decay as a function of time. A polymerization mechanism for the in situ supported metallocene catalysts is proposed for this behavior. During polymerization, the in situ supported metallocene catalysts may deactivate, but homogeneous metallocene species present in the reactor may form new active sites and compensate for deactivated sites.