Et(ind)zZrClz (C2H,(indenyl)zZrC12) confined inside regular pores of molecular sieves MCM-41 and VPIJ were prepared and used to polymerize propene with high activity. Stereoregularity, melting point and molecular weight of polypropene obtained were increased and the polymerization behavior was quite different from that prepared with homogeneous Et(ind)zZrC12. The small, regular and cylindrical pores of MCM-4 1 and VPI-5 suppress the formation of inactive binuclear complexes between metallocene and metallocene, or between metallocene and methylaluminoxane, resulting in stable active sites and high activity in propene polymerization. ' )Present address: Polymer Technology Lab.,

For a determination of the active site concentrations, [C*], the simultaneous kinetics and inhibition method using CO as a catalyst inhibitor were examined. It is noticed that this evaluation method is not quantitatively exact because MAO-activated alkyl Zr sites exist in dynamic equilibrium between dormant states and a chain propagating site and because some CO molecules coordinate even to inactive species. The number of active sites was evaluated on the assumption that two molecules of CO coordinate to each active center. The increase in Al/Zr ratio and temperature increased both the number of active sites and the value of k p for ethylene polymerization over Cp2ZrCl2/MAO. Especially, a drastic increase of activity is mainly due to a much higher value of k p above a Al/Zr ratio of 2000. A comonomer enhanced drastically the catalytic activity to more than 10 times for ethylene−propylene copolymerization over the rac-Me2Si(Ind)2ZrCl2/MAO system. This is due to the drastic increase in the propagating rate constant, k p, rather than the increase in the formation of new active sites by the addition of comonomer.

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