ETHYLENE-PROPYLENE COPOLYMERIZATION WITH 2-ARYLINDENE ZIRCONOCENES

Unbridged 2-arylindenylmetallocene complexes such as bis(2-phenylinden yl)zirconium dichloride in the presence of methylaluminoxane (MAO) are catalyst precursors for the synthesis of elastomeric polypropylenes. These catalysts are also active for the copolymerization of ethylene a nd propylene. Addition of small amounts of ethylene to a polymerizatio n system derived from the 2-arylindene metallocenes results in a large and nonlinear increase in the polymerization rate. This increase in r ate cannot be explained by the faster rate of ethylene insertion but i s likely the result of the activation of dormant catalyst sites by eth ylene. This ''ethylene effect'' is much larger for bis(2-phenylindenyl )zirconium dichloride/MAO ((2PhInd)(2)ZrCl2/MAO, 1/MAO) and bis[2-(3', 5'-bis(trifluoromethyl)phenyl)indenyl]zirconium dichloride/MAO ((CF3) (2)PhInd)(2)ZrCl2/MAO, 2/MAO) metallocene catalysts than for bridged r ac-ethylene-bis(indenyl)zirconium dichloride/MAO (EBIZrCl2/MAO, 3/MAO) metallocene. Copolymerization parameters for 1-3/MAO reveal that the unbridged 2-arylindene catalysts show a tendency toward random or slig htly blocky incorporation of comonomers (r(e)r(p) = 1.0-1.9 greater th an or equal to 1), Whereas the ansa-metallocene 3/MAO exhibits a tende ncy toward alternating comonomer distribution (r(e)r(p) = 0.5 < 1).