Ethene homopolymerization and copolymerization with 1-hexene for all methyl-substituted (RnC5H5-n)(2)ZrCl2/MAO catalytic systems: Effects of split methyl substitution

Ethene homopolymerization and copolymerization with 1-hexene were catalyzed by methyl-substituted cyclopentadienyl (Cp) zirconium dichlorides, (RnC5- H5-n)(2)ZrCl2 (R-n = H, Me, 1,2-Me-2, 1,3-Me-2, 1,2,3-Me-3, 1,2,4-Me-3, Me- 4, or Me-5), and methylaluminoxane. The polymers were characterized with Fo urier transform infrared, nuclear magnetic resonance, gel permeation chroma tography, and differential scanning calorimetry techniques. Generally, an i ncreasing number of methyl substituents on the Cp ligand results in lower l -hexene incorporation in the copolymer. The two catalysts with split methyl substitution (R-n = 1,3-Me-2 and R-n = 1,2,4-Me-3) show a higher comonomer response than their disubstituted and trisubstituted counterparts (R-n = 1 ,2-Me-2 and R-n = 1,2,3-Me-3). They even incorporate more 1-hexene than R-n = H and R-n = Me. These findings are qualitatively in agreement with the r esults of a theoretical study based on density functional calculations. The presence of comonomer does not influence the termination reactions after t he insertion of ethene. There is more frequent termination after each hexen e insertion with increasing comonomer incorporation except for the two cata lysts with split methyl substituents. The termination probability per inser ted comonomer is highest for the less substituted catalysts. (C) 2000 John Wiley & Sons, Inc.