SERIES ON HOMOGENOUS ZIEGLER-NATTA CATALYSTS .11. KINETICS AND STEREOCHEMICAL CONTROL OF PROPYLENE POLYMERIZATION INITIATED BY ETHYLENE BIS(4,5,6,7-TETRAHYDRO-1-INDENYL) ZIRCONIUM DICHLORIDE METHYL ALUMINOXANE CATALYST

The kinetics and sterochemical control of propylene polymerization initiated by rac-ethylene bis (4,5,6,7-tetrahydro-1-indenyl) zirconium dichloride/methyl aluminoxane (1/MAO) and by rac-ethylene bis (1-indenyl) zirconium dichloride/MAO (2/MAO) were investigated. The polymerization activities increase monotonically with temperature corresponding to an overall activation energy of 10.6 kcal mol-1. This is accompanied, however, by reduction of stereochemical control as reflected in the amount of the polypropylene (PP) soluble in low boiling solvent. At a temperature of 30-degrees-C and higher, polymerization initiated by 1/MAO produced no PP insoluble in refluxing n-heptane. Tritium radiolabeling showed that at [Al]/[Zr] greater-than-or-equal-to 3500 and 30-degrees-C, two-thirds of 1 becomes catalytically active. There are at least two kinds of active species formed in about equal amounts; one has more stereoselectivity, 10-20 times greater rate constant of propagation, and a factor of 5-15 faster chain transfer to MAO than the second kind of active species. This is also true at low [Al]/[Zr] of 350, except that the total amount of the two active species corresponds to only 13% of the [1]. Replacement of MAO with trimethyl aluminum resulted in the decrease of stereoselectivity and loss of catalytic activity proportional to the amount of replacement. A comparison was made with the polymers obtained with 2/MAO.