The effect of substituents at the indenyl ringon the catalytic activity of unbridged metallocene
dichlorides in ethylene polymerization
Polimery 1997, No 10, 591
Catalytic behavior was examined in the series of 2- and 1-substituted bisindenyl zirconium and hafnium complexes, (2-PhInd)2 ZrCl2, (2-PhInd)2HfCl2, (2-p-TolInd)2ZrCl2, (2-p-TolInd)2HfCl2, (1-MeInd)2ZrCl2, (1 -i-PrInd)2HfCl2, (1-cyclo-C6H11Ind)2ZrCl2, (2-n-BuInd) 2ZrCl2, and (2-A11-Ind)2ZrCl2. 2-Ph-substituted zirconocene showed higher activity in ethylene polymerization than did the unsubstituted indenyl complex under similar conditions, and provided polyethylene of the higher molecular weight. These catalytic features suggest the increase in activity to be caused probably by an increase in chain propagation rate. The lower productivity of (2-p-Tol-Ind)2ZrCl2 complex compared to (2-PhInd)2ZrCl2 is attributed to the electron donating effect of the methyl substituent at the phenyl ring suppressing the effect of the aryl substituent. The two hafnium analogs showed considerably lower activity as compared with zirconium complexes, the feature commonly observed on replacement of zirconium by hafnium. The most pronounced effect of 1-substituents on the metallocene activity was observed for the 1-Me and 1-i-Pr-substituted complexes. The activities of the complexes examined in ethylene polymerization were found to be linearly correlated with the electronic and steric substituent characteristics.