Standardized polymerizations of ethylene and propene with bridged and unbridged metallocene derivatives: A comparison

Abstract

Ethylene and propene were homopolymerized with 11 different metallocene-methylaluminoxane (MAO) catalysts 1-11 using a constant set of parameters. The catalytic activity of the two unbridged and 9 ansa-metallocenes as well as the properties of the polymers, such as molecular weight, width of molecular weight distribution, melting point, and, with polypropene, chain microstructure, were investigated. It was found that structure variations of the catalysts cause rather different catalytic behaviour, which further diversifies the performances with the two different monomers. In some cases this comparison allows insight into the nature of the influencing factors. 0 1992, Huthig & Wepf Verlag, Basel CCC 0025-1 16)3/92/$05,00 Standardized polymerizations of ethylene and propene with . . . Scheme 1: 6 : M t z Z r 7 : Mt=Hf 9 4-R=CH, (2 isomers) 5: R-H

Homo- and copolymerization of ethylene by cationic hafnocene catalysts based on tetrakis(pentafluorophenyl)borate

“…1. As already reported 9) , rac-Et(Ind) 2 HfCl 2 /MAO catalyst showed very low activities in ethylene polymerization, but rac-Et(Ind) 2 HfCl 2 / Me 2 PhNH N B(C 6 F 5 ) 4 /R 3 Al catalyst was much more active in ethylene polymerization than the MAO activated catalyst. Fig.…”

Influence of the catalyst and polymerization conditions on the long-chain branching of metallocene-catalyzed polyethenes

“…A lower activity in the homopolymerization of propene 38 is an indication that the insertion rate of the 1-olefins is slower than the insertion rate of ethene. When ␤-H elimination prevails, the slower insertion rate of the 1-olefin increases the probability of chain transfer.…”

Allyloxy- and benzyloxy-substituted pyridine-bis-imine iron(II) and cobalt(II) complexes for ethylene polymerization

“…The influence of substituents on the cyclopentadienyl (Cp) rings on the activity of the metallocene catalysts and on the MW of the resulting polymers has been the object of many studies. [6][7][8][9] Electronic and steric effects have been considered, but the lack of kinetic data, the different reaction conditions used by the authors that hinder an accurate comparison of the results and the difficulty of singling out the steric from electronic effects, do not allow sound conclusions to be drawn, not even about the influence on activity. Nevertheless, in general, electron releasing alkyl substituents on the Cp rings are reported to enhance catalytic activity, at least until steric hindrance inhibits monomer coordination.…”

“…5 The elucidation of ligand effects has been a central piece of work in olefin polymerizations over homogeneous catalysts, both metallocene and post-metallocene catalysts, as the catalytic activity and the polymer parameters such as molecular weight (MW) and molecular weight distribution (MWD) can be tailored through a rational ligand design at the transition metal center. Most investigations into ligand effects in such polymerizations have focused on the influence of the steric environment [6][7][8][9] and comparatively few have addressed the question how electronic changes in a ligand affect the metal center and its catalytic properties. [10][11][12][13] Electronic together with steric effects have at times been invoked to explain the influence of different cyclopentadienyl ligand substituents in metallocene complexes, e.g.…”