Ethylene/α-olefins cooligomerization versus copolymerization by zirconocene catalysts

Alternating Copolymerization of Ethylene and Propylene: Evidence for Selective Chain Transfer to Ethylene

“…The latter results in particular implies that chain transfer to ethylene might be quite common in ethylene/ R-olefin copolymerization, [45][46][47][48][49][50][51] particularly in those cases where the molecular weights for copolymerization are lower than the corresponding ethylene homopolymerizations. 7,52,53 Conclusions. The copolymerization of ethylene and propylene with ansa-(indenyl)(fluorenyl)zirconocenes yields highly alternating EP copolymers.…”

“…This selectivity helps explain the formation of quaternary centers and the much lower molecular weights we observe in copolymerization relative to homopolymerizations (Table ). The latter results in particular implies that chain transfer to ethylene might be quite common in ethylene/α-olefin copolymerization, − particularly in those cases where the molecular weights for copolymerization are lower than the corresponding ethylene homopolymerizations. ,, …”

Possible effects on the polyethene chain structure of trimethylaluminum coordination to zirconocene catalysts

“…Totally different results were reported by Rieger and Janiak11 and D'Agnillo et al12 They found that replacing MAO with TMA decreased the molecular weight of the polyethene produced but had only a slight influence on the MWD. The influence of alkylaluminum on olefin copolymerization and copolymer properties with (Me 5 Cp) 2 ZrCl 2 as a catalyst was studied by Michelotti et al,13 but its effect on homopolymerization with the same catalyst was not addressed. In a recent comprehensive work on the composition and structure of MAO solutions,14 we found that TMA acted as a separate chain‐transfer agent that reduced the molecular weight of polyethene produced with (Me 5 Cp) 2 ZrCl 2 .…”

Selective Chain Transfer Reactions in Metallocene Catalyzed Copolymerization of Ethylene with Allylbenzene

“…[1][2][3][4][5] Generally, chain termination via alkyl chain transfer to aluminum is described as a minor chain termination process for the metallocene-catalyzed olefin polymerization. [6][7][8][9][10][11] Recently we found that chain transfer to aluminum became a major chain transfer reaction when ethylene was copolymerized with allylbenzene. 12 In this communication, we report the copolymerization behavior of ethylene and allylbenzene with several metallocene catalysts having different ligand structures where chain transfer mode depends on the catalysts' structures.…”

“…It is known that two kinds of chain transfer reactions, β-H elimination and chain transfer to aluminum, prevail in olefin polymerization with metallocene/MAO catalysts. However, only a few publications that describe the predominant occurrence of chain transfer to aluminum during olefin polymerization have appeared in the scientific literature. − Generally, chain termination via alkyl chain transfer to aluminum is described as a minor chain termination process for the metallocene-catalyzed olefin polymerization. − Recently we found that chain transfer to aluminum became a major chain transfer reaction when ethylene was copolymerized with allylbenzene …”