Abstract
The relevance of chain end isomerization in ethylene and propylene homopolymerizations has been investigated using four Ct symmetric methylaluminoxane (MAO)-activated metallocene catalysts: rac-ethylenebis(1-indenyl)zirconium dichloride (1), rac-ethylenebis(2-(tert-butyldimethylsiloxy)-1-indenyl)zirconium dichloride (2), rac-ethylenebis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride (3), and rac-ethylenebis(1-(tert-butyldimethylsiloxy)-3-indenyl)zirconium dichloride (4). The amount of transvinylene groups in polyethylene and the amount of stereoinverted CH2D groups in poly(1-d-propylene) mere used as a measure for chain end isomerization. The isomerization process was more favored for 3/MAO than for 1/MAO, 2/MAO, and 4/MAO. The presence of the bulky electron-donating 2-siloxy substituent in 2/MAO drastically suppresses the isomerization reaction. Formation of trans-vinylene groups in polyethylene and d-[mrrm] stereoerrors in polypropylene were concluded to be mechanistically related. Monomer-assisted chain termination after isomerization is proposed to explain the presence of chain end bound trans-vinylene groups in polyethylenes produced with 1/MAO, 2/MAO, and 4/MAO.
| Original language | Undefined/Unknown |
|---|---|
| Pages (from-to) | 8534–8540 |
| Number of pages | 7 |
| Journal | Macromolecules |
| Volume | 33 |
| Issue number | 23 |
| Publication status | Published - 2000 |
| MoE publication type | A1 Journal article-refereed |