| Popis: |
Seventeen different phospholyl ligands were incorporated in a total of 22 zirconium complexes, (Phos) 2 ZrCl 2 , (Phos)(C 5 H 5 )ZrCl 2 , investigated in propylene polymerization catalysis using methylaluminoxane as cocatalyst. Atactic polypropylene with M n varying from 450 to >20 000 and vinylidene end groups (CH 2 C(Me)R) was obtained with activities up to 170 kg/g Zr·h. For the 11 diphospholyls of structure (2,5-R 2 C 4 H 2 P) 2 ZrCl 2 , catalytic activity was highest with substituents of moderate bulk adjacent to phosphorus (e.g., c -Pr, Ph), whereas complexes with two small (H) or two large (CMe 3 , SiMe 3 ) ligand substituents were inactive. It is hypothesized that optimum activity with MAO requires selective blocking of phosphorus lone pair coordination to aluminum, whilst allowing free propylene approach to the active site. The degree of polymerization increased steadily in the series of 2,5-disubstituted phospholyl complexes, dialkyl M n . |
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