PHOSPHOLYL CATALYSTS FOR OLEFIN POLYMERIZATION

Seventeen different phospholyl ligands were incorporated in a total of 22 zirconium complexes, (Phos)(2)ZrCl2, (Phos)(C5H5)ZrCl2, investigat ed in propylene polymerization catalysis using methylaluminoxane as co catalyst. Atactic polypropylene with M-n varying from 450 to > 20 000 and vinylidene end groups (CH2=C(Me)R) was obtained with activities up to 170 kg/g Zr . h. For the 11 diphospholyls of structure (2,5-R2C4H2 P)(2)ZrCl2, catalytic activity was highest with substituents of modera te bulk adjacent to phosphorus (e.g., c-Pr, Ph), whereas complexes wit h two small (H) or two large (CMe3, SiMe3) ligand substituents were in active. It is hypothesized that optimum activity with MAO requires sel ective blocking of phosphorus lone pair coordination to aluminum, whil st allowing free propylene approach to the active site. The degree of polymerization increased steadily in the series of 2,5-disubstituted p hospholyl complexes, dialkyl < alkyl-phenyl < diphenyl, suggesting tha t electronic factors are more important than steric factors in determi ning M-n. (C) 1998 Elsevier Science B.V.