Propylene Polymerization Using ansa‐Zirconocenes with Water/Pentafluorophenol‐Modified Methylaluminoxane

We have confirmed that water- and pentafluorophenol-modified isobutylmethylaluminoxane (W/PM-MMAO) enhances the productivity and stereoregularity of the yielded polymer and increases its molecular weight when propylene is polymerized using C 2 -symmetric ansa-zirconocenes. 13 C NMR analysis shows that when W/PM-MMAO is used as a cocatalyst with C 2 -symmetric ansa-zirconocenes, although the pentad peaks of the stereoerrors derived from enantiofacial misinsertion have still existed; those derived from the epimerization of the growing chain end that occurred with β-hydride elimination disappear. Therefore, we propose that W/PM-MMAO interacts more strongly to the cationic metal center of metallocene than does MMAO owing to steric and electronic effect, and W/PM-MMAO suppresses β-hydride elimination, resulting in the production of polypropylene with higher molecular weight and isotacticity. To the contrary, there was no significant difference in the structure of the yielded polymer when W/PM-MMAO was used with C s -symmetric ansa-zirconocenes. In the case of C s -symmetric ansa-zirconocene, the stereoerror is mostly the result of monomer insertion error, and small amount of stereoerror caused by skipped insertion, not from the epimerization of the polymer chain end that occurs after β-hydride elimination; therefore, there might not be any difference of the microstructure of yielded polymers between MMAO and W/PM-MMAO. It can be concluded that the both cases of C 2 - and C s -symmetric ansa-zirconocenes are used as a catalyst, and water and phenol modification of MMAO does not affect the monomer misinsertion which is one of the mechanisms of the stereoerrors.