NEW EVIDENCE OF THE PRESENCE OF INTERNAL ELECTRON-DONORS IN ACTIVE-SITES OF HETEROGENEOUS ZIEGLER-NATTA CATALYSTS

Poly(propylene) samples produced by heterogeneous Ziegler-Natta cataly sts containing different internal electron donors were fractionated by using temperature rising elution fractionation; some key fractions we re analyzed with C-13 NMR. It was found that internal electron donors with different structures can convert aspecific active sites into diff erent isospectrific ones. The employment of bis(2-ethylhexyl) phthalat e as internal electron donor leads to chemically inverted structures i n the atactic fraction. This suggests that an internal electron donor may also exist in the environment of aspecific active sites.