Effect of internal donors in propylene polymerization analyzed with the two-site model

The effect of internal donors of Ziegler‐Natta catalyst on stereoregularity in propylene polymerization was analyzed with the aid of the two‐site model analysis system. The amount of internal donor and that of external donor were varied. The probability in the selection of d (or l) monad in asymmetric site is contributed by both the amount of internal donor and that of external donor. With respect to the fraction of asymmetric site, the two‐site model enabled us to conceive that the new kinds of active centres are generated in specific cases where external donor is believed to be replacing weaker internal donor during polymerization. The effect of hydrogen concentration during polymerization is also discussed. © 2002 Society of Chemical Industry.