Effect of different donors on kinetics of Zn catalysts and molecular weight of the obtained polypropylene

Abstract

This paper studies MgCl 2/internal donor/TiCl 4//external donor/AlEt 3 catalytic systems where ethyl benzoate (E.B.) or 2,2,6,6 tetramethylpiperidine (TMPiP) are used as internal and external donors. E.B. as external donor does not change the molecular weight of the product with TMPiP as internal donor. The molecular weight of polypropylene decreases drastically and global productivity and stereoselectivity are very low with MgCl 2/internal Donor/TiCl 4//external donor/AlEt 3 when TMPiP is the external and internal donor. In this case the insoluble fraction in n-heptane is highly stereospecific and the molecular weight is similar to commercial products. We present a new explanation of these results, based on Ystenes proposal, comparing both precatalysts.