MICROSTRUCTURAL ANALYSIS OF POLYPROPYLENES PRODUCED WITH HETEROGENEOUS ZIEGLER-NATTA CATALYSTS

Microstructural analysis was carried out on five isotactic polypropyle nes produced with different heterogeneous Ziegler-Natta catalyst syste ms and different polymerization processes. The samples were fractionat ed according to stereostructure using a direct extraction method. Pent ad tacticities of unfractionated samples and selected fractions were d etermined by C-13 n.m.r. spectroscopy. I.r. isotacticities were also m easured. Statistical analysis of the polymerization mechanism was carr ied out on the basis of the two-site model from the pentad tacticities , and average lengths of meso and racemic sequences were determined. I n addition to atactic and isotactic materials produced at different ca talytic sites, the polypropylene samples contained syndiotactic materi al as stereoblocks in isotactic chains. On the basis of the analysis c arried out on the fractions, slight differences in the microstructure were found to exist between the samples produced by different processe s and catalyst types. These differences have a significant effect on a verage sequence lengths.