MICROTACTICITY DISTRIBUTION OF POLYPROPYLENES PREPARED WITH HETEROGENEOUS ZIEGLER-NATTA CATALYSTS

The microstructure of the isotactic parts of various polypropylene has been studied by **1**3C NMR spectroscopy. The isotacticity of the isotactic parts as determined by the mmmm pentad sequence ('microisotacticity') increases as the stereospecificity of the catalysts (isotactic index, II) employed increases. Several polypropylenes prepared with titanium-based catalysts were fractionated by using an elution column technique. The fractionation results show that two isospecific active centers reside in such catalysts.