Homogeneous Ziegler–Natta Catalysts and Synthesis of Anisotactic and Thermoplastic Elastomeric Poly (propylenes) Dedicated to Professor T. Keii on the Occasion of his seventieth birthday

Ziegler–Natta (ZN) catalysis is in a revival with vigorous activities and advances achieved in both heterogeneous and homogeneous systems. Most Ziegler–Natta catalysts have maximum activity at some optimal temperature; the activity decreases at both lower and higher temperature because of catalyst activation and deactivation, respectively. The microstructures of the polymer fractions have been determined by ¹³C-NMR and the steric sequence distributions are summarized in the chapter. In case of 70°C polymerization the fractions in the order of increasing solvent ranking show regular increases in the mmmm and mmmr pentads and regular decreases in the pentads having two or more replacements. The same holds true for all, but the −55°C/E fraction. The polymers obtained at 0°C have occasional reversals in the progressions of steric sequence distributions with respect to the solvent ranking. High level of isotactic polypropylene (PP) crystallizes in the α-modification; less stereoregular polypropylenes can also crystallize in the β and γ-modifications. The heterogeneity in the microstructures of ani-PP and the radio labeling determination of C^∗distribution showed that there are two or more catalytic species in the ansa-metallocene/MAO systems. The catalytic activity (A) of metallocene compound is strongly dependent on the amount of MAO used for activation. The results are summarized in the chapter.