HEMIISOTACTIC POLYPROPYLENE - A KEY POINT IN THE ELUCIDATION OF THE POLYMERIZATION MECHANISM WITH METALLOCENE CATALYSTS

An analysis of propylene polymerization in the presence of metallocene complexes was carried out on the basis of the alternating mechanism and formulated in terms of fundamental stereochemistry. A statistical approach allowed the calculation of pentad distribution for polypropylenes produced in the presence of isospecific, syndiospecific, and hemiisospecific catalysts. Comparison with experimental data published for hemiisotactic polypropylene confirmed the validity of the alternating mechanism but showed also the presence of successive additions at the same catalyst face.