ELASTOMERIC POLY(PROPYLENE) - PROPAGATION MODELS AND RELATIONSHIP TO CATALYST STRUCTURE

Propylene polymerizations were conducted with a number of chiral metallocene complexes of titanium, zirconium, and hafnium, and the polymers were characterized by C-13 NMR spectroscopy. In certain cases, elastomeric material is produced. The microstructure of the polymers prepared, as determined by C-13 NMR spectroscopy, has been simulated using several statistical models for propagation. The models are formulated in terms of different mechanisms for monomer insertion at the two, inequivalent coordination sites in this family of catalysts. This work has revealed that the microstructure of this polymer can be adequately described by more than one model and that a range of acceptable parameters exists for each of these models. Arguments are presented that the microstructure of elastomeric poly(propylene) is much more random than originally proposed and that if blocks of e.g., atactic sequences are present, they are, on average, very short.