Preparation of elastomeric polypropylene using metallocene catalysts: Catalyst design criteria and mechanisms for propagation

Abstract A series of unsymmetrical metallocene catalysts were prepared and used to polymerize propylene under a variety of conditions using methylaluminoxane as a cocatalyst. Zirconium and hafnium‐based catalysts were more active and more importantly, much more stable at conventional polymerization temperatures than titanium catalysts. By adjusting experimental conditions, it is possible to vary both the molecular weight of the polymer and also the degree of crystallinity. These properties significantly impact on the tensile properties of elastomeric poly(propylene) (ELPP) in a predictable manner. The microstructure of ELPP was characterized by 13C NMR spectroscopy and the pentad distributions were analyzed using several statistical models for propagation. This work has demonstrated that the microstructure of ELPP is probably not that of an isotactic‐atactic block copolymer.