Elastomeric polypropylenes from unbridged 2-phenylindene zirconocene catalysts: Temperature dependence of crystallinity and relaxation properties

The solid-state structure and physical behavior of an elastomeric polypropy lene (PP1) synthesized with unbridged 2-phenylindene zirconocene catalyst w ere examined using solid-state C-13 NMR spectroscopy, differential scanning calorimetry, wide-angle X-ray powder diffraction, and birefringence measur ements of relaxation behavior. Extraction of these elastomeric polypropylen es with boiling ether and heptane yielded three fractions of different mole cular weight and tacticity. The ether-soluble fraction is the lowest in iso tactic pentad content and exhibits no detectable crystallinity. For the oth er fractions and the parent homopolymer, the degrees of crystallinity estim ated from DSC and WAXD results are similar. The amount of the immobile phas e determined by solid-state NMR, however, appears much higher than the degr ee of crystallinity. An increase in temperature from 20 to 80 degrees C res ults in a loss in the relative fraction of mobile and immobile phase as mea sured by solid-state NMR and a corresponding loss in the percent crystallin ity as measured by DSC. The relaxation of polymer samples subjected to step shear as a function of increasing temperature was investigated using polar ized optical birefringence measurements. These studies revealed that the el astic network remains stable up to temperatures of 80 degrees C. Blends of atactic and isotactic polypropylene with similar average isotactic pentad c ontents as PP1 and its heptane-insoluble fraction were examined in comparis on. Despite their similar taciticities and degrees of crystallinity. the bl ends show no evidence of a network structure after being subjected to a ste p shear but instead relax back to an isotropic orientation.