ELASTOMERIC POLYPROPYLENES FROM UNBRIDGED (2-PHENYLINDENE)ZIRCONOCENECATALYSTS - THERMAL CHARACTERIZATION AND MECHANICAL-PROPERTIES

The properties of three elastomeric stereoblock polypropylene (PP) sam ples made with unbridged 2-phenylindene zirconocene catalysts were inv estigated. One of the characteristics of these catalysts is the abilit y to control the structure and properties of the polypropylenes by man ipulation of the reaction conditions. Samples PP1 and PP2 were prepare d to have similar tacticities las indicated by IR and NMR spectroscopy ) yet different molecular weights. The molecular weight of PP2 is appr oximately half the molecular weight of PP1. Sample PP3 has a molecular weight similar that of PP2 but is lower in isotactic pentad content. All three samples were separated into fractions that differ in their s olubilities in boiling ether and heptane. The fractionation appeared t o be governed by tacticity and molecular weight. Thermal analysis by d ifferential scanning calorimetry showed very broad melting endotherms. The broadness of the transitions and the relatively large standard de viations calculated for the enthalpy of fusion are indicative of a mul tiphase material. X-ray powder diffraction patterns of the three sampl es and their fr-actions (except the ether-soluble fractions) all showe d characteristic peaks of the a crystalline phase. The heptane-insolub le fractions of both PP1 and PP2 also exhibited gamma-phase reflection , whereas in the heptane-soluble fractions, that reflection is less ev ident. Tensile tests performed on PP1 and PP2 yielded a similar tensil e modulus for the two, indicating similar degrees of crystallinity. PP 1 exhibited better recovery properties, as measured in tests at 100% a nd 300% elongation.