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A strategy has been developed for the synthesis of thermoplastic elastomeric polypropylene based on the catalytic activity of the unbridged metallocene bis(2-phenylindenyl)zirconium dichloride [[(2-PhInd).sub.2]Zr[Cl.sub.2]. This catalyst was designed to isomerize between achiral and chiral coordination geometries during the polymerization reaction to produce atactic-isotactic stereoblock polymers. The metallocene precursor [(2-PhInd).sub.2]Zr[Cl.sub.2] in the presence of methylaluminoxane polymerizes propylene to yield rubbery polypropylene. The isotacticity of the polymer, described by the isotactic pentad content, increases with increasing propylene pressure and decreasing polymerization temperature to produce polypropylenes with an isotactic pentad content ranging from 6.3 to 28.1 percent., The stereochemistry of polyolefins strongly influences their properties. Isotactic polypropylene, consisting of a regular arrangement of stereocenters, is a crystalline thermoplastic with a melting point of '165°C, whereas atactic (stereorandom) [...]

Spectacular advances in organometallic chemistry over the past two decades have resulted in single-site catalysts that are revolutionizing production of polyethylene (PE) and isotactic polypropylene (iPP). This report describes an unanticipated benefit of metallocene-catalyzed semicrystalline polyolefins, namely welded joint strengths in PE/iPP laminates that can exceed the cohesive strength of the constituents. We propose that interracial polymer entanglements, established in the molten state and subsequently anchored in chain-folded lamellae upon crystallization, are responsible for this intrinsic property. The poor adhesion exhibited by traditional Ziegler-Natta-catalyzed polyolefins is shown to derive from the accumulation of amorphous polymer, a by-product of the polymerization reactions, at the interface. These results should facilitate fabrication and improve the properties of composites based on materials that dominate the plastics industry., Polypropylene (PP) is the thermoplastic polymer with the fastest expansion in production in the world, with an average annual growth rate of 9% since 1991 (1). Currently, worldwide PP resin [...]

Polypropylene is relatively new in the plastics world, a 1950s product of the academic work of Ziegler and Natta (1) and the Phillips Petroleum industrial labs of Banks and Hogan [...]