| Abstract: | Recent progress in transition metal catalyzed propylene polymerization based upon single-site catalysts and melt compounding of polypropylene is stimulating the development of novel polypropylene materials with unconventional property combinations such as improved low temperature toughness, low haze, elasticity, and improved toughness/stiffness balance. As a function of metallocene architectures, polypropylene microstructures can be varied over a very wide range in order to produce thermoplastic elastomers and highly flexible polymers as well as stiff engineering thermoplastics and fibers. Control of polypropylene molecular architectures, especially random placement of steric irregularities in the polypropylene main chain, and the addition of clarifiers represents the key to producing novel transparent polypropylenes. Metallocene-based ethene/1-olefin copolymers such as poly(ethylene-co-1-butene) are attractive blend components to afford either single-phase flexible or two-phase rigid blends with improved low temperature impact strength as a function of the 1-butene content. New families of polypropylene nanocomposites, containing nanowhiskers and anisotropic nanoparticles derived from organophilic layered silicates, exhibit effective matrix reinforcement at low filler content. |
