Tailoring the Physical Properties of Isotactic Polypropylene through Incorporation of Comonomers and the Precise Control of Stereo- and Regioregularity by Metallocene Catalysts

Random copolymers of propylene with ethylene, butene, and hexene comonomers have been prepared with different metallocene catalysts. The used catalysts have allowed a precise control of concentration of stereodefects and high degree of comonomer incorporation while maintaining high molecular mass and random distribution of comonomers. Incorporation of ethylene, butene, and hexene produces great enhancement of ductility, flexibility, and toughness, as compared to highly isotactic polypropylene, but with important differences in the values of elastic modulus and strength depending on the comonomer. In propylene−ethylene copolymers, the values of elastic modulus, ductility, toughness, and strength can be tuned by changing the concentrations of rr stereodefects and ethylene units, so that stiff and fragile plastics, highly flexible materials, and elastomers can be obtained. Propylene−butene copolymers behave as highly flexible materials with remarkable ductility and toughness and contemporary high strength and stiffness. Propylene−hexene copolymers are highly flexible materials with plastic resistance and strength that decrease with increasing hexene content. These outstanding properties are not easily accessible with propylene-based copolymers produced with traditional Ziegler−Natta catalysts because of nonrandom distribution of comonomers and non-homogeneous composition.